Resumo

RANDHAWA, Navneet Singh  e  KATIYAR, Prvan Kumar. Potentiodynamic Polarization Behavior and Microscopic Examination of Tungsten Carbide Hard Metal Materials in Supported Ammoniacal Medium. Port. Electrochim. Acta [online]. 2020, vol.38, n.3, pp.185-200. ISSN 0872-1904.  https://doi.org/10.4152/pea.202003185.

Electrochemical methods for the recycling of tungsten carbide (WC-10Co) resources suffer from passivation in the acidic medium caused by WO₃ and also in NaOH electrolytes, due to hydroxide formation. We found that an ammoniacal solution is a promising electrolyte for sustainable electrochemical dissolution of both tungsten (W) and cobalt (Co). The ammoniacal medium performs greatly when supported with Cl^-, SO₄^2- and CO₃^2- ions. Poor dissolution/corrosion tendency of WC-10Co in a diluted NH₄OH solution enhanced many folds in the presence of Cl^-, SO₄^2- and CO₃^2- ions. Among these supporting ions, Cl^- emerged as the most suitable for the electrochemical leaching of W and Co from the WC-10Co, accompanying the least noble behavior of WC-10Co. An electrolyte composed of 150 g/L of ammonia and 5% (w/v) of NH₄Cl yielded the maximum anodic current density. Microscopic examination of the electrochemically treated samples shows scattered active sites responsible for the oxidative dissolution of WC-10Co. The usefulness of W and Co dissolution in ammonia-additive salt followed the order NH₄OH-NH₄Cl>NH₄OH-(NH₄)₂SO₄>NH₄OH-(NH₄)₂CO₃.

Palavras-chave : ammoniacal electrolyte; electroleaching; electrodissolution; potentiodynamic; tungsten carbide.

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