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Irradiation-assisted stress corrosion cracking behavior of austenitic stainless steels applicable to LWR core internals.

Description: This report summarizes work performed at Argonne National Laboratory on irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels that were irradiated in the Halden reactor in simulation of irradiation-induced degradation of boiling water reactor (BWR) core internal components. Slow-strain-rate tensile tests in BWR-like oxidizing water were conducted on 27 austenitic stainless steel alloys that were irradiated at 288 C in helium to 0.4, 1.3, and 3.0 dpa. Fractographic analysis was conducted to determine the fracture surface morphology. Microchemical analysis by Auger electron spectroscopy was performed on BWR neutron absorber tubes to characterize grain-boundary segregation of important elements under BWR conditions. At 0.4 and 1.4 dpa, transgranular fracture was mixed with intergranular fracture. At 3 dpa, transgranular cracking was negligible, and fracture surface was either dominantly intergranular, as in field-cracked core internals, or dominantly ductile or mixed. This behavior indicates that percent intergranular stress corrosion cracking determined at {approx}3 dpa is a good measure of IASCC susceptibility. At {approx}1.4 dpa, a beneficial effect of a high concentration of Si (0.8-1.5 wt.%) was observed. At {approx}3 dpa, however, such effect was obscured by a deleterious effect of S. Excellent resistance to IASCC was observed up to {approx}3 dpa for eight heats of Types 304, 316, and 348 steel that contain very low concentrations of S. Susceptibility of Types 304 and 316 steels that contain >0.003 wt.% S increased drastically. This indicates that a sulfur related critical phenomenon plays an important role in IASCC. A sulfur content of <0.002 wt.% is the primary material factor necessary to ensure good resistance to IASCC. However, for Types 304L and 316L steel and their high-purity counterparts, a sulfur content of <0.002 wt.% alone is not a sufficient condition to ensure good resistance to IASCC. This is in distinct contrast to the behavior of their high-C ...
Date: January 31, 2006
Creator: Chung, H. M.; Shack, W. J. & Technology, Energy
Partner: UNT Libraries Government Documents Department

Resonant Auger studies of metallic systems

Description: Results of resonant Auger spectroscopy experiments are presented for Cu, Co, and oxidized Al. Sub-lifetime narrowing of Auger spectra and generation of sub-lifetime narrowed absorption spectra constructed from Auger yield measurements, were observed. Resonant Auger yields are used to identify three valence states of oxidized Al. Partial absorption yield spectra were derived giving detailed electronic information and thickness information for the various chemical states of the bulk metal, the passivating aluminum oxide layer, and the metal-oxide interface region. In addition, the total absorption yield spectrum for the oxidized Al sample was constructed from the partial yield data, supporting the consistency of the authors method.
Date: October 21, 1999
Creator: Coulthard, I.; Antel, W. J., Jr.; Frigo, S. P.; Freeland, J. W.; Moore, J.; Calaway, W. S. et al.
Partner: UNT Libraries Government Documents Department

Sodium Depletion on Glass Surfaces During Auger Analysis

Description: The kinetics of the depletion of sodium on glass surfaces during Auger Electron Spectroscopic analysis is investigated. The decay process is mathematically represented as a sum of two single decaying exponential functions. This behavior may be described by a mechanism that accounts for the neutralization of sodium ions by the electron beam. Sodium ions and neutral sodium atoms are depleted by several known processes.
Date: April 22, 1981
Creator: Whitkop, P.G.
Partner: UNT Libraries Government Documents Department

Anodically enhanced diffusion in Cu/Ag thin film couples

Description: Thin, 100-nm films of first silver and then copper were deposited consecutively onto pure single-crystal (111) silicon substrates by magneton sputter deposition. Controlled anodic current density was applied at room temperature to dissolve the outer copper film to varying depths approaching the copper/silver interface. Profiles of copper and silver concentration vs. depth below the anodically dissolved surfaces were subsequently obtained by argon ion sputtering and simultaneous Auger Electron Spectroscopy. Despite some intrinsic mixing during the profile analysis, there is clear evidence that diffusion of copper and silver into one another is enhanced by anodic currents at the outer copper surface. Preliminary interpretation leads the authors to believe that the effect is caused by surface formation of vacancies during anodic dissolution. The anodically generated vacancies can migrate as divacancies to the copper/silver interface where they enhance diffusion by the usual vacancy exchange mechanism.
Date: April 1, 1995
Creator: Jones, D.A. & Jankowski, A.F.
Partner: UNT Libraries Government Documents Department

Interface diffusion in polysynthetically-twinned TiAl

Description: The utility of polysynthetically-twinned (PST) TiAl, which contains a high density of parallel, atomically-flat interfaces within a set of identical crystallographic orientations, as a potential model system for a detailed investigation of interface diffusion is explored. Macroscopic PST crystals were grown in an optical float zone furnace. Thin films were cut from oriented crystals and polished with <112> directions normal to the film. After sputter cleaning, Ag was deposited on one side of the TiAl thin films. Auger spectra were obtained from these films over a wide range of sputter/anneal conditions. The Al and Ti concentrations were analyzed as well as the important impurity elements, S, Ar, C, N and O. Using the present data and existing knowledge of the microstructure and crystallography of PSI TiAl, the potential of this material for providing a detailed understanding of the atomistic mechanisms of interface diffusion is analyzed.
Date: December 1, 1997
Creator: Luzzi, D.E.; Imamura, D.; Inui, H.; Yamaguchi, M.; George, E.P.; Heatherly, L. et al.
Partner: UNT Libraries Government Documents Department

RF and structural characterization of new SRF films

Description: In the past years, energetic vacuum deposition methods have been developed in different laboratories to improve Nb/Cu technology for superconducting cavities. Jefferson Lab is pursuing energetic condensation deposition via Electron Cyclotron Resonance. As part of this study, the influence of the deposition energy on the material and RF properties of the Nb thin film is investigated. The film surface and structure analyses are conducted with various techniques like X-ray diffraction, Transmission Electron Microscopy, Auger Electron Spectroscopy and RHEED. The microwave properties of the films are characterized on 50 mm disk samples with a 7.5 GHz surface impedance characterization system. This paper presents surface impedance measurements in correlation with surface and material characterization for Nb films produced on copper substrates with different bias voltages and also highlights emerging opportunities for developing multilayer SRF films with a new deposition system.
Date: September 1, 2009
Creator: A.-M. Valente-Feliciano,H. L. Phillips,C. E. Reece,X. Zhao,D. Gu,R. Lukaszew,B. Xiao,K. Seo
Partner: UNT Libraries Government Documents Department

Sulfur-induced corrosion of Au(111) studied by real-time STM

Description: The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers (SAMs), use as a corrosion inhibitor, and as a chemical sensor. In this work, the interaction of sulfur with Au(111) at two different temperatures (300 K and 420 K) was studied by real-time scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). In the low coverage regime (&lt; 0.1 monolayer), S modifies the surface stress leading to a lateral expansion of the Au surface layer. An ordered ({radical}3 x {radical}3)R30{sup o} sulfur adlayer develops as the coverage reaches {approx}0.3 ML. With further increasing S coverage the Au(111) surface undergoes a dynamic rearrangement while forming a two-dimensional AuS phase: gold surface atoms are removed from regular terrace sites and incorporated into the growing gold sulfide phase resulting in the appearance of pits and irregularly shaped AuS islands. Gold sulfide prepared at room temperature exhibits short-range order; an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. Higher temperatures lead to decomposition of the AuS corrosion film. Formation of an ordered AuS phase via rapid step retraction rather than etch pit formation is observed during S-interaction with Au(111) surfaces at 420 K. Our results shed new light on the S-Au(111) interaction.
Date: November 2, 2004
Creator: Biener, M; Biener, J & Friend, C
Partner: UNT Libraries Government Documents Department

Analysis of potential component cleaning techniques. Final report, July 6, 1992--July 5, 1995

Description: Elevated temperature, elevated pressure water, supercritical carbon dioxide and helical resonator plasmas were investigated for potential use in surface cleaning. A surface analysis system consisting of X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy was used to evaluate surfaces exposed to water and supercritical carbon dioxide. Langmuir probe and silicon oxidation studies were used to evaluate the effect of oxygen plasmas on silicon surfaces. Silicon oxides were removed from silicon surfaces by water at temperatures above 260{degrees}C and pressures above 2000 psi; silicon oxidation and simultaneous dissolution of the oxide grown occurred under these conditions. A new approach for in-situ monitoring of subcritical and supercritical fluid density was devised.
Date: November 1, 1997
Creator: Hess, D.W.
Partner: UNT Libraries Government Documents Department

Optically driven surface reactions: Laser probes of surface dynamics

Description: Our efforts in the past three and a half years have been directed towards providing the ground work for applying REMPI detection to the dynamics of surface oxidation and desorption reactions. Our initial efforts addressed the oxidation of carbon films that had been prepared on metal supports. The photolysis of adsorbed N{sub 2}O was chosen as the initial oxygen atom source. However, a number of alternative O atom precursors were also evaluated. Results from Auger electron spectroscopy (AES), temperature programmed desorption (TPD), and state-resolved studies of the photochemistry of N{sub 2}O, NO{sub 2}, or O{sub 2} coadsorbed with carbon on Pt(111) have been obtained. In the last eighteen months, we have focused on a stringent test of current theories of femtosecond laser-induced desorption of CO/Cu(100). The results indicate that an electronic friction model is sufficient to account for essentially all of the results in this system, indicating that a predictive tool for femtosecond laser-induced surface chemistry may be in hand.
Date: March 11, 1997
Creator: Cavanagh, R.R. & King, D.S.
Partner: UNT Libraries Government Documents Department

Development of laser-plasma diagnostics using ultrafast atomic-scale dynamics. 96-ERD-046 final report

Description: Ultrashort laser pulse systems allow examination of intense, ultrafast laser-plasma interactions. More specifically, intense laser irradiation can induce short xuv/x-ray bursts from the surface of condensed phase targets. Ultrafast xuv/x-ray detection is needed to understand laser-plasma interactions in this dynamic regime. Support of the Stockpile Stewardship and Management Program requires this critical understanding. Our effort here has been to extend understanding of atomic-scale dynamics in such environments with the goal of developing next generation ultrafast xuv/x-ray diagnostics where the sensors will be the atoms and ions themselves and the time resolution will approach that of the induced atomic transitions ({approx} a few femtoseconds). Pivotal contributions to the rapidly developing field of highly nonperturbative interactions of ultrashort pulse lasers with atoms/ions have been made at this laboratory. In the visible/infrared wavelength regions the temporal and spectral content of ultrashort laser pulses are now reliably monitored within a single pulse using frequency resolved optical gating (FROG) which is based on rapid nonlinear optical processes such as the Kerr effect. New applications of this basic concept are still being developed. Corresponding detection for the xuv/x-ray wavelengths does not exist and is urgently needed in many laboratory programs. The FROG technique cannot be applied in the xuv/x-ray region. Current x-ray streak camera technology is limited to {approx}0.5 picosecond resolution.
Date: March 1, 1997
Creator: Bolton, P.R.; Kulander, K.C. & Boreham, B.W.
Partner: UNT Libraries Government Documents Department

Study of substrate diffusion in epitaxial n-type CdSe films grown on GaAs (001) by pulsed laser ablation

Description: N-type CdSe films with thicknesses of 470--630 nm were grown on (001) and 2{degree}-miscut GaAs wafers by ArF (193 nm) pulsed laser ablation of stoichiometric CdSe targets at platen temperatures (T{sub p}) of 250--425 C in vacuum and ambient Ar gas. Film-substrate interdiffusion was studied with Auger depth profiling, as well as energy dispersive x-ray fluorescent spectroscopy (EDS). Both techniques showed that extensive interdiffusion took place at the film-substrate interface for CdSe films grown at T{sub p} {ge} 355 C but was greatly reduced at T{sub p} = 250 C. Tilting the substrate to be approximately parallel to the ablation plume as well as decreasing the ambient gas pressure also reduced film-substrate interdiffusion.
Date: April 1, 1998
Creator: Park, J.; Rouleau, C.M. & Lowndes, D.H.
Partner: UNT Libraries Government Documents Department

Processing and characterization of SiC platelet/SiC composites

Description: Hot pressed {beta}-SiC and SiC matrix composites containing encapsulated {alpha}-SiC platelets were prepared and investigated. The Microstructures were characterized using electron microscopy, Auger electron spectroscopy, and x-ray diffraction. Prior to hot pressing, the platelets were either encapsulated with hydrated aluminum sulfate or yttrium hydroxycarbonate (later calcined to form alumina or yttria) from aqueous solutions, or oxidized to form a silica layer. The effect of these interfacial layers on toughness was described.
Date: March 1, 1995
Creator: Cao, J.J.; MoberlyChan, W.J.; De Jonghe, L.C.; Dalgleish, B. & Niu, M.Y.
Partner: UNT Libraries Government Documents Department

X-ray fluorescence/Auger-electron coincidence spectroscopy of vacancy cascades in atomic argon

Description: Argon L{sub 2.3}-M{sub 2.3}M{sub 2.3} Auger-electron spectra were measured in coincidence with K{alpha} fluorescent x-rays in studies of Ar K-shell vacancy decays at several photon energies above the K-threshold and on the 1s-4p resonance in atomic argon. The complex spectra recorded by conventional electron spectroscopy are greatly simplified when recorded in coincidence with fluorescent x-rays, allowing a more detailed analysis of the vacancy cascade process. The resulting coincidence spectra are compared with Hartree-Fock calculations which include shake-up transitions in the resonant case. Small energy shifts of the coincidence electron spectra are attributed to post-collision interaction with 1s photoelectrons.
Date: December 1, 1996
Creator: Arp, U.; LeBrun, T.; Southworth, S.H.; Jung, M. & MacDonald, M.A.
Partner: UNT Libraries Government Documents Department

Chemical and microstructural characterization of thermally grown alumina scales

Description: An experimental program has been initiated to evaluate the chemical, microstructural, and mechanical integrity of thermally grown oxide scales to establish requirements for improved corrosion performance in terms of composition, structure, and properties. Iron aluminides of several compositions were selected for the study. Oxidation studies were conducted in air and oxygen environments at 1000{degrees}C. The results showed that the scaling kinetics followed a parabolic rate law but that the rates in early stages of oxidation were significantly greater than in later stages; the difference could be attributed to the presence of fast-growing transient iron oxides in the layer during the early stages. Further, scale failure occurred via gross spallation, scale cracking, and nodule formation and was influenced by alloy composition. Auger electron spectroscopy of Ar-exposed specimens of ternary Fe-Cr-Al alloy showed sulfur on the gas/scale side of the interface; the sulfur decreased as the exposure time increased. Raman spectroscopy and ruby fluorescence were used to examine the scale development as a function of oxidation temperature. Ruby-line shift is used to examine phase transformations in alumina and to calculate compressive strains in thermally grown scales.
Date: September 1995
Creator: Natesan, K.; Richier, C. & Veal, B. W.
Partner: UNT Libraries Government Documents Department

Catalyzed hydrogenation of nitrogen and ethylene on metal (Fe, Pt) single crystal surfaces and effects of coadsorption: A sum frequency generation vibrational spectroscopy study

Description: High-pressure catalytic reactions and associated processes, such as adsorption have been studied on a molecular level on single crystal surfaces. Sum Frequency Generation (SFG) vibrational spectroscopy together with Auger Electron Spectroscopy (AES), Temperature Programmed Desorption (TPD) and Gas Chromatography (GC) were used to investigate the nature of species on catalytic surfaces and to measure the catalytic reaction rates. Special attention has been directed at studying high-pressure reactions and in particular, ammonia synthesis in order to identify reaction intermediates and the influence of adsorbates on the surface during reaction conditions. The adsorption of gases N{sub 2}, H{sub 2}, O{sub 2} and NH{sub 3} that play a role in ammonia synthesis have been studied on the Fe(111) crystal surface by sum frequency generation vibrational spectroscopy using an integrated Ultra-High Vacuum (UHV)/high-pressure system. SFG spectra are presented for the dissociation intermediates, NH{sub 2} ({approx}3325 cm{sup -1}) and NH ({approx}3235 cm{sup -1}) under high pressure of ammonia (200 Torr) on the clean Fe(111) surface. Addition of 0.5 Torr of oxygen to 200 Torr of ammonia does not significantly change the bonding of dissociation intermediates to the surface. However, it leads to a phase change of nearly 180{sup o} between the resonant and non-resonant second order non-linear susceptibility of the surface, demonstrated by the reversal of the SFG spectral features. Heating the surface in the presence of 200 Torr ammonia and 0.5 Torr oxygen reduces the oxygen coverage, which can be seen from the SFG spectra as another relative phase change of 180{sup o}. The reduction of the oxide is also supported by Auger electron spectroscopy. The result suggests that the phase change of the spectral features could serve as a sensitive indicator of the chemical environment of the adsorbates.
Date: December 15, 2004
Creator: Westerberg, Staffan Per Gustav
Partner: UNT Libraries Government Documents Department

Effect of Corrosion Film Composition and Structure on the Corrosion Kinetics of Ni-Cr-Fe Alloys in High Temperature Water

Description: Nickel alloys such as Alloy 600 undergo Stress Corrosion Cracking (SCC) in pure water at temperatures between about 260 C and the critical point. Increasing the level of Cr in Ni-Fe-Cr alloys increases SCC resistance in aerated and deaerated water. The mechanism is not understood. The effect of Cr composition on oxide microstructure and corrosion kinetics of Ni-Fe-Cr alloys was determined experimentally, to evaluate whether the anodic dissolution model for SCC can account for the effect of Cr on SCC. The alloy corrosion rate and corrosion product oxide microstructure is strongly influenced by the Cr composition. Corrosion kinetics are parabolic and influenced by chromium concentration, with the parabolic constant first increasing then decreasing as Cr increases from 5 to 39%. Surface analyses using Analytical Electron microscopy (AEM) and Auger Electron Spectroscopy (AES) show that the corrosion product film that forms initially on all alloys exposed to high purity high temperature water is a nickel rich oxide. With time, the amount of chromium in the oxide film increases and corrosion proceeds toward the formation of the more thermodynamically stable spinel or hexagonal Cr-rich oxides, similar to high temperature gaseous oxidation. Due to the slower diffusion kinetics at the temperatures of water corrosion compared to those in high temperature gaseous oxidation, however, the films remain as a mixture of NiO, mixed Ni, Fe and Cr spinels, NiCrO{sub 3} and FeCrO{sub 3}. As the amount of Cr in the film increases and the nature of the film changes from NiO to spinel or hexagonal oxides, cation diffusion through the films slows, slowing the corrosion rate. These observations are qualitatively consistent with an anodic dissolution SCC mechanism. However, parametric modeling of the SCC growth process, applying available creep, oxide rupture strain and corrosion kinetics data, indicates that the anodic dissolution mechanism accounts for only ...
Date: February 27, 2002
Creator: Rosecrans, P.M.; Lewis, N. & Duquette, D.J.
Partner: UNT Libraries Government Documents Department

Surface preparation and characterization of the icosahedral Al-Pd-Mn-Ga quasicrystal

Description: Auger electron spectroscopy and low-energy electron diffraction (LEED) provide basic information about the structure and composition of the fivefold surface of the quaternary quasicrystal, icosahedral Al67Pd4Mn21Ga8. Surface preparation techniques established previously for two of the icosahedral ternary alloys, Al-Pd-Mn and Al-Cu-Fe, appear to be similarly effective for Al-Pd-Mn-Ga. After annealing in the range 600-950 K, the surface concentration of Ga is constant and low. After annealing in the range 900-950 K, a good LEED pattern is obtained. LEED indicates that Ga changes the surface structure significantly.
Date: January 8, 2002
Creator: Heinzig, Mark; Jenks, Cynthia J.; Van Hove, Michel; Fisher, Ian; Canfield, Paul & Thiel, Patricia A.
Partner: UNT Libraries Government Documents Department

A Scanning Auger Microprobe analysis of corrosion products associated with sulfate reducing bacteria

Description: A Scanning Auger Microprobe analysis was performed on the corrosion products of an austenitic AISI type 304 SS after a potentiostatic polarization of one volt for ten minutes in a modified Postgate`s C media containing sulfate reducing bacteria. The corrosion products were characterized and mapped in local regions where pitting was observed. A critical evaluation of the applicability of this technique for the examination of microbially influenced corrosion (MIC) is presented.
Date: March 1, 1995
Creator: Sadowski, R.A.; Chen, G.; Clayton, C.R.; Kearns, J.R.; Gillow, J.B. & Francis, A.J.
Partner: UNT Libraries Government Documents Department

Effect of Microstructure on Low Temperature Cracking Behavior of EN82H Welds

Description: As-fabricated EN82H welds are susceptible to low temperature embrittlements in 54 degree C hydrogenated water. Values of J[sub]IC in water are typically 90% to 98% lower than those in air due to a fracture mechanism transition from microvoid coalescence to hydrogen-included intergranular fracture. Environmental J[sub]IC testing demonstrated that a high temperature (1093 degree C) anneal and furnace-cool alleviates the material's susceptibility to hydrogen-induced intergranular cracking. To identify metallurgical and compositional features that are responsible for the material's environment-sensitive behavior, detailed characterization of the microstructure and grain boundary chemistry for the as-fabricated and as-annealed materials was performed. Results from light optical microscopy, analytical electron microscopy, electron probe microanalysis, Auger electron spectroscopy and mechanical property characterization are used to provide insight into the observed low temperature embrittlement phenomenon. The key microstructural feature responsible for low temperature cracking in as-fabricated welds appears to be fine niobium and titanium-rich carbonitrides that cover most grain boundaries. These precipitates are effective hydrogen traps that promote hydrogen-induced intergranular cracking. Dissolution the fine carbonitrides during the 1093 degree C anneal reduces grain boundary trapping sites, which accounts for the improved fracture resistance displayed by the annealed weld. The role of strength level in promoting low temperature embrittlement is evaluated by cold-rolling the annealed weld to increase its yield strength from 280 to 640 MPa. The annealed and cold-rolled weld exhibits high toughness in 54 degree C water and shows no evidence of hydrogen-induced intergranular cracking, thereby demonstrating that strength is not a primary cause of low temperature embrittlement.
Date: April 30, 2001
Creator: Mills, W. J.; Brown, C. M. & Burke, M. G.
Partner: UNT Libraries Government Documents Department

Atomic and Molecular Photoelectron and Auger Electron SpectroscopyStudies Using Synchrotron Radiation

Description: Electron spectroscopy, combined with synchrotron radiation, was used to measure the angular distributions of photoelectrons and Auger electrons from atoms and molecules as functions of photon energy. The branching ratios and partial cross sections were a 130 measured in certain cases. By comparison with theoretical calculations, the experimental results are interpreted in terms of the characteristic electronic structure and ionization dynamics of the atomic or molecular sample. The time structure of the synchrotron radiation source was used to record time-of-flight (TOF) spectra o f the ejected electrons. The ''a double-angle-TOF'' method for the measurement of photoelectron angular distributions is discussed. This technique offers the advantages of increased electron collect ion efficiency and the elimination of certain systematic errors. Several results were obtained for Xe using photon energies in the range hv {approx_equal} 60-190 eV, where excitation and ionization of the inner-subshell 4d electrons dominates. The 4d asymmetry parameter {beta} exhibits strong oscillations with energy, in agreement with several theoretical calculations. As predicted, the 5p asymmetry parameter was observed to deviate strongly from that calculated using the independent-electron model, due to intershell correlation with the 4d electrons.
Date: January 1, 1982
Creator: Southworth, Stephen H.
Partner: UNT Libraries Government Documents Department


Description: Preventing the corrosion and oxidation of uranium is important to the continued development of advanced nuclear fuel technologies. Knowledge of the surface reactions of uranium metal with various environmental and atmospheric agents, and the subsequent degradation processes, are vitally important in 21st century nuclear technology. A review of the oxidation of actinide elements and their use in catalysis summarizes the present understanding of the kinetics and mechanisms of the reaction in dry and humid air. Researchers have recently used N{sub 2}{sup +} and C{sup +} ion implantation to modify the near surface region chemistry and structure of U to affect the nucleation and growth kinetics of corrosion and to passivate the surface. These researchers used Auger electron spectroscopy (AES) in conjunction with sputter depth profiling to show that the implanted surfaces had compositional gradients containing nitrides and carbides. In addition to chemical modification, ion implantation can create special reactive surface species that include defect structures that affect the initial absorption and dissociation of molecules on the surface, thus providing mechanical stability and protection against further air corrosion.
Date: April 21, 2005
Creator: Nelson, A J; Felter, T E; Wu, K J; Evans, C; Ferreira, J L; Siekhaus, W J et al.
Partner: UNT Libraries Government Documents Department