Nanorods of HfB2 from mechanically-activated HfCl4 and B-based powder mixtures

Besides being an established method of synthesis of nanomaterials and a method for inducing chemical reactions during grinding, high-energy ball-milling is further a way, with potential industrial applications, of activating powdered solids which react then at lower temperature than usual and possibly lead to the formation of original materials. Hafnium diborides with an AlB2 type-structure, which are difficult to obtain as single crystals, are synthesized in that way by a two-step process. It consists first in a mechanical activation stage of ph-HfCl4 + B and ph-HfCl4 + B + Mg powder mixtures, where ph-HfCl4 is a partially hydrated hafnium tetrachloride, then in an isothermal annealing treatment of the activated powders in flowing argon. According to the composition of the initial mixtures and to the time and temperature of the argon annealing treatment, either nanosized facetted grains or single crystalline nanorods of HfB2 are obtained.