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Thermophysical Properties of Laser-Sintered Zr–ZrB2 Cermets


  • J. Hellmann—contributing editor

  • This work was financially supported by the Ceramics and Nonmetallic Materials Program, Air Force Office of Scientific Research, under Grant No. FA9550-06-1-0163, NASA Langley Professor Program and NSF I/UCRC center grant. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which was sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U. S. Department of Energy. Research (thermal expansion, heat capacity, and thermal diffusivity measurements) conducted through the Oak Ridge National Laboratory's High Temperature Materials Laboratory User Program was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.

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Thermophysical properties between 293 and 1863 K were investigated for laser-sintered Zr–ZrB2 cermets containing 30, 50, and 70 wt% Zr. The measured values of coefficient of thermal expansion of Zr–ZrB2 cermets were larger than the predicted values due to the effect of Zr–O solid solution, which was formed during laser sintering. The order–disorder phase transition of Zr–O solid solution resulted in the sharp increase in heat capacity between 625 and 675 K. Thermal conductivities were calculated from measured densities, heat capacities, and thermal diffusivities. Thermal diffusivities at 473 K were 14.0, 12.2, and 8.0 mm2/s for 30Zr–ZrB2, 50Zr–ZrB2, and 70Zr–ZrB2, respectively. Thermal conductivities at 473 K were 38, 31, and 20 W·(m·K)−1 for 30Zr–ZrB2, 50Zr–ZrB2, and 70Zr–ZrB2, respectively. Electron contribution to thermal conductivity of the 70Zr–ZrB2 cermet was determined using electrical resistivity measurements, which shows that total thermal conductivity mostly came from the electron contribution at high temperatures (1073–1473 K) while the phonon contribution was very small.

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