A wide range of ceramic oxide materials can be used for crucibles, the type being dependent on the metal/alloy, the basicity of the melt and the foundry practice, whether erosion resistance or thermal shock resistance takes prominence.

The most common type, historically, are the aluminosilicate range; these were based on clays but now utilise the purer synthetic materials.  At one end of the range lies fused silica, with an excellent thermal shock resistance, whilst at the other extreme is fused alumina with a very good erosion resistance.

Magnesia generally offers better chemical and erosion resistance, but is better suited to the faster cycling times.  The most resistant material is zirconia, and there are many iterations of this to suit different applications.




The Aluminosilicates fill the gap between the important end members of the series, i.e. Silica and Alumina. They generally have lower working temperatures but they have the advantage of good thermal cycling capabilities and a good strength.

SILLIMANITE has the benefit of a very good thermal shock resistance but it has a poor erosion resistance in contact with metals.  It is therefore used in non-critical positions such as crucible outer sleeves or as containers for powder calcination.

MULLITE products have a greater alumina content and can be used in the air-melting of steels; it is better suited to acidic slags.  The material is used for one-shot applications, such as with pouring cups. and also support struts.

MULLITE F80 maximises the possibilites of a mullite material.  It is made from fused grain to enhance its thermal shock resistance and has an alumina boosted matrix for better erosion resistance.  It is well suited to use as a transfer ladle. SC MULLITE is a slip cast grade used for crucible sleeves and special shapes with a smooth finish.

Alternatively, if pre-heat problems limit the life of a ladle then an effective solution would be the FS60 product.  This is based on FUSED SILICA to confer an excellent thermal shock resistance; erosion resistance is maintained at a good level by alumina additions. Also suited to fire assay crucibles.


Chemical Properties

Sillimanite AM1
33.5 0.6 64.5 0.2
Mullite F80
20.5 0.05 79.0 0.2
Silica FS60
 59.5 0.25 39.5 0.6

Physical and Thermal Properties

Product AP (%) >BD (g/cc) CTE (x10-6/K) TC (W/m/K)
Sillimanite 22.0 2.35 na 1.5
Mullite F80
 19.0  2.58  na  1.6
Silica FS60
 25.0  1.90  na  na
AP=Apparent Porosity BD=Bulk Density CTE=Coefficient of Thermal Expansion TC=Thermal Conductivity