5.6.2.2 Corrosion
From Melts
The corrosion Mechanisms of ceramics exposed
to inorganic, non-metallic melts (such as molten salts, oxides,
slags or glasses) are different from those arising with molten
metals.
5.6.2.2.1 Non-metallic melts
The extent of the reaction between inorganic melts and ceramics
depends on a large number of factors. The most important of
these are:
- the viscosity of the melt,
- the acidity or basicity of the melt,
- the chemical composition and solubility of the reaction
products,
- the chemical composition of the principal and secondary
phases in the ceramic, and
- how easily the ceramic is wetted by the melt.
If it is necessary for ceramic materials to withstand melts,
in practice it is almost always necessary to rely on tests.
5.6.2.2.2 Molten metals
In contrast to the oxide ceramics, non-oxide materials
are more resistant to corrosion by metallic melts. Silicon
nitride is not wetted by most melts, but is not resistant
to molten copper in oxidising atmospheres. Due to its low
wettability, boron nitride is very resistant to most molten
metals.
Aluminium titanate (ATI) displays high resistance,
in particular to molten non-ferrous metals, again because
it is not easily wetted.
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