The large and dense rare earth (RE)-oxide inclusions in high-oxygen RE metal increase the risk of producing variable properties in RE steel. Consequently, a self-developed electrolysis cell was utilized for the produc...The large and dense rare earth (RE)-oxide inclusions in high-oxygen RE metal increase the risk of producing variable properties in RE steel. Consequently, a self-developed electrolysis cell was utilized for the production of low-oxygen La/Ce mischmetal. The electrolysis process and the origin of oxygen in mischmetal were comprehensively investigated. The results indicate that the reaction between La/Ce oxide and fluoride molten salt results in the formation of La/Ce oxy-fluoride. The deposition of oxy-fluoride at the bottom of the electrolysis cell is the primary factor contributing to the increased oxygen content in mischmetal. The comprehensive influence of oxide addition quantity, feeding interval, and electrolysis temperature on oxygen content, purity, and current efficiency using the response surface methodology model is revealed. The results for industrial experiment show that the purity of mishcmetal reaches higher than 99.78 wt.%, the oxygen content of mischmetal is only 0.0047 wt.% and the current efficiency of the electrolysis process achieves 80.79% under the optimized parameters of 225 kg/d, 30 s and 1069 ℃. The findings offer valuable insights into the application of molten salt electrolysis for the production of low-oxygen mischmetal.展开更多
Laser powder bed fusion(LPBF)is a widely used and well-developed approach in additive manufacturing.To meet the high material performance requirements of fourth-generation nuclear power reactors,the combination of LPB...Laser powder bed fusion(LPBF)is a widely used and well-developed approach in additive manufacturing.To meet the high material performance requirements of fourth-generation nuclear power reactors,the combination of LPBF processing with oxide dispersion strengthening(ODS)is currently of interest for the design and development of new materials.In this approach,nanoscale Y_(2)O_(3)particles are dispersed into the feeding powders to produce LPBF-ODS materials.Oxygen exposure and the introduction of oxygen into the solvation cell during LPBF are usually considered as detrimental processes that are impossible to eliminate completely.However,our understanding of these unavoidable processes is still limited.In this study,we developed a new LPBF-ODS design approach based on in situ oxygen content regulation during the LPBF process.The oxygen content of the environmental chamber was artificially adjusted using an online monitoring system to activate reactions between oxygen and the metallic elements for the in situ formation of dispersed oxide particles.Four batches of LPBF 304 L stainless steel samples were successfully processed under different oxygen levels to investigate the reinforcement effect of in situ chemical alloying.The results show that dispersed oxide particles were formed with an average nanoscale size of approximately 46 nm through the LPBF in situ alloying approach.The increase in the number density of oxide particles to 11.4 particles∕μm^(2)as the oxygen content increased played a role in refining and stabilizing the cellular structure.The yield strength of the in situ alloyed ODS material was enhanced(to up to~675 MPa)while its ductility was not significantly degraded(elongation of up to~39%).These tensile properties are competitive within the ranges reported for ODS alloys prepared by mechanical alloying.The main mechanisms for yield strength enhancement through interactions between nanoscale oxide particles and dislocation entanglement cells were analyzed.This study provides a new approach for the future preparation of high-performance LPBF-ODS alloys.展开更多
This study was conducted to investigate the air oxygen content inside and outside a Phyllostachys edulis forest in Qishan Forest Park throughout all four seasons.(1)Regarding the overall annual variation in oxygen con...This study was conducted to investigate the air oxygen content inside and outside a Phyllostachys edulis forest in Qishan Forest Park throughout all four seasons.(1)Regarding the overall annual variation in oxygen content in both environments,comparative analysis of the annual average oxygen concentration showed that the average inside the forest was 22.13%,while the value outside it was 21.39%.The annual average oxygen concentration inside the forest was 3.34%higher than that outside the forest.(2)Regarding the seasonal variation in oxygen content at both sites,the oxygen concentration inside the forest was consistently higher than that outside the forest in all four seasons.The oxygen concentrations inside the forest were 22.1%,21.9%,21.8%,and 21.5%in spring,summer,autumn,and winter,respectively,while outside the forest,they were 22.0%,21.8%,21.7%,and 21.4%for the same seasons,respectively.(3)The diurnal variation trends of oxygen concentration at both sites were similar throughout all four seasons,exhibiting a single-peak and double-trough curve pattern.The peak period occurred at 13:00 in spring,summer,and winter,and at 9:00 in autumn.The trough periods were observed at 7:00 and between 21:00 and 23:00 or at 5:00.展开更多
By measuring the content of oxygen and nitrogen in welds of six kinds of self-shielded flux-cored wires,the effect of oxygen on nitrogen content in weld is studied and the different absorptive mechanisms of nitrogen a...By measuring the content of oxygen and nitrogen in welds of six kinds of self-shielded flux-cored wires,the effect of oxygen on nitrogen content in weld is studied and the different absorptive mechanisms of nitrogen at a low oxygen level([O] lower than 0.02%) and a high oxygen level ([O] higher than 0.03%) have been discovered.The results indicate that the content of nitrogen in weld can be made lowest by modifying the composition of flux and controlling the content of oxygen to the range of 0.02%～0.03%.展开更多
The effects of different outer diameters and surface oxygen contents on the adsorption of heavy metals onto six types of multi-walled carbon nanotubes （MWCNTs） were investigated in an aqueous solution and lead was c...The effects of different outer diameters and surface oxygen contents on the adsorption of heavy metals onto six types of multi-walled carbon nanotubes （MWCNTs） were investigated in an aqueous solution and lead was chosen as a model metal ion. The results indicated that the percentage removal and adsorption capacity of lead remarkably increased with decreasing outer diameter due to larger specific surface area （SSA）. The SSA-normalized maximum adsorption capacity （qJSSA） and SSA-normalized adsorption coefficient （KdSSA） were strongly positively correlated with surface oxygen content, implying that lead adsorption onto MWCNTs significantly increases with the rise of oxygen content and decreases with decreasing SSA. The calculated thermodynamic parameters indicated that adsorption of lead on MWCNTs was endothermic and spontaneous. When the oxygen content of MWCNTs increased from 2.0% to 5.9%, the standard free energy （AGt） became more negative, which implied that the oxygenated functional groups increased the adsorption affinity of MWCNTs for lead. Through calculation of enthalpy （△H0）, AGO and free energy of adsorption （Ea）, lead adsorption onto MWCNTs was recognized as a chemisorption process. The chemical interaction between lead and the phenolic groups of MWCNTs could be one of the main adsorption mechanisms due to highly positive correlations between the phenolic groups and Kd/SSA or qm/SSA.展开更多
Experimental studies on the melting process of titanium aluminum alloy have been pursued from the viewpoint of contamination.TiAl alloys were prepared with vacuum induction melting(VIM)in calcia crucibles at 1873 K an...Experimental studies on the melting process of titanium aluminum alloy have been pursued from the viewpoint of contamination.TiAl alloys were prepared with vacuum induction melting(VIM)in calcia crucibles at 1873 K and 1923 K in order to determine the behavior of the oxygen content as a function of temperature,time and frequency of power.The experiment results showed that alloys were uncontaminated except for the increasing of oxygen content which was introduced from the reaction CaO(s)=Ca(in TiAl)+O(in TiAl),and the standard Gibbs energy of the reaction was determined to be△G0=274000102.8T(J/mol).Oxygen content increased slowly with the melting time by about 50×10-6 wt pct/min,and decreased with induction melting frequency.Lower superheat and higher melting frequency can be used to reduce oxygen content increasing rate.展开更多
Isothermal oxidation behaviors of Ti-45Al-2Fe-2Mo-1Cr intermetallics with different oxygen contents were studied under the condition of 950 °C, 100 h in air, and the oxidation kinetic parameters were also evaluat...Isothermal oxidation behaviors of Ti-45Al-2Fe-2Mo-1Cr intermetallics with different oxygen contents were studied under the condition of 950 °C, 100 h in air, and the oxidation kinetic parameters were also evaluated. The results show that the oxidation resistance of the TiAl intermetallics is negatively related to the oxygen content, and both the mass gain and thickness of oxide scale increase with the oxygen content. The sub-surface microstructure of the oxide scales varies with the oxygen content. Z phase is observed in the sub-surface area of the low-oxygen-content alloy, while the τ2(Al2FeTi) phase is found in the medium-oxygen-content and the high-oxygen-content alloys. The deterioration of oxidation resistance is due to the enhanced internal oxidation with the increase of oxygen content. It is possible to improve the oxidation resistance by controlling the oxygen content.展开更多
Ti-stabilized 321 stainless steel was prepared using an electric arc furnace, argon oxygen decarburization (AOD) furnace, ladle furnace (LF), and continuous casting processes. In addition, the effect of refining proce...Ti-stabilized 321 stainless steel was prepared using an electric arc furnace, argon oxygen decarburization (AOD) furnace, ladle furnace (LF), and continuous casting processes. In addition, the effect of refining process and utilization of different slags on the evolution of inclusions, titanium yield, and oxygen content was systematically investigated by experimental and thermodynamic analysis. The results reveal that the total oxygen content (TO) and inclusion density decreased during the refining process. The spherical CaO–SiO2–Al2O3–MgO inclusions existed in the 321 stainless steel after the AOD process. Moreover, prior to the Ti addition, the spherical CaO–Al2O3–MgO–SiO2 inclusions were observed during LF refining pro-cess. However, Ti addition resulted in multilayer CaO–Al2O3–MgO–TiOx inclusions. Two different samples were prepared by conventional CaO–Al2O3-based slag (Heat-1) and -TiO2-rich CaO–Al2O3-based slag (Heat-2). The statistical analysis revealed that the density of inclusions and the -TiOx content in CaO–Al2O3–MgO–TiOx inclusions found in Heat-2 sample are much lower than those in the Heat-1 sample. Furthermore, the TO content and Ti yield during the LF refining process were controlled by using -TiO2-rich calcium aluminate synthetic slag. These results were consistent with the ion–molecule coexist-ence theory and FactSage?7.2 software calculations. When -TiO2-rich CaO–Al2O3-based slag was used, the -TiO2 activity of the slag increased, and the equilibrium oxygen content significantly decreased from the AOD to LF processes. Therefore, the higher -TiO2 activity of slag and lower equilibrium oxygen content suppressed the undesirable reactions between Ti and O.展开更多
The effects of the calcination temperature on the oxygen content and magnetic properties of the nano- crystalline perovskite manganite Lao.75Sro.25MnO3±δ pre- pared by the sol-gel method were investigated. The h...The effects of the calcination temperature on the oxygen content and magnetic properties of the nano- crystalline perovskite manganite Lao.75Sro.25MnO3±δ pre- pared by the sol-gel method were investigated. The highest temperatures at which the samples were calcined were 973, 1073, 1273, and 1473 K. The X-ray diffraction （XRD） analyses indicate that all the samples have only a single phase with the R3c perovskite structure. As the calcination temperature and calcination time increase, the oxygen content in the samples increases from being deficient to being in excess of that in the stoichiometric formula. The crystallite size also increases from 23 to 283 nm. Magnetic measurements indicate that the sample calcined at 1073 K has the highest Curie temperature. This is owing to the fact that the crystallite cores of this sample have stoichiometric oxygen content. The dependence of the Curie temperature and the saturation magnetization on the calcination tem- perature are successfully explained.展开更多
In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phas...In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phase precursor method can achieve uniform mixing of components at the molecular level through multiple complexation reactions,and then realize the carbo/borothermal reduction reaction at a lower temperature to obtain ultrapure HfB2 powders.The as-resulted quasi-spherical HfB2 powders under the optimum conditions(atomic molar ratio M:B:C=1:2.8:10)calcined at 1500°C for 1 h have an average particle size of 205 nm and an oxygen content of 0.097 wt.%.Detailed analysis of the phase evolution of precursors shows that the formation of HfB2 particles is a mass diffusion mode from the external to internal HfO_(2)cores.We reveal that below 1300°C,HfC is not an intermediate product of HfB2 powder during the transition of precursors.Instead,HfC was formed as a by-product at high temperatures in the carbo/borothermal reduction process.The proposed formation mechanism of HfB_(2) is completely different from the traditional two-step transformation method.After the sintering of the ultrafine powders,the HfB_(2) ceramics show a relative density of 96.1%and superior mechanical properties compared to other works.Furthermore,by simply replacing the initial metal source,chlorinated group IV and V transitional metals(Ti,Zr,Ta,Nb)can also convert into high-purity and ultrafine diborides.This work shows that flocculating settling assisted carbo/borothermal reduction has potential in lot size production of various high-purity and ultrafine boride powders.展开更多
The metallurgical properties and fatigue life of bearing steel processed by electric furnace (EAF), ladle refining (LF-VD), continous casting (CC) and electroslag remelting (ESR) have been investigated. The main resul...The metallurgical properties and fatigue life of bearing steel processed by electric furnace (EAF), ladle refining (LF-VD), continous casting (CC) and electroslag remelting (ESR) have been investigated. The main results obtained are as follows: (1) Due to low oxygen content and dispersion inclusions in steel, the fatigue Life of LF-VD-IC or CC is three times as high as that of EAF steel; (2) The oxygen content in steel produced by CC process is about 9.0x10(-6), the carbon segregation (C/C(0)) is from 0.92 to 1.10 and the fatigue life of CC steel is equal to that of ladle refining ingot casting steel; (3) Although the amount of inclusion and oxygen in ESR steel is higher than that of LF-VD-IC or CC steel, the fatigue life of ESR steel is higher than that of the latter because of its fine and well dispersed inclusions.展开更多
The influence of dissolved oxygen content on the oxidative stability of a linked polymer solution (LPS) was studied by micro-filtration, dynamic light scattering and viscosity measurements. The results showed that at ...The influence of dissolved oxygen content on the oxidative stability of a linked polymer solution (LPS) was studied by micro-filtration, dynamic light scattering and viscosity measurements. The results showed that at the same temperature, the degree of the oxidative degradation of the LPS increased and the rapidity of the oxidative degradation was accelerated with the increase of the dissolved oxygen content. Consequently, the size of linked polymer coils (LPCs) of the LPS became small, and the plugging capability of the LPS decreased. At a fixed content of dissolved oxygen, with increasing degradation temperature, almost the same results were observed, namely, an increased degree of oxidative degradation, accelerated rapidity of the oxidative degradation and decreased plugging capacity, with decreased oxidative stability of LPS. At 90 °C, in the presence of oxygen, LPS lost its plugging capability after having been degraded for a period of time. But at 40 °C, LPS with low dissolved oxygen content could be stable for a long time. The decreased plugging ability of LPS after oxidative degradation is mainly caused by the decreased size and number of the LPCs due to the breaking of hydrolyzed polyacrylamide (HPAM) molecule segments and the structural changing of HPAM molecules.展开更多
The interfacial oxygen transfer rate is one of the main factors to control the composition of alloys.The commonly employed method of studying the interfacial oxygen transfer rate is the chemical composition analysis;h...The interfacial oxygen transfer rate is one of the main factors to control the composition of alloys.The commonly employed method of studying the interfacial oxygen transfer rate is the chemical composition analysis;however,it is difficult to be studied in situ.Here,a new method of measuring the oxygen transfer rate at the gas-slag and slag-metal interfaces was reported based on electrochemical analyses.The interfacial oxygen transfer rate in the smelting process of Inconel 718 superalloy was investigated at 1723,1773,1823,and 1873 K.The experimental results show that the electrochemical method can measure the real-time oxygen content;hence,this method is promising in controlling the oxygen content in alloys.As the temperature increased,both the equilibrium oxygen content and the rate of oxygen absorption increased significantly,and the increase was the most obvious when the temperature was 1873 K.The possible reason is that the increase in temperature weakens the mass transfer resistance of the electric double layer at the interface,thus accelerating the oxygen transfer rate.展开更多
The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper.Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the a...The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper.Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF-NdF_(3)melt after a lengthy period of pre-electrolysis purification at 1000℃(during which the oxygen content reduced from 413 to 150 mg/kg).The oxidation process of oxygen ions was found to have two stages:oxidation product adsorption and CO/CO_(2)gas evolution.The adsorption stage was controlled by diffusion,whereas the gas evolution was controlled by the electrochemical reaction.In comparison with oxygen content of 413 mg/kg,the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred.Fluorine-ion oxidation peaks that occurred at about 4.2 V vs.Li/Li+could be clearly observed in the reverse scanning processes,in which fluorine ions were oxidized and perfluorocarbons were produced,which resulted in an anode effect.展开更多
The complex fluoride, KNiF3, with perovskite structure was synthesized by refluxing KF and Ni（NO3）2·6H20 in ethanediol. The samples were characterized by X-ray diffraction（XRD）, transmission electron microsc...The complex fluoride, KNiF3, with perovskite structure was synthesized by refluxing KF and Ni（NO3）2·6H20 in ethanediol. The samples were characterized by X-ray diffraction（XRD）, transmission electron microscopy（TEM）, X-ray photoelectron spectroscopy（XPS）, and ultraviolet-visible diffuse reflectance speetroseopy（UV-Vis DRS）. The results indicate that the mean diameter of KNiF3 particles is about 30-60 nm and the oxygen content in the samples is ≤5%. The prepared KNiF3 shows obvious absorption peaks at 400-830 nm.展开更多
In the municipal solid waste incineration process,it is difficult to effectively control the gas oxygen content by setting the air flow according to artificial experience.To address this problem,this paper proposes an...In the municipal solid waste incineration process,it is difficult to effectively control the gas oxygen content by setting the air flow according to artificial experience.To address this problem,this paper proposes an optimization control method of gas oxygen content based on model predictive control.First,a stochastic configuration network is utilized to establish a prediction model of gas oxygen content.Second,an improved differential evolution algorithm that is based on parameter adaptive and t-distribution strategy is employed to address the set value of air flow.Finally,model predictive control is combined with the event triggering strategy to reduce the amount of computation and the controller's frequent actions.The experimental results show that the optimization control method proposed in this paper obtains a smaller degree of fluctuation in the air flow set value,which can ensure the tracking control performance of the gas oxygen content while reducing the amount of calculation.展开更多
Nd-Fe-B hot-pressed(HP) magnet prepared from melt-spun MQU-F flakes features coarse grains(CG)with the average size of both 200 nm(CGS) and 700 nm(CGL) at flake boundary.The grain growth at the flake boundary of Nd2 F...Nd-Fe-B hot-pressed(HP) magnet prepared from melt-spun MQU-F flakes features coarse grains(CG)with the average size of both 200 nm(CGS) and 700 nm(CGL) at flake boundary.The grain growth at the flake boundary of Nd2 Fe14B/α-Fe composite HP magnet before and after diffusion of low-melting-point Pr82Cu18 phase was investigated,revealing the indispensable role of surface RE-rich phase of meltspun flakes in the formation of CG in HP magnet.The dominant role of surface oxygen content of melt-spun flakes in the formation of CGL has been clarified with etching method.The HP magnet prepared from the etched flakes with dramatically decreased oxygen content exhibits the CG regions merely with homoge neous equiaxed CGS at flake boundary.Consequently,the coercivity(μ0 Hc) shows significant increase while remanent magnetization(μ0 Mr) inappreciable change.Further investigation with sieving method reveals the elimination of CGL via removal of the fine Nd-Fe-B flakes smaller than 54 μm due to their much higher oxygen content,confirming the dominant role of oxygen content in the formation of CGL.The quantitative analysis on the magnetic properties of the above HP magnets reveals the monotonic increase of coercivity(μ0 Hc) and negligible change of remanent magnetization(μ0 Mr) with decreased oxygen contents of Nd-Fe-B flakes.The maximum value of coercivity(μ0 Hc) increases from2.26 to 2.47 T as the oxygen content decreases from 0.1692 wt% to 0.079 wt%.展开更多
The effects of oxygen on the microstructure of Ti-47Al-0.7B （at. pct） alloy for as-cast automotive valves were investigated. Six alloys with oxygen content from 0.4 to 1.4 at. pct were prepared by induction melting ...The effects of oxygen on the microstructure of Ti-47Al-0.7B （at. pct） alloy for as-cast automotive valves were investigated. Six alloys with oxygen content from 0.4 to 1.4 at. pct were prepared by induction melting and centrifugal casting in CaO crucible under protective atmosphere. The microstructures were observed by optical microscopy （OM） and scanning electron microscope （SEM）. The results show that the increase of oxygen content led to grain refinement and enhanced the microhardness as well as the α2 volume fraction in the TiAl-based alloys.展开更多
The oxygen relief/absorption,superconduc— tivity and structure of(Bi_(1-x)Pb_x)_2Sr_2Ca_2— Cu_3O_y compounds have been studied by TGA, electrical resistance measurement and X-ray diffraction.The amount of oxygen whi...The oxygen relief/absorption,superconduc— tivity and structure of(Bi_(1-x)Pb_x)_2Sr_2Ca_2— Cu_3O_y compounds have been studied by TGA, electrical resistance measurement and X-ray diffraction.The amount of oxygen which can be re- leased and superconductivity of the compounds are correlative to Pb content.The release of oxygen in- creases when x less than 0.2 and decreases when x exceeds 0.2 with increasing x.The appropriate con- tent of Pb for superconductivity is in the range of 0.1<x<0.3,which corresponds to the relative large amount of oxygen that can be released.It is found according to electric resistance measurement that quenching is favourable to form the‘85K’phase and slow cooling the‘110K’phase.The experimen- tal results suggest that a relation exists between the superconductivity and the oxygen content in Bi sys- tem containing Pb.As the T_c of‘85K’phase de- creases and that of‘110K’phase increases with in- creasing oxygen content,it is possible that the effect of oxygen content in‘85K’phase and‘110K’ phase on the superconductivity is different.展开更多
The influence of oxygen content on the dielectric property of BiFeO3 ceramics is studied by experiment and firstprinciples calculation. The experimental result demonstrates that the dielectric constant of BiFeO3 is st...The influence of oxygen content on the dielectric property of BiFeO3 ceramics is studied by experiment and firstprinciples calculation. The experimental result demonstrates that the dielectric constant of BiFeO3 is strongly dependent on introduced oxygen and oxygen vacancies. By comparison with BiFeO3, the introduced oxygen and oxygen vacancies can lead to a reduction in dielectric constant of BiFeO5 at a lower frequency. The first-principles calculation also shows a similar result when photon energy is in a range of 2.0-4.1 eV. A likely explanation is that this oxygen content dependence may be ascribed to the distortion of Fe-O octahedron structure due to oxygen vacancies or excess oxygen ions in the crystal structure of BiFeO3.展开更多
基金supported by the National Natural Science Foundation of China(No.52101165)the Inner Mongolia Science and Technology Major Project(No.2020ZD0010)the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-CN-2021-3).
文摘The large and dense rare earth (RE)-oxide inclusions in high-oxygen RE metal increase the risk of producing variable properties in RE steel. Consequently, a self-developed electrolysis cell was utilized for the production of low-oxygen La/Ce mischmetal. The electrolysis process and the origin of oxygen in mischmetal were comprehensively investigated. The results indicate that the reaction between La/Ce oxide and fluoride molten salt results in the formation of La/Ce oxy-fluoride. The deposition of oxy-fluoride at the bottom of the electrolysis cell is the primary factor contributing to the increased oxygen content in mischmetal. The comprehensive influence of oxide addition quantity, feeding interval, and electrolysis temperature on oxygen content, purity, and current efficiency using the response surface methodology model is revealed. The results for industrial experiment show that the purity of mishcmetal reaches higher than 99.78 wt.%, the oxygen content of mischmetal is only 0.0047 wt.% and the current efficiency of the electrolysis process achieves 80.79% under the optimized parameters of 225 kg/d, 30 s and 1069 ℃. The findings offer valuable insights into the application of molten salt electrolysis for the production of low-oxygen mischmetal.
基金supported by the National Natural Science Foundation of China(Nos.U22B2067 and 52073176)。
文摘Laser powder bed fusion(LPBF)is a widely used and well-developed approach in additive manufacturing.To meet the high material performance requirements of fourth-generation nuclear power reactors,the combination of LPBF processing with oxide dispersion strengthening(ODS)is currently of interest for the design and development of new materials.In this approach,nanoscale Y_(2)O_(3)particles are dispersed into the feeding powders to produce LPBF-ODS materials.Oxygen exposure and the introduction of oxygen into the solvation cell during LPBF are usually considered as detrimental processes that are impossible to eliminate completely.However,our understanding of these unavoidable processes is still limited.In this study,we developed a new LPBF-ODS design approach based on in situ oxygen content regulation during the LPBF process.The oxygen content of the environmental chamber was artificially adjusted using an online monitoring system to activate reactions between oxygen and the metallic elements for the in situ formation of dispersed oxide particles.Four batches of LPBF 304 L stainless steel samples were successfully processed under different oxygen levels to investigate the reinforcement effect of in situ chemical alloying.The results show that dispersed oxide particles were formed with an average nanoscale size of approximately 46 nm through the LPBF in situ alloying approach.The increase in the number density of oxide particles to 11.4 particles∕μm^(2)as the oxygen content increased played a role in refining and stabilizing the cellular structure.The yield strength of the in situ alloyed ODS material was enhanced(to up to~675 MPa)while its ductility was not significantly degraded(elongation of up to~39%).These tensile properties are competitive within the ranges reported for ODS alloys prepared by mechanical alloying.The main mechanisms for yield strength enhancement through interactions between nanoscale oxide particles and dislocation entanglement cells were analyzed.This study provides a new approach for the future preparation of high-performance LPBF-ODS alloys.
基金Supported by Science and Technology Project of Beijing Municipal Administration Center of Parks (ZX2019ZX2017).
文摘This study was conducted to investigate the air oxygen content inside and outside a Phyllostachys edulis forest in Qishan Forest Park throughout all four seasons.(1)Regarding the overall annual variation in oxygen content in both environments,comparative analysis of the annual average oxygen concentration showed that the average inside the forest was 22.13%,while the value outside it was 21.39%.The annual average oxygen concentration inside the forest was 3.34%higher than that outside the forest.(2)Regarding the seasonal variation in oxygen content at both sites,the oxygen concentration inside the forest was consistently higher than that outside the forest in all four seasons.The oxygen concentrations inside the forest were 22.1%,21.9%,21.8%,and 21.5%in spring,summer,autumn,and winter,respectively,while outside the forest,they were 22.0%,21.8%,21.7%,and 21.4%for the same seasons,respectively.(3)The diurnal variation trends of oxygen concentration at both sites were similar throughout all four seasons,exhibiting a single-peak and double-trough curve pattern.The peak period occurred at 13:00 in spring,summer,and winter,and at 9:00 in autumn.The trough periods were observed at 7:00 and between 21:00 and 23:00 or at 5:00.
文摘By measuring the content of oxygen and nitrogen in welds of six kinds of self-shielded flux-cored wires,the effect of oxygen on nitrogen content in weld is studied and the different absorptive mechanisms of nitrogen at a low oxygen level([O] lower than 0.02%) and a high oxygen level ([O] higher than 0.03%) have been discovered.The results indicate that the content of nitrogen in weld can be made lowest by modifying the composition of flux and controlling the content of oxygen to the range of 0.02%～0.03%.
基金supported by the National High Technology Research and Development Program (863) of China (No.2007AA06Z334)the Scholarship Award for Excellent Doctoral Student granted by Ministry of Education and the Shanghai Jiao Tong University Innovation Fund for Postgraduates+1 种基金the State Key Laboratory of Pollution Control and Resource Reuse Foundation (No. PCRRY11009)the Program for Young Excellent Talents at Tongji University (No. 2010KJ026)
文摘The effects of different outer diameters and surface oxygen contents on the adsorption of heavy metals onto six types of multi-walled carbon nanotubes （MWCNTs） were investigated in an aqueous solution and lead was chosen as a model metal ion. The results indicated that the percentage removal and adsorption capacity of lead remarkably increased with decreasing outer diameter due to larger specific surface area （SSA）. The SSA-normalized maximum adsorption capacity （qJSSA） and SSA-normalized adsorption coefficient （KdSSA） were strongly positively correlated with surface oxygen content, implying that lead adsorption onto MWCNTs significantly increases with the rise of oxygen content and decreases with decreasing SSA. The calculated thermodynamic parameters indicated that adsorption of lead on MWCNTs was endothermic and spontaneous. When the oxygen content of MWCNTs increased from 2.0% to 5.9%, the standard free energy （AGt） became more negative, which implied that the oxygenated functional groups increased the adsorption affinity of MWCNTs for lead. Through calculation of enthalpy （△H0）, AGO and free energy of adsorption （Ea）, lead adsorption onto MWCNTs was recognized as a chemisorption process. The chemical interaction between lead and the phenolic groups of MWCNTs could be one of the main adsorption mechanisms due to highly positive correlations between the phenolic groups and Kd/SSA or qm/SSA.
文摘Experimental studies on the melting process of titanium aluminum alloy have been pursued from the viewpoint of contamination.TiAl alloys were prepared with vacuum induction melting(VIM)in calcia crucibles at 1873 K and 1923 K in order to determine the behavior of the oxygen content as a function of temperature,time and frequency of power.The experiment results showed that alloys were uncontaminated except for the increasing of oxygen content which was introduced from the reaction CaO(s)=Ca(in TiAl)+O(in TiAl),and the standard Gibbs energy of the reaction was determined to be△G0=274000102.8T(J/mol).Oxygen content increased slowly with the melting time by about 50×10-6 wt pct/min,and decreased with induction melting frequency.Lower superheat and higher melting frequency can be used to reduce oxygen content increasing rate.
基金Project(2014CB644002) supported by the National Key Fundamental Research and Development of ChinaProject(2017JJ2311) supported by the Natural Science Foundation of Hunan Province,ChinaProject(KFJJ11-7M) supported by the State Key Laboratory of Explosion Science and Technology,China
文摘Isothermal oxidation behaviors of Ti-45Al-2Fe-2Mo-1Cr intermetallics with different oxygen contents were studied under the condition of 950 °C, 100 h in air, and the oxidation kinetic parameters were also evaluated. The results show that the oxidation resistance of the TiAl intermetallics is negatively related to the oxygen content, and both the mass gain and thickness of oxide scale increase with the oxygen content. The sub-surface microstructure of the oxide scales varies with the oxygen content. Z phase is observed in the sub-surface area of the low-oxygen-content alloy, while the τ2(Al2FeTi) phase is found in the medium-oxygen-content and the high-oxygen-content alloys. The deterioration of oxidation resistance is due to the enhanced internal oxidation with the increase of oxygen content. It is possible to improve the oxidation resistance by controlling the oxygen content.
基金The authors gratcfully acknowledge the sup-port of the National Natural Science Foundation of China(Grant No.51374020)the State Key Laboratory of Advanced Metallurgy at theUniversity of Science and Technology Beijing(USTB)the JiuquanIron and Steel Group Corporation.
文摘Ti-stabilized 321 stainless steel was prepared using an electric arc furnace, argon oxygen decarburization (AOD) furnace, ladle furnace (LF), and continuous casting processes. In addition, the effect of refining process and utilization of different slags on the evolution of inclusions, titanium yield, and oxygen content was systematically investigated by experimental and thermodynamic analysis. The results reveal that the total oxygen content (TO) and inclusion density decreased during the refining process. The spherical CaO–SiO2–Al2O3–MgO inclusions existed in the 321 stainless steel after the AOD process. Moreover, prior to the Ti addition, the spherical CaO–Al2O3–MgO–SiO2 inclusions were observed during LF refining pro-cess. However, Ti addition resulted in multilayer CaO–Al2O3–MgO–TiOx inclusions. Two different samples were prepared by conventional CaO–Al2O3-based slag (Heat-1) and -TiO2-rich CaO–Al2O3-based slag (Heat-2). The statistical analysis revealed that the density of inclusions and the -TiOx content in CaO–Al2O3–MgO–TiOx inclusions found in Heat-2 sample are much lower than those in the Heat-1 sample. Furthermore, the TO content and Ti yield during the LF refining process were controlled by using -TiO2-rich calcium aluminate synthetic slag. These results were consistent with the ion–molecule coexist-ence theory and FactSage?7.2 software calculations. When -TiO2-rich CaO–Al2O3-based slag was used, the -TiO2 activity of the slag increased, and the equilibrium oxygen content significantly decreased from the AOD to LF processes. Therefore, the higher -TiO2 activity of slag and lower equilibrium oxygen content suppressed the undesirable reactions between Ti and O.
基金financially supported by the National Natural Science Foundation of China(No.NSF-11174069)the Natural Science Foundation of Hebei Province(No.E2011205083)+1 种基金the Key Item Science Foundation of Hebei Province(No.10965125D)the Key Item Science Foundation of the Education Department of Hebei Province(No.ZD2010129)
文摘The effects of the calcination temperature on the oxygen content and magnetic properties of the nano- crystalline perovskite manganite Lao.75Sro.25MnO3±δ pre- pared by the sol-gel method were investigated. The highest temperatures at which the samples were calcined were 973, 1073, 1273, and 1473 K. The X-ray diffraction （XRD） analyses indicate that all the samples have only a single phase with the R3c perovskite structure. As the calcination temperature and calcination time increase, the oxygen content in the samples increases from being deficient to being in excess of that in the stoichiometric formula. The crystallite size also increases from 23 to 283 nm. Magnetic measurements indicate that the sample calcined at 1073 K has the highest Curie temperature. This is owing to the fact that the crystallite cores of this sample have stoichiometric oxygen content. The dependence of the Curie temperature and the saturation magnetization on the calcination tem- perature are successfully explained.
基金financially supported by the National Science Fund for Distinguished Young Scholars(No.51825103)the National Science Fund for Excellent Young Scholars(No.52222208)+1 种基金the Major science and technology project of Anhui Province(No.008192841048)the HFIPS Director's Fund,CAS(No.BJPY2021B04,YZJJ202202-CX,YZJJKX202202).
文摘In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phase precursor method can achieve uniform mixing of components at the molecular level through multiple complexation reactions,and then realize the carbo/borothermal reduction reaction at a lower temperature to obtain ultrapure HfB2 powders.The as-resulted quasi-spherical HfB2 powders under the optimum conditions(atomic molar ratio M:B:C=1:2.8:10)calcined at 1500°C for 1 h have an average particle size of 205 nm and an oxygen content of 0.097 wt.%.Detailed analysis of the phase evolution of precursors shows that the formation of HfB2 particles is a mass diffusion mode from the external to internal HfO_(2)cores.We reveal that below 1300°C,HfC is not an intermediate product of HfB2 powder during the transition of precursors.Instead,HfC was formed as a by-product at high temperatures in the carbo/borothermal reduction process.The proposed formation mechanism of HfB_(2) is completely different from the traditional two-step transformation method.After the sintering of the ultrafine powders,the HfB_(2) ceramics show a relative density of 96.1%and superior mechanical properties compared to other works.Furthermore,by simply replacing the initial metal source,chlorinated group IV and V transitional metals(Ti,Zr,Ta,Nb)can also convert into high-purity and ultrafine diborides.This work shows that flocculating settling assisted carbo/borothermal reduction has potential in lot size production of various high-purity and ultrafine boride powders.
文摘The metallurgical properties and fatigue life of bearing steel processed by electric furnace (EAF), ladle refining (LF-VD), continous casting (CC) and electroslag remelting (ESR) have been investigated. The main results obtained are as follows: (1) Due to low oxygen content and dispersion inclusions in steel, the fatigue Life of LF-VD-IC or CC is three times as high as that of EAF steel; (2) The oxygen content in steel produced by CC process is about 9.0x10(-6), the carbon segregation (C/C(0)) is from 0.92 to 1.10 and the fatigue life of CC steel is equal to that of ladle refining ingot casting steel; (3) Although the amount of inclusion and oxygen in ESR steel is higher than that of LF-VD-IC or CC steel, the fatigue life of ESR steel is higher than that of the latter because of its fine and well dispersed inclusions.
文摘The influence of dissolved oxygen content on the oxidative stability of a linked polymer solution (LPS) was studied by micro-filtration, dynamic light scattering and viscosity measurements. The results showed that at the same temperature, the degree of the oxidative degradation of the LPS increased and the rapidity of the oxidative degradation was accelerated with the increase of the dissolved oxygen content. Consequently, the size of linked polymer coils (LPCs) of the LPS became small, and the plugging capability of the LPS decreased. At a fixed content of dissolved oxygen, with increasing degradation temperature, almost the same results were observed, namely, an increased degree of oxidative degradation, accelerated rapidity of the oxidative degradation and decreased plugging capacity, with decreased oxidative stability of LPS. At 90 °C, in the presence of oxygen, LPS lost its plugging capability after having been degraded for a period of time. But at 40 °C, LPS with low dissolved oxygen content could be stable for a long time. The decreased plugging ability of LPS after oxidative degradation is mainly caused by the decreased size and number of the LPCs due to the breaking of hydrolyzed polyacrylamide (HPAM) molecule segments and the structural changing of HPAM molecules.
基金gratefully express their appreciation to National Natural Science Foundation of China(Nos.51974153 and U1960203)the Joint Fund of State Key Laboratory of Marine Engineering and University of Science and Technology Liaoning(SKLMEA-USTL-201707)the China Scholarship Council(201908210457).
文摘The interfacial oxygen transfer rate is one of the main factors to control the composition of alloys.The commonly employed method of studying the interfacial oxygen transfer rate is the chemical composition analysis;however,it is difficult to be studied in situ.Here,a new method of measuring the oxygen transfer rate at the gas-slag and slag-metal interfaces was reported based on electrochemical analyses.The interfacial oxygen transfer rate in the smelting process of Inconel 718 superalloy was investigated at 1723,1773,1823,and 1873 K.The experimental results show that the electrochemical method can measure the real-time oxygen content;hence,this method is promising in controlling the oxygen content in alloys.As the temperature increased,both the equilibrium oxygen content and the rate of oxygen absorption increased significantly,and the increase was the most obvious when the temperature was 1873 K.The possible reason is that the increase in temperature weakens the mass transfer resistance of the electric double layer at the interface,thus accelerating the oxygen transfer rate.
基金the National Natural Science Foundation of China(No.51774145).The“Minjiang Scholar”Program of Department of Education,Fujian Province,China was also acknowledged.
文摘The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper.Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF-NdF_(3)melt after a lengthy period of pre-electrolysis purification at 1000℃(during which the oxygen content reduced from 413 to 150 mg/kg).The oxidation process of oxygen ions was found to have two stages:oxidation product adsorption and CO/CO_(2)gas evolution.The adsorption stage was controlled by diffusion,whereas the gas evolution was controlled by the electrochemical reaction.In comparison with oxygen content of 413 mg/kg,the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred.Fluorine-ion oxidation peaks that occurred at about 4.2 V vs.Li/Li+could be clearly observed in the reverse scanning processes,in which fluorine ions were oxidized and perfluorocarbons were produced,which resulted in an anode effect.
基金Supported by the National Natural Science Foundation of China(No.20671069)
文摘The complex fluoride, KNiF3, with perovskite structure was synthesized by refluxing KF and Ni（NO3）2·6H20 in ethanediol. The samples were characterized by X-ray diffraction（XRD）, transmission electron microscopy（TEM）, X-ray photoelectron spectroscopy（XPS）, and ultraviolet-visible diffuse reflectance speetroseopy（UV-Vis DRS）. The results indicate that the mean diameter of KNiF3 particles is about 30-60 nm and the oxygen content in the samples is ≤5%. The prepared KNiF3 shows obvious absorption peaks at 400-830 nm.
基金supported by the National Natural Science Foundation of China(62373017,62073006)and the Beijing Natural Science Foundation of China(4212032)。
文摘In the municipal solid waste incineration process,it is difficult to effectively control the gas oxygen content by setting the air flow according to artificial experience.To address this problem,this paper proposes an optimization control method of gas oxygen content based on model predictive control.First,a stochastic configuration network is utilized to establish a prediction model of gas oxygen content.Second,an improved differential evolution algorithm that is based on parameter adaptive and t-distribution strategy is employed to address the set value of air flow.Finally,model predictive control is combined with the event triggering strategy to reduce the amount of computation and the controller's frequent actions.The experimental results show that the optimization control method proposed in this paper obtains a smaller degree of fluctuation in the air flow set value,which can ensure the tracking control performance of the gas oxygen content while reducing the amount of calculation.
基金Project supported by the Ningbo Science and Technology Major (2017B10002,2019B10093)the National Natural Science Foundation of China (51671207,51301192)Zhejiang Province Technology Application Research (LGG19E010001)。
文摘Nd-Fe-B hot-pressed(HP) magnet prepared from melt-spun MQU-F flakes features coarse grains(CG)with the average size of both 200 nm(CGS) and 700 nm(CGL) at flake boundary.The grain growth at the flake boundary of Nd2 Fe14B/α-Fe composite HP magnet before and after diffusion of low-melting-point Pr82Cu18 phase was investigated,revealing the indispensable role of surface RE-rich phase of meltspun flakes in the formation of CG in HP magnet.The dominant role of surface oxygen content of melt-spun flakes in the formation of CGL has been clarified with etching method.The HP magnet prepared from the etched flakes with dramatically decreased oxygen content exhibits the CG regions merely with homoge neous equiaxed CGS at flake boundary.Consequently,the coercivity(μ0 Hc) shows significant increase while remanent magnetization(μ0 Mr) inappreciable change.Further investigation with sieving method reveals the elimination of CGL via removal of the fine Nd-Fe-B flakes smaller than 54 μm due to their much higher oxygen content,confirming the dominant role of oxygen content in the formation of CGL.The quantitative analysis on the magnetic properties of the above HP magnets reveals the monotonic increase of coercivity(μ0 Hc) and negligible change of remanent magnetization(μ0 Mr) with decreased oxygen contents of Nd-Fe-B flakes.The maximum value of coercivity(μ0 Hc) increases from2.26 to 2.47 T as the oxygen content decreases from 0.1692 wt% to 0.079 wt%.
文摘The effects of oxygen on the microstructure of Ti-47Al-0.7B （at. pct） alloy for as-cast automotive valves were investigated. Six alloys with oxygen content from 0.4 to 1.4 at. pct were prepared by induction melting and centrifugal casting in CaO crucible under protective atmosphere. The microstructures were observed by optical microscopy （OM） and scanning electron microscope （SEM）. The results show that the increase of oxygen content led to grain refinement and enhanced the microhardness as well as the α2 volume fraction in the TiAl-based alloys.
文摘The oxygen relief/absorption,superconduc— tivity and structure of(Bi_(1-x)Pb_x)_2Sr_2Ca_2— Cu_3O_y compounds have been studied by TGA, electrical resistance measurement and X-ray diffraction.The amount of oxygen which can be re- leased and superconductivity of the compounds are correlative to Pb content.The release of oxygen in- creases when x less than 0.2 and decreases when x exceeds 0.2 with increasing x.The appropriate con- tent of Pb for superconductivity is in the range of 0.1<x<0.3,which corresponds to the relative large amount of oxygen that can be released.It is found according to electric resistance measurement that quenching is favourable to form the‘85K’phase and slow cooling the‘110K’phase.The experimen- tal results suggest that a relation exists between the superconductivity and the oxygen content in Bi sys- tem containing Pb.As the T_c of‘85K’phase de- creases and that of‘110K’phase increases with in- creasing oxygen content,it is possible that the effect of oxygen content in‘85K’phase and‘110K’ phase on the superconductivity is different.
基金supported by the National Natural Science Foundation of China (Grant No. 60571063)
文摘The influence of oxygen content on the dielectric property of BiFeO3 ceramics is studied by experiment and firstprinciples calculation. The experimental result demonstrates that the dielectric constant of BiFeO3 is strongly dependent on introduced oxygen and oxygen vacancies. By comparison with BiFeO3, the introduced oxygen and oxygen vacancies can lead to a reduction in dielectric constant of BiFeO5 at a lower frequency. The first-principles calculation also shows a similar result when photon energy is in a range of 2.0-4.1 eV. A likely explanation is that this oxygen content dependence may be ascribed to the distortion of Fe-O octahedron structure due to oxygen vacancies or excess oxygen ions in the crystal structure of BiFeO3.
