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 ∼330 °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 P21/m (no. 11) with the lattice parameters a = 444.76(9) pm, b = 397.10(7) pm, c = 661.9(1) pm, and β = 111.93(1)°. The reaction enthalpies of the dehydration process were calculated by DSC to ∼87 kJ mol−1 (transformation: La(OH)3 to LaOOH), and to ∼54 kJ mol−1 (transformation: LaOOH to La2O3). Further, the activation energy EA = 76 kJ mol−1 of the transformation lanthanum hydroxide to lanthanum hydroxide oxide was estimated by isothermal TG studies. Article Outline