换热管漏磁检测磁化结构有限元分析

针对铁磁性换热管特点,以漏磁检测原理为基础,利用有限元分析软件,建立换热管漏磁检测磁化结构三维模型。研究换热管漏磁检测磁化结构中磁芯几何参数(磁芯内径d和中间磁芯长度l)改变时,换热管内表面圆柱形缺陷产生的漏磁场分布情况,得到磁感应强度轴向分量与径向分量随磁芯几何参数改变时的变化规律。     

Boosting the antimicrobial and Azo dye mineralization activities of ZnO ceramics by enhancing the light-harvesting and charge transport properties

Herein, we report the wet-chemical synthesis of a ferromagnetic nickel-doped ZnO (Zn_1-xNi_xO) nanocatalyst as a novel and visible-light-driven photocatalyst. Through X-ray diffraction, UV/Vis absorption, electronic studies, and current-voltage experiments, the effect of the ferromagnetic nickel dopant on the structural, optical, morphological, and electrical properties of the synthesized Zn_1-xNi_xO nanocatalyst was studied. The Ni-doping introduced the structural variation in the Zn_1-xNi_xO nanocatalyst, exhibiting a visible light-triggered optical band gap of 2.96 eV and an excellent current conductivity of 6.3 × 10⁻⁴ Sm⁻¹. Moreover, the synthesis of the Zn_1-xNi_xO catalyst at the nanoscale enhanced its surface energy, showing a robust affinity to stick with the dye and pathogenic microbes. The synergistic effects of all the mentioned features enable our Zn_1-xNi_xO nanocatalyst to efficiently generate and transport reactive oxygen species (ROS) under visible light illumination. Regarding antibacterial action, the as-synthesized Zn_1-xNi_xO nanocatalyst showed 1.7% higher activity against E. coli than that of the drug Ciprofloxacin. In addition, doped nanocatalysts mineralize almost 97% of the Allura red dye in just 80 min with a constant rate value of 0.036 min⁻¹. The impedance study and post-application XRD proposed that our Zn_1-xNi_xO nanocatalyst has good conductivity and structural stability. Applications studies show the unusual photocatalytic activity of as-synthesized Zn_1-xNi_xO nanocatalysts, which makes it a suitable candidate for industrial discharge treatment applications at the expense of solar light.     

Magnetic and magnetocaloric properties in melt-spun and annealed Ni42.7Mn40.8Co5.2Sn11.3 ribbons

The Ni_42.7Mn_40.8Co_5.2Sn_11.3 ribbons were prepared by melt spinning. After heat treatment, the martensitic transformation temperature and Curie temperature of austenite of the annealed ribbons increased remarkably. Inverse and direct magnetocaloric properties were investigated in the melt-spun and annealed ribbons. The effective refrigerant capacities for these ribbons were discussed in this paper.     

Magnetic properties and phase diagram of Ni50Mn50−xGax ferromagnetic shape memory alloys

We present the magnetic properties and the magnetic phase diagram of Ni₅₀Mn_50?xGa_x ferromagnetic shape memory alloys across a wide concentration range. Martensitic transformation, intermediate transformation, B2–L2₁ order–disorder transformation, Néel and Curie temperatures are determined for the prepared samples. The martensitic transformation temperature decreases with increasing Ga concentration and bends two times when crossing the Curie temperature and the intermediate-phase transformation temperature. Spontaneous magnetization and its composition dependence were also investigated. Composition dependence of the transformation temperatures and the spontaneous magnetization in the martensite phase of Ni₅₀Mn_50?xGa_x are compared with those of Ni₅₀Mn_50?xIn_x and Ni₅₀Mn_50?xSn_x, revealing a similarity in the NiMn-based alloy systems.     

Ferromagnetic ordering and mobility end-members for impurity diffusion in bcc Fe

Based on the experimental data available in the literature, the mobility end-members for impurity diffusion of twelve elements, i.e. Ag, Al, As, Au, Cu, Mo, Nb, Sb, Sn, Ti, W and Zn, in bcc Fe have been critically studied. The effect of ferromagnetic ordering is taken into consideration, which allows the dramatic change of kinetic behaviors around the Curie temperature to be considered. Comprehensive comparisons between the calculated and experimentally measured impurity diffusion coefficients are made, where the good agreement confirms not only the parameters obtained in this work but also the model developed by Jönsson. This work contributes to the establishment of a general mobility database to computationally study microstructure evolution upon heat treatment and performance prediction during service.     

Detection and measurement of surface cracks in ferromagnetic materials using eddy current testing

Eddy current testing is used to detect and quantify defects in electric conductive materials. Defects investigated are specifically mechanical, chemical and microstructural heterogeneities. In this scope, artificial defects simulating superficial cracks have been achieved in order to establish an eventual relationship between the orientation, the shape and the size of the defect in one hand, and the signature that it generates in the impedance plane on the other hand. We determine in the first stage the operating conditions for the minimization of all signals that may perturb the crack signal such as the background one. We have been able to detect easily a surface crack on ferromagnetic steel in a large range of the frequency. Curves allowing the discrimination between signals corresponding to the presence of cracks and those corresponding to a lift-off have been established. The limit depth has as well been determined and we found that this limit has no relationship with the depth of penetration of the eddy current. The operative parameters such as the diameter and the working mode of the probe, the excitation frequency and the setting of the measurement equipment have been optimized for the testing of the quality and the reliability of critical ferromagnetic steel parts.     

Effective magnetic permeability of ferromagnetic composites. Theoretical description and comparison with experiment

Two analytical methods based on the so-called local linearization of magnetostatic properties of composite materials with ferromagnetic inclusions in a non-magnetic matrix are described. These methods are applied to the experimental data obtained in Gorkunov et al. [Russ. J. Nondestruct. Test. 3 (2001) 186]. A qualitative agreement is obtained for the concentration values reported in that paper and a quantitative agreement is achieved at slightly different value of concentration. The conclusions are supported by direct numerical modeling.     

Magnetic, ferroelectric and magnetoelectric coupling properties of Fe-implanted BaTiO3 films

BaTiO₃ (BTO) nano-films were implanted with iron by means of ion-implantation. According to the results of X-ray diffraction (XRD) and Raman analysis, all the films are single-phase with tetragonal structure. Upon the increase of Fe dosage, on one hand, there is a decrease in c/a ratio of the unit cells. As the grain size and surface roughness of the Fe-implanted films decrease, the well crystallized film was obtained. Consequently, both decreasing of coercivity and boosting of magnetization were observed simultaneously. With the decline of the grain size and surface roughness during thermal treatment of the Fe-implanted films, there is an improvement of Fe distribution across the BTO matrix. Consequently, there is a decrease of coercivity and rise of magnetization. Upon the decrease of Fe dosage, on the other, there is a decline in magnetization, and a ferroelectric hysteresis loop is observed at a Fe dosage of 3.0 × 10¹⁴ cm^− 2. Additionally, the dependence of capacitance on the applied magnetic field and its frequency were also monitored.     

Ferromagnetism in Ga0.90Mn0.10As1 − yPy: From the metallic to the impurity band conduction regime

The magnetic properties of low temperature MBE grown Ga_0.90Mn_0.10As_1 − yP_y films with 0 < y < 0.20 have been studied as a function of the phosphorous content. The films are ferromagnetic for all phosphorous compositions. For y < 0.15 the conductivity type is metallic but above y > 0.15 it changes to impurity band conduction (IBC). In the IBC regime the main magnetic properties are profoundly modified: the saturation magnetization decreases from typically 50 emu/cm³ to 35 emu/cm³, the critical temperature drops sharply from 130 K to 45 K and the uniaxial magnetic anisotropy spectroscopy is strongly reduced.