Magnesia

Magnesia crucibles are an economical option for shorter runs of superalloy castings, cf. Zirconia, especially for larger castings associated with land turbines. They are also a less reactive alternative to Alumina with the more aggressive steels.  They do have a high thermal expansion which creates thermal stresses, so care needs to be taken with the cycling regime.

There are two versions available as isostatically pressed crucibles, plus a vibrocast version for larger items.

MAGNESIA MD is the standard magnesia product, used for a wide range of Ni-alloys in vacuum and air.  It also has excellent resistance to basic slags used for steels in air.

MAGNESIA SP has a spinel matrix to improve the thermal cycling capabilities by reducing the overall thermal expansion.  As it is solid-state sintered, with no added silicate phase, it has the best combination of erosion resistance plus thermal shock resistance of all the magnesia products; it can be used for the more aggressive Ni alloys containing strong reducing components.

MAGNESIA M1 is the vibrocast version, and so can be made into special shapes and larger crucibles. They are used for casting the larger blades and vanes for land-based turbines, and also for commercial melting of iron-based alloys in air when the environmental conditions are chemically basic.