Passive biocorrosion

Biocorrosion of stainless steel is caused by exopolymer-producing bacteria. It can be shown that Fe is accumulated in the biofilm [2.62]. The effect of bacteria on the corrosion behavior of the Mo metal surface has also been investigated by XPS [2.63]. These last two investigations indicate a new field of research in which XPS can be employed successfully. XPS has also been used to study the corrosion of glasses [2.64], of polymer coatings on steel [2.65], of tooth-filling materials [2.66], and to investigate the role of surface hydroxyls of oxide films on metal [2.67] or other passive films. 

This is a general name for a wide variety of corrosion processes that may be actively or passively influenced, or induced, by an even wider variety of microbiological organisms. The electrochemical reactions that occur always result in metal wastage, as with all other forms of corrosion the most active biocorrosion processes primarily involve sessile bacteria rather than planktonic bacteria, algae, or fungi. 

Passive biocorrosion tends primarily to promote general metal wastage under the biodeposit, which can increase the total iron levels in the recirculating cooling water, although pitting corrosion can also occur. 

It may also be difficult to distinguish between passive and active forms of biocorrosion, as they may occur at the same time biofilm accumulations on metal surfaces will naturally contain live organisms (including slime producers, sulfate reducers, and acid producers), as well as dead bacteria, excretion products, trapped particles, and perhaps oil and grease or other foulants. 

Some examples of bacterial species involved in passive biocorrosion are ... 

Dexter, S. C., Chandrasekaran, P., Zhang, H. J, and Wood, S., "Microbial Corrosion in Marine Environments Effect of Mi-crofouling Organisms on Corrosion of Passive Metals," Proc., Biocorrosion and Biofouling, H. Videla, Z. Lewandowski, R. Lutey, Eds., Buckman Laboratories, Int., Memphis, TN 1993, p. 171. 

---