Kinetics of oxide film growth on cobalt in neutral aqueous solutions

Abstract

The rate of oxide film thickening on Co was followed by measuring the open circuit potential in solutions of Cl 2 , Br 2 , SO 22 4 , NO 2 2 , NO 2 3 , PO 32 4 and WO 22 4 of varying concentrations until steady values were reached. In all the solutions studied, the steady state potentials E st. were reached from negative values denoting oxide film healing and growth. The rate of oxide film thickening was found to follow a direct logarithmic law as evident from the variation of the open circuit potential with the logarithm of the immersion time t. In solutions of the first five anions, the rate of oxide film growth decreased with increasing anions concentration. However, in solutions of PO 32 4 and WO 22 4 , the rate of the oxide film thickening increased with increasing concentration. The steady state potentials varied with the anions concentration according to straight line relationships. The significant role of the anions in the process of oxide film growth could be identified.

Corrosion Inhibition of Aluminium in 2 M Phosphoric Acid Using the Essential Oil of Mentha Pulegium Leaves

“…The use of green eco-friendly natural polymeric structures, extracted from leaves or seeds as corrosion inhibitors, is gaining large preference and interest due to its safe effect to the environment, practical use, low cost and renewable sources of materials [4][5][6]. The extent of inhibition by those compounds depends on the effective organic groups and increases in the order oxygen < nitrogen <sulfur < phosphorus [7,8]. Mentha pulegium, commonly known as pennyroyal, is one of mentha species and it is a native species of Europe, North Africa, and Asia.…”