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The literature contains information relating to the use in ceramics technology of active oxide powders prepared by calcining the salts at relatively low temperatures [1][2][3][4][5]. These powders are characterized by a large specific surface and considerable structural defectiveness which increase their consolidation activity and lowers the sintering temperature. However, active powders suffer from technological inadequacies which set limits to their use.It is well known that it is difficult to produce a dense green product from a fine-dispersion powder, and the use of fine-dispersion powders results in a higher firing shrinkage Cup to 25-28%). An increase in the molding pressure results in a slightly denser green product but increases the probability of overpressure cracking.Even in hot pressure-molding the use of active powders entails difficulties because their volume decreases by more than a factor of 14 in the molding process [3] so that active powders are used only as additives (20-30%) to improve the sintering of low-activity powders [2, 3].The technological properties of active powders can be improved by short-term dry grinding in a planetary mill [6].In this article the results are reported of an investigation of the properties of powders of A1203, Y203, and MgO after dry grinding in a planetary mill.The A1203 powder was produced by calcining chemically pure aluminoammonia alum for 2 h at 1300~ An x-ray analysis showed that the powder contained a-A1203.The MgO powder was produced by calcining analytically pure basic magnesium carbonate for 1 h at ll00~ and the Y203 powder by calcining chemically pure yttrium oxalate and analytically pure hydrated yttrium nitrate for 2 h at 800 and 600~ respectively.The calcination temperatures of the salts were the lowest practicable in accordance with the results of thermogravimetric analyses; the complete decomposition of the salts was verified by x-ray methods. D. I. Mendeleev Institute of Tectmolo~y, Moscow.

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The high temperatures used for melting glass and the special operational conditions of the refractories in glass-melting furnaces facilitate active interaction between the refractories accompanied by the accelerated destruction of individual elements of the lining and make it necessary to carry out more frequent maintenance shutdowns of the furnace as a whole~ Therefore, the useful life of refractories in glass-melting furnaces is affected not only by the corrosion of the refractories by the glass and the aggressive gas medium but also by the contact interaction between different refractory materials as is observed, e.g., at the bottom of glass-melting furnaces (contact between Bakor and chamotte refractories) in the port drums, and in components of the furnace superstructure (contact between Bakor and Dinas refractories) [;].It therefore seemed important to develop methods for studying the contact interaction between refractory materials since this would make it possible to estimate the behavior of refractory materials in contact one with another or through an intermediate layer of lime mortar at high temperatures (up to 1600~ and to forecast the possibility of using simultaneously various refractories in individual components of the lining of glass furnaces.There is no one method or apparatus used in Soviet practice for studying the contact interaction.According to non-Soviet data [2-5] such studies have been carried out in individual countries but the parameters of the tests were not standardized and to evaluate the contact interaction among refractory materials, apparatus were used which had been designed to study other properties of refractories (high-temperature strength, creep, etc.).We have now developed a method and the appropriate apparatus which make it possible to study the contact interaction between refractory materials over a wide range of temperatures (up to 1600~The essence of the method lies in the uniform heating of specimens under a load; the specimens lie one on top of another; heating continues until the specified test temperature is reached; there is a dwell at this temperature; this is followed by an evaluation of the contact interaction using various methods of physicochemical analysis.The laboratory apparatus for the tests consists of an electric resistance furnace with a specially designed device for loading the specimens.The furnace power is supplied from the mains via an RNO-250-10 transformer by means of a VRT-3 high-accuracy temperature regulator.A diagram of the apparatus is shown in Fig. I. The electric furnace consists of an internal alumina tube ! with a three-start rifling on the internal surface in which the heating elements 2 in the form of a spiral made from Pt 30-40% Rh are mounted.Between the alumina tube and the external metal housing 3 there are layers of high-temperature insulation 4 and a heat-insulated filling 5. The furnace is equipped with a loading device 6 which makes it possible to apply a load of 0.05-0.; MPa to the specimens as would be characteristic for the...

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