Study on Electrochemical Pickling

Behavior of Ferrosoferic Oxide in Reduction or Dissolution in Sodium Chloride Solution

Abstract

In order to clarify the removal mechanism of the scale on hot rolled strip steel by electrolytic reaction in sodium chloride solution, the behavior of ferrosoferic oxide, which is a main component of the scale, in reduction or dissolution was investigated.
Ferrosoferic oxide is not dissoluved by anodic dissolution only. When it is subjected to the treatment of catholic reduction, however, it reduces into the “amorphous substance” which can not be identified with X-ray diffraction, When the “amorphous substance” is subsequently subjected to the treatment of anodic dissolution, it dissoluves in the form of ferrous ions into the electrolyte.
The reactions is thought to proceed as shown below:
Anodic reaction: 2H₂O→O₂+4H⁺+4e^-
Cathodic reactions: Fe₃O₄+e^-→Amorphous substance
Anodic dissolutions subsequent to catholic reduction:
Amorphous substance →Fe₃₊+e^-
Amorphous substance →Fe₃O₄+e^-
2H₂O→O₂+4H⁺+4e^-
The dissolution rate of the “amorphous substance” increases with the increase of the temperature and the decrease of pH of the electrolyte.