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Shah Alam, Malaysia

Ramesh S.,University of Tenaga Nasional | Ramesh S.,University of Malaya | Tan C.Y.,University of Tenaga Nasional | Yeo W.H.,University of Tenaga Nasional | And 4 more authors.
Ceramics International | Year: 2011

The sinterability of Bi2O3-doped hydroxyapatite (HA) has been studied and compared with the undoped HA. Varying amounts of Bi 2O3 ranging from 0.05 wt% to 1.0 wt% were mixed with the HA. The study revealed that most sintered samples composed of the HA phase except for compacts containing 0.3, 0.5 and 1.0 wt% Bi2O3 and when sintered above 1100 °C, 1000 °C and 950 °C, respectively. In general, the addition of 0.5 wt% Bi2O3 was identified as the optimum amount to promote densification as well as to improve the mechanical properties of sintered HA at low temperature of 1000 °C. 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 1000 °C. A maximum Young's modulus of 119.2 GPa was measured for 0.1 wt% Bi2O3-doped HA when sintered at 1150 °C. Additionally, the ceramic was able to achieve highest hardness of 6.08 GPa and fracture toughness of 1.21 MPa m1/2 at sintering temperature of 1000 °C. © 2010 Elsevier Ltd and Techna Group S.r.l.

Sivakumar S.,University of Tenaga Nasional | Ramesh S.,University of Malaya | Chin K.L.,University of Tenaga Nasional | Tan C.Y.,University of Tenaga Nasional | Teng W.D.,Ceramics Technology Group
International Journal of Automotive and Mechanical Engineering | Year: 2011

A commercially available Y-TZP ceramic powder was fabricated under four different sintering profiles in order to investigate the effects of conventional single-stage sintering (SSS) with dwell times of 1 min and 2 h, respectively, compared with two-stage sintering (TSS), on the physical and mechanical properties of Y-TZP. Sintering was performed up to 1400°C at a ramp rate of 10°C/min. It was revealed that samples sintered via TSS yielded better properties than the SSS samples sintered at 1400°C using a dwell time of 2 h. In the hydrothermal ageing test, TSS samples did not undergo low-temperature degradation via the tetragonal to monoclinic phase transformation. Nevertheless, it was found by XRD analysis that Y-TZP ceramics sintered by the SSS method using a short dwell time of 1 min were effective in maintaining tetragonal phase stability after 50 h of exposure to superheated steam conditions. © Universiti Malaysia Pahang.

Shin B.,Pusan National University | Shin B.,Ceramics Technology Group | Lee H.,Pusan National University
Journal of Ceramic Processing Research | Year: 2014

WO3-TiO2 catalysts were prepared by an incipient wet-impregnation method for high-temperature selective catalytic reduction (SCR) of NOx. Structure, surface acidity, and catalytic performance of SCR catalyst according to WO3 content (4, 6, 8, and 10 wt.%) were characterized by morphological and spectroscopy analyses. The 10 wt.% WO3-TiO2 catalyst had high conversion efficiency due to the improvement of specific surface area, catalytic acidity, and monolayer capacity of TiO2 support. It was found that tungsten oxide species are dispersed in the interlayer between the grain and the grain boundary of TiO2 support in transmission electron microscopy. The WO3 affected the suppressed grain growth and the improved Brønsted acid sites that could provide much surface acidity by the grain boundary reinforcement. The structural interaction between the proper WO3 content and TiO2 support led to the existence of octahedrally and tetrahedrally coordinated WO3 structures on the surface in the Raman spectra. The enhanced catalytic activity of 10 wt.% WO3-TiO2 is attributed to the increase of the surface acidity (Brønsted acid sites) by the shell formation of WO3 species. © 2004 Hanyang University. All right reserved.

Ramesh S.,University of Malaya | Amiriyan M.,University of Tenaga Nasional | Meenaloshini S.,University of Tenaga Nasional | Tolouei R.,University of Tenaga Nasional | And 3 more authors.
Ceramics International | Year: 2011

The effect of employing a short sintering holding time of 12 min as compared to that of the commonly employed holding time of 120 min (2 h) on the properties of undoped and 1 wt% manganese oxide (MnO2)-doped Y-TZP ceramics were studied. Sintering studies was conducted over the temperature range of 1150-1600 °C. Bulk density, Young's modulus, Vickers hardness and fracture toughness tests were carried out on the sintered samples. The results revealed that the 12 min sintering holding time was effective in promoting densification of the 1 wt% MnO2-doped Y-TZP without sacrificing tetragonal phase stability or mechanical properties and incurring grain growth. Microstructure investigation by using the scanning electron microscope (SEM) of the fracture MnO2-doped Y-TZP samples which was subjected to rapid quenching in liquid nitrogen revealed distinct microstructural features believed to be associated with the presences of a transient liquid phase during sintering. A sintering mechanism was subsequently proposed to explain the densification behaviour of MnO2-doped Y-TZP ceramics. © 2011 Elsevier Ltd and Techna Group S.r.l.

Ubenthiran S.,University of Malaya | Ramesh S.,University of Malaya | Tan C.Y.,University of Malaya | Teng W.D.,Ceramics Technology Group
Applied Mechanics and Materials | Year: 2013

In this study oxygen vacancy concentration on 3Y - TZP ceramics was compared for sintered and aged samples in air and argon gas atmosphere. The sintering study was conducted over the temperature range 1250°C - 1500°C. Photoluminescence (PL) spectrums of the sintered samples were taken by laser with excitation wavelength 325nm. Two distinctive sharp and broad peaks were observed for the wavelength ~ 615 nm and ~ 580 - 600nm. The sample sintered at 1250 °C showed higher oxygen vacancy in both atmospheres. At the same time, argon gas sintered sample showed higher oxygen vacancy than air sintered sample. The emission band blue shifted after 1 h ageing for the sample sintered in 1500 °C in both atmospheres. XRD results on 1 hour aged sample sintered in argon gas atmosphere showed higher monoclinic phase than air sintered sample. © (2013) Trans Tech Publications, Switzerland.

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