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Chemistry and Physics of Point Defects in Advanced Ceramics
ZHOU Zhi-Gang,TANG Zi-Long
2009 Vol. 24 (3): 417426
Abstract(
3465 )
PDF(1429KB)(
2021
)
he structure and behavior of defects, especial point defects are the key to understand the structural imperfection of structuresensitive advanced ceramics and related devices. A conception of chemistry and physics, especially for electronics on the point defect in the advanced ceramics is briefly reviewed in the present work. Several achieved examples of defect engineering and microscopic control technology for improving some ceramics/devices of electric, magnetic, optical, mechanical and/or biological behavior by defect improve/rebuild are discussed. The knowledge of how defects influence the ceramics/device performance is revealed and point defects provide very useful tools for understanding their basic characteristics and to open up their potentiality of the new advanced ceramics/devices in the near future.
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Design, Preparation and Properties of Novel p-type Cu-based Chalcogenides as Transparent Conducting Materials
WU Li-Bin,HUANG FuQiang,JIANG Wan
2009 Vol. 24 (3): 427432
Abstract(
2935 )
PDF(919KB)(
1615
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Based on functional buildingblock with conducting slabs and transparent slabs, a new model was proposed in designing ptype Cubased chalcogenides, i.e.transparent conducting materials (TCMs) with layered structure. Under the guidance of the model, LaCuOTe and Sr3Cu2Sc2O5S2 are selected and studied as TCMs, taking into consideration of their layered structure from [Cu2Te2]/[Cu2S2] conducting slabs and [La2O2]/[Sr3Sc2O5] transparent slabs. The optical and transport properties of two compounds verify the validity and feasibility of the model in designing and finding novel TCMs. The two compounds show high conductivity of 1.65-2.9S·cm-1 and considerable wide bandgap of 2.3-3.1eV, indicating considerable high conductivity and high transparency.
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Structure and Properties of (K0.5Na0.5)1-2xSrx(Nb0.94 Sb0.06)O3 Lead-free Piezoelectric Ceramics
FAN Gui-Fen,LUWen-Zhong,RAO Yuan-Yuan
2009 Vol. 24 (3): 433437
Abstract(
3197 )
PDF(735KB)(
1540
)
Leadfree piezoelectric ceramics (K0.5Na0.5)1-2xSrx(Nb0.94 Sb0.06)O3 (abbreviated as KNSNS1000x) were synthesized by the conventional ceramic sintering technique. The structure and electrical properties of KNSNS1000x ceramics were investigated. The results of XRD indicate that KNSNS1000x ceramics have an orthorhombic structure. The proper content of Sr substitute increases the density of ceramics which reaches the maximum value of 4.411g/cm3 at x=0.008. With the increase of the amount of Sr, the Tc decreases and the temperature of orthorhombictetragonal phase transition (To-t) is almost a constant.In the temperature range from 0℃ to 200℃, dielectric constant of KNSNS1000x ceramics is independent of frequency. The KNSNS8 ceramics obtains the optimum piezoelectric properties: d33=155pC/N, kp=0.361,Qm=120,Np=2862,Pr=23μC/cm2,Ec=1.4kV/mm,ρ=4.411g/cm3.
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Effect of Organic Modification Temperature on the Microstructure of Nanoscale Titania
YAO Chao,DING Yong-Hong,LI Wei-Min,WANG Mao-Hua,LU Lu-De,WANG Xin
2009 Vol. 24 (3): 438442
Abstract(
3080 )
PDF(2703KB)(
2004
)
Nanoscale titania aqueous dispersion was prepared firstly, and then nanotitania particles was transfered into methylbenzene in which stearic acid was dissolved from water by distillation so that the surface modification was carried out in organic system. Nanoscale titania was modified with stearic acid at different temperatures.The samples were characterized by Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscope (XPS), thermogravimetry(TG), derivative thermogravimetry (DTG) and transmission electron microscopye(TEM). The results show that stearic acid is bound on the surface of nanoscale titania by bidentate structure, and even monolayer coverage is obtained. With modification temperature increasing, the crystallite size of nanoscale titania increase, the mass fraction of chemisorbed stearic acid on the surface of nanoscale titania decrease, and the thickness of stearic acid layer changes from 1nm to 2-3nm.The modification temperature has little effect on interactions between stearic acid and titania.
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Mechanism of the Doping Species Controlling the UV Photocatalytic Activity of Nitrogen Doped TiO2
LIU Hui-Jing,BAI Yuan,SUN Hong-Qi,JIN Wan-Qin
2009 Vol. 24 (3): 443447
Abstract(
3227 )
PDF(1547KB)(
3426
)
Nitrogendoped and pure TiO2 photocatalysts were synthesized by precipitation method using TiCl4 as titanium precursor. Both X-ray diffraction (XRD) and N2 adsorptiondesorption isotherms show that the asprepared samples consis of anatase phase except for trace brookite phase with mesoporous structure. X-ray photoelectron spectroscopy(XPS) confirms that the incorporated nitrogen element exists as the chemical state of NOx. The UV-Vis diffuse reflection absorption spectra (UV-Vis) reveal that the nitrogendoped TiO2 shows a new absorption region at 400-550nm. The photocatalytic activities of the nitrogendoped TiO2 utilized for the photodegradation of 4-chlorophenol (4-CP) are higher than those of the pure TiO2 under UV and visible light irradiation. The improved photocatalytic activities under UV light irradiation of the nitrogendoped TiO2 are attributed to the presence of NOx. With no influence on the energy gap of TiO2, NOx can extend the optical response of TiO2, excite more photoinduced electronsholes for photocatalysis and reduce the recombination probabilities of carriers.
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Effect of Heat Treatment Temperature on Energy Storage Ability of TiO2-WO3 Composite Photocatalyst
CAO Ling-Lin,YUAN Jian,CHEN Ming-Xia,SHANGGUAN Wen-Feng
2009 Vol. 24 (3): 448452
Abstract(
2871 )
PDF(1797KB)(
1776
)
TiO2-WO3 photocatalyst powder was made from TiO2 powder and soluble tungstic acid. The energy storage behavior was characterized by electrochemical galvanostatic method. Combined with XRD, TEM and BET, crystalline form and crystallinity changing of WO3 with heat treatment was studied. TiO2-WO3 composite materials have energy storage ability in electrochemical measurement. The crystallinity of WO3 has strong influence on samples’ performance. When WO3 is tungstite or amorphous, the TiO2-WO3 composites have no or quite low energy storage capacity. The energy storage capacity is improved with the crystallinty of WO3 increasing. The maximum of TiO2-WO3 energy storage capacity is 0.83×10-3 C·mg-1. But when the crystallinity of WO3 is high, the energy storage capacity decreases. And degradation experiment displays that Rhodamine B can be degraded in darkness by the TiO2-WO3 photocatalyst with energy storage ability, and the degradation efficiency reaches 11%.
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Synthesis of Novel Visible Light Driven BiVO4 Photocatalysts via Microemulsion Process and its Photocatalytic Performance
GE Lei,ZHANG Xian-Hua
2009 Vol. 24 (3): 453456
Abstract(
3503 )
PDF(1993KB)(
2484
)
The novel visiblelightdriven BiVO4 photocatalyst with tetragonal and monoclinic structures was synthesized via a reverse microemulsion method using Bi(NO3)3 and NH4VO3 as starting materials. The asprepared BiVO4 samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Xray photoelectron spectroscope (XPS). The photocatalytic activity of the BiVO4 powders was determined by degradation of methyl orange molecules in water under visible light irradiation (λ>400nm). The results revealed that the particle and crystallite sizes of the BiVO4 powders significantly depended on synthesis temperature of the reverse microemulsion solutions. The photocatalytic tests indicated that the synthesis temperature of the microemulsion solutions can significantly affect the visible light driven photocatalytic activities. The highest methyl orange degradation of 99.9% within 3h was achieved on the BiVO4 samples with mixed tetragonal and monoclinic phases.
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Preparation of Ti-Zr-V-O Catalytic Composite Material and its Selective Catalytic Reduction of NO
SHEN Yue-Song,ZHU She-Min,QIU Tai,SHEN Shu-Bao
2009 Vol. 24 (3): 457462
Abstract(
2823 )
PDF(2605KB)(
1966
)
A series of Ti-Zr-V-O catalytic composite materials were prepared by sol-gel method. Effect of doping zirconium on catalytic NOx activities of Ti-V-O composite catalysts was investigated, and effects of doping zirconium on crystal form, crystalline morphology, chemical composition, functional group structure and specific surface area of titanium-vanadium composite oxides were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy spectrum analysis (EDS), Fourier infrared spectrum (FT-IR) and N2 physical adsorption (BET method) respectively. The experimental results show that doping zirconium can inhibit anatase crystalline transformation, refine grain size, change the crystalline morphology and enhance the solid acidity of Ti-V-O composite catalysts. Consequently, the catalytic properties of Ti-Zr-V-O composite catalysts are improved. In the process of selective catalytic reduction of NO over Ti-Zr-V-O/ATS ceramics monolithic catalysts, using NH3 as reducing agent, doping zirconium widens the catalytic active zone to high temperature area about 100℃, and the highest NO conversion at 300℃ is increased by 17.3%.
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Fabrication of Morphology of One-dimensional Nano-γ-AlOOH via Hydrothermal Route
LU Guang-Wei,YANG Qi,DENG Yi-Da,HU Wen-Bin
2009 Vol. 24 (3): 463468
Abstract(
3479 )
PDF(7503KB)(
1912
)
One-dimensional nanostructure γ-AlOOH was fabricated via hydrothermal synthesis. And the effects of the processing parameters on structure of γ-AlOOH were investigated. The results show that γ-AlOOH nanorod can be achieved on the condition that AlCl3 density is lower than 0.2mol/L, pH value of reacting solution is lower than 7, and reacting temperature is set between 160℃ and 180℃; when pH value is higher than 7, γ-AlOOH is in the shape of nanoflake. Nanofiber with high slenderness ratio can be achieved on the condition that AlCl3 density is higher than 0.2mol/L, pH value is controlled between 5 and 6, and reacting temperature is set around 200℃ with adding surfactant SDBS.
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PC Nanofiber Reinforced PMMA Transparent Composites Incorporated with TiO2 NanoParticles
CHEN Lu-Song,HUANG Zheng-Ming,XUE Cong
2009 Vol. 24 (3): 469474
Abstract(
3007 )
PDF(2701KB)(
1871
)
Polycarbonate (PC) nanofiber reinforced polymethyl methacrylate (PMMA) transparent composites were developed by combination of co-axial electrospinning and hot-press technique. PMMA shell and PC core composite nanofibers were obtained through the coaxial-electrospinning and the nanofiber membranes were hot pressed into PC nanofiber reinforced PMMA transparent composites. TiO2 nano-particles of different contents were introduced into the shell (PMMA) and the core (PC) part of the composite nanofibers to shield ultraviolet transmittance of the resulting transparent composite. Distributions of the nano-particles in different parts of the core-shell structure of the composite nanofibers were observed, and the nanoparticle influences of different contents and locations on visible light transmittance, ultraviolet radiation shielding and mechanical properties of the composites were analyzed. The results show that the ultraviolet radiation shielding capacity and tensile properties can be enhanced when the nanoparticles are located within the shell part, with a little drop in the visible light transmittance. The nano-particles introduced into the core part induce significant improvement in mechanical performance without obvious impact on the visible light transmittance.
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Influence of Nano-hydroxyapatite on the Mechanical Properties of Short-carbon-fiber/Poly(methyl methacrylate) Bio-composites
ZENG Li-Ping,CAO Li-Yun,HUANG Jian-Feng,GUO Shen
2009 Vol. 24 (3): 475479
Abstract(
3196 )
PDF(1953KB)(
1726
)
An in-situ processing combined with solution co-mixing approach was developed in the preparation of poly(methyl methacrylate)(PMMA) matrix bio-composites using hydroxyapatite (HA) nano-particles and short carbon fiber (Cf) as reinforced materials. The influences of HA particles on the mechanical properties and microstructures of the HA-Cf/PMMA composites were investigated. The mechanical properties were tested by universal testing machine. The phase compositions and fracture surface morphologies of the asprepared HA-Cf/PMMA composites were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscope (FT-IR). The results show that the interface bonding between HA and PMMA matrix and the mechanical properties of HA-Cf/PMMA composites are obviously improved by surface modification of HA with lecithin as coupling agent. With the increase of lecithin-modified HA mass fraction, the flexural strength, tensile strength, compressive strength, flexural modulus and tensile modulus of the as-prepared HA-Cf/PMMA composites firstly increase and then decrease. When the surface modified HA particles mass fraction is 8%, the dispersion of HA nano-particles in PMMA matrix is uniform and the flexural strength, tensile strength, flexural modulus and tensile modulus of the HA-Cf/PMMA composites reach the maximum value.
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Preparation and Characterization of Porous Nano-dHA/PLA/BCP Scaffold
JI Jin-Gou,LI Xi,ZHOU Zhi-Guo,HU Cheng-Bo,XIA Zhi-Ning,HUANG Rui
2009 Vol. 24 (3): 480484
Abstract(
3045 )
PDF(2271KB)(
1955
)
To improve the hydrophilicity and to avoid sharp pH decrease during the degradation of polylactic acid/biphasic calcium phosphate ceramics (PLA/BCP) scaffold in solution, nano calcium deficient hydroxyapatite/polylactic acid/biphasic calcium phosphate (nano-dHA/PLA/BCP) scaffold was prepared by immersing assintered porous BCP scaffold in nano-dHA/PLA mixed solution followed by vacuum drying. The compressive strength of samples was measured by universal test machine. The porosity percentage of samples was investigated by Archimedes method. The surfaces of samples were analyzed by scanning electron microscope (SEM). The waterretention rate and pH value change of the samples incubating in phosphate buffered solution (PBS) were also studied. The results show that the compressive strength and waterretention rate of the nanodHA/PLA/BCP scaffold with rougher surface are improved. The pH decrease rate of nano-dHA/PLA/BCP scaffold is slower than that of PLA/BCP scaffolds incubating in PBS, and the surfaces have more bone-like apatite formation when incubating in simulated body fluid (SBF).
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Study on Porous Scaffold of Nano Hydroxyapatite/poly (ε-caprolactone) Bioactive Composite
SU Jia-Can,LI Ming,YU Bao-Qing,ZHANG Chun-Cai
2009 Vol. 24 (3): 485490
Abstract(
3240 )
PDF(2826KB)(
2005
)
Nano hydroxyapatite (n-HA) and its composite with poly(ε-caprolactone) (PCL) were fabricated by hydrothermally synthesized method, and the well interconnected macroporous nano-composite scaffolds with pore diameter from 200μm to 400μm were prepared by melt-cast/salt particle-leaching technique. The biological properties of the composite scaffolds were investigated through cell culture and animal implanted experimentation. The results show that porosity of the composite scaffolds increases with the increase of the quantity of the porogens used while the compressive strength decrease. The maximal porosity of the composite scaffold can reach 86% while its compressive strength is only 2.4MPa. The attachment ratio and proliferation of MG63 cells on the composite scaffolds increase with the increase of HA content in the composite, which are significantly higher than those of PCL alone. Histological examinations confirm that the new bony tissue could grow easily into the composite scaffold and directly integrate with the composite by bone-bonding. The results indicate that the n-HA/PCL composite scaffolds have excellent biocompatibility and bioactivity.
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Study on Mechanical Properties and Blood Compatibility of Carbon Nitride Film Deposited on NiTi Alloy
LIU Min,WANG Ji-Gang
2009 Vol. 24 (3): 491496
Abstract(
2939 )
PDF(3475KB)(
1740
)
Ti/CNx (x≈0.26), as well as Ti/DLC (Diamond-Like Carbon) and Ti/TiN gradient films were deposited on NiTi alloy substrates using DC (direct current) magnetron sputtering method. The mechanical properties concerning hardness and cohesion of the above three films were tested by using microhardness tester and scratch tester, respectively. The surface hydrophilicities of the three films were measured using contact angle measurement. The blood compatibilities of the substrate and the films were evaluated by hemolysis test and platelet adhesion test. The results indicate that the cohesion between Ti/CNx film and NiTi alloy substrate is excellent (63.6N). The hardness of the CNx film (23.01GPa) is nearly equal to that of the TiN film, which is somewhat higher than that of the DLC films. The results of surface hydrophilicity test and platelet adhesion test demonstrate that the hydrophilicity and blood compatibility of NiTi alloy are improved effectively by the modification with the Ti/CNx film. In comparison with Ti/TiN and Ti/DLC gradient films, Ti/CNx film has the minimum hemolysis ratio of 1.12%. Among the above gradient films, the Ti/CNx film has the best blood compatibilities, as indicated by the minimum amount of conglutinated platelets and the least deformation.
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Chemical Inhomogeneity of Plasma Sprayed Hydroxyapatite Coatings
LU Yu-Peng,XIAO Gui-Yong,LI Shi-Tong
2009 Vol. 24 (3): 497500
Abstract(
2767 )
PDF(2969KB)(
1547
)
Hydroxyapatite (HA) coatings were fabricated using plasma spraying method. The samples were polished along the direction parallel and vertical to the coating surface, respectively. Microstructure, element distribution and phase composition of the surface and crosssection of coaings were examined by a JXA-8800R electron probe microanalyser (EPMA) with a Link ISIS300 energy spectrum analyzer and a D/max-γB X-ray diffractometer (XRD). The results show that there exists chemical inhomogeneity in terms of chemical composition and phases in the coatings, corresponding to color differences in back scattering electron (BSE) images. The micro-regions with low P and low O contents are composed of amorphous, decomposed and recrystallized Ca-P phases. The difference in moltening degrees of HA particles during plasma spraying results in the inhomogeneity. Heat treatment eliminats the chemical inhomogeneity but results in the formation or spreading of cracks within the coatings.
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Preparation of Silica Hollow Microspheres with Special Surface Morphology by Biotemplate Method
CAO Feng,LI Dong-Xu,GUAN Zi-Sheng
2009 Vol. 24 (3): 501506
Abstract(
3179 )
PDF(3785KB)(
1736
)
Surface structured silica hollow microspheres were synthesized using the rape pollen grain as a biotemplate via a facile sol-gel method and a succedent calcinations process. Different surface morphologies were also achieved on the as-prepared silica microspheres by changing the ratio of tetraethyl orthosilicate (TEOS) to water in the silica sols. Differential scanning calorimetry (DSC), thermogravity (TG), energy disperse spectroscope (EDS) and scanning electron microscope (SEM) were used to characterize the pollen grain and the as-prepared silica hollow microspheres. The mechanism of morphology controlling in the microspheres fabrication was discussed in detail. The results indicate that the intine of pollen grain will be removed totally at 200℃, as a consequence hollow structure can be achieved in pollen grain. And the exine of pollen grain with the netlike morphology can be maintained under higher temperature, which makes the replication of the microstructure on microspheres surface possible. Along with quantity of colloidal particles deposited on pollen grain, the special surface morphology on the silica hollow microspheres will be adjustable.
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Preparation and Characterization of the Antibacterial Modified Montmorillonites Containing Quaternary Phosphonium Cations
TAN Shao-Zao,ZHENG Jia,CHEN Yin,XIE Yu-Shan,SHI Qing-Shan,OUYANG You-Sheng,CHEN Yi-Ben
2009 Vol. 24 (3): 507511
Abstract(
3192 )
PDF(1747KB)(
1614
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Four kinds of modified montmorillonites were prepared by introducing different content of hexadecyltriphenyl phosphonium cations into sodium montmorillonite (Na/MMT) through an ion-exchange method, and characterized using thermogravimetry (TGA), X-ray diffraction (XRD) and scanning electron microscope (SEM). Also the Zeta potentials and antibacterial activity of the modified montmorillonites were investigated. The onset temperatures of the decomposition for quaternary phosphonium cations in modified montmorillonites are all higher than 230℃, which have good thermal stability. For the montmorillonites, the interlayer spacings enlarge, the Zeta potentials increase and the antibacterial activity improves with the increase of the content of quaternary phosphonium cations. Na/MMT displays flake shape with the particles adhered and interwinded each other, while the modified montmorillonites are in irregular shape. QPC/MMT3 containing 23.55wt% quaternary phosphonium cations, possesses the minimal inhibitory concentration (MICs) against E.coli and S.aureus of 1.2g/L and 0.1g/L, respectively. After contacting the bacteria for 24h, 1.0g/L of QPC/MMT-3 is able to kill more than 99.9% E.coli, and nearly all the E.coli. Moreover, QPC/MMT-3 has good water resistance.
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Phytoliths in Mealies Corns and Preparation of SiO2 Nano-materials
CUI Peng,YUAN Shi-Ling,XU Gui-Ying
2009 Vol. 24 (3): 512516
Abstract(
2652 )
PDF(4016KB)(
1798
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Nanostructure SiO2 was prepared from mealies corns. The micron phytoliths were obtained after treatment with mixed acids, using the phytolith samples as raw materials, nano-silica was obtained through calcining at certain temperature after boiling in the nitric solution. And its structure was characterized by X-ray diffraction (XRD), optical microscope, transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectroscope (EDS) and Infrared Spectroscope (IR). The results show that the phytoliths are all dumbbelltype in cornstalks and leaves in the micro level; however they are located along or against vertically the lignose, respectively. The nanosilica with diameter of 103nm is obtained through calcination after boiling in HNO3 solution, and the nano SiO2 crosslink in higher temperature.
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Study on AlSb Polycrystalline Thin Films Material
SONG Hui-Jin,HE Jian-Xiong,WU Li-Li,ZHENG Jia-Gui,FENG Liang-Huan,LEI Zhi
2009 Vol. 24 (3): 517520
Abstract(
3267 )
PDF(1625KB)(
1600
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The structural, optical and electrical properties of AlSb polycrystalline thin films prepared by in co-evaporation vacuum were studied. The results show that the as-deposited AlSb thin films are amorphous phase. And the samples annealed above 540℃ present polycrystalline phases. The degree of transforming amorphous phase into polycrystalline phases depends on the annealing temperature and stoichiometrical composition. When the ratio of Al to Sb is 47.2∶52.8, the films display more obvious polycrystalline phase after annealing at 580℃. Furthermore, some irreversible changes of the conductivity take place in the annealed films during temperature increasing and decreasing processes. During the temperature increasing process, conductance activation energy (Ea) is 0.132eV. During the temperature decreasing process, Ea is 0.044eV from 200℃ to 270℃ and 0.32eV below 200℃. AlSb polycrystalline thin films are pdoping, indirect band semiconductor with absorption coefficient higher than 8×104cm-1. Open circuit voltage of TCO/CdS/AlSb photovoltaic device reaches 200mV.
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Characterization of MnO2 Aerogels Prepared via Supercritical Drying Technique
WEN Jian-Guo,RUAN Xiang-Yuan,ZHOU Zhen-Tao
2009 Vol. 24 (3): 521524
Abstract(
2313 )
PDF(1643KB)(
1707
)
The MnO2 aerogels were prepared from KMnO4 and allomaleic acid via solgel process and supercritical drying technique. The porous morphology, structure and composition of the aerogels were characterized by SEM, TEM, XRD, XPS, BET surface area, IR and TG/DSC. The effects of dehydration temperature on the aerogels structure were investigated. The results indicate that the proper mole ratio of reactants is favorable to the syntheses of MnO2 gels with the average valence states of manganese being close to 4.The resulting aerogels are hydrophilic, noncrystalline and monolithic porous materials with continuous, interpenetrate and threedimensional network structure, which consist of nanoscale MnO2 colloidal particles with mean particles size of 10nm and mean pore diameter of 100nm. The aerogels morphology maintain unchanged during the heat treatment of dehydration at conventional temperature.
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Photogenerated Cathodic Protection Properties of Nanosized TiO2/ Sb2O5 Coating
ZHOU Min-Jie,ZENG Zhen-Ou,ZHONG Li,ZHAO Guo-Peng
2009 Vol. 24 (3): 525530
Abstract(
3115 )
PDF(2851KB)(
1570
)
Nano-sized TiO2/Sb2O5 bilayer coatings were prepared on type 304 stainless steel substrate by solgel method. Surface morphology, structure and composition of the asprepared TiO2/Sb2O5 coatings were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS). The performance of photoelectrochemical and photogenerated cathodic protection of the coatings was investigated using the electrochemical method. SEM results indicate that the coating surface is continuous, uniform and dense, XRD results show that the coating is of anatase TiO2, XPS results indicate the outer and inner coatings are mainly composed of Ti, Sb, C and O elements. Moreover, the test results of the steady potential and polarization curves demonstrate that the nanosized TiO2/Sb2O5 bilayer coating has worsen photoelectrochemical properties than the plain nanosized TiO2 coating in 3% NaCl solution. Type 304 stainless steel coated with the bilayer coating can maintain cathodic protection for 4h in the dark after irradiation by UV illumination for 1h. In addition, a novel mechanism of the photogenerated cathodic protection for the bilayer coating is put forward.
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Preparation of Li4Ti5O12 with Hydration Titanium Dioxide for Electrochemical Hybrid Capacitor
ZANG Ge,BAO Li-Ying,SU Yue-Feng,WU Feng,CHEN Shi
2009 Vol. 24 (3): 531534
Abstract(
2704 )
PDF(1583KB)(
1812
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A novel pseudonanocrystalline Li4Ti5O12 spinel was prepared using hydration titanium dioxide as starting materials. Hydration titanium dioxide added with activated carbon, citric acid and lithium salt was heattreated at 800℃ in air for 12h after desiccation. The spinel shows a good lithiation performance. Its reversible capacity is more than 152.3mAh/g at current density of 85mA/g, the first chargedischarge efficiency is 99.3% and its chargedischarge potential is flat and steady. Then, the Li4Ti5O12/AC hybrid capacitors using Li4Ti5O12 as the anode and activated carbon as the cathode is assembled. Electrochemical tests show that at current density of 85mA/g, the specific capacity of Li4Ti5O12 electrode is 96.4mAh/g and the efficiency of hybrid capacitor is 96.5%.
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Effect of Graphitization on the Structures and Conducting Property of Carbon Nanotubes
ZHANG Lin-Lin,XU Fang-Fang,FENG Jing-Wei,RUAN Mei-Ling
2009 Vol. 24 (3): 535538
Abstract(
3261 )
PDF(1863KB)(
1784
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Turbostratic carbon nanotubes (CNTs) were treated in nitrogen atmosphere at 2700℃. Highresolution transmission electron microscope (HRTEM) was used to investigate the structural changes of CNTs. Meanwhile, the conducting property was measured via a selfbuilt setup installed in TEM. The structures of CNTs are found to change into bamboolike or tubular cones after graphitization. The apex angles of cones rang from 10° to 30°, and the tubular diameter ranges from 10nm to 40nm. Electron diffraction analysis reveals that an additional overlap angle is involved in the disclination operation of cones, suggesting the helicalconical structural characteristics of CNTs. The highly curved filamental structures are stabilized via interlayer coincidence site lattices of ∑13, ∑7, and ∑19type. The conducting measurement indicates that the helical conical CNTs are semiconductors.
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Preparation and Properties of Cobalt-Doped Ceria (CDC) for IT-SOFCs Anodes in Natural Gas
HAO Hong-Xia,LIU Rui-Quan
2009 Vol. 24 (3): 539544
Abstract(
3295 )
PDF(2290KB)(
1612
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Ce1-xCoxOy(x=0.10, 0.15, 0.20, 0.25, 0.30)(CDC) powders as the anode materials of intermediate temperature solid oxide fuel cells (IT-SOFCs) were prepared by sol-gel method. The NiO-CDC anodesupported cells were fabricated by drypressing process using Ce0.8Gd0.2O2-δ(GDC) as electrolyte and La0.8Sr0.2Co0.8Fe0.2O3-δ(LSCF)-Ce0.8Gd0.2O2-δ(GDC) as cathode. The crystal structure, morphology and chemical stability were investigated by XRD and SEM respectively. The performances of single cells were tested by using humidified natural gas(3% H2O) as fuel and oxygen as oxidant in the temperature range from 400℃ to 700℃. The results show that the anode of the cell has good openframework; The 50%NiO-50%Ce0.8Co0.2Oy(C20C80)anodesupported cell shows the best electrochemical performance among the eight cells composed of different anodes. The maximum current density and power density are 148.84mA/cm2 and 30.91mW/cm2 tested at 650℃, respectively.
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Fabrication of CoSb3/MoCu Thermoelectric Joint by One-step SPS and Evaluation
ZHAO De-Gang,LI Xiao-Ya,JIANG Wan,CHEN Li-Dong
2009 Vol. 24 (3): 545548
Abstract(
2958 )
PDF(2329KB)(
1625
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Mo-Cu alloy was applied as the electrode material in thermoelectric (TE) device using CoSb3based skutterudite compounds. Through adjusting the Cu content of Mo-Cu alloy, good thermal match between CoSb3 material and Mo50Cu50 alloy was achieved. By means of spark plasma sintering (SPS), Mo-Cu alloy was successfully joined with CoSb3 material through insertion of Ti layer. No crack was observed at the CoSb3/Ti/Mo-Cu interfacial area showing the joints were well bonded. SEM shows that an intermetallic compound (IMC) layer forms at the CoSb3/Ti interface and the IMC layer is identified as TiSb phase by the EDS analysis. After thermal aging, the thickness of TiSb phase increases. The high temperature reliability evaluation shows the joint has high thermal stability. The shear strength of joints decreases with the aging time increasing. The results of fourprobe measurement show that the interfacial resistance of joint is low and the contact electrical resistivity is 2030μΩ·cm2, which means the CoSb3/Ti/Mo-Cu joint exhibits a good electrical contact.
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Synthesis and Characterization of CeF3 via Ultrasound Assisted Route
LIU Yang,ZHAO Qing-lan,ZHAO Yan-Ba1,MA Xue-Hui,WU Zhi-Shen
2009 Vol. 24 (3): 549552
Abstract(
2876 )
PDF(596KB)(
1380
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CeF3 nanocrystals were successfully synthesized via ultrasound assisted route, which were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), powder Xray diffraction (XRD), ultraviolet (UV) spectroscope and photoluminescence spectrophotometer (PL). The results show that the shape and size of products are strongly depended on the ultrasonic time. With the increment of the ultrasonic time, the morphology of the CeF3 nanocrystals changes from “lantern” particles to uniform disklike particles. The UV absorption peak and the band-edge of the CeF3 nanocrystals exhibit a pronounced blue shift as the size of the particles decreasing, the PL intensity of CeF3 nanocrystals is related to the crystalline extent.
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Microwave Hydrothermal Synthesis of Hexagonal NaYF4 and Yb3+,Er3+-doped NaYF4 Microtubes
ZHANG Ling,ZHU Ying-Jie
2009 Vol. 24 (3): 553558
Abstract(
3150 )
PDF(5347KB)(
1903
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NaYF4 and Yb3+,Er3+doped NaYF4 (NaYF4∶Yb3+,Er3+) microtubes with a hexagonal structure were prepared by a simple microwave hydrothermal method at a relatively low temperature in a short period of time without using toxic trifluoroacetic acid. The starting reagents used in the preparation are Y(NO3)3 (also using Yb(NO3)3 and Er(NO3)3 in the case of doping), NaF, citric acid, NaOH and ethyl acetate, and deionized water is used as the solvent. The asprepared samples were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The effects of experimental parameters on the morphology and the crystal phase of the product were investigated. And the upconversion photoluminescence properties of the NaYF4∶Yb3+,Er3+ microtubes were investigated. NaYF4 microtubes with single hexagonal phase are obtained by microwave heating method at a lower temperature in a short period. The formation mechanism of NaYF4∶Yb3+,Er3+ microtubes is proposed. The prepared NaYF4∶Yb3+,Er3+ microtubes have high luminescence intensity.
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Epitaxial Growth of AlInGaN Quaternary Alloys by RF-MBE
WANG Bao-Zhu,WANG Xiao-Liang
2009 Vol. 24 (3): 559562
Abstract(
2892 )
PDF(1558KB)(
1761
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AlInGaN quaternary alloys were successfully grown on sapphire substrate by radiofrequency plasmaexcited molecular beam epitaxy (RF-MBE). AlInGaN quaternary alloys with different compositions were acquired by changing the Al cell’s temperature. The streaky RHEED patterns were observed during AlInGaN quaternary alloys growth. Scanning Electron Microscope (SEM), Rutherford backscattering spectrometry (RBS), X-Ray diffraction (XRD) and Cathodoluminescence (CL) were used to characterize the structural and optical properties of the AlInGaN alloys. The experimental results show that the AlInGaN quaternary alloys grow on the GaN buffer in the layerbylayer growth mode. When the Al cell’s temperature is 920℃, the Al/In ratio in the AlInGaN quaternary alloys is about 4.7,and the AllnGaN can acquire better crystal and optical quality. The X-ray and CL fullwidth at halfmaximum (FWHM) of the AlInGaN are 5arcmin and 25nm, respectively.
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Ultra-violet Stimulated Raman Scattering of SrWO4 Crystal
WANG Zheng-Ping,HU Da-Wei,ZHANG Huai-Jin,XU Xin-Guang,WANG Ji-Yang,SHAO Zong-Shu
2009 Vol. 24 (3): 563566
Abstract(
3951 )
PDF(1407KB)(
1500
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SrWO4 crystal with high optical quality was grown by Czochralski pulling method. The crystal sizes reached 22mm×40mm, and the weight was 72.3g. The transmittance range of SrWO4 crystal was measured to be 263-3200nm. By the singlepass configuration, ultraviolet stimulated Raman scattering (SRS) of SrWO4 crystal was realized. When the pump source was a 355nm picoseconds laser, three Stokes lines (366.44, 379.25, 392.98nm)were obtained. The pump threshold of the first Stokes line was only 169.76MW/cm2, and the corresponding Raman gain was 49.09cm/GW. The results show that SrWO4 crystal possesses many advantages such as wide transmittance spectrum, high optical damage threshold, low Raman pump threshold, and large gain coefficient, so the material will have good applications in Raman frequency shifting of ultra-violet laser.
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Effects of Different Dopants on the Growth and Phase Transition of Ba3Y(BO3)3 Crystal
PAN Shang-Ke,LU Sheng,DING Dong-Zhou,YANG Fan,REN Guo-Hao,WANG Guo-Fu
2009 Vol. 24 (3): 567570
Abstract(
2876 )
PDF(1317KB)(
1663
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Phase transition is harmful to the quality of Re doped Ba3Y(BO3)3 crystals. In order to obtain high quality Yb3+∶α-Ba3Y(BO3)3 crystal, Sr2+ ions co-doped Yb3+∶α-Ba3Y(BO3)3 crystal was grown with CZ method. Effect of various dopants and substitution sites on the growth and phase transition of Ba3Y(BO3)3 crystal were investigated. The phase transition temperature of 10at% Nd3+∶α-Ba3Y(BO3)3 crystal is 1099.6℃, which is lower than that of 10at% Yb3+∶α-Ba3Y(BO3)3 crystal (1145.3℃). Furthermore, the phase transition temperature of Nd3+∶α-Ba3Y(BO3)3 crystals is increased with the increase of the contentration of Nd3+ ions. For 10at%Yb3+∶α-Ba3Y(BO3)3 crystal, the melting point is increased and the phase transition temperature is decreased with the increase of the concentration of the codoped Sr2+ ions. The endothermic peak of phase transition disappears when the concentration of Sr2+ ions reaches 16at%, yet phase transition still exists with Sr2+ concentration of 5at% or 10at%.
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Structure Control of Ordered Mesoporous Carbon Spheres Prepared from Suspension-assist Evaporationinduced Selfassembly
LU Feng,LONG Dong-Hui,QIAO Wen-Ming,ZHAN Liang,LING Li-Cheng
2009 Vol. 24 (3): 571576
Abstract(
3055 )
PDF(3915KB)(
1718
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Ordered mesoporous carbon spheres (OMCs) were synthesized by suspensionassist evaporationinduced selfassembly of resorcinolfurfural oligomers and triblock copolymer F127. The effects of emulsifier concentration and stirring speed on the particle size and morphology of OMCs were investigated. The effects of F127/resoncinol ratio and reaction time of resorcinol with furfural on the mesostructure of OMCs were evaluated. It is found that the particle size can be controlled in the range from 60μm to 400μm by changing emulsifier concentration from 0.1vol% to 2.0vol% or stirring speed from 100r/min to 600r/min. The mesostructure of OMCs can be turned by varying the F127/resoncinol ratio or the reaction time of resorcinol with furfural. OMCs with 3-D body-centered cubic, 2-D hexagonal and wormlike mesostructures are obtained with the F127/resoncinol ratio of 0.008, 0.015 and 0.025, respectively.
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Preparation and Characterization of Mesoporous Iron-Oxide
XUE Hong-Tao,SHEN Shui-Fa,PAN Hai-Bo,XIE Chang-Huai
2009 Vol. 24 (3): 577580
Abstract(
2958 )
PDF(1448KB)(
2400
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Transition metal oxides are easy to form insoluble oligomer in reaction because of complicated oxidation states, so it is difficult to obtain the desired mesoporous structure. To resolve the problem, mesoporous iron oxide was synthesized by reacting a micellar phase of sodium dodecyl sulfate (SDS) with iron polymer solution which was prepared by controlling the proportion of sodium hydroxide and ferric chloride. Crystal structure and surface structure of the mesoporous iron oxide was characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analyse(TGA), Nitrogen adsorptiondesorption method and so on. The results show that mesoporous α-Fe2O3 can be obtained after calcining at 450℃ with OH-/Fe3+ ratio of 2.0. Its surface area is 146.5m2·g-1, BJH average diameter is 6.9nm, pore volume is 0.27cm3·g-1. The asprepared mesoporous iron oxide has better thermal stability, it still has surface area of 110.2m2·g-1 after calcination at 550℃.
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Synthesis and Characterization of Highsilica SAPO-5 from Metakolin
ZHOU Xin-Tao,LIU Qi-Feng,SU Da-Gen,LAI Lan-Mei
2009 Vol. 24 (3): 581585
Abstract(
2905 )
PDF(2112KB)(
1806
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Highsilica silicoaluminophosphate (SAPO-5) molecular sieves were hydrothermally synthesized using metakaoline with a certain activity as the silicon and aluminum sources, phosphoric acid as the phosphorus source and triethanolamine combined with cetyltrimethylammonium bromide (CTMABr) as the template agents. The sample was characterized by means of X-ray diffraction spectroscope (XRD), Infrared spectrum (IR), scanning electron microscope (SEM) and 29Si, 27Al MAS-NMR and X-ray photoelectron spectroscope (XPS), temperatureprogrammed desorption of adsorbed NH3. The results show that the crystallization of the SAPO-5 can be promoted by the addition of CTMABr. The synthesized SAPO-5 reveals pillarlike morphology with dimension of 20μm×5μm×5μm. The local environment of Si and Al changs greatly after reaction and many fourcoordinated structures such as Al(OP)4 and Si(AlO)4 are produced with the Si/Al ratio of 0.56. The acidity amount of the product is 0.578mmol/g and the ratio of the strong acid sites to the weak acid sites is 0.684.
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M-type Barium Hexaferrite with Excessive Divalent Iron Synthesized by Spark Plasma Sintering Method
WEI Ping,ZHAO Wen-Yu,WU Xiao-Yan,ZHANG Qing-Jie
2009 Vol. 24 (3): 586590
Abstract(
3170 )
PDF(3057KB)(
1635
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The precursor of M-type barium hexaferrite (BaM) with excessive divalent iron BaFe3+11.8Fe2+0.3O19 was prepared by chemical coprecipitation process in Ar atmosphere. The phase compositions, microstructures, and densities of sintered products synthesized by spark plasma sintering (SPS) method were investigated with XRD, SEM and Archimedes methods. The optimizing SPS condition for synthesizing singlephase and highcompactness BaM materials with excessive divalent iron is holding for 30min at 850℃ and 10MPa. The crystalline reaction process is composed of the decomposition of the precursor into α-Fe2O3 and Fe3O4 or γ-Fe2O3 at low temperature and the crystallization of BaM with excessive Fe2+ at hightemperature, without intermediate phase BaFe2O4 forming in the whole process. Saturation magnetization and coercivity of singlephase BaM materials with excessive divalent iron are of 58.2A·m2·kg-1 and 255kA·m-1, respectively, which imply that the excessive divalent irons spin upward at 2a site in FeO6 octahedron.
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Magnetroresistance and Currentvoltage Characteristics in La2/3Sr1/3MnO3/ZnO Composite Films
JIN Ke-Xin,ZHAO Sheng-Gui,TAN Xing-Yi,CHEN Chang-Le
2009 Vol. 24 (3): 591594
Abstract(
2805 )
PDF(1830KB)(
2135
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agnetroresistance and currentvoltage characteristics of the composite (La2/3Sr1/3MnO3)x/(ZnO)1-x films prepared by the pulsed laser deposition method on Si(100) substrates oxidized by SiO2 were investigated. XRD patterns indicate that ZnO and LSMO have (002) and (101) dominant orientations, respectively, and they form the coexisting system of two phases. Experimental results show the film with x=0.3 favors a semiconductive conduction and the film with x=0.4 exhibits the typical insulatormetal (I-M) transition. The films have the low field magnetoresistance(LFMR) effect and the nonlinear currentvoltage characteristics. The maximum LFMR value of the film with x=0.3 is about 28.8% at T=60K under an applied magnetic field of about 0.7T. The currentvoltage fitting shows that a great number of interface states appear at the depletion between La2/3Sr1/3MnO3 and ZnO grains due to the mismatch of the lattice.
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Effect of Anodized Aluminum Oxide Underlayer on the Magnetic Properties and Structure of Smtbco Magnetic Films
JIN Fang,LI Zuo-Yi,YAN Jun-Bing,LIN Geng-Qi
2009 Vol. 24 (3): 595598
Abstract(
2953 )
PDF(1853KB)(
1639
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A self-ordered hexagonal array of nanopore was fabricated by anodizing a thin film of Al on glass and subsequently SmTbCo perpendicular thin film was prepared on the AAO underlayer by magnetron sputtering. The vibrating sample magnetometer (VSM) measurement reveals that introducing anodized aluminum oxide (AAO) underlayer can increase the coercivity of SmTbCo thin film from 370kA/m to 530kA/m. With the decrease of hole diameter of AAO underlayer, the coercivity and remanence squareness ratio of SmTbCo magnetic thin film are increased. SEM observations indicate that the SmTbCo thin film deposited on the AAO underlayer consists of a column structure which is attributed to the AAO underlayer selfordered hexagonal array of nanopore structure, The enhancement of coercivity caused by heterogeneous structure extends SmTbCo thin film’s application in super high density perpendicular magnetic recording.
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Fabrication of Ba-Hexaferrite Quasi-single Crystals and their Magnetic Properties
LIU Jun-Liang,GUO Cui-Jing,ZHANG Wei,ZENG Yan-Wei
2009 Vol. 24 (3): 599601
Abstract(
3028 )
PDF(1895KB)(
1916
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Barium hexaferrite (BaFe12O19, BaM) with large uniaxial magnetocrystalline anisotropy is a key gyromagnetic material for the millimeter wave device. BaM quasi-single crystal materials with a grain orientation degree(GOD) of 99% were successfully fabricated by using nanosized single-domain BaM crystallites as the starting materials via press-forming in magnetic filed and sintering with minor liquid participation. The as-fabricated BaM quasi-single crystals were characterized with the saturation magnetization of 4654kA/m, the coercity field of 9.552kA/m and their formation mechanism was also discussed.
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Effect of Plused Negative Bias on Nucleation and Morphological Evolution of ZnO Films Deposited by Reactive Radio-frequency Magnetron Sputtering
FU Wei-Jia,LIU Zhi-Wen,GU Jian-Feng,LIU Ming,ZHANG Qing-Yu
2009 Vol. 24 (3): 602606
Abstract(
3075 )
PDF(2690KB)(
2084
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Using reactive radiofrequency magnetron sputtering, ZnO films were deposited on Si (001) substrates with plused negative bias. The atomic force microscopy was used to study the morphological evolution of ZnO films. The nucleation and growth behavior of the films are quantitatively characterized with the dynamic scaling theory. It is found that the island density of ZnO films increases and the grain size decreases with the increase of deposition time. Compared with the film depositions without bias, the stage of low-rate nucleation disappears due to the application of plused negative bias. The growth exponents of the nativedefect nucleation and the ionbombardment defect nucleation are determined to be (0.45±0.03) and (0.22±0.04), respectively. With the voltage of plused negative bias increasing, the island sizes and the roughness increase and the preferred orientation of the films is changed.
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Influence of Boron Doping on Growth Characteristic of Diamond Films Prepared by Hot Cathode DC Chemical Vapor Deposition
Lü Jiang-Wei,FENG Yu-Jie,PENG Hong-Yan,CHEN Yu-Qiang
2009 Vol. 24 (3): 607611
Abstract(
2935 )
PDF(1613KB)(
1612
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Borondoped diamond films were prepared by hot cathode DC chemical vapor deposition system with B(OCH3)3 as dopant. The influence of boron doping on growth characteristic of diamond films was investigated by plasma optical emission spectroscope, scanning electron microscope (SEM), Raman spectroscope, and X-ray diffraction (XRD). Comparing with the growth process for undoped diamond films, it is found that stable glow discharge can sustain for a long time at low boron doping concentration in hot cathode DC chemical vapor deposition system. The species of glow plasma radicals (Hα、Hβ、C2、CH) do not change after boron doping, while the concentration of C2 radical increases and the concentration of CH radical decreases. The growth rate of boron-doped diamond film increases to 0.65mg·cm-2·h-1. The borondoped diamond films possess well-faceted polycrystalline diamond with (111) dominant orientation, and the quality of boron-doped diamond films is improved in comparison with that of undoped diamond films. Boron atoms in the films are located at the substitutional site or interstitial site in diamond lattice, which do not destroy the diamond crystalline structure.
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Structure and Properties of Microarc Oxidation Coatings on SiCP/AZ31 Magnesium Matrix Composite
XUE Wen-Bin,JIN Qian,ZHU Qing-Zhen,MA Yue-Yu
2009 Vol. 24 (3): 612616
Abstract(
2627 )
PDF(2556KB)(
1397
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The protective ceramic coatings were prepared on SiC particle reinforced magnesium matrix composite by microarc oxidation (MAO) surface treatment technique. The surface morphology, cross-sectional microstructure and phase constituent of ceramic coatings were analyzed. And the microhardness profile, thermal shock resistance and electrochemical corrosion behavior of the coatings were measured. The ceramic coating consists of MgO, Mg2SiO4 and a few phases related to the electrolyte elements. Furthermore, a few residual SiC reinforced particles are also remained in the coatings. The maximum hardness of the coating is about HV800, which is at least five times higher than that of the uncoated composite substrate. The coatings do not detach from composite substrate after the coated samples undergo 100 thermal shocks, heating the sample to 500℃ and then quenching into water, which displays a good thermal shock resistance for the MAO coatings on SiCP/AZ31 composite. In addition, after MAO surface treatment, the corrosion resistance of the SiCP/AZ31 composite is greatly improved.
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Stress Analysis in the Preparation of Bi-layer Membranes by Co-sintering Process
QIU Ming-Hui,FENG Jun,FAN Yi-Qun,XU Nan-Ping
2009 Vol. 24 (3): 617622
Abstract(
2950 )
PDF(2414KB)(
1589
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Based on the theory of “constrained sintering”, stress of the membrane exerted by a rigid substrate was calculated. Results show that the tensile stress from supports can decrease driving force and consequently increase the sintering temperature of supported membranes. The optimal sintering temperatures, 1350℃ and 1180℃ for α-Al2O3 and ZrO2 supported membranes respectively, are determined by combining membrane strength and sintering driving force. Meanwhile, a method is proposed to calculate the stress developed in the co-sintering process of the supported multilayer membrane. For ZrO2/α-Al2O3 bi-layer membrane, the calculated results show that due to the contribution of the compressive stress, the sintering driving force increases and the α-Al2O3 membranes can be sintered effectively after co-sintering at 1200℃. Moreover, the top-layer ZrO2 membrane should be thicker than 10μm so as to exert sufficient compressive stress on the sub-layer α-Al2O3 membrane with thickness of 15μm.
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Combustion Synthesis of Ti3SiC2 in Air from 3Ti/Si/2C/0.2Al Powder Mixtures
LIANG Bao-Yan,WANG Ming-Zhi,SUN Jin-Feng,HAN Xin,LI Xiao-Pu
2009 Vol. 24 (3): 623626
Abstract(
2794 )
PDF(696KB)(
1293
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Ti3SiC2 based material was successfully synthesized by self combustion in air using mechanically activated 3Ti/Si/2C/0.2Al powders as starting materials. Phase composition and microstructure of the material were characterized by means of XRD and SEM, the composition of sample was determined through EDX. Mechanical alloying of 3Ti/Si/2C/0.2Al powder mixtures may refine the powder particles and produce the severe lattice distortion, which significantly improves the reaction activities of the powders. When the powder mixture is exposed to the air, it self-ignited spontaneously and self-propagating high temperature synthesis (SHS) of titanium silicon carbide (Ti3SiC2) is induced. After cooling, a porous sample is obtained. The sample is composed of Ti3SiC2,TiC and tiny amounts of oxide. The content of Ti3SiC2 in the sample is about 83wt%. Surface of the sample is relatively uniform and dense, but the fracture is rough and porous. Surface layer of the sample consists mainly of Al2O3 and TiO2 grains with a size of 24μm. The oxidation film thickness is 510μm. The inner of the sample is a mixture of Ti3SiC2 and TiC. Lath Ti3SiC2 grains are 2040μm in length and 24μm in width. TiC grains are about 3μm in dimension.
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Study on Polycrystalline C3N4 Prepared by Blast Shock
YU Yan-Wu,LIU Yu-Cun,ZHANG Hai-Long,CHEN Cui-Cui
2009 Vol. 24 (3): 627630
Abstract(
2855 )
PDF(1466KB)(
1488
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A new technique was developed to synthesize the superhard material C3N4 in which high pressure and temperature needed in the reaction were supplied by RDX explosive charge and dicyandiamide (C2H4N4) was used as the primary precursor. The structure, valencebond character and elemental composition of the sample prepared under 16GPa pressure were characterized by the scanning electron microscope (SEM), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy analysis (EDS) and infrared spectrometer (FTIR) respectively. The results show that the XRD pattern is in accordance with the theoretical value, i.e., α-C3N4, β-C3N4, graphite-C3N4 and intercrystal-C3N4 are recognised in the products. The mass ratio of carbon to nitrogen is about 1.00∶2.98 and nitrogen is mostly bonded with carbon by CN. Some hexagonal β-C3N4 particles with size of 2μm are observed through SEM. Powder of polycrystalline C3N4 is synthesized successfully and its formation mechanism is discussed.
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Oxidation Behaviors of the Pressureless Sintered ZrB2-SiC Composites
YAN Yong-Jie,ZHANG Hui,HUANG Zheng-Ren,LIU Xue-Jian
2009 Vol. 24 (3): 631635
Abstract(
2369 )
PDF(2361KB)(
2008
)
The pressureless sintering process of ZrB2-SiC composite ceramics was studied. The ceramic samples was prepared by using sol-gel synthesized ultra-fine ZrB2 powders as sources and different contents of Mo and/or B4C as sintering aids. The static oxidation behaviors of the sintered ZrB2-20wt%SiC composite ceramics using 4wt%Mo and 4wt%Mo-2wt%B4C additives were systemically analyzed. The results show that the composite ceramics oxidized quickly with visible ZrO2 particles on the surface above 1300℃/30min with pure Mo additive. While Mo-B4C additive is added, the protective liquid layer appears at 1300℃ and becomes thicker and uniform with the temperature rising. The composite ceramics present good oxidation resistance of which the flexural strength retains 86% of the value in room temperature after oxidiation at 1500℃ for 30min.
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Microstructure and Mechanical Property Analysis of AlN Ceramic with Mo-Ni-Cu Alloy Active Brazed Joints
ZHANG Ling-Yan,QIN Ming-Li,QU Xuan-Hui,LU Yan-Jie,ZHANG Xiao-Yong
2009 Vol. 24 (3): 636640
Abstract(
2687 )
PDF(2136KB)(
1585
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AlN ceramic is a highperformance electronic packaging material, but it is difficult to joint with metals directly. AlN ceramic and Mo-Ni-Cu alloy was brazed using 98(Ag28Cu)2Ti active filler alloy in vacuum. EBSD, EDS and XRD were used to study the microstructure and phases of bonding area and the surface of the sheared sample. The mechanical properties and hermeticity performance were measured. It is found that TiN exists in the interface of AlN ceramic, which indicate that there is a chemical bond between ceramic and filler metal, but there is a few of Ni-Ti intermetallics in the interface of MoNi-Cu alloy. TiN and AlN are found on the sheared fracture surface, which indicate that fracture occurrs from the bonding area near the AlN ceramic. The sample has good performance with gas leakage rate of 1.0×10-11Pa·m3/s, average bending strength of σb=78.55MPa and shear strength of στ=189.58MPa.
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