Well-Formed One-Dimensional Hydroxyapatite Crystals Grown by an Environmentally Friendly Flux Method

Abstract

Highly crystalline, well-developed hydroxyapatite (HAp) crystals were grown successfully for the first time by a flux cooling method at a temperature less than 500 °C under air pressure. Environmentally friendly growth was induced by heating a mixture of solute [Ca(NO 3 ) 2 • 4H 2 O, (NH 4 ) 2 HPO 4 , and KOH] and flux (KNO 3 and LiNO 3 ) at 400-500 °C and holding at this temperature for 10 h. After that, the mixture was cooled at various rates of 5, 200, and >1000 °C • min -1 (water quenching). The obtained HAp crystals, which had average sizes of up to 18.0 × 2.1 µm and aspect ratios of up to 8.6, were colorless and transparent. They had hexagonal prismatic one-dimensional (1-D) forms with pyramidal or truncated pyramidal end faces. The 1-D crystal forms and sizes were obviously dependent on the growth conditions, such as the holding temperature and the cooling rate of the high-temperature solution. High-resolution transmission electron microscopy (HR-TEM) images indicated that the grown HAp crystals were of a very good crystallinity. From the HR-TEM and X-ray diffraction, the 1-D HAp crystals, which were hexagonal cylinders ({101 j 0} faces), elongated in the 〈0001〉 directions.

Nanosized hydroxyapatite and other calcium phosphates: Chemistry of formation and application as drug and gene delivery agents

“…Numerous methods have been applied for the synthesis of fine particles of HAP, including reactions in solid state, [53][54][55][56] abrupt or continuous precipitation from solution, [57][58][59][60] hydrothermal processing, 61,62 electrospraying, 63 electrospinning, 64 flux cooling method, 65 spray pyrolysis, 66 ultrasound 67 and mechanochemical processing, 68,69 microwave irradiation-assisted precipitation, 70,71 microemulsion-and surfactant-assisted precipitation, [72][73][74][75][76] sol-gel syntheses based on hydrolysis of metal organic precursors, 77,78 and chemical vapor 79 and plasma deposition. 80 However, from the point of view of control over apatite structure and morphology, these methods could be roughly divided to low and high temperature ones.…”

Shape-controlled synthesis of F-substituted hydroxyapatite microcrystals in the presence of Na2EDTA and citric acid

“…F À was often used as the doping ion for a column hydroxyl or occupies a hydroxyl vacancy in HAp lattice in the synthesis of FHAp [25][26][27]31,49]. However, the reports demonstrating its effect on the growth of FHAp crystal are few.…”

“…Over the past decades, a number of synthetic routes have been developed to produce HAp and/or FHAp crystals with a variety of shapes and morphologies [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Owing to its simple synthetic processes and low total costs, hydrothermal technique is a highly efficient route to the preparation of HAp and/or FHAp crystals of high crystallinity with distinct morphological features.…”

Implementation of State Transfer Hamiltonians in Spin Chains with Magnetic Resonance Techniques

“…7 [123,124] and more recently by the flux method [125][126][127]. This same method has also been used to grow HAp [128]. Apatites have many diverse applications, from solid-state laser to fluorescent lamps, from phosphorus chemistry to geological probes.…”

“…Calcium apatites have also applications in biology, since they form the mineral part of bone and teeth. FAp and HAp have thus become common as biocompatible materials for bone replacement and coating of bone prostheses and their growth methods have been optimized [128].…”