5.6.1.3 Intergranular
Corrosion
The important corrosion mechanism here is
the dissolution of the glassy/crystalline material which is
present between the grains, particularly in liquid phase sintered
materials (LPS) such as LPSSIC, LPSN, LPBN or Al2O3 with <
99.5 % Al2O3 content.
The rate of corrosion depends on the solubility product, L,
of those ions in the intermediate phase that are relevant
to corrosion.
Intergranular corrosion can be significantly reduced through
the use of suitable intermediate phases with low solubility
products, or by enlarging the grains in the microstructure,
which is associated with a reduction in the grain boundary
area.
Solid-phase sintered materials (S-Al2O3, SSIC and SSN) and
hot pressed materials (HP-Al2O3, HPSIC etc.) show almost no
susceptibility to corrosion.
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