Electrochemical stability corrosion resistance

Titanium Carbide. Carbides of transition metals are known for their hardness, wear resistance and also for their high electrical conductivity, which makes them attractive as a refractory coating material for cutting tools or bearings. Only little work has been done on the electrochemical stability of transition metal carbides with the exception of TiC, where a corrosion and passivation mechanism was suggested by Hintermann et al. [119,120]. This mechanism was confirmed on amorphous TiC produced by metal-... 

Several recent reports describe using clay or other inorganic fillers to form CP composites. Polyani-line-polypyrrole composite coatings containing clay or yttria stabilized zirconia were electrodeposited onto AA 2024-T3 [158], with improved corrosion resistance of the substrate. Similarly, particulate-filled polyaniline and polypyrrole films on AA 2024-T3 were prepared electrochemically using a variety of fillers, including clay, carbon black, short carbon fiber, zirconia, and silica [159]. Again, enhanced corrosion performance for these composites was observed. 

Various types of carbon black have been used as the support for PEM fuel cells due to their low cost, high electronic conductivity, high corrosion resistance, and good chemical and electrochemical stabilities. Liu et al. reviewed carbon-type catalyst supports such as carbon black, nanostructured carbon, and mesoporous carbon for direct methanol fuel cells [3], The discussion is applicable to PEM fuel cells as well. 

Conductive sp -bonded diamond is being developed as an advanced catalyst support material. Boron-doped diamond thin-film electrodes possess excellent properties for this application, such as electrical conductivity, chemical inertness, extreme corrosion resistance, and dimensional stability. Compared with more commonly used sp -bonded carbon materials, diamond is highly resistant to electrochemical corrosion. For exam-... 

Electrochemical stability of the current collectors remains a significant technical challenge that must be considered throughout all aspects of research and development efforts. For example, over prolonged periods of operation, material corrosion may result in increased resistance, active material detachment, and inevitable significant performance loss. To address this... 

The support for the metal nano-particles turns out to be as important as the nano-particles for providing their dispersion and stability. Studies on electron transfer are particularly important for carbon-based materials because those materials, such as glassy carbon, graphite, fullerene, and diamond with different electronic and structural properties, have been proved to possess distinctly different electrochemical properties from each other (Ramesh and Sampath, 2003). Carbon supports provide high electronic conductivity, uniform catalyst dispersion, corrosion resistance, and sufficient access of gas reactants to the catalyst (Ismagilov et al, 2005). In addition to electrical conductivity and surface area, hydrophobicity, morphology, porosity, and... 

Because these alloys have been commercially developed, the full compositional, heat treatment and corrosion testing details are not available. It is difficult to identify the particular effects of R additions on the corrosion resistance of these alloys from the data shown, because of the absence of a systematic variation in the particular R addition or concentration. There is however, sufficient evidence in table 5 to suggest that R additions play a role in improving the corrosion resistance of Mg casting alloys, but it is difficult to draw conclusions regarding the nature of that role. As with other alloys, the corrosion resistance of Mg alloys is generally associated with the stability, solubility and defect structure of the naturally occurring oxide film, and the tendency for the various phases in the microstructure to act as local anodes and cathodes. Unfortunately there is no evidence in the literature to indicate whether or not R additions modify the properties of the surface oxide film on the cast Mg alloys or alter the electrochemical balance of the microstructure. 

In an aqueous solution, Mg(OH)2 is more difficult to dissolve than MgO, but it is still theoretically unstable in an acidic, neutral or weak alkaline aqueous solution according to the fi-pH diagram. Even if there is such a film on Mg, it cannot be thick or compact and, thus, offers only a limited level of protection for Mg. For the case of an Al substrate, its surface film consists of AI2O3, A1(0H)3 or a combination thereof which is electrochemically stable from weak acidic to weak alkaline. As a result, it can exist as a stable form on an Al surface and offer good corrosion protection for Al in many aqueous solutions. Therefore, the different thermodynamic stabilities of the surface films on Mg and Al in a natural aqueous solution should be the main reason for their different corrosion resistances. 

Many different metallic materials have been proposed and discussed in the scientific and patent literature. Because of their low density, typical lightweight metals such as aluminum and titanium are often used to manufacture metallic bipolar plates (Mepsted and Moore 2003). But owing to difficulties in stamping thin aluminum and titanium foils, most of the known designs use chemically etched plates. In addition, these metals and most of their alloys exhibit only poor stability in acidic conditions, as well as a strong tendency to form very thick and nonconductive oxide layers. Thus, the use of aluminum or titanium in PEFCs requires electrochemically dense and corrosion-resistant coatings. 

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