The vacuum volatilization kinetics of Pb in In-Pb solder was investigated.The results indicate a significant increase in the vacuum volatilization rates of Pb,25In-75Pb,40In-60Pb,and In with increasing temperatures fr...The vacuum volatilization kinetics of Pb in In-Pb solder was investigated.The results indicate a significant increase in the vacuum volatilization rates of Pb,25In-75Pb,40In-60Pb,and In with increasing temperatures from 923 to 1123 K,system pressure of 3 Pa and holding time of 30 min.The mass transfer coefficients and apparent activation energies of Pb and its alloys were determined at various temperatures.Additionally,a kinetics model was developed to describe Pb vacuum volatilization in high-temperature melts.It is obtained that the vapor mass transfer is the factor limiting the vacuum volatilization rates of Pb and In-Pb alloys under the above specified conditions.展开更多
The increasing demand for magnesium as a next-generation structural material highlights the significance of incorporating CaF_(2)as a catalyst to enhance the efficiency of vacuum carbothermal reduction of magnesium(VC...The increasing demand for magnesium as a next-generation structural material highlights the significance of incorporating CaF_(2)as a catalyst to enhance the efficiency of vacuum carbothermal reduction of magnesium(VCTRM).This study investigates the thermodynamic theory and catalytic mechanism of CaF_(2)in the VCTRM process.Catalytic reduction experiments and molecular dynamics simulations were conducted to gain a comprehensive understanding of the process.Thermodynamic calculations indicate that in vacuum carbothermal reduction,the primary reaction occurs between MgO and C.Analysis shows that CaF_(2)'s catalytic action primarily involves F^(-),Ca^(2+),and melt eutectic.Our experiments demonstrate that the addition of CaF_(2)significantly increases the reduction rate.Furthermore,the mass loss rate increases with both the quantity of CaF_(2)added and the holding time,stabilizing at additions over 5%.Experiments conducted at temperatures above the melting point of CaF_(2)exhibited a pronounced catalytic effect.The resultant magnesium showed optimal structure and crystallization,with a purity of 87.84%.Notably,while CaF_(2)remained in the residue,it was not detected in the condensate,confirming its catalytic role.Molecular dynamics simulations revealed that molten CaF_(2)sabotages the structure of magnesium oxide,with F^(-)dispersing onto the surface of MgO,thus enhancing the reaction between MgO and C to form CO.However,no chemical reaction was observed between C,MgO,and CaF_(2).The occurrence of the carbothermal reduction reaction at high temperatures depends on the concentration of the reducing agent C,with CaF_(2)influencing the reaction rate.This research elucidates the theoretical and mechanistic foundations of CaF_(2)-catalyzed VCTRM,aligning with the green energy-saving concept and significantly advancing the green and efficient VCTRM process.展开更多
Magnesium(Mg)alloys are widely used lightweight structural materials for automobiles and help reduce carbon emissions.However,their use increases the production of Mg alloy scrap,which is recycled at a much lower rate...Magnesium(Mg)alloys are widely used lightweight structural materials for automobiles and help reduce carbon emissions.However,their use increases the production of Mg alloy scrap,which is recycled at a much lower rate than aluminum,and its greater complexity poses challenges to existing recycling processes.Although vacuum distillation can be used to recycle Mg alloy scrap,this requires optimizing and maximizing metal recirculation,but there has been no thermodynamic analysis of this process.In this study,the feasibility and controllability of separating inclusions and 23 metal impurities were evaluated,and their distribution and removal limits were quantified.Thermodynamic analyses and experimental results showed that inclusions and impurity metals of separation coefficient lgβ_(i)≤-5,including Cu,Fe,Co,and Ni below 0.001 ppm,could be removed from the matrix.All Zn entered the recycled Mg,while impurities with-1<lgβ_(i)<-5 such as Li,Ca,and Mn severely affected the purity of the recycled Mg during the later stage of distillation.Therefore,an optimization strategy for vacuum distillation recycling:lower temperatures and higher system pressures for Zn separation in the early stage,and the early termination of the recovery process in the later stage or a continuous supply of raw melt can also prevent contamination during recycling.The alloying elements Al and Zn in Mg alloy scrap can be further recovered and purified by vacuum distillation when economically feasible,to maximize the recycling of metal resources.展开更多
Magnesium(Mg),as one of the most abundant elements in earth's crust,is the lightest structural metal with extensive applications across various industries.However,the performance of Mg-based products is highly dep...Magnesium(Mg),as one of the most abundant elements in earth's crust,is the lightest structural metal with extensive applications across various industries.However,the performance of Mg-based products is highly dependent on their impurity levels,and the lack of high-purity Mg,along with efficient purification method,has posed significant challenge to its widespread industrial adoption.This study investigates the impurity behavior in Mg ingots during the vacuum gasification purification process.Through the analysis of binary phase diagrams,iron(Fe)-based foam material was selected for the filtration and purification of Mg vapor in a vacuum tube furnace.A novel approach combining vacuum gasification,vapor purification,and directional condensation is proposed.The effect of filter pore sizes and filtration temperatures on the efficacy of impurity removal was evaluated.Experimental results demonstrate that Fe-based foam with a pore size of 60 ppi,at a filtration temperature of 773 K,effectively removes impurities such as calcium(Ca),potassium(K),sodium(Na),manganese(Mn),silicon(Si),aluminum(Al),and various oxides,sulfides,and chlorides from the vapor phase.Consequently,high-purity Mg with a purity level exceeding 5N3 was obtained in the condensation zone.展开更多
The feasibility of separation of lead anode slime with low silver by vacuum distillation was analyzed theoretically. The volatilization rates and mass fractions of elements, influenced by distillation temperature, hea...The feasibility of separation of lead anode slime with low silver by vacuum distillation was analyzed theoretically. The volatilization rates and mass fractions of elements, influenced by distillation temperature, heat preservation time and material thickness, were investigated under laboratory conditions. The experimental results indicate that almost all of lead and bismuth can be separated from silver-contained multicomponent alloy at 1 223 K for 45 min when the chamber pressure maintains at 10-25 Pa. Silver can be easily enriched in the residue and its mass fraction increases from 3.6% to 27.8% when the distillation temperature is between 1 133 K and 1 373 K. Due to the forming ofintermetallic compounds Cu2Sb, Cul0Sb3 and Ag3Sb, the antimony could not be evaporated completely during the vacuum distillation. EDS analysis indicates that the condensate has a columnar crystal structure.展开更多
Vacuum distillation is a technique suitable for low boiling and melting point materials,to remove the heavy and low vapor pressure impurities at low level.As indium has low melting point and high boiling point,it is s...Vacuum distillation is a technique suitable for low boiling and melting point materials,to remove the heavy and low vapor pressure impurities at low level.As indium has low melting point and high boiling point,it is suitable for refining by vacuum distillation.First,saturation vapor pressure for major elements in crude indium was calculated by the Clausius–Clay Prang equation,which could approximately predict the temperature and pressure during vacuum distillation process.Second,the activity coefficients for In–Cd,In–Zn,In–Pb,In–Tl at 1373 K,and In–Sn at 1573 K were acquired by means of molecular interaction on volume model.Vapor–liquid equilibrium composition diagrams of those above systems in crude indium were drawn based on activity coefficients.These diagrams could estimate the compositions of products in each process during the refinement of crude indium.Finally,1.2–1.6 ton crude indium was used per day when vacuum distillation experiments were carried out,and experimental results are in good agreement with the predicted values of the vapor–liquid equilibrium composition diagrams.展开更多
The aim of this paper is to experimentally investigate the behavior of magnesium and carbon monoxide vapor in the carbothermic reduction of magnesia at condensing zone temperatures ranging from 923 K to 1223 K.The pha...The aim of this paper is to experimentally investigate the behavior of magnesium and carbon monoxide vapor in the carbothermic reduction of magnesia at condensing zone temperatures ranging from 923 K to 1223 K.The phase,surface morphology,and composition of the condensates obtained were examined by means of scanning electron microscopy and energy-dispersive X-ray spectroscopy.The main findings of this paper include:the reverse reaction products,carbon and magnesium oxide,were formed following the process of magnesium vapor condensation,preventing two metal clusters from mutually combining.Moreover,the nearer the temperature of the condensation zone approached the liquid transformation temperature(810-910 K),the lower the rate of the reverse reaction between carbon monoxide and magnesium vapor.Decrease in the rate of the reverse reaction of magnesium was possible by controlling the condensation temperature.展开更多
Carbothermic reduction alumina in vacuum was conducted, and the products were analysed by means of XRD and gas chromatography. Thermodynamic analysis shows that in vacuum the initial carbothermic reduction reaction te...Carbothermic reduction alumina in vacuum was conducted, and the products were analysed by means of XRD and gas chromatography. Thermodynamic analysis shows that in vacuum the initial carbothermic reduction reaction temperature reduces compared with that under normal pressure, and the preferential order of products is Al404C, Al4C3, Al2OC, Al20 and A1. Experiment results show that the carbothermic reduction products of alumina are A1404C and A14C3, and neither A12OC, Al20 or Al was found. During the carbothermic reduction process, the reaction rate of Al203 and carbon decreases gradually with increasing time. Meanwhile, lower system pressure or higher temperature is beneficial to the carbothermic reduction of alumina process. A1404C is firstly formed in the carbothermic reaction, and then A14C3 is formed in lower system pressure or at higher temperature.展开更多
With the fast development of the application of magnesium based alloys,the demand for primary magnesium is increasing dramatically all over the world.The Pidgeon process is the most widely used process for producing m...With the fast development of the application of magnesium based alloys,the demand for primary magnesium is increasing dramatically all over the world.The Pidgeon process is the most widely used process for producing magnesium in China,but suffers from problems such as high energy,resource consumption and environmental pollution.While the process of vacuum carbothermal reduction to produce magnesium(VCTRM)has attracted more and more attention as its advantages,but it has not been well-practiced in industrial applications and there also is no comprehensive and quantitative analysis of this process.This study quantified the flows of resource and energy for the Pidgeon process and the VCTRM process,then compared and analyzed these two processes with each other from three aspects.The VCTRM process results in 63.14%and 69.16%lower of non-renewable mineral resources and energy consumptions when compared to the Pidgeon process,respectively.Moreover,the low energy consumption(2.675 tce vs.8.681 tce)and material to magnesium ratio(2.953:1 vs.6.429:1)of the VCTRM process,which lead to lower greenhouse gas(GHG)emissions(8.777 t vs.26.337 t)and solid waste generation(0.522 t vs.5.465 t)with a decrease of 66.67%and 90.45%,respectively.Results indicate that the VCTRM process is a more environmentally friendly process for magnesium production with high efficiency but low cost and low pollution,and it shows a good potential to be industrialized in the future after solving the bottleneck problem of the reverse reaction.展开更多
The carbothermal reduction-chlorination-disproportionation of alumina in vacuum was investigated by XRD and thermodynamic analysis. The experiments on alumina and graphite at 1643-1843 K in vacuum were carried out. Th...The carbothermal reduction-chlorination-disproportionation of alumina in vacuum was investigated by XRD and thermodynamic analysis. The experiments on alumina and graphite at 1643-1843 K in vacuum were carried out. The results demonstrate that AlCl3（g） reacts with Al2O（g） or Al（g） generated from the carbothermal reduction of alumina to form AlCl（g）, and the AlCl（g） disproportionates to aluminum and AlCl3（g） at a lower temperature and the reaction rate of AlCl（g） reaches 90% at 980 K and 100 Pa. The aluminum can absorb CO to catalyze its disproportionation to C and CO2, and react backward with CO to form Al4C3, Al2O3, C and CO2, resulting in the aluminum product containing C, Al4C3 and Al2O3. The impurities in the aluminum product decrease as the AlCl（g） disproportionation temperature decreases. AlCl3 condenses at a temperature approximated to the room temperature.展开更多
High purity （99.999% or 5N, mass fraction） indium （In） was obtained through vacuum distillation using a 2N （99%） In as input material under a dynamic vacuum of 5 Pa. The glow discharge mass spectrometry （GDMS）...High purity （99.999% or 5N, mass fraction） indium （In） was obtained through vacuum distillation using a 2N （99%） In as input material under a dynamic vacuum of 5 Pa. The glow discharge mass spectrometry （GDMS） was applied for the analysis of input material and the distilled indium. The results indicate that high-volatile impurities namely Cd, Zn, T1 and Pb can be removed from the indium matrix at the low fraction stage of 1 223 K for 120 min; Low-volatile impurities such as Fe, Ni, Cu, Sn can be reduced at the high fraction stage of 1 323 K for 120 min. The separation coefficient ,8i and activity coefficient Yi of impurities are calculated according to the experiments to fill the inadequate data of the thermodynamics.展开更多
In present work,we investigate production of magnesium by carbothermic reduction under vacuum conditions.The process was divided into two parts,one is reduction process,and the other one is condensation process.The ex...In present work,we investigate production of magnesium by carbothermic reduction under vacuum conditions.The process was divided into two parts,one is reduction process,and the other one is condensation process.The experimental results revealed that during reduction process,the gas-solid reaction between MgO and CO was not occurred at a temperature and pressure of 1723 K and 30-100 Pa respectively.So the main reduction reaction was MgO(_(s))+C(_(s))=Mg(_(g))+CO(_(g))(under vacuum)and reaction type belonged to solid-solid reaction.In Condensation Process,according to a contrast and analysis,the condensation quality of magnesium is associated with CO concentration.The resultant product C was formed and it followed magnesium vapor condensation which prevents mutual combination of two metal droplets to forms the compact condensation produces.Therefore,in order to compact morphological forms of magnesium crystal whiskers,we must control the technical conditions and find the method to separate the magnesium vapor and carbon monoxide.That's the key factor to get better crystalline structure.展开更多
To provide an accurate prediction of the product component dependence of temperature and pressure in vacuum distillation and give convenient and efficient guidance for the designing of the process parameters of indust...To provide an accurate prediction of the product component dependence of temperature and pressure in vacuum distillation and give convenient and efficient guidance for the designing of the process parameters of industrial production, according to the molecular interaction volume model(MIVM), the separation coefficient(β) and vapor-liquid equilibrium composition of Au-Ag alloy at different temperatures are calculated. Combined with the vapor-liquid equilibrium(VLE) theory, the VLE phase diagrams, including the temperature-composition(T-x) and pressure-composition(p-x) diagrams of Au-Ag alloy in vacuum distillation are plotted. The triple points and condensation temperatures of gold and silver vapors are calculated as well. The results show that the β decreases and the contents of gold in vapor phase increase with the distillation temperature increasing. Low pressures have positive effect on the separation of Ag and Au. The difference between the condensation temperatures of gold and silver is about 450 K in the pressure range of 1-10 Pa.展开更多
The activity of components of Sn-Zn binary alloy system was predicted based on the molecular interaction volume model （MIVM）. The calculated values are in good agreement with available experimental data of activitie...The activity of components of Sn-Zn binary alloy system was predicted based on the molecular interaction volume model （MIVM）. The calculated values are in good agreement with available experimental data of activities, which indicates that this model is of stability and reliability because the MIVM has a good physical basis. The vapor-liquid phase equilibrium of Sn-Zn alloy system in vacuum distillation was calculated as a function of the activity coefficient. The results show that the content of Sn in vapor phase is 4.2x 10-7 （mass fraction） while in liquid phase it is 90% （mass fraction） at 1 073 K, and the content of Sn in vapor phase increases with increasing the melt temperature and content of Sn in liquid phase. Vacuum distillation experiments were carried out on Sn-Zn alloy for the proper interpretation of the results of the MIVM in the temperature range of 973-1 273 K under pressures of 15-200 Pa. The experimental results show that the content of Sn in vapor phase is 5x 10 6 （mass fraction） while in liquid phase it is 90% （mass fraction） under the operational condition of 1 073 K, 100 rain and 15 Pa. The experimental results are in good agreement with the predicted values of the MIVM for Zn-Sn binary alloy system.展开更多
In an attempt to develop low-silver brazing filler metals used for hermetic sealing materials in the vacuum interrupter industry,the ternary Ag-50Cu-5Ga low-silver vacuum brazing filler metal was investigated.The melt...In an attempt to develop low-silver brazing filler metals used for hermetic sealing materials in the vacuum interrupter industry,the ternary Ag-50Cu-5Ga low-silver vacuum brazing filler metal was investigated.The melting temperature was measured by differential scanning calorimetry(DSC),and the brazability of Ag-50Cu-5Ga alloy on copper and metallized copper/kovar were ascertained at 850℃under 1×10-4 Pa in this article.The microstructures of the filler metal and the joints have been analyzed by using scanning electron microscopy(SEM),equipped with an energy dispersive spectroscopy.The results show that vacuum brazing was success to join with copper or metallized copper/kovar using Ag-50Cu-5Ga filler and reliable joints were obtained.There were Ag-rich phase,Cu-rich phase and a fine eutectic structure of Ag-based solid solution and Cu-based solid solution in the copper joints and the width of brazing seam is about 60μm.The joints of kovar alloy to copper after surface nickel plating was composed of AgCu eutectic phase,Ag,Cu,Cu2Ga and CuNi2 phase.The tensile strength was 167 MPa and 150 MPa,respectively.The tensile results of joints show that the joint strengths were equivalent to the traditional brazing filler metals.展开更多
By analyzing the gas expansion process from the upstream chamber via an orifice and a very rapid-opening ultra-high vacuum(UHV)gate valve to downstream one,the standard pressure analytical model basedon the dvnamic va...By analyzing the gas expansion process from the upstream chamber via an orifice and a very rapid-opening ultra-high vacuum(UHV)gate valve to downstream one,the standard pressure analytical model basedon the dvnamic vacuum calibration apparatus in millisecond range developed by Lanzhou Institute of Physics(LIP)is deduced theoretically and corrected by real gas characteristics and temperature changes.According to the Kuudsen criterion,there is no free molecular fow regime in the area in front of the orifice during the gas expansion,so the chocked fow approximation is adopted to reduce the difficulty of numerical computation Under this anproxiuatiou and the full opening of the rapid valve,the standard pressure expression is calculated theoretically,and the upstream chamber pressure and temperature changes are obtained by numerical simulation during the gas expansion from 100 kPa to 10kPa.Also,experiments are performed using capacitance diaphragmgauges(model CDG045Dhs),The uncertainties between the measured pressure and the simulated and theoretical ones are 10%and 4.65%,respectively,which indicates that the apparatus can generate predictable pressure changes in the millisecond rauge and the conceptual model can better approximate the calibration results.Einally,the orifice conductance,and the correction factors of real gas characteristics and temperature change to the standard pressure are calculated accordins to the simulation results:the corrected staudard pressure expression is obtained.展开更多
Thermodynamic calculation, ab initio molecular dynamics(AIMD) and vacuum decomposition experiments were performed to study the volatilization behaviors of Mo and S from molybdenite concentrate by vacuum decomposition....Thermodynamic calculation, ab initio molecular dynamics(AIMD) and vacuum decomposition experiments were performed to study the volatilization behaviors of Mo and S from molybdenite concentrate by vacuum decomposition. In thermodynamic calculation, starting decomposition temperatures of reactions were calculated, and saturated vapor pressures of Mo, S and Mo S2 were also analyzed. In AIMD, geometries of the Sn(n≤8), Mom(m≤8) and MomSn(m+n≤8) clusters have been optimized using density functional theory(DFT) with generalized gradient approximation(GGA). And these clusters were simulated in DFT with Cambridge Sequential Total Energy Package(CASTEP) code of Material Studio software. Structures and stabilities of these clusters before and after molecular dynamics simulations were discussed, and diffusion coefficients were also calculated. In vacuum decomposition experiments, relationship between heat preservation time and volatilization rate of Mo and S was obtained, while the constant temperature and chamber pressure were 1823 K and 5–35 Pa, respectively. Above all, both the theoretical and experimental results showed that volatilization behaviors of Mo and S during vacuum decomposition process of molybdenite concentrate were as follows: Mo could partly evaporate into the condensate in the form of clusters, and S could easily evaporate into the condensate.展开更多
Phosphorus is very difficult to remove during the purifying of metallurgical-grade silicon by metallurgical method.In this paper,phosphorus evaporation removal by vacuum arc furnace with electromagnetic stirring was i...Phosphorus is very difficult to remove during the purifying of metallurgical-grade silicon by metallurgical method.In this paper,phosphorus evaporation removal by vacuum arc furnace with electromagnetic stirring was investigated in vacuum weak oxidation atmosphere.The effects of refining time,electromagnetic stirring treatment and initial phosphorus content on the removal behavior of phosphorus in metallurgical-grade silicon were studied in detial. The result shows that the reduction of phosphorus using vacuum arc refining method was very obvious,especially in the first 10 minutes,and the removal rate of phosphorus increased with the refining time.Electromagnetic stirring is also benefit to the removal of phosphorus evaporation,which can be attributed to the improved mobility of phosphorus element from the internal to the surface(i.e.,improved kinetics condition)of melt.It was also observed that high purity sample could be obtained in the initial materials with low phosphorus content.展开更多
The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace.A numerical model for the electromagnetic-thermal-hydrodynamic coupling...The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace.A numerical model for the electromagnetic-thermal-hydrodynamic coupling fields have been developed by using the finite element method(FEM)and a 2D numerical simulation for electromagnetic、 temperature and velocity fields of metallurgical-grade silicon melting in vacuum induction furnace were performed with a software Multi-physics Comsol 3.5a in this paper.The results showed that the temperature field was dependent observably on input power of coils and induction heating times and the maximum temperature gradient in melting pool was 215K in holding time.With the silicon molted gradually a clockwise vortex was come into being for electromagnetic stirring in the smelting poor.The variation of velocity field in melting silicon is mainly influenced with the change of the current intensity and power frequency.The numerical predications of temperature distribution are in good agreement with experiments.展开更多
Vacuum chambers must fulfil ultra-high vacuum requirements while withstanding thermo-mechanical loads. This is particularly true in high energy particle accelerator where interactions of particles with matter may indu...Vacuum chambers must fulfil ultra-high vacuum requirements while withstanding thermo-mechanical loads. This is particularly true in high energy particle accelerator where interactions of particles with matter may induce thermal load, material activation, background… The choice of the material of the vacuum chamber is crucial for the final application. Metals such as stainless steel, copper and aluminium are usually used. Even with outstanding mechanical and physical properties, beryllium is used for very specific applications because of its cost and toxicity.Ceramics such as alumina are usually used for fast magnet vacuum chambers. With the next generation of high energy physics accelerator generation such as CLIC and TLEP, the problematic of high cyclic thermal load induced by synchrotron radiation is raised. This paper aims at defining some figures of merit of different materials with respect to several load scenarios and presents briefly their vacuum compatibility.展开更多
基金financially supported by the Fundamental Research Project of Yunnan Province,China(Nos.202301AW070020,202201AT070229,202105AC160091,202202AB080018).
文摘The vacuum volatilization kinetics of Pb in In-Pb solder was investigated.The results indicate a significant increase in the vacuum volatilization rates of Pb,25In-75Pb,40In-60Pb,and In with increasing temperatures from 923 to 1123 K,system pressure of 3 Pa and holding time of 30 min.The mass transfer coefficients and apparent activation energies of Pb and its alloys were determined at various temperatures.Additionally,a kinetics model was developed to describe Pb vacuum volatilization in high-temperature melts.It is obtained that the vapor mass transfer is the factor limiting the vacuum volatilization rates of Pb and In-Pb alloys under the above specified conditions.
基金supported by the Leading Talents of Industrial Technology in Yunnan Province[grant number 618820190024]the Yunnan Province Nonferrous Metal Vacuum Metallurgy Top Team[grant number 202305AS350012].
文摘The increasing demand for magnesium as a next-generation structural material highlights the significance of incorporating CaF_(2)as a catalyst to enhance the efficiency of vacuum carbothermal reduction of magnesium(VCTRM).This study investigates the thermodynamic theory and catalytic mechanism of CaF_(2)in the VCTRM process.Catalytic reduction experiments and molecular dynamics simulations were conducted to gain a comprehensive understanding of the process.Thermodynamic calculations indicate that in vacuum carbothermal reduction,the primary reaction occurs between MgO and C.Analysis shows that CaF_(2)'s catalytic action primarily involves F^(-),Ca^(2+),and melt eutectic.Our experiments demonstrate that the addition of CaF_(2)significantly increases the reduction rate.Furthermore,the mass loss rate increases with both the quantity of CaF_(2)added and the holding time,stabilizing at additions over 5%.Experiments conducted at temperatures above the melting point of CaF_(2)exhibited a pronounced catalytic effect.The resultant magnesium showed optimal structure and crystallization,with a purity of 87.84%.Notably,while CaF_(2)remained in the residue,it was not detected in the condensate,confirming its catalytic role.Molecular dynamics simulations revealed that molten CaF_(2)sabotages the structure of magnesium oxide,with F^(-)dispersing onto the surface of MgO,thus enhancing the reaction between MgO and C to form CO.However,no chemical reaction was observed between C,MgO,and CaF_(2).The occurrence of the carbothermal reduction reaction at high temperatures depends on the concentration of the reducing agent C,with CaF_(2)influencing the reaction rate.This research elucidates the theoretical and mechanistic foundations of CaF_(2)-catalyzed VCTRM,aligning with the green energy-saving concept and significantly advancing the green and efficient VCTRM process.
文摘Magnesium(Mg)alloys are widely used lightweight structural materials for automobiles and help reduce carbon emissions.However,their use increases the production of Mg alloy scrap,which is recycled at a much lower rate than aluminum,and its greater complexity poses challenges to existing recycling processes.Although vacuum distillation can be used to recycle Mg alloy scrap,this requires optimizing and maximizing metal recirculation,but there has been no thermodynamic analysis of this process.In this study,the feasibility and controllability of separating inclusions and 23 metal impurities were evaluated,and their distribution and removal limits were quantified.Thermodynamic analyses and experimental results showed that inclusions and impurity metals of separation coefficient lgβ_(i)≤-5,including Cu,Fe,Co,and Ni below 0.001 ppm,could be removed from the matrix.All Zn entered the recycled Mg,while impurities with-1<lgβ_(i)<-5 such as Li,Ca,and Mn severely affected the purity of the recycled Mg during the later stage of distillation.Therefore,an optimization strategy for vacuum distillation recycling:lower temperatures and higher system pressures for Zn separation in the early stage,and the early termination of the recovery process in the later stage or a continuous supply of raw melt can also prevent contamination during recycling.The alloying elements Al and Zn in Mg alloy scrap can be further recovered and purified by vacuum distillation when economically feasible,to maximize the recycling of metal resources.
基金supported by the Yunnan Province Nonferrous Metal Vacuum Metallurgy Top Team[No.202305AS350012]。
文摘Magnesium(Mg),as one of the most abundant elements in earth's crust,is the lightest structural metal with extensive applications across various industries.However,the performance of Mg-based products is highly dependent on their impurity levels,and the lack of high-purity Mg,along with efficient purification method,has posed significant challenge to its widespread industrial adoption.This study investigates the impurity behavior in Mg ingots during the vacuum gasification purification process.Through the analysis of binary phase diagrams,iron(Fe)-based foam material was selected for the filtration and purification of Mg vapor in a vacuum tube furnace.A novel approach combining vacuum gasification,vapor purification,and directional condensation is proposed.The effect of filter pore sizes and filtration temperatures on the efficacy of impurity removal was evaluated.Experimental results demonstrate that Fe-based foam with a pore size of 60 ppi,at a filtration temperature of 773 K,effectively removes impurities such as calcium(Ca),potassium(K),sodium(Na),manganese(Mn),silicon(Si),aluminum(Al),and various oxides,sulfides,and chlorides from the vapor phase.Consequently,high-purity Mg with a purity level exceeding 5N3 was obtained in the condensation zone.
基金Project(2010CI009) supported by Science Foundation of Yunnan Province,ChinaProjects(U1202271) supported by the National Natural Science Foundation of China
文摘The feasibility of separation of lead anode slime with low silver by vacuum distillation was analyzed theoretically. The volatilization rates and mass fractions of elements, influenced by distillation temperature, heat preservation time and material thickness, were investigated under laboratory conditions. The experimental results indicate that almost all of lead and bismuth can be separated from silver-contained multicomponent alloy at 1 223 K for 45 min when the chamber pressure maintains at 10-25 Pa. Silver can be easily enriched in the residue and its mass fraction increases from 3.6% to 27.8% when the distillation temperature is between 1 133 K and 1 373 K. Due to the forming ofintermetallic compounds Cu2Sb, Cul0Sb3 and Ag3Sb, the antimony could not be evaporated completely during the vacuum distillation. EDS analysis indicates that the condensate has a columnar crystal structure.
基金supported by the National Natural Science Foundation of China (No. 51104079 and U1202271)Fundamental Research of Yunnan Province (No. 2013FZ033)
文摘Vacuum distillation is a technique suitable for low boiling and melting point materials,to remove the heavy and low vapor pressure impurities at low level.As indium has low melting point and high boiling point,it is suitable for refining by vacuum distillation.First,saturation vapor pressure for major elements in crude indium was calculated by the Clausius–Clay Prang equation,which could approximately predict the temperature and pressure during vacuum distillation process.Second,the activity coefficients for In–Cd,In–Zn,In–Pb,In–Tl at 1373 K,and In–Sn at 1573 K were acquired by means of molecular interaction on volume model.Vapor–liquid equilibrium composition diagrams of those above systems in crude indium were drawn based on activity coefficients.These diagrams could estimate the compositions of products in each process during the refinement of crude indium.Finally,1.2–1.6 ton crude indium was used per day when vacuum distillation experiments were carried out,and experimental results are in good agreement with the predicted values of the vapor–liquid equilibrium composition diagrams.
基金Foundation item:Project(No.51304095)supported by National Natural Science Foundation of ChinaScience and Technology Planning Project of Yunnan Province,China(No.S2013FZ029)Personnel training Funds of Kunming University of Science and Technology,China(No.14118665).
文摘The aim of this paper is to experimentally investigate the behavior of magnesium and carbon monoxide vapor in the carbothermic reduction of magnesia at condensing zone temperatures ranging from 923 K to 1223 K.The phase,surface morphology,and composition of the condensates obtained were examined by means of scanning electron microscopy and energy-dispersive X-ray spectroscopy.The main findings of this paper include:the reverse reaction products,carbon and magnesium oxide,were formed following the process of magnesium vapor condensation,preventing two metal clusters from mutually combining.Moreover,the nearer the temperature of the condensation zone approached the liquid transformation temperature(810-910 K),the lower the rate of the reverse reaction between carbon monoxide and magnesium vapor.Decrease in the rate of the reverse reaction of magnesium was possible by controlling the condensation temperature.
基金Project(U0837604) supported by the Natural Science Foundation of Yunnan Province,ChinaProject(Jinchuan 201114) supported by the Pre Research Foundation of Jinchuan Group Ltd.,ChinaProject(2011148) supported by the Analysis and Testing Funds of Kunming University of Science and Technology,China
文摘Carbothermic reduction alumina in vacuum was conducted, and the products were analysed by means of XRD and gas chromatography. Thermodynamic analysis shows that in vacuum the initial carbothermic reduction reaction temperature reduces compared with that under normal pressure, and the preferential order of products is Al404C, Al4C3, Al2OC, Al20 and A1. Experiment results show that the carbothermic reduction products of alumina are A1404C and A14C3, and neither A12OC, Al20 or Al was found. During the carbothermic reduction process, the reaction rate of Al203 and carbon decreases gradually with increasing time. Meanwhile, lower system pressure or higher temperature is beneficial to the carbothermic reduction of alumina process. A1404C is firstly formed in the carbothermic reaction, and then A14C3 is formed in lower system pressure or at higher temperature.
基金the Yunnan Ten Thousand Talents Plan Industrial Technology Champion Project Foundation of China(No.YNWR-CYJS-2018-015)Basic Research Project of Yunnan Province(No.2019FB080).
文摘With the fast development of the application of magnesium based alloys,the demand for primary magnesium is increasing dramatically all over the world.The Pidgeon process is the most widely used process for producing magnesium in China,but suffers from problems such as high energy,resource consumption and environmental pollution.While the process of vacuum carbothermal reduction to produce magnesium(VCTRM)has attracted more and more attention as its advantages,but it has not been well-practiced in industrial applications and there also is no comprehensive and quantitative analysis of this process.This study quantified the flows of resource and energy for the Pidgeon process and the VCTRM process,then compared and analyzed these two processes with each other from three aspects.The VCTRM process results in 63.14%and 69.16%lower of non-renewable mineral resources and energy consumptions when compared to the Pidgeon process,respectively.Moreover,the low energy consumption(2.675 tce vs.8.681 tce)and material to magnesium ratio(2.953:1 vs.6.429:1)of the VCTRM process,which lead to lower greenhouse gas(GHG)emissions(8.777 t vs.26.337 t)and solid waste generation(0.522 t vs.5.465 t)with a decrease of 66.67%and 90.45%,respectively.Results indicate that the VCTRM process is a more environmentally friendly process for magnesium production with high efficiency but low cost and low pollution,and it shows a good potential to be industrialized in the future after solving the bottleneck problem of the reverse reaction.
基金Project (u0837604) supported by the Joint Funds of the National Natural Science Foundation of China and Yunnan Province
文摘The carbothermal reduction-chlorination-disproportionation of alumina in vacuum was investigated by XRD and thermodynamic analysis. The experiments on alumina and graphite at 1643-1843 K in vacuum were carried out. The results demonstrate that AlCl3（g） reacts with Al2O（g） or Al（g） generated from the carbothermal reduction of alumina to form AlCl（g）, and the AlCl（g） disproportionates to aluminum and AlCl3（g） at a lower temperature and the reaction rate of AlCl（g） reaches 90% at 980 K and 100 Pa. The aluminum can absorb CO to catalyze its disproportionation to C and CO2, and react backward with CO to form Al4C3, Al2O3, C and CO2, resulting in the aluminum product containing C, Al4C3 and Al2O3. The impurities in the aluminum product decrease as the AlCl（g） disproportionation temperature decreases. AlCl3 condenses at a temperature approximated to the room temperature.
基金Project(2009AA003) supported by Science and Technology Innovation Plan of Yunnan Province, China
文摘High purity （99.999% or 5N, mass fraction） indium （In） was obtained through vacuum distillation using a 2N （99%） In as input material under a dynamic vacuum of 5 Pa. The glow discharge mass spectrometry （GDMS） was applied for the analysis of input material and the distilled indium. The results indicate that high-volatile impurities namely Cd, Zn, T1 and Pb can be removed from the indium matrix at the low fraction stage of 1 223 K for 120 min; Low-volatile impurities such as Fe, Ni, Cu, Sn can be reduced at the high fraction stage of 1 323 K for 120 min. The separation coefficient ,8i and activity coefficient Yi of impurities are calculated according to the experiments to fill the inadequate data of the thermodynamics.
基金Foundation item:Project supported by National Natural Science Foundation of China(No.51304095)the Personnel Training Funds of Kunming University of Science and Technology,China(No.14118665)Educational Commission of Yunnan Province,China(No.14051618).
文摘In present work,we investigate production of magnesium by carbothermic reduction under vacuum conditions.The process was divided into two parts,one is reduction process,and the other one is condensation process.The experimental results revealed that during reduction process,the gas-solid reaction between MgO and CO was not occurred at a temperature and pressure of 1723 K and 30-100 Pa respectively.So the main reduction reaction was MgO(_(s))+C(_(s))=Mg(_(g))+CO(_(g))(under vacuum)and reaction type belonged to solid-solid reaction.In Condensation Process,according to a contrast and analysis,the condensation quality of magnesium is associated with CO concentration.The resultant product C was formed and it followed magnesium vapor condensation which prevents mutual combination of two metal droplets to forms the compact condensation produces.Therefore,in order to compact morphological forms of magnesium crystal whiskers,we must control the technical conditions and find the method to separate the magnesium vapor and carbon monoxide.That's the key factor to get better crystalline structure.
基金supported by the National Natural Science Foundation of China (No.52064029)Yunling Scholarship of Yunnan Province Ten-Thousand Plan,China (No.KKRC201952012)Yunnan Province Ten Thousand Talents Program-Youth Top Talent Project,China (No.2018-73)。
文摘To provide an accurate prediction of the product component dependence of temperature and pressure in vacuum distillation and give convenient and efficient guidance for the designing of the process parameters of industrial production, according to the molecular interaction volume model(MIVM), the separation coefficient(β) and vapor-liquid equilibrium composition of Au-Ag alloy at different temperatures are calculated. Combined with the vapor-liquid equilibrium(VLE) theory, the VLE phase diagrams, including the temperature-composition(T-x) and pressure-composition(p-x) diagrams of Au-Ag alloy in vacuum distillation are plotted. The triple points and condensation temperatures of gold and silver vapors are calculated as well. The results show that the β decreases and the contents of gold in vapor phase increase with the distillation temperature increasing. Low pressures have positive effect on the separation of Ag and Au. The difference between the condensation temperatures of gold and silver is about 450 K in the pressure range of 1-10 Pa.
基金Project(2012CB722803) supported by the Key Project of National Basic Research and Development Program of ChinaProject(2011FA008)supported by the Key Project of Science and Technology Program of Yunnan Province,China
文摘The activity of components of Sn-Zn binary alloy system was predicted based on the molecular interaction volume model （MIVM）. The calculated values are in good agreement with available experimental data of activities, which indicates that this model is of stability and reliability because the MIVM has a good physical basis. The vapor-liquid phase equilibrium of Sn-Zn alloy system in vacuum distillation was calculated as a function of the activity coefficient. The results show that the content of Sn in vapor phase is 4.2x 10-7 （mass fraction） while in liquid phase it is 90% （mass fraction） at 1 073 K, and the content of Sn in vapor phase increases with increasing the melt temperature and content of Sn in liquid phase. Vacuum distillation experiments were carried out on Sn-Zn alloy for the proper interpretation of the results of the MIVM in the temperature range of 973-1 273 K under pressures of 15-200 Pa. The experimental results show that the content of Sn in vapor phase is 5x 10 6 （mass fraction） while in liquid phase it is 90% （mass fraction） under the operational condition of 1 073 K, 100 rain and 15 Pa. The experimental results are in good agreement with the predicted values of the MIVM for Zn-Sn binary alloy system.
基金the National Key R&D Program of China(Grant No.2017YFB0305702).
文摘In an attempt to develop low-silver brazing filler metals used for hermetic sealing materials in the vacuum interrupter industry,the ternary Ag-50Cu-5Ga low-silver vacuum brazing filler metal was investigated.The melting temperature was measured by differential scanning calorimetry(DSC),and the brazability of Ag-50Cu-5Ga alloy on copper and metallized copper/kovar were ascertained at 850℃under 1×10-4 Pa in this article.The microstructures of the filler metal and the joints have been analyzed by using scanning electron microscopy(SEM),equipped with an energy dispersive spectroscopy.The results show that vacuum brazing was success to join with copper or metallized copper/kovar using Ag-50Cu-5Ga filler and reliable joints were obtained.There were Ag-rich phase,Cu-rich phase and a fine eutectic structure of Ag-based solid solution and Cu-based solid solution in the copper joints and the width of brazing seam is about 60μm.The joints of kovar alloy to copper after surface nickel plating was composed of AgCu eutectic phase,Ag,Cu,Cu2Ga and CuNi2 phase.The tensile strength was 167 MPa and 150 MPa,respectively.The tensile results of joints show that the joint strengths were equivalent to the traditional brazing filler metals.
基金the National Natural Science Foundation of China(No.61501212)。
文摘By analyzing the gas expansion process from the upstream chamber via an orifice and a very rapid-opening ultra-high vacuum(UHV)gate valve to downstream one,the standard pressure analytical model basedon the dvnamic vacuum calibration apparatus in millisecond range developed by Lanzhou Institute of Physics(LIP)is deduced theoretically and corrected by real gas characteristics and temperature changes.According to the Kuudsen criterion,there is no free molecular fow regime in the area in front of the orifice during the gas expansion,so the chocked fow approximation is adopted to reduce the difficulty of numerical computation Under this anproxiuatiou and the full opening of the rapid valve,the standard pressure expression is calculated theoretically,and the upstream chamber pressure and temperature changes are obtained by numerical simulation during the gas expansion from 100 kPa to 10kPa.Also,experiments are performed using capacitance diaphragmgauges(model CDG045Dhs),The uncertainties between the measured pressure and the simulated and theoretical ones are 10%and 4.65%,respectively,which indicates that the apparatus can generate predictable pressure changes in the millisecond rauge and the conceptual model can better approximate the calibration results.Einally,the orifice conductance,and the correction factors of real gas characteristics and temperature change to the standard pressure are calculated accordins to the simulation results:the corrected staudard pressure expression is obtained.
基金Projects(1202271,51104078)supported by the National Natural Science Foundation of ChinaProject(IRT1250)supported by the Program for Innovative Research Team in University of Ministry of Education of China
文摘Thermodynamic calculation, ab initio molecular dynamics(AIMD) and vacuum decomposition experiments were performed to study the volatilization behaviors of Mo and S from molybdenite concentrate by vacuum decomposition. In thermodynamic calculation, starting decomposition temperatures of reactions were calculated, and saturated vapor pressures of Mo, S and Mo S2 were also analyzed. In AIMD, geometries of the Sn(n≤8), Mom(m≤8) and MomSn(m+n≤8) clusters have been optimized using density functional theory(DFT) with generalized gradient approximation(GGA). And these clusters were simulated in DFT with Cambridge Sequential Total Energy Package(CASTEP) code of Material Studio software. Structures and stabilities of these clusters before and after molecular dynamics simulations were discussed, and diffusion coefficients were also calculated. In vacuum decomposition experiments, relationship between heat preservation time and volatilization rate of Mo and S was obtained, while the constant temperature and chamber pressure were 1823 K and 5–35 Pa, respectively. Above all, both the theoretical and experimental results showed that volatilization behaviors of Mo and S during vacuum decomposition process of molybdenite concentrate were as follows: Mo could partly evaporate into the condensate in the form of clusters, and S could easily evaporate into the condensate.
基金Item Sponsored by National Natural Science Foundation of China[No.U1137601]National Science and Technology Support Program[No.2011BAE03B01]+1 种基金Educational Commission Foundation of Yunnan Province[No.2001Z021]Natural Science Foundation of Yunnan Province[No.KKSY201252078]
文摘Phosphorus is very difficult to remove during the purifying of metallurgical-grade silicon by metallurgical method.In this paper,phosphorus evaporation removal by vacuum arc furnace with electromagnetic stirring was investigated in vacuum weak oxidation atmosphere.The effects of refining time,electromagnetic stirring treatment and initial phosphorus content on the removal behavior of phosphorus in metallurgical-grade silicon were studied in detial. The result shows that the reduction of phosphorus using vacuum arc refining method was very obvious,especially in the first 10 minutes,and the removal rate of phosphorus increased with the refining time.Electromagnetic stirring is also benefit to the removal of phosphorus evaporation,which can be attributed to the improved mobility of phosphorus element from the internal to the surface(i.e.,improved kinetics condition)of melt.It was also observed that high purity sample could be obtained in the initial materials with low phosphorus content.
基金Item Sponsored by the NSFC project (51066003u1137601) +1 种基金National science & technology support plan project (2011BAE03B01) Scientific Research Foundation Project (2010Y408) of Yunnan Province Education Department
文摘The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace.A numerical model for the electromagnetic-thermal-hydrodynamic coupling fields have been developed by using the finite element method(FEM)and a 2D numerical simulation for electromagnetic、 temperature and velocity fields of metallurgical-grade silicon melting in vacuum induction furnace were performed with a software Multi-physics Comsol 3.5a in this paper.The results showed that the temperature field was dependent observably on input power of coils and induction heating times and the maximum temperature gradient in melting pool was 215K in holding time.With the silicon molted gradually a clockwise vortex was come into being for electromagnetic stirring in the smelting poor.The variation of velocity field in melting silicon is mainly influenced with the change of the current intensity and power frequency.The numerical predications of temperature distribution are in good agreement with experiments.
文摘Vacuum chambers must fulfil ultra-high vacuum requirements while withstanding thermo-mechanical loads. This is particularly true in high energy particle accelerator where interactions of particles with matter may induce thermal load, material activation, background… The choice of the material of the vacuum chamber is crucial for the final application. Metals such as stainless steel, copper and aluminium are usually used. Even with outstanding mechanical and physical properties, beryllium is used for very specific applications because of its cost and toxicity.Ceramics such as alumina are usually used for fast magnet vacuum chambers. With the next generation of high energy physics accelerator generation such as CLIC and TLEP, the problematic of high cyclic thermal load induced by synchrotron radiation is raised. This paper aims at defining some figures of merit of different materials with respect to several load scenarios and presents briefly their vacuum compatibility.
