Analysis of corrosion in marine and acid environments is a complicated task,
involving the interaction of thermodynamic, kinetic and geometrical factors. Two
mathematical models which predict corrosion behaviour have been implemented for
personal computers.
The first program uses an assumption of unidirectional current flow to simplify the
prediction of potential distributions for systems of essentially cylindrical geometry
containing natural seawater-based electrolytes of differing strength. Using experimentally
determined electrochemical and flow rig data, experimental and theoretical results were
compared. The correlation between the two was shown to be poor, and this is attributed to
the unrepresentative nature of the electrochemical data input to the model.
The second model involves the synthesis of polarization curves. Several algorithms
to model passivating behaviour have been studied, and one was selected and incorporated
into the calculation routine. A number of kinetic and thermodynamic parameters are used
in algorithms describing such behaviour, along with activation, concentration and solution
polarization effects, for a number of redox reactions, which are then combined to produce
an overall potential-log current density curve.
Experimentally determined data for pure iron and different stainless steels in marine
and acid environments of differing dissolved oxygen content and temperature were obtained.
Theoretical models were constructed for each system, and compared to experimental data.
Excellent correlation between experimental and theoretical data was obtained for potential
ranges in excess of 2 V.
Trends in parameter values were discussed, and compared to published data. The
transition between stable and unstable passivity of stainless steels was shown to be
dependent on the oxygen reduction diffusion limited current density and the iron dissolution
reaction free corrosion current density, which in turn was linked to the dissolved oxygen
content and temperature of the electrolyte. A new model for the behaviour of stainless
steels in the transpassive region was proposed.
Date of Award | 1995 |
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Original language | English |
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Awarding Institution | |
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Computer Models of Corrosion in Passivating Systems
Phillips, S. S. (Author). 1995
Student thesis: PhD