Studies on Co-ordination Numbers of Aluminum and Sulfur in Aluminum Anodic Coatings by Fluorescent X-ray Method

Fundamental Studies on Coloring of Aluminum (Part 2)

Abstract

It was reported in the previous paper that the anodic coating of aluminum, which had been prepared from sulfo-salicylic acid or sulfuric acid solution as electrolyte, showed amorphous Al₂O₃, but at was proved by X-ray diffractiometry to be changed to γ-Al₂O₃ by heating at 800°C.
Various methods have been proposed in order to investigate the atomic bond an the amorphous state. It is believed that fluorescent X-ray method would be available for measurement of co-ordination numbers of atoms. Then, the authors attempted to determine chemical shift of the co-ordination numbers of Al and S in the above amorphous Al₂O₃ for measurement of these numbers.
The results obtained were as follows:
1) Both of aluminum atoms in the anodic coatings prepared from sulfo-salicylic acid and sulfuric acid solutions as electrolytes, had co-ordination numbers of 6-fold or 4-fold like that of γ-Al₂O₃. It proved that there was no significant difference in appearance between the both coatings.
2) The co-ordination numbers of sulfur in both of the anodic coatings were measured in the same manner as in aluminum. It was shown that the bonding of sulfur atoms was similar to that of SO₄^2--bond.