title: 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.
authors.affiliation: Clean Materials Technology Group, Department of Chemistry, University College London, Christopher Ingold Laboratories, London, UK. aqifanwar@ciitlahore.edu.pk
authors.forename: Aqif A
authors.initials: AA
authors.lastname: Chaudhry
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Knowles
authors.forename: Ihtesham
authors.initials: I
authors.lastname: Rehman
authors.forename: Jawwad A
authors.initials: JA
authors.lastname: Darr
mesh_terms: D002130:Calcium Phosphates / Q000138:chemical synthesis* / Q000737:chemistry; D002254:Carbonates / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D010316:Particle Size; D017640:Silicates / Q000737:chemistry*
chemical_list: D002130:Calcium Phosphates; D002254:Carbonates; D017640:Silicates