Low-iron bauxites of the Iksinskoe deposit

Iksinskoe-deposit bauxites (5 samples) with 65 – 75% Al₂O₃ were analyzed and used in ladle refractories which were tested in the lining of a ladle-furnace of a vacuum degassing plant. Their durability has turned out to be not inferior to that of mullite-corundum refractories based on commercial alumina.Translated from Ogneupory, Vol. 35, No. 1, pp. 13–17, January, 1994.     

Mullite corundum articles for electric furnace roofs

Conclusions Using a method developed by the Institute we produced an experimental batch of synthetic mullite-corundum refractories containing more than 72% Al₂O₃. The properties of these refractories exceed similar properties for regularly produced articles close in composition, which enables us to recommend them for use in the roofs of arc electric steel-melting furnaces.The experimental batch of synthetic mullite-corundum articles is being sent for testing in DSP-100 furnaces at the Chelyabinsk Metallurgical Combine.Translated from Ogneupory, No. 7, pp. 22–25, July, 1986.     

Effect of the basic properties of platelike corundum on its metal resistance

Conclusions It has been established that the wetting angle of sintered corundum by steel and the metal resistance of the corundum increase significantly with the concentration of Al₂O₃ and with its density.The size of the sintered corundum crystals, other things being virtually equal, does not have a significant effect on the angle of wetting by steel and on the metal resistance.An increase in the Al₂O₃ concentration in the initial aggregations of sintered corundum grains and an increase in their density help to improve the metal resistance of the corundum specimens made from that material.Translated from Ogneupory, No. 2, pp. 41–46, February, 1981.     

Resistance of corundum refractories to basic electric steel slags

Conclusions Upon reaction with slag corundum specimens exhibit a substitution of corundum by calcium hexa and di-aluminates. This process occurs most intensely in the bond part of the refractory and over the periphery of the fragment of fused corundum.The temperature of the eutectic between CaO·2Al₂O₃ and CaO·6Al₂O₃ is 1730 ± 10°C, and corresponds to the operating temperature of refractories in the slag belt of electric furnaces.The formation of calcium aluminates around the fragments of corundum and in the bonding part tends to reduce the refractories of the altered zones of material and the wear by fusion. Therefore corundum refractories are not reccomended for lining the slag belt of electric steel smelting furnaces.Translated from Ogneupory, No.5, pp. 41–44, May, 1970     

Changes in high alumina brick used in hot air stoves

Conclusions Aluminous brick made by the Semiluks Refractories Plant containing 60% Al₂O₃ sinters intensely, with sharp changes in properties and reductions in refractoriness from 1810 to 1750°C when used at temperatures of 1500–1600°C.The least-change zone and working zone of the refractory consist mainly of mullite and glassy substance. The amount of mullite increases in the direction from the least-change to the working zone.It is necessary to use high alumina refractories with a higher content of Al₂O₃ (70–72%), preferably with increased density, in order to increase the life of the linings in hot air stoves.Translated from Ogneupory, No. 6, pp.29–32, June, 1968.     

Effect of nickel nitrate on phase changes in mullite and mullite — Corundum refractories when heated in oxidizing and reducing conditions

Conclusions During heating in oxidizing atmospheres of mullite-corundum specimens with an addition of nickel nitrate at 500–900°C, NiO is formed, and an increase in temperature from 900 to 1500°C is characterized by the development of nickel spinel, NiAl₂O₄, the quantity of which increases with an increase in the content of the Ni(NO₃)₂ · 6H₂O, and the firing temperature.The high temperature diffractometric method showed that in the system 3Al₂O₃ · 2SiO₂-NiO heating in oxidizing conditions, and commencing at 1000°C, NiO decomposes the mullite with the formation of aluminonickel spinel, whose quantity rapidly increases with further temperature rise. At 1500°C the mullite is preserved in small quantities.The nickel spinel, formed as a result of heating to 1300°C the mullite-corundum refractory containing 25% Ni(NO₃)₂ · 6H₂O during firing in the silicon carbide mixture and in the hydrogen atmosphere at 1400°C for 30 min, in the main decomposes with the separation of metallic nickel and corundum. However, x-ray patterns confirm that in these conditions the nickel spinel is not completely decomposed.Translated from Ogneupory, No.5, pp.32–36, May, 1972.     

Refractories for lining blast furnaces

Conclusions At the Chasov Yar refractories combine we developed and introduced a technology for the production of chamotte kaolin refractories with a porosity of not more than 12% and a mass proportion of not less than 42% Al₂O₃ on the basis of chamotte from high-grade Polozhe kaolin, and also additions to the batch of finely milled mullite-corundum chamotte.Using the new technology we produced a batch of goods designated ShPD-42 for lining the shafts, bosh, and upper parts of blast furnaces of large capacity.Deceased.Translated from Ogneupory, No. 5, pp. 32–36, May, 1985.     

Sintering and some properties of mullite-corundum ceramic obtained from pure oxides

Conclusions The effect of the total concentration of SiO₂ and the method of preparation of the batch on the sintering and some of the properties of a mullite-corundum ceramic made from pure oxides has been studied.It is established that the sintering of the ceramic made from batches of various compositions containing mixtures of SiO₂ and Al₂O₃ is significantly more difficult than when analogous batches containing previously sintered mullite are used. With an increase in the concentration of Al₂O₃ in the batch with the previously synthesized mullite, the apparent density and strength increase while the open porosity decreases.The sintering of the mullite-corundum ceramic of the composition 10% SiO₂+90% Al₂O₃ containing previously sintered mullite differs from corundum and mullite by its significantly higher thermal-shock resistance.Translated from Ogneupory, No. 6, pp. 51–54, June, 1980.     

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.     

Cast refractories of the Al2O3-Cr2O3-CaO system

Conclusions In order to develop stable materials for glassmaking, we studied the physical and technological properties of the refractories belonging to the Al₂O₃-Cr₂O₃-CaO system that contain 5–20% CaO, 15–35% Cr₂O₃ and 45–80% Al₂O₃.The glass resistance of the refractories of the experimental systems (compositions) exceeds that of the BKCh-33 baddeleyite-corundum products by 3–5 times and their thermal shock resistance is superior to that of the well known chromium-containing refractories at comparable levels of mechanical properties.The developed refractories are recommended for the top or the bottom structures of the glassmaking furnaces depending on their glass resistance and thermal shock resistance and for making the refractory components of ferrous metallurgical units that are in contact with highly basic slags.Translated from Ogneupory, No. 3, pp. 23–26, March, 1989.     

Action of gaseous atmospheres and temperature on the properties of aluminosilicate refractories saturated with nickel catalyst

Conclusions Kaolin and kyanite-sillimanite refractories during heating in hydrogen up to 1500°C sinter intensely, as a result of which there is a sharp reduction in the porosity, and an alteration in other properties.All the tested aluminosilicate refractories containing 42–62% alumina when heated up to 1500°C in hydrogen rapidly lose their weight as a result of the reduction of the SiO₂, changing the structure of the surface layer, which is an active part of the catalyst carrier. These refractories cannot be recommended as carriers operating at high temperatures.The high-alumina refractories containing 79 and 90% Al₂O₃ have a much lower loss in weight, and during heating slightly change their porosity and other properties; they can be used as carriers for nickel catalysts.Translated from Ogneupory, No. 8, pp. 30–36, August, 1971.     

Synthesis and Properties of Fusion-Cast Refractories in the Al2O3 – ZrO2 System

The synthesis and properties of fusion-cast refractories in the Al₂O₃ – ZrO₂ system studied by x-ray phase analysis and petrography are reported. The phase composition of synthetic materials is represented by corundum and ZrO₂ monoclinic modification. Adding ZrO₂ results in a decrease in the size of corundum crystals. The corrosion resistance of the synthetic refractories increases with ZrO₂ concentration; still, further effort is needed to improve the fabricability of fusion-cast Al₂O₃ – ZrO₂-based refractories.     

Study of the service of high-alumina and kaolin refractories in the checkers and structure of blast-furnace stoves

Conclusions The structure of kaolin brick in the high-temperature zone of the stove after 6.7–7.2 years service at subcupola temperatures of 1300°C underwent substantive external and structural changes.In the structure of the stove made from high-alumina brick VGO-62 after six years service we detected substantially less change.In the kaolin brick of the upper rows of the checker three clearly defined zones are formed: working (slag), impregnated with alkalis, the transition zone (porcelain-type), and the least-changed zone. During the service of high-alumina refractories mullite crystallizes, which confirms the results of work carried out previously.Owing to the creep of kaolin and high-alumina refractories 4–5% shrinkage of the brick occurs in the upper rows of the checker, and at a depth of 2.5–6.0 m — 1.5–2.0%. The height of the checker diminishes under these conditions by 0.8–1.0 m.The densification of the structure of the upper rows of the checker corresponds to a reduction in porosity and an increase in the density of the brick.The temperature of initial deformation under load of 2 kg/cm² of the slagged kaolin refractories taken from the upper rows of the checker diminishes by 150–200°C, and in the lower layers of the checker it does not alter. This factor for high-alumina refractories in service increases by 160–190°C. In the high-temperature zone of the stoves it is desirable to test dense, high-alumina refractories containing 72–75% Al₂O₃.Translated from Ogneupory, No. 5, pp.14–19, May, 1972.     

Refractory Clays of the Southern Berlinskoe Deposit Studied for Technological Application

Clays sampled from three core sites of the southern area of the Berlinskoe deposit (Chelyabinsk District, Russia) are analyzed for potential technological application. The clays containing 30.9 – 35.73% Al₂O₃ have a refractoriness of 1670 – 1690°C. The clays can be used as a binder for fabricating chamotte refractories (sample 1) and as a material component for building structures (samples 2 and 3).     

Properties of RO-Y2O3-Al2O3-SiO2 glasses

The coefficient of linear expansion, glass-transition temperature, temperature at the orset of deformation (strain point), density. Young modulus, microhardness, crystallizability, and contact angle are studied as a function of the composition in RO–Y₂O₃–Al₂O₃–SiO₂ (R=Ca and/or Mg) glass systems. The composition ranges for glasses (with strain point >900°C and coefficient of linear expansion of (32–45)×10^–7°C^–1) that can be used for soldering silicon-nitride ceramics were established.Translated from Steklo i Keramika, No. 12, pp. 5–7, December, 1996     

Thermomechanical properties of ceramics in the systems Al2O3-TiO2 and Al2O3-TiO2-mullite

Conclusions We studied certain properties of ceramics in the systems Al₂O₃-TiO₂ and Al₂O₃-TiO₂-mullite, obtained by the use of the double-stage synthesis of aluminum titanate.We established the nature of the change in the high-temperature strength in relation to the ratio of Al₂O₃ and aluminum titanate. The maximum high-temperature strength (bending) at 1200°C is possessed by ceramic with a corundum matrix and a volume proportion of aluminum titanate equal to 40–45%.It is established that the addition of CaO + SiO₂ made in amounts of up to 1.0–1.5% contributes to the partial breakdown of the aluminum titanate in the compositions Al₂O₃-TiO₂ and the production of a ceramic with a bending strength of 160–190 N/mm² at 20–200°C, thermal-shock resistance 650–800°C, and thermal conductivity of 1.9–2.1 W/(m·K).We studied the effect of the mullite concentration on the properties of the ceramic in the system Al₂O₃-TiO₂-mullite. The introduction of mullite in amounts of not more than 50%, containing up to 3% of impurities, contributes to an increase in the ceramic's strength in the range 20–1300°C and in the thermal shock resistance.Translated from Ogneupory No. 2, pp. 22–26, February, 1988.     

Phase transformations in stabilized ZrO2-Al2O3 compositions and properties of zirconium-corundum refractories

Solid-phase reactions in mixtures of cubic ZrO₂ with different compositions synthesized by induction melting and Al₂O₃ with different thermal prehistories are investigated at a temperature of 1750°C. Data on the change in the principal engineering properties of zirconium-corundum refractories as a function of their chemical composition are obtained.Translated from Ogneupory, No. 12, pp. 5–8, December, 1995.     

Thermal stability of palladium on ceria-doped alumina

Several palladium on alumina and ceria/alumina catalysts were prepared and oxidized in air between 400 and 1000°C. The metal dispersion was determined by hydrogen titration of adsorbed oxygen. Dispersions above 50% were maintained on 0.2% Pd/Al₂O₃ up to 900°C. Adding 5.0% ceria, or increasing the metal loading to 2.5%, greatly reduces the thermal stability of the palladium, such that the dispersion falls rapidly at 600°C. The rates of methane oxidation (moles of CO₂/g Pd h) at 250°C and 5% excess oxygen are nearly equal on 0.22–2.50% Pd/3.5–5.2% CeO₂/Al₂O₃, dispersion 14–42%, and 0.20–0.46% Pd/Al₂O₃, dispersion 59–86%, but are 10 to 20 times lower than the rate on 2.3% Pd/Al₂O₃, dispersion 11%. The lower rate of methane oxidation on ceria-promoted and highly dispersed palladium on alumina might be due to the conversion of the palladium into less active palladium oxide during reaction.     

Mullite refractories from bauxites of the iksinskoe deposit

Bauxites with 76% Al₂O₃ and 2.65% Fe₂O₃ were used to produce mullite refractories and mixtures for steel-teeming ladles. Tests in service have shown that the strength of these refractories is no worse than or comparable with that of refractories based on commercial alumina and Chinese bauxites.Translated from Ogneupory, No. 2, pp. 28–31, February, 1995.     

More efficient utilization of alumina in refractories production

Conclusions An investigation was carried out of ways of utilizing commercial alumina more efficiently in refractories production by improving the composition of the products and the technology of their manufacture. Commercial alumina should be used mainly for the production of mullite refractories from synthetic mullite and of corundum refractories containing 90–99% Al₂O₃. Commercial alumina must be used for the production of spinel and spinel-containing refractories.More extensive use should be made of the alumina-containing waste from chemical plants for the production of refractories with a low mullite content, of ramming compounds, fusioncast refractories, and electrofused spinel as a substitute for chromite in roof bricks. To produce refractories with a higher Al₂O₃ content than can be achieved with kaolin more extensive use should be made of natural alumina-containing starting materials.Some mullite and corundum refractories should be produced with low porosity by using high molding pressures, actively sintering starting materials, and hydrostatic molding.Translated from Ogneupory, No. 8, pp. 33–39, August, 1978.