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Dehydration behaviour of hexadecyltrimethylammonium-exchanged smectite

School of Earth and Environmental Sciences, Seoul National University, Seoul 151-742, Korea

^* E-mail: lsyblue{at}hanmir.com

(Received 13 June 2001; revised 18 September 2002)

The dehydration of hexadecyltrimethylammonium (HDTMA)-exchanged smectites has been studied using X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The basal spacing of hydrated HDTMA-smectites changed with temperature. The 2.5 HDTMA-smectite (i.e. smectite treated with HDTMA equivalent to 2.5 times the CEC) showed a continuous increase in its basal spacing during dehydration up to 200°C, while the 1.2 HDTMA-smectite showed a significant decrease in basal spacing. It is assumed that the less ordered alkyl chains in the wet state in the interlayer region may be rearranged to ordered chains (e.g. all-trans conformation) during sequential dehydration. This results in a decrease in interlayer spacing in the phase with low organic packing density and a flat-lying array (i.e. 1.2 HDTMA-smectite), and a gradual increase in the basal spacing when the chains have a vertical configuration (2.5 HDTMA-smectite).

KEYWORDS: dehydration, hexadecyltrimethylammonium, smectite, X-ray diffractometry, differential scanning calorimetry, interlayer

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