THE EFFECT OF VARIOUS NUCLEATING AGENTS UPON THE CRYSTALLISATION OF CORDIERITE GLASS CERAMIC. S. M. Clark, G. N. Greaves, M. Oversluzien¹, G. Sankar², J. M. Thomas^2, CCLRC, Daresbury Laboratory, Warrington, WA4 4AD, UK, ¹Netherlands Organisation for Scientific Research, The Hague, The Netherlands, ²Royal Institution of Great Britain, 21 Albermarle Street, London, W1X 4BS, UK

Cordierite glass ceramics are of considerable relevance to the electronics packaging industry due to their high dielectric constant and their low coefficient of thermal expansion. Interest has also been shown in their optical properties for use in tunable lasers and solar concentrators. They are presently being produced in bulk quantities for use as catalyst supports in catalytic converters for car exhaust systems.

Cordierite glass ceramics can be made by heating a glass of the appropriate stoichiometry (Mg₂Al₄Si₅O₁₈) above the glass transition temperature. An intermediate crystalline phase known as u-cordierite is first formed as the final product alpha cordierite crystallises.

We have studied this reaction using time resolved powder diffraction, EXAFS and small angle scattering as well as conventional static measurements. The results of a detailed kinetic analysis will be presented together with a study of the effect of adding a number of nucleating agents to the reaction mixture.

An extension of the classical kinetic equations governing series reactions will also be presented.