Owen F. Devereux

Reactions at the corroding nickel electrode in molten sodium carbonate under CO/CO2 atmosphere

Abstract Anodic reactions at the CO, CO 2 |Ni electrode in molten sodium carbonate at 1000°C are examined in detail. Experimental polarization curves are fitted via a computer graphics procedure to a model employing five anodic reactions with activation, concentration and resistance polarization, and passivation. The resultant empirical parameters are interpreted in terms of absolute rate expressions describing possible anodic reactions. Three of the anodic reactions are found to be in accord with the findings at inert electrodes by previous investigators, i.e. oxidation of CO by two mechanisms and oxidation of carbonate, while the cathodic reaction is consistent with reduction of CO 2 . The remaining two anodic reactions were associated with the oxidation of nickel to Ni 2+ with formation of a NiO film above a passivation potential, and, at higher anodic overpotentials, oxidation of NiO to a higher oxide, e.g. Ni 2 O 3 . There is an indication of the formation of a third oxide at still higher anodic overpotentials.

Fatigue crack growth in 5052-H34 aluminum in vacuum and active gas environments

Center-notched sheet specimens of 5052-H34 aluminum alloy were fatigued at load ratios (R) of 0, 0.2, and 0.43. Crack growth rate at each value ofR was studied as a function of stress intensity amplitude (ΔK) and water vapor or oxygen pressure, referenced to vacuum and laboratory air. Crack rates at a givenR and ΔK were found to increase within the range defined by vacuum and air for a corresponding increase of water vapor pressure but remained essentially constant over the range of oxygen pressures tested. In water vapor a crack rate transition pressure (separating low pressure-low growth rates from high pressure-high growth rates), inversely related toR, was observed. Results are discussed in terms of several models predicting the critical pressure of an active gas environment. A mechanism involving hydrogen embrittlement and one involving a humidity dependent aluminum oxide modulus are both found to be plausible.

Electrochemistry of lead in simulated ground water environments

Abstract Lead and lead alloys are used commonly as moisture barriers for underground cables. Lead exhibits excellent corrosion resistance in a variety of environments, but areas of localized attack...

Microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 Wt pct Cu-2.0 wt pct Mn alloys

The microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 pct Cu-2.0 pct Mn alloy specimens solidified at various cooling rates were investigated. The equilibrium phases Al6Mn and θ-Al2Cu, which are observed in the conventionally solidified alloy in the as-cast condition, were not detected in rapidly solidified (melt-spun) material. Instead, the ternary compound Al20Cu2Mn3 was present in addition to the α phase, which was present in all cases. The morphological and kinetic nature of corrosion was investigated metallographically and through potentiostatic techniques in 3.5 wt pct NaCl aqueous solution. Corrosion of the as-cast material was described by two anodic reactions: corrosion of the intermetallic phases and pitting of the α-Al solid solution. The corrosion rate increased with cooling rate from that for the furnace-cooled alloy to that for the copper mold-cast alloy and, subsequently, decreased in the rapidly solidified alloy. In the heat-treated material, corrosion could be described by two anodic reactions: corrosion of Al20Cu2Mn3 precipitate particles and pitting of the α-Al matrix.

Liquid‐Line Corrosion of Nickel in Molten Sodium Carbonate

Liquid-line corrosion of nickel in molten sodium carbonate at 1000/sup 0/C under reduced air pressure was measured as a function of time and of air pressure. The observed attack profile approached a circular arc whose depth increased parabolically with time. Attack depth increased with air pressure from zero under an inert environment passed through a maximum, and decayed approximately hyperbolically at higher (subatmospheric) pressures. These observations are shown to be quantitatively consistent with rate control by the electron-transfer step of the cathodic process, reduction of peroxide.

The effect of solidification microstructure on the corrosion behavior of a columnar aluminum-copper alloy

The morphological and kinetic nature of corrosion of directionally solidified aluminum-4.5 wt pct copper alloy in the as-cast, solutionized and solutionized-and-aged conditions in air-saturated aqueous 3.5 wt pct NaCl solution were evaluated. In the solutionized and solutionized-and-aged conditions the intergranular attack and pitting are similar to those occurring in solutionized wrought alloys; the extent of attack at long times increases with increasing severity of solidification rate. The as-cast alloy exhibits a cored dendritic structure with significant formation of interdendritic nonequilibrium eutectic. Extensive inter dendritic corrosion of the α-phase containing more than 3.2 wt pct copper is seen; α containing less than 3.2 wt pct copper and the θ-Al2Cu phase are cathodic. Corrosion of the as-cast alloy is parabolic with time and increases with increasing severity of solidification rate in proportion to the amount of nonequilibrium second phase.

Coolant pH control for optimum ceramic grinding Part II Influence of the rebinder effect on the surface grinding of aluminum oxide

Variations in the grinding (machining) properties of aluminum oxide attributable to the Rebinder effect, an environment-caused variation in the hardness of rock, ceramic, or glass, were investigated using conventional surface grinding equipment. Systematic variation in normal force, tangential force, roughness average, waviness average, and post grinding flexural strength were attributable to the grinding condition (coarse or fine) and the pH of the coolant. Observations in this study are consistent with a ductile/brittle grinding transition for fine grinding, a brittle/brittle grinding transition for coarse grinding and pH control of plastic deformation.

Coolant pH control for optimum ceramic grinding. I. rebinder effect in polycrystalline aluminum oxide

The Rebinder effect, an environment-caused variation in the hardness of rock, ceramic, or glass, was investigated in polycrystalline aluminum oxide using conventional microhardness and electrochemical techniques. For an environment of pH-adjusted distilled water, both hardness and zeta potential were found to vary with pH. Maximum hardness and zero zeta potential were found to occur at pH 9.5. Observations in this study are consistent with a mechanism for the Rebinder effect in which changes in surface charge influence near-surface plastic deformation of surfaces and, thereby, hardness.

Alternating and Direct Current Electrochemical Studies of a Wool Wax-Based Corrosion Preventive Coating on Aluminum Alloy 2024

Abstract The corrosion behavior of Al 2024-T3 (UNS A92024) treated with a wool wax (lanolin)-based corrosion preventive coating in aqueous 0.5 M sodium chloride (NaCl) was studied using electrochem...

AC-induced pitting of tin-coated copper utility cables

Abstract Laboratory exposure tests involving chemicals commonly found in soil and an AC current flow between a tin-coated copper electrode and a surrounding electrolyte were conducted to provide data regarding the mechanism and rate of concentric neutral corrosion encountered in underground rural distribution systems. Experimental data supportive of an AC-induced pit initiation mechanism followed by autocatalytic pit growth are presented. In the absence of AC, the potential of tin-coated wire stabilizes at a more negative potential than that of bare copper wire, thus providing cathodic protection to exposed copper. In the presence of an AC signal, the potential of the tin-coated wire shifts to a more positive potential than that of the bare wire, indicating that AC-induced resistive currents on tin-coated samples passivate the tin coating, rendering it cathodic to the underlying copper. The large cathodic area leads to rapid pitting of the copper substrate at coating imperfections.