A Study On The Preparation Of LaAlO₃ By Hydrolyzing Of Lanthanum And Aluminium Alkoxides

Lanthanum aluminates crystal has gained extensive application with electron parts of apparatus, catalyzing, batteries of high temperature fuel. So ti is important to study high performance of lanthanum aluminates powders. In the methods of preparing lanthanum aluminates powders now, they paid not enough attention to the granularity and purity of the powders had not been controlled well. The paper uses the way of alkoxide-hydrolysis technique with the characteristic of high purity, ultra-fine granularity and high activity.In the paper, lanthanum alkoxide is prepared with alcohol used as solvent and AlCl₃ used as catalyst through the contrast of AlCl₃ and I₂.Calculate solubility of lanthanum alkoxide and discuss the catalyzing mechanism. Lanthanum aluminates alkoxide is attained by the reaction of lanthanum alkoxide with aluminates, aluminates alkoxide with lanthanum, lanthanum with aluminates and aluminates with lanthanum alkoxide which is acting. And discuss syntheses, character and structure of lanthanum aluminates alkoxide. In the process of alkoxide-hydrolysis, through controlling all kinds of factors, such as the concentration of the alkoxide, the amount of water and so on, found out their affections to the inside structure of colloid and powders character. Then the productions are dried by microwave drying, freezing drying etc, and changed into complex hydrate. The samples are roasted in different temperature and the lanthanum aluminates powders are prepared.The results show that through the metal La and Al acting with ethanol directly, lanthanum aluminate alkoxide can be gotten. The best suitable concentration of the catalyst AlCl₃ is 5mg/mL, and Ethanol is suitable for the preparation of lanthanum alkoxide with the metal concentration of 15mg/mL. In low pH value with the adding of oleic acid, it is good for controlling hydrolysis process and makes alkoxide hydrolyze slowly. Gel can be gotten at last. Drying the gel through freezing dry, small grains and good decentralization powders can be gotten. And then, the powders are roasted at 900℃, perfect phase lanthanum aluminate powders can be obtained. Its preparing process is easy, and 78nm powders can be gotten. Its synthesis temperature is 400-500℃lower than traditional solid phase method. AlCl₃ is a good catalyst for the synthesis of lanthanum alkoxide and lanthanum aluminium alkoxide. The more it is, the better it will be. The longer the carbon chain is, the less active it will be. So its velocity reacting with lanthanum will be slower. The concentration of the lanthanum alkoxide is 0.0466mol/L.Because of adding alcohol, the chance of alkoxide touching with water is smaller, so hydrolyzing velocity is decreased. At the same time, because of so many existing of-OR around, fall the activity of gel grains, reduce connecting chance of water with -OH of gel, and improve dispersing quality. Oleic acid can match with metal ion, low down alkoxide activity and decrease its hydrolyzing velocity. And it changes the structure of gel and control powder size. Lanthanum and aluminates alkoxide should be double metal alkoxide.