Abstract
A report is presented of the morphology and composition of the corrosion products formed on galvanized corrugated steel reinforcing bars immersed in 0·05–1·5M KOH solutions designed to simulate concrete pore environments. The morphology was studied by SEM of the in situ corrosion products and optical examination of transverse sections of the bar; phase identification was performed by X-ray diffraction and IR absorption analyses. Passivation events on the corrosion potential and corrosion intensity curves can be related to precipitation of prismatic Zn (OH)2 crystals which form a compact layer on the surface. Active corrosion is associated with formation of porous ZnO layers or precipitation of Zn(OH)2 in the solution rather than on the galvanized surface. A solution-precipitation mechanism involving ZnO and Zn(OH)2− 4 intermediate species is proposed for formation of the passivating Zn(OH)2 coating, although this scheme must be complemented to take account of the localized corrosion observed at pH < 12 in the first part of this study.
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