If the vapor pressure of a grown compound (and/or of the flux) is not negligible, the mirror furnace and the tetra-arc oven are not applicable. The growth has then to be carried out in welded containers (crucibles) made of inert refractory metals like tantalum, tungsten or molybdenum (melting points from 2600 to 3400°C). For sealing of crucibles a specially adjusted tetra-arc oven is used.

Tantalum crucibles

4-arc welding