Curated with aloha by
Ted Mooney, P.E. RET
The authoritative public forum
for Metal Finishing 1989-2025
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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
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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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