纳米SiO2形成柯石英的p-T相图

 使用纳米SiO₂粉体为原料，在2.0～4.2 GPa、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4.2 GPa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1 000 ℃以上转化为α-方石英。

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

With nanometer SiO₂ powder as initial material, the p-T phase diagram (2.0～4.2 GPa, 150～1200 ℃) of α-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 ℃.