Acid-base properties of single-phase aluminum oxides

It was found that the surface of single-phase aluminum oxides contains terminal, bridging, and hydrogen-bonded hydroxyl groups, which differ in both concentration and position of related absorption bands. A transition from -Al₂O₃ to -Al₂O₃ does not change the number of absorption bands, but the intensities of these bands decrease. The total concentration of Lewis acid sites in single-phase oxides increases from 2.5 to 5.34 µmol/m² for -Al₂O₃ and -Al₂O₃, respectively. As distinct from other species, -Al₂O₃ contains strong Lewis acid sites ((CO) = 2238 cm^–1). The total concentration of basic sites in aluminum oxides prepared by boehmite dehydration at 600, 800, and 1000°C decreases from 4.86 to 3.72 µmol/m².Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 141–146. Original Russian Text Copyright © 2005 by Kulko, Ivanova, Budneva, Paukshtis.     

Effect of pulsed plasma and high-current electron beam treatments on the structure and properties of nickel-based coatings

Using plasma-detonation technology (PDT), nickel-based powder (PGAN-33, PG-10N-01 and PG-19N-01) coatings 80–300 μm thick were deposited on a low-carbon St-3 steel substrate. Coatings were then subjected to additional treatment either by a high-current electron beam (HCEB) or by a high-velocity pulsed plasma jet until melting. The structure was analyzed using x-ray diffraction and conversion Mössbauer spectroscopy in the transmission and scattering modes. The morphology and elemental composition were studied using scanning electron microscopy and microanalysis. The micro-and nanohardness, volumetric wear, and corrosion resistance of the grown coatings were measured. It was found that, as the HCEB and PDT energy density increase, the phase composition changes, phase redistribution occurs, and new phases are formed. The last process is caused by mass transfer from the erosion plasmatron electrode and from a gas plasma jet, and interdiffusion of coating and substrate elements. After the exposure to concentrated energy fluxes, the coating surface roughness decreased. It is shown that physicochemical and mechanical characteristics of modified coatings improve in the case of optimum treatment conditions.     

Thermal expansion of niobium diselenide in the basal plane at low temperatures

The thermal expansion of a high-quality 2H-NbSe₂ single crystal is precisely measured in the basal plane and the temperature range 5.7–50 K. An anomaly of the thermal expansion in the basal plane is detected, and it is found to be caused by a superconducting transition. The change in thermal expansion coefficient α _ab is used to calculate the pressure derivative of the critical temperature (dT _c /dp _ab ) = (19.0 ± 2.0) × 10^?9 K/Pa, and this derivative agrees well with the reported data. An additional anomaly, which indicates a phase transition, is also detected in the pretransition range. The nature of the detected phase transition is discussed.     

Influence of silver on the galvanomagnetic properties and energy spectrum of mixed (Bi1− x Sbx)2Te3 crystals

An investigation is made of the temperature dependences of the resistivity in the range 4.2–300 K, the Hall effect, and the Shubnikov-de Haas effect in magnetic fields up to 40 T in (Bi_{1? x} Sb_x)₂Te₃Ag_y single crystals (0 ≤ x ≤ 0.75). Doping (Bi_{1? x} Sb_x)₂Te₃ crystals with silver showed that in Sb₂Te₃ and (Bi_{1? x} Sb_x)₂Te₃ crystals unlike Bi₂Te₃ silver exhibits acceptor properties. The angular and concentration dependences of the Shubnikov-de Haas effect were studied in (Bi_{1? x} Sb_x)₂Te₃Ag_y. It was established that the anisotropy of the ellipsoids of the upper valence band in Bi_0.5Sb_1.5Te₃ remains unchanged as a result of silver doping.     

Non-Stationary Photovoltage in Materials Science of Wide Band-Gap Semiconductors of Modern Adaptive Optics and Optoelectronics

Bulletin of the Lebedev Physics Institute - Non-stationary photovoltage excitation in silicon carbide and gallium oxide crystals is studied. The signal transient responses are measured, and the...     

Electrolyzed-reduced water protects against oxidative damage to DNA, RNA, and protein

The generation of reactive oxygen species is thought to cause extensive oxidative damage to various biomolecules such as DNA, RNA, and protein. In this study, the preventive, suppressive, and protective effects of in vitro supplementation with electrolyzed-reduced water on H₂O₂-induced DNA damage in human lymphocytes were examined using a comet assay. Pretreatment, cotreatment, and posttreatment with electrolyzed-reduced water enhanced human lymphocyte resistance to the DNA strand breaks induced by H₂O₂ in vitro. Moreover, electrolyzed-reduced water was much more effective than diethylpyrocarbonate-treated water in preventing total RNA degradation at 4 and 25°C. In addition, electrolyzed-reduced water completely prevented the oxidative cleavage of horseradish peroxidase, as determined using sodium dodecyl sulfate-polyacrylamide gels. Enhancement of the antioxidant activity of ascorbic acid dissolved in electrolyzed-reduced water was about threefold that of ascorbic acid dissolved in nonelectrolyzed deionized water, as measured by a xanthine-xanthine oxidase superoxide scavenging assay system, suggesting an inhibitory effect of electrolyzed-reduced water on the oxidation of ascorbic acid.     

Thermal conductivity and expansion of PbF2 single crystals

In order to check a phenomenon of the negative correlation between ionic and thermal conductivities of solid substances, we studied the thermal conductivity and expansion of cubic PbF₂ single crystals at 50–300 and 5.6–317 K, respectively. We found that lead difluoride had a thermal expansion coefficient α that was equal to (28.5 ± 0.3)10⁻⁶ K⁻¹ at 300 K, and a thermal conductivity coefficient k(T) was equal to 1.40 ± 0.07 W/(m K) at the same temperature. Thus, the thermal conductivity for PbF₂ is the lowest among fluorite-type MF₂ (M = Ca, Sr, Ba, Cd, Pb) thermal conductivities, whereas its fluoride-ion conductivity is the highest one among MF₂ (M = Ca, Sr, Ba, Cd, Pb) ionic conductors.

     

Structural phase transitions in CdTiO3

The reconstructive phase transition from the ilmenite-like CdTiO₃ modification to the perovskite modification is investigated thoroughly. It is revealed that the reconstructive transition is determined by size effects, results in the formation of the closest packing of the ilmenite CdTiO₃ structure, and is irreversible with a decrease in temperature. The perovskite CdTiO₃ modification undergoes displacive structural phase transitions at temperatures of 110, 220, and 380°C. The first displacive phase transition is isostructural, whereas the second and third transitions are associated with rotations of oxygen octahedra.     

Design optimization and forming methods for toroidal composite shells

Based on the example of a toroidal membrane, a model for calculating the winding trajectory and the shape of a shell billet and its transformation into given surface elements, as well as for calculating the shape of the membrane under an internal pressure loading, is developed. The problem of choosing optimum design variables and manufacturing parameters of the membrane is also investigated. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 147–164, March–April, 2006.