In summary, nano-crystalline titanium nitride powders were
synthesized by reactive ball milling of titanium and urea. The reactive
ball milling time can be reduced by increasing the rotation
speed of the milling machine. The grain size of the titanium nitride
powders was increased by prolonging the milling time. Based on
thermodynamic theory, it is predicted that the metal nitrides with
negative large formation enthalpy such as ZrN and HfN can be synthesized
by this simple method.