The morphology, microstructure, chemistry, electronic properties, and electrochemical behavior of a boron-doped nanocrystalline diamond (BDD) thin film grown on quartz were evaluated. Diamond optically transparent electrodes (OTEs) are useful for transmission spectroelectrochemical measurements, offering excellent stability during anodic and cathodic polarization and exposure to a variety of chemical environments. We report on the characterization of a BDD OTE by atomic force microscopy, optical spectroscopy, Raman spectroscopic mapping, alternating-current Hall effect measurements, X-ray photoelectron spectroscopy, and electrochemical methods. The results reported herein provide the first comprehensive study of the relationship between the physical and chemical structure and electronic properties of a diamond OTE and the electrode's electrochemical activity.

The structure and chemical composition of different variants of a commercial (SurTec 650 chromitAL) trivalent chromium process (TCP) conversion coating formed on AA7075-T6 are reported on. Comparison of coatings formed by immersion and spray was undertaken. Three different variants of the TCP coating were studied: 650 E, C and V. ICP-OES revealed similar concentrations of Cr in all three coating baths but differences in Zr, Zn, S (likely as sulfate), and Fe among the three. SEM and EDXS analysis revealed the coating forms (immersion and spray) over the entire alloy surface with some enrichment or thickening on and around intermetallic particles. The coatings generally consist of nodular particles (aggregates) that decorate the surface of all three coatings with the greatest number density seen for 650 E. Cracking and delamination were seen only for 650 C applied by immersion. The conversion coatings (immersion or spray) become more hydrophobic over a 7-day aging period in the laboratory air. Static water contact angles at day 7 are 60-90 o for all the coatings. Ellipsometry data indicated 650 E is the thickest of the three coatings at 95 nm after a 7-day aging period in the laboratory air. Overall, the thickness of the spray-coated films (3 min) is less than the immersion-coated

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The electrochemical properties (open-circuit potentials, anodic and cathodic polarization curve currents, and polarization resistances) were evaluated for AA7075-T6 alloys coated with three variants of a commercial trivalent chromium process (TCP) pretreatment coating. The coatings were formed on degreased and deoxidized aluminum alloy specimens. Measurements were made in oxygenated 0.5 M Na2SO4 and 3.5% NaCl. Comparison of coatings formed by immersion and spray was undertaken. The three coating variants were 650 chromitAL, versions E, V, and C. Similar concentrations of Cr were in all three coating baths but there were differences in Zr, Zn, S (likely as sulfate), and Fe among the three. TCP coatings formed by immersion exhibited electrochemical properties similar to those formed by spray. Overall, the greatest level of corrosion protection was provided by 650 E based on electrochemical data and results from a 14 d thin-layer mist (3.5% NaCl, 55°C) accelerated degradation test. The coating provides both anodic and cathodic protection in low-chloride electrolytes and functions as more of a cathodic inhibitor in high-chloride electrolytes. Rotating disk voltammetric data revealed the coating inhibits the reduction of dissolved oxygen by providing a diffusional barrier and possibly blocking sites for O2 chemisorption on the cathodically-active intermetallic phases.

We report on the physicochemical properties and anti-corrosion performance of a non-chromated Zr/Zn conversion coating (NCP) on AA2024-T3. The immersion coating was formed on polished, degreased and deoxidized specimens. Electrochemical methods were used to assess the corrosion inhibition provided by the coating in laboratory tests. The results were compared with environmental exposure tests to assess the stand-alone corrosion protection. Coated AA6061-T6 and 7075-T6 specimens were also used in the environmental tests. Electrochemical testing in naturally-aerated 0.5 M Na 2 SO 4 + 0.1% NaCl revealed that the NCP coating shifted E corr positive by about 250 mV, suppressed anodic more than cathodic current around E corr by at least a factor of 10x and shifted E pit more noble. The coating functions more as an anodic inhibitor through barrier layer protection. The coating provided excellent corrosion protection to all three alloys during a 14-day full immersion test in 0.5 M Na 2 SO 4 + 0.1% NaCl. However during 14-day neutral salt spray and thin-layer mist tests, NCP failed to provide much stand-alone corrosion protection to the aluminum alloys and the anti-corrosion properties were found to be inferior to TCP conversion coatings of comparable thickness. A 7-day beach exposure revealed the NCP coating also provides little resistance to galvanic corrosion on the aluminum alloys as compared to TCP coatings. The results demonstrate that laboratory evaluation of the anti-corrosion properties of non-chromated conversion coatings does not always reflect coating performance during accelerated degradation or environmental exposure. The inferior anti-corrosion behavior of NCP, as compared to TCP, is due to (i) inherent defect density of the former (i.e., reduced throwing power) and ( AA2024 and AA7075 are high-strength aluminum alloys that derive their properties from their alloying components. They are used on civilian and military aircraft because of their light weight and mechanical strength. 1,2 However, many of the constituent particles, such as the Al 2 CuMg phase (so-called S-phase) in AA2024 3,4 and Mg(ZnCuAl) 2 in AA7075, 5-8 lead to corrosion challenges. More noble intermetallic particles play a critical role in the corrosion susceptibility of aluminum alloys as they can give rise to localized corrosion, such as pitting and exfoliation, because of the formation of galvanic cells with the surrounding aluminum. [9][10][11] The intermetallic phases tend to function as cathodic sites supporting oxygen reduction, which can drive the localized dissolution of nearby aluminum. The shape, size and chemical composition of the intermetallic particles are determined by the processing route (heat-treatment and forming) carried out on the aluminum alloy. [9][10][11] Multilayer coating systems (conversion coating + primer + topcoat) are required to protect aerospace aluminum alloys from corrosion in service. Traditional coating systems contain hexavalent chromium (Cr(VI)) in both the conversion coating and primer, volatile orga...