ICMCTF2007 Session TS3P: TS4 Poster Session
Thursday, April 26, 2007 5:00 PM in Room Town & Country
Thursday Afternoon
Time Period ThP Sessions | Topic TS3 Sessions | Time Periods | Topics | ICMCTF2007 Schedule
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TS3P-1 Corrosion and Electrical Properties of Multi-layered Coatings on Stainless Steel for PEMFC Bipolar Plate Applications
W.-Y. Ho, C.-L. Chang (Mingdao University, Taiwan) Hard coatings play a continuously increasing role for protective applications in the field of wear and corrosion resistance. Specially, corrosion resistance, as well as electrical conductivity of coatings, is also interesting to potential applications for the metallic bipolar plates of PEMFC. In this study, multilayered coatings were designed to improve the properties of stainless steels in terms of corrosion and electrical conductivity. Many different nitrides, including TiN, CrN and even multi-layered TiN/CrN, CrN/Ti have been successfully deposited by cathodic arc deposition technique. The benefits of multi-layered coatings were attributed to inhibit the pinhole formation in the coatings and to the more noble behavior of CrN, as compared to that of TiN. When analyzing the polarization curves, all the coated samples present a better corrosion resistance with respect to the bare stainless steel substrate. The CrN/Ti multi-layered coatings provided the best corrosion resistance for coated stainless steels subjected to polarization and immersion test in 10 Vol.% H2SO4 solution. Additionally, CrN/Ti multi-layered coating exhibited better electrical conductivity as compared to TiN/CrN coating. Thus, as regards the coating with the higher corrosion and lower electrical resistance, the best candidates for PEMFC bipolar plate application are the CrN/Ti multi-layered coatings presented in this study. |
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TS3P-2 Effect of Calcium Phosphate and Serum Proteins on in Vitro Corrosion of Magnesium Alloys in Phosphate Buffer Saline Solution
C.L. Liu (City University of Hong Kong); Y. Xin (Tsinghua University); X. Tian (Harbin Institute of Technology); P.K. Chu (City University of Hong Kong) Development of new casting techniques has spurred research of degradable metal implants in prosthetic surgery. In the present study, the degradation susceptibility of AZ91 and ZK60 samples are measured in a phosphate buffer saline solution (PBS) in the presence of calcium phosphate and serum proteins at physiological temperature of 37±1°C. The magnesium alloys are subjected to immersion tests and electrochemical corrosion tests. Weight loss kinetic curves are measured and the surface analysis is performed by SEM with EDS. Our results reveal that deposition of the calcium phosphate layer on the surface of the magnesium alloys changes both the corrosion rate and corrosion resistance at open circuit potential (OCP). Addition of BSA also plays an important role in the corrosion behavior of the magnesium alloys in PBS, and it is mainly caused by adsorption and chelation effects between the BSA and sample surface. Addition of fibrinogen shows a similar but less pronounced effect than BSA. |
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TS3P-3 Deposition of Multiwalled Carbon Nanotubes from Solution
E. Widenkvist, J. Li, U. Jansson, H. Grennberg (Uppsala University, Sweden) Materials based on nanotubes may have potential applications in several different fields, such as field emitters, memory elements, sensors, actuators, hydrogen storage etc. In many suggested applications, in addition to the requirement of having carbon nanotubes with known chemical properties, it may be necessary to develop methods and techniques to control the lateral distribution of nanotubes onto different surfaces. We have developed a simple method for direct deposition of multiwalled carbon nanotubes (MWNTs) onto surfaces. The MWNTs are made soluble in a solution by microwave-assisted covalent sidewall functionalization. This method makes it possible to obtain nanotubes with a large number of different functional groups1. The nanotubes can then be adsorbed on different substrate areas directly from solution by a simple dipping procedure. This opens up the possibility to target adsorption of MWNT to specific surfaces by modifying the choice of functional groups attached to the nanotubes. We have studied the adsorption of MWNTs functionalized with octadecyl ester groups to silicon surfaces as well as silicon oxide surfaces. The results indicate a surface-dependent selectivity, with the MWNTs preferring hydrogen terminated silicon surfaces to silicon oxide surfaces. The potential of this method to obtain various selective structures will be discussed. Also the synthesis of nanocomposites by combination of a solution-based dipping technique and thin film deposition from a gas phase will be demonstrated. 1J. Li, H. Grennberg, Chem. Eur. J. 2006, 12, 3869-2875. |
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TS3P-4 Antimicrobial Efficacy of Photocatalytic TiO2 Coatings Prepared by Arc Ion Plating
C.J. Chung (Feng Chia University and Central Taiwan University of Science and Technology, Taiwan); H.I. Lin, J.L. He (Feng Chia University, Taiwan) TiO2 has been developed and applied extensively in form of coatings, in particular for its unique properties such as high photocatalytic activity, strong self-cleaning ability and non-toxicity. These coatings, which can be prepared via various processes have however not been proved yet to be antimicrobial. The research involves an arc ion plating method to produce TiO2 films on medical grade AISI 304 stainless steel. Antimicrobial efficacy is expected by proper control of coating parameters. Photocatalytic performance of the deposited specimens is tested with methylene blue solution, and antimicrobial efficacy is evaluated through the use of JIS Z2801:2000 industrial standard for better understanding the relation between photocatalytic effect and antimicrobial efficacy. The experimental result shows that columnar TiO2 film with an anatase phase structure can be prepared successfully within a proper coating parameter range. By increasing deposition time, the film initially consist of mainly rutile phase followed by anatase phase at later stage. Over a thickness of 2.5µm, photocatalytic efficiency of the deposited film presents the largest value, at the same time the antimicrobial activity (R) reaches the maximum value of 3.1. In addition to this, oxygen partial pressure as the coating parameter, favors the film crystallinity and anatase phase formation. As a result, its photocatalytic efficiency of the deposited film reaches maximum as well as antimicrobial activity of the deposited film progressively reaches the maximum value of 3.1 when oxygen partial pressure is increased. Photocatalytic efficiency and antimicrobial activity of deposited TiO2 film are thus dominantly determined by the presence of anatase phase. |
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TS3P-5 Enhancing Bioactivity and Corrosion Resistance of NiTi using Plasma Immersion Ion Implantation
Y.L. Chan (The University of Hong Kong); S.L. Wu, X.M. Liu (City University of Hong Kong); K.W.K. Yeung, W.W. Lu, A.H.W. Ngan, K.D.K. Luk (The University of Hong Kong); P.K. Chu (City University of Hong Kong); K.M.C. Cheung (The University of Hong Kong) Nickel Titanium (NiTi) alloy is a unique material displaying shape memory effect and superelastic property which makes it attractive to the orthopedics field. With its high nickel content of ~50%, there is concern on the safety use of this material for a long period of time inside the human body since, theoretically, NiTi alloy may release harmful nickel ions into the body due to corrosion under physiologic environment. Previous investigation had demonstrated that plasma immersion ion implantation (PIII) of oxygen into the surface could build up an oxide layer which increases the corrosion resistance of this shape memory alloy. In the present work, further implantation of sodium ions into this modified surface was aimed at enhancing its bioactivity. X-ray photoelectron spectroscopy (XPS) was used to investigate into the chemical composition of the modified surface. Simulated body fluid (SBF) immersion for 21 days proved that the implantation of sodium successfully enhanced the accumulation of calcium/phosphorus rich deposits on the modified surface. Anodic polarization scan proved that the sodium ion implantation did not affect the corrosion resistance of the oxygen implanted surface. Three point bending test revealed a change in mechanical property after PIII. However, superelasticity was still observed in the ion implanted NiTi. Differential scanning calorimetry (DSC)observed a change in the transition temperature of the substrate which likely attributes to the change in mechanical property. In conclusion, the PIII of oxygen and sodium ions into NiTi had enhanced its biaoctivity and corrosion resistance but at the same time induced changes in the mechanical property of this material. |
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TS3P-6 Preparation and Characterization of 1-D SnO2 Nanostuctures
C.-C. Kuo (National Tsing Hua University, Taiwan); J.-M. Wu, Y.-R. Lin, S.-Y. Tsai (Photovoltaics Technology Center, Taiwan); H.-C. Shih (National Tsing Hua University, Taiwan) High density and large quantity SnO2 nanostuctures were prepared by the thermal evaporation technique. The beak-like SnO2 nanorods were also successfully synthesized under different experimental parameters. The sources of these nanostructures were made from pure fine tin powder (99.95%) and pure oxygen under 1 Torr and 10 Torr argon flows at temperature in the range of 950-1000°C on silicon (100) and alumina oxide substrates. The semiconductive SnO2 nanowires showed a single crystalline rutile tetragonal structure. The morphology and microstructure were characterized by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selective area diffraction (SAD) and X-ray diffractometer (XRD). The morphology of beak-like nanorods are the thin nanowhiskers (the width of diameter is 40nm) growth on the rectangular cross-section nanorods (the width of diameter is 300nm). The angle between nanorods and thin nanowhiskers is ~ 120°-150°, and they may have potentials applying to the field emission property owing to this specific morphology. |
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TS3P-7 Size Effect of Tin Oxide Nanoparticles for High Capacity Lithium Battery Anode Materials
Y.-C. Chen (National Tsing Hua University, Taiwan); J.M. Chen, Y.-H. Huang, Y.-R. Lin (Industrial Technology Research Institute, Taiwan); H.-C. Shih (National Tsing Hua University, Taiwan) Tin oxide anode materials show high reversible capacity for secondary lithium batteries. However, the volume expansion of tin oxide will decrease the battery cycle life. In order to solve the expansion of tin oxide, the nanocomposite anode materials are synthesized. The nanocomposite anode materials are developed by sol-gel method. The nanocomposite materials(SnO2/C) show a kind of core-shell structure. The core material is the natural graphite(~10µm) and the shell is the nano tin oxide. The morphology and the nanostructure were characterized by JSM-6500F and the electrochemical tests were analyzed by Arbin BT2400. The tin oxide nanoparticles were smaller than 20nm and uniformly dispersed on the surface of the nature graphite. The tin oxide nanoparticles improved the cyclablility significantly relative to the bulk tin oxide particles. It is believed that the tin oxide nanoparticles decrease the effect of the volume expansion. The volume expansion of the tin oxide anode materials were suppressed by the nanocomposite structure(SnO2/C). |
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TS3P-8 Synthesis and Characterization of ZnO:Al Nanostructures on Silicon Substrates by Thermal Evaporation
C.-C. Lin (National Tsing Hua University, Taiwan); J.-M. Wu, Y.-R. Lin, S.-Y. Tsai (Photovoltaics Technology Center, Taiwan); H.-C. Shih (National Tsing Hua University, Taiwan) This work involves the formation and characterization of ZnO:Al nanostructures on the Al sputter-deposited Si (100) substrates by thermal evaporation. Aluminum thin film (~80nm) was first deposited on the silicon (100) by dc sputtering, and then followed by the growth of ZnO nanowires by the thermal evaporation. The condensed zinc vapor deposited on the aluminum film forms Al/Zn alloy, and the final structure of ZnO:Al was established when oxygen was admitted into the furnace. An oxidizing environment (1 Torr) was provided for pure zinc (99.9%) powder at 500°C-700°C. The results showed that highly symmetrical multipods and tetrapods of the ZnO:Al were formed on the Si substrates, which may have resulted from a vapor-liquid-solid mechanism. Typical widths of the nanostructures were about 30-100 nm and the lengths were up to 1 µm. The optical properties of the ZnO:Al was also compared with pure ZnO nanostructures in termsof the photoluminescence, cathodoluminescence, and the electron field emission characteristics. |
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TS3P-9 Capacitance-Voltage Characteristics of MOS Capacitors with Ge Nanocrystals Embedded in ZrO2 Gate Material
H.R. Lee (Korea Universtiy, Korea); S.J. Choi (Samsung Electronics Co., Korea); K. Cho (Korea University, Korea); S.S. Kim (Korea University) Capacitance versus voltage (C-V) curves of Ge-nanocrystal(NC)-embedded MOS capacitors are characterized in this work. Ge nanocrystals (NCs) were formed in a 20-nm thick gate ZrO2 layer by ion implantation and subsequent annealing procedures; after 74Ge+ ions at 15 keV with a dose of 1 x 10 16cm-2 were implanted into the gate layer at room temperature, the implanted layer was annealed at 800°C. High-resolution transmission electron microscopy and energy dispersive spectroscopy reveal the formation of the Ge NCs in a ZrO2 layer. Also, the C-V curves obtained for the MOS capacitors embedded with Ge NCs exhibit large flat-band voltage shifts, which indicate the presence of charge storages in the Ge NCs. Their hysteresis characteristics are greatly dependent on the voltage sweep range. The memory windows obtained from the Ge-NC-embedded MOS capacitors are larger than those from MOS capacitors without Ge NCs. The clockwise hysteresis observed from the C-V curves imply that electrons are trapped in a floating gate layer consisting of the Ge NCs present in a ZrO2 layer. |
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TS3P-10 Corrosion Resistance and Biocompatibility of ZrO2/HA Coating on Titanium by Electrochemical Method
H.C. Hsu (Central Taiwan University Science and Techology, Taiwan); J.S. Yang, F.T. Lin (Central Taiwan University of Science and Technology, Taiwan); W.F. Ho (Da-Yeh University, Taiwan); S.C. Wu (Central Taiwan University of Science and Technology, Taiwan) Titanium and its alloys widely use in medical and dental application. They have many excellent properties, include strength, corrosion resistance, and biocompatility. However, it is difficult to form a bond between living bone. Hydroxyapatite is a bioactive and osteoconductive material. There is an interest in producing and shortening the process toward osseointegration. The main objective of this study was to deposit ZrO2/HA coating on titanium by electrochemical method. Titanium was conducted in ZrO(NO3)2 solution and subsequent in a mixing solution of Ca(NO3)2 4H2O and (NH4)3PO4 3H2O. Deposition of HA/ZrO2 coating on titanium substrates were investigated by XRD, SEM/EDS, and polarization tests. Plate-like hydroxyapatite coating was found on Ti substrates by electrochemical deposition method. XRD indicated that HA, TiO2, and Ti peaks were detected. The polarization test in artificial saliva revealed that HA/ZrO2 coating on Ti exhibited a reduced current density, confirming the better corrosion resistance. The cell growth over the HA/ZrO2 coating showed better adhesion, spreading, and elongation. |
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TS3P-11 Synthesis of Segmented YSZ/Ni Nanofibers for Advanced Catalysis Application
D-Y. Wang, C.-C. Chu (Mingdao University, Taiwan) For a typical solid oxide fuel cell (SOFC), the unit cell PEN is composed of a YSZ/Ni anode, a YSZ electrolyte, and an LSM cathode. The microstructure of both electrodes needs to be designed to allow sufficient porosity for mass transfer for fuel and product gases within the fuel cell stack. In the mean time, the catalysts have to be distributed in an economic and homogeneous way on the convoluted electrode surfaces to support a sustainable electrochemical reaction in the triple-phase boundaries. The reaction kinetics depends on the distribution and the total number of those catalyst-based triple-phase boundaries. It is challenging to quantify the reaction kinetics based on such randomly distributed catalyst particles. In this research, a novel design of the YSZ/Ni SOFC anode, where the triple phase boundaries were created precisely in form of a large amount of junction rings on a bunch of tangled and segmented nanofibers of YSZ and Ni. The total reaction sites can be calculated according to the density, fiber diameter, and fiber length of the nanofibers and the number of segments of each fiber. The synthesis process takes advantage of the Anodic Aluminum Oxide (AAO) membrane as the template to assist the sequential growth of YSZ/NiO segmented nanofibers. The pore size of the AAO template is controlled within approximately 50-100nm, which provides the regulated fiber growth within the channels by CVD methods. After the removal of the AAO template by wet process, an effective anode electrode of high surface area with controllable catalysis reaction kinetics can be achieved. The influence of the process parameters on the overall SOFC efficiency will be analyzed. |
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TS3P-12 The Effect of Various Composed of SiO2 and HfO2 Thin Films on the Memory Properties of MOS Capacitors with Embedded Ni Nanocrystals.
F.-Y. Jian (National of Sun Yat-Sen University, Taiwan); T.-C. Chang (National Sun Yat-Sen University, Taiwan); P.-T. Liu (National Chiao Tung University, Taiwan); P.H. Yeh (National Tsing Hua University, Taiwan); M.-N. Tsai (National of Sun Yat-Sen University, Taiwan); C.-M. Chang (UMC (United Microelectronic Corporation) Device Department, Taiwan) Nonvolatile memory structures with Ni nanocrystals embedded in SiO2/ SiO2, HfO2/ HfO2-SiO2, and HfO2/SiO2 as blocking/tunnel layer have been characterized by capacitance voltage measurement. Our investigations demonstrated that using HfO2 as blocking layer and SiO2 as tunneling layer have given better program and erase efficiency. This result is due to the fact that electric field is mostly applied on the low k-value material, which is the SiO2 tunnel oxide. We also observed that the retention loss very quickly after program or erase. A frequency-dependent escape model is proposed to describe the retention of metal nanocrystals based memory. By our estimation, the electron would have high frequency to collide with the barriers. |