Effect of Cr(III) passivation layer on surface modifications of zinc-nickel coatings in chloride solutions

Surface chemical and morphological modifications of as-plated and Cr(III)-passivated monophasic zinc-nickel coatings induced by corrosion in chloride solutions are demonstrated. The passivated samples showed slower anodic dissolution, less significant de-alloying, smaller surface dezincification and lower coating cracking, as demonstrated by Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDX) of the surface and inductively coupled plasma atomic emission spectroscopy solution analysis. Surface characterization by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and SEM-EDS indicated simonkolleite as the main corrosion product for both, as-plated and Cr(III)-passivated coatings. In contrast, only for as-plated coating, which experienced higher cracking, new Ni containing phases (metallic Ni and NiO) were evidenced. The phase transition via selective dissolution of zinc is supposed to increase the concentration of the structural defects and could explain cracking in the non-passivated Zn-Ni coating.

     

Preparation,chemical features,structure and applications of membrane materials based on graphene oxide

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Potential Bounds in Nonpotential Two-Point Boundary - Value Problems

New conditions are suggested for the existence of solutions of two-point boundary -value problems. The situation is studied when monotone bounds of nonlinear terms do not guarantee the solvability of the problems. The approach developed is a combination of variational methods, simple fixed point principles, and methods of partially ordered spaces.     

Polyhalogenoheterocyclic compounds: Part 51. [1] Macrocycles from 4-alkoxy-tetrafluoropyridine derivatives

4-Alkoxy-tetrafluoropyridine derivatives were used as building blocks for the synthesis of 14- and 16-membered macrocyclic ring systems comprising pyridine and either poly-ether or amine subunits; two of the macrocycles were characterised by X-ray crystallography.     

Combined biologic (anaerobic-aerobic) and chemical treatment of starch industry wastewater

A combined biologic and chemical treatment of high-strength (total chemical oxygen demand [CODtot] up to 20 g/L), strong nitrogenous (total N up to 1 g/L), and phosphoric (total P up to 0.4 g/L) starch industry wastewater was investigated at laboratory-scale level. As a principal step for COD elimination, upflow anaerobic sludge bed reactor performance was investigated at 30 degrees C. Under hydraulic retention times (HRTs) of about 1 d, when the organic loading rates were higher than 15 g of COD/(L.d), the CODtot removal varied between 77 and 93%, giving effluents with a COD/N ratio of 4-5:1, approaching the requirements of subsequent denitrification. The activated sludge reactor operating in aerobic-anoxic regime (HRT of about 4 d, duration of aerobic and anoxic phases of 30 min each) was able to remove up to 90% of total nitrogen and up to 64% of COD tot from the anaerobic effluents under 17-20 degrees C. The coagulation experiments with Fe(III) showed that 1.4 mg of resting hardly biodegradable COD and 0.5 mg of phosphate (as P) could be removed from the aerobic effluents by each milligram of iron added.     

The Origin of115–130°C Thermoluminescence Bands in Chlorophyll-Containing Material

High-temperature thermoluminescence (TL) emitted in the temperature region from +50 to +150°C has been studied in a variety of chlorophyll-containing samples that were allowed to dry during the TL measurement. Analysis of the recorded traces by a multicomponent-fit-ting procedure revealed the existence of up to three bands of nonphotosynthetic origin with peak positions at62–75,114–128 and151–157°C and apparent activation energies of 27.0-28.8, 14.1-15.4 and 22.1-23.3 kcal/mol (the bands are denoted as HT₁ HT₂ and HT₃, respectively). Low-temperature treatment of leaves, incubation of algae in the presence of paraquat, exposure of algae or isolated thylakoids to a strong light, all conditions known to stimulate oxidative damage to membrane lipids, caused appearance of a small HT₁, band and significant rise in the intensity of the HT₂ band. The increase in the HT₂ component correlated positively with accumulation of conjugated dienes and malondialdehyde in thylakoids illuminated with a strong light. Different quenchers of active oxygen species and scavengers of free radicals added to preilluminated thylakoids or thylakoid lipid extracts before the TL measurements, as well as injection of argon into the TL measuring chamber, caused no changes in the intensity of the HT₂ emission. The HT₂ band in the thylakoids increased strongly upon addition of linoleate peroxidized by hydroxyradicals generated in the Fenton reaction but remained unchanged if the linoleate was oxidized with the use of lipoxygenase. We suggest that the HT₂ band arises due to thermal decomposition of lipid cyclic peroxides present in the samples. In turn, the decomposition reaction leads to formation of carbonyls in triplet state with following migration of excitation energy toward chlorophyll. Contrary to the HT₁, and HT₂ bands, the HT₃ band of TL cannot be associated with the thermolysis of lipid peroxidation products already present in the samples before starting the TL gradient.     

A (pi-extended tetrathiafulvalene)-fluorene conjugate. Unusual electrochemistry and charge transfer properties: the first observation of a covalent D(2+)-sigma-A(.-) redox state(1)

The synthesis of novel electrochemically amphoteric TTFAQ-sigma-A compounds (TTFAQ = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene, sigma = saturated spacer, A = polynitrofluorene acceptor) is reported. Their solution redox behavior is characterized by three single-electron reduction and one two-electron oxidation waves. Electrochemical quasireversibility of the TTFAQ(2+) state and a low E(ox) - E(red) gap ( approximately 0.25 V) for 3-(9-dicyanomethylene-4,5,7-trinitrofluorene-2-sulfonyl)-propionic acid 2-[10-(4,5-dimethyl-[1,3]dithiol-2-ylidene)-9,10-dihydroanthracen-9-ylidene]-5-methyl-[1,3]dithiol-4-ylmethyl ester (10) has enabled the electrochemical generation of the hitherto unknown transient D(2+)-sigma-A(.-) state as observed in cyclic voltammetry and time-resolved spectroelectrochemistry. The ground state of compound 10 was shown to be ionic in the solid but is essentially neutral in solution (according to electron paramagnetic resonance). The X-ray structure of an intermolecular 1:2 complex between 2-[2,7-bis(2-hydroxyethoxy)-9,10-bis(4,5-dimethyl-[1,3]dithiol-2-ylidene)-9,10-dihydroanthracene and 2,5,7-trinitro-4-bromo-9-dicyanomethylenefluorene, 14.(17)(2), reveals, for the first time, full electron transfer in a fluorene charge-transfer complex.