Rapid hydrothermal flow synthesis and characterisation of carbonate- and silicate-substituted calcium phosphates

Abstract

A range of crystalline and nano-sized carbonate- and silicate-substituted hydroxyapatite has been successfully produced by using continuous hydrothermal flow synthesis technology. Ion-substituted calcium phosphates are better candidates for bone replacement applications (due to improved bioactivity) as compared to phase-pure hydroxyapatite. Urea was used as a carbonate source for synthesising phase pure carbonated hydroxyapatite (CO3-HA) with ≈5 wt% substituted carbonate content (sample 7.5CO3-HA) and it was found that a further increase in urea concentration in solution resulted in biphasic mixtures of carbonate-substituted hydroxyapatite and calcium carbonate. Transmission electron microscopy images revealed that the particle size of hydroxyapatite decreased with increasing urea concentration. Energy-dispersive X-ray spectroscopy result revealed a calcium deficient apatite with Ca:P molar ratio of 1.45 (±0.04) in sample 7.5CO3-HA. For silicate-substituted hydroxyapatite (SiO4-HA) silicon acetate was used as a silicate ion source. It was observed that a substitution threshold of ∼1.1 wt% exists for synthesis of SiO4-HA in the continuous hydrothermal flow synthesis system, which could be due to the decreasing yields with progressive increase in silicon acetate concentration. All the as-precipitated powders (without any additional heat treatments) were analysed using techniques including Transmission electron microscopy, X-ray powder diffraction, Differential scanning calorimetry, Thermogravimetric analysis, Raman spectroscopy and Fourier transform infrared spectroscopy.

Hydroxyapatite for bone related applications derived from sea shell waste by simpleprecipitation method

“…The formation of CaCO 3 is assessed by the presence of a small peak at 712 cm −1 . Some literature [7,26] had reported the same information about this peak. The sharp intense peak at 3644 cm −1 suggests the presence of Ca(OH) 2 [27].…”

Synthesis of Nanostructured Hydroxyapatite via Controlled Hydrothermal Route

“…Subcritical conditions can be classified as mild (temperatures near to 100°C) or elevated (temperature up to 250°C). Many studies are done with synthesis temperature in the range from mild to elevated subcritical conditions (~100-240°C), showing the formation of various morphologies of particles with different sizes [18,19,21,37,39,48,53,55,60,80,86,87,89].…”

Aerosol assisted chemical vapour deposition of hydroxyapatite-embedded titanium dioxide composite thin films

“…Hydroxyapatite can be made via a number of ways such as batch co-precipitation or flow methods [Sadat-Shojai, 2013]. In flow methods such as Continuous Hydrothermal Flow Synthesis (CHFS), supercritical water can be used as a reagent to drive the rapid synthesis of HAp [Chaudhry, 2013], as well as a wide range of metal oxides [Kriedemann, 2015;Naik, 2015;Litwinowicz, 2014;Dunne, 2014]. CHFS made HAp nanoparticles and doped variants were also prepared [Chaudhry, 2008;Chaudhry, 2013;Gimeno-Fabra, 2015].…”