Inhibition Ability of Gluconates for Fresh Water Corrosion of Mild Steel Enhanced by Metal Cations

Abstract

Inhibition ability of gluconates for fresh water corrosion of mild steel changed with metal cations were investigated by immersion tests and electrochemical impedance spectroscopy (EIS) tests. The results of the tests showed that the inhibition ability of gluconates was enhanced by metal cations that have large "corrosion inhibitory effect of cation, Y", in model fresh water. Surface analysis showed that gluconate ligands and metal cations that have large Y can bond on mild steel and that they form a protective film on the steel. EIS analysis with an equivalent circuit suggested that metal cations that have large Y would reduce the area of defects in the protective film of gluconates.

Effects of metal cations on mild steel corrosion in 10 mM Cl− aqueous solution

“…Clear peak is observed (Fig 12 (b)) in the case of Zn 2+ among all experimental metal cations meaning that only Zn 2+ remains on the mild steel after immersion in the solution. Zn 2+ may precipitates as oxides or hydroxides [18,19] and make a chemical bond with the oxide film of mild steel in 10 mM Claqueous solution and forms a metal cation layer which inhibits the anodic and cathodic reactions, and protects the dissolution of metal [18,19]. These results correspond with other tests like as immersion tests and electrochemical tests.…”

“…Another possibility is that Zn 2+ directly makes a bond with OHof oxide film (oxide film contains so many OH -) and thus form a metal cation layer on the oxide film ( Fig. 13 (c)) [18,19]. Several studies also have shown that metal cations that have large X can easily bond with OHon the oxide film of mild steel [18,19,28,29].…”

“…Zn sol shows the lowest value of Q than other solutions of metal cation (Table 3). Q represents the structure of solution/metal interface and the area of defects in the protective film on the surface [19,22]. Otani et.…”

“…Otani et. al [19] reported that the decrease in Q indicates that Zn 2+ can decrease the defect in the protective film on the mild steel.…”

“…The mechanism of corrosion inhibition of metal cations is also unknown. By considering the corrosion rate of mild steel that depends on the metal cations [18,19], Clconcentration, pH [30,31] and dissolved oxygen, the present research purpose is to find out the effects of metal cations on corrosion of mild steel, and the mechanism of corrosion inhibition in 10 mM Claqueous solution at an equal level of pH.…”