Influence of mechanochemical activation on the sintering of cordierite ceramics in the presence of Bi2O3 as a functional additive

Due to its outstanding electrical characteristics, such as the low temperature expansion coefficient, low dielectric constant and good mechanical properties, cordierite, 2MgO⋅2Al2O3⋅ 5SiO2, is a very attractive high-temperature ceramic material. In order to accelerate the process of sintering, 2.50 mass% Bi2O3 has been added to the starting mixtures. Liquid phase sintering caused by the presence of bismuth-oxide lowers the temperature of cordierite formation. The mechanical activation of the starting mixtures (0–56 min in vibro-mill) additionally lowers sintering temperatures. The sintering process was performed at 1200, 1300, 1350 and 1400 °C, for 2 h. The particle size analysis (PSA) was employed in order to determine the changes in the particle size of the mechanically treated powders. The phase composition of the starting powders and sintered materials was analyzed by the X-ray diffraction method. Furthermore, scanning electron microscopy (SEM) was used in the analysis of the powder morphology.

Cordierite, whose composition is 2MgO⋅2Al2O3⋅ 5SiO2, is one of the phases of the ternary MgO–SiO2–Al2O3 system, among mullite, cristobalite, tridymite, enstatite, forsterite, sapphirine etc., [1]. Cordierite is widely used in glass–ceramic compositions for manufacturing multilayer circuit boards, catalytic converters, filters, kiln furniture, thermal insulation materials [2].The phase diagram of the ternary MgO–SiO2–Al2O3 system is presented at Fig. 6. A pink mark on the diagram represents the composition used in our experiments. We concluded that addition of 2.50 mass% Bi2O3 along with relatively short milling time of 56 minutes led to decrease in temperatures of both cordierite formation and its sintering process.Figure optionsDownload as PowerPoint slideHighlights
► The influence of mechanical activation on cordierite formation was studied.
► The Bi2O3 was added in order to improve its sintering process.
► Reducing the particle size allows lowering the temperature of cordierite formation.
► Sintering at 1300–1400 °C indicated at pure cordierite–mullite phase ceramics.