Process Integration Approach for the Efficient Synthesis of Metal Boride Ceramics

Inspired by the principle of process integration, a novel Self-propagating High-temperature Synthesis (SHS) route based on the combination of direct (DR) and borothermal (BR) reactions is proposed in this work for the synthesis of transition metal diborides. The aim is to identify the proper operating conditions that maximize the use of cheaper metal oxides as starting reactants instead of elemental powders, while still guaranteeing the self-propagating character of the synthesis process, by taking advantage of the excess heat generated by the DR reaction. A theoretical analysis based on accurate thermodynamic description of the reacting system is performed to evaluate the adiabatic temperatures of the combined DR-BR process, under different pressure conditions, for the synthesis of TiB2, ZrB2, and HfB2 transition metal diborides. The analysis outcomes have been validated by an experimental campaign, where SHS process was followed by a purification step to eliminate undesired byproducts (B2O3).