Study of personal hygiene concepts for future manned missions Final report

Personal hygiene concepts for long-duration manned space fligh

Electrochemical Behavior of AISI 304SS with Particulate Silica Coating in 0.1 M NaCl

This paper presents electrochemical behavior of AISI 304 stainless steel with a silica layer in a stagnant bulk solution of 0.1 M NaCl. Layers composed of densely packed 350 nm diam silica particles were deposited cathodically on stainless steel at a constant voltage by electrophoretic deposition (EPD). Quite smooth and crackfree silica layers less than about 80 μm in thickness were obtained and the thickness of the layer depended linearly on the deposition time. It is proposed that silica layers deposited by EPD can be used as simulated particulate layers to investigate localized corrosion of corrosion-resistant alloys under atmospheric environments. Electrochemical properties of silica-coated stainless steel samples in 0.1 M NaCl were investigated. The cathodic polarization behavior depended on the thickness of the silica layer; the limiting current density for oxygen reduction reaction decreased with increasing silica layer thickness. The effect of the silica layer on anodic polarization behavior was not remarkable.The work was performed under the Corrosion and Materials Performance Cooperative, DOE Cooperative Agreement Number: DE-FC28-04RW12252

The Influence of Dichromate Ions on Aluminum Dissolution Kinetics in Artificial Crevice Electrode Cells

Dissolution kinetics for pits and crevices in aluminum and the effect of dichromate ions on the dissolution kinetics were investigated by using artificial crevice electrodes. The aluminum artificial crevice electrodes were potentiostatically polarized over a range of potential in 0.1 M NaCl solution with and without dichromate ions. The anodic dissolution charge, and cathodic charges for the hydrogen and dichromate reduction reactions, were measured. The addition of dichromate ions did not suppress the active dissolution. This indicates that the mechanism of localized corrosion inhibition by dichromates is something other than anodic inhibition of Al dissolution in the pit or crevice environment. The relative amount of local cathodic reactions on Al was increased by the addition of dichromate because of the dichromate reduction. The initial dissolution of aluminum in a crevice was ohmic controlled. From the change in the dissolution current with time, the conductivity of the crevice and potential at the bottom of crevice were estimated. The conductivity and the bottom potential decreased with the ratio of cathodic charge of hydrogen evolution to anodic dissolution charge. The conductivity in the crevice and thus the dissolution current seem to be controlled by hydrogen evolution and only indirectly by dichromate concentration.This work was supported by the Air Force Office of Scientific Research under contract no. F49620-96-1-0479

Localized Corrosion Growth Kinetics in AA2024 Alloys

The kinetics of localized corrosion in AA2024 alloys were studied using the foil penetration technique. The growth kinetics for localized corrosion in AA2024-T3 exhibited a strong anisotropy, being slower in the short transverse or plate through-thickness direction than in either the longitudinal or long transverse directions. This growth rate anisotropy depended on the grain size and aspect ratio, and was different for different forms of AA2024-T3. The attack was primarily intergranular corrosion (IGC) at potentials of −610 mV SCE and higher in 1 M NaCl. The IGC growth rate was almost independent of potential over the range from −610 to +500 mV SCE, which suggests that only a small amount of the anodic dissolution current at the active IGC tip escapes from the IGC crevice. At lower potentials the attack was pit-like, and the rate of growth decreased with decreasing potential. Artificial aging of AA2024 to the T8 temper changed the attack from sharp IGC to selective grain dissolution, but the growth kinetics at high potentials were not strongly affected. The addition of nitrate increased the breakdown potential, and therefore decreased the growth kinetics in that region. At high potential, the nitrate had no effect. Sulfate addition had no significant effect at any potential studied.This work was supported by the United States Air Force Office of Scientific Research through grant no. F49620-99-1-0103

Pitting Corrosion of Metals: A Review of the Critical Factors

Pitting corrosion is localized accelerated dissolution of metal that occurs as a result of a breakdown of the otherwise protective passive film on the metal surface. This paper provides an overview of the critical factors influencing the pitting corrosion of metals. The phenomenology of pitting corrosion is discussed, including the effects of alloy composition, environment, potential, and temperature. A summary is then given of studies that have focused on various stages of the pitting process, including breakdown of the passive film, metastable pitting, and pit growth.Portions of this work and the preparation of this manuscript were supported by the United States Air Force Office of Scientific Research contracts F49620-96-1-0479 and F49620-96-0042 administered by Major H. De Long

Electrochemical Quartz Crystal Microbalance Study of Corrosion of Phases in AA2024

The electrochemical quartz crystal microbalance (EQCM) was used to directly measure the dissolution rate at cathodic potentials, and thus the cathodic corrosion rate, of thin-film analogs of phases in AA2024. Thin films of pure Al, Al-4% Cu, and Al2Cu were studied in 0.1 M NaCl containing 0, 10^-4, or 10^-2 M Cr2O7 . A range of cathodic potentials was studied for each material. The true cathodic current density was calculated from the difference of the net current density and the dissolution rate, which was determined by the EQCM. For pure Al and Al-4Cu, the cathodic corrosion rate was large relative to the net current density, so the true cathodic current density was considerably larger than the measured net current density. The cathodic current density was almost identical to the net current density for Al2Cu because the dissolution rate was very small compared to the cathodic reaction rate. Various potentials in the limiting oxygen reduction reaction region were examined, but the effect of the applied potential was small. The presence of dichromate in solution decreased both the cathodic corrosion rate and the cathodic current density on these thin-film analogs. In particular, it decreased more effectively the cathodic reaction rate on Al2Cu, which can support faster cathodic reaction rates.This work was supported by the United States Air Force Office of Scientific Research Grant no. F49620-96-1-0479 under the guidance of Dr. Paul Trulove

Effects of compressive stress on localized corrosion in AA2024-T3

The effect of compressive stress on intergranular corrosion (IGC) of AA2024-T3 was studied using a constant load and simultaneous electrochemical measurement. A specially designed electrochemical cell was used to compress a pillar-shaped sample and control the potential at a value that promoted IGC. The extent of IGC was assessed by metallurgical cross-sectional images. The effect of the compressive stress depended on the orientation of the stress relative to the elongated microstructure. Application of a compressive stress halfway to yield in the S or through-thickness direction significantly reduced the growth kinetics of IGC in the longitudinal direction, but did not eliminate it totally. The strain change during exposure also was used to quantify the change in radius of the cylindrical sample as a function of time during IGC growth. The effect of compression on reducing IGC was also assessed by the current density measured during potentiodynamic and potentiostatic polarization. The effects of residual compressive stress on IGC were studied using samples treated by low plastic burnishing (LPB), which produces a surface layer with high residual compressive stress. The results depended on the plane of the LPB treatment. A micro-capillary cell was used to measure corrosion behavior at different zones of the section of an LPB-treated sample. The breakdown potential was significantly higher in the zone with residual compressive stress than in the interior of the sample.This work was supported by the United States Air Force Office of Scientific Research through Grant No. F49620-02-1-0148

Corrosion Inhibition of AA2024-T3 by Vanadates

The speciation of vanadate solutions and the resultinginhibition of oxygen reduction and corrosion of AA2024-T3 wereinvestigated. 51V NMR is very useful for assessing vanadatespeciation. Clear metavanadate solutions contain nodecavanadate, which forms whenever the pH was decreased by theaddition of acid. Orange decavanadate solutions contain nomonovanadate, even when the pH is adjusted to high values.Monovanadate is a potent inhibitor in contrast to decavanadate. Inhibition by monovanadate seems to result from an adsorptionmechanism rather than reduction. Monovanadate effectivelyprotects S phase particles. Aging of high-pH decavanadatesolutions does not improve the inhibition performance or resultin complete depolymerization of the decavanadate