Superconducting TaC nanoparticle-containing ceramic nanocomposites thermally transformed from mixed Ta and aromatic mole
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Joseph Prestigiacomo Materials Sciences Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
Boris Dyatkinb) Chemistry Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
Syed Qadri and Ramasis Goswami Materials Sciences Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
Kenan Fears and Matthew Laskoski Chemistry Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
Michael Osofsky Materials Sciences Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
Teddy Keller Chemistry Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA (Received 25 January 2017; accepted 9 June 2017)
We report the structure and synthesis approach for obtaining a ceramic nanocomposite pellet comprising ;50 nm-sized TaC nanoparticles. A mixture of Ta metal powder and the carbon precursor 1,2,4,5-tetraphenylethynyl benzene, pelletized by vacuum pressing at 131 MPa, on further thermal treatment with Ar at 1400 °C yields such a ceramic composite. On air oxidation, the TaC nanoparticles are converted to Ta2O5 nanoparticles at 760 °C. Hardness measurements revealed that the composite exhibited a global hardness in the range of 1.23–1.57 GPa. However, nanoindentation studies showed that, locally, hardness of the TaC nanoparticles (;15 GPa) approached that of the densified TaC ceramic. Superconducting studies of the pellet consistently exhibited two transitions with Tc values of 10 K and 8.5 K, respectively, that corresponded to bulk TaC and to a component of unknown origin. The results discuss the morphological and constitutional characterizations of the TaC nanoparticle-containing composite.
I. INTRODUCTION
Tantalum carbide (TaC), similar to Hafnium carbide, has a melting point above 4000 °C and is among the most refractory binary compound known to date.1 TaC also has other impressive materials properties such as high hardness (19 GPa), high elastic modulus (537 GPa), and high electrical conductivity (.5 106 X1 m1 at 300 K).2,3 Such impressive properties enable this high-performance refractory material to play an important role in applications involving aggressive environments ranging from gas turbines to heat shields for hypersonic vehicles.4,5,6,7 Tantalum carbide is also used in refractory ceramic alloy materials, especially as components of tungsten carbide Contributing Editor: Xiaowei Yin a) Address all correspondence to this author. e-mail: [email protected] b) National Research Council Postdoctoral Fellow. DOI: 10.1557/jmr.2017.257
alloys.2 Furthermore, TaC is also known to be a superconductor with a Tc of 10.35 K.8 Transition-metal carbides are typically produced at extreme temperatures (above 2300 °C) and pressures (200–400 MPa) from component elements9–11; for example, the typical precursor materials for producing TaC are Ta powder and graphite.9 However, compaction under high temperature and pressure such as in the hot isostatic pressing (HIP)
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