Boron–MgO composite as an X-ray transparent pressure medium in the multi-anvil apparatus

Abstract

X-ray transparent material is very beneficial for in-situ X-ray experiments in the multi-anvil apparatus. We sintered machinable blocks of boron-MgO composite at 800-1000 °C under atmospheric pressure from a mixture of amorphous boron and brucite or Mg(OH) 2 . Machinability of composite blocks improved with increasing brucite content in starting material; brucite content higher than 15 wt.% showed reasonable machinability in forming various shapes such as octahedron, cylinder, and sleeve. We confirmed feasibility of the boron-MgO pressure medium through successfully generating lower mantle pressure (>23 GPa); its pressure generation efficiency is comparable to that of Cr 2 O 3 doped MgO pressure medium. The boron-MgO composite is expected to be an excellent thermal insulator owing to extremely low thermal conductivity of amorphous boron; we confirmed its better performance of thermal insulating through a comparative heating test with zirconia sleeve in Cr 2 O 3 doped MgO pressure medium. Constituting light elements, the boron-MgO composite has high X-ray transparency, which enables us to conduct various cutting edge X-ray measurements in large volume multi-anvil apparatus.

Thermal expansion of liquid Fe-S alloy at high pressure

“…S1. Trimmed octahedral pressure medium made from B+15 wt.% MgO (B85) was employed to minimize the absorption and diffraction of the sample environment (Xie et al, 2020). B85 gaskets were also used along the X-ray path instead of pyrophyllite gaskets.…”