Structure of organoclays - an X-ray diffraction and thermogravimetric analysis study

JOURNAL OF COLLOID AND INTERFACE SCIENCE

卷:277

Article

Xi, YF ; Ding, Z ; He, HP ; Frost, RL

关键词: montmorillonite;    dehydration;    dehydroxylation;    organoclay;    X-ray diffraction;    high-resolution thermogravimetric analysis;   

DOI  :  10.1016/j.jcis.2004.04.053

来源: Elsevier

【 摘 要 】

X-ray diffraction has been used to study the changes in the surface properties of a montmorillonitic clay through the changes in the basal spacings of montmorillonite (SWy-2) and surfactant-intercalated organoclays. Variation in the d-spacing was found to be a step function of the surfactant concentration. High-resolution thermogravimetric analysis (HRTG) shows that the thermal decomposition of SWy-2-MMTs modified with the surfactant octadecyltrimethylammonium bromide takes place in four steps. A mass-loss step is observed at room temperature and is attributed to dehydration of adsorption water. A second mass-loss step is observed over the temperature range 87.9 to 135.5 degreesC and is also attributed to dehydration of water hydrating metal cations such as Na+. The third mass loss occurs from 178.9 to 384.5 degreesC and is assigned to a loss of surfactant. The fourth mass-loss step is ascribed to the loss of OH units through dehydroxylation over the temperature range 556.0 to 636.4 degreesC. A model is proposed in which, up to 0.4 CEC, a surfactant monolayer is formed between the montmorillonitic clay layers; up to 0.8 CEC, a lateral-bilayer arrangement is formed; and above 1.5 CEC, a pseudotrimolecular layer is formed, with excess surfactant adsorbed on the clay surface. (C) 2004 Elsevier Inc. All rights reserved.

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