Dissolution and Protection of Aluminium Oxide in Corrosive Aqueous Media—An Ellipsometry and Reflectometry Study

Abstract

Dissolution of alumina has been studied from wafers in aqueous solution by means of ellipsometry and reflectometry. It was discovered that the dissolution of aluminium oxide is promoted by ethanol amines like N,N-bis(2-hydroxyethyl)glycine and triethanolamine, and that this dissolution is retarded by sodium dodecyl sulphate (SDS) and stopped by sodium dodecyl phosphate (SDP). The protective property of SDP to alumina is in perfect agreement with earlier found results which showed that SDP efficiently hinders the oxidation of aluminium pigment flakes in alkaline aqueous solution. Ethanol amines are used to regulate the pH in waterborne paints and printing ink formulations. However, the aggressive properties of ethanol amines to alumina are a problem for these kinds of formulations. This may be attributed to the formation of water soluble complexes between ethanol amines and Al(III). To increase the shelf life of aluminium pigments in waterborne formulations in the future, the ethanol amines then need to be replaced by other, less aggressive, bases if possible.

Keywords:

• Aluminium oxide
• ellipsometry
• ethanol amines
• reflectometry
• sodium dodecyl phosphate
• sodium dodecyl sulphate

The authors are grateful to Dr. Johan Hurtig and Lic. Eng. Björn Wickman at Chalmers University of Technology for help with preparation of the alumina modified silicon wafers in the clean room. The knowledge foundation and Carlfors Bruk AB are acknowledged for financial support.

Notes

Part of the special issue, Surface and Colloid Chemistry Without Borders: An International Festschrift for Professor Per Stenius on the Occasion of His 70th Birthday.