Function Of Chloride Ion Concentration Research Articles

International comparison on Ag|AgCl electrodes for pH measurement

The first practical comparison of the characteristics of Ag|AgCl electrodes prepared at different National Metrology Institutes (NMIs) has been carried out as a pilot study organised by the Consultative Committee for Amount of Substance (CCQM). Each NMI prepared at least three Ag|AgCl electrodes representative of those employed in their primary pH calibration facilities. The electrodes were sent to a coordinating laboratory where comparative measurements of their potential difference to a de facto reference, slope as a function of chloride ion concentration and electrochemical impedance were made. Electrodes from most NMIs were highly repeatable and consistent within the typical rejection criteria applied during production. An analysis of the electrode slopes in a phosphate buffer containing different concentrations of NaCl revealed the influence of variances in the Ag|AgCl electrodes between NMIs on the certified pH value of the buffer solution. The difference between NMIs is consistent with submitted values in CCQM-K9, although biases were smaller in the analysis here, suggesting the presence of other unknown contributions to the uncertainty such as cell design. The smaller biases observed in this work may also reflect improvements in the Ag|AgCl electrodes since CCQM-K9 was performed. Electrochemical impedance spectroscopy suggests a similar microstructure for electrodes prepared by most NMIs.

Study of the Substrate Effect in the KCl Adsorption onto Single-Crystal and Polycrystalline Gold Electrodes

Electron transfer kinetics in electrochemical systems is ubiquitous to natural and industrial processes. Thus a deep knowledge of all stages involved in the charge transfer at the electrode solution interface, which includes mass transport, adsorption and the role of the electrical double layer is highly desirable [1]. In particular, adsorption and the electrical double layer play a distinctive role in the charge transfer at electrode/solution interfaces, since they are essential part of reaction mechanisms, especially for reactions where more than one electron is transferred. Fueled by the importance of adsorption and the electric double-layer in the electrode kinetics, there has been published in the literature several works, but mainly focused on thermodynamic rather than kinetics [2-4].Here a qualitative study of the effect of the substrate and surface heterogeneities in the adsorption of chloride ions on gold surfaces is presented. With this goal in mind, we have performed a study of the adsorption of chloride ions at different concentrations (1 mM, 10mM 0.1M) disolved in HClO40.5 M on the surfaces of polycrystalline (pc) and gold (111) single crystal. Our results include the characterization of the system by using classic electrochemical techniques, such as cyclic voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and the novel intermodulated techniqued called Interfacial Capacitance Modulation (MIC) [5]. Figure 1 shows a comparison between the typical voltammetric responses as well as the double-layer capacitance vs. polarization behavior for polycristalline and (111) gold electrodes in contact with HClO4in absence and presence of KCl, respectively. After this characterization, EIS and MIC measurements are carried out. All our results are discussed qualitatively based on the relaxation of the double layer capacitance as a function of chloride ion concentration on the electrode solution interface.REFERENCES:[1] F.C. Anson, Acc. Chem. Res. 8 (1975) 400.[2] D.C. Grahame, Chem. Rev. 41 (1947) 441.[3] J. Lipkowski, W. Schmickler, D.M. Kolb, R. Parsons, J. Electroanal. Chem. 452 399, (1998) 193.[4] T. Pajkossy, D.M. Kolb, Electrochim. Acta 54 (2009) 3594.[5] E.R. Larios-Durán, R. Antaño-López, M. Keddam, Y. Meas, H. Takenouti, V. Vivier. Electrochim. Acta 55, (2010) 6292.

Localized Corrosion of Nuclear Grade Alloy 800 Under Steam Generator Layup, Startup and Operating Conditions

The localized corrosion resistance of nuclear-grade Alloy 800, which is one of the preferred steam generator (SG) heat exchange tube materials of CANDU and PWR reactors, was studied under simulated SG secondary side crevice chemistry conditions at ambient temperature as well as at elevated temperatures. Series of cyclic potentiodynamic polarization tests were performed to study the localized corrosion resistance of Alloy 800 as a function of chloride ion concentration in the SG crevice solution at 40°C, 150°C and 300°C. Based on the experimental results, empirical equations were provided for calculating the pitting potential of nuclear grade Alloy 800 in the SG secondary side crevice chemistries with different levels of chloride concentration at SG layup, startup and operating temperatures.

Electrochemical Kinetics of Anodic Ni Dissolution in Aqueous Media as a Function of Chloride Ion Concentration at pH Values Close to Physiological Conditions

AbstractWe have studied the electrochemical kinetics of anodic Ni dissolution as a function of chloride ion concentration, at pH 5, 6 and 7, in order to mimic the conditions of sweat samples. Our results show that the rate‐determining step for Ni dissolution in the mentioned pH range is the transfer of one first electron, as suggested by the Tafel slopes close to 0.120 V/decade. However, the reaction order in chloride ion varies from ca. 2 at pH 7 to values close to unity for pH values between 5 and 6. This finding is very important for sensor applications in sweat fluids since the sensitivity of the Ni electrode to chloride ions is higher in neutral solutions (pH ca. 7) compared to that in slightly acid solutions (pH between 5 and 6). Small variations in pH in real samples are expected so this change in sensitivity should be considered when sensing chloride ions in sweat fluids.

Structural Correspondence between Uranyl Chloride Complexes in Solution and Their Stability Constants

Pair-distribution functions (PDF)s were obtained from high-energy X-ray scattering (HEXS) data on a series of uranyl solutions as a function of chloride ion concentration. Analyses reveal that chloride forms only inner-sphere complexes with the uranyl, replacing inner-sphere waters such that the total uranyl coordination number decreases from 4.7 waters at [Cl(-)] = 0 m to 4.4 (1.7 water and 2.7 Cl(-)) at [Cl(-)] = 6.8 m. Some of the second-coordination sphere waters reorient upon uranyl inner-sphere chloride complexation in order to hydrogen bond with the bound anion. Similar data obtained on a series of solutions maintained at constant ionic strength are used to confirm structural assignments through determining stability constants for the addition of chloride to uranyl and comparison with published values. The stability constants, β(1) = 1.5(10) m(-1), β(2) = 0.8(4) m(-2), and β(3) = 0.4(1) m(-3), obtained in a series of solutions with constant ionic strength of 5.3 m, are in reasonable agreement with previously published results determined by solvent extraction. The agreement of stability constants supports our peak assignments for the PDF and thus our structural model for uranyl chloride complexes in solution. Using coordination numbers and speciation determined here as a function of chloride ion concentration, the monochloro species is found to have four coordinating waters in the uranyl equatorial plane, the dichoro species is found to be an equilibrium of three and two coordinating waters, and the trichloro species has only a single water in the equatorial plane. These values correspond to total average coordination numbers of 5, 4.3, and 4 for the mono-, di-, and trichlorouranyl complexes. From the equilibrium value of the dichloro species, it can be further estimated that ΔG = -0.5 kcal/mol for the conversion of five to four coordinate species. Overall, the HEXS data support the assertion that uranyl chloride correlations do exist and the results are not simply the result of solvent-ion effects.

Chloride ion detection by InN gated AlGaN∕GaN high electron mobility transistors

Real time chloride ion detection using InN gated AlGaN∕GaN high electron mobility transistors (HEMTs) was demonstrated. The InN thin film on the gate area of the HEMT provided fixed surface sites for reversible anion coordination. The drain current of the HEMT sensor exhibited increased a function of chloride ion concentration. The positive ions (Na+, Mg+2, and H+) in the chloride ion solutions showed no effect on the chloride ion concentration detection. The sensor was tested over a range of chloride ion concentrations from 100nMto100μM. The chloride ion HEMT sensors can be integrated with AlGaN∕GaN HEMT based pH and glucose sensors for exhaled breath condensate glucose monitoring technology. The HEMT based sensor can also be integrated into a wireless data transmission system for remote sensing applications.

Determination of the Ion-Pair Constant between Chloride Ion and Cationic-Coated, Silver SERS Substrates Using Competitive Complexation

The interaction of chloride ion with cationic-coated silver surface-enhanced Raman scattering (SERS) substrates was monitored using a competitive complexation technique. In this approach, the nitrate concentration is kept constant and the chloride ion concentration is varied. The change in the nitrate peak area, ΔANO3, is measured as a function of chloride ion concentration, CCl. The measured response is described by the following relationship: ΔANO3 = VCCl/(K + CCl). Using the value of Κ and the value of the ion-pair constant between the cationic coatings and nitrate ion, it is possible to extract the value of the ion-pair constant for chloride ion. The selectivities of the cationic coatings for nitrate, sulfate, and chloride ions are discussed.

Studies on the influence of chloride ion and pH on the corrosion and electrochemical behaviour of AZ91D magnesium alloy

The influence of chloride ion concentration and pH on the corrosion and electrochemical behaviour of die-cast and ingot-cast AZ91D alloy have been studied with a focus on the stability of microconstituents in these environments. The experimental techniques used include immersion studies, potentiodynamic polarization, X-ray diffraction and optical and scanning electron microscopy. The corrosion rate for the ingot and die-cast was very high in highly acidic solutions (pH 1–2) as compared to that in neutral and highly alkaline solutions (pH 4.5–12.0), and the rate increased with chloride ion concentration at all pH levels. In general, the die-cast showed a lower corrosion rate at all pH values and chloride ion concentrations. The open circuit corrosion potential shifted to more negative (more active) values with increase in concentration of chloride ions. Corrosion morphologies revealed more attack on primary α and eutectic α with increasing chloride concentration. In highly acidic conditions, corrosion attack was found on β (Mg17Al12) and eutectic α phase (α regions with higher Al content) while at pH 12.0 the ingot exhibited a pitting type of morphology. The corrosion product consisted of magnesium hydroxide, fallen β particles and magnesium–aluminium oxide; the amount of each component was found to be a function of chloride ion concentration and pH.

Effects of chloride ion and applied current density on the stress generation during anodic oxidation of tungsten in 0.1 M H 2SO 4 solution

Surface stresses developed during the anodic oxidation of tungsten in 0.1 M H 2SO 4 solution have been investigated as a function of chloride ion concentration and applied current density. Before the oxide film breakdown, specimens moved increasingly in a compressive direction with increasing chloride ion concentration. In contrast, after the oxide film breakdown, the reverse movement in a tensile direction was encountered and the amount of tensile deflection increased with increasing chloride ion concentration. Ac impedance measurements substantiated the existence of relatively stable tungsten-oxychlorides formed due to the incorporation of chloride ion in the anodic oxide film on tungsten during the oxide growth. The movement in the compressive stress direction due to chloride ion incorporation before the oxide film breakdown increased with decreasing applied current density. The present experiment results are discussed with respect to oxide film growth-related electrochemical reactions occurring both at the metal/oxide film interface and at the oxide film/electrolyte interface. The changes in the sign of deflection are well accounted for in terms of the combined effects of the increasing compressive stress development due to the substitution of chloride ion for oxygen vacancy and of the increasing tensile stress development due to the cation vacancy accumulation at the metal/oxide film interface with increasing chloride ion concentration.

Synthesis and characterization of Y 2O 3-ZrO 2 and Y 2O 3-CeO 2-ZrO 2 precursor powders

Thixotropic gels of the precursor powders of the titled compounds have been prepared by the addition of oxalic acid to the mixed solutions of metal salts at room temperature (≈ 27 °C). The clear sols of yttrium-zirconyl oxalate (YZO) and yttrium-cerium-zirconyl oxalate (YCZO) gelled within a few hours and were oven-dried at 40 °C. The various stages of gelation behaviour of the sols are explained on the basis of DLVO theory. By repeptizing the dried gel powders with water, concentrated sols were prepared. The gelation time as a function of chloride ion concentration is discussed for both sols. The nature of the temperature dependence of the dried gel powders was studied by means of thermogravimetric analysis and differential thermal analysis. Powder X-ray diffraction was used to study the crystallization behaviour of the dried amorphous gel powders. It is found that these powders crystallize in tetragonal phase when calcined at 850 °C for 1 h. Estimation of surface area and infra-red characterization have also been carried out for the prepared powders.

The effect of chloride ions on stress corrosion cracking of type 304 and type 316 austenitic stainless steels in sulfuric acid solution

Stress corrosion cracking of type 304 and type 316 austenitic stainless steels has been investigated as a function of chloride ion concentration in 0.82 kmol m −3 pure sulfuric acid solution at 353 K under a constant stress of 392 MPa by using a constant load method. At a concentration of up to approximately 2 × 10 −2 kmol m −3 type 316 has no SCC susceptibility as well as the result in the pure sulfuric acid solution, while type 304 has SCC susceptibility the same as that in the pure sulfuric acid solution except for a narrow concentration range of around 1 × 10 −3 kmol m −3, at which concentration type 304 has no or little SCC susceptibility. The behavior of type 304 at the narrow concentration range means that chloride ions serve as inhibitor for SCC. At higher concentrations of more than 2 × 10 −2 kmol m −3 the SCC susceptibility of both steels increases with increasing chloride concentration, which implies that chloride ions act as promotor for SCC. In addition, the logarithm relationship between time to failure and steady state elongation rate is found to become a good straight line with a slope of unity independent of the material and chloride concentration. The steady state elongation rate becomes a parameter for the prediction time to failure even in the mixed solution of sulfuric acid and the chloride ions. The present results obtained are qualitatively explained in terms of adsorption of chloride ions at crack tips through a SCC process.

Kinetics and mechanisms of the acid dissolution of goethite (α-FeOOH)

The initial rate of dissolution of several crystalline forms of goethite (α-FeOOH) has been measured as a function of solution conditions. These include hydrogen ion concentration, anion concentration (chloride or perchlorate) and temperature. For dissolution in HClO 4 the rate of reaction is first order with respect to hydrogen ion concentration and is independent of perchloric ion concentration. The rate determining step is thus a protonation of the surface. The activation energy in the presence of perchlorate ion is 23 kcal/mole and the rate of dissolution can be described by the simple collision theory. For dissolution in HCl the kinetics are more complex, the rate again being first order with respect to hydrogen ion concentration but also a function of chloride ion concentration. The results indicate that an adsorption complex is formed before dissolution occurs.

A Contribution to the Study of the Critical Pitting Potential of Oxide Covered Aluminum in aqueous chloride solutions

AbstractThe critical pitting potential of oxide covered aluminum electrodes in aqueous chloride solutions has been investigated as a function of chloride ion concentration, temperature, solution pH and oxide film thickness. The steady state critical pitting potential decreases with chloride ion concentration and increasing solution temperature. Solution pH in the range 5 to 9 has no effect on the breakdown potential. The role of the oxide film thickness is to slightly increase the critical potential for passivity breakdown and intiation of pitting. It is postulated that at the critical pitting potential, passivity breakdown occurs by a process of field assisted Cl adsorption on the hydrated oxide surface and formation of a soluble basic chloride salt with a lattice cation which readily goes in solution. This process of localized dissolution of the hydrated oxide film via formation of a soluble basic aluminum chloride salt, once initiated, is likely to continue in an “autocatalytic” fashion until the oxide is locally “penetrated” and dissolution of the substrate metal begins.

Reduction of stray-current attack in electrochemical machining

Stray current effects in electrochemical machining promote inferior surface finishes and poor dimensional tolerances. A study of the problem has been made using a segmented anode to measure weight losses in the stray current region as a function of chloride ion concentration. At intermediate chloride concentrations, the attack can be decreased by the formation of a passive film, but this effect is marred by heavy pitting. The growth of these pits has been retarded by the addition of anions that are capable of forming insoluble compounds in the pits. These additions can be made to chloride solutions in such a concentration that stray current attack is reduced but machining is not affected.

Solubility of cupric oxide in pure subcritical and supercritical water

THE DISSOLUTION, transport, and deposition of metallic oxides is an important factor in the operation of the high-pressure water circuit of modern power station boiler units. As feedwater purity improves, the relative importance of the metallic oxide impurities, which result largely from the corrosion of the water circuit containment itself, increases. A major parameter in each of the processes quoted above is the solubility of the oxide species in the high-temperature, high-pressure aqueous environment, but there is little data available for the systems of greatest practical significance, Fe304-H20, CuO-H20, and Cu20-H20. Sweeton et al. (8, 9) have studied the subcritical solubility of magnetite, Fe3O4, as a function of chloride ion concentration, while a small area of the supercritical solubility diagram for the system Fe304-H20 has been explored by Martynova (6). The measurements made by Pocock and Stewart (7) in the systems Cu-H20, Cu20-H20, and CuO-H20 were over a restricted range of pressure and temperature, and the results showed considerable scatter. In the present work, the solubility of cupric oxide, CuO, has been measured in pure water of pH 7.5 over the temperature range 50 to 550°C. and along a series of isobars between 3500 and 6000 p.s.i.g.

A Study of Scaling and Corrosion In Condenser Tubes Exposed to River Water

Abstract The series of tests reported give quantitative data on the rates of fouling and corrosion in 17 to 20 ft condenser tubes under simulated operating conditions using Neches River water as the cooling medium. Alloys tested were: 90–10 Cupro-nickel, aluminum-brass, Alclad aluminum, admiralty, three stainless steels, and alloy 77. Heat-transfer coefficients and Fanning friction factors were measured three times daily for 3 to 4 months. Several mechanisms of the fouling rate function were employed to compare the results. It appears that the heat-transfer coefficient is essentially linear with time and that the rate of fouling, initially at least, is not a function of velocity, but is a function of chloride-ion concentration (or hardness). The effects of weekly caustic addition, continuous cathodic protection, and river-water velocity were examined. Other river-water variables measured included pH, chloride-ion content, and hardness. The effects of these variables are discussed qualitatively. 3.3.2, 4.6.7, 7.4.2