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...

The chemical reactions between poly (acrylic acid) and cobalt (III) oxide and between poly (acrylic acid) and cobalt (III) fluoride were studied by Fourier Transform Infrared Spectroscopy. The results demonstrate the formation of cements between the metal and PAA aqueous solutions. Structural information was obtained from the observed frequency shifts of the absorption bands of the carboxylates groups in the cobalt (III) poly (acrylate) relative to those recorded for the purely ionic form. The results show that the bidentate bridging structure is the most likely to occur in both cases. Also, from the analysis of the corresponding coordination chemistry, an octahedral structure may be tentatively assigned to the cobalt (III) poly (acrylate).

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A time course of tissue ionic changes, and their relation to ultrastructural findings during reperfusion following a 15-min global ischemic brain insult was studied in a dog model. Parietal cortex was analyzed for Ca, Na, K, Mg and Fe in controls and after 10 min, 2, 4, and 8 h of reperfusion. After 8 h of reperfusion, the mean values (mumol/g tissue wet wt.) for Ca (control = 1.43, 8 h = 2.76) and Na (control 60.4, 8 h = 107.4) doubled and K (control = 90.4, 8 h = 48.5) decreased to half that of the control. Ultrastructural studies and subcellular localization of calcium in parietal cortex of in situ-fixed brains after 8 h showed cortical neurons with clumping of nuclear chromatin, dilatation of endoplasmic reticulum and disruption of plasma membranes. Large amounts of electron-dense precipitates of calcium were present within dilated astrocytic processes, synaptic vesicles, cytoplasm of edematous dendrites and mitochondria. Cortical neurons from postischemic dogs without reperfusion showed only slight chromatin clumping and edema of astrocytic processes, but no calcium accumulation. The large ionic shifts noted between 4 and 8 h of reperfusion, indicate a progressive inability of the cells to maintain normal transmembrane gradients of these ions and may reflect a membrane destructive process, as demonstrated ultrastructurally at 8 h. Enhanced calcium entry into the neuron during reperfusion appears to be a part of the cytotoxic mechanism leading to neuronal necrosis.

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