Department of Metallurgical Engineering, College of Mines and Earth Sciences, University of Utah, Salt Lake City, UT 84108, USA.
J Colloid Interface Sci. 2010 Apr 15;344(2):362-71. doi: 10.1016/j.jcis.2010.01.012. Epub 2010 Jan 14.
An experimental procedure is presented to order kaolinite particles on substrates for interrogation of the two basal plane surfaces by atomic force microscopy. Surface force measurements were performed between a silicon nitride tip and each of the two faces (silica tetrahedral face and alumina octahedral face) of kaolinite in 1 mM KCl solution at pH 4, 5, 6, 8 and 10, using atomic force microscopy. The colloidal force measurements reveal that the silica tetrahedral face of kaolinite is negatively charged at pH>4, whereas the alumina octahedral face of kaolinite is positively charged at pH<6, and negatively charged at pH>8. Such measurements have not been reported previously and the results suggest that the iso-electric point of the silica tetrahedral face is at pH<4, and that the iso-electric point of the alumina octahedral face lies between pH 6 and 8. These results contradict the generally accepted view that basal plane surfaces of kaolinite carry a permanent negative charge due to minor substitution of Al(3+) for Si(4+) in the silica tetrahedral layer, and suggest some surface charge dependency of the two faces with respect to solution pH. With this new information it may be possible to further explain the electrokinetic behavior of kaolinite particles, and their interactions in aqueous suspensions.
提出了一种实验程序，用于在基质上对高岭石颗粒进行排序，以便通过原子力显微镜对两个基面进行检测。在 pH 值为 4、5、6、8 和 10 的 1 mM KCl 溶液中，使用原子力显微镜在硅氮化物尖端和高岭石的两个面（四面体硅面和八面体铝面）之间进行了表面力测量。胶体力测量表明，高岭石的四面体硅面在 pH>4 时带负电荷，而高岭石的八面体铝面在 pH<6 时带正电荷，在 pH>8 时带负电荷。以前没有报道过这样的测量结果，结果表明四面体硅面的等电点在 pH<4，八面体铝面的等电点在 pH 6 和 8 之间。这些结果与高岭石基面由于硅四面体层中少量的 Al(3+)取代 Si(4+)而带有永久负电荷的普遍观点相矛盾，并表明两个面相对于溶液 pH 值具有一定的表面电荷依赖性。有了这些新信息，就有可能进一步解释高岭石颗粒的电动行为及其在水悬浮液中的相互作用。
