Effect of solid solution strengthening by iridium on the nucleation of dislocations in a molybdenum single crystal during nanoindentation

The nucleation of dislocations in single crystals of molybdenum and a Mo-1.5 at % Ir solid solution has been investigated by nanoindentation. In the curve of indentation of a Berkovich indenter into the single crystals, an abrupt transition from elastic to plastic deformation has been observed at a depth of 20–40 nm due to the nucleation of dislocations in the initially dislocation-free region under the contact. Alloying of molybdenum by iridium results in a twofold increase in shear stresses under which dislocations nucleated in the contact. Therefore, the solid solution impurity of iridium in molybdenum leads to an increase not only in the plastic strain resistance (to an increase in the hardness) but also in the elastic shear stresses under which dislocations are generated (homogeneously or heterogeneously) in the contact. The latter effect cannot be explained only by an increase in the elastic moduli because of its smallness; however, it is determined to a large extent by a higher degree of perfection of the solid solution crystal as compared to unalloyed molybdenum.     

Phase composition and structure of nanocrystalline products of solid-phase oxidative thermolysis of iron oxalate dihydrate

X-ray diffraction studies of the ultradisperse products of the solid-phase oxidative thermolysis of iron oxalate dehydrate are performed. Models are considered and diffraction patterns are calculated for the nanopowders of different crystalline modifications of iron oxide. Calculations are performed for the particles of various shapes and sizes, starting from one unit cell. Despite that the final product is the hematite phase, the reaction is shown to pass through the formation of particles with the ferrihydrite structure.     

Elastoplastic Deformation of Dispersion-Hardened Aluminum Tube Under External and Internal Pressure

Russian Physics Journal - The paper studies the elastoplastic deformation of the aluminum thick-walled tube hardened with incoherent particles under the external and internal pressure. The elastic...     

Stress-Strain State of Disperse-Hardened Aluminum Joint Tube Under Internal Pressure

Russian Physics Journal - The paper presents research into the stress-strain state of an interference-fit connected tube made of dispersehardened aluminum alloy and subjected to the uniform...     

Theoretical analysis of PPE measurements in liquids using a thermal-wave cavity

The photopyroelectric measurements in a thermal-wave cavity (PPE) were analyzed with a conventional one-dimensional approach and a three-dimensional approach. The calculations show that the dimensionality of the thermal-wave field in the cavity depends on the boundary conditions and the beam size of the applied laser. The study resulted in identifying ranges of heat transfer rates and cavity configurations for which accurate quantitative measurements of the thermal diffusivity of intracavity fluids can be made within the far simpler, but only approximate, one-dimensional approach conventionally adopted by users of thermal-wave cavities.     

Interaction of femtosecond pulses of a two-harmonic Ti:Sapphire laser with liquid media

The interaction of ultrashort laser pulses having wavelengths of 400 and 800 nm with liquid media, including organic solutions, has been experimentally studied. It is shown that transparent drops evaporate and boil (with partial mass ejection in the form of vapor and liquid fragments) in the field of ultrashort light pulse. A large-scale change in the spectrum of laser pulse during its interaction with a water particle is revealed. This change is caused by self-modulation of the light phase due to the Kerr optical nonlinearity of liquid and the formation of plasma. Filamentation in continuous liquid media is analyzed; specifically, the dependences of the number of filaments, the lasing spectrum width, the nonlinear-focusing distance, and the filamentation region diameter on the laser pulse power are measured. It is noted that there is a range of relative powers where the number of filaments very rapidly increases. It is shown that the spectral broadening at filamentation, observed for fixed pulse energy with a change in pulse width, overlaps the entire visible spectral range. This circumstance makes it possible to obtain width-tunable pulses and use them, e.g., in optoacoustic diagnostics of media.     

Iron Hydroxides—New Catalysts for Oxidation Reactions in Aqueous Solutions

The catalytic decomposition of H₂O₂ in the presence of SiO₂-supported amorphous and colloidal FeO(OH) is studied. An inactive Fe(IV) compound and a Fe(III) peroxo complex are found in the hydroxide composition. Possible mechanisms are discussed for H₂O₂ decomposition involving no free radicals. It is shown that lower hydrocarbons are oxidized in the systems, and their presence changes both the kinetics of H₂O₂ decomposition and the behavior of Fe(IV) and the peroxo complex.     

Study of the Influence of a Paraxial Porous Insert on Combustion of a Swirling Flow of a Mixture of Methane and Air

Russian Physics Journal - A study has been carried out on the influence of a paraxial porous insert on physical processes arising during the combustion of a swirling flow of a mixture of methane...     

Substrate selectivity and mechanism of oxidation of alkanes by peroxynitrous acid in aqueous solution

The relative rate constants (k_rel) were measured for the oxidation of alkanes (RH) by peroxynitrous acid (HOONO) in aqueous solutions at 25 °C. The krel values for the reactions of RH with HOONO and with OH radicals in the series of C₂-C₇ alkanes and the isotopic effects (c-C₆H₁₂/c-C₆D₁₂) agree. However, the k_rel value for methane was lower than for its reaction with OH. Possible reaction mechanisms are discussed. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 295–299, September–October, 2006.