High-performance graphite materials have important roles in aerospace and nuclear reactor technologies because of their outstanding chemical stability and high-temperature performance.Their traditional production meth...High-performance graphite materials have important roles in aerospace and nuclear reactor technologies because of their outstanding chemical stability and high-temperature performance.Their traditional production method relies on repeated impregnation-carbonization and graphitization,and is plagued by lengthy preparation cycles and high energy consumption.Phase transition-assisted self-pressurized selfsintering technology can rapidly produce high-strength graphite materials,but the fracture strain of the graphite materials produced is poor.To solve this problem,this study used a two-step sintering method to uniformly introduce micro-nano pores into natural graphite-based bulk graphite,achieving improved fracture strain of the samples without reducing their density and mechanical properties.Using natural graphite powder,micron-diamond,and nano-diamond as raw materials,and by precisely controlling the staged pressure release process,the degree of diamond phase transition expansion was effectively regulated.The strain-to-failure of the graphite samples reached 1.2%,a 35%increase compared to samples produced by fullpressure sintering.Meanwhile,their flexural strength exceeded 110 MPa,and their density was over 1.9 g/cm^(3).The process therefore produced both a high strength and a high fracture strain.The interface evolution and toughening mechanism during the two-step sintering process were investigated.It is believed that the micro-nano pores formed have two roles:as stress concentrators they induce yielding by shear and as multi-crack propagation paths they significantly lengthen the crack propagation path.The two-step sintering phase transition strategy introduces pores and provides a new approach for increasing the fracture strain of brittle materials.展开更多
The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed ...The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed nano powders(~50 nm average particle size), we are able to sinter W-10Re alloy to 98.4% density below 1200 ℃ while maintaining a fine grain size of 260 nm, and sinter molybdenum to 98.3% density below 1120 ℃ while maintaining a fine grain size of 290 nm. Compared to normal sintering,two-step sintering offers record-fine grain sizes and better microstructural uniformity, which translates to better mechanical properties with higher hardness(6.3 GPa for tungsten-rhenium and 4.0 GPa for molybdenum, both being the highest in all pressurelessly sintered samples of the respective material system)and larger Weibull modulus. Together with our previous demonstration in tungsten, we believe that twostep sintering is a general effective method to produce high-quality fine-grained refractory metals and alloys, and the lessons learned here are transferable to other materials for powder metallurgy.展开更多
With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies,the emission of pollutants such as SO_(2)and NO x has received unprecedented attention.Consideri...With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies,the emission of pollutants such as SO_(2)and NO x has received unprecedented attention.Considering the increase of the proportion of semi-dry desulfurization technology in the desulfurization process,several semi-dry desulphurization technologies such as flue gas circulating fluidized bed(CFB),dense flow absorber(DFA)and spray drying absorption(SDA)are briefly summarized.Moreover,a method for simultaneous treatment of SO_(2)and NOx in sintering/pelletizing flue gas by O_(3)oxidation combined with semidry method is introduced.Meantime,the effects of key parameters such as O_(3)/NO molar ratio,Ca SO_(3),SO_(2),reaction temperature,Ca/(S+2 N)molar ratio,droplet size and approach to adiabatic saturation temperature(AAST)on denitrification and desulfurization are analyzed.Furthermore,the reaction mechanism of denitrification and desulfurization is further elucidated.Finally,the advantages and development prospects of the new technology are proposed.展开更多
Gadolinium zirconate（Gd2Zr2O7） nanocrystals were prepared via two different combustion methods： citric acid combustion（CAC） and stearic acid combustion（SAC）. The effects of the different preparation methods on ...Gadolinium zirconate（Gd2Zr2O7） nanocrystals were prepared via two different combustion methods： citric acid combustion（CAC） and stearic acid combustion（SAC）. The effects of the different preparation methods on the phase composition, microtopography, and sintering densification of the resulting Gd2Zr2O7 nanopowders were investigated by thermal-gravimetric and differential thermal analysis（TG-DTA）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, and transmission electron microscopy（TEM） techniques. The results indicated that both methods could produce Gd2Zr2O7 nanopowders with an excellent defective fluorite structure. The reaction time was reduced by the SAC method, compared with the CAC method. The nanopowders synthesized by the two methods were different in grain size distribution. The resulting nanoparticle diameter was about 50 nm for CAC and 10 nm for SAC. After vacuum sintering, the sintered bodies also had a different relative density of about 93% and 98%, respectively. Thus the preparation of Gd2Zr2O7 nanopowders by SAC was the first choice to achieve the desired sintering densification.展开更多
A new two-step spark plasma sintering(TSS)process with low-temperature pre-sintering and high-temperature final sintering has been successfully applied to prepare the tungsten-particle(Wp)-reinforced bulk metallic gla...A new two-step spark plasma sintering(TSS)process with low-temperature pre-sintering and high-temperature final sintering has been successfully applied to prepare the tungsten-particle(Wp)-reinforced bulk metallic glass composites(Wp/BMGCs).Compared to normal spark plasma sintering(NS),the densification rate and relative density of Wp/BMGCs can be improved by selecting TSS with appropriate sintering pressure in the low temperature pre-sintering stage.However,the compressive strength and plastic strain of 30%Wp/BMGCs prepared by TSS are both higher than those of the samples prepared by NS.The TSS process can significantly enhance the compressive strength of 30%Wp/BMGCs by 12%and remarkably increase the plastic strain by 50%,while the trend is completely opposite for 50%Wp/BMGCs.Quasi-in situ experiments and finite element simulations reveal that uneven temperature distribution among particles during low-temperature pre-sintering causes local overheating at contact points between particles,accelerating formation of sintering neck between particles and plastic deformation of Wp.When the volume fraction of Wp is low,TSS can improve the interface bonding between particles by increasing the number of sintering necks.This makes the fracture mode of Wp/BMGCs being predominantly transgranular fracture.However,as the volume fraction of Wp increases,the adverse effects of Wp plastic deformation are becoming more and more prominent.The aggregated Wp tends to form a solid"cage structure"that hinders the bonding between particles at the interface;correspondingly,the fracture behavior of Wp/BMGCs is mainly dominated by intergranular fracture.Additionally,reducing the sintering pressure during the low-temperature pre-sintering stage of TSS has been shown to effectively decrease plastic deformation in Wp,resulting in a higher degree of densification and better mechanical properties.展开更多
Efficient and accurate simulation of unsteady flow presents a significant challenge that needs to be overcome in computational fluid dynamics.Temporal discretization method plays a crucial role in the simulation of un...Efficient and accurate simulation of unsteady flow presents a significant challenge that needs to be overcome in computational fluid dynamics.Temporal discretization method plays a crucial role in the simulation of unsteady flows.To enhance computational efficiency,we propose the Implicit-Explicit Two-Step Runge-Kutta(IMEX-TSRK)time-stepping discretization methods for unsteady flows,and develop a novel adaptive algorithm that correctly partitions spatial regions to apply implicit or explicit methods.The novel adaptive IMEX-TSRK schemes effectively handle the numerical stiffness of the small grid size and improve computational efficiency.Compared to implicit and explicit Runge-Kutta(RK)schemes,the IMEX-TSRK methods achieve the same order of accuracy with fewer first derivative calculations.Numerical case tests demonstrate that the IMEX-TSRK methods maintain numerical stability while enhancing computational efficiency.Specifically,in high Reynolds number flows,the computational efficiency of the IMEX-TSRK methods surpasses that of explicit RK schemes by more than one order of magnitude,and that of implicit RK schemes several times over.展开更多
In this work, a novel in-situ two-step pore-forming process in vacuum sintering(ITPVS) technique combining low-temperature processing to produce open pores through the interdiffusion among the intrinsic components in ...In this work, a novel in-situ two-step pore-forming process in vacuum sintering(ITPVS) technique combining low-temperature processing to produce open pores through the interdiffusion among the intrinsic components in the base steel, and subsequent high-temperature processing to further improve the porosities by the sublimation of Mn via previously formed open pores, was proposed to produce a lab-scale porous Fe Mn Al steel. For the first time, a high-Mn and high-Al steel with open and overall porosities of ~59.6 vol.% and ~63.7 vol.%(percent in volume, vol.%) was synthesized by isothermal holding of the quaternary elemental Fe/Mn/Al/C powder mixture at 640℃ for 1 h and the subsequent sintering at 1200℃ for 1 h. Elemental Al partly incorporated into/reacted with α-Fe and α-Mn after sintering at640℃ for 1 h, leading to the overall and open porosities promoting by ~26.6 vol.% and ~25.6 vol.%. After sintering at 1200℃, Fe Mn Al steel with increased porosities mainly comprising of austenite and α-Fe obtained. The compression strength and corresponding strain of the 1200℃-sintered porous specimen without crack on the surface was ~75 MPa and ~25%. The ITPVS technique takes advantage of using the intrinsic components like Al, Mn and Fe in steels to produce porous structure. This is beneficial to avoiding the contamination of the Fe Mn Al steel matrix caused by the employment of the foreign pore-forming agents.展开更多
A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination o...A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination of suitable process parameters in DMLS. The nonlinear transient model of the metals thermal conductivity for powder-to-solid transition was developed. The model uses solid thermal properties of material in liquid-phase zone, transitional ones in sintering or sintered zone and powder ones in unsintered zones of powder bed to predict, respectively. Sintering zone boundary was estimated by maximum temperature history profile. Experiments were carried out using multi-component Cu-based metal powder. Compared experimental and predicted results, the mean error of sintering depth and width are 7.8% and 14.4%, respectively, which confirms the accuracy of the FEM prediction.展开更多
Effects of various sintering methods such as spark plasma sintering(SPS), hot pressing(HP) and electric resistance sintering(ERS) on the microstructure and mechanical properties of commercial pure titanium(CP-Ti) powd...Effects of various sintering methods such as spark plasma sintering(SPS), hot pressing(HP) and electric resistance sintering(ERS) on the microstructure and mechanical properties of commercial pure titanium(CP-Ti) powder consolidations with particle size of <147 μm, <74 μm and <43 μm were studied. The smaller particle powders are densified to proceed at a higher rate. Dense titanium with relative density up to 99% is found to take place at 850 °C under 30 MPa of SPS and HP condition. However, in case of ERS, CP-Ti powders were densified almost at 950 °C under 30 MPa. The microstructure of sintered titanium is composed of equiaxed grains at 850-950 °C. The yield strength of sintered body composed of <43 μm powder is 858 MPa by using SPS at 850 °C under 30 MPa. When there is a higher content of small particle, the higher yield strength value is obtained both by using SPS and HP. However, when ERS is introduced, the highest yield strength is 441 MPa at 950 °C under 30 MPa, which shows much lower values than those by SPS and HP methods. ERS method takes much less sintering time compared with SPS and HP. Nevertheless, higher sintering temperature results in lower strength and elongation because of brittle fracture.展开更多
Thermal barrier coatings （TBCs） are mostly applied to hot components of advanced turbine engines to insulate the compo- nents from hot gas. The effect of sintering on thermal conductivity and thermal barrier effects...Thermal barrier coatings （TBCs） are mostly applied to hot components of advanced turbine engines to insulate the compo- nents from hot gas. The effect of sintering on thermal conductivity and thermal barrier effects of conventional plasma sprayed and nanostructured yttria stabilized zirconia （YSZ） thermal barrier coatings （TBCs） are investigated. Remarkable increase in thermal conductivity occurs to both typical coatings after heat treatment, The change of porosity is just the opposite. The grain size of the nanostructured zirconia coating increases more drastically with annealing time compared to that of the conventional plasma sprayed coating, which indicates that coating sintering makes more contributions to the thermal conductivity of the nanostructured coating than that of the conventional coating. Thermal barrier effect tests using temperature difference technique are performed on both coatings. The thermal barrier effects decrease with the increase of thermal conductivity after heat treat- ment and the decline seems more drastic in low thermal conductivity range. The decline in thermal barrier effects is about 80℃ for nanostructured coating after 100 h heat treatment, while the conventional coating reduces by less than 60 ℃ compared to the as-sprayed coating.展开更多
Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However...Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However,the sintering concurrently becomes increasingly more difficult with increasing Re contents.Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic(BCC)W is alloyed with more hexagonal-close-packed(HCP)Re,which results in inefficient pore removal in the final stage sintering.We showed that the conundrum can be resolved by pressureless two-step sintering(TSS)which suppresses acceler-ating final-stage grain growth,and our proposal is supported by the data of the critical densityρc that is required to start the second step for successful TSS at different W-Re compositions.Dense ultrafine-grained W-Re alloys with∼300 nm average grain size and up to 25 wt%Re were successfully produced.Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.展开更多
Aiming at the comprehensive utilization of the rare-earth resources and the preparation of the high-performance low-cost Nd-Fe-B magnets,sintered magnets with different Ce substitution amounts of 17.2 wt%,24.8 wt%and ...Aiming at the comprehensive utilization of the rare-earth resources and the preparation of the high-performance low-cost Nd-Fe-B magnets,sintered magnets with different Ce substitution amounts of 17.2 wt%,24.8 wt%and 31.8 wt%were prepared by intergranularalloy method.The influence of substitution of Ce for Nd on their microstructure and magnetic properties in this work was detailedly investigated.The results indicated that the remanence(Br)and the maximum energy product((BH)max)of the sintered magnets decreased monotonic ally with the increase in Ce substitution.However,the obvious enhancement of coercivity(Hcj)was also observed,which was mainly due to the improvement of microstructure and the smooth,continuous grain boundary(GB).It can be found that a reasonable Ce substitution of 24.8 wt%for the sintered magnets could promote the refinement of microstructure,leading to the realization of superior magnetic properties.It is expected that the investigations could be beneficial to offer a feasible method for preparing the high-performance low-cost Ce-doped magnets.展开更多
Temperature-dependent photoluminescence characteristics of organic-inorganic halide perovskite CH3NH3Pb I3-xClx films prepared using a two-step method on ZnO/FTO substrates were investigated. Surface morphology and ab...Temperature-dependent photoluminescence characteristics of organic-inorganic halide perovskite CH3NH3Pb I3-xClx films prepared using a two-step method on ZnO/FTO substrates were investigated. Surface morphology and absorption characteristics of the films were also studied. Scanning electron microscopy revealed large crystals and substrate coverage. The orthorhombic-to-tetragonal phase transition temperature was-140 K. The films＇ exciton binding energy was 77.6 ± 10.9 meV and the energy of optical phonons was 38.8 ± 2.5 meV. These results suggest that perovskite CH3NH3Pb I（3-x）Clx films have excellent optoelectronic characteristics which further suggests their potential usage in perovskitebased optoelectronic devices.展开更多
In order to develop AlN composites suitable for high average power electronic tube, AlN-W materials were prepared by spark plasma sintering. The effects of manufacture parameters on dielectric loss tangent and permitt...In order to develop AlN composites suitable for high average power electronic tube, AlN-W materials were prepared by spark plasma sintering. The effects of manufacture parameters on dielectric loss tangent and permittivity constant were investigated, which include powder-mixed method, milling time of high-energy ball milling, starting powder particle size, sintering temperature and holding time and adding amount of the conductive second phase. The results showed that A1N-W materials sintered at the temperature of 1700℃ holding for 5 min with 10 vol.% W showed the best dielectric loss tangent larger than 0.81 at the frequency 1 kHz-1 MHz. In addition, magnetic stirring mixed powder and lower sintering temperature led to the better propelties because of the higher porosity. The samples sintered from the starting AlN powder with smaller particle size also had the better properties.展开更多
Discrete element method （DEM） is used in the present paper to simulate the microstructural evolution of a planar layer of copper particles during sintering. Formation of agglomerates and the effect of their rearrang...Discrete element method （DEM） is used in the present paper to simulate the microstructural evolution of a planar layer of copper particles during sintering. Formation of agglomerates and the effect of their rearrangement on densification are mainly focused on. Comparing to the existing experimental observations, we find that agglomerate can form spontaneously in sintering and its rearrangement could accelerate the densification of compacts. Snapshots of numerical simulations agree qualitatively well with experimental observations. The method could be readily extended to investigate the effect of agglomerate on sintering in a three- dimensional model, which should be very useful for understanding the evolution of microstructure of sintering systems.展开更多
The distribution of remaining oil is often described qualitatively. The remaining oil distributed in the whole reservoir is calculated according to the characteristics of the space distribution of the saturation of re...The distribution of remaining oil is often described qualitatively. The remaining oil distributed in the whole reservoir is calculated according to the characteristics of the space distribution of the saturation of remaining oil. Logging data are required to accomplish this. However, many such projects cannot be completed. Since the old study of remaining oil distribution could not be quantified efficiently, the ＂dynamic two-step method＂ is presented. Firstly, the water cut of every flow unit in one well at one time is calculated according to the comprehensive water cut of a single well at one time. Secondly, the remaining oil saturation of the flow unit of the well at one time is calculated based on the water cut of the flow unit at a given time. The results show that ＂dynamic two-step method＂ has characteristics of simplicity and convenience, and is especially suitable for the study of remaining oil distribution at high water-cut stage. The distribution of remaining oil presented banding and potato form, remaining oil was relatively concentrated in faultage neighborhood and imperfect well netting position, and the net thickness of the place was great. This proposal can provide an effective way to forecast remaining oil distribution and enhance oil recovery, especially applied at the high water-cut stage.展开更多
Polycrystalline YBa2Cu3O6＋δbulks were synthesized by sol-gel method. Sintering processing played a vital role in the evolution of phase structure and microstructure, and thus significantly influenced their supercond...Polycrystalline YBa2Cu3O6＋δbulks were synthesized by sol-gel method. Sintering processing played a vital role in the evolution of phase structure and microstructure, and thus significantly influenced their superconducting properties. The influence of calcination temperature, sintering temperature, on the bulks structure, morphology and superconducting behaviors were investigated. The results showed that the oxygen content drastically increased with calcination temperature and sintering temperature. The SEM images revealed that the grains grew up monotonously with increase of calcination temperature. With increased calcination and sintering temperature, the resistivity was reduced gradually and the superconducting properties increased. Moreover, it was found that the optimal superconducting properties（with the highest superconducting transition temperature Tc^onset and the narrowest transition width ΔT） were obtained at calcination temperature of 900℃ and sintering temperature of 950 ℃.展开更多
At present,blast furnace ironmaking is still the main process for producing molten iron,and sinters are the main raw material for blast furnace ironmaking.A sinter with good metallurgical performance can not only ensu...At present,blast furnace ironmaking is still the main process for producing molten iron,and sinters are the main raw material for blast furnace ironmaking.A sinter with good metallurgical performance can not only ensure smooth operation of the blast furnace but also reduce the blast furnace fuel ratio and increase the molten iron production.Structure is the most important factor affecting the metallurgical properties of the sinter.Thus,the research progress of sinter pore and mineral phase structures was reviewed and the mechanism by which they influence sinter properties was expounded.Multiscale characterization methods for the sinter and their advantages and disadvantages were introduced,and the future research direction of sinter was discussed.展开更多
The Taguchi and analysis of variance (ANOVA) methods were applied to investigate the effects of the structural and operational parameters on the heat transfer performance of a vertical sinter cooling packed bed. The a...The Taguchi and analysis of variance (ANOVA) methods were applied to investigate the effects of the structural and operational parameters on the heat transfer performance of a vertical sinter cooling packed bed. The analysed parameters were the gas flow rate, the air inlet temperature, the sinter inlet temperature, the cooling bed diameter and the cooling bed height, all of which contain three levels. The purpose was to improve the heat transfer performance of a vertical sinter cooling bed. A numerical analysis model was established to assess the heat transfer performance with respect to the varying parameters and their different levels. This mathematical model was validated by using data from practical industrial processes. The Taguchi method for the L27 (35) orthogonal design experiment was selected to evaluate the impacts of the design parameters on the heat transfer performance and to acquire the optimum combination of parameters. The analysis of variance was applied to assess the impact weights and the order of significance of the design parameters. The results show that the sinter inlet temperature and cooling bed diameter have great influences and impact the exergy of the wasted heat recovery by 61.65% and 23.31%, respectively. However, the gas flow rate and the air inlet temperature have small effects on the response. Furthermore, the air and sinter inlet temperatures have the most significant impacts on the efficiency of heat transfer by 68.83% and 23.31%, respectively. The optimal parameter combination (A1B1C3D3E3) was obtained, and the optimal results were validated by confirmation tests.展开更多
基金Natural Science Foundation of Shanghai(24ZR1400800)he Natural Science Foundation of China(U23A20685,52073058,91963204)+1 种基金the National Key R&D Program of China(2021YFB3701400)Shanghai Sailing Program(23YF1400200)。
文摘High-performance graphite materials have important roles in aerospace and nuclear reactor technologies because of their outstanding chemical stability and high-temperature performance.Their traditional production method relies on repeated impregnation-carbonization and graphitization,and is plagued by lengthy preparation cycles and high energy consumption.Phase transition-assisted self-pressurized selfsintering technology can rapidly produce high-strength graphite materials,but the fracture strain of the graphite materials produced is poor.To solve this problem,this study used a two-step sintering method to uniformly introduce micro-nano pores into natural graphite-based bulk graphite,achieving improved fracture strain of the samples without reducing their density and mechanical properties.Using natural graphite powder,micron-diamond,and nano-diamond as raw materials,and by precisely controlling the staged pressure release process,the degree of diamond phase transition expansion was effectively regulated.The strain-to-failure of the graphite samples reached 1.2%,a 35%increase compared to samples produced by fullpressure sintering.Meanwhile,their flexural strength exceeded 110 MPa,and their density was over 1.9 g/cm^(3).The process therefore produced both a high strength and a high fracture strain.The interface evolution and toughening mechanism during the two-step sintering process were investigated.It is believed that the micro-nano pores formed have two roles:as stress concentrators they induce yielding by shear and as multi-crack propagation paths they significantly lengthen the crack propagation path.The two-step sintering phase transition strategy introduces pores and provides a new approach for increasing the fracture strain of brittle materials.
基金supports by the Natural Science Foundation of China(52074032,51974029,52131307,52071013)and“111”Project(No.B170003).Y.D.and J.L.acknowledge the support by Eni S.p.A.through the MIT Energy Initiative.
文摘The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed nano powders(~50 nm average particle size), we are able to sinter W-10Re alloy to 98.4% density below 1200 ℃ while maintaining a fine grain size of 260 nm, and sinter molybdenum to 98.3% density below 1120 ℃ while maintaining a fine grain size of 290 nm. Compared to normal sintering,two-step sintering offers record-fine grain sizes and better microstructural uniformity, which translates to better mechanical properties with higher hardness(6.3 GPa for tungsten-rhenium and 4.0 GPa for molybdenum, both being the highest in all pressurelessly sintered samples of the respective material system)and larger Weibull modulus. Together with our previous demonstration in tungsten, we believe that twostep sintering is a general effective method to produce high-quality fine-grained refractory metals and alloys, and the lessons learned here are transferable to other materials for powder metallurgy.
基金supported by the National Key Research and Development Program of China(No.2017YFC0210600)the National Natural Science Foundation of China(No.51978644)。
文摘With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies,the emission of pollutants such as SO_(2)and NO x has received unprecedented attention.Considering the increase of the proportion of semi-dry desulfurization technology in the desulfurization process,several semi-dry desulphurization technologies such as flue gas circulating fluidized bed(CFB),dense flow absorber(DFA)and spray drying absorption(SDA)are briefly summarized.Moreover,a method for simultaneous treatment of SO_(2)and NOx in sintering/pelletizing flue gas by O_(3)oxidation combined with semidry method is introduced.Meantime,the effects of key parameters such as O_(3)/NO molar ratio,Ca SO_(3),SO_(2),reaction temperature,Ca/(S+2 N)molar ratio,droplet size and approach to adiabatic saturation temperature(AAST)on denitrification and desulfurization are analyzed.Furthermore,the reaction mechanism of denitrification and desulfurization is further elucidated.Finally,the advantages and development prospects of the new technology are proposed.
文摘Gadolinium zirconate（Gd2Zr2O7） nanocrystals were prepared via two different combustion methods： citric acid combustion（CAC） and stearic acid combustion（SAC）. The effects of the different preparation methods on the phase composition, microtopography, and sintering densification of the resulting Gd2Zr2O7 nanopowders were investigated by thermal-gravimetric and differential thermal analysis（TG-DTA）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, and transmission electron microscopy（TEM） techniques. The results indicated that both methods could produce Gd2Zr2O7 nanopowders with an excellent defective fluorite structure. The reaction time was reduced by the SAC method, compared with the CAC method. The nanopowders synthesized by the two methods were different in grain size distribution. The resulting nanoparticle diameter was about 50 nm for CAC and 10 nm for SAC. After vacuum sintering, the sintered bodies also had a different relative density of about 93% and 98%, respectively. Thus the preparation of Gd2Zr2O7 nanopowders by SAC was the first choice to achieve the desired sintering densification.
基金financially supported by the National Natural Science Foundation of China(Nos.52371154,52090043,52175371 and 52271147)Guangdong Basic and Applied Basic Research Foundation(No.2023A1515012158)+1 种基金the Knowledge Innovation Program of Wuhan-Basic Researchthe Fundamental Research Funds for the Central Universities(No.2021GCRC003)。
文摘A new two-step spark plasma sintering(TSS)process with low-temperature pre-sintering and high-temperature final sintering has been successfully applied to prepare the tungsten-particle(Wp)-reinforced bulk metallic glass composites(Wp/BMGCs).Compared to normal spark plasma sintering(NS),the densification rate and relative density of Wp/BMGCs can be improved by selecting TSS with appropriate sintering pressure in the low temperature pre-sintering stage.However,the compressive strength and plastic strain of 30%Wp/BMGCs prepared by TSS are both higher than those of the samples prepared by NS.The TSS process can significantly enhance the compressive strength of 30%Wp/BMGCs by 12%and remarkably increase the plastic strain by 50%,while the trend is completely opposite for 50%Wp/BMGCs.Quasi-in situ experiments and finite element simulations reveal that uneven temperature distribution among particles during low-temperature pre-sintering causes local overheating at contact points between particles,accelerating formation of sintering neck between particles and plastic deformation of Wp.When the volume fraction of Wp is low,TSS can improve the interface bonding between particles by increasing the number of sintering necks.This makes the fracture mode of Wp/BMGCs being predominantly transgranular fracture.However,as the volume fraction of Wp increases,the adverse effects of Wp plastic deformation are becoming more and more prominent.The aggregated Wp tends to form a solid"cage structure"that hinders the bonding between particles at the interface;correspondingly,the fracture behavior of Wp/BMGCs is mainly dominated by intergranular fracture.Additionally,reducing the sintering pressure during the low-temperature pre-sintering stage of TSS has been shown to effectively decrease plastic deformation in Wp,resulting in a higher degree of densification and better mechanical properties.
基金supported by the National Natural Science Foundation of China(No.92252201)the Fundamental Research Funds for the Central Universitiesthe Academic Excellence Foundation of Beihang University(BUAA)for PhD Students。
文摘Efficient and accurate simulation of unsteady flow presents a significant challenge that needs to be overcome in computational fluid dynamics.Temporal discretization method plays a crucial role in the simulation of unsteady flows.To enhance computational efficiency,we propose the Implicit-Explicit Two-Step Runge-Kutta(IMEX-TSRK)time-stepping discretization methods for unsteady flows,and develop a novel adaptive algorithm that correctly partitions spatial regions to apply implicit or explicit methods.The novel adaptive IMEX-TSRK schemes effectively handle the numerical stiffness of the small grid size and improve computational efficiency.Compared to implicit and explicit Runge-Kutta(RK)schemes,the IMEX-TSRK methods achieve the same order of accuracy with fewer first derivative calculations.Numerical case tests demonstrate that the IMEX-TSRK methods maintain numerical stability while enhancing computational efficiency.Specifically,in high Reynolds number flows,the computational efficiency of the IMEX-TSRK methods surpasses that of explicit RK schemes by more than one order of magnitude,and that of implicit RK schemes several times over.
基金supported financially by the National Natural Science Foundation of China(Nos.51804239 and 51972252)the National Fundamental Research Funds for the Central Universities(WUT:2019IVB016)‘111 Project’of China(No.B17034).
文摘In this work, a novel in-situ two-step pore-forming process in vacuum sintering(ITPVS) technique combining low-temperature processing to produce open pores through the interdiffusion among the intrinsic components in the base steel, and subsequent high-temperature processing to further improve the porosities by the sublimation of Mn via previously formed open pores, was proposed to produce a lab-scale porous Fe Mn Al steel. For the first time, a high-Mn and high-Al steel with open and overall porosities of ~59.6 vol.% and ~63.7 vol.%(percent in volume, vol.%) was synthesized by isothermal holding of the quaternary elemental Fe/Mn/Al/C powder mixture at 640℃ for 1 h and the subsequent sintering at 1200℃ for 1 h. Elemental Al partly incorporated into/reacted with α-Fe and α-Mn after sintering at640℃ for 1 h, leading to the overall and open porosities promoting by ~26.6 vol.% and ~25.6 vol.%. After sintering at 1200℃, Fe Mn Al steel with increased porosities mainly comprising of austenite and α-Fe obtained. The compression strength and corresponding strain of the 1200℃-sintered porous specimen without crack on the surface was ~75 MPa and ~25%. The ITPVS technique takes advantage of using the intrinsic components like Al, Mn and Fe in steels to produce porous structure. This is beneficial to avoiding the contamination of the Fe Mn Al steel matrix caused by the employment of the foreign pore-forming agents.
文摘A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination of suitable process parameters in DMLS. The nonlinear transient model of the metals thermal conductivity for powder-to-solid transition was developed. The model uses solid thermal properties of material in liquid-phase zone, transitional ones in sintering or sintered zone and powder ones in unsintered zones of powder bed to predict, respectively. Sintering zone boundary was estimated by maximum temperature history profile. Experiments were carried out using multi-component Cu-based metal powder. Compared experimental and predicted results, the mean error of sintering depth and width are 7.8% and 14.4%, respectively, which confirms the accuracy of the FEM prediction.
基金Project(K0004130) supported by the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy,Korea
文摘Effects of various sintering methods such as spark plasma sintering(SPS), hot pressing(HP) and electric resistance sintering(ERS) on the microstructure and mechanical properties of commercial pure titanium(CP-Ti) powder consolidations with particle size of <147 μm, <74 μm and <43 μm were studied. The smaller particle powders are densified to proceed at a higher rate. Dense titanium with relative density up to 99% is found to take place at 850 °C under 30 MPa of SPS and HP condition. However, in case of ERS, CP-Ti powders were densified almost at 950 °C under 30 MPa. The microstructure of sintered titanium is composed of equiaxed grains at 850-950 °C. The yield strength of sintered body composed of <43 μm powder is 858 MPa by using SPS at 850 °C under 30 MPa. When there is a higher content of small particle, the higher yield strength value is obtained both by using SPS and HP. However, when ERS is introduced, the highest yield strength is 441 MPa at 950 °C under 30 MPa, which shows much lower values than those by SPS and HP methods. ERS method takes much less sintering time compared with SPS and HP. Nevertheless, higher sintering temperature results in lower strength and elongation because of brittle fracture.
基金National Natural Science Foundation of China (50771009, 50731001, 51071013)
文摘Thermal barrier coatings （TBCs） are mostly applied to hot components of advanced turbine engines to insulate the compo- nents from hot gas. The effect of sintering on thermal conductivity and thermal barrier effects of conventional plasma sprayed and nanostructured yttria stabilized zirconia （YSZ） thermal barrier coatings （TBCs） are investigated. Remarkable increase in thermal conductivity occurs to both typical coatings after heat treatment, The change of porosity is just the opposite. The grain size of the nanostructured zirconia coating increases more drastically with annealing time compared to that of the conventional plasma sprayed coating, which indicates that coating sintering makes more contributions to the thermal conductivity of the nanostructured coating than that of the conventional coating. Thermal barrier effect tests using temperature difference technique are performed on both coatings. The thermal barrier effects decrease with the increase of thermal conductivity after heat treat- ment and the decline seems more drastic in low thermal conductivity range. The decline in thermal barrier effects is about 80℃ for nanostructured coating after 100 h heat treatment, while the conventional coating reduces by less than 60 ℃ compared to the as-sprayed coating.
基金This work is financially supported by National Key R&D Pro-gram of China(no.2022YFB3700075)Natural Science Foundation of China(nos.52074032,51974029,52071013,52130407)+3 种基金Beijing Natural Science Foundation(no.2232084)Guangdong Basic and Applied Basic Research Foundation(no.2021B1515120033)Basic and Applied Basic Research Fund of Guangdong Province(no.BK20BE015)111 Project(no.B170003).
文摘Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However,the sintering concurrently becomes increasingly more difficult with increasing Re contents.Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic(BCC)W is alloyed with more hexagonal-close-packed(HCP)Re,which results in inefficient pore removal in the final stage sintering.We showed that the conundrum can be resolved by pressureless two-step sintering(TSS)which suppresses acceler-ating final-stage grain growth,and our proposal is supported by the data of the critical densityρc that is required to start the second step for successful TSS at different W-Re compositions.Dense ultrafine-grained W-Re alloys with∼300 nm average grain size and up to 25 wt%Re were successfully produced.Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.
基金financially supported by the Sichuan Province Science and Technology Support Program(No.2014GZ0090)the Key Technology and Development Program of PanXi Experimental Area(No.2016KJT0018).
文摘Aiming at the comprehensive utilization of the rare-earth resources and the preparation of the high-performance low-cost Nd-Fe-B magnets,sintered magnets with different Ce substitution amounts of 17.2 wt%,24.8 wt%and 31.8 wt%were prepared by intergranularalloy method.The influence of substitution of Ce for Nd on their microstructure and magnetic properties in this work was detailedly investigated.The results indicated that the remanence(Br)and the maximum energy product((BH)max)of the sintered magnets decreased monotonic ally with the increase in Ce substitution.However,the obvious enhancement of coercivity(Hcj)was also observed,which was mainly due to the improvement of microstructure and the smooth,continuous grain boundary(GB).It can be found that a reasonable Ce substitution of 24.8 wt%for the sintered magnets could promote the refinement of microstructure,leading to the realization of superior magnetic properties.It is expected that the investigations could be beneficial to offer a feasible method for preparing the high-performance low-cost Ce-doped magnets.
基金supported by the International Science and Technology Cooperation Program of Science and Technology Bureau of Changchun City,China(Grant No.12ZX68)
文摘Temperature-dependent photoluminescence characteristics of organic-inorganic halide perovskite CH3NH3Pb I3-xClx films prepared using a two-step method on ZnO/FTO substrates were investigated. Surface morphology and absorption characteristics of the films were also studied. Scanning electron microscopy revealed large crystals and substrate coverage. The orthorhombic-to-tetragonal phase transition temperature was-140 K. The films＇ exciton binding energy was 77.6 ± 10.9 meV and the energy of optical phonons was 38.8 ± 2.5 meV. These results suggest that perovskite CH3NH3Pb I（3-x）Clx films have excellent optoelectronic characteristics which further suggests their potential usage in perovskitebased optoelectronic devices.
文摘In order to develop AlN composites suitable for high average power electronic tube, AlN-W materials were prepared by spark plasma sintering. The effects of manufacture parameters on dielectric loss tangent and permittivity constant were investigated, which include powder-mixed method, milling time of high-energy ball milling, starting powder particle size, sintering temperature and holding time and adding amount of the conductive second phase. The results showed that A1N-W materials sintered at the temperature of 1700℃ holding for 5 min with 10 vol.% W showed the best dielectric loss tangent larger than 0.81 at the frequency 1 kHz-1 MHz. In addition, magnetic stirring mixed powder and lower sintering temperature led to the better propelties because of the higher porosity. The samples sintered from the starting AlN powder with smaller particle size also had the better properties.
基金supported by the National Natural Science Foundation of China (10972220, 11125211 and 11021262)973 Project(2012CB937500)
文摘Discrete element method （DEM） is used in the present paper to simulate the microstructural evolution of a planar layer of copper particles during sintering. Formation of agglomerates and the effect of their rearrangement on densification are mainly focused on. Comparing to the existing experimental observations, we find that agglomerate can form spontaneously in sintering and its rearrangement could accelerate the densification of compacts. Snapshots of numerical simulations agree qualitatively well with experimental observations. The method could be readily extended to investigate the effect of agglomerate on sintering in a three- dimensional model, which should be very useful for understanding the evolution of microstructure of sintering systems.
文摘The distribution of remaining oil is often described qualitatively. The remaining oil distributed in the whole reservoir is calculated according to the characteristics of the space distribution of the saturation of remaining oil. Logging data are required to accomplish this. However, many such projects cannot be completed. Since the old study of remaining oil distribution could not be quantified efficiently, the ＂dynamic two-step method＂ is presented. Firstly, the water cut of every flow unit in one well at one time is calculated according to the comprehensive water cut of a single well at one time. Secondly, the remaining oil saturation of the flow unit of the well at one time is calculated based on the water cut of the flow unit at a given time. The results show that ＂dynamic two-step method＂ has characteristics of simplicity and convenience, and is especially suitable for the study of remaining oil distribution at high water-cut stage. The distribution of remaining oil presented banding and potato form, remaining oil was relatively concentrated in faultage neighborhood and imperfect well netting position, and the net thickness of the place was great. This proposal can provide an effective way to forecast remaining oil distribution and enhance oil recovery, especially applied at the high water-cut stage.
基金Project supported by the National Natural Science Foundation of China(11564021)
文摘Polycrystalline YBa2Cu3O6＋δbulks were synthesized by sol-gel method. Sintering processing played a vital role in the evolution of phase structure and microstructure, and thus significantly influenced their superconducting properties. The influence of calcination temperature, sintering temperature, on the bulks structure, morphology and superconducting behaviors were investigated. The results showed that the oxygen content drastically increased with calcination temperature and sintering temperature. The SEM images revealed that the grains grew up monotonously with increase of calcination temperature. With increased calcination and sintering temperature, the resistivity was reduced gradually and the superconducting properties increased. Moreover, it was found that the optimal superconducting properties（with the highest superconducting transition temperature Tc^onset and the narrowest transition width ΔT） were obtained at calcination temperature of 900℃ and sintering temperature of 950 ℃.
基金The authors acknowledge the financial support from the National Natural Science Foundation of China(51474164,U1760101 and 51704216).
文摘At present,blast furnace ironmaking is still the main process for producing molten iron,and sinters are the main raw material for blast furnace ironmaking.A sinter with good metallurgical performance can not only ensure smooth operation of the blast furnace but also reduce the blast furnace fuel ratio and increase the molten iron production.Structure is the most important factor affecting the metallurgical properties of the sinter.Thus,the research progress of sinter pore and mineral phase structures was reviewed and the mechanism by which they influence sinter properties was expounded.Multiscale characterization methods for the sinter and their advantages and disadvantages were introduced,and the future research direction of sinter was discussed.
基金This work is supported by the National Key R&D Program of China(2017 YFB0304200)the National Natural Science Foundation of China(51734004).
文摘The Taguchi and analysis of variance (ANOVA) methods were applied to investigate the effects of the structural and operational parameters on the heat transfer performance of a vertical sinter cooling packed bed. The analysed parameters were the gas flow rate, the air inlet temperature, the sinter inlet temperature, the cooling bed diameter and the cooling bed height, all of which contain three levels. The purpose was to improve the heat transfer performance of a vertical sinter cooling bed. A numerical analysis model was established to assess the heat transfer performance with respect to the varying parameters and their different levels. This mathematical model was validated by using data from practical industrial processes. The Taguchi method for the L27 (35) orthogonal design experiment was selected to evaluate the impacts of the design parameters on the heat transfer performance and to acquire the optimum combination of parameters. The analysis of variance was applied to assess the impact weights and the order of significance of the design parameters. The results show that the sinter inlet temperature and cooling bed diameter have great influences and impact the exergy of the wasted heat recovery by 61.65% and 23.31%, respectively. However, the gas flow rate and the air inlet temperature have small effects on the response. Furthermore, the air and sinter inlet temperatures have the most significant impacts on the efficiency of heat transfer by 68.83% and 23.31%, respectively. The optimal parameter combination (A1B1C3D3E3) was obtained, and the optimal results were validated by confirmation tests.
