Department of Metallurgical Engineering, College of Mines and Earth Sciences, University of Utah, 135 South 1460 East, Room 412, Salt Lake City, UT 84112, USA.
J Colloid Interface Sci. 2011 Jul 1;359(1):95-103. doi: 10.1016/j.jcis.2011.03.043. Epub 2011 Mar 16.
The surface charge densities of the silica face surface and the alumina face surface of kaolinite particles, recently determined from surface force measurements using atomic force microscopy, show a distinct dependence on the pH of the system. The silica face was found to be negatively charged at pH>4, whereas the alumina face surface was found to be positively charged at pH<6, and negatively charged at pH>8. The surface charge densities of the silica face and the alumina face were utilized in this study to determine the interaction energies between different surfaces of kaolinite particles. Results indicate that the silica face-alumina face interaction is dominant for kaolinite particle aggregation at low pH. This face-face association increases the stacking of kaolinite layers, and thereby promotes the edge-face (edge-silica face and edge-alumina face) and face-face (silica face-alumina face) associations with increasing pH, and hence the maximum shear-yield stress at pH 5-5.5. With further increase in pH, the face-face and edge-face association decreases due to increasing surface charge density on the silica face and the edge surfaces, and decreasing surface charge density on the alumina face. At high pH, all kaolinite surfaces become negatively charged, kaolinite particles are dispersed, and the suspension is stabilized. The face-face association at low pH has been confirmed from cryo-SEM images of kaolinite aggregates taken from suspension which show that the particles are mostly organized in a face-face and edge-face manner. At higher pH conditions, the cryo-SEM images of the kaolinite aggregates reveal a lower degree of consolidation and the edge-edge association is evident.
高岭石颗粒的硅面和铝面的表面电荷密度最近通过原子力显微镜的表面力测量确定，显示出对系统 pH 值的明显依赖性。在 pH>4 时，发现硅面带负电荷，而在 pH<6 时，铝面带正电荷，在 pH>8 时带负电荷。在这项研究中，利用硅面和铝面的表面电荷密度来确定高岭石颗粒不同表面之间的相互作用能。结果表明，在低 pH 值下，硅面-铝面相互作用是高岭石颗粒聚集的主要原因。这种面对面的缔合增加了高岭石层的堆积，从而促进了边-面（边-硅面和边-铝面）和面对面（硅面-铝面）的缔合，随着 pH 值的增加，最大剪切屈服应力在 pH 5-5.5 时达到最大值。随着 pH 值的进一步增加，由于硅面和边缘表面的表面电荷密度增加，而铝面的表面电荷密度减小，因此面对面和边-面的缔合减少。在高 pH 值下，所有高岭石表面都带负电荷，高岭石颗粒分散，悬浮液稳定。从悬浮液中取的高岭石聚集体的低温扫描电镜图像证实了低 pH 值下的面对面缔合，表明颗粒主要以面对面和边-面的方式排列。在较高的 pH 值条件下，高岭石聚集体的低温扫描电镜图像显示出较低的固结程度，边缘-边缘的缔合很明显。
