Electrical-percolation effects in epoxy resin/ion-exchange resin/polyaniline anticorrosion composite materials

A new type of epoxy–polyelectrolyte anticorrosion protective material based on epoxy resin, ion-exchange resin, and polyaniline has been studied. Electrical-percolation transitions are observed after submerging stainless-steel plates coated with epoxy–polyelectrolyte compositions in a solution of NaCl. Conductivity data processed within a percolation model show that the modification of ion-exchange resin by polyaniline strongly influences the coating model parameters owing to changes in physicochemical and morphological properties of ion-exchange resin. It is established that the electrochemical response to the action of an aqueous salt solution can be controlled by variation of the material composition.     

Design and experience of HEU and LEU fuel for WWR-M reactors

Thin-walled WWR-M5 fuel elements were designed and manufactured and have been used successfully for 16 years; they contain twice as much uranium-235 as the WWR-M2 and WWR-M3 fuel elements. The fuel elements have been optimized with regard to their neutron physics and thermal-hydraulic parameters and fuel consumption has been minimized. The mean specific power in the core of the WWR-M reactor was raised to 230 kW l⁻¹, the measured maximum volume thermal specific power was 900±100 kW l⁻¹ and the surface specific power was 136±15 W cm⁻². The WWR-M5 fuel elements enable the power of the WWR-M pooltype reactor to be raised to 30 MW while simultaneously increasing the number of cells in the core available for experimentation by a factor of approximately two and reducing fuel element consumption. Reactor tests of WWR-M fuel elements with reduced fuel enrichment (36 and 21%) were carried out for a meat uranium density up to 2–3 g cm⁻³. Conversion of WWR-SM-type reactors to these fuel elements did not lead to a loss in reactivity and enabled their power to be increased to 20–30 MW.     

Measuring the mechanical recoil impulse of a polymeric target upon impact of a high power electron beam

A method for measuring the mechanical recoil impulse of a target produced by the relativistic electron beam of the Calamary accelerator is described. A detector based on a piezoelectric sensor is used in measurements. Results of measurements are presented for the mechanical recoil impulse produced by the relativistic electron beam with an energy as high as 300 keV, a current of up to 30 kA, and a duration of ~100 ns that is incident on an epoxy target. The energy flux density on the target surface is varied in the range of 1–10 GW/cm². The maximum measured impulse value is 0.32 N · s at an energy flux density of 10 GW/cm² (an energy fluence of 810 J/cm2).     

Magnetic properties of a low-density Bi-based HTSC

The preliminary results of the investigation of magnetic properties of a novel low-density superconducting material Bi_1.8Pb_0.3Sr₂Ca₂Cu₃O_x with a low density and microfoam structure are presented. The temperature, magnetic field, and time dependences of magnetization M have been measured. The experimental hysteresis loops M(H) are well described in the framework of the Val’kov-Khrustalev theory developed for type II granular superconductors.     

Effect of the method of preparation of a Nd2O3-MgO catalyst on its efficiency in the reaction of oxidative coupling of methane

It is shown that the decomposition of a mixture of nitrates or coprecipitated carbonates or hydroxides of Mg and Nd form catalysts manifesting similar catalytic properties, while the catalyst obtained by impregnation is more active but much less selective. The mechanism of formation of the catalytically active phase and the nature of the active sites are discussed.     

Electrodeposition, composition and structure of Zn—Cr alloys

The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg₂SO₄, which is reached at current density of about 20 A dm^–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a 3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a 2.67 Å, c 4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)₂. After 50 min sputtering, Zn and a mixture of Cr, Cr₂O₃ and Cr₇C₃ were found. The presence of organic C and O, probably from inclusions of PEG, were also detected.     

Titanate Composites for Core Catcher Donor Material in a Nuclear Reactor

Composites based on titanates compositions have been selected and tested. A technology for their production is proposed using high-alumina cement. Estimate of some of their properties is supplied making it possible to use these composites as donor materials in a reactor core catcher.     

Polyamide‐6‐b‐polybutadiene block copolymers: Synthesis and properties

Polyamide‐6 (PA6)/polybutadiene (PB) block copolymers were synthesized with macroactivators (MAs) based on hydroxyl‐terminated polybutadiene functionalized with diisocyanates and having three N‐acyllactam chain‐growing centers per molecule. Two different diisocyanates, hexamethylene diisocyanate and isophorone diisocyanate, were applied as precursors for the MAs. The sodium salt of ε‐caprolactam was chosen as an initiator. The influence of the MA type and concentration on the anionic ring‐opening polymerization of ε‐caprolactam at 180°C was studied. A large percentage of the gel fraction in the copolymers was estimated, indicating crosslinked macromolecules. The structure and phase behavior of the copolymers were investigated with differential scanning calorimetry, wide‐angle X‐ray scattering, thermogravimetric analysis, and dynamic mechanical thermal analysis. In the copolymers, only the PA6 chains crystallized, and the crystallinity depended on the PB content. Different glass‐transition temperatures for the PB blocks and PA6 blocks were observed, indicating microphase separation in the copolymers. The mechanical properties of the copolymers were studied by notched impact testing and hardness measurements. The impact strength increased linearly with the soft component concentration up to 10 wt % and reached values six times higher than those of the PA6 homopolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 711–717, 2003     

Plasmonic bandgap in random media

We present a dispersion theory of the surface plasmon polaritons (SPP) in random metal-dielectric nanocomposite (MDN) consisting of bulk metal embedded with dielectric inclusions. We demonstrate that embedding of dielectric nanoparticles in metal results in the formation of the plasmonic bandgap due to strong coupling of the SPP at the metal-vacuum interface and surface plasmons localized at the surface of nanoinclusions. Our results show that MDN can replace metals in various plasmonic devices, which properties can be tuned in a wide spectral range. Being compatible with waveguides and other photonic structures, MDN offers high flexibility in the plasmonic system design.