Thermal decomposition of dysprosium iron citrate

Abstract

The citrate gel process was used to synthesize ultrafine-grained, amorphous and crystalline Dy 3Fe 5O 12 (dysprosium iron garnet, DyIG). The citrate precursor is obtained on drying the citrate gel at 110°C and has the chemical composition Dy 3Fe 5(Cit) 25·36H 2O. The thermal decomposition of the hydrated citrate precursor was investigated by DTA, TG and DSC techniques, and gas and chemical analyses. An air atmosphere is found to be most suitable for the decomposition yielding stoichiometric DyIG. The decomposition consists of six steps. The dehydration step of the citrate precursor is followed by a low temperature decomposition of the citrate groups. The formation of a transient intermediate containing both citrate and carbonate groups is associated with evolution of CO, CO 2, water vapour and the burning-off of methylene groups in the temperature range 160–280° C. The citrate groups are completely destroyed in the temperature range 280–330 °C resulting in the formation of a carbonate which retains free CO 2 gas in the matrix. The final decomposition of the carbonate takes place between 330 and 450°C and yields ultrafine-grained amorphous DyIG, releases the trapped CO 2 above 450°C and crystallizes at 590°C. The citrate precursor and decomposed products were characterized by IR and NMR spectra, X-ray diffaction data and surface area measurements.