الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
-1-A literature survey of the different theories and concepts of corrosion and passivity of copper in the different environmental media is given, with particular emphasis on the behaviour of copper in sulphide
containing solutions.
2-from the potential-time curves of the copper electrode in aerated NaOH solutions in presence and absence of Na2S the following conclusions could be drawn:
i-In sulphide-free NaOH solutions, the steady-state open circut potential is reached from negative values indicating oxide film thickening,
ii-Addition of low concentrations of Na2S enhances oxide film thickening and the steady-state potential shifts more into the noble direction.
Increasing the S-ion content, on the other hand, causes the potential to oscillate into the active and noble directions during a time span
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which depends on Sion content and finally reaches a value in the noble direction which is less positive the higher the Sion concentration.
This shows the preferential formation of oxide and/or sulphide film.
iv-However,’in presence of higher Sion concentrations, the potential changes markedly to the more active direction denoting the formation of cuprous sulphide. Within this range of Sion concentration, the steady-state potential varies with [S according to:
Est = E° - 0.059 log ES 1 at 25°C.
while E° varies with the pH of solution to give straight line with a slope of 29 mV/pH unit.
v-The slope of 59-mV/log C: indicates a one electron transfer reaction which is attributed to the formation of CuSH as an intermediate step in the process of Cu2S formation according to the following reactions: ’
Cu + Sfl- CuSH- (ads)
CuSH (ads) = CuSH + e
2 CuSH + Na+ + OH = Cu2S + + H2O
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3- from the galvanostatic curves and the cyclic voltammograms of the Cu electrode in NaOH solutions devoid of and containing S ions the following features could be disclosed:
a-In S---free solutions, the galvanostatic curves and cyclicvoltammograms are characterized by three well defined anodic peaks and their corresponding cathodic ones. The anodic peaks are found to correspond successfully to the formation of a monolayer of Cu20, thick multilayer of CuO and finally Cu203 upon which 02 is evolved. The cathodic peaks correspond to the reduction of these oxides in a reverse manner.
b-Addition of Sions in increasing concentrations causes the following:
i- The formation of a new anodic peak at a potential around -0.70 V (NHE) whose charge amount increases markedly with increasing the Sion concentration,
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ii-The marked enlargement of the integrated charge amounts of the anodic peaks along the galvanostatic and the CVs and also in the region corresponding to the HCuO2 formation.
iii-The appearence of a composite cathodic reduction peak, (peaks)at a potential around (-0.76 to - 1.05 V NHE) due to the reduction of the formed sulphide.
4- from the coulometric reduction curves of the copper electrodes previously equilibrated in NaOH solutions in presence and absence of different Na2S addetives for different immersion times, the following results could
be summarized:
I- In S---free NaOH solution, the reduction process
at 0.03 mA/cm2 proceeds through two well defined
reduction steps at the following potentials
(against the NHE).
’ Step 1
Step 2
0.01 M
NaOH
- 0.28V
-0.52V
(NHE).
0.10 M
NaOH
- 0.26V
-0.56V
(NHE).
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The quantity of electricity (Q1) following along the first cathodic step is markedly smaller than that
following along the second one (Q2) in 0.01 M NaOH solutions, while the reverse is true in 0.10 M NaOH
i,e. Qi is much greater in comparison with Q2 at the same C.d. This may be due to the dissolution of part of the oxide’s in the concentrated solution than in
the dilute one. However, both quantities of electricity increase with immersion time, t, according to the relation:
log Q = a + b log t
II- from the cathodic polarization curves of Cu in both hydroxide solutions in presence of different concentrations of Na2S, the following conclusions could be drawn:
A- The presence of Sions, at any time of immersion, causes the partial disappearance of the first reduction step at -0.28V and the complete
disappearence of the second reduction step
reported in S—free solutions at -0.52V (NHE).
Thus, the presence of Sions causes Cu(OH)2 and Cu20 to be reduced directly to metallic Cu, instead
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of the expected sequence Cu(OH)2--)Cu20--) Cu.
B-In presence of higher concentration of S ions, the first step is completely disappeared after longer times
of immersion.
C-A new reduction step starts to be formed in presence of S ions at potentials around -0.910 V (NHE), due to the reduction of the formed cuprous sulphide. The quantity of electricity consumed during the reduction of this step is markedly increased with the immersion time according to the relation: log q = + 13’ log t.