الفهرس 
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Abstract
Summary
Corrosion of steel represents a phenomenon of negative impact economically and environmentally, since steel is widely used in concrete constructions and various industrial applications such as chemical manufacturing and oil refines industries. In the last decades, there was an increasing concern in the use of some classes of organic compounds especially oxygen, sulphur and nitrogen containing heterocyclic as corrosion inhibitors.
It is believed that the function of these inhibitors is to be adsorbed on the metal surface. One of the most widely used families of organic compounds is Schiff bases and their chemistry is essential material in many organic chemistry textbooks. The Schiff bases inhibitors have many advantages such as high inhibition efficiency, low price, low toxicity, and easy production.
The aim of the present study is to prepare some Schiff bases and then study their behavior as corrosion inhibitors of carbon steel in 1M hydrochloric acid.
This work includes three main parts:
1- The first part:
Introduction about corrosion(definition, forms, effects, and inhibition), corrosion inhibition of carbon steel in corrosive media then about Schiff bases as corrosion inhibitors.
2- The second part:
Synthesis of some Schiff base namely : N,N\-bis-(phenylmethylene) -1,8- diaminooctane (SB1), N,N\- bis- (2-hydroxy phenyl methylene) -1,8-diaminooctane (SB2), N,N\-bis-(4-Fluro- phenylmethylene)-1,8-diaminooctane (SB3), N,N\-bis-(4- bromo-phenylmethylene)-1,8-diaminooctane (SB4) , N,N\-bis-(phenylmethylene)- 1,4-diaminobenzene(SB5),N,N\-bis- (2-hydroxyphenylmethylene) -1,4-
Summary
diaminobenzene (SB6), N, N\-bis-(4-Fluro-phenylmethylene) -1,4-henylenediamine (SB7), N,N\-bis- (4-bromo-phenylmethylene) -1,4- diaminobenzene (SB8) .
- Elucidation of the structures of the obtained Schiff bases by the FTIR and
1HNMR analysis.
3- The Third part:
Evaluation of prepared Schiff bases (SB1-SB8) as corrosion inhibitors using different techniques.
1- Weight loss techniques
The weight loss of carbon steel specimens decreased in 1 M HCl. by using different concentrations of the prepared compounds (SB1-SB8). The results show that the inhibition efficiencies of the prepared compounds increase with increasing inhibitor concentrations. This means that, the presence of these compounds retard the corrosion (dissolution) of carbon steel in HCl acid medium, i.e., these compounds can act as corrosion inhibitors.
The maximum inhibition efficiency for each compound was achieved as corrosion inhibitor at 500 ppm .
- Schiff bases products can classified into two groups: 1st one is aromatic group (more efficient) and 2nd one is aliphatic group (less efficient). The corrosion inhibition efficiencies decrease according the following order: SB8 > SB7 > SB6 > SB5 > SB4 > SB3 > SB2 > SB1. Indicating the inhibition efficiency also depend on the nature of inhibitor.
- Thermodynamic parameters for adsorption process such as free energy (ΔGoads) enthalpy ( ΔHads ) and entropy (ΔSads) for the used inhibitors were determined.
- The values of ΔGads are in the range (-23.1 to -28.1), indicating that the adsorption mechanism of the prepared compounds on carbon steel in 1 M HCl solution is physisorption and chemisorption (mixed type).(mainly physical)The negative values of ΔHads reflect that the process is exothermic. The positive values of ΔSads
attributed to the increase of disorder due to the adsorption of only one inhibitor molecule by desorption of more water molecules.
2- Different Electrochemical Measurements
A- Potentiodynamic polarization measurements
The potentiodynamic polarization plots for carbon steel electrode in 1M HCl in the absence and presence of different concentrations of synthesized Schiff bases compounds (SB1 – SB8) were studied. The Tafel slopes reveal that the prepared compounds affected both the anodic and cathodic display which indicate that these inhibitors act as mixed type inhibitors) mainly cathodic).
B. Electrochemical Impedance Spectroscopy Measurements (EIS)
from the electrochemical impedance spectroscopy (EIS) measurements at OCP, the results indicate that the values of double layer capacitance (Cdl ) tend to decrease and charge transfer resistance (Rct) increase and inhibition efficiency (ηz) tends to increase by increasing the inhibitor concentrations.
3- Scanning electron microscope (SEM) and Energy dispersive X-ray (EDX) The results of both SEM and EDX techniques indicated that the inhibitor molecules form good protective films on the carbon surface which isolates the surface from 1MHCl.On the other hand the metal surface immersed in 1MCl without inhibitor appearslike full of pits and cavities.
from SEM: By using the inhibitors , the polar imino groups can form coordinate bonds with iron and hinder the dissolution of steel by forming adsorbed layer on the steel surface and there reduce the corrosion rate.
from EDX: The intensity of carbon steel in presence of inhibitors was reduced more and more than intensity in the absence of inhibitors. This indicated that these compounds act as corrosion inhibitors.
Finally, it was concluded that the Schiff bases prepared are efficient as corrosion inhibitors of carbon steel in hydrochloric acid medium.