For electro-polishing of the above steels we need to replace the combination of perchloric acid and ethanol, because of its being explosive under certain conditions. Is there a good substitution for it?
Hi Dr. Müller, various electrolytes are applicable to austenitic stainless steels. For example try these:
250 mL H2O, 750 mL H2SO4
300 mL H2O, 700 mL H3PO4
You can find more information in ASM Handbook vol9.
I used following solution for electro-polishing of 304 SS for EBSD measurement.
10% oxalic acid and 90% water at 6V. the holding time is short between 8 to 10 sec. of course it depends to sample area. smaller sample will be better in polishing quality.
if this solution does not work properly, I also have good experience with 4% Perchloric acid (HClO4) and 96% Ethanol (C2H6O) for electro polishing of 304 SS and Fe-Ni alloys.
Traditionally, the best composition for electropolishing (EP) of all austenitic stainless steels is 25 wt% sulfuric acid and 75 wt % phosphoric acid. No additional water is permitted. I am also inclined to make a rebuttal against the above said oxalic acid. At all it is an appropriate acid for EP of 18-8 SS and its Mo derivative S 316. The reason is simple: the solution required for EP should have low to moderate electrical conductivity. Also, it must be viscose enough. These two parameters are important because during EP we are supposed to remove picks more readily than that of crevices which means we have to provide a continuum in which electrical flux has a considerable difference at sharp points in comparison with flux at valleys. This can be provided only by the composition I mentioned earlier.
Safety is also another very important factor one should consider while electropolishing SS. Introducing perchloric acid, while very effective, it has a potential hazard of explosion at above 40 C. In an attempt to keep the bath in a sound position for opperation, you also need to measure the iron content of the bath constantly. Above, 4.3 mg/ml, the bath liquid shall be regenerated.
I know my answer seems long, but it worth reading. To further my answer, I advice you to study the effect of some surfactants such as Triton x-100 above its CMC to even enhance the result beyond what is achievable when working with standard solution.
sincerely
Aref
I use all mentioned formula, but i make mate the steel!or discoler to white like color.
I use all mentioned formula, but i make mate the steel!or discoler to white like color. can you suggest me some thing like inhibitor?
Electrochemical Polishing of Austenitic Stainless Steels
https://www.mdpi.com/1996-1944/13/11/2557
Materials 2020, 13(11), 2557; https://doi.org/10.3390/ma13112557
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