Synthesis of TaC and TaC from tantalum and graphite in the laser-heated diamond anvil cell

The pressure dependence of the onset of the formation of TaC and TaC from the elements has been investigated by in situ X-ray diffraction and pyrometry. TaC has been synthesized by the reaction of Ta and graphite at pressures between 8.6 and 14.3 GPa and at temperatures up to 2,300 K using a laser-heated diamond anvil cell. The products were characterized by X-ray diffraction. Ta and graphite begin to react around 1,100 K at ambient pressure conditions, and the reaction temperature increases with increasing pressure. A linear extrapolation of these data is consistent with recent observations of the formation of TaC at 90 GPa and 3,600 K. We show that diffusion of carbon into tantalum significantly changes the lattice parameter of up to 2 % in the pressure range of up to 19 GPa. In some experiments, TaC was formed concomitantly. The experimentally determined bulk modulus of TaC is = 286(5) GPa. Other tantalum carbide phases were not observed.