Toshimitsu Uchiyama

Ellipsometric Determination of Greasy Layer on Aluminum

The greasy layer remaining on aluminum as rolled is usually vaporized during annealing process; and contact angle is most commonly measured to check if the surface is free from the organic contaminations. In this paper, the possibility and limitations of applying ellipsometry for such a measurement were examined in the hope that the thickness of the greasy film might be determined more quantatively. Because of an complicated calculation of two-layer system consisting of both aluminum oxide film and the grease layer, an approximate method was used. The validity of this approximation was ascertained by measuring the built-up film of stearic acid on electropolished aluminum, the thickness of which had been previously known. The variation in the greasy layer thickness, thus measured with the specimens heated at variety of temperatures, indicates that the remaining oil on aluminum is almost completely depleted at temperatures higher than 400°C and then oxidation of aluminum takes palce instead.

Adhesion of polyethylene to aluminum heat treated in an inert gas atmosphere

The behavior of oxide films and oil existing on aluminum surfaces, heat treated in an inert gas atmosphere, and their effect on the adhesion of polyethylene to aluminum were investigated. The experimental results were compared with those obtained in aluminum heat treated in the air. The results obtained were as follows:(1) The growth rate of oxide films in the air strongly depended on the temperature and the film grew more than 100 A in thickness at 500°C for 5hr. However, the same heating condition produced only 50 A thick films in the inert atmosphere.(2) When heating was done in the air, the fluidity of oil decreased and the fixed oil layer was found as heat treatment proceeded. However, the heat treatment in the inert atmosphere resulted in the slight change of oil properties and produced a small amount of the fixed oil layer. Further, the oil removal from the surface did not occur rapidly in the inert atmosphere.(3) The heat treatment in the air accompanied the rapid oxide film growth and the considerable oil alteration. This resulted in a significant decrease in the peeling strength of the polyethylene film and shifted the peeling place from the polyethylene side to the oxide films side or the solid oil side. Contrary to this, the heating in the inert atmosphere did not accompany the strong oxide growth and the considerable oil alteration. Thus, the peeling strength, mainly associated with the cohesive failure at the polyethylene side, did not decrease rapidly and the shift of the peeling place was not noted.