Synthesis and characterisation of large chlorapatite single-crystals with controlled morphology and surface roughness

Abstract

This work describes the synthesis of chlorapatite single crystals using the molten salt method with CaCl2 as a flux. By manipulating the processing conditions (amount of flux, firing time and temperature, and cooling rates) it is possible to manipulate the crystal morphology from microscopic fibres to large crystals (up to few millimetre long and ~100 μm thick). The crystal roughness can be controlled to achieve very flat surfaces by changing the melt composition “in situ” at high temperature. The Young modulus and hardness of the crystals are 110 ± 15 and 6.6 ± 1.5 GPa respectively as measured by nanoindentation. Crystal dissolution in Hanks solution starts around the defects. Several in vitro assays were performed; ClAp crystals with different size and shape are biocompatible. Cell apoptosis was very low at 5, 10, and 15 days (Caspase-3) for all the samples. Proliferation (MTT) showed to be influenced by surface roughness and size of the crystals.

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

“…Last, one should very briefly mention on existence of carbonated HA (Lafon et al 2008;Tonegawa et al 2010;Yahia and Jemal 2010;Silvester et al 2014;Fleet 2015), chlorapatite (Kannan et al 2007;García-Tuñón et al 2012;Zhao et al 2013), as well as on a great number of CaPO 4 with various ionic substitutions (CaPO 4 with dopants) (Pan and Fleet 2002;Rey et al 2006;Kannan et al 2008;Boanini et al 2010b;Shepherd et al 2012;Adzila et al 2012;Grigg et al 2014;Š upová 2015). In principle, any ion in CaPO 4 might be substituted by other ion(s).…”

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

“…The crystals were vacuum‐filtered and washing was repeated three times. Subsequently they were sieved through a 63 μm mesh, and dried at 110°C for 24 h. The final samples consist mostly of millimeter sized‐ClAp single crystals with needle shape and characteristic microscopic roughness …”

Comparison of Physical-chemical and Mechanical Properties of Chlorapatite and Hydroxyapatite Plasma Sprayed Coatings

“…Regarding the synthesis of chlorapatite, several methods have been proposed [49, 50]. Precipitation methods in aqueous media do not lead generally to stoichiometric chlorapatite and the apatite obtained contains always hydroxide ions.…”

“…Several dry synthesis methods giving stoichiometric ClA with a high purity have been proposed. The reaction of CaCl 2 on Ca 3 (PO 4 ) 2 (800-1100°C) [50] results in ClA with a high yield, especially when using an excess of CaCl 2 , which can be removed by washing. Other methods can be used, especially Cl-OH ion exchange reactions on HA (800-1100°C), which offers the advantage of using an existing commercial product.…”

“…Comparison of the phase diagrams, CaO-P 2 O 5 for HA and CaCl 2 -Ca 3 (PO 4 ) 2 for ClA [50, 56] indicate a decomposition of HA on heating, whereby ClA melts without decomposition. This property is a major argument in favour of the use of ClA for producing plasma sprayed coatings: the formation of foreign phases is expected to be limited, except for the amorphous phase resulting of the quenching of a melted phase.…”