Graphs from a study of the thermal characterization of surfactant-modified montmorillonites
The montmorillonite (HM) was obtained from Hebei, China. The sample was purified by sedimentation and the <2 μm fraction was collected and dried at 90°C. The sample was ground through a 200 mesh sieve and sealed in a glass tube for use. As indicated by XRD (Zhu, J.X., He, H.P., Guo, J.G., Yang, D. and Xie, X.D. (2003) Arrangement models of alkylammonium cations in the interlayer of HDTMA+ pillared montmorillonite. Chinese Science Bulletin, 48, 368–372.), the montmorillonite collected contains minor illite and kaolinite. The CEC is 57.9 meq/100 g. The structural formula is [Na0.05Ca0.18Mg0.10] [Al1.58Fe0.03Mg0.39][Si3.77Al0.23]O10(OH)2·nH2O. The surfactant used in this study, provided by YuanJu Chem. Co., China, is hexadecyltrimethylammonium bromide (HDTMAB) with a purity of 99%.
Figure 1 shows DTA (Differential Thermal Analysis) and TG (Thermogravimetric) curves of (a) Na montmorillonite and (b) of neat HDTMAB. Figure 2 shows the DTA curves of the modified montmorillonites with different surfactant-packing density. Figure 3 is the DSC (Differential Scanning Caloimetry) curves of the neat surfactant and HM0.5 CEC, HM1.9 CEC, HM5.0 CEC. Figure 4 is the DSC curves of (a) HM1.9 CEC and (b) HM5.0 CEC, with three cycles of heating and cooling. Figure 5 TG curves of the modified montmorillonites with different surfactant-packing densities. Figure 6 shows the change in the surfactant decomposition temperature for modified montmorillonite as a function of the surfactant-packing density within the montmorillonite interlayer. The surfactant-packing density refers to the amount of the surfactant within the montmorillonite interlayer as shown in Table 1 of the associated text.