Pickle Stainless steel without HF
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Q. I am currently trying various chemical concoctions for pickling of stainless steel. All the solutions I've tried so far have had to contain HF.
Now I have managed to reduce the concentration of HF in my solution make up to just roughly 2% (solution is around 20% Nitric and 2% HF. However I would like to reduce this even further or even eliminate HF from my make up if at all possible.
Does anybody out there have a solution that can pickle stainless steel that is HF free or is less than 2% HF concentration. Any suggestions?Patrick Guckian
- Rep. of Ireland
A. Have you tried sulphuric anodic pickling as per Canning Handbook?
surface treatment shop - Stroud, Glos, England
A. Try using ammonium bifluoride as a replacement for the HF. We discontinued using HF several years ago and have switched to ammonium bifluoride for several processes including stainless steel pickling. It has some disadvantages over HF, but it is much safer to deal with. Start with a pickle that is in the range of 30-40% Nitric and 15 g/L of ammonium bifluoride. You will need to make additions of ammonium bifluoride as needed to control the etch rate.
A. Ammonium bifluoride mixed with diluted nitric acid will give you HF in the solution.Lesley Wendelrup
finishing chemicals - Sweden
for HF acid burns
[link is to Amazon]
A. Hi. Jon & Lesley are correct that you can get some of the pickling power of fluoride ions without using HF, and that this can reduce the possibility of exposure to concentrated HF. This does not, however, mean that ammonium bifluoride is 'safe' -- you can search the site for "HF replacement" or "Ammonium bifluoride" for several detailed discussions and a nuanced understanding of the issue.
Ted Mooney, P.E.
Pine Beach, New Jersey
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