Dissolution of magnesium was studied using an electrochemical flow cell combined with online analytics. The method has high sensitivity and congruency between electrochemical polarization experiments and magnesium concentrations detected downstream via inductively coupled plasma -mass spectroscopy (ICP-MS). The method used allowed quantification of magnesium dissolution during anodic and cathodic polarization and also without external currents, i.e. determination of dissolution rate at open circuit, which is not accessible by electrochemical techniques. The relationship between the applied current, and dissolved magnesium measured is presented and discussed in the broader context of past and recent works studying magnesium corrosion. The development of a surface film during anodic dissolution is described on the basis of an inventory of currents measured and applied. There exists a high demand for increased usage of magnesium (Mg) as a structural material in a range of technological applications where weight reduction is beneficial, such as transportation and portable electronics. Corrosion resistance of Mg and its alloys continues to be a major barrier to industrial uptake of Mg as a structural material. The dissolution characteristics of Mg therefore remain an important research topic, particularly in the present period where there are conflicting perspectives in the literature on the mechanisms of Mg dissolution in aqueous electrolytes. [1][2][3][4][5][6][7][8][9][10][11][12] In regards to the conflicting perspectives, they are nominally centered on the proposed theory of unipositive Mg (Mg + ), for which Petty et al.1 is the only paper to claim evidence for its existence. Interestingly, the evidence presented by Petty was descriptive with no experimental data, which was not atypical of the era. To date, no compounds containing Mg + have been isolated under atmospheric conditions, nor has any spectroscopic data ever been presented confirming even the transient appearance of such a species. This is important to note, because theories based on the existence of Mg + have been proposed in more recent years in the field of corrosion research, with no reasonable proof of its existence, 2-4,13-15 in spite of several historical papers providing alternative explanations to a Mg + theory. [16][17][18][19] Of relevance to Mg corrosion studies, the Mg + theory is purported to account for the so-called 'negative difference effect' (NDE), which is the phenomenon by which the amount of hydrogen evolved from a Mg electrode increases as the electrode potential is polarized anodically, to more noble potentials. According to the Mg + theory, superfluous hydrogen arises from a chemical reaction of Mg + with water at some unknown distance away from the metal surface. However, several alternate explanations of the NDE exist, with one plausible explanation for the NDE being the notion that the cathodic reaction is catalyzed by Mg dissolution as outlined recently, 10 which is consistent with the classic works noting enhanced 'reduci...

The dissolution of magnesium (Mg) has been investigated with an electrochemical flow cell coupled to downstream analysis. The setup allows for polarization experiments and simultaneous determination of the amount of dissolved magnesium ions via inductively coupled plasma -mass spectroscopy (ICP-MS). Additionally, Mg dissolution was compared to hydrogen evolution measurements in the flow cell and also in standard beakers. Experiments were performed in unbuffered NaCl and in buffered solutions of various pH to determine the influence of the pH on surface film stability and Mg dissolution. In borate buffer (pH 10.5), Mg(OH) 2 was found to be more stable than in unbuffered electrolyte. In the flow cell, the negative difference effect (NDE) was absent for low anodic polarization currents in a neutral buffered solution, whilst high anodic polarization currents and unbuffered electrolytes favored its existence. In beaker experiments, strong NDE was observed in a pH 10.5 buffer, and also in pH 7 and 3 buffers, but only at higher applied currents where the buffering capacity was locally overwhelmed. These observations validate the importance of the pH in near surface regions with respect to the stability of Mg-surface films and subsequent NDE.

a b s t r a c tMulti-element dissolution analysis of amorphous Fe 50 Cr 15 Mo 14 C 15 B 6 in 0.1 M H 2 SO 4 was investigated electrochemically and by coupled online mass spectrometry. We fully discuss the most important aspects of the application of the newly-developed methodology to study complex multi-elemental alloys. The resulting partial dissolution rates of Fe, Cr and Mo reflect the passive behavior and are compared to the measured total current density as function of time. The deviations between the added elemental dissolution currents and the measured total current density are discussed. Furthermore, the inferred growth of oxide thickness was correlated to results obtained from surface analysis.

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Ion transport through a Ca30 glass, a sodium ion (Na + ) conductor, has been induced by bombardment with a potassium ion (K + ) beam. The measurement of back side ion currents as a function of the ion beam kinetic energy by means of the recently developed BIIT (bombardment induced ion transport) approach allows determining the conductivity of the material. Measurement of this conductivity as a function of the temperature allows deriving the activation energy for ion transport as 0.99 eV ± 0.01 eV in perfect agreement with impedance spectroscopy. While the conductivity as well as the activation energy clearly correspond to the bulk property, i.e. the transport of Na + , depth profiling of the glass sample after the BIIT experiment exhibits K + profiles reaching up to 100 nm into the glass. Ultimately, modeling of the experimental data by means of the Nernst–Planck–Poisson theory provides access to a quantitative understanding of the conductivities and the diffusion profiles under the condition of competing Na + /K + ion transport.