La1-xSrxGa1-y MgyO3-δ(LSGM) electrolyte, La1-xSrxCr1-y MnyO3-δ( LSCM ) anode and La1-xSrxFe1-y MnyO3-aaaaaaa(LSFM) cathode materials were all synthesized by glycine-nitrate process (GNP). The microstructure and char...La1-xSrxGa1-y MgyO3-δ(LSGM) electrolyte, La1-xSrxCr1-y MnyO3-δ( LSCM ) anode and La1-xSrxFe1-y MnyO3-aaaaaaa(LSFM) cathode materials were all synthesized by glycine-nitrate process (GNP). The microstructure and characteristics of LSGM, LSCM and LSFM were tested via X-ray diffraction(XRD), scanning electron microcopy (SEM), A C impedance and four-probe direct current techniques. XRD shows that pure perovskite phase LSGM electrolyte and electrode (LSCM anode and LSFM cathode) materials were prepared after being sintered at 1400℃for 20 h and at 1000℃for 5 h, respectively. The max conductivities of LSGM (ionic conductivity), LSCM (total conductivity) and LSFM (total conductivity) materials are 0.02, 10, 16 S·cm-1 in the air below 850℃, respectively. The conductivity of LSCM becomes smaller when the atmosphere changes from air to pure hydrogen at the same temperature and it decreases with the temperature like metal. The porous and LSGM-based LSCM anode and LSFM cathode films were prepared by screen printing method, and the sintering temperatures for them were 1300 and 1250℃, respectively. LSGM and electrode (LSCM and LSFM) materials have good thermal and chemical compatibility.展开更多
In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respecti...In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respectively,dried at 110℃ for 24 h and heat treated at 800 and 1100 ℃,respectively.Then the apparent porosity,the cold modulus of rupture and the cold crushing strength were measured.The phase composition of castable matrix specimens treated under the same conditions and the influence of the curing temperature on the intermediate temperature strength of the castables were also analyzed.The results show that with the increase of the curing temperature,the hydration degree of calcium aluminate cement increases,which promotes the uniform distribution of hydration products with AI203 after decomposition,thus enhancing the intermediate temperature strength of castables.展开更多
A TTT diagram for th ie precipitation formed at some intermediate temperatures through cooling from high lemperalure parenl phase in a Cu-27 27Zn-3.73Al allay is established by means of dilatormetric measurement.The m...A TTT diagram for th ie precipitation formed at some intermediate temperatures through cooling from high lemperalure parenl phase in a Cu-27 27Zn-3.73Al allay is established by means of dilatormetric measurement.The morphology and structure of transformation products formed at some intermediate tem peratures isothermally through cooling from high temperature parent phase and up-quenching from DO_(3) parent phase are studied by metallographic.X-ray and electron microscopy analyses.Three regions in the two separate C curves are obtained according to different morphology of precipitate:rod-like a,plate-like bainite and a rods,and bainite plates.Prolonged aging makes bainite plate change gradually into a whose lattice parameters are no different from that of a formed equilibriumly from parent phase.The structure is almost orthorhombic long period structure for bainites formed from B_(2) and DO_(3) parent phase,but monoclinic for martensite from DO_(3).They correspond to the overlapping and separating of(1210)and(2010)diffraction peaks respectively,showing the lower degree of ordering in bainite.展开更多
The present work explores the application of La_(0.5)Sr_(0.5)Co_(0.95)Nb_(0.05)O_(3-δ)(LSCNO)perovskite as electrode material for the symmetric solid oxide fuel cell.Symmetric solid oxide fuel cells of thin-film LSCN...The present work explores the application of La_(0.5)Sr_(0.5)Co_(0.95)Nb_(0.05)O_(3-δ)(LSCNO)perovskite as electrode material for the symmetric solid oxide fuel cell.Symmetric solid oxide fuel cells of thin-film LSCNO electrodes were prepared to study the oxygen reduction reaction at intermediate temperature.The Rietveld refinement of syn-thesized material shows a hexagonal structure with the R-3c space group of the prepared perovskite material.Lattice parameter and fractional coordinates were utilized to calculate the oxygen ion diffusion coefficient for molecular dynamic simulation.At 973 K,the oxygen ion diffusion of LSCNO was 1.407×10^(-8)cm^(2)s^(-1) higher by order of one magnitude than that of the La_(0.5)Sr_(0.5)Co_(0.95)Nb_(0.05)O_(3-δ)(7.751×10^(-9)cm^(2)^(-1)).The results suggest that the Nb doping provide the structural stability which improves oxygen anion diffusion.The enhanced structural stability was analysed by the thermal expansion coefficient calculated experimentally and from molecular dynamics simulations.Furthermore,the density functional theory calculation revealed the role of Nb dopant for oxygen vacancy formation energy at Sr-0 and La-O planes is lower than the undoped structure.To understand the rate-limiting process for sluggish oxygen diffusion kinetics,80 nm and 40 nm thin films were fabricated using radio frequency magnetron sputtering on gadolinium doped ceria electrolyte substrate.The impedance was observed to increase with an increasing thickness,suggesting the bulk diffusion as a rate-limiting step for oxygen ion diffu-sion.The electrochemical performance was analysed for the thin-flm symmetric solid oxide fuel cell,which achieved a peak power density of 390 mW cm^(-2) at 1.02 V in the presence of H_(2) fuel on the anode side and air on the cathode side.展开更多
Ti-bearing high-entropy superalloys(HESAs)often suffer from severe intergranular embrittlement and terrible oxidation degradation at intermediate temperatures.Here we showcase that minor Si addition can effectively mi...Ti-bearing high-entropy superalloys(HESAs)often suffer from severe intergranular embrittlement and terrible oxidation degradation at intermediate temperatures.Here we showcase that minor Si addition can effectively mitigate the intergranular embrittlement and improve the oxidation resistance of the a(Ni_(2)Co_(2)FeCr)_(92) Ti_(4)Al_(4) HESA at 700℃ simultaneously.Experimental analysis revealed that the intergranu-lar G phase induced by 2 at%Si addition can effectively suppress the inward diffusion of oxygen along grain boundaries at 700℃,thus enhancing the tensile ductility of the alloy from∼8.3%to∼13.4%.Be-sides,the 2 at%Si addition facilitated the formation of a continuous Al_(2)O_(3) layer during oxidation,con-tributing to a remarkable reduction in the growth rate of the oxide scale to a quarter of the Si-free HESA.Our results demonstrate that Si can be a favorable alloying element to design advanced HESAs with syn-ergistically improved thermal-mechanical performance.展开更多
Intermediate temperature embritttement （ITE） is a general phenomenon in Ni alloys and recently was interpreted by dynamic strain aging （DSA）. The relationship between ITE and DSA was studied by a binary Ni-Bi allo...Intermediate temperature embritttement （ITE） is a general phenomenon in Ni alloys and recently was interpreted by dynamic strain aging （DSA）. The relationship between ITE and DSA was studied by a binary Ni-Bi alloy. The experimental alloy of well-controlled purity was produced by vacuum induction inching and then heat-treated properly. Tensile tests were performed at various tensile temperatures, and the elongation at fracture was used to indicate the ductility. In order to identify the mechanisms of fracture and ITE, fracture morphologies of the samples of low ductility were observed by scanning electron microscopy. According to the tensile ductility, Ni-Bi alloy shows an obvious embrittlement behavior in the intermediate temperature range （700--750℃ ）. However, the stress strain curves of Ni-Bi alloy and the fracture morphologies indicate that DSA does not exist over the whole temperature range. Based on the experimental results and literatures, the interpretation of DSA was then discussed and proved to be invalid for elucidating the general feature of ITE in Ni-Bi alloy and Ni-based superalloys.展开更多
Understanding the corrosion behavior of high entropy alloys(HEAs)after intermediate temperature fatigue is critical to prevent their catastrophic failures from the reduction of corrosion resistance.Here,we investigate...Understanding the corrosion behavior of high entropy alloys(HEAs)after intermediate temperature fatigue is critical to prevent their catastrophic failures from the reduction of corrosion resistance.Here,we investigated the corrosion behavior of CrMnFeCoNi HEA after 500℃ fatigue test with strain amplitudes of 0.2%and 0.5%.The intermediate temperature fatigue induced two types of precipitates,which were determined as Cr-richσphase and NiMn-rich L10 phase.Higher strain amplitude not only promoted precipitates generations but also spread the nucleation sites from intergranular to both intergranular and intragranular.Furthermore,we found that the deterioration in corrosion resistance of the alloy was derived from the increase of precipitates,which destroyed the stability of the passive film.The above results revealed that intermediate temperature fatigue impaired the stabilization of the solid solution state and subsequent corrosion resistance of CrMnFeCoNi HEA,where the higher strain amplitude led to more precipitates and more severe corrosion.展开更多
Proton conducting ceramic cells(PCCs)are an attractive emerging technology operating in the intermediate temperature range of 500 to 700℃.In this work,we evaluate the production of hydrogen at intermediate temperatur...Proton conducting ceramic cells(PCCs)are an attractive emerging technology operating in the intermediate temperature range of 500 to 700℃.In this work,we evaluate the production of hydrogen at intermediate temperatures by proton conducting ceramic cell electrolysis(PCCEL).We demonstrate a highperformance steam electrolysis owing to a composite positrode based on BaGd_(0.8)La_(0.2)Co_(2)O_(6-δ)(BGLC1082)and BaZr0.5Ce0.4Y0.1O3-δ(BZCY541).The high reliability of PCCEL is demonstrated for 1680 h at a current density as high as-0.8 A cm^(-2)close to the thermoneutral cell voltage at 600℃.The electrolysis cell showed a specific energy consumption ranging from 54 to 66 kW h kg^(-1)that is comparable to state-of-the-art low temperature electrolysis technologies,while showing hydrogen production rates systematically higher than commercial solid oxide ceramic cells(SOCs).Compared to SOCs,the results verified the higher performances of PCCs at the relevant operating temperatures,due to the lower activation energy for proton transfer comparing with oxygen ion conduction.However,because of the p-type electronic conduction in protonic ceramics,the energy conversion rate of PCCs is relatively lower in steam electrolysis.The faradaic efficiency of the PCC in electrolysis mode can be increased at lower operating temperatures and in endothermic conditions,making PCCEL a technology of choice to valorize high temperature waste heat from industrial processes into hydrogen.To increase the faradaic efficiency by optimizing the materials,the cell design,or the operating strategy is a key challenge to address for future developments of PCCEL in order to achieve even more superior techno-economic merits.展开更多
Compared with conventional electric power generation systems, the solid oxide fuel cell （SOFC） has many advantages because of its unique features. High temperature SOFC has been successfully developed to its commerc...Compared with conventional electric power generation systems, the solid oxide fuel cell （SOFC） has many advantages because of its unique features. High temperature SOFC has been successfully developed to its commercial applications, but it still faces many problems which hamper large-scale commercial applications of SOFC. To reduce the cost of SOFC, intermediate temperature solid oxide fuel cell （IT-SOFC） is presently under rapid development. The status of IT-SOFC was reviewed with emphasis on discussion of their component materials. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
The use of CO2-free energy sources for running SOEC （solid-oxide electrolysis cell） technologies has a great potential to reduce the carbon dioxide emissions compared to fossil fuel based technologies for hydrogen p...The use of CO2-free energy sources for running SOEC （solid-oxide electrolysis cell） technologies has a great potential to reduce the carbon dioxide emissions compared to fossil fuel based technologies for hydrogen production. The operation of the electrolysis cell at higher temperature offers the benefit of increasing the efficiency of the process. The range of the operating temperature of the SOEC is typically between 800 ~C and 1,000 ~C. Main sources of degradation that affect the SOEC stack lifetime is related to the high operating temperature. To increase the electrolyser durability, one possible solution is to decrease the operating temperature down to 650 ~C, which represents the typical operating range of the ITSE （intermediate temperature steam electrolysis）. This paper is related to the work of the JU-FCH project ADEL, which investigates different carbon-free energy sources with respect to potential coupling schemes to ITSE. A predominant focus of the analysis is put on solar concentrating energy systems （solar tower） and nuclear energy as energy sources to provide the required electricity and heat for the ITSE. This study will present an overview of the main considerations, the boundary conditions and the results concerning the development of coupling schemes of the energy conversion technologies to the electrolyser.展开更多
Intermediate temperature brittleness in alloys characterized as brittle fracture along grain boundaries(GBs)with less than 5%elongation to fracture(EF)at 600◦C–900◦C diminishes work hardening,leads to sudden failure ...Intermediate temperature brittleness in alloys characterized as brittle fracture along grain boundaries(GBs)with less than 5%elongation to fracture(EF)at 600◦C–900◦C diminishes work hardening,leads to sudden failure under load,and thus threatens the reliability during the service of alloys.Here,in a precipitation-strengthened CoNiCr alloy,through two grain boundary engineering(GBE)methods,fiber-likeγ′or topologically close-packed phase is introduced at GBs,which effectively optimizes the grain structure and prevents GB cracking under tensile stresses.GBEs not only alter the deformation mode from dislocation pairs to stacking faults and/or deformation twins,but also transform the failure mode from GB cracking to GB void formation,because the crack propagation along GBs is constrained by GB bridging phases.Consequently,our GBE approach enhances tensile EF from∼1%to∼10%and concurrently increases the yield strength from∼650 to∼770–850 MPa at 800◦C.A cavity growth model is then developed to illustrate the role of these bridging phases in GBs for ductility improvement.The fundamental philosophy utilized in the present work might be also applicable to other metallic materials.展开更多
Carbon dioxide（CO2） capture using magnesium oxide（MgO）-based adsorbents at intermediate temperatures has been regarded as a very prospective technology for their relatively high adsorption capacity,low cost, and w...Carbon dioxide（CO2） capture using magnesium oxide（MgO）-based adsorbents at intermediate temperatures has been regarded as a very prospective technology for their relatively high adsorption capacity,low cost, and wide availability. During the past few years, great effort has been devoted to the fabrication of molten salts-modified MgO-based adsorbents. The extraordinary progress achieved by coating with molten salts greatly promotes the COcapture capacity of MgO-based adsorbents. Therefore, we feel it necessary to deliver a timely review on this type of COcapturing materials, which will benefit the researchers working in both academic and industrial areas. In this work, we classified the molten saltsmodified MgO adsorbents into four categories:（1） homogenous molten salt-modified MgO adsorbents,（2） molten salt-modified double salts-based MgO adsorbents,（3） mixed molten salts-modified MgO adsorbents, and（4） molten salts-modified MgO-based mixed oxides adsorbents. This contribution critically reviews the recent developments in the synthetic method, adsorption capacity, reaction kinetics, promotion mechanism, operational conditions and regenerability of the molten salts-modified MgO COadsorbents. The challenges and prospects in this promising field of molten salts-modified MgO COadsorbents in real applications are also briefly mentioned.展开更多
The standard heat treatment of cast nickel base superalloy K403 is the solid solution treatment of 1210℃/4h, air cooling. It is very difficult to meet the requirements of Aviation Standard HB5155, in which the stre...The standard heat treatment of cast nickel base superalloy K403 is the solid solution treatment of 1210℃/4h, air cooling. It is very difficult to meet the requirements of Aviation Standard HB5155, in which the stress rupture life at 750℃ and 645MPa is longer than 50h. The results showed that the intermediate temperature stress rupture properties impaired by treatment of 1210℃/4h were due to precipitation of too small γ′ phase(<0.2μm) in grains and absence of the secondary carbides at grain boundaries. Microstructure containing the intergranular M6C carbides with envelope of γ′ and the residual coarse γ′ was obtained by means of 1180℃/4h treatment, therefore the stress rupture life was obviously increased to meet the demand of HB5155. The effect of γ′ size was also discussed from the view point of deformation mechanism in this paper.展开更多
1 Introduction The composite electrode of La0.6Sr0.4Co0.2Fe0.8O3(LSCF) and Ag was studied as a new air electrode system for reduced-temperature SOFCs.The LSCF/Ag composite electrodes were prepared by baking the LSCF e...1 Introduction The composite electrode of La0.6Sr0.4Co0.2Fe0.8O3(LSCF) and Ag was studied as a new air electrode system for reduced-temperature SOFCs.The LSCF/Ag composite electrodes were prepared by baking the LSCF electrode with various Ag solution infiltrated in the pores of the electrode.In all cases,the cathode polarization resistance was reduced,which may be brought from the catalytic activity of Ag metal.For example,the power density of LSCF electrode on anode supported cell was increased from 0....展开更多
Increasing density is one of the important factors for producing high quality powder metallurgy （PM） parts, which has beneficial effect on mechanical properties. One of the common techniques for achieving this goal ...Increasing density is one of the important factors for producing high quality powder metallurgy （PM） parts, which has beneficial effect on mechanical properties. One of the common techniques for achieving this goal is double compacting, which seems to be a potentially attractive method in PM route, also for Cr-Mo alloyed-steels. The objective of this research was to investigate the effect of first compacting pressure and intermediate annealing temperature on attaining higher densities and minimum interconnected porosity for Cr-Mo pre-alloyed steel. The effect of mentioned parameters was studied by measuring density, transverse rupture strength and macrohardness of repressed samples. The results show that for each first compacting pressure, the density range of repressed samples increases with the increasing annealing temperature up to a certain limit, due to C dissolution which causes free porosity and further densifieation. Annealing temperatures higher than optimum one should be avoided, since too much carbon dissolution results in harder and less deformable compacts. On the other hand, with regard to repressed density and other resulted properties, the amount of first compacting pressure offers considerable advantage in obtaining higher level of density and consequently improved mechanical properties.展开更多
The temperature distribution of COREX melter gasifier was studied by using a two-dimensional 1/30 scale thermal dynamic model.A set of operating conditions,such as radial distribution of direct reduction iron（DRI） t...The temperature distribution of COREX melter gasifier was studied by using a two-dimensional 1/30 scale thermal dynamic model.A set of operating conditions,such as radial distribution of direct reduction iron（DRI） to lump coal and coke volume ratio,coke charging location,coke charging amount and coke size,were taken into account.The results show that the temperature near the wall region decreases with the decrease of the radial distribution of DRI to lump coal and coke volume ratio.The temperature with central coke charging is higher than that without central coke column.Furthermore,the temperature significantly increases with the increase of central coke charging amount.With the increase of intermediate coke charging amount,the temperature near the wall region decreases while the temperature in the intermediate region increases.The temperature increases with the increase of coke size whether charging central coke or intermediate coke.展开更多
The oxidation behavior and kinetics of Ti_(2)AlC-20vol.%TiB_(2) composite at 600-900℃ in air were investigated.The results showed that the oxidation kinetics of the composite followed a logarithmic law within the giv...The oxidation behavior and kinetics of Ti_(2)AlC-20vol.%TiB_(2) composite at 600-900℃ in air were investigated.The results showed that the oxidation kinetics of the composite followed a logarithmic law within the given temperature range,which indicated that the composites had excellent oxidation resistance.The selective oxidation of Al in Ti_(2)AlC was greatly enhanced,which facilitated the formation of a continuous and dense protective layer of Al_(2)O_(3).Meanwhile,the existence of molten B_(2)O_(3) inhibited the outward diffusion of Ti and inward diffusion of oxygen,which prevented the growth of anatase TiO_(2) at 600℃ and rutile TiO_(2) at 700-900℃.Therefore,the incorporation of TiB_(2) completely inhibited the abnormally rapid oxidation of bulk Ti_(2)AlC at 600℃ and improved its oxidation resistance at 700-900℃.展开更多
High-entropy alloys(HEAs)commonly exhibit significant strength deficiencies and intermediate temperature brittleness(ITB)in the temperature range of 650-750°C,which greatly restricts their practical use in safety...High-entropy alloys(HEAs)commonly exhibit significant strength deficiencies and intermediate temperature brittleness(ITB)in the temperature range of 650-750°C,which greatly restricts their practical use in safety engineering.In this study,a novel coherent face-centered cubic(FCC)/L1_(2)HEA with multiple heterogeneous microstructures,including grain size and L1_(2)precipitates was developed.The newly designed HEA demonstrates outstanding mechanical properties across a broad temperature spectrum(25-750°C).At ambient temperature,the HEA displays a remarkable tensile strength of up to 1700 MPa and a tensile ductility of 15.9%.Notably,the HEA exhibits an impressive yield strength of 1 GPa in the intermediate temperature range,with minimal loss of ductility under high tensile stresses.The presence of the primary L1_(2)phase effectively stabilizes the grain boundaries(GBs),inhibiting crack propagation and oxygen diffusion along them.This mechanism prevents the formation of brittle phases at the GBs,thereby protecting the GBs and mitigating the issue of ITB.As a result,the HEA exhibits an intermediate temperature tensile strain surpassing 14%.The heterogeneous structural modulation strategy offers valuable insights into the tailored design of high-performance HEAs for advanced high-temperature structural applications in urgent demand.展开更多
In this communication,the electrical conductivities and thermal expansion studies of microwave sintered co-doped ceria Ce_(0.8)Y_(0.2-x)Dy_(x)O_(2-δ)(x=0,0.05,0.10,0.15 and 0.20) solid electrolyte materials for inter...In this communication,the electrical conductivities and thermal expansion studies of microwave sintered co-doped ceria Ce_(0.8)Y_(0.2-x)Dy_(x)O_(2-δ)(x=0,0.05,0.10,0.15 and 0.20) solid electrolyte materials for intermediate temperature solid oxide fuel cells(IT-SOFCs)synthesized by sol-gel auto-combustion method were discussed.Microwave sintering at 1300℃ for 30 min was used for making dense powder compacts.The relative densities of all the samples are noticed above 95%.Raman spectrum was characterized by the presence of a very strong band near 460 cm^(-1),which along with X-ray diffraction(XRD) analysis ascertain the sample formation with a single-phase cubic fluorite structure.The lattice parameter values were calculated from XRD patterns.SEM images show nearly uniform grains with distinct grain boundaries.The thermal expansion coefficients(TECs) are found to vary linearly with temperature and were measured in the range from 14.15 to 13.20×10^(-6)℃^(-1).The investigation on total ionic conductivity(TIC) was executed with variation in dopant concentration and relative oxygen vacancies.The impedance analysis reveals that the sample Ce_(0.80)Y_(0.10)Dy_(0.10)O_(2-δ) displays the highest TIC,i.e.,7.5×10^(-3) S·cm^(-1) at 500℃ and minimum activation energy 0.90 eV compared to others.With the highest TIC and minimum activation energy,the Ce_(0.80)Y_(0.10)Dy_(0.10)O_(2-δ)might be the possible material as the solid electrolyte in intermediate temperature SOFCs.展开更多
The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitatio...The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitation method with metal-nitrates as starting materials and mixed alkali (NaOH and Na2CO3) as a precipitating agent. The formation process of LSCCF from the precursors was monitored by TG-DSC, and the crystal structure and particles morphology of the precursors which were calcined at 600, 800, 1000 ℃ for 3 h were characterized using XRD, SEM technologies. Compared with the solid state reaction of constituent oxides, when the pH value of the precipitating solution was in the range of 9.1～9.5, the LSCCF powders from the precursors caclined at 800 ℃ for 3 h had high purity, homogeneous and single perovskite phase. The electrical conductivity of the LSCCF samples sintered at 1200 ℃ for 3 h, which was measured as a function of temperatures from 100 to 800 ℃ by DC four-probe method in air, decreased with x from 0.05 to 0.20. The value of electrical conductivity was almost equal because of Ca2+, Sr2+ co-dopant resulting in the 'mix effect' while x=0.10 or 0.15. The electrical conductivity of all doped samples was higher than 100 S·cm-1 at intermediate temperatures from 500 to 800 ℃, and there was good compatibility between the LSCCF cathode and Ce0.8Sm0.2O2 electrolyte.展开更多
基金Project supported by the National Natural Science Foundation of China (50204007)the Foundation of Yunnan Province (2005PY01-33)
文摘La1-xSrxGa1-y MgyO3-δ(LSGM) electrolyte, La1-xSrxCr1-y MnyO3-δ( LSCM ) anode and La1-xSrxFe1-y MnyO3-aaaaaaa(LSFM) cathode materials were all synthesized by glycine-nitrate process (GNP). The microstructure and characteristics of LSGM, LSCM and LSFM were tested via X-ray diffraction(XRD), scanning electron microcopy (SEM), A C impedance and four-probe direct current techniques. XRD shows that pure perovskite phase LSGM electrolyte and electrode (LSCM anode and LSFM cathode) materials were prepared after being sintered at 1400℃for 20 h and at 1000℃for 5 h, respectively. The max conductivities of LSGM (ionic conductivity), LSCM (total conductivity) and LSFM (total conductivity) materials are 0.02, 10, 16 S·cm-1 in the air below 850℃, respectively. The conductivity of LSCM becomes smaller when the atmosphere changes from air to pure hydrogen at the same temperature and it decreases with the temperature like metal. The porous and LSGM-based LSCM anode and LSFM cathode films were prepared by screen printing method, and the sintering temperatures for them were 1300 and 1250℃, respectively. LSGM and electrode (LSCM and LSFM) materials have good thermal and chemical compatibility.
基金The authors appreciate the financial support from National Natural Science Foundation of China(No.5157244,U1604252 and 5167225).
文摘In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respectively,dried at 110℃ for 24 h and heat treated at 800 and 1100 ℃,respectively.Then the apparent porosity,the cold modulus of rupture and the cold crushing strength were measured.The phase composition of castable matrix specimens treated under the same conditions and the influence of the curing temperature on the intermediate temperature strength of the castables were also analyzed.The results show that with the increase of the curing temperature,the hydration degree of calcium aluminate cement increases,which promotes the uniform distribution of hydration products with AI203 after decomposition,thus enhancing the intermediate temperature strength of castables.
基金supported by the National Natural Science Foundation
文摘A TTT diagram for th ie precipitation formed at some intermediate temperatures through cooling from high lemperalure parenl phase in a Cu-27 27Zn-3.73Al allay is established by means of dilatormetric measurement.The morphology and structure of transformation products formed at some intermediate tem peratures isothermally through cooling from high temperature parent phase and up-quenching from DO_(3) parent phase are studied by metallographic.X-ray and electron microscopy analyses.Three regions in the two separate C curves are obtained according to different morphology of precipitate:rod-like a,plate-like bainite and a rods,and bainite plates.Prolonged aging makes bainite plate change gradually into a whose lattice parameters are no different from that of a formed equilibriumly from parent phase.The structure is almost orthorhombic long period structure for bainites formed from B_(2) and DO_(3) parent phase,but monoclinic for martensite from DO_(3).They correspond to the overlapping and separating of(1210)and(2010)diffraction peaks respectively,showing the lower degree of ordering in bainite.
文摘The present work explores the application of La_(0.5)Sr_(0.5)Co_(0.95)Nb_(0.05)O_(3-δ)(LSCNO)perovskite as electrode material for the symmetric solid oxide fuel cell.Symmetric solid oxide fuel cells of thin-film LSCNO electrodes were prepared to study the oxygen reduction reaction at intermediate temperature.The Rietveld refinement of syn-thesized material shows a hexagonal structure with the R-3c space group of the prepared perovskite material.Lattice parameter and fractional coordinates were utilized to calculate the oxygen ion diffusion coefficient for molecular dynamic simulation.At 973 K,the oxygen ion diffusion of LSCNO was 1.407×10^(-8)cm^(2)s^(-1) higher by order of one magnitude than that of the La_(0.5)Sr_(0.5)Co_(0.95)Nb_(0.05)O_(3-δ)(7.751×10^(-9)cm^(2)^(-1)).The results suggest that the Nb doping provide the structural stability which improves oxygen anion diffusion.The enhanced structural stability was analysed by the thermal expansion coefficient calculated experimentally and from molecular dynamics simulations.Furthermore,the density functional theory calculation revealed the role of Nb dopant for oxygen vacancy formation energy at Sr-0 and La-O planes is lower than the undoped structure.To understand the rate-limiting process for sluggish oxygen diffusion kinetics,80 nm and 40 nm thin films were fabricated using radio frequency magnetron sputtering on gadolinium doped ceria electrolyte substrate.The impedance was observed to increase with an increasing thickness,suggesting the bulk diffusion as a rate-limiting step for oxygen ion diffu-sion.The electrochemical performance was analysed for the thin-flm symmetric solid oxide fuel cell,which achieved a peak power density of 390 mW cm^(-2) at 1.02 V in the presence of H_(2) fuel on the anode side and air on the cathode side.
基金the financial support from Hong Kong Research Grant Council(RGC)(Grant Nos.CityU 11214820,CityU 11209021,CityU 21205621,CityU 9360161 andC1017-21G)theNationalNatural Science Foundation of China(Grant Nos.52101151 and52101162)+3 种基金the Shenzhen Science and Technology Program(Grant No.SGDX20210823104002016)the Hong Kong Poly-technic University thanks the financial support from Hong Kong RGC(Grant Nos.25202719 and 15227121)the finan-cial support from National Natural Science Foundation of China(Grant No.52101135)the Shenzhen Science and Technology Program(Grant No.RCBS20210609103202012).
文摘Ti-bearing high-entropy superalloys(HESAs)often suffer from severe intergranular embrittlement and terrible oxidation degradation at intermediate temperatures.Here we showcase that minor Si addition can effectively mitigate the intergranular embrittlement and improve the oxidation resistance of the a(Ni_(2)Co_(2)FeCr)_(92) Ti_(4)Al_(4) HESA at 700℃ simultaneously.Experimental analysis revealed that the intergranu-lar G phase induced by 2 at%Si addition can effectively suppress the inward diffusion of oxygen along grain boundaries at 700℃,thus enhancing the tensile ductility of the alloy from∼8.3%to∼13.4%.Be-sides,the 2 at%Si addition facilitated the formation of a continuous Al_(2)O_(3) layer during oxidation,con-tributing to a remarkable reduction in the growth rate of the oxide scale to a quarter of the Si-free HESA.Our results demonstrate that Si can be a favorable alloying element to design advanced HESAs with syn-ergistically improved thermal-mechanical performance.
基金Item Sponsored by National Natural Science Foundation of China(51001011)Fundamental Research Funds for the Central Universities of China(FRF-TP-12-042A)Fok Ying Tong Education Foundation(141043)
文摘Intermediate temperature embritttement （ITE） is a general phenomenon in Ni alloys and recently was interpreted by dynamic strain aging （DSA）. The relationship between ITE and DSA was studied by a binary Ni-Bi alloy. The experimental alloy of well-controlled purity was produced by vacuum induction inching and then heat-treated properly. Tensile tests were performed at various tensile temperatures, and the elongation at fracture was used to indicate the ductility. In order to identify the mechanisms of fracture and ITE, fracture morphologies of the samples of low ductility were observed by scanning electron microscopy. According to the tensile ductility, Ni-Bi alloy shows an obvious embrittlement behavior in the intermediate temperature range （700--750℃ ）. However, the stress strain curves of Ni-Bi alloy and the fracture morphologies indicate that DSA does not exist over the whole temperature range. Based on the experimental results and literatures, the interpretation of DSA was then discussed and proved to be invalid for elucidating the general feature of ITE in Ni-Bi alloy and Ni-based superalloys.
基金the National Natural Science Foundation of China(Nos.52201072,12204143 and 52101013)the Natural Science Foundation of Hebei Province(No.E2020202009)+3 种基金the Technology Project of Hebei Education Department(No.QN2020150)the China Postdoctoral Science Foundation(No.2020M680843)the Central Funds Guiding the Local Science and Technology Development of Hebei Province(No.226Z1001G)the Central Funds Guiding the Local Science and Technology Development of Hebei Province(No.226Z1012G).
文摘Understanding the corrosion behavior of high entropy alloys(HEAs)after intermediate temperature fatigue is critical to prevent their catastrophic failures from the reduction of corrosion resistance.Here,we investigated the corrosion behavior of CrMnFeCoNi HEA after 500℃ fatigue test with strain amplitudes of 0.2%and 0.5%.The intermediate temperature fatigue induced two types of precipitates,which were determined as Cr-richσphase and NiMn-rich L10 phase.Higher strain amplitude not only promoted precipitates generations but also spread the nucleation sites from intergranular to both intergranular and intragranular.Furthermore,we found that the deterioration in corrosion resistance of the alloy was derived from the increase of precipitates,which destroyed the stability of the passive film.The above results revealed that intermediate temperature fatigue impaired the stabilization of the solid solution state and subsequent corrosion resistance of CrMnFeCoNi HEA,where the higher strain amplitude led to more precipitates and more severe corrosion.
基金The China Scholarship Council is acknowledged for the doctoral scholarship of Haoyu Zheng(201806160173)The German Federal Ministry for Education and Research is acknowledged for funding via the Project ARCADE(03SF0580A)。
文摘Proton conducting ceramic cells(PCCs)are an attractive emerging technology operating in the intermediate temperature range of 500 to 700℃.In this work,we evaluate the production of hydrogen at intermediate temperatures by proton conducting ceramic cell electrolysis(PCCEL).We demonstrate a highperformance steam electrolysis owing to a composite positrode based on BaGd_(0.8)La_(0.2)Co_(2)O_(6-δ)(BGLC1082)and BaZr0.5Ce0.4Y0.1O3-δ(BZCY541).The high reliability of PCCEL is demonstrated for 1680 h at a current density as high as-0.8 A cm^(-2)close to the thermoneutral cell voltage at 600℃.The electrolysis cell showed a specific energy consumption ranging from 54 to 66 kW h kg^(-1)that is comparable to state-of-the-art low temperature electrolysis technologies,while showing hydrogen production rates systematically higher than commercial solid oxide ceramic cells(SOCs).Compared to SOCs,the results verified the higher performances of PCCs at the relevant operating temperatures,due to the lower activation energy for proton transfer comparing with oxygen ion conduction.However,because of the p-type electronic conduction in protonic ceramics,the energy conversion rate of PCCs is relatively lower in steam electrolysis.The faradaic efficiency of the PCC in electrolysis mode can be increased at lower operating temperatures and in endothermic conditions,making PCCEL a technology of choice to valorize high temperature waste heat from industrial processes into hydrogen.To increase the faradaic efficiency by optimizing the materials,the cell design,or the operating strategy is a key challenge to address for future developments of PCCEL in order to achieve even more superior techno-economic merits.
基金the National Basic Research Program of China(No.2007CB936201)the National High Technology Research and Development Program of China(863 Program)(No.2006AAO3Z351)the Major International(Regional)Joint Research Program of China(No.50620120439,2006DFB51000).
文摘Compared with conventional electric power generation systems, the solid oxide fuel cell （SOFC） has many advantages because of its unique features. High temperature SOFC has been successfully developed to its commercial applications, but it still faces many problems which hamper large-scale commercial applications of SOFC. To reduce the cost of SOFC, intermediate temperature solid oxide fuel cell （IT-SOFC） is presently under rapid development. The status of IT-SOFC was reviewed with emphasis on discussion of their component materials. 2008 University of Science and Technology Beijing. All rights reserved.
文摘The use of CO2-free energy sources for running SOEC （solid-oxide electrolysis cell） technologies has a great potential to reduce the carbon dioxide emissions compared to fossil fuel based technologies for hydrogen production. The operation of the electrolysis cell at higher temperature offers the benefit of increasing the efficiency of the process. The range of the operating temperature of the SOEC is typically between 800 ~C and 1,000 ~C. Main sources of degradation that affect the SOEC stack lifetime is related to the high operating temperature. To increase the electrolyser durability, one possible solution is to decrease the operating temperature down to 650 ~C, which represents the typical operating range of the ITSE （intermediate temperature steam electrolysis）. This paper is related to the work of the JU-FCH project ADEL, which investigates different carbon-free energy sources with respect to potential coupling schemes to ITSE. A predominant focus of the analysis is put on solar concentrating energy systems （solar tower） and nuclear energy as energy sources to provide the required electricity and heat for the ITSE. This study will present an overview of the main considerations, the boundary conditions and the results concerning the development of coupling schemes of the energy conversion technologies to the electrolyser.
基金supported by the National Natural Science Foundation of China(Grant Nos.52201027 and 52471019)the Basic Science Center Program for Multiphase Media Evolution in Hypergravity of the National Natural Science Foundation of China(Grant No.51988101)+1 种基金the Zhejiang Provincial Natural Science Foundation of China(Grant No.LR24E010001)the Fundamental Research Funds for the Central Universities(Grant No.226-2024-00044).
文摘Intermediate temperature brittleness in alloys characterized as brittle fracture along grain boundaries(GBs)with less than 5%elongation to fracture(EF)at 600◦C–900◦C diminishes work hardening,leads to sudden failure under load,and thus threatens the reliability during the service of alloys.Here,in a precipitation-strengthened CoNiCr alloy,through two grain boundary engineering(GBE)methods,fiber-likeγ′or topologically close-packed phase is introduced at GBs,which effectively optimizes the grain structure and prevents GB cracking under tensile stresses.GBEs not only alter the deformation mode from dislocation pairs to stacking faults and/or deformation twins,but also transform the failure mode from GB cracking to GB void formation,because the crack propagation along GBs is constrained by GB bridging phases.Consequently,our GBE approach enhances tensile EF from∼1%to∼10%and concurrently increases the yield strength from∼650 to∼770–850 MPa at 800◦C.A cavity growth model is then developed to illustrate the role of these bridging phases in GBs for ductility improvement.The fundamental philosophy utilized in the present work might be also applicable to other metallic materials.
基金the Fundamental Research Funds for the Central Universities (2016ZCQ03)Beijing Excellent Young Scholar (2015000026833ZK11)+1 种基金the National Natural Science Foundation of China (51622801, 51572029, and 51308045)the Xu Guangqi grant
文摘Carbon dioxide（CO2） capture using magnesium oxide（MgO）-based adsorbents at intermediate temperatures has been regarded as a very prospective technology for their relatively high adsorption capacity,low cost, and wide availability. During the past few years, great effort has been devoted to the fabrication of molten salts-modified MgO-based adsorbents. The extraordinary progress achieved by coating with molten salts greatly promotes the COcapture capacity of MgO-based adsorbents. Therefore, we feel it necessary to deliver a timely review on this type of COcapturing materials, which will benefit the researchers working in both academic and industrial areas. In this work, we classified the molten saltsmodified MgO adsorbents into four categories:（1） homogenous molten salt-modified MgO adsorbents,（2） molten salt-modified double salts-based MgO adsorbents,（3） mixed molten salts-modified MgO adsorbents, and（4） molten salts-modified MgO-based mixed oxides adsorbents. This contribution critically reviews the recent developments in the synthetic method, adsorption capacity, reaction kinetics, promotion mechanism, operational conditions and regenerability of the molten salts-modified MgO COadsorbents. The challenges and prospects in this promising field of molten salts-modified MgO COadsorbents in real applications are also briefly mentioned.
文摘The standard heat treatment of cast nickel base superalloy K403 is the solid solution treatment of 1210℃/4h, air cooling. It is very difficult to meet the requirements of Aviation Standard HB5155, in which the stress rupture life at 750℃ and 645MPa is longer than 50h. The results showed that the intermediate temperature stress rupture properties impaired by treatment of 1210℃/4h were due to precipitation of too small γ′ phase(<0.2μm) in grains and absence of the secondary carbides at grain boundaries. Microstructure containing the intergranular M6C carbides with envelope of γ′ and the residual coarse γ′ was obtained by means of 1180℃/4h treatment, therefore the stress rupture life was obviously increased to meet the demand of HB5155. The effect of γ′ size was also discussed from the view point of deformation mechanism in this paper.
文摘1 Introduction The composite electrode of La0.6Sr0.4Co0.2Fe0.8O3(LSCF) and Ag was studied as a new air electrode system for reduced-temperature SOFCs.The LSCF/Ag composite electrodes were prepared by baking the LSCF electrode with various Ag solution infiltrated in the pores of the electrode.In all cases,the cathode polarization resistance was reduced,which may be brought from the catalytic activity of Ag metal.For example,the power density of LSCF electrode on anode supported cell was increased from 0....
文摘Increasing density is one of the important factors for producing high quality powder metallurgy （PM） parts, which has beneficial effect on mechanical properties. One of the common techniques for achieving this goal is double compacting, which seems to be a potentially attractive method in PM route, also for Cr-Mo alloyed-steels. The objective of this research was to investigate the effect of first compacting pressure and intermediate annealing temperature on attaining higher densities and minimum interconnected porosity for Cr-Mo pre-alloyed steel. The effect of mentioned parameters was studied by measuring density, transverse rupture strength and macrohardness of repressed samples. The results show that for each first compacting pressure, the density range of repressed samples increases with the increasing annealing temperature up to a certain limit, due to C dissolution which causes free porosity and further densifieation. Annealing temperatures higher than optimum one should be avoided, since too much carbon dissolution results in harder and less deformable compacts. On the other hand, with regard to repressed density and other resulted properties, the amount of first compacting pressure offers considerable advantage in obtaining higher level of density and consequently improved mechanical properties.
基金Item Sponsored by Fundamental Research Funds for Central Universities of China(090402021)
文摘The temperature distribution of COREX melter gasifier was studied by using a two-dimensional 1/30 scale thermal dynamic model.A set of operating conditions,such as radial distribution of direct reduction iron（DRI） to lump coal and coke volume ratio,coke charging location,coke charging amount and coke size,were taken into account.The results show that the temperature near the wall region decreases with the decrease of the radial distribution of DRI to lump coal and coke volume ratio.The temperature with central coke charging is higher than that without central coke column.Furthermore,the temperature significantly increases with the increase of central coke charging amount.With the increase of intermediate coke charging amount,the temperature near the wall region decreases while the temperature in the intermediate region increases.The temperature increases with the increase of coke size whether charging central coke or intermediate coke.
基金supported by the National Natural Science Foundation of China(Grant No.52071318).
文摘The oxidation behavior and kinetics of Ti_(2)AlC-20vol.%TiB_(2) composite at 600-900℃ in air were investigated.The results showed that the oxidation kinetics of the composite followed a logarithmic law within the given temperature range,which indicated that the composites had excellent oxidation resistance.The selective oxidation of Al in Ti_(2)AlC was greatly enhanced,which facilitated the formation of a continuous and dense protective layer of Al_(2)O_(3).Meanwhile,the existence of molten B_(2)O_(3) inhibited the outward diffusion of Ti and inward diffusion of oxygen,which prevented the growth of anatase TiO_(2) at 600℃ and rutile TiO_(2) at 700-900℃.Therefore,the incorporation of TiB_(2) completely inhibited the abnormally rapid oxidation of bulk Ti_(2)AlC at 600℃ and improved its oxidation resistance at 700-900℃.
基金supported by the National Natural Science Foundation of China(52404370,52171152)the Natural Science Foundation of Liaoning Province(2023-BS-012)the Institute of Metal Research Innovation Fund(2023-PY16).
文摘High-entropy alloys(HEAs)commonly exhibit significant strength deficiencies and intermediate temperature brittleness(ITB)in the temperature range of 650-750°C,which greatly restricts their practical use in safety engineering.In this study,a novel coherent face-centered cubic(FCC)/L1_(2)HEA with multiple heterogeneous microstructures,including grain size and L1_(2)precipitates was developed.The newly designed HEA demonstrates outstanding mechanical properties across a broad temperature spectrum(25-750°C).At ambient temperature,the HEA displays a remarkable tensile strength of up to 1700 MPa and a tensile ductility of 15.9%.Notably,the HEA exhibits an impressive yield strength of 1 GPa in the intermediate temperature range,with minimal loss of ductility under high tensile stresses.The presence of the primary L1_(2)phase effectively stabilizes the grain boundaries(GBs),inhibiting crack propagation and oxygen diffusion along them.This mechanism prevents the formation of brittle phases at the GBs,thereby protecting the GBs and mitigating the issue of ITB.As a result,the HEA exhibits an intermediate temperature tensile strain surpassing 14%.The heterogeneous structural modulation strategy offers valuable insights into the tailored design of high-performance HEAs for advanced high-temperature structural applications in urgent demand.
基金financially supported by the University Grants Commission,New Delhi,India,under the scheme of Faculty Development Program (No.Lr.APKA028/001/XIIPLAN)。
文摘In this communication,the electrical conductivities and thermal expansion studies of microwave sintered co-doped ceria Ce_(0.8)Y_(0.2-x)Dy_(x)O_(2-δ)(x=0,0.05,0.10,0.15 and 0.20) solid electrolyte materials for intermediate temperature solid oxide fuel cells(IT-SOFCs)synthesized by sol-gel auto-combustion method were discussed.Microwave sintering at 1300℃ for 30 min was used for making dense powder compacts.The relative densities of all the samples are noticed above 95%.Raman spectrum was characterized by the presence of a very strong band near 460 cm^(-1),which along with X-ray diffraction(XRD) analysis ascertain the sample formation with a single-phase cubic fluorite structure.The lattice parameter values were calculated from XRD patterns.SEM images show nearly uniform grains with distinct grain boundaries.The thermal expansion coefficients(TECs) are found to vary linearly with temperature and were measured in the range from 14.15 to 13.20×10^(-6)℃^(-1).The investigation on total ionic conductivity(TIC) was executed with variation in dopant concentration and relative oxygen vacancies.The impedance analysis reveals that the sample Ce_(0.80)Y_(0.10)Dy_(0.10)O_(2-δ) displays the highest TIC,i.e.,7.5×10^(-3) S·cm^(-1) at 500℃ and minimum activation energy 0.90 eV compared to others.With the highest TIC and minimum activation energy,the Ce_(0.80)Y_(0.10)Dy_(0.10)O_(2-δ)might be the possible material as the solid electrolyte in intermediate temperature SOFCs.
基金the National High-Tech Development Plan (2006AA05Z417)the Natural Science Foundation of Lia-oning Province (20062145)the Education department of Liaoning Province (05L073)
文摘The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitation method with metal-nitrates as starting materials and mixed alkali (NaOH and Na2CO3) as a precipitating agent. The formation process of LSCCF from the precursors was monitored by TG-DSC, and the crystal structure and particles morphology of the precursors which were calcined at 600, 800, 1000 ℃ for 3 h were characterized using XRD, SEM technologies. Compared with the solid state reaction of constituent oxides, when the pH value of the precipitating solution was in the range of 9.1～9.5, the LSCCF powders from the precursors caclined at 800 ℃ for 3 h had high purity, homogeneous and single perovskite phase. The electrical conductivity of the LSCCF samples sintered at 1200 ℃ for 3 h, which was measured as a function of temperatures from 100 to 800 ℃ by DC four-probe method in air, decreased with x from 0.05 to 0.20. The value of electrical conductivity was almost equal because of Ca2+, Sr2+ co-dopant resulting in the 'mix effect' while x=0.10 or 0.15. The electrical conductivity of all doped samples was higher than 100 S·cm-1 at intermediate temperatures from 500 to 800 ℃, and there was good compatibility between the LSCCF cathode and Ce0.8Sm0.2O2 electrolyte.
