Preparation of Cordierite below 1000°C via Bismuth Oxide Flux

Bismuth oxide has been found to be a useful flux for the preparation of dense body cordierite (Mg 2 Al 4 Si 5 O 18 ). The addition of as little as 2 at.% of bismuth ion to the appropriate stoichiometric mix of commercially available oxide starting materials gives fully dense cordierite after firing for 12 h at 1000°C. The lower‐temperature limit for this reaction is 960°C, with essentially no reaction occurring below this temperature. There is also a temperature‐dependent induction period prior to cordierite formation. The microstructure of the sintered body has the residual bismuth oxide flux distributed in discontinuous domains at the grain boundaries and at the triple points. The cordierite body has a dielectric constant of 5.0, unperturbed by the presence of the bismuth oxide.