Iridium crucibles are used to grow many types of crystals. They are generally cylindrical and range in capacity from 30 cm3 to several litres. An iridium crucible is typically made from a sheet of hot-rolled iridium or iridium powder. Typical wall thicknesses are 60 mils.
Iridium crucibles are also used to grow various metal oxide single crystals. These are used in the optical industry as well as in laser technology. For example, in the backlighting of mobile phones and in metal scanners.
The Czochralski technique is often used to grow these types of crystals. It involves slowly withdrawing a rotating single crystal seed from a molten oxide. This causes the molten oxide to solidify on the rotating crystal seed.
There are two problems with this method. First, the charge remains on the crucible and can decrease the lifetime of the crucible. Second, the crucible is heated too rapidly, causing the thermal mass of the crucible to be disrupted.
One possible method for reducing these problems is to weld-melt the iridium grains into smaller grains. In this way, the grain boundaries do not propagate as much. Weld melting can be done manually or by automated pulsing.
This can be done by charging the crucible slightly above its melting point. As this increases the concentration of the iridium, distortion is reduced. Similarly, when the crucible is encased in a thin film of zirconium oxide, the lifetime of the crucible is enhanced.
There are several different refractory materials that are suitable for these types of crucibles. Some of them include alumina, aluminized steel, and zirconium.