Effects of Si in Water on Corrosion Behavior of Hot-dip Galvanizing

Abstract

Effects of temperature and concentration of silicate anion in water on corrosion behavior of hot-dip galvanizing were investigated by immersion test, surface analysis, and cross-sectional observation. Immersion test using ion-exchanging water indicated that the corrosion rate decreased due to deterioration of water quality. X-ray fluorescence analysis revealed that much more Si exist on surface of hot-dip galvanizing sample after immersion test using deteriorated water compared to clean water. Now we prepared corroding liquid by adjusting the concentration of silicate anion using distilled water and sodium silicate in order to confirm the effect of concentration of silicate anion on corrosion rate by immersion test. In this test, higher concentration of silicate anion led to lower corrosion rate as well as in the immersion test using ion-exchanging water. Moreover, the influence on the corrosion inhibition by silicate anion was larger in corroding liquid at 60℃ than at 25℃. Glow discharge optical emission spectrometry revealed that more Si existed in the corrosion products on surface of hot-dip galvanizing immersed in 60℃ than in 25℃ water, and the thickness of corrosion products containing Si was about 20-30 nm by cross-sectional SEM image.