Thermophysical properties of reaction processed zirconium diboride

This dissertation focuses on the thermophysical properties of high purity zirconium diboride ceramics. These ceramics have shown promise for potential applications such as leading edge materials for next generation hypersonic vehicles. The overall goal of this work was to improve the understanding of the thermal properties and maximize the thermal conductivity of ZrB2 . Four main areas were investigated in this work. First, the sintering kinetics and the intrinsic thermal properties of reaction processed ZrB 2 were studied and compared to ZrB2 produced by hot pressing commercial powders. The reaction process produced ceramics with higher thermal conductivity and enhanced densification. Next, Hf impurity concentrations were varied showing that decreasing Hf content increased thermal conductivity. Finally, isotope enrichments were performed showing that lighter isotopes increased lattice frequency and subsequently thermal conductivity. Fully enriched Zr10B2 had a thermal conductivity of 145 W/m*K which is the highest value for ZrB2 reported to date. Scattering models based on quantum mechanics were used with density functional theory to analyze the effects of impurities and isotopes on the electron and phonon density of states. Overall, this work adds insight into the fundamental mechanisms behind the thermophysical properties of ZrB2. Tailoring compositions to reduce Hf content and adjusting boron isotope concentration has led to improved thermal properties at all temperatures. The processing conditions, reported properties, and insights gained from models will help the realization of ZrB2 as a leading edge material for the next generation of hypersonic vehicles.