纳米SiO_2形成柯石英的p-T相图

p-T Phase Diagram of Coesite Synthesized from Nanometer SiO_2 Powder

使用纳米SiO2粉体为原料，在2．0～4．2GPa、150～1200℃范围内进行了一系列的高压高温实验研究，得到了该压力温度范围内晶化产物α-石英与柯石英的p-T相图，而且该相图中的相边界在650℃以下斜率为负，在650℃以上基本水平。通过X射线衍射仪（XRD）、Raman光谱仪（Raman）、傅立叶红外光谱仪（FT-IR）、DSC-TGA差热分析仪（TG—DTA）等表征手段，发现纳米SiO2原粉中水分（包含Si—OH和吸附水）的存在能显著降低合成柯石英的温度和时间，在4．2GPa压力下得到了目前合成柯石英的最低温度190℃。常压下，合成的柯石英在800℃以下能够稳定存在，在1000℃以上转化为α-方石英。

With nanometer SiOz powder as initial material,the p-T phase diagram （2.0-4. 2 GPa, 150 -1 200 ℃） of a-quartz and coesite was obtained by a series of experiments under high pressure and high temperature,and the slope of the boundary in the phase diagram is negative below 650℃ and is basically horizontal above 650℃. By means of transmission electron microscopy（TEM）, X-ray diffractometer （XRD）, Raman spectrometry （Raman）, fourier transform infrared spectrometry （FT-IR）, thermogravimetry and differential thermal analysis measurements（TG-DTA）, the phenomenon that the water in the nanometer SiO2 can decrease the synthesis temperature of coesite and quicken reaction velocity was found,and the nanometer SiO2 can be crystallized into coesite under 4.2 GPa and 190 ℃, which is much lower than the synthesis temperatures of coesite that have been reported. Under ambient pressure,the coesite synthesized from nanometer SiO2 can stably exist at 800 ℃ and is transformed into cristobalite above 1 000 ℃.