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.     

Experimental investigation and thermodynamic simulation of the uranium oxide–zirconium oxide–iron oxide system in air

The behavior of melts and the phase composition of crystallization products of six compositions in the uranium oxide-zirconium oxide-iron oxide system in air have been investigated. It has been revealed that crystallized samples containing 20–50 wt % uranium oxide and 25–80 wt % iron oxide (the rest is zirconium oxide) consist of five crystalline phases and involve two types of eutectic structures. The possible factors responsible for this phenomenon have been considered.     

Nanomodification of SnO<Subscript>2</Subscript> films by doping with additives of copper and gold chlorides

The hydropyrolytic method was used to prepare samples of tin dioxide films without the doping additive, and also tin dioxide films with additives containing copper oxides and copper with gold. It was shown that by using doping additives it is possible to effectively control the ratio of the area of the film surface to its volume and, consequently, the adsorption ability of the sensor material.     

Encapsulation of urease in double‐layered hydrogels of macroporous poly(2‐hydroxyethyl methacrylate) core and poly(ethylene oxide) outer layer: fabrication and biosensing properties

Double‐layered hydrogels of super‐macroporous poly(2‐hydroxyethyl methacrylate) (PHEMA) cryogel core and poly(ethylene oxide) (PEO) hydrogel outer layer for encapsulation of the enzyme urease were constructed. The enzyme was entrapped into the pores of PHEMA cryogel by soaking and then the core was covered with a PEO layer. The leaking of urease from the core was prevented when the density of the PEO network was increased by incorporation of the crosslinking agent, poly(ethylene glycol) diacrylate. The hybrid system exhibited a nearly constant enzyme activity with time and maintained its structural integrity after several reactions of hydrolysis of urea. The potential of double‐layered hydrogels containing urease for establishment of water pollution with copper was investigated as well. Copyright © 2011 Society of Chemical Industry     

The influence of admixed micelles on the microstructural properties and global performance of cement-based materials

In this study, the influence of the admixed micelles (poly(ethylene oxide)-block-polystyrene micelles) on the microstructure and hydration rate of cement paste and more global performance of mortar were investigated. In cement paste, the cement hydration rate was only slightly influenced by the admixed micelles; on the other hand, the micelles lead to a reduced porosity and a denser matrix. The nano indentation combined with MIP and microstrutural analyses proves that the admixed micelles lead to a more uniform distribution of hydration products. In mortar, the compressive strength of the micelle-containing mortar was almost unaffected; the coefficient of water permeability was 3 orders of magnitude lower for the micelle-containing specimens, compared to the control (micelle-free) specimens. All experimental results indicate that the micelles act as nucleation sites for the formation of new hydration products and possibly induce defloculation of un-hydrated cement particles, resulting in a more uniform and homogeneous cement matrix.     

Silver–carbon electrocatalyst for air cathodes in alkaline fuel cells

A method for producing electrocatalysts containing silver supported on different carbons was developed. The catalysts were investigated in air (oxygen) diffusion electrodes in alkaline electrolyte (7 M KOH). Depending on the carbon support used, up to a threefold improvement in electrode performance was achieved compared with the activity of the uncatalysed carbon in this media. At ambient temperature and atmospheric pressure, a current density of 150 mA/cm^–2 was obtained at electrode potential 1.2 V vs zinc (0.75 vs HE). A correlation between electro catalytic activity and wetted surface area of the electrocatalysts was found.     

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.     

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.