Abstract
As a part of the study on sintering reactions, the thermal decomposition process of La(OH)3 was investigated by using T.G.A., D.T.A. and X-ray diffraction method. From the results thus obtained, the detailed mechanism of the decomposition was inferred.
(1) The thermo-gravimetric curves of specimens were obtained in air, N2, and CO2 gas. The thermal decomposition curves showed two stages for La(OH)3. The chemical reactions of these stages were determined as follow.
2La(OH)3→2LaO(OH)+2H2O (the initial stage)
2LaO(OH)→La2O3+H2O (the second stage)
(2) These reactions were found to be first order in various atmospheres. The rate constants for these two decomposition stages in air of La(OH) were represented by
k=1016exp(-23000/RT) (the initial stage)
k=1025exp(-42000/RT) (the second stage)
(3) It was recognized that La(OH)3 became La2O3 at about 600°C in air. The lattice constants of La2O3 obtained were a=3.945Å, c=6.151Å.
