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Breakage and cracks in polypropylene in chromic trioxide bath during photo etching

Q. I am etching on brass. After the Etching with ferric chloride [on eBay or Amazon], I pass the brass metal into chromic trioxide as a bright dip. But in the chromic trioxide bath all the plastic rollers and nozzles which are made of PP are breaking. Why? Be Detailed.

Shafiuddin A. Mohammed
metal coating shop - Dubai, United Arab Emirates
2007

A. Chromic acid is a very powerful oxidizing agent and polypropylene apparently will not stand up to it -- although you might want to double check that they actually are made of PP rather than nylon. PVC is more resistant, but not fully. Teflon will hold up, but if that is too soft for the nozzles and rollers, then you would need to use PVDF -- but it's very expensive.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

Thanks Ted.

Shafiuddin A. Mohammed
metal coating shop - Dubai, United Arab Emirates
December 3, 2008

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