We evaluated the thermal conductivity of HfB2-based ultra-high-temperature ceramics from laser flash diffusivity measurements in the 25°–600°C temperature range. Commercially available powders were used to prepare HfB2 composites containing 20 vol% SiC, some including TaSi2 (5 vol%) and Ir (0.5 or 2 vol%) additions. Samples were consolidated via conventional hot pressing or spark plasma sintering. Processing differences were shown to lead to differences in magnitude and temperature dependence of effective thermal conductivity. We compared results with measured values from heritage materials and analyzed trends using a network model of effective thermal conductivity, incorporating the effects of porosity, grain size, Kapitza resistance, and individual constituent thermal conductivities.
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Document Type: Research Article
Thermal Protection Materials & Systems Branch, NASA Ames Research Center, Moffett Field, California 94035
Molecular Physics Laboratory, SRI International, Menlo Park, California 94025
May 1, 2008