SHEN Yaqiang 1, LI Dongyun 1, XU Yang 1, GE Hongliang 1, XU Qiang 2, YANG Hui 2
(1. School of Materials and Chemistry, China Metrology University, Hangzhou 310018, Zhejiang, China; 2. School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, Zhejiang, China)
Abstract: In order to study the effect of ammonium fluoride on particle characteristics of alumina powder, industrial aluminum hydroxide micropowder was used as the raw material, together with different contents of ammonium fluoride. The mixtures were thoroughly grinded and refined, combined with washing to remove sodium, so as to prepare high-purity flaky alumina ultrafine powder. It was found that the addition of ammonium fluoride promoted the transformation of alumina from a transition phase to stable α-phase, along with enhanced productivity and purity of α-alumina. The phase transformation, particle morphology and the content of sodium ion in alumina were all dependent on the concentration of ammonium fluoride. It was hypothesized that the mass transport mode in alumina was altered owing to the presence of ammonium fluoride during the sintering process, thus influencing the phase transition and morphology of the alumina powder. The effect mechanism of the ammonium fluoride was proposed, while the growth model of the flaky alumina crystals was established.
Key words: high purity alumina; ammonium fluoride; mechanism of sodium removal; crystal growth model