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

Low temperature co-fired cordierite glass-ceramics were fabricated with K2O-MgO-Al2O3-SiO2 glasses. It was confirmed that alpha-cordierite crystals were precipitated from the glasses directly below 950 degrees C and at the higher temperature additional leucite crystals were formed. The calculation of crystallization activation energy (Ea) for a onefold alpha-cordierite was 230.77-279.81 kJ/mol; and the E-alpha of the concurrent precipitation of alpha-cordierite and leucite was 348.85-37433 kJ/mol, by Kissinger and Ozawa methods. Moreover, the Avrami constant (n) was calculated to be about 2 for onefold alpha-cordierite and to be 2.27-2.91 for the concomitant et-cordierite and leucite by the Augis-Bennett equation. Therefore, a bulk nucleation with one-dimensional crystal growth mechanism for alpha-cordierite was determined, which was verified by the results of Scanning Electron Microscope (SEM). The mechanisms for the concomitant alpha-cordierite and leucite changed from one-dimensional crystal growth to two-dimensional crystal growth with the variation of chemical composition. Furthermore, the alpha-cordierite glass-ceramics from the low-cost natural material exhibited good sintering capability below 950 degrees C, low dielectric constant (6.0-8.0) and loss (below 0.01), matchable thermal expansion (4.40-5.63 x 10(-6) K-1) and applicable flexural strength, which were essential for the application as low temperature co-fired ceramic (LTCC) substrates. (C) 2015-Elsevier EN. All rights reserved.