AFM analysis of initial stage of reaction between calcite and phosphate

A calcite surface reacted with phosphoric acid or phosphate in the initial stage was analyzed under an atomic force microscopy (AFM). The cleaved calcite was immersed in phosphoric acid or diammonium hydrogenphosphate under various conditions. The calcite dissolved upon immersion in phosphoric acid and many pits, oriented in a particular direction, were observed on the calcite surface. When the calcite was immersed in diammonium hydrogenphosphate, reaction products, also aligned in a particular direction, were observed on the calcite surface. X-ray diffraction analysis revealed that these products are carbonate-containing hydroxyapatite.