Ceramic Powders: Advances in Synthesis, Processing and Manufacturing
Session CA-1 - Advances in Powder Synthesis and Characterisation
CA-1:IL01 Adventures in Metal Oxide Nanomaterials
S. BANERJEE, University at Buffalo, The State University of New York & New York State Center of Excellence in Materials Informatics, Buffalo, NY, USA
S. BANERJEE, University at Buffalo, The State University of New York & New York State Center of Excellence in Materials Informatics, Buffalo, NY, USA
Scaling transition metal oxides to nanoscale dimensions substantially alters their phase stabilities and phase diagrams with tremendous consequences for the manifestation of unique physical phenomena. Such physical phenomena can be utilized to fabricate novel device constructs for logic circuitry, piezoelectric power generation, "smart windows", and Li-ion batteries.
In this talk, I will focus on our recent results on the influence of finite size and doping on the metal-insulator phase transitions of the binary vanadium oxide VO2. We have achieved substantial tunability of the critical transition temperature between -20 and 70°C through control of dimensionality morphology, and dopant concentration in hydrothermally prepared single-crystalline VO2 nanostructures. A combination of Raman microprobe analysis and electrical transport measurements provides a detailed mechanistic picture of the structural progression and local structure perturbations accompanying the phase transition. The tunability of the phase diagram portends applications of these materials as dynamically switchable glazings for energy efficient windows. We have further developed a novel series of quasi-1D vanadium oxide bronzes with the general formula MxV2O5 (M: K, Cu, Pb, Ca) wherein intercalating metal cations.
CA-1:IL02 Synthesis of Nanopowders by Aqueous Precipitation with Continuous Reactors
A. AIMABLE1, C. PAGNOUX1, F. ROSSIGNOL1, T. CHARTIER1, N. JONGEN2, A. TESTINO3, P. BOWEN2, 1SPCTS, CNRS, ENSCI, Université de Limoges, France; 2EPFL, Switzerland; 3Paul Scherrer Institute, Switzerland
Numerous routes are available for the synthesis of nanopowders. Among these routes, the low cost and simplicity of aqueous precipitation have succeeded in the controlled synthesis of numerous shapes, sizes and morphologies, at low temperature, and make this approach the most attractive for possible commercial developments. The control of the precipitate can be achieved with respect to its size, shape, and chemical composition, by thermodynamic considerations, as well as with the use of polymeric additives. For example, the precipitation conditions of ZnO were optimized in order to obtain redispersable particles of 60 nm. Also mesoporous powders (spinel, silica) with very high specific surface area can be obtained. The surface chemistry can be adjusted by further treatments in solution to get well-designed functionalized colloidal particles.
The low productivity of the synthesis of nanopowders is actually a critical point limiting their use in applied technologies and processes. Over recent years a new type of tubular plug flow reactor - the segmented flow tubular reactor (SFTR) - has been conceived and used to produce high quality powders in a continuous way. For example, 5 kg of ultrafine BaTiO3 (170nm), or the continuous synthesis of nanometric ZnO, could be achieved.
CA-1:L03 FAU Membrane for Organic-Template-Free Synthesis of Nanosized Zeolite Crystals
T.F. MASTROPIETRO2, E. DRIOLI1,2, T. POERIO1, 1National Research Council, Institute for Membrane Technology (ITM-CNR) c/o University of Calabria, Rende, Italy; 2Department of Environment and Territory and Chemical Engineering, University of Calabria Rende, Italy
An alternative approach to the synthesis of nanosized FAU zeolites has been developed. The alternative procedure does not require special equipment, produces nanocrystals with uniform particle size distribution in high yield and allows easy processing. The synthesis is carried out in "soft condition" at near ambient temperature (30°C) without using any organic template. A tubular alumina support, seeded with NaX particles of 2µm, anchored by dry-hydrothermal treatment, is used to address the crystallization process. The molar composition of the clear precursor suspension has been adjusted to achieve a high degree of supersaturation and produce a uniform and abundant nucleation. The reaction product can be purified by centrifugation and re-dispersion in aqueous solution. The XRD pattern of the sample exhibits the characteristic Bragg peaks corresponding to the FAU phase, but they are broad, due to the presence of very small particles. The particle size distribution curve obtained by DLS analysis is quite narrow, with a d50 value of 135 nm (d10 =115, d90=186), corresponding to the formation of nanocrystals of uniform particle dimensions.
Acknowledgements: The research under this project is co-funded by the European Union Seventh Framework Programme (FP7/2007–2013) under DEMCAMER project (NMP3-LA-2011-262840).
CA-1:L04 Nonclassical Crystallization of Zirconium Oxide and its Derivatives
B. WÓJTOWICZ, W. PYDA, AGH Univeristy of Science and Technology, Faculty of Materials Science and Ceramics, Department of Ceramics and Refractories, Kraków, Poland
Zirconium dioxide is one of the most commonly used ceramic materials. However, some issues still have not been fully studied. Nonclassical crystallization is among them. According to the nonclassical crystallization theory, in some conditions crystals grow by joining particles of a size of crystallization nuclei or even big crystallites. Such crystals often show different properties when compared to the classical crystals.
In this work, we examine nonclassical crystallization of the zironium oxide in two ways: the hydrothermal crystallization for over a dozen hours in concentrated strong base solution in case of stabilized zirconia and in the presence of mineralizer and selected polymers in case of pure zirconia.
Depending on the conditions of crystallization, the zirconia powders showed different morphologies - 3D assemblies of complex shape or needle like particles several dozen microns in lenght. TEM revealed that former ones are built from plates 100 nm in size. The 3D assemblies of zirconia recrystallize from new phase containing Zr, O, Na, F. Ageing in the strong bases revealed, that morphology of the obtained crystals is dependent on the stabilizer. 3YSZ crystalizes in the form of needles of the rhombus cross-section, while MgSZ needles are square in the cross-section.
CA-1:L06 Synthesis of Nano Size b-SiC by a Carbothermal Process from a SiO2-C Precursor Obtained by a Two-Step Sol-Gel Process with Base Catalyst
SUNG-IL YUN, DAE-SOON LIM, Korea University, Seoul, Korea; YUNG-CHUL JO, GYOUNG-SUN CHO, MI-RAE YOUM, SANG WHAN PARK, Interfacial Control Research Center, Korea Institute of Science and Technology, Seoul, Korea
The properties of SiC have important influences on the performance of sintered SiC, such as thermo-mechanical performance and electrical properties of sintered SiC. For the better properties of sintered SiC, fine SiC powders with narrow size distribution as well as high purity are necessary for the application to advanced industries. In this study, TEOS and phenol resin were used as Si and C liquid phase source. SiO2-C precursors varying C/Si mole ratios from 1.4 to 2.3 were fabricated by heat treating the dried SiO2/Phenol resin gel made by two step sol-gel processes with a base catalyst. β-SiC powders were synthesized by a conventional carbothermal reduction process using SiO2/C hybrid precursors at the temperature of 1200~1800℃ under vacuum atmosphere. β-SiC powders with size about 50 nm were synthesized at temperature below 1450 ℃. With increasing the synthesis temperature above 1500℃, rod shaped β-SiC powders start to be synthesized along with round shaped β-SiC powders that caused particle growth and the widening of the particle size distributions of synthesized β-SiC powders.
CA-1:L07 Ultradispersed Powder Raw Materials with High Chemical Homogeneity for Fine Grained Ceramics
E.A. TRUSOVA, K.V. VOKHMINTCEV, A.A. Baikov Institute of Metallurgy and Materials Science, RAS, Moscow, Russia
Technologically acceptable modified sol-gel technique was developed for obtaining ultradisperse raw materials Bi2O3, CeO2, Cr2O3, CuO, NiO, Y2O3, ZnO, ZrO2 with crystallite size of 4-120 nm. These powders have been developed to produce fine grained ceramics (grain size less than 3.0 microns) based on Bi2O3-ZnO composite. The problem of obtaining the compositions with high chemical homogeneity was solved by using ultradispersed powders consisting of ZnO nanoparticles (40-70 nm), decorated with 1 or 2 other metal oxides listed above. The formation of an interface on the surface of decorated nanoparticle was proved by use of Raman, FT-IR and UV-Vis spectroscopy. We have shown that the control of width and structure (indirect electronic transitions) of band gap of metal oxide powders can be achieved by varying their composition and dispersity. The obtained ZnO-Bi2O3 and ZnO-Cr2O3 powders have band gap width equal to 2.91 and 3.0 eV, respectively. Several fine grained Bi2O3-ZnO ceramic samples were obtained by liquid-phase sintering (750°C). It was shown, that nonlinearity coefficients of their volt-ampere characteristics were higher than the ones of conventional ceramics of the same chemical composition.
CA-1:L09 Studies on the Compositional Anomalies in Lanthanum Zirconate System Prepared by Co-Precipitation
A. CHOWDHURY1*, D. PRUSTY1, A. PATHAK1, A. CHINTHA1, B. MUKHERJEE2, 1R&D, Tata Steel Limited, Jamshedpur, India; 2Materials Research Centre, Indian Institute of Science, Bangalore, India. *Present address: Materials Science and Engineering, Indian Institute of Technology, Patna
The study set out to examine the compositional inconsistency in lanthanum zirconate system revealed the presence of non-stoichiometry in lanthanum zirconate powders when synthesized by co-precipitation route. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) investigations confirmed the depletion of La3+ ions in the system. Analyses using Vegard's law illustrated the La/Zr mole ratio in the sample to be around 0.45. An extra step of ultrasonication, introduced during the washing stage followed by the co-precipitation reaction, ensured the formation of stoichiometric La2Zr2O7. XRD analyses depicted significant peak shifts and huge difference in the Full Width at Half Maximum (FWHM) values for the two samples made with and without ultrasonication step. Noteworthy is also the difference between crystal sizes in these two samples which has been explained in the light of the formation of individual nuclei and their scope of growth within the precipitate core. The differential scanning calorimetry (DSC) analyses suggested pH 11 to be optimum for the synthesis of La2Zr2O7. The whole study also pointed towards the slow rate of activity of the lanthanum precursor which seemed to be predominantly responsible for this compositional inconsistency.
CA-1:L10 BaZr0.5Ce0.3Ln0.2O3-d (Ln=Y, Sm, Gd, Dy) Based Electrolyte for Intermediate Temperature Solid Oxide Fuel Cell
JUNFU BU, ZHE ZHAO, Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden
BaZr0.5Ce0.3Ln0.2O3-δ (Ln=Y, Sm, Gd, Dy) were synthesized successfully by using cost-effective solid state reactive sintering method from inexpensive raw materials of BaCO3, ZrO2, CeO2, Ln2O3 (Y2O3, Sm2O3, Gd2O3, Dy2O3) with 1 wt.% NiO as a sintering aid. The fully densified pellets can be prepared under sintering temperature of 1500 oC for 12 h. The grain size is larger than 1 um and in a narrow distribution. The conductivity of BaZr0.5Ce0.3Y0.2O3-δ, BaZr0.5Ce0.3Sm0.2O3-δ, BaZr0.5Ce0.3Gd0.2O3-δ and BaZr0.5Ce0.3Dy0.2O3-δ are 2.5×10-2 s cm-1, 0.5×10-2 s cm-1, 0.7×10-2 s cm-1, 4.3×10-2 s cm-1 respectively at 600 oC under air atmosphere.
CA-1:L11 High Energy Milling of ZrO2 - Reactivity Improvement and Application for the Synthesis of Ceramic Phosphate Pigments
N.O. GORODYLOVA, Z. DOHNALOVÁ, P. SULCOVÁ, University of Pardubice, Pardubice, Czech Republic
Zirconium dioxide is the most widely used zirconium precursor for ceramic synthesis. However, due to low reactivity of the low temperature polymorph, monoclinic-ZrO2 (m-), extreme conditions (high temperatures, pressure etc.) for its processing are required. Our research group is highly interested in the development of new thermally stable ceramic pigments and, recently complex zirconium phosphates were characterised as perspective colouring compounds for application in glazes. However employment of m-ZrO2 as an initial reagent in classical solid state reaction did not provide the desired phase composition or required too high temperatures. According to literature data, the transformation of m-ZrO2 into the reactive high temperature modifications, tetragonal and cubic, can be induced by milling and stabilized at ambient conditions. In our present study, high energy milling was performed as a pre-treatment stage of the zirconium precursor (m-ZrO2) in order to improve its reactivity in solid state reaction for the synthesis of complex zirconium phosphates.
Acknowledgment: The Ministry of Education, Youth and Sports of the Czech Republic, Project CZ.1.07/2.3.00/30.0021 "Enhancement of R&D Pools of Excellence at the University of Pardubice", financially supported this work.
CA-1:IL12 Continuous Production of Ceramic Nano Crystals using Supercritical Aqueous Solution
T. ADSCHIRI, WPI-AIMR, Tohoku University, Sendai, Japan
Variety of composite materials has been developed so far, but in many cases trade-off of the functions are of important issues: fabrication becomes difficult due to the significant increase of viscosity, and transparency of the polymer is sacrificed. To over come the trade off, controll of the nano-interface, namely the organic modification of NPs, is the key. For fabricating multi-functional materials, we proposed a continuous production process of organic modified ceramic nano crystals using supercritical hydrothermal conditions. Since the organic molecules and metal salt aqueous solutions are miscible under the supercritical state, and water molecule works as an acid/base catalyst for the reactions, organic-inorganic conjugate nanoparticles can be synthesized under the condition. The hybrid NPs show high affinity with the organic solvent or the polymer matrix, which leads to fabricate the organic inorganic hybrid nanomaterials with the compatible (trade-off) functions.
CA-1:L15 Effect of ammonium sulfate on morphology of Y2O3 nanopowders Obtained by Precipitation and its Impact on the Transparency of YAG Ceramics
H. TOMASZEWSKI, A. WAJLER, H. WEGLARZ, A. SIDOROWICZ, U. BRYKALA, K. JACH, Institute of Electronic Materials Technology, Department of Ceramics, Warsaw, Poland
As known fabrication of fully transparent YAG ceramics using solid-reaction method needs highly sinterable Y2O3 and Al2O3 powders. In this work, Taimicron TM-DR nanopowder was used as a source of alumina, and Y2O3 nanopowder with controlled morphology was prepared by AHC precipitation starting from nitrates. The effect of ammonium sulfate was intensively studied throughout the precipitation process. It was found that the morphology of precursors and sinterability of final Y2O3 powders were strongly affected by the addition of (NH4)2SO4. Transmittance of sintered YAG ceramics based on commercial alumina and prepared yttria powders showed that an optimum of ammonium sulfate addition exists. Mechanism of Y2O3 nanopowders properties regulation by the presence of ammonium sulfate in the precipitation process was widely studied and discussed.
CA-1:L16 Preparation of Ultradispersed Powders of Cobalt, Nickel, Molybdenum and Tungsten Oxides by Modified Sol-gel Technique
K.V. KOTSAREVA, E.A. TRUSOVA, A.A. Baikov Institute of Metallurgy and Materials Science, RAS, Moscow, Russia
During the last few decades great interest has been attracted to ultradispersed powders of Co, Ni, Mo and W oxides (MO). This is caused by their need for commercial production of fine grained ceramics, catalysts for petrochemistry, electrodes for new generation power source, gas sensors, photochromic and electrochromic facilities, multilayer capacitors.
Ultradispersed MO were obtained by modified sol-gel technique with use of different low-molecular structure direct agents (SDA). The particle sizes of obtained powders were 10-200 nm. All synthesized MO have been characterized using of XRD, TEM, BET and laser confocal microscopy. The optimal parameters of modified sol-gel synthesis have been determined: metal sources, SDAs, the qualitative and quantitative reaction medium compositions, calcination mode etc. The developed approach allows to synthesize MO nanoparticles with a given size, to vary it within 10-130 nm range with 20-30 nm precision.
CA-1:L19 Segregation and Color Change on (Cr,Ca) Codoped Nanocrystalline Tin Dioxide
D. GOUVEA, D.U. ROCHA, L.B. CALIMAN, Polytechnic School of the University of Sao Paulo, Sao Paulo, Brazil
The intense violet color and the high catalyst activity of Cr-doped SnO2 nanoparticles has motivated several authors to understand the solid solution formation and the oxidation state of chromium ions after synthesis. Recent work has demonstrated the ability of surface segregation in chromium-doped tin oxide system but the oxidation state is still misunderstood. Calcium addition changes the color of (Cr,Ca) codoped nanocrystalline tin dioxide pigments from violet to yellow simultaneously to a high particle size stabilization demonstrating that co-segregation could be associated to color change due to chemical environment change of chromium ions and specific surface area increase. High solubility of Cr+6 and Ca+2 allow us to determine the surface excess of both cations by ionic chromatography and the color change after surface solubilization.
Session CA-2 - Colloidal Processing
CA-2:IL01 Assembly of Nanoparticles and Inorganic-nanocellulose Hybrids into Functional Materials
L. BERGSTRÖM, Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden
The ability to control structure and functionality at all length scale has developed tremendously in the last decades. It is clear that optimal design of nanostructured materials require integration of various approaches to synthesize, functionalize, characterize and process the nanosized species for various applications.
We have previously demonstrated how it is possible to assemble iron oxide nanocrystals into superlattices with both translational and orientational order (mesocrystals) through evaporation-induced self-assembly. Here, we will present recent work on the structural evolution and the formation kinetics of large and highly ordered mesocrystals of nanocubes and nanospheres with a combination of gracing incidence small angle X-ray scattering, electron microscopy and modeling. I will also give an overview of recent research on the bio-inspired fabrication of multifunctional materials based on nanocellulose and inorganic nanoparticles. We will demonstrate how the microstructure and magnetic, mechanical, and optical properties of various inorganic-nanocellulose hybrids can be tailored by controlling the nucleation and growth of the inorganic nanoparticles onto the nanocellulose surfaces.
CA-2:IL02 Structuration of Ceramic Suspensions via Colloidal Processing: Simulations and Experiments
A. VIDECOQ, F. ROSSIGNOL, C. PAGNOUX, SPCTS, UMR 7315, ENSCI, CNRS, Limoges, France; D. Bochicchio, R. Ferrando, Dipartimento di Fisica, Genova, Italy
Many ceramic shaping processes are using the liquid route. Here, controlling the structure of colloidal suspensions is crucial in order to reliably adapt the suspension rheology to the process and to get the desired microstructure in the final part.
We believe that numerical simulations, which take into account the discrete nature of the colloids, may be of help in this goal. Indeed, we have developed and used simulation codes, and we propose to show how this kind of simulations can be employed to control the suspension stability and the suspension structure: particle ordering (formation of colloidal crystals), compactness of the aggregate network, percolation properties, etc. This will be illustrated in the case of a one-component system, and more interestingly in the case of a two-component system prone to heteroaggregation (i.e. when the two components bear opposite charges). Some of the simulation results will be compared to experimental characterizations of an alumina-silica-based system. We will emphasize on the main parameters controlling the structure of ceramic colloidal suspensions in both cases.
CA-2:L03 Colloidal Systems in the Fabrication of Advanced Ceramics and Composites
M. SZAFRAN, A. IDZKOWSKA, E. PAWLIKOWSKA, Warsaw University of Technology, Faculty of Chemistry, Inorganic Technology and Ceramics Department, Warsaw, Poland
Colloidal processing is playing now a very important role in production of ceramic materials and advanced composites. The crucial element of the technological process is to obtain green bodies with high homogeneity, advantageous microstructure and mechanical strength. Nowadays, the challenge is to design time-stable colloidal suspensions with low viscosity and high solid loading of well-dispersed particles. These materials find wide application from plastics industry, electronics and firearms to food industry.
Two types of advanced materials are presented in the study. First, shear-thickening fluids which base on nanosilica and poly(propylene glycols). Rheological properties of the suspensions will be discussed. These materials are applied to dampen and disperse energy in some devices. Another type of an advanced material is ceramic - polymer composite with low permittivity and loss tangent based on the barium-strontium titanate (BST). The material is obtained by tape casting method using shear-thinning fluids and measured up to 0.5 THz frequency.
This work has been financially supported by the The National Centre for Research and Development (agreement no PBS1/A5/19/2012 ) and by the National Science Centre ( No. DEC-2011/01/B/ST5/06295), Poland
CA-2:L04 Simulation of Colloidal Suspensions under Shear Flow
A. LAGANAPAN, A. VIDECOQ, M. BIENA, SPCTS, UMR 7315, ENSCI, CNRS, Limoges, France; D. BOCHICCHIO, R. FERRANDO, Dipartimento di Fisica, Genova, Italy; T. ALA-NISSILA, Department of Applied Physics, Aalto University School of Science, Aalto, Espoo, Finland
Colloidal suspensions have extensive applications in the ceramic industry hence various numerical studies are devoted in providing a model that can be used to optimize the production process and the final structure of ceramic materials.
Since a full-scale simulation of all the particles (colloids + solvent) is computationally impossible, most models work on simplified systems. The most simplified ones even ignore hydrodynamic interactions (HIs). However, several studies suggest that HIs influence the aggregation phenomena, moreover they are needed to study flowing suspensions. In order to include the HIs, we employ a technique that is a hybrid between Stochastic Rotation Dynamics for the solvent and Molecular Dynamics for the colloids.
We will show how we employ this technique to compute the viscosity of a colloidal suspension. We also use it to compare the aggregation phenomena in the simulations when HIs are taken into account and when they are not included. The effect of HIs on relevant quantities such as the percolation threshold in aggregating colloidal systems will be shown.
CA-2:L05 Challenges and Achievements in Fabrication of Ceramics by Techniques using in Situ Polymerization
P. WIECINSKA, M. BACHONKO, Warsaw University of Technology, Faculty of Chemistry, Warsaw, Poland
The leading role in fabrication of advanced ceramic materials is nowadays played by methods based on colloidal processes. These methods can provide good mechanical properties, homogeneous microstructure and simplify the manufacturing process. There is a group of colloidal shaping methods which use the in situ polymerization through which a macromolecular network is created, to hold ceramic particles together. As examples of these techniques gelcasting, gel-tape casting, gel-electrophoresis and methods linking gelcasting with UV-shaping or polymeric sponge method can be mentioned. There are several factors concerning polymerization conditions which have a big influence on the properties of final ceramic material such as: oxygen inhibition, degree of polymerization, polymeric shrinkage, monomer-ceramics interactions, etc. Authors examined the properties of selected monomers, resultant polymers and green ceramic tapes. Within research measurements of glass transition temperatures, degree of polymerization, polymeric shrinkage, rheological properties of ceramic suspensions and microstructure of ceramics were performed.
The project has been financially supported by the Ministry of Science and Higher Education of Poland (Grant No. IP2011 002171).
Session CA-3 - Shape Forming and Consolidation Mechanisms
CA-3:IL01 Direct Consolidation Techniques for Ceramics
J.M.F. FERREIRA, A. KAUSHAL, S.M. OLHERO, Department of Materials and Ceramics Engineering (DEMaC), CICECO, University of Aveiro, Aveiro, Portugal
Colloidal shaping techniques offer the opportunity to control the interaction forces between dispersed particles and their packing efficiency, and to increase the intimacy of powder mixtures in suspension. These benefits need to be preserved upon the consolidation step in order to obtain homogeneous green bodies, a key condition to enhance the reliability of final ceramic products. However, consolidation techniques involving liquid removal might lead to particle segregation phenomena that limit their useful application scope, mitigating the advantages of colloidal processing. This sort of drawbacks led to the development of several “direct consolidation techniques” in which low viscosity and highly concentrated suspensions are transformed into green bodies without liquid removal. The most common setting mechanisms (Gel Casting, Hydrolysis-Assisted Solidification, Direct Coagulation Casting, Starch Consolidation, Freeze Casting, etc.) and respective pros and cons will be reviewed. While some of them enable the consolidation of ceramic components with a varied range of shapes and dimensions and the green strength obtained is enough for outstanding the usual unmoulding stresses, this condition no more holds when micronized components with high aspect ratio are to be fabricated. To face this big challenge a new Epoxy Gel Casting technique was successfully developed, which enables the fabrication of ceramic micro components such as pillar arrays for high-frequency piezoelectric transducers and other Micro Electro Mechanical Systems (MEMS). Examples of PZT and lead free functional micro-components consolidated by Epoxy Gel Casting will be presented, demonstrating the potential of this new approach to mitigate the onerous and time consuming features of the state of the art micro-machining technologies.
CA-3:IL02 Manufacture and Benefit of Ceramic Composite Membranes by Plastic Processes
F. CLEMENS1, M. SALEHI1, 2, B. GROBETY2, J. KARBAUM3, M. ZWICK3, 1Lab. for High Performance Ceramics, Empa, Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Switzerlan; 2The Fribourg Center for Nanomaterials (FriMat) and Dept. of Geosciences, University of Fribourg, Fribourg, Switzerland; 3FGK, Forschungsinstitut für Anorganische Werkstoffe - Glas / Keramik - GmbH, Hoehr-GrenzhausenHoehr-Grenzhausen, Germany
Ceramic-polymeric compounds can be thermoplastic processed only by heating above the melting temperature of the polymeric binder. The advantage of this technique is the scalability in terms of green density, shape complexity and geometry by small modifications. These small modifications have typically no significant influence on the microstructure after sintering process. In the past oxygen separation membranes have been investigated by using different raw materials (e.g. BSCF and LSCF) and the talk will give an overview of the developments. Grain orientation and oxygen flux have been investigated on extruded and pressed samples. Non-deformed dead-end tubular membranes with wall thickness of 0.5 mm could be achieved after sintering with this processing technique. The gas-tightness test showed no leakage up to a pressure of 35 bar. To achieve higher mechanical properties, Al2O3 fibers and ZrO2 particles were used to reinforce the monolithic ceramic membrane. SEM analysis and phase composition were used to investigate the interface between the reinforcement material and the MIEC matrix. The mechanical properties decreased because of reaction between reinforcement and the matrix and increase in porosity. Interestingly the oxygen flux were not significantly influenced.
CA-3:L03 Transparent Tetragonal Zirconia Ceramics by Colloidal Processing of Nanoparticle Suspension
M. TRUNEC, CEITEC BUT, Brno University of Technology, Brno, Czech Republic; O. Bera, Faculty of Technology, University of Novi Sad, Novi Sad, Serbia
A reasonable transparency of birefringent tetragonal zirconia ceramics in visible light can only be reached using a fully dense and nanometre-sized microstructure. However, the use of nanoparticles represents one of the most challenging tasks in the field of bulk ceramics processing. This presentation introduces a simple method for consolidating low-concentrated nanoparticle suspensions into a bulk ceramics. The consolidation method was applied to a commercial 5 vol% zirconia nanosuspension with a particle size of 11-15 nm. The nanosuspension was first concentrated by osmotic dehydration in a liquid desiccant to 14 20 vol% of solid loading and then consolidated by centrifugation in non-porous moulds. It was shown, that homogenous plate samples with regular particle packing could be obtained from centrifuged bodies. The solid deposit with a relative density of 46% could be sintered to full density at a temperature as low as 1100°C. The advantage of regular particle packing by centrifugal compaction was utilized by fabricating transparent tetragonal zirconia ceramics. The real in-line transparency of 25% (0.5 mm thickness, 633 nm wavelength) was obtained for ceramics prepared by pressureless presintering and hot isostatic pressing at 1010°C for 3 h and 198 MPa of argon pressure.
CA-3:L04 Development of Aqueous Processing Routes for Alternative SOFC Materials in an Anode Supported Cell Design
M.C. VERBRAEKEN, M. CASSIDY, J.T.S. IRVINE, University of St Andrews, School of Chemistry, North Haugh, St Andrews, UK
Poor redox stability, sulphur and coking tolerance have been main drivers in finding alternative anode materials for the state-of-the-art Ni-cermets in Solid Oxide Fuel Cells (SOFC). A novel approach is to replace the Ni cermet with a redox stable, electronically conducting ceramic, whereas subsequent impregnation with electrocatalysts into the porous backbone can provide activity towards fuel oxidation. This concept has shown promising results in an electrolyte supported cell configuration on relevant SOFC scale. In this work we are now applying this concept to an anode supported cell configuration. The A-site deficient La0.20Sr0.25Ca0.45TiO3 shows good mechanical strength and is therefore chosen as substrate material. An aqueous tape casting process has been developed to produce the supports. Thick films could be cast through control of slip viscosity; the effect of solids content and binder system on rheological properties will be discussed. Thin electrolyte layers were subsequently deposited by either screen printing or tape casting and the assemblies co-fired. Flat ceramics with crack free dense electrolytes could be obtained. Optimisation of anode support microstructure to achieve optimum balance between mechanical strength, current collection and gas transport is ongoing.
CA-3:IL05 Consolidation of Alumina and Aluminium Oxynitride Powders using Hydrolysis of Aluminium Nitride
M.M. BUCKO, R. LACH, J. DOMAGALA, K. WOJCIECHOWSKI, AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Krakow, Poland
Aluminum oxynitride with spinel-type structure, γ-alon, is one of the materials with high potential for application as a refractory material. Alon materials, single-phase or composites, are characterized by good mechanical properties, high thermal shock resistance and a high corrosion and erosion resistance to molten metals and slags. Synthesis of γ-alon powders can be based on self-sustain high-temperature reaction (SHS) between aluminum and aluminum oxide powders. The SHS derived powders are relatively good sinterable, however they are characterized by poor compressibility. This work presents a simple method of compaction of γ-alon powders using the hydrolysis reaction of aluminum nitride, which is one of the by-products of SHS synthesis. The γ-alon powders with an addition of 10 mas.% of water were pressed at 100 MPa and kept in room temperature for a long time. After two weeks of storage they reach a strength level up to 30 MPa and an open porosity of less than 25%. These effects can be attributed to a formation of aluminum hydroxide phase (gibbsite) that bind bigger grains of γ-alon. Pressureless sintering of the compacts allows to achieve 95% of theoretical density at 1700°C during less than one minute. The same idea can be used for compaction of alumina powders.
CA-3:L06 Thick Film Processing Challenges in the Realisation of a Co-Fired Solid Oxide Fuel Cell Roll
M. CASSIDY, M. MACHADO, Y. KALECHEFF, M. ETCHES, J.T.S. IRVINE, University of St Andrews, School of Chemistry, St Andrews, UK
The Solid Oxide Fuel Cell Roll (SOFCRoll) is a novel design based on a double spiral. Combining structural advantages of tubular geometries with processing advantages of thick film methods, it utilises a single cofiring process. The initial concept used separate tape cast layers which were laminated before rolling. To optimise layer thickness to function, thinner screen printed layers were combined into the tape cast structure in 2nd generation cells. This presented several processing challenges, such as achieving dense electrolyte layers, maintaining porous electrode and current collecting layers and incorporation of integral gas channels. Performance has been promising with open circuit voltages close to 1V and cell power of over 400mW at 800°C, however cracking is still evident. Therefore further iterations are in development where thinner layers are sequentially cast, aiming to improve interfacial bonding and better match plasticity and burn out to reduce cracking. This paper discusses key aspects of understanding and controlling the behaviour and interaction of inks and slurries, such as plasticisation, particle dispersion and pore former addition, along with careful study and control of physical aspects of layer deposition such as the casting, printing, drying and firing.
CA-3:L07 Photopolymerization of Thin Ceramic Layers
P. FALKOWSKI, M. SZAFRAN, Faculty of Chemistry, Warsaw University of Technology, Warsaw, Poland
Shaping methods of advanced ceramic require application of diverse organic compounds which act as dispersants, binders, flocculants, plasticizers etc. If organic molecules have reactive double bond between two adjacent carbon atoms (C=C) it is possible to use such molecules as monomers in photopolymerization reaction. The photopolymerization reaction in ceramic processing gives a possibility to shape ceramic elements with complicated 3D structures (stereolithography) or to manufacture the ceramic tapes with complex surface topography (slip casting, tape casting, soft lithography). What is more, it is quite versatile technique which allows shaping ceramic-polymer composites or fully dense ceramics (after sintering).
In this work a photopolymerization of ceramic dispersions in UV curable monomer was used to manufacture thin ceramic layers by photo-tape casting method. The effect of particle size and powder concentration on viscosity, cure depth, polymerization shrinkage and relative density were investigated. In case of photopolymerization a photoinitiator concentration, conversion of double bond as well as oxygen inhibition were measured.
Acknowledgement: This work was financially supported by Polish National Centre for Research and Development (grant No. PBS1/A5/19/2012).
CA-3:L08 A Mixed SVD-neural Network Approach to Optimal Control of Ceramic Mould Manufacturing in Lost Wax Cast Processes
C. CARAMIELLO, S. IANNUZZI, Europea Microfusioni Aerospaziali, Morra de Sanctis (AV), Italy; D. D'ADDONA, University of Naples Federico II, Naples, Italy
We account for the problem of optimal control of ceramic mould manufacturing in lost wax cast processes with the aid of a mixed linear algebraic-statistical approach based on the employment of Singular Value Decomposition (SVD) and Neural Networks (NR).
We consider the peculiar aspect of minimizing ceramic inclusions occurrence in equiaxed superalloy turbine components which are manufactured resorting to gravitational pouring. The optimization consists in finding optimal extrema of scalar and/or vectorial functions of the type Rk→Rm i.e. Key Process Variable domain (KPV) vs. Target Variable domain (TV) over a large set of experimental data affected by acquisition noise and incomplete sampling leading to a typical sparse multiblock array.
The goal of the work consists in the assessment of possible significant statistical multivariate correlations amongst the KPV and TV when the dimension of domain space, k, has an order of magnitude of tens, in the presence of quasi-rank deficient input matrix.
Session CA-4 - Sintering, Grain Growth and Property/Microstructure Evolution and Characterization
CA-4:IL01 Recent Advances in Nano-scale Metallic and Ceramic Powder Sintering and Microstructure Evolution
O.A. GRAEVE, University of California, San Diego, La Jolla, CA, USA
A variety of techniques are currently available for the preparation of lightly agglomerated powders that result in controlled microstructures during sintering. This talk will present an overview of such techniques, with special emphasis on the effect of additives during sintering. Two model systems will encompass the bulk of the discussion, metallic glasses and high-temperature carbides. On metallic glasses, we will present fundamental phase stability and boundary structure of two Fe-based alloys and how sintering behavior can be modified by controlling surface interactions. We will also present the concept of a time-temperature-crystallinity diagram that can serve as a roadmap for determining changes in amorphous character with respect to time and temperature of sintering. Finally, we will describe sintering behavior of high-temperature carbides and the relation between powder morphology and size to sintered grain size. Special focus will be on tantalum carbide and the effect of transition metal additives on its synthesis and sintering effectiveness. Some of these additives include yttrium, zirconium, hafnium, niobium, and tungsten. Current progress and challenges will be discussed and analyzed.
CA-4:IL02 Fabrication of Translucent Silicon Nitride Ceramics by SPS
J. HOJO, W. YANG, M. INADA, N. ENOMOTO, Department of Applied Chemistry, Faculty of Engineering, Kyushu University, Fukuoka, Japan
Translucent Si3N4 ceramics are expected to be used for special optical applications in high-temperature and corrosive environment because of its thermal and chemical stability. In order to achieve high translucency, high density, and fine-grained microstructure appropriate sintering aids are required to reduce the light scattering by pores, grains and the grain-boundary phase. The spark-plasma sintering process was effective to obtain high-density sintered bodies with fine-grained microstructure. Another factor was the selection of sintering aid. The densification behavior, microstructure and translucency of sintered bodies were investigated in detail by using AlN-MgO, AlN-Y2O3 and Al2O3-Y2O3 sintering aids. When AlN-MgO and AlN-Y2O3 were used, SiAlON ceramics formed, exhibiting high translucency. Translucent Si3N4 ceramics were obtained when the content of sintering aid was small, even in Al2O3-Y2O3 system. For the translucency of Si3N4 ceramics using various oxide additives, most important was to reduce the difference in refractive index between grain and grain boundary phase. The translucent Si3N4 ceramics had excellent mechanical and thermal properties compared to translucent oxide ceramics.
CA-4:IL03 Densification and Microstructural Development in Anisotropic and Hierarchical Porous Ceramics
A. LICHTNER, H. SHANG, University of Washington; D. ROUSSEL, D. JAUFFRES, C. MARTIN, Université de Grenoble; R.K. BORDIA, Clemson University, Clemson, SC, USA
Porous ceramics are used in a broad range of electrochemical applications including electrodes for solid oxide fuel cells. These applications demand optimization of a multitude of properties many of which have conflicting requirements on the microstructure. The properties of interest are mechanical, thermal, electrical and ionic conductivity, gas diffusion and chemical reactivity. Materials with designed anisotropic and hierarchical microstructures have the potential to optimally address the requirements. In this presentation, results will be presented on the processing approaches to make these structures, the quantification of the 3D microstructure at different length scales and meso-scale simulations to simulate the mechanical and transport properties of these complex microstructures. The effect of external stresses during processing on the microstructural investigation has also been investigated. The results show that non-hydrostatic stresses lead to the development of anisotropic microstructures. There is a very strong effect of the scale of the microstructure on the induced anisotropy. These results, together with possible explanations for them, will be presented.
This research is supported by the USA's NSF, France's ANR and the Saint-Gobain Company.
CA-4:IL04 In Situ Platelet Reinforcement of Alumina and Zirconia Matrix Nanocomposites - One Concept Different Reinforcement Mechanisms
F. KERN, R. GADOW, University of Stuttgart - IFKB, Stuttgart, Germany
Zirconia-alumina composites are structural ceramics which due to their high strength and toughness are interesting in biomedical and engineering applications. Reinforcement of such materials with in situ formed platelets can improve fracture toughness and reliability, the mechanisms are however not yet fully understood. In this study alumina and zirconia based composites (ZTA and ATZ) reinforced with various hexaaluminates were investigated. In ZTA materials the main effect of platelets is the improvement of toughness as the the grain size distribution of the microstructure is broadened and transformability of the zirconia dispersion is improved. Crack deflection by platelets is unimportant, toughening is commonly achieved at the expense of strength and hardness. In case of zirconia based composites results are strongly depending on the type of stabilizer (Y-TZP or Ce-TZP) used and the type of hexaaluminates formed in situ. Here platelets can cause crack deflection and crack bridging. By variation of the composite recipes a multitude of compositions can be produced which have mechanical properties tailored for individual applications.
CA-4:IL05 Evolution of Microstructure during Sintering of Ceramics
SUK-JOONG L. KANG, Materials Interface Laboratory, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
In efforts to understand and analyze microstructural evolution during sintering, including grain growth and densification, numerous theoretical as well as experimental studies have been carried out in the last few decades. Several models and theories of densification and grain growth have been developed. The developed classical theories have been the basis for the interpretation and analysis of observed sintering phenomena until recently. In the development of the classical theories, use was always made of the assumption that the grain boundary is a perfect atom source/sink, which does not require energy for atom attachment/detachment. Our recent investigations, however, show that this assumption is not valid for faceted (atomically ordered) boundaries, which commonly appear in ceramics sintering. For systems with faceted boundaries, critical driving forces are needed for appreciable boundary migration and densification. Based on this result, a mixed control model of boundary migration (grain growth) is established and the principle of microstructural evolution is deduced. Recent experimental results for many systems support the applicability of the microstructure evolution principle for controlling the microstructure of ceramics during sintering.
CA-4:IL06 Atomistic Simulations from Dopant Segregation to Grain Boundary Complexions and Transparent Ceramics via a Microstructural Model
P. BOWEN1, U. ASCHAUER3, S. GALMARINI1, A. TEWARI1, S.C. PARKER2, F. NABIEI4, M. CANTONI4, C. HEBERT4, 1Laboratoire de Technologie des Poudres, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland; 2Department of Chemistry, University of Bath, Bath, UK; 3Materials Theory, ETH Zürich, Zurich, Switzerland; 4CIME, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
Ceramic properties are inherently linked to their chemical composition and microstructure. The transformation of a ceramic powder from a loose collection of particles into a sophisticated ceramic piece depends heavily on our capacity to control and modify the interfaces during processing and sintering. The use of dopants, which can segregate to both surfaces and grain boundaries during powder synthesis and sintering is a key phenomenon. Controlling grain growth and grain boundary composition is a key factor for the production of transparent polycrystalline ceramics such as yttrium aluminium garnet (YAG) and alumina. Using energy minimisation techniques the location, dopant concentration, grain boundary structure and, surface and interfacial energies have been investigated for a number of crystallographic surfaces in YAG and alumina for both single and copdoped ceramics. These data have then been used in a microstructural model to link these simulations with sintered grain sizes and grain boundary complexions. Atomistic modelling of a general grain boundary for Y-La doped alumina has shown very good agreement with high resolution analytical TEM showing a promising future for such simulation approaches.
CA-4:IL07 Ceramic Composites for Biomedical Applications: New Strategies for Tailoring Composition, Microstructure and Properties
P. PALMERO, L. MONTANARO, Dept. of Applied Science and Technology, Politecnico of Torino, Torino, Italy; J. CHEVALIER, V. GARNIER, Université de Lyon, INSA de Lyon, MATEIS UMR CNRS 5510, Villeurbanne, France
In the biomedical field, there is a strong requirement of long lasting devices based on new materials, presenting superior strength and toughness, optimal tribological properties and long term biocompatibility. In this frame, zirconia-toughened alumina (ZTA) composites have demonstrated their effectiveness for orthopaedic applications and recently the first composite femoral heads have been developed and commercialised. On the other side, tetragonal zirconia polycrystals (TZP) and zirconia-based composites have shown their feasibility for spine and especially oral implants, as these ceramics match biocompatibility, mechanical specifications and aesthetic properties, as required for dental applications. However, the main issue in these materials is keeping a homogeneous microstructure and a fine zirconia grain size, necessary to produce reliable biomedical devices with the expected performances. Most ZTA and TZP-based composites are currently produced by mechanical mixing of the constituent phases. This route can ensure neither a completely homogeneous dispersion of the second phase particles inside the zirconia matrix, nor even a rigorous tailoring of all the microstructural features of the sintered bodies.
In this frame, this work deals with a novel approach concerning both the materials design the and elaboration process of nano-composite materials, allowing an effective tailoring of the powder characteristics, final microstructure and properties, with the aim of fabricating biomedical devices characterized by a perfect reliability and a lifetime longer than 60 years. By this approach, a careful control and optimisation of the main ceramic processing steps is carried out, leading to robust relationships among composition, architecture and performances in terms of mechanical behaviour and durability. In particular, attention will be paid to the synthesis process of both alumina- and zirconia-based composite powders, by exploiting a simple but reliable powder coating method, able to assure the required microstructural features to the developed material; the drying and forming procedure will be optimized, being critical processing steps able to affect the green bodies homogeneity; finally, sintering will be optimized toward the fabrication of fully dense materials, in which a perfect tailoring of the microstructural parameters (grain size, distribution, morphological development of secondary phases) will be achieved.
CA-4:IL08 Grain Boundary Atomic Structures and Mechanical Properties in Oxide Ceramics
Y. IKUHARA, Institute of Engineering Innovation, The University of Tokyo, Tokyo, Japan; Nanostructures Res. Lab., Japan Fine Ceramics Center, Nagoya, Japan; WPI-AIMR Research Center, Tohoku University, Sendai, Japan
Doping ceramic materials with impurity ions have been a widespread technique for altering the properties of materials. In many cases, a macroscopic change is apparently observed, but characterizing the changes of the structure of the ceramics on the atomic scale remains a difficult task. Particularly in the case of ceramics, it is widely assumed that the dopants segregate to crystal defects (e.g. dislocations and grain boundaries (GBs)), as they are known to be sinks for impurity segregation. Recently, some studies have been performed on unraveling the atomic scale mechanism of dopant segregation to defects in GBs in ceramics. But, these researches have been mainly performed for the simple model GB with isovalent dopants w.r.t. the grain matrix. Because the number of ceramics and possible impurities are very large, a wide range of ceramic systems must be characterized to fully understand the segregation behavior at GBs in ceramics. In this study, complex dopants systems with aliovalent dopants and co-dopant are quantitatively investigated by combining high resolution scanning transmission electron microscopy (STEM) characterization and first principles calculations.
CA-4:IL09 Effect of Electrical Field and Atmosphere on the Processing of Nanocrystalline Zinc Oxide
B. DARGATZ, J. GONZALEZ, O. GUILLON, Otto Schott Institute of Materials Research, Friedrich Schiller University of Jena, Germany
The retention of nanocrystallinity in dense polycrystalline oxide materials is still a challenge, even with the application of stress-assisted methods like Spark Plasma Sintering. Interestingly, the combined effect of high heating rates and the presence of bound water seems to significantly promote densification of zinc oxide nanoparticles. Hence, dense nano-grained ZnO could be synthesized at a temperature of only 400 °C. In contrast, the sintering behavior of coarser powders is not affected by these conditions. The complementary roles of atmosphere, applied electrical field, pressure and heating rate on densification and coarsening mechanisms of zinc oxide will be highlighted in this talk.
CA-4:L11 Crystallization and Microstructural Evolution Process from Mechanically Alloyed Amorphous SiBCN Powder to Nano SiC/BN(C) Ceramic Sintered at Ultra-high Pressure and High Temperature
YU ZHOU, BIN LIANG, DECHANG JIA, ZHIHUA YANG, Harbin Institute of Technology, Harbin, P.R. China
The mechanically alloyed amorphous SiBCN powders were sintered at 1000, 1100, 1200, 1300 and 1400 °C under a pressure of 5 GPa for 30 min. The crystallization, the microstructural evolution, and the properties of the prepared ceramics were carefully studied by XRD, TEM, HRTEM, and property testing. Results show that the crystallization of β-SiC, turbostratic BN(C), and α-SiC in the amorphous matrix starts at about 1200 °C. Under a pressure of 5 GPa，When the powder is sintered at a temperature higher than 1300 °C, the prepared ceramics always consist of nano β-SiC, α-SiC, turbostratic BN(C), and amorphous body. With the increase of the sintering temperature, the ceramic crystallinity becomes higher, the grains get larger, and the amorphous content becomes lower. The bulk density increases with the increasing temperature. It is remarkable the fact that at 1100 °C, the nano-hardness and the Young's modulus of the prepared ceramics reach the maximum, about 30.2 GPa and 306.0 GPa, respectively. However, at temperature lower and higher than 1100 °C, the nano-hardness and the Young's modulus are both lower.
CA-4:L12 Sol-gel Derived Mullite-gahnite Composite
S. KURAJICA, E. TKALÈEC, V. MANDIC, I. LOZIC, University of Zagreb, Faculty of Chemical Engineering and Technology, Zagreb, Croatia; J. SCHMAUCH, University of Saarland, Saarbrücken, Germany
Mullite-gahnite composites with different phase-ratio were prepared by the sol-gel process. Crystallization path was determined by differential thermal analysis (DTA). X-ray diffraction (XRD) was used to study the development of crystal phases. Calcined amorphous precursors were further compacted and sintered. The course of thermal reactions is dominated by the intermediate formation of two spinel phases. The former phase was attributed to gahnite and the latter to Al-Si spinel. With temperature increase Al-Si spinel transforms to mullite releasing excess alumina, which reacts with amorphous SiO2-rich phase in the second step of mullitization. Zn loading decreases mullite and α-alumina while increases gahnite and amorphous phase. Mullite composition, temperatures and rates of the crystallization processes depend on the gahnite content. Microstructure was investigated by scanning electron microscopy (SEM). The observed microstructure, characterized by fine gahnite particles distributed among mullite acicular grains, is known to be highly favourable for ceramics with high mechanical requirements. The microstructure is also affected by the gahnite content, where the sample with the highest gahnite amount yields the largest mullite grains.
CA-4:L14 3D Phase-field Simulation and Characterization of Microstructure Evolution During Liquid Phase Sintering
H. RAVASH, J. VLEUGELS, N. MOELANS, Department of Metallurgy and Materials Engineering, KU Leuven, Heverlee (Leuven), Belgium
Liquid phase sintering (LPS) is widely used as a materials processing technique for high-temperature applications. In LPS, particle-particle contact size and distribution, 3-D coordination number, connectivity , and contiguity are important microstructure parameters which, to a large extent, determine the mechanical properties of the final materials. These features all depend on the grain size, solid volume fraction and dihedral angle during sintering.
The dihedral angle is an important parameter in LPS. It is the angle formed between the 2 solid-liquid interfaces at the intersection of a grain boundary with the liquid. A higher solid volume fraction, on the other hand, favors larger 3-D coordination number, connectivity , and contiguity. In practice, studying the correlation between these parameters and direct measurement of them is not a trivial task. Among them, 3-D measurement of dihedral angle is believed to be the most challenging one.
In the current study, phase-field modeling is employed to simulate LPS in two phase systems (solid and liquid). Simulations are performed for the different ratios of grain boundary to solid-liquid energies and the different solid volume fractions. To create initial structures with high solid volume fraction, an advanced particle packing algorithm is employed. An extended sparse bounding-box algorithm is used to speed-up the computations and makes it computationally efficient for 3D simulations. Contiguity, connectivity and, the three dimensional coordination number were measured in the self similar regime. The results were compared with empirical rules and experimental data and used to estimate the mean 3-D dihedral angle.
CA-4:L15 Development of High Properties Multilayered Ceramics
C. AHARONIAN, C. PAGNOUX, P.-M. GEFFROY, SPCTS, Limoges, France; N. TESSIER-DOYEN, GEMH, Limoges, France
The development of lightweight, cheap and high strength ceramics based on alumina or alumino-silicate compositions, is of interest in a wide variety of applications including aerospace or defense industries. Combination of different ceramic components in multilayered ceramic architectures may increase overall strength, toughness and thus impact resistance. The aim of this study is to develop inexpensive and easy processing multilayered multi-phase materials combining different oxide based constituents to improve mechanical properties mainly by inducing internal residual stresses.
Elaboration routes including tape casting allow designing several configurations of microstructures in layered composite ceramics. The monitoring of thermal expansion mismatch between the constituents during the thermal cycle of sintering is necessary to keep the integrity of samples. Ultrasonic pulse echography characterization and Charpy impact test have been performed to evaluate and compare the final properties. From macroscopic point of view, the performances of these multilayered materials are finally closely monitored by few parameters, such as density, Young's modulus and acoustic impedance.
CA-4:L16 Influence of Alumina Addition on Low Temperature Degradation of Y2O3-Coated Powder Based Y-TZP ceramics
FEI ZHANG, K. VANMEENSEL, J. VLEUGELS, Department of Metallurgy and Materials Engineering (MTM), KU Leuven, Leuven, Belgium; M. INOKOSHI, B. VAN MEERBEEK, I. NAERT, BIOMAT, KU Leuven, Leuven, Belgium
The influence of the addition of 0.25, 2 and 5 wt.% alumina on the mechanical properties and low temperature degradation (LTD) behaviour of 2, 2.5 and 3 mol% yttria-coated ZrO2 powder based Y-TZP ceramics was investigated. The ceramics were subjected to accelerated hydrothermal degradation in an autoclave in H2O at 134°C up to 40 hrs. X-ray diffraction and Raman spectroscopy were used to assess the LTD behaviour.
Incorporating the Y2O3 stabilizer by means of a coating method resulted in a higher LTD resistance without compromising the higher fracture toughness, compared to the co-precipitation method. Alumina additions did not significantly influence the mechanical properties of all Y-TZPs, but significantly increased the LTD resistance of Y-TZP ceramics with 0.25 wt.% alumina doped TZPs having the highest hydrothermal stability.
The LTD susceptibility of Y-TZP ceramics increased with decreasing yttria content. Independent on the yttria content, the LTD resistance of 0.25 wt% Al2O3 doped TZPs was substantially higher than that of ceramics containing 2 or 5 wt.% Al2O3, which had a comparable susceptibility. The highest LTD resistance for the 0.25 wt.% alumina doped ceramics could be correlated to the solubility limit of alumina in zirconia.
Session CA-5 - Innovation in Fabrication and Technology
CA-5:IL01 Space-selective Pulsed Heating for Fabrication of Submicrometer Ceramic Spherical Particles
N. KOSHIZAKI, Hokkaido University, Sapporo, Hokkaido, Japan; Y. Ishikawa, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Recently we found that submicrometer spherical particles of ceramic oxides (ZnO, TiO2, etc.) can be produced by irradiating low-fluence laser onto raw nanoparticles dispersed in liquid. In this process, raw nanoparticles are not vaporized nor ablated but melted by nanosecond laser irradiation to form liquid droplets, resulting in spherical particle formation by quenching. Thus, this process "laser melting in liquid" is evidently different from the conventional technique, "laser ablation in liquid" for nanoparticle fabrication using high-fluence laser irradiation in liquid.
Essential point of this technique is space-selective pulsed heating of the raw nanoparticles dispersed in liquid. Space selectivity is introduced by the difference in optical absorption coefficient between raw nanoparticles and surrounding liquid. Pulsed heating is provided by the nanosecond pulsed laser, which supplies sufficient energy to melt a particle before heat dissipation to the surroundings.
The spherical particles obtained by this technique have many advantages over nanoparticles due to their spherical shape. Examples of their various applications are demonstrated in the presentation.
CA-5:IL02 Hydrothermal Reactions for Synthesis/Preparation of Nano-Materials with Desired Shapes, Sizes and Structures for Oxides and Carbons
M. YOSHIMURA, Promotion Center for Global Materials Research, Dept. Mater.Sci. & Eng., National Cheng Kung University, Tainan, Taiwan, Professor Emeritus of Tokyo Institute of Technology, Japan
Hydrothermal reactions have more widely been recognized in natural and artificial systems on the earth1). Particularly, the formation, production, alteration, decomposition of all substances and materials in natural systems are always related with the action of water (aqueous solutions). The origin and development of life might be influenced by the action of aqueous solutions most probably around the hydrothermal vents in deep sea2). Not only the bio-systems but also artificial materials systems can be related to the actions of water.
In the present lectures, I will summarize Hydrothermal reactions on various natural and artificial materials. Hydrothermal Syntheses of Nano-particles3),ZrO2,CeO2, (Zr,Ce)O2,HAp, Fe3O4,TiO2,BaTiO3,etc. Nanostructured Films2,4) of BaTiO3, SrTiO3, LiCoO2 , BaWO4 CaWO4, HAp etc. ,and  Nanostructured Patterns5) of BaTiO3,Carbon,etc. established in our group will be reviewed. In the formation of films,
additional activation(s) with thermal one are very useful. Particularly electrochemistry is very attractive to prepare oxide films and patterns. Recent proposal: Growing Integration Layer[ GIL] method6) is also using electrochemistry to make oxide layer(s) on metallic material(s) to improve adhesion, anti-oxidation, bioactivity and/or other functionalities. A novel subject, "Hydrothermal Carbons"7-12) where various nano-carbon materials can be prepared by hydrothermal reactions, will be introduced. Recent Graphene and functionalized Graphene formation in solutions will be introduced13-14).
1) M. Yoshimura, J. Mater. Sci., 41  1299-1306 (2006)
2) M. Yoshimura and K. Byrappa, J. Mater. Sci., 43  2085-2103 (2008)
3) T. Taniguchi, M. Yoshimura, et al, J.Phys.Chem.C, 112(2008),4884,&113 (2009), 839-843, Y. Kolenko, M. Yoshimura et al, J. Phys.Chem.C, 111(2007)7306
4) D. Rangappa, M. Yoshimura et al, Mater. Res. Bull. 43(2008), 3155-3163
T. Watanabe and M. Yoshimura, Thin Solid Films, 515(2006), 2696-2699
5) M. Yoshimura, R. Gallage et al, Solid State Electrochem. 12(2008) 775-782, & .Am.Ceram. Soc., 91(2008),2083-2087, Thin Solid Films, 517(2009),4515
6) M. Yoshimura, N. Sugiyama et al, Mater. Sci. Eng. B,148(2008)2-6, & Acta Biomaterialia, 5(2009),1367-1373, Mater. Sci. Eng. B,161(2009),31-35
7) Y. Gogotsi and M. Yoshimura, Nature, 364,(1994),628-630
8) Wang Hao and M. Yoshimura, Chem . Phys. Letters, 348 (2001),7-10
9) W. Suchanek et al, J. Solid State Chem., 160(2001), 184-188
10) V.G. Pol, A. Gedanken, et al, Carbon, 42(2004)111-116
11) B. Basavalingu et al, J. Mater. Sci., 43(2007), 2153-2157
12) T. Watanabe, M. Yoshimura et al, Carbon, 44(2006), 799-802
13) J. Senthilnathan, M. Yoshimura et al, Sci. Reports, 3, 2414, Aug.12, 2013
14) J. Senthilnathan, M. Yoshimura et al, Carbon, to be published.
CA-5:IL03 Electronic/Ionic Conducting Oxide Particles Added Si Nanocomposite Fibers for High Performance Anodes for Li-Ion Battery
DONGHA KIM1, DAEHEE LEE1, JOOSUN KIM2, JOOHO MOON1, 1Department of Materials Science and Engineering, Yonsei University, Seoul, Republic of Korea; 2High-Temperature Energy Materials Research Center Korea Institute of Science and Technology, Seoul, Republic of Korea
Si is one of the most attractive anode materials as an alternative to conventional graphite anode because of abundance and higher theoretical capacity of 4,000 mAh g-1 than that of 372 mAh g-1 for graphite. Though high specific capacity, Si based anode suffers from drastic volume change (over 300%) induced pulverization and intrinsic low electrical conductivity, both of which lead to capacity fading and poor rate capability during the charge/discharge cycles. Herein, we designed one pot core-sheath composites fibers in which Si nanoparticles (NPs) are enclosed inside carbon hollow fiber with inner electronic/ionic conducting oxide nanoparticles by co-electrospinning. Encapsulating Si nanoparticles by hollow nanofibers allows alleviate significant volumetric change, while carbon sheath is not only rigid structure to release the inner Si volume expansion stress but also blocking directly contact between liquid electrolyte and Si NPs so as not to continually grow SEI. Furthermore, it also promotes the electrical conduction even in the absence of additional conducting carbon phase through inner oxide NPs which have high electronic/ionic conductivities, so that inner oxide NPs are able to facilitate the electron transport and the lithium diffusion, leading to high rate capability.
CA-5:IL04 Texture Developing and Some Properties of Ceramics by Colloidal Processing in a Strong Magnetic Field and Sintering
Y. SAKKA, CHUNFENG HU, K. TATO, T.S. SUZUKI, T. UCHIKOSHI, National Institute for Materials Science (NIMS), Tsukuba, Japan
The controlled development of texture is one of the ways for effectively improving properties of ceramics. We have demonstrated a new processing of textured ceramics with a feeble magnetic susceptibility by colloidal processing in a high magnetic field and subsequent heating. The principle of the process is that a crystal with an anisotropic magnetic susceptibility will rotate to an angle minimizing the system energy when placed in a magnetic field. Some trials have been presented to fabricate highly textured ceramics using template particles, changing magnetic susceptibility of different cationic doping, rotation magnetic field, etc. This processing can be applied to fabricate many kinds of textured ceramics with non-cubic structure, such as alpha-alumina, aluminium nitride, silicon carbide, silicon nitride, MAX phase materials, ZrB2, B4C, etc. Crystalline-textured controlled laminated composites can be fabricated by two methods: one is textured layered structure materials, such as textured MAX phase ceramics, and the other is using electrophoretic deposition by varying the angle between the vectors of electric field and magnetic field. Some anisotropic properties, such as mechanical properties, thermal conductivity, oxidation resistance, etc. will be demonstrated.
CA-5:IL05 Formation of Nanostructured Titania on High Aspect Ratio Microstructures: A Novel Wicking Material for Thermal Management
A.S. ZURUZI, Engineering Product Development Pillar, Singapore University of Technology and Design, Singapore
Due to the persistent trend of miniaturization, heat dissipation is an important issue that needs to be addressed in the coming generations of microelectronic components. Because of the large latent heat of vaporization, two-phase cooling technologies are attractive for thermal management in such components. In line with the trend of harnessing unique properties at the nanoscale to enhance the cooling performance, we demonstrate here a novel wicking material consisting of nanoporous TiO2 grown on Ti micropillars. Nanostructured titania was formed on high aspect ratio titanium structures using a simple technology involving oxidation in aqueous hydrogen peroxide followed by annealing. These high aspect ratio structures with nanostructured titania surface and titanium core have excellent hydrophillic properties which bodes well for thermal management applications. Compared to those using copper based wick materials, heat pipes using nanostructured titania/Ti ones have better capillary speed characteristics which decays at a slower rate.
CA:P01 Characterization of Calcium Phosphate Biomaterials
F. LAMONACA1, M. VASILE2, GRIMALDI1, A. NASTRO3, 1Department of Computer Science, Modeling, Electronic and System (DIMES), University of Calabria, Rende (CS), Italy; 2Medical School, Ovidius University of Constanta, Romania; 3Chemical Department, University of Calabria, Rende (CS), Italy
The sinterized hydroxyapatite is characterized by high crystallinity that makes it difficult to integrate in the bone turnover. Recently different methods to prepare Calcium Phosphate (CP) manufact characterized by different crystallinity are presented. For medical application lower crystallinity means a more similar behavior of the manufact respect to natural bones, and then a easier integration. In this paper we propose a new method to characterize the microstructure and composition of hydroxyapatite. The characterization method pointed out is based on measurement techniques used for civil engineering materials. Therefore, it is possible to assess that the obtained results depend only by the material under test and not by the specific measurement method. The experimental tests, were conducted on different CP manufact and on a compact bovine bone. Each one was characterized by XRD, HV test, SEM and porosity evaluation. Experimental results shows that the samples obtained thought hydrothermal treatment, have mechanical, chemical and physical characteristics much similar to the natural bone ones respect to the commercial ones.
CA:P03 Characteristic and Sinterability of Alumina-Zirconia-Yttria Nanoparticles Prepared by Different Chemical Methods
J. GRABIS, D. JANKOVICA, I. STEINS, I. SIPOLA, RTU Institute of Inorganic Chemistry, Salaspils, Latvia
The aim of the present work was to compare characteristics and sinterability of the Al2O3-ZrO2(Y2O3) nanoparticles produced by simple and effective microwave and molten salts methods and processed by using spark plasma sintering.
Experiments were performed by using Zr, Al, Y reagent grade salts. For molten salts (MS) synthesis the Zr, Al and Y salts were mixed with definite amount of NaCl and NaNO3. The microwave (MW) synthesis of dissolved salts with NH4OH or urea additives was conducting using MasterBTR reactor at 180 °C during 20 min at pressure about 26 bar.
The prepared powders by both methods and calcinated at 600 °C Al2O3-ZrO2-Y2O3(3 mol%) and Al2O3-ZrO2 nanoparticles with Al2O3 content above 10 wt.% consisted of t-Al2O3 and t-ZrO2 phases. The specific surface area of powders prepared by MS and MW synthesis were in the range of 79.3-166.0 m2/g and 101.2-124.7 m2/g respectively depending on the content of Al3O3 and synthesis parameters.
The prepared samples were densified by using spark plasma sintering (SPS-825-CE) in vacuum at 1300-1600 °C and 30 MPa. Densification of the particles starts at 850-900 °C and bulk materials with fine-grained microstructure and relative density in the range of 96-98.5% were obtained at 1500 °C.
CA:P05 Characterization and Preparation of High Lithium Ion Conductive NASICON-type Ceramics by Phosphate Assisted Sol-gel Method
E.C. BUCHARSKY, K.G. SCHELL, M.J. HOFFMANN, Karlsruhe Institute of Technology, Institute for Applied Materials, Ceramics in Mechanical Engineering, Karlsruhe, Germany
Ultrapure phase lithium titanium aluminum phosphate (LATP) solid electrolytes were prepared by the sol gel method. LATP glass was converted to glass-ceramic by heat treatment in the range 400-900 °C, the consolidation process being made by Field Assisted Sintering "FAST". The resulting phase composition, crystal structure and theoretical density were obtained from XRD measurements. Electrical properties of the samples, such as ionic conductivity, were calculated from the frequency response in the range 5 MHz - 50 Hz. The ionic conductivity of the sintered pellets was investigated and correlated with its density and crystal structure. The main reason for the conductivity enhancement seems to be ascribed to the increase of the sintered density and its pure phase, reaching a maximum of 10-3 S cm-1 at room temperature.
The mechanism of lithium ion conduction is not clearly understood yet. In this work, we review the structural properties, electrical conductivity, and electrochemical characterization of LATP materials.
CA:P06 Development of Highly Dispersed Hybrid Nanoalumina with the Sol-Gel Method
F. PETRAKLI1, D. SIOULAS2, A. TSETSEKOU1, 1School of Mining and Metallurgical Engineering N.T.U.A, Athens, Greece; 2Department of Materials Science and Engineering, University of Ioannina, Ioannina, Greece
A hybrid sol-gel method was employed to develop a uniform and highly dispersed alumina nanopowder in the presence of hyperbranched dendritic poly(ethylene)imine (PEI) acting as template material and complexation agent for aluminium ions. For this purpose, the hydrolysis and polycondensation reactions followed the compexation reaction between the Al precursor and PEI, whereas ammonium polymethacrylate was added to improve the powder dispersion. The as-formed nanopowder was characterized before and after calcination in the temperature range 200-1200 oC. For this purpose Scanning Electron Microscopy (SEM), Field Emission SEM, Transmission Electron Microscopy (TEM), X Ray Diffraction (XRD) Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric and Differential Thermal Analysis (TG-DTA), N2 porosimetry and ζ-potential measurements at different pH were carried out.
The analysis confirmed the successful formation of a boemite-PEI hybrid of uniform spherical crystals (~ 10 nm) and small agglomerates (~ 1 μm). Transformation of boemite is completed at 600 °C resulting in a stabilized γ-alumina which remains almost the only phase up to 1000 °C. This material is investigated regarding the shaping and sintering possibilities to develop nanostructured alumina.
CA:P07 Ceria-based Mixed Oxides UV Filters Obtained by an Innovated Sol-Gel Route for Photoprotection Application
J. FONSECA DE LIMA, J.L. CUNHA, O.A. SERRA, Department of Chemintry/FFCLRP, University of Sao Paulo, Ribeirao Preto, Sao Paulo, Brazil
Ceria, titania and zinc oxide individually have been investigated as UV filters in cosmetics and other applications. These oxides nanoparticles exhibit the ability to scatter UVB and UVA radiation; furthermore, the mechanism of these UV filters also involves UV light absorption leading to an appreciable photocatalytic activity (PA), which can catalyse the formation of many oxidizing reactive species. In order to decrease the PA rates, mixed oxides UV filters were synthesized by Sol-Gel method in a sealed autoclave, and using microwave radiation to take advantages of the different oxides properties and minimize their disadvantages. The ZnO:TiO2:CeO2 and ZnO:CeO2 were prepared using zinc acetate dehydrate, titanium tetraisopropoxide and cerium nitrate as starting materials. These reagentes were mixed in an appropriate stoichiometry to give a solution with desired Zn:Ti:Ce ratio. The solutions were submitted to different conditions of heat and pressure to obtain the solid systems. The mixed oxides were characterized by FTIR, DRX, SEM, TEM and DRS. The PA study was assessed by the conductometric determination method with an UV-Vis lamp to simulate the solar radiation. The systems showed high UV absorption and low PA. The mixed oxides systems are promising candidates as UV filters.
CA:P08 Study of Gamma Alumina Synthesis
R.R. RIBEIRO, H. DE PAIVA, M.V. SURMANI MARTINS, L. FIGUEIREDO DE MIRANDA, E.C. DE OLIVEIRA; R. CONS ANDRADES, A.H. MUNHOZ Jr., U.P. Mackenzie, Santo André, Sao Paulo, Brazil
Different samples of pseudoboehmite (PB) were synthesized through the sol-gel process, using aluminum nitrate as its precursor. The influence of variables on the synthesis and calcinations of the PB on the specific area of the obtained gamma-Alumina were studied. The variables were the ageing temperature (25 and 130o C), addition or no addition of polyvinyl alcohol to the precursor solution and the ageing time of the PB. The pH adjustment of the precursor solution was made by using ammonium carbonate. The products, which were obtained on the synthesis, each one obtained on a different condition, were then characterized by x-ray diffraction, specific area measurements through the BET process, and by thermal analysis (DTA, and TG). After characterization, the synthesis products were calcined at 500ºC, following the gamma-Alumina transformation, and the calcination products were characterized by the same methods (x-ray diffraction, BET, DTA and TG), but it were also obtained the desorption-absorption curves and the t-plot curves, for the micropore volume analysis of the samples. Finally, the results were analyzed following an experimental factorial planning and showed that high specific area gamma-Al2O3 (around 330m²/g) can be obtained through this process.
CA:P09 Synthesis and Characterization of Nanocomposite HA/α-Al2O3 Sol-Gel Powders for Biomedical Applications
N.H.A. CAMARGO, P. CORRÊA, P.F. FRANCZAK, E. GEMELLI, Santa Catarina State University - UDESC, Program in Materials Science and Engineering, Mechanical Engineering Department, Joinville - SC, Brazil
The calcium phosphate nanostructured bioceramics and nanocomposites with calcium phosphate matrix are subjects of research and have raised scientific, political, industrial and commercial interest because these biomaterials present differentiated properties from microporosity, bioactivity and cell adhesion on the surface of grain and micropores compared to conventional biomaterials. This work aimed at the wet synthesis of a nanostructured hydroxyapatite bone matrix for subsequent preparation of hydroxyapatite/α-Al2O3 sol-gel nanocomposite powders, at concentrations 1, 2, 3 and 5% in volume of nanocrystalline α-Al2O3 dispersed in inter-intragranular position in the hydroxyapatite matrix. The method used for the preparation of HA/α-Al2O3 nanocomposite powders was high-energy attrition milling. This method allows obtaining nanocomposite powders formed by fine particles with size smaller than 100nm. The technique of scanning electron microscopy served for observation of morphology, microstructure and nanostructure. The X-ray diffractometry, laser particle analysis method and differential thermal analysis technique were used to identify the phases, particle size and thermal behavior for nanostructured powders retrieved from the attrition milling.
CA:P11 Synthesis of Silicon Carbide from Graphite and Silicon Using Sodium
H. MORITO, H. YAMANE, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
Recently, we reported the formation of nano-particulate and porous bulk of SiC at 1000 K from a mixture of Si and amorphous carbon powder by the Na flux method. While this procedure yielded SiC when amorphous carbon was used as the carbon source, it did not afford SiC when graphite was used as the carbon source. The purpose of the present study is to find conditions under which SiC is formed by the reaction of Si and graphite with Na, and to characterize the morphology and crystal structure of the resulting SiC samples.
SiC was prepared by heating a mixture of graphite and Si powders with sodium at the temperature range 1173-1273 K. No formation of SiC was observed by heating the mixture without sodium at the same temperature range. The XRD reflection peaks from the SiC sample prepared at 1273 K were indexed with a cubic lattice parameter (a = 0.436 nm), which was identical to that of beta-type SiC. The sample was the aggregates of truncated hexagonal pyramid-shaped SiC crystals with a size of a few hundreds nanometers, as evidenced by scanning electron microscopy. Transmission electron microscopy and electron diffraction revealed that the crystals contained stacking faults along  of the cubic lattice of beta-type SiC.
CA:P14 A Thermodynamic Approach of the Alumina Powder Properties Prepared by Combustion Synthesis
R. IANOS, R. BABUTA, R. LAZAU, "Politehnica" University of Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Timisoara, Romania
Different fuels (valine, β-alanine, glycine and urea) were tested for obtaining nanocrystalline α-Al2O3 powders via solution combustion synthesis. Aluminium nitrate nonahydrate was used as an oxidizing agent. The resulted samples have been characterized by TG-DTA, SEM, XRD and BET measurements. Urea led to a self-propagated exothermic combustion reaction, whilst the other fuels led to smouldering combustion reactions. XRD patterns revealed that urea was the only fuel that enabled the formation of crystalline corundum directly from the combustion reaction. All the other fuels led to grey-black amorphous powders. For a better understanding of fuel action on alumina powder properties, the standard enthalpies of reaction were calculated. Even if the calculated standard enthalpies of reactions had relatively close values (valine: -1480 kJ/mol, β-alanine: -1452 kJ/mol, glycine: -1391 kJ/mol, urea: -1235 kJ/mol) and point that all combustion reactions should be highly exothermic, the real situation was different.Therefore, the various actions of the used fuels led to many uncertain aspects. The innovative explanation relied on the velocity of heat generation (kJ/sec), which was much higher in the case of urea-aluminium nitrate combustion reaction - as evidenced by thermal analysis.
CA:P15 Synthesis and Characterization of Nanocrystalline YAlO3 and Cr3+-doped YAlO3 Powders
R. IANOS, R.I. LAZAU, S. BORCANESCU, "Politehnica" University of Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Timisoara, Romania
Two different directions were approached in order to achieve pure YAlO3 and chromium-doped YAlO3 powders: solution combustion synthesis and the conventional solid state reaction. Yttrium nitrate, aluminium nitrate, urea and glycine were used as raw materials for combustion reactions. Yttrium oxide and aluminium oxide were used in the conventional method. The resulted samples were characterized by TG-DTA, XRD, CIEL*a*b* and SEM measurements. Single fuel recipes, based on urea or glycine, failed to yield single phase YAlO3. The use of urea and glycine fuel mixture triggered a very fast (28 seconds) and exothermic combustion reaction which enabled the formation of the desired perovskites (YAlO3, YAl0.95Cr0.05O3) directly from the combustion reaction, without any additional annealing. The obtained YAl0.95Cr0.05O3 had a pink colour and an average crystallite size around 50 nm. Subjecting the powder to further thermal treatment did not lead to a significant colour enhancement. In the case of the sample prepared by solid state reaction, the formation of pink single phase YAl0.95Cr0.05O3 was not achieved not even after annealing the starting raw materials at 1200 °C for 1 hour. In this case, the use of CaF2 as a mineralizer significantly enhanced the development of the pink colour.
CA:P18 Structural and Electrical Properties of (1-x)Pb (Zry Ti1-y)O3-xSm(Fe3+0.5, Nb5+0.5)O3 Ceramics Prepared by Conventional Solid State Synthesis and Sintered at Low Temperature
F. KAHOUL, L. HAMZIOUI, A. BOUTARFAIA, Université Kasdi Merbah, Département de Génie des Procédés, Faculté des Sciences Appliquée, Ouargla, Algérie; and Département de Chimie, Laboratoire de Chimie Appliquée, Université de Biskra, RP-Biskra, Algérie
The phase structure, microstructure and electrical properties of (1-x)Pb (Zry Ti1-y)O3-xSm(Fe3+0.5, Nb5+0.5)O3 (PZT-SFN) (with x = 2 %, 41%≤ y ≤57 %) piezoelectric ceramics prepared by the conventional solid state method, and effects of SFN and the Zr/Ti ratio content on the piezoelectric properties of PZT ceramics were investigated. A stable solid solution has been formed between PZT and SFN, and a morphotropic phase boundary of PZT-SFN ceramics is identiﬁed in the range of 51% ≤ y ≤55 %). The Curie temperature of PZT-SFN ceramics decreases with increasing at Zr/Ti ratio content. A higher εr value and a lower tan δ value are demonstrated for the PZT-SFN ceramics with y = 53 %. The PZT-SFN ceramics with y = 53 % has an enhanced electrical behavior of d31 ~ 115 pC/N, g31 ~18*10-3 m V/N, kp ~ 63 %, Qm ~ 454, εr ~ 1165, tan δ ~ 2.027 % and TC ~ 370 OC. As a result, PZT-SFN ceramics are promising candidate materials for the ﬁeld of lead piezoelectric materials and piezoelectric device.
CA:P19 Structural and Electrical Properties of Ca2+ Substituted Pb[(Zr0.52Ti0.48)0,98(Cr3+0.5, Ta5+0.5)0,02]0,96 P0,04 O 3 Ceramics
L. HAMZIOUI, F. KAHOUL, A. BOUTARFAIA, Université Kasdi Merbah Ouargla, Département de Génie des Procédés, Faculté des Sciences appliquée, Ouargla, Algérie; and Université Mohamed Khider Biskra, Laboratoire de Chimie Appliquée, Université de Biskra, RP-Biskra, Algérie
PbxCa1-x[(Zr0.52Ti0.48)0,98(Cr3+0.5, Ta5+0.5)0,02]0,96 P0,04 O 3 (x = 0,00, 0.02, 0.04, 0.06) ceramics were prepared using the conventional mixed-oxide route. The resultant samples were sintered at different temperatures and subsequently characterized in terms of both microstructure and dielectric properties to study effects of sintering behavior. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase and exhibits a phase transition from a rhombohedral phase to the coexistence of rhombohedral and tetragonal phases with an increase of sintering temperature. The grain size first increases up to x = 0.02 and then decreases. Comparing with the undoped ceramics, the dielectric properties of the Ca-doped PZT-PCTP specimens are significantly improved. The results show that the ceramics sintered at 1180 °C have optimum electrical properties for x= 0.02: a high dielectric constant (εr = 16800) at Tc, a low dissipation factor (tanδ = 0.009) and a low resistivity (ρ= 0.09 ×10+4) (Ω.cm) at 1 kHz, which indicates that the PZT-PCTP ceramics are promising for lead practical applications.
CA:P21 Microstructural Characterization of Activated Carbon Obtained from Waste Tyres
F. MAZZANTI, G. MAGNANI, S. GRILLI, ENEA-UTTMATF, Faenza, Italy; A. BRILLANTE, T. SALZILLO, University of Bologna, Italy; A. BRENTARI, E. BURRESI, Certimac s.c.a.r.l., Faenza, Italy
SOREME project (LIFE 11 ENV/IT/109) is aimed to the synthesis of innovative sorbent based on activated carbon obtained from the carbonization of waste tyres. Microstructural characterization was mainly performed in order to define crystallinity, morphology and porosity of the activated carbon powders obtained in different conditions. In particular, XRD analysis always revealed a partially crystalline structure with different crystallite size of the nanographitic structure. The disorder of these structures was determined by Raman spectroscopy. This evaluation was made on the basis of the ratio of the integrated area of the D and G bands typical of the graphitic structure. Finally, SEM was used to put in evidence the powder morphology. Mesopores and macropores were always revealed and the porosity changed as a function of the process conditions.
CA:P22 Reaction Mechanism of Mullite Formation in Alpha-Al2O3/Cristobalite Powder Systems
PEI-CHING YU, YUNG-WEI TSAI, FU-SU YEB, Department of Resources Engineering, National Cheng Kung University, Tainan, Taiwan
The reaction mechanism of mullite formation by a solid-state reaction in an α-Al2O3/cristobalite (SiO2) powder system and the diffusion between the two constituents were examined. Three α-Al2O3 powders with D50 values of 230, 320, and 400 nm were mixed with the same cristobalite powder of D50 430 nm in a stoichiometric composition of 3Al2O3∙2SiO2, giving samples of various particle number ratios of SiO2/Al2O3 that can be used to relating the constituent diffusion between SiO2 and Al2O3. Pressed samples prepared by the mixtures were heated at various temperatures. The results showed that mullite formation is related to the amorphization of cristobalite particles that take places during the thermal treatment. Then the Si component diffused into the α-Al2O3 particle to form mullite via nucleation and growth. A size reduction of α-Al2O3 particles lowered the temperature for cristobalite amorphization, resulting in the mullite formation temperature reduction. Mullite particles with a multi-domain structure were observed in the α-Al2O3 particle matrix. The crystal orientation and the particle size of the mullite were controlled by the α-Al2O3 matrix. These results indicated the α-Al2O3 particles act as hosts for mullite formation.
CA:P23 Synthesis and Sintering of Alumina-borides Powders Obtained by High-energy Ball Milling
V.R. CERQUEIRA1, J.J. PIERRI2, R. TOMASI2, E.M.J.A. PALLONE3, 1Departamento de Construção Civil (UNED-Imperatriz-MA); 2Universidade Federal de São Carlos - DEMa; 3Universidade de São Paulo - FZEA, Brazil
Aluminothermy activated by a high energy milling process has been utilized in the synthesis of composite powders of alumina and a variety of high hardness phases such as carbides and borides. An important advantage is the short time milling for the ignition of a self sustained reaction and the total reaction completion. The disadvantage is the large amount of alumina in the reaction products and the formation of large aggregated product particles. The milled products dispersed in high reactive alumina powder results in high hardness and wear resistant composites of alumina with nanometric inclusions of carbides and borides. This work objectified verifies experimentally the viability of synthesis and sintering of alumina-borides powders obtained by high-energy ball milling without dilution in alumina. Compositions in the system alumina/WB2 /TiB2 were considered. It was observed the effect of precursors on phase composition, the effect of the milling time on sintering behavior (pressureless sintering at 1600-1700 °C.The final microstructures where analyzed by SEM. The variations on products phase composition where attributed to the complexity of the system W-B which probably may be associated to the range of sintered densities(70 to 96%) and grain size and phase distribution.
CA:P24 Composition - Property Relations in Shear Thickening Fluids
L. WIERZBICK, M. LEONOWICZ, Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland
The studies revealed that silica fumed (SF), dispersed in various olygomers, forms shear thickening fluids (STF) having useful practical properties. Silica nano-powders, having various size and olygomers, with different molecular weight, were tested. It has been indicated, that the increasing volume fraction of a solid phase causes greater dilatancy effect. Higher molecular weight of the olygomer provides higher viscosity values, but the abrupt change of the viscosity is obtained at lower share rates. The highest viscosity value was obtained for the material composed of SF and poly(propylene) glycol PPG400, however, the best combination of the properties (high viscosity, obtained at high shear rate) represents the material composed of the SF and poly(ethylene) oxide PEO300. Change of the volume fraction of the SF and variation of the molecular weight of the olygomer enables tailoring of the STF properties.
The shear thickening fluid obtained was tested in the composite system, consisting of paraaramide fabric with colloidal insert, for the bulletproof properties, against parabellum 9 mm. Improved flexibility of such armour was demonstrated.
CA:P25 Freeze-granulation of Nanometric and Submicronic Barium Titanate Powders
A. WAJLER, A. SIDOROWICZ, H. WÊGLARZ, U. BRYKALA, K. JACH, Institute of Electronic Materials Technology, Warsaw, Poland
Transparent ferroelectric materials are used in a wide variety of electro-optical devices. Among them, great attention attracted last years transparent ferroelectric ceramics. Polycrystalline materials have many practical advantages over single crystals, but reaching the high optical quality of ceramics is difficult and strongly depends on all processing steps. One of the crucial points in preparation of porosity-free ceramics is proper adjustment of green bodies shaping. The main granulation method used in ceramic processing is spray drying but recently freeze-granulation gains increasing interest.
The work presents the attempts to produce barium titanate granulates basing on water suspensions of nanometric and submicronic powders. The relations between the type of BaTiO3 powder used, suspension solids content, amount of dispersant and binder, granulation process parameters and granulate properties were studied. The shape, size distribution, internal homogeneity and pore size distribution of the granules was evaluated.
The project "Preparation and properties of translucent barium titanate ceramics" is realized within the POMOST program of Foundation for Polish Science, co-financed from European Union, Regional Development Fund.
CA:P27 Study on Processing Conditions of Making RBSC Radiant Tube Using Centrifugal Casting
YOUNGSEOK KIM, DONG-IL CHUN, Inocera Inc., Yongin, South Korea
This study is designed to investigate effects of processing conditions on physical properties of RBSC radiant tube. For its many merits like high thermal efficiency and low pollutant emission, RBSC radiant tube will be used gradually for heat treat applications. Starting materials are composed of batch of SiC powders and thermo-set polymers that were mixed in a chamber at low temperature. Pouring it into the casting mold, tube was formed by centrifugal force and heat aid. The formed bodies were degreased to remove unnecessary polymers and infiltrated by molten Si at 1500 °C in vacuum. Though centrifugal casting has strong points like high density and high strength, it has a segregation problem resulting in cracks. The powder systems were binary or ternary. The ratio of each powder, RPM and solid loading were controlled to prevent segregation. Flexural strength, hardness and toughness were measured and microstructures were observed by SEM.
CA:P28 Manufacturing of Porous Ceramic Spheres using Biphasic Ceramic Phosphates, Hydroxyapatite and Beta Tricalcium Phosphate by a Mechanical Method without Additives or Binder
K.B. VIOLIN, T.S. GOIA, J.C. BRESSIANI, A.H.A. BRESSIANI, Materials Science and Technology Center - CCTM, Energy and Nuclear Research Institute - IPEN, Sao Paulo/SP, Brazil; K. ISHIKAWA, Department of Biomaterials, Faculty of Dental Science, Kyushu University, Fukuoka, Japan
The processing of porous ceramic spheres (PCS) has been developed for biphasic calcium phosphates (BCP), hydroxyapatite (HAp) and beta tricalcium phosphate (βTCP) in order to be used mostly as bone fillers and drug delivery systems. The importance of the PCS is due to better accommodation of them in order to fill empty spaces and also because is more friendly to cells and bone tissue growth. Also is important to obtain a surface roughness to increase the surface area in contact with the living tissue and their fluids. There are several methods used to achieve the PCS form and most of them use suspensions based on liquids immiscibility effect or additives. The aim of this work was to achieve PCS of BCP, HAp and βTCP with rough surface and varying size without use solutions or additives. The method proposed is based on a mechanical continuous movement of the particles, relying on the normal ability of the ceramic powders to aggregate themselves while rolling in a cylindrical container for long periods. The physical forces involved in the process, gravity, particle attraction, centripetal force and shocking make the ceramic rounds with golf ball appearance on its surface. With this method it was possible obtain PCS with 30% of porosity with rough surface and size between 1 to 4 mm.
CA:P29 Influence of the Ceramic Powders Crystallite Substructure on the Sintering Kinetics
B.A. TARASOV, M.S. YURLOVA, V.G. BARANOV, V.I. SKRITNIY, NRNU MEPHI, Russia
The specific surface area, average particle size, bulk density are the main parameters which taken into account to select the sintering conditions. However, the problem of accurately prediction of the required sintering program changes with using the different powder batches are still unsolved. The possibility of more precise control of the final product properties can be achieved by taken into account the influence of powder particles structure on the sintering kinetics.
Determining the relationship between sintering kinetics and thus fundamental characteristic as the crystallographic parameters of crystallites substructure will allow to better understanding of the particle defects structure impact on the shrinkage kinetics of powder.
In this work the impact of the powder particles substructure of TiN, obtained by the different ways, on the sintering kinetics, as well as its restructuring during sintering processing are examined.
CA:P31 Space Charge Contributions During the Intermediate Stage of Sintering
F. LEMKE, J. HÖTZER, M.J. HOFFMANN, B. NESTLER, IAM-KM, KIT, Karlsruhe, Germany
To analyze the basic mechanism during the densification of ceramic materials, theoretical sintering models with input of microstructural data and sintering data are usually used. A defect chemical approach to analyze sintering is still not very common despite of the good availability of literature data on the high temperature defect chemistry in bulk and at the grain boundaries (GB's) for model systems like SrTiO3. Diffusion coefficients based on defect chemical calculations were used with the Coble sintering equation to obtain densification rates as a function of temperature, oxygen partial pressures, doping, space charge potential and grain size. The results are compared to experimental data on SrTiO3 ceramics. It shows there is a strong contribution of the increased diffusion in the space charge layer at GBs to material transport during sintering especially for fine grained materials. It is proposed that an adapted model including space charge contributions reflects diffusion in bulk and at the GBs respectively, depending on particle size and defect concentration. Because the grain size distribution is not considered in the model, our results are assisted by phase-field simulations respecting the microstructural development during the sintering process.
CA:P32 Effect of Sintering on the Dispersion of Carbon Nanostructures in Ceramic Matrix Nanocomposites
O. TAPASZTO, M. MARKO, C. BALAZSI, L. TAPASZTO, Reseach Centre for Natural Sciences, Institute of Technical Physics and Materials Science, Budapest, Hungary
Carbon nanostructures are employed as filler materials for ceramic matrix composites in order to improve their mechanical, electrical or thermal properties. One of the major challenges is that nanostructures have a strong tendency toward agglomeration, whereupon the properties of the resulting composites are substantially deteriorated. Sustained efforts have been focused to achieve a better dispersion of nanostructures within the host matrix by using high efficiency milling, ultrasonic mixing, as well as the in-situ growth of carbon nanotubes. However, these methods aim to optimize the dispersion of the nanostructures in the starting powder mixture, before the sintering process. Therefore, it is important to understand how the dispersion of the nanostructures is altered during the sintering process itself. To study this, we have prepared Si3N4/carbon nanostructures composites from the same starting powder but using two different sintering methods: Hot Isostatic Pressing and Spark Plasma Sintering. To investigate the dispersion patterns in the sintered composites electron microscopy and neutron scattering measurements have been performed, revealing a substantial influence of the sintering process on the distribution patterns of carbon nanostructures within the ceramic matrix.
CA:P34 Effect of Different Sintering Processes on Microstructure of Alumina Ceramics
A.S.A. CHINELATTO1, A.L. CHINELATTO1, C. LAGO1, A. PEREIRA PINTO1, M.V. GELFUSO2, D. THOMAZINI2, 1Materials Engineering Departament, State University of Ponta Grossa, UEPG, Brazil; 2Mechanical Engineering Institute, Federal University of Itajubá, UNIFEI, Brazil
Structural ceramics, such as alumina, are widely used as industrial materials due to their properties such as hardness, chemical inertness and thermal insulation properties. However, low fracture toughness has limited applications of these materials. A way to overcome the low fracture toughness is to control the microstructure, seeking a refined and homogeneous microstructure. In this way, the aim of this study was to investigate the effect of different sintering processes on the microstructure of a commercial alumina ceramic. It was studied sintering in two steps and by microwaves. In sintering in two-steps, the samples are first heated to a higher temperature then cooled down to a lower temperature to suppress grain-boundary migration. In microwave sintering, microwaves directly interact with the particles within the pressed compacts and thereby provide rapid volumetric heating. This reduces processing time and results in energy saving. The sintered samples were characterized by apparent density, scanning electron microscopy and measurements of grain size. The results showed that two-steps sintering and microwave were effective to control the microstructure of alumina and that in two steps sintering it is essential to control the sintering steps to inhibit grain growth.
CA:P36 Effect of Alumina Addition on Mechanical Behavior and Fracture Properties of All-ceramics Zirconia Dental Materials
DONGJAO ZHANG1, DAWEI SONG1, YUNMAO LIAO2, XINMIN CHEN1,2, MIN WANG1,2, 1Prosthodontics,West China College of Stomatology Sichuan University, Chengdu, P.R. China; 2State Key Laboratory of Oral Diseases West China College of Stomatology Sichuan University, Chengdu, P.R. China
It was evaluated that initial crack angle affected the mechanical behavior and fracture properties of all-ceramics zirconia dental materials. In this study, samples containing 10 wt.% Al2O3 particles were prepared by cold isostatic pressing (200 MPa), sintered at 1500℃ for 5 h, and cut into different angles (30°, 60°, 90°). Commercial powders were investigated by bulk density and phase formation using Archimedes principle and X-ray diffraction (XRD). Bending strength and fracture load were determined at room temperature by three-point bending test. In order to study the fracture, we took and plotted points on coordinates, then generated fitting curves. Scanning electron microscopy (SEM) and atomic force microscope (AFM) were introduced to estimate the particle size of powders and observe the fracture surfaces. This study analysed the stress distribution of specimen with different incision samples by three dimensional finite element. No density difference was observed for a given alumina content. The majority phases of ceramics were t-zirconia and alumina before frature while m-zirconia, t-zirconia and alumina coexisted on the cross section of cracked samples. Specimen with original angle 30° had the best mechanical properties, the most tortuous crack propagation and the least obvious crack distribution. So this work may provide a reference for the materials selection, shape design and production process of all-ceramic crown and bridge.
CA:P37 Characterization of Magnesium-doped Hydroxyapatite Prepared by Sol-gel Process
S. ZIANI, S. MESKI, H. KHIREDDINE, Universite De Skikda, Universite De Bejaia, Algerie
Pure and doped hydroxyapatite (HA) nanocrystalline powders (Ca10-xMgx(PO4)6OH2) were synthesized using sol-gel process. For this, calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and phosphorous pentoxide were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg+2) especially from 0 to 10% (molar ratio) were incorporated as dopant into the calcium sol solution. The structure and morphology of the gels obtained after mixing the solutions were different, and their condensations in time depend on the quantities of magnesium added. The several powders resulting from the gels dried and sintered at 500°C for 1 h were characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and inductively coupled plasma (ICP). Additionally, their agglomeration, morphology, and particle size were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area of each sample was measured by the Brunauer–Emmett–Teller (BET) gas adsorption technique. The results of XRD, FTIR, and ICP values ranged between 0.45 and 2.11 mg/L indicated that the magnesium added in the calcium solution was incorporated in the lattice structure of HA so prepared, while those obtained by SEM and TEM confirmed the influence of Mg on their morphology (needle and irregular shape) and crystallite size, which is about 30–60 nm. The as-prepared powders had a specific surface area ranged between 6.37 and 27.60 m2/g.
CA:P38 Mechanical Characterization of Conventional and Non-conventional Sintering of Commercial and Lab-synthesized Y-TZP Zirconia for Dental Applications
A. PRESENDA, A. BORRELL, M.D. SALVADOR, Instituto de Tecnologia de Materiales, Universitat Politecnica de Valencia, Camino de Vera, Valencia, Spain; F.L. PENARANDA-FOIX, J.M. CATALA, Instituto de Aplicaciones de las Tecnologias de la Informacion y de las Comunicaciones Avanzadas (ITACA), Universitat Politecnica de Valencia, Valencia, Spain
Ceramics for dental applications have become increasingly important in the last decades. Particularly, the introduction of Y-TZP Zirconia as a material for elaboration of dental implants and prosthesis has provided a powerful tool to match the demands required for these replacements in terms of biocompatibility, toughness, hardness and optical properties. Several commercial zirconia-based materials are currently available on the market and strong efforts in research and development facilities are being made to improve processing of zirconia to fully consolidate dental pieces.
The purpose of this study is to characterize and compare the resulting properties of commercial and laboratory zirconia-based materials after sintering with a conventional technique and a non-conventional method: microwave heating. Two different commercial materials and two laboratory-synthesized powders are analyzed.
Results of this study suggest that a microwave zirconia furnace satisfies the general clinical requirements of manufacturing zirconia for dental use. Microwave energy provides a greater uniformity of heating, allowing the use of higher heating rates to increase productivity and save energy.
CA:P39 Sintering of AlO3-TiO2 Mixtures Obtained by High-energy Ball Milling
A. SARAIVA RAMOS1, M. APARECIDA DE SOUZA1, R. DE OLIVEIRA MAGNAGO3, 4, C. DOS SANTOS3, 4, C.A. ARAUJO DA SILVA3, B. DE ALMEIDA FORTES3, 1Universidade Federal de Alfenas, Instituto de Ciência e Tecnologia; 2Universidade Estadual Paulista, Departamento de Materiais e Tecnologia; 3Universidade Estadual do Rio de Janeiro, Faculdade de Tecnologia; 4Centro Universitário de Volta Redonda, Brazil
In this work, the preparation of Al2O3-TiO2 ceramics by high-energy ball milling varying the molar fraction in 1:1 and 3:1 was investigated. The powder mixtures were processed in a planetary mill at 250 rpm and a ball-to-powder weight ratio of 5:1, for 120min. Compacts were obtained by cold pressing at 100MPa. These specimens were heated at 1000◦C for 30min to promote the water evaporation, and subsequently sintered at 1500◦C for 240min. Samples were characterized by relative density, X-ray diffraction and Scanning electron microscopy. Hardness and fracture toughness were determined by Vickers Indentation Method. The crystallite sizes were lower than 420 and 560Å in Al2O3-TiO2 and 3Al2O3-TiO2 powders, respectively. After sintering, XRD analysis indicates Al2TiO5 and Al2O3/Al2TiO5 as major crystalline phases for Al2O3-TiO2 and 3Al2O3-TiO2 compositions, respectively. The relative density of the Al2O3-TiO2 ceramics was higher than 90% in both compositions. However, hardness and fracture toughness results of 10.7GPa or 10.5GPa and 3.2MPam1/2 or 2.6MPam1/2 for Al2O3-TiO2 and 3Al2O3-TiO2 mixtures respectively, indicates that microstructure duplex composed by Al2O3 and Al2TiO5 grains lead to improvement of toughness of these ceramics.
CA:P40 Comparison of Technological Properties of Ceramic Shell Moulds Based on Ethyl Silicate and Colloidal Silica Binders
M. MALEK1, H. MATYSIAK2, P. WISNIEWSKI2, K.J. KURZYDLOWSKI1, 1Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland; 2Functional Materials Research Centre, Warsaw University of Technology, Warsaw, Poland
The ceramic shell moulds manufacturing has become the technique for fabrication precision investment castings. The materials used to build the shell mould (binders and refractories) play significant role in manufacturing castings with proper quality. The binders used today are generally ethyl silicate and colloidal silica binders. In Polish industry the environmental divisions are forced to eliminate the use of ethyl silicate. Thus the objective of this paper is to demonstrate the advantages of new shell systems based on colloidal silica binders in the specific area of application such as replacement for current use ethyl silicate binders shell system. Comparison of full characteristic of manufacturing new shell (including thermal and mechanical behaviour, permeability and porosity structure) clearly shows that new solutions are very promising for future industrial application.
CA:P41 Effect of Particle Size of ZrO2(Y2O3) Powders on the Shrinkage of the Sintered Substrate with Coloring Gradient
C. DOS SANTOS1, P. CIPRIANO DA SILVA2, C.A. ARAÚJO DA SILVA1, B. DE ALMEIDA FORTES1, R. DE OLIVEIRA MAGNAGO1, 2, 1UERJ-FAT - Universidade do Estado do Rio de Janeiro, Brazil; 2UNIFOA, Brazil
ZrO2(Y2O3)-based ceramics with coloring gradient can facilitate the development of dental prosthesis by the improvement of esthetic properties. In this work, ZrO2 powders with different particle sizes were investigated. White and yellow zirconia powders (TOSOH Corporation-Japan) were characterized by particles size distribution using Nano Sight-LM20 analyzer. Furthermore, samples were characterized by X-Ray diffraction and Scanning Electron Microscopy. Compacts with two layers, one white and one yellow were uniaxially pressed at 80MPa and sintered at 15300C-120min. The yellow-powder presented average particles size of 180±66nm, while the white-powder presented particles size of 198±73nm. After sintering, full dense ceramics with tetragonal phase were obtained. The linear shrinkage of the yellow and white-layer was 22.75% and 22.05% respectively. This difference in shrinkage is important in the machining of prostheses in ceramic CAD/CAM systems, because they lead to difficulties in adapting this customized prosthesis in patients.