Patent ID: 7658996

Claim:
A brittle material formed of ultrafine particles, for use in an aerosol deposition method to form an article, the brittle material having been pretreated by (i) applying a mechanical impact force or a pressure to ultrafine particles to be crushed, and (ii) subjecting the crushed ultrafine particles to a heat treatment at a temperature not higher than the sintering temperature thereof, wherein the thus-heat-treated brittle material particle has the following characteristics: (a) primary particle diameter of 50 nm to 5 μm, (b) no piece of the ultrafine brittle material particles having a primary particle diameter of less than 50 nm is on the surface of the brittle material particle, (c) a polycrystal structure made of microcrystals, the microcrystal having a crystal grain diameter of 20 nm to 1 μm, and (d) contains defects, cracks or dislocations therein.