Alpacca Fortyfive
Stainless
- Joined
- Nov 16, 2007
- Location
- Leinster, Ireland
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.
Uses:
As a strong alkali, sodium hydroxide will attack and disolve the following metals:
Tin
Aluminium
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.
Keith
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.
Uses:
As a strong alkali, sodium hydroxide will attack and disolve the following metals:
Tin
Aluminium
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.
Keith