Thesis & Dissertations

Evaluation of the inhibitory effect of some plant extracts on the corrosion of mild steel in acidic media


Acids are widely used in acid pickling, industrial acid cleaning, acid descaling, oil well acidizing, and manufacturing processes in different industries. The commonly used acids are sulfuric acids and phosphoric acid. Also Phosphoric acid is a major chemical product, which has many important uses, especially in the production of fertilizers. Inhibitors are used in acid solutions in order to minimize corrosive attack of the metal or alloy. Although there are abundance of publications on all aspects of corrosion and its control, few references have been cited in literature to a research paper carried out in Lebanon in this field. The aim of this work is to create new and local research in Lebanon in the field of corrosion protection, providing an integrated model of inhibitor to retard the corrosion of steel in industrial acid cleaning systems and to do a comparison between sulfuric acid and phosphoric acid under the effect of the studied plants leaves extract, by using a new category of environmentally friendly plant leaf extract, which are widely cultivated in Lebanon. The known hazard effects of the most synthetic corrosion inhibitors are the motivation for the use of these natural products. Recently, Plant extracts have again become important as an environmentally acceptable, readily available and renewable source for a wide range of needed inhibitors. Plant extracts are viewed as an incredibly rich source of naturally synthesized chemical compounds that can be extracted by simple procedures with low cost. In this work, the inhibition efficiency of different plant extracts: Eucalyptus(Eu) and Prunus dulcis(PD) on the corrosion of mild steel in 0.5 M H2SO4,0.5 M H3PO4 ,and 50% H3PO4 acidic solutions was investigated electrochemically using electrochemical impedance spectroscopy (EIS) technique and Potentiodynamic polarization curves measurements. The major chemical constituent for each plant leaf extract were suggested using Fourier Transform Infrared Spectroscopy (FTIR). The results shows that as the concentration of the plant leaf extract increase, the inhibition efficiency increase. While the efficiency decrease as temperature increase. Theoretical fitting of different adsorption isotherm (Langmuir isotherm, ,Florry-Huggins isotherm, and Temkin model),and kinetic-Thermodynamic model was tested to clarify the nature of adsorption on mild steel surface. Thermodynamic parameters indicated that the inhibition of corrosion of mild steel by both plants leaves extract occurred by physical adsorption mechanism. The FTIR reported that Eu leaf extract contains a substance known citronellal, and the PD leaf extract contains a substance known as linoleic acid . The results showed that plant leaf extracts are more efficient in H2SO4 than in H3PO4 solutions, in the different concentration of the tested solution.


Fatmeh Toufiq Beqai


Ashraf Mostafa Abdel Gaber