Corrosion protection afforded by praseodymium conversion film on Mg alloy AZNd in simulated biological fluid studied by scanning electrochemical microscopy

Abstract

Surface passivation of AZNd Mg alloy with Pr(NO 3 ) 3 is studied using scanning electrochemical microscopy (SECM) in surface generation/tip collection (SG/TC) and AC modes. Corrosion protection afforded by the Pr treatment and the degradation mechanism in a simulated biological environment was examined on a local scale and compared with non-treated AZNd. SG/TC mode results revealed a drastic decrease in H2 evolution due to the Pr treatment. Mapping the local insulating characteristics using AC-SECM showed higher conductivity of the surface where H 2 evolution was most favorable. Keywordsscanning, studied, fluid, biological, simulated, corrosion, microscopy, protection, electrochemical, afforded, praseodymium, conversion, film, mg, alloy, aznd Disciplines Engineering | Physical Sciences and Mathematics Publication DetailsJamali, S. S., Moulton, S. E., Tallman, D. E., Forsyth, M., Weber, J., Mirabedini, A. & Wallace, G. G. (2015). Corrosion protection afforded by praseodymium conversion film on Mg alloy AZNd in simulated biological fluid studied by scanning electrochemical microscopy. Journal of Electroanalytical Chemistry, 739 211-217. AuthorsSeyed S. Jamali, Simon E. Moulton, Dennis E. Tallman, Maria Forsyth, Jan Weber, Azadehsadat Mirabedini, and Gordon G. Wallace AbstractSurface passivation of AZNd Mg alloy with Pr(NO 3 ) 3 is studied using scanning electrochemical microscopy (SECM) in surface generation/tip collection (SG/TC) and AC modes. Corrosion protection afforded by the Pr treatment and the degradation mechanism in a simulated biological environment was examined on a local scale and compared with nontreated AZNd. SG/TC mode results revealed a drastic decrease in H 2 evolution due to the Pr treatment. Mapping the local insulating characteristics using AC-SECM showed higher conductivity of the surface where H 2 evolution was most favorable.

Biodegradable Conducting Polymer Coating to Mitigate Early Stage Degradation of Magnesium in Simulated Biological Fluid: An Electrochemical Mechanistic Study

“…The subsequent drop of impedance observed at 48hr is related to break down of Pr conversion coating in the long term exposure to corrosive media which has been also reported in earlier studies. [25,27] Similar behavior is observed in the case of PrOx/20 BL PTC surface treatment (Figure 12d) suggesting insufficient protective efficiency of the Pr conversion coating in the long term due to instability of the conversion layer in presence of chloride. In contrast, a smaller change is observed in the impedance values for the specimens treated with 20 and 40 BLs of PTC (Figure 12b and c) and the consistent increase in the impedance value during the entire immersion time indicates the higher resistance of these surface layers against electrolytic break down.…”

“…The Oxygen (O) rich layer evident in Figures 5c and d indicates that the Pr conversion film was mainly composed of Pr oxide. [25] The sulfur (S) rich layer evident in Figure 5e represents the PTC film with a roughness that follows the surface profile of the Pr conversion coating.…”

“…In the case of combined Pr conversion film overlaid by 20 BL PTC coating (Figure 8d), strong positive feedback is observed indicating the predominant insulating characteristics of the surface which is comparable to the insulating characteristics of the Pr conversion coated AZNd (Figure 10a) with known insulating characteristics. [25] It is hypothesized that the insulating layer of PrOx in between the conducting PTC coating and AZNd surface interrupts any electrical connection between the PTC and AZNd while the inconsistent PTC coating with submicron thickness does not have required electrical conductivity characteristics to carry the AC signal. This is schematically illustrated in Figure 8b, with the R coating representing the impedance of the PTC layer being significant enough to effectively impede the AC signal at these frequencies.…”

“…Conversion coatings based on lanthanum (La), cerium (Ce) and praseodymium (Pr) have been shown to provide temporary protection to the underlying metal substrate and their protective properties for number of Mg alloys such as AZNd, [25,26] WE43, [27] AZ31, [28] AZ91, AM50, [29] AZ63 [30] and WE43 [31] have been studied. The majority of these studies have shown effective protection afforded by the rare earth element (REE) conversion coating in the short term that tends to deteriorate as exposure time to the corrosive environment increases.…”

Electro‐oxidation and reduction of H2 on platinum studied by scanning electrochemical microscopy for the purpose of local detection of H2 evolution

“…Sensing H 2 via electro‐oxidation at SECM tip has been utilized for studying corrosion of metals and electro‐catalytic activity of surfaces . SECM in SG/TC mode has been applied elsewhere in the reverse order for screening hydrogen oxidation reaction (HOR) where the H + generated electro‐catalytically at the substrate was reduced to H 2 at the tip and the reduction current was measured.…”