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Exploring the Synthesis Parameters and Spark Plasma Sintering of Tantalum Carbide Powders Prepared by Solvothermal Synthesis Braeden M. Clark, James P. Kelly, and Olivia A. Graeve* Kazuo Inamori School of Engineering, Alfred University, Alfred, NY 14802 *Author to whom correspondence should be addressed: Email: [email protected], Tel: (607) 871-2749, Fax: (607) 871-2354, URL: http://people.alfred.edu/~graeve/ ABSTRACT Tantalum carbide is a technologically important material for use in ultra-high temperatures and corrosive environments. In this report, we describe the scalability of a low temperature solvothermal method for the preparation of this useful material. X-ray diffraction shows phasepure powders with no change in average crystallite size or compound stoichiometry compared to synthesis in smaller batches, remaining at 25 nm and 0.94 respectively. Dynamic light scattering shows a slight decrease in particle size distribution with scale-up. Thermogravimetric analysis (TGA) in air shows a decrease in surface species on the powders, but the powders oxidize at a lower temperature when scaling the synthesis. Mass spectrometry performed alongside TGA in a helium atmosphere reveals that water is the most abundant species on the surface of the powders, but oxygen, carbon monoxide, carbon dioxide, and nitrogen are also detected. Oxygen analysis reveals that the oxygen content of the powders is high (>6%). The oxygen source and methods of decreasing oxygen content are discussed. Initial sintering trials were performed and demonstrate the need for further powder processing. INTRODUCTION Tantalum carbide is of special interest because of its high melting temperature (~4000 K), making it one of the most refractory ceramics known. In addition to being refractory, other properties have been investigated including mechanical strength, oxidation behavior, elasticity, superconductivity, electronic structure, thermodynamic properties and hardness [1-8]. Due to these properties, tantalum carbide is being investigated as a candidate material for use in space reentry vehicles, high Mach aircraft, and propulsion systems, where high temperatures and pressures are sustained. A novel solvothermal synthesis method has been used to successfully synthesize tantalum carbide and other non-oxide ceramic powders [9-10]. This technique makes use of fused-quartz tubes to allow observation of the reaction; however, this limits the amount of powder that can be synthesized per reaction (~3 g) and risks contamination from the reaction vessel. A scale-up synthesis using the same principles is done in a stainless-steel beaker to reduce contamination and demonstrate scalability of this process. EXPERIMENTAL PROCEDURE Reactants for the synthesis were prepared in an argon-filled glove box. The precursors consisted of 92.8 g tantalum (V) chloride (99.8%, Alfa Aesar, Ward Hill, MA) and 9.3 g of carbon (Lampblack 101, Degussa, Parsippany, NJ) and were mixed with a mortar and pestle.

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The powders were added to a 600 mL stainless-steel beaker along wit