Synthesis of Coesite from Ultra Fine Particles

Abstract

Coesite, a high pressure phase of SiO2, was synthesized without H2O or any other catalizing component at temperatures as low as 250°C from ultra fine particles (80 Å in diameter) of silica produced by the gas evaporation technique. The ultra fine particles were worked by a tetrahedral anvil type high pressure apparatus up to a pressure of 50 kbar at 450°C for 30 minutes and almost 100% of the particles were crystallized into coesite. Mechanically ground quartz and silica-gel of a few µm in size were also worked under the same condition. The reaction speed of recrystallization of the ultra fine particles was roughly estimated to be ten times or more that of particles of micron size.