Bismuth oxide has been found to be a useful flux for the preparation of dense body cordierite (Mg2Al4Si5O18). The use of as little as 2 atom% bismuth ion with the appropriate mixture of commercially available oxide starting materials serves to produce fully dense crystalline cordierite after firing at 1000 °C. The microstructure of the sintered body (92 w/o% cordierite, 8 w/o% bismuth oxide) has the residual bismuth oxide flux distributed in discontinuous domains at the grain boundaries and at the triple points. Physical properties such as thermal coefficient of expansion and dielectric constant are largely unperturbed by the presence of the flux.
Green tapes having high volume fraction solids loading have been fabricated from bismuth oxide-cordierite precursor powders. The subsequent firing at 1000 °C of laminated green tapes yields fully dense ceramic bodies of crystalline cordierite.