Tantalum carbide products from chemically-activated combustion synthesis reactions

Musa, Clara;Licheri, Roberta;Montinaro, Selena;Orru', Roberto;Cao, Giacomo

2017-01-01

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Abstract

A rapid route based on the use of small amounts of polytetrafluoroethylene to chemically activate and sustain the combustion synthesis reaction for the formation of TaC from its elements is successfully exploited in this work. Other than a reaction booster, the polymer is found to play also a role as a carbon source, so that part of graphite can be replaced by Teflon to produce a single phase material. A relevant importance in the activation of the synthesis reaction is provided by the intermediate phase TaF3, whose formation is clearly evidenced, along with that of Ta2C, by combustion front quenching experiments. Additive free TaC products with relative density up to about 98% and grains size less than 5 µm are finally obtained when combustion synthesized powders are processed for 20 min at 1800 °C by Spark Plasma Sintering. A further increase in the sintering temperature to 2050 °C and/or the dwell time to 30 min is found to negatively affect product densification. This outcome is mainly ascribed to the significant grains coarsening (above 20 µm) correspondingly observed as well as to other vapor-phase generating events, which could be more easily induced when powders are exposed to higher temperature conditions.