In-vessel corium catcher of a nuclear reactor

A new concept of an in-vessel corium melt catcher is proposed. The lower part of an elongated reactor vessel, which is filled with a sacrificial material of a proper composition, porosity, and arrangement, is used as such a catcher. The concept accounts of the scientific and design experience with the development of the ex-vessel corium catcher for the Tyan’van NPP with VVER-1000 reactors.     

Effect of Oxide Content on the Tribological and Physicomechanical Properties of Filled Polytetrafluoroethylene

The effect of the nature and the amount of oxide fillers on antifriction properties of polytetrafluoroethylene under dry friction conditions with different loads and slow sliding rates is studied. It is established that oxides with a high hardness increase the friction coefficient and reduce the wear resistance of filled polytetrafluoroethylene, but oxides with a low hardness do not give rise to an increase in friction coefficient for polytetrafluoroethylene with a marked increase in its wear resistance, and this is connected with formation of a separating layer at the surface of the friction pair.     

Capillary Transport of Low-Viscosity Liquids in Porous Metallic Materials under the Action of Gravitational Force

Proceeding from model considerations about the microstructure of a porous body and the quantitative characteristics that govern it in structural regularity criteria analytical solutions are suggested for describing capillary transport of a wetting liquid, including movement of it against gravitational force considering the possibility of partial draining of pore channels. Results of experimental studies of the rate of capillary impregnation and the rise of distilled water, ethanol, and acetone in highly porous specimens prepared from powders of copper, bronze, chromium-nickel steels, titanium and its alloys, discrete fibers of copper and titanium of different diameter, and also grids of different interweaving, are analyzed. Extensive possibilities are demonstrated for controlling capillary effects in porous structures of different construction using technological methods.     

Electromodulated reflectance study of self-assembled Ge/Si quantum dots

We perform an electroreflectance spectroscopy of Ge/Si self-assembled quantum dots in the near-infrared and in the mid-infrared spectral range. Up to three optical transitions are observed. The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band. The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and Δ(4) valleys of the Ge conduction band, and the localized hole states at the Γ point.     

Catalytic Conversion of Bioethanol to Ethylene

Dehydration of bioethanol to ethylene has been investigated on supported cerium-containing catalysts and with additives of lanthanum. It was established that the modification of the 3% Ce/γ-Al2O3 catalyst by lanthanum increases catalyst dispersion, thereby increasing yield of the main product ethylene. The highest yield of ethylene is observed on the CeLa/γ/-A12O3 catalyst under optimal conditions （space velocity： 6,000 hl, bioethanol concentration： 21.7 g/m3 and T = 400℃）.     

Basic sites on the surface of oxide catalysts responsible for oxidative methane coupling

The basic sites of various oxide catalysts for the oxidative dimerisation of methane were studied by FTIR spectroscopy of adsorbed molecular probes (chloroform and CO₂). The methods used are compared and the advantage of CO₂ as probe for specifying the basic sites is demonstrated. The strengths of the basic sites were seen to correlate with the spectral parameters of the surface carbonates. Differences in spectral responses of carbonates are attributed to the different states of oxygen participating in their formation. The concentration of the strongest sites was estimated. A study of the catalytic activity of this system indicates that the system's activity in oxidative methane coupling depends on the presence and concentration of strong basic sites on the catalyst surface.     

Hard Alloy WC – 24% Ni Obtained in the Solid Phase from Ultrafine WC, NiO, and C Powders. Part 1. Density and Structure of Specimens

We have studied the density and structure of specimens of the alloy WC – 24 mass% Ni, obtained by combining into one step the processes of synthesis of the metallic phase and compaction of the ultrafine mixture of WC – Ni powders by high-energy pressing and sintering. We have established that reduction of nickel monoxide by carbon occurs at temperatures of 650-750°C and does not affect the shrinkage process which in the case of sintering begins only at a temperature of 1050°C. High-energy pressing of briquettes sintered at the indicated temperature reduces their porosity from 30-25% down to 8-4%. Specimens of porosity <1% can be obtained by pressing at 1150°C or 1050°C in the case of triple pressing. Raising the temperature at which the briquettes are heated is accompanied by enlargement of the pores together with a decrease in the total porosity, but at temperatures of 1300°C (sintering) and 1250°C (pressing), the pore dimensions are sharply reduced. The high density of the specimens pressed at low temperature does not provide low electrical resistance, which suggests the presence of weakly connected boundaries. When the specimens are sintered and pressed in the solid phase, we observe the growth of tungsten carbide particles. It is most rapid at 1150-1250°C, while at 1050°C the particle growth process slows down. Reduction of the metal oxide when the powders are heated promotes formation of structure in the higher temperature range.     

Synthesis and properties of magnetite nanoparticles with peroxide-containing polymer shell and nanocomposites based on them

Magnetite nanoparticles (Fe₃O₄ NPs) with peroxide-containing polymer shell have been synthesized using the method of coprecipitation from the mixture solutions of Fe (II) and Fe (III) salts in the presence of peroxide-containing copolymer (PCC). Polymer shell presence has been proved by elemental and complex thermal analysis. Synthesized Fe₃O₄ NPs possess superparamagnetic properties. Their specific saturation magnetization decreases gradually from 65 to 54 A·m²·kg⁻¹ with increasing PCC concentration owing to the surface spin pinning effect caused by a polymer shell. The average sizes of Fe₃O₄ NPs estimated from the data of XRD analysis and magnetic measurements are in the range of 9–12 nm. The NP sizes determined by the DLS method lie in the range of 150–270 nm; this result is significantly larger than the sizes estimated by the two aforementioned methods evidencing a tendency for Fe₃O₄ NPs toward self-association. Cross-linked composite films based on polyvinyl alcohol have been obtained via radical curing initiated by the PCC shell of nanoparticles. The resulting composite films are magnetically sensitive films with rather high physico-mechanical properties (tensile strength reaches 48–67 MPa and relative elongation – 4%–21% depending on cross-linking degree), a priori non-toxic and biocompatible, which makes them promising materials for various applications.