Passivity and Corrosion of Cu–<Emphasis Type="BoldItalic">x</Emphasis>Zn (<Emphasis Type="BoldItalic">x</Emphasis> = 10–40 wt%) Alloys in Borate Buffer Containing Chloride Ions

The electrochemical behaviour of Cu–xZn alloys and of Cu and Zn metals was studied by cyclic voltammetry and chronopotentiometry in borate buffer, pH = 9.2, with and without the addition of chloride ions in the range from 0.01 m to 1 m. In general, the shape of voltammograms of four Cu–xZn alloys with 10 – 40 wt.% of zinc resembles that of copper more than that of zinc. With increasing zinc content several characteristics of zinc are observed. In borate buffer containing chloride anions, Cu–xZn alloys are susceptible to pitting corrosion. The breakdown potential, E_b, at which the current density in the passive region starts to increase abruptly, becomes more negative with increasing zinc content in the alloy. The general relationship E_b = a + b log c_NaCl held in all cases, with constants a and b, however, being dependent on the zinc content of the alloy and on the chloride concentration. The corrosion resistance of Cu–xZn alloys was less than that of copper metal but significantly greater than that of zinc.     

Effect of artificial weathering and temperature cycling on the performance of coating systems used for wooden windows

The effects of ultraviolet light irradiation and water spray and temperature cycling on the color stability of waterborne coating systems on spruce were investigated. The test samples were treated with three coating systems (white and brown pigmented acrylate waterborne coatings systems with different layering) from six producers. The artificial weathering was carried out based on standardized (504 h) and increased weathering parameters (504 h). Thirty cycles of temperature changes were performed. Discoloration suggesting the rate of degradation process and color stability was measured by a spectrophotometer in L*a*b* color space. The results showed greater color stability of white coating systems during both experiments. The producer of acrylate coatings with iodopropynyl butyl carbamate and permethrin as biocides and benzotriazole, silicon dioxide and methylsiloxane as additives was characterized by the best coatings performance. The most sensitive color parameter to describe the surface quality as a result of irradiation and water spray has proven to be a change of lightness. A tendency towards degradation with increasing lightness was observed during weathering. The effect of temperature itself on color change was minimal. Scanning electron microscopy and energy dispersive spectroscopy revealed microscopic changes of coatings caused by artificial weathering.     

The impact of natural and artificial weathering on the visual,colour and structural changes of seven tropical woods

This study investigates the effects of wood weathering on changes in its macroscopic and colour characteristics in connection with changes in its molecular and anatomical structure. Seven hardwoods suitable for outdoor architecture—bangkirai, cumaru, cumaru rosa, ipé, jatobá, kusia, and massaranduba—were exposed to the exterior out of ground contact for 1–36 months according to EN 927-3, and for 1–12 weeks in Xenotest with water spraying according to partly modified EN 927-6. With prolonged weathering, the following changes occurred in the top surfaces of all tropical woods: (1) visual—creation of longitudinal macro-cracks, (2) spectrophotometry and CIE-L ^? a ^? b ^? —darkening in exterior exposure mainly due to pollutants, except for ipé, and vice versa lightening in Xenotest, as well as greening and blueing in both modes of exposure, (3) FTIR—faster decrease of guaiacyl than syringyl lignin, absolute decrease of conjugated and unconjugated carbonyl groups in the newly formed lignin-polysaccharide-extractive substrate in the photo-oxidized and washed-out cell walls, and decrease of cellulose crystallinity, (4) SEM—damaging of cell-walls by micro-cracks, and their degradation by thinning. Connections between changes of the individual characteristics of weathered woods, for example, between the colour (ΔE*, etc.) and the molecular structure (carbonyls, etc.), were also determined.     

Direct measurement of the wetting behavior of individual carbon nanotubes by polymer melts: the key to carbon nanotube-polymer composites

Carbon nanotube wetting is the critical parameter for the development of nanocomposites yet, due to the lack of suitable methods of qualifying and, more importantly, quantifying nanoscale wetting and adhesion phenomena, it is often overlooked. Here, we discuss a qualitative approach that provides wetting/nonwetting information and present a microfluidics method to produce "nanodroplets" of polymers on individual carbon nanotubes which enable the direct quantification of contact angles.     

Selective digital filters with quadratic phase

A method for design of a new class of digital infinite impulse response filters realized as parallel connection of two all‐pass filters is presented in this paper. A new approach to approximation of quadratic phase of all‐pass filter at all frequencies is given. Chosen parallel structure offers opportunity for realization of filters with arbitrary shape phase. The presented algorithm is based on all‐pass filter phase approximation. Phases of both all‐pass filters approximate ideal quadratic phase in minimax sense at all frequencies. Such filters can be applied for chirp signal compression or expansion. Magnitude characteristic of described filters is very selective and elliptic‐like. Obtained filters are compared with elliptic filter and group delay corrector in cascade. For the same specifications, much better results are achieved by the proposed filters. Parallel connection of all‐pass filters introduces lower signal delay, and for a given maximal phase, approximation error demands less complex network. Examples to illustrate the proposed method are given. Copyright © 2016 John Wiley & Sons, Ltd.     

Microstructure and dislocation density evolutions in MgAlZn alloy processed by severe plastic deformation

Commercial MgAlZn alloy AZ31 was processed by hot extrusion and equal channel angular pressing (ECAP) known as EX-ECAP. Microstructure and defect structure evolution with strain due to ECAP were investigated by TEM, positron annihilation spectroscopy (PAS), and X-ray diffraction. Significant grain refinement was obtained by EX-ECAP. In the extruded condition relatively low density of dislocations was determined by PAS. Sharp increase of dislocation density occurred during the first two passes of ECAP, followed by the saturation and even a decline manifesting the dynamic recovery at higher strains. XRD line profile analysis confirmed the results of PAS with slightly higher values of dislocation densities in individual conditions. Detailed analysis of contrast factors allows to determine the type of dislocations and to draw conclusions about slip activation and its variations with strain. The influence of microstructure evolution on mechanical properties is discussed.     

The corrosion resistance of Nitinol alloy in simulated physiological solutions: Part 1: The effect of surface preparation

The corrosion behaviour of Nitinol alloy containing nearly equi-atomic composition of nickel and titanium and its constituent metals (nickel and titanium) was investigated in simulated Hanks physiological solution (pH value 7.5) and pH modified simulated Hanks physiological solution (pH values 4.5 and 6.5) and by electrochemical method of anodic potentiodynamic polarization at 37 °C. In this chloride-rich medium the corrosion stability of Nitinol is limited by the susceptibility to localized corrosion and is in that sense more similar to nickel than to titanium. The corrosion stability of Nitinol is strongly dependent on the surface preparation—grinding, polishing or chemical etching. Whereas a ground surface is not resistant to localized corrosion, polished and chemically etched surfaces are resistant to this type of corrosion attack. The reasons for this behaviour were investigated through metallurgical, topographical and chemical properties of the surface as a function of surface preparation. For that purpose, scanning electron microscopy combined with chemical analysis, confocal microscopy and X-ray photoelectron spectroscopy were used. The surface roughness decreased in the following order: chemically etched > ground > polished surface. Besides differences in topography, distinct differences in the chemical composition of the outermost surface are observed. Ground, rough surfaces comprised mainly titanium oxides and small amounts of nickel metal. Chemically etched and, especially, polished surfaces are composed of a mixture of titanium, nickel and titanium oxides, as studied by angle resolved X-ray photoelectron spectroscopy. These results emphasize the importance of detailed investigation of the metal surface since small differences in surface preparation may induce large differences in corrosion stability of material when exposed to corrosive environments.     

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Brewers' spent grain and thin stillage as raw materials in l‐(+)‐lactic acid fermentation

Brewer's spent grain (BSG) hydrolysates were used for l ‐(+)‐lactic acid (LA) fermentation by Lactobacillus rhamnosus ATCC 7469. In this study the effect of the addition of various amounts of thin stillage (TS) in BSG hydrolysate on LA fermentation parameters were evaluated. TS addition significantly increased utilization of glucose by up to 43.0%. In batch fermentation the highest LA concentration and volumetric productivity of 31.0 g/L, and 0.93 g/L/h, respectively, were obtained with the addition of 50% TS. L. rhamnosus cell viability also increased with the addition of 50% TS (by 2.4%). TS addition significantly increased free amino nitrogen concentration (by up to 209%) which is important for bacterial growth. A strong positive correlation between free amino nitrogen and LA concentration was noted. Compared with the results obtained in the batch fermentation (50% TS), significantly higher LA concentration, yield and volumetric productivity (54.8, 1.9 and 4.0%, respectively) were achieved in fed‐batch fermentation with glucose and TS addition. The results suggest that the combination of the by‐products of brewing and bioethanol industries could be suitable for LA production. Copyright © 2017 The Institute of Brewing & Distilling     

Lipid peroxidative damage on Cisplatin exposure and alterations in antioxidant defense system in rat kidneys: a possible protective effect of selenium

Cisplatin (Cis-diamminedichloroplatinum II, CP) is an important chemotherapeutic agent, useful in the treatment of several cancers, but with several side effects such as nephrotoxicity. The present study investigated the possible protective effect of selenium (Se) against CP-induced oxidative stress in the rat kidneys. Male Wistar albino rats were injected with a single dose of cisplatin (7 mg CP/kg b.m., i.p.) and selenium (6 mg Se/kg b.m, as Na(2)SeO(3), i.p.), alone or in combination. The obtained results showed that CP increased lipid peroxidation (LPO) and decreased reduced glutathione (GSH) concentrations, suggesting the CP-induced oxidative stress, while Se treatment reversed this change to control values. Acute intoxication of rats with CP was followed by statistically significant decreased activity of antioxidant defense enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and glutathione-S-transferase (GST). Treatment with Se reversed CP-induced alterations of antioxidant defense enzyme activities and significantly prevented the CP-induced kidney damage.