Phase formation and properties of the BaO-B2O3-SiO2 and -Al2O3 ceramics prepared via an aqueous suspension route

The low-temperature sintering ceramics based on the eutectic systems BaO-B2O3-SiO2 and -Al2O3 are fabricated by an aqueous suspension process at a sintering temperature of 900-940 degrees C. Sintering mechanism and physical properties, e.g., dielectric and thermal properties, of the low-temperature sintering ceramics have been investigated and discussed in detail in terms of their mineral phase compositions. The results indicate that the barium borate compounds with low melting characteristics can be easily obtained by the chemical combination of Ba(OH)(2)center dot 8H(2)O and an aqueous solution of H3BO3. In turn, the presence of the BaO-B2O3 composition in the low-temperature sintering ceramics can supply a liquid phase sintering aid for the mineral phase formation and the achievement of densification sintering. The addition of a SiO2 component to the BaO-B2O3 composition can cause the emergence of barium silicate phases and consequently achieves high coefficients of thermal expansion (11-17 ppm degrees C-1), whereas the introduction of an Al2O3 component to the BaO-B2O3-SiO2 composition can result in the formation of a hexacelsian phase, which can achieve a low permittivity and loss (permittivity: 7.1-7.4; loss: 5-7 x 10(-4)). The work may be referenced for the fabrication of LTCC materials with tailored physical properties. (C) 2012 Elsevier B.V. All rights reserved.