title: Phase stability and rapid consolidation of hydroxyapatite-zirconia nano-coprecipitates made using continuous hydrothermal flow synthesis.
abstract: A rapid and continuous hydrothermal route for the synthesis of nano-sized hydroxyapatite rods co-precipitated with calcium-doped zirconia nanoparticles using a superheated water flow at 450°C and 24.1 MPa as a crystallizing medium is described. Hydroxyapatite and calcium-doped zirconia phases in the powder mixtures could be clearly identified based on particle size and morphology under transmission electron microscopy. Retention of a nanostructure after sintering is crucial to load-bearing applications of hydroxyapatite-based ceramics. Therefore, rapid consolidation of the co-precipitates was investigated using a spark plasma sintering furnace under a range of processing conditions. Samples nominally containing 5 and 10 wt% calcium-doped zirconia and hydroxyapatite made with Ca:P solution molar ratio 2.5 showed excellent thermal stability (investigated using in situ variable temperature X-ray diffraction) and were sintered via spark plasma sintering to >96% sintered densities at 1000°C resulting in hydroxyapatite and calcium-doped zirconia as the only two phases. Mechanical tests of spark plasma sintering sintered samples (containing 10 wt% calcium-doped zirconia) revealed a three-pt flexural strength of 107.7 MPa and Weibull modulus of 9.9. The complementary nature of the spark plasma sintering technique and continuous hydrothermal flow synthesis (which results in retention of a nanostructure even after sintering at elevated temperatures) was hence showcased.
authors.affiliation: Christopher Ingold Laboratories, Department of Chemistry, University College London, London, UK. aqifanwar@ciitlahore.edu.pk
authors.forename: Aqif A
authors.initials: AA
authors.lastname: Chaudhry
authors.forename: Haixue
authors.initials: H
authors.lastname: Yan
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Viola
authors.forename: Mike J
authors.initials: MJ
authors.lastname: Reece
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Knowles
authors.forename: Kenan
authors.initials: K
authors.lastname: Gong
authors.forename: Ihtesham
authors.initials: I
authors.lastname: Rehman
authors.forename: Jawwad A
authors.initials: JA
authors.lastname: Darr
mesh_terms: D017886:Durapatite / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles; D010316:Particle Size; D033362:Powder Diffraction; D015040:Zirconium / Q000737:chemistry*
chemical_list: D017886:Durapatite; D015040:Zirconium; C028541:zirconium oxide