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Boric acid vs Borax pentahydrate


Are there any major differences between boric acid and borax pentahydrate in relation to a nickel sulfamate bath? We have a 50gal (189L) bath, using a boric concentration of 35g/l. We've added 6.5Kg of what we thought was boric acid, but after having problems with dissolving all the boric (at 130 F) we did some research on the 'boric' we received and find that it is borax pentahydrate. I can live with the excess boric until it diminishes, but am curious about the borax pentahydrate buffering properly. Is there a way to reduce the boric concentration safely with NaOH or another base? Would it be better to go the other way and drop the pH with sulfamic acid?

Thanks for any suggestions!
Jeff Carlson

First of two simultaneous responses -- 2006

I could not find exactly the compound that you mention in a chem reference handbook. From the two that were similar in name, it would appear that there is no cheap way of getting it out. Will it buffer? I doubt it. Have you found any difference in your plated product? Hardness, brittleness, solderability or other preferred properties? If not, you can probably continue to use the tank by adding the correct amount of boric acid.
For sure, look at the MSDS sheet for what you have. It can be nasty.
James Watts
Navarre, Florida

Second of two simultaneous responses -- 2006

Borax is the tetra sodium salt of boric acid. Being a salt it acidity is gone. It's buffering properties, which come from the acidity, were lost during it's synthesis between the acid and the corresponding base. Also, you know that the sodium present in the borax is a stress riser for a sulfamate bath. Depending on the added amount it may give somewhat stressed deposits.
Guillermo Marrufo

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