Synthesis of ultra-refractory transition metal diboride compounds

This paper critically evaluates methods used to synthesize boride compounds with emphasis on diborides of the early transition metals. The earliest reports of the synthesis of boride ceramics used impure elemental powders to produce multiphase reaction products; phase-pure borides were only synthesized after processes were established to purify elemental boron. Carbothermal reduction of the corresponding transition metal oxides emerged as a viable production route and continues to be the primary method for the synthesis of commercial transition metal diboride powders. Even though reaction-based processes and chemical synthesis methods are mainly used for research studies, they are powerful tools for producing diborides because they provide the ability to tailor purity and particle size. The choice of synthesis method requires balancing factors that include cost, purity, and particle size with the performance needed in expected applications.