Consolidation of nanocrystalline hydroxyapatite powder (original) (raw)
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Sintering effects on the densification of nanocrystalline hydroxyapatite
International Journal of Automotive and Mechanical Engineering, 2011
"The effects of sintering profiles on the densification behaviour of synthesized nanocrystalline hydroxyapatite (HA) powder were investigated in terms of phase stability and mechanical properties. A wet chemical precipitation method was successfully employed to synthesize a high purity and single phase HA powder. Green HA compacts were prepared and subjected to sintering in air atmosphere over a temperature range of 700°C to 1300°C. In this study two different holding times were compared, i.e. 1 minute versus the standard 120 minutes. The results revealed that the 1 minute holding time sintering profile was indeed effective in producing a HA body with high density of 98% theoretical when sintered at 1200°C. High mechanical properties such as fracture toughness of 1.41 MPa.m1/2 and hardness of 9.5 GPa were also measured for HA samples sintered under this profile. Additionally, XRD analysis indicated that decomposition of the HA phase during sintering at high temperatures was suppressed. http://www.doaj.org/doaj?currentYear=2013&id=1173077&go=1&func=abstract&fromYear=&toYear=
Pressureless sintering of nanocrystalline hydroxyapatite at different temperatures
Metals and Materials International, 2010
In this work, the sintering behaviour of hydroxyapatite (HA) at different temperatures was studied. Nano HA powders synthesized by sol-gel technique were uniaxially pressed at 30 MPa into pellets and cold isostatically pressed at 200 MPa. The pellets were sintered in air at temperatures ranging from 900 °C to 1400 °C with a holding time of 2 h. It was observed that, at a sintering temperature of 1200 °C when the material was composed of pure HA phase, the samples exhibited densities of > 98.5 % of the theoretical value and possessed a hardness value of 5.89 GPa. Decomposition of HA into the secondary phases of TCP and CaO was found to occur at 1300 °C and 1400 °C, respectively. Changes in the microstructure, relative density and hardness of the sintered HA ceramics with the sintering temperature were also analyzed. The variation in the hardness was found to be dependent on the relative density up to a threshold grain size limit of 2 μm. However, beyond this threshold, no correlation existed between the two properties. Porosity and grain size were found to play an important role in determining the properties of the sintered HA compacts.
Effects of sintering temperature on the properties of hydroxyapatite
Ceramics International, 2000
The sintering behaviour of hydroxyapatite (HA), the resulting microstructure and properties are influenced not only by the characteristics and impurities of the raw materials but also were found to be dependent on the thermal history during the fabrication process. This work is concerned with the effects of grain size on the relative density and hardness. A commercially available HA powder was cold isostatically pressed at 200 MPa and sintered at temperatures ranging from 1000 to 1450 °C with a dwell time of 2 hours. It has been found that, at the optimum sintering temperature of 1250 °C where the material is composed of pure hydroxyapatite phase, the samples exhibited densities >99% of theoretical value and possessed a hardness value of 6.08 GPa. Decomposition of HA starts to occur at approximately 1400 °C with the formation of TCP phase. The change in hardness was found to be dependent on the relative density up to a certain grain size limit. However, above this grain size limit, no correlation exists between the two properties. Porosity and grain size were found to play an important role in determining the properties of sintered hydroxyapatite compacts. http://ac.els-cdn.com/S0272884299000462/1-s2.0-S0272884299000462-main.pdf?\_tid=71666aca-e777-11e2-a713-00000aacb35f&acdnat=1373251276\_93a64089598e9ab649030079384185f2
Materials Chemistry and Physics, 2005
Hydroxyapatite (HAP) powder precursors have been used as starting material for biomedical applications, such as synthetic bone graft materials and scaffold for hard tissue engineering. Considering the numerous applications of hydroxyapatite, three different routes for HAP powders preparations was investigated. Two powders were prepared by chemical precipitation reactions at 100 °C and one by mechanochemical reaction. The powders were characterized using chemical analysis, surface area measurements, laser diffraction, X-ray diffraction (XRD) and SEM. The Ca/P ratios were varied from 1.67 to 1.58. The chemical composition, the crystallinity and the agglomeration characters depend on the preparation route. The effect of powder characteristics on the sinterability was investigated. Although, the thermal stability and hence the start of sintering dependents on the Ca/P ratio, the final sintering density and hence the mechanical properties depends on the agglomeration characteristics and the particle size distribution. Hydroxyapatite powder prepared by mechanochemical route have nano-sized crystallites with a uniform smaller agglomerated particle size distribution and have a butter sinterability.