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Electrolytic polishing

 

Dear experts,

I would like to know the electrolytic polishing solution for Palladium Silver based dental alloys with typical compositions of 59.8%Pd ¯ 28.1 Ag ¯ 6.0%In- 5.0%Sn (weight percent). I tried to use the following electrolytic solution: 50% alcohol ¯ 33% nitric acid ¯ 17% phosphoric acid, but I could not mix them for they suddenly boiled even though I just add only less then 10 ml phosphoric acid to 500 ml mixture of alcohol and nitric acid.

Thanks for giving me any suggestions.

Wenhua Guo
The Ohio State University - Columbus, Ohio

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Sounds like you need to check the strength of the acids BEFORE mixing them. Mixing reagent grades of acids with alcohol will produce some exciting results, as you have seen. The order in which you mix these chemicals will produce varied levels of stability at certain temperatures, therefore, ALWAYS mix at room temperature. Try adding the nitric acid to the phosphoric acid, then slowly add to the alcohol. The percentages by weight you gave are probably correct, however, the difference may be the acid strength in the condition it is in before mixing. Reagent grade, when compared to lab or technical grades, may be way too strong for your experiment, if that is what you are using. The reaction you are seeing could be the result of water in the phosphoric acid which would not bode too well with the nitric acid, the list goes on and on. The alloy you are attempting to polish should, of course, not be present during any of the mixing as this would guarantee a nasty episode(I have actually heard of this scenario...). Look at it this way, you make a few mistakes, and you learn!

Good luck! Jeff Swayze
- Kelowna, B.C., Canada