Glenn E. Stoner

Localized Corrosion Behavior of Alloy 2090—The Role of Microstructural Heterogeneity

Abstract The pitting and intergranular corrosion behavior of alloy AA 2090 (Al-2Li-3Cu, UNS A92090) in a 3.5 wt% NaCl solution was investigated. Techniques used included potentiodynamic polarization, galvanic couples, and pH measurements in simulated crevices. Polarization scans were performed on under-aged and peak-aged material to obtain the standard polarization parameters. Corroded specimens were examined with optical microscopy, scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDAX) to distinguish various local corrosion morphologies. Ingots were cast to approximate the subgrain boundary, T1 (Al2CuLi) phase, and Al-Cu-Fe constituent phases inherent in the alloy. These were then galvanically coupled to solution heat treated (SHT) 2090 to identify their role in local corrosion processes. Simulated crevices were produced by inserting pH micro-electrodes into crevices machined in 2090 blocks to measure pH versus time response in occluded environments. Based on the experiments...

Microstructural Effects on Electrocatalytic Oxygen Reduction Activity of Nano‐Grained Thin‐film Platinum in Acid Media

The oxygen reduction activity of thin-film platinum deposits on carbon and its relationship to catalyst microstructure has been investigated using rotating-disk-electrode techniques. The thin-film form of platinum is a viable tool for catalyst study as it can provide intrinsic activity data on finely divided carbon-supported platinum. Sputtered polycrystalline thin-film platinum deposits on carbon (loading from 6 to 200 μg/cm 2 ) have been characterized, and their oxygen reduction activity at 25 o C in 1M sulfuric acid determined. Catalyst characterization consisted of electrochemical surface-area measurement and establishing grain size, morphology, and lattice parameter using transmission electron microscopy

The Effect of Phosphoric Acid Concentration on Electrocatalysis

Phosphoric acid is the electrolyte used in the most advanced fuel cell developed for power generation and for on‐site integrated energy systems. Oxygen reduction kinetics in this electrolyte are relatively poor and thus limit the efficiency of such fuel cells. Therefore, in order to better understand oxygen interactions with platinum in these cells, oxygen adsorption and the kinetics of oxygen reduction reaction (ORR) were studied utilizing a Pt rotating disk electrode in several concentrations of highly purified . Although the kinetics of the ORR remained first order in all concentrations, it was found that its Tafel slope increased from ~110 mV/dec in low concentrations to ~134 mV/dec in 85 w/o. Anodic adsorption isotherms indicated that the higher concentrations also hindered adsorption of oxygen from solution. These effects were attributed to the blockage of electroactive sites by the adsorption of molecules.

A Modified Double Loop EPR Technique for Detection of Sensitization in Cast Stainless Steel

The double loop electrochemical potentiodynamic reactivation technique was developed to detect sensitization in wrought stainless steel. Because cast stainless steel has a different microstructure than wrought stainless steel, neither the double loop nor the single loop EPR technique has the selectivity required to detect sensitization. By using a modified double loop EPR technique in which the peak potential is raised to 450 mV vs. SCE, the sweep rate is slowed to 3 V/h , and the KSCN concentration is increased to 0.02 M, sensitization can be detected in cast stainless steel

Graphite Fiber‐Polymer Matrix Composites as Electrolysis Electrodes

The effect of electrolysis on graphite fiber-polymer matrix composites used as electrodes in a simulated seawater electrolyte was studied with interest in the impact of several composite construction variables. It was found that the electrochemical behavior is a function of the matrix polymer as well as the fiber orientation

Electrochemical impedance spectroscopy as a method to nondestructively monitor simulated in-service damage in a carbon fiber reinforced plastic

Electrochemical impedance spectroscopy has been utilized to nondestructively evaluate simulated, in-service, environmental and mechanical damage in a carbon fiber reinforced epoxy system. A continuous, unidirectional (0 degrees) fiber composite was subjected to immersion (water, sodium sulfate) and fatigue conditions, and subsequently submitted to electrochemical impedance testing. Definitive correlations between the value of the double layer capacitance and the amount of flexural fatigue or moisture uptake were observed. The changes in ths electrochemical parameter paralleled changes in the shear strength as a function of damage state.

Chromate-free corrosion resistant conversion coatings for aluminum alloys

Inorganic polycrystalline hydrotalcite, Li{sub 2}[Al{sub 2}(OH){sub 6}]{sub 2}{center_dot}CO{sub 3}{center_dot}3H{sub 2}O, coatings can be formed on aluminum and aluminum alloys by exposure to alkaline lithium carbonate solutions. This process is conducted using methods similar to traditional chromate conversion coating procedures, but does not use or produce toxic chemicals. The coating provides anodic protection and delays the onset of pitting during anodic polarization. Cathodic reactions are also inhibited which may also contribute to corrosion protection. Recent studies have shown that corrosion resistance can be increased by sealing hydrotalcite coated surfaces to transition metal salt solutions including Ce(NO{sub 3}){sub 3}, KMnO{sub 4} and Na{sub 2}MoO{sub 4}. Results from these studies are also reported.

The Influence of Composition and Microstructure on the Corrosion Behavior of Two AlLiX Alloys

Abstract The corrosion behavior of two AlLiCuZrGe alloys, with and without Mg, was studied. The types of corrosion tests conducted included exfoliation corrosion, crevice corrosion, constant immers...

Water Staining of Al 3104-H19 Can Body Stock: A Crevice Corrosion Study Utilizing the Double Crevice Assembly Test Method

Abstract An electrochemical technique was developed to detect the initiation and monitor propagation of water staining on Al 3104-H19 (UNS A93104). Water staining is a crevice corrosion phenomenon occurring between adjacent layers of coiled aluminum can stock in the presence of a condensed water phase. One of the main forms of water stain prevention consists of electrostatic application of oil-based post-lubricants to the can stock surface prior to shipment. A double crevice assembly (DCA) method was developed to induce water staining in the laboratory as observed in the field. The relative inhibiting performance of various post-rolling protective lubricants and the susceptibility of various can stock alloying compositions used in the industry then were compared. Susceptibility of a can stock coupon and the ability of a given post-lubricant to inhibit crevice corrosion was related directly related to the water stain initiation time (tstain) detected in the DCA technique by a negative shift in the electroc...