Corrosion Inhibitors for Metals and Alloys in an Alkaline Medium
This chapter discusses the corrosion inhibitor for an alkaline medium. Metals undergo corrosion in an acid medium, a basic medium, and a neutral medium. In all the mediums, the anodic reaction is dissolution of the metal. Corrosion inhibition studies have been evaluated at various temperatures. In general, corrosion inhibition decreases because at elevated temperature, desorption of adsorbed molecules takes place. A formulation consisting of 250 ppm p-nitrophenol and 50 ppm of Zn2+ offers a corrosion inhibition efficiency of 90% in controlling the corrosion of aluminum immersed in aqueous solution at pH 11. Atomic force microscopy reveals the formation of nanofilms on the metal surface in the presence of inhibitors. The inhibition effect is due to the adsorption of the inhibitor molecule on the metal surface. Adsorption may be physical adsorption or chemical adsorption, depending on the adsorption strength. Organic compounds not only offer electrons to the unoccupied metal orbital but also accept free electrons from the metal.