In this work, hydroxyapatite (HA) powders were synthesized using calcium hydroxide Ca(OH)2 and orthophosphoric acid H3PO4 via wet chemical precipitation method in aqueous medium. Calcium‐to‐phosphorus (Ca/P) ratio was set to 1.57, 1.67, 1.87 that yield calcium‐deficient HA, stoichiometric HA, and calcium‐rich HA, respectively. These synthesized HA powders (having different Ca/P ratio) were characterized in terms of particle size and microstructural examination. Then, the densification and mechanical properties of the calcium‐deficient HA, stoichiometric HA, and calcium‐rich HA were evaluated from 1000 to 1350°C. Experimental results have shown that no decomposition of hydroxyapatite phase was observed for stoichiometric HA (Ca/P = 1.67) and calcium‐deficient HA (Ca/P = 1.57) despite sintered at high temperature of 1300°C. However, calcium oxide (CaO) was detected for calcium‐rich HA (Ca/P = 1.87) when samples sintered at the same temperature. The study revealed that the highest mechanical properties were found in stoichiometric HA samples sintered at 1100–1150°C, having relative density of ~99.8%, Young's modulus of ~120 GPa, Vickers hardness of ~7.23 GPa, and fracture toughness of ~1.22 MPam1/2.
In this work, the sinterability of forsterite powder synthesized via solid‐state reaction was investigated. X‐ray diffraction (XRD) analyses indicate that the synthesized powder possessed peaks that correspond to stoichiometric forsterite. Scanning electron micrographs revealed that the powders were formed agglomerates, which were made up of loosely packed fine particles. Subsequently, the forsterite powders were cold isostatically pressed into a disk shape under 200 MPa and sintered in air at temperature ranging from 1200°C to 1500°C (interval of 50°C) with ramp rate of 10°C/min and dwelling time of 2 h. The sinterability of each sintered samples was examined in terms of phase stability, relative density, Vickers hardness, fracture toughness, and microstructural examination. XRD examination on all the sintered samples exhibited pure forsterite, in which the generated peaks were found to be in a good agreement with JCPDS card no. 34‐0189. The densification of forsterite progressed to reach a maximum relative density of ~91% at 1500°C. This study also revealed that high‐strength forsterite ceramic can be synthesized via solid‐state reaction as forsterite attained favorable mechanical properties, having fracture toughness of 4.88 MPam1/2 and hardness of 7.11 GPa at 1400°C.
Synthesis of phase-pure forsterite (Mg 2 SiO 4 ) is a challenging process that requires multiple steps including careful heat treatment and ball milling. In this work, the effects of temperature, time and ball milling duration in synthesizing forsterite powder were investigated. A comparison of 1000 and 1200°C heat treatment temperature with 1 min, 1, and 2 h of holding time during heat treatment was conducted. In addition, 1, 5, 7, and 10 h of milling time were selected as variables to identify optimum conditions for completion of reaction in forming pure forsterite powder. Based on the X-ray diffraction results, 1200°C heat treatment, 2 h of holding time, and 7 h of milling successfully produced single phase forsterite powders with crystallite size of 41 nm. The forsterite powder was compacted and sintered at temperatures ranging from 1200 to 1500°C. The highest hardness and fracture toughness of 7.11 GPa and 4.88 MPa m 1/2 were achieved when sintered at 1400°C, respectively. Meanwhile, the highest relative density of 91% was obtained for the sample sintered at 1500°C.
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