Morphological features of porous silicon carbide obtained via a carbothermal method

Samples of porous silicon carbide were obtained using sucrose or carbon and aerosil or silica mesoporous molecular sieves (SBA‐3, SBA‐15, KIT‐6 and MCF). Fibers content in silicon carbide samples is higher when the mesopore surface area of carbon materials derived from carbon‐silica composites is lower. Based on the found correlation between the morphology and porosity of SiC and mesopore surface area of the carbon component in the composites, a templating action of carbon in carbothermal reduction was suggested.     

Furfural Oxidation with Hydrogen Peroxide Over ZSM-5 Based Micro-Mesoporous Aluminosilicates

Micro-mesoporous aluminosilicates based on ZSM-5 zeolite, obtained by a dual template method, as well as in the presence of a dual-functional template (i.e. a Gemini-type surfactant), were tested in the oxidation of furfural with hydrogen peroxide. Even substantial changes in acidity and porosity of the catalysts result in minor variations of selectivity towards the desired products. Application of the synthesized zeolite-based materials in the oxidation of furfural with hydrogen peroxide leads to formation of 2(5H)-furanone (yield up to 28.5%) and succinic acid (up to 19.5%) as the main C4 reaction products. The kinetic model developed previously to treat the results for oxidation of furfural over sulfated zirconia was able to describe the data also for micro-mesoporous aluminosilicates.

Graphical Abstract

     

High-strain-rate superplasticity of nanocrystalline aluminum alloy 1570

The structure and mechanical properties of nanocrystalline aluminum alloy 1570 obtained by means of severe plastic deformation have been studied. Being tested in a temperature range from 300 to 400°C, the alloy exhibits high-strain-rate superplasticity. At 400°C, the superplasticity is manifested in a very broad range of strain rates, extending from 5 × 10^?3 to 1 s^?1.     

Ultrapurification of archaeological lead

Based on purification efficiency calculations for lead distillation, we developed a combined process for the ultrapurification of archaeological lead. We obtained pilot amounts of high-purity archaeological lead and PbO with the following contents of detrimental impurities: U, <2 ppb; Th, <1 ppb; Ni, Cu, Fe, Si, Ti, Mg, Al, Mn, Cr, V, Co, < 0.1 ppm; K, Ca, Zn, Cd, Ag, Sb, < 1 ppm. Lead of such purity can be used in low-background experiments as a protective shield material and in the growth of low-background PbWO₄ and PbMoO₄ scintillator crystals. From an isotope ratio, we were able to identify the origin of the archaeological lead.     

Asymmetric 1,2-diacylhydrazines as reagents for ionic flotation

The physicochemical properties (solubility, acidic-basic equilibria, stability to hydrolysis and oxidation, and kinetics of foam formation) of asymmetric 1,2-diacylhydrazines with the general formula C₆H₅C(O)NHNHC(O)R¹ (where R¹ = CH₃, C₂H₅, and C₃H₇) and CH₃C(O)NHNHC(O)R² (where R² = C₇H₁₅, C₉H₁₉, and C₁₀H₂₁), which are necessary to their evaluation as potential reagents, are investigated. By the example of 1-acetyl-2-octanoylhydrazine, it is shown that the reagents can be used for the removal of ions of Cu(II), Co(II), Ni(II), and Zn(II) ammonia solutions with low metal contents by the ion flotation method. The maximum degree of recovery at pH 9.8 was Cu(II) 88.0, Co(II) 98.0, Ni(II) 99.5, and Zn(II) 95.0. The residual concentration of metal ions corresponds to the regulations for the maximum permissible concentrations of tap water.     

A Gyrostabilizer Drift Model: Autonomous Identification by the Inverse Sensitivity Method

The concept of the inverse sensitivity problem is used to design a method for autonomous (on-board) identification of the drift velocity of a gyrostabilizer when there is no possibility for laboratory experimentation. Results obtained by this method on identification of the drift of a three-degree gyrostabilizer are given.__________Translated from Avtomatika i Telemekhanika, No. 5, 2005, pp. 146–155.Original Russian Text Copyright © 2005 by I. Shcherban, O. Shcherban.     

Template synthesis,structure, sorption properties and acidity of micro-mesoporous materials obtained from sol-precursor of zeolite BEA

Partially zeolitized micro-mesoporous materials (the total specific surface area S _BET  = 460–645 m²/g, mesopore volume V _meso  = 0.30–0.57 cm³/g, mesopore diameter D _meso  ≈ 5.6 nm, micropore volume V _micro  = 0.11–0.16 cm³/g, micropore diameter D _micro  ≈ 0.72 nm) and X-ray amorphous micro-mesoporous materials with uniform mesoporous structure (mesopore specific surface area S _meso  = 820–890 m²/g, total pore volume V _t  = 0.71–0.86 cm³/g, V _meso  = 0.53–0.67 cm³/g, D _meso  = 1.8–2.4 nm) were obtained by micellar templating of sol-precursor containing primary products of crystallization of zeolite BEA under conditions typical for forming of mesoporous molecular sieve MCM-41 (hydrothermal treatment at 100–130 °C for 3–5 days). It was found that the obtained X-ray amorphous micro-mesoporous materials contain secondary building units of zeolite BEA (five-membered rings of Si–O tetrahedra of BEA) and show acidic properties comparable to zeolite BEA.     

Photocatalytic activity of nanostructured composites based on layered niobates and C3N4 in the hydrogen evolution reaction from electron donor solutions under visible light

Nanostructured composites based on layered niobates KNb₃O₈, K₃Н₃Nb_10.8O₃₀ and HNb₃O₈ as well as C₃N₄ were obtained. It was established that the rate of hydrogen evolution from electron donors water solutions under visible light using composites niobate/C₃N₄ as photocatalysts significantly exceeds the rate value for an individual C₃N₄. This phenomenon was explained by an effective separation of photogenerated charges between the components of the composite and thus a decrease of the electron-hole recombination. Transition from an individual C₃N₄ to the composites niobate/C₃N₄ allows significantly extend the list of an effective electron donor compounds for the photocatalytic hydrogen evolution process.