Preparing ultramicro molybdenum nitride powders by high-energy mechanochemistry method

Using a mechanochemistry ball mill equipment specifically designed by the authors,the ultramicro molybdenum nitride powders were prepared by high-energy ball milling technology in ammonia atmosphere at room temperature.The structure and the particle size of the powders were investigated by X-ray Diffraction,Scanning Electronic Microscope and Transmission Electronic Microscope.The results show that with the grinding media to powder mass ratio being 8:1 and after 30 h of milling,the Mo2N of FCC structure were obtained,and the average particle size of the podwers was within 100 nm.It is found that the chemisorption of ammonia onto the fresh molybdenum surfaces created by milling was the dominated processes govering solid-gas reaction,and the energy inputed from the cumulative energy of grain-boundaries and lattice defects offered the activation energy for the transition from Mo-N chemisorption to molybdenum nitride.In addition,the change of Mo electronic undersaturation accelerated the bonding between Mo and N.During the high-engergy ball milling processing,the rotational speed of milling played a critical role in the reaction speed.