Natural graphite ahes and their effect on the properties of carbonized periclase refractories

The properties of Chinese natural graphite of grades FG+194 and FG+198 and their ashes are investigated. The extent of the effect of ash content in graphite on the technical parameters of carbonized periclase refractories with an increased carbon content is demonstrated. The advisability of using low-ash graphite for carbon-bearing refractories is justified. __________ Translated from Novye Ogneupory, No. 5, pp. 35–40, May, 2007.     

Thermomechanical and deformation properties of periclase and magnesia-spinel refractories

Conclusions The strength of periclase and magnesia-spinel refractories at normal temperatures varies in wide limits and is determined by the quantity, shape, dimensions, and distribution of the pores and microcracks. At high temperatures the degree of influence of the pores and microcracks on the strength is reduced.In the region of medium temperatures (600–1200°C) there is a temporary strengthening and an increase in E_d of the magnesia-spinel refractories, due to the internal stresses caused by the difference in the coefficient of linear thermal expansion of the spinels and periclase.With further increase in temperature the articles' strength and E_d are reduced as a result of the softening of the silicate bond. The abradability of the refractories depends slightly on the porosity but strongly on the compressive strength.The least creep is typical of refractories made of fused materials (PKhVP) with a comparatively low concentration of silicate phase, the viscous flow of which at temperatures above 1450°C determines the plastic deformation of the periclase and magnesia-spinel articles made industrially.Periclase refractories containing 2.5–3% silicates in the form of montichellite are brittle up to 1400°C and above this temperature they are elastoplastic, while articles and tiles containing up to 0.5% silicates in the form of Ca₂SiO₄ may be brittle up to 1600°C. They possess high thermomechanical properties and wear resistance in service in gate valves for steel ladles.The wear under friction of periclase tiles at various temperatures is determined by the crystal structure, the change in strength of the materials, and the state of the rubbing surfaces, and also by the adhesion and deformation reactions.Translated from Ogneupory, No. 1, pp. 7–14, January, 1983.     

Cast oxide refractories of a grainy structure. Initial compositions and the principles of molding

Conclusions The main principles in the technology of cast ceramic or refractory materials of a grainy structure are considered using some pure oxides or their compounds as an example.The general principles of the change in the rheological properties of the fine-grained suspensions as they are saturated by the grainy filler are considered.A process has been developed for cast-filled systems in inactive molds and it is shown that under specific conditions this method is as good as the method of vibrocasting in active molds.The semifinished product based on the grainy cast systems has adequate mechanical strength and low shrinkage when molded, dried, and sintered.Translated from Ogneupory, No. 6, pp. 6–11, June, 1985.     

The thermal conductivity of periclase and periclase — Spinel refractories

Conclusions It was established that it is possible to vary the thermal conductivity of periclase and periclase- spinel refractories within fairly wide limits by varying their phase composition and structure.Translated from Ogneupory, No. 3, pp. 48–50, March, 1975.     

Effect of the grain composition of the batch on the structure and properties of periclase refractories

Conclusions The structure and properties of periclase articles have been studied as a function of the quality of the powders and the grain composition of the batch. The possibility of obtaining periclase refractories with a high density (open porosity 8–12%) and heat resistance (11–16 heat cycles into water) is shown. In order to obtain strong dense articles with an enhanced heat resistance, it is recommended that dense powders with a fine-crystal structure be used; additional recrystallization during the high-temperature firing helps to strengthen the articles.The addition of 1% ZrO₂ improves the properties of the articles, which is the result of the strengthening of the diffusion processes capable of forming strong direct bonds between the periclase crystals in the aggregates and the bonding material.Deceased.Translated from Ogneupory, No. 2, pp. 52–57, February, 1979.     

Structure and properties of dense periclase refractories prepared from laminated granules

Conclusions On the basis of laminated granules we prepared dense periclase refractories with a higher thermal-shock resistance than that of ordinary articles prepared by sintering solid granules. The technical properties are determined by the degree of development of a fragmentary structure which depends on the size of the granules, the composition of their outside layer, and the composition of the bonding mass in the batch.With an increase in the dimensions of the laminated granules and addition to the composition of their outside layers of yttrium oxide or lanthanum zirconate and to the composition of the batch of solid grains of periclase of a smaller fraction in the articles, complex elements are produced which form the fragments of the structure. This increases the thermal-shock resistance of the goods. The porosity of the articles is reduced with a reduction in the amount of dispersed part of the batch and its additional sintering with the formation of closed pores. The strength of the articles is reduced with a rise in the amount and size of the channel pores, and there is its increase during the formation of additional bonds in the area of contacts between the bond and the aggregates of coarse grains.Translated from Ogneupory, No. 3, pp. 9–13, March, 1984.     

Production of refractories from Chinese periclase

Periclase refractories from Chinese periclase are produced by the Chasovo-Yarsky Refractory Plant. The refractories have been tested with positive results at a number of metallurgical works, and specifications have been established for articles.Translated from Ogneupory, No. 1, pp. 21 – 26, January, 1995.     

Effect of some properties of aluminosilicate refractories on their glass resistance

Conclusions The glass resistance of aluminosilicate blocks with similar porosity values depends mainly on the quantitative ratios of crystalline and glassy phases, their chemical composition, and the grain size of the mullite. The higher the crystalline phase concentration in the refractory (mullite and mullite+ corundum) the fewer the impurities (oxides of iron, titanium, calcium, sodium, potassium, etc.), and the coarser the grains of mullite, then the lower their corrosion by molten glass.An increase in the glass resistance of aluminosilicate blocks can be achieved by using pure clays and kaolins, and also by using high temperatures for firing, longer soaking periods, and also mineralizing additives.Translated from Ogneupory, No.6, pp. 40–44, June, 1970.     

Thermophysical and elastomechanical properties of grainy corundum-zircon refractories and the effect of these properties on the thermal-shock resistance

Conclusions The thermophysical properties (l/l ₀ and ) and the elastomechanlcal properties (E, G, _bend) of corundum-zircon specimens in the 20–1200°C interval with various concentrations and grain sizes of zircon and different grain sizes and types of the corundum and zircon components in the grain and bondings have been investigated. It is established that in particular temperature regions there is a connection between the criteria R and R calculated from the values of the properties and the number of heat changes before the onset of primary cracking and total destruction of the specimens.Translated from Ogneupory, No. 1, pp. 56–60, January, 1980.     

Effect of reaction of periclase and iron-chrome spinel on the properties of periclase-spinel refractories

Conclusions Using a typical composition of the type MgO-Mg(Al_1–x–yCr_xFe_y)₂O₄ a study was made of the effect of the processes involved in the processing and decomposition of solid solutions of periclase and spinels on the technical properties of the fired products.During cooling from 1600–1750°C decomposition occurs in the solid solutions of periclase and spinel; the crystals of spinel separating under these conditions are able to grow to large sizes which inevitably should lead to the development of stresses inside the periclase grains.The decomposition of the solid solution of periclase and spinel adversely affects the strength and thermal-shock resistance of the fired specimens.The best technical properties are possessed by combinations of periclase with small (up to 15%) quantities of high-alumina (x=0.16 and 0.46) spinels.The use of compositions of periclase with high-alumina spinels of the type x=0.16 and 0.46 enables us to obtain denser and more thermal-shock resistant refractories.Translated from Ogneupory, No.6, pp. 44–47, June, 1970.     

Heat-treatment effect on the properties of a zirconia ceramic with a grainy structure

Conclusions The heat treatment at 2000°C of zirconia ceramic with a grainy structure causes the destabilization of the ZrO₂-CaO solid solutions but this is not complete after a 200-h dwell; the electrosmelted ZrO₂ ceramic stabilized with CaO is more stable under these conditions. The ZrO₂-Y₂O₃ solid solutions have greater stability on heating.When the grainy-structure zirconia ceramic is subjected to an isothermal dwell at 2000°C there is a consequent reduction in the strength properties caused either by the decomposition if the solid solutions (CaO-stabilized ceramic) or by the growth of crystals (Y₂O₃-stabilized ceramic).Deceased.Translated from Ogneupory, No, 7, pp. 51–55, July, 1979.     

Interaction of periclase and corundum refractories with iron and iron-manganese melts

Conclusions The authors have experimentally investigated the reaction of periclase and corundum refractories with iron and iron-manganese melts. They propose a physicochemical scheme of the reaction, taking account of the characteristics of the composition and structure of the specimens. They show the influence of manganese and of the composition of the primary oxide phase on the character of the reaction. The coefficients of diffusion of the primary oxide phase in periclase grains have been determined.Translated from Ogneupory, No. 7, pp. 35–40, July, 1980.