The Measurement of the Composition of Surface Film on the Electrolytically Treated Steel Sheet in Chromic Acid Solution

Abstract

In order to determine the elemental Cr in the hydrated Cr oxide and the metallic Cr separately on the surface film of the electrolytically treated steel sheet in the chromic acid solution containing some catalyzer, we inuestigated the conditions of alkaline dissolution of the Cr oxide film and the metallic Cr using a fluorescent X-ray method and a coulometric method.
Furthermore, we calculated the thickness of the Cr oxide film by the measurements of the weight and the specific gravity of the Cr oxide film. The following results were obtained:
(1) A little metallic Cr is dissolved by immersion in NaOH solution containing H₂O₂.
(2) Metallic Cr is scarcely dissolved by immersion in 7.5 N NaOH solution at 90 to100°C for 5 min.
(3) In a coulometric method current efficiency in anodic dissolution of the metallic Cr is not affected by the NaOH concentration, anodic current density, interelectrode distance and thepresence of the Cr oxide, and shows about 100%.
(4) The weight of the Cr oxide corresponds to about 3 times of the weight of the elemental Cr in the Cr oxide and the specific gravity of the Cr oxide is 2.1-2.2.