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05-13-2008, 11:56 AM #1
Sodium hydroxide / caustic soda / lye : useful stuff
This is intended to summarise some of the uses of this stuff:
Sodium and potassium hydroxides are as strong alkalis as you can get. About the only practical difference is sodium is cheaper than potassium.
Strong alkalis will disolve most things organic, including skin fat and flesh. Generally an alkali burn is going to occur faster and go deeper than an acid burn, as alkalis react with fats/oils in your skin and flesh, turning them into soap (hence the soapy feeling if you get them on your skin), wheras most acids won't react or penetrate fatty acids (conc hydrofluoric is a v dangerous exception).
unless it gets in your eyes, a quick wash in a cheap weak acid such as vinegar or citric acid solution will neutralise the alkali.
As a strong alkali, sodium hydroxide will attack and disolve the following metals:
zinc (cadmium behaves closely enough to zinc that all i've written aplies to it too)
It will also attack chromium plating and copper, although ammonia is far better at dissolving copper:
It will therefore attack and if not totally disolve, then certainly weaken brazing and soft solder joints.
The reaction with those metals releases hydrogen gas.
Sodium hydroxide will not react with iron or steel, in fact the alkaline conditions will not allow rust to grow;
if you make the conditions oxidising, the black magnetic oxide will grow in its stead; hence the use of alkaline solutions of sodium nitrate for hot bluing baths.
For short periods of time, freshly cut or cleaned steel can be kept bright by keeping it in sodium hydroxide solution or solid.
If you can establish electrical contact between aluminium or zinc and rusty iron, then put them in sodium hydroxide, the reaction will electrolytically reduce at least some of the rust to iron metal (loose black powder), and make it much easier to remove.
You can get the same effect, much more controlably by attaching your work to the negative (black) lead of a battery charger, and a piece of scrap to the red lead, and submerge both bits in the hydroxide solution for a day or two.
If you use galvanized metal for the positive (red) electrode, and it zinc plates your work, just leaving it in the solution with the power turned off will disolve the zinc again.
Dilute solution works best, too strong and it conducts too well, so some fancy battery chargers will cut out, also anything that give bubbles through the stuff gives tiny droplets of spray which burn hell out of the lining of your nose and throat, a dilute solution is a lot less unpleasant in that respect, and if it gets on your skin or clothes too!
The electrolytic de rusting has "potential" to cause hydrogen embrittlement, so be careful on any stressed parts.
The ability to disolve fats and organic material makes sodium hydroxide an excellent paint stripper and de greaser its a lot less unpleasant to use than ammonia, but does require rinsing to remove the sodium hydroxide, wheras ammonia solution just evaporates, although any soaps it formed will remain behind unless rinsed.
Strong alkalis will disolve or severely weaken plant fibres and paper. Nylon is relatively resistant to strong alkalis, but polyester will turn to jelly. Polythene, PET and teflon appear to be relativly un affected.
As with most chemicals, the stronger the solution, the faster it works.
heat also increases the rate of reaction (rate approximately doubles per 10 deg celcius rise in temperature).
Left exposed to the air, sodium hydroxide will absorb carbon dioxide, and gradually become sodium carbonate (washing soda / soda ash). for most of our bucket chemistry, that's not too important, electrolysis with iron / steel electrodes will expell carbon dioxide, or reaction with quick or slaked lime will precipetate calcium carbonate, getting you your hydroxide back (useful for bluing baths).
When dissolving, in water, it will release heat, so, as with acids, always add to the water, and go slowly.
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05-13-2008, 02:52 PM #2
Sodium Hydroxide eats meat. People are made of meat. One drop in an eye will instantly and permanently blind that eye. Take proper precautions when dealing with the stuff, to include proper protective gear.
05-14-2008, 09:07 AM #3
Thanks, Ammonia, chlorine bleach.
I wasn't clear enough on not getting any chemical, especially a strong alkali in your eyes, or anywhere else personal.
Ammonia disolved in water is also a strong alkali, and will also attack and disolve Tin, Aluminium, zinc and cadmium, just as sodium hydroxide does.
Where ammonia really comes into its own is being able to disolve copper, hence its use in bore cleaners.
With first additions of ammonia, copper will become coated in greenish copper hydroxide, but with enough concentrated ammonia solution, the green will disolve giving a deep blue solution of a copper :ammonium complex.
Again, short exposure won't affect steel.
Because of the noxious vapour, you're unlikely to risk getting too much of a dose of ammonia; it is poisonous, and can gas you (William Burroughs called getting high on ammonia "the scrub woman's kick", more like masochistic!!), it can also burn flesh if you get it on your body, or blind you if it goes in your eyes.
Adding any of the strong alkalis (eg sodium or potassium hydroxides or carbonates, slaked or quick lime, chlorine bleach, cement) to a chemical compound of ammonia (e.g. ammonium nitrate or ammonium sulphate fertilizer, or even farmyard slurry or topsoil) will liberate ammonia gas.
I've mentioned chlorine bleach.
Sodium hyperchlorite always contains some sodium hydroxide, and so is very strongly alkaline. any addition of acid (even urine) will cause release of chlorine gas (poisonous, unpleasant and will set everything in the shop corroding).
Mixing hyperchlorite and ammonia is not good news!
at best it will be a waste of both, at worst it could go bang! (ClN3) that stuff is far too unstable to play with, al quaeda could do well to try it, it would thin their numbers out some, as they each collected Darwins
seriously, I messed with related compounds when I was in my teens, and even with tiny quantities was lucky just to get serious hearing loss, the stuff even goes off spontaneously.
05-14-2008, 11:30 AM #4
Another use for caustic soda is cleaning machines or tiled floors, a mixture of Laundy detergent, caustic soda and water is my general purpose cleaner 1% caustic for use inside the house 8% for cleaning machines. add cornflour to thicken if necessary (oven cleaner)
In high concentrations at high temperature it will dissolve glass
In all very handy for a material costing less than $1/lb
05-14-2008, 12:33 PM #5
Where do you buy it at???
05-14-2008, 01:44 PM #6
Where to get it
Ordinary hardware stores will likely have it but for cheap bulk buys, trade plumbing supply places will have it as drain cleaner.
Agricultural suppliers are also pretty good sources of chemicals:
Sodium hydroxide is sometimes used to treat straw, it breaks down some of the woody material and makes it possible for cattle to digest it better.
Ammonia has been used for the same purpose, with the advantage that the bugs in the animals' rumen (one of it's many stomachs) can use the ammonia to make protein.
Agricultural suppliers are also a good source for the following:
Phosphoric acid (milk scale remover)
Citric acid (used as disinfectant if there's a foot and mouth outbreak)
citric is a lot pleasanter to use than sulphuric for pickling copper.
Sulphuric has a high boiling point, so it won't evaporate, if you get it on your clothes, the water evaporates leaving more concentrated sulphuric which makes holes.
Use the citric as a good strong solution, as it stops the bugs setting up home in it, and keeps well.
sodium hyperchlorite (dairy disinfectant)
05-14-2008, 02:17 PM #7
possible electrolytic removal of lead.
I've been looking at the following link about conservation of lead and tin archaeological artifacts:
It talks about electrolytic reduction of corrosion products in a sodium hydroxide bath, and cautions not to allow the current to stop.
Does anyone want to experiment connecting a peice of scrap steel with lead on it to the red lead of the battery charger in a caustic bath to see if it disolves the lead but leaves the steel un marked?
The use of acids is out as the steel will rust....
Last edited by Alpacca Fortyfive; 05-14-2008 at 02:21 PM. Reason: dissleckseeeaaahh
05-14-2008, 02:59 PM #8
I can't say how things like this are viewed in places such as Ireland and Australia, but in many of the States in the good old U.S. of A. you'll be given a very suspicious look if you ask the local Pharmacist or fertilizer salesman about some of these chemicals. I used to mix my own blacking concoctions using caustic soda and one of the Nitrates or Nitrites and when they would ask what I intended to use it for I would tell them, "as an enema for my cow." That usually broke the tension.
05-14-2008, 03:32 PM #9
Caveat 1: Dissolving NaOH or KOH in water is STRONGLY
exothermic. Do it wrong and you boil the solution by
doing this. That's "bad."
Caveat 2: Washing soda (sodium carbonate) works every
bit as well as lye for electrolytic de-rusting and carries
much less attendant risk.
05-15-2008, 08:24 AM #10
Thanks & nitrates and dissolving abrasives
I have done the boiling trick by adding NaOH to hot water. it wasn't clever, especially as it was in the house with SWMBO present
Nitrates are getting difficult to get. In Britain, even NH4NO3 fertilizer is getting sticky to get. A friend who cures his own bacon, now has to buy "Curing salts" which is a mix of KNO3 and NaCl, the "authorities" are worried someone might make black powder with saltpeter.
Here in Ireland, fertiliser has been diluted for some time, although that didn't stop the bomb makers. What is now beginning to emerge, is the extent to which the British security forces were alleged to be helping the bombers. Some allegations even go as far as claiming that the bomb makers were planted British agents!!!
When I was doing blasting at college, the lecturer said that the IRA had been recrystallizing fertilizer (which has dense, non absorbant prills) to make absorbant nitate suitable for mixing with fuel oil.
Who knows, we might have to start extracting nitrates from s**t, as they did in the past. (you'd literaly be "passing" on the bacon).
Think I made a mistake, the stuff that goes bang is nitrogen tri chloride NCl3, other nitrogen and ammonium tri-halides are also extremly un-stable, with the solid ones; even the friction of drying shrinkage will set them off!
Forgot to say that the strong alkalis will also disolve aluminium oxide, so if we are sure that is what our abrasive is, a good long soak in a hot alkali solution should disolve alumina abraisive out of the surface of iron or steel work. It would do the same for tin oxide too, but I've not heard of it for years.
05-15-2008, 10:30 AM #11
05-15-2008, 10:57 AM #12
There's the solder remover! (pos bluing remover too)
Thanks for that!
anyone work in an analytical lab or have a friend who does?
it looks like an expensive drain cleaner (NaOH for lead)/ floor cleaner (NH4OH for copper) and battery charger combo although I'd be very cautious about generating hydrogen in a barrel, incase it did cause some brittleness, perhaps I'm over cautious on that risk?
Also, alkaline solutions are used to electrolyically strip chrome plating, even hard chrome. I wonder if it cautions against using on chrome plated bores?
Wholesale catering supplies places will likely have sodium hydroxide as drain cleaner
05-15-2008, 11:07 AM #13
05-15-2008, 11:26 AM #14
I'd still be cautious, I'm not trolling for a fight, and I'm sure that with product liability lawyers waiting for carcasses to feed on, the process would be shown to be pretty safe before anyone marketed it.
I checked out a couple of threads, here's 1:
Electrolysis And Hydrogen Embrittlement
embrittlement is sneaky, in my own field, I know that even a little pool of stagnant salt water is enough to cause failure of a metro rail through embrittlement (H2S generated in the puddle put H into the rail).
we generally don't know the alloys we're dealing with, so my vote is proceed with caution.
05-15-2008, 11:54 AM #15
I can promise you that hydrogen embrittlement is not going to be the main problem for rifle barrels that have been left in stagnant pools of salt water.
05-15-2008, 02:36 PM #16
Drain cleaners are often aluminum/NaOH mixtures. Check the
ingredients before using...!