الفهرس 
Chapter (I) Introduction and Aim of the workOnly 14 pages are availabe for public view
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Abstract
The present thesis aims to through a high light on the chemical and electrochemical behavior of silver electrode in acidic and alkaline media to investigate various factors affecting the formation of passive films formed on silver electrode and the role of silver oxide film as a catalyst for the electrooxidation of simple organic molecules. Also, study of corrosion and corrosion inhibition of silver electrode in acetic acid solutions as a product of ethnol electrooxidation in fuel cells.
Part (1) Study of chemical and electrochemical behavior of silver electrode in HCl solutions. Part (1) Section (A) Study chemical behavior of silver electrode in HCl solutions under pen circuit potential conditions, in this section:
i) The rate of formation of silver chloride film is decreased with increasing acid concentrations. In all studied solutions, the steady state potentials Est. were reached from negative values denoting the growth of AgCl film.
ii) The influence of temperature on the rate of formation of AgCl was discussed. Difference in behavior is noted according to the temperature range, film thickening is predominated at low temperature range (10-25C), whilst film destruction and dissolution is predominated at temperature more than 25C.
Part (1) Section (B) Study of electrochemical behavior of silver electrode in HCl solutions under galvanostatic polarization conditions, in this section the general size of the anodic potential-time curves was found to depend on magnitude of the polarizing current density, the acid concentration and the temperature of the solution. The data of the curves were characterized by the presence of various regions due to different electrochemical processes.
Part(1) Section (C) Study of electrochemical behavior of silver electrode in HCl solutions using cyclic voltammetry and potentiodynamic polarization measurements, in this section:
i) The cyclic voltammogram of silver electrode in HCl solution is characterized by the presence of pre-peak, Pa, which is related to the adsorption of Cl- ions on silver metal. Then the anodic peak, A1 is related to the formation of an ordered AgCl adlayer formed with the topmost Ag
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layer. Then the anodic peak A2 (during the reverse scan) is related to a three-dimensional (3D) growth of AgCl takes place on the electrode surface.
ii) The presence of two reduction peaks, C1, C2 and a hump, Pc, on the cathodic branch during the reverse scan could be related to the reduction of the formed AgCl passive film on the Ag substrate during anodic process.
iii) The formation of silver chloride film on silver electrode is affected by repetitive cycling, anodic potential scan limit, potential scan rate and HCl concentration.
Part (2) Study of chemical and electrochemical behaviour of silver electrode in acetic acid solutions. Part (2) Section (A) Study of chemical and electrochemical behaviour of silver electrode in acetic acid solutions under open circuit potential conditions, in this section:
i) The rate of destruction of silver oxide film increased with increasing acid concentration. In all studied solutions, the steady state potentials Est. were reached from positive values denoting the destruction of passive silver oxide film.
ii) The influence of temperature on the rate of destruction of silver oxide film was discussed. It was found that, the rate of destruction of silver oxide film increased with increasing temperature.
Part (II) Section (B) Study of electrochemical behaviour of silver electrode in acetic acid solutions under galvanostatic polarization conditions, in this section:
i) The general size of the anodic potential-time curves was found to depend on magnitude of the polarizing current density, the acid concentration and the presence of aggressive ions on the solution. The data of the curves were characterized by the presence of various regions due to different electrochemical processes.
ii) The initiation of pitting corrosion on Ag electrode in 5 M acetic acid solution in presence of NaClO3, NaClO4 and KNO3 decreases in the order:
ClO-3 < ClO-4 < NO-3
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Part (II) Section (C) Study of electrochemical behaviour of silver electrode in acetic acid solutions using cyclic voltammetry techniques, in this section:
i) The anodic- cathodic voltammetric response displays a small anodic peak A1 which is related to the dissolution of silver metal and or electroformation of Ag2O and two cathodic peaks, C1 which is related to the reduction of Ag2O and C2 related to the reduction of (CH3COOAg species) the accumulated dissolution products formed during the anodic half cycle.
ii) Urea and its derivatives were used as dissolution inhibitors, the inhibition efficiency, I.E., decreases in the order:
Urea < Thiourea < N-allylthiourea
Part (II) Section (D) Study of electrochemical behaviour of silver electrode in acetic acid solutions using the Tafel extrapolation method, in this section:
i) The corrosion of silver electrode in acetic acid was studied using potentiodynamic polarization technique in absence and presence of different concentrations of urea, thiourea and N-allylthiourea. These organic additives are mixed-type inhibitors. The inhibitive action of these compounds is based on the formation of salt complex and/or the adsorption of the protonated species on the metal surface according to Temkin adsorption isotherm.
ii) In presence of one and the same concentration of these additives, the inhibition efficiency, I.E., decreases in the order:
Urea < Thiourea < N-allylthiourea.
Part (3) Study of chemical and electrochemical behaviour of silver electrode in KOH solutions. Part (3) Section (A) Study of chemical behaviour of silver electrode in KOH solutions under open circuit potential conditions, in this section:
i) The rate of destruction of silver oxide film increased with increasing KOH concentration.
ii) The influence of temperature on the rate of formation and destruction of silver oxide film was discussed. Difference in behavior is noted according to the temperature range, film thickening is developed at low
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temperature range (10-20C), whilst film destruction and dissolution is predominated at temperature more than 20C.
Part (3) Section (B) Study of kinetics of electrooxidation of some alcohols at a modified silver electrode in KOH solutions using cyclic voltammetry technique, in this section:
Modified silver electrode was made by repetitive cyclic polarization at a sweep rate of 2.5 V/s for a period of 5 minutes in 0.1M KOH solution, for coating silver metal with a silver oxide layer. After the formation of silver oxide layer, the electrode was transferred into 0.1 M KOH solutions in absence and presence of alcohols.
The use of a modified silver electrode to catalyze the electrooxidation of ethanol methanol and isobutanol in 0.1 M KOH solution, as reductants in fuel cell industry, was studied using cyclic voltammetry technique.