Thermal genesis course and characterization of lanthanum oxide

La(NO3). 6H(2)O was used as a precursor to produce La2O3 at 650 degreesC in an atmosphere of air. Thermal processes occurred were monitored by means of thermogravimetry, differential thermal analysis, and gas-mass spectrometry. Infrared (IR)-spectroscopy, X-ray diffractometry and scanning electron microscopy characterized the intermediates and final solid products. The results showed that, La(NO3). 6H(2)O decomposes through nine endothermic weight loss processes. Five dehydration steps occurred at 90, 105, 150, 175 and 215 degreesC, leading to the formation of crystalline nitrate monohydrate, which decomposes to La(OH)(NO3)(2) at 410 degreesC. The latter, decomposes to La2O3 at 640 degreesC, via two different intermediates; LaO(NO3) at 440 degreesC, and non-stoichiometric unstable, La(O)(1.5)(NO3)(0.5) at 570 degreesC. The gaseous decomposition products as identified by gas-mass spectroscopy were water vapor, nitric acid and nitrogen oxides (NO, NO2 and N2O5). The final product La2O3 has a large crystalline containing pores, voids and cracks, with a surface area of 23 m(2) g(-1). Also it possessed Lewis acidic and basic sites, as indicated by Pyridine adsorption. (C) 2001 Elsevier Science B.V. All rights reserved.