Electrical properties and thermal expansion of cordierite and cordierite-mullite materials

Commercially available cordierite and mullite powders were used to obtain cordierite and composite materials with mullite content up to 65 wt.% by attrition milling, uniaxial pressing and sintering. The employed cordierite powders were the coarse, medium and fine single granulometric fractions and the binary mixtures of them with 30, 50 and 70 wt.% of the smaller size component. Mullite powder employed in composites was a 7 h-attrition milled one. The dielectric constant (ε), dielectric loss tangent (tan δ), resistivity (ρ) and thermal expansion coefficient (α) were measured. The influence of the porosity, mullite and glassy phase contents and grain size in the electrical parameters was analyzed. The thermal expansion coefficient as a function of the composition was studied.