Continuous Synthesis and Properties of Fine AlN Powder by Floating Nitridation Technique

Abstract

Fine AlN powder was synthesized continuously at 1350°-1550°C by the floating nitridation technique. The nitriding temperature was reduced by using ultrapure Al and N₂ gas as raw materials. The obtained AlN powder was pure with trace amounts of metallic impurities and oxygen. The primary particle size of AlN powder obtained was 0.1μm with 86% secondary particles in the range from 0.1 to 0.8μm. The hollow spherical powder was obtained when unreacted-Al remained. The formation process of the fine AlN powder was presumed to be constituted by several elementary reaction processes, i.e., formation of a thin oxide layer on Al particles; disintegration of the thin oxide layer; formation of an AlN layer; disintegration of the AlN layer; eruption of ultrafine Al droplets and Al vapor from the inside of particle; and formation of fine AlN particles by reaction of these Al's and N₂ gas. This AlN powder had good sinterability, and transparent AlN ceramics were obtained without any sintering aids.