Makio Mizuno

Degreasing of Metals by Organic Solvents

This paper deals with the nature of desorption of fatty acid molecules from metal surfaces. In the experiments, the metals such as Cu, Al, and Fe are immersed in a solution of n-hexadecane to which a small percentage of the radiolabeled palmitic acid is added, and then degreased by being immersed in a solution of, for example, petroleum benzine, acetone, trichloroethylene or alkali cleaning liquid. The radioactivity of the palmitic acid remained on the metal surface is measured by using Geiger-Muller counter with varying duration of cleaning. As a result, the desorption curves for various organic solvents under a few cleaning conditions are obtained. These desorption curves can be evaluated by both the velocity constant of desorption and the fraction of finally residual molecules. The results obtained from these experiments are summarized as follows:(1) Perfect degreasing can not be attained by any organic solvents, but the better results are obtained by alkali cleaning or electrolytic polishing.(2) As for a solvent of trichloroethylene, the velocity constant of desorption by ultrasonic cleaning is about thirteen times as higher as that by dipping. However, the fraction of finally residual molecules for the former might not become smaller than that for the latter.(3) As for a solvent of trichloroethylene at an elevated temperature of 55°C, both the velocity constant of desorption and the fraction of finally residual molecules become larger than those at room temperature.(4) The nature of desorption, i. e. the velocity constant of desorption and the fraction of finally residual molecules seem to be related to mutual affinities among the fatty acid, the solvent and the metal.(5) A strong bonding force between a fatty acid and a metal must be due not to physical adsorption, but to chemical adsorption.