Making sodium metal at home
Sodium is a very reactive metal. Contact with water may result in explosions due to releasing hydrogen gas.
When electrolyzing molten NaOH lye, realize that the hot lye of over 300°C is NASTY STUFF ! Be prepared for (small) explosions of back-reacting of Na metal with water vapor or oxygen at the anode. AVOID ANY CONTACT WITH SKIN AS THE HOT LYE CAUSES SEVERE BURNS !!! The hot lye may even burn through your clothes. So wear face protection, gloves and preferably an apron.
When using oil for capturing sodium by the 'carbon-method', be aware that the heat of the furnace may ignite it or its vapors.
Also be aware for suckback in this method, when you stop the furnace and as a result the underpressure in the retort sucks back, the oil does not come in the hot retort with explosions as a result ! Just keep the mouth of the pipe a few mm under the oil level and do not use a wide for the oil.
ALWAYS wear a face shield and gloves when handling sodium !
Sodium metal is one of the alkali metals which are soft and reactive and have relatively low melting points. They do not occur in a free metallic state in nature as they are too reactive. Sodium is the most common of them and it is a major component of table salt which is a compound with Chlorine. And it is found in Sodium hydroxide which is a strong base and used in lye.
The aim of the project "Preparation of sodium metal' is that it is possible with simple means to prepare sodium metal. There are hazards involved, see the safety box above. If you as a chemist really need sodium metal you can better buy it via ebay or a chemicals supply store. The aim is not to do shows with throwing Na metal on a pond or even into the loo which may cause bad accidents. There are two possibilities:
- Electrolysis of molten NaOH or NaCl.
- Chemical reduction of Na2CO3 or NaOH with magnesium or aluminum metal or carbon.
The metal itself is prepared by electrolyzing molten NaCl with the Downs cell and the early 20th century by the Castner process which used electrolysis of molten NaOH. Some amateur chemists who want to make sodium metal use this Castner method on a small scale basis. One guy made a very well-designed replica of the Castner cell which worked very good and had a good yield. This forum topic has an extensive description on this.
Cathode: Na+ + e --> Na
This is done by melting NaOH at 320°C and using a carbon or nickel anode (no iron as this corrodes) and a copper or iron cathode. The reactions which take place are:
Anode: 4OH- --> 2 H2O + O2 + 4e
There are however some issues when electrolyzing NaOH.
- As the sodium floats on the lye bath, precautions should taken place to prevent drifting of the sodium to the anode where it oxidizes again.
- Water vapor is formed at the anode which can react with the sodium and evolve hydrogen gas. Combined with the oxygen this may cause explosions which mght splatter the hot lye around and when this touches the skin this is NOT FUN.
- The temperature should be within a narrow range of 320 and 330°C as above 330°C the sodium metal dissolves in the lye and electrolysis will cease. This requires a good temperature control and thermocouple sheathing which is resistant to the lye.
After doing some not quite successful tests with the 'carbon method'(see more below) I was trying to electrolyze NaOH by using hardware shop grade NaOH pellets. However I watched this video
which discouraged me from doing the electrolysis due to the aforementioned issues.
First electrolysis test: could not collect the sodium
But Later on I made a setup for a simple test. I bought a stainless steel Senseo coffeepad container for a few $$ (8cm diameter, 20cm tall) which Icut off till 7cm tall. This would be the container in which the lye is to be electrolyzed. I surrounded this by two pieces of cell concrete (Ytong) breeze blocks with a cutout for the S/S container. I put two electrodes into it a nickel anode (which is also used in commercial Castner cells) and a copper cathode.
Now the party could begin. I put on my face shield and gloves and old winter coat for extra protection. I had a piece of Fermacell ready which I put over the bath during run and only open for pictures and collecting Na metal. Heck wat is is difficult to control the camera with gloves.... First I heated the NaOH pellets till they melted and started the current which was rather constant to 5 amperes. I used an auto light bulb in series to prevent a too high voltage and to exclude the risk of shorting (hence the bright incandescent light). I had made a copper small dipper to collect the Na droplets, but they were floating very quickly over the surface of the lye bath. Sometimes I only saw gas escape at the cathode and no sodium forming at all, so I suspected overheating of the bath (Na dissolves into the lye), so I measured the temperature and sometimes it heated over 340°C so I had to stop the already very low propane flame. Despite watching many Youtube videos showing a guy collecting the Na metal I did no succeed yet. So I stopped and let the lye freeze and cool down and put in into an airtight container to prevent attracting moisture.
Experiment Nov 2013
Next attempt: I used a stainless spoon dipper and put a nickel anode and a copper cathode into it. Small balls of lustrous sodium metal were appearing, but hard to collect. As the lye froze, the metal was sometimes still embedded in the lye. I used a copper wire with a piece of gauze in it but that filled with frozen lye. With tweezers I had slightly more success. So going on ...
In the Sciencemadness forum
I have discussed this.
The setup before the first run
Close detail of the setup
A look into the lye where very tiny sodium droplets are floating on the lye bath
Electrolysis running in another experiment (Nov 2013)
Collected sodium balls between frozen lye in a bottle with paraffin oil
But by the end of the 19th century the metal was made chemically by heating sodium carbonate with carbon to 1200°C. The reaction is:
Na2CO3 (liquid) + 2 C (solid) --> 2 Na (gas) + 3 CO (gas)
Over 1000°C this reaction is favorable also because the vapor pressure of sodium is well over 1 bar (boiling point 889°C). For making my own sodium metal I preferred this process. Electrolyzing NaOH or NaCl is a rather tedious job for an amateur chemist because of the Na metal floats on the liquid salts and is not easy to protect the hot molten metal from burning in air. But collecting sodium metal is easier than with the carbon method.
This method however requires capturing of the Na vapor under an oil bath, but that is easier to handle than it seems. The biggest challenge is to keep the retort airtight. At those temperatures, plain steel is easily attacked by oxygen from the air. Stainless steel is the best option. Actually, inert gas like Argon should be used to prevent oxidizing the metal vapor.
The setup with the retort in a sandbox
As the process requires temperatures of over 1000°C you need a furnace which reaches that temperature. That is rather easy if you have a propane burner. See this furnace page
for more info. As the sodium metal is released in gaseous state, the vapor should be condensed and collected where it cannot react with air or water. Mineral oil is a good option however it is flammable.