Electrochemical behavior of 304 stainless steel with electrodeposited niobium as PEMFC bipolar plates

In order to enhance the corrosion resistance of 304 stainless steel, niobium was electrodeposited on its surface in air- and water-stable ionic liquids. The electrochemical behaviors of bare and niobium-coated 304 stainless steel were evaluated by electrochemical tests in a simulated proton exchange membrane fuel cell (PEMFC) environment. The results showed that niobium could be electrodeposited on the surface of 304 stainless steel from ionic liquids, and a smooth and strong chemical inert compound film was obtained on the surface of 304 stainless steel, which was mainly composed of NbO and Nb₂O₅. The thin composite film acted as a barrier and remarkably improved the corrosion resistance of 304 stainless steel in the PEMFC environment.     

Two-and three-electrode impedance spectroscopic studies of graphite electrode in the first lithiation

The first lithiation of graphite electrode was investigated by electrochemical impedance spectroscopy （EIS） and scanning electron microscope （SEM） in a two-electrode button cell and a three-electrode glass cell. The results demonstrate that the study of the variation of EIS feature of the graphite electrode in the two-electrode button cell with electrode polarization potential decreasing in the first lithiation cannot be used to investigate the formation mechanism of the solid electrolyte interphase （SEI） film. However, the formation and growth process of the SEI film can be acquired by investigating the variation of EIS features of the graphite electrode in the three-electrode glass cell with the decrease of electrode polarization potential in the first lithiation. Moreover, the results also point out that the SEI film on graphite electrode is mainly formed between 1.0 and 0.6 V in the first lithiation.     

多孔Fe–C–P合金泡孔形貌、孔隙率、显微组织及力学性能的研究

Open cell steel foams were successfully fabricated through the powder metallurgy route using urea granules as the water leachable space holder in the present study. The influence of different amounts of phosphorus (0, 0.5wt%, 1wt%, 2wt%, and 4wt%) was investigated on the cell morphology, porosity, microstructure of cell walls, and mechanical properties of steel foams. The cell morphology and microstructure of the cell walls were evaluated using an optical microscope equipped with image processing software and a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. In addition, the compression tests were conducted on the steel foams using a universal testing machine. Based on microscopic images, the porous structure consists of spherical cells and irregularly shaped pores that are distributed in the cell walls. The results indicated that by increasing the phosphorus content, the porosity increases from 71.9% to 83.2%. The partially distributed ferrite and fine pearlite was observed in the microstructure of the cell walls, and α-Fe and Fe₃P eutectic extended between the boundaries of agglomerated iron particles. Furthermore, elastic and long saw-toothed plateau regions were observed before fracture in the compressional stress–strain curves. According to the results, by increasing the phosphorus content from 0 to 4wt%, the plateau region of the stress–strain curves shifts to the right and upward. Therefore, increasing phosphorus content causes improvement in the mechanical properties of steel foams.     

Silk Fibroin-modified Poly（butadiene） urethane Films and Their Effects on Fibroblast Viability

Surface-modified poly（butadiene）urethane （PBTU） films with silk fibroin （SF） were prepared by simple chemical method under the normal temperature. The physical properties and biological behaviour of the SF-modified PBTU film were evaluated. The results showed that the SF-modified PBTU films kept the tenacity and pliability very well, and could overcome rigid and brittle weaks of silk fibroin films. The morphology of SF in the PBTU film was dendritic aggregations, and the water-contact angle measurement indicated that the surface hydrophilicity of modified films was apparently enhanced. The biocompatibility of PBTU films was improved due to the change of surface components. The degree of platelet adhesion and the cell viability of rat embryo dermal fibroblasts seeded on PBTU films, SF films, and SF-modified PBTU films were measured by counting platelets before and after they contacted the films and MTT assay, respectively. The results indicated that platelet adhesion resistance and cell viability on the modified film were greatly superior to those on the PBTU film and the compound interface had good stability in the air.     

Silicon dots films deposited by spin-coating as a generated carrier addition layer of third generation photovoltaics

In this work, silicon ink composing of silicon powder and zinc oxide solution was formulated and spin-coated on quartz and n/p-Si substrates followed by drying the films under atmosphere at the temperature of 550°C. The results showed that this top-addition layer could be the highly promising layer for photo-generating carriers in third-generation photovoltaics to enhance blue-light absorption. X-ray diffraction and scanning electron microscopy techniques were used to study the presence of silicon and zinc oxide nano-crystallites. The thin films consisting of different energy bandgap of Si nanocrystals(～100 nm) with narrow bandgap and spherical Zn O:Bi nanocrystal(～20 nm) with wider bandgap could be obtained from the evidence of bandgap enlargement. The band gaps of the thin films were tunable by adjusting silicon dots density in Zn O:Bi film. Energy upshift of light absorption edge depended on the silicon dots density was observed in the range 1.6–3.3 eV related band gap enlargement by Tauc plot. Under illumination, a high photocurrent gain of the thin film comprised of low Si dots density coated on a quartz substrate was about 10~3 times higher compared with its dark current. This result is agreeably explained in terms of its lower superficial trap states at the interface between silicon and zinc oxide matrix. The composite layer can be applied to a third-generation solar cell with the efficiency 1.50% higher than that with a typical crystalline-Si solar cell.     

Analysis of magnetic mechanisms of 3d-doped ZnO diluted magnetic semiconductors by an abnormal peak on M-T curve

The crystallographic structures and magnetic properties of a Zn0.95Co0.05O thin film deposited on a C-sapphire substrate using a dual-beam pulsed laser deposition method were characterized. It was shown from crystallographic analysis that the film belongs to the wurtzite structure with the C-axis aligned with that of the substrate. Magnetic hysteresis loops were observed till up to room temperature. A small peak around 55 K was noticed on the magnetization vs. temperature curve. The corresponding temperature of the small peak is close to that of ‘the abnormal peak’ reported by X.M. Zhang et al. From the results obtained, no correlation was found between the abnormal peak and the quantum effects. The magnetic behaviors in the Zn0.95Co0.05O film cannot be explained by the ferromagnetism in diluted magnetic semiconductors. The magnetic mechanisms in ZnO-based diluted magnetic semiconductors are also discussed.     

Regional Δ<Superscript>14</Superscript>C patterns and fossil fuel derived CO<Subscript>2</Subscript> distribution in the Beijing area using annual plants

The level of atmosphericΔ14C and the fossil fuel derived CO 2 concentration in the Beijing area from May to September,2009, were systematically analyzed based on radiocarbon(14C)measurements of annual plants by accelerator mass spectrometry(AMS). The results show that the maximumΔ14C in Beijing was 29.6‰±2.2‰,and the minimum was–28.2‰±2.5‰,with a trend of decreasingΔ14C from the outer suburbs to inner suburbs to the urban center.This trend correlates well with increases in fossil fuel derived CO2 caused by human activities such as population density,industrial emissions and traffic,with lower values of atmosphericΔ14C associated with more intensive human activities.The fossil fuel derived CO 2 concentrations from May to September, 2009,ranged from 3.9±1.0 ppm to 25.4±1.0 ppm.It was calculated that each additional 1 ppm of CO2 from fossil fuels depleted the atmosphericΔ14C by approximately 2.70‰.This study suggests that 14C measurements of annual plants by AMS provide an effective method to rapidly trace fossil fuel derived CO2.     

Micro PEM Fuel Cells and Stacks

1 Results The effects of different operating parameters on micro proton exchange membrane (PEM) fuel cell performance were experimentally studied for three different flow field configurations (interdigitated,mesh,and serpentine).Experiments with different cell operating temperatures and different backpressures on the H2 flow channels,as well as various combinations of these parameters,have been conducted for three different flow geometries.The micro PEM fuel cells were designed and fabricated in-house through a deep UV lithography technique and the SU-8 photoresist was used as microstructure material for the fuel cell flow field plates.Results are presented in the form of polarization VI curves and PI curves under different operating conditions.The possible transport mechanisms associated with the parametric effects were discussed.Moreover,it was found that among the three flow patterns considered,significant improvements can be reached with a specified flow geometry.     

Preparation of Nano Silver/Silk Fibroin Composite Films

In this study, the outstanding biocompatibility of silk fibroin （SF） and the highly efficient anti-bacterial effect of nano silver （NS） were utilized to prepare SF/NS composite film with anti- bacterial property. The structure and property of the film were characterized. The results showed that the structure of SF in the film was mainly silk I. SF in the film was almost insoluble in water. The tensile strength of film with NS was significantly lower than that of films without NS. When the addition of NS was within the range of 0%-0.6%, the elongation at break had no significant difference. The antibacterial rate of the film on staphylococcus aurens and escherichia coil increased with the amount of NS. The minimum amount of NS in the fdm was O. 1% and the maximum amount was 0.5%.     

Fabrication of a TiO2-P25/(TiO2-P25+TiO2 nanotubes) junction for dye sensitized solar cells

The dye sensitized solar cell（DSSC）, which converts solar light into electric energy, is expected to be a promising renewable energy source for today’s world. In this work, dye sensitized solar cells, one containing a single layer and one containing a double layer, were fabricated. In the double layer DSSC structure, the under-layer was TiO₂-P25 film, and the top layer consisted of a mixture of TiO₂-P25 and TiO₂ nanotubes. The results indicated that the efficiency of the DSSC with the double layer structure was a significant improvement in comparison to the DSSC consisting of only a single film layer. The addition of TiO₂-P25 in the top layer caused an improvement in the adsorption of dye molecules on the film rather than on the TiO₂ nanotubes only. The presence of the TiO₂ nanotubes together with TiO₂-P25 in the top layer revealed the enhancement in harvesting the incident light and an improvement of electron transport through the film.     

Porous SiC ceramics fabricated by quick freeze casting and solid state sintering

Porous SiC ceramics with uniform microstructure were fabricated by quick freezing in liquid nitrogen and solid state sintering.Poly(vinyl alcohol)(PVA) was added as binder and pore morphology controller in this work.The microstructure and mechanical properties of porous SiC ceramics could be controlled by the composition of the aqueous slurries.Both solid content of the slurries and PVA content impacted on the pore structures and mechanical properties of the porous SiC ceramics.The solid content of slurries and PVA content varied from 60 to 67.5 wt%and 2-6 wt%,respectively.Besides,the grain morphology of ceramics was also tailored by changing the sintering temperature from 2050 to 2150 ℃.Porous SiC ceramics with an average porosity of 42.72%,flexural strength of 59.28 MPa were obtained at 2150 ℃ from 67.5 wt% slurries with 2 wt% PVA.     

Preparation of Cu（In,Ga）Se2 thin film by sputtering from Cu（In,Ga）Se2 quaternary target

Cu(In,Ga)Se2 (CIGS) thin films were prepared by directly sputtering Cu(In,Ga)Se2 quaternary target consisting of Cu:In:Ga:Se 25:17.5:7.5:50 at%. The composition and structure of CIGS layers have been investigated after annealing at 550 ℃ under vacuum and a Se-containing atmosphere. The results show that recrystallization of the CIGS thin film occurs and a chalcopyrite structure with a preferred orientation in the (112) direction was obtained. The CIGS thin film annealed under vacuum exhibits a loss of a portion of Se, while the film annealed under Se-containing atmosphere reveals compensation of Se. Several solar cells with three different absorber thicknesses were fabricated using a soda lime glass/Mo/CIGS/CdS/i-ZnO/ZnO:Al/Al grid stack structure. The highest conversion efficiency of 9.65% with an open circuit voltage of 452.42 mV, short circuit current density of 32.16 mA cm2 and fill factor of 66.32% was obtained on a 0.755 cm2 cell area.     

Effects of temperature and stress on the creep behavior of a Ni3Al base single crystal alloy

The creep behavior and microstructure of a Ni3Al base single crystal alloy IC6SX with [001] orientation under the testing conditions of 760 ℃/593 MPa, 980 ℃/205 MPa, and 1100 ℃/75 MPa were investigated. The experimental results showed that Alloy IC6SX had good creep resistance and its creep resistance at elevated temperatures was similar to the second generation nickel-base single crystal alloy containing Re. TEM analysis indicated that the dislocation configuration and movement pattern were different under different temperature and stress conditions. It has been found that under the test condition of 1070 ℃/137 MPa the dislocations moved within the γ channel during the primary creep stage, and the motion of dislocations were prevented by the matrix of γ′ phase, which reduced the creep rate of the alloy. In the secondary creep stage, dislocations cut into the γ′ phase from the γ/γ′ interface. However in the third creep stage, the dislocation pileups were observed in both γ and γ′ phase, and dislocation multiplication occurred when the dislocations with different Burgers vector met and reacted each other.     

Densification behavior of mechanically milled Cu–8 at% Cr alloy and its mechanical and electrical properties

Synthesis and consolidation behavior of Cu–8 at%Cr alloy powders made by mechanical alloying with elemental Cu and Cr powders,and subsequently,compressive and electrical properties of the consolidated alloys were studied.Solid solubility of Cr in Cu during milling,and subsequent phase transformations during sintering and heat treatment of sintered components were analyzed using X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The milled powders were compacted applying three different pressures(200 MPa,400 MPa and 600 MPa)and sintered in H2atmosphere at 900 1C for 30 min and at 1000 1C for 1 h and 2 h.The maximum densification(92.8%)was achieved for the sample compacted at 600 MPa and sintered for 1000 1C for 2 h.Hardness and densification behavior further increased for the compacts sintered at 900 1C for 30 min after rolling and annealing process.TEM investigation of the sintered compacts revealed the bimodal distribution of Cu grains with nano-sized Cr and Cr2O3precipitation along the grain boundary as well as in grain interior.Pinning of grain boundaries by the precipitates stabilized the fine grain structure in bimodal distribution.     

Effect of La0.8Sr0.2Co0.2Fe0.8O3-δ morphology on the performance of composite cathodes

In the present work,one dimensional La0.8Sr0.2Co0.2Fe0.8O3 δ(LSCF) nanofibers with the mean diameter of about 100 nm prepared by electrospinning were deposited on Gd0.2Ce0.8O1.9(GDC) electrolyte followed by sintering to form one dimensional LSCF nanofiber cathode. And LSCF/GDC composite cathodes were formed by introducing GDC phases into LSCF nanofiber scaffold using infiltration method. The polarization resistances for the composite cathode with an optimal LSCF/GDC mass ratio of 1/0.56 are 0.27,0.14 and 0.07 Ω cm2at 650,700 and750 1C,respectively,which are obviously smaller than 2.26,0.78 and 0.29 Ω cm2of pure LSCF nanofiber cathode. And the activation energy is1.194 eV,which is much lower than that of pure LSCF nanofiber cathode(1.684 eV). These results demonstrate that the infiltration of GDC into LSCF nanofiber scaffold is an effective approach to achieve high performance cathode for solid oxide fuel cells(SOFCs). In addition,the performance of composite cathode in this work was also compared with that of our previous nanorod structured LSCF/GDC composite cathode.     

Zr-pillared montmoril lonite supported cobalt nanoparticles for Fischer – Tropsch synthesis

In this article Fischer–Tropsch(FT) synthesis was studied over cobalt nanoparticles supported on modifed Montmorillonite(Zr-PILC).Co-loaded/Zr-PILC catalysts were synthesized by hydrothermal methods and were characterized by XRD,XRF,BET,H2-TPR,TGA and SEM techniques.FT reactions were carried out in fxed bed microreactor(T 225 1C,260 1C and 275 1C,P 1,5 and 10 bars).The FT-products obtained over Co-loaded/Zr-PILC catalysts showed increased selectivity of C2–C12hydrocarbons and decreased selectivity towards CH4and higher molecular weight hydrocarbons(C21) at a TOS of 2–30 h as compared to the Co-loaded/NaMMT catalysts.With increase in reaction temperature from225 1C to 275 1C,CO-conversion and CH4selectivity increases while that of C5+hydrocarbons decreases.Decrease in CH4selectivity while increase in C5+hydrocarbons and CO-conversion were observed on increasing the pressure of reaction.     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Effect of CuO addition on the sintering temperature and microwave dielectric properties of CaSiO3– Al2O3 ceramics

CuO-doped CaSiO3–1 wt% Al2O3 ceramics were synthesized via a traditional solid-state reaction method, and their sintering behavior,microstructure and microwave dielectric properties were investigated. The results showed that appropriate CuO addition could accelerate the sintering process and assist the densification of CaSiO3–1 wt% Al2O3 ceramics, which could effectively lower the densification temperature from1250 1C to 1050 1C. However, the addition of CuO undermined the microwave dielectric properties. The optimal amount of CuO addition was found to be 0.8 wt%, and the derived CaSiO3–Al2O3ceramic sintered at 1100 1C presented good microwave dielectric properties of εr?7.27,Q f?16,850 GHz and τf? 39.53 ppm/1C, which is much better than those of pure CaSiO3 ceramic sintered at 1340oC(Q f?13,109 GHz).The chemical compatibility of the above ceramic with 30 Pd/70 Ag during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between palladium–silver alloys and ceramics.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Properties of garnet-type Li6La3ZrTaO12 solid electrolyte films fabricated by aerosol deposition method

The garnet-type Li_6La_3ZrTaO_(12)(LLZT) solid electrolyte films were fabricated by aerosol deposition(AD)method.Ball-milled LLZT powder with a cubic garnet structure and a particle size of 1-2 urn was used as raw material and deposited directly on a SUS316L or a glass substrate via impact consolidation.As-deposited LLZT film has a cubic garnet structure but contains Li_2CO_3 and La_2Zr_2O_7 phases.SEM observation revealed that the film consists of LLZT particles fractured into submicron size.The impurity phase formation during AD process was caused by the local heating by the collision between LLZT particles and deposition surface and reaction with CO_2.The Li~+ ion conductivity of LLZT film was estimated to be 0.24 × 10~(-5)S cm~(-1) at room temperature.Electronic conductivity of LLZT film was confirmed to be around 10~(-12) S cm~(-1),indicating the dominant Li~+ ion conduction of LLZT film.     

Microstructure and growth kinetics of Ce and Y jointly modified silicide coatings for Nb–Ti–Si based ultrahigh temperature alloy

In order to protect Nb-Ti-Si based ultrahigh temperature alloy from oxidation, pack cementation processes were utilized to prepare Ce and Y jointly modified silicide coatings. The Ce and Y jointly modified silicide coating has a double-layer structure: a relatively thick (Nb, X)Si2 (X represents Ti, Cr and Hf elements) outer layer and a thin (Ti, Nb)5Si4 transitional layer. The pack cementation experiments at 1150 ℃ for 8 h proved that the addition of certain amounts of CeO2 and Y2O3 powders in the packs distinctly influenced the coating thickness, the contents of Si, Ce and Y in the (Nb, X)Si2 outer layers, and the density of cavities in the coatings. In order to study the effects of Ce and Y joint modification in the silicide coatings, both only Ce and only Y modified silicide coatings were also prepared for comparison. The mechanisms of the beneficial effects of Ce and Y are discussed. A pack mixture containing 1.5CeO2-0.75Y2O3 (wt%) powders was employed to investigate the growth kinetics of the Ce and Y jointly modified silicide coating at 1050, 1150 and 1250 ℃. It has been found that the growth kinetics obeyed parabolic laws and the parabolic rate constants were 109.20 mm2/h at 1050 ℃, 366.75 mm2/h at 1150 ℃ and 569.78 mm2/h at 1250 ℃, and the activation energy for the growth of the Ce and Y jointly modified silicide coating was 197.53 kJ/mol.