Effect of the silicon powder content on the properties of Al_2O_3-SiC-Me composites

By means of transient plastic phase process,the Al2O3-SiC-Me composites were produced throungh adding metal aluminium and silicon-powder to Al2O3-SiC materials.Under the condition of the same content of silicon and aluminium mixed-powder,the effect of silicon powder addition on properties of Al2O3-SiC-Me composites was studied by means of XRD and EPMA analyses in the temperature range of 300°C-1600°C.The results indicated that the content of metal phase in the sample at 1600°C increases with increasing silicon powder content.At the same time,when the temperature is lower than 1100°C,the strength of samples gradually increases with increasing temperature.However when the temperature is higher than 11000°C,the strength of samples gradually decreases with increasing temperature,and this change is very small.The results also indicated that at the same sintering temperature,the sample with 6%silicon powder has the maximum strength.     

Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties,electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated.The results indicated that with elevating the aging temperature from 100°C to 160°C,the aging response rate was greatly accelerated,and the UTS at peak aging condition decreased,while the corresponding TYS increased.However,the electrical conductivity of the alloy became higher.After aging for 24 h at 120°C,the peak UTS and TYS values were achieved as 591 MPa and 541 MPa,respectively;but the alloy achieved a lower conductivity,20.4 MS/m.When T6 temper was performed at 140°C for 14 h,the UTS decreased only by 1%of the former,whereas the TYS and the electrical conductivity increased obviously,which were up to 559 MPa and 22.6 MS/m,respectively.The major strengthening precipitates of the peak-aged alloy were GP zones andη′phase.The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature.There were obvious PFZs along the grain boundary both in T6 conditions aged at 140°C and 160°C.     

Performance of an activated carbon made from waste palm shell in simultaneous adsorption of SO_x and NO_x of flue gas at low temperature

This study examined the individual and simultaneous adsorption of SOx(SO2)and NOx(NO-NO2)on activated carbon prepared from waste palm shell.The adsorption process was examined in a fixed bed reactor at low temperatures(100 300°C).For individual adsorption without any catalytic activation,SOx showed good adsorption whereas NOx was very much poor.In the simultaneous adsorption of SOx and NOx,SOx showed greater adsorption affinity than NOx.For palm shell activated carbon(PSAC)impregnated with metal catalyst(Ni and Ce)the concentration adsorbed profile showed that the amount of SOx adsorbed decreased regularly,while the amount of the adsorbed NOx increased irregularly.The properties of the pure and impregnated PSAC were analyzed by BET,SEM and EDX.These investigations indicated that PSAC impregnated with metal catalyst is the determining factor in the adsorption of SOx and NOx simultaneously.     

Optimization of the process for preparing Al-doped ZnO thin films by sol-gel method

Transparent and conducting Al-doped ZnO thin films with c-axis-preferred orientation were prepared on glass substrate via sol-gel route.The physical and chemical changes during thermal treatment were analyzed by TG-DSC spectra and the crystallization quality was characterized by XRD patterns.The optimized preheating and post-heating temperatures were determined at～420°C and～530°C,respectively.From thermodynamic and kinetics views,we investigated the mechanism of orientation growth with(002) plane parallel to the substrates.The surface morphologies of the films,post-heated at 420°C,450°C,530°C and 550°C,respectively,were observed by SEM micrographs.The film post-heated at 530°C shows a homogenous dense microstructure and exhibits the minimum sheet resistance of 140Ω/Sq.The visible optical transmittance of all the films is beyond 90%.In addition,the annealing treatment in vacuum can contribute greatly to the electrical conductivity.     

Effects of temperature and pressure on the structural and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on fused silica via pulsed laser deposition (PLD) at substrate temperatures from 300°C to 800°C and ambient oxygen pressures ranging from 10?2 mTorr to 240 mTorr. X-ray diffraction (XRD) and Raman spectra indicated that wurtzite ZnO was obtained in all cases. The highly c-oriented ZnO films were obtained for oxygen pressures above 11 mTorr. The room-temperature photoluminescence (PL) spectra demonstrated that all the films exhibited strong near-band-edge (NBE) emission, while d...     

Examination of dynamic recrystallization during compression of AZ31 magnesium

This study aimed to investigate dynamic recrystallization(DRX)behavior during compression of magnesium alloy AZ31. Cylinder samples were cut from the extruded rod and hot rolled sheet AZ31 for compression test.The samples were compressed using a Gleeble 1500D at a temperature of 300℃and a strain rate of 0.01 s-1.Grain orientations and misorientation angles across grain boundaries for the tested samples were obtained by using electron backscatter diffraction(EBSD)technique.The results showed that strong basal texture was observed after 50%compression(ε=0.69)on both the extruded and hot rolled samples,which have different initial textures.It was observed that with increased strain,DRX grains gradually rotated to basal orientation,and grain boundaries with misorientation angle of near 30°was formed in the samples.At the strain of 0.69,a high fraction of high-angle(60°)boundaries was present in the extruded sample,whereas almost no high angle boundaries were observed in the hot rolled sheet sample.     

Preparation and properties of multi-wall carbon nanotube/SiC composites by aqueous tape casting

MWCNTS/SiC composites were fabricated by aqueous tape casting.High solid content(50 vol%) SiC slurries with sintering additives and multi-wall carbon nanotubes(MWCNTs) as reinforcements were prepared using Tetramethylammonium hydroxide as the dispersant.The stability of MWCNTs/SiC slurries was studied and characterized in terms of zeta potential and rheology measurements.The relative density of the composite was about 98%after hot-pressing at 1850°C(at 25 MPa in Ar for 30 min) .The hardness of the composites decreased with the increase in MWCNTs content.The flexural strength and the fracture toughness were 742.17 MPa and 4.63 MPa·m 1/2,respectively when the MWCNTs content was 0.25 wt%.Further increase in MWCNTs content to 0.50 wt%did not lead to the increase in mechanical properties.Most of MWCNTs were found to be located at SiC grain boundaries and the pull out of the MWCNTs was observed.     

Understanding of the influence of process parameters on the heat transfer behavior at the metal/die interface in high pressure die casting process

The current paper focuses on the influence of the process parameters on the peak values of the interfacial heat transfer coefficient(IHTC)at metal/die interface during high pressure die casting(HPDC)process.A"step shape"casting and AM50 alloy were used during the experiment.The IHTC was determined by solving the inverse thermal problem based on the measured temperature inside the die.Results show that the initial die surface temperature(IDST,TDI)has a dominant influence while the casting pressure and fast shot velocity have a secondary influence on the IHTC peak values.By curve fitting,it was found that the IHTC peak value(hmax)changes as a function of the IDST in a manner of hmax=e αTγ DI .Such relationship between the IHTC peak value and the IDST can also be found when the casting alloy is ADC12,indicating that this phenomenon is a common characteristic in the HPDC process.     

Preparation of TiO_2 thin film by the LPD method on functionalized organic self-assembled monolayers

In this paper,uniform titania(TiO2) films have been formed at 50°C on silanol SAMs by the liquid-phase deposition(LPD) method at a temperature below 100℃.OTS(Octadecyltrichloro-Silane) self-assembled monolayers(SAMs) on glass wafers were used as substrates for the deposition of titanium dioxide thin films.This functionalized organic surface has shown to be effective for promoting the growth of films from titanic aqueous solutions by the LPD method at a low temperature below 100°C.The crystal phase composition,microstructure and topography of the as-prepared films were characterized by various techniques,including X-ray diffraction(XRD) ,scanning electron microscopy(SEM) ,and atomic force microscopy(AFM) .The results indicate that the as-prepared thin films are purely crystallized anatase TiO2 constituted by nanorods after being annealed at 500°C.The pH values,concentration of reactants,and deposition temperatures play important roles in the growth of TiO2 thin films.     

Microstructure and texture evolution during warm compression of the magnesium alloy AZ31

The evolution of the microstructure and texture with strain during compression at 150℃of the magnesium alloy AZ31 has been investigated using the electron backscattered diffraction(EBSD)technique.The initial samples were chosen to have a strong basal plane texture with the crystal c-axes perpendicular to the compression direction.The EBSD data provide evidence concerning the relative activity of both{10-12}extension twinning and slip,and suggest that non-basalc+a slip is important in samples deformed to a strain of more than 0.2.The relative contributions of the twinning and the slip during deformation have been discussed based on the results above.     

Anisotropic plastic deformation behavior of as-extruded ZK60 magnesium alloy at room temperature

The anisotropic plastic deformation behavior of as-extruded ZK60 magnesium alloy at room temperature(RT)was investigated by compressive and tensile testing in different directions,i.e.the loading axis oriented at 0°,45°and 90°to the extrusion direction.The relationship between texture and plastic deformation behavior were examined.The results show that the extruded ZK60 alloy exhibits a strong ring fiber texture.The mechanical properties are strongly orientation dependent.In tension testing,the 0°specimen exhibited higher yield strength and lower elongation.In compression testing,however,ZK60 alloy exhibited almost the same yield strength in three directions.The anisotropic plastic deformation behavior is due to strong fiber texture and the lower symmetry of the hexagonal close packed(hcp)structure of ZK60 alloy. The correlation between texture and mechanical behaviour offers the possibility to improve the mechanical properties of magnesium alloy by optimization of the material production process.     

Improvement of warm formability of Al-Mg sheet alloys containing coarse second-phase particles

Several alloying elements involving Zr,Cu,Zn and Sc were added to Al-Mg sheet alloys in order to obtain an excellent combination of high strength and good high-temperature formability.Microstructural examination showed that coarse intermetallic particles were formed in the microstructure and their amounts changed with variations of the alloying elements. During warm rolling of thermomechanical treatments prior to warm deformation,the coarse particles initiated cracks,decreasing the warm formability.For healing the crack damage and further improving the warm formability,a process of hot isothermal press was developed and optimized to the sheet alloys.With this process,the biaxial stretch formability at 350°C was improved by 22%for an aluminum alloy containing a large amount of coarse particles.     

Low temperature synthesis of SiCN nanostructures

Silicon carbon nitride(SiCN) nanowires,nanorods and nanotubes have gained much attention due to their excellent field emission and photoluminescence properties.These nanostructures were usually grown using catalysts at high temperature(800-1000°C) .In this paper,synthesis of SiCN nanostructures at a temperature less than 500°C is reported.Various kinds of SiCN nanostructures were synthesized using microwave plasma chemical vapor deposition method.Gas mixtures of CH4,H2 and N2 were used as precursors and Si chips were inserted in the sample holder at symmetrical positions around the specimen as additional Si sources.Metallic gallium was used as the liquid medium in a mechanism similar to vapor-liquid-solid.Morphologies of the resultant were characterized by field emission scanning electron microscopy.Energy dispersive spectrometry and X-ray photoelectron spectroscopy were used to characterize their compositions and bonding states.     

Effect of Fe(Ⅲ) impurity on the electrochemical performance of LiFePO_4 prepared by hydrothermal process

Lithium iron phosphate(LiFePO4)was synthesized from LiOH,FeSO4 and H3PO4 by a hydrothermal process at 180℃.The samples were characterized by X-ray diffraction,scanning electron microscopy and chemical analysis.Electrochemical performance of the samples was tested in terms of charge-discharge capacity and cycling behavior.The results indicated that Fe(Ⅲ) impurity had obviously effect on the electrochemical properties of LiFePO4,and the formation of Fe 3+ was caused by the oxidation of Fe 2+ in the dissolving...     

Inducing effect of Pb(Zr_(0.4)Ti_(0.6))O_3 thin film derived by different processes in BiFeO_3/Pb(Zr_(0.4)Ti_(0.6))O_3 multilayer capacitor at room temperature

BiFeO3/PZT multilayer capacitor was prepared on Pt(100) /Ti/SiO2/Si(100) substrate.PZT buffer layer was derived by MOCVD method(label:PZT1) and sputtering method(label:PZT2) respectively.XRD analysis indicated that high(110) orientation of BFO in the BFO/PZT1 structure was achieved.SEM analysis indicated a better microstructure in the BFO/PZT1 structure compared with BFO/PZT2.The remnant polarization of the BFO/PZT1 was 82.5μC/cm2 at an applied voltage of 8 V,compared with that of 25.2μC/cm2 in the BFO/PZT 2 structure.The BFO/PZT1 multilayer exhibited little polarization fatigue(1.5%) upon 1×101 0switching cycles,at an applied voltage of 4 V.The leakage current density was about 2×10-7A/cm 2 at an applied voltage 4 V,in the BFO/PZT1 capacitor.All the results indicated that PZT can act as an inducing layer to the BFO and the MOCVD derived PZT has more inducing effect to the BFO thin film at room temperature.     

Novel wide band gap alloyed semiconductors,x(LiGaO_2)_(1/2)-(1-x)ZnO,and fabrication of their thin films

Oxide semiconductor alloys of x(LiGaO2) 1/2-(1-x) ZnO were fabricated by the solid state reaction betweenβ-LiGaO2 and ZnO and rf-magnetron sputtering.For the solid state reaction,the wurtzite-type single phases were obtained in the composition range of x≤0.38.The formation range of the alloys was wider than that of the(Mg1-xZnx) O system,because the β-LiGaO 2possesses a wurtzite-derived structure and approximately the same lattice constants with ZnO.The electrical resistivity and energy band gap of the 0.38(LiGaO2) 1/2-0.62ZnO alloyed ceramic were 0.45-cm and 3.7 eV,respectively,at room temperature.For the alloying by sputtering,the films consisting of the wurtzite-type single phase were obtained over the entire composition range of x(LiGaO2) 1/2-(1-x) ZnO.The energy band gap was controllable in the range from 3.3 to 5.6 eV.For the as-deposited film fabricated using the 0.4(LiGaO2) 1/2-0.6ZnO alloyed ceramic target,the energy band gap was 3.74 eV,and the electrical resistivity,carrier density and the Hall mobility at room temperature were 3.6-cm,3.4×1017 cm-3and 5.6 cm 2 V-1s-1,respectively.     

One-step synthesis route of the aligned and non-aligned single crystalline α-Si_3N_4 nanowires

This paper reports the bulk synthesis route of the aligned and non-aligned high-qualityα-Si 3 N4 nanowires(NWs) which were grown directly from the Si substrate by vapor phase deposition at 1050℃.The as-grown products were characterized by employing XRD,SEM,HRTEM and photoluminescence.The microscopic results revealed that the products consist of single crystalline aligned and non-alignedα-Si 3 N4 NWs having a same diameter range of 30-100 nm and different lengths of about hundreds of microns.The XRD observation revealed that the products consist ofα-phase Si 3 N4 NWs.The room temperature PL spectra indicated that the NWs have good emission property.The non-aligned NWs were formed at lower temperature as compared with aligned NWs.Our method is a simple and one-step procedure to synthesize the bulk-quantity and high-purity aligned and non-alignedα-Si 3 N4 NWs at a relatively low temperature.The possible growth mechanism was also briefly discussed.     

Straight SiO_x nanorod Y junctions

Novel straight silicon oxideSiOx(1x2) nanorod Y junctions have been synthesized on Si plate by thermal evaporation of mixed powders of silica and carbon nanofibers at 1300°C and condensation on a Si substrate without assistance of any catalyst.The synthesized samples were characterized by means of scanning electron microscopy,transmission electron microscopy,high resolution transmission electron microscopy,and energy dispersive X-ray spectroscopy.The results suggested that the straight nanorod Y junctions are amorphous and consist only of elements Si and O,and these rods with diameters about 50-200 nm have a neat smooth surface.The growth of such silicon oxide nanorods may be a result of the second nucleation on the surface of rods causing a change in the growth direction of silicon oxide nanorods developed.     

Effect of Cu seed on the synthesis and characterization of FeCo alloy nano-particles by using polyol method

Fine metal particles with uniform shape,narrow size distribution and high purity are increasingly needed for specific uses in high tech industrial application.We report the direct chemical synthesis of FeCo alloy particles using the mixture of FeCl2·4H2O,Co(Ac) 2·4H2O(Ac:acetate) and NaOH in ethylene glycol,and then obtained FeCo alloy particles better dispersed by adding the polyvinylpyrrolidone(PVP) and also the size could be controlled by adding copper.The prepared nano-particles were characterized using FESEM,XRD and VSM.The mean diameter of these particles was varied in the range of submicrometer to nanometer with metal-ion concentration.FeCo particles showed the typical soft magnetic properties.     

Superplasticity of Mg-5.8Zn-1Y-Zr alloy sheet fabricated by combination of extrusion and hot-rolling processes

Superplastic behaviors of quasicrystal phase containing Mg-5.8Zn-1Y-0.48Zr alloy sheets fabricated by combination of extrusion and hot-rolling processes have been investigated at temperature ranging from 623 to 753 K and at the strain rates ranging from 10 -4 to 10 -2 s -1 by uniaxial tensile tests.An excellent superplasticity with the maximum elongation to failure of 1020%was obtained at 753 K and the strain rate of 1.04×10-3s -1and its strain rate sensitivity,m,is as high as up to 0.75. The microstructure was stable during superplastic deformation due to the uniformly distributed fine quasicrystal particles. In addition,micro-cavities and their coalescences were observed in the superplastic deformation of the ZW61 magnesium alloy.Grain boundary sliding(GBS)was considered to be the main deformation mechanism during the superplastic deformation.Dislocation creep controlled by atom diffusion through grain boundaries or interior grains is suggested mainly to accommodate the GBS in superplastic deformation.