Measurement of ZrC properties up to 5000 K by fast electrical pulse heating method

Abstract

Abstract

Fast anharmonic free energy method with an application to vacancies in ZrC

“…Consequently we suggest the physical origin of the steep increase in heat capacity in ZrC x 51 is a combination of electron thermal excitations, electron-vibration coupling, and structural excitations on the carbon sub-lattice, predominantly the constitutional carbon vacancies that have been the focus of this paper, although there are also stoichiometry conserving intrinsic carbon Frenkel defects, which are beyond the scope of this work but discussed elsewhere. 50,51 Finally, it is interesting to note that while anharmonicity is the only term that suppresses C P in Fig. 9, the enhancing effects of the vacancy contribution are mainly due to the indirect effect of anharmonicity, insomuch as anharmonicity by lowering G form enhances the population of vacancies (e.g.…”

Electron and phonon interactions and transport in the ultrahigh-temperature ceramic ZrC

“…25,26 The PZ81 LDA 30 functional provides a satisfactory description of ZrC at low temperature, giving a zero-point-corrected T = 0 K value of a LDA = 4.667 Å, compared to an experimentally reported value of a exp = 4.694 Å. 6 The difference is similar in magnitude but opposite in sign to PBE, 31 however we choose to work with the LDA due to reported superior description of thermodynamics at high temperatures. 32 DFT calculations employ the projector-augmented wave (PAW) method, 33 with 4s and 4p-Zr electron included as valence states.…”

Carbides and Nitrides of Zirconium and Hafnium

“…The binary systems of zirconium and hafnium with nitrogen and carbon were studied experimentally from circa 1000 °C to liquidus temperatures and most of the systematic studies of phase equilibria were performed before 1970. New experimental results on melting temperature determination and thermodynamic properties of single phases were published since then [61,62,63,64,65,66], and an entirely new stream of thermodynamic data has emerged from ab initio computations [1,67,68,69].…”

“…Due to the microseconds timeframe of discharge, the heat losses can be neglected, and the total energy is known from the capacitor calibration. Recently, this approach was successfully applied for carbides and nitrides films 100 µm or thinner [61,63,64,65,66,161,162] and the first experimental data on fusion enthalpies and high temperature heat capacities of ZrC and ZrN were reported. The fusion enthalpy of ZrN was measured as 104 kJ/mol [65], and the fusion enthalpy of ZrC x was found to increase from 92 kJ/mol for ZrC to 111 kJ/mol for ZrC 0.95 .…”