Automotive degradation

The thermal degradation of mixtures of the common automotive plastics polypropylene, ABS, PVC, and polyurethane can produce low molecular weight chemicals (57). Composition of the blend affected reaction rates. Sequential thermolysis and gasification of commingled plastics found in other waste streams to produce a syngas containing primarily carbon monoxide and hydrogen has been reported (58). 

CSM is extensively used in constmction and electrical appHcations. This includes roofing membranes, automotive ignition boots and wire, toU compounds, and in some automotive hoses requiring good heat and oil resistance, eg, air conditioning and power steering. It is also used in nuclear power plants because of its exceUent resistance to radiation degradation. 

Wear. Eor a fixed amount of braking the amount of wear of automotive friction materials tends to remain fairly constant or increase slightly with respect to brake temperature, but once the brake rotor temperature reaches >200° C, the wear of resin-bonded materials increases exponentially with increasing temperature (26—29). This exponential wear is because of thermal degradation of organic components and other chemical changes. At low temperatures the practically constant wear rate is primarily controlled by abrasion, adhesion, and fatigue (30,31). 

As an example, when automotive catalytic mufflers and converters were introduced many years ago, the automobile industry required the petrochemical industry to eliminate lead from gasoline since lead degraded and reduced the effectiveness of the catalyst and caused the destruction of the gasoline. One set of industrial compounds that can harm catalysts are halogens, a family of compounds that include chlorine, bromine, iodine, and fluorine. Bromine, while not prevalent in industry, is present in chemical plants. Freons are fluorine compounds. Silicone is another compound that is deleterious to catalysts. It is used as a slip agent, or a lubricant, in many industrial processes. Phosphorous, heavy metals (zinc, lead), sulfur compounds, and any particulate can result in shortening the life of the catalyst. It is necessary to estimate the volume or the amount of each of those contaminants, to assess the viability of catalytic technologies for the application. 

Finally, it should be remembered that lifetime is not necessarily measured in time. For some products and some degradation mechanisms it could be the number of cycles of use, or, in automotive applications, the number of kilometres driven. 

The stability of electrocatalysts for PEMFCs is increasingly a key topic as commercial applications become nearer. The DoE has set challenging near-term durability targets for fuel cell technology (automotive 5,000 h by 2010 stationary 40,000 h by 2011) and has detailed the contribution of the (cathode) catalyst to these. In particular, for automotive systems as well as steady-state stability, activity after simulated drive cycles and start-stop transients has been considered. In practice, both these treatments have been found to lead to severe degradation of the standard state-of-the-art Pt/C catalyst, as detailed next. 

The other effect considered in this section deals with transients in a single fuel cell. The transient models examine step changes in potential and related phenomena (e.g., gas flow rates, water production, and current density). Hence, they are aimed at examining how a fuel-cell system handles different load requirements, which may occur during automotive operation or start up and shut down. They are not trying to model slow degradation processes that lead to failure or the transients associated with impedance experiments (i.e., potential or current oscillations). These types of models are discussed in section 7. 

SCI WGI Industrial, chemical and oil hoses SCI WG2 Automotive hose SCI WG3 Hydraulic hose SCI WG4 Hose test methods SC2 Physical and Degradation Tests SC2 WGI Physical properties SC2 WG2 Viscoelastic properties SC2 WG3 Degradation tests SC2 WG4 Application of statistical methods... 

M. Quintus et al., Chemical membrane degradation in automotive fuel cell -Mechanisms and mitigation, 2nd Annual International Symposium on Fuel Cell Durability Performance, Miami Beach, FL,7-8 Dec 2006... 

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