Streptococcus mutans soluble extracellular polymeric substances and sodium molybdate as mixed corrosion inhibitor for X70 steel.

In this work, the corrosion behavior and mechanism of X70 steel induced by soluble extracellular polymeric substances (s-EPS) extracted from Streptococcusmutans (S.mutans) and sodium molybdate as the mixed corrosion inhibitor in 3.5 wt% NaCl solution were investigated. Results of electrochemical measurements showed that the inhibition efficiency of single s-EPS or sodium molybdate increased with increase in concentration of inhibitor but the inhibition efficiency was not too high, while a synergistic effect existed when s-EPS and sodium molybdate were combined together to prevent X70 steel corrosion. The synergistic effect increased with increasing the concentration of s-EPS from 10 to 40 mg/L in the presence of 50 mg/L sodium molybdate, and the synergistic parameter can achieve 5.46. The mixed inhibitors simultaneously inhibited the anodic and cathodic corrosion of X70 steel clearly, which greatly promoted the activation energy of the corrosion reaction. Results from X-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy demonstrated that co-adsorption of s-EPS and [(OH)₄OMo–O–MoO(OH)₄]²⁻ led to the formation of a more homogeneous and protective film on the surface of X70 steel. All the adsorption of single and mixed inhibitors followed the Langmuir adsorption model according to the thermodynamic analysis. [ABSTRACT FROM AUTHOR]