The enrichment of surface passive film on stainless steel during biofilm development in coastal seawater

Abstract

The surface passive film on UNS S30400 alloy was characterized before and after biofilm development under different regimes of diurnal lighting in quiescent flowing coastal seawater. As exemplified by atomic force microscopy, the passive film grew under all test conditions with conspicuous variations in morphological features. X-ray photon spectroscopy illustrated an enrichment of the outer film by iron oxide and a progressive increase in the iron oxide/chromium oxide ratio with lighting. Mott-Schottky plots reflected the duplex nature of the film, comprising an outer n-type and an inner p-type configuration. The slopes of the plots showed a strong decrease in donor and acceptor densities with biofilm coverage and lighting, thus confirming passive film growth. These results provide new insights that passive film enrichment is an intrinsic process under practical marine conditions, and show that the evolution of the passive film is a key step to sustained passivity and/or its breakdown by microbial mechanisms.

Keywords:

• stainless steel in seawater
• marine biofilm
• sunlight
• passive film
• semiconductivity
• sustained passivity
• passivity breakdown

Acknowledgements

The authors thank the Director, CSIR – Central Electrochemical Research Institute, Karaikudi, India for his encouragement and support. The authors would like to especially thank K. Krishnamoorthy, T. Jeyaram and L. Subbiah for their invaluable technical support.

Conflict of interest disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

The supplemental material for this paper is available online at http://dx.doi.org/10.1080/08927014.2015.1062476

Additional information

Funding

This work was funded by the Council of Scientific and Industrial Research, New Delhi, India under the MULTIFUN theme of the 12^th Five Year Plan Programme.