Another Citric Acid Passivation Question
We are having a problem with citric acid passivation of 303 stainless steel. The parts continue to fail a 24-hour salt spray test. Currently we passivate for 30 min. Should we double the amount of time in the citric acid? Do you have any suggestions for us?
Q: We are having a problem with citric acid passivation of 303 stainless steel. The parts continue to fail a 24-hour salt spray test. Currently we passivate for 30 min. Should we double the amount of time in the citric acid? Do you have any suggestions for us? W. S.
A: I am not sure that doubling the time in the citric acid passivation bath will solve your problem. 303 stainless steel contains more sulfur than some of the other stainless steels and this excess sulfur can lead to possible failure in the salt spray test. Pre-cleaning of your 303 stainless steel with a good alkaline cleaner should help remove the excess sulfur from the surface. After good alkaline cleaning rinse thoroughly and then proceed to the passivation step.
You did not mention in your e-mail whether you are using a “home brew” or a commercial product. My preference is to use a commercial product. They are more stable and give more consistent results. I know of at least one vendor that manufactures a complete line of citric acid based passivating materials. A bonus is that if you use a commercial product should be able to call the vendor and get some technical support.
Related Content
-
Nanotechnology Start-up Develops Gold Plating Replacement
Ag-Nano System LLC introduces a new method of electroplating based on golden silver nanoparticles aimed at replacing gold plating used in electrical circuits.
-
How to Choose Between Sulfate and Chloride-Based Trivalent Chromium
There are several factors to consider when choosing between sulfate and chloride-based baths for trivalent chromium plating. Mark Schario of Columbia Chemical discusses the differences and what platers should keep in mind when evaluating options.
-
Advantages to Pumped Eductor Agitation
Not all agitation methods are created equally. Pumped agitation with eductor nozzles can improve process tanks and quickly show a reduction in operating costs while keeping staff safe, following environmental legislation and preventing pollution.
