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.