As is known, stabilizing slips not only improves their casting properties (fluidity, good mold filling, stability, etc. ) but also helps to form denser and better structured castings owing to the ordered packing of the separate particles. The particles of unstabigzed slip are packed as whole aggregates (floccules) that carry within their volume water-filled cavities which are preserved during molding. This increases the porosity of the castings and may form large pores and cavities, which is inadmissible for the service conditions of quartz immersion sheaths.The traditional method of stabilizing slips made of fused quartz (quartz glass) is gravitation blending [1][2][3][4], in which the quartz ceramic is not contaminated by impurities that contribute to crystallization of the glass when the articles axe being fired. The duration of the mixing depends on the original and prescribed parameters of the slip and equals 1-5 days.The mechanism of fused quartz slip formation has been fully described in [1, 5]; we note only that the double electric layer in this slip is formed by anions and cations of hydrogen whose number is very small because of the low quantity of silicic acid and water. The stability of the quartz slip is attained by ordered distribution of the dipoles of water around the ionized solid particles of SIO2, which ensures prolonged mixing of the slip.The production technology for quartz slipcast immersion sheaths at the Podolsk factory includes stabilizing by blending for 24 h [2]. In contrast to high-density quartz ceramics [1], quartz sheaths at the factory are made from slips of relatively low density (1.75-1.78 g/cm3). Such slips have a typically low content of silicic acid as indicated by the low calcination loss, equal to 0.2-0.3% and the slight fall in pH when the slip is being prepared. Thus, when the pH of a mixture of quartz glass and distilled water equals 6.56, then the pH of a slip of density 1.785 g/cm 3 is 5.76. For the pH of a mixture of quartz glass and water used at the factory for production purposes equal to 7.18-7.38, the pH of the slip having a density of 1.781 g/cm z is 7.21-7.49. A certain rise in pH in the latter case occurs because of the use of alkaline water and the entry into the slip of additions of high-alumina composition because of the grinding of uralit balls used for milling the quartz glass.As a result of this, the pH of the suspension proves to be unfavorable since the minimum viscosity of the quartz slip is reached in the acid region when pH ~ 5 [1, 5]. When pH z 5 the silicic acid is more stable and with a pH close to 7 its polymerization occurs rapidly, accompanied by separation of water and a reducUon in the concentration of H + [6]. All these factors indicate the unfavorable combination of the properties of a slip with pH z 7.In practice at the factory the slip factors come on the boundaries of the permissible limits; viscosity of slips is not high while the water content is high, and the density low. Thus, slip with pH = 7.21 has a viscosity of 57 St,* density 1....

Refractories containing in their composition carbon and oxygen-free compounds such as carbides, nitrides, borides, etc. are acquiring increasing practical value [i].Present and future areas of their use include the linings of converters and electric arc furnaces, refractories for ladle gate valves and teeming of steel in continuous billet casting machines, etc.In their interaction with molten metals these refractories exhibit specific features, some of which are discussed in this article.As a first approximation as the result of the high surface activity of oxygen and sulfur in it (their surface activity may exceed the content by tens of times) the surface of molten steel may be represented in the form of the highly electronegative anions 0 =-and S =-in coordination with the cations Fe 2+, Mn =+, etc.In interaction with the oxidizable elements of the refractories the anions form intermediate products all the way to oxides, including gaseous ones.The corrosion of carbon-containing refractories under the action of steel under equilibrium conditions may be represented in three stages [2]:at the steel--refractory contact under the action of surface-active oxygen, oxidation of the carbon occurs and a decarburized zone is formed; the decarburized zone with increased porosity rapidly forms a slag and the products of the interaction have decreased refractoriness, mechanical strength, and thermal coefficient of volumetric expansion differing from the original material; for these reasons the slagged layer of the refractory is rapidly washed away by the steel.The increase in metal resistance of a refractory with the addition of oxygen-free additions, particularly carbon, is the result of the following facts: frequently, the carbon addition is made by impregnation or precipitation from the gaseous or liquid phase into the finished refractory and the carbon partially replaces the porous spaces, mechanically preventing penetration of the molten metal; the products of gasification of the carbon pneumatically prevent penetration of the molten metal into the voids; in the microvolumes carbon deoxidizes the molten metal in contact with it and the highly active oxide forms of iron are converted into less active lower oxides all the way to the metallic state, a confirmation of which is the presence of beads of pure iron in the reaction zones of carbon-containing refractories after their wetting even by slag.To the products of gasification of carbon are added the gases entrapped in the void space and the gaseous products of reduction by carbon of the oxides of the refractory occurring according to reactions of the type:(SiO2, AI2Oa, ZrO~, ZrO=.SiO,, MgO era. )ml+Cso~C0g~+SiOg ~ AIOg~ era.These reactions occur both in the contact zone and in the thickness of the refractory with diffusion of CO and gaseous suboxides into the contact zone. In addition, the decomposition of oxygen-free compounds is possible according to reactions of the form SiaN4--+2N2+3Si.All-Union Refractory Institute.

We recommended for the lining of the shaft shoulders and the bottom and upper parts of the hearth the use of dense kaolin refractories containing 41-42% A1203 and with an open porosity of 8-12%, the technology for which is being introduced at the Chasov-Yar Refractories Combine. LITERATURE CITED

The temperature was measured by means of thermocouples fi~ed at a depth of 150 mm in the bottom and at a depth of 100 mm in the walls. The temperature readings were taken automatically by a PSR-1 recording potentiometer.A chrome--magnesite coating was applied to the dried lining; it consisted of 6@Jo ground sintered magnesite powder of grade , 40?0 of chrome--magnesite powder PKhMT , and 12% over 100% of magnesium sulfate solution with a density of 1.16-1.18 g/cm 3.The thickness of the coating layer on the bottom and at the bottom of the walls of the runner was 20-30 ram, and that at the tops of the walls was 10-15 ram.After connection of the runner to the furnace, the protective coating was dried by natural gas with the aid of a burner. At the end of discharge of the melt, the runner was conveyed to the runner fabrication section for cooling for 1-1.5 h in natural conditions. After cooling the runner was cleared of metal scale and slag; as a result, the thickness of the coating was reduced by 5-15 mm.At present at the Zaporozhstal' Works two steel tapping runners with monolithic linings have been made, and 200 melts have been discharged through them; the runners are still in service. At VNIImekhchermet plans are being drawn up for a mechanized system for making monolithic linings by a casting method and for repairing and demolishing them after service.The use of a monolithic lining instead of brickwork not only increases the durability of the furnace owing to the lack of a large number of seams, but also permits mechanization of the lining installation, and reduces the expenditure of labor and materials. A test of single-channel steel-tapping runners with cast linings in industrial conditions in comparison with brickwork at the Zaporozhstal' factory revealed that their times of preparation for melting are reduced from 0.66 to 0.42 h. Moreover, the process of preparation and repair of the cast lining and the deposition of a protective coating on its surface can be completely mechanized.