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Topic Date User

The Plastic Bolt 14-May-2007 At 8:52:38 PM AlanD

Message

On 14/05/2007 nmonteith wrote:
>Doesn't plastic UV degrade instead?

Yes it does, most plastics will contain UV stabilizers that assist in preventing UV degradation, but they only work for a finite amount of time. It also suffers from oxidation.

On 14/05/2007 dougo wrote:
>i think it probably depends on the specific plastic used. you can't use
>the word "plastic" to try and cover all plastics - they each have their
>own characteristics. just like saying metal rusts - some do, and some (like
>stainless) won't rust easily at all.

Only iron alloys rust
Only metal corrodes
Most materials oxidize :)

Now the technical bit ... fall asleep if you want.
All metals will suffer some sort of corrosion / oxidation, but sometimes it requires high temperatures to achieve. Stainless is oxidizing, but it is the chromium within the alloy that preferentially oxidizes, and it's this oxidation product that forms a continious layer on the stainless steel that prevents the iron within the stainless oxidizing. If this layer breaks down faster than it forms, then the stainless will corrode, hence why stainless is pretty poor in chloride or sulfide environments, typically in forms of microcorrosion such as pitting or stress corrosion cracking.