Microstructure of electrocorundum

Conclusions Investigation of the microsturcture of electrocorundum has shown that two types of micro structure are typical of standard electrocorundum:The first type is a hypidiomorphic structure and the accompanying phases fill the gaps between the corundum crystals; accompanying phases fill the gaps between the corundum crystals;The second type of corundum is represented by large fields, the diameters of which-attain several millimeters; the accompanying phases are present in the form of impurities in the body of the corundum fields.White electrocorundum, generally speaking, has a microstructure of the second type, but is marked by dendritic shapes and a considerable volume of cavities.     

Improving the thermal-shock resistance of corundum ceramic

Conclusions We have studied the effect of coarse-grained additives of electrocorundum, sintered mullite, SiC, and electrosmelted ZrO₂ on the thermal-shock resistance of a corundum ceramic obtained from a mixture of technical alumina and glass-forming oxides. New ceramic materials have been obtained with a higher thermal-shock resistance, a lower open porosity, and adequate strength. The materials can be used in the manufacture of articles to be operated under conditions of stringent thermal loading.Translated from Ogneupory, No. 2, pp. 44–48, February, 1982.     

Designing compositions for unshaped refractories using normal electrocorundum

The possibility of complete or partial replacement of scarce and expensive materials in the production of unshaped refractories by less scarce normal electrocorundum or waste of its production is studied. Ramming mixtures of type MMK-88 (TU 14-8-391-82) and MMK-74 (TU 14-8-337-80 with alterations Nos. 1–7) in which scarce electrofused corundum or high-alumina chamotte is replaced partially or fully by available normal electrocorundum are suggested. Mortars of a mullite-corundum or mullite composition using powders of normal electrocorundum and waste of its production are presented.     

Ramming bodies for the bottoms of soaking pit furnaces

Conclusions On the basis of sintered corundum and electrocorundum compositions were developed for ramming bodies containing phosphoric acid which can be recommended for making the bottoms of soaking pits.The specimens and articles made from these bodies by pressing and pneumatic tamping have excellent properties.Translated from Ogneupory, No.5, pp.32–36, May, 1970.     

Phase changes in fused oxide refractories in contact with semimild and stainless steels and their slags

Conclusions These studies show the significant reaction resistance of the articles made from electrocorundum to 20 sm steel and its slag. The slag and oxidation products of the 20Kh23N18 steel penetrate the articles made from grainy electrocorundum to a greater depth, causing the corrosion of the corundum grains.In the case of the fused silicon-containing periclase articles, the thickness of the least-changed zone, like the concentration in it of the basic phase (periclase), is significantly larger after the interaction with the 20Kh23N18 steel than with the 20 sm steel. As a result of the interaction with the oxidation products of the 20Kh23N18 steel, the appearance of a solid solution MgO-NiO can be seen in the periclase articles. The articles made from fused zircon-containing periclase can be recommended for industrial use in contact with a high-alloy, heat-resistant (stainless) steel while those made from electrocorundum are recommended for use with a semimild steel, e. g., in continuous casting with mechanical treatment on the liquid phase.Translated from Ogneupory, No. 1, pp. 42–45, January, 1980.     

Technology for high-alumina mortar in the Belokamensk Refractory Plant

Materials proposed for the production of a high-alumina mortar are investigated, namely, waste of melting of secondary aluminum, polishing powder of normal electrocorundum, and sintered corundum. A technology for the production of high-alumina mortars of three compositions has been developed for these materials. An experimental industrial batch of mortar composed of ShKN chamotte, polishing powder of normal electrocorundum, and DN2 clay has been manufactured and tested with a positive result. Production of the mortar has been introduced in the Belokamensk Refractory Plant.Translated from Ogneupory, No. 1, pp. 27 – 28, January, 1996.     

Use of Corundum Ceramics for Fine Milling of Various Materials

The wear resistance of corundum milling bodies developed by the authors is estimated compared to foreign analogs. It is established that domestic ceramics, with respect to its abrasion rate in milling electrocorundum and quartz sand, is not inferior to foreign ceramics. The kinetics of milling the specified materials is analyzed.__________Translated from Steklo i Keramika, No. 1, pp. 17 – 18, January, 2005.     

Effect of fibrous single crystals of mullite on the thermal-shock resistance of alumina

Conclusions A technology was developed for incorporating fibrous single crystal mullite into corundum products. Studies were made of the strength and thermal physical properties of the corundum reinforced with mullite fibers. Judging from the thermal-shock resistance and impact strength, corundum products with additions of fibrous single crystals of mullite are much better than corundum products without the additives.Translated from Ogneupory, No. 2, pp. 56–57, February, 1973.     

Vibratory densification of thermal insulation corundum products

Conclusions During vibratory densification, the bulk density and the angle of repose of the corundum bodies based on hollow granules and a porous filler depend on the type of the filler used and the size of its grains. The relative settling and the relative density of the bodies obtained after densification are related to their bulk density and the angle of repose.We established the dependence of the shrinkage during firing, the apparent density, and the strength of the fired products on the bulk density, the degree of settling, and the relative density of the specimens after vibratory densification. At a given density, the products based on the corundum granules exhibit higher strength.We developed large-sized corundum products of complex shape for thermal insulation at 1800°C under reducing conditions.Translated from Ogneupory, No. 4, pp. 28–32, April, 1986.     

Structural-mechanical properties of corundum bodies containing a porous filler

Conclusions We studied the structural-mechanical properties of granular corundum bodies in relation to the form, amount of additives consisting of surface active substances, and the type of porous filler.It was shown that a positive influence on the forming properties of the bodies based on spherical corundum and porous corundum briquet is exerted by the incorporation of technical lignosulfonate, and moreover it is most advantageous to use 0.5% solution for the spherical corundum and 2% solution for the briquet. An addition of GKZh-11 in amounts of 0.05% is desirable only for bodies based on spherical corundum. The addition of these agents increases the plasticity of the bodies on account of reducing the internal friction between the particles, and enables us to obtain articles with good properties.Translated from Ogneupory, No. 8, pp. 10–13, August, 1987.     

Thermal-shock resistance of corundum-mullite masses

Conclusions The thermal-shock resistance of corundum-mullite specimens of a grainy structure made from semidry masses is significantly increased with the formation of a porous matrix phase in the structure of the articles or with the creating of pores at the boundaries between the binding mass and the coarse grains of filler.Resistance to thermal shock in the vibrocompacted corundum-mullite masses in an ethyl silicate binder increases with the partial replacement of the coarse-grain corundum by sintered or acicular mullite and also with the addition of finely dispersed additions of SiC and quartz to the mass.Translated from Ogneupory, No. 1, pp. 45–48, January, 1982.     

Effect of preliminary heat treatment of alumina on the thermal-shock resistance and strength of corundum ceramics

Conclusions The firing temperature of the starting alumina is one of the important factors influencing the formation of the microstructure of corundum materials and determines the properties of the ceramics. At low alumina firing temperatures (1400°C) the structure of the specimens is finely crystalline. An increase in the firing temperature (to 1600–1750°C) causes an increase in the crystal sizes.The finely crystalline structure ensures a high strength in corundum materials, while the coarsely crystalline structure reduces it.The high thermal-shock resistance of specimens is determined by the formation of regular, random orientation, and close contacting crystals of corundum. An important role in this case, apparently, is played by the structure of the crystals. The thermal-shock resistance of the materials is favored by a combination of starting materials having different firing temperatures, namely, aluminas fired at 1750 and 1600°C.Translated from Ogneupory, No. 2, pp. 44–49, February, 1971.     

Effect of Andalusite Addition on Properties of Chrome-corundum Bricks

In order to improve the thermal shock resistance of chrome-corundum bricks, different amounts of andalusite were added to the formulation of chrome-corundum bricks to replace the equivalent white fused corundum with the same particle size. After mixing, shaping, drying and firing, the density, the cold strength, the cold wear resistance, the hot modulus of rupture and the thermal shock resistance were tested. XRD, SEM and elemental surface scanning were used to characterize the specimens. The results show that:(1) the volume expansion of andalusite mullitization reduces the apparent porosity of chrome-corundum bricks;(2) the density and the hardness of mullite are lower than those of corundum so the decrease of the corundum content in brick leads to the decrease of the bulk density, the strength and the cold wear resistance;(3) the cross-distributed columnar mullite in the matrix can effectively improve the hot modulus of rupture and the thermal shock resistance of the specimens;(4) considering comprehensively, the andalusite addition shall not exceed 18%.     

Effect of electromelted corundum crystal size and shape on the microstructure and permeability of porous ceramic

The effect of electrocorundum powder particle size and shape on its properties are studied. Results are presented for a study of the microstructure and permeability of porous ceramic based on electrocorundum with different particle sizes and shapes. The effect of production factors, and also air flow rate and the thickness of ceramic specimens on the air pressure drop ahead and after a specimen and the gas permeability coefficient are studied.     

几种防爆剂对浇注料透气性能的影响

研究了维尼纶防爆纤维(以下简称防爆纤维)的长度和加入量、金属铝粉的粒度和加入量以及偶氮二甲酰胺加入量对超低水泥刚玉质浇注料中≤1 mm的细料部分的透气度的影响。结果表明:这3种材料的加入均能提高试样透气度;随着它们加入量的增加,试样的透气度均增大,但当它们的加入量达到某一值后,试样透气度的增加均不明显;比较而言,金属铝粉对提高材料透气度的效果最明显,维尼纶防防爆纤维的次之,偶氮二甲酰胺的最小。     

Properties of highly refractory corundum ceramics containing glass phase,and their influence on the surface roughness after mechanical treatment

Conclusions We studied the strength and grain sizes of corundum ceramic containing glass phase and their relationships with the surface roughness during grinding and polishing.It is shown that the amount of glass phase formed in the corundum ceramic, regardless of the type of silica-containing additive, is determined by the concentration of silica in it.An increase in the amount of glass phase in the corundum ceramic reduces the size of its crystals, which in turn increases the strength and impact strength.The increase in the strength of the ceramic increases the roughness of the surface after the first polishing and reduces it after the final (clean) polishing. The presence of glass and the reduction in the crystal sizes of corundum in the ranges studied increase the purity of the surface of these ceramics after the final polishing.Translated from Ogneupory, No. 2, pp. 5–8, February, 1985.     

Porous materials based on corundum and aluminophosphate bond

Conclusions Highly porous corundum products obtained by using fluoroplastics have a relatively high strength in the green state (7 kg/cm² with an apparent density of 0.4 g/cm³), and a low apparent density after firing (0.23 g/cm³).The incorporation of aluminophosphate bond sharply increases the strength of the products after combustion of the organic part, and reduces the total shrinkage during heat processing from 30 to 4–5%.The use of electrofused corundum in place of commercial alumina reduces the concentration of organic constituent in the body to 18%; under these conditions the additional shrinkage at 1600°C of specimens fixed at 1000°C drops to 0.5–1%.Translated from Ogneupory,No.5, pp.46–50, May, 1972.     

Effect of surface — Active agents on the fine grinding kinetics of fired corundum pellets

Conclusions During the grinding of corundum pellets (briquettes) without additives in the initial period (up to 13 h) the low fired materials are more rapidly ground. With an increase in the dispersion grinding of low fired pellets is retarded. Additions of silicone substances during the grinding of corundum pellets fired at different temperatures, reducing the resistance to grinding, speed up the grinding process. The most effective of the additives investigated proved to be silicone liquid GkZh-94. The grinding process with additions of surface-active agents, and without them, for pellets fired at different temperatures obeys the basic law of grinding kinetics. Between the parameters m and k in this equation for corundum pellets we detected an inverse relationship which agrees well with theoretical ideas.Translated from Ogneupory, No. 7, pp. 42–46, July, 1973.     

Rheology of Plastic Molding Mixtures Based on Electromelted Corundum

The rheological and structural-mechanical properties of mixtures based on coarse-grained corundum with additives ensuring the production of porous permeable ceramics are considered. It is established that the joint use of different types of additives stabilizes the molding properties of the mixtures, when their composition and moisture vary, and makes it possible to modify the structural-mechanical type and, consequently, the molding conditions and to preserve the configuration of molded samples.     

Structure evolution of corundum concretes

Conclusions Structure evolution of the corundum concretes based on the binders of different compositions was studied.We demonstrated the effect of Cr₂O₃, CCLS, and technological (technical-grade) lignosulfonate on the strength gain of the cement stone and the concrete based on it, the phase composition of the cement stone and the concrete, their variation during the process of heat treatment, and on the microstructure.The ability of these additives to increase the degree of hydration of the high-alumina cement was established. The formation of a large quantity of aluminum hydroxide and calcium hydromonocarboaluminate confirm this fact.The evolution of a dense and strong structure of the corundum concrete based on the high-alumina cement and the occurrence of additional growth during the high-temperature firing process due to the formation of CA₆ and the solid solutions of corundum and CA₆ with Cr₂O₃ were shown.Translated from Ogneupory, No. 4, pp. 7–14, April, 1989.