INHIBITION EFFECT OF SODIUM BORO-GLUCONATE ON MILD-STEEL WITH AND WITHOUT NITRITE IONS IN LOW CHLORIDE-CONTAINING WATER

As an alternative for the replacement of chromate containing corrosion inhibitors for mild steel in cooling water systems, sodium boroglucon ate (SBG) has been evaluated by gravimetric and electrochemical method s in water containing 100 p.p.m. Cl- in an open system at ambient temp erature. An inhibitor efficiency of 90% has been obtained in the prese nce of optimum concentration (50 p.p.m.) of SBG alone. However, the in hibition efficiency tends to decrease after 48 h of immersion due to t he formation of soluble iron gluconate complexes. The formation of the complex is evident from the shift of the u.v. absorption peaks of Fe( II) and Fe(III) in the presence of gluconate ions. To stabilize the in hibitive action of SBG, NO2- ions were added in an equal mass ratio an d their combined effect was found to be very effective in maintaining inhibition efficiency up to 100 h of immersion.