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Alodine outgassing

I am experiencing contamination on an optical surface when an aluminum part which has been given an Alodine coating. The sample was initially baked out at 100 °C & the "outgassing" was experienced at 70C. Is there a spec for this? Is anodizing better?

Mike Hogan
- Lexington, Massachusetts
2003

70 °C is 158 °F which is too hot for bare aluminum chromate. The MIL Spec says not to bake any coatings over 140F. The gel breaks down when the water cooks off.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2003

Mike, Alodine or Iridite or Chem Film or ? are a chemical conversion coating. They form a very thin "gel" on the surface. 24 hour later, most of the water has evaporated, but not the water of hydration. You will see this in chemical formulas as a .H20 When you dry the part above 40 to 45C, you drive off the hydration and the gel literally turns to a non-adherent powder. So, do not bake. Yes, anodize is superior to chem film in nearly every aspect, but it costs more.

James Watts
- Navarre, Florida
2003

Please check treatment temperature requirement for this surface finish. I think the max rinse temp or blow air temp is 140 deg F which is lower than 100 °C.

Dado Macapagal
- Toronto, Ont
2003

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