EFFECTS OF ALUMINUM ION DISSOLVED IN ELECTROLYTE ON PROPERTIES OF ANODIC OXID FILM ON ALUMINIUM

EFFECTS ON PROPERTIES OF D.C. ANODIC OXID FILM IN SULPHURIC ACID PROCESS

Abstract

We have previously reported1) on the effects of working-condition on the properties of anodic oxid film on aluminum in this journal. In these experiments, however, we used the fresh sulphuric acid as the electrolyte. But, in the production practice, the electrolyte may be not always fresh, and therefore the effects of aluminum ion dissolved in electrolyte can not be neglected.
In this report, we studied these problem in our production shop and our laboratory. At first, we measured the increse of dissolved aluminum ion and th decrease of free sulphuric acid by daily analysis of electrolyte of our production shop. And then we studied the effects of aluminum ion which was dissolved in 15% sulphuric acid by adding aluminum sulphide on the properties of anodic oxid film.
The results are as follows.
(1) The increase of dissolved aluminum ion and the decrease of free sulphuric acid are proportional to the anodized area.
(2) The increase of dissolved aluminum ion is proportional to the decrease of electric conductivity of electorolyte
(3) The dissolved aluminum ion has not so remarkable effect on the thickness of film.
(4) As for the corrosion resistance of anodic oxid film, the small amount of dissolved aluminum ion has rather better effect, but it gradually lowers as the dissolved aluminum ion increases more than 0.2%.
(5) The abrasion resistance of anodic oxid film rapidly lowers as the dissolved aluminum ion increases.