Improving the quality of chamotte made from Berlinsk clay

Conclusions The optimum firing temperature for Berlinsk clay to convert it into chamotte is 1300–1330°C. Above this temperature the chamotte bloats and has a low apparent density (below 2.10 g/cm³). The fireclay goods should be made from chamotte with an average or high apparent density (2.14–2.30 g/cm³).The articles made with the overtired chamotte have a high porosity and low apparent density. It is not recommended for use in firebrick production.Translated from Ogneupory, No. 2, pp. 14–16, February, 1981.     

Cast (Self-Flow) Ceramic Castables. 4. Spreadability of Molding Systems and Some Properties of Mullite – Silicon Carbide Ceramic Castables

The rheological properties of molding systems are shown to depend on the spreadability of the mixture under the action of its own mass; some of the factors influencing the self-flow are determined, namely, the moisture content, the content of the filler, and the temperature of the mixture. The described self-flow castables based on a mullite HCBS and a SiC filler have a porosity of 18% after drying and 16 – 16.5% after heat treatment. Their ultimate bending strength is 45 MPa and the ultimate compressive strength is 110 MPa, which is higher than those of the known refractories of similar compositions. The temperature of 4% deformation of mullite – silicon carbide refractory heat treated at 1350°C and having C _Vf = 0.4 is 1710 – 1720°C, which is 70 – 80°C higher than that of a similar material molded by pressing and heat treated at 1500°C.     

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.     

Influence of heat treatment of fused mullite materials on their properties

Conclusion It is shown that the temperature of initial crystallization of glass spheres of mullite composition with diameters of less than 0.1 mm, in the metastable state, equals 935°C. The phase composition of the spheres of diameters from 0.1 to 0.5 mm varies. With an increase in the diameter of the spheres from 0.5 to 1–1.7 mm their properties vary slightly.Thermal processing of the spheres of mullite composition with different starting contents of mullite and glass in the mullite component influences the crystallization of the mullite and causes increases in the density at temperatures from 900–1300°C. The most rapid change in properties takes place in the spheres containing the maximum amount of glass phase (100%). In the 1300–1500°C range in all spheres, with different contents of glass phase in the starting condition, there is a variation in the density and in the mass proportion of mullite.An increase in soaking from 0.5 to 1.5 h at 1300 and 1500°C leads to an increase in the mullite content and a rise in the density of the glass spheres.During the firing of finely milled powders made of granules and spheres with different contents of glass phase and mullite, and also specimens prepared from these powders, with temperature rise the material's density and the amount of mullite are both increased, and the changes in these factors are identical. It is established that with increase in the mullite concentration in specimens of finely milled powders there are marked reductions in shrinkage, and apparent density; and an increase in the porosity of the specimens fired at 1750°c. There is much less change in the properties at 1700°c.Translated from Ogneupory, No. 4, pp. 7–10, April, 1990.     

A study of the process of hot pressing strontium zirconate

Conclusions The basic conditions for hot pressing samples of strontium zirconate were determined. An increase of temperature and pressure favors a sharp increase in the density of the obtained products. Samples with a relative density of more than 99% are obtained at 1450–1500°C, 200 kg/cm², and a holding time of 30 min.An intensive densification of strontium zirconate powder occurs above 1400°C; here, the viscosity is 10¹⁰–10¹¹ P.Translated from Ogneupory, No.5, pp. 41–45, May, 1969.     

Densification of RO2 type oxides during hot pressing

Conclusions The optimal conditions for obtaining high-density products by the hot pressing of pure oxides of the type RO₂ were established. In order to prepare high-density samples with simultaneous hot pressing and stabilization of the zirconium and hafnium dioxide the heating must be slowed down in the polymorphic interval (800–1200°C) to generate the necessary number of vacancies which ensure significant densification. The amount of stabilizer (calcium or magnesium oxide) should not be less than 7% (by weight). Prestabilized zirconium and hafnium dioxide can be sintered by hot pressing with heating without holding in the interval 800–1200°C to a relative density of 0.98–0.99 under a pressure of 160 kg/cm², and also with a holding time of 10 min and a temperature of 1700–1800°C (zirconium dioxide) and 2100–2200°C (hafnium dioxide).Fused quartz can be sintered by hot pressing to zero water absorption and a relative density of about 1.0 at 1400°C, a pressure of 200 kg/cm², and a holding time of 10 min.Deceased.Translated from Ogneupory, No. 2, pp. 36–40, February, 1969.     

High-temperature rheological properties of clay bodies and bodies plasticized with clay

Conclusions We determined the rheological properties of clay materials at elevated temperatures. With an increase in the temperature and pressure the structural-mechanical constants diminish, and the plasticity increases. The total proportion of elastic and plastic deformations reaches significant values (92–95%) in kaolins at 1450°C, and in Chasov-Yar clay at 1200–1250°C. It is in these conditions precisely that we obtain the densest thermal-pressed products.With optimum thermoplastic pressing temperatures the various clay materials have the closest viscosity and maximum yield point values.The best natural raw material for thermoplasticizing is Chasov-Yar clay, but it is possible to use other clay materials. It is possible to regulate the rheological properties of bodies by varying the compositions (filler + thermoplasticizer) of the bodies, the pressing temperature, and pressure.The rheological properties of mixtures of zircon and thermoplasticizer (10% Chasov-Yar clay) at 1450–1480°C facilitate the production of especially dense products for continuous steel casting. Tests carried out on continuous casting plant were successful.Translated from Ogneupory, No. 6, pp. 43–51, June, 1973.     

Structural features of Sc3TaO7

Conclusions The compound Sc₃TaO₇ synthesized at 1300°C has a monoclinic modification which is stable in vacuum in the 25–1700°C range. We detected a phase inversion of the monoclinic modification into the tetragonal at 1800°C, accompanied by a change in the chemical composition with respect to oxygen. We determined the temperature coefficients of linear expansion of the monoclinic modification of Sc₃TaO₇ in the 25–1700°C range, and detected a marked anisotropy of temperature expansion in the crystal lattice.The author wishes to thank O. N. Vasil'eva for assistance with the experiments.Translated from Ogneupory, No. 7/8, pp. 14–16, July–August, 1992.     

Dependence of the properties of chamotte on the firing regime of the briquette

Conclusions The physicomechanical properties and phase composition of chamotte depends on the composition of the gas medium, the firing temperature, and the cooling regime. In the briquettes fired at 1500°C in an oxidizing medium with the cooling temperature lowered from 1500 to 1200°C, the apparent density increases and the porosity decreases. In the briquettes fired in a reducing medium with the cooling temperature lowered from 1500 to 1300°C, there is a reduction in the apparent density and an increase in the porosity but with a further reduction of the cooling temperature to 1200°C, these properties change in the opposite direction.The apparent density of chamotte and its concentration of mullite is increased with a reduction in the cooling rate. The apparent density of the chamotte from the Polozhsk kaolin under analogous cooling conditions increases more rapidly than that from the Novoselitsk kaolin chamotte.The temperature interval in which the cooling rate effectively increases the apparent density of the chamotte fired in an oxidizing medium is 1500–1300°C. In a reducing medium this interval is shifted 100°C toward lower temperatures.The experiments have shown that an increase in the cooling rate of the fired briquettes at temperatures below 1200°C has only a very slight effect on the apparent density and porosity of the Novoselitsk kaolin chamotte. When the chamotte has been obtained from Polozhsk kaolin, a reduction in the cooling rate at temperatures below 1200°C, and particularly in a reducing medium, has a quite perceptible effect on the increase in apparent density and reduction of porosity of the material.Translated from Ogneupory, No. 3, pp. 22–26, March, 1982.     

Optimizing the properties of corundum-based thermal insulation products using the method of experimental planning

Conclusions In order to optimize the properties of the corundum-based thermal insulation products, a study was conducted on the effect of granulometry and the type of the filler using the method of experimental planning.It was shown that increasing the limiting size of the filler grains decreases the apparent density and the ultimate compressive strength independent of the type of the filler.Using the method of correlation-regression analysis, it was established that the weight content of the grains of the 2–3 mm fraction must not exceed 20% in the charge for obtaining products which can simultaneously satisfy the requirements of (low) apparent density and (high) ultimate compressive strength.Based on the complex studies, we worked out the production technology and obtained a trial batch of corundum-based thermal insulation products withstanding a service temperature up to 1750°C.Translated from Ogneupory, No. 6, pp. 15–17, June, 1987.     

Anorthite insulating refractory

Conclusions A technology was developed for manufacturing heat-insulating refractories with an anorthite composition and an apparent density of 0.3–0.4 g/cm³ or more using kaolin, semihydrated gypsum and stabilized foam. The proposed method guarantees a reduction in the production cycle, yielding cheap insulating brick, and the possibility of mechanizing the production processes.Anorthite ultralightweight refractories in terms of their basic factors correspond to insulating products made by foreign concerns for service at 1100–1260°C.Translated from Ogneupory, No.5, pp. 36–40, May, 1970.     

Lightweight foamed filler in granular form from raw kaolin

Conclusions The technological parameters were determined for the production by the foam method of a lightweight granulated filler of apparent density 0.5–0.7 g/cm³ from raw kaolin without the addition of a nonplastic material to the batch.When the operations are carried out separately, the duration of the production cycle is 2.5–3 h, which includes the firing of the porous lump material by passing flue gases through a layer up to 500 mm in depth and demonstrates that in principle it is possible to set up a line for the production of foam-kaolin filler by the new method. The filler can be used, e.g., with good results as aggregate for heat-insulation concrete.Translated from Ogneupory, No. 1, pp. 46–52, January, 1977.     

Role of sintering additives in the production of lime refractories

Conclusions A production technology is proposed for lime refractories covering the preparation of high-density lime clinker, followed by crushing, batching, adding waterproof bond, pressing the goods, and firing at 2020 K.The technology for obtaining high-density lime clinker resistant to atmospheric hydrolysis, includes milling CaCO₃ to a particle size of 100–150 m with simultaneous incorporation of sintering additives (2–6% TiO₂ or 2–4% titanium ferrites), and the use of water solutions of sulfite lye as bond; pelletizing and firing at 2020 K. The lime clinker has an apparent density of 2.75–3.03 g/cm³, and an open pelletizing and firing at 2020 K. The lime clinker has an apparent density of 2.75–3.03 g/cm³, and an open porosity of 3.4–9.8%.The lime products have an apparent density of 2.65–2.97 g/cm³, open porosity 4.4–16.4%, compressive strength 60–140 N/mm², and refractoriness under load 1610–1700°C and above.Translated from Ogneupory, No. 2, pp. 13–16, February, 1992.     

Thermophysical parameters of high-performance corundum insulation at 500–2100 K

Conclusions Measurements have been made on the thermal conductivity and thermal diffusivity for corundum refractories based on hollow granules having apparent densities of 0.3–0.6 g/cm³, as well as foam corundum ones at about 0.5 g/cm³, which cover the range 200–1700°C. A conduction model has been devised that gives a qualitative explanation of the temperature and porosity effects.Translated from Ogneupory, No. 5, pp. 33–38, May, 1988.     

A Study of Refractories from Baddeleyite Stabilized with Magnesium Oxide

It is shown that refractory articles can be produced from ZrO₂ on a forsterite binder based on natural baddeleyite with native grain composition. The articles have a high density (4.71 – 4.72 g/cm³), ultimate compressive strength (257.6 MPa), heat resistance (6 – 8 water heat cycles from 1300°C), and a low porosity (12.2%).     

Sintering and recrystallization of high-purity magnesia-alumina spinel during hot pressing

Conclusions A study was made of the densification and recrystallization of magnesia — alumina spinel of high dispersion during hot pressing in the temperature range 1200–1600°C, a pressure of 60–300 cm², and a holding time of 10–30 min.The relative density of 92–98% theoretical was achieved at 1300–1400°C, a pressure of 300 kg/cm², and a soaking of 10 min. The spinel of theoretical density with a finely crystalline homogeneous structure was obtained by hot pressing at 1450–1600°C.Intensive recrystallization of the spinels during hot pressing occurs in the temperature range ensuring maximum rate of densification (1450–1600°C).The rate of recrystallization of the spinel grains during hot pressing at 1400°C and a pressure of 300 kg/cm² and soakings of 10 and 30 min, has the order of 10^–6 cm/sec and the maximum for the grains of diameter from 2 to 6.Report read at a symposium on pure oxide sintering, Khar'kov, 1968.Deceased.Translated from Ogneupory, No.6, pp. 32–36, June, 1970.     

Strength of magnesia refractories in combined thermal cyclic and mechanical loading of them

Conclusions As the result of laboratory tests of periclase-chromite refractories produced by different methods (MKhS, MKhV, and MKhVP) under the combined action of thermocyclic and mechanical loads possibilities were revealed of the most effective use of them in relation to the service conditions of plasma and electric arc furnace linings. The results of production tests of MKhS, MKhV, and MKhVP refractories at various furnace lining operating temperatures agree with the laboratory data and make it possible to draw the following conclusions:MKhS parts, as the most heat resistant, may be used successfully in heating the furnace lining working surface to 1700–1750°C, which corresponds to a temperature on the boundary of spalling of the refractory of 1400–1500°C.An increase in the lining operating temperature to 1800–1900°C (1550–1650°C on the boundary of spalling) requires the use of refractories with a combination of such properties as heat resistance and high-temperature strength. These requirements are met to the greatest degree by MKhV parts.In the future for large tonnage plasma and electric arc furnaces with high mechanical loads MKhVP high-strength parts may be recommended for the lining. However, for successful use of these parts it is necessary to aim to increase their heat resistance.Translated from Ogneupory, No. 5, pp. 43–47, May, 1985.     

Temperature regime in a 130-ton converter lining during service

Conclusions The temperature of the working surface of the refractory structure during the heat alters from 800 to 1700°C, which adversely affects the wear resistance of the refractories.Intensifying the blow through the metal, regular operation of the converters (with minimum interheat downtime), rapid charging of metal scrap in the converter, and accurate batching of the powdered materials all improve the temperature cycle of the refractory structure, and reduce its wear.During the charging of metal scrap after easting the iron in the converter, the temperature of the structure in the interheat period drops only down to 1300°C, ensuring variations in it during the heating period in the limits 1300–1700°C.Foaming of the converter batch during blow reduces the overheating of the lining. As the lining wears away the heat loss through the structure increases, which can be excluded by using heat insulation.Translated from Ogneupory, No. 4, pp. 31–35, April, 1972.     

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.     

Lightweight refractories semidry-molded from Borovich clay

Conclusions It was shown in a laboratory investigation that in the production of lightweight chamotte refractories by semidry molding it is difficult to achieve the strength specified by the relevant All-Union State Standard. The strength depends mainly on the chemical and mineral composition and the properties of the binder clay and on the ash content of the burn-out additive.With high-sintering, semirefractory Lyubytin clay as binder and petroleum coke with an ash content below 1% as burn-out additive the finished refractory product had an apparent density of 1 g/cm³ and a cold-crushing strength of 7–17 kg/cm². The strength of the refractory was increased by adding a substance containing alkali or CaO to the batch, more particularly expanded perlite.An experimental batch of lightweight chamotte refractories of apparent density 1 g/cm³ was produced from Borovich plastic clay from the Ust'-Brynkino Sector and coal coke fines from a UDSC. Without added sintering substances the cold-crushing strength was 24–38 kg/cm² (i.e., 30 kg/cm² on average).Translated from Ogneupory, No. 6, pp. 9–15, June, 1976.