The efficiency of calcium gluconate in inhibiting the corrosion of mild steel in a neutral aqueous solution containing 60 ppm Cl−, a situation commonly encountered in cooling water systems, has been evaluated by the weight loss method. It was found that 200 ppm calcium gluconate resulted in 99% inhibition efficiency after 24 h but that this decreased to 60% after 7 days. The decrease in inhibition efficiency is attributed to the dissolution of the Fe2+–gluconate complex formed on the metal surface. The protective film formed on the metal surface consisted of an Fe2+–gluconate complex and Ca(OH)2.
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