Fusion-cast Refractories Research Articles

Application of Fused-Cast Refractories in the Smelting of Mineral Melts in Electric Furnaces

Application of Fused-Cast Refractories in the Smelting of Mineral Melts in Electric Furnaces

Formation of mullite in fused cast AZS refractories

Fused cast refractories, based on the system Al2O3-ZrO2-SiO2 (AZS), are used in industrial glass tanks and are in direct contact with the glass melt and/or the furnace atmosphere (combustion gases, evaporation products, and dusts) at temperatures up to 1600 °C. Three samples of AZS materials were studied, (i) the original AZS refractory as delivered from the refractory industry, (ii) AZS refractory thermally treated similar to furnace heat up over days and ending for 10 h at 1580 °C and (iii) AZS refractory thermally cycled 600 times between 1530 and 1580 °C after furnace heat up simulation.The samples were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) including Energy Dispersive X-ray analysis (EDX) and Electron Backscatter Diffraction (EBSD). In the untreated AZS, monoclinic ZrO2 (m-ZrO2) and Al2O3 were detected, while in AZS thermally treated at 1580 °C, mullite also occurred. Thermal cycling led to further increase in the mullite concentration and to a small concentration of tetragonal ZrO2 (t-ZrO2). The Al2O3 crystals as well as some of the ZrO2 had a blocky morphology. Surprisingly also formed mullite crystals were block and not needle-like. In the mullite as well as in the Al2O3 crystals tiny m-ZrO2 crystals were embedded which were formed during cooling in the production process from t-ZrO2 and were heavily twinned.

Physical Modeling and Simulation of the Cooling-Down of Fused-Cast Refractories

The accurate description of the interfacial heat transfer coefficient is of great significance for the accurate measurement of the temperature field in the process of casting cooling. In this paper, the solidification process of metallic tin in refractory mould was studied by physical simulation experiment, and the on-site temperature measurement of the mold structure was carried out. According to the temperature record, the numerical simulation method is used to realize the fitting of the calculated temperature and the measured temperature. The reversible method was used to calculate the interfacial heat transfer coefficient between the casting and the mould, and then the evolution of the internal temperature field of the casting during the cooling process was determined. The results show that the melt has a large shrinkage during the cooling process, and the interface heat transfer coefficient can reach 300 W·m-2·K-1, which provides a mathematical model for the annealing process of fused-cast refractories.

Refractory Corrosion Resistance in Molten Lead-Niobium Glass

It is shown that chromium-containing refractories containing more than 80% Cr2O3 are most corrosion-resistant in molten lead-niobium glass at 1440°C. Alongside good corrosion resistance fusion-cast high-chromium refractories are capable of providing prescribed glass electrophysical properties, obtained on contact with chromium refractory. The data provided point to the possibility of replacing platinum melting equipment during preparation of lead-niobium glass with use of a small bath electric melting furnace with a lining of fusion-cast high-chromium refractory.

THE PROBLEMS AND DEVELOPMENT PROSPECTS FOR THE FUSEDCAST REFRACTORIES PRODUCTION IN RUSSIAN FEDERATION

The current state analysis of the fused-cast refractory processing in Russia shows that the domestic manufacturers cover only the minimum requirement of the Russian glassmanufacturing plants in the middle-quality fused-cast baddeleyite-corundum refractories. The fused-cast highalumina refractories for the glass industry and also the chromecontaining refractories for the chemical industry are imported. The necessity is noticed in the article for the establishment and development of the fused-cast refractories production in light of both the best achievements of the foreign enterprises, the practical experience of the actual Russian enterprises, as well as taking into account the results of domestic science investigations. Ill. 3. Ref. 6. Tab. 2.

Investigation by neutron diffraction of texture induced by the cooling process of zirconia refractories

New fused cast refractories with a high content of zirconia have been developed to face corrosion in glass furnaces. The controlled cooling process is responsible for thermal gradients. So, thermal mismatches appear between core and edge zones of blocks. Besides, the multiphasic nature of ZrO2 based refractories is associated to thermal mismatches during cooling. Finally, the expansive transformation of ZrO2 can lead to stress generation.This paper is an application of neutron diffraction to study texture generated during the cooling process of zirconia based materials. In fact, it is shown that ZrO2 crystallographic variants have particular crystallographic texture regarding the main direction of the thermal gradient in the block. It was hypothesized that a selection of crystallographic variants could be done depending on the field stress. Tensile-compressive tests at high temperature have been done, to reproduce stress environment during the transformation of zirconia.

Preparation of Fusion-Cast Chromium-Spinelid Refractories Using Vessel Scrap

Results are provided for preparation of fusion-cast chromium-spinelid refractories using lumps of baddeleyite-corundum refractory waste after service in glass melting furnaces. It is shown that fusion-cast chromium-spinelid refractories, containing 31.2 and 50.4% Cr2O3 and prepared from a charge using broken vessel refractory, has improved corrosion resistance in molten mineral wool compared with fusion-cast baddeleyite-corundum and chromium-aluminum-zirconium refractories of commercial grades ER 1711, KhATs-30, and KhTs-45.

Numerical simulation of the cooling-down of high-zirconia fused-cast refractories

Abstract This study concerns high zirconia fused-cast refractories used in the glass industry. In situ temperature measurements have been performed in the casting structure during an actual casting of a tile. A two-dimensional mesh of the casting structure has been developed so as to perform numerical simulations. From temperature recordings, an interfacial heat transfer coefficient between the tile and the graphite mould has been determined, by an inverse method, by fitting the calculated temperatures with those measured. A similar procedure allowed the thermal conductivity and the heat capacity of the surrounding insulating medium to be determined. Then, the numerical model allowed the evolution of the temperature field, within the tile, to be determined. The influences of different parameters (mould thickness and thermal properties of the annealing medium) have been numerically tested, by comparison with the cooling-down kinetics of the tile.

Mechanical behavior characterization of high zirconia fused-cast refractories at high temperature: Influence of the cooling stage on microstructural changes

Today, the high quality level required by new applications of glass, imposes the use of high zirconia refractories (HZ). These are designed to operate in extreme condition and also require control of the making process. Elaborated by a fused cast process followed by a controlled cooling step, these materials exhibit specific thermo mechanical properties related to a microstructure containing monoclinic zirconia dendrites embedded into a silica–alumina glassy phase.

Fusion-cast chromium-bearing refractories — the most durable materials in aggressive melts

Information is presented on fusion-cast materials that have been developed in recent years on the basis of the systems Cr2O2–Al2O3–ZrO2–SiO2, Cr2O3–MgO–SiO2, and Cr2O3–MgO–Al2O3. Such materials have good service properties in mineral melts at high temperatures. It is shown that fusion-cast chromium-bearing refractories KhPL-85 and KhMG are as corrosion-resistant as chromium-oxide-based ceramic refractories in melts of alkali-free borosilicate glass E and basalt fibers.

Arc melting plant for synthesizing and producing fusion-cast refractories

Data are given on arc melting plant for synthesizing and producing fusion-cast refractories. The technical characteristics of experimental plant type EDP-600 with moving electrodes are such as to allow one to synthesize fused materials on the basis of the oxides Al2O3, MgO, Cr2O3, and ZrO2, and also allows one to produce refractory components for industrial glass-melting furnaces. The DSPM-1.5 arc furnace is recommended for the industrial production of fusion-cast baddeleyite-corundum, high-alumina, and chromium-bearing refractories.

Study of damage of high zirconia fused-cast refractories by measurement of Young's modulus

Young's modulus evolutions versus temperature have been studied for two high zirconia fused-cast refractories undergoing thermal solicitations up to 1700 °C. As well as the step of cooling from very high temperature of the manufacturing process, the first heating up can lead to the formation of internal stresses that are released by microcracking. Young's modulus has been assessed by using the impulse excitation technique at room and high temperature. Damage and healing phenomena for different temperatures are compared and discussed taking into account the physico-chemical evolutions. The effect of the allotropic transformation of zirconia, through its associated change of volume, is in particular emphasized. Furthermore, the behaviour of the glassy phase, responsible for healing at high temperature and damage at lower temperature by thermal expansion mismatch, is discussed.

Investigation of the thermomechanical properties of industrial refractories: the French programme PROMETHEREF

This paper summarises the work that has been done in the framework of the French programme PROMETHEREF. This programme was concerned with the thermomechanical properties at high temperature of two industrial refractories: fused-cast materials for glass melting and alumina castables for steel production. At high temperature, both materials exhibit creep, that has been characterised by tension, compression and bending tests. The microstructural mechanisms of deformation have been investigated and allowed the macroscopic viscoplasticity to be understood. Both types of materials exhibit damage processes that have also been characterised mechanically and microstructurally. The nature and the adhesion of the aggregates have been shown to have a great influence on the mechanical behaviour of the castables, as well as the continuous zirconia skeleton observed in high-zirconia fused-cast refractories by X-rays tomography.

Finite element simulations of the deformation of fused-cast refractories based on X-ray computed tomography

This work consists in building a 3D numerical model of the microstructure of a fused-cast refractory (two-phase material). Creep tests at temperatures as high as 1400°C reveal a major influence of the morphology of the phases on the material behavior. A possible 3D connectivity of the zirconia grains, related to the fabrication process, may explain the observed high creep resistance. In order to have a realistic representation of the microstructure, 3D pictures have been obtained using X-ray microtomography at the European Synchrotron Radiation Facility in Grenoble (ESRF). Volumetric tetrahedral grids are generated from the exploitation of these pictures using available meshing techniques. Finite elements calculations are performed to study the influence of the glassy phase content on the stiffness of the material. Simulations are compared with experiments. In particular the notions of geometrical and mechanical percolation are investigated numerically. High elastic stiffness is predicted, even for large amorphous phase contents. A percolation threshold is observed for the geometry of the hard phase (zirconia phase) but not for the Young’s modulus.

Fusion-Cast High-Chrome Refractories Synthesized in the Cr2O3 - MgO - SiO2 System

The synthesis and comprehensive study of fusion-cast refractories based on the Cr2O3 - MgO - SiO2 system containing more than 60% Cr2O3 are reported. Analyzed by x-ray diffractometry and petrography, the synthesized materials display a phase composition represented by a complex spinel and escolaite. Tested for stability by molten alkali-free borosilicate E-glass, the synthesized refractories are shown to be not inferior in corrosion resistance to a chromium oxide-based ceramic refractory.

Arc Furnace Assisted Carbothermal Decomposition of Zircon

Results of a thermodynamic analysis of the reduction of silicon from zircon are presented and a method for carbothermal desiliconization of zircon using arc furnace technology are proposed. Fused materials with a residual silicon concentration of 10 – 17% are prepared that can be used in the manufacture of fusion-cast refractories.

The Structure of Fusion-Cast High-Chrome Oxide Refractories in the Cr2O3 - MgO - Al2O3 System

The phase composition and structure of fusion-cast refractories composed of 57.0 – 84.2% Cr2O3, 4.3 – 36.1% MgO, 2.0 – 9.7% Al2O3, and 2.4 – 6.9% SiO2 have been studied by petrographic and x-ray spectral microprobe analysis methods. Refractories high in MgO with modulus M = (Cr2O3 +Al2O3)/MgO = 1.64 – 3.1 are shown to consist of spinel phase Mg(Cr, Al)2O4 and silicate glass. Refractory materials (80.8 – 84.2% Cr2O3, 4.3 – 4.7% MgO, 2.0 – 9.7% Al2O3, and 2.7 – 6.9% SiO2 with M = 18.7 – 20.2) are three-phase systems composed of spinel, escolaite, and glass phase. These materials, owing to their high corrosion resistance, have promising potentiality for practical applications.

Synthesis and Properties of Fusion-Cast Refractories in the Al2O3– B2O3System

Synthesis and properties of fusion-cast high-alumina refractories in the Al2O3 – B2O3 system are reported. Adding B2O3 is shown to improve density and fabricability of the fusion-cast products. As shown by x-ray diffractometry and petrographic analysis, the phase composition of synthetic products is represented by corundum and 9Al2O3 ċ 2B2O3 boroaluminate. Corrosion tests in molten industrial glasses have shown the potential use of these materials in the melting technology of VS-92-grade optical lead silicate glass.

Synthesis and Properties of Fusion-Cast Refractories in the MgO – Al2O3System

Synthesis and Properties of Fusion-Cast Refractories in the MgO – Al₂O₃System

Cathodoluminescence (CL) Microscopy Application to Refractories and Slags

Refractories are ceramic materials possessing high thermal shock properties and slag corrosion resistance, as well as creep resistance at high temperatures. They are used in large quantities in steel making furnaces, metal smelting vessels, and glass melting tanks, and are made from very refractory minerals such as lime, periclase, corundum, spinel, and zirconia. Slags are residual vitreous materials generated during steel refining processes. They cover a wide range of compositions and may contain pure oxides, silicates, and sulfides as well as fluoride phases, depending on the melting and smelting processes. These minerals exhibit spectacular cathodoluminescence color when bombarded with electrons. Cathodoluminescence (CL) microscopy, therefore, is a very effective technique for the characterization of refractory corrosion by slags. Studies in this paper include: (1) reaction of fluorine containing mold slags with ZrO2-C nozzle refractories, promoting crystallization of cuspidine [Ca4Si2O7(F,OH)2], (2) corrosion of fusion cast refractories and formation of glass defects in TV panel glassmaking furnaces, and (3) densification of spinel-based castable in steel melting induction furnace.