Various Types of Bubble-Containing Silica Glasses Fabricated by Sintering Powder Mixtures of Silica with Silicon Nitride.

Abstract

Bubble-containing silica glasses were fabricated by sintering amorphous silica powders with small amount of silicon nitride powders. Sintering was performed at 1800°C in N2 gas atmosphere. It was found that the addition of Si3N4 is effective for forming bubbles. By controlling the Si3N4 content, various types of bubble-containing silica glasses, such as the so-called the opaque silica glass and the foamed silica glass, could be obtained. Addition of 0.004mol% Si3N4 produced highly opaque silica glasses containing a large number of small bubbles, while 0.431mol% Si3N4 resulted in low-density foamed silica glasses containing large 1mm-sized bubbles. Wide variations of bubble size and density were observed on these glasses. Thermal conductivities were estimated and compared with several literature values. The relation between thermal conductivity and bubble density was discussed based on a model simulation.