For a few years I wanted to obtain my own optical cesium reference cell like those provided by Thorlabs1 or Precision Glassblowing2 but the relative high cost (~400 USD) for a glass container with a few milligrams of metal and shipping problems were a big discouragement. So I decided to build my own reference cell. One of the problems was to obtain the cesium. You can buy metallic cesium sealed in glass ampules but it is very difficult to buy a single gram or half. There is an evaporation method in witch cesium salt (e.g. cesium chloride) is mixed with another alkali metal with higher boiling point than cesium (e.g. lithium - boiling point: 1330 °C) which has a boiling point of 671 °C. Cesium is more reactive but the evaporation will move the reaction point towards creating more and more second alkali metal chloride salt. Cody presented this simple method in his YouTube video.3 This method is very simple but I’m not comfortable working with boiling cesium metal. Every method of obtaining metallic cesium needs temperatures above 500 °C and inert gas or vacuum.4

A week ago I stumbled on a interested paper from 1975 in which the authors presented a method of electrodeposition of the alkali metals from propylene carbonate.5 I had cesium chloride and rubidium chloride from plans on the method mentioned earlier. I ordered few ml of propylene carbonate, aluminum chloride and I think it worked like described in the paper. I just switched to graphite electrodes.

Small notes for recreating the reaction mentioned in that paper:

  • Heat the solution up to 40 °C, otherwise the conductivity will be low and the reaction will be very slow.
  • Monitor the temperature of the solution because it can start to boil and ignite when the current is to high.
  • Aluminum chloride is very dangerous.
  • All reagents have to be dry.

Below is a movie of me heating a few mg of deposited cesium. After the solvent evaporates the cesium spontaneously ignites.

The next thing to do is to build a box in which the cesium could be transferred into a glass vial without air.


References

  1. Thorlabs, GC25075-CS - Cesium Borosilicate Reference Cell ↩

  2. Precision Glassblowing, Cesium Vapor Cell, Pyrex ↩

  3. Cody’sLab, Isolating Cesium Metal, YouTube ↩

  4. David G. Lovering, Molten Salt Technology, Springer-Verlag US 1982, DOI:10.1007/978-1-4757-1724-2 ↩

  5. Jorné, J., Tobias, C.W. Electrodeposition of the alkali metals from propylene carbonate. J Appl Electrochem 5, 279–290 (1975). DOI:10.1007/BF00608791 ↩