Structural Transition of Nanometer SiO_2 Powders under High Pressure and High Temperature

The crystallization process of nanometer SiO 2 powder under high pressure and high temperature was investigated.The experiment results show that nanometer SiO 2 powder crystallizes to α -cristobalite with a little tridymite under normal pressure at 1 000~1 600 ℃,crystallizes to α -quartz under 2.0~3.5 GPa and 320~1 100 ℃,and crystallizes to coesite under 3.9 GPa and 320~1 100 ℃.The temperature of coesite formation from nanometer SiO 2 is much lower than that from common α -quartz.