Coating systems high-temperature resistant

A commercial application has been reported by Volkswagen for some EU6 vehicle applications of their new 1.6 and 2.0 1 TDI engines [72]. The system comprises a close coupled DOC followed in short distance by an SCR catalyst coated DPF. In addition, a slip catalyst with combined SCR and oxidation functionality is installed downstream of the DPF. The urea injection is located in-between the DOC and DPF components and a static mixer is used to improve distribution and evaporation within the limited space. Due to the high temperatures that can occur in this very close coupled position, a water-cooled urea injector was selected and the supply lines for the aqueous urea solution are made of highly temperature resistant materials. 

It is apvparent from the brief review and case study that oxide systems could be quite helpful to reduce or slow down the corrosion phenomenon of metallic systems. However, it could be dependent on the oxide system employed. Importantly the stability of oxide phases is very vital as it could undergo several changes during the operation depending on the temperatures of application environment. Dispersion of Si02 showed marked enhancement in the oxidation and corrosion resistance of the hybrid coatings at high temperatures. 

Other test media and techniques include post-emulsification penetrants, penetrants that form gels resistant to easy removal from entrapments, penetrants that concentrate dye constituents as their carrier Hquids evaporate during test processing, and penetrants that form strippable coatings in the developers. StiU other penetrant systems are formulated for use at abnormally low or high temperatures for special test appHcations. 

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