The effect of carbon within corrosion pits of iron in chloride solutions

ABSTRACT

Iron artificial pits have been used in this work to investigate the effect of a carbon-based black layer that can form within a pit during iron dissolution in HCl solutions. Commercial purity iron (99.5%) and high purity iron (99.99+%) have been compared, and a black layer has been observed only in the 99.5% iron pit. It has been found that the formation of a black layer within an iron artificial pit is potential dependent: it can form at applied voltages below 0.2 V(SCE), but not at 0.6 V(SCE). The presence of a black layer can decrease the rate of mass transport inside a pit, which may help to maintain the aggressive acidic solution in an active pit. This effect has been characterised quantitatively via potentiostatic and potential step methods. In addition, the black layer has also been found to induce a small extra resistance in the solution.

KEYWORDS:

• Iron
• artificial pit
• carbon
• solid corrosion product

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Trevor Rayment http://orcid.org/0000-0003-1168-1414

Additional information

Funding

This work was supported by National Natural Science Foundation of China 51501180; and Engineering and Physical Sciences Research Council grant EP/E045464/1. The author Xu was also funded by School of Metallurgy and Materials (University of Birmingham) and China Scholarship Council during his study in the UK.