Pitting corrosion of titanium by a freshwater strain of sulphate reducing bacteria (Desulfovibrio vulgaris)

Pitting corrosion of titanium (ASTM Grade 2) was investigated by exposing coupons (2.0 x 1.5cm) to a semi-continuous culture of sulphate reducing bacteria (SRB) strain Desulf-ovibrio vulgaris. The coupons were exposed to the SRB culture for 90 days along with a control set in uninoculated medium. During the course of the experiment sulphide was estimated at intervals of 4 days and the concentrations ranged from 0.2 to 0.4mM in the bulk medium. Epifluorescence microscopy revealed extensive colonization by the SRB and the cell count ranged from 10(4) to 10(5) celIs cm(-2). Optical microscopy revealed the presence of two types of pits; large hemispherical pits of similar to 2mm diameter and many micropits. Pitting was not observed in control coupons exposed to SRB free medium. SEM and CSLM pictures showed the corroded titanium surface with several micropits, along with typical rod shaped SRB cells in the pitted regions. EDAX analysis revealed peaks for Ti, O, N, C, Fe and P in the pitted region. XPS data showed clear peaks for titanium sulphur (three states) and phosphorous. The study reveals that at room temperature and in the presence of 0.2-0.4 mM of sulphide, as well as the putative phosphine, SRB can promote pitting corrosion of titanium by formation of titanium sulphide. (c) 2004 Elsevier Ltd. All rights reserved.