Effects of Ti additive on HPHT diamond synthesis in Fe-Ni-C system

Abstract

Diamond crystals with low nitrogen concentration were synthesized from the Fe-Ni-C system with Ti additive at high pressure and high temperature (HPHT) in a china-type cubic high pressure apparatus (CHPA). The synthesis pressure range was 4.8–5.2 GPa, and the temperature range was 1420–1600 K. The lowest synthesis pressure for diamond fell first and then rose with the increase of Ti additive. The color, shape, surface morphology and nitrogen impurity concentration of the synthesized diamond crystals were characterized using optical microscopy (OM), scanning electron microscopy (SEM) and micro Fourier transform infrared (FTIR) spectrometry. The results show that the Ti additive has significant effects on color, growth rate, crystal shape, surface morphology and nitrogen impurity concentration of the synthesized diamond crystals. The color of diamond crystals synthesized without Ti additive is yellow, while that with Ti additive becomes light and nearly colorless. The growth rate without Ti additive is higher than that with Ti additive. The crystal shapes of as-grown diamond crystals vary with the increase of Ti additive. The {111} crystal faces become dominant and some {311} crystal faces appear with the increase of Ti additive. The concentration of nitrogen impurity in diamond crystals without Ti additive is higher than that with Ti additive.