Thermogravimetric analysis of hydrotalcites based on the takovite formula NixZn6-xAl2(OH)16(CO3).4H2O

Abstract

High resolution thermogravimetric analysis (HRTG) coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of zinc-modified takovites of formulae (NixZn6-xAl2(CO3)(OH)16.4H2O) where x varies from 0 to 6. X-ray diffraction data indicate an increase in the crystallinity and decrease in the interlayer spacing of the materials with increase in the zinc composition. HRTG and mass spectrometry results indicate that water is lost in two major steps, with carbon dioxide coming off simultaneously at the second step. Further loss of CO2 occurred at higher temperatures due to decomposition of carbonate chemically bound to layer Zn2+ and Al3+ cations. The variations of the temperatures of dehydration and dehydroxylation/decarbonation with the zinc composition are discussed in terms of the effects of stabilisation of the layer structure, the electronegativity of the layer metals, the charge-to-size ratio of the layer cations and the layer-interlayer hydrogen bonding interactions.