Study on Reaction Mechanism of Reactive Ball Milling of Ti with Urea to Prepare TiN Powder

Abstract

Titanium nitride (TiN) powders were synthesized by reactive ball milling titanium (Ti) and urea at room temperature. The structure of the as-synthesized powders were analyzed by XRD,the urea decomposed temperature and the decomposed products were characterized by TG-FTIR,the morphology and the microstructure were observed by TEM and the component of the powders were analyzed by EELS. The powders milled for 70h were annealed at 800℃ in vacuum for 5h. The results show that TiN powders with grain size of 6-7nm can be synthesized by reactive ball milling Ti and urea for 70h. The XRD patterns of the annealed powders prove that the powders are single phase of TiN. In the milling progress,titanium reacts with the decomposed products of urea,ammonia gas (NH3) and cyanic acid (HNCO) to form TiN. With the milling time increasing,the activity and the defect energy of titanium increase,so the diffusion activation energy for nitrogen diffusing in titanium decreases. The diffusion distance also decreases because the new TiN layer between Ti and nitrogen can be brought by milling. With the content of TiN increasing,the nucleus of TiN are formed which grow to nano-crystalline.