Silica Microbubbles

Abstract:
Glass microbubbles 0.150 to 0.020 mm diameter, having a bulk density of 0.25 g/cc and a true density of 0.50 g/cc have been greatly improved by decreasing the alkali content and also by making them of vitreous silica. The improvements consist of marked decrease in moisture adsorption, enhanced electrical properties, and great increase in maximum use temperature. An acid leaching technique applied to the commercially available 18% alkali "Eccospheres" of Emerson & Cuming, Inc. reduces the alkali content to 6% and increases the maxim m use temperature from 500°C to 800°C. Formation from pure silica by a direct high temperature process to give a vitreous silica bubble retains the useful characteristics of the low-melting-alkali-glass bubble with the desirable properties of vitreous silica - low to negligible moisture adsorption, outstanding dielectric properties even at high temperature, and a safe use temperature for most applications of 1300°C. The feasibility of the direct process has been briefly demonstrated on pilot plant scale at 2 lb/hr rate.

Work on bonding the high temperature product into structural shapes is described.