Please enable JavaScript.
Coggle requires JavaScript to display documents.
ATMOSPHERIC AND HIGH TEMPERATURE CORROSION - Coggle Diagram
ATMOSPHERIC AND HIGH TEMPERATURE CORROSION
Atmospheric Corrosion
Important Variable
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 the critical humidity to form electrolyte (+)
Atmospheric parameters affecting corrosion
Temperature
Humidity
Wind speed
Smart Coatings
Paint systems with color-changing compounds, responding to pH changes that result from corrosion processes
Release of color dyes, on coating damage, from incorporated dye-filled micro-capsules
Piezo-electric thin film applications
Changes of coating compounds from non-fluorescent to fluorescent states, upon oxidation or complexing with metal cations
Fiber optics
High Temperature Corrosion
A form of corrosion that does not require the presence of a liquid electrolyte
Sulfidation implies sulfides
Sulfidation/oxidation implies sulfides plus oxides
Oxidation implies oxides
Carburization implies carbides
The increase of the carbon content of (the surface of) a steel due to interactions with the environment at elevated temperatures
Prevention
Minor alloying elements can exert an influence on the susceptibility to carburization of various alloys
Preoxidation and the subsequent formation of an oxide film will increase the resistance against decarburization
Austenitic steels carburize more readily than ferritic steels because of the high solubility of carbon in austenite
Nitridation
Beneficial Effect of Nitriding
Improve fatigue life
Improve corrosion resistance (except for stainless steels)
Increase wear resistance
Obtain a surface that is resistant to the softening effect of heat at temperatures up to the nitriding temperature
Obtain high surface hardness
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
