Anodic Dissolution of Zinc in Potassium Nitrate

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Anodic polarization of Be in both aqueous and nonaqueous media leads to a spalling or disintegration of the anode. The disintegration product is composed of shiny, metallic, crystalline particles embedded in a white brittle mass [BoO and/or Be(OH)2] as viewed under an optical microscope. Microstructural studies using scanning electron microscopy provide further proof for the nature and identity of the Be particles. Valency determinations from weight loss measurements give values between 0.34 and 1.75. These anomalous values are attributed to the production of Be by anodic disintegration rather than to a disproportionation reaction of monovalent Be. The "apparent" valency appears to be more a function of the nature of the anion than of the solvent. The apparent valency approaches 1.0 in LiC104/EtOH and KC1/aq and is fractional in LiC1/MeOH. Beryllium is passivated both in aqueous and nonaqueous media containing NO3-ions. Beryllium passivated in NaNOs/ MeOH has no electronic conduction; the surface when examined optically appears dark with shiny Be crystals on it. Thus anodic disintegration occurs even at potentials where passive oxides predominate on the surface.The seeming inapplicability of Faraday's law for the anodic dissolution of Be, Zn, Mg, A1, etc. has led to several inquiries into the fundamental aspects of uncommon valency (1-4). The formation of univalent cations as the first stage during anodic dissolution is partly accepted in the case of A1, In, etc. (5, 6 (DMF). Anodic disintegration studies in this laboratory were supplemented with microstructural studies using an optical microscope in the past. The preset%t study utilizes a scanning electron microscope also, which has a high resolution and large depth of focus. ExperimentalThe Be anodes had a purity greater than 99.00%. Circular disks of Be were machined, polished with emery paper, cleansed in an ultrasonic cleaner, degreased with CC14 and acetone, and dried in a desiccator. A specially constructed Teflon holder was used to hold these leak-proof Be disks in the electrolyte. The nonaqueous solvents methanol, ethanol, and dimethyl formamide were 99.9% pure. They were purified further by using Davison Type 4A molecular sieves. Valency determinations were carried out as described earlier (8). Prepurified N2 provided an inert atmosphere in the electrolysis cell. The water content of the electrolyte was determined at the end of each valency study by Karl-Fisher titrations.Several potential sweep experiments were carried out. Though a steady-state galvanostatic study is extremely simple the potential sweep method enables the evaluation of current density at all potentials within the range of interest and hence the pursuit of passivation stages in the reaction. A Wenking potentiostat externally modulated by an Elron function generator was used. The cyclic current (i) vs. After each valency study, the polarized electrodes were washed with methanol and dried. These were then used for optical and scanning electron microscopic (SEM) studies. In ce...

Section: Discussionmentioning

confidence: 55%

Section: Discussionmentioning

confidence: 62%

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Polarization Characteristics and Anodic Disintegration of Beryllium in Nonaqueous Solutions

Vaidyanathan

Straumanis

James

1974

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“…(D) At least in the case of chloride solutions, the presence of cuprous ion could be verified quantitatively. All these factors indicate that a distintegration mechanism, which has been proposed primarily for more reactive metals (beryllium, magnesium, cadmium, zinc) at low current densities (13)(14)(15)(16), is not likely to be of importance in the present anodic dissolution process. Measured apparent valences tended to reach a constant limiting value at high current densities.…”

Section: Discussionmentioning

confidence: 94%

Stoichiometry of Anodic Copper Dissolution at High Current Densities

Kinoshita

Landolt²,

Müller³

et al. 1970

l'he influence• of current density, flow rate and electrolyte composition on the stoichiometry of anodic copper dissolution was investigated under conditions comparable to those of electrochemical machining. Weight loss measurements, x-ray diffraction and chemical analysis were used for the characterization of the dissolution reaction. A sharp change in dissolution mechanism.coincidedwith the transition from active to transpassive dissolution. For active dissolution, an apparent valence of the dissolution process of two was found in sulfate and nitrate electrolytes; and of one in chloride electrolytes. For transpassive dissolution, mixed valences lying between 1 and 2 were found in all electrolytes. The mixed valences are interpreted to result from the simUltaneous production of monovalent and divalent reaction products, some of which are in solid form.

“…work of Straumanis and co-workers in Ref. (31)(32)(33) and in other works referenced in the abovementioned review article (30)], the suboxidation state finds support in numerous test results (25-80).…”

Section: To Explain the Present Results We Propose The Following Simu...mentioning

confidence: 74%

A Limitation to the Mixed Potential Concept of Metal Corrosion: Copper in Oxygenated Sulfuric Acid Solutions

Andersen

Ghandehari

Eyring

1975

The corrosion of copper in oxygenated sulfuric acid solutions was studied by means of weight‐loss and polarization curves. At a given potential, the rate of copper dissolution is greater in the presence than in the absence of oxygen reduction, which is contrary to the conventional theory of mixed potentials. An explanation of this phenomena is proposed on the basis of chemical attack by dissolved oxygen on the Cu+ ions which are intermediates in the electrochemical copper oxidation scheme. The model is further verified by results of varying the solution agitation rate, acid strength, and oxygen partial pressure.