Research On The Reaction Mechanism Between Y₂O₃ And Al₂O₃ In Molten Salt

Recently, Molten salt synthesis method has been the one of important methods of preparing inorganic powder. Having advantages of easy operation, low synthesis temperature, the product of controlled morphology and good dispersion make it attract more researches on it. YAG (Y3Al5O12) powder is the essential part of inorganic powder materials, being widely used in laser crystal and luminescent materials. At present, preparing YAG by molten salt synthesis have significant superiority and wide application prospect, however, the mechanism of this method requires thorough study. In this paper, using self-made nano-Y2O3 and micron-Al2O3 as raw materials to study the recreation and mechanism between Y2O3 and Al2O3.Firstly, nano-Y2O3 powder is fabricated by chemical precipitation method. The parameters such as the amount of ammonium bicarbonate, the type of dispersant and the process of cleaning, are analyzed and optimized, which affect particle size and morphology of Y2O3. As results, less NH4HCO3 would decrease particle size; different dispersant made unequal impacts on Y2O3, especially, PEG could increase its dispersibility. The process of cleaning have obviously influences in products, using ethanol would get smaller particles. By adjusting the parameters, spherical Y2O3 particles with 50nm size have been prepared.When using self-made nano-Y2O3 and micron-Al2O3 as raw materials, it is found that nano-Y2O3 particles with solid phase move in the molten salt and coat on a-AlO3, then form a AlO3@ nano-Y2O3 structure, in which interface the reaction started. The molten salt improve the movement of Y2O3 particles and uniform distribution of reactants, which is fluid in high temperature. This phenomenon of particles coating is different from solution-precipitation process and solution-diffusion process, the only two theories having been proposed.In the paper, the reaction between Y2O3 and Al2O3 in the molten salt with different temperature, the phase transition and morphology changing of YAG, both of them are analyzed. It is found that the main phase is YAM(Y4Al2O9) which is fabricated in the molten salt during 900℃-1100℃; When temperature increases to 1200℃, YAP(YA103) firstly appears; Then a large amount of YAG synthesized during 1300℃-1400℃, which become the only phase after heating at 1400℃. Different heating processes result in different phase transition, and the coating structure synthesizd in 900 ℃ is conducive to diffusion between raw materials, which shorten the reaction time.