Chlorapatite Conversion to Hydroxyapatite under High Temperature Hydrothermal Conditions

Abstract

The need for biomaterials in dental and orthopedic applications has increased as the world population ages. Synthetic calcium phosphate bioceramics and calcium phosphate cements are proved potential substitutes for bone and teeth due to their structural and crystallographic similarities with the biological apatites, and their biocompatibility but they show poor mechanical properties. Chlorapatite and hydroxyapatite whiskers with high aspect ratio can be used to improve this drawback. This work describes a method to transform chlorapatite single crystals into hydroxyapatite whiskers, suitable for the reinforcement of calcium phosphate bioceramics and calcium phosphate cements. Hydroxyapatite whiskers were obtained by treating chlorapatite single crystals in high-temperature hydrothermal conditions. The variable studied was furnace temperature with and without moisture conditions. The characterization of the chlorapatite and hydroxyapatite whiskers was carried out by SEM, XRD, EDS and FTIR. SXRD data were analyzed for the description of the chlorapatite structure.

Calcium orthophosphates

“…Finally, one should very briefly mention the existence of carbonated apatite, 489 - 495 chlorapatite 496 - 498 as well as a great number of various ion-substituted calcium orthophosphates 83 , 499 , 500 . Usually, they are of a non-stoichiometric nature, and there are too many of them to be mentioned in one review.…”

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.…”

Synthesis and Optimization of the Production of Millimeter‐Sized Hydroxyapatite Single Crystals by Cl−–OH− Ion Exchange

“…In both cases, in air and wet atmosphere [Figs. (a) and (a)], powder XRD shows systematic peak displacements with temperature toward the HA structure above 1450°C . There is also a secondary transformation to a monoclinic calcium phosphate without Cl − or OH − in the structure, identified by diffractions at 2θ = 30.7 and 34.5° .…”

“…Carbonate incorporations in the structure either in the anionic channel or PO 4 3− substitutions were ruled out by Single crystal x‐ray diffraction (SXRD). This band may be justified by the carbonation of spodiosite remaining on the surfaces of the ClAp from the fabrication process …”