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**22** 

 *Venezuela* 

**Reactive Sintering** 

Irene Barrios de Arenas

*"Dr Federico Rivero Palacio"* 

**of Aluminum Titanate** 

*Instituto Universitario de Tecnología* 

The high thermal shock resistance due to the negligible thermal expansion coefficient, additional to its low thermal conductivity and good chemical resistance makes the aluminum titanate (Al2TiO5) a suitable material for different technological applications. It is a ceramic material consisting of a mixture of alumina (Al2O3) and titania (TiO2) forming solid solution with stoichiometric proportion of the components: Al2O3·TiO2 or Al2TiO5. It is prepared by heating a mixture of alumina and titania at temperature above 1350°C, in air atmosphere. Pure Aluminum Titanate is unstable at temperatures above 750°C, when the solid solution decomposes, following a eutectoid reaction, into two separate phases Al2O3 and TiO2. For this reason Aluminum Titanate ceramics are doped usually with MgO, SiO2

Unfortunately, the expansion crystal structure anisotropy that promotes the low thermal expansion coefficients provokes microcracking, as a result of anisotropy of thermal expansion along the three primary axes of the crystal lattice (a single crystal of Aluminum Titanate expands along two axes and contracts on the third one when heated), therefore a low mechanical strength and, on the other hand, the low thermal stability below 1280°C

Aluminum Titanate ceramic materials have many technological applications, among others, as thermal insulation liner, soot particulate filter in diesel engines, spacing rings of catalytic converters, in the foundry crucibles, launders, nozzles, riser tubes, pouring spouts and

thermocouples for non-ferrous metallurgy and master moulds glass industries.

**2. Fundamentals of low thermal expansion coefficient aluminum titanate** 

There are two important features to achieve a very low thermal expansion coefficient, in crystalline ceramic structures highly anisotropic. The first aspect involves unit cell crystalline chemistry. The coefficients of thermal expansion of the crystal axes are controlled to develop solid solutions, in an attempt to ensure that the sum of the coefficients of the principal axes gives zero. In the case of polycrystalline ceramic materials, the volumetric

and ZrO2 in order to stabilize the solid solution structure.

**1. Introduction** 

restricts its technical use.

**(Al2TiO5) ceramics** 
