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The recent developments in the production of large-sized and intricate refractory products by casting from aqueous suspensions [1][2][3][4][5] call for an improved technology of obtaining the casting suspensions and an increased strength of the unfinished castings.The conventional method of obtaining A1203 suspensions includes milling the powder in steel mills, subsequently washing off the milled iron contaminant, and suspending the milled products in the optimum pH range [4][5][6]. However, this method involves a lengthy process (multiple decantation requiring a total duration up to 30 days) and a significant consumption of hydrochloric acid (up to 0.5 liter per i kg of material). Besides this, the castings obtained from such suspensions exhibit a relatively high shrinkage during the process of drying (up to 3-4%) and low strength [7,8] because of which it is not possible to produce large-sized intricate components. Furthermore, the low strength makes machining of the unfinished (raw) products difficult. Machining of the underfired or sintered products leads to an increased consumption of diamonds.Furthermore, the conditions have been established [9-13] for obtaining ceramic suspensions possessing considerable binding properties that ensure high strength of castings. Thus, a new method was proposed [13] for obtaining heat-resistant binders (including those based on A1203) by introducing small amounts of highly active additives having low values of ionic potential (BaO, SrO, CaO) into the composition of the low-activity materials (having high values of ionic potential) and for obtaining the suspensions by wet milling the materials in corundum-lined mills using corundum grinding bodies at predetermined pH values. The ultimate bend strength of the raw castings based on the additiveless GK alumina that was prepared using the new method was found to be 2-4 MPa and after drying it increased up to 5-8 MPa [13].Wet milling at elevated temperatures (owing to the occurrence of heat liberating processes) and optimum (for thinning) pH values forms the main condition for obtaining such suspensions. This makes it possible to carry out the process at the maximum possible concentration of the solid phase. In this case, one obtains polydispersed granular composition (size distribution) and a low content of the bound (bonded) liquid that subsequently determine the density of the semifinished product. This paper deals with the evaluation of three methods of preparing the suspensions: the commonly used method of suspending a powder milled in a vibrational mill and subsequently washed for removing the iron contaminant; suspending a powder milled in a corundum-lined vibrational mill using corundum balls; and suspending a powder wet-milled in a corundumlined ball mill using corundum balls under the optimum values of the moisture content and pH. In all the cases, the material:balls ratio was maintained at 1:6; and during wet milling, the material:balls:water ratio was equal to 1:6:0.5.An aluminous frit (sinter) containing a glass phase...

The use of ethyl silicate binders of an optimal composition makes it possible to produce east corundum articles with a mullite--corundum binder with excellent characteristics.The best combination of properties is found in the articles when binders of optimal composition, close to stoichiometric, are used in the hydrolysis reaction of the ethyl silicate.The destruction and sintering processes in the corundum casts in an ethyl silicate binder during heat treatment are produced by the destruction kinetics of the hydrolysis products of the ethyl silicate and by the presence in them of active SiO 2. The sintering of articles of such a composition begins at ~ ll00~The excellent thermal-shock resistance of the ceramic made from masses with ethyl silicate binders and the slower destruction of these ceramics result from the rational phase composition and structure of the material.

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