Effect of CaF2 and Na2SiF6 nucleating agents on the crystallization behavior and properties of MgO-Al2O3-SiO2 glass-ceramics

MgO-Al2O3-SiO2 (MAS) glass-ceramics were prepared by melt and sintering method, and the effects of two kinds of nucleating agents CaF2 (labeled as C-group) and Na2SiF6 (labeled as N-group) on the crystallization kinetics mechanism, crystallization behavior, physical and chemical properties of MAS glass-ceramics were investigated. Herein, differential scanning calorimetry (DSC), X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM), density, corrosion resistance, dielectric properties, coefficient of thermal expansion (CTE) and other tests were carried out to evaluate the performance of both parent glass and glass-ceramics samples. The results show that the nucleating agent of CaF2 and Na2SiF6 exhibit a significant influence on the characteristic temperatures of Tg and Tp, and crystallization kinetics of MAS parent glass. The Tg of C-group parent glass are slightly higher than that of N-group parent glass. The Avrami parameter n value for N-group and C-group parent glass are 3.8 and 2.5, which suggesting the main crystal phase in N-group and C-group parent glass present threedimensional and two-dimensional growth, respectively. However, the nucleating agent of CaF2 and Na2SiF6 present a negligible influence on the crystallization behavior, bulk density, acid resistance, CTE, dielectric constant and dielectric loss of MAS glass-ceramics. When the crystallization temperature increased from 900 to 1000 degrees C, the main crystal phase precipitated from the all these MAS glass-ceramics kept unchanged with & alpha;-cordierite phase (Mg2Al4Si5O18), and the grain size of these rod-like & alpha;-cordierite phase around 300-500 nm. All these two groups MAS glass-ceramics present low relative dielectric constant (& epsilon;r), which is ranges from 1.32 to 2.40, and the & epsilon;r of C-group glass-ceramics increases with increasing of the crystallization temperature. The MAS glass-ceramics samples also display low dielectric loss (tan & delta;), which is ranges from 0.42 x 10-2 to 4.93 x 10-2. This finding suggests the MAS glass-ceramics would be used as a potential candidate of dielectric materials for electronic devices, especially for high frequency applications.