Formation of spinel from a hydrotalcite-like compound at low temperature : Reaction between edges of crystallites

• Published in: Clays and clay minerals Vol. 45; no. 6; pp. 842 - 853
• Main Authors: HIBINO, T, TSUNASHIMA, A
• Format: Journal Article
• Language: English
• Published: Boulder, CO Clay Minerals Society 01.12.1997
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Experimental petrology; Mineralogy; Non silicates; models; spinel; oxides; grinding; transformations; X-ray diffraction; transmission electron microscopy; low temperature; carbonates; thermal analysis; hydrotalcite
• ISSN: 0009-8604; 1552-8367
• DOI: 10.1346/CCMN.1997.0450608

Abstract 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-CO 3 HTlc by exposure to aqueous Na 2 CO 3 . However, the Mg-Al-CO 3 HTlc reconstructed under particular conditions yields spinel (MgAl 2 O 4 ) at 400 °C. This temperature is very low, because Mg-Al-CO 3 HTlc that has been reported yields spinel at 900 °C after forming a Mg-Al double oxide. The reconstructed Mg-Al-CO 3 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-CO 3 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-CO 3 HTlc to spinel at 400 °C is the result of a reaction occurring between edges of crystallites.