Yohnosuke Suzuki

The effect of marine fouling on the ennoblement of electrode potential for stainless steels

Abstract Electrode potentials for 18 kinds of stainless steels and commercially pure titanium were measured in live sea water pumped up into the laboratory room through a 100m-long pipe, so that the specimens were fouled by only the brown slime. After 10 days of immersion, the electrode potentials for all the specimens attained to about 400mV(SCE). Deposited slime was examined under a scanning electron microscope and analyzed in terms of fluorescence. It was found that the slime was composed of living sea diatoms. Variations of electrode potential for stainless steel which had been immersed for 35 days were measured with successive removal of the deposited layer. The electrode potential remained noble after removal of the slime layer, while it decreased drastically after subsequent removal of a thin organic film under the slime layer. The ennoblement of the electrode potential is caused not by the metabolism but by the metabolite of the sea diatoms included in the thin organic film.

Stress corrosion cracking of pure copper in dilute ammoniacal solutions

Abstract Studies of the stress corrosion cracking (SCC) of 99.999% copper and Cu-Zn alloys containing up to 10 wt%Zn in NH 4 OH solution were made with varying concentrations (0.03–0.07 M) and temperatures (40–70°C). Stress corrosion cracking occurs on pure copper and all of the alloys under the condition in which thick tarnish film (Cu 2 O oxide film) forms. The path of cracking is transgranular for pure copper and alloys containing 1.3 wt%Zn. Crack propagation rates and times-to-failure estimated by the tarnish rupture theory, utilizing experimentally determined values of the fracture strain of film and the creep rate of specimens during SCC tests, are in good agreement with those observed under constant load.