The nanoparticles of Co1＋xMnxFe2-xO4 （0≤x ≤ 0.5） ferrite system are synthesized by solid-state reaction route using planetary ball milling technique to investigate structural, electrical and magnetic properties. ...The nanoparticles of Co1＋xMnxFe2-xO4 （0≤x ≤ 0.5） ferrite system are synthesized by solid-state reaction route using planetary ball milling technique to investigate structural, electrical and magnetic properties. The X-ray diffraction patterns confirm the inverse spinel structure with residual oxide phases. Three distinct regions of frequency response on dielectric constant are observed Co1.2sMn0.5Fe1.75O4 as determined by the Wayne Kerr Impedance Analyzer. The first two regions of frequency response 1.13-4.5 MHz and 4.5-6.5 MHz exhibit the normal behavior but the last region 6.5-10.5 MHz indicates its anomalous behavior due to concurrent contribution of O^2-, Fe^3＋, Co^2＋ and Mn^3＋ ions in the relaxation process for sintering effects （sintered at 700℃）. This anomalous behavior is found to be pronounced and significant for the sample of composition Co1.25Mn0.25Fe1.75O4, which may be suitable to be used in the frequency band filter over wide range of frequencies. The single peak of imaginary part of dielectric constant （ε＂） indicates that the conduction process in this sample is due to the grain boundary resistance. The pronounced increase of capacitance （C） as observed from 100 ℃ to 125 ~C in temperature dependent measurement （30-125℃） is expected to eause from the change of polarization across the grain boundary due to redistribution of ions by the thermal agitation. The variation of resistance （R） with temperature （30-125 ℃） is found to exhibit semieonducting behavior that resulted from the p-type carriers （Co^2＋/Co^3＋）. A significant increase of Z from 105 ℃ with the increase of temperature indicates the signature of phase transition from ferrimagnetic-to-ferromagnetic, which may be ascribed to the increase of Co content. The appearance of the single semicircular arc in the Cole-Cole plot may be attributed to the contribution of grain boundary resistance and correspond to the parallel equivalent circuit of resistor-capacitor （R-C） combination with single relaxation time. Saturation magnetization of Co1.25Mn0.25Fe1.75O4 and Co1.375Mn0.375Fe1.625O4 is found to be greater than the literature value （61.5 emu/g） of un-doped cobalt ferrite in the measurement of their initial magnetization using Lakeshore vibrating sample magnetometer. The negative real part of AC permeability of Co1.5Mn0.5Fe1.5O4 signifies the diamagnetic behavior in the frequency range 0.13-25.2 MHz and expected to cause from the formation of magnetic dipoles opposite to the applied field due to Mn^2＋ in the B site. The samples are expected to be suitable for dielectric heating and high frequency applications.展开更多
Wheel/rail rolling contact is a highly nonlinear issue affected by the complicated operating environment(including adhesion conditions and motion attitude of train and track system),which is a fundamental topic for fu...Wheel/rail rolling contact is a highly nonlinear issue affected by the complicated operating environment(including adhesion conditions and motion attitude of train and track system),which is a fundamental topic for further insight into wheel/rail tread wear and rolling contact fatigue(RCF).The rail gauge corner lubrication(RGCL)devices have been installed on the metro outer rail to mitigate its wear on the curved tracks.This paper presents an investigation into the influence ofRGCL on wheel/rail nonHertzian contact and rail surface RCF on the curves through numerical analysis.To this end,a metro vehicle-slab track interaction dynamics model is extended,in which an accurate wheel/rail non-Hertzian contact algorithm is implemented.The influence of RGCL on wheel/rail creep,contact stress and adhesion-slip distributions and fatigue damage of rail surface are evaluated.The simulation results show that RGCL can markedly affect wheel/rail contact on the tight curves.It is further suggested that RGCL can reduce rail surface RCF on tight curves through the wheel/rail low-friction interactions.展开更多
文摘The nanoparticles of Co1＋xMnxFe2-xO4 （0≤x ≤ 0.5） ferrite system are synthesized by solid-state reaction route using planetary ball milling technique to investigate structural, electrical and magnetic properties. The X-ray diffraction patterns confirm the inverse spinel structure with residual oxide phases. Three distinct regions of frequency response on dielectric constant are observed Co1.2sMn0.5Fe1.75O4 as determined by the Wayne Kerr Impedance Analyzer. The first two regions of frequency response 1.13-4.5 MHz and 4.5-6.5 MHz exhibit the normal behavior but the last region 6.5-10.5 MHz indicates its anomalous behavior due to concurrent contribution of O^2-, Fe^3＋, Co^2＋ and Mn^3＋ ions in the relaxation process for sintering effects （sintered at 700℃）. This anomalous behavior is found to be pronounced and significant for the sample of composition Co1.25Mn0.25Fe1.75O4, which may be suitable to be used in the frequency band filter over wide range of frequencies. The single peak of imaginary part of dielectric constant （ε＂） indicates that the conduction process in this sample is due to the grain boundary resistance. The pronounced increase of capacitance （C） as observed from 100 ℃ to 125 ~C in temperature dependent measurement （30-125℃） is expected to eause from the change of polarization across the grain boundary due to redistribution of ions by the thermal agitation. The variation of resistance （R） with temperature （30-125 ℃） is found to exhibit semieonducting behavior that resulted from the p-type carriers （Co^2＋/Co^3＋）. A significant increase of Z from 105 ℃ with the increase of temperature indicates the signature of phase transition from ferrimagnetic-to-ferromagnetic, which may be ascribed to the increase of Co content. The appearance of the single semicircular arc in the Cole-Cole plot may be attributed to the contribution of grain boundary resistance and correspond to the parallel equivalent circuit of resistor-capacitor （R-C） combination with single relaxation time. Saturation magnetization of Co1.25Mn0.25Fe1.75O4 and Co1.375Mn0.375Fe1.625O4 is found to be greater than the literature value （61.5 emu/g） of un-doped cobalt ferrite in the measurement of their initial magnetization using Lakeshore vibrating sample magnetometer. The negative real part of AC permeability of Co1.5Mn0.5Fe1.5O4 signifies the diamagnetic behavior in the frequency range 0.13-25.2 MHz and expected to cause from the formation of magnetic dipoles opposite to the applied field due to Mn^2＋ in the B site. The samples are expected to be suitable for dielectric heating and high frequency applications.
基金supported by the National Key Research and Development Program of China(Grant No.2020YFA0710902)the National Natural Science Foundation of China(Grant Nos.51735012,52072317,and UJ9A20110)the State Key Laboratory of Traction Power(Grant No.202JTPL-T08).
文摘Wheel/rail rolling contact is a highly nonlinear issue affected by the complicated operating environment(including adhesion conditions and motion attitude of train and track system),which is a fundamental topic for further insight into wheel/rail tread wear and rolling contact fatigue(RCF).The rail gauge corner lubrication(RGCL)devices have been installed on the metro outer rail to mitigate its wear on the curved tracks.This paper presents an investigation into the influence ofRGCL on wheel/rail nonHertzian contact and rail surface RCF on the curves through numerical analysis.To this end,a metro vehicle-slab track interaction dynamics model is extended,in which an accurate wheel/rail non-Hertzian contact algorithm is implemented.The influence of RGCL on wheel/rail creep,contact stress and adhesion-slip distributions and fatigue damage of rail surface are evaluated.The simulation results show that RGCL can markedly affect wheel/rail contact on the tight curves.It is further suggested that RGCL can reduce rail surface RCF on tight curves through the wheel/rail low-friction interactions.
