Symposium CO
Refractories: Developments in Raw Material, Production and Installation, Modelling, and Testing/Performance

Session CO-1 - Raw Materials

CO-1:IL01  New Calcium Magnesium Aluminate binders for High Performance Cefractory Castables
C. PARR, F. SIMONIN, C. WÖHRMEYER, C. ZETTERSTROM, Kernos SA, Neuilly sur Seine, France

Calcium magnesium aluminate (CMA) is a novel binder for refractory castables. It displays hydraulic properties as well an an instrincicorrosion resistance mechanism to prevent slag penetration and corrosion. Microcrystalline magnesium aluminate spinel is present which is homogeneously distributed between hydraulic calcium aluminate phases. This paper presents application studies of Magnesia containing castables based upon CMA for molten metal contact applications. Both pre-formed Magnesium Aluminate Spinel and Magnesia are combined in different model systems. Results show improved thermo mechanical properties and in particular excellent corrosion and penetration resistance when compared to reference systems. However, inside The ladle environment contains several destructive phenomena that occur simultaneously. Slag penetration, chemical dissolution, mechanical abrasion, and thermo-mechanical phenomena are all present and these are difficult to simulate in classical laboratory tests. Furthermore focus is given to a the post mortem analysis of CMA based castables after use inside ladles. Microstructure investigations of samples taken from ladle linings give an understanding of the mechanisms that lead to the improved performance of CMA based ladle castables.


CO-1:L04  Magnesium Fluoride Role on Alumina-magnesia Cement-bonded Castables
T.M. SOUZA, A.P. LUZ, V.C. PANDOLFELLI, Federal University of São Carlos (UFSCar), São Carlos, SP, Brazil

As spinel (MgAl₂O₄) containing refractory shows an outstanding slag corrosion resistance, to anticipate this phase generation (T < 1200°C) could improve the overall castable performance at high temperature. Mineralizing agents can be a suitable alternative to reduce spinel formation starting temperature. Nevertheless, only few studies have evaluated the effect of this sort of additive on the refractories’ properties. Considering this aspect, MgF₂-containing aqueous suspensions and alumina-magnesia cement-bonded compositions with and without magnesium fluoride were evaluated in order to better understand the role of this mineralizing additive in the castable’s phase evolution. The evaluated suspensions revealed that solid state reactions between reactive alumina and MgF₂ led to spinel formation at relatively low temperatures (800°C). Magnesium fluoride also reacted with calcium aluminate cement in the initial processing steps giving rise to CaF₂. Due to the presence of these two sorts of fluorides, a liquid phase was formed at temperatures close to 1000°C, increasing the MgAl₂O₄ generation rate. Phase transformations indicated in the suspensions showed a good correlation with the castables’ in situ hot elastic modulus measurements. Nevertheless, MgF₂ addition led to a marked thermal expansion, highlighting that an additional component to counterbalance the spinel expansion (such as fumed silica) must be simultaneously added to this sort of refractory material.


Session CO-2 - Testing

CO-2:IL01  Creep Testing of Refractories at Service Related Load Levels and Application for Material Simulation
SHENGLI JIN, H. HARMUTH, D. GRUBER, Montanuniversität Leoben, Leoben, Austria

During the operation of industrial vessels at high temperatures both elastic and inelastic behaviour of refractories may occur under intense thermomechanical loads. The latter one brings about an irreversible strain, which may cause mechanical failure of refractories and be responsible for the opening of joints. Besides material failure under tensile or shear loads, creep of refractories also may contribute to the occurrence of the irreversible strains. For quantitative assessment of the thermomechanical behaviour of an industrial vessel lining by the simulations, the accurate determination and description of creep behaviour of refractories at service related load levels is of importance. In this paper, a newly developed high temperature compressive creep testing equipment is introduced. Compared with conventional creep testing machines it enables the application of higher load levels as they occur under service conditions. A general testing procedure and displacement/time curves for various temperatures and loads are shown. For simulation purposes a Norton Bailey type creep law representing strain hardening is identified from the test results. An inverse evaluation procedure is performed for this purpose which exhibits high efficiency and robustness.


CO-2:IL02  Mechanical Properties of Refractories: Multi-scale Composite Approach from Grains to Material Level
M. HUGER, N. TESSIER-DOYEN, T. CHOTARD, SPCTS (UMR CNRS 7315), Centre Européen de la Céramique, Limoges, France

Refractory materials exhibit a heterogeneous microstructure consisting in coarse aggregates surrounded by fine grains that form an aggregate/matrix composite. This heterogeneous microstructure often leads to a complex mechanical behaviour during loading. This paper is devoted to the study of thermomechanical properties of several industrial and model refractory materials in relation with the evolution of their microstructure during thermal treatments. The aim is, in particular, to highlight the role of thermal expansion mismatches existing between the different phases which can induce damage at local scale. The resulting network of microcracks is well known to decrease elastic properties. Moreover, this network of microcracks can also strongly affect the thermal expansion at low temperature and the stress-strain behaviour in tension. Indeed, the occurrence of a large quantity of small precracks during the cooling stage after sintering, which enhances the development of a fracture process zone while loading, allows the decrease of the brittleness of the material which becomes in this case flexible. The large increase in strain to rupture, which results from this flexibility, is thus of a great interest for the enhancement of thermal shock resistance.


CO-2:L03  Mould Fluxes Viscosity and Surface Tension Influence on the Wear Mechanisms of Al2O3-C Nozzle
E. BRANDALEZE¹, M. ÁVALOS², ¹Metallurgical Department-DEYTEMA, Universidad Tecnológica Nacional-FRSN, Argentina; ²IFIR, Universidad Nacional de Rosario, Argentina

The deep understanding of the effect caused by mould fluxes on the wear mechanisms of Al2O3-C nozzle is relevant in order to avoid premature damage and to decrease the cost of the black refractories in the industry. In this paper, a post mortem study on a nozzle was carried out in order to identify the wear mechanisms caused during the continuous casting of billets. Physical properties such as viscosity and surface tension of the fluxes were determined at operation temperature (1550ºC), in order to correlate with the microstructural results obtained by light and scanning electron microscopy (SEM).  Also contact angle measurements were realized at high magnification. By EDS analysis the infiltrated flux chemical composition was determined. The study was completed by EBSD analysis.
The EBSD technique contributes to increase the knowledge on wear mechanisms because of the possibility to identify and localized phases together with crystalline condition. Nozzles possess a complex crystal structure coupled with anisotropic materials properties. The phases present, the grains orientation including planes and the properties of grain boundaries, have a large influence on the corrosion behaviour. Therefore, it is essential to have a characterization technique that can provide information such as: grain size, orientation, misorientation angle and phases. In this context, EBSD can provide relevant information on crystallographic and structural analysis of Al2O3-C nozzle including the insert material (ZrO2-C).


CO-2:IL05  Simulation of Refractory Fracture as a Tool for Advanced Material Testing
D. GRUBER, S. JIN, H. HARMUTH, Montanuniversität Leoben, Leoben, Austria

The work presented here deals with simulation assisted evaluation of fracture testing of ordinary ceramic refractory materials. Two tests are applied. One of them, a wedge splitting test, is already established for this purpose. An inverse evaluation procedure was established to derive more information from the test results: It enables the simultaneous determination of the specific fracture energy, the tensile strength and the Young's modulus. Moreover specific fracture energy can also be determined in the case that the test has to be interrupted at some residual load due to relatively low material brittleness. The other test method, a laser irradiation disc test, was developed in order to determine specific fracture energy and tensile strength for fine ceramic refractory materials behaving relatively brittle. From the time elapsed until crack initiation occurs (time t1) and a stable/instable transition of crack propagation takes place (time t2), respectively, the tensile strength and the specific fracture energy are calculated based on a simulation of the mode I fracture behaviour which applies the fictitious crack model according to Hillerborg.


CO-2:L06  Temperature Dependent Thermo-mechanical Behavior of Novel Alumina Based Refractories
A. BÖHM¹, C.G. ANEZIRIS², J. MALZBENDER¹, ¹Forschungszentrum Jülich GmbH, IEK-2, Jülich, Germany; ²Technical University Bergakademie Freiberg, Germany

Novel alumina based refractories are assessed with respect to their thermo-mechanical behavior from room temperature to 1000 °C within the framework of the DFG SPP "FIRE". The refractories are developed for use in slide gates or entry nozzles. The elastic behavior was investigated using an impulse excitation technique. Wedge splitting tests were used to determine the fracture resistance behavior. A comparison with in situ crack growth experiments permitted to gain insight into associated crack shielding mechanism. Evaluated materials characteristics and thermal shock resistance are compared to a standard refractory material, permitting a conclusion on the effect of the used additives (TiO2, ZrO2) on apparent elastic behavior, crack propagation and thermal shock resistance.


CO-2:L07  Digital Image Correlation as a Tool for Monitoring Crack Networks on the Surface of MgO-based Refractory Castable
R.G.M. SARACURA, R.B. CANTO, F. HILD, V.C. PANDOLFELLI, N. SCHMITT, DEMa,UFSCar, Sao Carlos-SP, Brasil; LMT-Cachan, ENS de Cachan/CNRS/UPMC, Cachan, France

Setting the composition of refractory castable to control cracking during curing and drying is one of the challenges to improve their lifetime. On the other hand, crack networks on hot surfaces are beneficial as they provide thermal stress release most likely inhibiting complete failure at high temperatures. Besides that, when the cracked and hot surface are in contact with liquid (e.g., slag) or gas, the chemical corrosion is faster, also reducing the refractory performance. Therefore, studies to better characterize crack network on surfaces are required. Digital Image Correlation (DIC) is a promising technique that allows displacement fields and discontinuities to be measured on a surface. In the present work, this technique was used to monitor the evolution of the crack network pattern on MgO-based castable. After a brief introduction of the DIC technique, the device used to characterize the effects of curing and drying of a plate at a temperature of 110°C is presented. Additionally, some experimental tests highlight the network profile and based on them some insights and technological implications are drawn.


CO-2:L08  Phosphate-based Anti-hydration Additive for Al2O3-MgO Refractory Castables
A.P. DA LUZ, T.M. SOUZA, V.C. PANDOLFELLI, Federal University of Sao Carlos (UFSCar), Sao Carlos, SP, Brazil; M.A.M. BRITO, Magnesita Refratarios S.A., Contagem, MG, Brazil

The main obstacle for a broader application of magnesia in refractory castables is related to the Mg(OH)2 formation, as such transformation may lead to processing drawbacks. Silica is one of the most applied anti-hydration additives in MgO-containing castables due to its low cost and effectiveness. Nevertheless, the use of silico-phosphates (presenting higher reactivity) seems to be a promising alternative to enhance the formation of magnesium-silicate-hydrated gels that act inhibiting MgO hydration and controlling brucite formation. This work aims to evaluate the performance of a commercial phosphate-based binder as an anti-hydration additive in Al2O3-MgO refractory castables and MgO aqueous suspensions. Thermodynamic calculations were carried out in order to predict the phase transformations steps. Flowability, thermogravimetric and mechanical tests were also performed for the characterization of the samples. Based on the simulated Pourbaix diagrams, two gels [Mg3Si2O5(OH)4 or Mg3Si4O10(OH)2] may be formed in the castables structure (depending on the Mg:Si molar ratio). Additionally, the blend of silica fume and the phosphate-based additive proved to be the most effective route to halt the Mg(OH)2 formation, so that castables with improved performance could be prepared.


CO-2:L09  Crystallographic Texture on High Zirconia Refractories
C. PATAPY, LMDC INSA Toulouse, Toulouse Cedex, France; F. GOURAUD, M. HUGER, R. GUINEBRETIERE, SPCTS UMR 7315 CNRS, Centre Européen de la Céramique, Limoges Cedex, France; N. GEY, M. HUMBERT, A. HAZOTTE, LEM3, UMR 7239 CNRS, Metz Cedex, France; D. CHATEIGNER, CRISMAT ENSICAEN, UMR 6508 CNRS, Caen Cedex, France; T. CHOTARD, SPCTS UMR 7315 CNRS, Centre Européen de la Céramique, Limoges Cedex, France

New compositions of refractory materials with a very high content of zirconia are being developed for the processing of special glasses. The use of these refractories requires good control of the manufacturing process to avoid critical flaws due to severe thermo-mechanical stresses. These materials exhibit a microstructure containing monoclinic zirconia dendrites embedded into a glassy phase.
The purpose of this study is to characterize the coupling between the microstructural texture and the cooling process of high zirconia refractories. The cooling stage creates an important thermal gradient between the core and the skin of the block. During this cooling process, zirconia crystallizes under the cubic (C) phase and then two phase transitions occur (cubic to tetragonal (T) and tetragonal to monoclinic (M)), which can influence the macroscopic mechanical properties. Neutron diffraction experiments have been performed, on samples from solidified blocks to evaluate the relationship between the thermal gradient of cooling and the crystallographic texture. It was shown that the stress field created during the cooling process manages the preferential orientation of zirconia crystals.


CO-2:L10  Corrosion Mechanism Analysis of Al2O3-SiC-C Castables
CHIEN-NAN PAN, Ceramic Materials Section (T62), New Materials Research & Development Dept., China Steel Corporation, Kaohsiung, Taiwan, R.O.C.

This study aims to analyze the corrosion mechanism of Al2O3-SiC-C castables for blast furnace main trough. The anti-oxidation property and corrosion of materials by slag were studied with residual lining investigation and microstructure analysis. Scanning electronic microscopy, EDX, optical microscopy, and Cathodoluminescence microscopy were used to identify grain distribution, ingredients, and mineral phases. Cathodoluminescence microscopy showed different fluorescent color to distinguish the brown corundum, alumina, spinel, and CaO low-melting phase etc., The results indicated that while carbon in the matrix of castables was oxidized, its non-wetting property to slag was reduced, then slag easily penetrated to material and formed CaO low-melting phases; In contrast, while the anti-oxidation property of material was better, the carbon in the matrix was not oxidized easily and material resisted the corrosion of slag. Furthermore, MgO of slag reacted with Al2O3 in the matrix and formed spinel, a continuous good corrosion resistance layer to reduce the corrosion of castables.
 
 
Session CO-3 - Products Development, Selection, Design and Use

CO-3:IL01  Refractory Castable Engineering
V.C. PANDOLFELLI, A.P. DA LUZ, Federal University of Sao Carlos, Materials Engineering Department, Sao Carlos, Brazil

Refractory castables are commonly used in risers for petrochemical fluid catalytic converters (FCC). Although such materials attain high erosion resistance, they do not usually present high good thermal shock performance and high hot mechanical strength at temperatures close to 800C. The aim of this work was to evaluate and optimize the thermo-mechanical properties of alumina-based castables designed for petrochemical applications by adding different amounts of a boron-based sintering additive able to speed up the densification at lower temperatures. Although the sintering additive induced liquid formation mainly above 800C, the hot elastic modulus profiles indicated that this phase presented a transient feature, as it was crystallized throughout subsequent heating cycles. Thermal fatigue effect (related to the thermal expansion mismatch of the formed borate phases) was also observed especially for the samples containing higher sintering additive content. Nevertheless, the boron-containing samples showed outstanding properties (high thermal shock and erosion resistances and enhanced hot modulus of rupture between 600-1000C) and this performance could be attained only with by using suitable amounts of this engineered sintering additive.


CO-3:IL02  A New Generation of Carbon Bonded Filters for Advanced Metal Melt Filtration
C.G. ANEZIRIS, M. EMMEL, S. DUDCZIG, Institute of Ceramic, Glass and Construction Materials, Technical University of Freiberg, Germany

A new generation of carbon bonded filters aims to improve the mechanical properties of metallic materials for security and light-weight constructions with the aid of surface functionalized filter materials based on so called "active" as well as "reactive" coatings. In case of the "active" coatings, the same chemistry as the chemistry of the primary or secondary inclusions that have to be removed are generated on carbon bonded filters. On the other hand, "reactive" coatings react with the dissolved gas in the melt (for instance, oxygen in steel melts) and create inclusions above the liquidus temperature of the melt that are deposited on the filter. With these approaches less primary and secondary fine inclusions below 10 µm pass the filter as well as less tertiary and quartenary inclusions are generated below the liquidus temperature. Studies in a confocal scanning laser microscope and in a novel steel casting simulator support the understanding of the functionality of the new coatings, and industrial trials give a first very promising picture of the effectiveness of the new filters.


CO-3:L04  Criteria to Select the Refractory Lining in Biomasses Co-combustion Reactors for Energy Production
D. OLEVANO, P. MICELI, U. MARTINI, A. DI DONATO, Centro Sviluppo Materiali SpA, Rome, Italy

The addition of biomasses in co-combustion reactors for energy production is becoming a promising way for reducing the use of non-renewable fossil fuels. However the presence of alkalis in biofuel can degrade more rapidly the refractory lining of the combustion chamber. The alkalis can penetrate in the refractory and dissolve material components, forming new liquid phases that physically degrade the coherence of the material, increasing the risk of refractory failure.
The use of selection criteria based on this degradation mechanism is useful to a proper choice of materials, limiting the traditional trial-and-error approach.
In this work an integrated approach helping the selection of materials is presented.
The approach integrates thermodynamics and laboratory experiments.
Thermodynamic evaluation of the chemical reactions between systems representing the refractory and the aggressive environment of the combustion chamber is used to predict the formation of new phases, potentially modifying the refractory structure. Laboratory experiments are performed to evaluate the extent of the modification.
The predictions obtained by the integrated approach have been validated on samples tested in real combustion chambers.


CO-3:IL05  Impact of Temperature and Oxygen Partial Pressure on Aluminum Phosphate in High Chrome Oxide Refractories
J.P. BENNETT¹, K.S. KWONG¹, J. NAKANO^{1, 2}, H. THOMAS¹, A. NAKANO¹, ¹National Energy Technology Laboratory, Albany, OR, USA; ²URS Corporation, Albany, OR, USA

Gasifiers are reaction vessels used to contain the high temperature/pressure severe service environment used to process carbon feedstock (coal and/or petcoke) and water in a reducing atmosphere (low oxygen partial pressure), resulting in the formation of CO and H2 (also called synthesis gas or syngas). Syngas is used as a feedstock in chemical production or power generation. By-products of gasification include: 1) unreacted carbon, 2) gases such as CO2 and H2S, and 3) slag formed from mineral or organometallic impurities. Molten slag formed during gasification can coalesce and flow down the gasifier sidewall, interacting with the refractory liner and causing wear by two main means - spalling (structural and chemical) and chemical dissolution. The gasifier is lined with a high Cr2O3 refractory liner used to contain the gasification environment and can contain up to 18 % porosity. Wear by structural spalling involves slag penetration into surface refractory pores, resulting in shear and separation of that penetrated layer from the underlying material. Spalling results in a significant reduction of refractory service life, and once completed, is a repetitive process. Phosphate additives in high Cr2O3 refractories are a recent innovation, and are known to reduce spalling and chemical dissolution. The phosphate additives, however, have been found to move within the refractory, with an unknown impact on wear. This paper will discuss how temperature and oxygen partial pressure impact phosphate movement.


CO-3:L08  Artificial Aggregates Obtained from Waste Alumina-rich Refractory Powder by the Cold Bonding Process
V. DUCMAN, Slovenian National Building and Civil Engineering Institute, Ljubljana, Slovenia

Recycled aggregate can either be produced by (i) crushing and grinding or, if the starting material is in powder form, (ii) by the application of high temperatures (foaming or sintering), or (iii) by a cold bonding process. The latter process, which is, from the energy point of view, considered to be more economical than others, is based on reaction mechanisms which are the same or similar to those which take place in concrete; at temperatures below 100°C. Cement with suitable additives, or else water glass and alkali activators, is usually used as the binding agent. The aim of the paper is to present the development of artificial recycled aggregates from the waste which remains after the crushing and grinding of used refractory products. In the study refractory cement, as well as potassium water glass, were used as binders. The aggregates obtained in this way were assessed by an analysis of their microstructure, strength, and porosity, and were tested as a constituent of concrete. The results confirmed that high quality aggregate can be obtained from waste alumina-rich refractory powder by means of the cold bonding process.

 
Session CO-4 - System Modeling and Simulation; Failure Analysis

CO-4:IL01  Multiphysics Modelling Applied to Refractory behaviour in Severe Environments
E. BLOND¹, T. MERZOUKI², N. SCHMITT³, M.-L. BOUCHETOU⁴, T. CUTARD⁵, A. GASSER¹, E. DE BILBAO⁴, J. POIRIER⁴, ¹Univ. Orléans, PRISME (EA4229), Polytech Orléans, Orléans; ²Univ. of Versailles Saint-Quentin, LISV (EA4048), Vélisy; ³ENS Cachan, LMT-Cachan (UMR 8535), Cachan; ⁴Univ. Orléans, CEMHTI (UPR3079), Orléans; ⁵Ecoles des Mines d'Albi Carmaux, ICA-Albi, Campus Jarlard, Albi CT Cédex, France

The design of refractory linings is mainly based on thermal computation, thermochemistry analyses and strong workman know-how. The mechanical design of these linings is often limited to simple thermo-elastic computations. Sometimes they are refined considering non-linear mechanical behaviour, even if corrosion often induces large swelling and strong evolution of the mechanical behaviour in service. The aim of this presentation is to briefly recast the irreversible thermodynamic framework in order to underline the implications of some basic thermodynamic concepts in term of refractory behaviour modelling. Then, the use of these concepts to develop fully 3D finite element simulations accounting simultaneously for thermal, mechanical and chemistry phenomena will be illustrated on the particular case of SiC-based refractory. Comparison between long duration oxidation test at high temperature and model prediction allows validating the proposed approach. Then, an extension to the industrial case of refractory lining in Waste to Energy plant will be illustrated. Finally, the interest of taking into account the thermo-chemo-mechanical coupling effects is clearly shown.


CO-4:IL02  Thermo-mechanical Modelling of Refractory Masonries
A. GASSER, E. BLOND, N. GALLIENNE, J.L. DANIEL, Univ. Orléans, Orléans, France; S. SINNEMA, Tata Steel, IJmuiden, The Netherlands; M. LANDREAU, CPM, Forbach, France

Many refractory linings of structures used in steel making industry are made of masonries containing joints with or without mortar between bricks. These joints play an important role in the thermo-mechanical behaviour of the masonry. So, it is necessary to take them into account during a numerical computation of a structure containing a refractory masonry. Since such masonries are built with hundreds of bricks, it is very time expensive to model each joint and each brick in a finite element computation. Therefore, the masonries are modelled by a homogeneous material that has a behaviour equivalent to that of the set of bricks and joints. The thermo-mechanical properties of this equivalent material were determined using a periodic homogenization method. They are temperature dependent and depend also on the joint states (open or closed in the two directions).
This approach was used in two applications:
- A simplified steel ladle to show the influence of different parameters: presence or not of joints, dry joints/mortar joints, thickness of mortar joints, masonry design (parallel, fish bone or radial), refractory material properties,
- A heating wall of a coke oven to determine the maximum pressure that the coal can apply on it during coking process.


CO-4:L03  Numerical Analysis on the Refractory Wear of the Blast Furnace Main Trough
C.M. CHANG, Y.S. LIN, WEN-TUNG CHENG, Department of Chemical Engineering, National Chung Hsing University, Taichung, Taiwan, R.O.C.; C.N. PAN, China Steel Corporation, Kaohsiung, Taiwan, R.O.C.

This study aims to numerically analyze the refractory wear of the blast furnace main trough. The three dimensional transient Navier-Stocks equation associated with the volume of fluid (VOF) was developed to describe the flow fields of air, molten iron and slag in the main trough of the blast furnace during tapping process; and then solved by the finite volume method (FVM) subject to the pressure implicit with split operator (PSIO). Based on the Newton's law of viscosity, the computed shear stress profile in the impingement region consists with the wear rate of main trough from the no. 4 blast furnace at China Steel Corporation (CSC BF4). The influence of the taphole angle and the ratio of iron to slag in tapping stream on the wall shear stress of main trough was also examined for the suggestion to minimize the refractory wear of blast furnace main trough in this work.


CO-4:IL04  Recent Development of the FactSage Thermodynamic Database for Ceramic Refractories
IN-HO JUNG, Mining and Materials Engineering, McGill University, Montreal,  Quebec, Canada

Thermodynamic database is very useful to analyze the complex chemical reactions happening in industrial process. An accurate thermodynamic database based on the physically sound thermodynamic models can provide accurate thermodynamic calculations for complex chemical reactions and phase diagrams related to industrial process. FactSage thermodynamic database has been widely used for the applications to pyrometallurgical process and refractories research. In this study, the recent progress of the FactSage database toward oxy-fluoride system will be presented and their applications to steelmaking process will be discussed.


CO-4:IL05  Modeling and In-plant Validation of Thermal Stresses in Steelmaking Ladles
P. GALLIANO, L. MARTORELLO, T. SIMARO, L. MUSANTE, M. ROSSI, H. ERNST, D. JOHNSON, Tenaris REDE AR, Argentina

A thermo-mechanical finite element model was developed by using Abaqus commercial software, in order to determine stress levels in a refractory lined steelmaking ladle shell during its first preheating stage. Thermal stresses in ladle shell were predicted and results were adjusted according to in plant measurements. Longitudinal and circumferential stresses due to the refractory lining thermal expansion were simulated by using a finite element model in which both working and safety refractory linings are considered. Stress-strain curves of lining materials at different temperatures were obtained through lab tests and were then used for model optimization. Additionally, creep behavior in the steel shell under tensile strength and different temperatures was also modeled taking into account results from laboratory tests. Finally, in-plant measurements were done by instrumenting the lower part of the ladle sidewall external shell with high temperature strain gauges and thermocouples. In this way, strain and temperature evolution during preheating process were determined. Predicted stress evolution showed good agreement with in plant measurements.


CO-4:IL06  Fine Element Modelling of the Blast Furnace Hearth Lining
P. PUT, S. SINNEMA, J. LIEFHEBBER, Tata Steel Europe, IJmuiden, The Netherlands

Experiences from the recent past years show that with increasing outputs, with the high coal injection levels, the current blast furnaces design (linings, hearth depth) is coming to its limitations. Knowledge needed to be prepared to anticipate on process changes and production level fluctuations is essential to increase installation availability. To be able to develop this knowledge the current behaviour of the blast furnace hearth lining is investigated. The investigations comprise amongst others post mortem analysis of hearth lining materials, output of online monitoring systems (acoustic, thermocouples, infra-red images) also both computational fluid dynamic (CFD) and finite element modelling (FEM).
The use of Finite Element Modelling of blast furnace linings will be illustrated. Findings from several analysis techniques are combined with this modelling tool. The finite element method is for instance powerful in translating observed temperature recordings at a hot spot into local wear and/or skull formation processes.


CO-4:IL07  Study of Reactive Impregnation and Phase Transformations during the Corrosion of High Alumina Refractories by Al2O3-CaO Slag
E. DE BILBAO¹, M. DOMBROWSKI¹, K. COFFIGNIER², N. TRAON³, T. TONNESEN³, J. POIRIER¹, E. BLOND⁴, ¹CNRS, CEMHTI UPR3079, Univ. Orléans, France; ²Polytech'Orléans, Univ. Orléans, France; ³RWTH Aachen University, Germany; ⁴Univ. Orléans, PRISME, France

Corrosion of refractories results from reactive transport namely, the transport of corrosive agents and the ensuing chemical reactions of those agents with the impregnated medium. On one hand, the transport involves either diffusion or impregnation according to the state of the corrosive agents and the microstructure of the host medium. On the other hand, chemical reactions may be very numerous and complex. This study focused on the reactive impregnation of Al2O3-CaO slag into a porous high alumina refractory.
Transport properties of the porous medium were assessed by performing gas permeability measurements and wicking tests.
Chemical reactions between the solid high alumina skeleton and Al2O3-CaO slag involve successive dissolution/precipitation mechanisms forming aluminates of lime. Contrary to the thermodynamical properties of the binary system, the kinetics of these solid/liquid reactions is not well known. Corrosion tests associated with quenching method, XRD and high temperature XRD were performed for a better understanding of the kinetics.


CO-4:IL08  Mechanisms of SiC Refractory High Temperature Corrosion by Molten Salts (Na, K, Ca, Cl, S) in Waste to Energy Facilities
J. POIRIER¹, P. PRIGENT², M.L. BOUCHETOU¹, E. DE BILBAO¹, E. BLOND³, J.M. BROSSARD⁴, ¹CEMHTI, CNRS / University of Orléans, France; ²TRB, Nesles; ³PRISME, University of Orléans, France; ⁴VEOLIA environment

Damage of SiC oxide bonded refractories in waste-to-energy facilities (WtE) has been characterized. Different phenomena were observed: wear by slag phases, volume expansion of tiles and fracture in different locations. The role of gas composition and tiles temperature profile has been emphasized: deposit composition, condensation of gaseous alkali chloride and formation of liquid phase. Gaseous alkali species are involved, not only in the formation of liquid phases, but also as a precursor of cristoballite formation around the SiC grains as well as in the rich alumina-silica matrix. On the hot face of the refractories, oxo-reduction reactions produce the formation of wollastonite.
Post-mortem analysis after several thousand hours of operation reveals three main corrosion mechanisms:
- Molten salt/slag attack (Na,K,Ca,sulphate phases),
- Salt condensation inducing new phase formation (SiO2-CaSO4-K2SO4 or K2O-Al2O3-SiO2),
- SiC oxidation, cristoballite and wollastonite crystallisations.
These mechanisms explain the volume expansion of SiC refractories observed in WtE plants and makes it possible to understand cracks propagation related to stress load.The relative contributions of chemical degradation mechanisms are discuss and different axes of improvement are suggested.


CO-4:IL09  Corrosion of Refractories in Incineration Processes: Changes in Microstructure, Properties and Performance
TH. TONNESEN, R. TELLE, RWTH Aachen University, Aachen, Germany

The demand of energy resources increases the amount of waste to energy processes and industrial gasification and incineration processes of biomass. Apart from process stability corrosion of the refractory lining is a limitation.
The corrosion mechanisms for different castables based on SiC, andalusite, calcium aluminate and spinel were examined in contact to slags and ashes of waste and biomass incineration processes with its high alkaline, phosphate, chlorine and sulfate concentrations. A thermodynamic model using the software package FactSage was worked out and applied on refractory compositions to predict phase formation and corrosion. Vapour phase corrosion experiments between 1000 and 1400°C with different waste and biomass feedstocks of crucibles and in a special tube furnace were performed to work out the gaseous corrosion in regard of condensation of aggressive vapors into a refractory with thermal gradient. Slag and post-mortem analyses were achieved to define dissolution behaviour. The corrosion experiments were applied on the matrix materials (CA-cement, CA6, spinel-cement, SiC fines) as well as on aggegates. Coupling effects of impregnation, microstructural and changing thermal properties such as expansion, permeability and strength change are discussed.
 
 
Poster Presentations

CO:P02  Microstructures and Corrosion Mechanisms in MgO-C Bricks in Contact with High-basicity and FeO-rich Slags
E. BENAVIDEZ, E. BRANDALEZE, Dto. Metalurgia-Deytema, FRSN-UTN, San Nicolás, Argentina; L. MUSANTE, P. GALLIANO, Tenaris REDE AR, Campana, Argentina

The MgO-C bricks are extensively used as lining work on different steel containers. Due to the high temperatures of the process, these refractories are subjected to severe wear and corrosion processes, principally in the area of contact with the slag. These slags have variable contents of CaO, SiO2, Al2O3, MgO and FeO, varying in composition according to the process stage.
In this paper, cup tests were performed at 1650 °C during 2 hours in air, using three kinds of MgO-C bricks. They were put in contact with two different grades of slags, one with high basicity (LF) and the other rich in FeO (HO). The corrosion degree and decarburization level suffered by the refractory materials were analyzed and compared. Microstructural observations were performed in order to postulate the probable corrosion mechanisms acting on each material. The results establish that, in the case of LF slag, the attack is carried mainly through the filler region (matrix). In the case of HO slag attack, it is observed that Fe is the main specie that diffuses through the matrix area of the bricks, and to a lesser extent through MgO grains. In both cases, the quality of the raw material used in manufacturing each refractory bricks, be playing an important role in the corrosion degree.