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The influence of firing temperature of 1000, 1100, 1200, 1300, 1400, 1580 °C and atmosphere (air and reducing) on the main properties of castable samples from low-cement silicon carbide castable grade of “NKBS” with a combined additive has been investigated. It was shown that, in air with an increase in the firing temperature in the range 1000—1580 °C, the content of silicon carbide in the castable samples decreases. Up to temperatures of 1200—1300 °C, the content of silicon carbide in the castable samples practically does not change, and oxidation slows down due to the formation of a viscous melt of a glassy phase of an alumina silicate composition on the surface of silicon carbide grains. An increase in the firing temperature above 1300 °C leads to a more intense oxidation of silicon carbide grains to SiO2, which causes a change in the porosity, density and strength of the samples. As a result of the carried out studies, it was found that, the using temperature in the air of the above mentioned low-cement silicon carbide castable should not exceed 1300 °C. It was found that, after firing in a reducing atmosphere in the temperature range of 1000—1580 °C in the samples of silicon carbide castable, the content of silicon carbide remains almost the same, and the density and strength increase, which ensures the efficiency of its use for lining thermal units operating in a reducing atmosphere up to temperatures of 1580 °C.

Ensuring compliance of the physical and mechanical properties of castable products with differentiated operating requirements is achieved by optimizing the grain size composition of the fireclay aggregate, using a microfiller with an increased content of aluminum oxide and reactive additives in the matrix component, choosing effective deflocculants and plasticizers additives, etc. The influence of aggregate type, its grain size composition, quartzcontaining additives (quartz-containing additive FS or a mixture of combined grinding of ɑ-form alumina and quartz-containing additive S), amount of cement grade of “VGTs-73” on water demand, flowability of freshly prepared mass and properties of castable samples from low-cement alumina-silica castable after thermal treatment at temperatures of 110, 800 and 1400 °C. It was found that, with a partial replacement of fireclay in the castable with brown alumina, an addition introduction of ɑ-form alumina and a quartzcontaining component, an increase in the amount of high-alumina cement grade of “VGTs-73” from 5 to 8 %, the water demand decreases and the castable flowability increases, the strength of castable samples increases before and after thermal treatment. As a result of the carried out research, a technology for the manufacture of low-cement alumina-silica castable with Al2O3 content 52—56 % has been developed and mastered in JSC “URIR named after A. S. Berezhnoy”.

The use of dispersing additives in the composition of concrete mixtures helps to reduce water demand, increase flow, increase strength after hardening in air. The effect of a new dispersant additive amount on a polycarbonate base in comparison with the currently used phosphate-containing additive on the structural and rheological properties of chamotte concrete from a mixture of the “SSHBD” grade and samples from it has been investigated. The optimal amount of new dispersant additive on the polycarbonate base has been established and it has been shown that, in its effect on the structural and rheological properties of concrete from a mixture of the “SSHBD” grade and the properties of samples from it, it is similar to the phosphate-containing additive used at present. The change nature of the concrete flowability is practically the same. "Vitality" (i.e. the time period during which the concrete mass is suitable for performing high-quality lining by vibrocasting) of the compared concretes is ~ 4 hours; cold crushing strength of concrete samples with additives after hardening in air for 7 days and heat treatment at a temperature of 110 °C, as well as cold crushing strength of samples after firing at a temperature of 1350 °C are practically the same. The use of new polycarbonate-based dispersant can be recommended for the preparation of chamotte concrete as an alternative phosphate-containing additive.

An influence of type and amount of a quartz­containing additive (silica fume and pulverized silica) on the properties of concrete and samples from it before and after thermal treatment was investigated. It has been established that, the partial replacement of expensive high­alumina cement in the concrete with the quartz­containing additive improves a flowability of concrete and provides an increase in the strength of concrete samples. Optimal was the addition of domestic pulverized sili-ca in an amount of 2 wt. %. The compositions of mullite­corundum and mullite­siliceous mixtures with the pulverized silica addition in the optimal amount and a reduced content of high alumina cement (in comparison with the mullite­corundum concrete manufactured by JSC “URIR named after A. S. Berezhnoy”) have been developed. Concrete samples from mullite­corundum concrete of the developed composition with the pulverized silica addition were characterized by a higher cold crushing strength after 3 days of air hardening and thermal treatment at 110 and 1400 C (87 and 108 N/mm2, respectively) compared with samples from mullite­corundum concrete without the quartz­containing additive (52 and 70 N/mm2). Petrographic studies have established that, the introduction of quartz­containing additives in the optimum amount in the concrete composition contributes to better sintering of concrete. In the presence of quartz­containing additives in the binder mass of concrete samples, crystallization of mullite and calcium hexaaluminate was intensified, as well as anorthite formation. The production of mullite­corundum concrete with the quartz­containing additive (pulverized quartz) has been mastered at JSC “URIR named after A. S. Berezhnoy”.

The amount influence of the “Carbonxide” additive on the properties of pressed silicon-carbide products on the nitride-silicon-containing binder has been studied. The optimal amount of the indicated additive was established. On the basis of carried out studies, it can be concluded that, along with the addition of ferrosilicon and petroleum coke, in the manufacture of carbide-silicon products on a nitride-silicon-containing binder with a thickness of more than 50 mm, the “Carbonxide” additive can be used. The use of the “Carbonxide” additive instead of the addition of ferrosilicon and petroleum coke as part of the refractory batch contributes to the creation of microporous structure of the material and the binder formation of multiphase composition (Si3N4, β-sialon, β-SiC, AlN), which generally increases the refractory strength. Products with the “Carbonxide” addition in the amount of 2.5 % (in excess of 100 %) are characterized by the following indicators of physico-chemical properties: content, mass %: SiC — 71.0, Si residual— 0.41, N — 7.15; cold crushing strength — 216.0 N/mm2, open porosity — 16.8 %, apparent density — 2.58 g/cm3, refractoriness under load 0.2 N/mm2 —> 1700 оC and meet the requirements of the technical conditions for the brand KKNK.

The influence researches of high alumina cement brand of “VGTS-73” and disperse brown fused corundum ratio on the properties of mullite corundum concrete brand of “MКBС” have been carried out. As a result of carried out researches the expediency of amount decreasing of the high alumina cement brand of “VGTS-73” with specific surface area of 7000 cm2/g from 20 to 15 % and amount increasing of the disperse brown fused corundum from 10 to 15 % in the composition of mullite corundum concrete brand of “MКBС” has been determined. It promotes to strength increasing of samples from this concrete after thermal treatment at a temperature of 1450 оC by 44 % (from 104 up to 150 N/mm2), refractoriness by 60 оC (from 1660 up to 1720 оC) and thermal shock resistance by 30 % (from 7 up to 9 thermal cycles) at preservation of long working time of the concrete mix, as well as to decreasing of production costs. Manufacturing of the mullite corundum concrete brand of “MКBС” with improved composition was put into production at the PJSC “THE URIR NAMED AFTER A. S. BEREZHNOY”.

Data on some novel kinds of refractory articles and materials developed and produced by the Berezhnoy Ukrainian Research Institute for Refractories (Berezhnoy UkrNIIO) are presented. Corundum articles with Sialon binder and unshaped materials of various kinds (ramming mixtures, dry mixtures, traditional and low-cement refractory concretes) containing normal electrocorundum or refractory scrap instead of the costly white electrocorundum are described.

Silicon carbide refractory materials and specimens of silicon nitride and silicon oxynitride are tested under high-temperature attack from reducing (H2 and CO) and oxidizing gases (O2, air) and from molten slag, alkalis, and iron. It is shown that nitride-based refractory materials are prone to change their properties, structure, and resistance when exposed to molten slag, iron, and alkalis. Silicon oxynitride and silicon nitride resist attack from carbon monoxide and alkali and provide protection to silicon carbide used as the refractory lining for blast furnaces.

The optimum compositions of oxygen-free mixtures for manufacture of nitride-based refractory bonds are reported. A technology for manufacturing chamotte refractory materials with a compound nitride-based bond is developed. The newly designed materials exhibit improved physicomechanical properties and enhanced durability against attack by alkalis and molten slag.

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.

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.

Formation of a combined nitride-containing binder for mullite-alumina refractories is studied. An optimal combination is found to consist of 80% crystalline silicon, 10% silicon carbide, and 10% aluminum, magnium, or zirconium oxide. Mullite-alumina refractories with selected binders showed high resistance to the effects of slag, alkali, and iron.

A study of the formation of sialon in a charge based on the Ovruchsk quartzite and fine aluminum powder established that the density of the products increases with increasing content of the aluminum fines in the body (from 40 up to 60%). The material fired at 1450°C in nitrogen atmosphere consists ofβ-sialon, corundum, and a small quantity of aluminum nitride and silicon oxynitride as impurities.

The technological parameters of the production of silicon carbide refractories with a silicon nitride binder are investigated. An experimental industrial batch of refractories has been produced by the Semiluki Refractory Plant and shipped to the Kaustic Production Association to be used in linings of reactors for the production of aluminum chloride.

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 β-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.

The synthesis of a combined nitride-containing binder is described. The main parameters for the production of corundum refractories with the combined nitride-containing binder are determined. The refractories have a high resistance to the effect of slag melts.