F. S. Kaplan

Development, introduction into production, and service of unfired quartz refractories

ConclusionsA method of centrifugal forming of quartz refractories based on highly concentrated suspensions of fused quartz has been developed under laboratory and production conditions.The method of unfired quartz refractories with hydrothermal strengthening of centrifugally cast parts has been introduced into production.Quartz refractories for pouring and treatment of steel have successfully passed production tests.

Centrifugal casting of ceramics and the properties of the castings

ConclusionsIt was established that the circumferential velocity maintained during the centrifugal casting process has a significant effect on the porosity of the castings. The effect of the rheological behavior of the original HCBS is also significant.We carried out a comparative analysis of the rheological properties of the HCBS of fused quartz having different pH values with the parameters of their centrifugal casting and the porosity of the obtained castings.As in the case of slip casting, unfired quartz ceramics were obtained according to the method of centrifugal casting. These ceramics exhibit high levels of mechanical properties after undergoing a hydrothermal treatment or a strengthening treatment in alkaline solutions.The possibility of using the method of centrifugal casting for shaping the refractories based on the casting systems containing a granular filler (the keramobeton-type systems) was established.

Centrifugal casting of ceramics. Main parameters and the regularities of the process

ConclusionsUsing HCBS of fused quartz, we studied and analyzed the main regularities of the centrifugal casting process of ceramic products.The procedure for calculating the magnitude of the centrifugal pressure during the molding process and a nomogram establishing the relationship between the rotational frequency of the mold, the diameter of the product being molded, and the circumferential velocity of centrifugal forming were presented. Based on the integral curves of grain size distribution of the castings, the degree of layering in their solid phase was characterized.The volume fraction of HCBS, the circumferential velocity and the temperature maintained during the molding process, and the coefficient of excess solid phase form the most important and decisive technological parameters of the process of centrifugal forming.The method of centrifugal casting makes it possible to accelerate the molding process by several tens of times as compared to slip casting. In this case, the porosity of the castings amounts to 12–20%.

Effect of the structural parameters of refractories on their slag impregnation in the units used for vacuum refining of steels

ConclusionsWe studied the effect of the specific features of the pore structure (porosity) and the wetting characteristics of the refractories on their depth of impregnation in the units used for vacuum refining of steels. The changes occurring in the pore space of the refractories during their service were examined. Minimum impregnation occurs in the materials having an insignificant content of the glass phase, a branched pore structure, and a large total volume of fine pores (in particular, pores measuring <1 μm in radius).

Unfired quartz nozzles for teeming of steel

ConclusionsUnfired quartz nozzles hardened by hydrothermal treatment for teeming of steel are no poorer in life than fired. In addition in contact with aggresive (manganese) steels the wear of the unfired ceramic is somewhat less. There was no penetration of the unfired material by the products of interaction of the metal with the refractory during service.Unfired nozzles based on suspensions produced by grinding in an acid medium and stabilized in an alkaline medium showed the least wear in service.

Highly concentrated suspensions of nontransparent fused quartz and materials based on them

ConclusionsOn the basis of nontransparent quartz glass, using the wet milling method in a porcelain mill and uralit balls, we obtained casting suspensions with volume concentrations of solid phase equal to 70–73%. By means of stabilization with mechanical gravitation stirring we attained a sharp reduction in the slips viscosity, and increases in density and strength.We demonstrated the considerable influence of the concentration of the suspension during wet milling on the porosity and strength of the cast. A technology was developed with which, on the basis of the suspension of nontransparent quartz glass, we can obtain green articles with a porosity of 13.3–15% and a bending strength of up to 2 MPa. Using this slip we prepared samples of unfired ceramic with σbend up to 30 MPa which is comparable with the strength of fired materials.

Highly concentrated ceramic binder suspensions. Colloidal component and binding (bonding) properties

ConclusionsWe carried out depletion and enrichment (concentration) of the original suspension of quartz sand and obtained suspensions and castings based on them by varying Cccnd in the 0.01–2.22% range with respect to the total weight of the solid phase.The colloidal component is characterized by a specific surface Ssp=260 m2/g (average superficial particle diameter davs=9.5 nm). Its content determines Ssp of the suspensions to a large extent; Ssp was varied in the 0.96–8.30 m2/g range by varying Cccnd.The most significant effect of Cccnd on the strength properties of the castings was established. Depending on Cccnd, the parameter σbnd changes by 60 times (from 0.1 up to 6.0 N/mm2), the porosity changes from 10.7 up to 18%, and the loss on ignition changes from 0.04 up to 0.35%.

HIGHLY CONCENTRATED CERAMIC BONDING SUSPENSIONS. MECHANISM AND FEATURES OF STRUCTURE FORMATION DURING DRYING

ConclusionsUsing as an example castings of VKVS of acid and acid-amphoteric compositions we studed the main rules governing their structure formation in the process of drying.The drying process at the first stage (reduction in moisture content by 0.5–1.2%) is characterized by shrinkage (0.05–0.3%), and in the latter stages by a gradual expansion 0.017–0.08%).We established a relationship between the various factors of dispersion in the VKVS and the expansion of the castings based on them, and showed that a decisive influence on the magnitude of the expansion is exerted by the concentration in the suspension of particles measuring less than 0.1 μm.We put forward a scheme for structure formation during drying of the casting, including three stages: shrinkage of the casting on account of the removal of physical-mechanical moisture; expansion of the casting on account of the action of repulsive forces between the colloidal particles, developing with an increase in the concentration of the latter, in the intergrain spaces, during removal of moisture; and finally the strengthening of the developed contacts on account of the formation of siloxane bonds.During the making of the goods based on VKVS we should take into consideration the stresses developing on account of the nonsimuitaneous occurrence of the processes of expansion and shrinkage across the thickness of the casting, and we need to select grinding and dispersion factors for the VKVS, bearing in mind the dimensions an required technical properties of the articles.

Rheological and technological properties of zirconia suspensions stabilized with various amounts of calcium oxide

ConclusionsA study was made of the rheological and technological characteristics of suspensions. The presence of different types of flow is noted. We identified the influence of the phase composition on the nature of the rheological curves. We studied the rheological properties of calcium zirconate, and identified the optimum conditions for casting water suspension.The change in the rheological properties of the suspensions is interpreted from the viewpoint of the magnitude of hydration and kinetically bonded liquid. We demonstrated the link between the rheological properties of the heterophase suspensions and the change in ζ-potential.The change in the rheological properties of the suspension by means of small amounts of surface-active agents of the organic alcohol types in the optimum pH range makes it possible to obtain articles with outstanding properties, including those from compositions containing CaO right up to calcium zirconate.

Influence of oxide additions on the sintering of corundum refractories

Influence des oxydes de Mg, Ti et Cr et de leurs melanges sur la structure du corindon fritte