Olga Lahodny-Šarc

The influence of pH on the inhibition of corrosion of iron and mild steel by sodium silicate

Abstract The inhibition of iron and mild steel in solutions of sodium silicate of different concentration and pH has been studied by means of potentiostatic and potentiokinetic polarization measurements. The mechanism of formation of protective layers formed in the presence of inhibitor has been discussed on the basis of experimental measurements and literature data. The difference in the protective action due to the presence of sodium silicate as distinguished from the effect of the alkaline media has been demonstrated. The influence of the metal corrosion products in the formation of the protective layers has also been investigated.

Corrosion inhibition of carbon steel in the near neutral media by blends of tannin and calcium gluconate

The efficiency of tannin/calcium gluconate blends, as corrosion inhibitors for carbon steel in near neutral water media, heva been studied.Synrgistic behaviour of two components blend of different concentrations has been demonstrated in solutions prepared with distilled and a tap water. The anodic character of the inhibitor was recognised by the shift of corrosion potential to more positive values and a decrease of the passivation current on potentiodynamic polarisation curves. The cathodic inhibition was also recognised by slowing down the cathodic current of the polarisation run.Soluble iron tannate chelate has been observed as a dark blue flux flowing down from the metal surface into solution of tannin in the tap water, resulting in a corrosion process. Tannin decreased the pH of tap water.Calcium gluconate added in tannin solutions increases the pH maintaining it in the near neutral region enabling the precipitation of a low soluble protctive iron tannate and metal gluconate.

Corrosion Inhibition of Carbon Steel by Blends of Gluconate/Benzoate at Temperatures Up to 60°C

The inhibition of carbon steel in solutions of mixtures of calcium- and zinc-gluconate with sodium benzoate was investigated in the temperature range from 25° to 60°C, under atmospheric conditions in stagnant solutions prepared with the tap water. The efficiency and the mechanism of inhibition were estimated by potentiodynamic polarization measurements. The influence of the concentration and the ratio of gluconate/benzoate on the anodic reaction and an observed cathodic effect, indicating slowing down the oxygen reduction process, relevant to the concentration of zinc ions, have been demonstrated. The performed inhibition of carbon steel, as shown by polarization data, may be attributed to the adsorption of gluconate along with benzoate or/and to the formation of a low soluble iron gluconate complex on the metal surface. The inhibition is enhanced by the cathodic polarization mechanism resulting in the precipitation of a zinc hydroxide film, due to the local cathodic gradient of hydroxyl ions. Gluconates act also as sequestring agents preventing a deposition of calcium carbonate from hard waters. Results obtained by electrochemical measurements were confirmed by immersion tests, and could be of interest for the application in cooling water treatement systems, and for the injection water in oil and gas recovery. Investigated compounds are environmentally acceptable being non-toxic and non-polluting.