On the high-pressure behavior of periodic mesoscale SBA-16 silica/carbon composites: studies at 10 GPa between 25 and 1800 °C

Abstract

We report on the structural transformations of carbon filled SBA-16 mesoporous silica at 10 Gigapascal pressure and temperatures between 25 and 1800 °C in a multi-anvil apparatus. The silica begins to crystallize in the coesite structure at 400 °C under retention of the mesophase order. An irregular mesostructure of crystalline coesite is observed for samples treated at 800 °C. Formation of crystalline stishovite and graphite under mesoscale phase separation is observed at 1000 °C and 1300 °C. From a temperature of 1400 °C, the stishovite phase transforms into coesite and graphite transforms into diamond, respectively. The diamond phase adopts a micron-sized platelet-like morphology at 1400–1800 °C. The diamond crystallite size was determined to be 9–12 nm.

Keywords:

• mesoporous silica
• carbon composites
• stishovite
• coesite
• diamond

Acknowledgements

We gratefully acknowledge the financial support from Lehigh University and the Carnegie Institution of Washington. We thank Liwei Deng, Yao Wu, Li Zhang, and Alexander Goncharov for technical assistance.