Pressureless sintering of nanocrystalline hydroxyapatite at different temperatures

Abstract

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.

Characteristics and properties of hydoxyapatite derived by sol–gel and wet chemical precipitation methods

“…However, if the decomposition forms α-TCP as the secondary phase instead, this formation could not be attributed to nonstoichiometric HA. Instead, the formation could be due to the formation of an intermediate phase, oxyapatite, which shows the gradual loss of the radical OH À (dehydroxylation) when heated at atmospheric conditions [19]. According to Fathi et al [21], pure HA powder derived from the sol-gel was only obtained after the powder was subjected to calcination at 600 1C, whereas the powder could be decomposed into β-TCP and CaO at 700 1C [21,26].…”

“…Therefore, although wet chemical precipitation and sol-gel methods have been classified as the simple routes employed in producing HA [17,18] and are able to produce high-purity HA [19], the production of HA nanoparticle with expected morphology via these method remain challenging mainly because of the raw materials used for synthesis. This paper reports the comparison of the characteristics of nanocrystalline HA powders synthesized via wet chemical precipitation and novel sol-gel synthesis by using different raw materials.…”

Chemical Treatment, Characterization and Electrical Properties of Utilization Biowaste Hydroxyapatite Nanocrystalline

“…(6). Secondly, the increase of charge carrying proton density due to OH -and O 2-leads to ... (6) And/or to an OH -ions interacting with the double bonded oxygen of a PO 4 3-groups as follows:…”

“…Synthetic HAP with well defined properties offers a good, safer alternative bone graft material which can help the body to repair bone defects 6,7 . Recently, HAP has found interesting applications in other areas such as a support for adsorption of bacteria or viruses, for ammonia catalysis, as a catalyst support material, support bone ingrowths and osseointegration when used in orthopaedic, dental and maxillofacial applications [16][17][18][19][20] .…”

“…Everyday million tons of eggshells are generated as biowaste around the globe. Eggshell represents 11 % of the total weight of the egg and is largely composed of calcium carbonate (minerals calcite) 97 % and organic matter 3% [1][2][3][4][5][6][7][8][9][10] . This material is an unwanted byproduct after the production of eggs and egg derivatives.…”