Behavior In Acidic Solutions Research Articles

Influence of vacuum annealing on structures and properties of Al[sbnd]Ti[sbnd]Si[sbnd]N coatings with corrosion resistance

The corrosion behaviors in 10wt% H2SO4 solution of the AlTiSiN coatings, deposited on 316L stainless steel using multi-arc ion plating then vacuum annealed at 700°C, 800°C and 900°C for 2h, was investigated. The microstructures, compositions and surface morphologies of the coatings were characterized by utilizing X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS) and scanning electron microscope (SEM) analyses. The adhesion strength and corrosion behavior of coatings were measured by scratch test and electrochemical polarization curves, respectively. The results indicated that the as-deposited coatings were mainly comprised of solid solution (Ti,Al)N phase and amorphous Si3N4 phase. With increasing annealing temperature, the solid solution gradually decomposed into fcc-TiN and fcc-AlN phases and further into hcp-AlN phase. The defects on coating surface and adhesion strength of coatings were improved simultaneously. The electrochemical results revealed that all coated samples had better corrosion resistance than the substrate, and the coatings annealed at 800°C exhibited the best corrosion behavior in acid solutions. This was caused by the formation of amorphous Si3N4 phase and anti-corrosion hcp-AlN phase.

Chitosan as a Natural Polymer for Heterogeneous Catalysts Support: A Short Review on Its Applications

Chitosan, a bio-based polymer which has similar characteristics to those of cellulose, exhibits cationic behavior in acidic solutions and strong affinity for metals ions. Thus, it has received increased attention for the preparation of heterogeneous catalysts. Recent studies demonstrated that chitosan-based catalysts had high sorption capacities, chelating activities, stability and versatility, which could be potentially applied as green reactants in various scientific and engineering applications. This study intends to review the recent development of chitosan-based catalysts, particularly in the aspects of the main mechanisms for preparing the materials and their applications in environmental green chemistry. Studies on the preparation of catalyst nanoparticles/nanospheres supported on chitosan were also reviewed.

Studies on pigments of the myxomycete Physarum nudum. II. Separation and optical properties of the pigments from plasmodia cultured in darkness

The paper presents the data on Separation and some optical properties of the pigments obtained from the plasmodium of the myxomycete <i>Physarum nudum</i> grown in the dark. Pigment Separation was performed by means of thin-layer chromatography with celulose MN 300 as adsorbent and with the solvent: tert.-butylalcohol, H<sub>2</sub>O, 3N NH<sub>4</sub>OH at the ratio 5:2:1 In these conditions the chromatograms revealed 12 coloured bands from which pigments were eluted and their absorption spectra as well as the spectra of fluorescence emission were determined. The isolated pigments differ from one another by their physical properties (different Rf values, localization of absorption maxima, and behaviour in acid solution). Nevertheless, certain analogies perceptible between particular pigments per-mitted to distinguish 3 families of the studied pigments demonstrating similar properties.

Спектрофотометричне визначення аскорбінової кислоти з використанням бісмутовмісного 18-молібдодифосфату

Reactions of formation and reduction of bismuth substituted 18-molybdophosphate (18-MBPC) with ascorbic acid (Asc) have been investigated. 18-MBPC is reduced by Asc in the presence of Bi(III) ions at the ratio of Asc:18-MBPC 1:1 and 2:1 with formation of, respectively, two- and four-electron reduced heteropoly blues. Their spectra are similar to the spectra of metalsubstituted heteropoly blues with Keggin structure and have an absorption maximum at 690 nm. Selective, rapid and simple method was developed for the determination of Asc. Benefits of using the 18-MPBC as analytical reagent are high sensitivity and rate of reduction rate, including the behavior in acid solutions. The limit of detection was of 2.6·10 –6 mol/l ( l = 1 cm ), and e was of 1.15·10 4 mol –1 ·l·cm –1 .

Corrosion Protection of Mild Steel in Acid Solutions Using Red Cabbage Dye

Red cabbage dye (RCD) and its inhibitory effect on the corrosion of mild steel in 1 N HCl and 1 N H3PO4 was investigated by weight loss and electrochemical methods. RCD was a good inhibitor for mild steel corrosion in acid solutions, affecting anodic and cathodic reactions. The inhibition efficiency increased with RCD concentrations, with more pronounced effects observed in HCl. The effect of temperature on corrosion inhibition was studied and kinetic activation parameters were calculated and discussed. The inhibition mechanism of RCD on the mild steel surface was related to the dye make up and behavior in acid solutions.

LEACHING KINETICS OF COPPER FROM CHALCOPYRITE CONCENTRATE IN NITROUS-SULFURIC ACID

Treating chalcopyrite flotation concentrates by hydrometallurgical techniques seems to be the most convenient method for leaching copper due to concerns over air pollution and regulations regarding the emission of sulfur dioxide that result from smelting. In this study, the leaching recovery-time trajectories of bulk chalcopyrite concentrate obtained from a flotation plant in the Kastamonu region of Turkey are presented. The effects of various parameters were elucidated in the nitrous-sulfuric acid electrolyte (CNaNO2:0.05 M-0.15 M, CH2SO4:1 M) at a moderate temperature (80-120 °C). A high level of copper recovery (98%) from bulk chalcopyrite concentrate was obtained under a total pressure of 6 atm at 120°C within 2 h when using small amounts of nitrite species due to their autocatalytic behavior in acidic solutions. The kinetics were well correlated with the shrinking core model for the diffusion controlled mechanism with an apparent activation energy of 34.06 kJ·mol -1 . Elemental sulfur was the primary leaching product on the mineral surface, as confirmed using XRD and SEM/EDX. The semi-empirical equation explaining the reaction rate under the present conditions was expressed as follows:   t T e C X

Shape-controlled platinum nanocrystals on boron-doped diamond

Platinum nanocrystals with different shapes are generally produced by wet-chemical synthesis in colloidal solutions. In this study, we shaped electrochemically Pt nanocrystals on highly boron doped diamond electrodes without adding surfactants or additives. Their shapes were controlled by varying deposition potential during electrodeposition process, as confirmed with high resolution scanning electron microscope. Their crystallography of Pt nanocrystals was analyzed through hydrogen adsorption/desorption behavior in acidic solutions. Oxygen reduction reactions on these nanocrystals were investigated, indicating shape dependence. The discussion on shaping mechanism reveals that hydrogen evolution reaction is deemed to be responsible.

Dissolution of low-grade chalcopyrite concentrate in acidified nitrite electrolyte

Copper sulfides are generally treated by flotation followed by smelting. However, concerns over air pollution have made governments tighten their regulations regarding the emission of sulfur dioxide. Thus, hydrometallurgical techniques seem to be the most convenient methods to selectively extract non-ferrous metals. In this study, the leaching kinetics of copper from low-grade concentrate by nitrite salt was investigated. The probabilities of several chemical reactions and the products formed were explained based on literature data and thermodynamic analysis. The copper concentrate was obtained from a flotation plant in the Kastamonu region of Turkey. Leaching experiments were conducted in sulfuric acid electrolyte (0.5M–2.0M) containing nitrite compounds (0.025M–0.15M) at a moderate temperature (80–120°C). A high level of copper recovery (96%) from low-grade chalcopyrite concentrate was obtained under a total pressure of 6atm at 120°C within 2h when using small amounts of nitrite species due to their autocatalytic behavior in acidic solutions. Elemental sulfur was the primary leaching product on the mineral surface, as confirmed using XRD and SEM/EDX analysis, and the formation of the sulfur layer inhibited leaching rate at later stage of dissolution process.

Influence of Ozonation Processes on the Microbial Degradation of Surfactants

Abstract The influence of ozonation of aqueous solutions of non-ionic surfactants was investigated in this study. The research was conducted using solutions of amine oxide based surfactants. These surfactants constitute a particular class of non-ionic surfactants that exhibit cationic behaviour in acid solution, they show good foaming properties and are skin compatible. The ozonation process was carried out at 25°C in a stirred tank reactor for 30 min, where gaseous ozone was bubbled. The degree of mineralization achieved after the ozonation process was evaluated by measuring the total organic carbon before and after ozonation. The influence of ozonation on biodegradability of the solutions was studied using the biodegradation test by Pseudomonas putida . Biodegradation efficiency of the ozonated amine oxides based surfactants was also evaluated. It was found that the effectiveness of ozonation depended on the chemical structure of surfactant molecule. Ozonation only slightly improved biodegradation of these surfactants.

Pseudo-Capacitive and Electrocatalytic Properties of Electrochemically Modified Graphite Electrode in Different Solutions

A graphite electrode (GE) was electrochemically modified by recurrent galvanic pulses. The pseudo-capacitive behavior in acidic and neutral solutions and the electrocatalytic property in HCl and HNO3 solutions of the modified graphite electrode (MGE) were evaluated by cyclic voltammetry (CV). We found that the MGE exhibited a considerable pseudo-capacitance (the specific capacitance was high up to 1.730 F·cm - 2 ) in H2SO4 solution and excellent pseudo-capacitive behavior was obtained in HCl solution as well except for a narrow potential window. This was due to the excellent electrocatalytic activity of the MGE toward the chlorine evolution reaction (the onset potential of chlorine evolution was negatively shifted 238 mV). However, the MGE showed no pseudo-capacitive behavior in HNO3 solution but did show electrocatalytic activity toward the reduction of nitric acid. Compared with the pseudo-capacitive behavior in acidic solutions, the potential window of the MGE in neutral solution was substantially broadened and its energy density improved greatly eventually even though the corresponding peak current density decreased.

Electroreduction of Oximes: Substituent Effects and Behavior in Acidic Solutions

not Available.

The corrosion behavior of Fe–10Cr nanocrystalline coating

Fe–10Cr nanocrystalline (nc) coatings with a grain size of 20–30 nm were synthesized on glass substrates by magnetron sputtering. The corrosion behavior was investigated in 0.05 mol/L H 2SO 4 + 0.25 mol/L Na 2SO 4 and 0.05 mol/L H 2SO 4 + 0.5 mol/L NaCl solution by polarization curves, EIS and Mott–Schottky analysis. The results showed that compared to Fe–10Cr cast alloy, the active dissolution of the coating was accelerated; the passive film contained more Cr and therefore the coating was easier to passivate. The passive films formed on Fe–10Cr nc and cast alloy exhibited n-type semiconducting behavior in acidic solutions without Cl − and p-type semiconducting behavior in acidic solutions with Cl −. The lower breakdown potential for both materials in the solution with Cl − is related to the p-type passive film formed on them. For Fe–10Cr nc, lower donor density and increased Cr content were responsible for the chemical stability of the passive film.

Letter to the Glyco-Forum: The Karl Meyer Award for glycoconjugate research.

As time has passed, knowledge of the seminal contributions of Dr. Meyer to glycobiology and the burgeoning area of proteoglycan research have become less familiar to those in the field. In this issue, Glycobiology is pleased to reproduce a perspective on Dr. Meyer prepared by one of the first awardees, Dr. Vincent Hascall. How well I remember my confusion in 1991. I was presenting Dr. Ulf Lindahl to the Society for Complex Carbohydrates as the first Karl Meyer awardee when I learned, quite unexpectedly, that there were to be two awards granted. I felt very honored when I understood that the second award was for me! In the intervening years since Lindahl and I became the first awardees for our work with glycosaminoglycans and proteoglycans, the award has been granted to a stellar series of researchers who have established the breadth and depth of what is now glycobiology. Karl Meyer (see Figure 1) is often considered the father of glycosaminoglycan research. His contributions to our knowledge of the structures of hyaluronan, chondroitin sulfate, and keratan sulfate (three of the four classes of glycosaminoglycans) certainly merit such consideration, and it is very appropriate for the society to honor his work and his memory through the award that bears his name. The perspective that follows was first presented as a poster at Hyaluronan 2000, an international meeting held in Wrexham, Wales (Kennedy et al., 2002). It provides an overview of Meyer and his work in the context of his time. It focuses on hyaluronan, the simplest of the glycosaminoglycans, and the molecule that continues to amaze those of us who work with it for its diversity and importance in a wide variety of normal and pathological processes. On behalf of the recipients of this singular honor, I hope you will enjoy this perspective and pause to reflect on Meyer's seminal contributions at the annual Society for Glycobiology meeting each year when the new honoree receives the Karl Meyer Award. At the time that Meyer initiated his pioneering research on hyaluronan, previous work had been done in the area that he no doubt knew of and found useful in placing his work in its proper context. A French chemist, Portes, reported in 1880 that a ``mucin'' isolated from vitreous differed from similar preparations from cornea and cartilage in its behavior in acid solutions, and he called it a Fig. 1. Karl Meyer, circa 1958 (photo courtesy of Gerard Armand).

Corrosion behaviour in acid solution of (Ti, Cr)Nx films deposited on glass

Some (Ti, Cr)Nx films were deposited on a glass substrate by reactive cathodic sputtering. This kind of substrate was chosen to evaluate the electrochemical properties of the deposit without any galvanic coupling with a metal substrate. The TiCr ratio in the coatings was varied by using different TiCr area ratios in the cathode. Auger analysis and X-ray diffraction were used to characterize the chemical composition and the microstructure of the various nitride coatings produced. The X-ray diffraction characterization of the bimetallic nitrides showed the presence of an f.c.c. structure with diffraction peaks which are situated between those of the TiN and CrN phases. As the chromium amount increases, we observed the shift of these peaks towards the CrN peaks and the appearance of a structure which is increasingly microcrystalline. Chromium adjunction appeared to be interesting as far as the corrosion resistance of titanium nitride is concerned.

Medium dependence of the spectroscopic and photophysical properties of Ru(bpy) 2(HAT) 2+. The effect of solvent, pH and binding to polyelectrolytes

In order to assess its usefulness as a probe for medium properties, the absorption, emission and excited state decay behaviour of Ru(bpy) 2(HAT) 2+ (bpy,2,2′-bipyridyl; HAT, 1,4,5,8,9,12-hexaazatriphenylene) were studied in various solvents, low temperature ethanol—methanol glasses, perfluorinated ionomer membranes (Nafion), in the presence of DNA or synthetic polynucleotides and in a solution of sodium polystyrenesulphonate (PSSS). The emission intensity and lifetime are quenched in acid solution and in protic solvents, increasing in the order H 2O < ethanol (EtOH) < dimethylsulphoxide) DMSO) < CH 3CN. The p K a values for the first two protonations of the HAT ligand in Ru(bpy) 2(HAT) 2+ (p K a1 = − 2.5, p K a2 = −4.3) have been determined. The spectroscopic and emission lifetime properties of the complex in Nafion membranes depend markedly on the swelling solvent and membrane hydration. The acidity of the H +-form membrane at different degrees of hydration was estimated by comparison with the absorption behaviour in acid solution. In the presence of DNA in aqueous solutions, the absorption of the complex is markedly altered, resembling that in low temperature glasses, and a 400% increase in the emission intensity and lifetime is observed. Spectroscopic changes are less marked with single-stranded than with double-stranded polynucleotides and very sensitive to the presence of salt cations. They increase in the order poly(dG).poly(dC) < poly[d(GC)] < poly(dA).poly(dT) < calf thymus DNA (CT-DNA) < poly[d(AT)] (dG, deoxyguanylic acid; dC, deoxycytidylic acid; dA, deoxyadenylic acid; dT, deoxythymidylic acid). Results are consistent with the partial intercalation of the complex into DNA, with a preference for AT stretches.

Direct evidence for the involvement of domain III in the N-F transition of bovine serum albumin.

The domain III of bovine serum albumin containing residues 377-582 of the protein sequence was isolated and its behaviour in acid solution was studied. The fragment was found to undergo structural transformations over the pH range 3.5-4.5 known to cause N-F transition in serum albumin. On the other hand, an albumin fragment that was devoid of domain III was unable to exhibit such a transition. These results were consistent with a mechanism where N-F transition involves the separation of domain III from the rest of the albumin starts at about pH 4.3 and is completed at pH 3.5.

Ruthenium dioxide: a new electrode material. I. Behaviour in acid solutions of inert electrolytes

The electrochemical behaviour of RuO2 film electrodes, prepared by the thermal decomposition of Ru Cl3 on metallic supports has been investigated in solutions of inert electrolytes. Steady-state pot entiostatici/E curves, cyclic voltammetry and charging curves are presented. The procedure for the preparation of electrodes is described.

Anodic and Cathodic Behavior of Maraging Steel in Acid Solution

Nickel maraging steel polarization behavior in acidic solutions, noting corrosion potential dependence on pH

Dissolution of AgO in Acid and Alkaline Media

THE oxide AgO is a diamagnetic, monoclinic, stoichiometric Ag(I)–Ag(III) oxide1,2. Its behaviour in acid solutions is well known: it dissolves as bivalent silver with 1.98 effective magnetons perion3,4. The nature and parameters of the magnetic complex do not depend critically on the stabilizing acid5, namely, nitric, sulphuric, perchloric, hydrofluoric or orthophosphoric. It has cylindrical magnetic symmetry, as most of the bivalent silver complex compounds6. The dissolution of AgO in alkaline solutions, however, is a well-known process in regard to the solubility, although the nature of the product is only speculative. Studies of the variation of the solubility with pH have led to the formulation of the dissolution products:

Bovine serum albumin and its behaviour in acid solution.

Bovine serum albumin and its behaviour in acid solution.