A Silver-Based Electrocontact Material Dispersion-Strengthened with Zinc,Tin, and Titanium Oxides

Technical Physics - A new silver-based electrocontact material dispersion-strengthened with nanopowders of zinc, tin, and titanium oxides has been obtained. The microstructure and elemental...     

Study of Diffusion Bonding of 45 Steel through the Compacted Nickel Powder Layer

The microstructure of the transition zone and powder spacer, the concentration distribution of chemical elements over the width of the diffusion-bonded joint, and microhardness of 45 steel–compacted Ni powder spacer–45 steel layered composites formed by diffusion bonding have been investigated. It has been shown that the relative spacer thickness χ < 0.06 is optimal for obtaining a high-quality joint has been formed under a compacting pressure of 500 MPa. The solid-state diffusion bonding is accompanied by sintering the nickel powder spacer and the formation of the transition zone between the spacer and steel. The transition zone consists of solid solution of nickel in the α-Fe phase and ordered solid solution of iron in nickel (FeNi₃).     

Determination of diagnostically important free and conjugated bile acids in blood plasma by high-performance liquid chromatography

A procedure was proposed for the determination of free bile acids and their conjugates in blood plasma by the reversed-phase HPLC using the column Lichrospher 100 RP-18 (250 + 4.6 mm) with gradient elution and UV-detection at 206 nm. The procedure allowed the simultaneous determination of diagnostically important cholic acids, tauro-and glyco-cholates in blood plasma of patients with no preliminary separation of the analytes into subtypes. The bile acids and their conjugates were isolated from the sample matrix by solid phase extraction in a Sep-Pack C18 cartridge. The limits of detection were 0.11–0.15 mM for free acids and 0.015–0.025 mM for conjugates.     

Properties of Epoxy Systems with Clay Nanocomposites

Different types of montmorillonite clays are often used for the modification of thermoplastic polymers. In the case of epoxy systems, the presence of the clays can complicate the cure process. Therefore, the influence of montmorillonite concentration and the temperature regime on the cure rate and mechanical properties of the composite material obtained is investigated in this paper.     

Rhodium(I)-NHC Complexes Bearing Bidentate Bis-Heteroatomic Acidato Ligands as gem-Selective Catalysts for Alkyne Dimerization

A series of Rh(κ²-BHetA)(η²-coe)(IPr) complexes bearing 1,3-bis-hetereoatomic acidato ligands (BHetA) including carboxylato (O,O), thioacetato (O,S), amidato (O,N), thioamidato (N,S), and amidinato (N,N), have been prepared by reaction of the dinuclear precursor [Rh(μ-Cl)(IPr)(η²-coe)]₂ with the corresponding anionic BHetA species. The Rh^I-NHC-BHetA compounds catalyze the dimerization of aryl alkynes, showing excellent selectivity for the head-to-tail enynes. Among them, the acetanilidato-based catalyst has shown an outstanding catalytic performance reaching unprecedented TOF levels of 2500 h⁻¹ with complete selectivity for the gem-isomer. Investigation of the reaction mechanism supports a non-oxidative pathway in which the BHetA ligand behaves as proton shuttle through intermediate κ¹-HBHetA species. However, in the presence of pyridine as additive, the identification of the common Rh^IIIH(C≡CPh)₂(IPr)(py)₂ intermediate gives support for an alternative oxidative route.     

Microstructure and properties of a copper electrocontact material with a nanodispersed titanium dioxide additive

The influence of TiO₂ nanopowder additive on the microstructure, physicomechanical properties, and performance characteristics of a copper-based composite is studied. The properties of the composites are compared with those of pure copper compacts. The microstructure and state of the composite’s working surface after performance tests are examined. It is shown that, when the amount of TiO₂ grows, the hardness of the material rises and the arc quenching effect is enhanced.     

Determination of glyphosate and its biodegradation products by chromatographic methods

Conditions were selected for the separation of the herbicide glyphosate (N-(phosphonomethyl)glycine) and products of its microbiological utilization as N-acylated derivatives by ion-exchange liquid chromatography. The order of the elution of compounds on a Repro-Gel H column with UV detection correlates with their structures. The detection limits of the derivatives (wavelength 210 nm) are as follows (ng): glyphosate, 30; glycine and sarcosine, 20 and 43, respectively; aminomethylphosphonic acid, 45. The detection limit of methylphosphonic acid is 14 μg. Glyphosate and its biodegradation products were separated by thin-layer chromatography on plates with silica gel in the system isopropanol-5% aqueous ammonia solution (1: 1).     

Size effects in electronic and breakdown processes during barrier electric discharge in disperse systems

The differences in the breakdown characteristics of barrier electric discharge (BED) in air and disperse systems (air + ZrO₂) at 77 and 300 K are determined by polarization, plasma-forming medium charge deposition on the ZrO₂ surface, and surface effects on the duration and mechanism of electron avalanches changing with the sizes of air voids between oxide surfaces (E/P ∼ const, T ∼ const). Original Russian Text ? M.M. Aliev, E.A. Zelenkova, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 978–984.     

Chromatographic determination of morpholine and products of its microbiological degradation

A combination of thin-layer chromatography (TLC) with high-performance liquid chromatography (HPLC) was shown to be efficient in determining the intermediate products of the utilization of thiomorpholine with ligninolytic basidiomycete fungus Bjerkandera adusta VKM F-3477. The chromatographic mobility of the products of microbiological degradation of thiomorpholine was studied on Sorbfil PTSKh-P-V plates in the systems of chloroform-methanol-25% aqueous ammonia (80: 20: 2) for determining cyclic amines and isopropanol-25% aqueous ammonia (70: 30) for determining thio acids. The optimum conditions were selected for the separation of thiomorpholine and the formed metabolites by ion-exchange chromatography and reversed-phase chromatography.