Dense ceramics of single-crystalline-phase osumilite synthesized by solid-state reaction

Solid-state reactions of ultrafine particles of magnesium hydroxide and barium carbonate with kaolin were investigated to obtain dense osumilite ceramics. Hexacelsian, μ-cordierite and α-cordierite were found to crystallize prior to the formation of osumilite above 1200 °C. Dense ceramics of single-crystalline-phase osumilite were obtained by a delicate compositional adjustment around the nominal formula of osumilite 2MgO·BaO·3Al2O3·9SiO2, because it hardly showed any solid solution formation. Single-phase osumilite ceramics showed a linear thermal expansion coefficient of 2.7×10−6 K−1 (RT–900 °C), a relative dielectric constant of 5.6 and a dielectric loss of 5×10−5 at 1 MHz. The osumilite ceramics prepared in the present work may fulfill the requirement from various applications.