The effect of Cu content on the high temperature oxidation properties of the phase change material(PCM)Al-Cu-Si alloys was studied.The oxidation kinetics curves at 600◦C were achieved for Al-Cu-Si alloys with 35-55%Cu...The effect of Cu content on the high temperature oxidation properties of the phase change material(PCM)Al-Cu-Si alloys was studied.The oxidation kinetics curves at 600◦C were achieved for Al-Cu-Si alloys with 35-55%Cu,which all follow the cubic law.With an increase in the Cu content from 35 to 55%,the weight gain decreases from 5.75 to 3×10^(−4) g/cm^(2) after 96 h isothermal oxidation.The oxidation rate also decreases with Cu content,the maximum and minimum rates are 1.52 and 0.32×10^(−5) g/cm^(2)•h,a nearly 4 times difference.Oxidation does not change the phase composition of Al-Cu-Si alloys,but coarsens the microstructure.The latent heat and the starting temperature of phase change after 96 h oxidation at 600◦C have variations of less than 10%and 6◦C,respectively,indicating that the Al-Cu-Si alloys have good thermal stability after high temperature oxidation.展开更多
The oxidation properties of silver alloy powders and microstructures of oxidized powders have been investigated by thermo gravity analysis(TGA), scanning electron microscopy(SEM) and wave dispersive X ray spectrosco...The oxidation properties of silver alloy powders and microstructures of oxidized powders have been investigated by thermo gravity analysis(TGA), scanning electron microscopy(SEM) and wave dispersive X ray spectroscopy(WDEX). Ag Sn RE alloy powders have been oxidized completely at 610 ℃ within 60 min, with an external pure silver scale forming around each oxidized particle. It is useful to produce electrical contact composites. The excellent oxidation properties of Ag Sn RE alloy powders are attributed to the ideal microstructure of the oxidized powders.展开更多
The quantitative relationship between microstructure and properties of austenitic Fe-28Mn-xAl-1C（x=10 and 12 wt.%）low-density steels was evaluated using Rietveld method to refine X-ray diffraction（XRD）patterns.The...The quantitative relationship between microstructure and properties of austenitic Fe-28Mn-xAl-1C（x=10 and 12 wt.%）low-density steels was evaluated using Rietveld method to refine X-ray diffraction（XRD）patterns.The results showed that a typical three-phase austenitic steel was obtained in the forged Mn28Al10（i.e.Fe-28Mn-10Al-1C）steel,which included about 92.85 wt.% γ-Fe（Mn,Al,C）（austenite）,5.28 wt.%（Fe,Mn）_3AlC_（0.5）（κ-carbide）,and 1.87 wt.% α-Fe（Al,Mn）（ferrite）.For the forged Mn28Al12（i.e.Fe-28Mn-12Al-1C）steel,nevertheless,only about 76.64 wt.% austenite,9.63 wt.%κ-carbide,9.14 wt.%ferrite and 4.59 wt.% Fe_3Al（DO_3）could be obtained.Nanometerκ-carbide and DO_3 were mainly distributed in austenite grains and at the interface between austenite and ferrite,respectively.The forged Mn28Al10 steel had a better combination of strength,ductility and specific strength as compared with the forged Mn28Al12 steel.The ductility of the forged Mn28Al12 steel was far lower than that of the forged Mn28Al10 steel.The oxidation kinetics of Mn28Al10 steel oxidized at 1323 Kfor 5-25 h had two-stage linear rate laws,and the oxidation rate of the second stage was faster than that of the first stage.Although the oxidation kinetics of Mn28Al12 steel under this condition also had two-stage linear rate laws,the oxidation rate of the second stage was slower than that of the first stage.When the oxidation temperature increased to 1373K,the oxidation kinetics of the two steels at 5-25 hhad only onestage linear rate law,and the oxidation rates of the two steels were far faster than those at 1323K for5-25 h.The oxidation resistance of Mn28Al12 steel was much better than that of Mn28Al10 steel.Ferrite layer formed between the austenite matrix and the oxidation layer of the two Fe-Mn-Al-C steels oxidized at high temperature.展开更多
Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface s...Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size （La） of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing （d（002）） increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m 2 . The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.展开更多
Titanium and its alloys are widely used in the aerospace, marine, and biomedical industry due to their unique bulk properties such as high strength-to-weight ratio and melting temperature, good corrosion resistance, a...Titanium and its alloys are widely used in the aerospace, marine, and biomedical industry due to their unique bulk properties such as high strength-to-weight ratio and melting temperature, good corrosion resistance, and favorable biocom- patibility. However, in some applications, com- ponents made of titanium or titanium alloys exhibit poor wear resistance under stationary or dynamic loading as well as contact corrosion manifested by the relatively negative standard electrode potential （-1.63 V ） . In order to improve the surface properties of titanium and its alloys, several techniques such as PVD （ physical vapor deposition ） /CVD （chemical vapor deposition ） coatings,展开更多
A series of copper manganese oxides were prepared using a selective etching technique with various amounts of ammonia added during the co-precipitation process. The effect of the ammonia etching on the structure and c...A series of copper manganese oxides were prepared using a selective etching technique with various amounts of ammonia added during the co-precipitation process. The effect of the ammonia etching on the structure and catalytic properties of the copper manganese oxides was investigated using elemental analysis, nitrogen physisorption, X-ray powder diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduc- tion, and Oz temperature-programmed desorption combined with catalytic oxidation of CO. It was found that ammonia can selectively remove copper species from the copper manganese oxides, which correspondingly generates more defects in these oxides. An oxygen spillover from the man- ganese to the copper species was observed by H2 temperature-programmed desorption, indicating that ammonia etching enhanced the mobility of lattice oxygen species in these oxides. The Oz tem- perature-programmed desorption measurements further revealed that ammonia etching improved the ability of these oxides to release lattice oxygen. The improvement in redox properties of the copper manganese oxides following ammonia etching was associated with enhanced catalytic performance for CO oxidation.展开更多
C/SiC volume ratios in carbon fiber-reinforced carbon-silicon carbide(C_(f)/C-SiC)composites may influence greatly mechanical and oxidation properties of the composites,but have not been well investigated yet.Herein,C...C/SiC volume ratios in carbon fiber-reinforced carbon-silicon carbide(C_(f)/C-SiC)composites may influence greatly mechanical and oxidation properties of the composites,but have not been well investigated yet.Herein,C_(f)/C-SiC composites with different C/SiC volume ratios were fabricated by chemical vapor infiltration(CVI)technique through alternating the thickness of a pyrocarbon(PyC)interlayer.The composites with C/SiC volume ratios of 0.37 and 0.84 exhibited the better comprehensive mechanical properties.The CS0.37 showed the highest flexural strength of 340.6 MPa,and CS0.84 had the maximum tensile strength of 139.1 MPa.The excellent mechanical properties were closely related to the relatively low C/SiC volume ratios and porosities,optimum interfacial bonding and reduced matrix micro-cracks.The composite with a low C/SiC volume ratio of 0.10 showed the best anti-oxidation performance due to its high SiC content.The oxidation mechanisms at 1100℃and 1400℃were discussed by considering the effect of the C/SiC volume ratios,pores and matrix micro-cracks,oxidation of carbon phase and SiC.展开更多
The effects of Ca addition on the microstructure and oxidation properties of a new Mg alloy were studied.The oxidation behavior of the alloys was analyzed by thermal analysis and material characterization of the alloy...The effects of Ca addition on the microstructure and oxidation properties of a new Mg alloy were studied.The oxidation behavior of the alloys was analyzed by thermal analysis and material characterization of the alloys exposed in flame environment;and both electrical and induction furnaces.Moreover,the surface layers were characterized using field emission scanning electron microscopy,and X-ray diffraction technique.It was found that increasing the Ca addition reduces the grain size and increases the fraction of the secondary phases,and enhances the mechanical properties.Moreover,increasing the Ca contents resulted in the formation of a dense CaO/MgO layer on the surface prohibited the oxygen diffusion and assisted in protection of the substrate against further oxidation.Therefore,ignition temperature was increased from 680℃ to 890℃ after addition of the Ca element.The mechanical properties and ignition behavior of the current materials was compared with the literature which it showed an excellent combination of the properties in the developed alloys.展开更多
Natural intercalation of the graphite oxide, obtained as a product of Hummer＇s method, via ultra-sonication of water dispersed graphite oxide has been carried out to obtain graphene oxide（GO） and thermally reduced ...Natural intercalation of the graphite oxide, obtained as a product of Hummer＇s method, via ultra-sonication of water dispersed graphite oxide has been carried out to obtain graphene oxide（GO） and thermally reduced graphene oxide（RGO）.Here we report the effect of metallic nitrate on the oxidation properties of graphite and then formation of metallic oxide（MO） composites with GO and RGO for the first time. We observed a change in the efficiency of the oxidation process as we replaced the conventionally used sodium nitrate with that of nickel nitrate Ni（NO_3）_2, cadmium nitrate Cd（NO_3）_2,and zinc nitrate Zn（NO_3）_2. The structural properties were investigated by x-ray diffraction and observed the successful formation of composite of MO–GO and MO–RGO（M = Zn, Cd, Ni）. We sought to study the effect on the oxidation process through optical characterization via UV-Vis spectroscopy and Fourier Transform Infrared（FTIR） spectroscopy.Moreover, Thermo Gravimetric Analysis（TGA） was carried out to confirm 〉 90% weight loss in each process thus proving the reliability of the oxidation cycles. We have found that the nature of the oxidation process of graphite powder and its optical and electrochemical characteristics can be tuned by replacing the sodium nitrate（NaNO_3） by other metallic nitrates as Cd（NO_3）_2, Ni（NO_3）_2, and Zn（NO_3）_2. On the basis of obtained results, the synthesized GO and RGO may be expected as a promising material in antibacterial activity and in electrodes fabrication for energy devices such as solar cell, fuel cell,and super capacitors.展开更多
Fresh Pd/CeO/AlOclose coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these...Fresh Pd/CeO/AlOclose coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for CHoxidation. XRD and XPS results indicated that well-crystallized CeOparticles were formed during calcinations at 800 °C, which made CeOan effective promoter. HRTEM revealed that Pd particles found on the edge of CeOover the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H-TPR and XPS results also implied that the interaction between well-crystallized CeOand Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.展开更多
The phase compositions and properties of Ti3SiC2-based composites with SiC addition of 5%-30% in mass fraction fabricated by in-situ reaction and hot pressing sintering were studied. SiC addition effectively prevented...The phase compositions and properties of Ti3SiC2-based composites with SiC addition of 5%-30% in mass fraction fabricated by in-situ reaction and hot pressing sintering were studied. SiC addition effectively prevented TiC synthesis but facilitated SiC synthesis. The Ti3SiC2/Ti C-SiC composite had better oxidation resistance when SiC added quantity reached 20% but poorer oxidation resistance with SiC addition under 15% than Ti3SiC2/TiC composite at higher temperatures. There were more than half of the original SiC and a few Ti3SiC2 remaining in Ti3SiC2/Ti C-SiC with 20% SiC addition, but all constituents in Ti3Si2/TiC composite were oxidized after 12 h in air at 1500 °C. The oxidation scale thickness of TS30, 1505.78 μm, was near a half of that of T,2715 μm, at 1500 °C for 20 h. Ti3SiC2/Ti C composite had a flexural strength of 474 MPa, which was surpassed by Ti3SiC2/TiC-SiC composites when SiC added amount reached 15%. The strength reached the peak of 518 MPa at 20% SiC added amount.展开更多
Molybdenum-based catalysts for the gas-phase oxidation of propylene with air were investigated. Various types of silica-supported molybdenum oxide and molybdenum-bismuth mixed oxide cata- lysts were prepared from inor...Molybdenum-based catalysts for the gas-phase oxidation of propylene with air were investigated. Various types of silica-supported molybdenum oxide and molybdenum-bismuth mixed oxide cata- lysts were prepared from inorganic and organometallic molybdenum precursors using wet impregnation and physical vapor deposition methods. The epoxidation activities of the prepared cata- lysts showed direct correlations with their nanostructures, which were identified using transmission electron microscopy. The appearance of a partly or fully crystalline molybdenum oxide phase, which interacted poorly with the silica support, decreased the selectivity for propylene oxide for- mation to below 10%; non-crystalline octahedrally coordinated molybdenum species anchored on the support gave propylene oxide formations greater than 55%, with 11% propylene conversion. Electrochemical characterization of molybdenum oxides with various morphologies showed the importance of structural defects. Direct promotion by bismuth of the epoxidation reactivities over molybdenum oxides is disputed.展开更多
Superfine cerium-zinc oxides Ce1-xZnxO2-x with x = 0, 0.1, 0.3, 0.5, and 1.0 were obtained by grinding Ce（SO4）2·4H2O, ZnSO4·7H2O and NH4HCO3 under the condition of surfactant PEG-400 being present at room ...Superfine cerium-zinc oxides Ce1-xZnxO2-x with x = 0, 0.1, 0.3, 0.5, and 1.0 were obtained by grinding Ce（SO4）2·4H2O, ZnSO4·7H2O and NH4HCO3 under the condition of surfactant PEG-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts, drying at 80°C, and calcining.The precursor and its calcined samples were characterized using thermogravimetry and differential thermal analyses（TG/DTA）, UV-vis absorption spectroscopy, X-ray powder diffraction（XRD）, and scanning electron microscopy（SEM）.The results showed that superfine Ce1-xZnxO2-x behaved as an excellent UV-shielding material.The ZnO-doped CeO2 can facilitate the formation of crystalline state CeO2.The catalytic ability of products used in air oxidation of castor oil was investigated.The results showed that the catalytic abilities of products decreased with increasing zinc amount.展开更多
Transparent conductive aluminum doped zinc oxide（ZnO：Al,AZO） films were prepared on glass substrates by rf（radio frequency） magnetron sputtering from ZnO： 3wt% Al_2O_3 ceramic target. The effect of argon gas pre...Transparent conductive aluminum doped zinc oxide（ZnO：Al,AZO） films were prepared on glass substrates by rf（radio frequency） magnetron sputtering from ZnO： 3wt% Al_2O_3 ceramic target. The effect of argon gas pressure（PAr） was investigated with small variations to understand the influence on the electrical, optical and structural properties of the films. Structural examinations using X-ray diffraction（XRD） and scanning electron microscopy（SEM） showed that the ZnO：Al thin films were（002） oriented. The resistivity values were measured by four-point probe with the lowest resistivity of 5.76×10^（-4） Ω？cm（sheet resistance=9.6 Ω/sq. for a thickness=600 nm） obtained at the PAr of 0.3 Pa. The transmittance was achieved from ultravioletvisible（UV-VIS） spectrophotometer, 84% higher than that in the visible region for all AZO thin films. The properties of deposited thin films showed a significant dependence on the PAr.展开更多
ZnO tetrapods were synthesized by a typical thermal vapor-solid deposition method in a horizontal tube furnace.Structural characterization was carried out by transmission electron microscopy （TEM） and select-area el...ZnO tetrapods were synthesized by a typical thermal vapor-solid deposition method in a horizontal tube furnace.Structural characterization was carried out by transmission electron microscopy （TEM） and select-area electron diffraction （SAED）,which shows the presence of zinc blende nucleus in the center of tetrapods while the four branches taking hexagonal wurtzite structure.The electrical transport property of ZnO tetrapods was investigated through an in-situ nanoprobe system.The three branches of a tetrapod serve as source,drain,and ＂gate＂,respectively;while the fourth branch pointing upward works as the force trigger by vertically applying external force downward.The conductivity of each branch of ZnO-tetrapods increases 3-4 times under pressure.In such situation,the electrical current through the branches of ZnO tetrapods can be tuned by external force,and therefore a simple force sensor based on ZnO tetrapods has been demonstrated for the first time.展开更多
An effective procedure has been developed to synthesize the functionalized graphene oxide grafted by maleic anhydride grafted liquid polybutadiene（MLPB-GO）. Fourier transform spectroscopy and X-ray photoelectron spe...An effective procedure has been developed to synthesize the functionalized graphene oxide grafted by maleic anhydride grafted liquid polybutadiene（MLPB-GO）. Fourier transform spectroscopy and X-ray photoelectron spectroscopy indicate the successful functionalization of GO. The NR/MLPB-GO composites were then prepared by the co-coagulation process. The results show that the mechanical properties of NR/MLPB-GO composites are obviously superior to those of NR/GO composites and neat NR. Compared with neat NR, the tensile strength, modulus at 300% strain and tear strength of NR composite containing 2.12 phr MLPB-GO are significantly increased by 40.5%, 109.1% and 85.0%, respectively. Dynamic mechanical analysis results show that 84% increase in storage modulus and 2.9 K enhancement in the glass transition temperature of the composite have been achieved with the incorporation of 2.12 phr MLPB-GO into NR. The good dispersion of GO and the strong interface interaction in the composites are responsible for the unprecedented reinforcing efficiency of MLPB-GO towards NR.展开更多
In-situ growing carbon nanotubes （CNTs） directly on carbon fibers （CFs） always lead to a degraded tensile strength of CFs and then a poor fiber-dominated mechanical property of carbon/carbon composites （C/ Cs）. ...In-situ growing carbon nanotubes （CNTs） directly on carbon fibers （CFs） always lead to a degraded tensile strength of CFs and then a poor fiber-dominated mechanical property of carbon/carbon composites （C/ Cs）. To solve this issue, here, a novel carbon fiber-based multiscale reinforcement is reported. To synthesize it, carbon fibers （CFs） have been first grafted by graphene oxide （GO）, and then carbon nanotubes （CNTs） have been in-situ grown on GO-grafted CFs by catalytic chemical vapor deposition. Characterizations on this novel reinforcement show that GO grafting cannot only nondestructively improve the surface chemical activity of CFs but also protect CFs against the high-temperature corrosion of metal catalyst during CNT growth, which maintains their tensile properties. Tensile property tests for unidirectional C/Cs with different preforms show that this novel reinforcement can endow C/C with improved tensile properties, 32% and 87% higher than that of pure C/C and C/C only doped with in-situ grown CNTs. This work would open up a possibility to fabricate multiscale C/Cs with excellent global performance.展开更多
In this communication, we report the results of the studies on electrical properties of Zn0.95Cr0.05O nanoparticles synthesized using sol-gel method. X-ray diffraction （XRD） and transmission electron microscopy （TE...In this communication, we report the results of the studies on electrical properties of Zn0.95Cr0.05O nanoparticles synthesized using sol-gel method. X-ray diffraction （XRD） and transmission electron microscopy （TEM） measurements were performed for the structural and microstructural behaviors of the nanoparticles. Rietveld analysis was carried out to confirm the single phasic nature. High resolution TEM （HRTEM） confirms the nanoscale nature and polycrystalline orientations in the samples. Dielectric response has been understood in the context of universal dielectric response （UDR） model along with the Koop＇s theory and Maxwell - Wagner （M-W） mechanism. Variation in ac conductivity with frequency has been discussed in detail in terms of power law fits. Results of the impedance measurements have been explained on the basis of crystal cores and crystal boundary density. Cole - cole behavior has been studied for the impedance data. For potential application of nanoparticles, average normalized change （ANC） in impedance has been estimated and discussed in the light of size effects and oxygen vacancies.展开更多
The structure,the morphology and the thermal,optical and the surface properties of nanocrystalline CeO_2 doped with Mn have been studied by X-ray diffraction（XRD）,field-emission transmission electron microscopy（FE-...The structure,the morphology and the thermal,optical and the surface properties of nanocrystalline CeO_2 doped with Mn have been studied by X-ray diffraction（XRD）,field-emission transmission electron microscopy（FE-TEM）,energy-dispersive X-ray analysis,thermogravimetric analysis,UV–Vis absorption spectroscopy and Fourier transform infrared spectroscopy.The XRD results confirmed the successful incorporation of Mn into the CeO_2 lattice through the formation of nanoscale face-centered cubic solid solution.The FE-TEM observations supported the nanocrystalline nature of the solid solutions.The presence of structural defects and their role on the band gap have been discussed on the basis of absorption spectral studies.The structural differences correlate with results from temperature-programmed reaction（TPR）experiments with H_2 consumption.The TPR measurements showed an enhanced bulk reduction at much lower temperatures,indicating increased oxygen mobility in the samples,which enable to enhanced oxygen diffusion at lower temperatures.展开更多
基金The work is supported by the Chengdu Science and Technology Project(No:2019-YF05-01332-SN)the National Natural Science Foundation of China(No:51678488).
文摘The effect of Cu content on the high temperature oxidation properties of the phase change material(PCM)Al-Cu-Si alloys was studied.The oxidation kinetics curves at 600◦C were achieved for Al-Cu-Si alloys with 35-55%Cu,which all follow the cubic law.With an increase in the Cu content from 35 to 55%,the weight gain decreases from 5.75 to 3×10^(−4) g/cm^(2) after 96 h isothermal oxidation.The oxidation rate also decreases with Cu content,the maximum and minimum rates are 1.52 and 0.32×10^(−5) g/cm^(2)•h,a nearly 4 times difference.Oxidation does not change the phase composition of Al-Cu-Si alloys,but coarsens the microstructure.The latent heat and the starting temperature of phase change after 96 h oxidation at 600◦C have variations of less than 10%and 6◦C,respectively,indicating that the Al-Cu-Si alloys have good thermal stability after high temperature oxidation.
文摘The oxidation properties of silver alloy powders and microstructures of oxidized powders have been investigated by thermo gravity analysis(TGA), scanning electron microscopy(SEM) and wave dispersive X ray spectroscopy(WDEX). Ag Sn RE alloy powders have been oxidized completely at 610 ℃ within 60 min, with an external pure silver scale forming around each oxidized particle. It is useful to produce electrical contact composites. The excellent oxidation properties of Ag Sn RE alloy powders are attributed to the ideal microstructure of the oxidized powders.
基金funded by the National Natural Science Foundation of China (Grant No.51674004)Education Department of Anhui Province of China (Grant Nos.KJ2016A104 and KJ2017A805)
文摘The quantitative relationship between microstructure and properties of austenitic Fe-28Mn-xAl-1C（x=10 and 12 wt.%）low-density steels was evaluated using Rietveld method to refine X-ray diffraction（XRD）patterns.The results showed that a typical three-phase austenitic steel was obtained in the forged Mn28Al10（i.e.Fe-28Mn-10Al-1C）steel,which included about 92.85 wt.% γ-Fe（Mn,Al,C）（austenite）,5.28 wt.%（Fe,Mn）_3AlC_（0.5）（κ-carbide）,and 1.87 wt.% α-Fe（Al,Mn）（ferrite）.For the forged Mn28Al12（i.e.Fe-28Mn-12Al-1C）steel,nevertheless,only about 76.64 wt.% austenite,9.63 wt.%κ-carbide,9.14 wt.%ferrite and 4.59 wt.% Fe_3Al（DO_3）could be obtained.Nanometerκ-carbide and DO_3 were mainly distributed in austenite grains and at the interface between austenite and ferrite,respectively.The forged Mn28Al10 steel had a better combination of strength,ductility and specific strength as compared with the forged Mn28Al12 steel.The ductility of the forged Mn28Al12 steel was far lower than that of the forged Mn28Al10 steel.The oxidation kinetics of Mn28Al10 steel oxidized at 1323 Kfor 5-25 h had two-stage linear rate laws,and the oxidation rate of the second stage was faster than that of the first stage.Although the oxidation kinetics of Mn28Al12 steel under this condition also had two-stage linear rate laws,the oxidation rate of the second stage was slower than that of the first stage.When the oxidation temperature increased to 1373K,the oxidation kinetics of the two steels at 5-25 hhad only onestage linear rate law,and the oxidation rates of the two steels were far faster than those at 1323K for5-25 h.The oxidation resistance of Mn28Al12 steel was much better than that of Mn28Al10 steel.Ferrite layer formed between the austenite matrix and the oxidation layer of the two Fe-Mn-Al-C steels oxidized at high temperature.
基金supported by the National Basic Research Program of China (No. 2011CB605602)
文摘Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size （La） of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing （d（002）） increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m 2 . The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.
文摘Titanium and its alloys are widely used in the aerospace, marine, and biomedical industry due to their unique bulk properties such as high strength-to-weight ratio and melting temperature, good corrosion resistance, and favorable biocom- patibility. However, in some applications, com- ponents made of titanium or titanium alloys exhibit poor wear resistance under stationary or dynamic loading as well as contact corrosion manifested by the relatively negative standard electrode potential （-1.63 V ） . In order to improve the surface properties of titanium and its alloys, several techniques such as PVD （ physical vapor deposition ） /CVD （chemical vapor deposition ） coatings,
基金supported by the National Basic Research Program of China (973 Program,2013CB934104)the China Postdoctoral Science Foundation(2014M560202)~~
文摘A series of copper manganese oxides were prepared using a selective etching technique with various amounts of ammonia added during the co-precipitation process. The effect of the ammonia etching on the structure and catalytic properties of the copper manganese oxides was investigated using elemental analysis, nitrogen physisorption, X-ray powder diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduc- tion, and Oz temperature-programmed desorption combined with catalytic oxidation of CO. It was found that ammonia can selectively remove copper species from the copper manganese oxides, which correspondingly generates more defects in these oxides. An oxygen spillover from the man- ganese to the copper species was observed by H2 temperature-programmed desorption, indicating that ammonia etching enhanced the mobility of lattice oxygen species in these oxides. The Oz tem- perature-programmed desorption measurements further revealed that ammonia etching improved the ability of these oxides to release lattice oxygen. The improvement in redox properties of the copper manganese oxides following ammonia etching was associated with enhanced catalytic performance for CO oxidation.
基金financially supported by the National Key R&D Program of China(Grant No.2018YFF01013600)the National Natural Science Foundations of China(Grant Nos.U20A20242,52022101,51802313,51902315)+1 种基金the Research Fund of Youth Innovation Promotion Association of Chinese Academy of Sciences,China(Grant Nos.Y201830 and 2021190)the Liaoning Revitalization Talents Program and the National Science and Technology Major Project(No.2017-VI-0020-0093)。
文摘C/SiC volume ratios in carbon fiber-reinforced carbon-silicon carbide(C_(f)/C-SiC)composites may influence greatly mechanical and oxidation properties of the composites,but have not been well investigated yet.Herein,C_(f)/C-SiC composites with different C/SiC volume ratios were fabricated by chemical vapor infiltration(CVI)technique through alternating the thickness of a pyrocarbon(PyC)interlayer.The composites with C/SiC volume ratios of 0.37 and 0.84 exhibited the better comprehensive mechanical properties.The CS0.37 showed the highest flexural strength of 340.6 MPa,and CS0.84 had the maximum tensile strength of 139.1 MPa.The excellent mechanical properties were closely related to the relatively low C/SiC volume ratios and porosities,optimum interfacial bonding and reduced matrix micro-cracks.The composite with a low C/SiC volume ratio of 0.10 showed the best anti-oxidation performance due to its high SiC content.The oxidation mechanisms at 1100℃and 1400℃were discussed by considering the effect of the C/SiC volume ratios,pores and matrix micro-cracks,oxidation of carbon phase and SiC.
基金the Advanced Research and Technology of Magnesium (ARTofMag) research core for their help and support for this study.
文摘The effects of Ca addition on the microstructure and oxidation properties of a new Mg alloy were studied.The oxidation behavior of the alloys was analyzed by thermal analysis and material characterization of the alloys exposed in flame environment;and both electrical and induction furnaces.Moreover,the surface layers were characterized using field emission scanning electron microscopy,and X-ray diffraction technique.It was found that increasing the Ca addition reduces the grain size and increases the fraction of the secondary phases,and enhances the mechanical properties.Moreover,increasing the Ca contents resulted in the formation of a dense CaO/MgO layer on the surface prohibited the oxygen diffusion and assisted in protection of the substrate against further oxidation.Therefore,ignition temperature was increased from 680℃ to 890℃ after addition of the Ca element.The mechanical properties and ignition behavior of the current materials was compared with the literature which it showed an excellent combination of the properties in the developed alloys.
文摘Natural intercalation of the graphite oxide, obtained as a product of Hummer＇s method, via ultra-sonication of water dispersed graphite oxide has been carried out to obtain graphene oxide（GO） and thermally reduced graphene oxide（RGO）.Here we report the effect of metallic nitrate on the oxidation properties of graphite and then formation of metallic oxide（MO） composites with GO and RGO for the first time. We observed a change in the efficiency of the oxidation process as we replaced the conventionally used sodium nitrate with that of nickel nitrate Ni（NO_3）_2, cadmium nitrate Cd（NO_3）_2,and zinc nitrate Zn（NO_3）_2. The structural properties were investigated by x-ray diffraction and observed the successful formation of composite of MO–GO and MO–RGO（M = Zn, Cd, Ni）. We sought to study the effect on the oxidation process through optical characterization via UV-Vis spectroscopy and Fourier Transform Infrared（FTIR） spectroscopy.Moreover, Thermo Gravimetric Analysis（TGA） was carried out to confirm 〉 90% weight loss in each process thus proving the reliability of the oxidation cycles. We have found that the nature of the oxidation process of graphite powder and its optical and electrochemical characteristics can be tuned by replacing the sodium nitrate（NaNO_3） by other metallic nitrates as Cd（NO_3）_2, Ni（NO_3）_2, and Zn（NO_3）_2. On the basis of obtained results, the synthesized GO and RGO may be expected as a promising material in antibacterial activity and in electrodes fabrication for energy devices such as solar cell, fuel cell,and super capacitors.
基金Project supported by the National Natural Science Foundation of China(21173153)the National Hi-tech Research Development Program of China(863 Program,2013AA065304)the Sichuan Science and Technology Agency Supported Project(2012FZ0008)
文摘Fresh Pd/CeO/AlOclose coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for CHoxidation. XRD and XPS results indicated that well-crystallized CeOparticles were formed during calcinations at 800 °C, which made CeOan effective promoter. HRTEM revealed that Pd particles found on the edge of CeOover the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H-TPR and XPS results also implied that the interaction between well-crystallized CeOand Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.
基金Project(51302206)supported by the National Natural Science Foundation of ChinaProject(2013JK0925)supported by Shaanxi Provincial Department of Education,China+1 种基金Project(SKLSP201308)supported by the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,ChinaProject supported by the State Scholarship Fund,China
文摘The phase compositions and properties of Ti3SiC2-based composites with SiC addition of 5%-30% in mass fraction fabricated by in-situ reaction and hot pressing sintering were studied. SiC addition effectively prevented TiC synthesis but facilitated SiC synthesis. The Ti3SiC2/Ti C-SiC composite had better oxidation resistance when SiC added quantity reached 20% but poorer oxidation resistance with SiC addition under 15% than Ti3SiC2/TiC composite at higher temperatures. There were more than half of the original SiC and a few Ti3SiC2 remaining in Ti3SiC2/Ti C-SiC with 20% SiC addition, but all constituents in Ti3Si2/TiC composite were oxidized after 12 h in air at 1500 °C. The oxidation scale thickness of TS30, 1505.78 μm, was near a half of that of T,2715 μm, at 1500 °C for 20 h. Ti3SiC2/Ti C composite had a flexural strength of 474 MPa, which was surpassed by Ti3SiC2/TiC-SiC composites when SiC added amount reached 15%. The strength reached the peak of 518 MPa at 20% SiC added amount.
基金A support by VEGA grant 2/0129/13 is acknowledged by I.V.
文摘Molybdenum-based catalysts for the gas-phase oxidation of propylene with air were investigated. Various types of silica-supported molybdenum oxide and molybdenum-bismuth mixed oxide cata- lysts were prepared from inorganic and organometallic molybdenum precursors using wet impregnation and physical vapor deposition methods. The epoxidation activities of the prepared cata- lysts showed direct correlations with their nanostructures, which were identified using transmission electron microscopy. The appearance of a partly or fully crystalline molybdenum oxide phase, which interacted poorly with the silica support, decreased the selectivity for propylene oxide for- mation to below 10%; non-crystalline octahedrally coordinated molybdenum species anchored on the support gave propylene oxide formations greater than 55%, with 11% propylene conversion. Electrochemical characterization of molybdenum oxides with various morphologies showed the importance of structural defects. Direct promotion by bismuth of the epoxidation reactivities over molybdenum oxides is disputed.
基金supported by the Natural Scientific Foundation of Guangxi Province (No. 0832111)the Large Apparatus Cooperation Community Net Foundation of Guangxi Province, China (No. 695-2008-108)the Undergraduate Innovation Foundation of School of Chemistry and Chemical Engineering of Guangxi University
文摘Superfine cerium-zinc oxides Ce1-xZnxO2-x with x = 0, 0.1, 0.3, 0.5, and 1.0 were obtained by grinding Ce（SO4）2·4H2O, ZnSO4·7H2O and NH4HCO3 under the condition of surfactant PEG-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts, drying at 80°C, and calcining.The precursor and its calcined samples were characterized using thermogravimetry and differential thermal analyses（TG/DTA）, UV-vis absorption spectroscopy, X-ray powder diffraction（XRD）, and scanning electron microscopy（SEM）.The results showed that superfine Ce1-xZnxO2-x behaved as an excellent UV-shielding material.The ZnO-doped CeO2 can facilitate the formation of crystalline state CeO2.The catalytic ability of products used in air oxidation of castor oil was investigated.The results showed that the catalytic abilities of products decreased with increasing zinc amount.
基金Funded by the Key Projects in the National Science&Technology Pillar Program during the Twelfth Five-year Plan Period(No.2011BAJ04B04)
文摘Transparent conductive aluminum doped zinc oxide（ZnO：Al,AZO） films were prepared on glass substrates by rf（radio frequency） magnetron sputtering from ZnO： 3wt% Al_2O_3 ceramic target. The effect of argon gas pressure（PAr） was investigated with small variations to understand the influence on the electrical, optical and structural properties of the films. Structural examinations using X-ray diffraction（XRD） and scanning electron microscopy（SEM） showed that the ZnO：Al thin films were（002） oriented. The resistivity values were measured by four-point probe with the lowest resistivity of 5.76×10^（-4） Ω？cm（sheet resistance=9.6 Ω/sq. for a thickness=600 nm） obtained at the PAr of 0.3 Pa. The transmittance was achieved from ultravioletvisible（UV-VIS） spectrophotometer, 84% higher than that in the visible region for all AZO thin films. The properties of deposited thin films showed a significant dependence on the PAr.
基金supported by the China Scholarship Council (CSC) (No.20083019)Fundamental Research Funds for the Central Universities (Nos.21611603,21611424,and 216113143)+1 种基金Jinan University Start-up Funds (No.50624019)the Knowledge Innovation Program of the Chinese Academy of Sciences (No.KJCX2-YW-M13)
文摘ZnO tetrapods were synthesized by a typical thermal vapor-solid deposition method in a horizontal tube furnace.Structural characterization was carried out by transmission electron microscopy （TEM） and select-area electron diffraction （SAED）,which shows the presence of zinc blende nucleus in the center of tetrapods while the four branches taking hexagonal wurtzite structure.The electrical transport property of ZnO tetrapods was investigated through an in-situ nanoprobe system.The three branches of a tetrapod serve as source,drain,and ＂gate＂,respectively;while the fourth branch pointing upward works as the force trigger by vertically applying external force downward.The conductivity of each branch of ZnO-tetrapods increases 3-4 times under pressure.In such situation,the electrical current through the branches of ZnO tetrapods can be tuned by external force,and therefore a simple force sensor based on ZnO tetrapods has been demonstrated for the first time.
基金financially supported by the National Natural Science Foundation of China(No.51363006)Science and Technology innovation key project of Hainan province(No.ZDXM20120090)National Science and Technology support project(No.2013BAF08B02)
文摘An effective procedure has been developed to synthesize the functionalized graphene oxide grafted by maleic anhydride grafted liquid polybutadiene（MLPB-GO）. Fourier transform spectroscopy and X-ray photoelectron spectroscopy indicate the successful functionalization of GO. The NR/MLPB-GO composites were then prepared by the co-coagulation process. The results show that the mechanical properties of NR/MLPB-GO composites are obviously superior to those of NR/GO composites and neat NR. Compared with neat NR, the tensile strength, modulus at 300% strain and tear strength of NR composite containing 2.12 phr MLPB-GO are significantly increased by 40.5%, 109.1% and 85.0%, respectively. Dynamic mechanical analysis results show that 84% increase in storage modulus and 2.9 K enhancement in the glass transition temperature of the composite have been achieved with the incorporation of 2.12 phr MLPB-GO into NR. The good dispersion of GO and the strong interface interaction in the composites are responsible for the unprecedented reinforcing efficiency of MLPB-GO towards NR.
基金supported by the National Natural Science Foundation of China (Nos.51432008,51502242,U1435202,and 51202194)the Research Fund for the Doctoral Program of Higher Education of China (No.20126102110013)the Key Grant Project of Chinese Ministry of Education (No.313047)
文摘In-situ growing carbon nanotubes （CNTs） directly on carbon fibers （CFs） always lead to a degraded tensile strength of CFs and then a poor fiber-dominated mechanical property of carbon/carbon composites （C/ Cs）. To solve this issue, here, a novel carbon fiber-based multiscale reinforcement is reported. To synthesize it, carbon fibers （CFs） have been first grafted by graphene oxide （GO）, and then carbon nanotubes （CNTs） have been in-situ grown on GO-grafted CFs by catalytic chemical vapor deposition. Characterizations on this novel reinforcement show that GO grafting cannot only nondestructively improve the surface chemical activity of CFs but also protect CFs against the high-temperature corrosion of metal catalyst during CNT growth, which maintains their tensile properties. Tensile property tests for unidirectional C/Cs with different preforms show that this novel reinforcement can endow C/C with improved tensile properties, 32% and 87% higher than that of pure C/C and C/C only doped with in-situ grown CNTs. This work would open up a possibility to fabricate multiscale C/Cs with excellent global performance.
基金financial support in the form of UGC (BSR) Meritorious Fellowship (No.: F.25-1/2014-15(BSR)/7-156/2007(BSR))financial support in the form of UGC (BSR) Meritorious Fellowship (No.: F.25-1/2013-14(BSR)/7-156/2007(BSR))
文摘In this communication, we report the results of the studies on electrical properties of Zn0.95Cr0.05O nanoparticles synthesized using sol-gel method. X-ray diffraction （XRD） and transmission electron microscopy （TEM） measurements were performed for the structural and microstructural behaviors of the nanoparticles. Rietveld analysis was carried out to confirm the single phasic nature. High resolution TEM （HRTEM） confirms the nanoscale nature and polycrystalline orientations in the samples. Dielectric response has been understood in the context of universal dielectric response （UDR） model along with the Koop＇s theory and Maxwell - Wagner （M-W） mechanism. Variation in ac conductivity with frequency has been discussed in detail in terms of power law fits. Results of the impedance measurements have been explained on the basis of crystal cores and crystal boundary density. Cole - cole behavior has been studied for the impedance data. For potential application of nanoparticles, average normalized change （ANC） in impedance has been estimated and discussed in the light of size effects and oxygen vacancies.
基金the Deanship of Scientific Research at King Saud University for its funding this Prolific Research Group(PRG-1436-26)
文摘The structure,the morphology and the thermal,optical and the surface properties of nanocrystalline CeO_2 doped with Mn have been studied by X-ray diffraction（XRD）,field-emission transmission electron microscopy（FE-TEM）,energy-dispersive X-ray analysis,thermogravimetric analysis,UV–Vis absorption spectroscopy and Fourier transform infrared spectroscopy.The XRD results confirmed the successful incorporation of Mn into the CeO_2 lattice through the formation of nanoscale face-centered cubic solid solution.The FE-TEM observations supported the nanocrystalline nature of the solid solutions.The presence of structural defects and their role on the band gap have been discussed on the basis of absorption spectral studies.The structural differences correlate with results from temperature-programmed reaction（TPR）experiments with H_2 consumption.The TPR measurements showed an enhanced bulk reduction at much lower temperatures,indicating increased oxygen mobility in the samples,which enable to enhanced oxygen diffusion at lower temperatures.
