Formation of Spinel from a Hydrotalcite-Like Compound at Low Temperature: Reaction between Edges of Crystallites
The thermal decomposition behavior of hydrotalcite-like compounds (HTlcs) prepared by reconstruction of calcined HTlcs is described. From the results of X-ray diffraction (XRD), it seems that dicarboxylate intercalates of HTlc calcined at 500 °C are completely reconstructed to Mg-Al-CO3 HTlc by exposure to aqueous Na2CO3. However, the Mg-Al-CO3 HTlc reconstructed under particular conditions yields spinel (MgAl2O4) at 400 °C. This temperature is very low, because Mg-Al-CO3 HTlc that has been reported yields spinel at 900 °C after forming a Mg-Al double oxide. The reconstructed Mg-Al-CO3 HTlc that yields spinel at 400 °C is obtained when the following conditions are fulfilled: the crystallites of the starting dicarboxylate intercalates are coagulated tightly and the calcined HTlcs and reconstructed materials are not ground. The Mg-Al-CO3 HTlc reconstructed under these conditions contains only 55–70% of carbonate anions required by stoichiometry. Therefore, we conclude that the transformation of reconstructed Mg-Al-CO3 HTlc to spinel at 400 °C is the result of a reaction occurring between edges of crystallites.
Key WordsDouble Hydroxide Grinding Hydrotalcite Reconstruction Spinel Thermal Decomposition
Unable to display preview. Download preview PDF.
- Bratton RJ. 1969. Coprecipitates yielding MgAl2O4 spinel powders. Am Ceram Soc Bull 48:759–762.Google Scholar
- Brindley GW, Kikkawa S. 1979. A crystal-chemical study of Mg,Al and Ni,Al hydroxy-perchlorates and hydroxy-car-bonates. Am Mineral 64:836–843.Google Scholar
- Chibwe K, Jones W. 1989b. Intercalation of organic and inorganic anions into layered double hydroxides. J Chem Soc, Chem Commun 926–927.Google Scholar
- Hokazono S, Nagai H, Kato A. 1991. Synthesis of spinel powder by the homogeneous precipitation method. Nippon Kagaku Kaishi 275–280.Google Scholar
- Ingram L, Taylor HFW. 1967. The crystal structures of sjögrenite and pyroaurite. Mineral Mag 36:465–479.Google Scholar
- Miyata S, Kumura T. 1973. Synthesis of new hydrotalcite-like compounds and their physico-chemical properties. Chem Lett 843–848.Google Scholar
- Narita E, Kaviratna P, Pinnavaia TJ. 1991. Synthesis of het-eropolyoxometalate pillared layered double hydroxides via calcined zinc-aluminium oxide precursors. Chem Lett 805–808.Google Scholar
- Rouxhet PG, Taylor HFW. 1969. Thermal decomposition of sjögrenite and pyroaurite. Chimia 23:480–485.Google Scholar