Service of chamotte articles in furnaces for melting aluminum

Chamotte bricks are studied after service in the tank of a furnace for melting secondary aluminum. The deterioration of the lining is caused by the reducing action of molten aluminum mainly on the silica contained in the refractory. It is inferred that high-alumina refractories are more suitable for such furnaces.     

Review of corrosion of refractory in gaseous environment

Advancing high temperature technologies pushes the envelope of the service conditions to new extremes. However, corrosion of refractories substantially decreases the service life and causes unscheduled shutdown of manufacturing and processing plants. In this paper, corrosion of refractories in gaseous environments is reviewed. The corrosion mechanisms of alumina refractories, including alumino-silicates and zirconia as oxide, and silicon carbide as non-oxide refractory are emphasized due to their broad array of applications. It is shown that carbonaceous atmosphere and water vapor are detrimental for the oxide refractories. Interaction with water vapor leads to formation of the volatile species and subsequent recession of the refractories. Carbonaceous atmosphere leads to the decomposition of even mullite, which is categorized as neutral refractory due to its excellent thermochemical stability. Oxidizing atmosphere with water vapor dominates the corrosion of non-oxide refractories. Presence of impurities, even parts per million level, in the gas stream such as alkali vapor and halogens can alter the corrosion mechanisms and favor “hot corrosion.”     

Status and Progress of Refraetories for Aluminum Smelting Furnaces

Status and state-of-the-art progress on research,development and application of refractories for aluminum smelting furnaces and holding furnaces were reviewed and discussed in the present paper.The main types of aluminum smelting furnaces and smelting processes,and the service conditions of refractories and the requirements for refractory lining were also described and discussed.     

Corrosion of Disposing Urban Domestic Wastes on Refractories for Cement Rotary Kilns

Corrosion of burning urban domestic wastes to alkali-resistant bricks and spalling-resistant high alumina bricks was researched by static crucible method and SEM in order to choose refractories for cement rotary kilns for collaboratively disposing wastes. The result indicates that the main corrosion mechanism is slag permeation and corrosion; the emitted high temperature gases containing alkali,sulfur and chlorine during burning the wastes react with refractories forming low melting point sulfate,chloride and compound salts,which metamorphose the refractories,and the loose metamorphic layer is easy to spall under thermal stress. So,corrosion resistance and spalling resistance shall be taken into account when choosing refractories for cement rotary kilns for collaboratively disposing wastes. It is suggested that decomposition furnaces should adopt spalling resistant high alumina bricks and anti-coating Si C castables,and preheating equipment should adopt high strength alkali-resistant bricks and castables.     

有色金属火法冶炼用耐火材料及其发展动向

根据近些年来有色重金属与轻金属火法冶炼工艺技术的发展,从有色重金属与轻金属火法冶炼条件的特点分析与阐述了所用耐火材料发展的动向,着重介绍了有色金属冶炼炉如:闪速炉、澳斯麦特炉、艾萨炉、诺兰达炉、转炉、连续炼铜炉、氧气底吹熔池直接炼铅炉(QSL炉)、铅锌密闭鼓风炉(ISP炉)、粗锌精馏炉、锌浸出渣挥发回转窑、碱石灰法回转窑、焙烧炉、铝电解槽、铝熔化炉以及硅热还原法制原镁等窑炉关键部位所用的耐火材料。另外,为了给上述冶炼炉的关键部位选择合适的耐火材料,还对一些耐火材料组元的抗FeO-SiO2渣侵蚀,抗炉渣与锍的渗透以及在炉衬工作面形成保护层等方面进行了分析与论述。此外,化学热力学计算与现场试验结果表明,含碳耐火材料不适宜用在重有色金属冶炼炉。还介绍了不同品种的镁铬耐火材料与碳化硅质耐火材料以及Al2O3-Cr2O3-尖晶石材料,并对含Cr2O3耐火材料存在的问题与解决途径做了分析与建议。     

Evaluation of Corrosion Resistance of Refractory Materials in Furnaces for Melting Frit Glazes

The corrosion resistance of refractories to frit melts applied at the Velor Nompany (city of Orel) are investigated. Based on the results of the study, it is proposed to replace the refractory MKS, which is currently used in furnaces for melting frit glazes, by the refractory material KMTs that is more resistant to frit melts.     

Cladding and corrosion characteristics of magnesium-aluminum spinel refractory by alkaline slag during alkali recovery

The alkaline slag produced during alkali recovery might cause harm to the furnace's refractory components. The seat-drop technique and static dry pan method are used to explore the cladding features and corrosion characteristics of alkaline slag on the surface of magnesia-alumina spinel refractory in this paper. SEM-EDS and XRD are used to study the microstructure, fundamental changes, and compound composition of the molten cladding and interfacial layers, as well as the trends of slag column alterations. Factsage 7.2 software is used to model the interaction between the molten slag and the refractory. The results demonstrate that the wettability process of the slag column is impeded in a reducing environment. Combine with the results of the thermodynamic simulate, it is found that the formation and transformation of a large number of high melting point compounds in a reducing atmosphere is the decisive reason for the inhibition of wettability. Temperature increases promote the production of high melting points substances such as magnesium silicate and sodium metal aluminate, which alters the micro-morphology of the materials and improves slag resistance and permeability resistance of refractories.     

Methods of determining the corrosion resistance of glass-tank refractories

Conclusions When laboratory investigations are being carried out to find resistant refractories for glass tank furnaces it is desirable to make simultaneous use of indirect and direct methods of assessing corrosion resistance.The use of indirect methods for determining corrosion resistance in refractories permits us to explain the nature of the interaction between the refractory and glass, to study the nature and properties of the reaction products, and also to select refractories that form with the glass the most infusible or viscous reaction products for subsequent investigation in molten glass.The direct methods permit direct determination of the rate of corrosion of refractories by glass at working temperatures and allow us to recommend the most corrosion resistant refractories for tests in service conditions.In laboratory conditions we established that the most corrosion resistant refractories in regard to original glass used for obtaining slag sitalls are bakor-33 and dense zirconium refractory. This may be explained by the formation of viscous reaction products in the contact layer which have a protective action on the refractory.Translated from Ogneupory, No. 5, pp. 56–60, May, 1967.     

Development and Application of Refractory Materials for Molten Aluminum Applications

Two new refractory materials have been developed for use in molten aluminum contact applications that exhibit improved corrosion and wear resistance leading to improved thermal management through reduced heat losses caused by refractory thinning and wastage. The development of these materials was based on an understanding of the corrosion and wear mechanisms associated with currently used aluminum contact refractories through physical, chemical, and mechanical characterization and analysis performed by Oak Ridge National Laboratory (ORNL) and the University of Missouri, Rolla Rolla (UMR), along with their industrial partners, under the ITP Materials project "Multifunctional Metallic and Refractory Materials for Energy Efficient Handling of Molten Metals." Spent castable refractories obtained from a natural gas-fired reverberatory aluminum alloy melting furnace were analyzed, leading to identification of several refractory degradation mechanisms and strategies to produce improved materials. The newly developed materials have been validated through an R&D industrial trial.     

REQUIREMENTS OF REFRACTORIES FOR ELECTRIC FURNACES1

This article is essentially a survey, giving, however, not generalized statements, but a definite discussion of the refractories problems now existing in the important electric furnace processes. After summarizing some of the general refractory requirements of electric furnace work, the author discusses the specific conditions and refractory requirements in steel, iron, and non-ferrous metal melting, smelting furnaces for producing iron, ferro-alloys and calcium carbide, anti in furnaces for melting refractory materials. The article closes with a summary of outstanding present developments. Varied conditions probably make an ideal, universal refractory almost impossible of attainment. The relatively cheap refractories standardized in fuel-fired furnaces have been very largely used in electric furnaces. There is, however, a growing use for specialized “super-refractories,” even at greatly increased cost, that will stand various especially severe conditions in certain kinds of work. Important recent developments are higher firing temperatures, the use of high aluminous fire clays, and increased experimental work on fused refractories. The commercial production of sufficiently high firing temperatures, and the development of satisfactory bonds for special refractories are at present perplexing problems.     

Interaction of magnesium-containing refractories and melts of optical glass

The interaction of magnesium-containing refractory materials and optical glasses is considered. It is shown that in most cases such materials cannot be used in glass melting because their corrosion resistance is lower than in conventional refractories owing to the formation of stones and crystalline inclusions in the glass. It is possible to use magnesium-containing refractories for melting high-lead glass.     

Use of aluminum phosphate as a bond for refractory corundum products and washes

Summary The use of aluminum phosphate is desirable for preparing corundum products and washes based on commercial calcined alumina.A composition was developed ensuring strong bonding of corundum refractories and also of corundum refractories with steel and graphite.The bonded refractory components (corundum) are tightly held on graphite components of thermocouples after 15 h operation in the walls of electric arc furnaces at 2000°C.Aluminophosphate bond increases the spalling resistance of corundum products and also raises their strength.     

REFRACTORIES AND REFRACTORY CEMENTS FOR THE NONFERROUS FOUNDRY1

Development in refractory linings for the various furnaces encountered in the nonferrous foundry industry is outlined, and figures given showing the present trend. These include open-flame, crucible, and electric furnaces. The open-flame furnaces formerly used firebrick linings, but silicon-carbide and high alumina refractories are coming into use. The crucible furnace linings show a decided preference for silicon-carbide refractories, while the electric furnaces are partial to the alumina and mullite bearing types. Progress in the manufacture of refractory cements and their use in the various types of furnaces is discussed. Data are given which indicate that the use of the proper types of cements for maintaining furnace linings of similar composition is becoming more general.     

Reaction of high-alumina refractory with chromium vapors in vacuum

Conclusions The main cause of the failure of high-alumina refractory of mullite composition during service in vacuum furnaces is the chemical reaction of chromium vapors with the alumina, as a result of which a readily melting vitreous silicate substance is formed together with gaseous silicon monoxide and corundum with chromium dissolved in it. Therefore, in order to increase the life of linings of vacuum furnaces it is necessary to use high-alumina refractories with a maximally high content of Al₂O₃.Translated from Ogneupory, No. 6, pp. 38–40, June, 1969.     

Thermodynamic calculation and microstructure characterization of spinel formation in MgO–Al2O3–C refractories

In this paper, by simulating the gas phase conditions inside the MgO–Al₂O₃–C refractories during continuous casting process and combining with thermodynamic analysis, as well as SEM analysis, the gas-gas and gas-solid formation of MA spinel were clarified in carbon containing refractories. Thermodynamic calculations showed that gas partial pressure of CO, O₂ and Mg could meet the formation and stable existence conditions of MA spinel in MgO–Al₂O₃–C refractories under service environment, and nitrogen could not affect the formation of MA spinel at 1550 °C in the thermodynamic condition. The formation processes of MA spinel were analyzed experimentally under embedding carbon atmosphere. The carbon-coated alumina powders in MgO–Al₂O₃–C refractories prevented the direct contact between magnesia and alumina. Mg gas was formed by carbon thermal reaction, then reacted with alumina (gas-solid) and gas containing aluminum (gas-gas) to generate MA spinel. Through gas-gas or gas-solid reaction, the formation of MA spinel was effectively controlled. By means of SEM analysis, a two-layer structure with dense outer spinel layer and loose inner layer was formed in MgO–Al₂O₃–C refractories.     

Increasing the lining life of arc furnaces for melting of cobalt

Conclusions Experimental refractory parts and a ramming mixture produced from baddeleyite concentrate have been successfully tested under conditions of the pyrometallurgical processes for production of cobalt.The chemical composition and microstructure of magnesite and baddeleyite refractories after service in production furnaces for melting of cobalt were investigated.It is desirable to line these furnaces differentially. The point of maximum wear, the charging hole, is lined with castable refractories, the side walls in the zone of entry of the electrodes with granular baddeleyite mixture-base sintered refractories, and the zone of the journals with monolithic shaped inserts produced from baddeleyite ramming mixture. The remaining portion of the lining must be made of increased density magnesite brick. Such a lining method makes it possible to substantially lengthen the furnace campaign and reduce repair costs, which in general leads to an increase in their productivity.Translated from Ogneupory, No. 2, pp. 48–51, February, 1989.     

Creep strain recovery of an in situ spinel-forming refractory castable under loading/unloading compressive creep conditions

Creep strain recovery after unloading has been well studied for metals and certain ceramic composites; however, it has not yet been investigated for ordinary ceramic refractories applied in industrial furnaces. The present study explores the question whether creep strain recovery can be observed in ordinary ceramic refractories to justify its consideration in the design of such refractories and refractory linings. To this end, the dependence of creep strain recovery on different loading conditions was investigated for a high-alumina in situ spinel-forming castable, commonly used as refractory lining of steel ladles in secondary steel metallurgy. Several loading/unloading compressive creep tests were performed at 1300 °C for different loading histories. Creep strain recovery was observed to occur and it was significantly affected by the holding time and degree of unloading. A longer holding time for the loading period was found to increase the internal stress, which is the driving force for creep strain recovery. In addition, the findings indicate that a higher excess of internal stress over external stress after unloading induces higher strain recovery.     

Interactions of high-chromia refractory materials with infiltrating coal slag in the oxidizing atmosphere of a cyclone furnace

The mechanism of high-chromia refractory failure in the oxidizing atmosphere of cyclone furnaces differs from the reducing atmosphere in gasifiers. In this paper, postmortem analysis was conducted to investigate the changes in the microstructures of exposed high-chromia refractory caused by its interaction with infiltrating coal slag under cyclone furnace conditions. The effects of the temperature level and viscosity of the molten slag were also investigated. Postmortem analysis confirmed that the form of Fe found in the slag in an oxidizing atmosphere was Fe₂O₃ rather than FeO, the phase present in a reducing atmosphere of gasifiers. Furthermore, the higher melting temperature of Fe₂O₃ weakened the slag penetration and chemical corrosion in an oxidizing atmosphere. As coal slag infiltrated a high-chromia refractory, Fe₂O₃ in the slag reacted with Cr₂O₃ until Fe₂O₃ was depleted in the penetrating slag. Cr₂O₃ was dissolved in the slag because of the permeation of the slag in large pores of the refractory. The depth of the slag penetration increased as the temperature increased because of its lower viscosity at higher temperature.     

Isothermal corrosion testing of frit furnace refractories

In this paper, the corrosion behaviour of aluminosilicate type refractories in frit melts is studied in an isothermal corrosion test setup. A refractory brick of largely andalusite and sillimanite composition was compared to another refractory brick of mullite and sillimanite composition, both of which were made by different manufacturers for use in different frit furnaces. The industrial frit used for corrosion tests was a commercial product used in a wall tile glaze formulation. Corrosion tests conducted under isothermal conditions provide quantitative and reproducible data about the corrosion performance of refractories. In this study, tests were performed by partially immersing a 15 mm × 15 mm × 115 mm refractory specimen into a frit melt at temperatures between 1404 and 1504 °C. The effects of temperature, duration of exposure and the refractory brick type were investigated using a statistically designed set of experiments. The ANOVA (analysis of variance) table indicated that temperature and test duration were the most important factor effects, as expected. Increasing both temperature and exposure duration led to an increased amount of corrosion as measured by the cross-sectional area loss of the corroded refractory specimen. Postmortem microstructural analysis was also done on the specimens, with extensive amount of ZnO·Al₂O₃ precipitation observed along the frit–refractory interface, where crystals of mullite and alumina were also found to precipitate. Increasing the amount of exposure time and temperature produced more ZnO·Al₂O₃ precipitation. As identified by SEM-EDS analysis, mullite crystals were in the needle-like morphology, while alumina crystals were generally cubic. Additional experiments were conducted by rotating the specimens in the melt at 50 rpm of rotational speed. Due to the reduction of boundary layer thickness, more dissolution was observed from the rotated specimens. In all specimens, corrosion was more pronounced in the bond phase than through the large filler grains of mullite and andalusite.     

Operation of type OKB-2126 furnaces for production of molten and cast refractory materials

Conclusions Literature and experimental data on operation of type OKB-2126 furnaces in melting of various refractory materials is summarized. The use of their temperature in melting into an overflow is proposed as a universal index of the basic properties of molten refractories. The relationships of the basic melting parameters and the operating indices of type OKB-2126 arc furnaces to the temperature of the metal being poured were established. The maximum melting point the material of which it is desirable to produce by melting into an overflow was determined. The data obtained may be used in evaluation of the melting parameters of new forms of refractory materials and also for determination of the operating indices of more powerful furnaces.Translated from Ogneupory, No. 5, pp. 38–42, May, 1989.