Corrosion of superalloys in molten glass - Electrochemical characterization of the passive state
Résumé
In the glass industry, the lifetime of many metallic parts in contact with molten glass is mainly controlled by high temperature corrosion. The degradation of the alloys immersed in the molten glass is governed by oxido-reduction reactions. Then electrochemical techniques were developed for the characterization of the alloys corrosion. The aim of this paper is to describe the corrosion behavior of superalloys containing about 30% of chromium in a soda-lime molten glass at 1050°C and to determine the mechanism of passivation. Classical electrochemical methods with adapted experimental apparatus are suitable for the characterization of alloys corrosion in molten glasses. The electrochemically measured corrosion rates are in good accordance with the thickness losses of an industrial component. All the tested high chromium alloys are spontaneously in an active state, corresponding to a corrosion rate of a few cm/year. In the passive state, these alloys can be protected by the presence of a thin chromia layer on their surface. Chromia protection allows at least a one magnitude decrease in corrosion rates. The three following methods are efficient to reach a passive state : addition of oxidizing agents to the glass, temporary anodic protection and preoxidation. The erosion phenomena has been shown on a rotating electrode. In the case of a passive scale damage, a favourable galvanic coupling allows a restoration of the protective layer.
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