Acidic dissolution mechanism of natural fluorapatite .1. Milli- and microlevels of investigations

Two different levels of acidic dissolution of natural fluorapatite crystals were investigated. The millilevel (i.e. for the whole crystals) was studied by a flow installation and optical microscopy. Dissolution process at this level was found to be determined by the dislocation structure of crystals, resulting in permanent increasing of dissolution rates for the whole crystals. The microlevel (i.e. for single etch pits) was studied by scanning electron microscopy. Dissolution process at this level was found to have random irregularities equal to 1.15 +/- 0.05 mu m, which appeared to be close to dimensions of the dislocation blocks. Both levels of acidic dissolution of natural fluorapatite were found to correspond with diffusion-controlled, polynuclear and etch-pit formation mechanisms, proposed in literature for dissolution of chemically pure apatites.