Papers by Author: R. Tolouei

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Authors: R. Tolouei, Singh Ramesh, Chou Yong Tan, Mahdi Amiriyan, Wan Dung Teng
Abstract: Grain size dependences of Vickers microhardness and indentation fracture toughness in fully dense hydroxyapatite bioceramics without additives were studied. The nanostructure and highly pure Hydroxyapatite powders produced by wet chemical precipitation method were used as starting material. After uniaxial and cold isostatic pressing, the green HA samples sintered at temperatures ranging from 1000 °C to 1300 °C with one minute holding time. Dense compacts with grain sizes in the nanometer to micrometer range were processed. The average grain size of HA compact sintered at 1000 °C was around 500 nm. Grain size increased to 3 µm when the compacts were sintered at a higher temperature. The average microhardness value of sintered HA decreased with an increased in grain size. Indentation fracture toughness for HA compacts of 700 nm grain size was 1.41±0.4 MPa.m1/2 which is similar to fracture toughness of human cortical bone.
Authors: R. Tolouei, Chou Yong Tan, Ramesh Singh, Iis Sopyan, Wan Dung Teng
Abstract: The effects of adding a small amount of nano silica in hydroxyapatite (HA) on the sinterability and mechanical properties of hydroxyapatite were studied. The starting HA powder was synthesized using a novel wet chemical precipitation method. Different amount of silica powder was mechanically mixed with the synthesized HA. The green samples were subsequently cold isostatically pressed at 200 MPa. Sintering in air was accomplished by firing the green samples at temperatures ranging from 1050°C to 1250°C. Sintered samples were analyzed to determine phase composition and mechanical properties. The XRD analysis revealed that with increasing the amount of silica in the HA powder, decomposition of HA to TCP occurred at sintering temperature higher than 1050°C. The bulk density of all silica-doped samples decreased through the temperature range studied. In agreement with the bulk density trend, the increasing silica additives in HA depleted the Young’s modulus and Vickers hardness of the HA body. The study revealed that the addition of silica have an adverse effect on the sintered properties of hydroxyapatite bioceramics.
Authors: Wei Hong Yeo, Ramesh Singh, Chou Yong Tan, K.L. Aw, R. Tolouei, H. Kelvin, Iis Sopyan, Wan Dung Teng, E. Hoque
Abstract: The aim of this work is to study the phase stability and sinterability of bismuth oxide (Bi2O3) doped HA ranging from 0.05 wt% to 1 wt%. The green samples were sintered in air at temperature ranging from 1000oC to 1400oC. In this experiment, the results from XRD analysis revealed that the stability of HA phase was disrupted when addition of 0.3, 0.5 and 1.0 wt% Bi2O3 were used and when samples sintered above 1100oC, 1000oC and 950oC, respectively. In general, HA containing 0.5 wt% of Bi2O3 and when sintered at 1000oC was found to be beneficial in enhancing densification, Young’s modulus, Vickers hardness and fracture toughness. Throughout the sintering regime, the highest value of relative bulk density of 98.7% was obtained for 0.5 wt% Bi2O3-doped HA when sintered at 1000oC. A maximum Young’s modulus of 119.2 GPa was observed for 0.1 wt% Bi2O3-doped HA when sintered at 1150oC. Additionally, 0.5 wt% Bi2O3-doped HA was able to achieve highest hardness of 6.04 GPa and fracture toughness of 1.21 MPam1/2 at sintering temperature of 1000oC. Furthermore, the Young’s modulus of HA was found to vary linearly with bulk density.
Authors: K.L. Aw, R. Tolouei, Ramesh Singh, Chou Yong Tan, Wei Hong Yeo, H. Kelvin, Iis Sopyan, Wan Dung Teng
Abstract: The sinterability of hydroxyapatite (HA) powder synthesized through a novel wet chemical method (HAp) and a wet mechanochemical method (HAwm) was investigated over a temperature range of 1000oC to 1400oC in terms of phase stability, bulk density, hardness and fracture toughness. The results indicated that the sinterability of HAp powder were significantly better than HAwm powder. Moreover, the XRD traces of HAwm sintered samples showed signs of decomposition into TTCP when sintered at 1300oC and above. Densification of ~98% of theoretical density was attained by HAp compacts at 1100oC while the HAwm compacts exhibited only ~96% of theoretical density even at 1350oC with no significant increase of density at 1400oC. The Vickers hardness of HAp showed increasing trend for temperature range of 1000oC to 1100oC with the compacts attaining HV of ~7 GPa at 1100oC. Subsequently, the hardness decreased with increasing sintering temperature though the value does not dropped below ~5 GPa. Similarly, HAwm compacts showed an increasing trend from 1000oC to 1300oC with the largest HV attained was ~4.57 GPa. Further increased in sintering temperature resulted in the decreased of Vicker’s hardness. Moreover, the HAp samples reached a maximum fracture toughness of ~0.9 MPam1/2 at 1050oC while the HAwm attained maximum KIc of only ~0.7 MPam1/2 at 1300oC.
Authors: Ramesh Singh, R. Tolouei, Chou Yong Tan, K.L. Aw, Wei Hong Yeo, Iis Sopyan, Wan Dung Teng
Abstract: In the present work, densification of synthesised hydroxyapatite (HA) bioceramic prepared via chemical precipitation method was investigated. HA samples was prepared by compaction at 200 MPa and sintered at temperatures ranging from 800°C to 1400°C. The results revealed that the HA phase was stable for up to sintering temperature of 1250°C. However, decomposition of HA was observed in samples sintered at 1300°C with the formation of tetra-calcium phosphate (TTCP) and CaO. Samples sintered above 1400°C were found to melt into glassy phases. The bulk density increases with increasing temperature and attained a maximum value of 3.14 gcm-3 at 1150°C whereas maximum hardness value of 6.64 GPa was measured in HA sintered at 1050°C. These results are discussed in terms of the role of grain size.
Authors: Chou Yong Tan, Ramesh Singh, R. Tolouei, Iis Sopyan, Wan Dung Teng
Abstract: The sinterability of magnesium oxide (MgO) doped hydroxyapatite (HA) ranging from 1 to 10 wt% when sintered at 1150°C was investigated in terms of phase stability, bulk density, Young’s modulus, Vickers hardness and fracture toughness. The addition of up to 1 wt% MgO as sintering additive was found to be beneficial in promoting the densification of HA. Further addition of MgO in the HA matrix would deteriorate its densification properties. Similar results were observed for its stiffness and Vickers hardness. Nevertheless, the fracture toughness of HA was greatly enhanced by the incorporation of 5 wt% MgO. An increased toughness of up to 35% was obtained for the MgO-doped HA when compared to the undoped HA. This improvement is associated to the smaller grain size of the doped sample as compared to the undoped HA.
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