The valence bond structure of substitutional BCC based Ta-W alloys is studied using characteristic crystal （CC） theory. This theory is based on cluster statistics of random alloys. By studying the correlativity betw...The valence bond structure of substitutional BCC based Ta-W alloys is studied using characteristic crystal （CC） theory. This theory is based on cluster statistics of random alloys. By studying the correlativity between energy and volume of the CC in Ta- W alloys, the valence bond structure of CC is determined by the energy and shape method. Then, following additive law of CC, the valence bond structure of Ta-W alloys is calculated. It is found that the outer shell valence electronic distribution of Ta-W Mloys shows a continuous change in the whole composition range. The covalent electrons ec （dc, sc, and pc） increase, whereas near free electrons ef decrease with increasing W concentration. The bond length and single-bond radius decrease, whereas bond energy and bond valence increase with increasing W concentration. The mechanism of solid solution strengthening of Ta-W alloys is analyzed based on their valence bond structure.展开更多
The characteristic crystal model is applied to the study of phase stability and thermodynamics in substitutional bcc-based Ta-W alloys.The basic principle and method of alloy thermodynamics which is described by the c...The characteristic crystal model is applied to the study of phase stability and thermodynamics in substitutional bcc-based Ta-W alloys.The basic principle and method of alloy thermodynamics which is described by the characteristic crystal model is introduced in detail.The Gibbs energy of various phases including both disordered and ordered phases of the Ta-W system are evaluated.The phase diagram of Ta-W alloys is assessed and predicted.The results are in good agreement with experiments and better than that of first principle.展开更多
A series of mesoporous Ta and Ta-W oxides have been prepared and employed as solid acid catalysts for the dehydration of fructose and glucose to 5-hydroxymethylfurfural(HMF).Solid state 31 P MAS NMR spectroscopic resu...A series of mesoporous Ta and Ta-W oxides have been prepared and employed as solid acid catalysts for the dehydration of fructose and glucose to 5-hydroxymethylfurfural(HMF).Solid state 31 P MAS NMR spectroscopic results using trimethylphosphine(TMP)as a probe molecule show that the acid strength and the ratio of Br?nsted to Lewis acid sites increase gradually with the addition of tungsten in tantalum oxide.It is found that high sugar conversion and HMF selectivity are achieved over catalyst with relatively high ratios of Br?nsted to Lewis acid sites.Unexpected stoichiometric excess of formic acid relative to levulinic acid can be observed mainly because of direct decomposition of fructose over Lewis acid sites.The addition of 2-butanol leads to the increase of sugars conversion and the HMF selectivity,especially for the catalyst with high ratio of Br?nsted to Lewis acid sites.Among them,Ta7W3 oxide catalyst shows 54%HMF selectivity and good reusability with the addition of 2-butanol by extracting HMF from aqueous phase and removing humins deposed on the surface of the catalyst.展开更多
基金supported by Xiangtan University Doctor Research Foundation(GrantNo.08QDZ32)
文摘The valence bond structure of substitutional BCC based Ta-W alloys is studied using characteristic crystal （CC） theory. This theory is based on cluster statistics of random alloys. By studying the correlativity between energy and volume of the CC in Ta- W alloys, the valence bond structure of CC is determined by the energy and shape method. Then, following additive law of CC, the valence bond structure of Ta-W alloys is calculated. It is found that the outer shell valence electronic distribution of Ta-W Mloys shows a continuous change in the whole composition range. The covalent electrons ec （dc, sc, and pc） increase, whereas near free electrons ef decrease with increasing W concentration. The bond length and single-bond radius decrease, whereas bond energy and bond valence increase with increasing W concentration. The mechanism of solid solution strengthening of Ta-W alloys is analyzed based on their valence bond structure.
基金supported by the 45th China Postdoctoral Science Foundation (Grant No.20090451101)the Xiangtan University Postdoctoral Science Foundation
文摘The characteristic crystal model is applied to the study of phase stability and thermodynamics in substitutional bcc-based Ta-W alloys.The basic principle and method of alloy thermodynamics which is described by the characteristic crystal model is introduced in detail.The Gibbs energy of various phases including both disordered and ordered phases of the Ta-W system are evaluated.The phase diagram of Ta-W alloys is assessed and predicted.The results are in good agreement with experiments and better than that of first principle.
文摘A series of mesoporous Ta and Ta-W oxides have been prepared and employed as solid acid catalysts for the dehydration of fructose and glucose to 5-hydroxymethylfurfural(HMF).Solid state 31 P MAS NMR spectroscopic results using trimethylphosphine(TMP)as a probe molecule show that the acid strength and the ratio of Br?nsted to Lewis acid sites increase gradually with the addition of tungsten in tantalum oxide.It is found that high sugar conversion and HMF selectivity are achieved over catalyst with relatively high ratios of Br?nsted to Lewis acid sites.Unexpected stoichiometric excess of formic acid relative to levulinic acid can be observed mainly because of direct decomposition of fructose over Lewis acid sites.The addition of 2-butanol leads to the increase of sugars conversion and the HMF selectivity,especially for the catalyst with high ratio of Br?nsted to Lewis acid sites.Among them,Ta7W3 oxide catalyst shows 54%HMF selectivity and good reusability with the addition of 2-butanol by extracting HMF from aqueous phase and removing humins deposed on the surface of the catalyst.
