Mineralogical Transformation and Electrochemical Nature of Magnesium-Rich Primers during Natural Weathering

Pathak, S.S.; Blanton, Michael D.; Mendon, Sharathkumar K.; Rawlins, James W.

doi:10.3390/met4030322

Cited by 7 publications

(10 citation statements)

References 11 publications

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“…As is common for outdoor exposure, and as was found in this Mg-Li study, carbonate compounds are formed and can be considered along with the usual oxide/hydroxide compounds. 2,24,30,[32][33][34][36][37][38] The stability of a carbonate compound depends on the concentration of the carbonate ion as a function of pH, as the carbonate ion can participate in proton exchange reactions according to the stability of its variously protonated species as a function of pH. 39 The total concentration of each carbonate species present as a function of pH can be calculated as expressed by Eq.…”

Section: Resultsmentioning

confidence: 99%

Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium

2018

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Predicting the stability of chemical compounds as a function of solution chemistry is crucial towards understanding the electrochemical characteristics of materials in real-world applications. There are several commonly considered factors that affect the stability of a chemical compound, such as metal ion concentration, mixtures of ion concentrations, pH, buffering agents, complexation agents, and temperature. Chemical stability diagrams graphically describe the relative stabilities of chemical compounds, ions, and complexes of a single element as a function of bulk solution chemistry (pH and metal ion concentration) and also describe how solution chemistry changes upon the thermodynamically driven dissolution of a species into solution as the system progresses towards equilibrium. Herein, we set forth a framework for constructing chemical stability diagrams, as well as their application to Mg-based and Mg-Zn-based protective coatings and lightweight Mg-Li alloys. These systems are analyzed to demonstrate the effects of solution chemistry, alloy composition, and environmental conditions on the stability of chemical compounds pertinent to chemical protection. New expressions and procedures are developed for predicting the final thermodynamic equilibrium between dissolved metal ions, protons, hydroxyl ions and their oxides/hydroxides for metal-based aqueous systems, including those involving more than one element. The effect of initial solution chemistry, buffering agents, complexation agents, and binary alloy composition on the final equilibrium state of a dissolving system are described by mathematical expressions developed here. This work establishes a foundation for developing and using chemical stability diagrams for experimental design, data interpretation, and material development in corroding systems.

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Section: Resultsmentioning

confidence: 99%

Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium

2018

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“…This observation is predicting the surface becoming homogenous with the passage of exposure periods of the coating in the solution. Blucher et al (2001) and other researchers have observed that for aluminum metal exposed in NaCl solution polluted by CO 2 in the environment, the surface is inhibited by corrosion products due to the cathodic reduction of oxygen and anodic dissolution of metal by high pH [54][55][56][57]. In this study the formation of passive films that stifle the anodic dissolution of coating are as follow:…”

Section: Electrochemical Impedance Spectroscopy (Eis) Evaluation Of Cmentioning

confidence: 94%

Corrosion Resistance Properties of Aluminum Coating Applied by Arc Thermal Metal Spray in SAE J2334 Solution with Exposure Periods

Lee

Singh

Ismail

et al. 2016

Metals

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Arc thermal metal spray coating provides excellent corrosion, erosion and wear resistance to steel substrates. This paper incorporates some results of aluminum coating applied by this method on plain carbon steel. Thereafter, coated panels were exposed to an environment known to form stable corrosion products with aluminum. The coated panels were immersed in Society of Automotive Engineers (SAE) J2334 for different periods of time. This solution consists of an aqueous solution of NaCl, CaCl 2 and NaHCO 3 . Various electrochemical techniques, i.e., corrosion potential-time, electrochemical impedance spectroscopy (EIS) and the potentiodynamic were used to determine the performance of stimulants in improving the properties of the coating. EIS studies revealed the kinetics and mechanism of corrosion and potentiodynamic attributed the formation of a passive film, which stifles the penetration of aggressive ions towards the substrate. The corrosion products that formed on the coating surface, identified using Raman spectroscopy, were Dawsonite (NaAlCO 3 (OH) 2 ) and Al(OH) 3 . These compounds of aluminum are very sparingly soluble in aqueous solution and protect the substrate from pitting and uniform corrosion. The morphology and composition of corrosion products determined by scanning electron microscopy and energy dispersive X-ray analyses indicated that the environment plays a decisive role in improving the corrosion resistance of aluminum coating.

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“…1 Over the past few years, a commercial organic coating system containing a Mg-rich primer (MgRP) has been developed for the active corrosion protection of aerospace aluminum alloys. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The commercial MgRP coating system consists of a surface pretreatment, an epoxy resin with metallic Mg pigment and, where applicable, a polyurethane topcoat. The active corrosion protection of any Al alloy is provided by galvanic coupling of more active Mg pigment in the primer which is active compared to the more noble AA2024-T351 substrate.…”

mentioning

confidence: 99%

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Full Immersion: a Galvanic Throwing Power Investigation Using a Scanning Vibrating Electrode Technique

Kannan

Glover

McMurray

et al. 2018

J. Electrochem. Soc.

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The scanning vibrating electrode technique (SVET) was employed to examine the effect of 'galvanic throwing power' and the distance over which a Mg-rich primer (MgRP) provided sacrificial anode-based cathodic protection to AA2024-T351. Three systems were investigated in full immersion conditions where the same MgRP was used with three different pretreatments: Non-film forming (NFF), trivalent chromium pretreatment (TCP) and anodization with a chromate seal (ACS). Experiments were conducted with two coating/defect area ratios and three parameters were monitored: 1) the maximum peak height of local anodes, inferring the location and intensity of pits, 2) the current density profile at the coating/defect interface (CDI) region and 3) total integrated anodic and cathodic current density values of defined areas in the defect region moving progressively away from the CDI. The NFF-based system was shown to provide the superior galvanic throwing power and a quasi-steady-state galvanic current distribution was detected in the defect region adjacent to the CDI indicating enhanced cathodic activity in response to the MgRP. High resistance between the MgRP and the substrate, due to the thickness of the pretreatment layer, appeared to mediate galvanic interactions in the case of TCP and ACS-based systems.

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Mineralogical Transformation and Electrochemical Nature of Magnesium-Rich Primers during Natural Weathering

Cited by 7 publications

References 11 publications

Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium

Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium

Corrosion Resistance Properties of Aluminum Coating Applied by Arc Thermal Metal Spray in SAE J2334 Solution with Exposure Periods

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Full Immersion: a Galvanic Throwing Power Investigation Using a Scanning Vibrating Electrode Technique

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