The Inhibition Effect of Potassium Iodide on the Corrosion of Pure Iron in Sulphuric Acid

The use of inorganic inhibitors as an alternative to organic compounds is based on the possibility of degradation of organic compounds with time and temperature. The inhibition effect of potassium iodide on the corrosion of pure iron in 0.5？M H2SO4 has been studied by weight loss. It has been observed from the results that the inhibition efficiency (IE%) of KI increases from 82.17% to 97.51% with the increase in inhibitor concentration from 1·10？4 to 2·10？3？M. The apparent activation energy () and the equilibrium constant of adsorption () were calculated. The adsorption of the inhibitor on the pure iron surface is in agreement with Langmuir adsorption isotherm. 1. Introduction Corrosion is the deterioration of materials by chemical interaction with their environment [1]. Corrosion can cause disastrous damage to metal and alloy structures causing economic consequences in terms of repair, replacement, product losses, safety, and environmental pollution [2]. Several protective measures are taken to control and prevent corrosion. One of these is the use of corrosion inhibitors, which are usually chemical substances; when added in a small concentration to a corrosive medium, they reduce effectively the corrosion of the metal and/or alloy [3, 4]. The use of corrosion inhibitors constitutes one of the most economical ways to mitigate the corrosion rate [5]. The corrosion and corrosion protection of iron in corrosive environments have attracted the attention of many investigators [6–8]. Iron plays a central role as one of the most widely used materials in our daily life because of its so many applications [9]. The inhibition efficiency depends on the parameters of the corrosive system [pH, temperature, duration, metal composition, etc.] and on the nature of the inhibitor [10]. Sulfuric acid is one of the most aggressive acids for iron and its alloys and is often used during cleaning, pickling, descaling, acidizing, and so forth [11, 12]. The inhibitor molecules get bonded to the metal surface by chemisorption, physisorption, or complexation with the polar groups acting as the reactive centers in the molecules [13]. 2. Experimental 2.1. Materials The weight loss experiments were conducted in a 150？mL beaker; the electrolyte volume is 100？mL. Julabo thermostat brand keeps the electrolyte at the desired temperature (±0.1°C). The test pieces were mechanically polished with emery paper (a coarse paper was used initially and then progressively finer grades were employed, 400 to 1200 grade). The specimens were weighed by electronic digital analytical balance with five