Magnetic and microwave properties of glass-coated amorphous ferromagnetic microwires

Glass-coated amorphous FeCuNbSiB microwires were prepared by Taylor-Ulitovsky technique. X-ray diffractometry and scanning electron microscopy were used to investigate the microstructure and morphology of the glass-coated microwires respectively. The vibrating sample magnetometer and vector network analyzer were used to study the magnetostatic and microwave properties of glass-coated microwires. The experimental results show that the effective anisotropy of an array of 150 microwires of 10 mm in length is large than that of one microwire of 10 mm in diameter and an array of 150 microwires of 1 mm in diameter. The natural ferromagnetic resonance takes place as the microwave magnetic component is perpendicular to the microwires axis, and the electric dipole resonance takes place as the microwire is long or the short microwire concentration is moderate. The natural ferromagnetic resonance shifts to higher frequency with the larger microwire concentration. The electric dipole resonance is governed by the microwires length and concentration. The glass-coated FeCuNbSiB microwires can be used to design EMI filters and microwave absorbing materials.     

Giant magneto-impedance effect of two paralleled amorphous microwires

Giant magneto-impedance（GMI）is effectively enhanced by the mutual magnetic interaction between two amorphous microwires.A comparative study on GMI properties of a single wire and two wires arranged in parallel mode was reported in this work.Two-peak（TP）of impedance characteristic is presented when the dc external field changed from 0 to 320 A m^-1in two-wire system,which is attributed to successive magnetization process in two wires induced by their magnetic interaction.And the evolution of single peak to TP phenomenon,when the distance between two wires is upto 8 mm,evidences a distance dependence of transformation from successive magnetization to simultaneous via a corresponding distance dependence of magnetostatic interactions.It is proposed that the recombination of magnetic interaction and the shielding effect results in a distance dependency of GMI response.When the distance is 8 mm,the magnetization process is close to synchronous between two wires,which give rises to higher circular permeability and better GMI response.The impedance ratio DZ/Z increases from74.5 % of single wire to 172.4 % at 10 MHz.However,when the distance is upto 12 mm,the magnetic interaction is weak and magnetization process is completely independent,and GMI response decreases,relatively.This indicates that the GMI response could be effectively improved in a two-wire connection with an opticaldistance,which is promising and useful for the application of high-performance GMI sensors.     

Dimensional absorption high-frequency properties of the cast glass coated microwires

Correlation between frequency of natural ferromagnetic resonance of the cast glass coated amorphous microwires and high-frequency absorption of a composite material from this microwire is investigated. The article is published in the original.     

Magnetic properties of microwires and filiform nanostructures with elongated magnetic inclusions

We developed technological procedures for preparation of filiform nanostructures (FNSs) on the basis of stretching microwires with magnetic material cores. It is shown that disruptions of the microwire core occur for these materials during technological process of stretching due to relatively high melting temperature of magnetic alloys. As a result, FNSs with elongated magnetic inclusions are produced. An installation for the production of FNSs as well as an experimental complex for measuring magnetic properties of the produced magnetic FNSs is described in this paper. The morphology of the produced FNSs from microwires with magnetic bistability is investigated by means of scanning electron microscopy, while magnetic properties, such as magnetic response with remagnetizing pulses, hysteresis loop, and coercive force, are investigated on the developed experimental complex. The magnetic interaction during remagnetizing processes of several microwires with different coercive forces assembled in a bunch, as well as the reaction of a bunch assembled from a big number of bistable mirowires of two types with different coercive forces (soft magnetic and hard magnetic cores) upon increasing external magnetic field are also investigated. Some potential applications of the produced magnetic structures are suggested.     

Effect of a glass shell on the crystallization of Fe- and Co-based amorphous microwires

Crystallization of amorphous Fe_73.9B_13.2Si_10.9C₂ and Co_73.6B_11.2Si₁₃C₂ microwires in a glass isolation (shell) upon heating has been studied by X-ray diffraction. Crystallization of the core of an amorphous microwire starts at temperatures above 400°C. No noticeable effect of the glass shell on the crystallization of the Fe-based microwire was observed. The crystallization of the Co-based microwires with a glass shell begins at a lower temperature than the crystallization of those without a shell. There has been observed a difference in the effect of the glass shell on the crystallization of microwires of different chemical compositions.     

Relating residual stress and microstructure to mechanical and giant magneto-impedance properties in cold-drawn Co-based amorphous microwires

The effect of cold-drawing on the tensile property and giant magneto-impedance (GMI) effect of melt-extracted Co-based amorphous microwires was evaluated through detailed analyses of the distribution of residual stress and microstructural evolution. The tensile ductility and tensile strength increased gradually with cross-sectional area reduction ratio (R) until 51%, and decreased with further deformation. The microwire with R = 51% exhibits the highest tensile ductility of 1.09% and tensile strength of 4320 MPa. Structural and thermodynamic analyses reveal that it is the mechanical deformation rather than thermal activation that induces the precipitation of nanocrystals and arrests the quick extension of shear bands leading to the enhanced ductility. Interestingly, the GMI effect also attains the maximum value of 160% at 10 MHz when R = 51% (30% larger than that of the as-cast wires), before decreasing with further cold-drawing. Such an identical evolution trend of both tensile and GMI properties can be ascribed to two underlying mechanisms: the generation of longitudinal and circumferential residual stresses and the growth of deformation-induced nanocrystals during cold-drawing. The role of residual stress is established herein not only as a trigger to accelerate the amorphous-to-nanocrystalline phase transformation but also as a decisive contributor to the mechanical and GMI performance. The unique simultaneous improvement of both mechanical and GMI properties of cold-drawn Co-based microwires opens up new possibilities for a variety of engineering applications, such as high-performance magnetic, stress and biological sensors.     

Magnetic microstructure of amorphous,nanocrystalline, and nanophase ferromagnets

The magnetic microstructure of nanostructured ferromagnets is represented by an ensemble of stochastic magnetic domains—regions with dimensions of the length of magnetic orientation coherency. It is shown that the curves displaying the approach of magnetization to saturation make it possible to determine the dimension of the element of the micromagnetic structure, i.e., the size of the stochastic domain and the constant of the effective anisotropy in this element, the size of the element of the nanostructure and the constant its local anisotropy, as well as the dimensionality of the exchange-coupled ferromagnetic nanoparticles.     

Experimental measurement of residual stresses in microwires

Methods of measurement of residual stresses in cast amorphous microwires are submitted. The obtained experimental results confirm the earlier given theoretical conclusions.     

Magnetic properties of Fe75Si10B15 amorphous metallic wires

Effects of the temperature of a preliminary treatment, specimen length, and elastic tensile stresses on magnetic properties of amorphous metallic wires of composition Fe₇₅Si₁₀B₁₅ have been investigated. It has been revealed that the temperature of the pretreatment and the length of the wires have important influence on their magnetic properties. As the wire length decreases, a segment appears in the functional dependence of the differential magnetic permeability of the wire on the external magnetic field where the permeability remains constant, which indicates a change in the fundamental mechanism of magnetization of the wire. It has been shown that the behavior of the experimental functional dependence of the coercive force and differential permeability on applied tensile stresses may be explained in the context of the model of propagation of domain walls that separate oppositely magnetized domains in the core of the wire with allowance for the dissipative term.     

超长五重对称铜微米线的水热合成

利用简单水热法制备了高质量的超长铜微米线,并采用X射线衍射(XRD)仪、扫描电镜(SEM)氮气吸附表征了产品的结构和形貌、织构性质。结果表明,所得铜微米线具有五重对称的正五棱柱状孪晶结构。铜微米线的形成,被归因于CTAB对铜{100}面的吸附和铜晶体结构内部张力的协同作用。并且研究了产品对过氧化氢辅助的罗丹明B的催化脱色性能。在微米铜上过氧化氢辅助的罗丹明B脱色反应的表观反应速率常数(ka=0.004 84 min~(-1))为体相铜的(k_a=0.0014 min~(-1))3.5倍,这归因于前者较高比表面积和微米尺寸。本制备方法具有产率高(高达85.9%)、操作简单等优点,易于放大制备。     

Empirical models for long-term localised corrosion of cast iron pipes buried in soils

ABSTRACT

Empirical models are proposed for the progression of maximum depth of localised corrosion of cast iron pipes, based on data for pipes buried in 67 different backfill clay and sandy soils for up to 129 years. Early corrosion increases with increased inhomogeneity of the backfill soil and with greater availability of free water at the soil–pipe wall interface. Longer term corrosion is correlated with free water availability and occurs at a much slower rate. In most cases, the free water is fresh, oxygenated rainwater, known to be corrosive, but may also include some groundwater. Statistical uncertainty in pit depth is estimated and factors are proposed to allow for different annual rates of precipitation.     

玻璃包覆纯铜微丝耐腐蚀性能及电学性能

制备硼硅酸盐玻璃包覆纯铜微丝,其主要尺寸范围为：铜丝直径4-30μm,玻璃包覆层厚度2-8μm;对微丝的耐腐蚀性能和电学性能进行评价。结果表明：玻璃包覆纯铜微丝在中性盐雾实验条件下,抗潮热盐雾腐蚀时间在240 h以上;对于外径25μm、包覆层厚度3.2μm和外径18μm、包覆层厚度2.5μm玻璃包覆纯铜微丝,平均击穿电压分别达到1 174 V和774 V,耐击穿电压分别在1 050 V和660 V以上;外径25μm、包覆层厚度3.2μm的玻璃包覆纯铜微丝抗软化击穿温度大于400℃。     

In situ structural investigation of amorphous and nanocrystalline Fe40Co38Mo4B18 microwires

Thermal evolution of the structure of glass-coated nanocrystalline FeCoMoB microwire during its devitrification has been studied. It is shown that annealing at the temperature above 411 °C leads to the formation of crystalline α-FeCo grains with diameter ∼12 nm. Annealing at higher temperature increases the crystalline weight fraction up to 40% at 565 °C. However, crystalline grains size increases very weakly to ∼13 nm. The thermal expansion coefficient of nanocrystalline microwire decreases by one half comparing to that of the amorphous precursor.     

Magnetic field annealing of FeCo-based amorphous alloys to enhance thermal stability and Curie temperature

Annealing temperatures and applied magnetic fields are two important parameters for the performance modification of magnetic alloys.This article investigated the effect of different annealing temperatures on crystallization condition,magnetic properties and thermal stability of the amorphous magnetic alloy Co₃₆Fe₃₆Si_4.8B1_9.2Nb₄(at%).Results indicate that the annealing temperature can significantly affect the size and content of precipitated ...     

Effect of nanocrystallization on giant magnetoimpedance effect of Fe-based microwires

We studied giant magnetoimpedance (GMI) effect and magnetic properties of Fe_70.8Cu₁Nb_3.1Si_14.5B_10.6 and Fe_71.8Cu₁Nb_3.1Si₁₅B_9.1 Finemet microwires. We observed that GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored either controlling magnetoelastic anisotropy of as-cast FeCuNbSiB microwires, and/or controlling their structure by heat treatment or by changing the fabrication conditions. High GMI effect has been observed in as-prepared Fe-rich and heat treated microwires with nanocrystalline structure.