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Dissolution and electrochemical properties of molybdenum carbide (Mo2C) in basic solutions

Abstract : The dissolution and electrochemical properties of molybdenum carbide were investigated using a number of electrochemical techniques, including general corrosion tests (GCT), linear voltammetry (LV), potential controlled electrolysis (PCE) and Scanning Electrochemical Microscopy (SECM), in basic media (0.5−4 M NaOH and 1 M NaHCO3/Na2CO3, pH 9.1–11.3). It was shown that the Mo2C corrosion potential (Ecorr) shifted towards negative values from -0.39 to -0.96 V/SCE with an increase of the OH- concentration and did not depend on the CO32- concentration in the electrolyte. LV measurements in carbonate buffer (pH 9.2), evidenced three potential regions: passivation from Ecorr to -0.2 V/SCE, pseudopassivation from -0.25 to 0 V/SCE and anodic dissolution (transpassivation) at E > 0.1 V/SCE. The potentials delimiting the mentioned regions decreased with the increase of the OH- concentration, becoming undistinguished in 2 M NaOH. The Mo2C dissolution rate (kdiss) in the transpassive state was estimated using LV data. In 4 M NaOH at -0.1 V/SCE, kdiss reached 430 mg cm-2 h-1 and decreased with the decrease of the OH- concentration and the electrolysis potential. The Mo2C dissolution current efficiency varied between 12 and 13 F mol-1 Mo2C, proving the formation of the intermediate products of a carbon oxidative degradation during PCE. The presence of C2O42- and non-identified aromatic compounds in the electrolytes after Mo2C dissolution was ascertained, using capillary zone electrophoresis. Scanning electrochemical microscopy (SECM) confirmed the formation of a pseudopassive film and demonstrated the increase of its thickness with the increase of the applied potential. The effect of the presence of Mo2C on the irradiated UC fuel dissolution rate and the mechanisms involved are discussed.
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Submitted on : Monday, April 14, 2008 - 3:13:59 PM
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A. Maslennikov, C. Cannes, B. Fourest, N. Boudanova, Vincent Vivier, et al.. Dissolution and electrochemical properties of molybdenum carbide (Mo2C) in basic solutions. Radiochimica Acta, R Oldenbourg Verlag GMBH, 2007, 95, pp.399-408. ⟨10.1524/ract.2007.95.7.399⟩. ⟨in2p3-00273136⟩



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