AN EXTERNALLY-HEATED HIGH-TEMPERATURE DIAMOND-ANVIL CELL. Y. Fei and H. K. Mao, Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, N.W., Washington, DC 20015.

We have developed an externally heated high-temperature diamond-anvil cell that is capable of achieving pressures greater than 125 GPa at temperatures up to 1100 K. The cell was accordingly modified from the Mao-Bell type cell to optimize pressure generation at high temperature. The major modifications include (1) inconel piston-cylinder, (2) thermally insulating the piston-cylinder from the lever arm body, and (3) a double- ring alignment system on the piston to freely retract and advance the piston at high temperature. High temperatures were achieved by a large sleeve-shaped platinum-wire heater fitted around the protruding portion of the piston-cylinder and a small molybdenum-wire heater around the diamond anvils. Combined with synchrotron x-ray diffraction techniques, we can now obtain isothermal compression data for various materials at high temperatures, and in-situ measurements of phase transitions at high pressure and temperature. Experiments on MgO, FeO, and FeS were conducted under hydrostatic or quasi-hydrostatic conditions, using neon as a pressure transmitting medium.