Effect of gasketing and assembly design: a novel 10/3.5 mm multi-anvil assembly reaching perovskite pressures

Abstract

A new design of multi-anvil assembly and modified gasket characteristics with octahedron and truncation edge lengths of 10 and 3.5 mm is presented for reaching pressures and temperatures over 24 GPa and 2000 °C, respectively. Partially dehydroxylated pyrophyllite half-gaskets with a tapered design fully nesting the octahedron have been employed to prevent excessive octahedron extrusion between the cubes. The assembly utilizes an axially placed thermocouple through the octahedral center, allowing two samples to be present at identical high P–T conditions on either side of the thermocouple during a run. A third sample can be used as a packing around the thermocouple, so long as that sample is inert with respect to the thermocouple and surrounding material. The temperature gradient within the sample locations has been well characterized using two-pyroxene thermometry in the CaO–MgO–SiO₂ system and numerical modeling calculations. The results indicate a good agreement in gradient shape, although the numerical model appears to under-estimate the magnitude of temperature change. The assembly maintains stable temperatures and provides low failure rates.

Keywords:

• Anvil cells
• High pressure
• High temperature
• Pressure calibration

Acknowledgements

The authors would like to thank Eiji Ito for his hospitality in Japan and his significant insights into multi-anvil assembly design. Reviews of the manuscript by Dan Frost and Rick Secco were very useful and we gratefully acknowledge their help. We also thank Andreas Jallas, our intrepid technician, whose job was to make the endless permutations of assemblies and gaskets. This work was funded by the Swiss National Science Foundation, grant numbers 2100-066903-01/1 and 200020-103722/1.