自然海水中で貴化したステンレス鋼自然電位に及ぼす環境条件の影響
1995 年 44 巻 6 号 p. 355-363
詳細
1995 年 44 巻 6 号 p. 355-363
When stainless steels are immersed in natural sea water, biofilm begins to develop on their surface to make electrode potential (Esp) of the steels ennobled up to approximately 400mV vs. SCE, which enhances possibility of localized corrosion. In this paper, effect of environmental factors on activity of biofilm on the steels in natural sea water was investigated. Firstly, steels were immersed in natural sea water for 14-16 or 30 days from 1991 to 1994 to measure Esp vs. time of steels in various seasons. Attained value of Esp in winter was lower than that in the other seasons. Under conditions where sunlight was allowed to illuminate steels, Esp decreased by about 100mV around noon every day and returned to their stationary ennobled value at night. This effect of sunlight was observed for 316 steels with Esp values more noble than 200mV vs. SCE. Different from sunlight, a fluorescent lamp for cultivating plants made no significant effect for the Esp. Therefore, following experiments were carried out under the condition of turning on the lamp. To study effect of other environmental factors on activity of biofilm, ennobled steels were immersed in abiotic sea water adjusted to various temperatures (5-95°C), pH (2-10), salinities (3-45‰) or applied potentials (-500-300mV vs. SCE). As the next step of experiments, the samples were transfered to abiotic sea water under natural condition and subsequent behavior of Esp was measured to examine whether Esp of them were maintained after these treatments. Ennobled Esp of the steels was not maintained in abiotic sea water adjusted to temperatures higher than 60°C for 24 hours, pH 2 and 3 for 24 hours, salinity of 45‰ for 96 hours or applied potential of -500mV vs. SCE for 5 hours.
