Researchers at Singapore’s government-led Agency for Science, Technology and Research (A*STAR) are developing a technique to use molybdate as a corrosion inhibitor on carbon steel (CS) alloys. While CS represents the largest class of alloys in use today, the researchers explain that CS corrosion is a huge cost.
Seeking a safer alternative to toxic inhibitors, Yong Teck Tan and colleagues from the National University of Singapore and the Singapore Institute of Manufacturing Technology are exploring molybdate as an alternative. Molybdate is non-toxic, and it protects CS from corrosion by competitive adsorption against chloride ions (Cl−) on the passive film surface. Moreover, in the presence of calcium cations, it can deposit a layer of calcium molybdate (CaMoO4).
“Previous studies using electrochemical techniques have focused on corrosion inhibition efficiency at a particular time, which provides a snapshot of the level of corrosion at that instant,” Tan explains. “Depending on whether it was assessed over short or long timescales, different conclusions were drawn.”
Tan’s research team used an electrochemical method to estimate the extent of corrosion over the entire duration of the investigation. “Even though molybdate resulted in a slightly higher passive current in the later stages, faster passivation in the early stages resulted in a lower overall level of corrosion,” Tan says.
The researchers found that incomplete coverage of CS by the CaMoO4 led to slightly higher corrosion rates compared with untreated surfaces. By controlling the composition of the molybdate solution, however, the CaMoO4 film covered the entire surface, resulting in improved corrosion resistance.