Electrocatalytic water splitting(EWS)driven by renewable energy is vital for clean hydrogen(H2)production and reducing reliance on fossil fuels.While IrO_(2) and RuO_(2) are the leading electrocatalysts for the oxygen...Electrocatalytic water splitting(EWS)driven by renewable energy is vital for clean hydrogen(H2)production and reducing reliance on fossil fuels.While IrO_(2) and RuO_(2) are the leading electrocatalysts for the oxygen evolution reaction(OER)and Pt for the hydrogen evolution reaction(HER)in acidic environments,the need for efficient,stable,and affordable materials persists.Recently,transition-metal borides(TMBs),particularly metal diborides(MDbs),have gained attention due to their unique layered crystal structures with multicentered boron bonds,offering remarkable physicochemical properties.Their nearly 2D structures boost electrochemical performance by offering high conductivity and a large active surface area,making them well-suited for advanced energy storage and conversion technologies.This review provides a comprehensive overview of the critical factors for water splitting,the crystal and electronic structures of MDbs,and their synthetic strategies.Furthermore,it examines the relationship between catalytic performance and intermediate adsorption as elucidated by first-principle calculations.The review also highlights the latest experimental advancements in MDb-based electrocatalysts and addresses the current challenges and future directions for their development.展开更多
High-entropy diborides(HEBs)have attracted extensive research due to their potential ultra-high hardness.In the present work,the effects of transition metals(TM)on lattice parameters,electron work function(EWF),bondin...High-entropy diborides(HEBs)have attracted extensive research due to their potential ultra-high hardness.In the present work,the effects of transition metals(TM)on lattice parameters,electron work function(EWF),bonding charge density,and hardness of HEBs are comprehensively investigated by the first-principles calculations,including(TiZrHfNbTa)B_(2),(TiZrHfNbMo)B_(2),(TiZrHfTaMo)B_(2),(TiZrNbTaMo)B_(2),and(TiHfNbTaMo)B_(2).It is revealed that the disordered TM atoms result in a severe local lattice distortion and the formation of weak spots.In view of bonding charge density,it is understood that the degree of electron contribution of TM atoms directly affects the bonding strength of the metallic layer,contributing to the optimized hardness of HEBs.Moreover,the proposed power-law-scaled relationship integrating the EWF and the grain size yields an excellent agreement between our predicted results and those reported experimental ones.It is found that the HEBs exhibit relatively high hardness which is higher than those of single transition metal diborides.In particular,the hardness of(TiZrNbTaMo)B_(2)and(TiHfNbTaMo)B_(2)can be as high as29.15 and 28.02 GPa,respectively.This work provides a rapid strategy to discover/design advanced HEBs efficiently,supported by the coupling hardening mechanisms of solid solution and grain refinement based on the atomic and electronic interactions.展开更多
Structural and mechanical properties of several rare-earth diborides were systematically investigated by first principles calculations. Specifically, we studied XB2 , where X=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu in ...Structural and mechanical properties of several rare-earth diborides were systematically investigated by first principles calculations. Specifically, we studied XB2 , where X=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu in the hexagonal AlB2 , ReB2 , and orthorhombic OsB2 -type structures. The lattice parameters, bulk modulus, bond distances, second order elastic constants, and related polycrystalline elastic moduli （e.g., shear modulus, Young’s modulus, Poisson’s ratio, Debye temperature, sound velocities） were calculated. Our results indicate that these compounds are mechanically stable in the considered structures, and according to ＂Chen’s method＂, the predicted Vickers hardness shows that they are hard materials in AlB2 - and OsB2 -type structures.展开更多
The potential applications of transition metal diborides(TMB_2) in extreme environments are particularly attractive but still blocked by some intrinsic properties such as poor resistances to thermal shock and oxidatio...The potential applications of transition metal diborides(TMB_2) in extreme environments are particularly attractive but still blocked by some intrinsic properties such as poor resistances to thermal shock and oxidation. Since surface plays a key role during grain growth and oxygen adsorption, an insight into the surface properties of TMB_2 is essential for understanding the materials performance and accelerating the development of ultra-high temperature ceramics. By employing two-region modeling method, the stability and oxygen adsorption behavior of TMB_2 surfaces were investigated by first-principles calculations based on density functional theory. The effects of valance electron concentration on the surface stability and oxygen adsorption were studied and the general trends were summarized. After analyzing the anisotropy in surface stability and oxygen adsorption, the observed grain morphology of TMB_2 were well explained, and it was also predicted that YB_2, HfB_2 and TaB_2 may have better initial oxidation resistance than ZrB_2.展开更多
Ceramic materials have obvious advantages in thermal stability,but impedance mismatch limits their ability to attenuate electromagnetic(EM)waves.Herein,a novel series of high-entropy(V_(0.2)Nb_(0.2)Zr_(0.2)Ta_(0.2)X_(...Ceramic materials have obvious advantages in thermal stability,but impedance mismatch limits their ability to attenuate electromagnetic(EM)waves.Herein,a novel series of high-entropy(V_(0.2)Nb_(0.2)Zr_(0.2)Ta_(0.2)X_(0.2))B_(2)(X=Mo,Ti,and Hf)ceramics were successfully synthesized via ultrafast high-temperature sintering(UHS)apparatus based on joule heating.The results indicated that the effect of high-entropy component on the magnetic loss of the system was relatively small,but the effect on the dielectric loss was larger.Among them,the(V_(0.2)Nb_(0.2)Zr_(0.2)Ta_(0.2)Ti_(0.2))B_(2)(HEB-Ti)sample demonstrated superior absorbing properties due to relatively moderate dielectric loss and optimal EM impedance matching.Moreover,because of its relatively moderate attenuation constant,it could achieve the maximum penetration of the EM wave and the minimum reflection after absorbing wave.As a result,the minimum reflection loss(RL_(min))was as low as−40.7 dB,and the effective absorption band covered the entire low-frequency range from 2 to 8 GHz.Its excellent absorption performance was mainly due to the synergistic effect of various dielectric attenuation mechanisms,including defect polarization,dipole polarization,and conduction loss.Furthermore,thermogravimetric(TG)analysis showed that the sample exhibited excellent thermal stability and could withstand temperatures up to 550℃in air and 1000℃in an argon gas environment.The relevant work could provide meaningful references for the design of new high-performance ceramic wave-absorbing materials.展开更多
Understanding the initial oxidation mechanism is critical for studying the oxidation resistance of high-entropy diborides.However,related studies are scarce.Herein,the initial oxidation mechanism of(Zr_(0.25)Ti_(0.25)...Understanding the initial oxidation mechanism is critical for studying the oxidation resistance of high-entropy diborides.However,related studies are scarce.Herein,the initial oxidation mechanism of(Zr_(0.25)Ti_(0.25)Nb_(0.25)Ta_(0.25))B_(2)high-entropy diborides(HEB_(2)-1)is investigated by first-principles calculations at the atomic level.By employing the two-region model method,the most stable surface of HEB_(2)-1 is determined to be(1120)surface.The dissociative adsorption process of the oxygen molecule on the HEB_(2)-1-(1120)surface is predicted to proceed spontaneously,where OeO bond breaks and each oxygen atom is chemisorbed on the most preferable hollow site.The adsorption energy and the diffusion barrier of the oxygen atom on the(1120)surface of HEB_(2)-1 are in the vicinity of the average level of the cor-responding four individual diborides.In addition,ab initio molecular dynamics simulations indicate a high initial oxidation resistance of HEB_(2)-1 at 1000 K.Our results are beneficial to further designing the high-entropy diborides with excellent oxidation resistance.展开更多
Oxidation resistance is critical for high-entropy diborides(HEBs)to be used as thermal structural components under oxygen-containing high-temperature environments.Here,we successfully realize the exploitation of(Zr,Ta...Oxidation resistance is critical for high-entropy diborides(HEBs)to be used as thermal structural components under oxygen-containing high-temperature environments.Here,we successfully realize the exploitation of(Zr,Ta,Cr,W)B2 HEBs with superior oxidation resistance by comprehensively screening their compositions.To be specific,21 kinds of HEB-xTM(x=0–25 mol%,TM=Zr,Ta,Cr,and W)samples are fabricated via an ultrafast high-temperature sintering technique.The as-fabricated HEB-5Cr samples show the best oxidation resistance at 1673 K among all the samples.Subsquent oxidation investigations further confirm the as-fabricated HEB-5Cr samples possess superior oxidation resistance with the parabolic oxidation behavior across 1473–1773 K.Such superior oxidation resistance is believed to result from the multi-component synergistic effects.Particularly,the Ta^(5+)and W^(4+)cations with high ionic field strengths can promote the formation of 4B–O–4B linkages between[BO4]tetrahedrons by charge balance,which can stabilize the threedimensional skeletal structure of B_(2)O_(3)glass and consequently result in an improved viscosity of the B_(2)O_(3)glassy layer.In addition,the ZrO_(2)and Cr_(2)O_(3)with high melting points can dissolve into the B_(2)O_(3)glass to increase its glass transition temperature,leading to an enhanced viscosity of the B_(2)O_(3)glassy layer.展开更多
The advance in communication technology has triggered worldwide concern on electromagnetic wave pollution.To cope with this challenge,exploring high-performance electromagnetic(EM)wave absorbing materials with dielect...The advance in communication technology has triggered worldwide concern on electromagnetic wave pollution.To cope with this challenge,exploring high-performance electromagnetic(EM)wave absorbing materials with dielectric and magnetic losses coupling is urgently required.Of the EM wave absorbers,transition metal diborides(TMB2)possess excellent dielectric loss capability.However,akin to other single dielectric materials,poor impedance match leads to inferior performance.High-entropy engineering is expected to be effective in tailoring the balance between dielectric and magnetic losses through compositional design.Herein,three HE TMB2 powders with nominal equimolar TM including HE TMB2-I(TM=Zr,Hf,Nb,Ta),HE TMB2-2(TM=Ti,Zr,Hf,Nb,Ta),and HE TMB2-3(TM=Cr,Zr,Hf,Nb,Ta)have been designed and prepared by one-step boro/carbothermal reduction.As a result of synergistic effects of strong attenuation capability and impedance match,HE TMB2-1 shows much improved performance with the optimal minimum reflection loss(RL_(min))of-59.6 dB(8.48 GHz,2.68 mm)and effective absorption bandwidth(EAB)of 7.6 GHz(2.3 mm).Most impressively,incorporating Cr in HE TMB2-3 greatly improves the impedance match over 1-18 GHz,thus achieving the RLmin of-56.2 dB(8.48 GHz,2.63 mm)and the EAB of 11.0 GHz(2.2 mm),which is superior to most other EM wave absorbing materials.This work reveals that constructing high-entropy compounds,especially by incorporating magnetic elements,is effectual in tailoring the impedance match for highly conductive compounds,i.e.,tuning electrical conductivity and boosting magnetic loss to realize highly efficient and broadband EM wave absorption with dielectric and magnetic coupling in single-phase materials.展开更多
In order to improve the lifespan of spot-welding electrodes used for welding zinc coated steel sheets, titanium diboride was deposited onto their surface after precoating nickel as an intermediate layer. The microstru...In order to improve the lifespan of spot-welding electrodes used for welding zinc coated steel sheets, titanium diboride was deposited onto their surface after precoating nickel as an intermediate layer. The microstructures and phase compositions of TiB2 and Ni coatings were characterized by SEM and XRD. The coating hardness was measured using a microhardness tester. The results indicate that a satisfactory TiB2 coating is obtained as a result of the intermediate nickel layer acting as a good binder between the TiB2 coating and the copper alloy substrate. Owing to its capacity of deforming, the precoated nickel layer is dense and crack free, while cracks and pores are observed in the TiB2 coating. The hardness of the TiB2/Ni coating decreases with the increase of voltage and capacitance because of the diffusion of copper and nickel and the oxidation of the coating materials. Because of the good thermal and electrical conductivities and high hardness properties of TiB2, the deformation of the electrode with TiB2/Ni coating is reduced and its spot-welding life is by far prolonged than that of the uncoated one.展开更多
By using cyclic and linear sweep voltammetry,the electrochemical deposition behaviors of Mg^2＋ and B^3＋ in fluorides molten salts of KF-MgF2 and KF-KBF4 at 880℃ were investigated,respectively.The results show that ...By using cyclic and linear sweep voltammetry,the electrochemical deposition behaviors of Mg^2＋ and B^3＋ in fluorides molten salts of KF-MgF2 and KF-KBF4 at 880℃ were investigated,respectively.The results show that the electrochemical reduction of Mg^2＋ is a one-step reaction as Mg^2＋＋2e-→Mg in KF-1%MgF2 molten salt,and the electrochemical reduction of B^3＋ is also a one-step reaction as B^3＋＋3e-→B in KF-KBF4 （1%,2% KBF4） molten salts.Both the cathodic reduction reactions of Mg^2＋ and B^3＋ are controlled by diffusion process.The diffusion coefficients of Mg^2＋ in KF-MgF2 molten salts and B^3＋ in KF-KBF4 molten salts are 6.8×10^-7 cm^2/s and 7.85×10^-7 cm^2/s,respectively.Moreover,the electrochemical synthesis of MgB2 by co-deposition of Mg and B was carried out in the KF-MgF2-KBF4 （molar ratio of 6：1：2） molten salt at 750℃.The X-ray diffraction analysis indicates that MgB2 can be deposited on graphite cathode in the KF-MgF2-KBF4 molten salt at 750℃.展开更多
Transition metal diborides based ultrahigh temperature ceramics(UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity a...Transition metal diborides based ultrahigh temperature ceramics(UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy(HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm2 s^-1 and 0.51 W m^-1K^-1, respectively. In addition, it exhibits high compressive strength of3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is a novel strategy in making UHTCs thermal insulating.展开更多
High entropy diborides are new categories of ultra-high temperature ceramics,which are believed promising candidates for applications in hypersonic vehicles.However,knowledge on high temperature thermal and mechanical...High entropy diborides are new categories of ultra-high temperature ceramics,which are believed promising candidates for applications in hypersonic vehicles.However,knowledge on high temperature thermal and mechanical properties of high entropy diborides is still lacking unit now.In this work,variations of thermal and elastic properties of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) with respect to temperature were predicted by molecular dynamics simulations.Firstly,a deep learning potential for Ti-Zr-Hf-Nb-Ta-B diboride system was fitted with its prediction error in energy and force respectively being 9.2 meV/atom and 208 meV/A,in comparison with first-principles calculations.Then,temperature dependent lattice constants,anisotropic thermal expansions,anisotropic phonon thermal conductivities,and elastic properties of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) from 0℃to 2400℃were evaluated,where the predicted room temperature values agree well with experimental measurements.In addition,intrinsic lattice distortions of(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) were analyzed by displacements of atoms from their ideal positions,which are in an order of 10^(-3) A and one order of magnitude smaller than those in(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C.It indicates that lattice distortions in(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) is not so severe as expected.With the new paradigm of machine learning potential,deep insight into high entropy materials can be achieved in the future,since the chemical and structural complexly in high entropy materials can be well handled by machine learning potential.展开更多
Designing active,robust and cost-effective catalysts for the nitrogen reduction reaction(NRR) is of paramount significance for sustainable electrochemical NH3 synthesis.Transition-metal diborides(TMB_2)have been recen...Designing active,robust and cost-effective catalysts for the nitrogen reduction reaction(NRR) is of paramount significance for sustainable electrochemical NH3 synthesis.Transition-metal diborides(TMB_2)have been recently theoretically predicted to be a new class of potential NRR catalysts,but direct experimental evidence is still lacking.Herein,we present the first experimental demonstration that amorphous FeB_2 porous nanosheets(a-FeB_2 PNSs) could be a highly efficient NRR catalyst,which exhibited an NH3 yield of 39.8 μg h^(-1) mg^(-1)(-0.3 V) and a Faradaic efficiency of 16.7%(-0.2 V),significantly outperforming their crystalline counterpart and most of existing NRR catalysts.First-principle calculations unveiled that the amorphization could induce the upraised d-band center of a-FeB_2 to boost d-2π~* coupling between the active Fe site and ~*N_2 H intermediate,resulting in enhanced ~*N_2 H stabilization and reduced reaction barrier.Out study may facilitate the development and understanding of earth-abundant TMB_2-based catalysts for electrocatalytic N_2 fixation.展开更多
Transition metal diborides(TMB_(2)s)are the materials of choice in extreme environments due to their excellent thermal and chemical stabilities.However,the degradation of oxidation resistance of TMB_(2)s at elevated t...Transition metal diborides(TMB_(2)s)are the materials of choice in extreme environments due to their excellent thermal and chemical stabilities.However,the degradation of oxidation resistance of TMB_(2)s at elevated temperature still hinders their applications.To cope with this challenge,it is effective to incorporate rare earth elements to form high-entropy transition and rare-earth metal diborides(HE TMREBs).To obtain thermodynamically stable single-phase structures for HE TMREB_(2)s,a“16×16 mixed enthalpy matrix”is constructed using first-principles calculations to predict the single-phase formation ability of120 two-component diborides(TCBs).Through the use of the“16×16 mixed enthalpy matrix”of TCBs,specific combinations of TMB_(2)s and REB_(2)s that are most likely to form single-phase HE TMREB_(2)s are confirmed.Subsequently,based on the energy distribution of the local mixing enthalpies of all possible configurations,the enthalpy and entropy descriptors of HE TMREB_(2)s(RE=Sc,Lu,Tm,Er,Ho and Dy)are investigated.It is found that the mixing enthalpy plays a critical role in the stability of the single-phase HE TMREB_(2)s,i.e.,HE TMREB_(2)s are enthalpy-stabilized materials.The experimental results further confirm that enthalpy dominates the thermodynamic domain and drives the stability of REB_(2)s in HE TMREB_(2)s.This study validates that enthalpy-stabilized HE TMREB_(2)s can further expand the compositional space of ultrahigh temperature ceramics(UHTCs)and is expected to further improve the oxidation resistance and high temperature properties of UHTCs.展开更多
Structural and lattice dynamical properties of ReB2,RuB2,and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation.The present results show ...Structural and lattice dynamical properties of ReB2,RuB2,and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation.The present results show that these compounds are dynamically stable for the considered structure.The temperature-dependent behaviors of thermodynamical properties such as internal energy,free energy,entropy,and heat capacity are also presented.The obtained results are in good agreement with the available experimental and theoretical data.展开更多
We have performed low temperature resistivity p（T） and specific heat C（T） measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperatu...We have performed low temperature resistivity p（T） and specific heat C（T） measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is -4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat γn=4.51 mJmol^-1K^2 and the Debye temperature θD=419 K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/γnTc = 2.84 exp（-1.21Tc/T）. This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.展开更多
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners...Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB_(2)provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB_(2)and(1-100)NbB_(2)surface can be substituted by Al to form(Al,Nb)B_(2)intermedia layers.In addition,a layer of NbAl_(3)-like compound(NbAl_(3)')can cover the surface of NbB_(2)with the orientation relation of(1-100)[11-20]NbB_(2/)/(110)[110]NbAl_(3)'.Both of the(Al,Nb)B_(2)and NbAl_(3)'intermedia layers contribute to enhancing the nucleation potency of NbB_(2)particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys.展开更多
The physical and mechanical properties of metal matrix composites were improved by the addition of reinforcements. The mechanical properties of particulate-reinforced metal-matrix composites based on aluminium alloys ...The physical and mechanical properties of metal matrix composites were improved by the addition of reinforcements. The mechanical properties of particulate-reinforced metal-matrix composites based on aluminium alloys （6061 and 7015） at high temperatures were studied. Titanium diboride （TiB2） particles were used as the reinforcement. All the composites were produced by hot extrusion. The tensile properties and fracture characteristics of these materials were investigated at room temperature and at high temperatures to determine their ultimate strength and strain to failure. The fracture surface was analysed by scanning electron microscopy. TiB2 particles provide high stability of the alumin- ium alloys （6061 and 7015） in the fabrication process. An improvement in the mechanical behaviour was achieved by adding TiB2 particles as reinforcement in both the aluminium alloys. Adding TiB2 particles reduces the ductility of the aluminium alloys but does not change the microscopic mode of failure, and the fracture surface exhibits a ductile appearance with dimples formed by coalescence.展开更多
This paper predicts the elastic and thermodynamic characteristics of TiB2 crystal through the method of density functional theory within the generalized gradient approximation （GGA）. The five independent elastic con...This paper predicts the elastic and thermodynamic characteristics of TiB2 crystal through the method of density functional theory within the generalized gradient approximation （GGA）. The five independent elastic constants （Cij）, the bulk modulus （B0）, the dependence of bulk modulus （B0） on temperature T and pressure P and the coefficient of thermal expansion （αL） at various temperatures have been evaluated and discussed. According to calculation, the bulk modulus will increase with increasing pressure while decrease with the increasing temperature. The coefficient of thermal expansion is consistent with the famous Griineisen＇s law when the temperature is not too high. The obtained results agree well with the experimental and other theoretical results.展开更多
An Al2O3-TiB2 nanocomposite was successfully synthesized by ball milling of Al, TiO2 and two B source materials of B2O3 （system （1）） and H3BO3 （system （2））. Phase identification of the milled samples was exami...An Al2O3-TiB2 nanocomposite was successfully synthesized by ball milling of Al, TiO2 and two B source materials of B2O3 （system （1）） and H3BO3 （system （2））. Phase identification of the milled samples was examined by Xray diffraction. The morphology and microstructure of the milled powders were monitored by scanning electron microscopy and transmission electron microscopy. It was found that the formation of this composite was completed after 15 and 30 h of milling time in systems （1） and （2）, respectively. More milling energy was required for the formation of this composite in system （2） due to the lubricant properties of HaBO3 and also its decomposition to HBO2 and B2O3 during milling. On the basis of X-ray diffraction patterns and thermodynamic calculations, this composite was formed by highly exothermic mechanically induced self-sustaining reactions （MSR） in both systems. The MSR mode took place around 9 h and 25 h of milling in systems （1） and （2）, respectively. At the end of milling （15 h for system （1） and 30 h for system （2）） the grain size of about 35-50 nm was obtained in both systems.展开更多
基金financial support from the Scientific and Technological Research Council of Türkiye(223M182).
文摘Electrocatalytic water splitting(EWS)driven by renewable energy is vital for clean hydrogen(H2)production and reducing reliance on fossil fuels.While IrO_(2) and RuO_(2) are the leading electrocatalysts for the oxygen evolution reaction(OER)and Pt for the hydrogen evolution reaction(HER)in acidic environments,the need for efficient,stable,and affordable materials persists.Recently,transition-metal borides(TMBs),particularly metal diborides(MDbs),have gained attention due to their unique layered crystal structures with multicentered boron bonds,offering remarkable physicochemical properties.Their nearly 2D structures boost electrochemical performance by offering high conductivity and a large active surface area,making them well-suited for advanced energy storage and conversion technologies.This review provides a comprehensive overview of the critical factors for water splitting,the crystal and electronic structures of MDbs,and their synthetic strategies.Furthermore,it examines the relationship between catalytic performance and intermediate adsorption as elucidated by first-principle calculations.The review also highlights the latest experimental advancements in MDb-based electrocatalysts and addresses the current challenges and future directions for their development.
基金financially supported by the Science Challenge Project(No.TZ 2018002)。
文摘High-entropy diborides(HEBs)have attracted extensive research due to their potential ultra-high hardness.In the present work,the effects of transition metals(TM)on lattice parameters,electron work function(EWF),bonding charge density,and hardness of HEBs are comprehensively investigated by the first-principles calculations,including(TiZrHfNbTa)B_(2),(TiZrHfNbMo)B_(2),(TiZrHfTaMo)B_(2),(TiZrNbTaMo)B_(2),and(TiHfNbTaMo)B_(2).It is revealed that the disordered TM atoms result in a severe local lattice distortion and the formation of weak spots.In view of bonding charge density,it is understood that the degree of electron contribution of TM atoms directly affects the bonding strength of the metallic layer,contributing to the optimized hardness of HEBs.Moreover,the proposed power-law-scaled relationship integrating the EWF and the grain size yields an excellent agreement between our predicted results and those reported experimental ones.It is found that the HEBs exhibit relatively high hardness which is higher than those of single transition metal diborides.In particular,the hardness of(TiZrNbTaMo)B_(2)and(TiHfNbTaMo)B_(2)can be as high as29.15 and 28.02 GPa,respectively.This work provides a rapid strategy to discover/design advanced HEBs efficiently,supported by the coupling hardening mechanisms of solid solution and grain refinement based on the atomic and electronic interactions.
文摘Structural and mechanical properties of several rare-earth diborides were systematically investigated by first principles calculations. Specifically, we studied XB2 , where X=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu in the hexagonal AlB2 , ReB2 , and orthorhombic OsB2 -type structures. The lattice parameters, bulk modulus, bond distances, second order elastic constants, and related polycrystalline elastic moduli （e.g., shear modulus, Young’s modulus, Poisson’s ratio, Debye temperature, sound velocities） were calculated. Our results indicate that these compounds are mechanically stable in the considered structures, and according to ＂Chen’s method＂, the predicted Vickers hardness shows that they are hard materials in AlB2 - and OsB2 -type structures.
基金supported by the National Natural Sciences Foundation of China under Grant No.51672064 and No.U1435206Beijing Municipal Science & Technology Commission under Grant No.D161100002416001
文摘The potential applications of transition metal diborides(TMB_2) in extreme environments are particularly attractive but still blocked by some intrinsic properties such as poor resistances to thermal shock and oxidation. Since surface plays a key role during grain growth and oxygen adsorption, an insight into the surface properties of TMB_2 is essential for understanding the materials performance and accelerating the development of ultra-high temperature ceramics. By employing two-region modeling method, the stability and oxygen adsorption behavior of TMB_2 surfaces were investigated by first-principles calculations based on density functional theory. The effects of valance electron concentration on the surface stability and oxygen adsorption were studied and the general trends were summarized. After analyzing the anisotropy in surface stability and oxygen adsorption, the observed grain morphology of TMB_2 were well explained, and it was also predicted that YB_2, HfB_2 and TaB_2 may have better initial oxidation resistance than ZrB_2.
基金supported by the National Key R&D Program of China(No.2024YFB3816600)the Guangxi Natural Science Foundation(No.2022GXNSFAA035527)+4 种基金the Natural Science Foundation of Tianjin(Nos.23JCZDJC00150 and 22JCZDJC00080)the Science and Technology Major Project of Ningbo(No.2021Z123)the Yongjiang Talent Introduction Programme(No.2021A-108-G)the Youth Fund of the Chinese Academy of Sciences(No.JCPYJJ-22030)Guilin University of Technology Research Startup Fund(No.RD2100000621).
文摘Ceramic materials have obvious advantages in thermal stability,but impedance mismatch limits their ability to attenuate electromagnetic(EM)waves.Herein,a novel series of high-entropy(V_(0.2)Nb_(0.2)Zr_(0.2)Ta_(0.2)X_(0.2))B_(2)(X=Mo,Ti,and Hf)ceramics were successfully synthesized via ultrafast high-temperature sintering(UHS)apparatus based on joule heating.The results indicated that the effect of high-entropy component on the magnetic loss of the system was relatively small,but the effect on the dielectric loss was larger.Among them,the(V_(0.2)Nb_(0.2)Zr_(0.2)Ta_(0.2)Ti_(0.2))B_(2)(HEB-Ti)sample demonstrated superior absorbing properties due to relatively moderate dielectric loss and optimal EM impedance matching.Moreover,because of its relatively moderate attenuation constant,it could achieve the maximum penetration of the EM wave and the minimum reflection after absorbing wave.As a result,the minimum reflection loss(RL_(min))was as low as−40.7 dB,and the effective absorption band covered the entire low-frequency range from 2 to 8 GHz.Its excellent absorption performance was mainly due to the synergistic effect of various dielectric attenuation mechanisms,including defect polarization,dipole polarization,and conduction loss.Furthermore,thermogravimetric(TG)analysis showed that the sample exhibited excellent thermal stability and could withstand temperatures up to 550℃in air and 1000℃in an argon gas environment.The relevant work could provide meaningful references for the design of new high-performance ceramic wave-absorbing materials.
基金support from the National Key Research and Development Program of China(No.2021YFA0715801)the National Natural Science Foundation of China(Nos.52122204 and 51972116)Guangzhou Basic and Applied Basic Research Foundation(No.202201010632).
文摘Understanding the initial oxidation mechanism is critical for studying the oxidation resistance of high-entropy diborides.However,related studies are scarce.Herein,the initial oxidation mechanism of(Zr_(0.25)Ti_(0.25)Nb_(0.25)Ta_(0.25))B_(2)high-entropy diborides(HEB_(2)-1)is investigated by first-principles calculations at the atomic level.By employing the two-region model method,the most stable surface of HEB_(2)-1 is determined to be(1120)surface.The dissociative adsorption process of the oxygen molecule on the HEB_(2)-1-(1120)surface is predicted to proceed spontaneously,where OeO bond breaks and each oxygen atom is chemisorbed on the most preferable hollow site.The adsorption energy and the diffusion barrier of the oxygen atom on the(1120)surface of HEB_(2)-1 are in the vicinity of the average level of the cor-responding four individual diborides.In addition,ab initio molecular dynamics simulations indicate a high initial oxidation resistance of HEB_(2)-1 at 1000 K.Our results are beneficial to further designing the high-entropy diborides with excellent oxidation resistance.
基金the financial support from the National Key Research and Development Program of China(2021YFA0715801)the National Natural Science Foundation of China(52122204)。
文摘Oxidation resistance is critical for high-entropy diborides(HEBs)to be used as thermal structural components under oxygen-containing high-temperature environments.Here,we successfully realize the exploitation of(Zr,Ta,Cr,W)B2 HEBs with superior oxidation resistance by comprehensively screening their compositions.To be specific,21 kinds of HEB-xTM(x=0–25 mol%,TM=Zr,Ta,Cr,and W)samples are fabricated via an ultrafast high-temperature sintering technique.The as-fabricated HEB-5Cr samples show the best oxidation resistance at 1673 K among all the samples.Subsquent oxidation investigations further confirm the as-fabricated HEB-5Cr samples possess superior oxidation resistance with the parabolic oxidation behavior across 1473–1773 K.Such superior oxidation resistance is believed to result from the multi-component synergistic effects.Particularly,the Ta^(5+)and W^(4+)cations with high ionic field strengths can promote the formation of 4B–O–4B linkages between[BO4]tetrahedrons by charge balance,which can stabilize the threedimensional skeletal structure of B_(2)O_(3)glass and consequently result in an improved viscosity of the B_(2)O_(3)glassy layer.In addition,the ZrO_(2)and Cr_(2)O_(3)with high melting points can dissolve into the B_(2)O_(3)glass to increase its glass transition temperature,leading to an enhanced viscosity of the B_(2)O_(3)glassy layer.
基金supports from the National Natural Science Foundation of China(Grant Nos.51972089,51672064,and U1435206).
文摘The advance in communication technology has triggered worldwide concern on electromagnetic wave pollution.To cope with this challenge,exploring high-performance electromagnetic(EM)wave absorbing materials with dielectric and magnetic losses coupling is urgently required.Of the EM wave absorbers,transition metal diborides(TMB2)possess excellent dielectric loss capability.However,akin to other single dielectric materials,poor impedance match leads to inferior performance.High-entropy engineering is expected to be effective in tailoring the balance between dielectric and magnetic losses through compositional design.Herein,three HE TMB2 powders with nominal equimolar TM including HE TMB2-I(TM=Zr,Hf,Nb,Ta),HE TMB2-2(TM=Ti,Zr,Hf,Nb,Ta),and HE TMB2-3(TM=Cr,Zr,Hf,Nb,Ta)have been designed and prepared by one-step boro/carbothermal reduction.As a result of synergistic effects of strong attenuation capability and impedance match,HE TMB2-1 shows much improved performance with the optimal minimum reflection loss(RL_(min))of-59.6 dB(8.48 GHz,2.68 mm)and effective absorption bandwidth(EAB)of 7.6 GHz(2.3 mm).Most impressively,incorporating Cr in HE TMB2-3 greatly improves the impedance match over 1-18 GHz,thus achieving the RLmin of-56.2 dB(8.48 GHz,2.63 mm)and the EAB of 11.0 GHz(2.2 mm),which is superior to most other EM wave absorbing materials.This work reveals that constructing high-entropy compounds,especially by incorporating magnetic elements,is effectual in tailoring the impedance match for highly conductive compounds,i.e.,tuning electrical conductivity and boosting magnetic loss to realize highly efficient and broadband EM wave absorption with dielectric and magnetic coupling in single-phase materials.
基金Project (50575069) supported by the National Natural Science Foundation of China
文摘In order to improve the lifespan of spot-welding electrodes used for welding zinc coated steel sheets, titanium diboride was deposited onto their surface after precoating nickel as an intermediate layer. The microstructures and phase compositions of TiB2 and Ni coatings were characterized by SEM and XRD. The coating hardness was measured using a microhardness tester. The results indicate that a satisfactory TiB2 coating is obtained as a result of the intermediate nickel layer acting as a good binder between the TiB2 coating and the copper alloy substrate. Owing to its capacity of deforming, the precoated nickel layer is dense and crack free, while cracks and pores are observed in the TiB2 coating. The hardness of the TiB2/Ni coating decreases with the increase of voltage and capacitance because of the diffusion of copper and nickel and the oxidation of the coating materials. Because of the good thermal and electrical conductivities and high hardness properties of TiB2, the deformation of the electrode with TiB2/Ni coating is reduced and its spot-welding life is by far prolonged than that of the uncoated one.
基金Project(50804010) supported by the National Natural Science Foundation of ChinaProject(2007CB210305) supported by the National Basic Research Program of China
文摘By using cyclic and linear sweep voltammetry,the electrochemical deposition behaviors of Mg^2＋ and B^3＋ in fluorides molten salts of KF-MgF2 and KF-KBF4 at 880℃ were investigated,respectively.The results show that the electrochemical reduction of Mg^2＋ is a one-step reaction as Mg^2＋＋2e-→Mg in KF-1%MgF2 molten salt,and the electrochemical reduction of B^3＋ is also a one-step reaction as B^3＋＋3e-→B in KF-KBF4 （1%,2% KBF4） molten salts.Both the cathodic reduction reactions of Mg^2＋ and B^3＋ are controlled by diffusion process.The diffusion coefficients of Mg^2＋ in KF-MgF2 molten salts and B^3＋ in KF-KBF4 molten salts are 6.8×10^-7 cm^2/s and 7.85×10^-7 cm^2/s,respectively.Moreover,the electrochemical synthesis of MgB2 by co-deposition of Mg and B was carried out in the KF-MgF2-KBF4 （molar ratio of 6：1：2） molten salt at 750℃.The X-ray diffraction analysis indicates that MgB2 can be deposited on graphite cathode in the KF-MgF2-KBF4 molten salt at 750℃.
基金supported by the National Natural Science Foundation of China (Nos. 51672064 and U1435206)
文摘Transition metal diborides based ultrahigh temperature ceramics(UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy(HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm2 s^-1 and 0.51 W m^-1K^-1, respectively. In addition, it exhibits high compressive strength of3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is a novel strategy in making UHTCs thermal insulating.
基金supported by Natural Sciences Foundation of China under Grant No.51972089 and No.51672064。
文摘High entropy diborides are new categories of ultra-high temperature ceramics,which are believed promising candidates for applications in hypersonic vehicles.However,knowledge on high temperature thermal and mechanical properties of high entropy diborides is still lacking unit now.In this work,variations of thermal and elastic properties of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) with respect to temperature were predicted by molecular dynamics simulations.Firstly,a deep learning potential for Ti-Zr-Hf-Nb-Ta-B diboride system was fitted with its prediction error in energy and force respectively being 9.2 meV/atom and 208 meV/A,in comparison with first-principles calculations.Then,temperature dependent lattice constants,anisotropic thermal expansions,anisotropic phonon thermal conductivities,and elastic properties of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) from 0℃to 2400℃were evaluated,where the predicted room temperature values agree well with experimental measurements.In addition,intrinsic lattice distortions of(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) were analyzed by displacements of atoms from their ideal positions,which are in an order of 10^(-3) A and one order of magnitude smaller than those in(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C.It indicates that lattice distortions in(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) is not so severe as expected.With the new paradigm of machine learning potential,deep insight into high entropy materials can be achieved in the future,since the chemical and structural complexly in high entropy materials can be well handled by machine learning potential.
基金supported by the National Natural Science Foundation of China (51761024)the CAS ‘‘Light of West China” Program, ‘‘Feitian Scholar” Program of Gansu Provincethe Foundation of A Hundred Youth Talents Training Program of Lanzhou Jiaotong University。
文摘Designing active,robust and cost-effective catalysts for the nitrogen reduction reaction(NRR) is of paramount significance for sustainable electrochemical NH3 synthesis.Transition-metal diborides(TMB_2)have been recently theoretically predicted to be a new class of potential NRR catalysts,but direct experimental evidence is still lacking.Herein,we present the first experimental demonstration that amorphous FeB_2 porous nanosheets(a-FeB_2 PNSs) could be a highly efficient NRR catalyst,which exhibited an NH3 yield of 39.8 μg h^(-1) mg^(-1)(-0.3 V) and a Faradaic efficiency of 16.7%(-0.2 V),significantly outperforming their crystalline counterpart and most of existing NRR catalysts.First-principle calculations unveiled that the amorphization could induce the upraised d-band center of a-FeB_2 to boost d-2π~* coupling between the active Fe site and ~*N_2 H intermediate,resulting in enhanced ~*N_2 H stabilization and reduced reaction barrier.Out study may facilitate the development and understanding of earth-abundant TMB_2-based catalysts for electrocatalytic N_2 fixation.
基金the National Natural Science Foundation of China(Nos.51772027 and 51972089)。
文摘Transition metal diborides(TMB_(2)s)are the materials of choice in extreme environments due to their excellent thermal and chemical stabilities.However,the degradation of oxidation resistance of TMB_(2)s at elevated temperature still hinders their applications.To cope with this challenge,it is effective to incorporate rare earth elements to form high-entropy transition and rare-earth metal diborides(HE TMREBs).To obtain thermodynamically stable single-phase structures for HE TMREB_(2)s,a“16×16 mixed enthalpy matrix”is constructed using first-principles calculations to predict the single-phase formation ability of120 two-component diborides(TCBs).Through the use of the“16×16 mixed enthalpy matrix”of TCBs,specific combinations of TMB_(2)s and REB_(2)s that are most likely to form single-phase HE TMREB_(2)s are confirmed.Subsequently,based on the energy distribution of the local mixing enthalpies of all possible configurations,the enthalpy and entropy descriptors of HE TMREB_(2)s(RE=Sc,Lu,Tm,Er,Ho and Dy)are investigated.It is found that the mixing enthalpy plays a critical role in the stability of the single-phase HE TMREB_(2)s,i.e.,HE TMREB_(2)s are enthalpy-stabilized materials.The experimental results further confirm that enthalpy dominates the thermodynamic domain and drives the stability of REB_(2)s in HE TMREB_(2)s.This study validates that enthalpy-stabilized HE TMREB_(2)s can further expand the compositional space of ultrahigh temperature ceramics(UHTCs)and is expected to further improve the oxidation resistance and high temperature properties of UHTCs.
文摘Structural and lattice dynamical properties of ReB2,RuB2,and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation.The present results show that these compounds are dynamically stable for the considered structure.The temperature-dependent behaviors of thermodynamical properties such as internal energy,free energy,entropy,and heat capacity are also presented.The obtained results are in good agreement with the available experimental and theoretical data.
基金Supported by the National Natural Science Foundation of China, the Knowledge Innovation Project of Chinese Academy of Sciences, and National Basic Research Programme of China under Grant Nos 2003CCC01000, 2005CB32170X and 2006CB921301.
文摘We have performed low temperature resistivity p（T） and specific heat C（T） measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is -4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat γn=4.51 mJmol^-1K^2 and the Debye temperature θD=419 K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/γnTc = 2.84 exp（-1.21Tc/T）. This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.
基金supported by the National Natural Science Foundation of China(51871138)Science and Technology Commission of Shanghai Municipality(19010500400)the 111 project(No.D16002)。
文摘Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB_(2)provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB_(2)and(1-100)NbB_(2)surface can be substituted by Al to form(Al,Nb)B_(2)intermedia layers.In addition,a layer of NbAl_(3)-like compound(NbAl_(3)')can cover the surface of NbB_(2)with the orientation relation of(1-100)[11-20]NbB_(2/)/(110)[110]NbAl_(3)'.Both of the(Al,Nb)B_(2)and NbAl_(3)'intermedia layers contribute to enhancing the nucleation potency of NbB_(2)particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys.
文摘The physical and mechanical properties of metal matrix composites were improved by the addition of reinforcements. The mechanical properties of particulate-reinforced metal-matrix composites based on aluminium alloys （6061 and 7015） at high temperatures were studied. Titanium diboride （TiB2） particles were used as the reinforcement. All the composites were produced by hot extrusion. The tensile properties and fracture characteristics of these materials were investigated at room temperature and at high temperatures to determine their ultimate strength and strain to failure. The fracture surface was analysed by scanning electron microscopy. TiB2 particles provide high stability of the alumin- ium alloys （6061 and 7015） in the fabrication process. An improvement in the mechanical behaviour was achieved by adding TiB2 particles as reinforcement in both the aluminium alloys. Adding TiB2 particles reduces the ductility of the aluminium alloys but does not change the microscopic mode of failure, and the fracture surface exhibits a ductile appearance with dimples formed by coalescence.
基金Supported by Special Foundation for Young Teacher of Xinyang Normal University,China (Grant No 20072012)the Science and Technology Foundation of Henan Province,China (Grant No 082300410050)
文摘This paper predicts the elastic and thermodynamic characteristics of TiB2 crystal through the method of density functional theory within the generalized gradient approximation （GGA）. The five independent elastic constants （Cij）, the bulk modulus （B0）, the dependence of bulk modulus （B0） on temperature T and pressure P and the coefficient of thermal expansion （αL） at various temperatures have been evaluated and discussed. According to calculation, the bulk modulus will increase with increasing pressure while decrease with the increasing temperature. The coefficient of thermal expansion is consistent with the famous Griineisen＇s law when the temperature is not too high. The obtained results agree well with the experimental and other theoretical results.
文摘An Al2O3-TiB2 nanocomposite was successfully synthesized by ball milling of Al, TiO2 and two B source materials of B2O3 （system （1）） and H3BO3 （system （2））. Phase identification of the milled samples was examined by Xray diffraction. The morphology and microstructure of the milled powders were monitored by scanning electron microscopy and transmission electron microscopy. It was found that the formation of this composite was completed after 15 and 30 h of milling time in systems （1） and （2）, respectively. More milling energy was required for the formation of this composite in system （2） due to the lubricant properties of HaBO3 and also its decomposition to HBO2 and B2O3 during milling. On the basis of X-ray diffraction patterns and thermodynamic calculations, this composite was formed by highly exothermic mechanically induced self-sustaining reactions （MSR） in both systems. The MSR mode took place around 9 h and 25 h of milling in systems （1） and （2）, respectively. At the end of milling （15 h for system （1） and 30 h for system （2）） the grain size of about 35-50 nm was obtained in both systems.
