Douglas M. Mattox

Experimental observation of the thermocapillary driven motion of bubbles in a molten glass under low gravity conditions

An experiment was carried out on board a Space Processing Applications Rocket with the aim of demonstrating bubble migration in molten glass due to a temperature gradient under low gravity conditions. During the flight, a sample of a sodium borate melt with a specific bubble array, contained in a platinum/fused silica cell, was subjected to a well defined temperature gradient for more than 4 minutes. Photographs taken at one second intervals during the experiment clearly show that the bubbles move toward the hot spot on the platinum heater strip. This result is consistent with the predictions of the theory of thermocapillary driven bubble motion.

Mixed crystallisation modes in glass-ceramic enamel

The crystallisation of a glass-ceramic enamel system in which two modes of crystallisation are observed is described in some detail. During the coating fusion, uncontrolled, spontaneous devitrification of kalsilite occurs throughout the glass. In a post heat treatment process a controlled, intentionally nucleated crystallisation of the matrix occurs. The preferential diffusion of iron from the substrate, through the glassy phase of the biphasal system during fusion is observed. The implication of this behaviour on adherence is noted.