Enhancement of Electric Conductivity in Transparent Glasse—Ceramic Nanocomposites of Bi2O3—BaTiO3 Glasses

The frequency and temperature dependent electrical conductivity measurements for heat-treated binary glass system with composition of （lO0-x）Bi203-xBaTi03 （x = 20, 30, 40 and 50, in mol%） were carried out. The glass was prepared by melt quenching technique and their corresponding glass-ceramic nanocomposites were obtained by suitable heat treatment. Nanostructured behavior and electrical properties of these glasses and their corresponding glass-ceramic nanocomposites were studied. X-ray diffraction （XRD） and differential scanning calorimetry confirmed the amorphous nature of the glasses. Moreover, XRD patterns of the samples indicate nanocrystallites embedded in the glass matrix. The Fourier transform infrared spectroscopy （FT-IR） spectral analysis showed that the band positions of glass system are within the wave number range of Bi06, Bi03 and Ti06 structural units. It is observed that the electrical conductivity is enhanced by 102-103 times in the transparent glass-ceramic nanocomposite phase. With further heat treatment, the conductivity decreased considerably in the stage of glass-ceramic nanocomposite phase as compared with the glassy phase sample. Therefore, partially devitrified phase is more suitable as cathode material in secondary batteries compared to its vitreous or fully crystalline counterpart. The conduction mechanism was confirmed to obey the adiabatic small polaron hopping （SPH）. AC conductivity measurements were performed as a function of temperature and frequency, showing a very slow increasing rate at low temperatures and then a fast rate at higher temperatures.     

Effects of Strontium,Magnesium Addition,Temperature Gradient,and Growth Velocity on AI-Si Eutectic Growth in a UnidirectionaUy-solidified Al-13 wt% Si Alloy

Al-Si eutectic growth mechanism was investigated in a directionally-solidified AI-1 3 wt% Si alloy with different strontium （Sr） and magnesium （Mg） additions, growth velocities and temperature gradients. Macro- and micro- scale metallographic analyses revealed that addition level of Sr and Mg, temperature gradient and growth velocity are important factors affecting stability of solidifying AI-Si eutectic front and the final morphology of eutectic grains in the solidified A1-13 wt% Si alloys. By varying （tailoring） these factors, a variety of eutectic grain structures and morphologies such as planar front, cellular structure, a mix of cellular and columnar, or equiaxed dendrites, can be obtained. Increasing temperature gradient, reducing growth velocity, or decreasing Sr and Mg contents is beneficial to stabilizing planar growth front of eutectic grains, which is qualitatively in accordance with constitutional supercooling criterion for binary eutectic growth. In contrast, adding more Sr and Mg, increasing growth velocity, or decreasing temperature gradient produces large constitutional supercooling, leading to columnar-equiaxed transition （CET） of eutectic structure, which can be interpreted on the basis of Hunt＇s Model. It is also found that both solute concentration and solidification variables have significant impact not only on eutectic growth, but also on gas porosity formation.     

Microstructure,Phase Transformation,Precipitation Behavior and Mechanical Properties of P/M Cu40Zn-1.0 wt% Ti Brass Alloy via Spark Plasma Sintering and Hot Extrusion

The effect of titanium addition on the microstructure and mechanical properties of brass Cu4OZn has been studied via the powder metallurgy （P/M） route. The water-atomized Cu4OZn-1.0 wt% Ti alloy powder was consolidated at different temperatures in the range of 400-600℃ using spark plasma sintering （SPS） and hot extrusion subsequently. Results show that the super-saturated solid solution titanium element in rapidly cooled brass Cu4OZn powder created high chemical potential for a precipitate reaction, showing significant grain refinement effects on the consolidated Cu4OZn matrix. Consequently, excellent mechanical properties were obtained by precipitation hardening and work hardening after sintering and extrusion, with yield strength of 390 MPa, ultimate tensile strength of 617 MPa, and Vickers micro-hardness of 192 HV, which are 28.7%, 23.4%, and 23.9% higher values than those of extruded Cu4OZn brass, respectively.     

Role of Double Oxide Film Defects in the Formal ion ol’ Gas Porosity in Commercial Purity and Sr-containing A1 Alloys

The role of double oxide film （bifilm） defects in the formation of gas porosity in commercial purity and Srcontaining AI alloys was investigated by means of a reduced pressure test （RPT） technique. The liquid metal was poured from a height into a crucible to introduce oxide defects into the melt. The melt was then subjected to different ＂hydrogen addition＂ and ＂holding in liquid state＂ regimes before RPT samples were taken. The RPT samples were then characterized by determining their porosity parameters and examining the internal surfaces of the pores formed in them by scanning electron microscopy. The results indicated oxide defects as the initiation sites for the growth of gas porosity, both in commercial purity and Sr-containing AI alloys. The results also rejected reduction of the surface tension of the melt, increase in the volumetric shrinkage and reduction in interdendritic feeding as the possible causes of an increase in the porosity content of the AI castings modified with strontium. The change in the composition of the oxide layers of double oxide film defects was suggested to be responsible for this behaviour.     

Fabrication of Shape-Controlled Au Nanoparticles in a TiO2-Containing Mesoporous Template Using UV Irradiation and Their Shape-Dependent Photocatalysis简

A SiO_2-TiO_2 template with ordered tubular mesochannels has been prepared by the sol—gel method.Au nanorods are deposited in the tubular mesochannels of the SiO_2—TiO_2 template,and the shape of Au is changed from nanorods to nanospheres by ultraviolet irradiation during thermal deposition.The photocatalytic activity of mesoporous SiO_2—TiO_2 with/without Au nanorods/nanospheres is evaluated.Deposition of Au in the mesoporous SiO_2—TiO_2 template enhances the photocatalysis of TiO_2.Interestingly,the sample containing Au nanorods exhibits higher photocatalytic activity than that with Au nanospheres.Photocatalysis by exciting surface plasmon resonance is not detected in the composite samples regardless of the shape of the deposited Au nanoparticles.     

Isothermal Oxidation Behavior of Dysprosium/S-Doped β-NiAl Alloys at 1200°C

A β-NiAl alloy with normal purity, a S-doped and a Dy and S co-doped b-NiAl alloys were prepared by arc-melting and their corresponding S contents were less than 20×10 6, 33×10-6 and 22×10-6, respectively. The isothermal oxidation behavior of the alloys at 1200° C was investigated and the extent of S segregation at the scalee alloy interface was determined by scanning Auger microscopy. S-doping had no significant effect on the phase transformation rate from q- to a-Al2O3, while the addition of Dy retarded this process. For the Sdoped alloy, scale rumpling occurred only after 2 h thermal exposure and numerous large voids were observed at the scalee alloy interface where S segregated. In contrast to this, the oxide scale formed on the Dy and S co-doped alloy still remained flat even after 50 h isothermal oxidation and only small voids existed at the interface where S segregation was not detected.     

Optical and Microstructural Characterisations of Pulsed rf Magnetron Sputtered Alumina Thin Film

Alumina thin films were deposited on fused quartz and SS304 substrate by pulsed rf magnetron sputtering with both direct and reactive methods. The films were characterised by energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy and atomic force microscopy to reveal the microstructure, surface morphology and topography of thin films. Transmittance and reflectance of alumina thin film were evaluated after deposition on the quartz substrate. Transmittance of the quartz remains almost un-altered when alumina was deposited by the reactive sputtering. A marginal decrease of ~4% in the transmittance of quartz was, however, observed after deposition of alumina by direct sputtering. Infrared emittance of the substrate also remains almost constant after deposition of thin alumina film. Further, as-deposited alumina on SS304 obtained by both direct and reactive sputtering process was amorphous in nature. However, after annealing crystalline peaks were observed.     

Fabrication of (Ti,Hf)-rich NiTiHf Alloy Using Graphitic Mold and Crucible

In this research, fabrication of a(Ti,Hf)-rich NiTiHf alloy by using vacuum induction melting(VIM) process and a graphitic crucible was investigated. For this purpose, casts with the nominal composition of Ni49Ti36Hf15 were prepared in graphitic crucible and mold. Optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS), X-ray diffraction(XRD), and differential scanning calorimetry(DSC) tests were employed to characterize the samples. Results demonstrated that microstructure of the first cast was composted of a B2 austenite phase as well as a great amount of two differently formed(Ti,Hf)C carbides.Moreover, no austenite 4 martensite transformation peak was detected in the DSC curve of this sample,indicating a drastic decline in the transformation temperatures. In the succeeding cast, however, owing to the formation of carbide layers on the inner surfaces of the graphitic crucible and mold during the initial casting process, the amounts of carbides decreased remarkably. This cast exhibited transformation temperatures above100° C, while XRD pattern denoted the presence of B190 monoclinic martensite phase at room temperature.All in all, results confirmed that VIM process using graphitic mold and crucible can be considered as an appropriate method for the fabrication of(Ti,Hf)-rich NiTiHf high temperature shape memory alloys.     

Influence of Features of Interphase Boundaries on Mechanical Properties and Fracture Pattern in Metal--Ceramic Composites

The results of a theoretical study on the influence of strength of interphase boundaries in metal-ceramic composite on macroscopical characteristics of composite response such as strength, deformation capacity, fracture energy and fracture pattern are presented. The study was conducted by means of computer-aided simulation by means of movable cellular automaton method taking account of a developed ＂mesoscopical＂ structural model of particle-reinforced composite. The strength of interphase boundaries is found to be a key structural factor determining not only the strength properties of metal-ceramic composite, but also the pattern and rate of fracture. The principles for achievement of the high-strength values of particle/binder interfaces in the metal-ceramic composition due to the formation of the wide transition zones （areas of variable chemical composition） at the interphase boundaries are discussed. Simulation results confirm that such transition zones provide a change in fracture mechanism and make the achievement of a high-strength and a high deformation capacity of metal-ceramic composite possible.     

Corrosion Behavior of Extruded near Eutectic Al—Si—Mg and 6063 Alloys

In this work,a comparison study on corrosion behavior of extruded near eutectic Al—12.3%Si—0.26%Mg and 6063 alloys has been carried out by mass loss test in 4%H₂SO₄ aqueous solution in the open air and potentiodynamic polarization test in 3.5 wt.%NaCI aqueous solution.Results indicate that the corrosion resistance of the near eutectic Al—Si—Mg alloy is less than that of 6063 alloy.Macro/microscopy and scanning electron microscopy results clearly show the difference of the corrosion progress of these two alloys in 4%H₂SO₄ aqueous solution.The corrosion type of 6063 alloy is pitting corrosion.The Mg₂Si and AlFeSi particles and surface defects act as nucleation sites for pitting,and the amount and distribution of them have a significant effect on the pitting behavior.For the near eutectic alloy,there are two types of corrosion cells. One is between the extruded primaryα-AI and the eutectic,the other is between the eutectic Al and eutectic Si particles.Combination of these two types of corrosion cells leads to a lower corrosion resistance,a higher mass loss of the near eutectic alloy compared with 6063 alloy,and the formation of the paralleling corroded grooves.     

Development and Characterization of Al2O3 Dispersed Al/Mg/Cu/Ti Matrix Composite

The effect of dispersion with different weight fractions of Al2O3 particles in metallic matrices （AI/Mg/Ti/Cu） fabricated by powder metallurgy was investigated. In the case of 15 wt% Al2O3 reinforced composites, peak hardness was attained which subsequently decreased with increasing the content of Al2O3. A correlation between the microhardness and nanomechanical properties at submicron scale was examined for all the composites. Specific strength and specific modulus were measured in order to figure out the performance of the composites.     

Mo^6＋ Modified （K0.5Na0.5）NbO3 Lead Free Ceramics： Structural,Electrical and Optical Properties

Lead free polycrystalline ceramics （K0.5Na0.5）Nb（1-x）MoxO3 （x = 0, 0.02, 0.04, 0.06 and 0.08） have been synthesized via solid state reaction method. The formation of single phase perovskite structure up to 6 mol% of Mo^6＋ has been confirmed by X-ray diffraction pattern. Impedance spectroscopy reveals that bulk resistance decreases with increasing temperature, which indicates negative temperature coefficient of resistance （NTCR） behaviour of the compounds. The diffuse reflectance spectroscopy results indicate a red shift of the band gap energy of K0.5Na0.5NbO3 （KNN, from 4.28 to 3.61 eV） with increasing Mo^6＋ concentration due to structural modification. The photoluminescence spectra of doped samples are composed of two emission bands at room temperature. One emission band is near band edge ultraviolet （UV） emission （354 nm） and other is visible emission band （-397 nm） which may explore the possibility of these ceramics to be used in optical device applications.     

Electrochemical Study of Diffusion Bonded Joints between Micro-duplex Stainless Steel and Ti6Al4V Alloy

In the present study, corrosion behavior of diffusion bonded joints formed between micro-duplex stainless steel （MDSS） and Ti6AI4V alloy （TiA） （at 900 ~C for 60 min under 4 MPa uniaxial pressure in vacuum） was investigated in 1 mol/L HCI and 1 mol/L NaOH solutions using various electrochemical measurements such as open circuit potential （OCP）, electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization （PD）. For comparison, corrosion behavior of base metals （MDSS and TiA） was also evaluated. Bonded joint was characterized by light optical microscopy and scanning electron microscopy using backscattered electron mode. The layer wise σ phase and λ ＋ FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were - 556.4 MPa and -420.2 MPa, respectively.     

Hydrothermal Synthesis of CsxWO3 and the Effects of N2 Annealing on its Microstructure and Heat Shielding Properties

Cesium tungsten bronze(Cs_xWO_3) powders were synthesized by hydrothermal reaction at 190 ℃ by using sodium tungstate and cesium carbonate as raw materials,and the effects of N_2 annealing on the microstructure and near-infrared(NIR) shielding as well as heat insulation properties of Cs_xWO_3 were investigated.The results indicated that the synthesized Cs_xWO_3 powders exhibited hexagonal Cs_(0.32)WO_3crystal structure,and subsequent N_2 annealing could further improve the crystallinity of CsxW03 particles.Moreover,the NIR shielding and heat insulation properties of Cs_xWO_3 could be further improved after N_2annealing at appropriate temperature for a period of time.Particularly,the 500 ℃-annealed Cs_xWO_3 products in the N_2 atmosphere showed the best NIR shielding and heat insulation properties.When the N_2 annealing temperature was higher than 700 ℃,the NIR shielding properties decreased again.The 800 ℃-annealed samples in the N_2 atmosphere showed higher visible light transmittance,however,the NIR shielding properties were lower than that of the non-annealed samples.     

Achieving Large-area Bulk Ultrafne Grained Cu via Submerged Multiple-pass Friction Stir Processing

Large-area bulk ultrafine grained (UFG) pure Cu was successfully prepared by multiple-pass overlapping friction stir processing(FSP) under additional rapid cooling.Overlapping FSP did not exert a significant effect on the microstructure and mechanical properties of the FSP UFG Cu.Similar average grain size was achieved in the transitional zone(TZ) of the multiple-pass FSP sample compared to that in the nugget zone of the single-pass FSP sample,and the TZ exhibited a strong{111}〈112〉type A fiber shear texture.Very weak softening occurred in the TZ of the multiple-pass FSP UFG Cu,resulting in a relatively uniform hardness distribution throughout the whole processed zone.A high yield strength of w310 MPa and a uniform elongation of w13%were achieved in the bulk FSP UFG Cu.This study provides an effective strategy to prepare large-area bulk UFG materials.     

Flower-shaped CuO Nanostructures： Synthesis, Characterization and Antimicrobial Activity

In the present work, flower-like CuO nanostructures were synthesized by reflux condensation method without using any surfactants or templates. Structural analysis by X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR） and Raman studies revealed the formation of highly crystalline single phase CuO, exhibiting monoclinic structure. Morphological analysis by field emission scanning electron microscopy （FESEM） showed flower-shaped CuO hierarchical architecture made up of interpenetrating self-assembled nanosheets. Optical analysis by UV-Vis diffused reflectance spectra （DRS） exhibited considerable blue-shift in the optical band gap due to quantum confinement effect. Photoluminescence （PL） spectrum showed both UV as well as visible emissions. The antibacterial activity of flower-shaped CuO nanostructures were tested against gram-positive （Bacillus subtilis, Bacillus thuringiensis） and gram-negative （Salmonella paratyphi, Salmonella paratyphi-a, Salmonella paratyphi-b, Escherichia coil and Pseudomonas aeruginosa） bacteria. Also, the antifungal activity of CuO was investigated against Aspergillus niger, Rhizopus oryzae, Aspergi/lus flavus, Cladosporium carrionii, Mucor, Penicilliurn notatum and Alternaria alternata. Results demonstrate that the flower-shaped CuO nanostructures act as an effective antimicrobial agent against pathogenic bacteria and fungi.     

Microstructures and Hardness Properties for β-Phase Ti-24Nb-4Zr-7.9Sn Alloy Fabricated by Electron Beam Melting

Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for the precursor powder and 2.5 GPa for the solid, EBM-fabricated products. The powder and solid product microstructures were examined by optical and electron microscopy. X-ray diffraction analyses showed that they had bcc β-phase microstructure. However, it was found by transmission electron microscopy that the EBM-fabricated product had plate morphology with space -100-200 nm. Although the corresponding selected area diffraction patterns can be indexed by β-phase plus α＂-martensite with orthorhombic crystal structure, the dark-field analyses failed to observe the α＂-martensite. Such phenomenon was also found in deformed gum metals and explained by stress-induced diffusion scattering due to phonon softening.     

Plasmon-enhanced Performance of Dye-sensitized Solar Cells Based on Electrodeposited Ag Nanoparticles简

In the present work,pulse current deposition is used to deposit evenly distributed and uniformly sized Ag nanoparticles onto a TiO_2 nanotube array as photoelectrode in dye-sensitized solar cells(DSSCs),and the size and amount of loading Ag nanoparticles are controlled by the pulse deposition time.Due to the enhanced light absorption and electron—hole separation caused by plasmon effect,DSSCs based on Ag-modified TiO_2nanotube arrays show higher energy conversion efficiencies than those based on bare nanotubes with the same tube length.Particularly,DSSC based on nanotubes modified using pulse deposition time 1 s/3 s delivers the highest energy conversion efficiency of 1.68%and the largest short-circuit current of 4.37 mA/cm~2,while DSSC consisting of bare nanotubes exhibits efficiency of 1.20%and short-circuit current of2.27 mA/cm~2,which represents a 40%enhancement of cell efficiency in DSSC based on Ag-modified TiO_2nanotubes.It is also noted that overly long pulse deposition time will not further increase DSSC efficiency due to agglomeration of Ag particles.For example,when the pulse deposition time is increased to 2 s/6 s,DSSC based on Ag-modified nanotubes exhibits a lower efficiency of 1.42%.Moreover,high-concentration TiCl_4treatment on TiO_2 nanotube arrays can further increase the energy conversion efficiencies to 3.82%and2.61%for DSSC based on Ag-modified TiO_2 nanotubes and DSSC based on bare TiO_2 nanotubes,respectively,by significantly creating more surface area for dye loading.     

Crystallographic Analysis of Isothermally Transformed Bainite in 0.2C-2.0Mn-1.55Si-0.6Cr Steel Using EBSD

The crystallography of bainite,transformed isothermally at 450℃in 0.2C-2.0Mn-1.5Si-0.6Cr steel,was investigated by electron backscatter diffraction(EBSD) analysis.The orientation relationship(OR) was found to be closer to Ntshiyama-Wassermann(N-W) than Kurdjumov—Sachs orientation relationship.Bainite microstructure consisted of parallel laths forming a morphological packet structure.Typically,there were three different lath orientations in a morphological packet.These orientations were dictated by a three specific N—W OR variants sharing the same {111} austenite plane.A packet of bainite laths with common {111} austenite plane was termed as crystallographic packet.Generally,the crystallographic packet size corresponded to the morphological packet size.Locally,crystallographic packets with only two dominant orientations were observed.This indicates strong local variant selection during isothermal bainite transformation.The relative orientation between the variants in crystallographic packets was found to be near 60°/<110>.This appears to explain the strong peak observed in the grain boundary misorientation distribution near 60°.Bainite also contained pronounced fraction of boundaries with their misorientation in the range of 2.5°—8°with quite widely dispersed rotation angles.Spatially these boundaries were found to locate inside the bainite laths,forming lath-like sub-grains.     

Hydrochlorination of Acetylene Using SiC Foam Supported Structured C/Au Catalysts

AuCl3 loaded structured catalysts were prepared on SiC foam supported with pre-coated activated carbon layers. The catalytic properties of the structured catalysts towards hydrochlorination of acetylene were tested in a fixed- bed reactor with the AuCl3 loaded on activated carbon pellets as a reference. For isopyknic catalysts, the structured catalyst with only one fifth of the Au amount as that was used on the reference catalyst exhibited even a little higher acetylene conversion and much better stability than the latter no matter what the gas hourly space velocities of acetylene were used. The results indicated that the more homogeneous distribution of AuCl3 particles and better heat transfer along the fixed-bed reactor originated from the low pressure drop and high thermal conductivity of the SiC foam supported structured catalysts might be able to account for their improved efficiency and stability. It is befieved that these novel structured C/Au catalysts can be potentially applied in VCM industrialization in view of their greatly reduced cost and much prolonged life.