Mullite-corundum refractories with silicon carbide for linings of transportable mixers

Investigations of the technology of mullite-corundum refractories containing silicon carbide and used for linings of transportable mixers are described. It is shown that an addition (10%) of silicon carbide to a mullite-corundum mixture ensures a high slag resistance. Mixers lined with mullite-corundum refractories with silicon carbide have shown high service properties, namely, 720 pourings of cast iron with 5 hot repairs. Translated from Ogneupory, No. 3, pp. 26–29, March, 1995.     

Life of stopper heads in continuous steel casting

Conclusions Chamotte heads with 5, 10 and 15% graphite differ from conventional chamotte by high thermal endurance, thermal conductivity and wear resistance. The increased rigidity of stopper heads with a graphite content of 5 to 15% used in combination with magnesite sleeves enhances the formation of longitudinal cracks.Chamotte specimens fired at 1230° C are endowed with high wear-resistance. They differ from conventional chamotte refractories by higher thermal endurance and provide for good stopper service in reladling killed steel.High-alumina SP-9-type heads made at Chasov-Yar Combine wear less in intermediate ladles and are endowed with greater thermal strength than chamotte heads.The higher quality of the chamotte heads under conditions of Stalino Metallurgical Plant in comparison to that of Krasnoye Sormovo Plant is not only due to the quality of the refractory but also to such factors as the rate and degree of preheating intermediate ladles before filling with metal, careful placement of the stoppers, and use of graphite packing around the teeming head.Despite higher wear SP-12-type chamotte heads made at Chasov-Yar Combine allowed normal teeming of rimmed steel in 50 ton ladles.To ensure a steady service of the stoppers in continuous steel casting the preheating of intermediate ladles of 1300 and the use of precooled stoppers are recommended.     

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.     

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.     

Quality and economy of refractories

Conclusions The development of new forms of refractories must be based on the use of all forms of raw material, including the lowest grades. Beneficiation of raw material must be done for a purpose and be based on technical necessity, cost effectiveness, and ecological desirability.It is necessary to develop at accelerated rates the production of unformed and unfired refractories and to locate it preferentially in plants producing fireclays and having avilable various forms of inexpensive raw material.Newly created methods must answer the requirements of production of high quality parts, full mechanization, provision of atmospheric cleanliness, and cost effectiveness in the production and use of them.Investigators and production personnel must concentrate their attention on the solution of problems of a sharp decrease or the elimination of formation of dust in firing raw materials in rotating kilns and effective utilization of the dust caught in refractory production.Scientific-research institutes together with production plants and design organizations must develop and use modern instruments and on the basis of them develop new accelerated and automated methods of quality inspection of semifinished products and finished refractory production (chemical and phase composition, nondestructive methods for determining the physicomechanical, thermophysical, and other properties).Extending the service life of lining under the action of slag, metal, a gaseous medium, and thermal impacts must be done by guniting, cooling of the lining and refractory parts with air, water, and steam, and the introduction of new lining designs.Translated from Ogneupory, No. 7, pp. 4–9, July, 1982.     

Refractory fiber from natural starting materials

Refractories and Industrial Ceramics - The feasibility was demonstrated of producing refractory fiber from high-alumina chamotte of calcined Arkalyk clay. The fiber properties conform to the...     

Changes in the properties of Novoselits kaolin during heating

Conclusions Intensive dehydration and breakdown of kaolin briquette occurs at 400–600°C. Preliminary calcination of the kaolin at temperatures of up to 700°C reduces its cracking propensity with subsequent thermal shock which should favorably affect the reduction in dust emission and the formation of fine fractions of chamotte when it is being fired in rotary kilns.Surface-active agents (0.2–1%) reduce the cracking of raw kaolin specimens during thermal shock at 700°C, but to a less degree than preliminary dehydration.The sharpest change in the properties of kaolin briquette occurs at 1000–1250°C between the first and second exothermic effects.Additions of quartz sand appreciably increase the water absorption and porosity of kaolin chamotte, and reduce the apparent density, while additions of Gibbsite have a slight effect on the properties of the chamotte.Translated from Ogneupory, No. 5, pp. 40–47, May, 1971.     

Sialon-containing silicon carbide refractories

Conclusions We worked out the technology of sialon-containing silicon carbide refractories for lining the shafts of blast furnaces. It was shown that addition of MgO in combination with the waste products of the oxides of the rare-earth elements improves the strength and the other properties of the products fired at 1550°C in nitrogen atmosphere.The sialon-containing silicon carbide refractories exhibit a high resistance to the action of slags and are recommended for lining the lower portion of the shaft and the bosh of blast furnaces.Translated from Ogneupory, No. 5, pp. 6–8, May, 1992.