The effects of crystallite size on the physicochemical properties and surface defects of pure monoclinic ZrO_(2) catalysts for isobutene synthesis were studied.We prepared a series of monoclinic ZrO_(2) catalysts with...The effects of crystallite size on the physicochemical properties and surface defects of pure monoclinic ZrO_(2) catalysts for isobutene synthesis were studied.We prepared a series of monoclinic ZrO_(2) catalysts with different crystallite size by changing calcination temperature and evaluated their catalytic performance for isobutene synthesis from syngas.ZrO_(2) with small crystalline size showed higher CO conversion and isobutene selectivity,while samples with large crystalline size preferred to form dimethyl ether(DME)instead of hydrocarbons,much less to isobutene.Oxygen defects(ODefects)analyzed by X-ray photoelectron spectroscopy(XPS)provided evidence that more ODefectsoccupied on the surface of ZrO_(2) catalysts with smaller crystalline size.Electron paramagnetic resonance(EPR)and ultraviolet–visible diffuse reflectance(UV–vis DRS)confirmed the presence of high concentration of surface defects and Zr3+on mZrO_(2)-5.9 sample,respectively.In situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS)analysis indicated that the adsorption strength of formed formate species on catalyst reduced as the crystalline size decreased.These results suggested that surface defects were responsible for CO activation and further influenced the adsorption strength of surface species,and thus the products distribution changed.This study provides an in-depth insight for active sites regulation of ZrO_(2) catalyst in CO hydrogenation reaction.展开更多
TNAs (Titanium dioxide nanotube arrays) were synthesized by electrochemical anodization and these TNAs were annealed in different gas atmosphere such as argon, air, hydrogen and nitrogen. This annealing in different...TNAs (Titanium dioxide nanotube arrays) were synthesized by electrochemical anodization and these TNAs were annealed in different gas atmosphere such as argon, air, hydrogen and nitrogen. This annealing in different atmosphere brought variation in crystallite size (27 - 33 nm), which influences on electrochemical properties. The specific capacity of Ar, Air, N2 and H2-annealed TNAs was around ~165, 185, 177 and 190 mAh g~, respectively. The crystallite size of anatase TNAs seemed to be responsible for the change in lithium storage capacity, indicating that structural changes of TNAs were playing major role in electrochemical properties.展开更多
We investigated the structural and optical properties of ZnO thin films as an n-type semiconductor. The films were deposited at different precursor molarities using an ultrasonic spray method. In this paper we focused...We investigated the structural and optical properties of ZnO thin films as an n-type semiconductor. The films were deposited at different precursor molarities using an ultrasonic spray method. In this paper we focused our attention on a new approach describing a correlation between the crystallite size and optical gap energy with the precursor molarity of ZnO thin films. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along the c-axis. The maximum value of the crystallite size of the films is 63.99 nm obtained at 0.1 M. The films deposited with 0.1 M show lower absorption within the visible wavelength region. The optical gap energy increased from 3.08 to 3.37 eV with increasing precursor molarity of 0.05 to 0.1 M. The correlation between the structural and optical properties with the precursor molarity suggests that the crystallite size of the films is predominantly influenced by the band gap energy and the precursor molarity. The measurement of the crystallite size by the model proposed is equal to the experimental data. The minimum error value was estimated by Eq. (4) in the higher crystallinity.展开更多
A series of Co_(3) O_(4) catalysts was prepared by ammonia(Co-AP) and oxalate(Co-OP) precipitation,solgel(Co-SG),and urea hydrothermal(Co-UH) methods,and their physicochemical properties were characterised by numerous...A series of Co_(3) O_(4) catalysts was prepared by ammonia(Co-AP) and oxalate(Co-OP) precipitation,solgel(Co-SG),and urea hydrothermal(Co-UH) methods,and their physicochemical properties were characterised by numerous techniques including X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),nitrogen sorption,X-ray photoelectron spectroscopy(XPS),temperature-programmed reduction of H_(2)(H_(2)-TPR),temperature-programmed desorption of O_(2)(O_(2)-TPD),and temperature-programmed desorption of NH_(3)(NH_(3)-TPD).The catalytic activity of each catalyst was estimated for the catalytic combustion of vinyl chloride(VC) emissions.The crystallite size of the Co_(3) O_(4) catalyst was found to be well correlated with the amounts of surface-adsorbed oxygen species and number of acid sites on the catalyst surface,and consequently,determined several physicochemical properties of the catalyst.Of the catalysts studied here,the Co-AP catalyst exhibits the smallest crystallite size,which increases the specific surface area and the concentration of Co^(2+) on the catalyst surface.This,in turn,enhances the redox property,oxygen mobility,and the number of acid sites associated with the Co-AP catalyst.In fact,the Co-AP catalyst exhibits the best catalytic activity for VC combustion at 360℃and does not produce any chlorinated by-products.展开更多
To improve oil quality,ZSM-22/SAPO-11 composite molecular sieves were synthesized by adding ZSM-22 into a synthetic gel of SAPO-11 for n-decane hydroisomerization.The mass ratios of ZSM-22/(ZSM-22+SAPO-11)in the compo...To improve oil quality,ZSM-22/SAPO-11 composite molecular sieves were synthesized by adding ZSM-22 into a synthetic gel of SAPO-11 for n-decane hydroisomerization.The mass ratios of ZSM-22/(ZSM-22+SAPO-11)in the composite molecular sieves were optimized and the optimal ZSM-22/SAPO-11 composite(ZS-9)was obtained.The electrostatic repulsions between the ZSM-22 precursors and the SAPO-11 crystalline nuclei produced small ZSM-22 and SAPO-11 crystallites in ZS-9,which increased the specific surface area and mesopore volume and thereby exposed more acid sites.In comparison with conventional SAPO-11,ZSM-22 and their mechanical mixture,ZS-9 with smaller crystallites and the optimal medium and strong Brønsted acid centers(MSBAC)content displayed a higher yield of branched C_(10) isomers(81.6%),lower cracking selectivity(11.9%)and excellent stability.The correlation between the i-C_(10) selectivity and the MSBAC density of molecular sieves indicated that the selectivity for branched C_(10) isomers first increased and then decreased with increasing MSBAC density on the molecular sieves,and the maximum selectivity(87.7%)occurred with a density of 9.6×10^(−2)μmol m^(−2).展开更多
By optimizing the orystallization condition, a procedure for the synthesis of small crystallite zeolite ZSM-5 was developed. Compared with the larger crystallite ZSM-5. the smaller one exhibits higher catalytic perfor...By optimizing the orystallization condition, a procedure for the synthesis of small crystallite zeolite ZSM-5 was developed. Compared with the larger crystallite ZSM-5. the smaller one exhibits higher catalytic performance in aromatization reaction of propane.展开更多
Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride con...Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride containing solutions. In this research, commercially pure α-Ti top coating having good pitting potential(~1293 mV_(SCE)), high microhardness(HV_(0.025): 263.03) and low wear rate was applied on a CP-Al coated Mg-based alloy using high pressure cold spray technology. Potentiodynamic polarization(PDP) curves indicated that the probability of transition from metastable pits to the stable pits for cold spayed(CS) Al coating is considerably higher compared to that with the CS Ti top coating(for Ti/Al/Mg system). In addition, CS Ti top coating was in the passivation region in most pH ranges even after 48 h immersion in 3.5 wt% NaCl solution. The stored energy in the CS Ti top coating(as a passive metal) was presumed to be responsible for the easy passivation. Immersion tests indicated no obvious pits formation on the intact CS Ti top coating surface and revealed effective corrosion protection performance of the CS double layered noble barrier coatings on Mg alloys in 3.5 wt% NaCl solution even after 264 h.展开更多
The excited localized surface plasmon(LSP)in metallic nanoparticles is known to relax through several processes such as electron-electron scattering,electron-phonon coupling,and phonon-phonon scat-tering.In the curren...The excited localized surface plasmon(LSP)in metallic nanoparticles is known to relax through several processes such as electron-electron scattering,electron-phonon coupling,and phonon-phonon scat-tering.In the current research,the ultrafast electron-phonon(e-ph)coupling relaxation processes for different average sizes and crystallinity of chemically synthesized silver nanoparticles were evaluated utilizing transient absorption spectroscopy.The nanoparticle size and crystallinity of similar linear dimension polycrystalline spherical and monocrystalline cubic nanoparticles ranging from ca.30-60 nm was related to their electron relaxation time constants and revealed very different dependencies.For the monocrystalline nanocubes,the electron-phonon coupling was not dependent on the cube edge length,while for the polycrystalline nanospheres,it was linearly decreasing with diameter.We demonstrate that the e-ph coupling time constant could be used to evaluate crystallinity and crystallite size in plasmonic metal nanoparticles when the size(surface area)of the nanoparticle is known.展开更多
A low-cost rout for modification the polyacrylontrile(PAN) precursor fibers was developed.The approach involved pretreatment PAN precursor fibers with UV irradiation for various periods of time before the fibers wer...A low-cost rout for modification the polyacrylontrile(PAN) precursor fibers was developed.The approach involved pretreatment PAN precursor fibers with UV irradiation for various periods of time before the fibers were stabilized.The effect of UV irradiation on the chemical structure,orientation factor,density,crystallite size and morphology of the fibers in the process of stabilization was characterized by use of fourier transform infrared spectroscopy(FTIR),float-sink procedure,X-ray diffraction(XRD),scanning electron microscope(SEM),respectively.The results showed that UV irradiation could increase the density of the fibers in stabilization process.FTIR analysis indicated that the cyclization of nitrile groups was initiated at room temperature by UV irradiation.The transformation of C≡N groups to C=N ones was accelerated in the process of stabilization.The orientation factor of irradiated fibers was also increased.The crystallite size was decreased at first and increased later,and the better irradiation time of UV was 3 min according to the XRD test.SEM analysis indicated that irradiation could decrease the internal and surface defects of the stabilized fibers treated at 300 ℃.展开更多
Carbon nanotube (CNT)/maleic acid anhydride (MAH)-grafted polypropylene (PP) composites were prepared by in situ grafting method. Infrared spectroscopy showed that the CNTs were linked to PP by MAH grafting. The...Carbon nanotube (CNT)/maleic acid anhydride (MAH)-grafted polypropylene (PP) composites were prepared by in situ grafting method. Infrared spectroscopy showed that the CNTs were linked to PP by MAH grafting. The microstructures and calorimetry analysis indicated that the crystallization behaviors of the filled and unfilled PP were quite different. The addition of CNTs dramatically reduced the spherulite size, increased crystallization rate and improved the thermal stability of PP. These results confirmed the expected nucleant effect of CNT on the crystallization of PP. Scanning and transmission electron microscopy showed that the CNTs were dispersed homogeneously, indicating that the original CNT bundles were separated into individual tubes by the grafting.展开更多
The kinetic data of solid state polycondensation of PET and its copolymers are determined.It is shown that the reaction rate of copolycondensation is higher than that of PET polyconden-sation, and increases with the c...The kinetic data of solid state polycondensation of PET and its copolymers are determined.It is shown that the reaction rate of copolycondensation is higher than that of PET polyconden-sation, and increases with the comonomers content. But the reaction rate of copolycondensationin melt state of this kind of copolymers is lower than that of PET. It is considered that the chemi-cal reactivity of comonomer is the main factor which affect the polycondensation in melt state,whereas the aggregative structure of the polymer is the main factor in solid state. The crystallinity and crystallite size of the copolymers have been measured by X-ray method.展开更多
Ca3Co4O9 is a p-type semiconducting material that is well-known for its thermoelectric(TE),magnetic,electronic,and electro-optic properties.In this study,sol–gel autoignition was used to prepare Ca3Co4O9 at different...Ca3Co4O9 is a p-type semiconducting material that is well-known for its thermoelectric(TE),magnetic,electronic,and electro-optic properties.In this study,sol–gel autoignition was used to prepare Ca3Co4O9 at different calcination temperatures(773,873,973,and 1073 K)and time(4,6,8,10,12,and 14 h)using starch as a fuel.The phase and microstructure of the prepared Ca3Co4O9 powder were investigated.Thermogravimetry–differential thermal analysis(TGA)confirms that the final weight loss occurred at 1073 K to form Ca3Co4O9 stable powder.The variable-pressure scanning electron microscopy(VP-SEM)images show that the size of powder particles increases from 1.15 to 1.47μm as calcination time increases from 4 to 12 h,and the size remains almost constant thereafter.A similar pattern is also observed on the increment of the crystallite size and percentage of crystallinity with X-ray diffraction(XRD)analysis.The highest crystallinity is found about 92.9%when the powder was calcinated at 1073 K for 12 and 14 h with 458 and 460Åcrystallite size,respectively.Energy dispersive X-ray spectroscopy(EDS)analysis demonstrates that the calcinated powder has a high intensity of Ca,Co,and O with uniform distribution.High-resolution transmission electron microscopy(HRTEM)images prove that there is no distinct lattice distortion defect on the crystal structure.展开更多
The NiO-Cu composite films were deposited on a glass substrate at various substrate temperatures by DC reactive magnetron sputtering technique. The effect of substrate temperature on the structural, optical, morpholog...The NiO-Cu composite films were deposited on a glass substrate at various substrate temperatures by DC reactive magnetron sputtering technique. The effect of substrate temperature on the structural, optical, morphological and electrical properties of the films was mainly investigated. X-ray diffraction studies revealed that when the substrate temperature increased to above 200 ℃, the preferred orientation tended to move to another preferred site from (220) to (111) and had a band gap values increased with increasing substrate observed that the grain size and root mean square stable cubic structure. The optical transmittance and temperature. From the morphological studies, it was roughness were increased with increasing substrate temperature. The electrical resistivity of the film decreased to 0.017 Ωcm at high substrate temperature of 400 ℃.展开更多
HfO2/SiO2 multilayer films were deposited on BK7 glass substrates by electron beam evaporation method. The effects of annealing at the temperature between 200 and 400 ℃ on residual stresses have been studied. It is f...HfO2/SiO2 multilayer films were deposited on BK7 glass substrates by electron beam evaporation method. The effects of annealing at the temperature between 200 and 400 ℃ on residual stresses have been studied. It is found that the residual stress of as-deposited HfO2/SiO2 multilayers is compressive. It becomes tensile after annealing at 200 ℃, and then the value of tensile stress increases as annealing temperature increases. And cracks appear in the film because tensile stress is too large when the sample is annealed at 400 ℃. At the same time, the crystallite size increases and interplanar distance decreases with the increase of annealing temperature. The variation of residual stresses is corresponding with the evolution of structures.展开更多
Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route ...Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route B_(C)(i.e.,rotated 90° in the same sense between each pass).The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope(OM),X-ray diffraction(XRD),tensile test(at room temperature),and scanning electron microscope(SEM).The results show that the main strengthening phase of the alloy is MgZn_(2),whose content increases apparently after ECAP,the dislocation density increases by one order of magnitude,the hardness value of the 1 pass ECAPed sample increases by 53 %,the ultimate tensile strength(UTS)increases by 29 %,and the true strain increases by 15.4 %.But the further increase in the strength with the passes increasing would cost a slight drop in the true strain.The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.展开更多
A method of ultrasonic treatment (UST) was first used to modify the structure and electrochemical performance of nickel hydroxide for the active material of nickel series alkaline batteries. The experimental results...A method of ultrasonic treatment (UST) was first used to modify the structure and electrochemical performance of nickel hydroxide for the active material of nickel series alkaline batteries. The experimental results showed that UST was an effective method to improve the electrochemical performance of β-Ni(OH)2 such as specific discharge capacity, discharge potential, electrochemical reversibility and oxygen evolution over-potential. The results of electrochemical impedance spectroscopy, powder X-ray diffraction and particle size distribution indicated that the improvement of the performance of β-Ni(OH)2 through UST was attributed to the reduction of the charge-transfer resistance (Rt) and the diffusion impedance (Zw), which resulted from the decrease of the crystallite and particle size and the increase of interlayer spacing. Diffusion coefficient of proton DH of ultrasonic treated β-Ni(OH)2 gained by CV tests was 1.13 × 10^-11 cm^2/s, and the average discharge specific capacity of ultrasonic treated β-Ni(OH)2 electrode was 301 mAh/g.展开更多
基金financially supported by the Natural Science Foundation of China(21978312,21908235 and 21802155)the Key Research Program of Frontier Sciences,CAS(QYZDB–SSW–JS C043)+1 种基金Foundation of State Key Laboratory of Highefficiency Utilization of Coal and Green Chemical Engineering(2019-KF-05 and 2018-K22)Supported by Shanxi Scholarship Council of China and Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province are also greatly appreciated。
文摘The effects of crystallite size on the physicochemical properties and surface defects of pure monoclinic ZrO_(2) catalysts for isobutene synthesis were studied.We prepared a series of monoclinic ZrO_(2) catalysts with different crystallite size by changing calcination temperature and evaluated their catalytic performance for isobutene synthesis from syngas.ZrO_(2) with small crystalline size showed higher CO conversion and isobutene selectivity,while samples with large crystalline size preferred to form dimethyl ether(DME)instead of hydrocarbons,much less to isobutene.Oxygen defects(ODefects)analyzed by X-ray photoelectron spectroscopy(XPS)provided evidence that more ODefectsoccupied on the surface of ZrO_(2) catalysts with smaller crystalline size.Electron paramagnetic resonance(EPR)and ultraviolet–visible diffuse reflectance(UV–vis DRS)confirmed the presence of high concentration of surface defects and Zr3+on mZrO_(2)-5.9 sample,respectively.In situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS)analysis indicated that the adsorption strength of formed formate species on catalyst reduced as the crystalline size decreased.These results suggested that surface defects were responsible for CO activation and further influenced the adsorption strength of surface species,and thus the products distribution changed.This study provides an in-depth insight for active sites regulation of ZrO_(2) catalyst in CO hydrogenation reaction.
基金Acknowledgments This work is supported by the National Natural Science Foundation of China (Grand No. 21271114) Tsinghua University independent research and development fund (20111080982) and Program for Changjiang Scholars and Innovative Research Team in University (IRT13026).
文摘TNAs (Titanium dioxide nanotube arrays) were synthesized by electrochemical anodization and these TNAs were annealed in different gas atmosphere such as argon, air, hydrogen and nitrogen. This annealing in different atmosphere brought variation in crystallite size (27 - 33 nm), which influences on electrochemical properties. The specific capacity of Ar, Air, N2 and H2-annealed TNAs was around ~165, 185, 177 and 190 mAh g~, respectively. The crystallite size of anatase TNAs seemed to be responsible for the change in lithium storage capacity, indicating that structural changes of TNAs were playing major role in electrochemical properties.
文摘We investigated the structural and optical properties of ZnO thin films as an n-type semiconductor. The films were deposited at different precursor molarities using an ultrasonic spray method. In this paper we focused our attention on a new approach describing a correlation between the crystallite size and optical gap energy with the precursor molarity of ZnO thin films. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along the c-axis. The maximum value of the crystallite size of the films is 63.99 nm obtained at 0.1 M. The films deposited with 0.1 M show lower absorption within the visible wavelength region. The optical gap energy increased from 3.08 to 3.37 eV with increasing precursor molarity of 0.05 to 0.1 M. The correlation between the structural and optical properties with the precursor molarity suggests that the crystallite size of the films is predominantly influenced by the band gap energy and the precursor molarity. The measurement of the crystallite size by the model proposed is equal to the experimental data. The minimum error value was estimated by Eq. (4) in the higher crystallinity.
基金financially supported by the National Key Research and Development Program of China(No.2016YFC0204300)the National Natural Science Foundation of China(Nos.21922602 and 21577035)the Fundamental Research Funds for the Central Universities(No.222201717003)。
文摘A series of Co_(3) O_(4) catalysts was prepared by ammonia(Co-AP) and oxalate(Co-OP) precipitation,solgel(Co-SG),and urea hydrothermal(Co-UH) methods,and their physicochemical properties were characterised by numerous techniques including X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),nitrogen sorption,X-ray photoelectron spectroscopy(XPS),temperature-programmed reduction of H_(2)(H_(2)-TPR),temperature-programmed desorption of O_(2)(O_(2)-TPD),and temperature-programmed desorption of NH_(3)(NH_(3)-TPD).The catalytic activity of each catalyst was estimated for the catalytic combustion of vinyl chloride(VC) emissions.The crystallite size of the Co_(3) O_(4) catalyst was found to be well correlated with the amounts of surface-adsorbed oxygen species and number of acid sites on the catalyst surface,and consequently,determined several physicochemical properties of the catalyst.Of the catalysts studied here,the Co-AP catalyst exhibits the smallest crystallite size,which increases the specific surface area and the concentration of Co^(2+) on the catalyst surface.This,in turn,enhances the redox property,oxygen mobility,and the number of acid sites associated with the Co-AP catalyst.In fact,the Co-AP catalyst exhibits the best catalytic activity for VC combustion at 360℃and does not produce any chlorinated by-products.
基金The authors gratefully acknowledge the financial support of Science Foundation of China University of Petroleum,Beijing(Grant No.KYJJ2012-03-03).
文摘To improve oil quality,ZSM-22/SAPO-11 composite molecular sieves were synthesized by adding ZSM-22 into a synthetic gel of SAPO-11 for n-decane hydroisomerization.The mass ratios of ZSM-22/(ZSM-22+SAPO-11)in the composite molecular sieves were optimized and the optimal ZSM-22/SAPO-11 composite(ZS-9)was obtained.The electrostatic repulsions between the ZSM-22 precursors and the SAPO-11 crystalline nuclei produced small ZSM-22 and SAPO-11 crystallites in ZS-9,which increased the specific surface area and mesopore volume and thereby exposed more acid sites.In comparison with conventional SAPO-11,ZSM-22 and their mechanical mixture,ZS-9 with smaller crystallites and the optimal medium and strong Brønsted acid centers(MSBAC)content displayed a higher yield of branched C_(10) isomers(81.6%),lower cracking selectivity(11.9%)and excellent stability.The correlation between the i-C_(10) selectivity and the MSBAC density of molecular sieves indicated that the selectivity for branched C_(10) isomers first increased and then decreased with increasing MSBAC density on the molecular sieves,and the maximum selectivity(87.7%)occurred with a density of 9.6×10^(−2)μmol m^(−2).
文摘By optimizing the orystallization condition, a procedure for the synthesis of small crystallite zeolite ZSM-5 was developed. Compared with the larger crystallite ZSM-5. the smaller one exhibits higher catalytic performance in aromatization reaction of propane.
基金the financial support received from the National Science Foundation (NSF-CMMI 2131441) under the direction of Dr.Alexis Lewis。
文摘Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride containing solutions. In this research, commercially pure α-Ti top coating having good pitting potential(~1293 mV_(SCE)), high microhardness(HV_(0.025): 263.03) and low wear rate was applied on a CP-Al coated Mg-based alloy using high pressure cold spray technology. Potentiodynamic polarization(PDP) curves indicated that the probability of transition from metastable pits to the stable pits for cold spayed(CS) Al coating is considerably higher compared to that with the CS Ti top coating(for Ti/Al/Mg system). In addition, CS Ti top coating was in the passivation region in most pH ranges even after 48 h immersion in 3.5 wt% NaCl solution. The stored energy in the CS Ti top coating(as a passive metal) was presumed to be responsible for the easy passivation. Immersion tests indicated no obvious pits formation on the intact CS Ti top coating surface and revealed effective corrosion protection performance of the CS double layered noble barrier coatings on Mg alloys in 3.5 wt% NaCl solution even after 264 h.
基金NET 2 scheme(European Union’s Horizon 2020 Research and Innovation Program,grant No.685451)co-funded by the Research Council of Lithuania(LMTLT),agreement No.S-M-ERA.NET-21-2,the National Science Centre of Poland,project No.2020/02/Y/ST5/00086+1 种基金the Saxon State Ministry for Science,Culture and Tourism(Germany),grant No.100577922as well as from the tax funds on the basis of the budget passed by the Saxon state parliament.
文摘The excited localized surface plasmon(LSP)in metallic nanoparticles is known to relax through several processes such as electron-electron scattering,electron-phonon coupling,and phonon-phonon scat-tering.In the current research,the ultrafast electron-phonon(e-ph)coupling relaxation processes for different average sizes and crystallinity of chemically synthesized silver nanoparticles were evaluated utilizing transient absorption spectroscopy.The nanoparticle size and crystallinity of similar linear dimension polycrystalline spherical and monocrystalline cubic nanoparticles ranging from ca.30-60 nm was related to their electron relaxation time constants and revealed very different dependencies.For the monocrystalline nanocubes,the electron-phonon coupling was not dependent on the cube edge length,while for the polycrystalline nanospheres,it was linearly decreasing with diameter.We demonstrate that the e-ph coupling time constant could be used to evaluate crystallinity and crystallite size in plasmonic metal nanoparticles when the size(surface area)of the nanoparticle is known.
基金supported by Unité de Catalyse et Chimie du Solide (UCCS)sponsor of scholarship: China scholarship council and School of Environment, Tsinghua University
基金Funded by the National Natural Science Foundation of China (No. 51073098)the State Key Laboratory of Polymer Material Engineering(Sichuan University) (Nos.KF200901 and 2030925123008)
文摘A low-cost rout for modification the polyacrylontrile(PAN) precursor fibers was developed.The approach involved pretreatment PAN precursor fibers with UV irradiation for various periods of time before the fibers were stabilized.The effect of UV irradiation on the chemical structure,orientation factor,density,crystallite size and morphology of the fibers in the process of stabilization was characterized by use of fourier transform infrared spectroscopy(FTIR),float-sink procedure,X-ray diffraction(XRD),scanning electron microscope(SEM),respectively.The results showed that UV irradiation could increase the density of the fibers in stabilization process.FTIR analysis indicated that the cyclization of nitrile groups was initiated at room temperature by UV irradiation.The transformation of C≡N groups to C=N ones was accelerated in the process of stabilization.The orientation factor of irradiated fibers was also increased.The crystallite size was decreased at first and increased later,and the better irradiation time of UV was 3 min according to the XRD test.SEM analysis indicated that irradiation could decrease the internal and surface defects of the stabilized fibers treated at 300 ℃.
基金supported by the National Natural Science Foundation of China(Nos.50772033,50372020)the Natural Science Fund in Hunan Province,China(No.2007FJ3003).
文摘Carbon nanotube (CNT)/maleic acid anhydride (MAH)-grafted polypropylene (PP) composites were prepared by in situ grafting method. Infrared spectroscopy showed that the CNTs were linked to PP by MAH grafting. The microstructures and calorimetry analysis indicated that the crystallization behaviors of the filled and unfilled PP were quite different. The addition of CNTs dramatically reduced the spherulite size, increased crystallization rate and improved the thermal stability of PP. These results confirmed the expected nucleant effect of CNT on the crystallization of PP. Scanning and transmission electron microscopy showed that the CNTs were dispersed homogeneously, indicating that the original CNT bundles were separated into individual tubes by the grafting.
文摘The kinetic data of solid state polycondensation of PET and its copolymers are determined.It is shown that the reaction rate of copolycondensation is higher than that of PET polyconden-sation, and increases with the comonomers content. But the reaction rate of copolycondensationin melt state of this kind of copolymers is lower than that of PET. It is considered that the chemi-cal reactivity of comonomer is the main factor which affect the polycondensation in melt state,whereas the aggregative structure of the polymer is the main factor in solid state. The crystallinity and crystallite size of the copolymers have been measured by X-ray method.
基金This research study was supported by the Ministry of Education Malaysia(MOE)for the FRGS Grant(R.J130000.7824.4F723)Universiti Teknologi Malaysia(UTM)research grant(Q.J130000.2524.17H83).
文摘Ca3Co4O9 is a p-type semiconducting material that is well-known for its thermoelectric(TE),magnetic,electronic,and electro-optic properties.In this study,sol–gel autoignition was used to prepare Ca3Co4O9 at different calcination temperatures(773,873,973,and 1073 K)and time(4,6,8,10,12,and 14 h)using starch as a fuel.The phase and microstructure of the prepared Ca3Co4O9 powder were investigated.Thermogravimetry–differential thermal analysis(TGA)confirms that the final weight loss occurred at 1073 K to form Ca3Co4O9 stable powder.The variable-pressure scanning electron microscopy(VP-SEM)images show that the size of powder particles increases from 1.15 to 1.47μm as calcination time increases from 4 to 12 h,and the size remains almost constant thereafter.A similar pattern is also observed on the increment of the crystallite size and percentage of crystallinity with X-ray diffraction(XRD)analysis.The highest crystallinity is found about 92.9%when the powder was calcinated at 1073 K for 12 and 14 h with 458 and 460Åcrystallite size,respectively.Energy dispersive X-ray spectroscopy(EDS)analysis demonstrates that the calcinated powder has a high intensity of Ca,Co,and O with uniform distribution.High-resolution transmission electron microscopy(HRTEM)images prove that there is no distinct lattice distortion defect on the crystal structure.
基金the University Grants Commission(UGC),New Delhi(File No. F.40-419/2011(SR)) for providing the financial assistance to carry out the above work
文摘The NiO-Cu composite films were deposited on a glass substrate at various substrate temperatures by DC reactive magnetron sputtering technique. The effect of substrate temperature on the structural, optical, morphological and electrical properties of the films was mainly investigated. X-ray diffraction studies revealed that when the substrate temperature increased to above 200 ℃, the preferred orientation tended to move to another preferred site from (220) to (111) and had a band gap values increased with increasing substrate observed that the grain size and root mean square stable cubic structure. The optical transmittance and temperature. From the morphological studies, it was roughness were increased with increasing substrate temperature. The electrical resistivity of the film decreased to 0.017 Ωcm at high substrate temperature of 400 ℃.
基金the National Natural Science Foundation of China under Grant No.10704078
文摘HfO2/SiO2 multilayer films were deposited on BK7 glass substrates by electron beam evaporation method. The effects of annealing at the temperature between 200 and 400 ℃ on residual stresses have been studied. It is found that the residual stress of as-deposited HfO2/SiO2 multilayers is compressive. It becomes tensile after annealing at 200 ℃, and then the value of tensile stress increases as annealing temperature increases. And cracks appear in the film because tensile stress is too large when the sample is annealed at 400 ℃. At the same time, the crystallite size increases and interplanar distance decreases with the increase of annealing temperature. The variation of residual stresses is corresponding with the evolution of structures.
基金financially supported by the National Natural Science Foundation of China (Nos.51175138, 50875072 and 51575153)the Program for New Century Excellent Talents in University (No.NCET-13-0765)。
文摘Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route B_(C)(i.e.,rotated 90° in the same sense between each pass).The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope(OM),X-ray diffraction(XRD),tensile test(at room temperature),and scanning electron microscope(SEM).The results show that the main strengthening phase of the alloy is MgZn_(2),whose content increases apparently after ECAP,the dislocation density increases by one order of magnitude,the hardness value of the 1 pass ECAPed sample increases by 53 %,the ultimate tensile strength(UTS)increases by 29 %,and the true strain increases by 15.4 %.But the further increase in the strength with the passes increasing would cost a slight drop in the true strain.The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.
文摘A method of ultrasonic treatment (UST) was first used to modify the structure and electrochemical performance of nickel hydroxide for the active material of nickel series alkaline batteries. The experimental results showed that UST was an effective method to improve the electrochemical performance of β-Ni(OH)2 such as specific discharge capacity, discharge potential, electrochemical reversibility and oxygen evolution over-potential. The results of electrochemical impedance spectroscopy, powder X-ray diffraction and particle size distribution indicated that the improvement of the performance of β-Ni(OH)2 through UST was attributed to the reduction of the charge-transfer resistance (Rt) and the diffusion impedance (Zw), which resulted from the decrease of the crystallite and particle size and the increase of interlayer spacing. Diffusion coefficient of proton DH of ultrasonic treated β-Ni(OH)2 gained by CV tests was 1.13 × 10^-11 cm^2/s, and the average discharge specific capacity of ultrasonic treated β-Ni(OH)2 electrode was 301 mAh/g.