S. Ramesh | University of Malaya, Malaysia (original) (raw)
Papers by S. Ramesh
Science and Technology of Advanced Materials, 2007
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8th IEEE International Conference on Computer and Information Technology Workshops, CIT Workshops 2008, 2008
This paper describes an approach to implementing technology-assisted problem solving (TAPS) packa... more This paper describes an approach to implementing technology-assisted problem solving (TAPS) package using desktop virtual reality interface that brings together a 3-D model of an engineering mechanics problem in an interactive manner. It provides the user with a self-study environment in which to solve an engineering mechanics problem in mechanical engineering course. The package guides the user to solve a problem in a step-by-step approach and graphical environment. Integrating components such as 2-D, 3-D and stereoscopic images provides dynamic learning environment and guidance so that the learner can analyze the necessary actions to be taken in the virtual environment. Preliminary evaluation indicated that the TAPS package has great potential to aid teaching and thus provide an effective learning environment.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4568520&tag=1
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Composites Part B-Engineering, 2013
Over the years new coating design and technology for structures have received much attention main... more Over the years new coating design and technology for structures have received much attention mainly due to the demand for longer life span and durability. Conventional coating general consists of few homogeneous layers being deposited on the parent material or substrate. These layers are very vulnerable to cracking followed by de-bonding due to mismatch thermo-mechanical property. To avoid such coating failures, functionally graded material (FGM) is proposed in the coating design. Hence, this study analyzes FGM plates subjected to transverse load with clamped edges. Three configurations were considered. The first involves a two-layer plate in which a homogeneous coating layer was coated on a homogeneous substrate. The second involves a two layer system with the first layer as a FGM coating followed by the homogeneous substrate and the final configuration was a three layer system. The top and bottom layers are homogenous coating and substrates respectively, and the interlayer is composed of FGM. The Young's modulus of FGM plates is assumed to vary in the thickness direction based on the sigmoid functions and the Poisson's ratio remain constant throughout the FGM plate. The analysis was carried out in the context of two-dimensional elasticity theory and the method of superposition was used to find a series solution. The deflections, strains, and stresses were evaluated and the differences between the elastic behaviors of all three design configurations were investigated.
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5th Kuala Lumpur International Conference on Biomedical Engineering, BIOMED 2011, Held in Conjunction with the 8th Asian Pacific Conference on Medical and Biological Engineering, APCMBE 2011, 2011
Thermal analysis of hydroxyapatite formation through dry mechanochemical method has been studied.... more Thermal analysis of hydroxyapatite formation through dry mechanochemical method has been studied. The calcium phosphate was synthesized using calcium hydroxide and di-ammonium hydrogen phosphate as the precursors. The ball milling of 1/6 ball-powder mass ratio was employed on mixtures of calcium hydroxide and di-ammonium hydrogen phosphate in three different speeds 170, 270 and 370 rpm for 15 h. As ball-milled powders were then sintered at 1150, 1250 and 1350°C for 2 h, then subjected to TGA, XRD and FTIR for phase characterization. Calcium phosphates with ammonium are phases of the material. The ammonium is trace of phosphorus precursor. Choosing condition of the process and type of precursors determines type of reactions and its products.
http://link.springer.com/chapter/10.1007/978-3-642-21729-6_30
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2012 International Conference on Materials Science and Nanotechnology, ICMSN 2012, 2013
Biphasic calcium phosphate powders doped with zinc (Zn-doped BCP) were synthesized via sol-gel te... more Biphasic calcium phosphate powders doped with zinc (Zn-doped BCP) were synthesized via sol-gel technique. Different concentrations of Zn have been successfully incorporated into biphasic calcium (BCP) phases namely: 1%, 2%, 3%, 5%, 7%, 10% and 15%. The synthesized powders were calcined at temperatures of 700-900°C. The calcined Zn-doped BCP powders were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential and thermogravimetric analysis (TG/DTA) and field-emission scanning electron microscopy (FESEM). X-ray diffraction analysis revealed that the phases present in Zn-doped are hydroxyapatite, β- TCP and parascholzite. Moreover, FTIR analysis of the synthesized powders depicted that the bands of HPO4 increased meanwhile O-H decreased with an increase in the calcination temperature. Field emission scanning electron microscopy (FESEM) results showed the agglomeration of particles into microscale aggregates with size of the agglomerates tending to increase with an increase in the dopant concentration.
http://www.scientific.net/KEM.531-532.614
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Multi-functional Materials and Structures - International Conference on Multifunctional Materials and Structures, 2008
Strontium is one of metallic elements found in bones and teeth. It is an essential substance in p... more Strontium is one of metallic elements found in bones and teeth. It is an essential substance in preventing osteoporosis and has the ability to regenerate, preserve, and even restore bone growth. Synthesizing Sr-doped HA powder is of great importance accordingly. Here we present Sr-doped HA powders prepared via sol-gel procedure using calcium nitrate and diammonium hydrogen phosphate as the precursors. Strontium nitrate was used as the dopant source, and its concentration was varied from 2∼15 %. An ammoniacal solution was heated until a white gel was obtained. The obtained gel was then dried and subsequently subjected to 900°C calcination. Characterization on the obtained powder was conducted using XRD, FTIR, and FESEM. XRD measurement had shown that the powder contained hydroxyapatite phase only. Morphological evaluation by FESEM measurement shows that the particles of the Sr -doped HA agglomerates are globular in shape with an average size of 1-2 μm in diameter. Meanwhile, the primary particles have a diameter of 50-150 nm in average. It is likely Sr has played an important role as a calcination or sintering additive, causing more progressive densification of particles.
http://www.scientific.net/AMR.47-50.928
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International Conference on Advances in Materials and Processing Technologies, AMPT 2009, 2011
The sinterability of magnesium oxide (MgO) doped hydroxyapatite (HA) ranging from 1 to 10 wt% whe... more 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 MgOdoped 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.
http://www.scientific.net/AMR.264-265.1849
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8th International Conference on Fracture and Strength of Solids 2010, FEOFS2010, 2011
Metal-organic framework MOF-5 (i.e. IRMOF-1) with the chemical structure of Zn4O(BDC)3 were succe... more Metal-organic framework MOF-5 (i.e. IRMOF-1) with the chemical structure of Zn4O(BDC)3 were successfully synthesized using room temperature synthesis approach of direct-mixing method ans liquid-crystal templating method. The metal clusters organic linker used was benzenedicarboxylic acid (BDC). Direct-mixing approach resulted in MOF-5 with tetragonal cell while the liquid-crystal templating method resulted in cubic structure. The metal/linker ratios were varied from 0.1 to 1 to study the effect of metal linker on the formation of MOF-5 materials and their characteristics. The crystallinity of the evacuated framework MOF-5 materials were increased when the metal/organic linker ratios were increased from 0.3 to 0.5. However, the cubic structure of the evacuated framework was relatively disrupted at metal/linker ratio 0.7.
http://www.scientific.net/KEM.462-463.1103
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Journal of Electroanalytical Chemistry, 2004
A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-... more A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-nitrate soft-combustion process at low temperature. The annealed powders were characterized by XRD to confirm the phase formation of the stoichiometric product, Ni2(MoO4)3 in its non-lithiated state. The morphology of the annealed product was found to be composed of soft agglomerates embedded by ultrafine spherical grains. Electrochemical redox properties of the synthesized product were confirmed by employing the new material as a cathode in lithium-containing test cells in an aprotic electrolyte environment (1 M LiPF6 in EC+DMC). Slow scan cyclic voltammetry (SSCV) confirmed the redox behavior corresponding to the reduction/oxidation of the transition metals, Ni and Mo between the potential window of 3.5-1.5 V. The lithium insertion/extraction process was confirmed by galvanostatic measurements on the test cells and they exhibited well discernible discharge/charge profiles with a reversible capacity of 170 mAh/g over the potential window of 3.5-1.5 V after the first charge/discharge cycle. Nevertheless, the discharge capacity was found to deteriorate slowly upon repeated cycling, which might presumably be due to disproportion reaction of the host structure beyond the extent of insertion of two lithium ions.
http://www.sciencedirect.com/science/article/pii/S0022072804001779
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Journal of Electroanalytical Chemistry, 2004
A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-... more A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-nitrate soft-combustion process at low temperature. The annealed powders were characterized by XRD to confirm the phase formation of the stoichiometric product, Ni2(MoO4)3 in its non-lithiated state. The morphology of the annealed product was found to be composed of soft agglomerates embedded by ultrafine spherical grains. Electrochemical redox properties of the synthesized product were confirmed by employing the new material as a cathode in lithium-containing test cells in an aprotic electrolyte environment (1 M LiPF6 in EC+DMC). Slow scan cyclic voltammetry (SSCV) confirmed the redox behavior corresponding to the reduction/oxidation of the transition metals, Ni and Mo between the potential window of 3.5-1.5 V. The lithium insertion/extraction process was confirmed by galvanostatic measurements on the test cells and they exhibited well discernible discharge/charge profiles with a reversible capacity of 170 mAh/g over the potential window of 3.5-1.5 V after the first charge/discharge cycle. Nevertheless, the discharge capacity was found to deteriorate slowly upon repeated cycling, which might presumably be due to disproportion reaction of the host structure beyond the extent of insertion of two lithium ions.
http://www.sciencedirect.com/science/article/pii/S0022072804001779
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The Medical journal of Malaysia, 2008
Improvement of the mechanical properties of hydroxyapatite (HA) can be achieved by the incorporat... more Improvement of the mechanical properties of hydroxyapatite (HA) can be achieved by the incorporation of metal. In addition, incorporation of strontium ion into HA crystal structures has been proved effective to enhance biochemical properties of bone implant. In this research, strontium-doped HA powder was developed via a sol-gel method to produce extraordinarily fine strontium-doped HA (Sr-doped HA) powder. XRD measurement had shown that the powder contained hydroxyapatite phase only for all doping concentration except for 2%, showing that Sr atoms have suppressed the appearance of beta-TCP as the secondary phase. Morphological evaluation by FESEM measurement shows that the particles of the Sr-doped HA agglomerates are globular in shape with an average size of 1-2 microm in diameter while the primary particles have a diameter of 30-150 nm in average.
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Materials and Manufacturing Processes, 2008
The use of response surface methodology for minimizing the surface roughness in machining titaniu... more The use of response surface methodology for minimizing the surface roughness in machining titanium alloy, a topic of current interest, has been discussed in this article. The surface roughness model has been developed in terms of cutting parameters such as cutting speed, feed, and depth of cut. Machining tests have been carried out using CVD (TiN-TiCN-Al2O3-TiN) coated carbide insert under different cutting conditions using Taguchi's orthogonal array. The experimental results have been investigated using analysis of variance (ANOVA). The results indicated that the feed rate is the main influencing factor on surface roughness. Surface roughness increased with increasing feed rate, but decreased with increasing cutting speed and depth of cut. The predicted results are fairly close to experimental values and hence, the developed models can be used for prediction satisfactorily.
http://www.tandfonline.com/doi/abs/10.1080/10426910701774700#.UdZ2pqyTX1U
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Malaysian Journal of Microscopy, 2011
In this research, (X)PZT-(1-X)PMN ceramics (where X is 0.25, 0.5 and 0.75) were achieved from a c... more In this research, (X)PZT-(1-X)PMN ceramics (where X is 0.25, 0.5 and 0.75) were achieved from a conventional mixed-oxide method. Lead Zirconate titanate (PZT) powders with composition near the morphotropic phase boundary have been synthesized via a microemulsion processing route. Modified mixed oxides method was used for obtaining single phase Lead Magnesium niobate (PMN) powder with high relative density (98% of T.D.) and good electrical properties (dielectric constant of ≈10 4 at room temperature). Two-step sintering (TSS) has been applied to suppress the accelerated grain growth of PZT-PMN composite compacts in the last sintering stage. The produced samples with high PZT content showed low densities due to the low compaction ratio of PZT powder. The dielectric properties of PZT-rich and PMN-rich materials were high (dielectric constant of about 0.7×10 3 and 1×10 3 was measured for PZT-rich and PMN-rich ceramics, respectively) while the other sample exhibited lower dielectric properties. The X-ray diffraction analysis of the sintered samples indicated that PZT-PMN ceramic was produced successfully with traces of pyrochlore phase formed in the structure.
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Trends in Biomaterials and Artificial Organs, 2009
Strontium doped hydroxyapatite (Sr-doped HA) nanopowder has been synthesized using a sol-gel meth... more Strontium doped hydroxyapatite (Sr-doped HA) nanopowder has been synthesized using a sol-gel method. The concentration of strontium was varied at 2, 5, 10 and 15 mol%. The as synthesized powders were calcined at temperatures of 500-900°C. The calcined white Sr-doped HA powders were characterized using differential and thermogravimetric analysis (TG/DTA), field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Morphological evaluation by FESEM measurement shows that the particles of the Sr-doped HA agglomerates are globular in shape with an average size of 1-2 mm in diameter while the primary particles have a diameter of 30-150 nm in average. The calcined powders contained hydroxyapatite phase only for all doping concentration except for the smallest doping concentration, 2 mol%, where â-TCP appeared as the secondary phase. This indicates that the substitution of Sr atoms for Ca atoms have stabilized the HA phase, leading to the inhibition of the appearance of â-TCP phase upon high temperature calcination. Even, for 2 mol% Sr-doped HA, the appearance of â-TCP peak only started to appear at a temperature as high as of 900°C, compared to non-Sr doping HA which appeared at a temperature below 800°C.
medind.nic.in/taa/t09/i2/taat09i2p105.pdf
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Materials Science Forum, 2011
The nanocrystalline HA powders were produced through sol-gel method which employed calcium nitrat... more The nanocrystalline HA powders were produced through sol-gel method which employed calcium nitrate tetrahydrate [Ca(NO3)2.4H2O] and diammonium hydrogen phosphate [(NH4)2HPO4] as calcium and phosphorous precursors. Sodium ion (Na+) is one of the trace elements found in biological apatite and believed to have important effect in its performance. The concentrations of sodium dopant were varied from 0 mol% until 15 mol% by using sodium nitrate (NaNO3) as the source of dopant. Characterization of nanopowders was investigated by using X-ray diffraction (XRD), Fourier transform infra red (FTIR) and Transmission Electron Microscope (TEM). XRD analysis revealed that there are no other phases exist in the synthesized powder, evinced single phase of HA and a trend shows an increase of cristallinity with increase of sodium dopant concentration. While the TEM images showed evidence that the particle sizes were bigger with the increasing sodium concentration, showing the effect of sodium dopant on the densification of the powder.
http://www.scientific.net/MSF.694.128
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Journal of Materials Science, 1996
The sintering behaviour of Y-TZP ceramics, their resulting microstructures and properties are inf... more The sintering behaviour of Y-TZP ceramics, their resulting microstructures and properties are influenced not only by the characteristics of the raw materials but also were found to be dependent on the thermal history during the fabrication process. It is generally understood that fracture toughness increases as grain size increases up to a certain limit but in the present investigation, the results obtained challenge this view. The work is concerned with grain size dependence on the mechanical properties, in particular on the fracture toughness. Two commercially available powders based on two different processing techniques (i.e. coated and co-precipitated) were studied. It has been found that both materials exhibited different fracture toughness trends. Smaller grains of coated Y-TZP resulted in high fracture toughness > 12 MPa m1/2 while the opposite effect was seen in the co-precipitated material which showed enhanced fracture toughness with increasing grain size above a certain lower limit from a nonconventional heat treatment.
http://link.springer.com/article/10.1007%2FBF01152158
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Ceramics International, 2013
In the present work, the sintering behaviour of HA particles prepared via the wet precipitation m... more In the present work, the sintering behaviour of HA particles prepared via the wet precipitation method (HAp) and wet mechanochemical technique (HAwm) was investigated. The sintering behaviour of a commercial HA powder (HAc) was also studied for comparison purpose. All the three powders were characterised in terms of particle size, Ca/P ratio and crystal size. Green samples were prepared and sintered in air at temperatures ranging from 1000 degrees C to 1400 degrees C. The sintered bodies were studied in terms of the phase stability, relative density, Young's modulus, Vickers hardness, fracture toughness and grain size. The results indicated that HAwm samples suffered phase decomposition while the HAp and HAc sintered samples showed no phase disruption throughout the temperature range employed. The HAp samples exhibited the overall best densification and properties when compared to the HAc and HAwm samples. Furthermore, the results showed that mechanical properties of sintered samples were governed by both the bulk density and the grain size.
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International Conference on Advances in Materials and Processing Technologies, AMPT 2009, 2011
In the present work, densification of synthesised hydroxyapatite (HA) bioceramic prepared via che... more 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.
http://www.scientific.net/AMR.264-265.1856
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4th Kuala Lumpur International Conference on Biomedical Engineering 2008, Biomed 2008, 2008
The effects of doping small amounts of TiO2 up to 5 wt% on the sintering behaviour of alumina (Al... more The effects of doping small amounts of TiO2 up to 5 wt% on the sintering behaviour of alumina (Al2O3) was studied. Green samples were prepared and pressureless sintered in air at temperatures ranging from 1250°C to 1600°C, at a furnace ramp rate of 10°C/min. and soaking time of 2 hours. Sintered samples were characterized to determine bulk density, hardness and Young's modulus. It has been found that all the doped samples exhibited higher bulk density than the undoped samples. The bulk density increases with increasing temperature and attained a maximum value of 3.9 Mgm-3 for samples doped with 1.0 wt% TiO2 at 1450°C. The addition of 1 wt% TiO2 when sintered at 1450°C was found to be the most beneficial throughout the studied range as the samples exhibited the highest Young's modulus of 381 GPa and Vickers hardness of 16.5 GPa as compared to 256.7 GPa and 11.2 GPa for the undoped alumina. Titanium oxide doping is one economical way of improving the densification of Al2O3 without affecting mechanical properties.
http://link.springer.com/chapter/10.1007/978-3-540-69139-6_89
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Journal of Materials Science, 2000
The sintering behaviour of alumina-Y-TZP composites prepared by slip-casting technique were studi... more The sintering behaviour of alumina-Y-TZP composites prepared by slip-casting technique were studied. Slip-cast samples containing varying amounts of Y-TZP ranging up to 90 vol% were prepared and evaluated. Sintering studies were carried out at 1450 degrees C to 1600 degrees C. Sintered samples were characterised where appropriate to determine phases present, grain sizes, bulk density and mechanical properties. Good correlation was obtained between the calculated prepared powder density and experimental results. The sintered bulk density of the composites was observed to increase with increasing Y-TZP content and sintering temperature up to 1550 degrees C. Maximum hardness values (> 14 GPa) were obtained for all samples containing < 60 vol% Y-TZP and when sintered at 1550 degrees C. It has been found that the additions of up to 50 vol% Y-TZP was effective in suppressing Al2O3 grain growth.
http://link.springer.com/content/pdf/10.1023%2FA%3A1004837516291.pdf
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Science and Technology of Advanced Materials, 2007
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8th IEEE International Conference on Computer and Information Technology Workshops, CIT Workshops 2008, 2008
This paper describes an approach to implementing technology-assisted problem solving (TAPS) packa... more This paper describes an approach to implementing technology-assisted problem solving (TAPS) package using desktop virtual reality interface that brings together a 3-D model of an engineering mechanics problem in an interactive manner. It provides the user with a self-study environment in which to solve an engineering mechanics problem in mechanical engineering course. The package guides the user to solve a problem in a step-by-step approach and graphical environment. Integrating components such as 2-D, 3-D and stereoscopic images provides dynamic learning environment and guidance so that the learner can analyze the necessary actions to be taken in the virtual environment. Preliminary evaluation indicated that the TAPS package has great potential to aid teaching and thus provide an effective learning environment.
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4568520&tag=1
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Composites Part B-Engineering, 2013
Over the years new coating design and technology for structures have received much attention main... more Over the years new coating design and technology for structures have received much attention mainly due to the demand for longer life span and durability. Conventional coating general consists of few homogeneous layers being deposited on the parent material or substrate. These layers are very vulnerable to cracking followed by de-bonding due to mismatch thermo-mechanical property. To avoid such coating failures, functionally graded material (FGM) is proposed in the coating design. Hence, this study analyzes FGM plates subjected to transverse load with clamped edges. Three configurations were considered. The first involves a two-layer plate in which a homogeneous coating layer was coated on a homogeneous substrate. The second involves a two layer system with the first layer as a FGM coating followed by the homogeneous substrate and the final configuration was a three layer system. The top and bottom layers are homogenous coating and substrates respectively, and the interlayer is composed of FGM. The Young's modulus of FGM plates is assumed to vary in the thickness direction based on the sigmoid functions and the Poisson's ratio remain constant throughout the FGM plate. The analysis was carried out in the context of two-dimensional elasticity theory and the method of superposition was used to find a series solution. The deflections, strains, and stresses were evaluated and the differences between the elastic behaviors of all three design configurations were investigated.
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5th Kuala Lumpur International Conference on Biomedical Engineering, BIOMED 2011, Held in Conjunction with the 8th Asian Pacific Conference on Medical and Biological Engineering, APCMBE 2011, 2011
Thermal analysis of hydroxyapatite formation through dry mechanochemical method has been studied.... more Thermal analysis of hydroxyapatite formation through dry mechanochemical method has been studied. The calcium phosphate was synthesized using calcium hydroxide and di-ammonium hydrogen phosphate as the precursors. The ball milling of 1/6 ball-powder mass ratio was employed on mixtures of calcium hydroxide and di-ammonium hydrogen phosphate in three different speeds 170, 270 and 370 rpm for 15 h. As ball-milled powders were then sintered at 1150, 1250 and 1350°C for 2 h, then subjected to TGA, XRD and FTIR for phase characterization. Calcium phosphates with ammonium are phases of the material. The ammonium is trace of phosphorus precursor. Choosing condition of the process and type of precursors determines type of reactions and its products.
http://link.springer.com/chapter/10.1007/978-3-642-21729-6_30
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2012 International Conference on Materials Science and Nanotechnology, ICMSN 2012, 2013
Biphasic calcium phosphate powders doped with zinc (Zn-doped BCP) were synthesized via sol-gel te... more Biphasic calcium phosphate powders doped with zinc (Zn-doped BCP) were synthesized via sol-gel technique. Different concentrations of Zn have been successfully incorporated into biphasic calcium (BCP) phases namely: 1%, 2%, 3%, 5%, 7%, 10% and 15%. The synthesized powders were calcined at temperatures of 700-900°C. The calcined Zn-doped BCP powders were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential and thermogravimetric analysis (TG/DTA) and field-emission scanning electron microscopy (FESEM). X-ray diffraction analysis revealed that the phases present in Zn-doped are hydroxyapatite, β- TCP and parascholzite. Moreover, FTIR analysis of the synthesized powders depicted that the bands of HPO4 increased meanwhile O-H decreased with an increase in the calcination temperature. Field emission scanning electron microscopy (FESEM) results showed the agglomeration of particles into microscale aggregates with size of the agglomerates tending to increase with an increase in the dopant concentration.
http://www.scientific.net/KEM.531-532.614
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Multi-functional Materials and Structures - International Conference on Multifunctional Materials and Structures, 2008
Strontium is one of metallic elements found in bones and teeth. It is an essential substance in p... more Strontium is one of metallic elements found in bones and teeth. It is an essential substance in preventing osteoporosis and has the ability to regenerate, preserve, and even restore bone growth. Synthesizing Sr-doped HA powder is of great importance accordingly. Here we present Sr-doped HA powders prepared via sol-gel procedure using calcium nitrate and diammonium hydrogen phosphate as the precursors. Strontium nitrate was used as the dopant source, and its concentration was varied from 2∼15 %. An ammoniacal solution was heated until a white gel was obtained. The obtained gel was then dried and subsequently subjected to 900°C calcination. Characterization on the obtained powder was conducted using XRD, FTIR, and FESEM. XRD measurement had shown that the powder contained hydroxyapatite phase only. Morphological evaluation by FESEM measurement shows that the particles of the Sr -doped HA agglomerates are globular in shape with an average size of 1-2 μm in diameter. Meanwhile, the primary particles have a diameter of 50-150 nm in average. It is likely Sr has played an important role as a calcination or sintering additive, causing more progressive densification of particles.
http://www.scientific.net/AMR.47-50.928
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International Conference on Advances in Materials and Processing Technologies, AMPT 2009, 2011
The sinterability of magnesium oxide (MgO) doped hydroxyapatite (HA) ranging from 1 to 10 wt% whe... more 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 MgOdoped 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.
http://www.scientific.net/AMR.264-265.1849
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8th International Conference on Fracture and Strength of Solids 2010, FEOFS2010, 2011
Metal-organic framework MOF-5 (i.e. IRMOF-1) with the chemical structure of Zn4O(BDC)3 were succe... more Metal-organic framework MOF-5 (i.e. IRMOF-1) with the chemical structure of Zn4O(BDC)3 were successfully synthesized using room temperature synthesis approach of direct-mixing method ans liquid-crystal templating method. The metal clusters organic linker used was benzenedicarboxylic acid (BDC). Direct-mixing approach resulted in MOF-5 with tetragonal cell while the liquid-crystal templating method resulted in cubic structure. The metal/linker ratios were varied from 0.1 to 1 to study the effect of metal linker on the formation of MOF-5 materials and their characteristics. The crystallinity of the evacuated framework MOF-5 materials were increased when the metal/organic linker ratios were increased from 0.3 to 0.5. However, the cubic structure of the evacuated framework was relatively disrupted at metal/linker ratio 0.7.
http://www.scientific.net/KEM.462-463.1103
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Journal of Electroanalytical Chemistry, 2004
A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-... more A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-nitrate soft-combustion process at low temperature. The annealed powders were characterized by XRD to confirm the phase formation of the stoichiometric product, Ni2(MoO4)3 in its non-lithiated state. The morphology of the annealed product was found to be composed of soft agglomerates embedded by ultrafine spherical grains. Electrochemical redox properties of the synthesized product were confirmed by employing the new material as a cathode in lithium-containing test cells in an aprotic electrolyte environment (1 M LiPF6 in EC+DMC). Slow scan cyclic voltammetry (SSCV) confirmed the redox behavior corresponding to the reduction/oxidation of the transition metals, Ni and Mo between the potential window of 3.5-1.5 V. The lithium insertion/extraction process was confirmed by galvanostatic measurements on the test cells and they exhibited well discernible discharge/charge profiles with a reversible capacity of 170 mAh/g over the potential window of 3.5-1.5 V after the first charge/discharge cycle. Nevertheless, the discharge capacity was found to deteriorate slowly upon repeated cycling, which might presumably be due to disproportion reaction of the host structure beyond the extent of insertion of two lithium ions.
http://www.sciencedirect.com/science/article/pii/S0022072804001779
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Journal of Electroanalytical Chemistry, 2004
A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-... more A new framework type LixNi2(MoO4) 3 [0 ≤ x ≤ 4] polyanion compound was synthesized via a glycine-nitrate soft-combustion process at low temperature. The annealed powders were characterized by XRD to confirm the phase formation of the stoichiometric product, Ni2(MoO4)3 in its non-lithiated state. The morphology of the annealed product was found to be composed of soft agglomerates embedded by ultrafine spherical grains. Electrochemical redox properties of the synthesized product were confirmed by employing the new material as a cathode in lithium-containing test cells in an aprotic electrolyte environment (1 M LiPF6 in EC+DMC). Slow scan cyclic voltammetry (SSCV) confirmed the redox behavior corresponding to the reduction/oxidation of the transition metals, Ni and Mo between the potential window of 3.5-1.5 V. The lithium insertion/extraction process was confirmed by galvanostatic measurements on the test cells and they exhibited well discernible discharge/charge profiles with a reversible capacity of 170 mAh/g over the potential window of 3.5-1.5 V after the first charge/discharge cycle. Nevertheless, the discharge capacity was found to deteriorate slowly upon repeated cycling, which might presumably be due to disproportion reaction of the host structure beyond the extent of insertion of two lithium ions.
http://www.sciencedirect.com/science/article/pii/S0022072804001779
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The Medical journal of Malaysia, 2008
Improvement of the mechanical properties of hydroxyapatite (HA) can be achieved by the incorporat... more Improvement of the mechanical properties of hydroxyapatite (HA) can be achieved by the incorporation of metal. In addition, incorporation of strontium ion into HA crystal structures has been proved effective to enhance biochemical properties of bone implant. In this research, strontium-doped HA powder was developed via a sol-gel method to produce extraordinarily fine strontium-doped HA (Sr-doped HA) powder. XRD measurement had shown that the powder contained hydroxyapatite phase only for all doping concentration except for 2%, showing that Sr atoms have suppressed the appearance of beta-TCP as the secondary phase. Morphological evaluation by FESEM measurement shows that the particles of the Sr-doped HA agglomerates are globular in shape with an average size of 1-2 microm in diameter while the primary particles have a diameter of 30-150 nm in average.
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Materials and Manufacturing Processes, 2008
The use of response surface methodology for minimizing the surface roughness in machining titaniu... more The use of response surface methodology for minimizing the surface roughness in machining titanium alloy, a topic of current interest, has been discussed in this article. The surface roughness model has been developed in terms of cutting parameters such as cutting speed, feed, and depth of cut. Machining tests have been carried out using CVD (TiN-TiCN-Al2O3-TiN) coated carbide insert under different cutting conditions using Taguchi's orthogonal array. The experimental results have been investigated using analysis of variance (ANOVA). The results indicated that the feed rate is the main influencing factor on surface roughness. Surface roughness increased with increasing feed rate, but decreased with increasing cutting speed and depth of cut. The predicted results are fairly close to experimental values and hence, the developed models can be used for prediction satisfactorily.
http://www.tandfonline.com/doi/abs/10.1080/10426910701774700#.UdZ2pqyTX1U
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Malaysian Journal of Microscopy, 2011
In this research, (X)PZT-(1-X)PMN ceramics (where X is 0.25, 0.5 and 0.75) were achieved from a c... more In this research, (X)PZT-(1-X)PMN ceramics (where X is 0.25, 0.5 and 0.75) were achieved from a conventional mixed-oxide method. Lead Zirconate titanate (PZT) powders with composition near the morphotropic phase boundary have been synthesized via a microemulsion processing route. Modified mixed oxides method was used for obtaining single phase Lead Magnesium niobate (PMN) powder with high relative density (98% of T.D.) and good electrical properties (dielectric constant of ≈10 4 at room temperature). Two-step sintering (TSS) has been applied to suppress the accelerated grain growth of PZT-PMN composite compacts in the last sintering stage. The produced samples with high PZT content showed low densities due to the low compaction ratio of PZT powder. The dielectric properties of PZT-rich and PMN-rich materials were high (dielectric constant of about 0.7×10 3 and 1×10 3 was measured for PZT-rich and PMN-rich ceramics, respectively) while the other sample exhibited lower dielectric properties. The X-ray diffraction analysis of the sintered samples indicated that PZT-PMN ceramic was produced successfully with traces of pyrochlore phase formed in the structure.
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Trends in Biomaterials and Artificial Organs, 2009
Strontium doped hydroxyapatite (Sr-doped HA) nanopowder has been synthesized using a sol-gel meth... more Strontium doped hydroxyapatite (Sr-doped HA) nanopowder has been synthesized using a sol-gel method. The concentration of strontium was varied at 2, 5, 10 and 15 mol%. The as synthesized powders were calcined at temperatures of 500-900°C. The calcined white Sr-doped HA powders were characterized using differential and thermogravimetric analysis (TG/DTA), field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Morphological evaluation by FESEM measurement shows that the particles of the Sr-doped HA agglomerates are globular in shape with an average size of 1-2 mm in diameter while the primary particles have a diameter of 30-150 nm in average. The calcined powders contained hydroxyapatite phase only for all doping concentration except for the smallest doping concentration, 2 mol%, where â-TCP appeared as the secondary phase. This indicates that the substitution of Sr atoms for Ca atoms have stabilized the HA phase, leading to the inhibition of the appearance of â-TCP phase upon high temperature calcination. Even, for 2 mol% Sr-doped HA, the appearance of â-TCP peak only started to appear at a temperature as high as of 900°C, compared to non-Sr doping HA which appeared at a temperature below 800°C.
medind.nic.in/taa/t09/i2/taat09i2p105.pdf
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Materials Science Forum, 2011
The nanocrystalline HA powders were produced through sol-gel method which employed calcium nitrat... more The nanocrystalline HA powders were produced through sol-gel method which employed calcium nitrate tetrahydrate [Ca(NO3)2.4H2O] and diammonium hydrogen phosphate [(NH4)2HPO4] as calcium and phosphorous precursors. Sodium ion (Na+) is one of the trace elements found in biological apatite and believed to have important effect in its performance. The concentrations of sodium dopant were varied from 0 mol% until 15 mol% by using sodium nitrate (NaNO3) as the source of dopant. Characterization of nanopowders was investigated by using X-ray diffraction (XRD), Fourier transform infra red (FTIR) and Transmission Electron Microscope (TEM). XRD analysis revealed that there are no other phases exist in the synthesized powder, evinced single phase of HA and a trend shows an increase of cristallinity with increase of sodium dopant concentration. While the TEM images showed evidence that the particle sizes were bigger with the increasing sodium concentration, showing the effect of sodium dopant on the densification of the powder.
http://www.scientific.net/MSF.694.128
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Journal of Materials Science, 1996
The sintering behaviour of Y-TZP ceramics, their resulting microstructures and properties are inf... more The sintering behaviour of Y-TZP ceramics, their resulting microstructures and properties are influenced not only by the characteristics of the raw materials but also were found to be dependent on the thermal history during the fabrication process. It is generally understood that fracture toughness increases as grain size increases up to a certain limit but in the present investigation, the results obtained challenge this view. The work is concerned with grain size dependence on the mechanical properties, in particular on the fracture toughness. Two commercially available powders based on two different processing techniques (i.e. coated and co-precipitated) were studied. It has been found that both materials exhibited different fracture toughness trends. Smaller grains of coated Y-TZP resulted in high fracture toughness > 12 MPa m1/2 while the opposite effect was seen in the co-precipitated material which showed enhanced fracture toughness with increasing grain size above a certain lower limit from a nonconventional heat treatment.
http://link.springer.com/article/10.1007%2FBF01152158
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Ceramics International, 2013
In the present work, the sintering behaviour of HA particles prepared via the wet precipitation m... more In the present work, the sintering behaviour of HA particles prepared via the wet precipitation method (HAp) and wet mechanochemical technique (HAwm) was investigated. The sintering behaviour of a commercial HA powder (HAc) was also studied for comparison purpose. All the three powders were characterised in terms of particle size, Ca/P ratio and crystal size. Green samples were prepared and sintered in air at temperatures ranging from 1000 degrees C to 1400 degrees C. The sintered bodies were studied in terms of the phase stability, relative density, Young's modulus, Vickers hardness, fracture toughness and grain size. The results indicated that HAwm samples suffered phase decomposition while the HAp and HAc sintered samples showed no phase disruption throughout the temperature range employed. The HAp samples exhibited the overall best densification and properties when compared to the HAc and HAwm samples. Furthermore, the results showed that mechanical properties of sintered samples were governed by both the bulk density and the grain size.
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International Conference on Advances in Materials and Processing Technologies, AMPT 2009, 2011
In the present work, densification of synthesised hydroxyapatite (HA) bioceramic prepared via che... more 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.
http://www.scientific.net/AMR.264-265.1856
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4th Kuala Lumpur International Conference on Biomedical Engineering 2008, Biomed 2008, 2008
The effects of doping small amounts of TiO2 up to 5 wt% on the sintering behaviour of alumina (Al... more The effects of doping small amounts of TiO2 up to 5 wt% on the sintering behaviour of alumina (Al2O3) was studied. Green samples were prepared and pressureless sintered in air at temperatures ranging from 1250°C to 1600°C, at a furnace ramp rate of 10°C/min. and soaking time of 2 hours. Sintered samples were characterized to determine bulk density, hardness and Young's modulus. It has been found that all the doped samples exhibited higher bulk density than the undoped samples. The bulk density increases with increasing temperature and attained a maximum value of 3.9 Mgm-3 for samples doped with 1.0 wt% TiO2 at 1450°C. The addition of 1 wt% TiO2 when sintered at 1450°C was found to be the most beneficial throughout the studied range as the samples exhibited the highest Young's modulus of 381 GPa and Vickers hardness of 16.5 GPa as compared to 256.7 GPa and 11.2 GPa for the undoped alumina. Titanium oxide doping is one economical way of improving the densification of Al2O3 without affecting mechanical properties.
http://link.springer.com/chapter/10.1007/978-3-540-69139-6_89
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Journal of Materials Science, 2000
The sintering behaviour of alumina-Y-TZP composites prepared by slip-casting technique were studi... more The sintering behaviour of alumina-Y-TZP composites prepared by slip-casting technique were studied. Slip-cast samples containing varying amounts of Y-TZP ranging up to 90 vol% were prepared and evaluated. Sintering studies were carried out at 1450 degrees C to 1600 degrees C. Sintered samples were characterised where appropriate to determine phases present, grain sizes, bulk density and mechanical properties. Good correlation was obtained between the calculated prepared powder density and experimental results. The sintered bulk density of the composites was observed to increase with increasing Y-TZP content and sintering temperature up to 1550 degrees C. Maximum hardness values (> 14 GPa) were obtained for all samples containing < 60 vol% Y-TZP and when sintered at 1550 degrees C. It has been found that the additions of up to 50 vol% Y-TZP was effective in suppressing Al2O3 grain growth.
http://link.springer.com/content/pdf/10.1023%2FA%3A1004837516291.pdf
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