Topotaxial replacement of chlorapatite by hydroxyapatite during hydrothermal ion exchange

Conversion of Calcium Fluorapatiteinto Calcium Hydroxyapatite under Alkaline Hydrothermal Conditions

“…In contrast, Yanagisawa et al (11) have reported that the conversion of ClAp to OHAp proceeds under alkaline hydrothermal conditions. This reaction on ClAp crystals begins at low temperatures (3003C), and occurs along both of the a-and c-axes by a topotaxial dissolution}precipitation mechanism.…”

“…Recently, Yanagisawa et al (11) have studied the ionexchange process under alkaline hydrothermal conditions, and observed that the ion exchange in ClAp single crystals was accelerated by using alkaline solutions. The ClAp single crystals were converted into OHAp single crystals under alkaline hydrothermal conditions at temperatures as low as 3003C in 6.25 M KOH solution for 12 h. The ionexchange reaction under these conditions is conducted by a topotaxial dissolution and precipitation process, which enhances the conversion of the ClAp to OHAp without changing the original dimension and shape of the ClAp crystals.…”

Effect of Metal Ions of Chlorapatites on the Topotaxial Replacement by Hydroxyapatite under Hydrothermal Conditions

“…Recently, Yanagisawa et al (11) have proposed a di!erent mechanism of the anion exchange in CaClAp structure. The exchange of Cl\ ions with OH\ in the synthetic CaClAp single crystals proceeded in concentrated alkaline solutions under hydrothermal conditions at much lower temperatures than that by the solid state mechanism.…”

“…Although the Cl}OH ion exchange reaction in the CaClAp crystals has been widely investigated under alkaline hydrothermal conditions (11), there is a lack of information regarding the e!ect of the metal ions in the chlorapatite structure on the topotaxial replacement process. Hence, the goal of the present work is to determine the experimental conditions (temperature) that enhance the topotaxial ion exchange reaction on CaClAp, strontium chlorapatite (hereafter referred to SrClAp) and barium chlorapatite (hereafter referred to BaClAp) single crystals.…”

Nanoscale conversion of chlorapatite into hydroxyapatite using ultrasound irradiation

“…Topotactic, i.e. shape preserving, conversion of chlorapatite and other phosphocalcic apatite into hydroxyapatite has already been described in hydrothermal conditions from well-crystallized powders [24,25]. These approaches required strong alkalinity (KOH, 6.25 M), high temperatures (> 4 300 °C) and relatively long reaction times (> 12 h) but allowed for conversion of large crystals (several mm).…”