A Study On Preparation Of Lanthanum Aluminate And As The Application Of Crucible Material

The lanthanum aluminate belongs to perovskite structure, with high thermal andchemical stability. The LaAlO3expected to be used as the high chemical activity of thealloy melting crucible materials, such as rare earth hydrogen storage alloy, Nd-Fe-Balloys, samarium-cobalt alloy, etc. Therefore, this research was carried out. Byresearching on all of the synthetic methods, a synthetic method with short process,single structure and high efficiency was determined and the synthetic mechanism of thismethod was investegated. Based on experiments of high temperature reaction ofLanthanum aluminate with active metal such as Ca, Nd, LaNi5and so on, the chemicalstability was investegated. The ways and effects of Lanthanum aluminate compoundingon the suface of other crucible materials was investegated too.1By using of the methods of direct solid phase synthesis, such as La₂O₃and Al₂O₃,Al2O3and La₂（CO₃）₃·nH₂O, Al（OH）₃, La₂（CO₃）₃·nH₂O and so on, because of smallcontact area among materials, the synthesis was not complete and there ware impuritiesin the product; By using of the methods of Coprecipitation method（chloride system,nitrate system）, it has a great difficulty in precipitation, filtration and washing, and has acomplex process and a low synthesis efficiency; By using of the methods of indirectsolid phase synthesis including the preparation of Lanthanum hydroxide fromlanthanum oxide by hydrothermal method, the uniform mixing with aluminumhydroxidem and the high temperature calcination, It has a very easy filtering process, acomplete synthesis and a high synthesis efficiency.2The synthetic mechanism of solid phase synthesis was investegated by mean ofTG-DTA and X-ray diffraction. Research show that highly active intermediate LaOOHand AlOOH obtained in the heating process of mixture of Lanthanum hydroxide andaluminum hydroxide can be decomposed into lanthanum aluminate.3Lanthanum aluminate powders can not react with LaNi5at1450℃, while it canreact significantly with metal Ca at1100℃, but the rate was lower than that of alumina.Meanwhile, Lanthanum aluminate crucible can react slightly with metal Nd at1200℃,so it is obviously superior to corundum crucible.4To prolong the service life of magnesia crucible, the experiments of vacuumpress impregnating process and coating process were carried out. The attachment effect of vacuum press impregnating process is superior to that of coating process, so it is aneffective method to improve the properties of ordinary crucibles.