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Atmospheric and High Temperature Corrosion - Coggle Diagram
Atmospheric and High Temperature Corrosion
Atmospheric Corrosion
Important variables
Time of wetness
relative humidity, hygroscopic nature of the corrosion products
contaminants
SOx, atmospheric salinity (NaCl), NOx
Temperature
high temperature increase electrochemical corrosion rates
increase electrolyte evaporation
increase critical humidity to form electrolyte
Parameters affecting corrosion
humidity
temperature
wind speed
Smart Coatings
fiber optics
piezo-electric thin film application
release of color dyes, on coating damage, from incorporated dye-filled micro-capsules
Changes of coating compounds from non-fluorescent to fluorescent states, upon oxidation or complexing with metal cations.
Paint systems with color-changing compounds, responding to pH changes that result from corrosion processes.
High Temperature Corrosion
dominant corrosion products
Nitridation
Beneficial Effect
obtain high surface hardness
increase wear resistance
improve fatigue life
improve corrosion resistance (except for stainless steels)
obtain a surface that is resistant to the softening effect of heat at temperatures up to the nitriding temperature
carburization implies carbides
sulfidization/oxidation implies sulfides plus oxides
sulfidation implies sulfides
oxidation implies oxides
Oxide Properties
film should have good adherence, to prevent flaking and spalling
melting point of the oxide should be high
oxide should have low vapor pressure to resist evaporation
oxide film and metal should have close to the same thermal expansion coefficients
film should have high temperature plasticity to accommodate differences in specific volumes of oxide and parent metal and differences in thermal expansion
film should have low electrical conductivity and low diffusion coefficients for metal ions and oxygen