Structure of organoclays--an X-ray diffraction and thermogravimetric analysis study.
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 degrees C 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 degrees C 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 degrees C. 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.
Xi
Yunfei
Y
Inorganic Materials Research Group, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
Ding
Zhe
Z
He
Hongping
H
Frost
Ray L
RL
D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D009930:Organic Chemicals / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D013818:Thermogravimetry; D014961:X-Ray Diffraction
D000538:Aluminum Silicates; D009930:Organic Chemicals; D000077215:Clay