Prospects for using aluminosilicate refractories for aluminum electrolyzers. Part 2. Resistance of aluminosilicate refractories to the action of commercial electrolyte

Data are provided for laboratory studies of the resistance of aluminosilicate refractories to the action of commercial electrolyte. It is established that refractory ShPD_M-45, prepared using a mullite-corundum chamotte, is most resistant to electrolyte action. Results are provided for studies in the change of mineral composition and phase transformations in aluminosilicate refractories during reaction with commercial electrolyte. It is shown that long-prismatic titanium-containing mullite is more resistant to the action of the fluoride ion than short-prismatic material. __________ Translated from Novye Ogneupory, No. 10, pp. 26–32, October 2007. Part 1 of the article was published in Novye Ogneupory No. 9 (2007).     

Prospects for using aluminosilicate refractories for aluminum electrolyzers. Part 1. Features of the structure of aluminosilicate refractories intended for aluminum electrolyzers

Comparative analysis is provided for the structure and properties of aluminosilicate refractories grade ShPD. It is established that refractory ShPD_M-45, produced with the use of an addition of mullite-corundum chamotte surpasses in all characteristics refractories prepared by the normal technology. Refractory ShPD_M-45 may be recommended for use in aluminum electrolyzers. __________ Translated from Novye Ogneupory, No. 9, pp. 20–23, September 2007.     

Wetting of aluminosilicate refractories with cast iron

Conclusions The magnitude of the wetting angle of molten cast iron on aluminosilicate refractories depends on the structure, phase composition, and physicochemical properties of the solid material and the melt. An increase in the temperature from 1140 to 1500°C causes the wettability of the refractories by molten cast iron to increase as a result of the increase in the content and chemical activity of the liquid phase in the refractory.An increase in the open porosity of sintered kaolin refractories from 8 to 16% results in a decrease in the wetting angle of cast iron at 1350 and 1500°C from 122 to 108° and from 119 to 102°, respectively; at 1140°C the wetting angle increases with the open porosity.The largest wetting angles of cast iron occur on high-density mullite and kaolin refractories containing a minimum of glass phase.Translated from Ogneupory, No. 5, pp. 35–38, May, 1978.     

Corrosion of aluminosilicate refractories by molten aluminum and melts based upon it in melting and casting units

Corrosion mechanisms are proposed for aluminosilicate refractories by molten aluminum taking account of new ideas about physicochemical reaction of molten aluminum with refractory.With a negative volumetric effect for aluminum reactions with components of aluminosilicate refractories reaction products will not form a continuous film, and with a positive volumetric effect the reaction products will split pores and cause material cracking. Aporous aluminum oxide film will not be a barrier for the reaction of aluminum with refractory. The possibility for aluminosilicate refractories of wetting by molten aluminum and the size of pores permeable for penetration of molten aluminum in relation to presence or absence of antiwetting additions are determined.     

Abrasion resistance of aluminosilicate refractories for rotary kilns

Conclusions An investigation was carried out of the abrasion resistance of aluminosilicate refractories for rotary kilns by two methods, viz., on a sandblaster and on a grinding wheel. The first method gave more precise and reliable results. The test conditions on a sandblaster are optimal with an air pressure of 1.5 kgf/cm².The results of the investigation of the abrasion resistance and its variation with the elastic and strength properties of aluminosilicate brick were evaluated by methods of mathematical statistics. It was found that the abrasion resistance of aluminosilicate refractories depends largely on the strength and elastic modulus of the product.The abrasion resistance determined on a sandblaster is a reliable criterion for a prediction of the potential durability of refractories in the cold zones of rotary kilns.The bricks produced by the Novomoskovsk Refractories Plant from semiacid clays are more resistant to abrasion than the chamotte bricks produced by that Plant, a fact which is demonstrated by the performance of these brick types in the rotary kilns of the Achinsk Alumina Combine and the Magnezit Combine.Translated from Ogneupory, No. 5, pp. 42–46, May, 1978.     

Wettability of aluminosilicate refractories with molten steel

Conclusions An increase in the Al₂O₃ content of the base causes the wetting angle of steel 10kp to increase with an increase in the temperature from 1490 to 1620°C.Chromium-nickel steel wets refractories to a greater degree than rimmed steel. In this case the wetting angle is largest on mullite-corundum refractories containing 75–78% Al₂O₃.The introduction of small amounts of modifying additives in the form of MgO and Cr₂O₃+ ZrSiO₄ into mullite-corundum and corundum refractories causes the wetting angle to increase by 7–10° and helps to increase the resistance of the refractory materials to the action of rimmed steel.Translated from Ogneupory, No. 4, pp. 53–56, April, 1978.     

Main factors affecting the thermal stability of aluminosilicate refractories

It is shown that the partial pressure of oxygen and thermocycling in variable gas media are the main factors characterizing the thermal stability of aluminosilicate refractories. The obtained functional dependences of the variation of the properties of the refractories are described by equations.     

Obtaining aluminosilicate refractories by the hydrothermal method

Conclusions On the basis of aluminosilicate bond made from heat-processed hydrated alumina and quartz sand in the molecular ratio of Al₂O₃: SiO₂=32, in conditions of autoclave processing at 800–1000 kg/cm² in a period of 8–12 h, it is possible to obtain unfired aluminosilicate refractories with quite high physico-chemical factors.During the heating of the specimen after autoclave processing to the temperature of sintering, their strength diminishes to a small extent, which makes it possible to use these refractories directly in structures.The high strength of aluminosilicate refractories after autoclave processing is due to the formation of a gel-like hydrated aluminosilicate upon the interaction of Al(OH)₃ with SiO₂.The technology developed for the production of unfired autoclave firebrick and high-alumina refractories permits us to obtain large products which make it possible to industrialize their transportation and laying, and to reduce the number of joints in the lining.Translated from Ogneupory, No.1, pp.15–19, January, 1967.     

Changes in the properties of aluminosilicate refractories under prolonged reducing conditions

Conclusions Studies of corundum and aluminosilicate refractories of dense and granular structures in an atmosphere of hydrogen and dissociated ammonia at 1200, 1500, and 1700°C in periods of 175 and 50 h showed that the resistance of the products increases with an increase in the alumina concentration and density. The maximum resistance is exhibited by corundum products. In the aluminosilicate refractories there is some additional sintering of the material with the separation of mullite and glass. Simultaneously on the surface of the specimens we detected deeper mineralogical changes, accompanied by the decomposition of the mullite, with the formation of corundum, silicon monoxide, and glass.The changes in the phase composition are accompanied by a change in the structure, and an increase in the creep. Considering that a reduction in the temperature of 100°C causes a reduction in the creep by approximately a half [26], it can be recommended that corundum refractories should be used (under a load of 2 kg/cm²) in a reducing atmosphere at temperatures of up to 1550–1600°C, sillimanite up to 1450–1500°C, kaolin and chamotte (high-grog) up to 1300°C, with a reduction in the load and an increase in the density, the temperature of application for the products examined, especially corundum, can be increased.Translated from Ogneupory, No.5, pp.26–32, May, 1972.     

Measuring the high-temperature strain and creep in nonfired refractories

Instrumentation and methodology for the experimental study of high-temperature strain and creep under load in phosphate-bonded nonfired refractories are described. Results for nonfired aluminosilicate, corundum, silicon nitride, and other refractory composites are reported. __________ Translated from Novye Ogneupory, No. 4, pp. 121–125, April, 2006.     

Creep of aluminosilicate refractories

Conclusions Investigations were made of the creep of industrial aluminosilicate refractories of various types, differing as regards the original materials, phase composition, the properties of the glass phase, and the structure. The results of the investigations characterize the plastic properties of materials in a fairly broad range of temperatures and stresses.Translated from Ogneupory, No. 7, pp. 39–43, July, 1969.     

Silicon carbide refractories with a sialon binder

An investigation concerning molding of silicon carbide refractories with a sialon binder was carried out. It is shown that the alumina-containing component plays an important role in the synthesis of the sialon binder. A corundum addition to the composition of silicon carbide refractories ensures higher parameters for the refractory as compared to a mullite addition. With an increase in the content of crystalline silicon the strength of silicon carbide refractories grows sharply due to the increased amount of -sidalon. Refractories with elevated contents of sialon in the binder have better resistances to alkali, slag, and molten metal than refractories with binders containing silicon nitride.Translated from Ogneupory, No. 4, pp. 2–4, April, 1995.     

Change in structure and some properties of industrial aluminosilicate refractories under prolonged anneals at high temperatures

Conclusions A study was made of the change in the structure and some properties of aluminosilicate refractories after prolonged heat processing at 1350–1500°C. The changes in the structure of the refractories occur mainly after heating at 1500°C, and consist in the redistribution of the glassy phase and some increase in the mullite crystals. In the fireclay refractories there was an increase in the quantity of glass phase, because of which its porosity sharply diminished.The change in the structure in aluminosilicate refractories is much lower than in pure-oxide materials, so the properties of these refractories after prolonged heating hardly change.Translated from Ogneupory, No. 6, pp. 27–30, June, 1970.     

Effect of boron nitride addition on some properties of aluminosilicate refractories

Conclusions An addition of 10–60 wt.% of boron nitride significantly alters the thermal conductivity, thermal expansion, and the elastic modulus of aluminosilicate refractories.As the boron nitride content is increased from 1–60% the strength of specimens heated in a nitrogen atmosphere with an oxygen content of 0.02% decreases.During cyclic heat treatment in an oxidizing atmosphere between 900 and 20°C additional bonds develop between the particles of the aluminosilicate and the oxygen-free additive. As a result the strength of the specimen increases.The thermal shock resistance of the specimens increases with an increase in the amount of boron nitride addition. Specimens with 40–50% boron nitride addition are in practice insensitive to temperature drops in the range 20–2400°C.Aluminosilicate refractories with the addition of 30–40 wt.% of boron nitride can be used as lining material in high temperature systems with brief nonsteady or cyclic work schedules.Translated from Ogneupory, No. 4, pp. 36–39, April, 1968.     

The physical and mechanical properties of alumina-based ultralow cement castable refractories

In this study, the effects of the type of alumina on the physical, chemical and mechanical properties of the ultralow cement castable (ULCC) refractories were investigated. Brown fused alumina, tabular alumina and rotary bauxite-based ULCC refractories were prepared by mixing each type of alumina with silicon carbide, carbon, cement, metallic silicon and microsilica. The density, porosity and cold crushing strength (CCS) of the refractory castables were measured after drying at 110 °C for 24 h and firing at 1450 °C for 5 h. The slag penetration resistance of the refractory castables was determined using slag corrosion tests. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) were used to characterize the castables. It was found that all three refractory castables had strong slag penetration resistance and that the tabular alumina-based refractory castable had the largest specific cold crushing strength with an acceptable percent of porosity among the refractory castables.     

Industrial test batch of carborundum refractories with silicon nitride binder

Conclusions The production process developed at the All-Union Institute of Refractories and tested at the Semiluki Plant showed that the properties of carborundum refractories prepared with a silicon nitride binder are superior to the popular carborundum bricks made with silica binders.A final conclusion on carborundum refractories with silicon nitride binders will be made on the basis of industrial performance.It is recommended that the authors investigate the homogeneity of specimens from different muffles as well as that of one specimen. Furthermore, a method for the elimination of free silicon has to be suggested and the behavioral changes of refractories with free silicon observed at elevated temperatures and in oxidizing medium.     

Corrosion of oxide bonded silicon carbide refractories by molten salts in solid waste-to-energy facilities

Oxide bonded silicon carbide refractories are used successfully in solid waste-to-energy facilities (WtE). They are submitted to severe thermo-chemical stresses that limit their performance. Even if the corrosion resistance of silicon carbide is high, wear and failure of refractory lining are currently observed.For a better understanding of corrosion mechanisms, oxide bonded silicon carbide refractories, collected in the combustion chamber of several WtE facilities, were examined. The main mechanisms of corrosion, according to the environment of refractories, were determined. The chemical composition and the nature of the corrosive agents were calculated from the thermo-chemical modeling. They are mainly condensed phases of sulfates and chlorides (CaSO₄, K₂SO₄, Na₂SO₄, KCl, and NaCl). In service conditions, these molten salts react with the SiC aggregates and the matrix of the refractories to form low melting compounds.The post-mortem analyses showed the formation of para-wollastonite in the porosity and around the SiC grains, on the hot face of refractory tiles. Other phases such as cristobalite and microline (KAlSiO₈) were also formed down to the core of refractories. The volume expansion created by the formation of new mineral phases (cristobalite, para-wollastonite) causes the formation of micro cracks in the refractory lining.In this paper, the degradation mechanisms of oxide bonded silicon carbide refractories are presented and the main research developments for the future are discussed.     

Differentiated use of refractories in blast furnace linings

Properties of aluminosilicate, silicon carbide, and carbon refractories and mixtures used for lining blast furnaces and recommended for the future are presented. Recommendations are given for changing the design of some lining zones with the aim of increasing their endurance and reliability in service.     

Development of fireclay aluminosilicate refractory from lithomargic clay deposits

Lithomargic clay until now has not been utilised to produce refractory bodies due to its low plasticity. In this work, the development and evaluation of fireclay refractory material produced from lithomargic clay deposit has been studied by addition of clay binder. Three formulations were prepared by mixing, semi-dry moulding, drying and firing at temperatures ranging from 1200 to 1400 °C. The fired samples were investigated to determine their physical properties such as bulk density, apparent porosity, linear firing shrinkage, and cold crushing strength. The chemical and mineralogical compositions were also determined. The results show that the linear firing shrinkage values were within limits acceptable for refractory clays. The cold crushing strength increases as temperature increased to 1400 °C. Cold crushing strength increased with increasing binder content. The increase of the highly refractory phases (cristobalite and mullite) and the densification of the bricks due to the presence of fluxing agents were responsible for the high cold crushing strength values. The investigated properties indicate that lithomargic clay underlying bauxite deposits could be used to produce fire clay aluminosilicate refractories.     

Resistance of silicon carbide referactories to the effect of aluminum melt and aluminum chloride vapor

Silicon carbide refractories with binders of silicon nitride and silicon oxynitride are compared with dense aluminum silicate refractories. It is shown that silicon carbide refractories possess high stability in aluminum melts and vapors of aluminum chloride, whereas aluminosilicate refractories are severely damaged under these conditions. Silicon carbide refractories with a binder of silicon nitride possess the highest resistance to the effect of the tested aggressive factors and are recommended for operation in aluminum melts and gaseous aluminum chloride media.Translated from Ogneupory, No. 12, pp. 2–5, December, 1995.