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      20 June 2018, Volume 46 Issue 6 Previous Issue    Next Issue
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    REVIEW
    Preparation, Properties and Applications of Nanopaper Substrates for Flexible Electronics
    Gang CHEN, Cong-xing PENG, Yu-di KUANG, Yong ZENG, Peng-hui ZHU, Ri-hui YAO, Hong-long NING, Zhi-qiang FANG
    2018, 46 (6): 1-10.   DOI: 10.11868/j.issn.1001-4381.2016.000803
    Abstract ( 956 ( PDF (4869KB)( 699 Citation

    In recent years, "green" cellulose nanopaper made of nanocellulose has been considered as an alternative substrate for flexible electronics due to its unsurpassed quintessential physical and chemical properties, for example, biodegradability, light mass, mechanical flexibility, transparency, thermal stability, and compatible with well-established roll-to-roll manufacturing techniques. Nanopaper substrates for flexible electronics have gradually been a hotspot of research in academic and industrial community due to the increasing environmental concerns on electronic waste. The latest progresses in nanopaper substrates for flexible electronics were reviewed. The preparation, properties, and device applications of nanopaper substrates were elucidated in details, with specific emphasis on the current application status of nanopaper substrates in organic thin-film transistors, solar cells, and organic light emitting diodes. Moreover, several personal insights on the existing challenges and future research direction of nanopaper substrates were considered based on current advances.

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    Hydride Phases and Hydride Orientation in Zirconium Alloys
    Wen ZENG, Bai-feng LUAN, Na LIU
    2018, 46 (6): 11-18.   DOI: 10.11868/j.issn.1001-4381.2016.001027
    Abstract ( 1076 ( PDF (921KB)( 636 Citation

    As a fuel cladding materials of the nuclear reactor, water side corrosion and hydrogen absorption generated in zirconium alloys which due to the embrittlement of matrix and hydrogen induced delayed cracking. The hydride phases, hydride orientation and the effect of hydride orientation on mechanical properties of zirconium alloys were reviewed. The crystallographic orientation relationship between α-Zr matrix and hydrides(γ and δ), the effect of texture, Q value, stress and annealing temperature on hydride orientation, the effect of hydride orientation on mechanical properties of zirconium alloy were primarily discussed. Meanwhile, the current problems were analyzed, for example, the mechanism of hydride orientation was not clear, the mechanism of hydride stress reorientation was controversial, etc. It was pointed out that the hydride orientation, crystallographic orientation relationship between hydrides and Zr matrix, hydride stress reorientation in Zr alloys require further investigation. Furthermore, the research on the hydrides in domestic new type high performance Zr alloy needs to be carried out.

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    Evaluation of Irradiation Properties for Fusion Structural Materials
    Pei HE, Wei-zhi YAO, Jian-ming LYU, Xiang-dong ZHANG
    2018, 46 (6): 19-26.   DOI: 10.11868/j.issn.1001-4381.2016.001564
    Abstract ( 762 ( PDF (888KB)( 532 Citation

    On the basis of specific irradiation conditions in fusion reactor, the advantages and limitations of the main proposed irradiation facilities including ion irradiation, fission neutron irradiation, spallation neutron irradiation and fusion neutron irradiation were compared and evaluated.Ion accelerators, fission reactors and theory and modeling are expected to continue to play an indispensable role in studying the irradiation effect of fusion materials before the 14MeV neutron source is available. The corresponding relation between irradiation data from real fusion neutron and irradiation data from ion, fission neutron or spallation neutron irradiation has to be verified by irradiation using 14MeV high flux neutron source (e.g. IFMIF). The construction of powerful, economy-efficient fusion materials irradiation facility and the development of multi-scale numerical simulation are the inevitable choices to facilitate the commercialized application of fusion materials.

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    RESEARCH ARTICLE
    Preparation and Characterization of Pt/buckypaper Catalytic Layer Based on Pt/CNTs Catalyst for Fuel Cells
    Shi-yao ZHU, Ping LI, Li-cheng YE, Jun-sheng ZHENG, Yuan GAO
    2018, 46 (6): 27-35.   DOI: 10.11868/j.issn.1001-4381.2017.000173
    Abstract ( 882 ( PDF (4104KB)( 168 Citation

    In order to increase the utilization of the precious metal catalysts in proton exchange membrane fuel cells, a new type of Pt/buckypaper catalytic layer with gradient structure was designed and prepared. Carbon nanotubes (CNTs) pretreated using ultrasonic method in mixed acid were used as the support of Pt catalyst. The Pt/buckypaper catalytic layer with Pt/CNTs gradient distribution was fabricated by simple filtration method. Several techniques such as scanning electron microscope, energy-dispersive X-ray spectroscope were utilized to characterize the microstructure and morphology of the catalyst and catalytic layer as well as the Pt distribution. The electrocatalytic performance of the catalyst and catalytic layer were measured by cyclic voltammetry and linear sweep voltammetry methods. The results show that the Pt particles were well dispersed on the CNTs support and the Pt particle size of Pt/CNTs was about 2.4nm. The electrochemical specific area (ECSA) of Pt/CNTs is similar to that of commercial Pt/C catalyst, while its specific mass activity and electrochemical stability were much higher than those of Pt/C. The ECSA of Pt/buckypaper catalytic layer can basically maintain the value of Pt/CNTs, indicating a high utilization of Pt. The novel gradient structure of catalytic layer manifests its promising applications in fuel cells.

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    Effects of Y Doping Content on Visible-light Photocatalytic Property of N-BiVO4
    Min WANG, Jin HAN, Yu ZHANG, Mei-yan YOU, Guang-jun YANG, Tian-yu CHAI, Tong ZHU
    2018, 46 (6): 36-42.   DOI: 10.11868/j.issn.1001-4381.2016.000591
    Abstract ( 666 ( PDF (3848KB)( 225 Citation

    Y doped N-BiVO4 photocatalysts were synthesized by a sol-gel method using rice stem as template. The photocatalysts were characterized by XPS, XRD, SEM, BET and UV-Vis DRS methods. The results show that all samples are monoclinic phase and Y doping does not change the crystallinity of N-BiVO4. The addition of nitrogen and yttrium inhibits the growth of crystalline grain and reunion, which can decrease the average grain size and increase the specific area of N-BiVO4, and leds to narrower band-gap and red-shift of optical absorption band. The effects of doping component on photocatalytic activity are evaluated by measuring the degradation of azocarmine B under visible light irradiation. 6Y-N-BVO has an optimal photocatalytic effect and the degradation rate of AZB in 50min is 97%, which is much higher than that of N-BVO(68%) and 6Y-BVO(72%).

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    Preparation of Hollow Fe3O4 Nanospheres & Spongy Carbon Composite and Its Characterization of Electrochemical Performance
    Zhao YANG, Jin-ping YANG, Jing WANG, Shao-wei YAO, Gang LIU
    2018, 46 (6): 43-50.   DOI: 10.11868/j.issn.1001-4381.2016.001319
    Abstract ( 619 ( PDF (3340KB)( 288 Citation

    Using FeCl3·6H2O as iron source, the hollow spheres-in-porous three-dimension (3D)-nanostructure denotes the structure of the hollow Fe3O4 nanospheres & spongy carbon composite was synthesized by the disposable solvothermal method. The effect of the preparation methods and the proportion ratio on the electrochemical properties of the samples was investigated. The phase, composition and morphology of the hollow Fe3O4 nanosphere & spongy carbon composites were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The specific surface area and pore size distribution of the specimen were characterized by nitrogen adsorption-desorption isotherm method. Galvanostatic cycling test was carried out with a LAND CT2001C battery test system to characterize the electrochemical performance. The electrochemical experiment results indicate that the sample exhibits the better electrochemical properties with the synchronization solvothermal method and compound ratio Fe3O4 & C=2:1. The reversible specific capacity remains 1302.6mAh·g-1 up to 100 cycles at the current density of 0.1A·g-1. A homogeneous distribution of hollow Fe3O4 nanospheres(ϕ135nm) in the spongy carbon conductive 3D-network significantly enhances the effective contact with electrolyte and increases electrochemical reaction area, so that improves electrochemical performance of the composite material.

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    Effect of Co-doped Concentration on Microstructure and Photoelectric Properties of Na-Al Co-doped ZnO Thin Films
    Yi-chuan CHEN, Yue-hui HU, Ke-yan HU, Xiao-hua ZHANG, Fan TONG, Wei-qiang SHUAI, Zi-xuan LAO
    2018, 46 (6): 51-56.   DOI: 10.11868/j.issn.1001-4381.2016.000915
    Abstract ( 747 ( PDF (2518KB)( 268 Citation

    Sodium and aluminum (Na-Al) co-doped ZnO thin films (NAZO) were prepared on the quartz glass substrate by sol-gel spin-coating method. The effect of different Na-Al co-doped concentration on crystallization, microstructure and photoelectric properties of ZnO films were investigated. The results show that all NAZO thin films samples grow along the c-axis of the preferred orientation; appropriate Na-Al co-doped concentration can improve the ZnO films crystallization, increase the carrier mobility; meanwhile, six columnar grain structure crystal particles can be observed on the NAZO films surface. With the changing of Na-Al co-doped concentration, the highest mean optical transmittance reaches 95%. Because of the difference of the solid solution ratio, the appropriate concentration can improve the efficiency of doping Na-Al element, which enhances the carrier concentration of the film inside and the resistivity decreases; the lowest resistivity of NAZO thin films is 4.7×10-2Ω·cm.

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    Microstructures and Mechanical Properties of ZL114A Alloy Under Cold Welding State
    Zhen-zhong FAN, Tong WAN, Duan-zhi WANG, Kun-peng WANG, Sheng-qiang WANG, Du-peng HE
    2018, 46 (6): 57-64.   DOI: 10.11868/j.issn.1001-4381.2016.001410
    Abstract ( 926 ( PDF (9532KB)( 324 Citation

    The microstructure and mechanical properties of ZL114A alloy after cold welding were studied by using SEM, EDS, OM, Vickers hardness and WDW-100KN universal tensile tester, the temperature field distribution was calculated by the SYSWELD FEM simulation. The results show that the largest molten pool and peak temperature are 6mm and about 512℃, which are obtained in the 20V and 24A process parameters. The average tensile strength, yield strength, elongation and HV hardness at T6 state are 334, 276MPa, 7.4% and 68HV, which are changed to 156, 108MPa, 12.8% and 60HV after the cold welding process of the ZL114A alloy, leading to a decline of strength by 53.3% and 60.9%, together with an increase of elongation by 72.9%. The same mechanical properties are attained in the cold welding of ZL205A alloy and the normal processing 4mm round hole, the average tensile strength, yield strength and elongation are 232, 218MPa and 3.8%. The primary and binary eutectic Si phases are shown as a spherical morphology at T6 state, dimple fracture is the main fracture mechanism, accompanying with numbers of intergranular fracture. The material organization is changed from the T6 state into the solid solution state after the cold welding process, the silicon particles that distributed nearby the grain boundaries are gathered together and the Mg and Si elements are distributed in the grain boundary area coincidentally, the Cu, V and Mn elements are dissolved into the primary Al matrix, some Al2Cu phases are precipitated along the grain boundary.

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    Effect of Dispersed Precipitates on Recrystallized Grain Size of 3003 Aluminum Alloy
    Yuan-chun HUANG, Tian-cheng XU, Zheng-bing XIAO, Xian-wei REN, Guang-ze JIA
    2018, 46 (6): 65-72.   DOI: 10.11868/j.issn.1001-4381.2016.000260
    Abstract ( 912 ( PDF (8305KB)( 338 Citation

    Regarding the grain coarsening issue of 3003 aluminum alloy cold rolled plate during recrystallization annealing, optical microscopy, scanning electron microscopy(SEM), energy spectrum analysis, X-ray diffraction and transmission electron microscopy were used to investigate the mechanism for the effect of dispersed precipitates, including their kinds, size and distribution on the recrystallization grain size, which were formed during homogenization annealing and intermediate annealing. The results indicate that the recrystallization starting temperature of 3003 aluminum alloy cast-rolling plate is 540℃; the coarse dispersed phases that formed during the homogenization annealing process facilitate the recrystallization, while the fine ones restrain the recrystallization; the fine dispersed phases that formed during the intermediate annealing have a weak effect on the recrystallization; there is no dispersed phases in the plate after intermediate annealing at 500℃ for 200s; at this time, recrystallization occurs prior to the precipitate of dispersed phase; there are many fine AlMnSi phase precipitates in the plate after intermediate annealing at 500℃ for 2h; the optimum homogenization annealing temperature range of 3003 aluminum alloy is between 560℃ and 580℃.

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    Effect of Rare Earth Gd on Corrosion Resistance of AZ31 Magnesium Alloy
    Jun LIU, Jin-ling ZHANG, Zhi-bo QU, Yan-chong YU, Bing-she XU, She-bin WANG
    2018, 46 (6): 73-79.   DOI: 10.11868/j.issn.1001-4381.2016.001178
    Abstract ( 669 ( PDF (3570KB)( 270 Citation

    The corrosion behavior of AZ31 magnesium alloy with different Gd contents in 3.5%(mass fraction) Na2SO4 solution was investigated by mass loss method. The effect of rare earth Gd on microstructure, corrosion rate and corrosion morphology of AZ31 magnesium alloy was analyzed by optical microscope (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that adding rare earth Gd can improve the corrosion resistance of AZ31 magnesium alloy significantly. When the Gd content is less than 4.12%, the corrosion resistance of the alloy increases with the increase of Gd content, but when the Gd content is more than 4.12%, the corrosion resistance of the alloy declines at a certain degree with the increase of Gd content. This is mainly caused by the content of Gd, which exacerbates the micro-galvanic corrosion effect between the precipitation phase and matrix phase, and thereby results in the decline of the corrosion resistance of the alloy. So when the content of Gd is 4.12%, AZ31 magnesium alloy has the optimum corrosion resistance.

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    Microstructure Evolution and Prediction of Alloy 617 During Hot Deformation Based on Dynamic Recrystallization
    Huai-shen ZHU, Yi-hong NIE, Shuai ZHAO, Bao-zhong WANG
    2018, 46 (6): 80-87.   DOI: 10.11868/j.issn.1001-4381.2016.001499
    Abstract ( 815 ( PDF (5275KB)( 556 Citation

    The hot compressive experiments of nickel-based alloy 617 were carried out at the different deformation conditions on a Gleeble-3500 thermal-simulator.The rule of the process parameters on the dynamic recrystallization microstructure evolution of alloy 617 under different deformation conditions were analyzed.Microstructure evolution models of dynamic recrystallization were constructed based on computational analyzed on the experiment data including strain-stress curves and metallographic photos.The models were implanted into finite element software Deform-3D in order to predict microstructure evolution during hot forging.The results show that the simulated results are in good agreement with the actual results, prediction control on the microstructure of alloy 617 during hot forging is achieved and the accuracy of models is verified.

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    Effect of Marine Fouling Organisms Adhesion on Formation of Calcareous Deposits Formed by Cathodic Protection on Surface of Q235 Carbon Steel
    Xiao-long LI, Jie ZHANG, Xin ZHANG, Jiang-wei WANG, Hui-hui XU, Ji-zhou DUAN, Bao-rong HOU
    2018, 46 (6): 88-94.   DOI: 10.11868/j.issn.1001-4381.2016.001264
    Abstract ( 547 ( PDF (5215KB)( 285 Citation

    The effect of fouling organisms adhesion on the formation of calcareous deposits in the ocean environment was simulated by immersion test. The corrosion morphologies, the calcareous deposits composition, the corrosion kinetics of Q235 steel and fouling organisms adhesion were investigated by the methods of SEM, EDS, EIS, mass loss method and fluorescence microscope observation. The results show that the electrochemical impedance modulus value and capacitive reactance arc of the samples of forming calcareous deposits after fouling organisms adhesion are greater than the bare steel samples, but it is less than the samples of forming calcareous deposits without fouling organisms adhesion. The results show that fouling organisms adhesion can inhibit the formation of calcareous deposits and cause calcareous deposits to protect metal performance degradation. The Ca/Mg ratio of same sample gradually decreases with the increase of experimental periods, and this shows that the ability of large fouling organisms to inhibit the formation of calcareous deposits is stronger.Mass loss experiments show that large fouling organisms can inhibit local corrosion.

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    Microstructure Evolution of Sn-35Bi-1Ag/Ni-P/Cu Solder Joints During Post-reflow Cooling and Isothermal Aging
    Han-qiao LU, Yu-long LI, Xiao YU, Wei-feng LONG, Jian-feng JIANG
    2018, 46 (6): 95-100.   DOI: 10.11868/j.issn.1001-4381.2017.000412
    Abstract ( 636 ( PDF (3914KB)( 238 Citation

    Two kinds of rapid and slow cooling solder joints of Sn-35Bi-1Ag/Ni-P/Cu were prepared by reflow soldering and then cooling in water and oven, respectively. The kinetics of two kinds of layers were investigated using isothermal aging. Scanning electron microscope and energy dispersive spectrum were employed to characterize the microstructure and composition of the interfacial layers. Experimental results show that the structure of rapid-cooling interface is composed of (Ni, Cu)3Sn4+Ni3P, while the slow-cooling interface consisting of (Ni, Cu)3Sn4+Ni3P+(Cu, Ni)6Sn5.During the isothermal aging process, the growth of (Ni, Cu)3Sn4 layer slows down for the thin Ni-P gradually depleting, but the (Cu, Ni)6Sn5 layer follows the dynamics of the square root of aging time. The growth of interface IMCs is overall controlled by the diffusion mechanism, and these two kinds of interfacial layers eventually exhibit the composite lamellar structure of (Cu, Ni)6Sn5+(Ni, Cu)3Sn4+(Cu, Ni)6Sn5.The IMCs layer thickness in slow-cooling solder joints is greater than that in rapid-cooling solder joints under the same condition during soldering and aging. The growth rates of total IMCs are 4.670×10-18m2/s for slow-cooling joints, 3.816×10-18m2/s for rapid-cooling joints, respectively. It indicates that the cooling rate affects the aging behavior of solder joints during soldering and service.

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    Effect of Carbon Fiber Coating on Thermal Conductivity of Carbon Fiber Reinforced Lithium Alumina Silicate Glass-ceramics Composites
    Chang-qing YU, Li CHEN, Yu-chen PEI
    2018, 46 (6): 101-105.   DOI: 10.11868/j.issn.1001-4381.2017.001159
    Abstract ( 792 ( PDF (3037KB)( 346 Citation

    The carbon fibers with two and four order graphite intercalation were fabricated by high temperature heat treatment of carbon fibers coated by lithium-silicate sol using sol impregnation method. After that, the as-prepared carbon fibers were applied to synthesize carbon fiber reinforced lithium alumina silicate (Cf/LAS) glass-ceramic composites. The results indicate that the increase of sintering temperature and the formation of graphite intercalated compounds on the surface of carbon fibers can significantly improve the thermal conductivity of Cf/LAS composites. Compared to the Cf/LAS composites without coatings 1.1-1.3W/(m·K), the thermal conductivity of Cf/LAS composites with coating treatment increases from 1.3W/(m·K) to 2.2W/(m·K), with the increase of 70%.

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    Effects of LaPO4 Coating on Properties of Carbon Fiber Reinforced SiBCN Ceramic Matrix Composites
    Xi TAN, Wei LIU, La-mei CAO, Sheng-long DAI
    2018, 46 (6): 106-112.   DOI: 10.11868/j.issn.1001-4381.2017.000188
    Abstract ( 915 ( PDF (5044KB)( 277 Citation

    A novel lanthanum monazite (LaPO4) coating was applied on two-dimensional woven continuous carbon fibers by a simple hydrothermal method. Then a Cf/LaPO4/SiBCN ceramic matrix composite(CMCs) was fabricated via subsequent RTM (resin transfer moulding) & PIP (polymer impregnation and pyrolysis) technology. Microstructure observation shows that most of the carbon fibers are coated uniformly with a layer of lanthanum monazite with the thickness of 500nm and there is no obvious chemical contamination between the coating and fiber/matrix during high temperature pyrolysis process. Cf/SiBCN, Cf/PyC/SiBCN and Cf/BN/SiBCN composites were also made to be compared with Cf/LaPO4/SiBCN composites in three-point bending test, fracture toughness test and oxidation test. The results show that Cf/LaPO4/SiBCN composites obtain at least 30% improvement in fracture toughness; in 1350℃/50h oxidation test, Cf/LaPO4/SiBCN composites have the lowest mass loss and the fibers are protected effectively by the coatings, demonstrating the significant increasing in oxidation resistance. Overall, compared with other mentioned coatings, the lanthanum monazite coating enhances much more the high temperature performance of the carbon fiber reinforced SiBCN ceramic matrix composites and promotes the high temperature application potential of the composites.

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    Preparation and Properties of Composites of R-PET and Surface Modified Aramid Fiber
    Ya-bo LI, Ning-ning CAO, Yu-ying ZHENG, Wen-qing ZHENG
    2018, 46 (6): 113-119.   DOI: 10.11868/j.issn.1001-4381.2016.001290
    Abstract ( 645 ( PDF (2048KB)( 242 Citation

    Phthalic anhydride was used to corrode the aramid fibers (AFs) in order to improve the interfacial compatibility between AFs and recycled polyethylene terephthalate (R-PET). Besides, the intrinsic viscosity and the mechanical properties of the composites of AFs/R-PET could be improved to realize the transformation from waste products to engineering plastics because phthalic anhydride was also the chain extender of R-PET. FE-SEM, XPS, DSC, TG and MFR were used to study the surface morphology and element contents of AFs and the impact fracture morphology, crystallinity and liquidity of the AFs/R-PET composites. The results show that the surface roughness of AFs and the surface oxygen content are increased with the increase of etching time. Compared with the pure R-PET, AFs/R-PET composites are easier to crystallize and the composites have higher bending strength and impact strength. The maximum intrinsic viscosity of the composites reaches 0.9343dL·g-1 and the mechanical properties achieve optimal values when AFs are corroded for 6h.

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    Characteristics of Al Coatings Fabricated by Detonation Gun Spray on Polymer-based Composites
    Yong-jing CUI, Jing-ying HAO, Chang-liang WANG, Bo YU, Zhi-hui TANG
    2018, 46 (6): 120-124.   DOI: 10.11868/j.issn.1001.4381.2017.000655
    Abstract ( 781 ( PDF (1392KB)( 411 Citation

    0.45mm thick Al coatings were deposited by detonation gun spraying (D-gun) on polymer-based composites. The characteristics of the coatings, including micro structure, phase composition and bonding strength, were investigated by means of SEM, EDS, XRD and mechanical testing machine; electrical conductivity and electromagnetic shielding properties were then tested according to GJB 2604-1996 and GJB 6190-2008 respectively. The results indicate that D-gun sprayed Al coating, with bond strength 8.63MPa and porosity about 1.26%, is superior to that of conventional flame spray and plasma spray; D-gun sprayed Al coating, with electrical resistivity 0.181mΩ/□ and 1-40GHz electromagnetic shielding effectiveness above 60dB, is an ideal candidate for electromagnetic shielding utilizing.

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    Preparation and Damping Properties of PMN/CB/PF/ⅡR Composite
    Jian LI, Ming DU, Zhi-xiong HUANG
    2018, 46 (6): 125-131.   DOI: 10.11868/j.issn.1001-4381.2016.001120
    Abstract ( 525 ( PDF (3053KB)( 172 Citation

    The aim of this study was to investigate the damping properties of butyl rubber (ⅡR) composite filled with conductive carbon black and piezoelectric ceramics particles (PMN). Factors such as the content of PMN and CB, external force and its frequencies, polarization and modulus of polymer matrix on the damping properties of the composite were studied by DMA analysis. The results show that with the same external force, only when the frequency of external force is matched with the modulus of the composite, the mass fraction of PMN is 50% and CB is 5%, the damping peak can reach its maximum value, the damping coefficient maximum reaches 0.81, the damping temperature range is -35-60℃, and with optimum damping property. And the damping peak of polarized sample is higher than that of unpolarized.

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    Predication and Experimental Verification on Mechanical Properties of Three-dimensional and Four-direction Braided Composites
    Shan-ying XU, Huan-cheng TAN, Yu-pu GUAN, Lu-lu LIU
    2018, 46 (6): 132-140.   DOI: 10.11868/j.issn.1001-4381.2016.001135
    Abstract ( 848 ( PDF (6351KB)( 308 Citation

    In order to predict the elastic constants of 3D four-direction braided composites, unit cell model was established for braided composites with 20°, 30°, 45° braided angle respectively. The elastic properties of the interior cell and the surface cell were predicted using both the stiffness volume average method and the numerical analysis method, and all quasi-static tensile tests were performed on MTS machine. The experimental results, theoretical analysis and numerical simulation results were analyzed. It is found that the axial tensile modulus decreases, and the transverse tensile modulus and transverse shear stiffness increases with the increase of braiding angles because of the decrease of the component of carbon fiber stiffness in the direction of the carrier movement and the increase of the transverse component of carbon fiber stiffness. Tests reveal that the stress-strain curve for the extension tests of specimen of 20° braided angle exhibit linear elastic type, the stress-strain curve of 30° specimen shows nonlinear characters, the stress-strain curve of 45° specimen shows bilinear relation, but the transverse tensile stress-strain curves of all the specimens are basically linear. Combining the longitudinal and transverse tensile test results with the theoretical and numerical data, it is found that the stiffness volume average method and the numerical analysis methods are able to predict the stiffness in the direction of the carrier movement of 3D braided composites well. However, the prediction precision for the transverse stiffness of specimen is not satisfactory, mainly because these methods neglect the interface damage between the fiber and the matrix in tests.

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    Photo-oxidative Degradation Behavior and Comprehensive Evaluation Model of LDPE Based on Improving Principal Components Analysis
    Jun DAI, Hua YAN, Lian-yong SANG, Zhi-de HU, Han-song ZHANG
    2018, 46 (6): 141-147.   DOI: 10.11868/j.issn.1001-4381.2017.001624
    Abstract ( 808 ( PDF (859KB)( 217 Citation

    The artificial accelerated aging test of low density polyethylene (LDPE) was carried out for different time periods up to 64 days under UV environment to study the photo-oxidative degradation behavior and the rule. The influence on mechanical properties, chemical structure, thermal stability and melting property evolution of LDPE after photo-oxidation aging was studied by mechanics experiments, attenuated total reflection infrared spectroscopy (ATR-FTIR), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Analytic hierarchy procedure (AHP) was used to determine the weighing values for assessment index of LDPE, and the photo-oxidative degradation comprehensive evaluation model of LDPE was established on the base of improving traditional principal components analysis (PCA). The results show with increasing aging time, the tensile strength, bending strength and impact strength of LDPE are declined by 39.7%, 32.3% and 96.4%, respectively. The concentration of carbonyl and hydroxyl groups are increased, the rupture of molecular chain is intensified. The initial thermal decomposition temperature and melting temperature peak value are declined and the LDPE surface microstructure is seriously damaged and the aging is severe. The comprehensive evaluation parameters exhibit changing trend in three stages. The evaluation results of improved PCA are more reasonable and all the above-mentioned shows that improved PCA is appropriate for the comprehensive evaluation of photo-oxidative degradation behavior of LDPE.

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