The characteristics and generation mechanism of（Ti,Nb,V）（C,N） precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of（Ti,Nb,V）（C,N） phases exist—a Ti-V-r...The characteristics and generation mechanism of（Ti,Nb,V）（C,N） precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of（Ti,Nb,V）（C,N） phases exist—a Ti-V-rich one and an Nb-rich one—in the form of single or complex precipitates. The sizes of the single Ti-V-rich（Ti,Nb,V）（C,N） precipitates are mostly within 5 to 10 μm, whereas the sizes of the single Nb-rich precipitates are mostly 2–5 μm. The complex precipitates are larger and contain an inner Ti-V-rich layer and an outer Nb-rich layer. The compositional distribution of（Ti,Nb,V）（C,N） is concentrated. The average composition of the single Ti-V-rich phase is（Ti_（0.511）V_（0.356）Nb_（0.133））（CxNy）, whereas that for the single Nb-rich phase is（Ti_（0.061）V_（0.263）Nb_（0.676））（C_xN_y）. The calculation results based on the Scheil–Gulliver model in the Thermo-Calc software combining with the thermal stability experiments show that the large phases precipitate during the solidification process. With the development of solidification, the Ti-V-rich phase precipitates first and becomes homogeneous during the subsequent temperature reduction and heat treatment processes. The Nb-rich phase appears later.展开更多
The precise construction of chiral molecules is a core research area in chemical science and technology.Among the plethora of reported synthetic methods,asymmetric catalysis has emerged as one of the most efficient an...The precise construction of chiral molecules is a core research area in chemical science and technology.Among the plethora of reported synthetic methods,asymmetric catalysis has emerged as one of the most efficient and direct ways to obtain optically pure chiral compounds.This article mainly reviews the recent progress of asymmetric catalysis made by Chinese chemists from the following aspects:the development of new chiral ligands,transition metal-catalyzed asymmetric reactions,asymmetric organocatalytic reactions,and new strategies for asymmetric catalysis.This review does not intend to be comprehensive;only representative examples are selected to highlight the important progress made in this field.Finally,a brief outlook is given on the development of novel chiral ligands/catalysts,new enantioselective reactions,and their applications in chiral drugs and agricultural chemicals.展开更多
Poly（ethylene oxide） （PEO） was controllably grafted from styrene-b-（ethylene-co-propylene）-b-styrene （SEPS） backbones by combining lithiation of styrenic units and living monomer-activated anionic ring-opening...Poly（ethylene oxide） （PEO） was controllably grafted from styrene-b-（ethylene-co-propylene）-b-styrene （SEPS） backbones by combining lithiation of styrenic units and living monomer-activated anionic ring-opening polymerization of ethylene oxide （EO） monomers with the aid of co-initiators triisobutyl aluminum. The as-synthesized SEPS-g-PEO copolymers were characterized by SEC, 1H-NMR, FTIR, SAXS, AFM and DSC. When the branch length is relatively small, increase of PEO fraction leads to the increase of the correlation length between neighboring hard domains, but the degree of correlation reduces. When the branch length is relatively large, the phase-separated structures become random both in terms of size and spatial correlation, and macro-phase separated structures appear. The crystallization behavior of the PEO branches can be effectively inhibited in SEPS-g-PEO, so no significant crystallization takes place until the fraction of PEO branches is 20.1 wt%, which greatly promotes the rapid delivery of hydrophilic drugs in the hot-melting pressure- sensitive adhesives （HMPSAs） based on SEPS-g-PEO. Their cumulative release amount of a model drug could achieve 80%, more than twice the value in the HMPSAs based on linear PEO-containing styrenic block copolymers.展开更多
文摘The characteristics and generation mechanism of（Ti,Nb,V）（C,N） precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of（Ti,Nb,V）（C,N） phases exist—a Ti-V-rich one and an Nb-rich one—in the form of single or complex precipitates. The sizes of the single Ti-V-rich（Ti,Nb,V）（C,N） precipitates are mostly within 5 to 10 μm, whereas the sizes of the single Nb-rich precipitates are mostly 2–5 μm. The complex precipitates are larger and contain an inner Ti-V-rich layer and an outer Nb-rich layer. The compositional distribution of（Ti,Nb,V）（C,N） is concentrated. The average composition of the single Ti-V-rich phase is（Ti_（0.511）V_（0.356）Nb_（0.133））（CxNy）, whereas that for the single Nb-rich phase is（Ti_（0.061）V_（0.263）Nb_（0.676））（C_xN_y）. The calculation results based on the Scheil–Gulliver model in the Thermo-Calc software combining with the thermal stability experiments show that the large phases precipitate during the solidification process. With the development of solidification, the Ti-V-rich phase precipitates first and becomes homogeneous during the subsequent temperature reduction and heat treatment processes. The Nb-rich phase appears later.
基金supported by major research plan“Precise Construction of Multilevel Chiral Substances”of the National Natural Science Foundation of China(grant nos.91956000,92256000,and 92256303).
文摘The precise construction of chiral molecules is a core research area in chemical science and technology.Among the plethora of reported synthetic methods,asymmetric catalysis has emerged as one of the most efficient and direct ways to obtain optically pure chiral compounds.This article mainly reviews the recent progress of asymmetric catalysis made by Chinese chemists from the following aspects:the development of new chiral ligands,transition metal-catalyzed asymmetric reactions,asymmetric organocatalytic reactions,and new strategies for asymmetric catalysis.This review does not intend to be comprehensive;only representative examples are selected to highlight the important progress made in this field.Finally,a brief outlook is given on the development of novel chiral ligands/catalysts,new enantioselective reactions,and their applications in chiral drugs and agricultural chemicals.
基金financially supported by the National Natural Science Foundation of China (Nos.51673034 and 51233005)the Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry (Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,No.110000R088)
文摘Poly（ethylene oxide） （PEO） was controllably grafted from styrene-b-（ethylene-co-propylene）-b-styrene （SEPS） backbones by combining lithiation of styrenic units and living monomer-activated anionic ring-opening polymerization of ethylene oxide （EO） monomers with the aid of co-initiators triisobutyl aluminum. The as-synthesized SEPS-g-PEO copolymers were characterized by SEC, 1H-NMR, FTIR, SAXS, AFM and DSC. When the branch length is relatively small, increase of PEO fraction leads to the increase of the correlation length between neighboring hard domains, but the degree of correlation reduces. When the branch length is relatively large, the phase-separated structures become random both in terms of size and spatial correlation, and macro-phase separated structures appear. The crystallization behavior of the PEO branches can be effectively inhibited in SEPS-g-PEO, so no significant crystallization takes place until the fraction of PEO branches is 20.1 wt%, which greatly promotes the rapid delivery of hydrophilic drugs in the hot-melting pressure- sensitive adhesives （HMPSAs） based on SEPS-g-PEO. Their cumulative release amount of a model drug could achieve 80%, more than twice the value in the HMPSAs based on linear PEO-containing styrenic block copolymers.
