ELectrokinetic studies on oxidized aluminium surfaces

Abstract

Phenomena occurring at the metal- and metal oxide-electrolyte interface are of enormous fundamental and technological interest. This paper reports experimental and theoretical findings on electrokinetic potentials obtained for aluminium and aluminium oxide surfaces in contact with simple electrolytes. The correlation of electrokinetic parameters with corrosion phenomena is a new development, which the authors regard as having wide implications in surface oxidation studies and related fields. The streaming potential technique has been used to determine zeta potentials. An automatic recording apparatus has been employed for quick measurement of electrokinetic parameters, a capability which is essential for the study of reactive surfaces and/or substrates. This apparatus records streaming potential-pressure curves in approximately 10–20 s (or less if desired) as compared to about 50 min necessary by older methods. Aluminium metal, oxidized aluminium, and pure alumina powders have been investigated. Adsorption isotherms for simple and complex ions, respectively, and an explanation of the specific adsorption phenomena have been deduced from electrokinetic measurements. The electrokinetic behaviour of aluminium oxidized in air or water is found intermediate to that of aluminium metal and pure alumina, respectively. The isoelectric points obtained at constant ionic strengths of 1 × 10 −3M range from a pH = 6 to pH = 9, and depending on the extent of surface oxidation, the former have been shown rather sensitive functions of pH. An attempt to correlate the degree of surface oxidation to the observed data has been made.