Dissolution mechanism of calcium apatites in acids: A review of literature

Figure 1 A dissolution process according to the diffusion and kinetically controlled models. C_s: Solute concentration on the surface; C_i: Solute concentration on the interface; C_b: Solute concentration in bulk. Reprinted from Ref.[34] with permission.

Figure 2 A dissolution process according to the mono- and polynuclear models. A: Mononuclear model; B: Polynuclear model in one crystal step; C: Polynuclear model in multiple steps: birth and spread; D: Spiral model. Reprinted from Ref.[34] with permission.

Figure 3 A typical etch pit on the surface of calcium apatites. A: Top view and a model of its evolution during dissolution. Arrows represent relative step velocities displaying different facets; B: View through the [001] direction in the (100) surface. The exposed step faces can be seen to be un-equivalent owing to the opposite orientations of the orthophosphate groups. Reprinted from Ref. [118] with permission; C: Schematic of the evolution of hexagonal etch pits. Four differently colored arrows represent relative step velocities. Reprinted from Ref. [120] with permission.

Figure 4 A schematic representation of surface protonation of apatites at different solution pH. Reprinted from Ref. [119] with permission.

Figure 5 Surface of a crystal according to Kossel[168]. The various types of imperfections are shown. Reprinted from Ref. [34] with permission.

Figure 6 An example of etched crystal surface of natural fluorapatite with typical hexagonal etch pits. Bar 10 μm