The anodic corrosion of gold has been studied in concentrated chloride solutions as a function of chloride concentration and pH. Results are discussed in terms of five potential regions: active, prepassive, active‐to‐passive transition, passive, and transpassive. The existence of HAuCl2 with a dissociation constant of the order of 1 to 10 and a mechanism for the active dissolution of gold are postulated. The relation between the breakdown of the passivating film in the transpassive region and the gold dissolution and chlorine evolution reactions is discussed.

We have built a particle analyzer capable of real-time detection and characterization of individual particles. Particle analysis is accomplished by pulsed laser ablation of a particle followed by time-of-fiight mass spectrometry of the resulting atomic and molecular ions. The detected ions are characteristic of a particle's

The corrosion mechanism of copper at 373 and 300 K in the presence of submieron (NH~)2SO4 particle deposits has been investigated. Several in situ techniques have been used to monitor the corrosion process in real time. At and above the critical relative humidity of (NH4)2SO4, dissolution of Cu is followed by formation of Cu20, oxidation of Cu(I) ions to Cu (II) ions, and precipitation of antlerite [Cu3(SO4)(OH)4], broehantite [Cu4(SO4)(OH)6], or posnjakite [Cu4(SQ)(OH)~ -HzO]. The amount of corrosion product formed increases with amount of (NH4)2SQ particles, relative humidity (RH), and temperature. The in situ techniques allowed us to confirm and refine the individual steps in the multistep mechanism proposed in earlier work. ~ ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 155.69.4.4 Downloaded on 2015-06-18 to IP

The effect of submicron-sized (NH4)2SQ particles on the corrosion of copper has been investigated in air-H20 mixtures at 373 K and relative humidities (RH) of 65, 75, and 88%. At 65% RH, (NH~)2SO4 particles do not affect the oxidation of copper. At 75 % RH, the "critical relative humidity" of (NH4)2SO4, localized formation of Cu20 and a basic copper sulfate, brochantite [Cu4(SO4)(OH)6] or antlerite [Cu~(SO~)(OH)4], isobserved, depending on the amount of particles deposited. At 88% RH, sufficient water is absorbed by the particles to form a solution that spreads over a large surface area. A continuous thick layer of Cu20 forms rapidly and becomes overgrown by antlerite crystals. Beneath the oxide scale, the copper substrate is locally corroded. The present work clearly demonstrates that ammonium sulfate particles, which are a major constituent of urban atmospheric dust, are an important factor in the formation of patina on copper.

The corrosion of sputter-deposited aluminum and A1-0.5 weight percent Cu alloy thin film metallizations and of highpurity aluminum foil has been investigated in dilute aqueous HF solutions. Using ac and dc electrochemical techniques and optical and electron analytical techniques, the solution and metallurgical conditions that lead to localized breakdown of the passivating film and subsequent micropitting of aluminum and the alloy have been established. Micropitting occurs at potentials as negative as the open-circuit potential, which for aluminum is 1.2V negative of the oxide breakdown potential, i.e., the pitting potential. Al2Cu precipitates in the alloy depolarize the cathodic reaction causing an increase in pit density and in the rate of pit growth.

Characterization of materials in situ offers a new window of opportunity for several areas of science, including electrochemistry, biology, chemistry, physics, and medicine. At the present time, few research groups are working toward building more versatile microscopes that extend modern microscopy to studies in situ in liquids. Smyrl's group, for example, demonstrated that by using a modified near-field scanning optical microscope (NSOM), with a home-built tuning fork, it is possible to obtain in situ topography in liquids together with functional imaging (FI) on some model systems. 1 William's group 2 modified an atomic force microscope (AFM) to study the onset of pits on austenitic stainless steels, by using it as a scanning electrochemical microscope (SECM). They also modified a confocal microscope to obtain a photoelectrochemical microscopy (PEM) and reported images with resolution of the order of 0.5 m. 3 Smyrl's group has also used PEM to study precursor sites for pitting in polycrystalline Ti with a resolution in the order of 100 nm. 4 In the present work, we show that by using a modified near-field scanning optical microscope (NSOM), with a home-built tuning fork, one can obtain high resolution optical images concurrently with the topography of different systems while the substrate (sample) and the probe are immersed in the liquid. This technique has been used to show, for the first time, metastable pitting experiments in a 25% Cr duplex stainless steel (DSS) UNS S32550.It is well established that MnS inclusions are the main cause of pitting in commercial stainless steels. 2,3,5,6 However, in highly alloyed steels (as in the case of duplex stainless steels), the cause for pitting is a more complex phenomenon, mainly because of the presence of different precursors (not only MnS inclusions) and because of the development of metastable pits preceding stable pitting. 7 In the present work we briefly describe the method for obtaining concurrent topography and optical imaging by using an optical fiber with an apex smaller than 100 nm. The optical image is obtained by using a three-way connector that allows the focusing of a laser light through the fiber to illuminate the sample, and at the same time, that allows the collection of the reflected light. After finding, analyzing, and isolating the particles in some areas of a DSS sample, prior to the corrosion tests, they were imaged in situ in both 3.5% NaCl and 1 M HCl solutions. Then, the metastable pitting process was initiated with further imaging of the selected areas. ExperimentalTip preparation.-All NSOM probes were prepared from type F-AS optical fiber (3.7 m in core diameter with 125 Ϯ 2 m of cladding and 245 Ϯ 15 m of polymer coating), which were obtained from Newport Corporation. The optical fibers were pulled with a commercial pulling machine (from Sutter). After pulling the fibers they were observed under a 63 times magnification microscope to check the shape of the fiber before it could be mounted in the fork. The apex of the fibers were 100 nm or l...

Amorphous Tb-Fe thin films prepared by dual magnetron cosputtering were exposed to air at 200 °C in order to investigate the evolution of the films as they oxidize. Magnetic properties of the films were measured using a vibrating-sample magnetometer and torque magnetometer and are interpreted in light of the structure of the films as revealed by Auger electron spectroscopy and composition-depth profiling. This leads to a detailed and self-consistent description of the oxidation process. At first a uniform and homogeneous oxidation layer grows from the surface toward the substrate. This layer has a high magnetization and low intrinsic anisotropy and consists of an intimate mixture of oxidized Tb and metallic TbxFe(1−x). The initially high intrinsic anisotropy of the unoxidized region decreases relatively quickly, while the composition changes only slowly as this region shrinks. When the oxidation layer reaches the substrate, two oxide phases (Fe2O3 and Tb2O3) begin to grow at the surface exposed to air.

This feature discusses measuring the levels of equipment damage caused by airborne substances and determining the effect of ionic particles on the corrosion mechanism.