The photodissociation dynamics of 2-bromopentane at -234 nm has been investigated by utilizing ion-velocity map imaging technique. The mapped images of Br（2P3/2） （denoted as Br） and Br（2p1/2） （denoted as Br＊）...The photodissociation dynamics of 2-bromopentane at -234 nm has been investigated by utilizing ion-velocity map imaging technique. The mapped images of Br（2P3/2） （denoted as Br） and Br（2p1/2） （denoted as Br＊） fragments were analyzed by means of the speed and angular distributions, respectively. The speed distributions can be fitted with two Gaussian components which are correlated to the two independent reaction paths on the excited po- tential energy surfaces （PES）. The high-energy component is from the prompt dissociation along the C-Br stretching mode, while the low-energy one is related to the dissociation from the coupling of the C-Br stretching and bending modes. Relative quantum yield is measured to be 0.892 for Br in the photodissociation of 2-bromopentane at 234 nm. Combining the anisotropy parameter with the relative quantum yield of Br and Br fragments, the contributions of the excited 3Q0, 3Q1, and 1Q1 states to the products Br and Br were derived. The effect of alkyl branching on the mechanism of photodissociation was discussed by comparing the photodissociation processes of four isomers of bromopentane.展开更多
采用光学显微镜、扫描电镜、能谱分析和力学性能测试等手段,对油气滑半连续铸造φ254 mm 6061铝合金圆棒的均匀化态微观组织和后续锻造轮毂过程进行研究。结果表明,铸锭偏析层中含Fe相的数量、大小和形貌,与锻造成形、裂纹形成扩展和轮...采用光学显微镜、扫描电镜、能谱分析和力学性能测试等手段,对油气滑半连续铸造φ254 mm 6061铝合金圆棒的均匀化态微观组织和后续锻造轮毂过程进行研究。结果表明,铸锭偏析层中含Fe相的数量、大小和形貌,与锻造成形、裂纹形成扩展和轮毂力学性能有着直接的关系。当Fe含量由0.32%降低到0.22%,均匀化温度由550℃提高到约570℃,保温13 h时,铸锭R/2处均匀化态组织中Al_(2)Cu相完全回溶、MgSi相少量残留、AlFeSi相更断续弥散,β-AlFeSi相的面积分数由1.08%减少到0.73%,MgSi相的面积分数由1.11%减少到0.67%;同时,偏析层区域的均匀化组织中β-AlFeSi相和MgSi相的富集量明显减少,β-AlFeSi相的最大尺寸由60.2μm减小到29.9μm,面积分数由1.57%减少到0.89%,减少变形过程中粗大脆硬β-AlFeSi相周围区域的应力集中。此时,锻造轮毂成形性最好,有效的抑制了锻造裂纹的产生,轮毂本体的抗拉强度由322 MPa提高到378 MPa,伸长率由10.2%提高到12.2%。展开更多
We employed a melt ultrasonic treatment near the liquidus to prepare a high-thermal-conductivity Al-4Si-2Ni-0.8Fe-0.4Mg alloy.The influences of various ultrasonic powers on its microstructure,mechanical properties,and...We employed a melt ultrasonic treatment near the liquidus to prepare a high-thermal-conductivity Al-4Si-2Ni-0.8Fe-0.4Mg alloy.The influences of various ultrasonic powers on its microstructure,mechanical properties,and thermal conductivity were investigated.It is shown that near-liquidus ultrasonication significantly refines the alloy grains and eutectic structure,synergistically improving the alloy’s mechanical properties and thermal conductivity.Specifically,the grain size decreased by 84.5%from 941.4 to 186.2μm.Increasing the ultrasonic power improved the thermal conductivity of the alloy slightly and significantly enhanced its mechanical properties.At an ultrasonic power of 2100 W,the tensile strength,yield strength,elongation rate,and thermal conductivity were 216 MPa,142 MPa,6.3%,and 169 W/(m·k),respectively.展开更多
文摘The photodissociation dynamics of 2-bromopentane at -234 nm has been investigated by utilizing ion-velocity map imaging technique. The mapped images of Br（2P3/2） （denoted as Br） and Br（2p1/2） （denoted as Br＊） fragments were analyzed by means of the speed and angular distributions, respectively. The speed distributions can be fitted with two Gaussian components which are correlated to the two independent reaction paths on the excited po- tential energy surfaces （PES）. The high-energy component is from the prompt dissociation along the C-Br stretching mode, while the low-energy one is related to the dissociation from the coupling of the C-Br stretching and bending modes. Relative quantum yield is measured to be 0.892 for Br in the photodissociation of 2-bromopentane at 234 nm. Combining the anisotropy parameter with the relative quantum yield of Br and Br fragments, the contributions of the excited 3Q0, 3Q1, and 1Q1 states to the products Br and Br were derived. The effect of alkyl branching on the mechanism of photodissociation was discussed by comparing the photodissociation processes of four isomers of bromopentane.
基金Funded by the Zhaoqing Xijiang Innovation and Entrepreneurship Team Project Funding of China(No.2017A0109004)。
文摘We employed a melt ultrasonic treatment near the liquidus to prepare a high-thermal-conductivity Al-4Si-2Ni-0.8Fe-0.4Mg alloy.The influences of various ultrasonic powers on its microstructure,mechanical properties,and thermal conductivity were investigated.It is shown that near-liquidus ultrasonication significantly refines the alloy grains and eutectic structure,synergistically improving the alloy’s mechanical properties and thermal conductivity.Specifically,the grain size decreased by 84.5%from 941.4 to 186.2μm.Increasing the ultrasonic power improved the thermal conductivity of the alloy slightly and significantly enhanced its mechanical properties.At an ultrasonic power of 2100 W,the tensile strength,yield strength,elongation rate,and thermal conductivity were 216 MPa,142 MPa,6.3%,and 169 W/(m·k),respectively.
