Dependence of the magnetic properties of an amorphous metal alloy on its nanoporosity

Magnetic and structural properties of an amorphous alloy based on iron are investigated. The properties and state of the alloy are changed under hydrostatic pressure of up to 1.3 GPa. An increase in the pressure leads to a linear increase in the maximum magnetic induction and a linear decrease in the remanence. Two nanopore fractions with average sizes of ～20 and 150 nm are revealed in the alloy with the use of small-angle x-ray diffraction. The application of the pressure decreases the size of nanopores and increases the average distance between their boundaries, i.e., increases the average sizes of continuity regions in the alloy. It is established that the relative change in the magnetic characteristics is linearly related to the change in the size of the continuity regions in the alloy. Upon extrapolation to zero nanoporosity, the remanence reduces to zero. The inference is made that the nanopores play a dominant role (as compared to other structural defects) in the magnetic properties of the alloy.     

Energy of the frequency-elastic effect in solids

A decrease in the frequency of skeletal vibrations (frequency-elastic effect) has been measured using Raman spectroscopy, and the stretching of backbone interatomic bonds in polyethylene molecules under elastic tensile loading of oriented polyethylene fibers has been measured using X-ray diffraction. It has been found that there are differences in the sign and magnitude of the changes in the zero-point energy and the work of the external force. The energy of the frequency-elastic effect has been explained in terms of the influence exerted by the initial (before loading) anharmonic stretching of backbone bonds and the force of anharmonic pressure, with the separation of the anharmonic (potential) component of the zero-point energy of the solid. A change in the frequency of vibrations corresponds to a change in the harmonic component of the zero-point energy. The loading with an external force causes a redistribution of the zero-point energy components. An energy analysis of the loaded quantum anharmonic oscillator has confirmed the conclusion regarding the mechanism of energy transfer and revealed that, under loading, there is a redistribution of the average values of the kinetic and potential components of the internal energy of the oscillator.     

Characteristics of elementary acts in the kinetics of metal fracture

Experimental studies of the fracture kinetics of polycrystalline metals have led to the problem of the barrier and activation volume of elementary fracture acts. A model is proposed where the field binding one atom to its environment in a metal is represented by equivalent bonds directed along three orthogonal axes. These bonds are described using the Morse potential, whose parameters are found from the values of the Young’s modulus and the linear thermal expansion coefficient for metals. The validity of the model is checked by comparing the results obtained with metal sublimation data. The values of the barrier and activation volume of elementary fracture acts are determined for 15 polycrystalline metals. The levels of local overstresses are estimated. The theoretical breaking strengths of the metals are calculated.     

Thermal expansion of polymers subjected to low-amplitude temperature cycling

The temperature dependence of the thermal expansion of polymers subjected to small harmonic temperature oscillations about certain base temperatures near the glass transition range is considered. The conformational component of the expansion as a function of temperature is calculated in terms of the conformational transition kinetics. The temperature dependences of the expansion and the expansion vs. oscillation phase shift are analyzed with allowance for the vibrationally anharmonic component. The thermal expansion of polyvinylacetate at base temperatures of 295–320 K, oscillation frequencies of 0.3 and 0.1 Hz, and an oscillation amplitude of 0.8 K are studied experimentally. The measured and calculated data for the expansion and expansion vs. temperature phase shift are shown to be in good agreement.     

Determination of the activation energy for complicated relaxation processes

Different methods are considered for analyzing the temperature dependence of the relaxation rate in the Arrhenius form. It is emphasized that the possible changes in the barrier to elementary acts with variations in temperature should be taken into account in order to determine the relaxation activation energy correctly. Changes in the barrier to elementary acts are illustrated using experimental data on the temperature-frequency dependence of the dielectric relaxation in polymers. A theoretical approach offering realistic activation energies is proposed.     

Deformations and stresses around submicroscopic cracks in loaded polymers

Structure deformations upon loading of oriented films of polycaproamide (Kapron) or polypropylene when submicroscopic cracks (dimensions of hundreds of Ångstroms) have appeared in the samples in high concentration (up to 2 · 10¹⁵ cm^–3) have been studied by x-ray diffraction methods at low and large angles. It has been established that the appearance of submicro-cracks causes relieving of the regions adjacent to them along the loading axis (extent about 1000 Å) and an increase in stress in the lateral zone relative to the crack, which is manifested in an intensification of the stretching of these zones.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 51–58, January–February, 1972.     

The strength properties of acicular single crystals of polyoxymethylene

The strength properties of acicular formations of polyoxymethylene, obtained by the directed polymerization of trioxane whiskers, have been studied. It has been found that the acicular single crystals obtained in this process exhibit a high strength.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 266–270, March–April, 1970.     

Effect of hydrostatic pressure on submicrocrack formation in oriented polymers

Small-angle x-ray scattering has been used to obtain a quantitative estimate of the concentration and size of the submicrocracks in Kapron and polypropylene equally extended at 1 and 1500 atm. Direct evidence of the retarding effect of pressure on fracture development has been obtained.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga: Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 917–921, September–October, 1971.     

Correlation of the elastic characteristics of Arimid PM with the elasticity modulus of its crystal lattice

Studies were made of the elastic characteristics (longitudinal elasticity modulus, elastic recovery) of Arimid PM fibers and of the longitudinal elasticity modulus of the crystal lattice of these samples. The elasticity modulus of the crystallites was determined by x-ray diffraction studies of loaded fibers. It is shown that the studied samples practically instanteneously recover their starting length after removing the load; the sample and its crystal lattice have comparatively low elasticity moduli with nearly identical values. Based on this data, reasons are discussed for the high elastic recovery of Arimid fibers and for the low elasticity modulus of its crystal lattice.Leningrad Branch, All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 5, pp. 771–773, September–October, 1972.     

Energetics of an adiabatically-loaded excited anharmonic oscillator

The dependence of the energy characteristics on an adiabatically slowly increasing external force is determined analytically for an anharmonic oscillator. The analytical results are confirmed by a numerical calculation. The nature of the force dependences of the energy characteristics are determined and discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 153–157 (January 1997)