Synthesis of n‐HAP using different precursors and dependence of Vickers hardness on the structure by tuning sintering temperature

Abstract

Three sets of starting materials Ca(NO3)2·4H2O and (NH4)2HPO4; Ca(OH)2 and H3PO4; Ca(OH)2 and (NH4)2HPO4 were chosen for the preparation of different precursors of hydroxyapatite nanoparticles (n‐HAP) by wet chemical precipitation technique denoted by HAP‐1, HAP‐2, HAP‐3. X‐ray diffraction (XRD) studies show that n‐HAP of all three types exhibited single‐phase in the as‐prepared condition. Transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) studies of as‐prepared samples showed characteristic needle‐like particles with a width of 5 nm, which were fully crystalline exhibited by the lattice fringe in HRTEM, and single‐phase demonstrated by SAED patterns. The samples were pelletized and annealed at varying temperatures in the range of 600°C–1400°C. The results indicated that HAP‐1 and HAP‐3 samples showed phase decomposition at 1400°C to form β‐tricalcium phosphate (β‐TCP) while for HAP‐2 no such decomposition occurred up to 1400°C. Data from the Vickers hardness test revealed that the hardness value up to 2.5 GPa was attained at the sintering temperature of 1200°C for HAP‐1 and HAP‐3. The hardness values are consistently higher for HAP‐2 than HAP‐1 and HAP‐3 at all sintering temperatures and attained a value of 3 GPa at 1200°C. Thus, synthesizing n‐HAP by using H3PO4; Ca(OH)2 bestows highest Vickers hardness.

In-vitro physicochemical characterization of a novel type of bone-defect-filling granules—BpNcCaP in comparison to deproteinized bovine bone (Bio-Oss ®)

“…However, the sintering process also significantly enhanced the hardness of xenogeneic bone grafts. Similar changes are also found in the production of synthetic HAp [49]. In comparison, our granules were produced in a biomimetic precipitation process and did not involve a sintering process.…”

Enhanced mechanical properties and biocompatibility of hydroxyapatite scaffolds by magnesium and titanium oxides for bone tissue applications

“…Then, the heating rate is increased to 2 °C/min up to 1200 °C with a soaking time of 1 h to complete the heat treatment process. This process ensures that the scaffolds are fully formed and hardened, creating a strong and durable structure [ 45 ].…”

Biomimetically precipitated nanocrystalline hydroxyapatite

“…The results demonstrated that the phosphate compound that gave more amount of phosphate ions would prepare HAP more efficiently [28]. Ishtiaque et al prepared nano-HAP by wet chemical precipitation and concluded that starting materials would influence the thermal stability and hardness of HAP [29]. To this end, commercially available chemical reagents would be used as an alternative by dissolving in a water solution to generate a uniform precipitate and a high-purity nano-powder material would be obtained after post-reaction processing.…”