Elastomers can swell and/or degrade in chemical
seal environments through reactions with the polymer backbone and cross-link
system, or by reactions with the filler system. In the semiconductor industry,
this degradation can be seen in increased contamination and reduced seal life.
Polymer Backbone and Cross-link:
Nucleophilic Attack-main mechanism for
cross-linking. However, when it occurs in chemical media, it may lead to
excessive cross-linking and embrittlement.
Dehydrofluorination-attack resulting in the
formation of unsaturated bonds on the fluorocarbon backbone. It can be caused
by the attack of primary and secondary aliphatic amines.
Oxidation—degradation of carbon black fillers
Chemical Attack—i.e., HF acid attack of silica
Residual Gas Contamination
Special Chemical Environments:
Vacuum—volatile condensable material
(VCM) 125°C 10-6 Torr JPL
ISO 1817 (Liquids)
ASTM D471, D1460, D3137 (Liquids)
The most common measure of chemical compatibility
for a chemical seal is volume swell. The following formula is used in reporting
volume swell measurements. This takes into account dimensional changes in all
three dimensions, and is more relevant than specific dimensional change readings
for a chemical seal.
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