Corrosion behaviour of solar reflector coatings on AA 2024T3 – an electrochemical impedance spectroscopy study

Kumar, C. S.; Rao, V. Shankar; Raja, V.S.; Sharma, Anand; Mayanna, S. M.

doi:10.1016/s0010-938x(01)00082-8

Cited by 24 publications

(5 citation statements)

References 11 publications

(11 reference statements)

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“…It means Al-5 Mg coating has a higher corrosion resistance than the Al coating after 1 h of immersion in 3.5 wt.% NaCl solution. The phase-frequency Bode plots of both coatings at high frequency reveal the oxide film formation, as has been suggested by other authors [52][53][54][55][56]. The Al-5 Mg coating exhibits around a -80° phase angle maxima at 100 kHz due to the surface properties where this coating shows dense and uniform morphology as well as a high contact angle.…”

Section: Electrochemical Impedance Spectroscopy (Eis) With Immersion ...supporting

confidence: 79%

Role of 5 wt.% Mg Alloying in Al on Corrosion Characteristics of Al-Mg Coating Deposited by Plasma Arc Thermal Spray Process

Jeong

Singh

2023

Materials

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The corrosion of steel structures in coastal areas is a major issue. Therefore, in the present study, the protection against the corrosion of structural steel is carried out by depositing 100 μm thick Al and Al-5 Mg coatings using a plasma arc thermal spray process, immersing them in 3.5 wt.% NaCl solution for 41 days (d). To deposit such metals, one of the best known processes, arc thermal spray, is frequently used, but this process has severe defects and porosity. Thus, to minimize the porosity and defects of arc thermal spray, a plasma arc thermal spray process is developed. In this process, we used normal gas to create plasma instead of argon (Ar) and nitrogen (N2) with hydrogen (H) and helium (He). Al-5 Mg alloy coating exhibited uniform and dense morphology, where it reduced more than four times the porosity compared to Al, where Mg fills the voids of the coating, resulting in greater bond adhesion and hydrophobicity. The open circuit potential (OCP) of both coatings exhibited electropositive values due to the formation of native oxide in Al, while in the case of Al-5 Mg, the coating is dense and uniform. However, after 1 d of immersion, both coatings showed activation in OCP, owing to the dissolution of splat particles from the corner where the sharp edges are present in the Al coating, while Mg preferentially dissolved in the Al-5 Mg coating and made galvanic cells. Mg is galvanically more active than Al in the Al-5 Mg coating. Due to the capacity of the corrosion products to cover the pores and defects, both coatings stabilized the OCP after 13 d of immersion. The total impedance of the Al-5 Mg coating is gradually increased and is higher than the Al, which can be attributed to the uniform and dense coating morphology where Mg dissolves and agglomerates to form globular corrosion products and deposit over the surface, thereby causing barrier protection. The defect bearing corrosion products on Al coating led to the cause having a higher corrosion rate than the Al-5 Mg coating. A total of 5 wt.% mg in the Al coating improved the corrosion rate by a rate of 1.6 times compared to the pure Al in the 3.5 wt.% NaCl solution after 41 d of immersion.

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Section: Electrochemical Impedance Spectroscopy (Eis) With Immersion ...supporting

confidence: 79%

Role of 5 wt.% Mg Alloying in Al on Corrosion Characteristics of Al-Mg Coating Deposited by Plasma Arc Thermal Spray Process

Jeong

Singh

2023

Materials

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“…It is observed that SPCN1 and SPCN2 exhibit one time constant around −52° on 11 and 71 Hz, respectively, owing to the deposition of treatment film while AC and SPCN3 show two different time constants at different frequencies ( Figure 6a). Middle frequency attributed to the treatment/corrosion products while lower frequency shows the characteristics of the coating [34,[60][61][62][63]. The SPCN3 sample shows highest shifting in phase angle maxima at −62° on 120 Hz while at lower frequency i.e., 0.03 Hz exhibit at −13°.…”

Section: Electrochemical Impedance Spectroscopy (Eis)mentioning

confidence: 96%

Effect of Sodium Phosphate and Calcium Nitrate Sealing Treatment on Microstructure and Corrosion Resistance of Wire Arc Sprayed Aluminum Coatings

et al. 2020

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Aluminum coating was deposited by arc thermal spraying process onto the steel substrate for the corrosion protection in aggressive environment. However, the arc thermal sprayed coating possesses defects in the coating. Thus, it is important to reduce the defects and enhance the corrosion resistance properties of the deposited coating using post-treatment. In the present study, we have used different concentrations of sodium phosphate mono basic (NaH2PO4) with 0.1 molar (M) calcium nitrate [Ca(NO3)2] as post-treatment solution to fill out the defects of the Al coating. It was observed by scanning electron microscopy (SEM) that 1 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample exhibited 71% reduction in defects compared to as coated samples. X-ray diffraction (XRD) was performed to determine the phases formed on the coating surface after treatments. XRD confirms the formation of sodium aluminum hydrogen phosphate (Na3Al(OH)(HPO4)(PO4)) and brushite (Ca(HPO4)(H2O)2) as composite oxides on the Al coating. Electrochemical results show that 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample has exhibited the highest charge transfer resistance and the lowest corrosion current density after 89 days of exposure in 3.5 wt.% NaCl solution. The enhancement in corrosion resistance of 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample attributed to the formation of adherent, sparingly soluble, and stable corrosion products. The volume fraction result of the corrosion products formed on 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample after 89 days of exposure in 3.5 wt.% NaCl using XRD confirms the highest amount of Bayerite (α-Al(OH)3) deposition, thus, the corrosion rate of this sample was the lowest.

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“…Damage function (D) also offers important information in the corrosion behaviour of coatings. It gives a quantitative measure of degradation of impedance modulus over a period of immersion [28]. D is evaluated as follows: Corrosion current, I Corr , is calculated from anodic and cathodic Tafel slopes from the linear polarisation plots using the Stern-Geary equation given below, and results are shown in Table 3:…”

Section: Breakpoint Frequency Is Given Bymentioning

confidence: 99%

“…Equivalent electrical circuit models were developed to fit the experimental impedance data and to estimate the electrochemical parameters of porous and barrier layers [6,[15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Frequencies as low as 1 mHz were used to evaluate the barrier layer resistance and capacitance values from Bode plots in the aforementioned studies.…”

Section: Introductionmentioning

confidence: 99%

Porous Layer Characterization of Anodized and Black-Anodized Aluminium by Electrochemical Studies

et al. 2012

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Three types of black anodic coatings, namely, black dyeing (BD), inorganic colouring (IC), and electrolytic colouring (EC) were prepared by conventional type II sulphuric acid anodizing on Al6061 alloys. Electrochemical behaviour of these coatings was studied by exposure to 3.5% wt sodium chloride solution for prolonged immersion periods up to 360 hours. The porous layer characteristics of all sealed, fresh and autosealed coatings were investigated by means of electrochemical impedance spectroscopy (EIS). An equivalent circuit that reproduces the a.c. impedance results of porous aluminium oxide films is proposed. The breakpoint frequency and damage function analysis were carried out to analyse the coating's electrochemical behaviour. Corrosion morphology was studied by scanning electron microscopy. It was observed that BD and IC behaved in a very similar manner to sulphuric acid anodising (SAA). However EC was behaving in an entirely different manner. Among all colouring methods BD was showing very less values. All these findings were further confirmed by linear polarisation studies. No major evidence of localised corrosion or pitting of the black anodic coatings was observed in SEM micrographs.

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Corrosion behaviour of solar reflector coatings on AA 2024T3 – an electrochemical impedance spectroscopy study

Cited by 24 publications

References 11 publications

Role of 5 wt.% Mg Alloying in Al on Corrosion Characteristics of Al-Mg Coating Deposited by Plasma Arc Thermal Spray Process

Role of 5 wt.% Mg Alloying in Al on Corrosion Characteristics of Al-Mg Coating Deposited by Plasma Arc Thermal Spray Process

Effect of Sodium Phosphate and Calcium Nitrate Sealing Treatment on Microstructure and Corrosion Resistance of Wire Arc Sprayed Aluminum Coatings

Porous Layer Characterization of Anodized and Black-Anodized Aluminium by Electrochemical Studies

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