Figure 1. Kaolinite clay formation |
The bond between two sheets is strong and, also, it is the primary bond. However, the stack of two sheets (with thickness 7.2 Ã… [Angstrom]) is not a form of clay yet. Many layers of this basic kaolinite unit make a kaolinite clay particle. Figure 3.3 shows an electron photomicrograph of well-crystallized kaolinite clay particles.
Figure 2. Electron photomicrograph of kaolinite clay |
From the picture, it can be estimated that the diameter of a particle is about 5 μm, and the thickness of the particle is about one-tenth of that (i.e., 0.5 μm). Thus, it is required to have about 700 layers of the basic unit to make a kaolinite clay particle in the picture. The bond between each basic silica and aluminum sheet unit is the one between exposed OH- and satisfied O2- and is called a hydrogen bond. This bond is not as strong as the previous atomic bond (primary bond) but much stronger than the bond between exposed O2- and O2- in case of montmorillonite clay, which will be discussed later. Hydrogen bond is categorized as a primary bond in many literatures, but it shall be noted that this is a marginally strong bond. Because of its nature of bonds within the kaolinite particle, this clay is rather stable, has less swelling and shrinking characteristics, and is less problematic.