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Introduction

A Downs Cell uses electrolysis to remove chlorine gas from molten sodium chloride to produce sodium metal.
Would you like to know more?

Why?

Since sodium metal is

  • a fun material
  • too expensive for our budget
  • made from cheap and readily available (non-iodized) table salt
  • produced by a very simple reaction

it is therefore desirable to produce it ourselves and should also be a fairly simple feat.

How?

  • Temperatures of roughly 800 °C (1500 F) are needed to melt the NaCl, this is easily accomplished using the Charcoal Foundry.
  • Only 8VDC are needed, a computer power supply can provide us with 12VDC.
  • Iron and carbon electrodes are easy to obtain.

All that remains is to design and build a suitable container for the reaction.

Problems

Some technical challenges that need to be overcome:

  • Apparatus must be able to withstand 800 °C
  • What do you do with 800 °C chlorine gas?
  • The container will probably have to be made of metal, how do you get electricity to the electrodes without touching the container or the liquid NaCl?
  • How do you collect, cool, and store 800 °C sodium without it contacting water or oxygen?

How the pros do it

Downs Cell Patent


NOTE: Although this page only describes the process for producing sodium metal from a downs cell, other metals can also be produced. Calcium chloride melts at a temperature of 772 C (much less if it is di or hexahydrate) and can be used to produce calcium metal using the same process.

Project Cheat Sheet

  • Melting point of NaCl = 1074 K, 801 °C, 1473.8 °F
  • Melting point of Na = 370.87 K, 97.72 °C, 207.9 °F
  • Sodium is produced at the (-) electrode, chlorine gas at the (+) electrode
  • Chlorine is harmful in concentrations as low as 30 ppm
  • Density of Sodium (near r.t.) 0.968 g·cm−3
  • Density of NaCl 2.165 g/cm3


Possible Designs

Possible Design Ver. 1.0

This is a fairly cheap, disposable design. The cell is composed of pipe nipples, pipe fittings, wire, ceramic beads and uses the Charcoal Foundry to provide the necessary heat. The entire reaction is contained within the network of pipes. It has an open middle column so that the NaCl can be observed directly. This allows the operator to make sure that the NaCl is molten and allows them to monitor the level of the NaCl and add more as necessary. Since Na is less dense than NaCl, the molten Na will float on top of the molten NaCl. This also causes the fluid level in the (-) pipe to be higher than the other two pipes, allowing the Na to flow up out of the cell. The electrodes are copper wire that is threaded through the ends of the pipe and down into the two vertical side columns. A series of ceramic beads are strung onto the wire to prevent it from contacting the pipes. The pipe from the (-) side of the cell is placed directly into a container of mineral oil. This provides reasonable protection to the Na from O2. This container is also covered to prevent the mineral oil from contacting O2 and igniting. A good way of disposing of the Cl2 has yet to be determined. One possible method involves using a second electrolysis cell to generate H2 which could be burned with the Cl2 in an HCl oven and then dissolved in water to produce useful hydrochloric acid. It may also be possible to dissolve the Cl2 in water and then dispose of the water.