We use Ferric Chloride in a spray etching application to etch 304 Stainless Steel. We are having problems and cannot determine what they are. We do not have a scientific background and are just looking for a few simple answers. When the bath is new it seems to work beautifully. Then at some point we start to get peculiar undesirable results.
We use 45 Baume Ferric Chloride and etch at 45°. The Ferric is less than 3% hyrdro-chloric acid when received.
The following website I put up clearly demonstrates the problems with photos.1.) What is actually happening in these pictures? Is part of the steel decomposing faster than other parts?
2.) What measuring equipment should we be using to monitor the Ferric Chloride? We have been measuring it's Baume with a hydrometer but should we also be measuring the pH or anything else? If so, what type of instruments and what are the ranges that they need to be?3.) I've heard of regeneration. Is regeneration of the Ferric Chloride safe to do with HCL (Muriatic)? By safe I mean are there any harmful / flammable fumes generated? Do I need to make sure that the HCL stays at 3%? And how much tolerance is there with it?
I feel like I'm on the right track here but need some good advice or confirmation.