Iridium crucibles are used to grow high melting oxides in the optical and laser industries. They are also useful in high temperature investigations.
In 1912, Sir William Crookes made experiments with an iridium crucible. He claimed to have melted copper and lead in the crucible without damage. Aside from the crucible itself, iridium can also be enhanced with a thin film of zirconium oxide.
The crucible is a cylindrical object, generally made of welded sheet. It is enclosed in a refractory enclosure. Normally, the wall is 60 mils thick. Typical crucibles contain 500 hours of molten oxide.
If a crucible is not conditioned properly, it can fail. The failure can be brittle fracture, melting, or reaction with an oxidising atmosphere. Depending on the material and the size and shape of the crucible, the failure may be catastrophic or not.
The condition of an iridium crucible can be regulated by pulsating the weld. For example, a pulsed weld can condition the bottom and sidewalls of an iridium crucible. Pulsed weld puddling can be performed by using a TIG, GTAW, or laser welder.
When puddling is carried out for long periods of time, the walls of the crucible can undergo considerable penetration. This results in reduced useable life. To avoid this, the crucible is conditioned to a selected height by pulsating the weld.
An iridium crucible can be damaged due to the growth of grain boundaries. The last part of the crystal to solidify is usually contaminated with defects.