Preparation of nano-sized TiN coated alpha -Si sub 3 N sub 4 particles

alpha -Si sub 3 N sub 4 particles coated with 10 and 25 vol% nano-sized TiN were prepared by coating the surface of the Si sub 3 N sub 4 particles with TiO sub 2 , followed by nitridation. Coating by TiO sub 2 was accomplished by dispersing alpha -Si sub 3 N sub 4 powders (0.16 and 1.6 g l exp -1 ) in a solution of TiCl sub 4 , urea and aqueous HCl, and heating at 105 deg C for 130 and 190 min. The success of the coating procedure was confirmed by TEM observation with electron diffraction and EDX analysis. Zeta potential measurements suggest that the TiO sub 2 coating on the surface of Si sub 3 N sub 4 particles occurs at a pH between 3.7 and 4.3 by the attractive force of opposite charges. When the TiO sub 2 on the surface of the Si sub 3 N sub 4 is nitrided with NH sub 3 gas at 1000 deg C, it is completely changed to TiN of uniform particle size (20 nm). (Ultimate aim is to produce silicon nitride matrix composites containing a continuous titanium nitride network, which would be machinable via electric discharge machining (EDM).)