Pressureless Sintering Of Zirconium Diboride Obtained By Combustion SynThesis

Magnetohydrodynamic (MHD) direct power generation has the potential to significantly increase the thermal efficiency of coal fired power plants. Materials for MHD electrodes should have high melting points, high electrical and thermal conductivities, and excellent thermal shock and corrosion resistance. Zirconium diboride (ZrB2), which belongs to the class of ultra-high temperature ceramics (UHTC), is a promising material for this application. Mechanically activated self-propagating high-temperature synThesis (MASHS) is an attractive method for its fabrication. Previous studies have shown that zirconium diboride can be fabricated from inexpensive oxides of zirconium and boron (ZrO2 and B2O3) using magnesium as a reducing agent and sodium chloride as an inert diluent. It was determined that for the highest conversion of ZrO2 and B2O3 to ZrB2, the concentration of Mg in the ZrO2/B2O3/Mg/NaCl mixture should be higher by 20% than the stoichiometric one and the mixture should include 30 wt% NaCl. However, 100% conversion was not achieved and the obtained product was a loose powder. In the present work, pressureless sintering of ZrB2 obtained by magnesiothermic MASHS was studied for its purification and densification. The effects of additives (boron carbide and molybdenum silicide) and operating parameters (milling time and initial density) on the density and composition of the final product were investigated. The experiments have confirmed the effectiveness of both additives in converting the remaining oxides to ZrB2. It has been shown that milling, pressing, and adding boron carbide are needed for enhancing the sinterability of zirconium diboride