High temperature corrosion
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"Hot corrosion" is a mechnism of "high temperature corrosion", others include high temperature oxidation, sulfidation and carbonization.
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[edit] Hot corrosion by sulfates
Two types of sulfate-induced hot corrosion are generally distinguished : Type I takes place above the melting point of sodium sulfate and Type II occurs below the melting point of sodium sulfate but in the presence of small amounts of SO3.
In Type I the protective oxide scale is dissolved by the molten salt. Sulfur is released from the salt and diffuses into the metal substrate forming discrete grey/blue colored aluminum or chromium sulfides so that, after the salt layer has been removed, the steel cannot rebuilt a new protective oxide layer.
The same kind of attack has been observed for potassium and magnesium sulfate.
[edit] Hot corrosion by vanadium
Most fuels contain small traces of vanadium. The vanadium is oxidized to different vanadates. Molten vanadates present as deposits on metal can flux oxide scales. Furthermore, the presence of vanadium accelerates the diffusion of oxygen through the fused salt layer to the metal substrate. The presence of sodium in a ratio of 1:3 gives the lowest melting point and most be avoided. This melting point of 535 degrees can cause problems on the hot spots of the engine like piston crowns, valve seats, and turbochargers.
[edit] Hot corrosion by lead
Lead can form a low melting slag capable of fluxing protective oxide scales.
[edit] See also
- [1] - High temperature oxidation
[edit] External links
- [2] - Definition
- [3] - Hot corrosion phenomena
- [4] - Hot corrosion of materials (pdf)
- [5] - Hot corrosion information
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