Cobalt-containing core-shell nanoparticles on the surface of poly(tetrafluoroethylene) microgranules

Cobalt-containing nanoparticles have been prepared via thermal decomposition of cobalt acetate on the surface of poly(tetrafluoroethylene) (PTFE) microgranules forming a fluidized bed over the surface of hot mineral oil. Using transmission electron microscopy, the average size of the cobalt-containing nanoparticles has been determined to be 3.6 nm. The composition and structure of the nanoparticles have been determined by x-ray diffraction, extended x-ray absorption fine structure spectroscopy, and electron paramagnetic resonance, and the magnetic properties of the synthesized nanomaterial have been studied. The results indicate that the nanoparticles have a core-shell structure, with a metallic cobalt core (?10 vol%) and a shell consisting of three phases: Co₃O₄ (?80%) and small amounts of CoO and CoF₂ (?10%). The fluoride phase results from the interaction of the nanoparticles with surface fluorine atoms of the PTFE microgranules.     

Influence of Hydrogen on the Equilibrium of a Dislocation Submicrocrack in α-Iron

Numerical methods are used to analyze the influence of hydrogen on the fracture of steels with bcc lattice by the mechanism of microcleavage. The behavior of submicrocracks at the head of a dislocation pileup is studied under uniaxial tension. In the case of delivery of hydrogen by merged dislocations of the pileup into the submicrocrack, it loses stability due to the adsorption decrease in the specific surface energy earlier than it becomes possible under the action of the pressure of hydrogen in the crack. We deduce the dependences of the fracture stress on the specific surface energy and the amount of hydrogen delivered by dislocations into the submicrocrack. The influence of hydrogen condensed on dislocations on the formation of submicrocracks is significant. We establish the relationship between the amount of hydrogen condensed on dislocations, the concentration of diffusing hydrogen in the metal, and rapid degradation of mechanical properties of steel even for small concentrations of dissolved hydrogen.     

Paramagnetism of melanoprotein fibres

Experimental EPR studies of the properties of more than 200 melanoprotein samples from human hair were conducted. The EPR signal from keratin associates was found for the first time. Conclusions were drawn from the temperature dependences of the keratin signal parameters concerning the structural states of the protein polymer: melting, glass transition, dehydration. Arguments in support of localization of paramagnetic centers on the surface of bound keratin tetramers are presented. The temperature evolution of the parameters of the EPR signal of melanin was investigated. It was shown that the material of pigment granules corresponds to a small organic semiconductor with E ∼ 0.15 eV. __________ Translated from Khimicheskie Volokna, No. 6, pp. 49–54, November–December, 2006.     

Angular dependence of the FMR linewidth and the anisotropy of the relaxation time in iron garnets

This work is devoted to the problem of extracting the contribution of the anisotropy of relaxation to the angular dependence of the FMR linewidth and to the opportunity of determining the values of the parameters of relaxation. The results of the FMR study of films based on the yttrium iron garnet prepared by the method of liquid-phase epitaxy are given. The orientational dependence of the linewidth has been calculated using the traditional method of measuring an FMR spectrum and a method based on scanning at an angle to the resonance field for obtaining the minimum linewidth. A model for calculating the linewidth has been proposed that takes into account the anisotropy of the relaxation term in the equation of motion of the magnetic moment. The model leads to a dependence that agrees well with the experimental data, which makes it possible to state that the anisotropy of relaxation most likely takes place in the samples under consideration at the temperatures employed.     

Nature of Hydrogen Brittleness of Structural Steels

We generalize the results of investigations performed at the Paton Institute of Electric Welding and aimed at elucidating the nature of the reversible hydrogen brittleness of structural steels. The state of the problem is analyzed, and a methodical approach is proposed for studying the problem at the atomic level. New ideas of the mechanism of reversible hydrogen brittleness are formulated, and their experimental substantiation is presented. It is shown that these ideas are useful for refining the methods of prevention of hydrogen embrittlement in steel structures while they are in production or in operation under conditions of hydrogen adsorption.     

The Effect of Morphology and Particle-Size Distribution of VT20 Titanium Alloy Powders on the Mechanical Properties of Deposited Coatings

Powder Metallurgy and Metal Ceramics - The surface morphology of coatings produced from spherical and nonspherical VT20 titanium alloy powders with different particle-size distributions has been...     

Micromechanical Aspects of Reversible Hydrogen Embrittlement

We present experimental data confirming the known regularities of reversible hydrogen embrittlement of structural steels. We analyze some aspects of this complicated phenomenon at the atomic, dislocation, microstructural, and macrostructural levels and show that the defective structure of a metal plays a decisive role in all stages of reversible hydrogen embrittlement.