Experimental data for carbides (ZrC, TaC) in the vicinity of melting region under fast electrical pulse heating


S. Onufriev1, A. Savvatimskiy1 and V. Yanchuk1

1Joint Institute for High Temperatures Russian Academy of Sciences, Moscow, Russia

Keywords: pulse heating; current; thermophysics; high temperature
property: resistivity; enthalpy; melting point
material: carbides; ZrC; TaC

Refractory carbides are widely used in high-temperature apparatus, in particular in atomic industry and in aerospace technologies. However there is a significant lack of thermophysical data for these substances especially at very high temperatures. The available data on enthalpy of solid ZrC up to the vicinity of the melting point and its heat of fusion are given in handbook [1]. No data exist on both resistivity and enthalpy of TaC in the vicinity of the melting point of this very refractory carbide. It is supposed that melting temperature for TaC is 4200 K. Temperature dependences of resistivity for ZrC and TaC are also presented in [1], but for temperatures lower melting point. Most data on carbides are obtained by conventional stationary methods having usual temperature limitation around 2200 K [1]. The investigation of carbides properties at the melting point by steady-state methods is very difficult because of the high melting temperature and fragility of carbides. We believe that fast microsecond heating offers considerable advantages in respect to the conventional methods for the experimental investigation of carbides at very high temperatures.

Resistivity of carbides has a positive temperature coefficient dR/dT, which is similar to that of metals. The latter makes pulse current heating technique applicable for investigation of carbides at high temperature. Resistivity ( alt ) of ZrC and TaC versus enthalpy is measured by pulse electrical heating. The duration of electrical current is 10 microseconds. It is shown that the slope of resistivity dependence on enthalpy is changing at the melting point, just as for the most metals. Experimental data on resistivity, enthalpy at the melting point and heat of fusion were obtained for ZrC and TaC in the vicinity of the melting point. Measured data for ZrC are in a good agreement with published data in [1].

Additional experimental data were obtained for TaC for thin specimens (2-8 microns). These thin specimens were obtained by a magnetron scattering technique at quartz surface. The resistivity values turned out to be ~ 10-fold higher than for bulk TaC specimens at the same enthalpy values.

Acknowledgments The work was supported by a scientific grant No.10-08-00114a of the Russian Foundation for Basic Research (RFBR) and by a scientific grant of Presidium of Russian Academy of Sciences (P-12)

References
  1. High refractory elements and compounds. Handbook. R.B.Kotelnikov, S.N.Bashlykov, Z.G.Galiakbarov, A.I.Kashtanov. Ed. “Metallurgia”, Moscow, 1969 (in Russian)

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