Cordierite Mg2Al

A more interesting substitution involves replacing two tetrahedral Al ions by one Be and one Si ion. This results in the stoichiometric end-member Mg2BeAl2SigOjg from normal cordierite Mg2Al Si Ojg and produces changes in lattice parameters as well as in thermal expansion behavior (see Table 1-9). From room temperature to 800°C, the average linear thermal expansion coefficient increases from 11.7 X 10 K in stoichiometric... 

Therefore it would be sheer folly to attempt developing a glass-ceramic with a stable assemblage of cordierite (Mg2Al Si50jg) and P-eucryptite (LiAlSiO ), even though it would seem useful to have sudi a phase mixture to achieve a zero coefficient of thermal expansion in a high-temperature material. 

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