EXCHANGEABLE ION AND THERMAL TREATMENT EFFECTS ON BASAL SPACINGS OF Al-HYDROXY PILLARED MONTMORILLONITES

摘要

Al-hydroxy intercalated clays (ALHICs) obtained from different parent clays were used to investigate the interactions between oligomers and clay surface layers. The thermal stability of ALHICs obtained from natural, Cs-, Ca-, Ba-, Fe-, Cu- or Ce-montmorillonites has been investigated by studying the relationship between basal spacing and calcination temperature. X-ray diffraction has shown that the basal spacing of ALHICs obtained from Cu-montmorillonite calcined at 550℃ is 13.4 A, different from basal spacings of ALHICs obtained from Fe-montmorillonite (16.0 A) and other parent clays (16.7 A). Thermograms for AlHICs obtained from natural, Fe- and Ce-montmorillonites displayed distinct steps at 225 and 650℃, attributed to the dehydration of Al_(13) oligomers, and the dehydroxylation of the surface layer, respectively. By contrast, thermograms of ALHICs obtained from Cu-montmorillonite displayed one step between 250 and 700℃ for both dehydration and dehydroxylation. Moessbauer parameters showed that Fe~(3+) octahedra in octahedral sheets are distorted in pillared interlayered clay (PILC) obtained from Cu-montmorillonite and undistorted in that obtained from Fe-montmorillonite. The difference in thermal stability for the various ALHICs is attributed to the retention of some of the original cations after intercalation with Al_(13) oligomers, which induces several interactions between the oligomers and the clay surface layers.