Evolution of metal nitriding and hydriding reactions during ammonia plasma-assisted ball milling

Nanocrystalline metal nitride and hydride powders were prepared using plasma-assisted ball milling in ammonia gas (NH3-P-milling) via an in situ synthesis reaction. The gas-solid reactions were triggered by a short duration of plasma milling of Mg and Ti under a constant pressure of ammonia gas, and the products in the two systems were nanocrystalline Mg3N2 and TiN, TiH2 after 10 h, respectively. During the NH3-P-milling of Ti powder, TiH2 and TiN were formed during the initial stages of milling, and then, the TiH2 decomposed during further milling upon reaction with N radicals, transforming into the TiN phase. In contrast, no chemical reaction occurred between NH3 and Mg/Ti after 10 h of C-milling. The discharge plasma activated and decomposed the ammonia gas and activated the surface of the powders, which, together with the mechanical effect of high-energy ball milling, accelerated the gas-solid reactions.