52079

Is a swab with IPA and test using a general UV scan vs a blank an acceptable way to determine the part is clean.  

May 6, 2009

We have a stainless steel roller that was passivated using Sodium hydroxide, Citric acid, and Nitric acid. Washed with purified water, air dried and swabbed with IPA to test by general UV scan. The cleaning has been done four times but keeps failing. Any suggestions?

Carlos Nadal
chemist - Miami, Florida

What do you mean by "failing"? That will help people determine what the problem might be.

As for IPA, the test assumes that whatever contamination is there will be dissolved by IPA and thus show up on the scan. This isn't necessarily true. You might want to try other solvents. Also, remember that salts aren't necessarily going to be dissolved by organic solvents. That could be your problem right there. This touches on the issue of what you mean by failure.

Christian M. Restifo
- Pittsburgh, PA

After re-reading your post, I understand it to mean that you're having some type of contaminant show upon the scan.

Your process doesn't seem like a good one to remove organics. NaOH, citric, and nitric acids will not do a good job of removing oils or the like. You need a good cleaner with some surfactants to emulsify or otherwise dissolve the organics. I suggest you contact your vendor for ideas. Keep in mind that all raw metals can have rust preventatives, machining/forming oils, and general oils/dust/dirt on them.

Christian M. Restifo
- Pittsburgh, PA