Galvanic corrosion mechanism

There are different forms of corrosion. General (uniform) and galvanic corrosion mechanisms were mainly considered in this chapter. Other kinds of corrosion such as pitting, stress cracking, and hydrogen induced cracking are not covered in this introductory book but can be learned from a number of excellent books such as [1]. 

The basic mechanisms involved in graphitic corrosion are familiar and easily understood. Hence, remedial and preventive measures are relatively simple to implement. Although commonly categorized as a form of dealloying, graphitic corrosion has much in common with galvanic corrosion. 

Corrosion may be uniform or be intensely localized, characterized by pitting. The mechanisms can be direct oxidation, e.g. when a metal is heated in an oxidizing environment, or electrochemical. Galvanic corrosion may evolve sufficient hydrogen to cause a hazard, due to ... 

The basic objective of the conversion coating process is to provide a corrosion-resistant film that is integrally bonded chemically and physically to the base metal and that provides a smooth and chemically inert surface for subsequent application of a variety of paint films. The conversion coating processes effectively render the surface of the basis material electrically neutral and immune to galvanic corrosion. Conversion coating on basis material coils does not involve the use of applied electric current to coat the basis material. The coating mechanisms are chemical reactions that occur between solution and basis material.1-4... 

Gallium tribromide, 72 356 Gallium trichloride, 72 356 Gallium trihalides, 72 356, 357-358 Gallium triiodide, 72 356 Gallopamil, 5 121-122 molecular formula and structure, 5 119t Galvanic corrosion, 7 804-806 as failure mechanism, 26 983 in industrial water treatment,... 

In this study, the investigations were concentrated on the polishing of the Ai alloys and the adhesion/barrier metal (Ti) in the slurries containing A1,03 abrasive, phosphoric acid, citric acid and hydrogen peroxide. The electrochemical analyses, including the potentiodynamic polarization and galvanic corrosion measurements, have been used to elucidate the electrochemical mechanism of the removal selectivity in Al CMP. 

The first chapter constitutes an introduction to corrosion and various forms of corrosion such as general or uniform or quasi-uniform corrosion, galvanic corrosion, stray current corrosion, localized corrosion, such as pitting and crevice corrosion, metallurgically influenced and microbiologically influenced corrosion, mechanically assisted corrosion and environmentally induced cracking. 

The unstable behavior of some solder-replacement adhesives has been attributed to galvanic corrosion. Similar to most corrosion mechanisms, condensed or absorbed moisture on the surface and dissimilar metals are required to form a galvanic cell. The silver filler acts as a cathode while the substrate metallization acts as an anode and is oxidized. In the case of tin-lead solder surfaces, the solder, which has a lower electrochemical potential (0.13 V) than silver (0.79 V), becomes the anode at which corrosion and oxidation occur. A smaller potential difference between a copper surface and silver accounts for some improvement in contact resistance over the solder-silver couple. 

Carbon itself has been successfully used as a biomaterial. Carbon based fibers used in composites are known to be inert in aqueous (even seawater) environments, however they do not have a track record in the biomaterials setting. In vitro studies by Kovacs [1993] disclose substantial electrochemical activity of carbon fiber composites in an aqueous environment. If such composites are placed near a metaUic implant, galvanic corrosion is a possibility. Composite materials with a polymer matrix absorb water when placed in a hydrated environment such as the body. Moisture acts as a plasticizer of the matrix and shifts the glass transition temperature towards lower values [Delasi and Whiteside, 1978], hence a reduction in stiffness and an increase in mechanical damping. Water immersion of a graphite epoxy... 

A new method was developed using a modified polishing device for measuring galvanic corrosion during chemical mechanical planarization (CMP) of copper and tantalum [22]. CMP is used to pofish on a microscopic scale. In most cases, this is done using a colloidal slurry of abrasive microscopic particles. 

The LSP mechanism proposes that SCC results from the effect of the structure ahead of the crack tip [61]. This mechanism assumes that a galvanic corrosion between active sites (weakened passive site) and surroimding passive surfaces produces large anodic currents at the rupture site. Repassivation of the active sites is prevented by the presence of weakened passive films on the surface. It has been su ested that the weakened passive film... 

---