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Thermodynamic and Kinetic Study for
Corrosion of Al-Si-Cu/Y2O3 Composites |
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This study involves the effect of
yttria with three wt. % (1, 2 and 3 %) on the corrosion behavior
of Al-Si-Cu alloy in 0.1 N NaOH solution by potentiostat at four
different temperatures 303, 313, 323 and 333 K. Corrosion
parameters for these composite materials were determined by
Tafel extrapolation method such as corrosion potentials Ecorr,
corrosion current densities icorr and Tafel slopes bc and ba.
The results of electrochemical study indicates that Al-Si-Cu/1 %
yttria gave the lowest corrosion rate due to behaviour of yttria
as protective layer which cover the metallic surface and
enhances the passive film of Al2O3, while 2 and 3 % yttria may
be behave as sufficient cathode leading to increasing the
corrosion of base alloy because of the inhomogenous structure of
an metal matrix composite which must be considered in designing
a corrosion protection system. Thermodynamic study was achieved
to estimate thermodynamic quantities of corrosion process DG, DS
and DH. The results show spontaneous the corrosion in 0.1 N NaOH
through the negative values of Gibbs free energy for composites
and the lowest spontaneous process was for Al-Si-Cu/1 % yttria,
the change in entropy values were positive and the lowest value
was for Al-Si-Cu/1 % yttria. Also the change in enthalpy values
was positive referring to endothermic nature of corrosion
process. Kinetic study was applied using Arrhenius equation to
estimate activation energies and the highest activation energy
was for Al-Si-Cu/1 % yttria, this means that this composite need
most energy to surmount the energy barrier. The relationship
existed between values of the activation energy (Ea) and
logarithm of pre-exponential factor (log A) for different
material suggesting the operation of a compensation effect in
kinetics of corrosion. This suggests that, the corrosion
reaction proceeds on surface sites, which were associated with
different energies of activation. |
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