The Point Defect Model for Bi-Layer Passive Films

Macdonald, Digby D.; Englehardt, George

doi:10.1149/1.3496427

Cited by 79 publications

(37 citation statements)

References 23 publications

(70 reference statements)

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“…No active‐to‐passive transition was evident in Region 1, indicating that the active state did not exist in sulphide‐containing solutions, whereas a typical active‐to‐passive transition existed in Region 2, which showed an increase in the current density; details of the reactions are described in the subsequent section. Our previous work, which is cited in this paper, showed unequivocally that, in the presence of sulphide in Region 1, the passive film has a bi‐layer structure comprising a compact barrier layer of cuprous sulphide and a precipitated outer layer of either cuprous or cupric sulphide, depending on the exact conditions.…”

Section: Resultsmentioning

confidence: 71%

Long‐term polarisation and immersion for copper corrosion in high‐level nuclear waste environment

Kong

Dong

et al. 2017

Materials & Corrosion

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Long‐term polarisation and immersion for copper corrosion were investigated in chloride‐containing sulphide solutions. Results showed that no active state exists for copper in sulphide‐containing solutions, whereas a typical active‐to‐passive transition exists in the second passivation region, indicating a hydroxyl activation effect on copper. After the sulphide passive film broke down, the pitting area was re‐passivated by hydroxide ions; however, if the chloride and sulphide concentrations were both high, then there was no second passivation and the copper would dissolve rapidly. The corrosion resistance and the film thickness both increased with increasing immersion time and an average corrosion rate of 51.2 µm/year was obtained in aerobic solution, which was much higher than in bentonite or under deoxygenated conditions. Moreover, several local corrosion pits appeared after 1‐year immersion and this would occur at the beginning of storage.

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Section: Resultsmentioning

confidence: 71%

Long‐term polarisation and immersion for copper corrosion in high‐level nuclear waste environment

Kong

Dong

et al. 2017

Materials & Corrosion

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“…According to the point defect model, [38,49,50,51] the thickness of the barrier oxide layer through which tunneling must occur can be written as:Lss=1−αεV+g where ε is the electric field strength, and g is a function of pH and the standard rate constants for film formation at the metal/barrier layer (m/bl) interface and the dissolution rate at the bl/s interface, among other parameters (see Equation (3)). Substitution of Equation (10) into Equation (8) yields the tunneling current as:i=truei0^e−trueβ^(1−αε)Ve−βg.…”

Section: Discussionmentioning

confidence: 99%

Studies on Pitting Corrosion of Al–Cu–Li Alloys Part III: Passivation Kinetics of AA2098–T851 Based on the Point Defect Model

et al. 2019

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In this paper, the passivation kinetics of AA2098–T851 was investigated by a fundamental theoretical interpretation of experimental results based on the mixed potential model (MPM). The steady state passive layer formed on the AA2098–T851 in NaHCO3 solution in a CO2 atmosphere upon potentiostatic stepping in the anodic direction followed by stepping in the opposite direction was explored. Potentials were selected in a way that both anodic passive dissolution of the metal and hydrogen evolution reaction (HER) occur, thereby requiring the MPM for interpretation. Optimization of the MPM on the experimental electrochemical impedance spectroscopy (EIS) data measured after each potentiostatic step revealed the important role of the migration of Al interstitials in determining the kinetics of passive layer formation and dissolution. More importantly, it is shown that the inequalities of the kinetics of formation and dissolution of the passive layer as observed in opposite potential stepping directions lead to the irreversibility of the passivation process. Finally, by considering the Butler–Volmer (B–V) equation for the cathodic reaction (HER) in the MPM, and assuming the quantum mechanical tunneling of the charge carriers across the barrier layer of the passive film, it was shown that the HER was primarily controlled by the slow electrochemical discharge of protons at the barrier layer/solution (outer layer) interface.

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“…(3). According to the point defect model [13][14][15][16][17][18], the thickness of the barrier oxide layer through which the tunnelling occurs can be expressed as…”

Section: Quantum Tunnelling Definition Of Current Densitymentioning

confidence: 99%

Re-defining the kinetics of redox reactions on passive metal surfaces

Macdonald

Qiu

2020

J Solid State Electrochem

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It is known that the kinetics of redox reactions occurring on the surfaces of passive metals depend upon the properties of the passive film, ostensibly due to quantum mechanical tunnelling (QMT) of electrons and holes between the metal and the redox couple at the barrier layer/solution (bl/s) interface. In this paper, the tunnelling probability is used to inter-convert the exchange current densities for the redox reactions occurring at the bl/s interface and on the hypothetical bare metal surface. We review our previous work on combining QMT theory with the point defect model (PDM), which provides an analytical expression for the bl thickness as a function of voltage. By combining QMT theory and the PDM, we derive a modified form of the generalized Butler-Volmer equation that requires as input only the kinetic parameters for the redox reaction on the hypothetical bare surface and parameters contained in the PDM. The application of the theory is illustrated with reference to the corrosion of carbon steel in concrete pore solution, to calculating the corrosion potential of, and crack growth rate in, sensitized type 304 SS in boiling water reactor (BWR) coolant circuits, and the use of hydrogen oxidation on platinum to determine the thickness of the bl as a function of voltage and temperature. This illustrates a new, powerful technique for probing the formation of passive films on metal surfaces.

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The Point Defect Model for Bi-Layer Passive Films

Cited by 79 publications

References 23 publications

Long‐term polarisation and immersion for copper corrosion in high‐level nuclear waste environment

Long‐term polarisation and immersion for copper corrosion in high‐level nuclear waste environment

Studies on Pitting Corrosion of Al–Cu–Li Alloys Part III: Passivation Kinetics of AA2098–T851 Based on the Point Defect Model

Re-defining the kinetics of redox reactions on passive metal surfaces

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