We investigated the influence of the growth temperature, O_(2) flow, molar ratio between Ga_(2)O_(3) powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire(0001) substrat...We investigated the influence of the growth temperature, O_(2) flow, molar ratio between Ga_(2)O_(3) powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire(0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga_(2)O_(3) illustrate that β-Ga_(2)O_(3) growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga_(2)O_(3) films was produced when the O_(2) flow was 20 sccm. To guarantee that β-Ga_(2)O_(3) films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga_(2)O_(3) powder should be set at 10 : 1.展开更多
Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the...Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the addition of additive AlF_(3)(0,0.5%,1.0%,1.5%,2.0%and 2.5%,by mass)on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB_(2)-ZrO_(2)-SiC composite powder can be synthesized by carbothermal reduction at 1500℃in flowing argon atmosphere;ZrB_(2) and ZrO_(2) are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB_(2) increases,the amounts of m-ZrO_(2) and SiC decrease,and the total amount of non-oxides ZrB_(2),SiC and ZrC gradually increases;the optimal soaking time is 3 h;(3)compared with the sample without AlF_(3),the sample with 0.5% AlF_(3) has decreased m-ZrO_(2)amount,noticeably increased ZrB_(2) amount but decreased SiC amount;however,when the addition of AlF_(3) increases from 0.5%to 2.5%,the m-ZrO_(2) amount increases,the ZrB_(2)amount decreases,and the SiC amount changes slightly;the optimum AlF_(3)addition is 0.5%.展开更多
For the purpose of exploring a potential process to produce FeMn,the effects of microwave heating on the carbothermal reduction characteristics of oxidized Mn ore was investigated.The microwave heating curve of the mi...For the purpose of exploring a potential process to produce FeMn,the effects of microwave heating on the carbothermal reduction characteristics of oxidized Mn ore was investigated.The microwave heating curve of the mixture of oxidized Mn ore and coke was analyzed in association with the characterization of dielectric properties.The comparative experiments were conducted on the carbothermal reductions through conventional and microwave heatings at temperatures ranging from 973 to 1373 K.The thermogravimetric analysis showed that carbothermal reactions under microwave heating proceeded to a greater extent and at a faster pace compared with those under conventional heating.The metal phases were observed in the microstructures only under microwave heating.The carbothermal reduction process under microwave heating was discussed.The electric and magnetic susceptibility differences were introduced into the thermodynamics analysis for the formation of metal Mn.The developed thermodynamics considered that microwave heating could make the reduction of MnO to Mn more accessible and increase the reduction extent.展开更多
A thermodynamical calculation shows that AlN powders were synthesized in the process bythe overall reaction Al2O3(s)+3C(s)+N2(g)=2AlN(s)+3CO(g) and its minimum reaction tem-perature T0=1852 K, if all reactants and pro...A thermodynamical calculation shows that AlN powders were synthesized in the process bythe overall reaction Al2O3(s)+3C(s)+N2(g)=2AlN(s)+3CO(g) and its minimum reaction tem-perature T0=1852 K, if all reactants and products were in standard states. ln the practicalexperiments, AlN phase appeared obviously at only 1300℃, the major reasons are related to thepartial pressure of its gaseous product pco and the mixed free energy. The synthesis temperaturecould be lowered by either increasing N2 flow rate or elevating N2 pressure. On the other hand，as the temperature decreases, the equilibrium constant Km also reduces, and the reducing ratestrongly depends on the temperature： the lower the temperature, the higher the rate.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 of MgO and Al_(2)O_(3) in argon flow at low pressure allows to lower the onset temperature of metal vapor formation.Thermodynamic calculations indicate that metal formation begins at 1400 an...The carbothermal reduction of MgO and Al_(2)O_(3) in argon flow at low pressure allows to lower the onset temperature of metal vapor formation.Thermodynamic calculations indicate that metal formation begins at 1400 and 1700 K for a primary vacuum(1000 Pa),respectively,for Mg and Al.In the experimental section,concentrated solar energy was used for the process heating in order to favor energy savings.The products of the reaction between MgO or Al_(2)O_(3) and 2 varieties of carbon(graphite,carbon black)in flowing argon atmosphere at a total pressure of around 1000 to 1600 Pa were studied using X-ray diffraction,and microstructure observations revealed the formation of metallic nanopowders with some by-products.Metallic conversions close to 45 wt%and 52 wt%,respectively,for Mg and Al,were obtained.The low conversion yield of the carbothermal reduction of MgO can be attributed to a backward reaction reforming MgO powder and to a sintering process between oxide particles at high temperature.Aluminum production challenge is to avoid formation of undesired by-products:Al_(2)O,Al_(4)C_(3) and Al-oxycarbides.Advantages and weaknesses of the used process are described and some improvements are proposed to increase metallic yields.展开更多
Most of researchers believed that the developments on the condensation of magnesium produced by carbothermic reduction just concentrated on two process routes:the“quench”route and the“solvent”route.But this paper ...Most of researchers believed that the developments on the condensation of magnesium produced by carbothermic reduction just concentrated on two process routes:the“quench”route and the“solvent”route.But this paper will briefly analyzes the major challenges in magnesium vapor condensation during the vacuum carbothermic reduction of calcined dolomite,on equipment upgrade,heat transfers alter,to achieve condensation control and production collection.Solutions are then proposed using theoretical calculations and experiment results.Comparative analysis of the experiment results shows that the burning and even explosion of condensation products during the vacuum carbothermic reduction of calcined dolomite are mainly due to the burning of crystallized powder magnesium,which results from the self-ignition of alkali metals.Finally,this paper proposes a multistage condensation solution to improve traditional vacuum condensation equipment.And result show that the condensation equipment can effectively mitigate the burning and loss during condensation,also the morphology of the condensation products clearly improved,the grain size increased,and the oxidation rate decreased.The potassium/sodium vapor and the magnesium vapor were separately condensed.展开更多
The effects of mechanical activation on particle size distribution,crystalline phase,morphology,and mechanical energy storage of nickel slag were studied.Then,the direct reduction experiments of mechanically activated...The effects of mechanical activation on particle size distribution,crystalline phase,morphology,and mechanical energy storage of nickel slag were studied.Then,the direct reduction experiments of mechanically activated nickel slag mixed with reducing agent graphite powder were performed under conditions of 873-1273 K and reduction for 30-70 min.The results show that after 12 h of activation,90%of the nickel slag has a particle diameter less than 1.05 pm,and the total energy storage is 1790.4 kJ mol^(-1).With the extension of the mechanical activation duration,the intensity of the dift'raction peaks of the main crystalline phases Fe_(2)SiO_(4) and Mg2SiO4 in the nickel slag decreases.Mechanical activation is also an effective means to enhance the reduction of nickel slag.With the extension of the activation time,the reduction effect of the nickel slag and metallization degree increase.After 12 h of mechanical activation,the nickel slag was reduced at 1273 K for 70 min,and the metallization degree of the reduced product could reach 83.12%.展开更多
High-quality ferrovanadium nitride(FeV45N,FeV55N and Fe65N)was fabricated using the raw materials of Fe_(3)O_(4),V_(2)O_(5) and graphite via carbothermal reduction nitridation method.Compared with the traditional meth...High-quality ferrovanadium nitride(FeV45N,FeV55N and Fe65N)was fabricated using the raw materials of Fe_(3)O_(4),V_(2)O_(5) and graphite via carbothermal reduction nitridation method.Compared with the traditional methods,it shortens the production process of ferrovanadium nitride by avoiding the preparation of ferrovanadium.The effects of C/O molar ratio and reaction temperature on phase transition,density,carbon,oxygen and nitrogen contents and microstructure were investigated.The appropriate C/O molar ratio is crucial to obtain the products with high nitrogen content.It is also found that a higher temperature is beneficial for the densification,and the density of the products obtained at 1550℃ is much higher than that at 1500℃.Moreover,a higher temperature contributes to the increase in nitrogen content owing to the higher reaction kinetics.The carbothermal reduction nitridation method is proved to be a facile route to fabricate cost-effective ferrovanadium nitride and is possible to be applied for industrial production.展开更多
Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate(VTC) were investigated. It was found that calcium compounds had great effects on the metallization rate of the reducti...Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate(VTC) were investigated. It was found that calcium compounds had great effects on the metallization rate of the reduction product, the order of the metallization rate of reduction product being CaCO3 > no additive > CaSO4 > CaCl2, which indicated that the addition of CaCO3 was more conducive to promoting the reduction of iron than other calcium compounds. Gas analysis showed that there were mainly two processes in the carbothermic reduction of VTC, a solid–solid and a solid–gas reaction. The concentrations of CO and CO2 were highest when CaCO3 was added, while that in a roasting system decreased the most when CaCl2 was added. X-ray diffraction(XRD) analysis showed that calcium compounds could change the reduction process of ilmenite in VTC. The phase compositions of the reduction products were changed from metallic iron(Fe) and anosovite(FeTi2O5) to metallic iron(Fe) and perovekite(CaTiO3) when calcium compounds were added. Additionally, CaSO4 and CaCl2 could significantly promote the growth of metallic iron particles, though the existence of Fe-bearing Mg2TiO4 in reduction products was not conducive to the reduction of iron. The formation of FeS would further hinder the reduction of iron after adding CaSO4.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
The carbothermic reduction of vanadium titanomagnetite concentrate(VTC)with the assistance of Na_(2)CO_(3)was conducted in an argon atmosphere between 1073 and 1473 K.X-ray diffraction and scanning electron microscopy...The carbothermic reduction of vanadium titanomagnetite concentrate(VTC)with the assistance of Na_(2)CO_(3)was conducted in an argon atmosphere between 1073 and 1473 K.X-ray diffraction and scanning electron microscopy were used to investigate the phase transformations during the reaction.By investigating the reaction between VTC and Na_(2)CO_(3),it was concluded that molten Na_(2)CO_(3)broke the structure of titanomagnetite by combining with the acidic oxides(Fe_(2)O_(3),TiO_(2),Al_(2)O_(3),and SiO_(2))to form a Na-rich melt and release FeO and MgO.Therefore,Na_(2)CO_(3)accelerated the reduction rate.In addition,adding Na_(2)CO_(3)also benefited the agglomeration of iron particles and the slag–metal separation by decreasing the viscosity of the slag.Thus,Na_(2)CO_(3)assisted carbothermic reduction is a promising method for treating VTC at low temperatures.展开更多
The formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate(VTC)by adding CaCO3 was investigated.Thermodynamic analysis was employed to show the feasibility of calcium titan...The formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate(VTC)by adding CaCO3 was investigated.Thermodynamic analysis was employed to show the feasibility of calcium titanate formation by the reaction of ilmenite and Ca CO3 in a reductive atmosphere,where ilmenite is more easily reduced by CO or carbon in the presence of CaCO3.The effects of CaCO3 dosage and reduction temperature on the phase transformation and metallization degree were also investigated in an actual roasting test.Appropriate increase of CaCO3 dosages and reduction temperatures were found to be conducive to the formation of calcium titanate,and the optimum conditions were a CaCO3 dosage of 18 wt%and a reduction temperature of 1400°C.Additionally,scanning electron microscopy–energy dispersive spectrometry(SEM–EDS)analysis shows that calcium titanate produced via the carbothermic reduction of VTC by CaCO3 addition was of higher purity with particle size approximately 50μm.Hence,the separation of calcium titanate and metallic iron will be the focus in the future study.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
The Gibbs free energy and critical reaction conditions of preparing Mg and Ca metal by carbothermic reducing calcined dolomite were calculated and analyzed.New thermodynamic criterion for reduction reaction,including ...The Gibbs free energy and critical reaction conditions of preparing Mg and Ca metal by carbothermic reducing calcined dolomite were calculated and analyzed.New thermodynamic criterion for reduction reaction,including the critical temperature and vacuum degree,was studied.The results show that:when T/P^(0.0449)<1199.2,neither MgO nor CaO can be reduced by carbon;when T/P^(0.0449)≥1199.2 and T/P^(0.0462)<1350.9,MgO can be reduced while CaO can not be;when T/P^(0.0462)≥1350.9,both MgO and CaO can be reduced.According to the requirements,we can obtain only Mg,Mg first then Ca,Mg and Ca simultaneously by controlling temperature,vacuum degree or both of them properly,by carbothermic reducing calcined dolomite.展开更多
As alkali additive, KCl catalyzes effectively the carbothermic reduction of pre-oxidized ilmenite, and the catalytic effect becomes more remarkable as the amount of KCl increases. During the carbothermic reduction, th...As alkali additive, KCl catalyzes effectively the carbothermic reduction of pre-oxidized ilmenite, and the catalytic effect becomes more remarkable as the amount of KCl increases. During the carbothermic reduction, the gaseous product consists mainly of CO, and the partial pressure of which increases with reaction temperature. The EPMA and XPS of the partially reduced ilmenite ore and that of the used graphite as reductant showed that the potassium ions enter both ilmenite particles and graphite powders during reduction. The above-mentioned phenomena result in the distortion of ilmenite and carbon structure by potassium ions and reaction activity of carbon and ilmenite was enhanced. As a result, the overall carbothermic reduction was catalyzed by KCl.展开更多
A computer monitoring thermogravimetric system was used to study the effect of alkali chlorides(MCl, M=Li, Na, K and Cs) on the carbothermic reduction of pre oxidized ilmenite in the course of a linear rise in tempera...A computer monitoring thermogravimetric system was used to study the effect of alkali chlorides(MCl, M=Li, Na, K and Cs) on the carbothermic reduction of pre oxidized ilmenite in the course of a linear rise in temperature from 600 ℃ to 1 000 ℃. The experimental results indicate that all the alkali chlorides can speed up the reduction process of pre oxidized ilmenite, moreover, KCl is the most effective catalyst of the chlorides, while the catalytic effects of LiCl and CsCl are relatively weaker. It seems that the catalytic mechanism of LiCl is different from those of the other alkali chlorides. The cross sectional morphology of the partially reduced pre oxidized ilmenite particles and the distribution of potassium ions within them were examined by means of scanning electronic microscopy and electronic probe microanalysis, respectively, which shows that the reduction proceeds topochemically and the alkali ion enriches at the periphery of the particles.[展开更多
Among nitride fibers,aluminum nitride(AlN)fibers have been developed for various advanced applications due to their mechanical flexibility,high thermal conductivity,and excellent electrical insulation and chemical sta...Among nitride fibers,aluminum nitride(AlN)fibers have been developed for various advanced applications due to their mechanical flexibility,high thermal conductivity,and excellent electrical insulation and chemical stability.This article presents an overview on the recent progress of AlN fibers.The properties of AlN,particularly the thermal conductivity of AlN in polymer matrix composites are introduced.Afterward,two major approaches,carbothermal reduction and nitriding polycrystalline alumina fiber,for the preparation of AlN fibers are discussed.The carbothermal reduction includes electrospinning,solution blow spinning,and chemical vapor deposition.Furthermore,some perspectives on the future directions for the preparation and application of fibrous AlN are highlighted.This review is expected to provide readers with valuable guidance on the preparation of AlN fibers and inspire researchers to explore more potential applications.展开更多
Carbothermal reduction using biochar(BC)is a green and effective method of synthesizing BCsupported nanoscale zero-valent iron(nanoFe^(0))composites.However,the effect of BC surface area on the structure,distribution,...Carbothermal reduction using biochar(BC)is a green and effective method of synthesizing BCsupported nanoscale zero-valent iron(nanoFe^(0))composites.However,the effect of BC surface area on the structure,distribution,and performance such as the heavy metal uptake capacity of nanoFe^(0)particles remains unclear.Soybean stover-based BCs with different surface areas(1.7−1472 m^(2)/g)were prepared in this study.They have been used for in-situ synthesis BCs-supported nanoFe^(0)particlesthrough carbothermal reduction of ferrous chloride.The BCs-supported nanoFe^(0)particles were found to be covered with graphene shells and dispersed onto BC surfaces,forming the BC-supported graphene-encapsulated nanoFe^(0)(BC-G@Fe^(0))composite.These graphene shells covering the nanoFe^(0)particles were formed because of gaseous carbon evolved from biomass carbonization reacting with iron oxides/iron salts.Increasing BC surface area decreased the average diameters of nanoFe^(0)particles,indicating a higher BC surface area alleviated the aggregation of nanoFe^(0)particles,which resulted in higher heavy metal uptake capacity.At the optimized condition,BC-G@Fe^(0)composite exhibited uptake capacities of 124.4,121.8,254.5,and 48.0 mg/g for Cu^(2+),Pb^(2+),Ag^(+),and As^(3+),respectively(pH 5,25℃).Moreover,the BC-G@Fe^(0)composite also demonstrated high stability for Cu^(2+)removal from the fixed-bed continuous flow,in which 1 g of BC-G@Fe^(0)can work for 120 h in a 4 mg/L Cu^(2+)flow continually and clean 28.6 L Cu^(2+)contaminated water.Furthermore,the BC-G@Fe^(0)composite can effectively immobilize the bioavailable As^(3+)from the contaminated soil,i.e.,5%(w)of BC-G@Fe^(0)composite addition can immobilize up to 92.2%bioavailable As^(3+)from the contaminated soil.展开更多
In view of the difficulty of extracting iron from Bayer red mud,a new idea of adding laterite nickel ore into red mud was proposed to prepare a high value-added product.Toward this,the influences of laterite nickel or...In view of the difficulty of extracting iron from Bayer red mud,a new idea of adding laterite nickel ore into red mud was proposed to prepare a high value-added product.Toward this,the influences of laterite nickel ore on thermodynamic reaction,slagging and smelting reduction of extracting iron from red mud were studied.The results indicated that the product of extracting iron from red mud(R100)was changed with the addition of laterite nickel ore(R70L30).The slag of R100 was strongly basic,while the R70L30 was weakly acidic with composition closer to the ideal blast furnace slag.The metal recovery of R100 was 75.16%and that of R70L30 was 94.05%.At the same temperature,the slag viscosity of R70L30 was significantly lower than that of R100,which proved that laterite nickel ore can adjust the basicity,reduce melting point of slag and improve metal recovery.Because Fe,Ni and Cr in red mud and laterite nickel ore can be reduced sufficiently,a low Ni–Cr alloy cast iron can be directly prepared.展开更多
基金supported by the National Natural Science Foundation of China under Grant 62104024, Grant 11875097, Grant 12075045, Grant 11975257, Grant 11961141014, and Grant 62074146the Fundamental Research Funds for the Central Universities under Grant DUT19RC (3)074the Natural Science Foundation of Liaoning Province under Grant 2021MS124, Grant 2022020474JH2/1013。
文摘We investigated the influence of the growth temperature, O_(2) flow, molar ratio between Ga_(2)O_(3) powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire(0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga_(2)O_(3) illustrate that β-Ga_(2)O_(3) growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga_(2)O_(3) films was produced when the O_(2) flow was 20 sccm. To guarantee that β-Ga_(2)O_(3) films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga_(2)O_(3) powder should be set at 10 : 1.
基金supported by National Natural Science Foundation of China(52172031 and 51872266)Henan Provincial Science and Technology Research Project(222102230030).
文摘Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the addition of additive AlF_(3)(0,0.5%,1.0%,1.5%,2.0%and 2.5%,by mass)on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB_(2)-ZrO_(2)-SiC composite powder can be synthesized by carbothermal reduction at 1500℃in flowing argon atmosphere;ZrB_(2) and ZrO_(2) are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB_(2) increases,the amounts of m-ZrO_(2) and SiC decrease,and the total amount of non-oxides ZrB_(2),SiC and ZrC gradually increases;the optimal soaking time is 3 h;(3)compared with the sample without AlF_(3),the sample with 0.5% AlF_(3) has decreased m-ZrO_(2)amount,noticeably increased ZrB_(2) amount but decreased SiC amount;however,when the addition of AlF_(3) increases from 0.5%to 2.5%,the m-ZrO_(2) amount increases,the ZrB_(2)amount decreases,and the SiC amount changes slightly;the optimum AlF_(3)addition is 0.5%.
基金This work was financially supported by the National Natural Science Foundation of China(No.51704083).
文摘For the purpose of exploring a potential process to produce FeMn,the effects of microwave heating on the carbothermal reduction characteristics of oxidized Mn ore was investigated.The microwave heating curve of the mixture of oxidized Mn ore and coke was analyzed in association with the characterization of dielectric properties.The comparative experiments were conducted on the carbothermal reductions through conventional and microwave heatings at temperatures ranging from 973 to 1373 K.The thermogravimetric analysis showed that carbothermal reactions under microwave heating proceeded to a greater extent and at a faster pace compared with those under conventional heating.The metal phases were observed in the microstructures only under microwave heating.The carbothermal reduction process under microwave heating was discussed.The electric and magnetic susceptibility differences were introduced into the thermodynamics analysis for the formation of metal Mn.The developed thermodynamics considered that microwave heating could make the reduction of MnO to Mn more accessible and increase the reduction extent.
文摘A thermodynamical calculation shows that AlN powders were synthesized in the process bythe overall reaction Al2O3(s)+3C(s)+N2(g)=2AlN(s)+3CO(g) and its minimum reaction tem-perature T0=1852 K, if all reactants and products were in standard states. ln the practicalexperiments, AlN phase appeared obviously at only 1300℃, the major reasons are related to thepartial pressure of its gaseous product pco and the mixed free energy. The synthesis temperaturecould be lowered by either increasing N2 flow rate or elevating N2 pressure. On the other hand，as the temperature decreases, the equilibrium constant Km also reduces, and the reducing ratestrongly depends on the temperature： the lower the temperature, the higher the rate.
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the Programme“Investissements d’Avenir”(Investment for the Future)of the Agence Nationale de la Recherche(National Agency for Research)of the French State under award number ANR-10-LABX-22-01-SOLSTICE through the funding of the post-doctoral position of J.Puig.
文摘The carbothermal reduction of MgO and Al_(2)O_(3) in argon flow at low pressure allows to lower the onset temperature of metal vapor formation.Thermodynamic calculations indicate that metal formation begins at 1400 and 1700 K for a primary vacuum(1000 Pa),respectively,for Mg and Al.In the experimental section,concentrated solar energy was used for the process heating in order to favor energy savings.The products of the reaction between MgO or Al_(2)O_(3) and 2 varieties of carbon(graphite,carbon black)in flowing argon atmosphere at a total pressure of around 1000 to 1600 Pa were studied using X-ray diffraction,and microstructure observations revealed the formation of metallic nanopowders with some by-products.Metallic conversions close to 45 wt%and 52 wt%,respectively,for Mg and Al,were obtained.The low conversion yield of the carbothermal reduction of MgO can be attributed to a backward reaction reforming MgO powder and to a sintering process between oxide particles at high temperature.Aluminum production challenge is to avoid formation of undesired by-products:Al_(2)O,Al_(4)C_(3) and Al-oxycarbides.Advantages and weaknesses of the used process are described and some improvements are proposed to increase metallic yields.
基金Foundation item:Supported by National Natural Science Foundation of China(No.51304095)Science and Technology Planning Project of Yunnan Province,China(No.S2013FZ029)the personnel training Funds of Kunming University of Science and Technology,China(No.14118665).
文摘Most of researchers believed that the developments on the condensation of magnesium produced by carbothermic reduction just concentrated on two process routes:the“quench”route and the“solvent”route.But this paper will briefly analyzes the major challenges in magnesium vapor condensation during the vacuum carbothermic reduction of calcined dolomite,on equipment upgrade,heat transfers alter,to achieve condensation control and production collection.Solutions are then proposed using theoretical calculations and experiment results.Comparative analysis of the experiment results shows that the burning and even explosion of condensation products during the vacuum carbothermic reduction of calcined dolomite are mainly due to the burning of crystallized powder magnesium,which results from the self-ignition of alkali metals.Finally,this paper proposes a multistage condensation solution to improve traditional vacuum condensation equipment.And result show that the condensation equipment can effectively mitigate the burning and loss during condensation,also the morphology of the condensation products clearly improved,the grain size increased,and the oxidation rate decreased.The potassium/sodium vapor and the magnesium vapor were separately condensed.
基金the National Natural Science Foundation of China(No.51774224)for the funding of this research.
文摘The effects of mechanical activation on particle size distribution,crystalline phase,morphology,and mechanical energy storage of nickel slag were studied.Then,the direct reduction experiments of mechanically activated nickel slag mixed with reducing agent graphite powder were performed under conditions of 873-1273 K and reduction for 30-70 min.The results show that after 12 h of activation,90%of the nickel slag has a particle diameter less than 1.05 pm,and the total energy storage is 1790.4 kJ mol^(-1).With the extension of the mechanical activation duration,the intensity of the dift'raction peaks of the main crystalline phases Fe_(2)SiO_(4) and Mg2SiO4 in the nickel slag decreases.Mechanical activation is also an effective means to enhance the reduction of nickel slag.With the extension of the activation time,the reduction effect of the nickel slag and metallization degree increase.After 12 h of mechanical activation,the nickel slag was reduced at 1273 K for 70 min,and the metallization degree of the reduced product could reach 83.12%.
基金The authors gratefully acknowledge financial support from the National Natural Science Foundation of China(Grant No.51734002).
文摘High-quality ferrovanadium nitride(FeV45N,FeV55N and Fe65N)was fabricated using the raw materials of Fe_(3)O_(4),V_(2)O_(5) and graphite via carbothermal reduction nitridation method.Compared with the traditional methods,it shortens the production process of ferrovanadium nitride by avoiding the preparation of ferrovanadium.The effects of C/O molar ratio and reaction temperature on phase transition,density,carbon,oxygen and nitrogen contents and microstructure were investigated.The appropriate C/O molar ratio is crucial to obtain the products with high nitrogen content.It is also found that a higher temperature is beneficial for the densification,and the density of the products obtained at 1550℃ is much higher than that at 1500℃.Moreover,a higher temperature contributes to the increase in nitrogen content owing to the higher reaction kinetics.The carbothermal reduction nitridation method is proved to be a facile route to fabricate cost-effective ferrovanadium nitride and is possible to be applied for industrial production.
基金financially supported by the National Natural Science Foundation of China(No.51674018)
文摘Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate(VTC) were investigated. It was found that calcium compounds had great effects on the metallization rate of the reduction product, the order of the metallization rate of reduction product being CaCO3 > no additive > CaSO4 > CaCl2, which indicated that the addition of CaCO3 was more conducive to promoting the reduction of iron than other calcium compounds. Gas analysis showed that there were mainly two processes in the carbothermic reduction of VTC, a solid–solid and a solid–gas reaction. The concentrations of CO and CO2 were highest when CaCO3 was added, while that in a roasting system decreased the most when CaCl2 was added. X-ray diffraction(XRD) analysis showed that calcium compounds could change the reduction process of ilmenite in VTC. The phase compositions of the reduction products were changed from metallic iron(Fe) and anosovite(FeTi2O5) to metallic iron(Fe) and perovekite(CaTiO3) when calcium compounds were added. Additionally, CaSO4 and CaCl2 could significantly promote the growth of metallic iron particles, though the existence of Fe-bearing Mg2TiO4 in reduction products was not conducive to the reduction of iron. The formation of FeS would further hinder the reduction of iron after adding CaSO4.
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financially supported by the National Key R&D Program of China(No.2018YFC1900500)the National Natural Science Foundation of China(Nos.21908231,51774260,51804289,and 51904286)+2 种基金the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(No.QYZDJ-SSW-JSC021)the CAS Interdisciplinary Innovation Teamthe Special Project for Transformation of Major Technological Achievements in Hebei Province,China(No.19044012Z)。
文摘The carbothermic reduction of vanadium titanomagnetite concentrate(VTC)with the assistance of Na_(2)CO_(3)was conducted in an argon atmosphere between 1073 and 1473 K.X-ray diffraction and scanning electron microscopy were used to investigate the phase transformations during the reaction.By investigating the reaction between VTC and Na_(2)CO_(3),it was concluded that molten Na_(2)CO_(3)broke the structure of titanomagnetite by combining with the acidic oxides(Fe_(2)O_(3),TiO_(2),Al_(2)O_(3),and SiO_(2))to form a Na-rich melt and release FeO and MgO.Therefore,Na_(2)CO_(3)accelerated the reduction rate.In addition,adding Na_(2)CO_(3)also benefited the agglomeration of iron particles and the slag–metal separation by decreasing the viscosity of the slag.Thus,Na_(2)CO_(3)assisted carbothermic reduction is a promising method for treating VTC at low temperatures.
基金the National Natural Science Foundation of China(No.51674018)。
文摘The formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate(VTC)by adding CaCO3 was investigated.Thermodynamic analysis was employed to show the feasibility of calcium titanate formation by the reaction of ilmenite and Ca CO3 in a reductive atmosphere,where ilmenite is more easily reduced by CO or carbon in the presence of CaCO3.The effects of CaCO3 dosage and reduction temperature on the phase transformation and metallization degree were also investigated in an actual roasting test.Appropriate increase of CaCO3 dosages and reduction temperatures were found to be conducive to the formation of calcium titanate,and the optimum conditions were a CaCO3 dosage of 18 wt%and a reduction temperature of 1400°C.Additionally,scanning electron microscopy–energy dispersive spectrometry(SEM–EDS)analysis shows that calcium titanate produced via the carbothermic reduction of VTC by CaCO3 addition was of higher purity with particle size approximately 50μm.Hence,the separation of calcium titanate and metallic iron will be the focus in the future study.
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appreciate the Ministry of Edu-cation of the People’s Republic of China and Chongqing University with National Undergraduates Innovating Experi-mentation Project 1210611007.
文摘The Gibbs free energy and critical reaction conditions of preparing Mg and Ca metal by carbothermic reducing calcined dolomite were calculated and analyzed.New thermodynamic criterion for reduction reaction,including the critical temperature and vacuum degree,was studied.The results show that:when T/P^(0.0449)<1199.2,neither MgO nor CaO can be reduced by carbon;when T/P^(0.0449)≥1199.2 and T/P^(0.0462)<1350.9,MgO can be reduced while CaO can not be;when T/P^(0.0462)≥1350.9,both MgO and CaO can be reduced.According to the requirements,we can obtain only Mg,Mg first then Ca,Mg and Ca simultaneously by controlling temperature,vacuum degree or both of them properly,by carbothermic reducing calcined dolomite.
基金Item Sponsored by National Natural Science Foundation(59774026)
文摘As alkali additive, KCl catalyzes effectively the carbothermic reduction of pre-oxidized ilmenite, and the catalytic effect becomes more remarkable as the amount of KCl increases. During the carbothermic reduction, the gaseous product consists mainly of CO, and the partial pressure of which increases with reaction temperature. The EPMA and XPS of the partially reduced ilmenite ore and that of the used graphite as reductant showed that the potassium ions enter both ilmenite particles and graphite powders during reduction. The above-mentioned phenomena result in the distortion of ilmenite and carbon structure by potassium ions and reaction activity of carbon and ilmenite was enhanced. As a result, the overall carbothermic reduction was catalyzed by KCl.
基金Project supported by the National Natural Science Foundation of China
文摘A computer monitoring thermogravimetric system was used to study the effect of alkali chlorides(MCl, M=Li, Na, K and Cs) on the carbothermic reduction of pre oxidized ilmenite in the course of a linear rise in temperature from 600 ℃ to 1 000 ℃. The experimental results indicate that all the alkali chlorides can speed up the reduction process of pre oxidized ilmenite, moreover, KCl is the most effective catalyst of the chlorides, while the catalytic effects of LiCl and CsCl are relatively weaker. It seems that the catalytic mechanism of LiCl is different from those of the other alkali chlorides. The cross sectional morphology of the partially reduced pre oxidized ilmenite particles and the distribution of potassium ions within them were examined by means of scanning electronic microscopy and electronic probe microanalysis, respectively, which shows that the reduction proceeds topochemically and the alkali ion enriches at the periphery of the particles.[
基金National Natural Science Foundation of China(No.52173059)。
文摘Among nitride fibers,aluminum nitride(AlN)fibers have been developed for various advanced applications due to their mechanical flexibility,high thermal conductivity,and excellent electrical insulation and chemical stability.This article presents an overview on the recent progress of AlN fibers.The properties of AlN,particularly the thermal conductivity of AlN in polymer matrix composites are introduced.Afterward,two major approaches,carbothermal reduction and nitriding polycrystalline alumina fiber,for the preparation of AlN fibers are discussed.The carbothermal reduction includes electrospinning,solution blow spinning,and chemical vapor deposition.Furthermore,some perspectives on the future directions for the preparation and application of fibrous AlN are highlighted.This review is expected to provide readers with valuable guidance on the preparation of AlN fibers and inspire researchers to explore more potential applications.
基金the USDA National Institute of Food and Agriculture(NIFA),grant No.2020–65210–30763.
文摘Carbothermal reduction using biochar(BC)is a green and effective method of synthesizing BCsupported nanoscale zero-valent iron(nanoFe^(0))composites.However,the effect of BC surface area on the structure,distribution,and performance such as the heavy metal uptake capacity of nanoFe^(0)particles remains unclear.Soybean stover-based BCs with different surface areas(1.7−1472 m^(2)/g)were prepared in this study.They have been used for in-situ synthesis BCs-supported nanoFe^(0)particlesthrough carbothermal reduction of ferrous chloride.The BCs-supported nanoFe^(0)particles were found to be covered with graphene shells and dispersed onto BC surfaces,forming the BC-supported graphene-encapsulated nanoFe^(0)(BC-G@Fe^(0))composite.These graphene shells covering the nanoFe^(0)particles were formed because of gaseous carbon evolved from biomass carbonization reacting with iron oxides/iron salts.Increasing BC surface area decreased the average diameters of nanoFe^(0)particles,indicating a higher BC surface area alleviated the aggregation of nanoFe^(0)particles,which resulted in higher heavy metal uptake capacity.At the optimized condition,BC-G@Fe^(0)composite exhibited uptake capacities of 124.4,121.8,254.5,and 48.0 mg/g for Cu^(2+),Pb^(2+),Ag^(+),and As^(3+),respectively(pH 5,25℃).Moreover,the BC-G@Fe^(0)composite also demonstrated high stability for Cu^(2+)removal from the fixed-bed continuous flow,in which 1 g of BC-G@Fe^(0)can work for 120 h in a 4 mg/L Cu^(2+)flow continually and clean 28.6 L Cu^(2+)contaminated water.Furthermore,the BC-G@Fe^(0)composite can effectively immobilize the bioavailable As^(3+)from the contaminated soil,i.e.,5%(w)of BC-G@Fe^(0)composite addition can immobilize up to 92.2%bioavailable As^(3+)from the contaminated soil.
基金financially supported by the Center of Ecological Collaborative Innovation for Aluminum Industry in Guangxi and the Special Project for Innovation-driven Development of Guangxi(No.AA17202001).
文摘In view of the difficulty of extracting iron from Bayer red mud,a new idea of adding laterite nickel ore into red mud was proposed to prepare a high value-added product.Toward this,the influences of laterite nickel ore on thermodynamic reaction,slagging and smelting reduction of extracting iron from red mud were studied.The results indicated that the product of extracting iron from red mud(R100)was changed with the addition of laterite nickel ore(R70L30).The slag of R100 was strongly basic,while the R70L30 was weakly acidic with composition closer to the ideal blast furnace slag.The metal recovery of R100 was 75.16%and that of R70L30 was 94.05%.At the same temperature,the slag viscosity of R70L30 was significantly lower than that of R100,which proved that laterite nickel ore can adjust the basicity,reduce melting point of slag and improve metal recovery.Because Fe,Ni and Cr in red mud and laterite nickel ore can be reduced sufficiently,a low Ni–Cr alloy cast iron can be directly prepared.
