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.
Inorganic Materials Research Group, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
Yunfei
Y
Xi
Zhe
Z
Ding
Hongping
H
He
Ray L
RL
Frost
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