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Progress in Improvement Methods of Carbon Nanotube/Metal Contact
CHEN Chang-Xin, JIN Tie-Ning, ZHANG Ya-Fei
2012 Vol. 27 (5): 449457
Abstract(
3736 )
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Owing to its unique structure and excellent properties, carbon nanotube (CNT) has been widely used to construct various nanodevices. The contact between CNTs and metal electrodes plays a key role in CNT-based devices and directly influences device performance. Therefore, the improvement of the CNT/electrode contact is an important aspect in the study of CNT devices. In this paper, recent research progress on the improvement methods of the CNT/metal contact is reviewed. Typical contact optimization methods and their principles and processes are introduced. The resulting contact characteristics and device performances by applying these improvement methods are also discussed. On this basis, the features of these different improvement methods are compared.
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CO Sensing Properties of TiO2 Based on the p-n Transition Induced by Carbon Monoxide at High Temperatures
ZHANG Jian-Wei, SUN Fang-Jie, LI Xiao-Gan, YU Jun, WANG Jing, YAN Wei-Ping, TANG Zhen-An
2012 Vol. 27 (5): 458462
Abstract(
2575 )
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Rutile TiO2 based semiconductor-type sensors were investigated for sensing CO within the temperature range from 600℃ to 800℃. The sensor showed p-type behavior to CO (20-2000 mg/m3) when tested in oxygen concentrations varied from 10% to 2% between 600℃ and 700℃. The response of the sensor decreased significantly as the temperature increased from 600℃ to 700℃ approaching to one. However, when the temperature was above 750℃, an n-type behavior of the sensor to CO was observed. This n-type response further increased when the temperature increased to 800℃. AC impedance was employed to study the conduction behaviors of the TiO2 thick film in both varied oxygen concentrations and CO environment at 800℃. The results indicate that the change of the oxygen ion/vacancy concentrations in the bulk TiO2 is probably the reason for the p-n conduction transition induced by CO.
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Structure and Electrochemical Characteristics of Ti-V-based Solid Solution/AB5-type La-Mg-based Alloy Composite Hydrogen Storage Material
WANG Yan-Zhi, ZHAO Min-Shou
2012 Vol. 27 (5): 463468
Abstract(
2942 )
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Composite hydrogen storage alloy Ti0.10Zr0.15V0.35Cr0.10Ni0.30 + 5wt% La0.85Mg0.25Ni4.5Co0.35Al0.15 was prepared by two-step arc melting. X-ray diffractometry (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) show that the main phase of the composite alloy consists of V-based solid solution phase with BCC structure and C14 Laves phase with hexagonal structure, while secondary phase also exists in the composite alloy. Electrochemical studies show that distinct synergetic effect appears during the composite process. The real maximum discharge capacity of the composite alloy electrode is 361.8 mAh/g at 303 K, and the low temperature dischargeability (LTD) of the composite alloy electrode is 4.05 times as high as that of the matrix alloy electrode at 233 K. The high rate dischargeability (HRD), the charge–transfer resistance (Rct) and the exchange current density (I0) of the composite alloy electrode are 26.87 % bigger, 37.25 mΩ lower and 115.45 mA/g higher than that of the matrix alloy electrode, respectively. The hydrogen diffusion coefficient (D) in the bulk of the composite alloy is 6.13×10-10 cm2/s bigger than that of the matrix alloy.
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Solubility Rules of Negative Electrolyte V2(SO4)3 of Vanadium Redox Flow Battery
ZHAO Jian-Xin, WU Zeng-Hua, XI Jing-Yu, QIU Xin-Ping
2012 Vol. 27 (5): 469474
Abstract(
2791 )
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The solubility of V(III) species in negative electrolyte of all vanadium redox flow battery (VRB) was studied and the solubility parameters of V(III) species at various concentrations of H2SO4 and different temperatures were preliminarily obtained. The results showed that dissolution of V(III) was an exothermic process. The solubility of V(III) decreased with temperature (15-40℃). Also, the presence of V(III) in the solution was a V-O-V dimmer. The solubility of V(III) decreased with the increasing of H2SO4 and low concentration of H2SO4 would keep high concentration of V(III) stable for a long time. Especially, concentration of V(III) could reach 2.730 mol/L with 1 mol/L H2SO4 at 30℃. Electrochemical properties was further investigated by experiment, the results revealed that V(III)-H2SO4 solution was an irreversible system for V(III)/V(II) redox reaction. Increasing of concentration of H2SO4 had great benefit to improve the reversibility of V(III)/V(II) redox reaction.
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Synthesis of LiFePO4 Using FePO4 Produced by Electrolyzing Fe1.5P Waste Slag
LIU Yan, WANG Gui-Xin, YAN Kang-Ping, LI Cheng-Jia
2012 Vol. 27 (5): 475479
Abstract(
2786 )
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Fe1.5P waste slag was galvanostatically electrolyzed without separator in a H3PO4 aqueous solution using graphite as the cathode, and the electrolyte color turned from achromatism to yellow after electrolysis. Light yellow powder was finally obtained by adjusting the value of pH using ammonia water, filtering, washing and drying in sequence. The results of XRD and TG-DTA showed that the as-electrolyzed product was FePO4·2H2O. The as-obtained FePO4·2H2O was mixed well with LiOH·H2O and glucose to form a rheological phase precursor by using ethanol as a dispersing agent. LiFePO4/C composite was synthesized successfully by calcining the above precursor at 700℃ in an Ar atmosphere. The electrolysis process was investigated via a potentiodynamic polarization method. The structure, morphology and electrochemical performance of the as-synthesized LiFePO4/C composite were characterized by XRD, SEM and cyclic voltammetry, respectively. There was no impurity indexed peaks from Fe1.5P raw material, and the oxidization potential and the reduction potential were at 3.54 V and 3.33 V, respectively. The good experimental results indicated that electrolysis of Fe1.5P waste slag using an anode bag can eliminate the effect of impurities from raw material and the polarization between lithium ion intercalation and de-intercalation was low.
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Fabrication of Aluminate for Scandia Doped Dispenser Cathode and Emission Property
CUI Yun-Tao, WANG Jin-Shu, LIU Wei, WANG Xi, WANG Kai-Feng
2012 Vol. 27 (5): 480484
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2786 )
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Barium calcium aluminate (4BaO:CaO:Al2O3) was synthesized via liquid phase co-precipitation and solid phase mixing respectively and sintered in hydrogen atmosphere. Scandia doped tungsten powders were prepared in a new process of spray drying combined with two-step hydrogen reduction. During the preparation of scandia doped impregnated cathodes, a series of procedures, including pressing, sintering, impregnating, water cleaning and annealing were taken to obtain the impregnated cathodes. The results show that Ba5CaAl4O12 is formed after high temperature sintering. After impregnation, scandia doped impregnated cathodes with porous sub-micron structure are obtained. For full activation at 1150℃, the cathode surface is covered by a Ba-Sc-O active substance layer with a preferable atomic ratio, leading to its good emission property with space charge limited current density of 37.89 A/cm2 at 850℃.
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Fabrication and Characterization of Er3+:Yb3+ Co-doped Phosphosilicate Fibers
ZHANG Ze-Xue, JIANG Zuo-Wen, PENG Jing-Gang, DAI Neng-Li, LI Hai-Qing, YANG Lü-Yun, LI Jin-Yan
2012 Vol. 27 (5): 485488
Abstract(
2367 )
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Fabrication process of efficient Er3+:Yb3+ co-doped phosphosilicate fibers by modified chemical vapor deposition (MCVD) was reported. The process is combined with the solution doping technique where the codopant of aluminum is absolutely removed. It shows that the backward deposition process can be adapted to incorporate low viscosity phosphate glass and the reason of the porous layer with a higher phosphorus content which is fabricated in that process was discussed in details. The limiting of the back-transfer of energy from erbium ions to ytterbium ions and the suppressing the onset of Yb-ASE are demonstrated by fluorescence spectrum of the perform of phosphosilicate. It shows the efficient energy transfer in this broad absorption, ytterbium-sensitized erbium fiber. The performances of double-cladding Er3+:Yb3+ co-doped fiber lasers (EY-DCFLs) are also studied experimentally. The maximum output power is about 3.2 W by using a 4 m fiber, with a slope efficiency of 30%.
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Preparation of CeO2 Nanopowders by Hydrolysis and Oxidation of Cerium Carbide
WU Yi-Qing, NI Jian-Sen, DU Ya-Nan, HU Peng-Fei, DING Wei-Zhong, GENG Shu-Hua
2012 Vol. 27 (5): 489494
Abstract(
2673 )
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An effective route for the synthesis of CeO2 nanopowders on a large scale was presented. High-quality CeO2 nanopowders composed of nanoparticles with size of 3-5 nm were prepared by hydrolysis and oxidation of cerium carbide. The experimental variables which can tune the BET surface area of CeO2 nanopowders, including hydrolysis reaction temperature, reaction time, as well as feed ratio of cerium carbide, were systematically. Experimental results indicate that the lower hydrolysis temperature (around room temperature), higher feed ratio (1:20 (g/mL)), and proper reaction time (18 h) can product CeO2 nanopowders with higher surface area. The intermediate outcome Ce(OH)3 and aimed product CeO2 obtained with the optimized experimental variables (hydrolysis of cerium carbide powder at constant temperature (30℃) for 18 h in the suspension with feed ratio of 1:20 (g/mL) and dried at 80℃ for 4 h in the air) were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED), and UV-visible absorption spectrometer. It is found that the Ce(OH)3 is composed of a large quantity of rodlike nanostructures with length of 50-100 nm and diameter of 5-20 nm and the CeO2 nanopowders have higher UV-Vis absorbance property. Furthermore, the CeO2 nanopowders possess fine CO catalytic performance.
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Effect of Fe on the Selective Catalytic Reduction of NO by NH3 at Low Temperature over Mn/CeO2-TiO2 Catalyst
WU Da-Wang, ZHANG Qiu-Lin, LIN Tao, GONG Mao-Chu, CHEN Yao-Qiang
2012 Vol. 27 (5): 495500
Abstract(
2696 )
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The Mn/CeO2-TiO2 catalyst was prepared using manganese oxide as active component, CeO2-TiO2 as support. Effect of the addition of Fe on the performance of NH3-SCR over Mn/CeO2-TiO2 at low temperature was investigated. These catalysts were characterized by BET surface area, H2 temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscope (XPS). The activity result shows that the SCR performance of Mn/CeO2-TiO2 is obviously enhanced by the introduction of Fe. The Mn-Fe/CeO2-TiO2 catalyst shows high NO conversion within a wide temperature range of 113-250℃. The characterization results show that the introduction of Fe promotes the dispersion of manganese species on the surface of CeO2-TiO2, and the reduction temperature of manganese species shifts to lower temperature. The XPS analysis indicates that the valence of surface Mn on Mn-Fe/CeO2-TiO2 is +4, while the Fe mainly exists as +3 of Fe2O3, and the strong interaction happens between the Fe and the support.
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Rapid Synthesis of Mesoporous Nickel Phosphates under Microwave Assisted Hydrothermal Condition
LI Xu-Ying, TAN Juan, YANG Jian-Hua, LIU Jing, YANG Fei
2012 Vol. 27 (5): 501506
Abstract(
2785 )
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Mesostructured nickel phosphate (MW-NiPO-2) was rapidly synthesized in the presence of cationic surfactant by a microwave assisted hydrothermal process. The synthesis parameters, microwave irradiation temperature and time, OH-/P and Ni/P molar ratios of the precursor, were systematically investigated and optimized. The characterizations of the materials obtained by the two different procedures, Sol-Gel method and microwave assisted hydrothermal process, were carried out by ICP, FT-IR, TEM and N2 physisorption. The results show that MW-NiPO-2 can be obtained at relatively low temperature (60℃). When the microwave radiation temperature was 100℃, the mesostructured phase formed in an extremely short period about 0.25 h. Ordered MW-NiPO-2 can be obtained under microwave irradiation for 1 h at 100℃, when OH-/P and the Ni/P molar ratios of the precursor are 2.0 and 0.7, respectively. In contrast, it took at least 24 h for completion via Sol-Gel method. MW-NiPO-2 and SG-NiPO-2 possess similar structure and composition while MW-NiPO-2 exhibites a worm-like appearance other than piled nanotubes. In comparison with the sample synthesized via Sol-Gel method, MW-NiPO-2 possesses a relatively high BET surface area (334.4 m2/g) and pore volume (0.318 cm3/g).
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PZT Powders Synthesized by Hydrothermal Method
ZHU Kong-Jun, ZHU Ren-Qiang, DONG Na-Na, GU Hong-Hui, QIU Jin-Hao, JI Hong-Li
2012 Vol. 27 (5): 507512
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3104 )
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Lead zirconate titanate (PZT) powders with single-phase, cubic morphology and average size of 1 μm were synthesized using hydrothermal methods. Effects of KOH concentration, hydrothermal treatment time and Pb excess were investigated. The results show that KOH concentration has an important influence on the solid solubility of Pb ion in A-site of PZT perovskite structure. The concentration of Pb2+ vacancies increased with the increase of OH- concentration. However, this kind of deficiency could be compensated by adding more Pb ions in the raw materials, and more Pb ions were needed to add with higher alkaline concentration in the starting solution. But excessive compensation of Pb ions would result in the appearance of the second phase.
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Study on Hemostatic Materials of Mesoporous Silicon Dioxide Doped Ca and Ag with Antibacterial Properties
CHEN Yu, LI Wen-Rui, XU Can, SU Jia-Can, LI Ming, LIU Chang-Sheng
2012 Vol. 27 (5): 513518
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3147 )
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An antibacterial hemostatic material of mesoporous silicon oxide gel doped with Ca and Ag (m-SCA) gel was fabricated by using cetyltrimethylammonium bromide(CTAB) as templates and Sol-Gel process. The results showed that m-SCA with mesoporous structure had the surface area of 416 m2/g and pore size of around 2 nm. The m-SCA with high surface area and good clotting function could significantly shorten the prothrombin time (PT) and activated partial thromboplastin time (APTT). The m-SCA containing a small quantity of Ag had no obvious effects on its clotting properties while Ca in m-SCA could promote clotting. The m-SCA doped 0.02wt% Ag without cytotoxicity had good antibacterial properties against E.coli. Animal experimental results showed that the m-SCA could control hemorrhage and shorten the bleeding time of rabbit ear wound, showing good hemostatic properties. It suggestes that the m-SCA is a good hemostatic material with antibacterial properties.
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Improvement of Antibacterial Properties of Stainless Steel by Combining Plasma Cu and Thermal Diffusion
ZHANG Xiang-Yu, JIANG Li, HUANG Xiao-Bo, MA Yong, FAN Ai-Lan, TANG Bin
2012 Vol. 27 (5): 519523
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2591 )
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The duplex treatment consisting of plasma surface alloyed with copper followed by thermal diffusion under the bombardment of glow was carried out on AISI 304 stainless steel in order to improve its antibacterial properties. The antibacterial properties against Gram-negative E.coli ATCC10536 and Gram-positive S.aureus ATCC25923 of the untreated and duplex-treated stainless steel were investigated by using a spread plate method. The microstructure, chemical composition and the change of the chemical state of copper on the surface of the duplex treated stainless steel were characterized using scanning electron microscope (SEM), glow discharge optical emission spectroscope (GDOES) and X-ray photoelectron spectroscope (XPS). The results show that the antibacterial rates gradually rise with increase of the contact time between the bacteria and the copper-alloyed stainless steel, and the alloyed surface exhibits excellent antibacterial properties against both E.coli and S.aureus within 12 h. The copper concentration on the alloyed surface reaches to 5.7wt% and the thickness of the alloyed layer is about 2.7 µm. XPS analysis indicated that Cu ions was released when the copper-alloyed surface contacted with bacterial solution, which led to death of the bacteria.
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Synchrotron XRD Study on the Nacre of Freshwater Bivalve H. cumingii Lea
YAN Xiao-Hui, WANG Sheng-Nan, DU Bo, WANG Xiao-Xiang
2012 Vol. 27 (5): 524528
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2850 )
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Synchrotron XRD was used to study internal stress of nacre and microstructure of individual nacre tablet in the shell of freshwater bivalve H. cumingii Lea. The diffraction patterns show some biopolymers (intra-crystalline organic matrix) are occluded inside nacre tablets during biomineralization, causing that nacre powder exhibits tensile- like internal stress which is strongly anisotropic along different vectors of the reciprocal lattice. The characteristic of internal stress suggests that the intra-crystalline organic matrix is most probably arranged in the specific form. And line profile analysis which is conducted with the synchrotron XRD patterns of heated and unheated nacre powder samples, further confirms that the intra-crystalline organic matrix is adsorbed on (002) atomic planes of nacre tablets. The findings will facilitate the study on the formation mechanism and the strengthening and toughening mechanism of the nacre and provide theoretical basis for designing new organic-inorganic composite with high performances and cultivating pearl.
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Optimal Process Parameters for 3Y-TZP/TiN Conductive Polycrystal by Taguchi Method
WANG Cui-Feng, CHIOU Shi-Yung, OU Keng-Liang, CAI Zhang-Ting
2012 Vol. 27 (5): 529535
Abstract(
2505 )
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For the manufacturing of 3mol% Yttria- tetragonal Zirconia polycrystal (3Y-TZP) with 30wt% of Titanium Nitride (TiN) (3Y-TZP/TiN) powders, Taguchi method was used to selected the process parameters including sintering step variation, crushing time of TiN powder, the first step sintering duration and second step sintering temperature to be the controlling factors. The characterization features of sintered samples such as fracture toughness, flexural strength, hardness, relative density and electric resistance were explored through L9 orthogonal array. By analysis of variance (ANOVA), the optimal parameter settings for each response factor were obtained and tested through confirmation experiments. The results indicate that the optimal process parameters contain 8 h crushing time of TiN powder, two - steps sintering processes including the 1450℃ temperature with no duration for the first step and 1150℃ temperature and 20 h duration for the second step, and the average flexural strength of 736.75 MPa and fracture toughness of 7.545 MPa•m1/2 are obtained. In addition, the degree of the process parameter effects on the sintered samples is found in the series of the sintering duration of the first step, sintering step variation, size of TiN particles and the sintering temperature of the second step. Meanwhile, fracture toughness depends significantly on the ratio of tetragonal phase to monoclinic phase and attends to be 9.275 MPa·m1/2 when the ratio is getting to the maximum. The average electric resistance for 3Y- TZP/ TiN is measured to be 3.26 m?·cm. These samples can be electric-discharge machined.
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Effect of Target Composition and Sputtering Parameters on Microstructure and Mechanical Properties of Vanadium Carbide Films
SHEN Jie, LI Guan-Qun, LI Yu-Ge, LI Ge-Yang
2012 Vol. 27 (5): 536540
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2624 )
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To improve the crystalinity and mechanical properties of the films sputtering with carbide target, a series of vanadium carbide films were prepared by magnetron sputtering in an argon atmosphere using the stoichiometric VC target (n(C):n(V)=1:1) and substoichiometric VC target (n(C):n(V)=0.75:1). Energy-dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy and nanoindentation were employed to characterize their composition, microstructure and mechanical properties. The results show that for the VC target (n(C):n(V)=1:1), only when the Ar pressure is between 2.4 Pa and 3.2 Pa, the films can obtain fine crystallized structure and attain high hardness, of which the highest hardness is 28 GPa. For the V-rich VC target, fine crystallized films and high hardness (31.4 GPa) could be gained in lower Ar pressure (0.6-1.8 Pa). Compared with argon pressure and substrate temperature, target composition is the main factor of the film composition, microstructure and mechanical properties, thus proper increasing the content of metal component of the target is a more effective way to get VC films with good crystalinity and high hardness.
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Preparation and Characterization of Micro-coiled Carbon Fibers
LI Ning, KOU Kai-Chang, CHAO Min, ZHANG Dong-Na, WU Guang-Lei, MA Li-Peng
2012 Vol. 27 (5): 541544
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2425 )
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Carbon microcoils (CMCs) were synthesized by the catalytic decomposition of acetylene using nickel sulfide particles as the catalyst which prepared by solvothermal method. The morphology and microstructure of the catalyst and micro-coiled carbon fibers were examined by SEM, FT-IR and XRD. The results showed that the catalyst was regular hexagonal phase nickel sulfide with its diameter of 1-2 μm and a smooth surface. CMCs have double helix structure, rectangular cross-section and identical coil diameter. The molecular structure of CMCs contained both unsaturated –C=C– and saturated –CH2– and –CH3 groups. The microstructure of CMCs was of poor degree of order with a low graphitization degree, containing a certain amount of amorphous carbon and crystal defects.
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Friction of Pyrolytic Carbon Coating Prepared by Gradient CVD on Medical Carbon/Carbon Composites Surface
NI Xin-Ye, TANG Xiao-Bin, LIN Tao, GENG Chang-Ran, CAI Lei-Ming, GU Wei-Dong, CHEN Da
2012 Vol. 27 (5): 545549
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2805 )
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Pyrolytic carbon coating was prepared by gradient chemical vapor deposition (CVD) on medical carbon/carbon composites surface. Microstructure, friction coefficient and wear capacity of the pyrolytic carbon cating were investigated. The results show that the pyrolytic carbon coating is covered densely by spherical pyrdytic carbon with dimension of about 20 μm, and close, multi-layer pyrolytic carbon is shown on the fracture. Compared with carbon/carbon composite prepared by asphalt impregnated/carbonization, the friction coefficient of the byrolytic carbon coating is higher in the dry friction whereas in wet friction of simulated human joints, its friction coefficient is lower. The wear loss of the pyrolytic carbon coating is much smaller than that of the latter in dry and wet friction. It suggests that medical carbon/carbon composites surface prepared by gradient CVD can improve the wear resistance of the carbon/carbon composites.
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Microstructure Characterization and Thermal Conductivity Analysis of Plasma Sprayed ZrO2 Coatings
WANG Yong-Zhe, WU Wei, HUA Jia-Jie, ZENG Yi, ZHENG Xue-Bin, ZHOU Ying, WANG Hu
2012 Vol. 27 (5): 550554
Abstract(
6555 )
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Yttria stabilized zirconia coatings were deposited using two different sets of parameters (N1, N2 coating). The microstructure features, such as total porosity and large porosity, were quantified by means of scanning electron microscope and image analysis. The three-dimensional distribution of microcracks and segmentation cracks was successfully revealed by the X-ray microscopy in the scanning electron microscope with three-dimensional microtomography capability. So the relationship between microstructure and thermal conductivity was found. At room temperature, thermal conductivity of N2 was lower than that of N1 due to larger pores and microcracks. At 1000℃ thermal conductivity of N1 was lower for the sintering of microcracks. The segmentation cracks formed by the propagation of microcracks could effectively reduce the thermal conductivity at high temperature.
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Porous Titanium Treated by Nitric Acid with Varied Concentration and the Bioactivity in Vitro
XU Bin, ZHAO Chao-Yong, CAI Bing, FAN Hong-Song
2012 Vol. 27 (5): 555560
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4459 )
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Surface modification is expected to further activate the titanium implant and has been widely used in dense titanium surface. In this study, porous titanium fabricated by a slurry foaming method was treated by nitric acid solution with different concentrations. Micrometer-sized acid-etched pits were observed on the inner-pore walls of porous titanium and the morphology varied a little with nitric acid concentration. However, the ability to deposit apatite on the treated porous titanium surface changed obviously with nitric acid concentration. The samples treated by nitric acid solution at a ratio of 1:1 and 1:5 (V(HNO3):V(H2O)) showed the best apatite-forming ability. Compared with that non-treated porous titanium, the samples were treated by nitric acid at the ration of 1:1 and 1:5 (V(HNO3):V(H2O)) showed higher MG63s cells viability, better cells adhesion and spreading with cells both on the surface and inside the pores. The results showed that nitric acid treatment, a simple process with less impurity introduced and good penetration inside porous titanium was an effective method to prepare bioactive porous titanium.
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