plating, anodizing, & finishing Q&As since 1989
Trying electroless CoFe deposition
Q. Hi, I'm interested in deposit electroless CoFe alloys. I've already tried citrate bath pH 7 but it simply doesn't work. There's any additive I could use to prevent Fe2+ - Fe3+ oxidation?Mauro Ribeiro
A. I have never tried electroless Fe/Co, only pure cobalt. It too suffers from oxidation to the trivalent state and in the lab I found I had to bottle the solution immediately after using it and make sure the air was expelled by squeezing the bottle and then screwing the top down. This was necessary with either sodium hypophosphite or hydrazine as the reducing agent. I found that I could agitate using a peristaltic pump to take "air" from the top of the tank and pump it into the base. This was excellent because I could fit a close fitting lid and so conserve heat and nearly eliminate evaporation. After a few minutes the air would be replaced by the hydrogen given off by the plating process. I ran the process overnight giving 0.007in coatings.
At pH7 iron is easily oxidised by air so you try the same. Can you start the agitation with nitrogen? I doubt if any additive will prevent oxidation of ferrous to ferric.
Q. Very interesting your idea of pumping air out of the cell. In my case, I tried to avoid Fe3+ oxidation using ascorbic acid. However in this case the deposition simply didn't work. I think a reaction between the reducing agent and the ascorbic acid took place. Have you been studying the Co/Fe system yet?Mauro Ribeiro
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