Study of the differences of thermal stability of Mg-Al-CO3 and Zn-Al-CO3 hydrotalcite

The structures of Mg-Al-CO3 and Zn-Al-CO3 hydrotalcites have been studied by means of XRD, IR and TG-DTA. Although both have the same crystal structures, their thermal stabilities are quire different. During the thermal decomposition process, Mg-Al-CO3 hydrotalcite exhibits two steps-desorption of interlayer water occurs at 200 degreesC, followed by dehydroxylation of the brucite-like layers and loss of carbonate at 400 degreesC, Zn-Al-CO3 hydrotalcite decomposes in one step-the desorption of interlayer water, structural water and carbon dioxide occurred at the same time at 200 degreesC. The results of a theoretical study indicate that the bond strengths of OH-CO3-OH and OH-H2O-CO3-OH in Mg-Al-CO3 hydrotalcite are stronger than those in Zn-Al-CO3 hydrotalcite. It has been shown that the thermal stability of Mg-Al-CO3 hydrotalcite is higher than that of Zn-Al-CO3 hydrotalcite.