http://hdl.handle.net/1811/24626 2013-06-19T03:34:06Z 2013-06-19T03:34:06Z Davenport, Alison J. Bardwell, Jennifer A. Isaacs, Hugh S. MacDougall, Barry Frankel, Gerald S. Schrott, Alex G. http://hdl.handle.net/1811/46658 2012-12-29T00:08:25Z 1993-01-01T00:00:00Z

In Situ Studies of Passive Film Chemistry using X-ray Absorption Spectroscopy Davenport, Alison J.; Bardwell, Jennifer A.; Isaacs, Hugh S.; MacDougall, Barry; Frankel, Gerald S.; Schrott, Alex G. The passive film on sputter-deposited thin film Fe and Fe-26Cr electrodes has been examined using in situ X-ray Absorption Near Edge Spectroscopy (XANES). During the x-ray spectroscopic measurements, samples were maintained under potentiostatic control in pH 8.4 borate buffer. The passive film on both Fe and Fe-26Cr is formed from the metal without any detectable losses due to dissolution. Cathodic reduction leads to a loss of Fe from the film in both cases, but substantially less Fe is lost in the case of Fe-26Cr. Transpassive dissolution of Cr from Fe-26Cr only occurred on the second potential cycle after the film had been enriched in Cr due to the reductive dissolution of Fe. Simultaneous collection of both the Fe and Cr x-ray absorption edges provides quantitative information on the relative amounts of material lost during passivation and reduction.

1993-01-01T00:00:00Z Davenport, Alison J. Bardwell, Jennifer A. Isaacs, Hugh S. MacDougall, Barry Frankel, Gerald S. Schrott, Alex G. Baek, Y. Frankel, G. S. http://hdl.handle.net/1811/45451 2012-12-28T23:51:00Z 2003-01-01T00:00:00Z

Electrochemical Quartz Crystal Microbalance Study of Corrosion of Phases in AA2024 Baek, Y.; Frankel, G. S. 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.

2003-01-01T00:00:00Z Baek, Y. Frankel, G. S. Ramgopal, T. Schmutz, P. Frankel, G. S. http://hdl.handle.net/1811/45448 2012-12-29T00:04:02Z 2001-01-01T00:00:00Z

Electrochemical Behavior of Thin Film Analogs of Mg (Zn,Cu,Al)2 Ramgopal, T.; Schmutz, P.; Frankel, G. S. The electrochemical behavior of the intermetallic phase Mg(Zn, Cu, Al)2 was studied using thin film compositional analogs prepared by flash evaporation. Characterization by scanning electron microscopy, atomic force microscopy, and Auger electron spectroscopy depth profiles indicated that the films were single phase, laterally homogeneous, and homogeneous through the thickness. Experiments in deaerated 0.5 M NaCl showed that the addition of 18 atom % Cu to MgZn2 raised the open circuit potential (OCP) by about 150 mV and the breakdown potential by 170 mV. The attack seemed to be localized dealloying. In high pH solutions where Mg(OH)2 was stable, the films were susceptible to a more classical form of localized breakdown. The breakdown and the repassivation potentials increased with increasing copper concentration. Cyclic polarization curves on these films show the presence of Zn reduction peaks in the cathodic part of the downward potential scan. OCP playback experiments on the intermetallic thin films showed that the Mg(Zn, Cu, Al)2 phase is very active over a wide range of compositions in neutral solutions at the OCP of the 7xxx series alloy.

2001-01-01T00:00:00Z Ramgopal, T. Schmutz, P. Frankel, G. S. Xia, Lin Akiyama, Ejii Frankel, Gerald McCreery, Richard http://hdl.handle.net/1811/45447 2012-12-28T23:55:25Z 2000-01-01T00:00:00Z

Storage and Release of Soluble Hexavalent Chromium from Chromate Conversion Coatings Equilibrium Aspects of CrVI Concentration Xia, Lin; Akiyama, Ejii; Frankel, Gerald; McCreery, Richard The release of soluble CrVI species by a chromate conversion coating (CCC) was monitored quantitatively by ultraviolet-visible spectroscopy. By careful selection of measurement wavelength (339 nm), the CrVI concentration could be determined without regard to solution pH or CrVI speciation. The CrVI concentration in solution over a CCC reached an equilibrium value that depended on pH, ionic strength, and the ratio of the CCC surface area to the solution volume (A/V). In separate experiments, the adsorption of CrVI by synthetic CrIII hydroxide to form a CrIII-CrVI mixed oxide was observed, and also led to an equilibrium concentration of CrVI in solution. The equilibrium CrVI concentration was determined for a variety of A/V values on both AA1100 and AA2024-T3 aluminum alloys. The results are inconsistent with release mechanisms based on the solubility of a CrVI salt in the solution or depletion of CrVI from the CCC. However, the observed concentrations are consistent with a mechanism similar to a Langmuirian adsorption-desorption equilibrum of CrVI on a porous, insoluble CrIII hydroxide matrix. The CrIII hydroxide matrix has a finite number of CrVI binding sites and exhibits a nonlinear relationship between solution and solid CrVI concentrations governed by an equation similar to a Langmuir adsorption isotherm. The proposed model incorporates reversible adsorption and de-sorption of CrVI, with adsorption favored at low pH during formation of the CCC, and desorption favored in field conditions. The model quantitatively predicts the observed concentrations after determining the binding constant from fits to the data. The model explains the capacity of a CCC to release active CrVI corrosion inhibitor and provides strong evidence that CrVI storage in a CCC involves reversible formation of a CrVI-O-CrIII mixed oxide.

2000-01-01T00:00:00Z Xia, Lin Akiyama, Ejii Frankel, Gerald McCreery, Richard Sehgal, A. Frankel, G. S. Zoofan, B. Rokhlin, S. http://hdl.handle.net/1811/45446 2012-12-28T23:55:43Z 2000-01-01T00:00:00Z

Pit Growth Study in Al Alloys by the Foil Penetration Technique Sehgal, A.; Frankel, G. S.; Zoofan, B.; Rokhlin, S. The foil penetration technique was used to study pit growth in AA1100-O and AA2024-T3. Preliminary work on AA1100-O foils of different thicknesses indicated that the pit growth rate increased with increasing applied potential, suggesting that pit growth was not under transport control. Foil penetration experiments were also carried out on AA2024-T3 foils of a given thickness, at open circuit as well as anodic potentials. Dichromate ions and other oxidizing agents were added to some test solutions. Dichromate ions were shown to have little influence on the pit growth rate at controlled anodic potentials, even when added in large concentrations. However, dichromate ions effectively inhibited pitting at open circuit when present in very small amounts. Polarization curves of AA2024-T3 in 1 M NaCl with various additives show a large effect of dichromate ions in the cathodic region and no effect in the anodic region. These observations suggest that chromate (or its reduction product) acts as a cathodic inhibitor. Examination of penetrated samples was performed by optical and scanning electron microscopies, as well as by microradiography.

2000-01-01T00:00:00Z Sehgal, A. Frankel, G. S. Zoofan, B. Rokhlin, S. Schmutz, P. Frankel, G. S. http://hdl.handle.net/1811/45445 2012-12-28T23:55:55Z 1998-01-01T00:00:00Z

Corrosion Study of AA2024-T3 by Scanning Kelvin Probe Force Microscopy and In Situ Atomic Force Microscopy Scratching Schmutz, P.; Frankel, G. S. The localized corrosion of AA2024-T3, and the behavior of intermetallic particles in particular, were studied using different capabilities of the atomic force microscope (AFM). The role of intermetallic particles in determining the locations and rates of localized corrosion was determined using scanning Kelvin probe force microscopy in air after exposure to chloride solutions. Al-Cu-Mg particles, which have a noble Volta potential in air because of an altered surface film, are actively dissolved in chloride solution after a certain induction time. Al-Cu-(Fe, Mn) particles are heterogeneous in nature and exhibit nonuniform dissolution in chloride solution as well as trenching of the matrix around the particles. Light scratching of the surface by rastering with the AFM tip in contact mode in chloride solution results in accelerated dissolution of both pure Al and alloy 2024-T3. The abrasion associated with contact AFM in situ resulted in the immediate dissolution of the Al-Cu-Mg particles because of a destabilization of the surface film.

1998-01-01T00:00:00Z Schmutz, P. Frankel, G. S. Schmutz, P. Frankel, G. S. http://hdl.handle.net/1811/45444 2012-12-29T00:08:10Z 1998-01-01T00:00:00Z

Characterization of AA2024-T3 by Scanning Kelvin Probe Force Microscopy Schmutz, P.; Frankel, G. S. Volta potential mapping of AA2024-T3 on surfaces was performed with an atomic force microscope. A linear relation was found between the Volta potential measured in air and the corrosion potential in aqueous solution for a range of pure metal samples, indicating that this potential is a measurement of the practical nobility of the surface. Large differences in the Volta potential of intermetallic particles in AA2024-T3 and the matrix phase resulted in a potential map with high contrast that clearly identifies the location of the particles. All intermetallic particles, including the Mg-containing S-phase particles, had a Volta potential noble to that of the matrix. Surface films on the particles and the matrix were found to have strong effects on the potential, and probably explain the noble nature of the Mg-containing particles, which have been reported to be active to the matrix in solution. The effect of these surface films was examined by refreshing the sample surface using different techniques. Lateral heterogeneities in certain intermetallic particles were also revealed.

1998-01-01T00:00:00Z Schmutz, P. Frankel, G. S. Zhao, Jun McCreery, Richard L. Frankel, Gerald http://hdl.handle.net/1811/45443 2012-12-28T23:46:57Z 1998-01-01T00:00:00Z

Corrosion Protection of Untreated AA-2024-T3 in Chloride Solution by a Chromate Conversion Coating Monitored with Raman Spectroscopy Zhao, Jun; McCreery, Richard L.; Frankel, Gerald The behavior of chromate conversion coatings (CCCs) on the aluminum aircraft alloy AA 2024-T3 was examined by several types of experiments, using Raman spectroscopy as a primary technique. First, Raman spectra of the CCC film made from a commercial process revealed a Raman feature characteristic of Cr(VI) which was distinct from Raman bands of pure CrO4^−2 or Cr2O7^−2. Second, Raman spectroscopy was used to monitor migration of chromate species from a CCC film to an initially untreated alloy sample. The release of chromate from a CCC was demonstrated, as was redeposition of a chromate film on the fresh alloy surface. Formation of a Raman-observable Cr(VI)-containing deposit was more rapid in or near pits in the untreated alloy sample, and the deposit was spectroscopically very similar to the original CCC film. The initially untreated alloy became much less active toward corrosion after migration of chromate from the nearby CCC film, with the polarization resistance increasing by at least two orders of magnitude and the pitting potential increasing by 60 mV. The results clarify the mechanism of self-healing exhibited by CCC films, in which chromate species released from the CCC migrate to an actively corroding region and stop aluminum dissolution. The migrating chromate is selectively deposited at active corrosion sites, either by forming an insoluble Al/chromate is selectively deposited at active corrosion sites, either by forming an insoluble Al/chromate precipitate or by adsorption by previously formed corrosion.

1998-01-01T00:00:00Z Zhao, Jun McCreery, Richard L. Frankel, Gerald Frankel, G. S. http://hdl.handle.net/1811/45442 2012-12-28T23:40:04Z 1998-01-01T00:00:00Z

Pitting Corrosion of Metals: A Review of the Critical Factors Frankel, G. S. 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.

1998-01-01T00:00:00Z Frankel, G. S. Frankel, G. S. Scully, J. R. Jahnes, C. V. http://hdl.handle.net/1811/45441 2012-12-28T23:52:53Z 1996-01-01T00:00:00Z

Repassivation of Pits in Aluminum Thin Films Frankel, G. S.; Scully, J. R.; Jahnes, C. V. The effect of metal film thickness on repassivation of pits in sputter-deposited Al thin films was investigated in chloride solutions. The repassivation potential and the critical current density, which is the pit current density below which pits stop growing, were determined for pits in Al thin films ranging from 100 Ǻ to 43 μm in thickness. The repassivation potential first decreased as thickness increased from 100 to 4350 Ǻ, and then increased as the film thickness increased further. This behavior was found to be a consequence of the pit current-density/potential relationship. The critical current density, a more informative parameter, decreased for increasing metal film thickness, even when the repassivation potential increased. The critical current density is the minimum current density needed to maintain the critical pit environment and prevent repassivation. The repassivation potential for a given metal film thickness is the potential at which the pit current density drops below the critical value. Mass-transport and ohmic resistance both increase as the metal film thickness increases, but the former enhances pit stability and the latter destabilizes pitting in this system. Pit repassivation, and thus stability, are strongly influenced by mass-transport considerations for pits in very thin pits, even though dissolution at low potentials is not under pure mass-transport control. Ohmic effects become increasingly important as the film thickness increases.

1996-01-01T00:00:00Z Frankel, G. S. Scully, J. R. Jahnes, C. V. Brusic, V. Frankel, G. S. Roldan, J. Saraf, R. http://hdl.handle.net/1811/45440 2012-12-29T00:07:32Z 1995-01-01T00:00:00Z

Corrosion and Protection of a Conductive Silver Paste Brusic, V.; Frankel, G. S.; Roldan, J.; Saraf, R. One of the possible uses for a conductive paste is as an adhesive in interconnect technology that could replace PbSn solder. The interconnections are expected to perform under a variety of environmental conditions, and with an applied voltage. Thus knowledge of their corrosion and dissolution resistance is of utmost importance. This is a study of the dissolution and protection of polymer/metal composite films, prepared with a high loading of silver or gold particles. Electrochemical tests were conducted in a droplet of triple-distilled water with or without benzotriazole (BTA) and BTA derivatives. Results indicate that, in spite of some protection obtained by the polymer, silver paste dissolution at high anodic potentials is rapid, reaching values of 10^-1 A/cm2, which corresponds to a catastrophic silver removal rate of at least 35.6 nm/s. With a reservoir of azole in the corrosive environment, this rate can be reduced by up to five orders of magnitude. This azole effect greatly reduces the probability of electrolytic silver migration, but the Ag dissolution rate is still higher than the anodic activity shown by Au paste under the same conditions.

1995-01-01T00:00:00Z Brusic, V. Frankel, G. S. Roldan, J. Saraf, R. Frankel, G. S. Jahnes, C. V. Brusic, V. Davenport, A. J. http://hdl.handle.net/1811/45439 2012-12-28T23:53:57Z 1995-01-01T00:00:00Z

Repassivation Transients Measured with the Breaking-Electrode Technique on Aluminum Thin-Film Samples Frankel, G. S.; Jahnes, C. V.; Brusic, V.; Davenport, A. J. The breaking-electrode technique was used to study repassivation transients of small, fresh metal areas of Al exposed to a conductive electrolyte at a range of potentials. The peak current density measured within the first few microseconds after breaking was found to be ohmically limited, with an ohmic resistance that is substantially higher than that measured minutes after breaking. The current decay during the first 3 s was recorded and found to be exponential in nature. By plotting the data as log i vs. (it)^-1/2, it is concluded that oxide growth was better.represented by the direct logarithmic law than by high-field kinetics. Cathodic current transients having a complex shape were observed at low potentials. It is suggested that oxide growth at potentials slightly above the reversible potential for oxide formation retards the water reduction reaction. The advantages and limitations of the breaking-electrode technique are discussed.

1995-01-01T00:00:00Z Frankel, G. S. Jahnes, C. V. Brusic, V. Davenport, A. J. Brusic, V. Frisch, M. A. Eldridge, B. N. Novak, F. P. Kaufman, F. B. Rush, B. M. Frankel, G. S. http://hdl.handle.net/1811/45436 2012-12-28T23:48:28Z 1991-01-01T00:00:00Z

Copper Corrosion With and Without Inhibitors Brusic, V.; Frisch, M. A.; Eldridge, B. N.; Novak, F. P.; Kaufman, F. B.; Rush, B. M.; Frankel, G. S. The utility of copper interconnects may ultimately depend on the ability to protect copper from corrosion. We have studied the capacity of lH-benzotriazole (1H-BTA) to provide a protective and stable surface film able to withstand harsh chemical and thermal environments. The film was characterized with electrochemical techniques, in situ ellipsometry, ex situ time-of-flight static secondary ion mass spectrometry, high-temperature mass spectrometry, and accelerated temperature and humidity tests. Several important passivating film properties (thickness, degree of polymerization, thermal stability, corrosion resistance) depend critically on the details of the film preparation conditions. The best corrosion protection is offered by the thin film formed on an oxidized Cu surface. This film has also shown the slowest growth kinetics and the highest degree of polymerization in the Cu-BTA structure.

1991-01-01T00:00:00Z Brusic, V. Frisch, M. A. Eldridge, B. N. Novak, F. P. Kaufman, F. B. Rush, B. M. Frankel, G. S. Frankel, G. S. Stratmann, M. Rohwerder, M. Michalik, A. Maier, B. Dora, J. Wicinski, M. http://hdl.handle.net/1811/45435 2012-12-28T23:56:19Z 2007-01-01T00:00:00Z

Potential control under thin aqueous layers using a Kelvin Probe Frankel, G. S.; Stratmann, M.; Rohwerder, M.; Michalik, A.; Maier, B.; Dora, J.; Wicinski, M. Kelvin Probes can be modified to control as well as monitor potential. The design and operation of two different Kelvin Probe Potentiostats (KPPs) are described in this paper. One approach uses a permanent magnet and double coil to oscillate the needle at a fixed frequency, an AC backing potential, and software analysis and control schemes. This technique can also control the distance between the tip and sample, thereby tracking the topography of the sample. Both KPPs were used to make measurements on Type 304L stainless steel under thin layers of electrolyte. Cathodic polarization curves exhibited a limiting current density associated with oxygen reduction. The limiting current density varied with solution layer thickness over a finite range of thickness. Anodic polarization curves on 304L in a thin layer of chloride solution resulted in pitting corrosion. The breakdown potential did not vary with solution layer thickness. However, the thin layer was observed to increase in volume remarkably during pit growth owing to the absorption of water from the high humidity environment into the layer with ionic strength increased by the pit dissolution. The open circuit potential (OCP) and solution layer thickness were monitored during drying out of a thin electrolyte layer. Pitting corrosion initiated, as indicated by a sharp drop in the OCP, as the solution thinned and increased in concentration.

2007-01-01T00:00:00Z Frankel, G. S. Stratmann, M. Rohwerder, M. Michalik, A. Maier, B. Dora, J. Wicinski, M. Ruan, Shiling Wolfe, Douglas A. Frankel, Gerald S. http://hdl.handle.net/1811/45423 2012-12-29T00:01:48Z 2004-01-01T00:00:00Z

Statistical modeling and computer simulation of intergranular corrosion growth in AA2024-T3 aluminum alloy Ruan, Shiling; Wolfe, Douglas A.; Frankel, Gerald S. An extension of a brick wall model developed in a previous paper (Technometrics, to appear) was used to describe intergranular corrosion in AA2024-T3 aluminum alloys. The extended model simulates the behavior of corrosion paths at intersections of grain boundaries within the metal sample. Situations considered include the cases where a corrosion path might assume an upward turn, skip an intersection (not turn) or split into branches. The splitting of a corrosion path results in a smaller median of the minimum order statistic while the other factors increase the median of the minimum order statistic. Moreover, a larger number of grain layers increases the minimum path length for a sample with given thickness. With a proper combination of these factors, the extended model is able to provide a good fit to the experimental data developed by the foil penetration technique.

2004-01-01T00:00:00Z Ruan, Shiling Wolfe, Douglas A. Frankel, Gerald S. Kim, Yeong Ho Frankel, G. S. http://hdl.handle.net/1811/45422 2012-12-28T23:39:34Z 2007-01-01T00:00:00Z

Effect of Noble Element Alloying on Passivity and Passivity Breakdown of Ni Kim, Yeong Ho; Frankel, G. S. Welding of stainless steels can generate welding fumes containing carcinogenic hexavalent chromium (Cr^+6). To mitigate this problem, a new Ni-Cu-Pd welding consumable alloy has been developed. The addition of a small amount of Cu and Pd in Ni enhances the galvanic compatibility of Ni with stainless steels and improves its localized corrosion behavior. In this paper, the artificial pit electrode technique and X-ray photoelectron spectroscopy were used to study the benefits of Cu and Pd alloying. The passive film on Ni-10Cu-1Pd alloy mainly consisted of outer Ni-hydroxide and inner oxide, and the noble elements Pd and Cu apparently did not contribute to the formation of the passive film. However, Pd catalyzed the reduction of Cu at the bottom of artificial pits, which enhanced the cathodic reaction and thus ennobled the protection potential, making stable pit growth more difficult. This catalytic effect of Pd also prevented the propagation of deep pits in a test using a thin foil crevice sample.

2007-01-01T00:00:00Z Kim, Yeong Ho Frankel, G. S. Iannuzzi, M. Young, T. Frankel, G. S. http://hdl.handle.net/1811/45421 2012-12-28T23:53:24Z 2006-01-01T00:00:00Z

Aluminum Alloy Corrosion Inhibition by Vanadates Iannuzzi, M.; Young, T.; Frankel, G. S. The inhibition of Al alloy corrosion by vanadates was studied in this work. Vanadium speciation is very complicated and vital to the inhibition efficacy. Critical conditions for decavanadate polymerization from clear metavanadate solutions were investigated. Decavanadate only formed when metavanadate was added to solutions of pH 3 or less. It was not possible to change the pH of a metavanadate solution without forming decavanadates, creating an orange-colored solution. According to ^51 V nuclear magnetic resonance, monovanadates were present only in clear metavanadate solutions; orange solutions always contained decavanadates and never contained monovanadates. Orange decavanadate solutions containing 0.5 M NaCl at pH 8.71 exhibited no significant inhibition of the oxygen reduction reaction and increasing decavanadate concentration was detrimental. In contrast, clear metavanadate solutions containing monovanadate exhibited strong inhibition of the oxygen reduction reaction, to a level similar to chromate. At a fixed pH, increased NaVO3 concentration in clear metavanadate solutions increased inhibition efficiency.

2006-01-01T00:00:00Z Iannuzzi, M. Young, T. Frankel, G. S. Meng, Qingjiang Frankel, G. S. http://hdl.handle.net/1811/45410 2012-12-29T00:01:08Z 2004-01-01T00:00:00Z

Effect of Cu Content on Corrosion Behavior of 7xxx Series Aluminum Alloys Meng, Qingjiang; Frankel, G. S. The corrosion behavior of 7xxx aluminum alloys with various Cu content was investigated using polarization and electrochemical impedance spectroscopy (EIS) techniques. Two breakdown potentials were found in Cu-containing alloys in deaerated chloride solution, and the values increased logarithmically with increasing Cu content. However, in aerated chloride solution, polarization resistance as determined by EIS decreased with increasing Cu content. The first breakdown potential corresponded to transient dissolution associated with attack of the fine hardening particles and the surrounding solid solution in a thin surface layer. The second breakdown potential was associated with combined intergranular and selective grain attack. The correlation between the microstructure, especially Cu content, and corrosion behavior was made by composition analysis of the grain boundary regions including precipitate free zone and grain boundary precipitates as well as the matrix by scanning transmission electron microscopy. The corrosion potential increased with increasing alloy Cu content in aerated chloride solutions because of enhanced rates of oxygen reduction. This degraded the corrosion resistance despite the increase in the breakdown potentials with Cu content.

2004-01-01T00:00:00Z Meng, Qingjiang Frankel, G. S. Leblanc, Patrick P. Frankel, G. S. http://hdl.handle.net/1811/45409 2012-12-29T00:08:13Z 2004-01-01T00:00:00Z

Investigation of Filiform Corrosion of Epoxy-Coated 1045 Carbon Steel by Scanning Kelvin Probe Force Microscopy Leblanc, Patrick P.; Frankel, G. S. The mechanism for filiform corrosion (FFC) is thought to involve oxygen diffusion through the tail to the active head. The primary cathodic region is near the back of the head (at the head/tail boundary), where oxygen concentration is higher, and the primary anodic region is at the front edge of the head of the filament. Although there is experimental support for this mechanism, a high-resolution description of the FFC process has not been presented. The aim of this study was to provide detailed information about the mechanism of FFC on coated steel using the high spatial resolution of scanning Kelvin probe force microscopy. Segments of active filaments were successfully investigated through 150 and 300 nm thin epoxy coatings in air of 93% relative humidity. Volta potential and topographic maps showed separation of active anodes and cathodes in the head and revealed the presence of voids associated with delamination of the coating along the edge of the tail. The morphology of filaments and Volta potential distributions were strongly dependent on the film thickness. Differences in growth characteristics were explained by mass transport considerations.

2004-01-01T00:00:00Z Leblanc, Patrick P. Frankel, G. S. Liu, Xiaodong Frankel, G. S. http://hdl.handle.net/1811/45383 2012-12-28T23:56:27Z 2006-01-01T00:00:00Z

Effects of compressive stress on localized corrosion in AA2024-T3 Liu, Xiaodong; Frankel, G. S. 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.

2006-01-01T00:00:00Z Liu, Xiaodong Frankel, G. S. Zhang, Weilong Ruan, Shiling Wolfe, D. A. Frankel, G. S. http://hdl.handle.net/1811/45382 2012-12-28T23:53:13Z 2003-01-01T00:00:00Z

Statistical model for intergranular corrosion growth kinetics Zhang, Weilong; Ruan, Shiling; Wolfe, D. A.; Frankel, G. S. A statistical model has been developed to predict the anisotropy of intergranular corrosion (IGC) kinetics and effect of microstructure on IGC kinetics in high strength AA2024-T3 alloys. The methodology is to estimate the statistical distribution of minimum IGC path length that will be found through the thickness of a given thickness ST sample using the principle of order statistics. A brick-wall model is adopted for wrought Al alloy microstructure and different distributions of grain dimension are assumed for the purpose of the estimation of total IGC path length. Numerical stimulation using a gamma distribution model stimulated the anisotropy of localized corrosion in AA2024-T3 alloys, which quite agrees with the growth rate anisotropy experimentally determined by the foil penetration technique. Some limitations regarding the statistical model are discussed. The statistical model provides a new approach to predicting and quantifying localized corrosion kinetics on basis of the alloy microstructure.

2003-01-01T00:00:00Z Zhang, Weilong Ruan, Shiling Wolfe, D. A. Frankel, G. S. Frankel, G. S. Newman, R. C. Jahnes, C. V. Russak, M. A. http://hdl.handle.net/1811/44645 2012-12-28T23:57:53Z 1993-01-01T00:00:00Z

On the Pitting Resistance of Sputter-Deposited Aluminum Alloys Frankel, G. S.; Newman, R. C.; Jahnes, C. V.; Russak, M. A. The pitting behavior of sputter-deposited Al binary alloy thin films was studied. Pitting and repassivation potentials were determined in 0.1M NaCl for samples in freshly deposited and air-aged states. Aging for several years in laboratory air increased the pitting potential for some of the alloy systems but had no effect on others. The repassivation potentials, meaningful values for pits in thin films, were found to be very close to the pitting potentials of freshly-deposited films for many alloy systems. Stable pits initiate in these Al binary alloys at potentials just above the value at which they would repassivate, indicating that pit growth considerations control the pitting process. By determining the pit anodic current density just before passivation it is shown that alloying improves pitting resistance through a reduction in the ability of pits to maintain the critical local environment necessary for growth. The influences of alloying on the passive film chemistry and on the tendency of the metal to repassivate (depassivation pH) are secondary in nature.

1993-01-01T00:00:00Z Frankel, G. S. Newman, R. C. Jahnes, C. V. Russak, M. A. Brusic, V. Frankel, G. S. Schrott, A. G. Petersen, T. A. Rush, B. M. http://hdl.handle.net/1811/44644 2012-12-29T00:06:17Z 1993-01-01T00:00:00Z

Corrosion Inhibition of Cobalt with a Thin Film of Cu-BTA Brusic, V.; Frankel, G. S.; Schrott, A. G.; Petersen, T. A.; Rush, B. M. Electrochemical techniques, ellipsometry and x-ray photoelectron spectroscopy were used to evaluate the use of benzotriazole, alone or in combination with boric acid/borate buffer and dilute copper sulfate for the protection of cobalt. The data indicate that in slightly alkaline solutions benzotriazole is a strong inhibitor for cobalt corrosion, whereas in water and neutral solutions it produces a barely measurable effect. In the presence of benzotriazole and Cu^+2 ions, spontaneous reduction of copper ions leads to the formation of a thin film of Cu-BTA on the cobalt surface. This film acts as a corrosion protector that is better than benzotriazole, with a significant reduction of the corrosion rate even during subsequent exposure to solutions without inhibitors.

1993-01-01T00:00:00Z Brusic, V. Frankel, G. S. Schrott, A. G. Petersen, T. A. Rush, B. M. Frankel, G. S. Schrott, A. G. Isaacs, H. S. Horkans, J. Andricacos, P. C. http://hdl.handle.net/1811/44643 2012-12-29T00:09:25Z 1993-01-01T00:00:00Z

Behavior of Cu(P) and Oxygen Free High Conductivity Cu Anodes under Electrodeposition Conditions Frankel, G. S.; Schrott, A. G.; Isaacs, H. S.; Horkans, J.; Andricacos, P. C. Films formed on Cu(P) (with 0.1 atom percent P) and oxygen free high conductivity Cu anodes in electroplating solutions were studied by a newly developed gravimetric technique, electrochemical methods, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. The black film formed on Cu(P) in Cl^− -containing solutions was found to resemble a porous sponge composed of CuCl but laden with concentrated CuSO_4 solution. The gravimetric experiments show that the difference between the buoyancy-corrected measured mass change and the charge-equivalent mass change has two components: a reversible part that comes and goes as the current is turned on and off, and an irreversible part that remains on the surface and increases in mass with time as dissolution proceeds. The reversible part of the mass change arises from the weight of the diffusion layer. The irreversible part results from the anodic film, which increases linearly in mass with charge density but at a rate that is independent of current density. P inhibits the disproportionation of Cu^+1 that results in the poorly adherent anodic film that forms on OFHC Cu anodes.

1993-01-01T00:00:00Z Frankel, G. S. Schrott, A. G. Isaacs, H. S. Horkans, J. Andricacos, P. C. Frankel, G. S. Dukovic, J. O. Brusic, V. Rush, B. M. Jahnes, C. V. http://hdl.handle.net/1811/44642 2012-12-28T23:55:45Z 1992-01-01T00:00:00Z

Pit Growth in NiFe Thin Films Frankel, G. S.; Dukovic, J. O.; Brusic, V.; Rush, B. M.; Jahnes, C. V. Pit growth was studied in 80Ni-20Fe sputtered thin films by analysis of images of the growing pits. The pit current density was found to increase with pit growth potential until reaching a limiting value. The limiting current density increased with decreasing film thickness. The mass-transfer resistance to the active pit wall exceeds by an order of magnitude that predicted from a simple radial-diffusion model. It is suggested that the undercut, remnant passive film collapses over the pit wall causing a constriction. A voltage component calculation matches the data rather well and indicates that pit growth below the limiting current density is limited by a combination of ohmic, concentration, and surface activation considerations.

1992-01-01T00:00:00Z Frankel, G. S. Dukovic, J. O. Brusic, V. Rush, B. M. Jahnes, C. V. Zhang, Weilong Frankel, G. S. http://hdl.handle.net/1811/44564 2012-12-29T00:05:08Z 2003-01-01T00:00:00Z

Transitions between pitting and intergranular corrosion in AA2024 Zhang, Weilong; Frankel, G. S. The pitting and intergranular corrosion (IGC) behavior of various tempers of AA2024 was investigated in 1 M NaCl. The breakdown potentials associated with pitting or IGC were determined. The breakdown potentials were found to be almost independent of sample orientation for any given temper. Artificial aging had a strong effect on polarization behavior and localized corrosion morphology. The anodic polarization curves of AA2024 in the solution heat treated and water-quenched condition, T3, and T3+ tempers exhibited two breakdown potentials, whereas overaged AA2024-T8, T8+ , and solutionized and furnace cooled AA2024 exhibited only one breakdown potential. When two breakdown potentials were observed, the more active one was found to be related to the transient dissolution of S phase Al2CuMg particles leading to pitting while the noble one was thought to result primarily from initiation and growth of IGC. The breakdown potentials decreased with increasing aging time at 190°C, and only one breakdown potential was measured for T8 and T8+ tempers. Unlike the T3 temper, no sharp IGC was found for these tempers. Selected granular attack from breakdown of the copper-depleted matrix was believed to be the cause for localized corrosion in the T8 and T8+ tempers. The effect of nitrate and sulfate ions on the localized corrosion behavior was also studied.

2003-01-01T00:00:00Z Zhang, Weilong Frankel, G. S. Liu, Xiaodong Frankel, G. S. Zoofan, B. Rokhlin, S. I. http://hdl.handle.net/1811/44563 2012-12-28T23:45:09Z 2006-01-01T00:00:00Z

Transition from Intergranular Corrosion to Intergranular Stress Corrosion Cracking in AA2024-T3 Liu, Xiaodong; Frankel, G. S.; Zoofan, B.; Rokhlin, S. I. The transition of intergranular corrosion (IGC) to intergranular stress corrosion cracking (IGSCC) in AA2024-T3 was studied using microfocal X-ray radiography, scanning electron microscopy (SEM), and electrochemistry. A constant potential was applied in 1 M NaCl solution, and a fixed elastic tensile displacement was applied in the transverse direction using a modified ASTM G49 jig. In this orientation, IGC grows primarily along the elongated grain boundaries in the longitudinal and transverse directions, parallel to the applied stress. SEM and X-ray radiography provided insightful images of the transition to IGSCC. Linking of the individual IGC sites occurred at the edges of the elongated grains, resulting in transition of the IGC sites into IGSCC that was nominally normal to the applied stress. This coalescence process was discontinuous in nature, as evidenced by arrest marks on the fracture surface and oscillations in the measured current.

2006-01-01T00:00:00Z Liu, Xiaodong Frankel, G. S. Zoofan, B. Rokhlin, S. I. Huang, Tsai-Shang Frankel, G. S. http://hdl.handle.net/1811/44562 2012-12-29T00:08:37Z 2007-01-01T00:00:00Z

Kinetics of sharp intergranular corrosion fissures in AA7178 Huang, Tsai-Shang; Frankel, G. S. During service in structural aircraft applications, AA7178 has been found to develop sharp intergranular corrosion (IGC) fissures, a special form of attack. A new laboratory approach to quantify the kinetics of sharp IGC fissure growth was developed in this work. Sharp IGC fissures, similar to those formed in service, grew in samples that were given an electrochemical pre-treatment and then exposed in a humid environment. The time for the first sharp IGC fissure to penetrate the thin sample was determined by visual observation of the back side of the sample. The depth of the sharp IGC fissure was determined by serial sectioning. The kinetics measured by this approach did not represent the fastest rates, but rather the rates of long sharp IGC fissures. Relative humidity had no measurable effect on fissure kinetics, indicating that there was little connection of the local sharp IGC fissure region with the outside environment. AA7178 in the as-received and T7 conditions exhibited slower sharp IGC fissure rates than in the T6 condition. The sharp IGC fissures were found to be filled with corrosion products, which possibly exert a stress that could play an important role in driving fissure growth. It is suggested that the sharp IGC fissure could be a form of SCC.

2007-01-01T00:00:00Z Huang, Tsai-Shang Frankel, G. S. Schmutz, P. Guillaumin, V. Frankel, G. S. Lillard, R. S. Lillard, J. A. http://hdl.handle.net/1811/44561 2012-12-28T23:39:01Z 2003-01-01T00:00:00Z

Influence of Dichromate Ions on Corrosion Processes on Pure Magnesium Schmutz, P.; Guillaumin, V.; Frankel, G. S.; Lillard, R. S.; Lillard, J. A. The corrosion behavior of Mg is of interest because of its growing use as an alloy in the transportation industry and also because it is a major component of some intermetallic phases in Al alloys, such as the deleterious S (Al2CuMg)-phase found in AA2024-T3. Pure Mg corrodes rapidly in a chloride-containing solution and even dissolves in water if the surface hydroxide is damaged by scratching the surface, for example. Uniform dissolution is drastically reduced in NaCl solutions (from 0.01 to 0.5 M) with the addition of very dilute concentrations of dichromate (10-4 M). However, it is replaced by a strong localized attack in the form of fast filiform-like attack. On a large-grained sample with a defined defect structure, the attack can be seen to propagate at twin boundaries. Orientation imaging microscopy analysis found that corrosion was limited to planes near {0001} orientations with propagation being in prismatic directions. Auger electron spectroscopy analysis shows that interaction of chromate with the Mg hydroxide results in incorporation of reduced chromium ions in the hydroxide surface layer. Formation of a more resistant surface film could explain the very local nature of the corrosion in this case. The interaction between dichromate ions and Mg hydroxide can also explain the higher corrosion resistance of S-phase particles in chloride solutions containing dilute dichromate, although differences in the surface film formed compared to pure Mg are observed. Sputter-etching of the surface in order to assess the depth of the attack revealed that very hard or isolating corrosion products difficult to sputter are produced along the filiform path and that chromium compounds are not integrated in the corrosion products. Focused ion beam sectioning followed by scanning electron microscopy investigation of the sectioned area, demonstrates the presence of a continuous protective surface film. Adhesion between the Mg hydroxide and the metal is lost at the location of the corrosion filament, suggesting that the mechanism of propagation is similar to filiform corrosion under a coating. The depth of attack is a couple of micrometers with large cracks present within the corroded area that could induce severe surface damage.

2003-01-01T00:00:00Z Schmutz, P. Guillaumin, V. Frankel, G. S. Lillard, R. S. Lillard, J. A. Tada, Eiji Frankel, G. S. http://hdl.handle.net/1811/44560 2012-12-29T00:06:49Z 2007-01-01T00:00:00Z

Electrochemical Behavior of AISI 304SS with Particulate Silica Coating in 0.1 M NaCl Tada, Eiji; Frankel, G. S. 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.

2007-01-01T00:00:00Z Tada, Eiji Frankel, G. S. Tada, Eiji Frankel, G. S. http://hdl.handle.net/1811/44559 2012-12-28T23:50:55Z 2007-01-01T00:00:00Z

Effects of Particulate Silica Coatings on Localized Corrosion Behavior of AISI 304SS under Atmospheric Corrosion Conditions Tada, Eiji; Frankel, G. S. The effects of a coating of silica particles on the localized corrosion behavior of AISI 304 stainless steel (304SS) during drying of thin electrolyte layers in controlled relative humidity environments were investigated by measurements of the transients of open-circuit potential (OCP) and galvanic current. The silica coatings were composed of spherical silica particles and were deposited on 304SS by cathodic electrophoretic deposition. It was confirmed that the silica layer worked very well as a host layer to soak up electrolyte solutions and that it remained intact under wet and dry conditions. OCP and galvanic current transients indicated that the silica layer affected propagation more than initiation of pitting corrosion. The propagation of pitting corrosion for silica-coated samples was slower than for uncoated 304SS.

2007-01-01T00:00:00Z Tada, Eiji Frankel, G. S. Liu, Xiaodong Frankel, G. S. Zoofan, B. Rokhlin, S. I. http://hdl.handle.net/1811/44558 2012-12-28T23:42:22Z 2004-01-01T00:00:00Z

Effect of applied tensile stress on intergranular corrosion of AA2024-T3 Liu, Xiaodong; Frankel, G. S.; Zoofan, B.; Rokhlin, S. I. The effect of uniaxial tensile stress on intergranular corrosion (IGC) of AA2024-T3 was studied using the foil penetration technique. Standard ASTM G49 fixed-displacement jigs were modified to allow the use of sheet samples, which were then attached to an electrochemical cell as in the foil penetration setup. The time for IGC to penetrate samples of varying thickness was monitored. This method provides a new approach to bridge the gap between IGC and intergranular stress corrosion cracking (IGSCC). Samples with various orientations relative to the rolling direction were studied in 1.0 M NaCl at controlled anodic potentials. Potentiodynamic polarization measurements indicated that the two breakdown potentials typically observed for AA2024-T3 were lower for stressed samples than for unstressed samples, and the current at a given potential was higher. The penetration rate depended on potential and was higher for stressed samples than for unstressed samples. The primary form of attack above the higher breakdown potential was IGSCC, whereas pitting dominated between the two breakdown potentials. Stress had a larger effect on penetration rate at higher applied potentials, indicating that pitting is less susceptible to the effects of stress than a properly oriented IGC crevice. The effects of stress on the penetration rates in various orientations were strongly linked to the anisotropic microstructure. X-ray microfocal radiography and optical microscopy of cross-sections were used to characterize IGSCC defects in thin penetrated foils. In certain orientations, crack faces were parallel rather than perpendicular to the stress direction as a result of the constraints of the microstructure on the orientation of the IGC. Implications for the mechanisms of IGC and IGSCC are discussed.

2004-01-01T00:00:00Z Liu, Xiaodong Frankel, G. S. Zoofan, B. Rokhlin, S. I. Leblanc, P. Frankel, G. S. http://hdl.handle.net/1811/44557 2012-12-28T23:49:37Z 2002-01-01T00:00:00Z

A Study of Corrosion and Pitting Initiation of AA2024-T3 Using Atomic Force Microscopy Leblanc, P.; Frankel, G. S. The corrosion behavior of a population of microstructural inclusions in AA2024-T3 and the interactions between individual inclusions were investigated using atomic force microscopy-based techniques. The results showed that Al-Cu-Fe-Mn intermetallic particles were cathodic in nature and interacted strongly with their surroundings. For large exposed areas, it was found that pitting initiated at a few Al2CuMg particles, which became active upon film breakdown even though scanning Kelvin probe force microscopy measurements in air showed they were noble with respect to the matrix prior to the exposure. The size and location of the cathodic regions proved to be critical issues. Accelerated matrix dissolution took place for exposed areas containing a large area fraction of Al-Cu-Fe-Mn inclusions. The location of the cathodic sites had a strong influence on the local chemistry of the environment and controlled the corrosion behavior of the surface. Potentiodynamic measurements made using a remote cathode indicated no copper redeposition around the pit and on the matrix, in contrast with open-circuit exposure, where active cathodic inclusions modify the local pH. It was also found that pits generated at Al2CuMg inclusions became ennobled as a result of Cu enrichment but did not become active cathodic sites.

2002-01-01T00:00:00Z Leblanc, P. Frankel, G. S. Akiyama, E. Markworth, A. J. McCoy, J. K. Frankel, G. S. Xia, L. McCreery, R. L. http://hdl.handle.net/1811/44556 2012-12-28T23:37:31Z 2003-01-01T00:00:00Z

Storage and Release of Soluble Hexavalent Chromium from Chromate Conversion Coatings on Al Alloys Kinetics of Release Akiyama, E.; Markworth, A. J.; McCoy, J. K.; Frankel, G. S.; Xia, L.; McCreery, R. L. The release of chromate ions from chromate conversion coatings (CCCs) on Al alloys was studied, and the effect of aging of CCCs on the chromate release kinetics was investigated. Chromate release from CCCs into aqueous solutions was monitored by measuring the change in the chromate concentration in solution using UV-visible spectroscopy. Heat-treatment of the CCC greatly reduced the chromate release rate. The chromate release rate also decreased with increasing aging time at room temperature. A diffusion-control model was proposed based on the notion that the CCC in an aqueous solution is a porous, two-phase structure consisting of a solid phase with adsorbed Cr(VI) species that is in local Langmuir-type equilibrium with an interpenetrating solution phase. This model results in a concentration gradient of soluble Cr(VI) in the solution phase of the CCC as chromate is released. The concentration and diffusion coefficients of soluble Cr(VI) in CCC were estimated. The estimated diffusion coefficient tended to decrease with aging time, suggesting that the CCC is modified with aging time.

2003-01-01T00:00:00Z Akiyama, E. Markworth, A. J. McCoy, J. K. Frankel, G. S. Xia, L. McCreery, R. L. Sehgal, A. Lu, D. Frankel, G. S. http://hdl.handle.net/1811/44555 2012-12-28T23:42:59Z 1998-01-01T00:00:00Z

Pitting in Aluminum Thin Films Supersaturation and Effects of Dichromate Ions Sehgal, A.; Lu, D.; Frankel, G. S. The growth of pits in 209 nm thick Al films in chloride solutions with and without dichromate ions was examined using image analysis of the growing pits to determine pit current density. In pure chloride solutions, the pit current density decreased at high potentials after reaching a maximum value, and then was almost independent of applied potential. A hysteresis in the pit current density-potential behavior was observed during downward stepping of the potential from high values. This is a result of a combination of supersaturation of the pit electrolyte followed by salt film formation, and changes in mass transport from hydrogen bubbles that increase convection and lift the remnant passive film away from the dissolving surface. In solutions containing dichromate ions, the corrosion and repassivation potentials shifted in the noble direction, and rather large metastable pits formed at the open circuit. A large concentration of dichromate ions was needed to inhibit pit growth. In dichromate solutions, subsequent pit growth at higher potentials often initiated at the edge of the open-circuit pits. The rate of pit growth was lower for these pits because the remnant passive film layer was not easily lifted up at these sites, and thus created a barrier for mass transport away from the dissolving pit edge.

1998-01-01T00:00:00Z Sehgal, A. Lu, D. Frankel, G. S. Markworth, A. J. Sehgal, A. Frankel, G. S. http://hdl.handle.net/1811/44554 2012-12-29T00:02:16Z 1999-01-01T00:00:00Z

Oxidation of Zr-2.5 Nb Nuclear Reactor Pressure Tubes A New Model Markworth, A. J.; Sehgal, A.; Frankel, G. S. The corrosion and associated deuterium (D) uptake of Zr alloy nuclear reactor pressure tubes have been studied for over 40 years. Zircaloy tubes exhibit rapid D ingress after a period of in-reactor exposure, and have been replaced with tubes fabricated from the more resistant Zr-2.5 wt % Nb alloy. Recently, however, a small percentage of Zr-2.5 Nb tubes have been found to contain high D contents. There is currently no clear understanding of the mechanism for this increased D uptake, and concern exists that an increasing number of high-D tubes will develop with time. A new model for Zr-2.5 Nb corrosion is presented in this paper. The rate of corrosion is shown to be dependent on the rate of transformation of the protective inner oxide layer (closer to the metal) to a porous outer layer. The mechanism of this transformation is not known and should be the subject of future investigations. It is assumed in the model that zirconia chemically dissolves into the solution at the pore bottom. The rate of this dissolution reaction depends on the local pH, which increases if there is a buildup of deuteroxyl ions generated in the cathodic part of the Zr corrosion reaction. A mathematical description of this model, containing several parameters with unknown values, is presented. Assigning certain values to these parameters results in predictions of oxide formation (and thus D buildup) that correspond well with observations.

1999-01-01T00:00:00Z Markworth, A. J. Sehgal, A. Frankel, G. S. Zhang, Weilong Frankel, G. S. http://hdl.handle.net/1811/44553 2012-12-29T00:07:47Z 2002-01-01T00:00:00Z

Localized Corrosion Growth Kinetics in AA2024 Alloys Zhang, Weilong; Frankel, G. S. 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.

2002-01-01T00:00:00Z Zhang, Weilong Frankel, G. S. Schmutz, P. Frankel, G. S. http://hdl.handle.net/1811/44551 2012-12-29T00:00:41Z 1999-01-01T00:00:00Z

Influence of Dichromate Ions on Corrosion of Pure Aluminum and AA2024-T3 in NaCl Solution Studied by AFM Scratching Schmutz, P.; Frankel, G. S. The localized corrosion of pure aluminum, AA2024-T3 alloy, and in particular the behavior of the intermetallic particles in AA2024-T3 were studied using a technique of scratching the surface with atomic force microscopy (AFM) tips. In situ AFM scratching provides information regarding the protectiveness of the surface film. Scratching of aluminum by rastering the surface with the AFM tip in contact mode in 0.5M NaCl resulted in accelerated uniform dissolution in the rastered area. Slow pumping of the solution through the AFM cell during scratching, however, resulted in the development of sustained localized corrosion. Scratching in a stagnant 0.5 M NaCl solution containing 10-4 M Na2Cr2O7 also resulted in the development of large pits. For higher dichromate concentrations (0.005 and 0.05 M), neither accelerated dissolution nor pitting was observed, most probably because of the formation of harder chromium containing surface oxide. AFM scratching of AA2024-T3 in 0.01 M NaCl resulted in the immediate dissolution of the Al-Cu-Mg particles because of a destabilization of the surface film during light scratching. The addition of very dilute concentrations of dichromate (10-4 M) to 0.5 M NaCl completely suppressed the corrosion of the Al-Cu-Mg particles during AFM scratching, but breakdown in the matrix occurred in a similar fashion as for pure aluminum. The addition of 0.005 M dichromate to 0.5 M NaCl again suppressed localized breakdown for low applied force during scratching, but pits formed at the Al-Cu-Mg particles at high forces. Higher dichromate concentration (0.05 M) did not completely suppress the localized breakdown at Al-Cu-Mg particles, but the amount and lateral spreading of the dissolution was much smaller.

1999-01-01T00:00:00Z Schmutz, P. Frankel, G. S. Akiyama, E. Frankel, G. S. http://hdl.handle.net/1811/44550 2012-12-28T23:52:51Z 1999-01-01T00:00:00Z

The Influence of Dichromate Ions on Aluminum Dissolution Kinetics in Artificial Crevice Electrode Cells Akiyama, E.; Frankel, G. S. 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.

1999-01-01T00:00:00Z Akiyama, E. Frankel, G. S. Clark, William J. Ramsey, Jeremy D. McCreery, Richard L. Frankel, Gerald S. http://hdl.handle.net/1811/44549 2012-12-28T23:53:26Z 2002-01-01T00:00:00Z

A Galvanic Corrosion Approach to Investigating Chromate Effects on Aluminum Alloy 2024-T3 Clark, William J.; Ramsey, Jeremy D.; McCreery, Richard L.; Frankel, Gerald S. The effects of chromate treatment on the corrosion of an aluminum/copper aircraft alloy were examined with a galvanic corrosion apparatus composed of two electrodes and a zero resistance ammeter. Combinations of pure Al, pure Cu, and AA2024-T3 electrodes were immersed in 0.1 M NaCl solution, which was saturated with air, O2, or argon. Selection of electrode material or differential aeration resulted in partial segregation of corrosion reactions, with one electrode becoming a net cathode and the other a net anode. For the case of an Al/Cu galvanic cell, chromate significantly reduced the observed cathodic current on Cu but had little effect when added to the Al cell. For an AA2024/AA2024 couple, chromate decreased the observed current when present in either the net anode or net cathode compartments. The results indicate that CrVI in solution, or CrVI pretreatment, inhibits O2 reduction on Cu sites. Inhibition is preceded by a spike in the reduction current, implying that CrIII is formed at approximately a monolayer level on Cu. The results for CrVI effects on the AA2024/AA2024 galvanic couple are consistent with observed polarization curves. Considering the results in their entirety, CrVI acts as a strong irreversible cathodic inhibitor on Cu and AA2024, but the results do not exclude the action of CrVI as an anodic inhibitor on AA2024-T3.

2002-01-01T00:00:00Z Clark, William J. Ramsey, Jeremy D. McCreery, Richard L. Frankel, Gerald S. Iannuzzi, M. Frankel, G. S. Kovac, J. http://hdl.handle.net/1811/44537 2012-12-29T00:02:26Z 2007-01-01T00:00:00Z

A study of the mechanisms of corrosion inhibition of AA2024-T3 by vanadates using the split cell technique Iannuzzi, M.; Frankel, G. S.; Kovac, J. The mechanisms of corrosion inhibition of AA2024-T3 by vanadates were studied in this work using the split cell technique and polarization curves. The electrochemical behavior of clear solutions containing metavanadates and orange solutions containing decavanadates was clearly distinctive. Injection of metavanadates to the cathode side of the different split cell setups greatly reduced the galvanic current, indicating a potent inhibition of the oxygen reduction kinetics. The galvanic current never exhibited a transient current peak, suggesting that metavanadates inhibit AA2024-T3 corrosion by a mechanism that does not involve electrochemical reduction. Injection of metavanadate to the anode side of the different split cells had no effect on the galvanic current. Injection of orange decavanadate to the cathode side of the AA2024-T3 split cell resulted in a large current peak, associated with the electrochemical reduction of decavanadate. However, decavanadates did not impart significant corrosion protection.

2007-01-01T00:00:00Z Iannuzzi, M. Frankel, G. S. Kovac, J. Frankel, G. S. Schrott, A. G. Davenport, A. J. Isaacs, H. S. Jahnes, C. V. Russak, M. A. http://hdl.handle.net/1811/44528 2012-12-29T00:08:04Z 1994-01-01T00:00:00Z

X-Ray Absorption Study of Electrochemically Grown Oxide Films on AlCr Sputtered Alloys II. In Situ Studies Frankel, G. S.; Schrott, A. G.; Davenport, A. J.; Isaacs, H. S.; Jahnes, C. V.; Russak, M. A. The chemistry of chromium in the passive film on sputter-deposited chromium and AlCr thin films has been investigated in situ in an electrochemical cell under potential control by studying x-ray absorption near edge structure. At high potentials, Cr in the AlCr alloys was oxidized to the 6-valent state. Depending on the rate of potential increase, 6-valent chromium either dissolved from the alloy or was trapped in the passive film where it was electroactive, i.e., the valence state could be reversibly switched between the 3- and 6-valent states by changing the applied potential. The kinetics of these processes were investigated. Ex situ x-ray photoelectron spectroscopy measurements indicated that, during slow scanning at low potentials, the composition of both the surface oxide and underlying metallic layers changed. These changes resulted in a structure that was susceptible to transpassive dissolution of Cr at potentials above 0.2 V(MSE).

1994-01-01T00:00:00Z Frankel, G. S. Schrott, A. G. Davenport, A. J. Isaacs, H. S. Jahnes, C. V. Russak, M. A. Frankel, G. S. Davenport, A. J. Isaacs, H. S. Schrott, A. G. Jahnes, C. V. Russak, M. A. http://hdl.handle.net/1811/44527 2012-12-29T00:00:15Z 1992-01-01T00:00:00Z

X-Ray Absorption Study of Electrochemically Grown Oxide Films on Al-Cr Sputtered Alloys I. Ex situ Studies Frankel, G. S.; Davenport, A. J.; Isaacs, H. S.; Schrott, A. G.; Jahnes, C. V.; Russak, M. A. Oxides grown electrochemically in a borate buffer solution on the surface of sputter-deposited AlCr alloy films were studied by x-ray absorption near edge structure (XANES). The measurements were made in air immediately following polarization in solution. The oxides were also examined with x-ray photoelectron spectroscopy (XPS). The effects of alloy composition and thickness as well as applied potential were studied. Cr( VI) was found in the oxides if the applied potential was sufficiently high. The Cr(VI) was enriched at the interface with the electrolyte and the proportion of Cr(VI) in the oxide was higher for alloy films containing more Cr. The Cr(VI) in the oxides could be reversibly reduced to Cr(III) and reoxidized to Cr(VI) by subsequent potentiostatic treatments in solution.

1992-01-01T00:00:00Z Frankel, G. S. Davenport, A. J. Isaacs, H. S. Schrott, A. G. Jahnes, C. V. Russak, M. A. Brusic, V. Frankel, G. S. Rush, B. M. Schrott, A. G. Jahnes, C. Russak, M. A. Petersen, T. http://hdl.handle.net/1811/44526 2012-12-28T23:39:53Z 1992-01-01T00:00:00Z

Corrosion and Passivation of Fe and FeN Films Brusic, V.; Frankel, G. S.; Rush, B. M.; Schrott, A. G.; Jahnes, C.; Russak, M. A.; Petersen, T. The role of nitrogen in corrosion and passivation of thin Fe-N films was studied. Sputtered films with different levels of nitrogen were characterized for composition, conductivity, stress, and crystallinity. Corrosion and passivation of the films were evaluated by electrochemical measurements combined with in situ ellipsometry and ex situ x-ray photoelectron spectroscopy. The results indicate that in deaerated solutions the primary action of N is to reduce the catalytic activity of the surface for the hydrogen reaction and thereby reduce corrosion. In aerated solutions the corrosion rate increases with N content. Kinetics of the protective oxide formation as a function of potential, percent N, and the presence of borate buffer are discussed in detail. The work is relevant to the behavior of oxide-free Fe-N surfaces in contact with mild, nearly neutral electrolytes, such as could be used in fabrication of magnetic recording heads.

1992-01-01T00:00:00Z Brusic, V. Frankel, G. S. Rush, B. M. Schrott, A. G. Jahnes, C. Russak, M. A. Petersen, T. Frankel, G. S. Rush, B. M. Jahnes, C. V. Farrell, C. E. Davenport, A. J. Isaacs, H. S. http://hdl.handle.net/1811/44525 2012-12-28T23:56:20Z 1991-01-01T00:00:00Z

Repassivation Transients Measured with Thin Film Breaking Electrodes Frankel, G. S.; Rush, B. M.; Jahnes, C. V.; Farrell, C. E.; Davenport, A. J.; Isaacs, H. S.

1991-01-01T00:00:00Z Frankel, G. S. Rush, B. M. Jahnes, C. V. Farrell, C. E. Davenport, A. J. Isaacs, H. S. Brusic, V. Russak, M. Schad, R. Frankel, G. Selius, A. DiMilia, D. Edmonson, D. http://hdl.handle.net/1811/44524 2012-12-28T23:58:28Z 1989-01-01T00:00:00Z

Corrosion of Thin Film Magnetic Disk: Galvanic Effects of the Carbon Overcoat Brusic, V.; Russak, M.; Schad, R.; Frankel, G.; Selius, A.; DiMilia, D.; Edmonson, D. Thin film magnetic disks are usually coated with a layer of carbon or silica to improve wear properties, enhance flyability, and reduce environmental degradation of the underlying metal layers. In this paper we investigated the effect of dc and RF sputter deposited carbon overcoats on the corrosion behavior of the magnetic layers using electrochemical techniques and a corrosive gas chamber. Corrosion test samples were characterized by optical microscopy, ellipsometry, scanning electron microscopy (SEM), and scanning Auger spectroscopy (SAM) in order to establish the mechanism of corrosion. Corrosion of the magnetic layer was found to be galvanically coupled to the carbon overcoat and influenced by several disk processing parameters.

1989-01-01T00:00:00Z Brusic, V. Russak, M. Schad, R. Frankel, G. Selius, A. DiMilia, D. Edmonson, D. Davenport, A. J. Isaacs, H. S. Frankel, G. S. Schrott, A. G. Jahnes, C. V. Russak, M. A. http://hdl.handle.net/1811/44523 2012-12-28T23:53:02Z 1991-01-01T00:00:00Z

In Situ X-Ray Absorption Study of Chromium Valency Changes in Passive Oxides on Sputtered AlCr Thin Films under Electrochemical Control Davenport, A. J.; Isaacs, H. S.; Frankel, G. S.; Schrott, A. G.; Jahnes, C. V.; Russak, M. A.

1991-01-01T00:00:00Z Davenport, A. J. Isaacs, H. S. Frankel, G. S. Schrott, A. G. Jahnes, C. V. Russak, M. A. Frankel, G. S. Russak, M. A. Jahnes, C. V. Mirzamaani, M. Brusic, V. A. http://hdl.handle.net/1811/44522 2012-12-29T00:04:13Z 1989-01-01T00:00:00Z

Pitting of Sputtered Aluminum Alloy Thin Films Frankel, G. S.; Russak, M. A.; Jahnes, C. V.; Mirzamaani, M.; Brusic, V. A. Metallic films with thickness on the order of hundreds or thousands of angstroms are extensively used in the electronics industry. Due to obvious dimensional limitations, such thin films may be very susceptible to performance degradation resulting from corrosion. In this study, pitting of Al alloy thin films has been investigated. An advantage to studying thin films is that it is possible to produce alloys by thin film deposition techniques that are not easily produced by conventional metallurgical methods. Recent reports have described the exceptional pitting and corrosion resistance of thin film aluminum alloys (1-3). These alloys were metastable solid solutions produced by sputter deposition containing up to 15 atomic % solute which is far in excess of the equilibrium solubility. In this study, we have taken a similar approach to look at a wide compositional range of several Al alloys.

1989-01-01T00:00:00Z Frankel, G. S. Russak, M. A. Jahnes, C. V. Mirzamaani, M. Brusic, V. A. Iannuzzi, M. Frankel, Gerald S. http://hdl.handle.net/1811/36524 2012-12-29T00:10:06Z 2007-01-01T00:00:00Z

Mechanisms of Corrosion Inhibition of AA2024-T3 by Vanadates Iannuzzi, M.; Frankel, Gerald S. The mechanisms of corrosion inhibition of AA2024-T3 by vanadates were studied using chronoamperometry, polarization curves and adsorption isotherms. The electrochemical behaviour of clear solutions containing metavanadates and orange solutions containing decavanadates was clearly distinctive. Metavanadates reduced the kinetics of oxygen reduction to an extent similar to chromates. Corrosion inhibition of AA2024-T3 by metavanadates was very rapid and it might occur by the formation of an adsorbed layer. Reduction of clear metavanadate solution was very slow. Approximately 35 min were required to develop a monolayer of a reduced vanadate species. The adsorption of the inhibitor likely blocked reactive sites on intermetallic particles, discouraging the oxygen reduction reaction (ORR). Adsorption of the inhibitor on the Al matrix could also displace Cl- ions, increasing the stability of the passive film and reducing the breakdown of S-phase particles. In contrast, decavanadates were shown to be poor inhibitors of the ORR. A sharp current spike was observed after injection of decavanadates for both Cu and AA2024-T3 at various applied cathodic potentials. Integration of the current peaks suggested the formation of several monolayers of a reduced vanadate species. The formation of several monolayers was in line with the poor performance of decavanadates as inhibitors of AA2024-T3 corrosion.

2007-01-01T00:00:00Z Iannuzzi, M. Frankel, Gerald S. Liu, Xiaodong Frankel, Gerald S. Zoofan, B. Rokhlin, S. I. http://hdl.handle.net/1811/36523 2012-12-28T23:57:44Z 2007-01-01T00:00:00Z

In-situ Observation of Intergranular Stress Corrosion Cracking in AA2024-T3 under Constant Load Conditions Liu, Xiaodong; Frankel, Gerald S.; Zoofan, B.; Rokhlin, S. I. A specially designed setup was used to apply a constant load to a thin sheet sample of AA2024-T3 and, using microfocal X-ray radiography, to observe in situ the resulting intergranular stress corrosion cracking (IGSCC) from the exposed edge of the sample. The growth of and competition between multiple IGSCC sites was monitored. In many experiments twin cracks initiated close to each other. Furthermore, the deepest crack at the beginning of every experiment was found to slow or stop growing, and was then surpassed by another crack that eventually penetrated through the sample. These observations cannot be explained by the theory of fracture mechanics in inert environments. The possible mechanisms underlying the competition between cracks are discussed.

2007-01-01T00:00:00Z Liu, Xiaodong Frankel, Gerald S. Zoofan, B. Rokhlin, S. I.