A TTT diagram for th ie precipitation formed at some intermediate temperatures through cooling from high lemperalure parenl phase in a Cu-27 27Zn-3.73Al allay is established by means of dilatormetric measurement.The m...A TTT diagram for th ie precipitation formed at some intermediate temperatures through cooling from high lemperalure parenl phase in a Cu-27 27Zn-3.73Al allay is established by means of dilatormetric measurement.The morphology and structure of transformation products formed at some intermediate tem peratures isothermally through cooling from high temperature parent phase and up-quenching from DO_(3) parent phase are studied by metallographic.X-ray and electron microscopy analyses.Three regions in the two separate C curves are obtained according to different morphology of precipitate:rod-like a,plate-like bainite and a rods,and bainite plates.Prolonged aging makes bainite plate change gradually into a whose lattice parameters are no different from that of a formed equilibriumly from parent phase.The structure is almost orthorhombic long period structure for bainites formed from B_(2) and DO_(3) parent phase,but monoclinic for martensite from DO_(3).They correspond to the overlapping and separating of(1210)and(2010)diffraction peaks respectively,showing the lower degree of ordering in bainite.展开更多
The transformation process and the products of long term isothermal transformation around the kinetic B_s temperature(the bay temperature in TTT diagram)in Fe-C-Mo alloys have been investigated.It was found that,at th...The transformation process and the products of long term isothermal transformation around the kinetic B_s temperature(the bay temperature in TTT diagram)in Fe-C-Mo alloys have been investigated.It was found that,at the final stage of intermediate transformation,a kind of granular structure formed accompanying the growth of bainitic ferrite.In comparison with the carbide Mo_2C in the bainitic ferrite plates or blocks,the carbide m granular eutectoid has been determined to be cementite containing a tiny bit of molvbdenum,(Fe,Mo)_3C.展开更多
Precisely tuning.the micro-nanoscale characteristics and synergistic effect of metal-acid sites to regulate the distribution of hydroconversion products are significant but challenging.The protonated carbocation inter...Precisely tuning.the micro-nanoscale characteristics and synergistic effect of metal-acid sites to regulate the distribution of hydroconversion products are significant but challenging.The protonated carbocation intermediates triggered by tandem reaction on metal-acid region hinder target product formation due to their high reactivity and instability.Supported M/Zeolite hydroconversion catalysts,which often excel in simple synthesis,ease of separation and recyclability.However,they usually consist of sterically unconstrained metal centers which are isolated from acid sites,only providing limited coupling-selectivity to target product.Herein,metal nanoparticles enveloped in acidic zeolite frameworks were developed and used for investigating the process of hydroalkylation of benzene to cyclohexylbenzene.We show that appropriate metal encapsulation comprising adequate efficient metal-acid units successfully avoids the more thermodynamically favorable hydrogenation of cyclohexene to cyclohexane,but steers to alkylation of cyclohexene with benzene to cyclohexylbenzene.This resulted in the highest cyclohexylbenzene yield of 47.7%among the reported work,and surpassed the performance of all supported M/Zeolite catalysts.Experimental and theoretical results supported that the abundant bifunctional metal-acid units enhance the activation frequency and probability of intermediate cyclohexene.This work might provide insights for the integration strategy of dual active site and guidance for the construction of efficient"metal-acid balance"in tandem reactions.展开更多
The influence of carbon content on the mechanical properties of high yield strength bridge steel has been in- vestigated. The results show that the excellent mechanical properties and corrosion resistance are obtained...The influence of carbon content on the mechanical properties of high yield strength bridge steel has been in- vestigated. The results show that the excellent mechanical properties and corrosion resistance are obtained for the steel with carbon content of 0.03% -0. 05% （mass percent）. According to the results, a new weathering bridge steel plate with carbon content of 0. 045% （mass percent） has been developed. The appropriate controlled cooling process should be taken due to the results of CCT （continuous cooling transformation） and TTT （time-temperature-transformation） to ensure both microstructure and mechanical properties. CCT curve of the newly developed steel shows that when accelerated cooling speed is higher than 5 ℃/s, the intermediate transformation products can be formed. The TTT curve displays that the intermediate transformation temperature ranges from 600 to 530 ℃. Yield strength of the newly developed steels reaches 500 MPa, and their elongation and toughness are excellent.展开更多
基金supported by the National Natural Science Foundation
文摘A TTT diagram for th ie precipitation formed at some intermediate temperatures through cooling from high lemperalure parenl phase in a Cu-27 27Zn-3.73Al allay is established by means of dilatormetric measurement.The morphology and structure of transformation products formed at some intermediate tem peratures isothermally through cooling from high temperature parent phase and up-quenching from DO_(3) parent phase are studied by metallographic.X-ray and electron microscopy analyses.Three regions in the two separate C curves are obtained according to different morphology of precipitate:rod-like a,plate-like bainite and a rods,and bainite plates.Prolonged aging makes bainite plate change gradually into a whose lattice parameters are no different from that of a formed equilibriumly from parent phase.The structure is almost orthorhombic long period structure for bainites formed from B_(2) and DO_(3) parent phase,but monoclinic for martensite from DO_(3).They correspond to the overlapping and separating of(1210)and(2010)diffraction peaks respectively,showing the lower degree of ordering in bainite.
文摘The transformation process and the products of long term isothermal transformation around the kinetic B_s temperature(the bay temperature in TTT diagram)in Fe-C-Mo alloys have been investigated.It was found that,at the final stage of intermediate transformation,a kind of granular structure formed accompanying the growth of bainitic ferrite.In comparison with the carbide Mo_2C in the bainitic ferrite plates or blocks,the carbide m granular eutectoid has been determined to be cementite containing a tiny bit of molvbdenum,(Fe,Mo)_3C.
基金This work was financially supported by the National Natural Science Foundation of China(No.22278380)China Postdoctoral Science Foundation(Nos.2021M692911,2022T150589,2023TQ0319,and 2023M743174)+1 种基金Excellent Youth of Henan Province(No.242300421122)Zhongyuan postdoctoral innovative talent support program(No.ZYYCYU202012174).
文摘Precisely tuning.the micro-nanoscale characteristics and synergistic effect of metal-acid sites to regulate the distribution of hydroconversion products are significant but challenging.The protonated carbocation intermediates triggered by tandem reaction on metal-acid region hinder target product formation due to their high reactivity and instability.Supported M/Zeolite hydroconversion catalysts,which often excel in simple synthesis,ease of separation and recyclability.However,they usually consist of sterically unconstrained metal centers which are isolated from acid sites,only providing limited coupling-selectivity to target product.Herein,metal nanoparticles enveloped in acidic zeolite frameworks were developed and used for investigating the process of hydroalkylation of benzene to cyclohexylbenzene.We show that appropriate metal encapsulation comprising adequate efficient metal-acid units successfully avoids the more thermodynamically favorable hydrogenation of cyclohexene to cyclohexane,but steers to alkylation of cyclohexene with benzene to cyclohexylbenzene.This resulted in the highest cyclohexylbenzene yield of 47.7%among the reported work,and surpassed the performance of all supported M/Zeolite catalysts.Experimental and theoretical results supported that the abundant bifunctional metal-acid units enhance the activation frequency and probability of intermediate cyclohexene.This work might provide insights for the integration strategy of dual active site and guidance for the construction of efficient"metal-acid balance"in tandem reactions.
基金Item Sponsored by National Natural Science Foundation of China(50571016,50571089)National Key Basic Research and Development Program of China(2004CB619102)National High Technology Research and Development Program of China(2006AA03Z507)
文摘The influence of carbon content on the mechanical properties of high yield strength bridge steel has been in- vestigated. The results show that the excellent mechanical properties and corrosion resistance are obtained for the steel with carbon content of 0.03% -0. 05% （mass percent）. According to the results, a new weathering bridge steel plate with carbon content of 0. 045% （mass percent） has been developed. The appropriate controlled cooling process should be taken due to the results of CCT （continuous cooling transformation） and TTT （time-temperature-transformation） to ensure both microstructure and mechanical properties. CCT curve of the newly developed steel shows that when accelerated cooling speed is higher than 5 ℃/s, the intermediate transformation products can be formed. The TTT curve displays that the intermediate transformation temperature ranges from 600 to 530 ℃. Yield strength of the newly developed steels reaches 500 MPa, and their elongation and toughness are excellent.
