Papers by Author: Chou Yong Tan

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Authors: K.Y. Sara Lee, K.M. Christopher Chin, Ramesh Singh, Chou Yong Tan, Wan Dung Teng, I. Sopyan
Abstract: The present work is on the synthesis of forsterite (Mg2SiO4) powder using talc and magnesium oxide powders as the starting materials followed by a heat treatment process. Sintering behavior and mechanical properties of the forsterite bodies were evaluated from 1200°C to 1500°C. Forsterite phase were detected in samples without any secondary phases at all sintering temperatures. A very high fracture toughness of 4.9MPa.m1/2 and Vickers hardness of 7.1GPa were measured for samples sintered at 1400°C, thus indicating the viability of this ceramic for biomedical application.
Authors: Ramesh Singh, K.L. Aw, C.H. Ting, Chou Yong Tan, Iis Sopyan, Wan Dung Teng
Abstract: The effect of adding small amounts of copper oxide (CuO) on the sintering and mechanical properties of alumina ceramic was studied. Samples were prepared and fired in air atmosphere at temperatures ranging from 1400oC to 1600oC. Sintered samples were characterized to determine phase present, bulk density, hardness and grain size. The results indicated that all the doped samples could be sintered to high density > 3.85 Mgm−3 when compared to the undoped alumina. According to the XRD analysis, the α-Al2O3 phase was not disrupted by the dopant addition. Although the hardness of the CuO-doped material was higher when sintered below 1550°C, the maximum hardness of 21 GPa was measured for the undoped ceramics when sintered at 1600°C. The lower hardness of the doped samples could be attributed to the increased in grain size with increasing sintering temperature.
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: Lai Kuan Lee Samuel, Chou Yong Tan, Ramesh Singh, Boon Kar Yap, Ranna Tolouei, Mahdi Amiriyan
Abstract: Hydroxyapatite (HA) is by far the closest match to the human bone in terms of chemical composition. Furthermore, HA boasts excellent biocompatibility thus earning its reputation for human bone replacement. However, HA lacks desirable mechanical properties (i.e. hardness, fracture toughness, etc.). Due to the poor heat conductivity of ceramics, it is hypothesized that HA when sintered via conventional pressureless sintering, smaller ramp rates are advantageous as oppose to larger ramp rates. These advantages can be observed as improved densification along with improved mechanical properties. In the present work, the sintering profile for the HA green bodies were held at 1 minute in comparison to the usual 2 hours holding time. The applied ramp rates were 2 °C/min, 5 °C/min and 10 °C/min. Sintering temperatures were set to 1000, 1100, 1200, and 1300 °C. Sample characterization was then reviewed in the aspects of phase stability, % shrinkage, bulk and relative density, Young’s modulus, Vickers hardness, as well as fracture toughness. The results revealed that sintering with shorter holding time yielded an improvement in the mechanical properties of HA. It was observed that sintering HA with a 2 °C/min ramp rate does not result in the formation of extrageneous phases even when sintered to 1300 °C. Similarly at 2 °C/min and 1300 °C, densification was observed to be 99.05 %. In addition, Young’s modulus recorded its highest value (117.03 GPa) when sintered with a ramp rate of 2°C/min. It was also observed that sintering HA at a ramp rate of 2°C/min produced a hardness value of 5.88 GPa (improvement of 0.68 GPa when compared with 2 hours holding time).
Authors: Ranna Tolouei, Singh Ramesh, Chou Yong Tan, Meenaloshini Satgunam, Mahdi Amiriyan
Abstract: Hydroxyapatite (HA) is among the leading ceramic materials for hard tissue replacement implants. Despite the excellent bioactivity of HA, low toughness has limited the application of these materials to non-load bearing areas. The sinterability of nanocrystalline hydroxyapatite (HA) powder via new heating profile for conventional pressureless sintering was studied. The starting nanocrystalline HA powder was synthesized by wet chemical precipitation method. After uniaxial pressing followed by isostatic pressing, HA powder compacts are sintered over the temperature range of 1000°C to 1300°C. Different holding time of 1 minute and 120 minutes was applied as a heating profile of HA samples. The results revealed that new heating profile was effective in producing a HA body with high density of 98% when sintered at 1200°C. Subsequently, mechanical properties such as fracture toughness and hardness, of HA compacts increased with decrease in grain size. HA showed the highest hardness of 9.51 GPa and fracture toughness of 1.41 MPa.m1/2 when sintered at 1100 °C. XRD analysis indicated that decomposition of HA phase during sintering at high temperatures do not occur. Short holding time leads to finer microstructure of HA and subsequently better mechanical properties.
Authors: Mojgan Ahmadrezaei, Andanastuti Muchtar, Norhamidi Muhamad, Chou Yong Tan
Abstract: A recently reported promising new perovskite oxide cathode material, Ba0.2Sr0.8Co0.8Fe0.2O3−δ, (BSCF) (with x = 0.2 and y = 0.8) of high purity for intermediate-temperature solid oxide fuel cells (IT-SOFCs) was synthesised in the current work by using the co-precipitation method. The result indicated a precursor with a well-defined composition of fine particle size, high homogeneity, and high reactivity. After calcining has been developed at 900°C, the individual oxides from ammonium oxalate were alloyed into nanostructured perovskite (with x = 0.2 and y = 0.8) Ba0.2Sr0.8Co0.8Fe0.2O3 of high purity. The thermal properties, phase constituents, surface area and microstructure of the samples were characterised by TGA, XRD, BET, SEM and EDX techniques respectively. The results show that the BSCF powders have cubic perovskite-type structure with fine particle size, high surface area and high homogeneity. The current method employed is found to be very reliable for the synthesis of BSCF.
Authors: Kok Fong Lim, Muchtar Andanastuti, Rusnah Mustaffa, Chou Yong Tan
Abstract: Hydroxyapatite (HA)-zirconia nanocomposite is synthesised by mixing as-synthesised HA with commercially available yttria-stabilised zirconia nanopowder using wet ball milling. The sample is consolidated using uniaxial pressing followed by cold isostatic pressing. The composites containing 0 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, and 5 wt% zirconia are prepared and sintered at 1100, 1200, and 1300 °C. Results from the X-ray diffraction (XRD) and density analyses show that the proposed approach produced a highly dense sample (>98.8%) with minimum amount of impurity, which is suitable for dental applications.
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.
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