Conversion of Calcium Fluorapatiteinto Calcium Hydroxyapatite under Alkaline Hydrothermal Conditions

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

“…Recently, the present authors (17) have found that the apatite structure plays an important role on limiting the topotaxial ion exchange process. The conversion of calcium #uorapatite (hereafter abbreviated as CaFAp) to CaOHAp proceeds only at high temperature (8003C) in a concentrated KOH solution (10 M), because of the high stability of the CaFAp under hydrothermal conditions.…”

“…The formation of the very large holes might be due to the dissolution of the Cl\-rich solid solution in the alkaline solution. The dissolution of the apatite has been found to occur under alkaline hydrothermal conditions at high temperatures (17).…”

Synthesis and ionic conduction of apatite-type materials

“…Cal0(PO4)6F: single crystals were prepared at 1200 ~ by a flux method using KF as flux with CaHPO42H20, C a C O 3 and CaF 2 as solutes. Hydroxyapatite Cal0(POn)6F2.x(OI-[)x may be synthesised by further hydrothennal treatments of Cal0(PO4)6F 2 in concentrated KOH solutions at 600-800 ~ [19]. This method is very useful for the synthesis of apatite-type single crystals.…”

“…Some apatite-type single crystals may be synthesised by a flux method [17,19]. Single crystals of NaLag(GeO4)602 were obtained at 950 ~ using Na2CO 3 (30 mol% excess to compensate the evaporation of NazO), LazO 3 and GeOa as starting materials with PbO-B:O3-Na:O mixture as flux [ 17].…”

Hydroxylapatite nanoparticles: fabrication methods and medical applications

“…Hydrothermal processes can be further classified into two categories: (i) hydrothermal conversion and (ii) hydrothermal crystal growth techniques. [128]) into HAp in aqueous media, usually with the aid of calcium, phosphate and/or alkaline sources to control the Ca/P ratio of HAp particles [129][130][131][132][133][134][135]. Hydrothermal conversions of poorly soluble calcium salts such as CaCO 3 (from coral [136][137][138], seashells [139,140], aragonite or calcite crystals [141,142]) and CaSO 4 · 2H 2 O [124] into HAp have also been studied, and the conversion mechanism-ion exchange, dissolution and recrystallization-has been discussed.…”