Near equiatomic FeCo alloys: Constitution, mechanical and magnetic properties

Alloys based on the near-equiatomic FeCo offer exceptional magnetic properties. The equiatomic alloy was ‘invented’ in 1929, it offers a saturation hardly lower than that of the maximum obtained for Fe-0.35Co, with higher permeability and a lower coercivity than the latter. However, this alloy remained without industrial application, mainly because of its extreme brittleness. Only with the addition of a third element did it become possible to impart sufficient ductility for cold-rolling, and develop applications as laminated products. The addition of 2 wt% vanadium (1932) led to the ubiquitous FeCo-2V, or Permendur. It not only imparts, given appropriate heat-treatments, sufficient ductility, but also increases significantly the resistivity of the alloy while having little impact on the saturation.From a scientific point of view, the FeCo alloys, with their B2 structure below 730 °C, fall in the interesting category of ordered compounds. The ordering reaction has significant influence on the mechanical and magnetic properties and has therefore prompted a number of investigations. Not surprisingly, the vast majority of the work published to date concerns the FeCo-2V or its variants, rather than the binary alloy or other ternary systems. Recently though, alternative compositions, or improvement on the basic FeCo-2V have been put forward.This review attempts to summarise the current knowledge about the constitution, mechanical and magnetic properties of these alloys, focussing on the general properties of bulk FeCo and FeCo-X alloys (developed for applications such as rotor or stator laminations in motors). Recent development of nanocomposite and nanocrystalline materials such as HITPERM are not considered. A review of this developments is available in [McHenry ME, Willard MA, Laughlin DE. Amorphous and nanocrystalline materials for applications as soft magnets. Prog Mater Sci 1999;44:291-433]. An overview is given of work undertaken to date on various FeCo-X ternary system, with emphasis on the influence of these ternary additions on microstructure and characteristics of the phase diagram. The problem of the kinetics of ordering is given particular attention. Magnetic and mechanical properties are then discussed with emphasis on the relationship between microstructure and properties, and the main quantitative theories put forward are assessed again data gathered from the literature. It is shown that, while some points are clearly understood, a number of question remains in different areas which are outlined.     

Rheological properties of magnetic and electro-active nanoparticles in non-polar liquids

The rheological properties of two non-polar liquids [silicone oil or perfluorinated oil (FC70)] containing various types of particles, barium titanate, nickel and iron oxide, were investigated as functions of solid loading, particle size and shear rate. All the particles were synthesised in-house. The viscosities of either silicone oil or FC70 containing different solid loadings (10, 20 and 30 g/L) were measured over the shear rate range of 0.10–10 s⁻¹. All the nanofluids showed shear-thinning behaviour within this range and the viscosities increased with the increase of concentrations of nanoparticle and with the decrease of particle size. The highest increase of viscosity was found to be caused by nickel particles in silicone oil due to the formation of Ni network.     

Rheological behavior of carbon nanotube and graphite nanoparticle dispersions

Dispersions containing nanoparticles (nanofluids) are mixtures with unique properties, and their transport properties depend on the three-dimensional network or microstructure of the nanoparticles, which can be affected by various factors including shear stress, particle loading, and temperature. In this research, we studied the rheological behaviors of dispersions containing two different carbon morphologies: multiwalled carbon nanotubes (rodlike nanoparticles with L/D = 30), and graphite particles (disklike nanoparticles with L/D = 0.025). All nanofluids showed shear thinning behavior in steady shear measurements and those containing nanotubes had lower power law indices than graphite dispersions. Shear stress broke down the microstructure network and oriented both rodlike and disklike nanoparticles in the dispersions. The presence of a modest amount of nanotubes in the graphite nanofluid affected the microstructure of the dispersion and caused a remarkable decrease in its power law index. Microstructures of nanofluids strongly depended on the dispersant chemistry used to stabilize the particles, and high temperature may cause dispersant failure. Mechanical methods for dispersing the particles affected the geometry of the nanoparticles and therefore the rheological properties of the nanofluids. In the creep recovery tests, the compliance of graphite nanofluids quickly returned to zero when the stress was removed, while nanotube dispersion with high nanotube loading showed an elastic response during recovery. These results suggest that the microstructure in the dispersions is affected by nanoparticle morphology, dispersant chemistry, and shear stress.     

Dynamic mechanical,electrical and magnetic properties of ferrite filled styrene-isoprene-styrene

The dynamic mechanical, electrical and magnetic properties of highly filled magnetic polymeric composites containing 75 to 85 wt % barium ferrite in a thermoplastic elastomer matrix styrene-isoprene-styrene (SIS), are reported. The dependence of the properties on the volume fraction of the filler has been investigated. It is shown that the toughness and shore hardness of the composite may be correlated to its dynamic mechanical parameters. The use of coupling agents for surface treatment of ferrites has been shown to improve the magnetic properties of the composite due to better filler dispersion.     

Rheological and mechanical properties of surface modified multi-walled carbon nanotube-filled PET composite

Poly(ethylene terephthalate) (PET)/multi-walled carbon nanotube (MWCNT) composites were prepared by in situ polymerization. To improve the dispersion of MWCNTs in PET matrix, the surface modified MWCNTs having acid groups (acid-MWCNT) and diamine groups (diamine-MWCNT) were used. The functional groups on the surface of modified MWCNTs were confirmed by infrared (IR) spectrometry. SEM analysis showed better dispersion of diamine-MWCNTs as compared to pristine-MWCNTs and acid-MWCNTs in the PET. The reaction between PET and diamine-MWCNTs was evidenced by the shifting of the G band to a higher frequency in Raman spectroscopy and an increase of the complex viscosity in rheological properties. The composites containing functionalized MWCNTs showed a large increase in the tensile strength and modulus. The PET/diamine-MWCNT composites showed maximum tensile strength and modulus increases by 350% and 290% at 0.5 and 2.0 wt%, respectively, as compared to pure PET.     

Rheological and mechanical properties of polypropylene prepared with multi-walled carbon nanotube masterbatch

In this study, the effects of polypropylene-grafted maleic-anhydride-treated multi-walled carbon nanotubes (PP-MWNTs) on the viscoelastic behaviors and mechanical properties of a polypropylene-(PP)-based composite system were examined. The PP-MWNT/PP composites were prepared via melt mixing with a 3:1 ratio of PP-g-MA and acid-treated MWNTs at 220 degrees C. The surface characteristics of the PP-MWNTs were confirmed via Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The viscoelastic behavior and mechanical properties of the PP-MWNT/PP composites were confirmed using a rheometer and an ultimate testing machine (UTM). The storage and loss moduli increased with increasing PP-MWNT content. The critical intensity stress factor (K(IC)) of the PP-MWNT/PP composites at high filler loading was also higher than that of the MWNT/PP composites. In conclusion, the viscoelastic behavior and mechanical properties of MWNT/PP can be improved by grafting MWNTs to PP-g-MA.     

Rheological and mechanical properties of poly(butylene terephthalate)-modified epoxy resins

Poly(butylene terephthalate) (PBT) was used as modifier for epoxy resin. With the incorporation of 7.5 wt% PBT, the resin became a gel as shown by rheological measurements in steady shear, thixotropic loop and dynamic shear mode. The gel was very stable on storage. An abrupt change of rheological properties occurred at the dissolution temperature of the PBT spherulites. The PBT modifier did not impair mechanical properties of the cured resins, yet a moderate improvement in toughness was achieved.     

端基四肽聚异戊二烯的合成表征及流变性能

文中对四肽封端的聚异戊二烯的合成方法和流变性能进行了初步探索。首先采用新癸酸钕/二异丁基氢化铝/二氯二甲基硅稀土催化剂体系催化异戊二烯聚合,得到了相对分子质量可控,窄分布(1.09~1.4),顺1,4结构含量高(96%)的聚异戊二烯。聚合4 h后用二氧化碳封端得到端羧基聚异戊二烯(PI-COOH)。非水滴定结果表明羧基封端率高(100%)。然后PI-COOH与四肽(Boc-(ala)_4-NH_2)缩合形成端基为四肽的聚异戊二烯(PI-4A)。流变测试结果表明,与PI-COOH相比,PI-4A中四肽的分子间氢键作用使得储能模量提高了约1000倍;并且在升温过程中氢键被逐渐破坏,模量快速下降,在50℃时大部分氢键断裂。     

Ultrafine magnetic particles dispersed in silica: Characterization of cobalt iron citrate precursor and magnetic properties

Ultrafine magnetic particles dispersed in a silica matrix were successfully obtained by treatment of a cross-linked cobalt iron citrate precursor, synthesized by a modified Pechini route, with 0.001 M K₂Cr₂O₇ at 130 °C. The IR and NMR spectroscopic characterization of the precursor gel containing Co²⁺ and Fe³⁺ shows that the citric acid reacts with the metallic ions by coordination, the ethylene glycol by esterification and the tetraethylorthosilicate by substitution. SQUID measurements of the composite indicate superparamagnetic behavior. The blocking temperature, from the peak of the zero-field-cooled measurements, was 3 K at 1000 Oe. The magnetic diameter calculated using Langevin's equation was 4 nm.     

Some magnetic and mechanical properties of fibre-reinforced nickel and nickel-iron alloys

Composites containing tungsten wires reinforcing nickel and nickel-iron alloy matrices have been fabricated by a filament winding-electroplating technique and a considerable improvement in the tensile strength was achieved relative to the unreinforced matrix. The presence of the fibres was found to have a significant influence on the magnetic properties of the composites measured in the direction of the fibre axes. In composites having a matrix with a negative magnetostriction, the maximum permeability decreased with increasing volume fraction, V _f, and was also dependent on the fibre diameter and the magnitude of the magnetostriction. In cases where the matrix had a positive magnetostriction the maximum permeability was observed to increase with increasing V _f, reaching a peak value at V _f0.1. It was suggested that the presence of stresses induced in the matrix during cooling from the heat-treatment temperature, due to the difference in the thermal expansion between the fibre and matrix, could explain this magnetic behaviour. By theoretical considerations, the peak was shown to coincide approximately with the volume fraction at which the maximum, uniaxial elastic stress was expected to form in the matrix. Above this volume fraction the uniaxial and transverse stresses became sufficiently high to cause plastic deformation in the entire matrix leading to the observed fall in the maximum permeability, although in all cases the value remained above that shown by the unreinforced matrix.     

Characterization of mechanical properties of FeCrBSiMnNbY metallic glass coatings

This article investigates mechanical characteristics of Fe-based metallic glass coatings. A series of the coatings were fabricated by conventional wire-arc spray process. The microstructure of the coating was characterized by means of X-ray diffraction, scanning election microscopy equipped with energy dispersive X-ray analysis, transmission electron microscopy, and differential scanning calorimeter. The coating is very dense smooth, adhering well and with no cracking. The microstructure of the coating consists of amorphous phase and α(Fe,Cr) nanocrystalline phase. The nanocrystalline grains with a size of 30 to 60 nm are homogenously dispersed in the amorphous phase matrix. The crystallization temperature of the amorphous phase is about 545 °C. The mechanical properties, such as porosity, adhesive strength, microhardness, elastic modulus, and abrasive wear resistance, were analyzed in detail. The experimental results indicate that the coating has high microhardness (15.74 GPa), high elastic modulus (216.97 GPa), and low porosity (1.7%). The average adhesive strength value of the coating is 53.6 MPa. The relationship between abrasive wear behavior and structure of the coating is discussed. The relatively wear resistance of metallic glass coating is about 7 and 2.3 times higher than that of AISI 1045 steel and 3Cr13 martensite stainless steel coating, respectively. The main failure mechanism of metallic glass coating is brittle failure and fracture. The Fe-based metallic glass coating has excellent wear resistance.     

Characterization and dissolution properties of ketoprofen in binary and ternary solid dispersions with polyethylene glycol and surfactants

The effect of incorporation of an anionic [sodium dodecyl sulfate (SDS) or dioctylsulfosuccinate (DSS)] or nonionic [Tween 60 (TW60)] surfactant on the properties of ketoprofen solid dispersions in polyethylene glycol 15000 (PEG) has been investigated. Physicochemical and morphological properties of the various solid systems were determined by differential scanning calorimetry, hot stage microscopy, X-ray powder diffraction analysis, and scanning electron microscopy. The results from dissolution studies, performed according to the USP 24 basket method, indicated that all ternary dispersed systems were significantly (p < 0.001) more efficacious than the corresponding binary ones, by virtue of the additive wetting and solubilizing effect due to the presence of the surfactant. The relative effectiveness of the incorporated surfactant was in the same order as found in phase-solubility studies (i.e., SDS > DSS > TW60). With regard to the solid dispersion preparation method, coevaporated products always gave better results than the corresponding cofused ones; however, this effect was statistically significant (p < 0.001) only in the initial phase of the dissolution process. The most effective solid dispersion was the 10-80-10 w/w drug-PEG-SDS ternary coevaporate, which allowed dissolution of 50% drug after only 6 min (in comparison with > 120 min for drug alone and 17 min for the binary coevaporate) and dissolution of about 100% drug after 30 min (in comparison with > 120 min for the binary coevaporate).     

Electrorheological and dielectric properties of polypyrrole dispersions

The electrorheological (ER) response and dielectric properties of the polypyrrole (PPy) dispersions in mineral oil were investigated. Various PPy particles were synthesized controlling the amount of oxidant and surfactant to investigate the effect of these variables on the ER response. The ER response increases with the oxidant and surfactant amount, passes through a maximum, and then decreases with the oxidant and surfactant amount. However, the decrease in the ER response at large surfactant amounts is not so significant compared to that at large oxidant amounts. The increase in the ER response with the oxidant and surfactant amount arises from the enhanced particle polarization originated from the increased PPy conductivity. The decrease in the ER response at large oxidant amounts seems to arise from the increased conduction between the PPy particles, while that at large surfactant amounts arises from the decreased particle polarization.     

Characterization of mechanical properties in the Ir---Nb---Zr intermetallic system

The mechanical properties of very high melting intermetallic compounds are examined in the Ir---Nb---Zr system. The Ir---Nb---Zr system contains two related high temperature L1₂ intermetallic compounds, Ir₃Nb and Ir₃Zr, with similar lattice parameters and melting points of 2450 and 2280°C respectively. Microhardness and compression tests show that the Ir₃Nb possesses twice the strength of the Ir₃Zr despite their marked similarities in electronic structure and cohesive properties. Furthermore, preliminary studies of a ternary L1₂ compound of composition Ir_0.71Nb_0.21Zr_0.08 show that it has a high temperature strength greater than that of either of the binary systems. Total energy electronic structure calculations confirm the similarity in the cohesive properties of the binary compounds, and point to differences in the density of states at the Fermi level as a possible reason for their dissimilar mechanical behavior.     

Rheological Characterization of Tear Substitutes

The steady state viscosity as a function of shear rate was determined for eight commerical tear substitutes and compared with data for high molecular weight sodium hyaluronate solutions. The Zero shear viscosity at steady state varied more than 100-fold from about 2 to 300 cP. Many samples were Newtonian, while some samples exhibited a varying degree of shear thinning (psedudoplastic) behaviour. The results are discussed in realation to the rheological behaviour of normal tears and mucin.     

Rheological Characterization of Hydroxypropylcellulose Gels

The present paper describes the rheological properties of hydroxypropylcellulose (HPC) gels formulated in propylene glycol (PG), water, ethanol, and mixtures of these components. The effects of molecular weight, polymer concentration, and solvent composition on the apparent viscosity and flow characteristics have been studied by continuous shear rheometry. The HPC gels are shear thinning and do not exhibit significant yield or hysteresis in their rheograms. The apparent viscosity increases with increasing molecular weight and concentration of the polymer, as expected. Although not so pronounced at lower concentrations (≤ 1.5%), HPC gels tend to become increasingly non-Newtonian with increasing molecular weight at higher polymer concentrations (3%). A mathematical model has been proposed for the prediction of viscosities of HPC gels. There exists a high degree of dependence on molecular interactions between various solvent molecules in the prediction of mixture viscosities in ternary systems. The effects of solvent composition on the viscoelastic behavior of these gels have also been examined by dynamic mechanical analysis. The HPC gels are highly viscoelastic and exhibit greater degrees of elasticity with increased PG content in ternary solvent mixtures with water and ethanol. The study also suggests that dynamic mechanical analysis could prove to be a useful tool in the determination of zero-shear viscosities, viscosities that are representative of most realistic situations.     

Low-temperature mechanical and magnetic properties of the reduced activation martensitic steel

Mechanical and magnetic properties as well as their relationship in the reduced activation martensitic (RAM) steel were investigated in the temperature range from --90°C to 20°C. Charpy impact tests show that the ductile-to-brittle transition temperature (DBTT) of the RAM steel is about --60°C. Low-temperature tensile tests show that the yield strength, ultimate tensile strength and total elongation values increase as temperature decreases, indicating that the strength and plasticity below the DBTT are higher than those above the DBTT. The coercive field (H_C) in the scale of logarithm decreases linearly with the increasing temperature and the absolute value of the slope of lnH_C versus temperature above the DBTT is obviously larger than that below the DBTT, also confirmed in the T91 steel. The results indicate that the non-destructive magnetic measurement is a promising candidate method for the DBTT detection of ferromagnetic steels.     

Rheological Characterization of Tear Substitutes

Abstract

The steady state viscosity as a function of shear rate was determined for eight commerical tear substitutes and compared with data for high molecular weight sodium hyaluronate solutions. The Zero shear viscosity at steady state varied more than 100-fold from about 2 to 300 cP. Many samples were Newtonian, while some samples exhibited a varying degree of shear thinning (psedudoplastic) behaviour. The results are discussed in realation to the rheological behaviour of normal tears and mucin.