Galvanostatic Stripping Research Articles

Revealing Nanoscale Passivation Films and Their Role in Reactivity in Lithium-Mediated Ammonia Synthesis

Ammonia is an indispensable component of modern fertilizers and a key nitrogen source in chemical synthesis, making it one of the highest-volume commodity chemicals.1–3 However, its synthesis via the Haber-Bosch process contributes significantly to global carbon emissions, motivating the development of alternative pathways for ammonia synthesis.4–6 Of many alternative methods, an electrochemical lithium-mediated process is one of the most promising. Since its initial implementations,7–9 novel cell designs10–12 and electrolytes13–15 have greatly improved the selectivity and productivity of lithium-mediated electrochemical ammonia synthesis (LiMEAS), but questions persist regarding the mechanism of nitrogen fixation and the role of lithium in this process (Figure 1a). In particular, many in the literature have alluded to the possible importance of lithium passivation species, commonly known as the solid electrolyte interphase (SEI), but their small length-scale and reactivity make direct observation challenging.11,13,15 In this work, we leveraged a multiscale approach to reveal connections between device-scale performance and nanoscale passivation behavior in LiMEAS. We used four model systems, varying the presence of proton donor (no proton donor or 0.1 M ethanol), and the feed gas (Ar or N2), which allowed us to examine the influence of the two reactive components in LiMEAS which are not usually present for lithium metal electrodeposition in the literature: proton donor and nitrogen. For each model system, we quantified major reaction products (Figure 1b, f). Ammonia and lithium nitride were measured by the salicylate colorimetric assay,16 hydrogen by online gas chromatography (GC), and residual lithium by galvanostatic stripping. We used scanning electron microscopy to observe microscale morphology, and to gain deeper insights into nanoscale surface morphology, we implemented cryo-electron microscopy (cryo-EM) (Figure 1c-d, g-h). Cryo-EM is a powerful technique that enables high-resolution observation of beam-sensitive metallic lithium and SEI materials by holding them at cryogenic temperatures, which preserve their native state.17 In addition to nanoscale morphological information, cryo-EM provided chemical information in the form of selected-area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS), which were paired with X-ray photoelectron spectroscopy (XPS) to develop an understanding of the chemistry of the interphase.Our results indicate that the proton donor governs reactivity toward nitrogen reduction in LiMEAS via its influence on the SEI. In the absence of proton donor, the lithium deposit forms a passivating, mosaic-structured SEI that preserves the deposited lithium, regardless of whether the feed gas is argon or nitrogen (Figure 1e). With the addition of ethanol, the surface changes significantly. The resultant SEI does not passivate the lithium, allowing it to react with nitrogen and other electrolyte components (Figure 1i). This permeable SEI appears to be mosaic in structure, with organic phases dominated by ethanol breakdown products, and its formation is key to the functionality of lithium-mediated ammonia synthesis. These findings can help guide the development of optimal SEIs for selectivity and stability of LiMEAS, and beyond that, offer insights into the characteristics of the lithium SEI at a reactive rather than passivated interface. Figure 1. (a) Schematic of possible lithium reactions. (b) and (f) Faradaic efficiencies of quantified reaction products, with no proton donor (b) and with ethanol present (f). (c-d) and (g-h) Cryo-TEM images of material deposited with no proton donor (c-d), and with ethanol present (g-h). (e) and (i) schematics of surface reactivity, with no proton donor (e) and with ethanol present (i). References J. W. Erisman, M. A. Sutton, J. Galloway, Z. Klimont, and W. Winiwarter, Nat. Geosci., 1, 636–639 (2008).G. R. Maxwell, Synthetic Nitrogen Products, Kluwer Academic Publishers, New York, (2004).FAO, World fertilizer trends and outlook to 2022, (2019).J. G. Chen et al., Science, 360 (2018).G. Soloveichik, Nat. Catal., 2, 377–380 (2019).Z. J. Schiffer and K. Manthiram, Joule, 1, 10–14 (2017).F. Fichter, P. Girard, and H. Erlenmeyer, Helv. Chim. Acta, 13, 1228–1236 (1930).A. Tsuneto, A. Kudo, and T. Sakata, Chem. Lett., 22, 851–854 (1993).A. Tsuneto, A. Kudo, and T. Sakata, J. Electroanal. Chem., 367, 183–188 (1994).N. Lazouski, M. Chung, K. Williams, M. L. Gala, and K. Manthiram, Nat. Catal., 3, 463–469 (2020).S. Z. Andersen et al., Energy Environ. Sci, 13, 4291–4300 (2020).K. Li et al., ACS Energy Lett., 30, 35 (2021).N. Lazouski et al., ACS Catal., 12, 5197–5208 (2022).B. H. R. Suryanto et al., Science, 372, 1187–1191 (2021).K. Li et al., Science, 374, 1593–1597 (2021).H. Verdouw, J. A. Van Echteld, and E. M. L. Dekkers, Water Res., 12, 399–402 (1977).Y. Li et al., Science, 358, 506–510 (2017). Figure 1

Manganese fractionation analysis in specific soil and sediment samples

Manganese has been determined in soil- and sediment samples taken from selected regions with high manganese concentrations anthropogenic and/or geogenic. The total content of manganese in chosen sediment- and soil samples has been determined applying FAAS after microwave digestion and the manganese fractions after sequential extraction procedures using galvanostatic stripping chronopotentiometry. The highest content of manganese has been determined in sediment from Hôrka (6243.6 ± 56.2 mg kg-1), while the lowest value has been obtained in the sediment from Kráľová (278.6 ± 3.9 mg kg-1). Using a modified Tessier’s procedure it was found, that manganese in sediments from Kráľová is associated mainly with the carbonate fraction (>50%), while in sediments from Lozorno and Hôrka it is associated primarily with the Mn and Fe oxide fraction (80% and 42% respectively).

A Novel Electrochemical Method for Analysis of Thin Metal Films and Bilayers for Application in the PCB Industry

The fabrication and assembly of printed circuit boards (PCBs) involves the layering of metals onto an insulating substrate prior to the addition of electronic components. The interfaces between these metal layers are often subject to metal-metal interdiffusion, formation of brittle intermetallics and corrosion, compromising the integrity of the PCB-component solder joints. We have recently developed environmentally sustainable, non-toxic methodologies for application of metal PCB finishes using Deep Eutectic Solvents (DESs) as a novel solvent medium.1-3 Here we focus on the characterisation of metal-metal interfaces in DES media quantifying interfacial structure, layer thickness and morphology using a range of electrochemical and microscopy techniques, including chronoamperometry, cyclic voltammetry (CV) and novel simultaneous thickness electrochemical potential (STEP) measurements coupled with neutron reflectivity (NR.) We have developed the STEP methodology to ascertain some, if not all, of the same information that NR provides. Deposition of Ag and Cu layers has been carried out in different configurations onto Au substrates and characteristic STEP traces are presented for each upon galvanostatic stripping. The STEP methodology facilitates the identification and quantification of each metal layer by galvanostatic dissolution, which is comparable with time resolved NR measurements. The characteristic features of the STEP measurements are discussed including the shape and potential of the dissolution trace. The degree of mixing between the layers is qualitatively determined from E vs. t traces, along with the layer composition and thickness for systems in which layers remain discrete. In summary, we present a new, accessible and inexpensive technique, which probes the thickness, composition and interfacial mixing between layers in PCB metal systems using DES electrolytes and galvanostatic stripping methodologies. [1] A. D. Ballantyne, G. Forrest, M. Goosey, A. Griguceviciene, J. Juodkazyte, R. Kellner, A. Kosenko, R. Ramanauskas, K. S. Ryder, A. Selskis, R. Tarozaite and E. Veninga, Circuit World, 2012, 38(1), 21-29. [2] K. S. Ryder, A. D. Ballantyne, D. Price and T. Perrett, The PCB Magazine, February 2012, 22-30. [3] A. P. Abbott, S. Nandhra, S. Postlethwaite, E. L. Smith, and K. S. Ryder, Phys. Chem. Chem. Phys., 2007, 9, 3735–3743. Figure 1

Interfacial Film Driven Morphological Evolution of a Mg Anode with Galvanostatic Cycling - Application to Mg Batteries

Controlling the morphology of metal anodes is required for the energy storage community to push beyond the limiting energy density of Li ion battery technology. Lithium metal and its tendency to form dendrites is one example where morphological control restricts the replacement of the limiting graphite intercalation anode. Increased energy density and elimination of the dendrite problem are two often argued benefits for moving to a battery chemistry based on Mg as opposed to Li. Few accounts exist in the literature describing what changes in the morphology of electrochemically cycled Mg electrodes occur at relevant rates and capacities necessary for viable metal anode function. We take on the challenge of describing morphology development and its impact at relevant electrodeposition and electrodissolution current densities (1 to 6 mA/cm2) during the first hundred cycles of a model Mg anode. In these studies, Mg electrodeposition is conducted onto Au and Pt electrodes of varying degree of orientation and texture in chloride containing ether-based electrolytes (i.e., chloroaluminate, MgCl2modified Mg complexes) to generate Mg surfaces with controlled facet populations exposed to the electrolyte. We demonstrate that substrate, electrolyte (anion and solvent), and electrodeposition parameters can be used to control the initial crystallographic orientation of these model anode films. First cycle galvanostatic stripping of a fraction of the anode film followed by atomic force microscopy and Kikuchi diffraction allows measurement of the degree of anisotropy and orientation dependence of dissolution. Analytical electron microscopy (cross-section) methods show that high rate galvanostatic cycling yields continual re-nucleation and growth of the cycled layer that readily incorporates electrolyte constituents as filmed interfaces. The altered surface energetics due to these interfaces results in the formation of voids and eventual porosity within the cycled layer. This structural evolution imposes impedance changes for that cycled layer that show up in the chronopotentiometric traces generated during cycling. We use the orientation information learned from diffraction and structural data to parameterize a phase field model that describes early stage evolution of both structure and electrochemical response. This work shows that morphology control extends to structural changes other than dendrite formation; changes that can potentially impact anode performance. The ramification of other performance limiting attributes such as porosity on lost metal capacity and lost mechanical integrity of cycled Mg will be discussed. This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000. Figure 1

Simultaneous and Sequential Extraction Protocols as Tools for Determination of Zinc Bioavailability in Dried Anaerobic Sludge

Abstract Production of unsettleable sewage sludge with high water content is one of the problems of intensification of industrial activities and environmental protection. Sewage sludge with low toxic metals concentrations can be utilized as fertilizer and soil conditioner in agriculture. For determination of metal bioavailability, a wide range of extraction protocols and fractionation analyses can be used. We studied the distribution and quantified the leaching and bioavailability of zinc from dried anaerobic sludge by simultaneous, multi-step and three different sequential extraction protocols. For determination of zinc, the galvanostatic stripping chronopotentiometry (SCP) and electrothermal atomic absorption spectrometry (ETAAS) were used. The distribution of Zn in sequential extraction protocols was determined using a fivestep chemical fractionation procedures (BCR, Tessier and Van Hullebusch protocols). The potential bioavailability (0.9% NaCl, 0.1 mol/dm3 HCl, 0.1 mol/dm3 HNO3, 0.1 mol/dm3 CH3COOH, 0.1 mol/dm3 Na2EDTA, 0.1 mol/dm3 CaCl2, 0.1 mol/dm3 MgCl2, 0.1 mol/dm3 (NH4)2C2O4.H2O extraction) and pseudo total (aqua regia extraction and ETAAS analyses) content of Zn in sludge was determined. The amount of aqua regia extractable zinc in sludge samples was 650 ± 12 mg/kg (d.w.). We found out that the zinc was extractable from anaerobic sludge in first hour of contact time for all tested agents. Zinc was extracted with highest efficiency by 0.1 mol/dm3 (NH4)2C2O4.H2O, 0.1 mol/dm3 HCl and 0.1 mol/dm3 Na2EDTA. Sequential extraction protocols showed that the maximum extractable amount of zinc 126.3 ± 2.6 mg Zn / kg d.w. was bound to organic matter and sulfides. High concentrations of zinc in residual fractions were leachable under extraction conditions of strong acids only.

Galvanostatic Stripping Chronopotentiometric Study for Determination of Selenium: Pharmacokinetic Application in Experimental Mice

The aim of this study was to determine the selenium content in various tissues of the mouse employing the galvanostatic stripping chronopotentiometry (SCP) technique and to investigate the distribution profile of selenium as well as its pharmacokinetics in a mouse model. The animals received 0.25 μg/g Se orally for 5 days. Samples of whole blood and various tissues comprising kidney, liver and brain were harvested from mice and then analysed for Se content employing the SCP technique. The SCP method was validated over Se concentration range of 10 – 100 ng/mL and showed good linearity (r² > 0.999). The precision (over 5 days) of the assay in various mouse tissues (liver, kidney, and brain) ranged from 0.03 to 2.9% with accuracy results that varied from -6.69 to 0.28%. The mean (n = 5) recoveries of Se from the mouse tissues ranged from 93.31 to 100.28%. The lower limit of Se detection in the mouse tissues was 0.2 ng/mL. The present method was successfully applied in evaluating the distribution of Se in various tissues as well as its pharmacokinetics in the mouse model. The Se tissue concentrations in the mouse model showed that the maximum Se levels in most tissues were attained within 3-4 days following its administration. Furthermore, the pharmacokinetic profile of Se in the mouse model indicates that the element is slowly absorbed from the gastrointestinal tract (GIT) reaching a plateau in 4 days and then it is slowly eliminated from the body with a half-life of about 4.5 days. The present SCP method was employed to analyse Se in various mouse tissues. The method was characterized by excellent performance parameters necessary for the determination of Se in biological matrices. Se distributes in whole blood as well as into various tissues of the mouse with high concentrations in the kidney and liver and low levels in the blood and brain tissues. The absorption of Se from the GIT was very slow and the data suggest that the elimination of Se seems to be through the kidney at a very slow rate as well. The data of the present study thus suggest that Se remains in the mouse body for a long period of time.

Estudio para la recuperación de herramientas recubiertas con nitruro de cromo mediante ensayos galvanostáticos

The improvement of the corrosion, wear and tribological behaviour by searching for new materials has entailed a greater expansion of PVD technology. Introduction of PVD systems in the industry is a real fact because this technique has been able to develop coatings whose response for many applications goes beyond used them until now. However the evolution of this technology requires minimize the economic costs in order to be a competitive process. A way to achieve this objective consists on recover the tool when the life time of the coating has finished or when deposition process has failed. Bringing this idea in the industry requires the stripping methods’ development due to surface’s tool must be clean —without coating’s remainders—, before a new deposition process. Current work shows galvanostatic stripping of chromium nitride coating deposited by two different PVD techniques: cathodic arc and magnetron sputtering. The electrochemical method has exhibited more advantages than chemical methods reported in literature, such a high sensitivity to detect final point of CrN coating stripping, capability to determinate structure of the coating —number of coatings, chemical composition, thickness…—, short times of the process and minimum damage on the substrate. These entire characteristics do possible think about a new deposition process on the stripped tool.

Electrochemical Preparation of Nanograin Sized Dy-Co-Bi Alloy Thin Films by Cyclic Electrodeposition and Their Magnetism

The electrochemical preparation of the nanograin sized Dy-Co-Bi ternary rare earth alloy thin films were investigated by cyclic electrodeposition at room temperature. The electrodeposition was carried out by cyclic electrolysis between two potentials with voltage scan rates in the range from 0.01 to 0.10 V s -1 . Experimental results indicated that the optimum cyclic potentials were the upper potential within a range from -0.80 to -1.20 V and the lower potential within a range from -2.30 to -2.60 V, and only low DyCl 3 concentrations were suitable to prepare homogeneous, crack-free, and nano-sized Dy-Co-Bi thin films. The potentiostatic and galvanostatic stripping techniques were used for electrochemical characterization of the prepared Dy-Co-Bi thin films. The prepared thin films were amorphous characterized by X-ray diffraction. The magnetic measurements of the nanograin sized Dy -Co-Bi thin films showed that they had a spin-glass-like behavior and an unusual characteristic time at 100 K.

Determination of cadmium, lead, and copper in margarines and butters by galvanostatic stripping chronopotentiometry.

A galvanostatic stripping chronopotentiometric (GSCP) method for the simultaneous determination of cadmium, lead, and copper in commercial margarines and butters is described. Quantitative analyses of heavy metals in the mineralized fat samples, except standard addition method, were carried out automatically. The mean concentrations of Cd(II), Pb(II), and Cu(II) in different types of margarines and butters varied from 9.1 to 26.2, 9.2-14.2, 298.2-364.0 microg x kg(-)(1), respectively, that is below the legal requirements. The detection limits are 0.02, 0.02, and 0.06 microg x L(-)(1) for Cd(II), Pb(II) and Cu(II), while the reproducibilities are 3.3, 5.7, and 2.0%, respectively. The comparable precision (RSD = 0.76-4.5 and 0.87-4.9%) and recovery (96.7-102.2% and 96.1-103.2%) for the proposed GSCP and standard GFAAS methods, demonstrate the benefit of GSCP method in the routine analysis of heavy metal ions in fats.

Chemical and phase compositions of zinc + nickel alloys determined by stripping techniques

Zinc-nickel alloys were obtained from a bath with a high concentration of ammonium chloride that was previously used to prepare the alloys under industrial conditions. These industrial alloys were characterized with the usual ex situ techniques, while in the present case potentiodynamic and galvanostatic stripping methods were used. Three substrates with different characteristics were selected and in all cases the stripping techniques were shown to be a reliable method for fast determination of both the chemical and phase composition of electrodeposited zinc-nickel alloys. With the plating conditions used in the present work, the oxidation potentials of α- and η-phases coincided with those observed in other cases, while the γ-phase was oxidized at a significantly more positive potential. This fact could be attributable to a very low value of the exchange current density of zinc from this phase. Moreover, the analysis of the composition of the alloys with different thicknesses revealed that the deposition of the nickel-rich α-phase was favoured in the initial stages of the process.

A study of galvanic corrosion during coulometric dissolution of galvannealed steel

Galvanostatic stripping is used as a coating structure analysis technique for galvannealed steel sheet. The thickness of the coating determined in this way is underestimated by about 20% compared to the thickness measured by chemical dissolution. This study has shown that pH, electrolyte composition and current density affect coulometric measurements. Because of additional galvanic current between zinc rich zinc-iron phases and more noble phases (iron rich zinc-iron phases), hydrogen evolves during anodic stripping. This is especially observed at low current density. Also the duration of coulometric anodic dissolution cannot give the actual coating thickness. Potentiodynamic analysis tends to show that potentials observed on galvanostatic stripping curves are the result of different iron-zinc phase layers.

Determination of manganese in water samples by galvanostatic stripping chronopotentiometry in a flow-through cell

A flow-through electrochemical cell, with a porous working electrode made of crushed glassy carbon, was used for the complete electrochemical deposition of the MnII species from a flowing sample solution at +1.2 V versus an Ag–AgCl reference electrode. The deposit was then dissolved galvanostatically by applying a current of between –50 and –1000 µA while monitoring the potential of the working electrode. The measured potential values were mapped into the memory of a computer, enabling the dt/dE versus E relationship and the corresponding chronopotentiometric transition times to be obtained directly. The analyte concentration was directly calculated from this value by making use of Faraday's law. The flow rate, deposition potential, pH and dissolution current were optimized. The influence of Pb2+, Fe2+, Fe3+, surfactants, EDTA and humic acids on the analytical signal was studied. The method elaborated was used for analyses of water samples.

Absolute analysis of trace metals through galvanostatic stripping chronopotentiometry with signal accumulation

An electrochemical flow-through cell with a porous working electrode made of vitreous carbon particles and plated with mercury was used for the absolute determination of Pb using galvanostatic stripping chronopotentiometry in a flow system. After completing the potentiostatic electrodeposition of the analyte from the flowing sample solution the flow was stopped and oxygen in the solution inside the pores of the electrode was removed by reducing it. The deposit was then stripped by applying a constant current of 50 to 1000 μA and the measured potential vs time (E vs t) data were converted to the dt/dE vs E dependence by a memory mapping technique. Owing to the thin layer properties of the cell, the stripping/deposition steps could be repeated reproducibly enabling the accumulation of the signals while improving the signal to noise ratio. The method was also found to be suitable for the simultaneous determination of Cd, Pb and Cu. The experimental conditions, computerized data handling and signal processing have been investigated. Water, grass and sediment samples were analyzed for traces of Pb.

Composition Determination of Electrodeposited NiSn and PbSn Alloys Using Stripping Voltammetry at a Rotating Ring‐Disk Electrode

A new method has been developed for determining the composition of and alloys electrodeposited on a rotating disk electrode. The method makes use of a ring‐disk assembly combined with potentiodynamic or galvanostatic stripping voltammetry. According to the method the alloy is first deposited on the disk electrode and subsequently transferred to a stripping medium where it is anodically dissolved. During disk dissolution, Sn in the alloy dissolves in the +2 oxidation state and further oxidizes to Sn4+ on the ring electrode. The disk charge is proportional to the total amount of deposit while the ring charge is proportional to the total amount of Sn in the deposit. In addition to permitting composition determination, this method provides information about the phase structure of the electrodeposited alloy.

Electrodeposition of zinc + nickel alloy phases and electrochemical stripping studies of the anomalous codeposition of zinc

The electrodeposition of zinc + nickel alloy phases has been studied on platinum, glassy carbon and nickel film electrodes to investigate the depolarization and the anomalous codeposition of zinc. A model involving the coupling of charge transfer and heterogeneous interaction is proposed to calculate the partial Zn currents during the deposition of the α-phase of Zn + Ni in the absence of mass transfer limitations. Potentiodynamic and galvanostatic stripping techniques have been used to characterize the chemical and phase compositions of Zn + Ni films deposited under various conditions. The stripping results demonstrate the strong inhibition of nickel deposition by submonolayer amounts of underpotentionally deposited zinc. Earlier models on anomalous codeposition of zinc are examined critically, and the new experimental and theoretical results are used to show that anomalous deposition is caused mainly by two factors. They are the effect of electrode potential on the deposition of various zinc + nickel phases from the same electrolyte and the influence of underpotentially deposited zinc on the polarization for nickel deposition.

Potentiodynamic and Galvanostatic Stripping Methods for Characterization of Alloy Electrodeposition Process and Product

Potentiodynamic and galvanostatic stripping techniques have been applied towards the characterization of zinc‐nickel alloy deposition process and product. The current‐potential relations required to recover the equilibrium and kinetic properties of alloys have been obtained for the eutectic, solid solution, and intermediate phase types of alloys. The galvanostatic stripping response shows a series of plateau regions, and the potentiodynamic response reveals a peak structure. These stripping responses have been employed to determine the chemical and phase compositions of electro‐deposited zinc‐nickel alloys, evaluate their corrosion resistance, and estimate the equilibrium potentials of various zinc‐nickel phases (α, γ, and η‐phases). The zinc‐nickel deposition process has been characterized through evaluation of partial currents due to alloy components and the current efficiency of alloy deposition. The design of multiple layered zinc‐nickel alloy films for the protection of steel is discussed on the basis of the accelerated corrosion behavior of the γ‐phase and the equilibrium potentials of the phases.

Determination of bismuth by electrochemical stripping analysis: Elimination of interferences by using a mercury film electrode modified with tri-n-octylphosphine oxide, and application to copper alloys

A mercury film electrode modified with a film consisting of tri-n-octylphosphinc oxide in a poly(vinyl chloride) matrix is used for a galvanostatic stripping determination of bismuth in copper and copper alloys. The method can be used to determine from 0.002 to 0.5% of bismuth. It is very selective, simple and rapid. The precision and accuracy are good and the only serious interference is caused by tin(IV).

Determination of arsenic by galvanostatic stripping analysis and its application to steels

Arsenic can be determined by galvanostatic stripping analysis with a modified gold-film electrode, prepared by simultaneous electro-deposition of gold and arsenic on a glassy-carbon support. This initially deposited arsenic is stripped from the film before the electrode is used for the analysis, but its presence during the formation of the film apparently leads to uniformly distributed crystallization sites for the subsequent determination of arsenic, so that the precision of the determination is better than that obtained with an unmodified gold-film electrode. The pre-electrolysis is performed potentiostatically in a stirred solution of 7 M hydrochloric acid, at a potential from −0.10 to −0.35 V ( vs. Ag/AgCl). If the galvanostatic stripping step is performed in quiescent solution after a 6-sec rest-period, at a current of 2–12 μA, then for a 100-sec pre-electrolysis time the calibration curve is linear up to an arsenic concentration of about 2 μg ml and the limit of determination is 8 ng ml . In the analysis of steel, the arsenic must first be separated by selective extraction of arsenic(III) bromide into toluene and back-extraction into the supporting electrolyte. A single extraction is virtually 100% quantitative. The relative error of the determination in steels is a few per cent and the results are in good agreement with the certified values for reference materials and with the results obtained by X-ray fluorescence analysis.

Anion Effects on the Dissolution of Steel in ECM Binary Electrolyte Systems

Steady-state potentiostatic polarization, galvanostatic stripping, and current efficiency measurements were carried out on mild steel (Type 1020) anodes in O2‐stirred solutions of to which increasing amounts of were added. A salt layer is formed at steel anodes in solutions. A precipitate is deposited from this salt layer onto the anode surface and is converted to a protective anodic film at sufficiently anodic potentials. In the presence of Cl− ions, the salt layer becomes more soluble and the protectiveness of the anodic film is lessened. With increasing Cl− ion concentration, a family of curves with increasing current in the passive region is obtained. If the anodic film is formed by the direct oxidation of the anode surface (as in mixtures), a different family of curves is obtained. For the case where a noncomplexing, film-dissolving anion, such as , is present , a third family of curves is found. This behavior is related to the interaction between the type of film‐dissolving anion present in solution, and the type of anodic film formed on the electrode surface.

Electrochemical Measurement of the Available Surface Area of Carbon‐Supported Platinum

The measurement of charge consumed in the galvanostatic stripping of adsorbed oxygen or hydrogen from carbon‐supported platinum surfaces gave a measure of the area of platinum in contact with solution. A combination of the two methods proved superior to either used alone. The combination compensated for the charge consumed on the carbon with sufficient accuracy to permit measurements down to the region where the platinum area is 1/100 of the support area. Comparison with x‐ray diffraction measurements suggests that, with high platinum concentrations on low area carbons, standard platinum deposition techniques yield electrodes in which much of the platinum surface is not in contact with solution.