Characteristic features of hysteresis in soft-magnetic amorphous alloys upon structural relaxation

The influence of structural relaxation on the hysteresis of soft-magnetic amorphous alloys in the case when structural relaxation proceeds above the Curie temperature is investigated. The results of the present study and previous works, in which similar studies were conducted for alloys with structural relaxation observed below the Curie temperature, have been generalized. The entire set of experimental data obtained makes it possible to formulate the recommendations regarding the choice of the annealing conditions for softmagnetic amorphous alloys.     

Characteristic features of hysteresis in soft-magnetic amorphous alloys upon structural relaxation

The influence of structural relaxation on the hysteresis of soft-magnetic amorphous alloys in the case when structural relaxation proceeds above the Curie temperature is investigated. The results of the present study and previous works, in which similar studies were conducted for alloys with structural relaxation observed below the Curie temperature, have been generalized. The entire set of experimental data obtained makes it possible to formulate the recommendations regarding the choice of the annealing conditions for softmagnetic amorphous alloys.     

Magnetic properties and microstructure of electrodeposited Fe−P amorphous alloy

Electrodeposited Fe–P amorphous alloy has been characterized in terms of magnetic properties and the microstructure. The Fe–P electrodeposits show amorphous structure with phosphorus contents of about 20 at%. The formation of the amorphous structure depends mainly on the phosphorus content. The amorphous Fe–P alloy shows typical soft magnetic properties such as low coercive force and high permeability. The coercive force (Hc) decreases with the low temperature annealing, and the lowestHc is about 0.05 oersted. This reduction inHc can be attributed to structural relaxation. The amorphous phase is crystallized at temperatures above 300°C accompanying a drastic increase inHc. The stable crystalline phase is Fe₃P.     

Structural evolutions and electrochemical behaviors of Co-B alloys as anode materials for alkaline secondary batteries

Co-B alloys were synthesized via a chemical reduction method, and adopted as anode materials for alkaline secondary batteries. The structural evolutions and the electrochemical behaviors of the as-prepared Co-B alloys with increasing heat-treating temperatures were analyzed with X-ray diffraction (XRD), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and charge-discharge test. It is found that the Co-B alloys treated at various temperatures show high reversibility. And the electrochemical activities were found to be dependent on the structural evolutions of the Co-B alloys. The amorphous Co-B alloy treated at 50 °C achieves an excellent discharge capacity of 304 mAh/g in the first cycle, while the Co-B alloy treated at 500 °C shows superior cyclicity.     

Crossover effect for elastic moduli of amorphous metallic alloys

The structural relaxation in glass-forming melts and glasses is responsible for such a phenomenon as the crossover effect when the dependence of physical properties (such as the elastic modulus, volume, refractive index, etc.) upon isothermal annealing of materials (preliminarily heat-treated at lower temperatures) is described by a curve with an extremum. The paper presents the results of the investigation into the crossover effect for the elastic moduli of amorphous alloys obtained upon quenching from the liquid state in the form of a ribbon 15–70 μm thick.     

Crossover effect for elastic moduli of amorphous metallic alloys

The structural relaxation in glass-forming melts and glasses is responsible for such a phenomenon as the crossover effect when the dependence of physical properties (such as the elastic modulus, volume, refractive index, etc.) upon isothermal annealing of materials (preliminarily heat-treated at lower temperatures) is described by a curve with an extremum. The paper presents the results of the investigation into the crossover effect for the elastic moduli of amorphous alloys obtained upon quenching from the liquid state in the form of a ribbon 15–70 μm thick.     

Structural Relaxation in Amorphous Magnetic Screens

The structural relaxation is studied in amorphous magnetic screens produced by plasma deposition and explosive compacting from an amorphous metallic ribbon. Investigations are performed by different methods, such as differential scanning calorimetry (DSC), measurements of magnetic hysteresis properties, X-ray powder diffraction analysis, and electron probe X-ray microanalysis. It is found that the structural relaxation in the objects studied proceeds in the same way as in rapidly quenched glasses.     

电沉积Ni-Fe-P非晶态合金镀层变温晶化的研究

用差热分析的方法研究了电沉积Ｎｉ－Ｆｅ－Ｐ非晶态合金镀层的变温晶化过程。通过实验得出不同铁含量的Ｎｉ－Ｆｅ－Ｐ合金在不同加热速度下的开始晶化温度、结束晶化温度,并计算出其晶化激活能。对不同Ｆｅ含量镀层的晶化激活能进行比较发现,Ｆｅ元素在Ｎｉ－Ｆｅ－Ｐ合金镀层中具有稳定非晶态组织的作用。     

Variant of the Relaxation and Retardation Spectra for Amorphous Crystalline Synthetic Fibres

The relaxation (retardation) spectrum of amorphous crystalline synthetic fibres is totally determined by the mean statistical relaxation (retardation) time and the structural coefficient that essentially characterizes the intensity of the relaxation (creep) process. With respect to the physical meaning, the relaxation function (retardation function) is obtained by integration of the relaxation (retardation) spectrum. Methods are developed for determining the relaxation and retardation spectra.     

Drug-Biopolymer Dispersions: Morphology- and Temperature- Dependent (Anti)Plasticizer Effect of the Drug and Component-Specific Johari–Goldstein Relaxations

Amorphous molecule-macromolecule mixtures are ubiquitous in polymer technology and are one of the most studied routes for the development of amorphous drug formulations. For these applications it is crucial to understand how the preparation method affects the properties of the mixtures. Here, we employ differential scanning calorimetry and broadband dielectric spectroscopy to investigate dispersions of a small-molecule drug (the Nordazepam anxiolytic) in biodegradable polylactide, both in the form of solvent-cast films and electrospun microfibres. We show that the dispersion of the same small-molecule compound can have opposite (plasticizing or antiplasticizing) effects on the segmental mobility of a biopolymer depending on preparation method, temperature, and polymer enantiomerism. We compare two different chiral forms of the polymer, namely, the enantiomeric pure, semicrystalline L-polymer (PLLA), and a random, fully amorphous copolymer containing both L and D monomers (PDLLA), both of which have lower glass transition temperature (T_g) than the drug. While the drug has a weak antiplasticizing effect on the films, consistent with its higher T_g, we find that it actually acts as a plasticizer for the PLLA microfibres, reducing their T_g by as much as 14 K at 30%-weight drug loading, namely, to a value that is lower than the T_g of fully amorphous films. The structural relaxation time of the samples similarly depends on chemical composition and morphology. Most mixtures displayed a single structural relaxation, as expected for homogeneous samples. In the PLLA microfibres, the presence of crystalline domains increases the structural relaxation time of the amorphous fraction, while the presence of the drug lowers the structural relaxation time of the (partially stretched) chains in the microfibres, increasing chain mobility well above that of the fully amorphous polymer matrix. Even fully amorphous homogeneous mixtures exhibit two distinct Johari–Goldstein relaxation processes, one for each chemical component. Our findings have important implications for the interpretation of the Johari–Goldstein process as well as for the physical stability and mechanical properties of microfibres with small-molecule additives.     

Wettability of amorphous and nanocrystalline Fe<Subscript>78</Subscript>B<Subscript>13</Subscript>Si<Subscript>9</Subscript> substrates by molten Sn and Bi

The wettability of amorphous and annealing-induced nanocrystalline Fe₇₈B₁₃Si₉ ribbons by molten Sn and Bi at 600 K was measured using an improved sessile drop method. The results demonstrate that the structural relaxation and crystallization in the amorphous substrates do not substantially change the wettability with molten Bi because of their invariable physical interaction, but remarkably deteriorate the wettability and interfacial bonding with molten Sn as a result of changing a chemical interaction to a physical one for the atoms at the interface.     

Relation between nanocrystallization and structural relaxation in the Fe<Subscript>73.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> alloy

Based on X-ray powder diffraction data available in the literature on nanocrystallization of the rapidly quenched amorphous alloy Fe_73.5Cu₁Nb₃Si_13.5B₉ (Finemet) and our data on the deformation of the alloy during crystallization, it has been established that the formation of a nanostructure is associated with the structural relaxation in the amorphous state and its own features after the rapid quenching.     

Etude des propriétés viscoélastiques de quelques mélanges polybutène-1 – polypropène

Viscoelastic properties of polybutene-1—polypropene blends were investigated in the β-relaxation range. Those blends show only òne relaxation peak and are assumed to be compatible in the amorphous phase. These results permit to corroborate our former assumption concerning the influence of the relative length of the alkyl group in polyolefin blends.     

Fe-B非晶态合金中电子转移问题的DFT研究

利用一系列原子簇模型 Fen B2 (n=1～ 4)对 Fe- B非晶态合金的电子结构 ,用 DFT方法进行高水平的量子化学计算 ,结果表明 ,模型体系 Fen B2 (n=1～ 4)中 ,B原子供给 Fe原子电子 ,这与非晶态合金的实验结果一致 ;模型体系不存在类似于 Ni- B非晶态合金中 B- B近距离接触 ,为了比较 ,也选择了单硼原子簇 Fen B(n=1～ 4)模型 ,计算结果与实验不符 ,说明双硼原子簇模型 Fen B2 能在一定程度上反映 Fe- B非晶态合金的局域结构特征。     

Atomic mechanisms of glass formation in metallic alloys, tendency to glass formation, and structural models

The factors affecting the tendency of metallic alloys to glass formation have been discussed. The most commonly accepted structural models of amorphous alloys are considered. The Ni₈₀B₂₀ and Ni₈₀Zr₂₀ alloys are studied by the molecular dynamics method. It is demonstrated that the amorphization of these alloys occurs through the same mechanism of formation of low-dimensional nanometric dendrite-like compounds that nucleate in the liquid phase, persist upon glass transition, disturb the order in a metal matrix, and, thus, prevent the transition to the crystalline state.     

Atomic mechanisms of glass formation in metallic alloys, tendency to glass formation, and structural models

The factors affecting the tendency of metallic alloys to glass formation have been discussed. The most commonly accepted structural models of amorphous alloys are considered. The Ni₈₀B₂₀ and Ni₈₀Zr₂₀ alloys are studied by the molecular dynamics method. It is demonstrated that the amorphization of these alloys occurs through the same mechanism of formation of low-dimensional nanometric dendrite-like compounds that nucleate in the liquid phase, persist upon glass transition, disturb the order in a metal matrix, and, thus, prevent the transition to the crystalline state.     

Ultrafine Ni–Co–W–B amorphous alloys and their activities in benzene hydrogenation to cyclohexane

Quaternary Ni–Co–W–B amorphous alloys were prepared by chemical reduction of the aqueous solution of nickel and cobalt salts and sodium tungstate with potassium borohydride. The catalytic activities of the as-prepared materials were measured through liquid phase hydrogenation of benzene under moderate pressure. In comparison with Ni–Co–B, the as-prepared Ni–Co–W–B amorphous alloys showed superior activity, attributable to the promoting effect of tungsten on the microstructure of the alloys as revealed by XPS, XRD and DSC measurements.     

Glass transition dynamics and structural relaxation of PLLA studied by DSC: Influence of crystallinity

Poly(l-lactic acid), PLLA, in amorphous and semi-crystalline forms were studied by DSC, in order to investigate both molecular dynamics and structural relaxation features, and to understand the influence of the crystalline confinement on the segmental mobility of the intra-spherulitic amorphous phase. Experimental data were generated after submitting the materials to different thermal histories below T_g and were treated with a model based on the configurational entropy concept, allowing to extract a series of physical-meaningful parameters and to obtain the temperature dependence of the relaxation times. The main features of the relaxation process in the glassy state (activation energy of the glassy state and x) and the fragility index were found to be apparently insensitive to crystallinity. Significant differences between the two materials were detected in both the position of the glass transition temperature and the width of the distribution of relaxation times. In the framework of the Adam and Gibbs theory, it is suggested that for the semi-cristalline PLLA the mobility of the amorphous chains is more or less restricted, depending on their distance to the rigid lamellar walls or on the intra-lamellar thickness; this will imply that their conformational motions will take place at different temperatures, typically above the glass transition temperature of the (unconfined) bulk amorphous phase.     

Nonlinear stress-strain behavior of glassy polymers

We have attempted to provide a unified account of the structural relaxation and mechanical properties of glassy polymers by reviewing recent results of a predictive model. One would like to understand how the effects of structural relaxation influence the performance of amorphous solids. The physics of glassy polymers is still evolving and the functional relationships between relaxation and deformation have not been firmly established. However, significant progress has already been made that can be utilized in solving problems in the large deformation of polymers. Equations have been derived that can be applied to provide quantitative prediction of the nonlinear stress-strain relationships as a function of physical aging, strain rate, temperature, external stress field, and the filler concentration in composites.