Synthesis of ultra-fine tantalum carbide powders by a combinational method of sol-gel and spark plasma sintering

Tantalum carbide (TaC) nanopowders were synthesized by a novel method combining the sol-gel and spark plasma sintering (SPS) processes using tantalum pentachloride (TaCl5) and phenolic resin as the sources of tantalum (Ta) and carbon (C), respectively. Gels of Ta-containing chelate with good uniformity and high stability were prepared by solution-based processing. The products with the structure of carbon-coated tantalum pentoxide (Ta2O5) were obtained after pyrolysis at 800 °C. Further heat treatment by SPS resulted in the fast formation of TaC at a relatively low temperature. The effects of the C/Ta molar ratio in the raw materials and the heat treatment temperature on the prepared powders were investigated. With increase in the C/Ta molar ratio from 3.75 to 4.25, the synthesis temperature, oxygen content and average crystallite size of the TaC powders decreased. Furthermore, the oxygen content of the powders prepared at the C/Ta molar ratio of 4.25 could be reduce by increasing the heat treatment temperature from 1400° to 1600°C, which unfortunately also induced a mean crystallite size increase from 30 to 100 nm. The TaC powders obtained at a comparatively low C/Ta molar ratios of 4.25 at 1500 °C had an average particle size of about 50 nm and a low oxygen content of about 0.43 wt%.