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

Abstract

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 °C 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 H 2O and CO 2 evolution were observed at 175 and 265 °C, 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 °C. The onset of Ni 6MnO 8 crystallization was detected by XRD in samples heated at 300 °C. Together with Ni 6MnO 8, NiMnO 3 was detected by XRD in samples heated at 500 °C. According to the voltammetry, the further reconstruction of oxides took place above 600 °C. NiMnO 3 and Ni 6MnO 8 were converted to spinel (Ni,Mn) 3O 4 occurring together with NiO. These oxides were observed in diffraction patterns of samples heated at high temperatures (800–1100 °C).