Silica, the commonest material in nature, is used as the basic material in silicate technology. The extensive use of quartz sands and quartzites, particularly in a finely dispersed state, has made it necessary to study the processes of dry and wet milling various types of silica [1-3].By contrast with the coarsely dispersed or low-concentration quartz suspensions [4, p. 254; 5, p. 220], the high-concentration, comparatively finely dispersed suspensions of quartz sand seem promising for refractory technology since, after dewatering, these suspensions form a strong material. The study of such suspensions which have properties similar to those of vitreous silica [3, pp. 34-142] is of interest in the task of using these materials as a binding agent for ceramic concretes [6], as mixtures for molding light weight Dinas articles, as refractory solutions, coatings, and plastic refractories.

The value of the porous heat-insulation refractories continues to increase [1][2][3][4]. Foam ceramic of a mullite composition appears to be a promising material but we have seen no published reports on production or property data.We have studied how to obtain mineralized foams from suspensions of a mullite composition [5] and have done research on the optimum formation conditions and on some of the properties of the material after sintering. The suspensions had a polydispersed composition and contained* 32% of fractions finer than 3 ~m; 11% of 3-5 #m; 21%, 5-10 ~m; 30% 10-20 #m; and 6?0, coarser than 20 vm. The concentration of a previously stabilized, untreated suspension of density 2.08 g/cm 3 and pH 3.20 was adiusted by dilution with water~ In order to obtain three-phase foams (foam masses), the suspensions were mixed with two-phase foams with a glue-resin foaming agent whose properties have been already studied in [6]. the volume shrinkage on molding ShV~ and the foam ceramic sintered ,qhtot. at 1480~ (total shrinkage -"V ' the apparent density Papp, the total porosity Ptot; and the ultimate compressive stress o comp) ; Vf/Vs = 4.5. Fig. 2. Dependence of the log viscosity ~ and the shear velocity ~ on the shear stress P of the aqueous suspension of mullite with C V = 0.40 (1); the two-phase foam with Cg = 0.95 (2); and the three-phase mineralized foams obtained from them with K V equal to 2.84 (3); 5.6 (4); 8.5 (5); and 11.4 (6).

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One of the trends in replacing design elements made of costly nickel alloys for volume isothermal working of heat-resistant alloys at 850-I000~ is the use of insulating backing tiles and reinforcement of the stamps with ceramic inserts.It is desirable to use muliitecontaining refractories for making these components because the presence of the glass phase increases the mechanical strength in the range 800-I000~[i]. Large mullitic articles can be obtained by the slip method [2]. The rheological and bonding properties of mullite suspensions have now been thoroughly investigated [3][4][5]. However, data on the production of ceramic material of a granular structure for operation at elevated temperatures are almost unavailable.It is known [3] that it is desirable to use mullite and electrocorundum as the filler for granular specimens.The present article* makes an assessment of the temperature relationship for the strength of the specimens based on mullite suspensions with various original concentrations of A1203 with and without filler, and shows the possibility of using such materials for design elements.The starting material for making the specimens consisted of scrapmullite refractories in fractions minus 0.05 mm, and high-alumina chamotte VGSh-85 (intermediate product) produced by the Semiluksk refractories factory.The suspensions were prepared by wet ba!imilling using quartz (bearing in mind the pickup of amorphous silica in fractions minus 0.05 mm) and corundum linings.