Thesis (M.S., Materials Science) -- University of Idaho, 2015 | Magnetohydrodynamic direct power extraction can potentially increase the efficiency of power generation in coal-based power plants by producing electricity directly out of ionized exhaust, through the use of electrodes. Transition metal diborides, such as HfB2 and ZrB2, show promise as a material for such electrodes. Despite research on individual borides, little is known about the mechanical, electrical, thermal, and oxidation resistance of HfB2-ZrB2 solid solutions for the MHD electrode application. In the present work, spark plasma sintering was used to consolidate HfB2-ZrB2 powder prepared by high energy ball milling. Microstructural characteristics of both the milled powders and SPSed specimens were studied by X-ray diffraction and scanning electron microscopy. Density, Vickers micro-indentation hardness, indentation fracture toughness and electrical resistivity of such SPSed specimens were measured. Also examined were the effects of additives, Gd2O3, LaB6, Hf, Zr, and Ta, on Hf0.5Zr0.5B2, which generated greater densification and smaller grain size.