Various types of bubble-containing silica glasses fabricated by sintering powder mixtures of silica with silicon nitride

Bubble-containing silica glasses were fabricated by sintering amorphous sil ica powders with small amount of silicon nitride powders, Sintering was per formed at 1800 degreesC in Ng gas atmosphere, It was found that the additio n of Si3N4 is effective for forming bubbles. By controlling the Si3N4 conte nt, various types of bubble-containing silica glasses, such as the so-calle d the opaque silica glass and the foamed silica glass, could be obtained. A ddition of 0.004 mol%Si3N4 produced highly opaque silica glasses containing a large number of small bubbles, while 0.431 mol%Si3N4 resulted in low-den sity foamed silica glasses containing large 1 mm-sized bubbles, Wide variat ions of bubble size and density were observed on these glasses. Thermal con ductivities were estimated and compared with several literature values, The relation between thermal conductivity and bubble density was discussed bas ed on a model simulation.