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Abstract
The corrosion problem is a great problem, which faced the world
from the last years until now, we can’t hide this problem from our live
but we can reduce it “ inhibit” in the metals or their alloys by several
methods as the environment need. This work discuss the corrosion of
α-brass in 2M HCl.
This work contains four basic chapters
Chapter one “ INTEODUCTION ”
This chapter discusses:
1- General aspects of corrosion
Definition of corrosion
Classification of corrosion
Various forms of corrosion
Electrochemical theory of corrosion
Physical and mechanical properties of copper and brasses
Application of copper and copper alloys
Corrosion of copper and copper alloys
Copper and high copper alloys
Corrosion prevention of copper and its alloys
Corrosion inhibitors
Theory of corrosion inhibition
Corrosion monitoring techniques
2- Literature survey of brass and copper corrosion
Chapter two “ EXPERIMENTAL AND TECHNIQUES’
It includes the chemical composition of the investigated material,
preparation of the used hydrochloric acid solution, the used
phenlhydrazone derivatives solutions and procedures used for the
corrosion measurements such as a weight loss and polarization
techniques.
Chapter three “ RESULTS AND DISCUSSION”
It deals with the results obtained and their discussion
Evaluation of the inhibitor efficiency by weight loss method for all
the seven compounds in 2M HCl at 30 ± 10 C revealed that the
inhibitor efficiency increases with the concentration. Careful
inspection of these results showed that, at the same inhibitor
concentration, the order of inhibition efficiencies is as follow:
I) For first group compounds:
D > B > A > F
II) For second group compounds:
E > C > A > G
These phenlhydrazone derivatives obey Temkin’s adsorption
isotherm showing that the inhibition is by adsorption.
The degree of surface coverage (θ) for the inhibitors on the metal
surface increases with increasing their concentrations in the corrosive
medium. The action of the inhibitors in the aggressive acid was
assumed to be due to their adsorption at the metal /solution interface.
Synergetic effect of phenlhydrazone derivatives and KI on α-brass
corrosion inhibition in 2M HCl was studied . The results indicate that
the % inhibition increased in presence of 1x10-3 M KI.
The effect of temperature on the corrosion inhibition of α-brass in 2M
HCl was determined over the temperature range 30-550 C using
weight loss measurements. The rate of corrosion increases with
increasing the temperature thus a decrease in the inhibition efficiency
occurs which indicate that the inhibition occurs through physical
adsorption of the additives. Thermodynamic functions of activation
were calculated in presence of different concentrations of
phenlhydrazone derivatives.
The effect of phenlhydrazone derivatives on the cathodic and anodic
polarization of α-brass in 2M HCl was investigated. Corrosion rate
decreased with increase of concentration of the phenlhydrazone
derivatives together with increase in both cathodic and anodic
polarization, but the corrosion inhibition has a great effect on the
cathodic polarization. Variation of inhibition efficiency with the
structure of phenlhydrazone derivatives was interpreted in terms of
the number of absorption sites in the molecule and their electron
charge density, molecular size, mode of adsorption and the polar
effect of the substituent groups. The order of increased inhibition
efficiency for α-brass corrosion in 2M HCl at all concentrations in the
range 1x10-6 - 1.3x10-5 by polarization technique is as follow :
I) For first group compounds:
D > B > A > F
II) For second group compounds:
E > C > A > G
The effect of phenlhydrazone derivatives on the pitting corrosion of
α-brass was investigated from potentiodynamic anodic polarization.
The following points were obtained:
a) An increase of inhibitor concentration causes the shift of the pitting
potential into more positive values.
b) Inhibition afforded by these compounds using the same different
concentrations of the additives decreases in the following order :
I) For first group compounds:
D > B > A > F
II) For second group compounds:
E > C > A > G
Skeletal representation of the proposed mode of adsorption of the
investigated phenylhydrazone derivatives indicates the active
adsorption centers in the phenylhydrazone derivatives. These
compounds can be adsorbed in a flat orientation on the α- brass
surface. The order of decreasing the percentage inhibition efficiency
of the investigated inhibitors in the corrosive solutions was as follow:
I) For first group compounds:
D > B > A > F
II) For second group compounds:
E > C > A > G
In conclusion, weight loss measurements, polarization
potentiodynamic anodic polarization and Skeletal representation
support the assumption that corrosion inhibition primarily takes place
through adsorption of the inhibitors on α-brass surface. Agreement
among these different independent techniques indicates the validity of
the obtained results.
Chapter four “General discussion”
This thesis contains 178 references, 88 Figures, 19 Tables, Arabic and
English Summaries.