Chloride-containing Solutions Research Articles

MS4, a seminaphthofluorescein-based chemosensor for the ratiometric detection of Hg(ii)

The synthesis and photophysical characterization of Mercury Sensor 4, MS4, an aniline-derivatized seminaphthofluorescein-based dye that contains a pyridyl-amine-thioether ligand analogous to that employed in the previously reported Zinspy (ZS) Zn(II) sensor family (Nolan and Lippard, Inorg. Chem. 2004, 43, 8310–8317) are reported. Sensor MS4 provides single-excitation, dual-emission ratiometric detection of Hg(II) in aqueous solution. A ∼4-fold ratiometric change (λ624/λ524) is observed upon introduction of Hg(II) to an aqueous chloride-containing solution of MS4 at pH 8. In this milieu, MS4 shows selectivity for Hg(II) over a background of environmentally relevant alkali and alkaline earth metals, a number of divalent first-row transition metals, and its Group 12 congeners Zn(II) and Cd(II).

Thrombin stimulation of Cl −/HCO 3− exchange in human platelets

The presence of one acidifying Cl −/HCO 3 − exchange mechanism in human platelets has not been previously reported. This paper demonstrates that this mechanism does function and that it increases its activity after stimulation with thrombin. On resuspension of BCECF-loaded platelets in a chloride-free medium (gluconate replaced) that contains bicarbonate, cytosolic pH (pHi) increased and stabilized after 10 min at an alkaline value. After addition of 50 mM NaCl, pHi fell rapidly reaching steady state in the succeeding 5 min. The stilbene derivative 4-acetamido-4′-isothiocyanato stilbene-2,2′ disulfonic acid (SITS) inhibited both, the alkalization in chloride-poor solution and the recovery from the alkaline load after chloride enrichment. The decline in pHi was observed whether chloride was delivered to the solution in the form of LiCl or NaCl, or when the later was applied after blockage of the Na +/H + exchanger. The recovery in chloride-containing solution was in contrast to the effect of a similar change in osmolarity by addition of 50 mM sodium gluconate that did not produced a significant variation of pHi. Posterior addition of NaCl after 5 min in high gluconate reproduced the pHi fall of the control experiment. Alkali loads produced by 25 mM trimethylamine hydrochloride (TMA) were also counteracted by HCO 3 −-equivalent efflux via Cl −/HCO 3 − exchange. One of the major observations of the present study is that HCO 3 − equivalent efflux was twice as high when the platelets were previously stimulated with 0.1 IU of thrombin, but thrombin did not produce significant changes of the pHi recovery rate in a bicarbonate-free solution. The increase of the decline in pHi elicited by preexposure to thrombin was still observed in the presence of an inhibitor of the Na +/H + exchange or in sodium-free solutions. It is concluded that a Na-independent Cl −/HCO 3 − exchange mechanism mediates the recovery of pHi from alkalosis in platelets and that thrombin activates this exchanger by a direct regulatory pathway.

Fatigue behavior of AISI 347 stainless steel in various environments

The aim of this study is to investigate the influence of environmental factors, including pH, chloride ion, and pitting inhibitor, on the fatigue properties of AISI 347 stainless steel. Systematic fatigue tests, including both high-cycle fatigue (HCF, S-N curves) and fatigue crack growth (FCG, da/dN-ΔK curves), have been conducted in air and several aqueous environments. Results showed the HCF strength was markedly reduced in an acid solution and in a chloride-containing solution, as compared to the air value. An addition of pitting inhibitor could restore the HCF strength in salt water back to the level in atmospheric air by preventing the formation of corrosion pits and decreasing the corrosion rate. However, the corresponding stage II FCG rates in all given environments were almost equivalent. These results indicated that the variation of chemistry in bulk environment exerted more influence on the fatigue crack nucleation than on the extension of long fatigue cracks.

Passivity and passivity breakdown of 304 stainless steel in alkaline sodium sulphate solutions

The passivity and passivity breakdown of 304 stainless steel were investigated in 0.25 M Na2SO4solutions of pH 10. The effect of applied potential and the presence of Cl− ions in the electrolyte were also studied. Different electrochemical methods such as open circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used. The results showed that the steel electrode passivates under open circuit conditions and also under potentiostatic control. The rate of passive film thickening under open circuit conditions follows a simple logarithmic law. Addition of Cl− ion shifts the polarization curves in the active direction and above a critical chloride concentration, [Cl− ] ≥ 0.15 M, pitting corrosion occurs and the pitting potential, E pit, decreases linearly with the logarithm of [Cl−]. The addition of sulphate ions to the chloride-containing solutions was found to inhibit the pitting process, and at [SO2- 4] ≥ 0.25 M, a complete immunity to pitting corrosion was recorded. The impedance measurements provided support for film thickening and film breakdown reactions. An equivalent circuit model which consists of a pure resistor, R Ω, in series with a parallel combination of a pure resistor, R p, and a constant phase element, Q, was proposed to describe the electrode/electrolyte interface. The passive film thickness was found to increase with applied potential up to a critical value of 0.3 V. At higher voltages, breakdown of the passive film occured.

Effect of Low-Temperature Plasma Nitriding on Corrosion of 304L Stainless Steel in Sulfate and Chloride Solutions

Conventional plasma nitriding of stainless steels is carried out at about 550°C which leads to an increase of hardness, but also to a decrease of the corrosion resistance. The latter can be avoided by low-temperature nitriding at 380-450°C. Anodic behavior of low-temperature nitrided 304L steel was examined here in at pH 3, 6, and 9, and in at pH 3. The corrosion resistance of nitrided steel was in the chloride-free solution at pH 3 lower than that of unnitrided steel, whereas in the near-neutral solutions the resistance was higher. In the chloride-containing solution, nitrided steel exhibited much higher resistance to pitting corrosion than unnitrided steel. Nitrogen accelerated anodic oxidation in the initial stages of polarization, and promoted the subsequent passivation. X-ray photoelectron spectrometry analysis indicated the presence of nitrogen-rich species and large amounts of hydrated oxides and of on corroded nitrided steel. It is proposed that the improved resistance of nitrided steel to pitting corrosion can be related to the enhanced anodic reactivity of nitrogen-containing steel which results in the formation of oxide deposits and also in an accumulation of protective nitrogen-rich species. © 2004 The Electrochemical Society. All rights reserved.

Improving corrosion resistance of magnesium-based alloys by surface modification with hydrogen by electrochemical ion reduction (EIR) and by plasma immersion ion implantation (PIII)

Magnesium-based hydrides are well known that they have a high hydrogen-storage capacity. In this study, two different methods have been provided for hydrogen surface modification of high purity magnesium (hp Mg) and AZ91 magnesium alloy. One was electrochemical ion reduction (EIR) of hydrogen from an alkaline electrolyte on such Mg-based cathode. The other was plasma immersion ion implantation (PIII or PI 3) into Mg-based substrate. The depth profile of H-modified surfaces was described by Auger electron spectroscopy (AES) and by secondary ion mass spectrometry (SIMS) measurements. Corrosion testing was carried out in Avesta cell by potentiodynamic polarisation in chloride-containing aqueous solutions of pH 7 and pH 12. A greatly significant improvement in the corrosion resistance of H-modified surfaces was verified.

Pitting Resistance of Diffusion-Alloyed Carbon Steels

Pitting corrosion is a dangerous type of corrosion fracture of metals observed, as a rule, in solutions containing oxidizers (e.g, oxygen) and, at the same time, activating chlorine ions and ions of other halogens. In this case, bounded regions of the metal suffer fracture. However, since the surface damaged by pitting plays the role of an anode, the corrosion process runs at a high rate due to the contact with the remaining part of the surface playing the role of a practically nonpolarized cathode. This leads to the formation of deep point defects and pits. The principal electrochemical condition required for the development of pitting is the shift of potential to a value more positive than a certain critical value called the potential of pitting formation EPT . According to the generalized experimental data, pitting corrosion is typical of the metals and alloys readily susceptible to passivation, i.e., of iron, stainless steels, aluminum and its alloys, titanium, etc. [1–5]. The resistance of metals and alloys to this type of corrosion is determined, on one hand, by the nature, composition, structure, and state of the surface and, on the other hand, by the solution, its composition (i.e., aggressive ions), and temperature. In the present work, to study the pitting resistance of carbide layers obtained on 35, 45, and U7A steels after treatment according to the technology of diffusion carbide surface alloying (DCSA), the specimens were subjected to electrochemical and long-term corrosion tests in chloride-containing solutions.

Interfacial Void Model for Corrosion Pit Initiation on Aluminum

A model for pit initiation during galvanostatic anodic etching of aluminum in acid chloride-containing solutions was developed. The predictions were compared to experimental potential transients and pit-size distributions. The model presumed that pits initiated from subsurface nanoscale voids, which were exposed by uniform corrosion. Void concentrations fit from potential transients depended on times of caustic and acid exposure before etching, in agreement with prior characterization of the voids by positron annihilation measurements. The model yielded realistic predictions of the effect of applied current density and temperature on the potential transients. The effective void concentration was found to increase with the chloride concentration in the etching solution; this suggested that higher chloride concentrations inhibit passivation of newly exposed voids, enhancing their survival probability. On the whole, the interfacial void model provided a promising quantitative description of pit initiation during anodic etching. © 2004 The Electrochemical Society. All rights reserved.

Pitting initiation and propagation of hypoeutectoid iron-based alloy with inclusions of martensite in chloride-containing nitrite solutions

Pitting initiation and propagation of hypoeutectoid iron-based alloy with inclusions of martensite in chloride-containing nitrite solutions

Pitting initiation and propagation of hypoeutectoid iron-based alloy with inclusions of martensite in chloride-containing nitrite solutions

The pitting initiation and the pitting propagation of a hypoeutectoid iron-based alloy with inclusions of martensite in nitrite solutions containing chloride ions were studied by various electrochemical techniques. It was shown, by scanning reference electrode technique (SRET), that pitting occurred only on the martensite phase rather than hypoeutectoid areas. Anodic polarization behaviors of martensite electrode in nitrite solution with and without chloride ions are similar to those of hypoeutectoid electrode: both of martensite and hypoeutectoid electrodes were passive and the passive films could be broken by chloride ion. However, the open circuit potential of martensite electrode is more negative than that of hypoeutectoid electrode, and the passive current density of martensite electrode in the solution containing chloride ions was larger than that of hypoeutectod electrode. It was shown, by Mott-Schottky analysis, that the passive film of martensite electrode in the solution containing chloride ions had a higher donor concentration than that of hypoeutectoid electrode. There was a galvanic interaction between martensite and hypoeutectoid electrodes and it was this interaction that induced and accelerated the pitting corrosion on martensite area. Current and potential fluctuations, which reflected pitting initiation, were observed when martensite and hypoeutectoid electrodes were coupled together.

The initial stages of palladium deposition onto Pt(1 1 1)

The electrodeposition of Pd onto Pt(1 1 1) from PdCl 2 and PdSO 4 containing solutions was studied by cyclic voltammetry and in situ scanning tunnelling microscopy. Pd deposition starts by forming a pseudomorphic monolayer in both cases. While in the presence of chloride this monolayer is deposited at underpotentials, its formation in chloride-free solution is kinetically hindered to such an extent that the deposition peak is shifted negative of the equilibrium potential. Detailed structure information has been obtained from STM data about the Pd layer as well as the co-adsorbed anions. Bulk deposition from the chloride-containing solution proceeds via a quasi layer-by-layer fashion. However, the particular electrochemical properties of the first Pd monolayer disappear only after deposition of the equivalent of four more Pd layers. The electrochemical behaviour of such films is similar to that of a rough Pd(1 1 1) surface. Pd bulk deposition from chloride-free solution leads to the formation of three-dimensional clusters from the very beginning. About 10 ML equivalents are needed in that case to completely cover the first Pd monolayer.

Electrochemical characterization of copper surface modified by n-alkanethiols in chloride-containing solutions

The self-assembled monolayers (SAMs) of three n-alkanethiols, 1-octadecanethiol (C18SH), 1-dodecanethiol (C12SH), and 1-hexanethiol (C6SH), were formed on the fresh copper surface pretreated by nitric acid etch. The surface properties of the alkanethiol modified copper electrode in chloride-containing solutions were electrochemically characterized. The polarization measurements have shown that alkanethiol SAMs onto copper were able to protect effectively the underlying copper against corrosion. The cyclic voltammetric results, together with FT-IR measurements, showed that alkanethiol SAMs had quite good anodic inhibition at the lower anodic potentials, but this inhibition action gradually lost because of removal of SAMs from the copper substrate with the increase of anodic potentials. Alkanethiol SAMs were proved to be defective by scanning Kelvin probe (SKP) measurements. Electrochemical noise (EN) experiments have shown that SAMs-covered copper electrode suffered pitting attack in HCl solutions. The formation mechanism of pits was explained in this paper.

Influence of Dichromate Ions on Corrosion Processes on Pure Magnesium

The corrosion behavior of Mg is of interest because of its growing use as an alloy in the transportation industry and also because it is a major component of some intermetallic phases in Al alloys, such as the deleterious S -phase found in AA2024-T3. Pure Mg corrodes rapidly in a chloride-containing solution and even dissolves in water if the surface hydroxide is damaged by scratching the surface, for example. Uniform dissolution is drastically reduced in NaCl solutions (from 0.01 to 0.5 M) with the addition of very dilute concentrations of dichromate However, it is replaced by a strong localized attack in the form of fast filiform-like attack. On a large-grained sample with a defined defect structure, the attack can be seen to propagate at twin boundaries. Orientation imaging microscopy analysis found that corrosion was limited to planes near {0001} orientations with propagation being in prismatic directions. Auger electron spectroscopy analysis shows that interaction of chromate with the Mg hydroxide results in incorporation of reduced chromium ions in the hydroxide surface layer. Formation of a more resistant surface film could explain the very local nature of the corrosion in this case. The interaction between dichromate ions and Mg hydroxide can also explain the higher corrosion resistance of S-phase particles in chloride solutions containing dilute dichromate, although differences in the surface film formed compared to pure Mg are observed. Sputter-etching of the surface in order to assess the depth of the attack revealed that very hard or isolating corrosion products difficult to sputter are produced along the filiform path and that chromium compounds are not integrated in the corrosion products. Focused ion beam sectioning followed by scanning electron microscopy investigation of the sectioned area, demonstrates the presence of a continuous protective surface film. Adhesion between the Mg hydroxide and the metal is lost at the location of the corrosion filament, suggesting that the mechanism of propagation is similar to filiform corrosion under a coating. The depth of attack is a couple of micrometers with large cracks present within the corroded area that could induce severe surface damage. © 2003 The Electrochemical Society. All rights reserved.

Influence of the rare earth content on the electrochemical behaviour of Al–Mg–Er alloys

The electrochemical behaviour of a number of Al–Mg alloys with increasing content of erbium (rare earth metal) has been evaluated. To this end borate solutions with or without chloride have been used. The examined alloys show a complex microstructure, in which the Al solid solution coexists with such intermetallic compounds as Al 3Mg 2, Al 66.7Mg 23.3Er 10 (τ) and Al 3Er. In chloride-free solutions the alloys exhibit a good electrochemical behaviour independent of composition and microstructure. In chloride-containing solutions the intermetallic compounds have a strong influence due to the difference in electrochemical activity between these phases and the Al matrix; local galvanic cells form affecting the stability of the protective superficial oxide and lead to an accelerated localised corrosion attack. The presence of erbium is beneficial; the analysis of the anodic polarisation curves reveals a progressive increase in the passive range with increasing rare earth concentration.

Effect of nitric oxide on electrolyte transport across the porcine proximal colon.

The effect of nitric oxide (NO) on ion transport in the porcine proximal colon was investigated in slide-stripped epithelia mounted in Ussing chambers. The serosal addition of the NO-donors sodium nitroprusside (SNP, 0.5 mM) or S-nitroso-N-acetylpenicillamine (SNAP, 0.5 mM) induced a steep increase of short-circuit current ( I(sc)). The stimulatory effect of SNP on I(sc) could not be blocked by piroxicam or tetrodotoxin. Potassium channel inhibitors (quinidine, tetraethylammonium or barium) added serosally reduced the SNP- or SNAP-induced increases of I(sc). In chloride-free solutions, the SNP-induced increase of I(sc) was smaller than in chloride-containing solutions. Cl(- )and Na(+) flux measurements demonstrated that SNP diminished Cl(-) and Na(+) net absorption. Pre-treatment with barium was able to block the inhibitory effect of SNP on NaCl net absorption totally. NO effects on paracellular pathways were assessed by measuring flux rates of [(14)C]-D-mannitol. SNP did not change unidirectional D-mannitol flux rates. In conclusion, NO inhibits NaCl net absorption in the proximal colon of pigs by acting directly on the enterocyte. The antiabsorptive (and/or prosecretory) effect of NO depends on a functional basolateral potassium conductance.

Chemical Oxidation of an АМг-3 Type Alloy in Alkaline Molybdate-Containing Solutions

A possibility to obtain conversion coatings (CCs) on an АМг-3 type aluminum alloy from alkaline molybdate-containing solutions (pH 12.8) is studied instead of its chromating. The effect of converting solution components on the resistance of thus obtained CCs to local anodic activation in the chloride-containing solutions is studied by using corrosion-electrochemical methods. It is shown that protective properties of molybdate-containing CCs can be improved by adding nitrates and silicates to the converting solution. It is found that sealing these CCs in hot water enhances their corrosion resistance to the level of chromate coatings.

Electrochemical Reactivity of Zirconium-Based Bulk Metallic Glasses

ABSTRACTAmorphous Zr-(Ti)-(Nb)-Al-Cu-Ni alloy samples were prepared by melt-spinning and copper mould casting in an argon atmosphere and characterized regarding their microstructure and thermal behavior. Their anodization behavior in aqueous environments with pH= 0.5 – 13 was studied by electrochemical polarization techniques in combination with surface analytical investigations, i.e. SEM/EDX, AES. In chloride-containing solutions the macroscopic corrosion resistance of bulk amorphous alloys is affected by the presence of heterogeneities, such as concentrated cluster zones of selected components or crystalline defects. Pitting phenomena are studied in neutral and acidic chloride solutions and as a result a local corrosion mechanism is proposed. The cathodic reactivity of alloy samples at different microstructural states and after pre-etching in fluoride solutions was investigated. After pre-etching melt-spun amorphous samples exhibit a significant increase in surface reactivity as expressed by a drastic increase in electrochemical capacities and in cathodic current densities as well as by a significant reduction of overpotentials for the hydrogen reduction reaction. The hydrogen sorption behavior was studied on samples galvanostatically charged at various cathodic current densities by means of XRD, DSC, TEM and thermal desorption analysis TDA. At room temperature Zr-based alloys absorb hydrogen up to H/M=1.65 mainly by interstitial solution of hydrogen atoms in the amorphous structure. The effect of absorbed hydrogen on the thermal stability and the crystallization behavior is described.

Characterization of electrodeposited WO 3 films and its application to electrochemical wastewater treatment

WO 3 films have been prepared on to IrO 2-coated Ti substrate by cathodic deposition, and as-deposited and annealed films have been characterized using XRD, TEM, Raman and FT-IR spectroscopy. The as-deposited film consists of nanocrystalline, orthorhombic WO 3·H 2O and this phase transforms to amorphous WO 3 by annealing at 250 °C and to monoclinic WO 3 by annealing at and above 350 °C. The as-deposited and annealed films have been used as anodes for electrochemical decomposition of phenol in aqueous solutions with and without chloride ions. The monoclinic WO 3 anodes prepared by annealing at 350 and 400 °C show relatively high electrochemical activity in the chloride-containing solution. In addition, the anodes possess high chemical and physical stabilities: very low dissolution rate of WO 3 during the electrolysis and good adhesion to the substrate. Thus, WO 3 anodes may be promising materials for anodic oxidation of bio-refractory organics in wastewater, although further improvement of electrochemical activity is needed for more effective decrease in total organic carbons in wastewater.

Analysis of concentration boundary layer in thallium (III) extraction with butyl acetate using membrane modules of different length

The development of concentration boundary layer (CBL) inside the hollow fibers, based on the experimental data from membrane-based solvent extraction of thallium (III) from chloride-containing acidic solutions with butyl acetate, was investigated. The experiments have been performed using three laboratory made contactors, consisting of hydrophobic polypropylene or polyvinylidene fluoride fibers of different length. The feed solution flowed inside the fibers, while the organic phase was pumped counter-currently at the module shell side. The influence of aqueous flow rate on the mean mass transfer coefficient in the aqueous phase was investigated. The tube-side Sherwood number was proportional to the Graetz number raised to powers ranging between 0.4 and 0.81. A model for the determination of CBL thickness and entry length was developed and used for the numerical analysis of the process. The entry length, i.e. the axial distance from the fiber inlet at which CBL reaches the axis of the fibers, was directly proportional to the aqueous phase flow rate and inversely proportional to the number of fibers in a module.

Scanning Tunneling Microscopy Investigation of Silver Deposition upon Au(111) in the Presence of Chloride

Using electrochemical measurements and in situ scanning tunneling microscopy (STM), we confirm the process of Ag growth and the overlayer structures of Ag underpotential deposition (upd) on Au(111) in the presence or absence of chloride anions. There are four distinct structures of the Ag adlayer on Au(111) in the presence of chloride. Adlayer structures (√3 × √3)R30°, (√19 × √19)R37°, (√13 × √13)R46°, and (6 × 6) are formed as a function of potential, and these structures are clearly matched to the features in a cyclic voltammogram. Compared with the (4 × 4) structure of Ag upd on Au(111) in a pure 0.1 M HClO4 solution, overlayer structures of Ag on Au(111) in a chloride-containing solution are more loosely packed. Therefore, we conclude that the structures of the Ag overlayer on Au(111) strongly interact with chloride anions, suggesting the bilayer structure is composed of both Ag and Cl.