Thermal behaviour of Ni-Mn layered double hydroxide and characterization of formed oxides

Thermal behaviour of the Ni-Mn layered double hydroxide (LDH) with Ni/Mn molar ratio equal to 2 prepared by coprecipitation was studied in temperature range 200-1100 degreesC by thermal analysis (TG/DTA/EGA), powder X-ray diffraction (XRD), infrared spectroscopy and voltammetry of microparticles. A loss of interlayer water (dehydration) and sample decomposition accompanied by H2O and CO2 evolution were observed at 175 and 265 degreesC, respectively. Thermal decomposition of Ni-Mn LDH resulted in formation of a predominantly amorphous. mixture of oxides. A relatively high content of amorphous part was observed in samples heated at 200-500 degreesC. The onset of Ni6MnO8 crystallization was detected by XRD in samples heated at 300 degreesC. Together with Ni6MnO8, NiMnO3 was detected by XRD in samples heated at 500 degreesC. According to the voltammetry, the further reconstruction of oxides took place above 600 degreesC. NiMnO3 and Ni6MnO8 were converted to spinel (Ni,Mn)(3)O-4 occurring together with NiO. These oxides were observed in diffraction patterns of samples heated at high temperatures (800-1100 degreesC). (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.