Abstract
We investigated the influence of calcination conditions to fabricate dispersible hydroxyapatite (HAp) nanocrystals via calcination with an anti-sintering agent, poly(acrylic acid, calcium salt) (PAA-Ca), surrounding the nanocrystals. First, two kinds of low crystallinity HAp nanoparticles with spherical morphology (58 nm in diameter) and rod-shaped morphology (around 350 nm in length) were synthesized by wet chemical processes, and then coated with PAA-Ca in aqueous media. The HAp/PAA-Ca mixture was dried and calcined at 800 or 1,000 °C for 1 h. The resultant mixture was finally washed with aqueous media to remove CaO—the thermally decomposed product of PAA-Ca—surrounding the nanocrystals. The calcination-induced sintering between the nanocrystals was efficiently prevented by increasing the amount of PAA-Ca, but the increased amount of PAA-Ca also led to the formation of CaCO3 due to the incomplete thermal decomposition of PAA-Ca at 800 °C for 1 h. Highly dispersible and phase pure HAp nanocrystals could be obtained by calcination at higher temperature (1,000 °C). We also found that calcium ions were migrated from the anti-sintering agent into the HAp nanocrystals, and the degree of calcium ion migration varied by the nature of the low crystallinity HAp nanoparticles and the calcination temperature.
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Acknowledgments
The SEM observations, FT-IR measurements, XRD measurements, and XPS analyses were performed at the Institute of Dental Research, Osaka Dental University. This study was supported in part by JSPS KAKENHI (Grant-in-Aid for Scientific Research (C); Grant Number 25463061) and Osaka Dental University Research Funds (No. 13-07). The authors are grateful for the help offered by Dr. Syuji Fujii (Osaka Institute of Technology, Osaka, Japan) in facilitating access to the laser-diffraction particle size analyzer.
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Okada, M., Omori, Y., Awata, M. et al. Influence of calcination conditions on dispersibility and phase composition of hydroxyapatite crystals calcined with anti-sintering agents. J Nanopart Res 16, 2469 (2014). https://doi.org/10.1007/s11051-014-2469-0
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DOI: https://doi.org/10.1007/s11051-014-2469-0