Hydrogen-based mineral phase transformation(HMPT)technology has demonstrated its effectiveness in separating iron and enriching rare earths from Bayan Obo refractory ores.However,further research is needed to clarify ...Hydrogen-based mineral phase transformation(HMPT)technology has demonstrated its effectiveness in separating iron and enriching rare earths from Bayan Obo refractory ores.However,further research is needed to clarify the phase composition and floatability of rare earths obtained after HMPT owing to the associated phase transformations.This study explored the mineralogical characteristics and separation behavior of rare earths in HMPT-treated iron tailings.Process mineralogy studies conducted via BGRIMM process mineralogy analysis and X-ray diffraction revealed that the main valuable minerals in the tailings included rare-earth oxides(9.15wt%),monazite(5.31wt%),and fluorite(23.52wt%).The study also examined the impact of mineral liberation and gangue mineral intergrowth on flotation performance.Flotation tests achieved a rare-earth oxide(REO)grade of 74.12wt% with a recovery of 34.17% in open-circuit flotation,whereas closed-circuit flotation resulted in a REO grade of 60.27wt% with a recovery of 73%.Transmission electron microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy revealed that monazite remained stable during the HMPT process,while bastnaesite was transformed into Ce_(7)O_(12)and CeF_(3),leading to increased collector consumption.Nonetheless,the HMPT process did not significantly affect the flotation performance of rare earths.The enrichment of fluorite in the tailings highlighted its further recovery potential.The integration of HMPT with magnetic separation and flotation presents an efficient strategy for recovering rare earths,iron,and fluorite from Bayan Obo ores.展开更多
The paper reports on the atomic investigation aboutβphase in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope(HAADF-ST...The paper reports on the atomic investigation aboutβphase in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM)corrected by atomic Cs.By using HAADF-STEM,the rectangularβphases were observed in the underage and peak aging stages in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy.Theβphase could be precipitated from the previously precipitatedβphase,and theβphase grew in steps when it was precipitated.A special transition structure of three atomic layer thicknesses was first observed at the edge of theβphase and the structure of this interface is probably as theβ/Mg_(1) interface for the analysis of thermodynamic characterization and electronic characterization.Theβ'phase and theβ_(H) structure were precipitated only at the edge of the length directions of theβphase.Theβ'phase continues to grow into aβphase directly without the formation ofβ_(1) phase,resulting in an increase in the length of theβphase,which is discovered for the first time.展开更多
Recent studies have shown that the La-and Y-hydrides can exhibit significant superconducting properties under high pressures.In this paper,we investigate the stability,electronic and superconducting properties of LaYH...Recent studies have shown that the La-and Y-hydrides can exhibit significant superconducting properties under high pressures.In this paper,we investigate the stability,electronic and superconducting properties of LaYH_(x)(x=2,3,6 and 8)under 0-200 GPa.It is found that LaYH_(2) stabilizes in the C2/m phase at ambient pressure,and transforms to the Pmmn phase at 67 GPa.LaYH_(3) stabilizes in the C2/m phase at ambient pressure,and undergoes phase transitions of C2/m→P2_(1)/m→R3m at 12 GPa and 87 GPa,respectively.LaYH_(6) stabilizes in the P4_32_12 phase at ambient pressure,and undergoes phase transitions of P4_(3)2_(1)2→P4/mmm→Cmcm at 28 GPa and 79 GPa,respectively.LaYH_(8) stabilizes in the Imma phase at 60 GPa and transforms to the P4/mmm phase at 117 GPa.Calculations of the electronic band structures show that the P4/mmm-LaYH_(8) and all phases of LaYH_(2) and LaYH_(3) exhibit metallic character.For the metallic phases,we then study their superconducting properties.The calculated superconducting transition temperatures(T_c)are 0.47 K for C2/m-LaYH_(2) at 0 GPa,0 K for C2/m-LaYH_(3) at 0 GPa,and 55.51 K for P4/mmm-LaYH_(8) at 50 GPa.展开更多
Effects of collectors(butyl xanthate(BX), O-isopropyl-N-sulfur ethyl carbamate(Z-200) and emulsified kerosene), dereagent(sodium sulfide) and depressant thioglycollic acid(TGA) on the flotation of chalcocite and molyb...Effects of collectors(butyl xanthate(BX), O-isopropyl-N-sulfur ethyl carbamate(Z-200) and emulsified kerosene), dereagent(sodium sulfide) and depressant thioglycollic acid(TGA) on the flotation of chalcocite and molybdenite were investigated through flotation. The first principle theory was adopted to understand the difference of their surfaces and reaction between minerals and reagents. Results of flotation tests revealed that selectivity of emulsified kerosene is the best of three collectors in separation of chalcocite and molybdenite, though the others also display excellent collecting properties. Sodium sulfide can effectively remove collectors adsorbed on chalcocite surface, and TGA is an effective depressant of chalcocite at pH 8-9. Through first principle study, molybdenite displays relatively stronger covalence property while bonding interaction between copper atoms in chalcocite enhanced its ionicity. Bonding interaction is weaker in reaction of TGA and molybdenite, so it shows higher hydrophobicity and better flotability. Therefore, TGA is an effective inhibitor in the separation.展开更多
First-principles calculations based on density functional theory were performed to study the effect of alloying on the thermodynamic stability of MgH2 hydride （rutile and fluorite structures） with transitional meta...First-principles calculations based on density functional theory were performed to study the effect of alloying on the thermodynamic stability of MgH2 hydride （rutile and fluorite structures） with transitional metals （TM=Sc, Ti, Y） and group IIA elements （M=Ca, Sr, Ba）. The results indicate that fluorite structure of these hydrides are more stable than its relative rutile structure at low alloying content （less 20%）, structural destabilization of MgH2 appears in the alloying cases of Ti, Sr and Ba respectively. The structure-transition point from rutile structure to fluorite structure is at around 20% for MgH2-TM, and about 40% for MgH2-M. The formation enthalpy of fluorite Mg0.5Ba0.52 is about 0.3 eV and higher than that of fluorite MgH2, indicating that its hydrogen-desorption temperature at atmospheric pressure will be much lower than that of pure MgH2. Good consistency between experimental and calculated data suggests that above-adopted method is useful to predict structural transition and properties of MgH2 based hydrides for hydrogen storage.展开更多
Monazite((Ce,La)PO_(4))is one of the major types of light rare earth minerals from which the light rare earth elements cerium(Ce)and lanthanum(La)are economically extracted.Flotation is extensively used to recover fin...Monazite((Ce,La)PO_(4))is one of the major types of light rare earth minerals from which the light rare earth elements cerium(Ce)and lanthanum(La)are economically extracted.Flotation is extensively used to recover fine-grained monazite.Sodium oleate(NaOL)is considered as the collector with strong collecting ability for monazite flotation.However,this study shows that its collecting ability is still limited.In this paper,a phosphonic acid,nonane-1,1-bisphosphonic acid(C9-BPA),was employed as the novel collector in place of NaOL.Flotation experiments show that even when the C9-BPA dosage is less than one-fifth of the NaOL dosage,the monazite recove ry using C9-BPA as the collector is approximately 22 wt%higher than that using NaOL.The mechanism by which C9-BPA adsorbs on monazite was investigated using zeta potential,infrared(IR)spectroscopy and X-ray photoelectron spectroscopy(XPS)measurements as well as first-principles calculations.Zeta potential measurements show a more significant decrease in the zeta potentials of monazite after the addition of C9-BPA compared to those after the addition of NaOL.For C9-BPA-treated monazite,the characteristic peaks of C9-BPA are observed in the IR and C 1 s XPS spectrum,whereas for monazite treated by NaOL,no characteristic peak of NaOL was observed.Experimental results show that C9-BPA has a stronger affinity towards the monazite surface than NaOL as confirmed by the higher adsorption energy of CP-BPA on the monazite surface(-204.22 kJ/mol)than NaOL(-48.48 kJ/mol).This study demonstrates an extensive application value and prospect of C9-BPA in monazite flotation and helps design novel collectors with strong collecting ability for monazite flotation.展开更多
Fourier transform infrared (FTIR) spectroscopy has beenextensively employed in flotation research. The work done by theauthor and co-workers has been reported. A comparison has been madeamong the different FTIR spectr...Fourier transform infrared (FTIR) spectroscopy has beenextensively employed in flotation research. The work done by theauthor and co-workers has been reported. A comparison has been madeamong the different FTIR spectroscopic techniques, e.g., transmissionFTIR spectroscopy, diffuse reflectance infrared Fourier transform(DRIFT) spectroscopy, and attenuated total reflectance (ATR) FTIRspectroscopy.展开更多
Oxidation corrosion of steels usually occurs in contact with the oxygen-contained environment, which is accelerated by high oxygen concentration and irradiation. The oxidation mechanism of steels is investigated by th...Oxidation corrosion of steels usually occurs in contact with the oxygen-contained environment, which is accelerated by high oxygen concentration and irradiation. The oxidation mechanism of steels is investigated by the adsorption/solution of oxygen atoms on/under body-centered-cubic(bcc) iron surfaces, and diffusion of oxygen atoms on the surface and in the near-surface region. Energetic results indicate that oxygen atoms prefer to adsorb at hollow and long-bridge positions on the Fe(100) and(110) surfaces, respectively. As the coverage of oxygen atoms increases, oxygen atoms would repel each other and gradually dissolve in the near-surface and bulk region. As vacancies exist, oxygen atoms are attracted by vacancies, especially in the near-surface and bulk region. Dynamic results indicate that the diffusion of O atoms on surfaces is easier than that into near-surface, which is affected by oxygen coverage and vacancies. Moreover, the effects of oxygen concentration and irradiation on oxygen density in the near-surface and bulk region are estimated by the Mc Lean’s model with a simple hypothesis.展开更多
In this paper,FXL-14 (tetradecyl iminobimetyl phosphonic acid) as a collector for floating wolframite without Pb^(2+) and its adsorption mechanism were studied by electrochemical method.Flotation experiment results sh...In this paper,FXL-14 (tetradecyl iminobimetyl phosphonic acid) as a collector for floating wolframite without Pb^(2+) and its adsorption mechanism were studied by electrochemical method.Flotation experiment results showed that in the wide range of pH value activation of FXL-14 collecting wolframite with Pb^(2+) was not needed.Wolframite—carbon paste electrode and small-amplitude triangular potential sweep were used to measure the electro-double-layer capacitance of wolframite in the FXL-14 solution (with and without of the presence of 1×10^(-4)MPb^(2+)).It is showed that in spite of concentration of Pb^(2+) in the flotation processing,with FXL-14 (800mg/l) the electro-double-layer capacitance was bigger than with FXL-14 (800mg/l) and Pb^(2+).展开更多
Two-dimensional(2D)transition metal carbides known as MXenes belong to a new branch of 2D material family,and their fundamental properties vary with their compositions and surface functionalizations.In this study,the ...Two-dimensional(2D)transition metal carbides known as MXenes belong to a new branch of 2D material family,and their fundamental properties vary with their compositions and surface functionalizations.In this study,the structural and ideal mechanical properties of M2C-type MXenes and their functionalized M2CT2 MXenes(M=Ti,Zr,Hf;T=O,F,OH)were systematically examined via first-principles methods.The stress–strain curves of the MXenes under homogenous biaxial and uniaxial tension are identified,and the fundamental quantities(e.g.,Young’s modulus,in-plane stiffness,and Poisson’s ratio)are addressed.With significantly higher strength and extended critical strains,the M2CO2 MXenes exhibit optimal flexibility when compared with that of M2C,M2CF2,and M2C(OH)2.Additionally,Hf2CT2 exhibits optimal tensile performance under uniaxial or biaxial tension when compared to that of Ti2CT2 and Zr2CT2.The Young’s modulus,in-plane stiffness,and Poisson’s ratio of MXenes with different surface functionalization increase in a sequence corresponding to OH\F\O.Furthermore,the effects of vacancy on the mechanical properties of MXenes are further explored and indicate that vacancy can significantly weaken the tensile properties of MXenes that are considered.Moreover,vacancy also results in a certain anisotropy of stress along armchair and zigzag directions even under the biaxial tension condition.展开更多
As one of the main materials in the practical application.of superconductor,lead(Pb)has been used to manufacture superconducting AC power cable,and some weak current fields.With the development of manufacturing,techno...As one of the main materials in the practical application.of superconductor,lead(Pb)has been used to manufacture superconducting AC power cable,and some weak current fields.With the development of manufacturing,technology,more and more researchers focus on exploring the physical and chemical properties of cryogenic superconducting materials,instead of blindly pursuing the improvement of the superconducting transition temperature(T_(c)).In this paper,the structural properties and superconducting transition temperature under high pressure of Pb have been studied by first-principles calculations.It has shown that Pb can withstand the compressive strain up to 10%while the lattice structure remains stable,indicated by the calculations of phonon band structures.From 0%to 10%compressive strain,there is neither a band-gap nor changing of the band structure.The.changing of electronic DOS.at the Fermi level leads to a decreasing of T_(c).Our calculations show that Pb is a stable elemental metallic superconductor even under high pressure,which explains the reason why it has been used in practical productions.展开更多
First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the to...First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the total magnetic mo- ment mainly originates from the p--d hybridization of Cu-N and Cu-O as well as p--p coupling interaction between N and O at the Fermi level. The Zn34Cu2035N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the （Cu, N）-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.展开更多
Doping is an effective approach for improving the photovoltaic performance of Cu2 ZnSnS4（CZTS）. The doping by substitution of Cu atoms in CZTS with Li and Ag atoms is investigated using density functional theory. Th...Doping is an effective approach for improving the photovoltaic performance of Cu2 ZnSnS4（CZTS）. The doping by substitution of Cu atoms in CZTS with Li and Ag atoms is investigated using density functional theory. The results show that the band gaps of Li（2 x）Cu2（1-x）ZnSnS4 and Ag（2 x）Cu2（1-x）ZnSnS4 can be tuned in the ranges of 1.30-3.43 and 1.30-1.63 eV, respectively. The calculation also reveals a phase transition from kesterite to wurtzite-kesterite for Li（2 x）Cu2（1-x）ZnSnS4 as x is larger than 0.9. The tunable band gaps of Li（2 x）Cu2（1-x）ZnSnS4 and Ag（2 x）Cu2（1-x） ZnSnS4 make them beneficial for achieving band-gap-graded solar cells.展开更多
First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in(111)orientation.By considering the spin-orbit inter...First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in(111)orientation.By considering the spin-orbit interaction,for stoichiometric surface,the topological states keep robust for six-bilayer case,and can be recovered in the three-bilayer film,which are guaranteed by time-reversal symmetry and inverse symmetry.For reduced surface doped by non-magnetic Bi or magnetic Mn atom,localized three-fold symmetric features can be identified.Moreover,band structures show that the non-trivial topological states stand for non-magnetic substitutional Bi atom,while can be eliminated by adsorbed or substitutional magnetic Mn atom.展开更多
In this work,the equilibrium structure,electronic and elastic properties of L1_(2)-ordered Co-Al-W and Co-Al-W-X(X=Ti and Nb)phase were calculated,using first-principles calculations.Among six nonequivalent sites(Al_(...In this work,the equilibrium structure,electronic and elastic properties of L1_(2)-ordered Co-Al-W and Co-Al-W-X(X=Ti and Nb)phase were calculated,using first-principles calculations.Among six nonequivalent sites(Al_(1),Al_(2),Co_(3),Co_(4),W_(5),W_(6)),Ti and Nb prefer to occupy the W_(6)site,since the formation enthalpy of the system is lowest when Ti and Nb occupy the W。site.Both Ti and Nb most affect the density of states of Al atoms.Compared with the Al_(2) site,which is the sub-preference site of Ti and Nb,the density of states of Al atoms is higher with the addition of Ti and Nb in the W_(6)site,which means that the latter system is more stable.According to the bulk modulus B,shear modulus G,Young's modulus E,hardness Hv and Poisson's ratioσ,for Co_(3)(AI,W)alloy,the addition of Ti and Nb in the W_(6)site decreases its hardness hut increases its duetility.This work cnnfirms that Ti and Nh can stahilize the Cag(Al,W)alloy and have a positive effect in solving the relatively poor ductility of this alloy,which has important implications for the development of cobalt.based alloys.展开更多
The impacts of strain and polar discontinuities on the performance of superlattices have attracted widespread attention. Using first-principles calculation, we study the polarization and piezoelectricity of PbTiO3/KTa...The impacts of strain and polar discontinuities on the performance of superlattices have attracted widespread attention. Using first-principles calculation, we study the polarization and piezoelectricity of PbTiO3/KTa03 （PTO//KTO） superl^ttices with strain and polsr discontinuities. The strain caused by lattice mismatch between the superlattice and the substrate induces lattice distortion, the displacement of each atom and dynamical charge transfer between the Ti atom or Ta atom and the 0 atoms in the PTO//KTO superlattice. With more compressive or less tensile strain, the polarization value increases linearly, piezoelectric tensor e31 （e32） increases while e33 and e25 （e16） increase negatively. Polarity discontinuity caused by the interracial charge will produce large irreversible polarization. Proved by F-point phonons of PTO//KTO superlattices of different strain values, the polar discontinuity and the piezoelectric properties are just weakly dependent on temperature as found in PTO//KTO superlattices.展开更多
The flotation results of a phosphate ore are improved by replacing the conventional collectors of fatty acids with composite collectors. The synergistic effect on the froth characteristics in systems using composite c...The flotation results of a phosphate ore are improved by replacing the conventional collectors of fatty acids with composite collectors. The synergistic effect on the froth characteristics in systems using composite collectors has then been studied, and the concept of 'mixed hemimicellae' has been proposed in the adsorption of composite collectors at the air/solution interfaces.展开更多
The properties and collecting ability of a new collector,monoalkyl ester phosphoric acid(P538),for the flotation of rare earth minerals are described in the paper.The mechanism of P538 adsorption on the surfaces of mo...The properties and collecting ability of a new collector,monoalkyl ester phosphoric acid(P538),for the flotation of rare earth minerals are described in the paper.The mechanism of P538 adsorption on the surfaces of monazite or bastnaesite is explored by modern measuring techniques,such as IR and ESCA,etc.展开更多
The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site（OIS）. A...The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site（OIS）. As the concentration of He atoms in ThO2 increases, the strain induced by the He atoms increases and the octahedral interstitial site is not large enough to accommodate a large cluster, such as a He hexamer. We considered three different Schottky defect（SD） configurations（SD1, SD2, and SD3）. When He atoms are located in the SD sites, the strain induced by the He atoms is released and the incorporation and binding energies decrease. The He trimer is the most stable cluster in SD1. Large He clusters, such as a He hexamer, are also stable in the SDs.展开更多
Within the framework of density functional theory calculations,the structural,vibrational,and electronic properties of Zr_(n )C_(n-1)(n=2,3,and 4)and their functionalized MXenes have been investigated.We find that the...Within the framework of density functional theory calculations,the structural,vibrational,and electronic properties of Zr_(n )C_(n-1)(n=2,3,and 4)and their functionalized MXenes have been investigated.We find that the most stable configurations for Zr-C MXene are the ones that the terminal groups F,O,and OH locate on the common hollow site of the superficial Zr layer and its adjacent C layer.F and OH-terminated Zr_3C_(2 )and Zr_4C_(3 )have small imaginary acoustic phonon branches aroundΓpoint while the others have no negative phonon modes.The pristine MXenes(Zr_2C,Zr_3C_(2 )and Zr_4C_3)are all metallic with large DOS contributed by the Zr atom at the Fermi energy.When functionalized by F,O and OH,new hybridization states appear and the DOS at the Fermi level are reduced.Moreover,we find that their metallic characteristic increases with an increase in n.For(Zr_(n )C_(n-1))O_2,Zr_2CO_(2 )is a semiconductor,Zr_3C_2O_(2 )is a semimetal,and Zr_4C_3O_(2 )becomes a metal.展开更多
基金the financial support received from the Key Program of National Natural Science Foundation of China(No.52130406)the National Key R&D Program of China(Nos.2021YFC2901000 and 2022YFC2905800)+1 种基金the General Program of National Natural Science Foundation of China(No.52274253)Natural Science Foundation Innovation Group Project of Hubei Province,China(No.2023AFA044)。
文摘Hydrogen-based mineral phase transformation(HMPT)technology has demonstrated its effectiveness in separating iron and enriching rare earths from Bayan Obo refractory ores.However,further research is needed to clarify the phase composition and floatability of rare earths obtained after HMPT owing to the associated phase transformations.This study explored the mineralogical characteristics and separation behavior of rare earths in HMPT-treated iron tailings.Process mineralogy studies conducted via BGRIMM process mineralogy analysis and X-ray diffraction revealed that the main valuable minerals in the tailings included rare-earth oxides(9.15wt%),monazite(5.31wt%),and fluorite(23.52wt%).The study also examined the impact of mineral liberation and gangue mineral intergrowth on flotation performance.Flotation tests achieved a rare-earth oxide(REO)grade of 74.12wt% with a recovery of 34.17% in open-circuit flotation,whereas closed-circuit flotation resulted in a REO grade of 60.27wt% with a recovery of 73%.Transmission electron microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy revealed that monazite remained stable during the HMPT process,while bastnaesite was transformed into Ce_(7)O_(12)and CeF_(3),leading to increased collector consumption.Nonetheless,the HMPT process did not significantly affect the flotation performance of rare earths.The enrichment of fluorite in the tailings highlighted its further recovery potential.The integration of HMPT with magnetic separation and flotation presents an efficient strategy for recovering rare earths,iron,and fluorite from Bayan Obo ores.
基金financially supported by the National Natural Science Foundation of China(Grant No.51825101)the National Key Research and Development Program of China(Grant No.2016YFB0701201)。
文摘The paper reports on the atomic investigation aboutβphase in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM)corrected by atomic Cs.By using HAADF-STEM,the rectangularβphases were observed in the underage and peak aging stages in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy.Theβphase could be precipitated from the previously precipitatedβphase,and theβphase grew in steps when it was precipitated.A special transition structure of three atomic layer thicknesses was first observed at the edge of theβphase and the structure of this interface is probably as theβ/Mg_(1) interface for the analysis of thermodynamic characterization and electronic characterization.Theβ'phase and theβ_(H) structure were precipitated only at the edge of the length directions of theβphase.Theβ'phase continues to grow into aβphase directly without the formation ofβ_(1) phase,resulting in an increase in the length of theβphase,which is discovered for the first time.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12364003,11804131,11704163,12375014,and 11875149)the Natural Science Foundation of Jiangxi Province of China (Grant Nos.20232BAB211022 and 20181BAB211007)。
文摘Recent studies have shown that the La-and Y-hydrides can exhibit significant superconducting properties under high pressures.In this paper,we investigate the stability,electronic and superconducting properties of LaYH_(x)(x=2,3,6 and 8)under 0-200 GPa.It is found that LaYH_(2) stabilizes in the C2/m phase at ambient pressure,and transforms to the Pmmn phase at 67 GPa.LaYH_(3) stabilizes in the C2/m phase at ambient pressure,and undergoes phase transitions of C2/m→P2_(1)/m→R3m at 12 GPa and 87 GPa,respectively.LaYH_(6) stabilizes in the P4_32_12 phase at ambient pressure,and undergoes phase transitions of P4_(3)2_(1)2→P4/mmm→Cmcm at 28 GPa and 79 GPa,respectively.LaYH_(8) stabilizes in the Imma phase at 60 GPa and transforms to the P4/mmm phase at 117 GPa.Calculations of the electronic band structures show that the P4/mmm-LaYH_(8) and all phases of LaYH_(2) and LaYH_(3) exhibit metallic character.For the metallic phases,we then study their superconducting properties.The calculated superconducting transition temperatures(T_c)are 0.47 K for C2/m-LaYH_(2) at 0 GPa,0 K for C2/m-LaYH_(3) at 0 GPa,and 55.51 K for P4/mmm-LaYH_(8) at 50 GPa.
基金provided by the National Natural Science Foundation of China(No.51274255)the Innovation Driven Plan of Central South University(No.2015CX005)+1 种基金the Postdoctoral Research Station of Central South UniversityCo-Innovation Centre for Clean and Efficient Utilization of Strategic Metal Mineral Resources
文摘Effects of collectors(butyl xanthate(BX), O-isopropyl-N-sulfur ethyl carbamate(Z-200) and emulsified kerosene), dereagent(sodium sulfide) and depressant thioglycollic acid(TGA) on the flotation of chalcocite and molybdenite were investigated through flotation. The first principle theory was adopted to understand the difference of their surfaces and reaction between minerals and reagents. Results of flotation tests revealed that selectivity of emulsified kerosene is the best of three collectors in separation of chalcocite and molybdenite, though the others also display excellent collecting properties. Sodium sulfide can effectively remove collectors adsorbed on chalcocite surface, and TGA is an effective depressant of chalcocite at pH 8-9. Through first principle study, molybdenite displays relatively stronger covalence property while bonding interaction between copper atoms in chalcocite enhanced its ionicity. Bonding interaction is weaker in reaction of TGA and molybdenite, so it shows higher hydrophobicity and better flotability. Therefore, TGA is an effective inhibitor in the separation.
文摘First-principles calculations based on density functional theory were performed to study the effect of alloying on the thermodynamic stability of MgH2 hydride （rutile and fluorite structures） with transitional metals （TM=Sc, Ti, Y） and group IIA elements （M=Ca, Sr, Ba）. The results indicate that fluorite structure of these hydrides are more stable than its relative rutile structure at low alloying content （less 20%）, structural destabilization of MgH2 appears in the alloying cases of Ti, Sr and Ba respectively. The structure-transition point from rutile structure to fluorite structure is at around 20% for MgH2-TM, and about 40% for MgH2-M. The formation enthalpy of fluorite Mg0.5Ba0.52 is about 0.3 eV and higher than that of fluorite MgH2, indicating that its hydrogen-desorption temperature at atmospheric pressure will be much lower than that of pure MgH2. Good consistency between experimental and calculated data suggests that above-adopted method is useful to predict structural transition and properties of MgH2 based hydrides for hydrogen storage.
基金Project supported by the National Key Research and Development Program of China(2019YFC0408300)the Excellent Youth Foundation of IMUST(2017YQL05)+7 种基金the Key Program for International S&T Cooperation Projects of China(2019YFE012999)the Science Fund for Distinguished Young Scholars of Hunan Province(2020JJ2044)the Young Elite Scientists Sponsorship Program of Hunan Province,China(2018RS_(3) 011)Hubei Key Laboratory for Efficient Utilization and Agglomeration of Metallurgic Mineral Resourcesthe National Natural Science Foundation of China(U2067201,51774328,51674045,51404300)the National 111Project of China(B14034)Inner Mongolia Natural Science Foundation(2020LH05027,2019MS05039)。
文摘Monazite((Ce,La)PO_(4))is one of the major types of light rare earth minerals from which the light rare earth elements cerium(Ce)and lanthanum(La)are economically extracted.Flotation is extensively used to recover fine-grained monazite.Sodium oleate(NaOL)is considered as the collector with strong collecting ability for monazite flotation.However,this study shows that its collecting ability is still limited.In this paper,a phosphonic acid,nonane-1,1-bisphosphonic acid(C9-BPA),was employed as the novel collector in place of NaOL.Flotation experiments show that even when the C9-BPA dosage is less than one-fifth of the NaOL dosage,the monazite recove ry using C9-BPA as the collector is approximately 22 wt%higher than that using NaOL.The mechanism by which C9-BPA adsorbs on monazite was investigated using zeta potential,infrared(IR)spectroscopy and X-ray photoelectron spectroscopy(XPS)measurements as well as first-principles calculations.Zeta potential measurements show a more significant decrease in the zeta potentials of monazite after the addition of C9-BPA compared to those after the addition of NaOL.For C9-BPA-treated monazite,the characteristic peaks of C9-BPA are observed in the IR and C 1 s XPS spectrum,whereas for monazite treated by NaOL,no characteristic peak of NaOL was observed.Experimental results show that C9-BPA has a stronger affinity towards the monazite surface than NaOL as confirmed by the higher adsorption energy of CP-BPA on the monazite surface(-204.22 kJ/mol)than NaOL(-48.48 kJ/mol).This study demonstrates an extensive application value and prospect of C9-BPA in monazite flotation and helps design novel collectors with strong collecting ability for monazite flotation.
文摘Fourier transform infrared (FTIR) spectroscopy has beenextensively employed in flotation research. The work done by theauthor and co-workers has been reported. A comparison has been madeamong the different FTIR spectroscopic techniques, e.g., transmissionFTIR spectroscopy, diffuse reflectance infrared Fourier transform(DRIFT) spectroscopy, and attenuated total reflectance (ATR) FTIRspectroscopy.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFE0302400 and 2017YFA0402803)the National Nature Science Foundation of China(Grant Nos.11735015,52071314,51871207,U1832206,12075274,U1967211,52171084)Hefei Advanced Computing Center。
文摘Oxidation corrosion of steels usually occurs in contact with the oxygen-contained environment, which is accelerated by high oxygen concentration and irradiation. The oxidation mechanism of steels is investigated by the adsorption/solution of oxygen atoms on/under body-centered-cubic(bcc) iron surfaces, and diffusion of oxygen atoms on the surface and in the near-surface region. Energetic results indicate that oxygen atoms prefer to adsorb at hollow and long-bridge positions on the Fe(100) and(110) surfaces, respectively. As the coverage of oxygen atoms increases, oxygen atoms would repel each other and gradually dissolve in the near-surface and bulk region. As vacancies exist, oxygen atoms are attracted by vacancies, especially in the near-surface and bulk region. Dynamic results indicate that the diffusion of O atoms on surfaces is easier than that into near-surface, which is affected by oxygen coverage and vacancies. Moreover, the effects of oxygen concentration and irradiation on oxygen density in the near-surface and bulk region are estimated by the Mc Lean’s model with a simple hypothesis.
文摘In this paper,FXL-14 (tetradecyl iminobimetyl phosphonic acid) as a collector for floating wolframite without Pb^(2+) and its adsorption mechanism were studied by electrochemical method.Flotation experiment results showed that in the wide range of pH value activation of FXL-14 collecting wolframite with Pb^(2+) was not needed.Wolframite—carbon paste electrode and small-amplitude triangular potential sweep were used to measure the electro-double-layer capacitance of wolframite in the FXL-14 solution (with and without of the presence of 1×10^(-4)MPb^(2+)).It is showed that in spite of concentration of Pb^(2+) in the flotation processing,with FXL-14 (800mg/l) the electro-double-layer capacitance was bigger than with FXL-14 (800mg/l) and Pb^(2+).
基金supported by the National Natural Science Foundation of China(Nos.11605273 and 11847064)the Shanghai Municipal Science and Technology Commission(No.16ZR1443100)
文摘Two-dimensional(2D)transition metal carbides known as MXenes belong to a new branch of 2D material family,and their fundamental properties vary with their compositions and surface functionalizations.In this study,the structural and ideal mechanical properties of M2C-type MXenes and their functionalized M2CT2 MXenes(M=Ti,Zr,Hf;T=O,F,OH)were systematically examined via first-principles methods.The stress–strain curves of the MXenes under homogenous biaxial and uniaxial tension are identified,and the fundamental quantities(e.g.,Young’s modulus,in-plane stiffness,and Poisson’s ratio)are addressed.With significantly higher strength and extended critical strains,the M2CO2 MXenes exhibit optimal flexibility when compared with that of M2C,M2CF2,and M2C(OH)2.Additionally,Hf2CT2 exhibits optimal tensile performance under uniaxial or biaxial tension when compared to that of Ti2CT2 and Zr2CT2.The Young’s modulus,in-plane stiffness,and Poisson’s ratio of MXenes with different surface functionalization increase in a sequence corresponding to OH\F\O.Furthermore,the effects of vacancy on the mechanical properties of MXenes are further explored and indicate that vacancy can significantly weaken the tensile properties of MXenes that are considered.Moreover,vacancy also results in a certain anisotropy of stress along armchair and zigzag directions even under the biaxial tension condition.
文摘As one of the main materials in the practical application.of superconductor,lead(Pb)has been used to manufacture superconducting AC power cable,and some weak current fields.With the development of manufacturing,technology,more and more researchers focus on exploring the physical and chemical properties of cryogenic superconducting materials,instead of blindly pursuing the improvement of the superconducting transition temperature(T_(c)).In this paper,the structural properties and superconducting transition temperature under high pressure of Pb have been studied by first-principles calculations.It has shown that Pb can withstand the compressive strain up to 10%while the lattice structure remains stable,indicated by the calculations of phonon band structures.From 0%to 10%compressive strain,there is neither a band-gap nor changing of the band structure.The.changing of electronic DOS.at the Fermi level leads to a decreasing of T_(c).Our calculations show that Pb is a stable elemental metallic superconductor even under high pressure,which explains the reason why it has been used in practical productions.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61274128)the Natural Science Foundation of Chongqing City, China (Grant Nos. 2011BA4031 and 2013jjB0023)+1 种基金the Education Commission of Chongqing City, China (Grant No. KJ120608)the Chongqing Normal University,China (Grant No. 09XLS04)
文摘First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the total magnetic mo- ment mainly originates from the p--d hybridization of Cu-N and Cu-O as well as p--p coupling interaction between N and O at the Fermi level. The Zn34Cu2035N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the （Cu, N）-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.
基金Supported by the National Natural Science Foundation of China under Grant No 61674073the Science and Technology Planning Project of Guangdong Province under Grant No 2017A050506056+1 种基金the Key Basic and Applied Research Project of Guangdong Province under Grant No 2016KZDXM021the Project of International as well as Hongkong,Macao and Taiwan Science and Technology Cooperation Innovation Platform in Universities in Guangdong Province under Grant No 2015KGJHZ028
文摘Doping is an effective approach for improving the photovoltaic performance of Cu2 ZnSnS4（CZTS）. The doping by substitution of Cu atoms in CZTS with Li and Ag atoms is investigated using density functional theory. The results show that the band gaps of Li（2 x）Cu2（1-x）ZnSnS4 and Ag（2 x）Cu2（1-x）ZnSnS4 can be tuned in the ranges of 1.30-3.43 and 1.30-1.63 eV, respectively. The calculation also reveals a phase transition from kesterite to wurtzite-kesterite for Li（2 x）Cu2（1-x）ZnSnS4 as x is larger than 0.9. The tunable band gaps of Li（2 x）Cu2（1-x）ZnSnS4 and Ag（2 x）Cu2（1-x） ZnSnS4 make them beneficial for achieving band-gap-graded solar cells.
文摘First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in(111)orientation.By considering the spin-orbit interaction,for stoichiometric surface,the topological states keep robust for six-bilayer case,and can be recovered in the three-bilayer film,which are guaranteed by time-reversal symmetry and inverse symmetry.For reduced surface doped by non-magnetic Bi or magnetic Mn atom,localized three-fold symmetric features can be identified.Moreover,band structures show that the non-trivial topological states stand for non-magnetic substitutional Bi atom,while can be eliminated by adsorbed or substitutional magnetic Mn atom.
基金This work was supported by the National Natural Science Foundation of China(Grant Numbers 51971118,51771102,51471098).
文摘In this work,the equilibrium structure,electronic and elastic properties of L1_(2)-ordered Co-Al-W and Co-Al-W-X(X=Ti and Nb)phase were calculated,using first-principles calculations.Among six nonequivalent sites(Al_(1),Al_(2),Co_(3),Co_(4),W_(5),W_(6)),Ti and Nb prefer to occupy the W_(6)site,since the formation enthalpy of the system is lowest when Ti and Nb occupy the W。site.Both Ti and Nb most affect the density of states of Al atoms.Compared with the Al_(2) site,which is the sub-preference site of Ti and Nb,the density of states of Al atoms is higher with the addition of Ti and Nb in the W_(6)site,which means that the latter system is more stable.According to the bulk modulus B,shear modulus G,Young's modulus E,hardness Hv and Poisson's ratioσ,for Co_(3)(AI,W)alloy,the addition of Ti and Nb in the W_(6)site decreases its hardness hut increases its duetility.This work cnnfirms that Ti and Nh can stahilize the Cag(Al,W)alloy and have a positive effect in solving the relatively poor ductility of this alloy,which has important implications for the development of cobalt.based alloys.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11372085 and 10902029the Shenzhen Science and Technology Project under Grant No JCYJ20150625142543461
文摘The impacts of strain and polar discontinuities on the performance of superlattices have attracted widespread attention. Using first-principles calculation, we study the polarization and piezoelectricity of PbTiO3/KTa03 （PTO//KTO） superl^ttices with strain and polsr discontinuities. The strain caused by lattice mismatch between the superlattice and the substrate induces lattice distortion, the displacement of each atom and dynamical charge transfer between the Ti atom or Ta atom and the 0 atoms in the PTO//KTO superlattice. With more compressive or less tensile strain, the polarization value increases linearly, piezoelectric tensor e31 （e32） increases while e33 and e25 （e16） increase negatively. Polarity discontinuity caused by the interracial charge will produce large irreversible polarization. Proved by F-point phonons of PTO//KTO superlattices of different strain values, the polar discontinuity and the piezoelectric properties are just weakly dependent on temperature as found in PTO//KTO superlattices.
文摘The flotation results of a phosphate ore are improved by replacing the conventional collectors of fatty acids with composite collectors. The synergistic effect on the froth characteristics in systems using composite collectors has then been studied, and the concept of 'mixed hemimicellae' has been proposed in the adsorption of composite collectors at the air/solution interfaces.
文摘The properties and collecting ability of a new collector,monoalkyl ester phosphoric acid(P538),for the flotation of rare earth minerals are described in the paper.The mechanism of P538 adsorption on the surfaces of monazite or bastnaesite is explored by modern measuring techniques,such as IR and ESCA,etc.
基金Project supported by the Program of International S&T Cooperation,China(Grant No.2014DFG60230)the National Natural Science Foundation of China(Grant Nos.11605273,21571185,U1404111,11504089,21501189,and 21676291)+1 种基金the Shanghai Municipal Science and Technology Commission,China(Grant No.16ZR1443100)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA02040104)
文摘The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site（OIS）. As the concentration of He atoms in ThO2 increases, the strain induced by the He atoms increases and the octahedral interstitial site is not large enough to accommodate a large cluster, such as a He hexamer. We considered three different Schottky defect（SD） configurations（SD1, SD2, and SD3）. When He atoms are located in the SD sites, the strain induced by the He atoms is released and the incorporation and binding energies decrease. The He trimer is the most stable cluster in SD1. Large He clusters, such as a He hexamer, are also stable in the SDs.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11605273,21571185,U1404111,11504089,21501189,21676291the Shanghai Municipal Science and Technology Commission 16ZR1443100the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA02040104)
文摘Within the framework of density functional theory calculations,the structural,vibrational,and electronic properties of Zr_(n )C_(n-1)(n=2,3,and 4)and their functionalized MXenes have been investigated.We find that the most stable configurations for Zr-C MXene are the ones that the terminal groups F,O,and OH locate on the common hollow site of the superficial Zr layer and its adjacent C layer.F and OH-terminated Zr_3C_(2 )and Zr_4C_(3 )have small imaginary acoustic phonon branches aroundΓpoint while the others have no negative phonon modes.The pristine MXenes(Zr_2C,Zr_3C_(2 )and Zr_4C_3)are all metallic with large DOS contributed by the Zr atom at the Fermi energy.When functionalized by F,O and OH,new hybridization states appear and the DOS at the Fermi level are reduced.Moreover,we find that their metallic characteristic increases with an increase in n.For(Zr_(n )C_(n-1))O_2,Zr_2CO_(2 )is a semiconductor,Zr_3C_2O_(2 )is a semimetal,and Zr_4C_3O_(2 )becomes a metal.
