An electrochemical impedance study of Alloy-22 in NaCl brine at elevated temperature: II. Reaction mechanism analysis

Macdonald, Digby D.; Sun, Adan; Priyantha, Namal; Jayaweera, Palitha

doi:10.1016/j.jelechem.2004.05.032

Cited by 151 publications

(169 citation statements)

References 11 publications

(27 reference statements)

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“…It has been demonstrated previously [41][42][43] that the PDM can readily explain the observations of the passive state on Alloy-22. Characterization work 41,[44][45][46] has demonstrated that the passive film on Alloy-22 has a distinct layered structure with the inner layer primarily comprising Cr(III) oxide, so it is assumed in the optimization that point defective Cr 2 O 3 is the principal composition of the barrier layer.…”

Section: Results and Analysis By Numerical Optimizationmentioning

confidence: 80%

The Kinetics of Nucleation of Metastable Pits on Metal Surfaces: The Point Defect Model and Its Optimization on Data Obtained on Stainless Steel, Carbon Steel, Iron, Aluminum and Alloy-22

Lü

Engelhardt

Kursten

et al. 2016

J. Electrochem. Soc.

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The theory of the kinetics of metastable pit nucleation in terms of the Point Defect Model (PDM) has been applied the first time to describing the evolution of the nucleation rate of metastable pits on a variety of metallic substrates. The PDM successfully accounts for the experimental data that have been reported in the literature on stainless steel, carbon steel, iron, aluminum, and Alloy-22, and which are judged to be reliable and reproducible. Important fundamental parameters related to metastable pitting such as total number density of pitting nucleation sites, dissolution time of the cap over the pit, energy related to absorption of the aggressive ions into oxygen vacancies in the surface of the barrier layer, vacancy condensation rate, and the time at which the nucleation rate of metastable pits is maximum were obtained from the optimization of the PDM on the experimental data, as reported in the present paper. The values obtained for those parameters are in good agreement with values and observations reported elsewhere. The present work successfully demonstrates the capacity of the PDM in accounting for experimental observations of metastable pitting and that the PDM can be applied as an underlying theory for studying and understanding metastable pitting on metal surfaces. The passive state is not perfectly protective and passivity breakdown occurs for various reasons, giving rise to enhanced general corrosion rate or to localized corrosion. Localized passivity breakdown is especially of great concern, because it results in the nucleation and propagation of pits and the subsequent nucleation and growth of cracks provided that there is sufficient tensile stress in the system to initiate crack nucleation at the stress raiser represented by the pit. Metastable pitting, in which passivity breakdown occurs followed immediately by repassivation, is now well-accepted as being an integral part of the process of pitting corrosion on a metal or alloy, culminating in the accumulation of damage via the development of stable pits. It is also well-recognized that repassivation reflects the failure on the part of the pit nucleus to establish a spatial separation between the local cathode and the local anode with the former occurring on the external surfaces and the latter taking place in the nucleus, which is necessary for the buildup and maintenance of the aggressive conditions of high [Cl − ] and high [H + ] (low pH) that cause the pits to grow as stable pits, until they, too, die via delayed repassivation (due to the inability of the pit to maintain separation of the local cathode and the local anode, because of the limited availability of resources of the cathodic depolarizer on the external surfaces).Numerous authors have reported metastable pit nucleation rate data measured under more-or-less well-defined conditions. Williams et al.1-3 reported a good proportional correspondence for Type 304L SS between the nucleation frequency of metastable pits and the frequency of occurrence of propagating (stable) pits, that ...

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Section: Results and Analysis By Numerical Optimizationmentioning

confidence: 80%

The Kinetics of Nucleation of Metastable Pits on Metal Surfaces: The Point Defect Model and Its Optimization on Data Obtained on Stainless Steel, Carbon Steel, Iron, Aluminum and Alloy-22

Lü

Engelhardt

Kursten

et al. 2016

J. Electrochem. Soc.

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“…As it is known, chromium significantly affects protective properties of the conversion layer: even a brief contact with air and/or aqueous media is sufficient to create a thin oxide layer on the electrode surface, which prevents further active chromium dissolution and penetration of the corrosive medium into the depth [25]. The passive oxide layer consists of an inner barrier layer and an outer precipitated oxide/hydroxide (porous) layer [26][27][28]. Usually the passive oxide systems are modelled by an equivalent electrical circuit (EEC) composed of two consecutive parallel (RC) sub-circuits in series with R s (resistance of the solution layer between the reference electrode and the working one).…”

Section: Tests Of Electrochemical Impedance Spectramentioning

confidence: 99%

Characterization of Cr–ZrO2 composite coatings electrodeposited from Cr(III) bath

Bikulčius¹,

Češūnienė²,

Selskienė³

et al. 2018

chemija

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The aim of this work was to incorporate ZrO 2 particles into a Cr matrix within the research work aimed at obtaining metal matrix composite coatings (CrZrO 2 ) under direct current and to evaluate their protective properties. A CrZrO 2 composite coating was deposited from an electrolyte based on trivalent chromium sulphate with formate-urea as a complexing agent containing various concentrations of ZrO 2 . Cross-section investigations have revealed that ZrO 2 particles incorporated into the Cr coating are uniformly distributed. The results indicate that ZrO 2 particles influence the microhardness, morphology and corrosion behaviour of Cr-ZrO 2 composite coatings obtained from the Cr(III) bath. Keywords: zirconium, electrodeposited films, SEM, XPS, EIS, interfaces INTRODUCTIONHard chromium electrodeposition is extensively used in modern industry as it provides good corrosion and wear resistances of the coatings obtained. Commonly, chromium coatings are deposited from hazardous hexavalent chromium baths. In view of a very high toxicity of Cr(VI) compounds, the development of an alternative hexavalent chromium plating process is urgently needed. According to the EU Regulation (EC) No. 1907/2006 the use of chromium trioxide baths for functional and decorative chromium plating will be forbidden or severely limited after 1 September 2017.Among many potential alternatives, trivalent chromium (Cr(III)) plating is considered as a very promising technology to replace conventional hexavalent Cr plating. Inasmuch as Cr coatings deposited in Cr(III) baths do not feature such good properties as Cr coatings deposited in Cr(VI) baths, efforts have been made to improve them by various methods.Electrochemical codeposition of inert particles in a metal matrix is a suitable technique to produce composite materials with new exploitation properties. Different hard dispersion phases distinguish themselves for different electrical conductivity and surface charge, therefore, to incorporate one or another hard disperse phase into a metallic matrix, specific deposition conditions are required [1].One of popular ceramic particles is ZrO 2 . It is known [2,3] that ZrO 2 has many superior properties, such as high G. Bikulčius, A. Češūnienė, A. Selskienė, A. Grigucevičienė, V. Jasulaitienė The aim of this work was to form a Cr(III)-ZrO 2 composite in an environment-friendly Cr(III) bath under the conditions of constant current and to study the incorporation of ZrO 2 disperse particles into the Cr matrix, the elemental composition of the Cr-ZrO 2 composite, surface microhardness (HV), surface morphology (SEM, XPS) and corrosion resistance (OCP, Tafel and EIS). EXPERIMENTALCr-ZrO 2 composite coatings were deposited from the Cr(III) bath containing Cr 2 (SO 4 ) 3 6H 2 O (150 g l -1 ), H 3 BO 3 (30 g l -1 ), Na 2 SO 4 (60 g l -1 ), Al 2 (SO4) 3 18H 2 O (120 g l -1 ), NaF (20 g l -1 ), HCOONa (27 g l -1 ), NH 2 COONH 2 (g l -1 ) under a 30 l h -1 agitation flow of compressed air with a direct current density of 0.2 A cm -2 and pH 2.0 at 20°C. This...

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“…The conversion shown in (8) has been done in order to relate pure capacitance values ( ) to the thickness of passive film layers, according to the following equation [48,49]: . Nevertheless, neglecting some variations in the surface roughness and the dielectric constant, the capacitive response under different conditions can give an indication of how the passive film thickness changes with the changing system conditions.…”

Section: Equivalent Circuit and Interpretationmentioning

confidence: 99%

Corrosion Behaviour of a Highly Alloyed Austenitic Alloy UB6 in Contaminated Phosphoric Acid

Boudalia

Guenbour

Bellaouchou

et al. 2013

International Journal of Corrosion

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The influence of temperature ∘ C) on the electrochemical behaviour of passive films anodically formed on UB6 stainless steel in phosphoric acid solution (5.5 M H 3 PO 4 ) has been examined by using potentiodynamic curves, electrochemical impedance spectroscopy, and Mott-Schottky analysis. UB6 stainless steel in contaminated phosphoric acid is characterised by high interfacial impedance, thereby, illustrating its high corrosion resistance. The obtained results show that the films behave as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. This behaviour is assumed to be the consequence of the semiconducting properties of the iron oxide and chromium oxide regions which compose the passive film.

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An electrochemical impedance study of Alloy-22 in NaCl brine at elevated temperature: II. Reaction mechanism analysis

Cited by 151 publications

References 11 publications

The Kinetics of Nucleation of Metastable Pits on Metal Surfaces: The Point Defect Model and Its Optimization on Data Obtained on Stainless Steel, Carbon Steel, Iron, Aluminum and Alloy-22

The Kinetics of Nucleation of Metastable Pits on Metal Surfaces: The Point Defect Model and Its Optimization on Data Obtained on Stainless Steel, Carbon Steel, Iron, Aluminum and Alloy-22

Characterization of Cr–ZrO2 composite coatings electrodeposited from Cr(III) bath

Corrosion Behaviour of a Highly Alloyed Austenitic Alloy UB6 in Contaminated Phosphoric Acid

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