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.



induction_melting_cruciblesZirconia C, M, Y, zircon

Zirconia is the most resistant oxide material to almost all metals and alloys.  Zirconia crucibles are supplied in a stabilised form to lock in the crystal structure and assure good thermal cycling capabilities.  Stabilising agents include CaO, MgO, Y2O3.

ZIRCONIA C, calcia (CaO) stabilised, has a very good thermal shock resistance and can be reused over several days. The ZIRCONIA C2 variant was designed for improved erosion resistance combined with a good thermal shock resistance.  It is generally used for melting in air, and is suitable for steels, nickel alloys and precious metals.

For superalloys, the high performance grade is ZIRCONIA M, magnesia (MgO) stabilised.  It has a fine structure and low silica content and is fired to a high temperature.  This all contributes to low reactivity, with the most aggressive alloys, and high erosion resistance.  Suited for the high specification alloys melted under vacuum, the products are used in the aerospace, power, medical and precious metal industries.

ZIRCONIA Y, yttria (Y2O3) stabilised, is the most stable variant for thermal cycling.  Yttria has excellent resistance to reduction, reserving this version for the more testing alloys.

ZIRCONIA E is a grade used for atomising nozzles; its high purity and high density assure maximised erosion resistance under harsh conditions.  As a crucible, is suited to constant conditions, such as with continuous casting and also with extremely aggressive alloys with which most crucibles will react.

ZIRCON crucibles are used for melting precious metals, especially for refining platinum group alloys applications involving glassy and siliceous slags.  ZIRCON performs well with many non-ferrous metals and alloys, especially aluminium. Zircon is not “wetted” by aluminium, so is relatively unreactive; it also copes very well with thermal cycling.


Chemical Properties

Product SiO2(%) Fe2O3(%) CaO(%) MgO(%) ZrO2 (%) Y2O3(%)
Zirconia C 1.3 0.1 4.1 0.2 93.0
Zirconia C2 0.8 0.1 3.6 0.3 94.4
Zirconia M 0.6 0.1 0.2 2.8 95.6
Zirconia Y 0.8 0.1 0.2 0.2 90.2 7.2
Zirconia E 0.2 0.02 0.1 2.5 96.6
Zircon N 33.0 0.2 0.1 0.2 64.5

Physical and Thermal Properties

Product AP (%) >BD (g/cc) CTE (x10-6/K) TC (W/m/K)
Zirconia C 21.0 4.37 8.1 1.5
Zirconia C2 19.0 4.58  8.1 1.6
Zirconia M 20.6 4.46 8.1 0.8-1.5
Zirconia Y 22.8 4.49  8.1 0.8-1.5
Zirconia E 8.5 5.20  na na
Zircon N 13.5 3.80 4.6 1.7
AP=Apparent Porosity BD=Bulk Density CTE=Coefficient of Thermal Expansion TC=Thermal Conductivity