cleaning brass... with nitric acid

I searched the group and found some references to cleaning very badly
tarnished brass (in my case they are tubes for a carburetor, turned
near black from a rough life I guess). Among the suggestions was
ammonia and H2O, and vinegar and salt, ketchup, and a 2% nitric and
H2O mix. In the shop the only thing I have from the above list is
nitric, so I tried it.
I heated the water in a kettle, then poured it in a glass cup... added
a splash of nitric and dropped in the brass tubes. It fizzled a bit,
then after about 10 minutes or so, it was done the fizz. I added
another splash of Nitric and bingo, that second bit really, really
cranked up the results. These parts came out looking brand new... an
outstanding before/after difference. I would estimate the first bit
was at 3%, the second was at 7% or so... give or take..
This led me to a few questions. It seems the Nitric lost its punch
after soaking the part in there for a bit? I am no chemist, so this
may seem obvious to those in the know. Does a chemical reaction cause
it to weaker as it gets working on cleaning the brass.
Because Nitric is kind of a pain in the butt to get, I was kind of
hoping that I could have a little container of it that I could keep
and just use it as I have parts to restore, then cap it off for the
next time.... but from my experience today, I will have to neutralize
and discard the batch after each round.
Any useful, positive info is very much appreciated!
Reply to
rbce2003
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Yup, it reacts with the metal and becomes less active. Good thing you diluted it that much or your pipes would have been GONE. I can remember cleaning off platinum mesh electrodes in a chemistry course that had copper plated onto them. A quick dunk in a beaker of concentrated acid left a big cloud of brown nitrogen oxides and a green solution of copper nitrate. Best done in a fume hood. Took less than a second. Nitric acid is kind of like hydrochloric acid, basically a gas dissolved in water. The fumes will rapidly eat/rust anything in the room, best kept in a fume hood since even a closed container of it will outgas somewhat. Not something you really want to stick on a shelf with other chemicals.
Hydrochloric acid may be a little easier to get, does similar things to copper, just not as fast. Has the same storage problem as nitric acid.
Vinegar/salt solution is a little easier to concoct, but will preferentially eat the zinc out of brass leaving a salmon pink surface of copper. This has to be manually polished off. Ammonia will attack brass and may make thin sections brittle. Ketchup has vinegar and salt in it, much diluted, see above.
If you HAVE to use a brightening solution continually, see if you can find some Birchwood Casey cartridge case cleaner. This works with no after effects on the workpiece and isn't too nasty to store afterwards, although it is very poisonous, use rubber gloves. It won't creep out of the container and rust everything in sight, anyway. Supposedly, there's some citric-based cleaners out there for brass, haven't seen them, haven't tried them, but would be a lot safer than any of the above. Don't forget you're actually eating the surface away and changing the part's dimensions, may be more of a slip fit afterwards than before.
Stan
Reply to
stans4
Copper is below hydrogen in the reactivity table, and a simple acid such as hydrochloric will not attack. It will dissolve copper oxides or other corrosion, but not the unoxidized copper. Hydrochloric acid will, as you mentioned, leach the zinc out of brass.
Nitric acid is different. It is an oxidizing agent as well as an acid, and will attack elemental copper.
John Martin
Reply to
John Martin
I have been using Lysol toilet bowl cleaner on old brass car parts before polishing
Reply to
Stupendous Man
-------------------------------------------------- What about justice , as in 14th Amndmnt to our Constitution ?
Reply to
werty

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