The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remark...The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in 87Sr/86Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made 87Sr/86Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the prefer-ential release of Sr from dissolving solid phase and the fluctuation of 87Sr/86Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.展开更多
To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were stud...To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml0.80Mg0.20（Ni2.90Co0.50-Mn0.30Al0.30）x （x=0.68, 0.70, 0.72, 0.74, 0.76） alloys and Cu-substituted Ml0.80Mg0.20（Ni2.90Co0.50-yCuyMn0.30Al0.30）0.70 （y=0, 0.10, 0.30, 0.50） alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi5 phase, a LaNi3 phase, and a minor La2Ni7 phase;in addition, in the case of Cu-substitution, the Nd2Ni7 phase appears and the LaNi3 phase vanishes. Ther-modynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with in-creasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ame-liorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.展开更多
In this contribution, two important crystallographic concepts for the formation of a series of block structures associated with channeling have been compared: chemical twinning and crystallographic shear. Twin planes ...In this contribution, two important crystallographic concepts for the formation of a series of block structures associated with channeling have been compared: chemical twinning and crystallographic shear. Twin planes respectively shear planes besides formed channels serve as a sink for charge carriers or, when the oxidation state of metal ions can be reduced, as a reservoir for intercalated lithium. In this way, Wadsley-Roth shear phases such as niobium tungsten oxide exhibit channels for ultra-fast lithium-ion diffusion. They are in focus as anode material for super-batteries, superb in terms of energy respectively power density, charging time, cycle life and safety. It should be noted that the transition metal to oxygen ratio TM/O = 21/55 of the title compound is a Fibonacci number quotient. Also, the crystal lattice can be traced back to Fibonacci geometry. When replacing only 0.0213 tungsten atoms in the formula with less expensive titanium, a TM/O ratio of 0.381966 =ϕ<sup>2</sup> can be adapted besides an average valence electron concentration of 2⋅ϕ<sup>-2</sup>, where represents the most irrational number of the golden mean. The additional disorder caused by even such small titanium replacement and accompanied oxygen vacancies could fasten up the already high lithium diffusion further. Ultrasonic treatment may be applied besides thermal cycling to prepare phase-pure of the highest electrochemical performance. A replacement of oxygen by some fluorine atoms is an obvious synthesis possibility, but the higher binding energy expected between lithium and fluorine in contrast to oxygen may rather hinder than promote lithium diffusion.展开更多
Typical feed gas mixtures used in technological and other plasmas may give rise to reaction networks involving several hundred reactions.Such chemistries are often too large to be used in full reactor simulations and ...Typical feed gas mixtures used in technological and other plasmas may give rise to reaction networks involving several hundred reactions.Such chemistries are often too large to be used in full reactor simulations and it is therefore desirable to construct reduced chemistry networks which mimic as closely as possible the behavior of the full chemistry but employ far fewer individual reactions and species.Constructed chemistries are available from the Quantemol database (QDB) and two approaches to constructing reduced chemistry from these chemistries based on (a) physical intuition and (b) sensitivity analysis of dominant reaction pathways,are explored.In doing this it is necessary to consider different pressure and power regimes.Reduced chemistry sets are presented for CF4/O2/N2/H2,for which 396 reactions and 52 species are reduced to 71 reactions and 26 species,and for pure O2,for which 45 reactions and 10 species are reduced to 34 reactions.展开更多
基金the Ministry of Science and Technology of China (Grant No. 95-pre-39).
文摘The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in 87Sr/86Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made 87Sr/86Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the prefer-ential release of Sr from dissolving solid phase and the fluctuation of 87Sr/86Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.
基金supported by the National Natural Science Foundation of China(Nos.21303157 and 21106123)the Natural Science Foundation of Hebei Province,China(No.B2012203104)+1 种基金the China Postdoctoral Science Foundation Project(2013M541201)the Research Fund for the Doctoral Program of Higher Education of China(20131333120008)
文摘To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml0.80Mg0.20（Ni2.90Co0.50-Mn0.30Al0.30）x （x=0.68, 0.70, 0.72, 0.74, 0.76） alloys and Cu-substituted Ml0.80Mg0.20（Ni2.90Co0.50-yCuyMn0.30Al0.30）0.70 （y=0, 0.10, 0.30, 0.50） alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi5 phase, a LaNi3 phase, and a minor La2Ni7 phase;in addition, in the case of Cu-substitution, the Nd2Ni7 phase appears and the LaNi3 phase vanishes. Ther-modynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with in-creasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ame-liorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.
文摘In this contribution, two important crystallographic concepts for the formation of a series of block structures associated with channeling have been compared: chemical twinning and crystallographic shear. Twin planes respectively shear planes besides formed channels serve as a sink for charge carriers or, when the oxidation state of metal ions can be reduced, as a reservoir for intercalated lithium. In this way, Wadsley-Roth shear phases such as niobium tungsten oxide exhibit channels for ultra-fast lithium-ion diffusion. They are in focus as anode material for super-batteries, superb in terms of energy respectively power density, charging time, cycle life and safety. It should be noted that the transition metal to oxygen ratio TM/O = 21/55 of the title compound is a Fibonacci number quotient. Also, the crystal lattice can be traced back to Fibonacci geometry. When replacing only 0.0213 tungsten atoms in the formula with less expensive titanium, a TM/O ratio of 0.381966 =ϕ<sup>2</sup> can be adapted besides an average valence electron concentration of 2⋅ϕ<sup>-2</sup>, where represents the most irrational number of the golden mean. The additional disorder caused by even such small titanium replacement and accompanied oxygen vacancies could fasten up the already high lithium diffusion further. Ultrasonic treatment may be applied besides thermal cycling to prepare phase-pure of the highest electrochemical performance. A replacement of oxygen by some fluorine atoms is an obvious synthesis possibility, but the higher binding energy expected between lithium and fluorine in contrast to oxygen may rather hinder than promote lithium diffusion.
文摘Typical feed gas mixtures used in technological and other plasmas may give rise to reaction networks involving several hundred reactions.Such chemistries are often too large to be used in full reactor simulations and it is therefore desirable to construct reduced chemistry networks which mimic as closely as possible the behavior of the full chemistry but employ far fewer individual reactions and species.Constructed chemistries are available from the Quantemol database (QDB) and two approaches to constructing reduced chemistry from these chemistries based on (a) physical intuition and (b) sensitivity analysis of dominant reaction pathways,are explored.In doing this it is necessary to consider different pressure and power regimes.Reduced chemistry sets are presented for CF4/O2/N2/H2,for which 396 reactions and 52 species are reduced to 71 reactions and 26 species,and for pure O2,for which 45 reactions and 10 species are reduced to 34 reactions.
