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Queensland University of Technology, Centre for Instrumental and Developmental Chemistry, Brisbane, Queensl., Australia
The hydroxyl deformation modes of kaolins have been studied by Fourier transform (FT) Raman spectroscopy. Kaolinites showed well-resolved bands at 959, 938 and 915 cm -1 and an additional band at 923 cm-1. For dickites, well-resolved bands were observed at 955, 936.5 915 and 903 cm-1. Halloysites showed less-resolved Raman bands at 950, 938, 923 and 895 cm-1. The first 3 bands were assigned to the librational modes of the 3 inner-surface hydroxyl groups and the 915 cm-1 band was assigned to the libration of the inner hydroxyl group. The band in the 905 to 895 cm-1 range was attributed to "free" or non-hydrogen-bonded inner-surface hydroxyl groups. The 915-cm-1 band contributed approximately 65% of the total spectral profile and was a sharp band with a bandwidth of 11.8 cm-1 for dickite, 14.0 cm-1 for kaolinites and 17.6 cm-1 for halloysites. Such small bandwidths suggest that the rotation of the inner hydroxyl group is severely restricted. For the inner-surface hydroxyl groups, it is proposed that the hydroxyl deformation modes are not coupled and that the 3 inner-surface deformation modes are attributable to the three OH2-4 hydroxyls of the kaolinite structure. For intercalates of kaolinite and halloysite with urea, a new intense band at approximately 903 cm-1 was observed with concomitant loss in intensity of the bands at 959, 938 and 923 cm-1 bands. This band was assigned to the non-hydrogen-bonded hydroxyl libration of the kaolinite-urea intercalate. Infrared reflectance (IR) spectroscopy confirms these band assignments.
This record provided courtesy of AGI/GeoRef.
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