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Structural and mechanical stability of rare-earth diborides 被引量:4
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作者 Haci Ozisik Engin Deligoz +1 位作者 Kemal Colakoglu Gokhan Surucu 《Chinese Physics B》 SCIE EI CAS CSCD 2013年第4期369-376,共8页
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
关键词 ab initio calculations elastic properties HARDNESS rare-earth diborides
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Atomic-level insights into the initial oxidation mechanism of high-entropy diborides by first-principles calculations 被引量:1
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作者 Yiwen Liu Hulei Yu +1 位作者 Hong Meng Yanhui Chu 《Journal of Materiomics》 SCIE CSCD 2024年第2期423-430,共8页
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
关键词 High-entropy diborides Oxidation First-principles calculations
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Enhanced oxidation resistance of high-entropy diborides by multicomponent synergistic effects
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作者 Zhongyu Tang Zihao Wen +2 位作者 Lei Zhuang Hulei Yu Yanhui Chu 《Science China Materials》 SCIE EI CAS CSCD 2024年第10期3392-3400,共9页
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
关键词 high-entropy diborides composition screening oxidation resistance synergistic effects
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Electronic structures and strengthening mechanisms of superhard high-entropy diborides 被引量:3
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作者 Gang Yao William-Yi Wang +9 位作者 Pei-Xuan Li Ke Ren Jia-Qi Lu Xing-Yu Gao De-Ye Lin Jun Wang Yi-Guang Wang Hai-Feng Song Zi-Kui Liu Jin-Shan Li 《Rare Metals》 SCIE EI CAS CSCD 2023年第2期614-628,共15页
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
关键词 High-entropy diborides(HEBs) Hardness Electronic structure Lattice distortion POWER-LAW
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General trends in surface stability and oxygen adsorption behavior of transition metal diborides(TMB_2) 被引量:1
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作者 Wei Sun Fuzhi Dai +2 位作者 Huimin Xiang Jiachen Liu Yanchun Zhou 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2019年第4期584-590,共7页
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
关键词 Transition metal diborides FIRST-PRINCIPLES calculation Surface energy GRAIN morphology OXIDATION resistance
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Enabling highly efficient and broadband electromagnetic wave absorption by tuning impedance match in high-entropy transition metal diborides (HETMB_(2)) 被引量:8
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作者 Weiming ZHANG Fu-Zhi DAI +6 位作者 Huimin XIANG Biao ZHAO Xiaohui WANG Na NI Rajamallu KARRE Shijiang WU Yanchun ZHOU 《Journal of Advanced Ceramics》 SCIE CAS CSCD 2021年第6期1299-1316,共18页
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
关键词 transition metal diboride(TMB2) high-entropy(HE)ceramics electronic structure microwave absorption dielectric and magnetic losses coupling
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TiB_2/Ni coatings on surface of copper alloy electrode prepared by electrospark deposition 被引量:13
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作者 罗成 熊翔 董仕节 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2011年第2期317-321,共5页
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
关键词 titanium diboride electrospark deposition COPPER ELECTRODE NICKEL COATING
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Electrochemical behaviors of Mg^(2+) and B^(3+) deposition in fluoride molten salts 被引量:3
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作者 石忠宁 李敏 +3 位作者 李兰兰 高炳亮 胡宪伟 王兆文 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2011年第7期1655-1659,共5页
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
关键词 magnesium diboride ELECTRO-DEPOSITION fluoride molten salts diffusion coefficient
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Amorphization activated FeB_(2) porous nanosheets enable efficient electrocatalytic N_(2) fixation 被引量:4
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作者 Ke Chu Weicong Gu +3 位作者 Qingqing Li Yaping Liu Ye Tian Wuming Liu 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2021年第2期82-89,I0004,共9页
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
关键词 Electrocatalytic nitrogen fixation Transition-metal diborides Amorphization Density functional theory
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Lattice dynamical and thermodynamical properties of ReB_2,RuB_2,and OsB_2 compounds in the ReB_2 structure 被引量:1
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作者 E.Deligoz K.Colakoglu Y.O.Ciftci 《Chinese Physics B》 SCIE EI CAS CSCD 2012年第10期355-361,共7页
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
关键词 ab initio calculations lattice dynamical properties thermodynamical properties diborides
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Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2
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作者 刘广同 金灏 +6 位作者 李政 耿红霞 车广灿 金铎 孙连峰 解思深 雒建林 《Chinese Physics Letters》 SCIE CAS CSCD 2008年第2期687-690,共4页
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
关键词 TRANSITION-TEMPERATURE HEAT DEPENDENCE diborides TRANSPORT STATES
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High-temperature mechanical properties of aluminium alloys reinforced with titanium diboride (TiB_2) particles 被引量:6
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作者 J.Ooro 《Rare Metals》 SCIE EI CAS CSCD 2011年第2期200-205,共6页
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
关键词 metal-matrix composites aluminium high-temperature properties titanium diboride
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First principle study on the elastic and thermodynamic properties of TiB_2 crystal under high temperature 被引量:5
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作者 王春雷 余本海 +2 位作者 霍海亮 陈东 孙海滨 《Chinese Physics B》 SCIE EI CAS CSCD 2009年第3期1248-1252,共5页
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
关键词 titanium diboride density functional calculations bulk modulus coefficient of heat expansion
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Influence of B source materials on the synthesis of TiB_2-Al_2O_3 nanocomposite powders by mechanical alloying 被引量:3
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作者 Majid Abdellahi Javad Heidari Rahman Sabouhi 《International Journal of Minerals,Metallurgy and Materials》 SCIE EI CAS CSCD 2013年第12期1214-1220,共7页
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
关键词 NANOCOMPOSITES POWDERS ALUMINA titanium diboride mechanical alloying
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Preparation of wettable TiB2-TiB/Ti cathode by electrolytic boronizing for aluminum electrolytic 被引量:3
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作者 HUANG You-guo WANG Yi +2 位作者 ZHANG Xiao-hui WANG Hong-qiang LI Qing-yu 《Journal of Central South University》 SCIE EI CAS CSCD 2019年第10期2681-2687,共7页
According to the problems of short life and low strength of TiB2 coating cathode for current technology in aluminium electrolysis industry,this work synthesized TiB2-TiB/Ti gradient composite with TiB2 coating and TiB... According to the problems of short life and low strength of TiB2 coating cathode for current technology in aluminium electrolysis industry,this work synthesized TiB2-TiB/Ti gradient composite with TiB2 coating and TiB whiskers in metallic Ti matrix by a electrolytic boronizing method based on similar density and thermal expansivity of the three materials.The phase composition and morphology of the cross-section were determined by X-ray diffraction(XRD),scanning electronic microscope(SEM)and X-ray energy dispersive spectrum(EDS).The results show that uniform TiB2 layer with a thickness of 8-10μm is continuously coated on the surface while the TiB whisker connected with TiB2 layer was embedded dispersedly into the matrix.The TiB crystal whisker has a maximum length of about 220μm.The growth rate of TiB2 and TiB is enhanced by the strong reduction of B4C.The novel gradient design of the composite helps to extend life and improve strength of the TiB2 cathode in aluminium electrolysis. 展开更多
关键词 aluminium electrolysis electrolytic boronizing titanium diboride gradient materials
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Effect of NaCl on synthesis of ZrB2 by a borothermal reduction reaction of ZrO2 被引量:2
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作者 Yu Wang Yue-dong Wu +3 位作者 Ke-han Wu Shu-qiang Jiao Kuo-chih Chou Guo-hua Zhang 《International Journal of Minerals,Metallurgy and Materials》 SCIE EI CAS CSCD 2019年第7期831-838,共8页
ZrB2 powders were synthesized via a borothermal reduction reaction of ZrO2 with the assistance of NaCl under a flowing Ar atmosphere. The optimal temperature and reaction time were 1223 K and 3 h, respectively. Compar... ZrB2 powders were synthesized via a borothermal reduction reaction of ZrO2 with the assistance of NaCl under a flowing Ar atmosphere. The optimal temperature and reaction time were 1223 K and 3 h, respectively. Compared with the reactions conducted without the addition of NaCl, those performed with the addition of an appropriate amount of NaCl finished at substantially lower temperatures. However, the addition of too much NaCl suppressed this effect. With the assistance of NaCl, a special morphology of polyhedral ZrB2 particles covered with ZrB2 nanosheets was obtained. Moreover, the experimental results revealed that the special morphology was the result of the combined effects of B2O3 and NaCl. The formation of the special microstructure is explained on the basis of the “dissolution–recrystallization” mechanism. 展开更多
关键词 ZIRCONIUM DIBORIDE borothermal reduction ultra-high temperature ceramics dissolution-recrystallization mechanism
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Preparation and Microstructure of Porous ZrB_2 Ceramics Using Reactive Spark Plasma Sintering Method 被引量:2
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作者 袁辉平 李俊国 +1 位作者 SHEN Qiang ZHANG Lianmeng 《Journal of Wuhan University of Technology(Materials Science)》 SCIE EI CAS 2015年第3期512-515,共4页
Zirconium oxide (ZrO:) and boron carbide (B4C) were added to ZrB2 raw powders to prepare ZrB2 porous ceramics by reactive spark plasma sintering (RSPS). The reactions between ZrO2 and B,C which produce ZrB2 and... Zirconium oxide (ZrO:) and boron carbide (B4C) were added to ZrB2 raw powders to prepare ZrB2 porous ceramics by reactive spark plasma sintering (RSPS). The reactions between ZrO2 and B,C which produce ZrB2 and gas (such as CO and B2O3) result in pore formation. X-Ray Diffraction results indicated that the products phase was ZrB2 and the reaction was completed after the RSPS process. The porosity could be controlled by changing the ratio of synthesized ZrB2 to raw ZrB2 powders. The porosity of porous ceramics with 20 wt% and 40 wt% synthsized ZrB2 are 0.185 and 0.222, respectivly. And dense ZrB:SiC ceramic with a porosity of 0.057 was prepared under the same conditions for comparison. The pores were homogeneously distributed within the microstructure of the porous ceramics. The results indicate a promising method for preparing porous ZrB:based ceramics. 展开更多
关键词 zirconium diboride porous ceramic reactive spark plasma sintering
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Preparation of TiB_2 coatings by electroplating in molten salt 被引量:1
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作者 LI Jun LI Bing DONG Zheng'e 《Rare Metals》 SCIE EI CAS CSCD 2005年第3期261-266,共6页
Titanium diboride (TIB2) coatings were prepared by electroplating in fluoride-chloride electrolytes (KF-KC1) containing K2T1F6 and KBF4 as the electrochemically-active components. An attempt was made to correlate ... Titanium diboride (TIB2) coatings were prepared by electroplating in fluoride-chloride electrolytes (KF-KC1) containing K2T1F6 and KBF4 as the electrochemically-active components. An attempt was made to correlate the thermodynamic prediction and experimental observations. Thick, adherent, and uniform TtB2 coatings were obtained and the coating microhardness reaches the value of 33 GPa. The effects of the current density on the mechanical properties, structures, and morphologies of the coatings were studied. XRD analysis indicates that the preferred orientation of the coatings is (001), which is in accordance with the prediction of the two-dimensional crystal nuclei theory. Thermodynamic prediction and experimental results show that some phases such as TixCy and BaCb are absent at the interface, which indicates the substrate and coatings bind mechanically or physically. Some cracks exist at the interface, which is attributed to the difference between the coefficients of thermal expansion of TiB2 and graphite. 展开更多
关键词 ELECTRODEPOSITION titanium diboride COATINGS molten salt
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Electronic Structure and Chemical Bond of Titanium Diboride 被引量:1
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作者 闵新民 《Journal of Wuhan University of Technology(Materials Science)》 SCIE EI CAS 2003年第2期11-14,共4页
Titanium diboride was calculated by the density function and discrete variational (DFT-DVM) method to study the relation between structure and properties.Titanium and its first-nearest boron atoms form a strong covale... Titanium diboride was calculated by the density function and discrete variational (DFT-DVM) method to study the relation between structure and properties.Titanium and its first-nearest boron atoms form a strong covalent bond,so TiB 2 has high melting point,hardness and chemical stability.Titanium atom releases two electrons to form Ti 2+ ions,and a boron atom gets one electron to come into B- ion.B- takes the sp2 hybrid and forms σ bonds to link other boron atoms in the same layer.The other one 2p z orbital of every B- ion in the same layer interacts each other to form the π molecular orbital,so TiB 2 has fine electrical property.The calculated density of state is close to the result of XPS experiment of TiB 2.Mainly Ti3d and B2p atomic orbitals contribute the total DOS near the Fermi level. 展开更多
关键词 titanium diboride PROPERTY CALCULATION electronic structure chemical bond
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First-principle study on the physical properties of ultra-incompressible ReB_2 被引量:1
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作者 Chunlei WANG Qiuju SUN Xuanyu SONG Benhai YU 《Acta Metallurgica Sinica(English Letters)》 SCIE EI CAS CSCD 2009年第4期284-290,共7页
The elastic and physical characteristics of ReB2 crystal have been predicted through a method of density functional theory within the generalized gradient approximation (GGA). Five independent elastic constants are ... The elastic and physical characteristics of ReB2 crystal have been predicted through a method of density functional theory within the generalized gradient approximation (GGA). Five independent elastic constants are C11=662 GPa, C12=150 GPa, C13=146 GPa, C33=1090 GPa and Caa=263 GPa. The bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (γ) and the ratio of linear com- pressibility coefficient along the a- and c-axis crystal direction (Ka/Kc) are 356 GPa, 305 GPa, 711 GPa, 0.167 and 1.758, respectively. In addition, the dependence of bulk modulus (B) on temperature (T) and pressure (p) as well as the coefficient of thermal expansion (αL) at various temperatures are evaluated and discussed. The coefficient of thermal expansion is consistent with the famous Grüneisen's law when the temperature is less than 1500 K. Our results agree well with the other experimental results. 展开更多
关键词 Rhenium diboride Density functional calculations Bulk modulus Coefficient of thermal expansion
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