AVS1996 Session AS+BI-WeA: Corrosion and Bio-Corrosion

Wednesday, October 16, 1996 2:00 PM in Room 105B

Wednesday Afternoon

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2:00 PM		AS+BI-WeA-1 The Use of Soft X-ray Absorption Microspectroscopy in the Study of Bacterial Corrosion at Surfaces B. Tonner (University of Wisconsin, Milwaukee) X-ray absorption microscopy has many potential uses in the study of the interaction of micro-organisms with solid surfaces. In this work, we present results of the spectroscopic analysis of Mn containing compounds that are by-products of Mn oxidizing and Mn reducing bacterial life cycles. The identification of the chemical composition of Mn compounds produced by bacteria is possible using high resolution near edge spectroscopy, in combination with spectra from reference compounds. An advantage of microXANES imaging in biological problems, is the extended sampling depth which can penetrate through 'contamination' layers. The use of soft x-ray microscopy with spatial resolution of 100nm will be discussed in the context of bacterial corrosion problems.
2:20 PM		AS+BI-WeA-2 Effects of Marine Biocorrosion on the Polyurethane - Stainless Steel Interface M. Patterson (State University of New York, Buffalo); J. Gardella, Jr. (AVS) The chemical mechanisms related to adhesion between Texin 985, a polyetherurethane segmented block copolymer, and 316 L stainless steel (16-18% Cr, 10-14% Ni, 2-3% Mo) are investigated using X-ray Photoelectron Spectroscopy (XPS), Static Secondary Ion Mass Spectrometry (SSIMS) and Fourier-Transform Infrared Spectroscopy (FTIR) in grazing-angle mode. The FTIR results indicate that the urethane hard segment of the coating interacts with the metal oxide layer through hydrogen bonding of the amide group carbonyl. A 180 degree peel test is used to confirm that hydrogen bonding and weaker intermolecular forces are the primary forces of adhesion. The XPS and SSIMS results indicate that diffusion of iron into the coating may also play a role; this will be confirmed by depth profiling and imaging using SIMS. The same techniques are used to characterize the steel and coating surfaces prior to adhesion, and to study the de-adhesion of the coating following a two-part simulated marine corrosion experiment. Cathodic disbondment is simulated by exposure of the coated steel to ASTM seawater, following the creation of a fault in the coating. Biocorrosion is simulated by growth and attachment of a biofilm containing the bacteria Pseudomonas aeruginosa onto the steel surface in a flow-through reactor. Biofilm inaging is accomplished using Confocal Scanning Laser Microscopy (CSLM). Calculations of the differences in the relative percentages of Fe, Cr, and Ni on the exposed and control coupons are accomplished using the Statistical Analysis System (SAS) procedures PROC MANOVA and PROC DISCRIM.
2:40 PM		AS+BI-WeA-3 In Situ Surface Enhanced Raman Spectroscopy of Biopolymer Adhesion at Metal/Liquid Interfaces J. Rahn, G. Souza, R. Georgiadis (George Washington University) The microbially-induced corrosion of copper is an important problem because of large economic losses as well as release of toxic Cu\super ++\ ions into the aqueous environment. Bio-corrosion is mediated by the formation of a biopolymer conditioning film which facilitates surface biofouling. The conditioning film consists of a variety of exopolymers (including proteins and polysaccharides) secreted by micro-organisms. One proposed pathway for bio-corrosion of copper involves adhesion of acidic polysaccharides which are present in conditioning films and which are known to bind divalent cations. However, the mechanism is poorly understood as very few spectroscopic studies have been used to follow this process.\super 1-3\ We report the first application of SERS (surface-enhanced Raman spectroscopy) to study adhesion in the initial stages of biopolymer adhesion on metal surfaces from aqueous electrolyte solutions. Initial in situ experiments focus on obtaining vibrational spectroscopic signatures for model systems such as acidic polysaccharides, monosaccharides, or corrosion inhibitors on metal surfaces. Vibrational spectra of adsorbates on bare metal surfaces will be compared to spectra taken on surfaces modified by protein adsorption and on metal surfaces which have been modifed by self assembled monolayer films. \super 1\Ishida, K.P; Griffiths, P.R. J. Colloid Interface Sci. 160, 190 (1993). \super 2\Geesey, G.G.; Iwaoka, T.; Griffiths, P.R. J. Colloid Interface Sci. 120, 370 (1987). \super 3\Geesey, G.G.; Mittelman, M.W.; Iwaoka, T.; Griffiths, P.R. Mater. Perf. 2/86, 37 (1986).
3:00 PM		AS+BI-WeA-4 Organic Diffusion into Stainless Steel Surface due to Biofilm Colonization J. Pendyala, R. Avci (Montana State University) We report the effects of biofilm colonization on the surface chemistry of stainless steel in the first 20-60 \Ao\ . A mixed culture biofilm of Pseudomonas aeruginosa, Pseudomonas fluorescens and Klebsiella pneumoniae was grown on the surface of polished 304 stainless steel for 18 days. The surface chemistry, before and after exposures, was determined by using (small spot) x-ray photoelectron spectroscopy and (imaging) time of flight secondary ion mass spectroscopy. Careful analyses of the data show that during 18 days of exposure to aqueous media alone (control experiments), the surface did not change appreciably and has the same features as that of the coupon before exposure. In contrast, the surface of the coupon exposed to the biofilm shows diffusion of organic materials involving C and N into the oxide layer of the stainless steel.
3:20 PM		AS+BI-WeA-5 Comparison of Pb and Cu Corrosion Rates in Potable Water Systems Treated with Various Phosphate Inhibitors S. Vesecky, R. Friedman, D. Silverman, E. Cortez (Monsanto Company); T. Murrell, D. Goodman (Texas A&M University) Prevention of lead and copper corrosion in potable water systems is vital for protecting the public health. In 1991, the EPA mandated the Lead and Copper rule which limits the 90th percentile first draw concentrations measured at-the-tap to 15 ppb for Pb and 1.3 ppm for Cu. Corrosion of Pb and Cu can be controlled by the addition at the water utilities of various phosphate inhibitors, namely: phosphoric acid, zinc orthophosphate or blended (poly/ortho) phosphates. The purpose of this study is to compare the effects of different inhibitors on film formation on Pb and Cu test coupons. The coupons were exposed to various phosphate treatments for controlled amounts of time in water having similar pH, alkalinity and hardness. The coupons were analyzed using low voltage SEM to obtain a qualitative view of the film morphology and to quantify the film thickness. XPS and other spectroscopic measurements were used to determine the elemental and chemical compositions, and XPS sputter depth profile analysis measured the concentration gradients of various elements at different depths into the films. Electrochemical impedance spectroscopy in conjunction with a rotating cylinder electrode was used to estimate the corrosion rates of Pb and Cu. The efficacy of the films for decreasing corrosion depended on the incorporation of various species in the surface film. XPS and corrosion rate studies were also performed on model thin films of Cu and Pb exposed to water with highly controlled conditions. These studies augmented our fundamental understanding of film formation.
3:40 PM		AS+BI-WeA-6 An XPS Study of Electrochemically-Induced Oxide Formation in the Presence of Carboxylic Acid Corrosion Inhibitors on Aluminum and Copper Surfaces J. Mowlem, I. Kroun, L. Bartley (Texaco Fuels & Lubricants Technology Department) A study of the oxidation of aluminum and copper surfaces induced by electrochemical corrosion was examined by x-ray photoelectron spectroscopy (XPS). The electrochemical experiments were conducted in ASTM D1384 corrosive water containing 100 ppm each of sulfate, chloride, and bicarbonate ions introduced as sodium salts in the presence of carboxylic acid corrosion inhibitors which affected the oxide formation significantly. The differences between the Al and Cu surfaces were correlated to the observed differences in effectiveness of corrosion protection for the two materials. In addition, the surface films formed in the presence of tolyltriazole, an effective copper corrosion inhibitor, were probed on the Cu surface. Carbon, nitrogen, and oxygen 1s lineshapes, as well as, the Al 2s and 2p and the Cu 2p lines were monitored. Identification of several surface moieties were observed.
4:00 PM		AS+BI-WeA-7 Surface Oxidation Studies of Hot Isostatically Pressed Al-Cu-Fe Quasicrystalline Powders P. Pinhero, J. Anderegg, P. Thiel (Iowa State University) From an applied science perspective, gas atomized powders are a very versatile form of quasicrystalline alloys. Plasma spraying techniques allow these powders to be sprayed onto a wide variety of substrates. The icosahedral material, Al\sub 63\Cu\sub 25\Fe\sub 12\, is chosen because of its current commercial interest. To make these powders more accessible to conventional surface probes, we employ a hot-isostatic-press which produces solid forms with well defined surfaces. These surfaces are then exposed to various oxidizing environments (vacuum and atmosphere, dry and humid) in order to mimic possible real-world environments that may be encountered by the coatings. Oxide formation is examined by x-ray photoelectron spectroscopy. We find that on the quasicrystalline samples, oxidation induces surface segregation of the aluminum and formation of a thin passivating layer of aluminum oxide. Water can increase the thickness of the oxide from ~10=C5 to ~100=C5. These results are compared with data for crystalline phases.
4:20 PM		AS+BI-WeA-8 Enhancement in Nickel Oxidation Rates by Simultaneous Sputtering with Argon Ions J. Carrazza, P. Pereira (Intevep S.A.); F. Zaera (University of California, Riverside) The effect of Ar ion bombardment on the oxidation of nickel films was studied by XPS. In the absence of any ion beams, exposure of nickel surfaces to oxygen leads to the moderately rapid formatiomonolayers thick) nickel oxide overlayer. At room temperature the oxygen uptake stops once this limit is reached, but at higher temperatures the slow growth of a thicker oxide is seen. The diffusion coefficient for oxygen through the forming NiO film was determined to be about 2x10\super -18\ cm\super 2\/s at 625 K. The simultaneous impingement of argon ions on the surface during Ni oxidation was found to accelerate the process, and beam current densities as low as 0.01 \mu\A/cm\super 2\ were found to be sufficient to induce nickel oxide growth past the 3-5 ML limit at room temperature. The oxidation rate was found to be roughly proportional to both the ion flux and the square of the oxygen pressure. The build-up of a NiO film during these Ar\super +\-ion/oxygen treatt of a higher probability for O\sub 2\ molecular desorption from the surface and a higher atomic oxygen mobility into the bulk. Also, the oxide films prepared at low temperatures display a feature in the Ni 2p XPS spectra around 853.2 eV which could be assigned to partially reduced nickel, Ni\super +x be annealed out above 400 K. Further heating above 600 K leads to the diffusion of oxygen atoms into the bulk and to the partial reduction of the surface nickel to its metallic state.
4:40 PM		AS+BI-WeA-9 A Multi-Analytical Approach to Localized Corrosion Studies using Small Area Analysis and TOF-SIMS E. Principe, P. Lindley, G. Strossman, D. Spaulding (Charles Evans and Associates) Significant improvements in several areas of XPS (X-ray Photoelectron Spectroscopy) hardware and design have resulted in increased sensitivity and improved detection limits, while greatly reducing the practical minimum analysis area. With the latest generation of XPS instrumentation spectral acquisition and chemical state mapping can be accomplished from regions with a spatial resolution of 10 microns. TOF-SIMS (Time-Of-Flight Secondary Ion Mass Spectroscopy) combines high elemental sensitivity, high mass resolution and monolayer depth resolution. TOF-SIMS is also capable of generating secondary ion images at spatial resolutions on the order of 0.2 microns. The benefits of a combined surface analytical approach involving small area XPS and TOF-SIMS are explored through studies involving localized corrosion of sputter deposited thin film alloys containing aluminum, tungsten, and nitrogen. Small area XPS can provide quantitative chemical state information within and surrounding pits on a physical scale previously unrealized. TOF-SIMS contributes molecular information with submicron spatial resolution at detection limits in the range of 1-100ppm. The composition, chemistry, and localized distribution of anions surrounding pitted regions is emphasized.