Sealed argon tubes

To make a vacuum-tight feedthrough to fill the tube with noble gas, Farny prepared a simple manifold for filling with argon.

Kovar - Boro seals

Farny's first intention was to make a bulb using boro glass and kovar wire.

Kovar is an alloy developed for sealing to boro glass. The wire should be degreased, then heated to 800-900°C (red-orange colour) and left at this temperature for several minutes.

This procedure produces an oxide layer on the surface of the wire. The glass doesn't seal to the metallic surface, but does to the oxide and forms a strong seal.

The seal should have a gray colour. Metallic colour means too thin an oxide layer (weak seal) and black colour is too thick.

Farny heated the wire for 5 minutes, and during this process the wire is also degassed from impurities. 30 minutes of heating is recommended to completely remove impurities.

Tungsten - Boro seals

Tungsten isn't ideal for feedthroughs due to tiny cavities in the wire, however Farny tried it anyways.

Farny left the wire in flame for ~2 minutes to form a slight yellow oxide.

This successfully sealed 3 tubes for ~24 hours.

Dumet - lead glass

Farny explored Dumet and lead glass and had great success, with the only disadvantage being more difficult annealing.

I will avoid this combination as lead glass is difficult to find suppliers for and dangerous to work with.