Crystallization mechanisms and properties of α-cordierite glass–ceramics from K2O–MgO–Al2O3–SiO2 glasses

Abstract

Low temperature co-fired cordierite glass–ceramics were fabricated with K2O–MgO–Al2O3–SiO2 glasses. It was confirmed that α-cordierite crystals were precipitated from the glasses directly below 950°C and at the higher temperature additional leucite crystals were formed. The calculation of crystallization activation energy (Eα) for a onefold α-cordierite was 230.77–279.81kJ/mol; and the Eα of the concurrent precipitation of α-cordierite and leucite was 348.85–374.33kJ/mol, by Kissinger and Ozawa methods. Moreover, the Avrami constant (n) was calculated to be about 2 for onefold α-cordierite and to be 2.27–2.91 for the concomitant α-cordierite and leucite by the Augis–Bennett equation. Therefore, a bulk nucleation with one-dimensional crystal growth mechanism for α-cordierite was determined, which was verified by the results of Scanning Electron Microscope (SEM). The mechanisms for the concomitant α-cordierite and leucite changed from one-dimensional crystal growth to two-dimensional crystal growth with the variation of chemical composition. Furthermore, the α-cordierite glass–ceramics from the low-cost natural material exhibited good sintering capability below 950°C, low dielectric constant (6.0–8.0) and loss (below 0.01), matchable thermal expansion (4.40–5.63×10−6K−1) and applicable flexural strength, which were essential for the application as low temperature co-fired ceramic (LTCC) substrates.