Aluminum Titanate

Solid-state reaction of alumina and titania at temperatures greater than 1350 °C results in the synthesis of aluminum titanate. The generated powder may be sintered at temperatures of 1400 °C–1600 °C in air based on its reactivity. Aluminum titanate develops a psuedobrookite crystal structure.

Ceramics made from aluminum titanate display very good resistance to thermal shock. This is mainly because of its very low thermal expansion coefficient, which is due to the substantial anisotropy in the properties of the material.

While expansion in the direction of the a and b-axes is positive, in the direction of the c-axis it is is negative. Besides producing virtually zero thermal expansion, this causes microcracks to develop in the sintered material, resulting in the moderately low strength of the material. Additives such as MgO and SiO2 are used to curtail strength degradation and strengths up to 100 MPa have been cited for experimental materials.

Key Properties

Table 1 illustrates the key properties of aluminum titanate.

Table 1. Typical physical properties for aluminum titanate

Property
Density 3-3.4 g.cm-3
Modulus of Rupture @ RT 30 MPa
Modulus of Rupture @ 1000 °C 60 MPa
Young's modulus 20 GPa
Thermal expansion (20-600 °C) 0-1 x10-6 K-1
Thermal expansion (600-1000 °C) 1-2 x 10-6 K-1
Thermal conductivity (RT-1000 °C) < 2 W.m.K-1
Maximum service temperature 1000 °C continuous
1100 °C intermittent
Thermal shock resistance Excellent
Resistance to molten metals Good

Applications

The low thermal conductivity and exceptional thermal shock resistance together with the optimal chemical resistance to molten metals (mainly aluminum) enable the material to fulfil a number of metal contact applications in the foundry sector including plugs, crucibles, pouring spouts, riser tubes, launders and ladles.

Components manufactured using aluminum titanate display considerably longer service life compared to competing materials such as fused silica and calcium silicate.

In addition, aluminum titanate is used in the automotive sector as an insulating liner for exhaust manifolds where there is a necessity to lessen heat loss in advance of a turbocharger. In this article, the metal exhaust manifold is cast around the shaped aluminum titanate liner. The discrepancy in the thermal expansion between the aluminum titanate and the steel manifold during cooling preserves the ceramic in compression, thus overcoming the issues related to its low strength.

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