Electric Arc Synthesis of Nonstoichiometric Tantalum Carbides with a Face-Centered Cubic Lattice

In this paper, we report experimental results that show the feasibility of synthesizing ultrarefractory materials, namely crystalline phases of cubic tantalum carbide with a face-centered cubic lattice and different carbon-to-tantalum ratios. Experimental powder was synthesized using a low-voltage direct current arc discharge ignited in open air to heat up mixtures of different compositions (tantalum–carbon). The implementation of the nonvacuum electric arc method was carried out due to the self-shielding effect of the reaction zone of the arc reactor due to the sudden generation of CO and CO₂ gases. The synthesis yielded tantalum carbides TaC_0.77, TaC_0.84, TaC_0.92, and TaC_1.00 with lattice parameters of 4.4194, 4.4322, 4.4448, and 4.4588 Å, respectively. The lattice parameters were determined by X-ray diffractometry. The morphological features of tantalum carbide powder particles obtained by vacuum-free electric arc synthesis were determined using scanning electron microscopy. The method of synchronous thermal analysis detected some differences in the oxidation processes of the resulting crystalline phases when heated in air. For the first time, cubic tantalum carbide phases with different stoichiometry were obtained in a series of experiments performed using vacuum-free arc synthesis.