Crystallization process and growth mechanism for hexagonal prism of strontium hydroxyapatite by urea hydrolysis

Add time:08/04/2019    Source:sciencedirect.com

Strontium hydroxyapatite (SrHAp) is not only used as drug carrier material for bone disease treatment, but also has application prospect in bone tissue engineering. But SrHAp is prepared with by-products strontium hydrogen phosphate (SrHP) and strontium phosphate (TSrP), which requires accurate process optimizations and adjustments to circumvent the undesirable morphology products. The integral hexagonal prism crystals of SrHAp were successfully synthesized by urea hydrolysis at ambient pressure and without any strong acids and bases. Similarly, variable by-products are classified and investigated for their effects on crystallization process of strontium hydroxyapatite via monitoring the urea hydrolysis time-dependent products. The crystallization process of SrHAp can be divided into four stages based on the crystallographic results for the samples acquired by XRD and SEM studies during the entire synthesis processes. In the first stage, SrHP is formed (0–0.17 h); secondly, SrHP is converted into SrHAp (0.17–4 h); TSrP is obtained (4–8 h) at the third stage; and at last, TSrP is transformed into SrHAp (8–24 h), especially the amount of SrHAp obtained at 24 h was the sum of the second and fourth stages. Simultaneously, the growth mechanism of SrHAp crystals was proposed, considered of the formation energy of Gibbs-Thomson crystal plane and Born-Lande lattice energy. By calculating the interfacial energy γ(h k l) of different crystal planes, the γ(1 0 0) of hexagonal prism plane family m{1 0 0} is 1.3 × 10−5U0, the γ(0 0 1) of parallel double-plane family c{0 0 1} is 7.5 × 10−6U0, the normal growth rate of Ic{0 0 1} ≫ Im{1 0 0}. Accordingly, the growth mechanism for the preferential c axis growth maintaining the hexagonal prism shape is derived.

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