The thermal transformation from lanthanum hydroxide to lanthanum hydroxide oxide

The thermal transformation from lanthanum hydroxide (La(OH)(3)) to lanthanum oxide (La2O3) results in two successive endothermic effects, caused by a loss of water. Thermal analysis (DTA/TG, DSC), and high-temperature powder X-ray diffraction (HT-XRD) were used to characterize this process. Lanthanum hydroxide oxide (LaOOH) was obtained as temporary product at similar to 330 degrees C. The structure of lanthanum hydroxide oxide was characterized by X-ray powder diffraction methods and subsequent Rietveld refinement. LaOOH crystallizes in the monoclinic space group P2(1)/m (no. 11) with the lattice parameters a = 444.76(9) pm, b = 397.10(7) pm, c = 661.9(1) pm, and beta = 11 1.93(1)degrees. The reaction enthalpies of the dehydration process were calculated by DSC to similar to 87 kJ mol(-1) (transformation: La(OH)(3) to LaOOH), and to similar to 54 kJ mol(-1) (transformation: LaOOH to La2O3). Further, the activation energy E-A = 76 kJ mol(-1) of the transformation lanthanum hydroxide to lanthanum hydroxide oxide was estimated by isothermal TG studies. (c) 2005 Published by Elsevier B.V.