THE EFFECT OF THE REPLACEMENT OF FREE SILICA BY ALUMINA AND ZIRCONIA IN ELECTRICAL PORCELAIN1

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Abstract
Effect on electrical porcelain of the replacement of free silica by alumina and zirconia.—Since it had been suggested that free silica may be detrimental to the mechanical and the dielectric strengths of electrical porcelain, a series of sixteen batches was prepared in which various proportions of the free silica were replaced, weight for weight, by alumina, zirconia or combinations of both, and bars and disks, after burning at cone 8 l/2 to 9 or at cone 12, were tested for shrinkage, transverse strength, impact strength, heat resistance, absorption of moisture and dye penetration. The results show that resistance to sudden temperature changes can be greatly improved by substituting zirconia,—that the danger of overburning can be greatly decreased by substituting alumina and that the mechanical strengths can be increased by substituting either or both; but in the case of dielectric strength, no improvement was obtained by substituting for the free silica.

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