Joe H. Payer

An X-ray photo-electron spectroscopic investigation of the air-formed film on copper

Abstract The composition and the structure of the film formed on copper by exposure to ambient air for 24 h were investigated by X-ray photo-electron spectroscopy (XPS). This characterization of the native oxide on copper provides a basis for subsequent exposures in mixed flowing gas systems. Using angle-resolved XPS, it was observed that only the univalent, diamagnetic Cu + species was present in the film. The film was modelled as a two-layer structure with an inner layer of Cu 2 O and an outer layer comprising adventitious hydrocarbon and bound hydroxyl and water, with determined thicknesses of approximately 1.6 and 0.8 nm, respectively.

Effects of microstructure on the corrosion behavior of CoCr porous coatings on orthopedic implants

Cobalt-chromium alloy porous coatings have become increasingly popular as a means of achieving a stable, longer lasting fixation on orthopedic implants. However, sintering heat treatments cause changes in the microstructure that result in changes in the corrosion behavior of the porous coatings. Experiments were conducted to examine the effects of microstructure on the corrosion of CoCr porous coatings. Four distinct microstructures were characterized. Light microscopy revealed microstructures A and B had relatively fewer carbides and a large-grain structure, microstructures C and D displayed a finer grain size with significant carbide formation, predominantly within grains and fusion zones. Accelerated anodic corrosion experiments were conducted to study the localized attack of each microstructure. Experiments were conducted using metallographically polished porous-coated disks for durations of 1, 4, 16, 24, and 72 h. The disks were examined with SEM and EDS to observe preferential attack and element depletion. Results showed a progressive dissolution of the matrix, with preferential attack of the grain boundaries and regions adjacent to the carbides due to sensitization. A precipitation layer was found to be Cr-rich and possibly composed of chromium hydroxide or a chromium orthophosphate. In addition, the solution became yellow in color with longer exposure times, possibly due to the presence of chromate ions, as indicated by an increased chromium level detected by AAS.

Determination of the oxygen reduction products on ASTM A516 steel during cathodic protection

The electrochemistry of steel in aerobic and anaerobic aqueous alkaline solutions was studied with or without forced convection to investigate the cathodic processes occurring on steel exposed by defects in polymer coated steel pipe. The results are relevant to the mechanistic understanding of the effect of cathodic protection on the disbonding of fusion bonded epoxy (FBE) coatings on steel. Moderate (pH9.8) and strongly (pH14) alkaline aqueous solutions were used to simulate the water layers at the cathodically polarized steel surface on the soil-side of buried pipe. A rotating gold ring and steel disc electrode (RRDE) in alkaline aqueous electrolyte equilibrated with 1atm oxygen over solution was used to measure the rotation rate dependent current for the electroreduction of oxygen, O2, on an ASTM A516 steel disc and the resulting peroxide generation, which was determined by monitoring the oxidation current on the gold ring. An appreciable fraction of the oxygen reduction current on the steel disk gave rise to peroxide generation over a wide range of potentials, from −0.2 to −0.9V vs SCE in 1M KOH. The observation of peroxide generation is noteworthy, because oxidizing agents, such as peroxide and its decomposition products, superoxide and hydroxy radical, can degrade the polymers used for coating pipelines. As result, oxidative degradation of polymer or interfacial compounds may be a cause of the accelerated disbonding observed for protective coatings on steel pipelines under cathodic protection.

Devitrification of Fe-Based Amorphous Metal SAM 1651 and the Effect of Heat-Treatment on Corrosion Behavior

Devitrification of amorphous alloys is a process in which thermodynamically preferable crystalline phases form from the metastable amorphous phase. The corrosion behavior of the crystalline phases and the remaining amorphous material is likely to be different from that of the fully amorphous material and could have detrimental effects on the corrosion resistance of the devitrified material. The effect of heat-treatment on the corrosion behavior of an Fe-based bulk metallic glass Fe 48 Cr 15 Mo 14 C 15 B 6 Y 2 [structural amorphous metal (SAM) 1651] was examined, which revealed a degradation in the corrosion resistance of SAM 1651 upon annealing at 700°C. However, the partially devitrified material still exhibited good corrosion resistance even in the highly aggressive environments of 6 M HCl. The preferential corrosion sites of nanoscale in both fully amorphous and partially devitrified materials were identified with transmission electron microscope analysis. The corrosion resistance of both fully amorphous and partially devitrified materials was explained in terms of chemical and structural characteristics of the alloys.

Characterization of the Corrosion Products of Crevice Corroded Alloy 22

The crevice corrosion performance of Alloy 22 was tested under potentiostatic polarization more positive than the repassivation potential in 4 M NaCl solution at 100°C. Under this aggressive condition, crevice corrosion initiated under the crevice contacts and four stages of corrosion behavior were observed: initiation, propagation, stifling (corrosion slowed), and arrest (corrosion stopped). During the exposure, dark green deposits were found on the uncorroded metal surface around the crevice contacts, light green precipitations were found in the test solution, and the solution color changed from clear to light green. After exposure, loose black corrosion products were found under the crevice contacts. Surface analyses at the sites of varying corrosion penetrations showed similar composition depth profiles, and the results indicated that a 3-5 nm thick, chromium-rich oxide film was formed on the alloy surface. The composition depth profiles indicated that the crevice corrosion occurred by a uniform, nonselective dissolution. Surface analysis results showed that the corrosion products in the crevice were rich in O, enriched with Mo and W, and depleted of Ni and Cr relative to the bulk alloy. A solution analysis showed that Ni was the main element dissolved into the solution during the exposure.

Effects of Ca and H2O2 added to RPMI on the fretting corrosion of Ti6Al4V

Titanium and its alloys have demonstrated considerable success in various surgical procedures including orthopedic, dental, and cardiovascular surgery. However, particulate debris from corrosion and wear is present in a considerable quantity in tissue local to the implant. This study evaluated the effect of Ca, since it is present in both serum and bone, and H2O2, since it is produced through local inflammation, on the amount of titanium release. Four sets of Ti6Al4V plates and Ti6Al4V screws were used. Each set was designated to one of four solutions: RPMI (cell culture growth media), RPMI with CaCl2, RPMI with CaCO3, and RPMI with H2O2. A fretter was used to cause corrosion by creating micromotion between two screws and a two-hole plate of Ti6Al4V. After fretting for 72 h, weight loss of the plate and screws and the amount of Ti and vanadium (V) in solution was used to assess the amount of fretting corrosion which had occurred. Results of weight loss and Ti in solution indicated that the presence of H2O2 increased the amount of particulate debris produced in RPMI as compared with RPMI alone. The addition of CaCl2 to RPMI also increased both weight loss and Ti in solution compared with RPMI alone. The addition of CaCO2, however, did not give values significantly different from RPMI alone. Comparison of weight loss and Ti in solution indicated that the increase in fretting corrosion was not different between RPMI with CaCl2 and RPMI with H2O2. The particulate wear debris from the four solutions was black in color and the size of the particulate produced was compared using a Coulter Multisizer. The results indicated that particles produced in the four solutions were not different, with mean values between 1.324 and 1.100 microns, and they were similar in size to the particulate found in tissues surrounding failed total hip replacements. In order to better understand the role of Ca in the fretting corrosion of Ti6Al4V, energy dispersive x-ray analysis (EDXA) using SEM was used to determine elemental composition of one countersink surface of a plate which had been run four times in RPMI with CaCl2. The presence of Ca in the bulk was not significant (% composition < 0.5%). However, Ca was present in two surface particles which were examined at a magnification of 55,000, with a Ca% composition of 63.2% and 19.2%. While results from this study indicate that both soluble Ca(CaCl2) and H2O2 increase the fretting corrosion of Ti6Al4V, the insoluble form of Ca, which would be found in bone and hydroxyapatite, has no effect. These data indicate that it is important to specify the media used in corrosion, dissolution, and elution experiments.

Galvanic Corrosion during Processing of Polysilicon Microelectromechanical Systems The Effect of Au Metallization

Immersion in aqueous hydrofluoric acid (HF), a standard processing step in fabricating microelectromechanical systems devices, causes rougher and weaker polycrystalline silicon (polysilicon) films in the presence of Au metallization and leads to relatively thick surface oxides. The origin of these effects is the galvanic corrosion that takes place due to the difference in electrochemical potential between the noble Au metallization and the polysilicon in HF solution, resulting in the accelerated formation of a porous surface layer due to corrosion of the silicon. The electrochemical behavior and the evolving microstructural morphology are correlated. In HF solution, Si is dissolved and porous silicon (PS) is formed. The PS first develops along the polysilicon grain boundaries and then extends into the grain interiors. After rinsing in water and exposure to air, the pore walls form the usual oxide, leading to a Si/SiO 2 composite with a gradient in composition-from a high fraction of SiO 2 near the surface to 100% Si deeper into the polysilicon. Inasmuch as the galvanic corrosion requires positively charged holes, these effects can be minimized by using n-type dopants in the polysilicon and performing the HF immersion in the absence of illumination.

Composition of Copper Tarnish Products Formed in Moist Air with Trace Levels of Pollutant Gas: Hydrogen Sulfide and Sulfur Dioxide/Hydrogen Sulfide

The objective of the work reported here was to characterize the tarnish products formed on copper during the early stages of exposure to moist air with trace levels of pollutant gas, in particular hydrogen sulfide and sulfur dioxide/hydrogen sul ide. As determined by x-ray photoelectron spectroscopy and coulometric reduction (chronopotentiometry), the exposure of copper to 50 ppb hydrogen sulfide at 23°C and 70% relative humidity was found to produce a tarnish layer consisting of Cu 2 O and Cu 2 S. Addition of 75 ppb sulfur dioxide to a 50 ppb hydrogen sulfide, moist air environment at 23°C and 70% relative humidity encouraged the growth of a thicker tarnish product layer, with proportionally more Cu 2 O in the Cu 2 O/Cu 2 S structure.

Metal Oxide/Metal pH Sensor: Effect of Anions on pH Measurements

Abstract The electrochemical growth of iridium oxide on iridium (IrOx/ Ir) electrodes for use as pH sensors was examined. Usefulness of the electrodes was evaluated in a variety of solutions with a...

Chapter 1 – Cost of corrosion in the United States

Publisher Summary This chapter develops an estimate of the total economic impact of metallic corrosion in the United States and identifies national strategies to minimize the impact of corrosion. Corrosion costs result from (1) equipment and structure replacement, (2) loss of product, (3) maintenance and repair, (4) the need for excess capacity and redundant equipment, (5) corrosion control, (6) designated technical support, (7) design, (8) insurance, and (9) parts and equipment inventories. It was determined that the total direct cost of corrosion in the United States is approximately