Synthesis of metal boride nanoparticles by using thermal plasmas

Metal boride nanoparticles have very useful physical and chemical properties, such as high melting points, wear resistance, and chemical inertness, and they are receiving attention as functional materials such as a non-noble catalyst for water electrolysis. The synthesis of boride compounds, however, requires very high temperatures. Thermal plasmas can evaporate boron and metal raw materials in the high-temperature core region; then, the composite is produced in the form of a nanoparticle due to a steep temperature gradient in the tail region of the thermal plasma jet. Conventionally, a radio-frequency (RF) thermal plasma system is used to synthesize high purity nanoparticles, and the production of metal boride nanoparticles by using a triple- direct current (DC) thermal plasma system has been reported recently. The characteristics of metal boride nanoparticles, including the mean size and core–shell structure, are controlled by operating conditions such as the flow rate and the species of the plasma-forming gas. Research applications for the produced metal boride nanoparticles is developing in the fields of novel soft material for nuclear radiation shielding and water-splitting catalyst for hydrogen production.