Inhibition of acidic corrosion of iron by some Carrageenan compounds

Abstract

INTRODUCTION Iron is the most used of all the metals in several fields of industry. Iron and similar metals can be exposed to corrosion in connection with environmental conditions. The corrosion rate varies subject to structure of ions and molecules, kind of ion, concentration of ion, kind of solution and kind of materials 1,2. Especially in environments containing Cl-ions, corrosion of metals is unavoidable, as Cl-ion is an active one, it forces oxide formation on metal surface. This increases the corrosion rate of metal 2. Organic additives are commonly used to reduce the corrosion of iron in acidic medium 3-8. The inhibition efficiency of such compounds may function by adsorption on the iron surface, the adsorption process depends mainly on certain physico-chemical properties of the molecules such as, functional groups, steric factors, aromaticity, electron density at the donor atoms, π-orbital character of donating electron 9,10 and also on the electronic structure of the molecules. The inhibition efficiency increases with increasing the number of atomic rings 11,12. ABSTRACT The corrosion inhibition of some sulfated water soluble natural polymer (carrageenan) compounds on the corrosion of iron in 1M HCl was studied using weight loss and galvanostatic polarization measurements. The percentage inhibition efficiency was found to increase with increasing concentration of inhibitor and with decreasing temperature. The inhibitive action of these compounds was discussed in terms of blocking the electrode surface by adsorption of the molecules. The adsorption process follows a Langmuir adsorption isotherm. The effect of temperature on the rate of corrosion in the absence and presence of these compounds was also, studied. Some activation thermodynamic parameters were calculated.