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C.H. Ting,S. Ramesh,C.Y. Tan,N.I. Zainal Abidin,W.D. Teng,I. Urriés,L.T. Bang 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.8
In the present work, the effect of low temperature sintering, focusing on varying the sintering holding times on the mechanicalproperties, microstructure and low temperature degradation behavior of undoped and MnO2-doped Y-TZP ceramics wereinvestigated. Green samples were sintered at temperatures ranging from 1100 to 1250 oC at varying holding times rangingfrom 12 min. to 480 min. The sintered bodies were characterized in terms of bulk density, Vickers hardness, fracturetoughness, phase stability and grain size. The results indicated that the relative density of above 95%, Vickers hardness of 14GPa and fracture toughness of 5 MPam1/2 were obtained when sintered at lower sintering temperature (below 1250 oC) andlonger sintering times for MnO2-doped Y-TZP samples. Grain growth was marginal and the average grain size of all samplesranged between 0.14 and 0.28 µm. The results indicated that the grain growth kinetics was influenced mainly by the sinteringtemperature and not by the sintering holding time. The addition of MnO2 was found to be beneficial in enhancing densificationand mechanical properties of Y-TZP particularly at low sintering temperature of 1100 oC and low holding time of 12 min. Thelow-temperature degradation experiment conducted in superheated steam indicated that all the samples did not transformedto the monoclinic symmetry, attributed mainly to the lower grain size sintered at relatively low sintering temperatures
S.M. Kwa,S. Ramesh,L.T. Bang,Y.H. Wong,W.J. Kelvin Chew,C.Y. Tan,J. Purbolaksono,H. Misran,W.D. Teng 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.2
The sintering of yttria-tetragonal zirconia polycrystals (Y-TZP) is commonly carried at a predefined temperature using a long holding time of 2 hours. This often has resulted in grain coarsening which affects the mechanical properties of the sintered body and low temperature degradation (LTD) behaviour of the ceramic when exposed to moist environment. In this research, the effect of using a short holding time of 1 min. during sintering coupled with small amounts (0.5 and 1 wt%) of manganese oxide, MnO2 as dopant on the mechanical properties and LTD behaviour of 3 mol% Y-TZP were investigated. The results showed that the mechanical properties improved significantly with the addition of 0.5 wt% MnO2 for the 1-min. and 12-min. holding time samples when compared to 2 hours holding time sintered at the same temperature of 1350 ℃. Nevertheless, regardless of the holding time employed, the 1 wt% MnO2 addition was not effective in improving the mechanical properties and ageing resistance of Y-TZP ceramic.
Han, C.,Udalski, A.,Choi, J.-Y.,Yee, J. C.,Gould, A.,Christie, G.,Tan, T.-G.,Szymań,ski, M. K.,Kubiak, M.,Soszyń,ski, I.,Pietrzyń,ski, G.,Poleski, R.,Ulaczyk, K.,Pietrukowicz, P.,Kozłow IOP Publishing 2013 ASTROPHYSICAL JOURNAL LETTERS - Vol.762 No.2
<P>We report the discovery of a planetary system from observation of the high-magnification microlensing event OGLE-2012-BLG-0026. The lensing light curve exhibits a complex central perturbation with multiple features. We find that the perturbation was produced by two planets located near the Einstein ring of the planet host star. We identify four possible solutions resulting from the well-known close/wide degeneracy. By measuring both the lens parallax and the Einstein radius, we estimate the physical parameters of the planetary system. According to the best-fit model, the two planet masses are similar to 0.11 M-J and 0.68 M-J and they are orbiting a G-type main-sequence star with a mass similar to 0.82 M-circle dot. The projected separations of the individual planets are beyond the snow line in all four solutions, being similar to 3.8 AU and 4.6 AU in the best-fit solution. The deprojected separations are both individually larger and possibly reversed in order. This is the second multi-planet system with both planets beyond the snow line discovered by microlensing. This is the only such system (other than the solar system) with measured planet masses without sin i degeneracy. The planetary system is located at a distance 4.1 kpc from the Earth toward the Galactic center. It is very likely that extra light from stars other than the lensed star comes from the lens itself. If this is correct, it will be possible to obtain detailed information about the planet host star from follow-up observation.</P>
Properties of hydroxyapatite synthesize by wet chemical method
S. Ramesh,S. Adzila,C.K.L. Jeffrey,C.Y. Tan,J. Purbolaksono,A.M. Noor,M.A. Hassan,I. Sopyan,W.D. Teng 한양대학교 세라믹연구소 2013 Journal of Ceramic Processing Research Vol.14 No.4
The sintering behavior of a commercial HA and synthesized HA was investigated over the temperature range of 700 o C to 1400 o C in terms of phase stability, bulk density, Young’s modulus and Vickers hardness. In the present research, a wet chemical precipitation reaction was successfully employed to synthesize a submicron, highly crystalline, high purity and single phase stoichiometric HA powder that is highly sinteractive particularly at low temperature regimes below 1100 o C. It has been revealed that the sinterability of the synthesized HA was significantly greater than that of the commercial HA. The temperature for the onset of sintering and the temperature required to achieve densities above 98% of theoretical value were approximately 150 o C lower for the synthesized HA than the equivalent commercial HA. Nevertheless, decomposition of HA phase upon sintering was not observed in the present work for both powders.
Crack-tip constraint analysis of SENB specimen under creep condition
G. C. Jiao,W. Z. Wang,S. J. Tan,C. Yu,Y. Z. Liu 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2
A higher-order asymptotic C(t)-A2(t)-M approach was used to investigate the crack-tip stress of single edge notched bend (SENB)specimen in a power-law creeping material under plane strain conditions. Comprehensive calculations were made of SENB specimenwith a/W = 0.59 by using higher-order asymptotic C(t)-A2(t)-M approach, higher-order asymptotic C(t)-A2(t) approach and finite elementanalysis; the latter two methods were used to check the constraint significance and the calculation accuracy of C(t)-A2(t)-M approach,respectively. The results show that the stress components qq s obtained from the higher-order asymptotic C(t)-A2(t)-M solution agreedwell with that of finite element analysis, however, which gradually deviated from the results of C(t)-A2(t) approach as the distance faraway from the crack tip for small-scale creep stage.
Tan, X.P.,Liu, J.L.,Jin, T.,Hu, Z.Q.,Hong, H.U.,Choi, B.G.,Kim, I.S.,Jo, C.Y.,Mangelinck, D. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.580 No.-
The creep deformation of three single crystal Ni-based superalloys with various Ru contents has been investigated to clarify the effect of Ru additions at very high temperatures and low stresses conditions. The creep properties were significantly improved by Ru additions under the conditions of 1150<SUP>o</SUP>C/100MPa and 1180<SUP>o</SUP>C/70MPa. It is noted that obvious γ' phase dissolution occurs during the entire creep deformation at very high temperatures. It differs from the typical high-temperature creep curves that a short incubation period occurs before the primary creep stage during the creep deformation at very high temperatures. Ru additions are able to produce denser interfacial dislocation networks and improve the stability and homogeneous configuration of interfacial dislocations; and promote the high-temperature stability of γ' phase and formation of perfect γ' rafting. It is thus shown that Ru additions reduce the minimum creep rate, and prolong the secondary creep stage accordingly. The topological inversion of γ/γ' microstructure did not occur under both conditions. The origin of the rapid increase of creep rate is closely relevant to the unstable propagation of micro-cracks in the vicinity of porosity in necked regions.
C.K. Ng,S. Ramesh,C.Y. Tan,C.Y. Ching,N. Lwin,A. Muchtar 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.5
In the present work, the effect of manganese oxide (MnO2) additions (0, 0.5, 1 and 5 wt%) on the properties of ceria-dopedscandia stabilized zirconia (10Sc1CeSZ) was investigated over the temperature range of 1400 oC to 1550 oC. The results showedthat the addition up to 1 wt% had negligible effect on the mechanical properties of the ceramic. The samples containing upto 1 wt% MnO2 attained above 97.5% relative density, Vickers hardness of 13-14 GPa and fracture toughness of about3 MPam1/2. In addition, it was revealed that the 0.5 wt% MnO2 addition was beneficial in suppressing the cubic zirconia graingrowth i.e. the highest average grain size was measured at 4.9 µm when sintered at 1550 oC as compared to 9.9 µm measuredfor the undoped zirconia when sintered at the same temperature. On the other hand, the addition of 5 wt% MnO2 was foundto be detrimental to the densification and properties of the zirconia, particularly when sintered at higher temperatures. Thiswas attributed to the accelerated grain growth of the doped samples, i.e. the grain size increased by 2 fold, to 18.6 µm whensintered at 1550 oC.
Tan, X.P.,Liu, J.L.,Jin, T.,Hu, Z.Q.,Hong, H.U.,Choi, B.G.,Kim, I.S.,Jo, C.Y. Elsevier Sequoia 2011 Materials science & engineering. properties, micro Vol.528 No.29
The addition of 3wt% ruthenium (Ru) has been found to improve the creep rupture lives of a single crystal Ni-based superalloy under both conditions of 1100<SUP>o</SUP>C/150MPa and 1000<SUP>o</SUP>C/310MPa. Creep curve analysis indicates that the creep mechanisms are different from each condition. The improvement of creep rupture lives by 3wt% Ru addition is discussed not only from the view of dislocation movement but also the γ' phase evolution. The change of γ/γ' lattice misfit in the initial microstructure is believed to be the key role of Ru on the high-temperature creep deformation. The larger negative lattice misfit caused by an addition of 3wt% Ru induces smaller and more regular γ' particles in the initial state, as well as denser dislocation networks at the γ/γ' interface during creep. These two aspects are crucial to the high-temperature creep rupture life. In addition, a little topologically close-packed (TCP) phases are observed after creep rupture in the two experimental alloys.
Chang, Y.T.,Coombs, G.,Ling, T.,Balaji, V.,Rodrigues, C.,Mikamo, H.,Kim, M.J.,Rajasekaram, D.G.,Mendoza, M.,Tan, T.Y.,Kiratisin, P.,Ni, Y.,Barry, W.,Xu, Y.,Chen, Y.H.,Hsueh, P.R. Elsevier Science Publishers ; Elsevier Science Pub 2017 International Journal of Antimicrobial Agents Vol.49 No.6
This study was conducted to investigate the epidemiology and antimicrobial susceptibility patterns of Gram-negative bacilli (GNB) isolated from intra-abdominal infections (IAIs) in the Asia-Pacific region (APR) from 2010-2013. A total of 17 350 isolates were collected from 54 centres in 13 countries in the APR. The three most commonly isolated GNB were Escherichia coli (46.1%), Klebsiella pneumoniae (19.3%) and Pseudomonas aeruginosa (9.8%). Overall, the rates of extended-spectrum β-lactamase (ESBL)-producing E. coli and K. pneumoniae were 38.2% and 24.3%, respectively, and they were highest in China (66.6% and 38.7%, respectively), Thailand (49.8% and 36.5%, respectively) and Vietnam (47.9% and 30.4%, respectively). During 2010-2013, the rates of ESBL-producing E. coli and K. pneumoniae isolates causing community-associated (CA) IAIs (collected <48@?h after admission) were 26.0% and 13.5%, respectively, and those causing hospital-associated (HA) IAIs were 48.0% and 30.6%, respectively. Amikacin, ertapenem and imipenem were the most effective agents against ESBL-producing isolates. Piperacillin/tazobactam displayed good in vitro activity (91.4%) against CA ESBL-producing E. coli. For other commonly isolated Enterobacteriaceae, fluoroquinolones, cefepime and carbapenems exhibited better in vitro activities than third-generation cephalosporins. Amikacin possessed high in vitro activity against all GNB isolates (>80%) causing IAIs, except for Acinetobacter calcoaceticus-baumannii (ACB) complex (30.9% for HA-IAI isolates). All of the antimicrobial agents tested exhibited <45% in vitro activity against ACB complex. Antimicrobial resistance is a persistent threat in the APR and continuous monitoring of evolutionary trends in the susceptibility patterns of GNB causing IAIs in this region is mandatory.