Diffusion Paths for Interstitial Impurities in Different Polymorphic Modifications of Niobium Silicide Nb<Subscript>5</Subscript>Si<Subscript>3</Subscript>

Structural models of the α, β, and γ modifications of Nb₅Si₃ silicides, which are used as a reinforcing phase in composites obtained in situ based on the Nb?Si system, have been constructed by computer simulation methods. A geometric analysis of unit cells is performed using the H-poisk program to estimate the voids existing in the structures. The results of measuring the number of voids and their sizes are reported. A conclusion about possible diffusion paths of interstitial boron, carbon, nitrogen and oxygen atoms is drawn based on the calculation results, and the solubility of these impurities in the structure of each Nb₅Si₃ modification is estimated.     

Substitution of barium for strontium in hydroxovanadate structure

A possibility of substitution of barium for strontium in Sr₁₀(VO₄)₆(OH)₂ is studied by X-ray powder diffraction and IR spectroscopy. According to X-ray powder diffraction data, single-phase solid solutions Sr_{10 ? x} Ba _x (VO₄)₆(OH)₂ are formed with x = 0–2.5 with an increase in the unit cell parameters.     

Oxidation of polyethylene inhibited with a phenolic antioxidant under the conditions of contact with metallic zinc

The inhibiting power of a phenolic antioxidant upon introduction into polyethylene contacting with metallic zinc was examined. Conditions at which zinc enhances the inhibiting effect of the antioxidant were determined, and the mechanism responsible for this effect was suggested.     

Possibilities of surface-sensitive X-ray methods for studying the molecular mechanisms of interaction of nanoparticles with model membranes

The processes of structural rearrangement in a model membrane, i.e., an arachic acid monolayer formed on a colloidal solution of cerium dioxide or magnetite, are studied in situ in real time by the methods of X-ray standing waves and 2D diffraction. It is shown that the character of the interaction of nanoparticles with the monolayer is determined by their nature and sizes and depends on the conditions of nanoparticle synthesis. In particular, the structure formation in the monolayer–particle system is greatly affected by the stabilizer (citric acid), which is introduced into the colloidal solution during synthesis.     

Stability of silver clusters in mordenites with different SiO2/Al2O3 molar ratio

The stability and decay of silver clusters characterized by absorption bands 320 and 285 nm incorporated in mordenites with different SiO₂/Al₂O₃ molar ratios were studied under ambient conditions. Significantly different rates of disappearance of these two bands were the basis for assigning them to different silver species. Oxidation converts the clusters peaking at 320 and 285 nm into other silver clusters characterized by absorption bands at 310 and 240 nm, respectively. The oxidation of silver clusters peaking at 285 nm is significantly faster than that at 320 nm. The stability of both original clusters decreases with acid site strength that, in its turn, depends on Si0₂/Al₂O₃ molar ratio. The minimum lifetime of clusters peaking at 320 and 285 nm equal to ca. 40 and 20 days, respectively, was observed for mordenite characterized by the strongest acid sites. For mordenites possessing weaker acid sites, the lifetime of these clusters is found to be more than 50 months. The oxidation of silver clusters is reversible, and re-reduced silver clusters were revealed to possess the same electron structure as original ones.     

Direct central impact of different elastic bodies of rotation

A direct central collision of two bodies of revolution is studied. A nonstationary mixed boundary-value problem with an unknown moving boundary is formulated. Its solution is represented by a series in term of Bessel functions. An infinite system of Volterra equations of the second kind for the unknown expansion coefficients is derived by satisfying the boundary conditions. The basic characteristics of the collision process are determined depending on the physic-mechanical properties of the bodies. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the dynamics of the interaction of metal particles with a Langmuir single layer upon an increase in the surface pressure

X-ray studies of dipalmitoylphosphatidylcholine (DPPC) single layers on the surface of a liquid provide detailed information on the interaction of metal particles with a single layer upon an increase in the surface pressure up to the collapse. Two complementary X-ray methods are used: grazing incidence diffraction and the X-ray standing waves method. The experimental results obtained for a single layer formed on a colloidal solution of magnetite nanoparticles reveal that the increase in the surface pressure is accompanied by an increase in the concentration of nanoparticles near the surface. In a series of experiments where metal particles of submicron size are sputtered onto a DPPC single layer, a sharp decrease in the intensity of the fluorescence yield from metal atoms is observed while the single layer is compressed. These data suggest that metal particles deposited onto the surface of a single layer were extruded into the aqueous subphase.     

A representative of p,p,p-trihalogenylides: synthesis and structure

The representative of P,P,P-trichloroylides-5-methyl-2-phenyl-4-(trichlorophosphoranylidene)-2,4-dihydro-3H-pyrazol-3-one-was synthesized. Its constitution was confirmed by 1H, 13C, and 31P NMR spectroscopy and by X-ray analysis. Some chemical properties were studied and compared with ones of P,P,P-trimethylylide-5-methyl-2-phenyl-4-(trimethylphosphoranylidene)-2,4-dihydro-3H-pyrazol-3-one. DFT calculations of the model molecules were carried out.     

Diamondlike nanocomposite a-C:H:Cr Coatings: Structure,mechanical, and tribological properties

The results from a comprehensive investigation of the structure, phase and chemical composition, microhardness, and nanomechanical and tribological properties of chromium-doped coatings of hydrogenised amorphous carbon a-C:H:Cr are presented. The coatings are deposited via reactive magnetron sputtering in an Ar + C₂H₂ + N₂ gas mixture at various volume concentrations of nitrogen and acetylene. It is found that the carbon in the coatings is formed as disordered mixtures of domains with tetrahedral (sp ³) and hexagonal (sp ²) carbon coordinations. In addition, the doping metal in the coating consists of nanosized inclusions of metallic chromium and its carbide and nitride phases. Additional nitrogen doping resulting in the formation of chromium nitride is shown to improve the micromechanical and tribological properties of the obtained coatings.