Downs cell

A downs cell proper is used to produce sodium metal and chlorine gas by electrolysis of sodium chloride (possibly fluxed by calcium chloride). It's patented, etc. We use the term more generally to describe any apparatus that performs electrolysis on molten metal salts to produce pure metals, and does it in a gravitically efficient way.

Construction

Materials

• Refractory clay capable of withstanding molten alkali metals
• Nickel, graphite, or platinum electrodes
• A DC power source capable of 7-10V x 10kA/m² over a sustained period.
• Wire to connect the power source to the anode/cathode
• A heat source (if required) to supplement the resistive heating of the power supply to maintain the molten salt

Design

File:1501756-DownsCell.png

In general, the structures can be made of iron, covered by refractory material where it would otherwise contact the electrolyte.

Tank

Lidded, with five holes:

1. Electrolyte input (smaller lidded hole in roof)
2. Residue ducting output (hole in roof or high on side)
3. Product ducting output (hole in side above waterline, preferably near waterline
4. Anode input (small hole in bottom)
5. Cathode input (small hole in bottom)

• Downs uses an iron pot with a refractory lining.
• The lid does not (technically) touch the bath, so it can be made of anything. A hinge for support is a good idea. A slot for the residue duct and a lidded hole for the electrolyte would not be difficult.

Residue ducting

The residue is traditionally a halide (chlorine) gas, but if a hydroxide or carbonate were used, it would not be. It must surround and cover the anode, therefore it must contact the bath.

Product ducting

The product is traditionally a liquid alkali metal (sodium), but this too is not certain. It must surround and cover the anode, therefore it must contact the bath.

Anode

• Downs uses graphite or carbon

Cathode

• Downs uses iron or copper

Operation

Principle

The yield is limited by two things:

• The amount of product in the electrolyte input
• The total amps of current run through the cell at the minimum voltage or higher. It's the coulombes, not the joules.

Normal operation

1. Attach (or pour in) the electrodes at the base of the tank
2. Place the ducting into the vat, covering the anode and cathode appropriately
3. (If necessary) charge the ducting with inert gas.
4. (If necessary) direct the residue ducting to a chemical washing apparatus
5. Close or attach the lid
6. Fill the tank with electrolyte
7. (If necessary) heat the bath
8. (If necessary) wet the bath (to allow initial conduction)
9. Apply current at normal voltage but minimal amperage.
10. Wait until conduction is steady
11. Apply full current
12. Repeat
    1. If necessary, remove residue from residue container or maintain washer
    2. If necessary, remove product from product container
    3. If necessary, add more electrolyte
    4. If necessary, maintain DC power source
13. Until you have sufficient product
14. Disconnect DC power source
15. Damp the heat source
16. Clear residue container / washer
17. Clear product container