TW法による3La_2O_3・2WO_3の合成

概要

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The gel of 3La2O3·2WO3 composition was prepared by the TW method from the starting mixture containing La(NO3)3 aqueous solution and WO3 powder with each small amount of tetraethyl orthosilicate (TEOS) and 2M-HCl as a catalyst, which was heated at a fixed temperature in the range of 800°C to 1200°C for 30 min. In the obtained material (the sample No.1), the formation of 3La2O3·2WO3 began at about 800°C and was most remarkable at 1000°C. However, in the case of the sample No.1, the diffraction lines for 7La2O3·8WO3, α-La2W2O9, La2O3, β-La2W2O9 and γ-La2WO6 were observed in addition to those for 3La2O3·2WO3. Therefore, pure 3La2O3·2WO3 in a single phase was not obtained at any heating temperature. Whereas in the case of the sample No.4, which was obtained by heating the gel with 8.99×10-3 mol KCl at 1000°C for 30 min, almost pure 3La2O3·2WO3 was obtained in a single phase, though slight γ-La2WO6 and β-La2W2O9 were present. It was thought that 3La2O3·2WO3 was obtained as a degradation product of 7La2O3·8WO3, simultaneously as a product of the reaction of La2O3 and γ-La2WO6 in the progress of its decomposition when a part of β-La2W2O9 decomposed to γ-La2WO6. Furthermore, it was thought that α-La2W2O9 was transformed into β-La2W2O9, because the minimum in intensity of α-La2W2O9 was corresponding well to the maximum in that of β-La2W2O9.
社団法人粉体粉末冶金協会の論文
2006-05-15