Collaborative Research: Bulk synthesis of stishovite near ambient pressure and temperature

University Of Texas At Arlington, Arlington TX

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: The project targets synthesis of stishovite, a form of SiO2 (silica) and one of the hardest materials known to mankind at hydrothermal conditions. Presently, this precious form of silica can only be attained at extremely high pressure (ca. 100,000 times atmospheric pressure) in a technically very difficult and expensive process that yields only small quantities. The new approach of this project mimics geological conditions, and grows the crystals from aqueous solutions in bulk quantities. The process occurs close to ambient pressure and temperature conditions, and consequently, will be inexpensive and scalable. This facilitates new applications of stishovite as an abrasive, in cutting tools, and as a hard ceramic material in other applications. TECHNICAL DETAILS: Stishovite, a polymorph of silica (SiO2), is - together with cubic boron nitride - only second in hardness to diamond. Moreover, among the hardest materials known it is the only oxide, thus naturally resistant against degradation through oxidation. Despite these outstanding properties, stishovite is not used as an engineering material, because it can be synthesized only at pressures above 8 GPa. Although technically feasible, the high-pressure route is not scalable and rather expensive. In this project, a kinetically controlled hydrothermal synthesis approach for stishovite is being developed. The process occurs near ambient pressure and temperature conditions and is similar to the industrial production of quartz crystals. The difference to industrial quartz growth is that instead of quartz seed crystals, stishovite seed crystals are employed. The temperature gradient in the autoclave system allows for the supersaturation of the silicate solution in the growth chamber and the kinetically controlled growth of the stishovite seed crystals from the supersaturated solution. The experiments are guided by computations that explore and predict optimal synthesis conditions. The research is a seminal approach to synthesize high pressure phases near ambient conditions from solution which suggests a transformational impact on the synthesis of high-pressure phases. The project is training graduate students in high-pressure and hydrothermal synthesis techniques and computational materials chemistry. The results from the research are part of the graduate level course "Solid State Chemistry".