(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperatu...(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperature properties.This study systematically investigates the mechanical properties of(NbZrHfTi)C high-entropy ceramics by employing first-principles density functional theory,combined with the Debye-Grüneisen model,to explore the variations in their thermophysical properties with temperature(0–2000 K)and pressure(0–30 GPa).Thermodynamically,the calculated mixing enthalpy and Gibbs free energy confirm the feasibility of forming a stable single-phase solid solution in(NbZrHfTi)C.The calculated results of the elastic stiffness constant indicate that the material meets the mechanical stability criteria of the cubic crystal system,further confirming the structural stability.Through evaluation of key mechanical parameters—bulk modulus,shear modulus,Young’s modulus,and Poisson’s ratio—we provide comprehensive insight into the macro-mechanical behaviour of the material and its correlation with the underlying microstructure.Notably,compared to traditional binary carbides and their average properties,(NbZrHfTi)C exhibits higher Vickers hardness(Approximately 28.5 GPa)and fracture toughness(Approximately 3.4 MPa⋅m^(1/2)),which can be primarily attributed to the lattice distortion and solid-solution strengthening mechanism.The study also utilizes the quasi-harmonic approximation method to predict the material’s thermophysical properties,including Debye temperature(initial value around 563 K),thermal expansion coefficient(approximately 8.9×10^(−6) K−1 at 2000 K),and other key parameters such as heat capacity at constant volume.The results show that within the studied pressure and temperature ranges,(NbZrHfTi)C consistently maintains a stable phase structure and good thermomechanical properties.The thermal expansion coefficient increasing with temperature,while heat capacity approaches the Dulong-Petit limit at elevated temperatures.These findings underscore the potential of(NbZrHfTi)C applications in ultra-high temperature thermal protection systems,cutting tool coatings,and nuclear structural materials.展开更多
Mg_(2)V_(2)O_(7)is the most promising candidate for low-temperature co-fired ceramic(LTCC)multilayer devices.Selecting the appropriate precursors strongly requires reliable thermodynamic properties to be defined accur...Mg_(2)V_(2)O_(7)is the most promising candidate for low-temperature co-fired ceramic(LTCC)multilayer devices.Selecting the appropriate precursors strongly requires reliable thermodynamic properties to be defined accurately.In this study,the structural parameters of the Mg_(2)V_(2)O_(7)at ambient temperature indicate that it is crystallized in space group of P2_(1)/c.Notably,Mg_(2)V_(2)O_(7)has low lattice thermal conductivity(k_(L))of 4.77,5.12,and 4.52 W/m K,along the a,b,and c axes,respectively,which originates from the large phonon scattering rate and low phonon group velocity.The α-Mg_(2)V_(2)O_(7)←→β-Mg_(2)V_(2)O_(7) and β-Mg_(2)V_(2)O_(7)←→γ-Mg_(2)V_(2)O_(7)polymorphic transitions occur at 743℃and 908℃with enthalpy change of 1.82±0.04 kJ/mol and 1.51±0.04 kJ/mol,respectively.The endothermic effect at 1083℃ with an enthalpy change of 26.54±0.26 kJ/mol is related to the congruent melting of γ-Mg_(2)V_(2)O_(7).In addition,the molar heat capacity of Mg_(2)V_(2)O_(7) was measured utilizing drop calorimetry at high temperatures.The measured thermodynamic properties were then applied to select precursors for preparing Mg_(2)V_(2)O_(7)via a solid-state reaction,indicating that the V_(2)O_5 and Mg(OH)_(2) precursors are strongly recommended due to their thermodynamic superiority.展开更多
The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory....The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory.The results indicate that W-Ti alloys except W_(8)Ti_(8) are thermodynamically stable.The modulus and hardness of W-Ti alloys are smaller than those of pure tungsten and gradually decrease with increasing Ti concentration.However,their B/G ratios and Poisson's ratios exceed those of pure tungsten,suggesting that the introduction of Ti decreases the mechanical strength while enhancing the ductility of W-Ti alloys.The thermal expansion coefficients for W-Ti alloys all surpass those of pure tungsten,indicating that the introduction of titanium exacerbates the thermal expansion behavior of W-Ti alloys.Nevertheless,elevated pressure has the capacity to suppress the thermal expansion tendencies in titanium-doped tungsten alloys.This study offers theoretical insights for the design of nuclear materials by exploring the mechanical and thermodynamic properties of W-Ti alloys.展开更多
Density(p),speed of sound(u),viscosity(η),and refractive index(n_(D))were measured for pure acetonitrile,trichloroethene,and tetrachloroethene,as well as their binary mixtures at temperatures T=(293.15,298.15,303.15)...Density(p),speed of sound(u),viscosity(η),and refractive index(n_(D))were measured for pure acetonitrile,trichloroethene,and tetrachloroethene,as well as their binary mixtures at temperatures T=(293.15,298.15,303.15)K and at ambient pressure(81.5 kPa).From the experimental data,excess molar volume(V_(m)~E),thermal expansion coefficients(α),deviations in isentropic compressibility(Δκ_(S)),viscosity(Δ_η),and refractive index(Δn_(D))were calculated.These values were then correlated using the Redlich-Kister polynomial equation,with fitting coefficients and standard deviations determined.Additionally,the Prigogine-Flory-Patterson(PFP)theory and the Extended Real Associated Solution(ERAS)model were employed to correlate the excess molar volume,while the Perturbed Chain Statistical Associating Fluid Theory(PC-SAFT)was used to predict the density of mixtures.展开更多
Magnesium and its compounds are recognized as favorable materials for structural uses,primarily due to their lightweight nature and remarkable specific strength.This research employed first-principles methodologies to...Magnesium and its compounds are recognized as favorable materials for structural uses,primarily due to their lightweight nature and remarkable specific strength.This research employed first-principles methodologies to investigate how pressure affects the crystal structure along with the elastic and thermodynamic characteristics of MgXY_(2)(X=Zn,Cd,and Y=Ag,Au,Cu)compounds.All analyses were implemented via the Perdew-Burke-Ernzerhof variant of the Generalized Gradient Approximation alongside a plane-wave ultrasoft pseudopotential approach.The findings on the elastic constants indicated that these MgXY_(2)compounds have maintained their stability at pressures up to 500 kBar.These constants informed detailed assessments of properties like elastic modulus,Poisson’s ratio,Vickers hardness,and material anisotropy.The Quantum Espresso software was utilized to calculate melting points,Debye temperature,and minimum thermal conductivity values.A temperature range spanning from 0 to 800 K allowed for an evaluation of vibrational energy,free energy,entropy,and specific heat capacity metrics.The anticipated physical attributes suggest significant potential for these magnesium compounds in biomedical fields.展开更多
The micellization behavior and thermodynamic properties of cetyltrimethylammonium bromide(CTAB)in single lithium chloride(LiCl),potassium chloride(KCl),magnesium chloride(MgCl_(2))and calcium chloride(CaCl_(2))solutio...The micellization behavior and thermodynamic properties of cetyltrimethylammonium bromide(CTAB)in single lithium chloride(LiCl),potassium chloride(KCl),magnesium chloride(MgCl_(2))and calcium chloride(CaCl_(2))solutions were investigated at 288.15318.15 K.Result showed that the critical micelle concentration(CMC)values of CTAB in all solutions decreased to a minimum value around 298.15 K and then increased with further increasing the temperature.In all cases,the CMC values decreased with increasing salt concentration at each temperature.Additionally,the introduction of any single salt resulted in a reduction of CMC values for CTAB,attributed to the combined effects of counterions and entropy-driven interactions.The observed trend for CMC values was as follows:CMCH_(2)O>CMCKCl>CMCLiCl>CMCCaCl_(2)>CMCMgCl_(2).Furthermore,standard thermodynamic parameters,including standard free energy of micellization(ΔDG_(m)^(0)),standard enthalpy of micellization(ΔDH0m)and standard entropy of micellization(DS0 m),were calculated based on the obtained CMC values.The negative values ofΔDG_(m)^(0)indicated that the formation of CTAB micelles was a spontaneous behavior.The variations inΔDH0m andΔDS_(m)^(0)suggested that micellization was primarily entropy-driven at temperatures between 288.15 and 298.15 K,while it was influenced by both entropy and enthalpy from 298.15 to 318.15 K.Fourier transform infrared spectroscopy(FTIR)and transmission electron microscope(TEM)were employed to further explore the effects of salts on the micellization behavior of CTAB.展开更多
The effects of pressure on the structural stability,elasticity,electronic properties,and thermodynamic properties of Al,Al_(3)Cu,Al_(2)Cu,Al_(4)Cu_(9),AlCu_(3),and Cu were investigated using first-principles calculati...The effects of pressure on the structural stability,elasticity,electronic properties,and thermodynamic properties of Al,Al_(3)Cu,Al_(2)Cu,Al_(4)Cu_(9),AlCu_(3),and Cu were investigated using first-principles calculations.The experimental results indicate that the calculated equilibrium lattice constant,elastic constant,and elastic modulus agree with both theoretical and experimental data at 0 GPa.The Young's modulus,bulk modulus,and shear modulus increase with increasing pressure.The influence of pressure on mechanical properties is explained from a chemical bond perspective.By employing the quasi-harmonic approximation model of phonon calculation,the temperature and pressure dependence of thermodynamic parameters in the range of 0 to 800 K and 0 to 100 GPa are determined.The findings demonstrate that the thermal capacity and coefficient of thermal expansion increase with increasing temperature and decrease with increasing pressure.This study provides fundamental data and support for experimental investigations and further theoretical research on the properties of aluminum-copper intermetallic compounds.展开更多
The effects of the Rashba spin–orbit interaction and external electric and magnetic fields on the thermodynamic properties of parabolic quantum dots are investigated.An explicit partition function is derived,and ther...The effects of the Rashba spin–orbit interaction and external electric and magnetic fields on the thermodynamic properties of parabolic quantum dots are investigated.An explicit partition function is derived,and thermodynamic quantities,including specific heat,entropy,and magnetic susceptibility,are analyzed.The behavior of Shannon entropy-related thermodynamic quantities is examined under varying magnetic fields and Hamiltonian parameters through numerical analysis.The results reveal a pronounced Schottky anomaly in the heat capacity at lower temperatures.The susceptibility exhibits a progressive enhancement and transitions to higher values with changes in the quantum dot parameters.In the presence of the Rashba spin–orbit interaction,the specific heat increases with temperature,reaches a peak,and then decreases to zero.Additionally,the susceptibility increases with theβparameter for varying Rashba spin–orbit interaction coefficients,and at a fixed temperature,it further increases with the Rashba coefficient.展开更多
Based on the location of bromine substituents and conjugation matrix, a new substituent po- sition index ~X not only was defined, but also molecular shape indexes Km and electronega- tivity distance vectors Mm of diph...Based on the location of bromine substituents and conjugation matrix, a new substituent po- sition index ~X not only was defined, but also molecular shape indexes Km and electronega- tivity distance vectors Mm of diphenylamine and 209 kinds of polybrominated diphenylamine （PBDPA） molecules were calculated. Then the quantitative structure-property relationships （QSPR） among the thermodynamic properties of 210 organic pollutants and 0X, K3, M29, M36 were founded by Leaps-and-Bounds regression. Using the four structural parameters as input neurons of the artificial neural network, three satisfactory QSPR models with network structures of 4：21：1, 4：24：1, and 4：24：1 respectively, were achieved by the back-propagation algorithm. The total correlation coefficients R were 0.9999, 0.9997, and 0.9995 respectively and the standard errors S were 1.036, 1.469, and 1.510 respectively. The relative mean deviation between the predicted value and the experimental value of Sθ, AfHe and △fGθ- were 0.11%, 0.34% and 0.24% respectively, which indicated that the QSPR models had good stability and superior predictive ability. The results showed that there were good nonlinear correlations between the thermodynamic properties of PBDPAs and the four structural pa- rameters. Thus, it was concluded that the ANN models established by the new substituent position index were fully applicable to predict properties of PBDPAs.展开更多
First principles calculations are preformed to systematically investigate the elastic and thermodynamic properties of Re2N at high pressure and high temperature. The Re2N exhibits a clear elastic anisotropy and the el...First principles calculations are preformed to systematically investigate the elastic and thermodynamic properties of Re2N at high pressure and high temperature. The Re2N exhibits a clear elastic anisotropy and the elastic constants C11 and C33 vary rapidly in comparison with the variations in C12, C13 and C44 at high pressure. In addition, bulk modulus B, elastic modulus E, and shear modulus Gas a function of crystal orientations for Re2N are also investigated for the first time. The tensile directional dependences of the elastic modulus obey the following trend： [0001] [1211] [1010] [1011]EEEE〉〉〉 . The shear moduli of Re2N within the （0001） basal plane are the smallest and greatly reduce the resistance of against large shear deformations. Based on the quasi-harmonic Debye model, the dependences of Debye temperature, Grüneisen parameter, heat capacity and thermal expansion coefficient on the temperature and pressure are explored in the whole pressure range from 0 to 50 GPa and temperature range from 0 to 1600 K.展开更多
Electronic structure and elastic properties of Al_(2)Y,Al_(3)Y,Al_(2)Gd and Al_(3)Gd phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The g...Electronic structure and elastic properties of Al_(2)Y,Al_(3)Y,Al_(2)Gd and Al_(3)Gd phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The ground state energy and elastic constants of each phase were calculated,the formation enthalpy(ΔH),bulk modulus(B),shear modulus(G),Young's modulus(E),Poisson's ratio(ν)and anisotropic coefficient(A)were derived.The formation enthalpy shows that Al_(2)RE is more stable than Al_(3)RE,and Al-Y intermetallics have stronger phase stability than Al-Gd intermetallics.The calculated mechanical properties indicate that all these four intermetallics are strong and hard brittle phases,it may lead to the similar performance when deforming due to their similar elastic constants.The total and partial electron density of states(DOS),Mulliken population and metallicity were calculated to analyze the electron structure and bonding characteristics of the phases.Finally,phonon calculation was conducted,and the thermodynamic properties were obtained and further discussed.展开更多
The effect of pressure on structural, mechanical properties as well as the temperature dependence of thermodynamic properties of TiAl alloy are investigated by implementing first-principles calculations. The results s...The effect of pressure on structural, mechanical properties as well as the temperature dependence of thermodynamic properties of TiAl alloy are investigated by implementing first-principles calculations. The results show that the volume decrea-ses with the pressure increasing. We calculated the CtJ at various pressures and all the results satisfy mechanical stability crite-ria, thus the TiAl alloy is mechanically stable. The elastic constants？ bulk modulus and shear modulus calculated are well in a-greement with the calculated values at zero the pressure. The bulk modulus and shear modulus increase with the pressure in-creasing, which reflects the deformation resistance, and accordingly, deformation resistance can be strengthened with the in-crease of pressure. The brittle nature of TiAl alloy turns to ductile nature in 10 - 20 GPa . The Debye temperature, linear ther-mal expansion and heat capacity are calculated using the quasi-harmonic Debye model under the pressure ranging from 0 to 50 GPa and the temperature ranging from 0 to 1 000 K, which are useful to investigate the effect of temperature and pressure on thermodynamic parameters. Finally, electronic structure is calculated at various pressures,and it can be found that the peak intensity decreases with increasing pressure and the the strength of d-d orbital of Ti is weakened but the ductility is enhanced.展开更多
The geometric structures,electronic absorption spectrum,and thermodynamic pro-perties of 3-（4-N-maleimido）-phenyl-2,4-dihydro-2H-1,3-benzoxazine molecule were studied at the B3LYP/6-311＋G＊ level by density functio...The geometric structures,electronic absorption spectrum,and thermodynamic pro-perties of 3-（4-N-maleimido）-phenyl-2,4-dihydro-2H-1,3-benzoxazine molecule were studied at the B3LYP/6-311＋G＊ level by density functional theory.The results show that three rings of this molecule are in different planes.In gas,absorption wavelength of the lowest energy excitation was obtained at 503 nm,and solvents made it blue-shifted by 3-7 nm,both corresponding to the electron transition of HOMO → LUMO.At 298.15 K,the standard molar formed enthalpy and free energy of the title compound molecule were-549.43 and-273.37 kJ·mol-1,respectively.展开更多
Refractory high-entropy alloys(RHEAs)are emerging as new materials for high temperature structural applications because of their stable mechanical and thermal properties at temperatures higher than 2273 K.In this stud...Refractory high-entropy alloys(RHEAs)are emerging as new materials for high temperature structural applications because of their stable mechanical and thermal properties at temperatures higher than 2273 K.In this study,the mechanical properties of MoNbTaTiW RHEA are examined by applying calculations based on first-principles density functional theory(DFT)and using a large unit cell with 100 randomized atoms.The phase calculation of MoNbTaTiW with CALPHAD method shows the existence of a stable body-centered cubic structure at a high temperature and a hexagonal closely packed phase at a low temperature.The predicted phase,shear modulus,Young’s modulus,Poisson’s ratio,and hardness values are consistent with available experimental results.The linear thermal expansion coefficient,vibrational entropy,and vibrational heat capacity of MoNbTaTiW RHEA are investigated in accordance with Debye-Grüneisen theory.These results may provide a basis for future research related to the application of RHEAs.展开更多
Adsorption of atrazine, prometryne and prometon was determined on six soils with different physical and chemical properties. The adsorption isotherms of three herbicides could well fit Freundlich equation. On all of s...Adsorption of atrazine, prometryne and prometon was determined on six soils with different physical and chemical properties. The adsorption isotherms of three herbicides could well fit Freundlich equation. On all of six soils, adsorption of herbicides increased in the order: atrazine ≈prometon<prometryne. This order is quite the same to the calculation result of by means of excess thermodynamic properties of triazine. The Freundlich adsorption constants, K f, showed to have good correlation with organic matter(OM%) of soils for each of these herbicides, suggesting that OM is the main factor, which dominates in the adsorption process of these triazine herbicides.展开更多
The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L1_2 structure Al_3Tm and Al_3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion c...The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L1_2 structure Al_3Tm and Al_3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al_3Tm and A_3Lu keep their dynamical stabilities in L1_2 structure up to 100 GPa. The elastic properties and Debye temperatures for Al_3Tm and Al_3 Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices AG, AU, AZ, and the threedimensional（3D） curved surface of Young＇s modulus. The calculated results show that Al_3Tm and Al_3Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al_3Tm and Al_3Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications.展开更多
To understand deeply the structural, elastic and thermodynamic characteristics of AI2X （X= Sc, Y） compounds in C15 type （space number 227） Cu2Mg structure, we have performed ab-initio density functional theory wit...To understand deeply the structural, elastic and thermodynamic characteristics of AI2X （X= Sc, Y） compounds in C15 type （space number 227） Cu2Mg structure, we have performed ab-initio density functional theory within the local density approximation （LDA） and the generalized gradient approximation （GGA）. The thermodynamic properties of the considered structures are obtained through the quasi-harmonic Debye model. We have presented the results on the basic physical parameters, such as the lattice constant, bulk modu- lus, pressure derivative of bulk modulus, second-order elastic constants, Zener anisotropy factor, Poissongs ratio, Youngts modulus, and isotropic shear modulus. In order to gain further information, the pressure- and temperature-dependent behaviour of the volume, bulk modulus, thermal expansion coefficient, heat capacity, entropy, Debye temperature and Griineisen parameter were also evaluated over a pressure range of 0-20 GPa for Al2Sc and 0-17 GPa for Al2Y compound and a wide temperature range of 0-2000 K for both compounds. The obtained results were compared with the other reported values.展开更多
The hydriding/dehydriding thermodynamic properties of the slurry system formed by suspending La rich mischmetal nickel hydrogen storage alloy (MlNi 5) in Benzene (C 6H 6) were investigated. The pressure compositi...The hydriding/dehydriding thermodynamic properties of the slurry system formed by suspending La rich mischmetal nickel hydrogen storage alloy (MlNi 5) in Benzene (C 6H 6) were investigated. The pressure composition isotherms for both the alloy powder and the slurry suspended with MlNi 5 were measured at several temperatures(10, 20, 30, 40 ℃). The standard enthalpy of formation Δ H ° and standard entropy of formation Δ S ° for the alloy powder with and without benzene were determined respectively. The experimental results show that the values of Δ H ° and Δ S ° for the hydriding reaction of hydrogen storage alloy (MlNi 5) of the slurry system and the gas solid system are all very close.展开更多
Ab initio molecular orbital calculations have been performed at Hartree-Fock （HF）, second-order Mrller-Plesset （MP2）, and hybrid density functional theory （DFT） B3LYP levels with 6-31G^＊＊ basis set to investig...Ab initio molecular orbital calculations have been performed at Hartree-Fock （HF）, second-order Mrller-Plesset （MP2）, and hybrid density functional theory （DFT） B3LYP levels with 6-31G^＊＊ basis set to investigate the low sensitive explosive trans-1,4,5,8-tetranitro-1,4,5,8- tetraazadecalin （TNAD） and its seven bicyclic isomers. Their molecular geometries, electronic structures, thermodynamic properties, and detonation performances were predicted and compared. The relationships between structures and various properties were discussed in detail. The calculated results agree well with the available experimental data, and suggest that some compounds may be novel potential candidates of high energy density materials （HEDMs） with performances better than TNT （2,4,6-trinitrotoluene） and similar to RDX （1,3,5-trinitro-1,3,5-triazacyclohexane）.展开更多
基金supported by the National Natural Science Foundation of China(Nos.92166105 and 52005053)High-Tech Industry Science and Technology Innovation Leading Program of Hunan Province(No.2020GK2085)the Science and Technology Innovation Program of Hunan Province(No.2021RC3096).
文摘(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperature properties.This study systematically investigates the mechanical properties of(NbZrHfTi)C high-entropy ceramics by employing first-principles density functional theory,combined with the Debye-Grüneisen model,to explore the variations in their thermophysical properties with temperature(0–2000 K)and pressure(0–30 GPa).Thermodynamically,the calculated mixing enthalpy and Gibbs free energy confirm the feasibility of forming a stable single-phase solid solution in(NbZrHfTi)C.The calculated results of the elastic stiffness constant indicate that the material meets the mechanical stability criteria of the cubic crystal system,further confirming the structural stability.Through evaluation of key mechanical parameters—bulk modulus,shear modulus,Young’s modulus,and Poisson’s ratio—we provide comprehensive insight into the macro-mechanical behaviour of the material and its correlation with the underlying microstructure.Notably,compared to traditional binary carbides and their average properties,(NbZrHfTi)C exhibits higher Vickers hardness(Approximately 28.5 GPa)and fracture toughness(Approximately 3.4 MPa⋅m^(1/2)),which can be primarily attributed to the lattice distortion and solid-solution strengthening mechanism.The study also utilizes the quasi-harmonic approximation method to predict the material’s thermophysical properties,including Debye temperature(initial value around 563 K),thermal expansion coefficient(approximately 8.9×10^(−6) K−1 at 2000 K),and other key parameters such as heat capacity at constant volume.The results show that within the studied pressure and temperature ranges,(NbZrHfTi)C consistently maintains a stable phase structure and good thermomechanical properties.The thermal expansion coefficient increasing with temperature,while heat capacity approaches the Dulong-Petit limit at elevated temperatures.These findings underscore the potential of(NbZrHfTi)C applications in ultra-high temperature thermal protection systems,cutting tool coatings,and nuclear structural materials.
基金supported by the National Key Research and Development Program of China(No.2022YFC3901001-1)the National Natural Science Foundation of China(Grant No.U1902217)financial support from the Chinese Scholarship Council(CSC No.202106050084)。
文摘Mg_(2)V_(2)O_(7)is the most promising candidate for low-temperature co-fired ceramic(LTCC)multilayer devices.Selecting the appropriate precursors strongly requires reliable thermodynamic properties to be defined accurately.In this study,the structural parameters of the Mg_(2)V_(2)O_(7)at ambient temperature indicate that it is crystallized in space group of P2_(1)/c.Notably,Mg_(2)V_(2)O_(7)has low lattice thermal conductivity(k_(L))of 4.77,5.12,and 4.52 W/m K,along the a,b,and c axes,respectively,which originates from the large phonon scattering rate and low phonon group velocity.The α-Mg_(2)V_(2)O_(7)←→β-Mg_(2)V_(2)O_(7) and β-Mg_(2)V_(2)O_(7)←→γ-Mg_(2)V_(2)O_(7)polymorphic transitions occur at 743℃and 908℃with enthalpy change of 1.82±0.04 kJ/mol and 1.51±0.04 kJ/mol,respectively.The endothermic effect at 1083℃ with an enthalpy change of 26.54±0.26 kJ/mol is related to the congruent melting of γ-Mg_(2)V_(2)O_(7).In addition,the molar heat capacity of Mg_(2)V_(2)O_(7) was measured utilizing drop calorimetry at high temperatures.The measured thermodynamic properties were then applied to select precursors for preparing Mg_(2)V_(2)O_(7)via a solid-state reaction,indicating that the V_(2)O_5 and Mg(OH)_(2) precursors are strongly recommended due to their thermodynamic superiority.
基金Funded by National Key R&D Program of China(No.2021YFB3802300)the National Natural Science Foundation of China(No.52171045)the Joint Fund(No.8091B022108)。
文摘The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory.The results indicate that W-Ti alloys except W_(8)Ti_(8) are thermodynamically stable.The modulus and hardness of W-Ti alloys are smaller than those of pure tungsten and gradually decrease with increasing Ti concentration.However,their B/G ratios and Poisson's ratios exceed those of pure tungsten,suggesting that the introduction of Ti decreases the mechanical strength while enhancing the ductility of W-Ti alloys.The thermal expansion coefficients for W-Ti alloys all surpass those of pure tungsten,indicating that the introduction of titanium exacerbates the thermal expansion behavior of W-Ti alloys.Nevertheless,elevated pressure has the capacity to suppress the thermal expansion tendencies in titanium-doped tungsten alloys.This study offers theoretical insights for the design of nuclear materials by exploring the mechanical and thermodynamic properties of W-Ti alloys.
基金Bu-Ali Sina University for providing financial support for conducting this study。
文摘Density(p),speed of sound(u),viscosity(η),and refractive index(n_(D))were measured for pure acetonitrile,trichloroethene,and tetrachloroethene,as well as their binary mixtures at temperatures T=(293.15,298.15,303.15)K and at ambient pressure(81.5 kPa).From the experimental data,excess molar volume(V_(m)~E),thermal expansion coefficients(α),deviations in isentropic compressibility(Δκ_(S)),viscosity(Δ_η),and refractive index(Δn_(D))were calculated.These values were then correlated using the Redlich-Kister polynomial equation,with fitting coefficients and standard deviations determined.Additionally,the Prigogine-Flory-Patterson(PFP)theory and the Extended Real Associated Solution(ERAS)model were employed to correlate the excess molar volume,while the Perturbed Chain Statistical Associating Fluid Theory(PC-SAFT)was used to predict the density of mixtures.
基金support of the National Center for High Performance Computing(UHe M)#1012332022#。
文摘Magnesium and its compounds are recognized as favorable materials for structural uses,primarily due to their lightweight nature and remarkable specific strength.This research employed first-principles methodologies to investigate how pressure affects the crystal structure along with the elastic and thermodynamic characteristics of MgXY_(2)(X=Zn,Cd,and Y=Ag,Au,Cu)compounds.All analyses were implemented via the Perdew-Burke-Ernzerhof variant of the Generalized Gradient Approximation alongside a plane-wave ultrasoft pseudopotential approach.The findings on the elastic constants indicated that these MgXY_(2)compounds have maintained their stability at pressures up to 500 kBar.These constants informed detailed assessments of properties like elastic modulus,Poisson’s ratio,Vickers hardness,and material anisotropy.The Quantum Espresso software was utilized to calculate melting points,Debye temperature,and minimum thermal conductivity values.A temperature range spanning from 0 to 800 K allowed for an evaluation of vibrational energy,free energy,entropy,and specific heat capacity metrics.The anticipated physical attributes suggest significant potential for these magnesium compounds in biomedical fields.
基金The support of National Natural Science Foundation of China(22208198 and 22478232)is gratefully acknowledged。
文摘The micellization behavior and thermodynamic properties of cetyltrimethylammonium bromide(CTAB)in single lithium chloride(LiCl),potassium chloride(KCl),magnesium chloride(MgCl_(2))and calcium chloride(CaCl_(2))solutions were investigated at 288.15318.15 K.Result showed that the critical micelle concentration(CMC)values of CTAB in all solutions decreased to a minimum value around 298.15 K and then increased with further increasing the temperature.In all cases,the CMC values decreased with increasing salt concentration at each temperature.Additionally,the introduction of any single salt resulted in a reduction of CMC values for CTAB,attributed to the combined effects of counterions and entropy-driven interactions.The observed trend for CMC values was as follows:CMCH_(2)O>CMCKCl>CMCLiCl>CMCCaCl_(2)>CMCMgCl_(2).Furthermore,standard thermodynamic parameters,including standard free energy of micellization(ΔDG_(m)^(0)),standard enthalpy of micellization(ΔDH0m)and standard entropy of micellization(DS0 m),were calculated based on the obtained CMC values.The negative values ofΔDG_(m)^(0)indicated that the formation of CTAB micelles was a spontaneous behavior.The variations inΔDH0m andΔDS_(m)^(0)suggested that micellization was primarily entropy-driven at temperatures between 288.15 and 298.15 K,while it was influenced by both entropy and enthalpy from 298.15 to 318.15 K.Fourier transform infrared spectroscopy(FTIR)and transmission electron microscope(TEM)were employed to further explore the effects of salts on the micellization behavior of CTAB.
基金Funded by the National Key R&D Program of China(No.2021YFB3802300)the Foundation of National Key Laboratory of Shock Wave and Detonation Physics(No.JCKYS2022212004)the National Natural Science Foundation of China(No.52171045),and the Joint Fund(No.8091B022108)。
文摘The effects of pressure on the structural stability,elasticity,electronic properties,and thermodynamic properties of Al,Al_(3)Cu,Al_(2)Cu,Al_(4)Cu_(9),AlCu_(3),and Cu were investigated using first-principles calculations.The experimental results indicate that the calculated equilibrium lattice constant,elastic constant,and elastic modulus agree with both theoretical and experimental data at 0 GPa.The Young's modulus,bulk modulus,and shear modulus increase with increasing pressure.The influence of pressure on mechanical properties is explained from a chemical bond perspective.By employing the quasi-harmonic approximation model of phonon calculation,the temperature and pressure dependence of thermodynamic parameters in the range of 0 to 800 K and 0 to 100 GPa are determined.The findings demonstrate that the thermal capacity and coefficient of thermal expansion increase with increasing temperature and decrease with increasing pressure.This study provides fundamental data and support for experimental investigations and further theoretical research on the properties of aluminum-copper intermetallic compounds.
文摘The effects of the Rashba spin–orbit interaction and external electric and magnetic fields on the thermodynamic properties of parabolic quantum dots are investigated.An explicit partition function is derived,and thermodynamic quantities,including specific heat,entropy,and magnetic susceptibility,are analyzed.The behavior of Shannon entropy-related thermodynamic quantities is examined under varying magnetic fields and Hamiltonian parameters through numerical analysis.The results reveal a pronounced Schottky anomaly in the heat capacity at lower temperatures.The susceptibility exhibits a progressive enhancement and transitions to higher values with changes in the quantum dot parameters.In the presence of the Rashba spin–orbit interaction,the specific heat increases with temperature,reaches a peak,and then decreases to zero.Additionally,the susceptibility increases with theβparameter for varying Rashba spin–orbit interaction coefficients,and at a fixed temperature,it further increases with the Rashba coefficient.
文摘Based on the location of bromine substituents and conjugation matrix, a new substituent po- sition index ~X not only was defined, but also molecular shape indexes Km and electronega- tivity distance vectors Mm of diphenylamine and 209 kinds of polybrominated diphenylamine （PBDPA） molecules were calculated. Then the quantitative structure-property relationships （QSPR） among the thermodynamic properties of 210 organic pollutants and 0X, K3, M29, M36 were founded by Leaps-and-Bounds regression. Using the four structural parameters as input neurons of the artificial neural network, three satisfactory QSPR models with network structures of 4：21：1, 4：24：1, and 4：24：1 respectively, were achieved by the back-propagation algorithm. The total correlation coefficients R were 0.9999, 0.9997, and 0.9995 respectively and the standard errors S were 1.036, 1.469, and 1.510 respectively. The relative mean deviation between the predicted value and the experimental value of Sθ, AfHe and △fGθ- were 0.11%, 0.34% and 0.24% respectively, which indicated that the QSPR models had good stability and superior predictive ability. The results showed that there were good nonlinear correlations between the thermodynamic properties of PBDPAs and the four structural pa- rameters. Thus, it was concluded that the ANN models established by the new substituent position index were fully applicable to predict properties of PBDPAs.
基金Project (11204007) supported by the National Natural Science Foundation of ChinaProject (2012JQ1005) supported by Natural Science Basic Research Plan of Shaanxi Province,ChinaProject (2013JK0638) supported by the Education Committee Natural Science Foundation of Shaanxi Province,China
文摘First principles calculations are preformed to systematically investigate the elastic and thermodynamic properties of Re2N at high pressure and high temperature. The Re2N exhibits a clear elastic anisotropy and the elastic constants C11 and C33 vary rapidly in comparison with the variations in C12, C13 and C44 at high pressure. In addition, bulk modulus B, elastic modulus E, and shear modulus Gas a function of crystal orientations for Re2N are also investigated for the first time. The tensile directional dependences of the elastic modulus obey the following trend： [0001] [1211] [1010] [1011]EEEE〉〉〉 . The shear moduli of Re2N within the （0001） basal plane are the smallest and greatly reduce the resistance of against large shear deformations. Based on the quasi-harmonic Debye model, the dependences of Debye temperature, Grüneisen parameter, heat capacity and thermal expansion coefficient on the temperature and pressure are explored in the whole pressure range from 0 to 50 GPa and temperature range from 0 to 1600 K.
基金This work is supported by the Key Technologies Research and Development Program of Liaoning Province(2013201018).
文摘Electronic structure and elastic properties of Al_(2)Y,Al_(3)Y,Al_(2)Gd and Al_(3)Gd phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The ground state energy and elastic constants of each phase were calculated,the formation enthalpy(ΔH),bulk modulus(B),shear modulus(G),Young's modulus(E),Poisson's ratio(ν)and anisotropic coefficient(A)were derived.The formation enthalpy shows that Al_(2)RE is more stable than Al_(3)RE,and Al-Y intermetallics have stronger phase stability than Al-Gd intermetallics.The calculated mechanical properties indicate that all these four intermetallics are strong and hard brittle phases,it may lead to the similar performance when deforming due to their similar elastic constants.The total and partial electron density of states(DOS),Mulliken population and metallicity were calculated to analyze the electron structure and bonding characteristics of the phases.Finally,phonon calculation was conducted,and the thermodynamic properties were obtained and further discussed.
基金National Natural Science Foundation of China(Nos.U1610123,51674226,51574207,51574206,51274175)International Cooperation Project of the Ministry of Science and Technology of China(No.2014DFA50320)+3 种基金Science and Technology Major Project of Shanxi Province(No.MC2016-06)International Science and Technology Cooperation Project of Shanxi Province(No.2015081041)Research Project Supported by Shanxi Scholarship Council of China(No.2016-Key 2)Transformation of Scientific and Technological Achievements Special Guide Project of Shanxi Province(No.201604D131029)
文摘The effect of pressure on structural, mechanical properties as well as the temperature dependence of thermodynamic properties of TiAl alloy are investigated by implementing first-principles calculations. The results show that the volume decrea-ses with the pressure increasing. We calculated the CtJ at various pressures and all the results satisfy mechanical stability crite-ria, thus the TiAl alloy is mechanically stable. The elastic constants？ bulk modulus and shear modulus calculated are well in a-greement with the calculated values at zero the pressure. The bulk modulus and shear modulus increase with the pressure in-creasing, which reflects the deformation resistance, and accordingly, deformation resistance can be strengthened with the in-crease of pressure. The brittle nature of TiAl alloy turns to ductile nature in 10 - 20 GPa . The Debye temperature, linear ther-mal expansion and heat capacity are calculated using the quasi-harmonic Debye model under the pressure ranging from 0 to 50 GPa and the temperature ranging from 0 to 1 000 K, which are useful to investigate the effect of temperature and pressure on thermodynamic parameters. Finally, electronic structure is calculated at various pressures,and it can be found that the peak intensity decreases with increasing pressure and the the strength of d-d orbital of Ti is weakened but the ductility is enhanced.
基金Sponsored by the Supporting Project of Sichuan Province Key Technology Support Program (2011ZG0247)Sichuan Province Education Office Natural Science Foundation (10ZC080)
文摘The geometric structures,electronic absorption spectrum,and thermodynamic pro-perties of 3-（4-N-maleimido）-phenyl-2,4-dihydro-2H-1,3-benzoxazine molecule were studied at the B3LYP/6-311＋G＊ level by density functional theory.The results show that three rings of this molecule are in different planes.In gas,absorption wavelength of the lowest energy excitation was obtained at 503 nm,and solvents made it blue-shifted by 3-7 nm,both corresponding to the electron transition of HOMO → LUMO.At 298.15 K,the standard molar formed enthalpy and free energy of the title compound molecule were-549.43 and-273.37 kJ·mol-1,respectively.
基金the NSF EPSCoR CIMM project under the award#OIA-1541079 and DoD support under the W911NF1910005 contractComputational simulations were supported by the Louisiana Optical Network Infrastructure(LONI)with the supercomputer allocation loni_mat_bio12.
文摘Refractory high-entropy alloys(RHEAs)are emerging as new materials for high temperature structural applications because of their stable mechanical and thermal properties at temperatures higher than 2273 K.In this study,the mechanical properties of MoNbTaTiW RHEA are examined by applying calculations based on first-principles density functional theory(DFT)and using a large unit cell with 100 randomized atoms.The phase calculation of MoNbTaTiW with CALPHAD method shows the existence of a stable body-centered cubic structure at a high temperature and a hexagonal closely packed phase at a low temperature.The predicted phase,shear modulus,Young’s modulus,Poisson’s ratio,and hardness values are consistent with available experimental results.The linear thermal expansion coefficient,vibrational entropy,and vibrational heat capacity of MoNbTaTiW RHEA are investigated in accordance with Debye-Grüneisen theory.These results may provide a basis for future research related to the application of RHEAs.
文摘Adsorption of atrazine, prometryne and prometon was determined on six soils with different physical and chemical properties. The adsorption isotherms of three herbicides could well fit Freundlich equation. On all of six soils, adsorption of herbicides increased in the order: atrazine ≈prometon<prometryne. This order is quite the same to the calculation result of by means of excess thermodynamic properties of triazine. The Freundlich adsorption constants, K f, showed to have good correlation with organic matter(OM%) of soils for each of these herbicides, suggesting that OM is the main factor, which dominates in the adsorption process of these triazine herbicides.
基金Project supported by the Scientific Technology Plan of the Educational Department of Liaoning Province and Liaoning Innovative Research Team in University,China(Grant No.LT2014004)the Program for the Young Teacher Cultivation Fund of Shenyang University of Technology,China(Grant No.005612)
文摘The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L1_2 structure Al_3Tm and Al_3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al_3Tm and A_3Lu keep their dynamical stabilities in L1_2 structure up to 100 GPa. The elastic properties and Debye temperatures for Al_3Tm and Al_3 Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices AG, AU, AZ, and the threedimensional（3D） curved surface of Young＇s modulus. The calculated results show that Al_3Tm and Al_3Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al_3Tm and Al_3Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications.
文摘To understand deeply the structural, elastic and thermodynamic characteristics of AI2X （X= Sc, Y） compounds in C15 type （space number 227） Cu2Mg structure, we have performed ab-initio density functional theory within the local density approximation （LDA） and the generalized gradient approximation （GGA）. The thermodynamic properties of the considered structures are obtained through the quasi-harmonic Debye model. We have presented the results on the basic physical parameters, such as the lattice constant, bulk modu- lus, pressure derivative of bulk modulus, second-order elastic constants, Zener anisotropy factor, Poissongs ratio, Youngts modulus, and isotropic shear modulus. In order to gain further information, the pressure- and temperature-dependent behaviour of the volume, bulk modulus, thermal expansion coefficient, heat capacity, entropy, Debye temperature and Griineisen parameter were also evaluated over a pressure range of 0-20 GPa for Al2Sc and 0-17 GPa for Al2Y compound and a wide temperature range of 0-2000 K for both compounds. The obtained results were compared with the other reported values.
文摘The hydriding/dehydriding thermodynamic properties of the slurry system formed by suspending La rich mischmetal nickel hydrogen storage alloy (MlNi 5) in Benzene (C 6H 6) were investigated. The pressure composition isotherms for both the alloy powder and the slurry suspended with MlNi 5 were measured at several temperatures(10, 20, 30, 40 ℃). The standard enthalpy of formation Δ H ° and standard entropy of formation Δ S ° for the alloy powder with and without benzene were determined respectively. The experimental results show that the values of Δ H ° and Δ S ° for the hydriding reaction of hydrogen storage alloy (MlNi 5) of the slurry system and the gas solid system are all very close.
基金The project was supported by NNSFC (Nos. 10576030 and 10576016) and the Innovation Project for Postgraduates in the Universities of Jiangsu Province (AD20116)
文摘Ab initio molecular orbital calculations have been performed at Hartree-Fock （HF）, second-order Mrller-Plesset （MP2）, and hybrid density functional theory （DFT） B3LYP levels with 6-31G^＊＊ basis set to investigate the low sensitive explosive trans-1,4,5,8-tetranitro-1,4,5,8- tetraazadecalin （TNAD） and its seven bicyclic isomers. Their molecular geometries, electronic structures, thermodynamic properties, and detonation performances were predicted and compared. The relationships between structures and various properties were discussed in detail. The calculated results agree well with the available experimental data, and suggest that some compounds may be novel potential candidates of high energy density materials （HEDMs） with performances better than TNT （2,4,6-trinitrotoluene） and similar to RDX （1,3,5-trinitro-1,3,5-triazacyclohexane）.
