Based on experimental results in which VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at%V nanocomposite, a VH/MgH2 in- terface is designed and constituted in this work. A first-princ...Based on experimental results in which VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at%V nanocomposite, a VH/MgH2 in- terface is designed and constituted in this work. A first-principles plane-wave pseudopo- tential method based on Density Functional Theory (DFT) has been used to investigate the vanadium alloying effects on the dehydrogenating properties of magnesium hydride, i.e., MgH2. A low absolute value of the negative heat of formation of VH/MgH2 interface compared with that of MgH2 indicates that vanadium hydrides befit to improve the dehydrogenating properties of MgH2. Based on the analysis of the density of states (DOS) and the total valence electron density distribution of MgH2 before and after V alloying, it was found that the improvement of the dehydrogenating properties of MgH2 caused by V alloying originates from the increasing of the valence electrons at Fermi level (EF) and the decreasing of the HOMO-LUMO gap ( Δ E H ?L) after V alloying. The catalysis effect of V on dehydrogenating kinetics of MgH2 may attribute to a stronger bonding between V and H atoms than that between Mg and H atoms, which leads to nucleation of the α-Mg at the VH/MgH2 interface in the MgH2-V systems easier than that in pure MgH2 phase.展开更多
Precipitates,including silicides and Ti3 Al(α2)phase,and alloying elements distribution in a near a titanium alloy Ti65(Ti-5.8 Al-4.0 Sn-3.5 Zr-0.5 Mo-0.3 Nb-1.0 Ta-0.4 Si-0.8 W-0.05 C)after solution treatment and ag...Precipitates,including silicides and Ti3 Al(α2)phase,and alloying elements distribution in a near a titanium alloy Ti65(Ti-5.8 Al-4.0 Sn-3.5 Zr-0.5 Mo-0.3 Nb-1.0 Ta-0.4 Si-0.8 W-0.05 C)after solution treatment and aging process were characterized by using transmission electron microscopy(TEM)and atom probe tomography(APT).Quantitative composition analysis and TEM observation indicate that the silicides fit to(Ti,Zr)6(Sl,Sn)3.Zr exhibits aβ-stabilizing effect in near a titanium alloys but is weaker than otherβstabilizing elements.The enriching tendency of the alloying elements in the retainedβphase is in the order of Zr<Nb<Ta<Mo<W.The experimental results are rationalized by the relative stability of alloying elements in the a andβphases and the mobility of these atoms in the matrix.An enrichment of Si in theα2 phase over theαmatrix phase is noticed,which is attributed to the lower formation energy of Si in theα2 phase.展开更多
文摘Based on experimental results in which VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at%V nanocomposite, a VH/MgH2 in- terface is designed and constituted in this work. A first-principles plane-wave pseudopo- tential method based on Density Functional Theory (DFT) has been used to investigate the vanadium alloying effects on the dehydrogenating properties of magnesium hydride, i.e., MgH2. A low absolute value of the negative heat of formation of VH/MgH2 interface compared with that of MgH2 indicates that vanadium hydrides befit to improve the dehydrogenating properties of MgH2. Based on the analysis of the density of states (DOS) and the total valence electron density distribution of MgH2 before and after V alloying, it was found that the improvement of the dehydrogenating properties of MgH2 caused by V alloying originates from the increasing of the valence electrons at Fermi level (EF) and the decreasing of the HOMO-LUMO gap ( Δ E H ?L) after V alloying. The catalysis effect of V on dehydrogenating kinetics of MgH2 may attribute to a stronger bonding between V and H atoms than that between Mg and H atoms, which leads to nucleation of the α-Mg at the VH/MgH2 interface in the MgH2-V systems easier than that in pure MgH2 phase.
基金The authors acknowledge the helpful suggestions from Prof.Shangzhou Zhang and Dr.Yujing Liu.And TEM experimental assistance is kindly provided by Jiao Liu.
文摘Precipitates,including silicides and Ti3 Al(α2)phase,and alloying elements distribution in a near a titanium alloy Ti65(Ti-5.8 Al-4.0 Sn-3.5 Zr-0.5 Mo-0.3 Nb-1.0 Ta-0.4 Si-0.8 W-0.05 C)after solution treatment and aging process were characterized by using transmission electron microscopy(TEM)and atom probe tomography(APT).Quantitative composition analysis and TEM observation indicate that the silicides fit to(Ti,Zr)6(Sl,Sn)3.Zr exhibits aβ-stabilizing effect in near a titanium alloys but is weaker than otherβstabilizing elements.The enriching tendency of the alloying elements in the retainedβphase is in the order of Zr<Nb<Ta<Mo<W.The experimental results are rationalized by the relative stability of alloying elements in the a andβphases and the mobility of these atoms in the matrix.An enrichment of Si in theα2 phase over theαmatrix phase is noticed,which is attributed to the lower formation energy of Si in theα2 phase.
