Abstract:In order to understand more clearly the nature of the anodic film formed on aluminum and its alloys, and the mechanism of inhibition of corrosion by chromates, a novel investigation has been made on the anodic film formed on AA1060 using X-ray photoelectron spectroscopy. The goal has been to elucidate whether the interaction of CrO 4 2Ϫ on Al alloy surfaces is in certain aspects analogous to that of MoO 4 2Ϫ on stainless steel surfaces and investigate whether a bipolar mechanism is applicable to aluminum surfa… Show more
“…We have earlier shown that aluminum hydroxide films, which impart lesser corrosion resistance than aluminum oxide passive films, are susceptible to chloride ingress, while aluminum oxide films formed by deprotonation of hydrated films by chromate are protected. 57 Hence, we consider this hydration to be the reason for the observed activation.…”
Electrochemical techniques were employed to study the nature of individual interactions between the chemicals constituting a widely used commercial chromate conversion-coating treatment and the main constituents of AA2024-T3 alloy, namely, Al ͑99.999%͒, Al 2 Cu, Al-Al 2 Cu galvanic couple, and AA2024-T3 alloy. The samples were pretreated using chromate, ferricyanide, fluoride, tetrafluoroborate, and hexafluorozirconate, prior to electrochemical corrosion tests. The results were compared with untreated ͑control͒ samples. For the first time, the chemical interaction of aluminum with hexafluorozirconate has been studied. Maximum activation was observed in the case of hexafluorozirconate pretreatment, which also decreased the interfacial tension and increased surface wetting. The electrochemistry of the control and pretreated ͑except for hexafluorozirconate pretreatment͒ AA2024-T3 and Al 2 Cu were found to be similar. The cathodic electron transfer reaction rate for oxygen reduction was found to be enhanced by the presence of copper in the systems. The enhancement was proportional to the copper content. The cathodic reaction on all systems was inhibited by chromate. Aluminum was observed to undergo cathodic corrosion, leading to an enrichment of the surface copper content and subsequent enhancement of the cathodic electron transfer reaction.
“…We have earlier shown that aluminum hydroxide films, which impart lesser corrosion resistance than aluminum oxide passive films, are susceptible to chloride ingress, while aluminum oxide films formed by deprotonation of hydrated films by chromate are protected. 57 Hence, we consider this hydration to be the reason for the observed activation.…”
Electrochemical techniques were employed to study the nature of individual interactions between the chemicals constituting a widely used commercial chromate conversion-coating treatment and the main constituents of AA2024-T3 alloy, namely, Al ͑99.999%͒, Al 2 Cu, Al-Al 2 Cu galvanic couple, and AA2024-T3 alloy. The samples were pretreated using chromate, ferricyanide, fluoride, tetrafluoroborate, and hexafluorozirconate, prior to electrochemical corrosion tests. The results were compared with untreated ͑control͒ samples. For the first time, the chemical interaction of aluminum with hexafluorozirconate has been studied. Maximum activation was observed in the case of hexafluorozirconate pretreatment, which also decreased the interfacial tension and increased surface wetting. The electrochemistry of the control and pretreated ͑except for hexafluorozirconate pretreatment͒ AA2024-T3 and Al 2 Cu were found to be similar. The cathodic electron transfer reaction rate for oxygen reduction was found to be enhanced by the presence of copper in the systems. The enhancement was proportional to the copper content. The cathodic reaction on all systems was inhibited by chromate. Aluminum was observed to undergo cathodic corrosion, leading to an enrichment of the surface copper content and subsequent enhancement of the cathodic electron transfer reaction.
“…With regards to the progression of Cr(III) adsorption onto nanoboehmite surfaces, they [203] concluded that initial Cr(III) adsorption onto nanoboehmite under alkaline conditions occur by hydroxyl ligand exchange which leads to inner-sphere binding of Cr(OH) 4 −monomers, but at Cr(III) concentration in solution >20 ppm these monomers polymerize into clusters. Chromate ions are reported by several authors [204][205][206][207] to inhibit both hydration and deprotonation of anodic oxide films on aluminum.…”
Section: What Makes Chromium Sealing Unique and Accounts For Its Actimentioning
Increasing demands for environmental accountability and energy efficiency in industrial practice necessitates significant modification(s) of existing technologies and development of new ones to meet the stringent sustainability demands of the future. Generally, development of required new technologies and appropriate modifications of existing ones need to be premised on in-depth appreciation of existing technologies, their limitations, and desired ideal products or processes. In the light of these, published literature mostly in the past 30 years on the sealing process; the second highest energy consuming step in aluminum anodization and a step with significant environmental impacts has been critical reviewed in this systematic review. Emphasis have been placed on the need to reduce both the energy input in the anodization process and environmental implications. The implications of the nano-porous structure of the anodic oxide on mass transport and chemical reactivity of relevant species during the sealing process is highlighted with a focus on exploiting these peculiarities, in improving the quality of sealed products. In addition, perspective is provided on plausible approaches and important factors to be considered in developing sealing procedures that can minimize the energy input and environmental impact of the sealing step, and ensure a more sustainable aluminum anodization process/industry.Coatings 2020, 10, 226 2 of 55 sealing methods. Furthermore, the applicability of another hitherto popular sealing process; chromate sealing, is currently limited to essential parts in the aerospace industry due to toxicological, health, and environmental implications traced to Cr(VI) employed in the process [7][8][9][10][11][12][13][14][15][16]. On the other hand, the advantages of another industrially utilized sealing process; the nickel fluoride (cold) sealing process is limited by the toxicity of nickel salts which narrows its range of application, and introduces added costs due to post-sealing wastewater treatments and management [17][18][19][20]. Further efforts at sealing anodized aluminum at temperatures lower than that used in hydrothermal (high temperature) sealing, have led to much variety in the chemical constitution and operating temperatures of sealing baths [21]. On the basis of temperature at which the sealing step is carried out, sealing can be classified into three major categories; high temperature, mid-temperature, and room-temperature or cold sealing. In this work sealing at temperatures from 0 to 40 • C is classified as low temperature sealing, from ≥ 40 • C to 70 • C as intermediate or mid temperature sealing, and sealing at temperatures > 70 • C as high temperature sealing.
“…All XPS Spectra were taken at 90 • take off angle with respect to the sample surface and all spectra were corrected for charging by using the C 1 s line of adventitious carbon at 284.6 eV as a reference. All curve fitting followed the methods outlined by Savitsky and Golay [11], and Sherwood [12], as well as procedures developed over the years by Halada and Clayton [13][14][15] using CASA software version 1.001. XPS was performed on select samples to determine the surface (depth analysis 5-10 nm) chemical changes taking place on the spool material and the resulting printed 3D structures.…”
Featured Application: Detailed chemical and structural changes to polylactid acid (PLA) from source material through 3D printing needs to be quantified in order to use PLA 3D printed structures for specific applications. This work was specifically motivated for specific applications for in situ synthesis of silver nanoparticles on printed PLA surfaces used in antimicrobial applications and the development and characterization of PLA constructs for tissue engineering.Abstract: Polylactic acid (PLA) is an organic polymer commonly used in fused deposition (FDM) printing and biomedical scaffolding that is biocompatible and immunologically inert. However, variations in source material quality and chemistry make it necessary to characterize the filament and determine potential changes in chemistry occurring as a result of the FDM process. We used several spectroscopic techniques, including laser confocal microscopy, Fourier transform infrared (FTIR) spectroscopy and photoacousitc FTIR spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) in order to characterize both the bulk and surface chemistry of the source material and printed samples. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to characterize morphology, cold crystallinity, and the glass transition and melting temperatures following printing. Analysis revealed calcium carbonate-based additives which were reacted with organic ligands and potentially trace metal impurities, both before and following printing. These additives became concentrated in voids in the printed structure. This finding is important for biomedical applications as carbonate will impact subsequent cell growth on printed tissue scaffolds. Results of chemical analysis also provided evidence of the hygroscopic nature of the source material and oxidation of the printed surface, and SEM imaging revealed micro-and submicron-scale roughness that will also impact potential applications.
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