Bacterial phosphating of mild (unalloyed) steel

Mild (unalloyed) steel electrodes were incubated in phosphate-buffered cult ures of aerobic, biofilm-forming Rhodococcus sp, strain C125 and Pseudomona s putida mt2, A resulting surface reaction leading to the formation of a co rrosion-inhibiting vivianite layer was accompanied by a characteristic elec trochemical potential (E) curve. First, E increased slightly due to the int eraction of phosphate with the iron oxides covering the steel surface. Subs equently, E decreased rapidly and after 1 day reached -510 mV, the potentia l of free iron, indicating the removal of the iron oxides, At this point, o nly scattered patches of bacteria covered the surface. A surface reaction, in which iron was released and vivianite precipitated, started. E remained at -510 mV for about 2 days, during which the vivianite layer grew steadily , Thereafter, E increased markedly to the initial value, and the release of iron stopped. Changes in E and formation of vivianite were results of bact erial activity, with oxygen consumption by the biofilm being the driving fo rce,These findings indicate that biofilms may protect steel surfaces and mi ght be used as an alternative method to combat corrosion.