الفهرس 
Historical overview on corrosionOnly 14 pages are availabe for public view
 |  | from | 154 |  |  |
| | | from | 154 | | |
Abstract
The corrosion problem is a great problem, which faced the world from the last years til now, we can’t hide this problem from our live but we can reduce “inhibit” it in the metals by several methods as the environment need. This work discusses the corrosion of carbon steel in 0.5 M HCl in the absence and presence of three different organic compounds.
This work contains three basic chapters
Chapter one: “INTRODUCTION“
This chapter discusses: corrosion theory, causes of corrosion, corrosion migration, types of inhibitors, Literature survey of carbon steel corrosion and aim of this study.
Chapter two: ”EXPERIMENTAL AND TECHNIQUES”
It includes the chemical composition of the investigated material, preparation of the used hydrochloric acid solution, the used organic compounds, solutions and procedures used for the corrosion measurements such as a weight loss and electrochemical techniques, as well as, surface investigation.
Chapter three: ”RESULTS AND DISCUSSION”
It deals with the results obtained and their discussion and this chapter is divided into three sections:
Section (A):
Evaluation of the inhibitor efficiency by weight loss method in the presence and absence of different concentrations from the three organic compounds in 0.5 M HCl at 25 ± 1o C. Data reveled that the inhibitor efficiency increases with the concentration. The order of inhibition efficiency of investigated compounds in 0.5M HCl is found to be:
Inhibitor (A) > Inhibitor (B) > Inhibitor (C)
These organic compounds adsorbed on carbon steel surface according to Langmuir adsorption isotherm, showing that the inhibition is controlled by adsorption process. The degree of surface coverage (θ) for the inhibitors on the metal surface increases with increasing the concentration in the corrosive medium. The effect of temperature on the corrosion inhibition of carbon steel in 0.5 M HCl was determined over the temperature range 25-55 0C using weight loss measurements. The rate of corrosion increases with raising the temperature together with decrease in inhibition efficiency, indicating that the inhibition occurs through physical adsorption of the additives on carbon steel surface. Also some Thermodynamic functions of activation were calculated and discussed.
Section (B):
The inhibitive effect of organic compounds on the cathodic and anodic polarization curves of carbon steel in 0.5 M HCl was investigated. It is found that, the corrosion current density is decreased with increasing of concentration of the organic compounds. Variation of inhibition efficiency with the structure of organic compounds was interpreted in terms of the number of adsorption sites in the molecule and their electron charge density.
The results obtained from (EIS) show that the corrosion reactions in the absence and presence of organic compounds occurred under charge transfer control. The increase in concentration of the inhibitors leads to an increase in the value of the charge transfer resistance (Rct) and decrease in the double layer capacitance (Cdl) of the corroding carbon steel interface with increasing in the inhibitor concentration. This behaviour suggests an increase of the surface coverage of the inhibitor due to the adsorption process at the carbon steel surface.
The new technique electrochemical frequency modulation (EFM) was used as a rapid and non-destructive technique for corrosion rate measurements. Corrosion current densities (icorr) obtained with this technique was in good agreement with those obtained from Tafel extrapolation technique. In addition of the causality factors were good internal check for verifying the validity of data obtained by this technique.
The inhibition efficiency of the investigated organic compounds by the differant electrochemical techniques follow the order:
Inhibitor (A) > Inhibitor (B) > Inhibitor (C)
Section (C):
SEM and EDX experiments were carried out in order to verify if the investigated organic compounds are in fact adsorbed on carbon steel surface. SEM shows that carbon steel surfaces suffer from severe corrosion attack in the blank corroded sample. In contrast, in presence of the organic compounds the metallic surface seems to be less affected by corrosion where the specimen surfaces were less damaged.
EDX spectra show additional lines, demonstrating the existence of C (owing to the carbon atoms of organic compounds). Also, shows that the C and N materials covered the specimen surface. Owing to the inhibitor, existence.
In conclusion:
The weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM) measurements, and surface examinations analysis support the assumption that corrosion inhibition primarily takes place through adsorption of the investigated organic compounds on the carbon steel surface. Agreement among these different independent techniques indicates the validity of the obtained results.