Passivation.
Passivation.
(OP)
Group:
What is the advantage of passivation; are there any cheaper alternatives? Will using corrosion resistant SS help?
Thank in advance for all your help.
Regards,
-mechantaeus
What is the advantage of passivation; are there any cheaper alternatives? Will using corrosion resistant SS help?
Thank in advance for all your help.
Regards,
-mechantaeus
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Work Hard and Work Smart.





RE: Passivation.
RE: Passivation.
We use it to mean making the surface of a part selectively non-reactive.
We prepare ceramics for brazing though an aqueous plating process. The goal is to make a surface that will bond readily and well with standard braze alloys. However we may prepare parts here and ship them elsewhere.
Brazing is both a physical and a chemical joining so you have a surface ready to react chemically. If that surface reacts with oxygen you can get an oxide layer that will hinder a good bond between the braze alloy and the ceramic underlying the oxide layer. It is like painting over rust. It will look good but will not hold well.
To prevent this we do a final, quick dip that will passivate the surface and make it less reactive or selectively non-reactive.
Often passivation is to protect a finish and prevent discoloration.
One way to passivate is to do a final rinse in deionized water. In our experience this can help prevent discoloration of final parts.
I suppose the final rise could also be considered passivation.
Tom
RE: Passivation.
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RE: Passivation.
RE: Passivation.
The only problem with the first meaning is that it leads some people to believe that the acid wash process creates the passive film rather than simply removing contamination which hinders its formation; a small but important distinction.
Incidentally, a acid wash can also pickle. This process is the removal by dissolution of surface layers of the alloy. After oxidation the surface can have lower levels of chromium than the bulk composition and if this layer isn't removed then the lower chromium surface produces a passive film which is "weaker" (actually thicker, but less effective in preventing corrosion). Some passivation is done with strong enough acid than some pickling occurs, which is why some people think passivation creates the corrosion resistance. After welding when scale forms and is removed abrasively, pickling must be done to remove the chromium-depleted surface. At the same time oxide particles are also removed, so two important things are done in one process. As if this isn't confusing enough, the weld's corrosion resistance is still inferior because there can remain some microscopic chromium-depleted regions around manganese sulfide inclusions in the weld zone. Electropolishing or chemical polishing can remove these pit-initiating zones and restore full corrosion resistance.
Too much information?
RE: Passivation.
-mechantaeus
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Work Hard and Work Smart.