“Green rust”, iron solubility and the role of chloride in the corrosion of steel at high pH

✍ Scribed by K.K. Sagoe-Crentsil; F.P. Glasser

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 374 KB
• Volume: 23
• Category: Article
• ISSN: 0008-8846
• DOI: 10.1016/0008-8846(93)90032-5

✦ Synopsis

The solubility of iron, as well as nature of the solid corrosion products, influences greatly the kinetics and mechanism of reaction of steel embedded in cement or concrete.

At high pH, ferric iron has a very low solubility, <lmM/l, and spinel, which passivates steel, is obtained as the solid corrosion product. However, at pH -13, low chloride ion concentrations are inimical to spinel formation; the solubility-limiting solid corrosion product is instead "green. rust" layer-structured hydrate containing both Fe z+ and Fe j+ and Cl~

In the range lO-15mM/l chloride, iron solubility at pH -13 increases abruptly from nearzero to ~170-180n~I/I.

The enhanced solubility of iron, probably as an aqueous chlorocomplex, allows it to be transported. The resulting mobility with subsequent precipitation from the complex results in corrosion product being disseminated within the paste.