Machinable boron-doped diamond as a practical heating element in multi-anvil apparatuses

Area of Science:

• Materials Science
• High-Pressure Geophysics
• Diamond Anvil Cell Technology

Background:

• Boron-doped diamond (BDD) is an ideal heating element for multi-anvil apparatuses due to its refractory nature and X-ray transparency.
• The extreme hardness of diamond limits the manufacturability of BDD heating elements, hindering their widespread application.
• Difficulty in fabricating BDD tubes restricts its use in high-pressure, high-temperature research.

Purpose of the Study:

• To develop a machinable boron-doped diamond (MBDD) material for easier fabrication of heating elements.
• To evaluate the performance of MBDD heaters in generating ultrahigh temperatures under high-pressure conditions.
• To enable advanced measurements of melt properties under Earth's mantle conditions.

Main Methods:

• Sintering of MBDD by annealing a mixture of BDD powder and pitch (C_nH_2n+2) in Argon at 1273 K for 5 hours.
• Fabrication of MBDD tubes using a lathe or computer numerical control (CNC) machine.
• Testing the heating performance of MBDD heaters in a multi-anvil apparatus, achieving temperatures over 3300 K at 15 GPa.

Main Results:

• Successfully sintered machinable BDD (MBDD) with BDD powder bound by <10 wt.% graphite.
• MBDD tubes of various dimensions (e.g., 1.2/0.7/4.0 mm outer/inner diameter/length) were manufactured.
• MBDD heaters demonstrated comparable ultrahigh temperature generation (>3300 K) to conventional BDD heaters, melting Al₂O₃ at 15 GPa.
• Low graphite content in MBDD minimally affected heating performance due to limited graphite-diamond conversion.

Conclusions:

• MBDD offers a practical solution for fabricating high-performance heating elements for multi-anvil apparatuses.
• The excellent machinability and comparable heating performance of MBDD facilitate its application in high-pressure research.
• Stable temperature generation over 3300 K with MBDD enables crucial measurements of melt physicochemical properties under mantle conditions.