High-temperature calibration of a multi-anvil high pressure apparatus

Fusion and solidification of Al and Ag samples, as well as Fe-93-Al-3-C-4, Fe-56-Co-37-Al-3-C-4, and Fe-57.5-Co-38-Al-1-Pb-0.5-C-3 alloys (in wt%), have been investigated at 6.3GPa. Heater power jumps due to heat consumption and release on metal fusion and solidification, respectively, were used to calibrate the thermal electromotive force of the thermocouple against the melting points (mp) for Ag and Al. Thus, obtained corrections are +100 degrees C (for sample periphery) and +65 degrees C (center) within the 1070-1320 degrees C range. For small samples positioned randomly in the low-gradient zone of a high pressure cell, the corrections should be +80 degrees C and +84 degrees C at the temperatures 1070 degrees C and 1320 degrees C, respectively. The temperature contrast recorded in the low-gradient cell zone gives an error about +/- 17 degrees C. The method has been applied to identify the mp of the systems, which is especially important for temperature-gradient growth of large type IIa synthetic diamonds.