Crystal structure of single phase and low sintering temperature of α-cordierite synthesized from talc and kaolin

Abstract

Cordierite body with the formulation of 2.8MgO·1.5Al2O3·5SiO2 was prepared from talc and kaolin as the basic raw materials. Following glass crystallization technique the glass powder was successfully heat treated at 900 °C for 2 h to form a single-phase α-cordierite. The crystal structure of α-cordierite was analysed using X-ray diffraction technique and the Rietveld structural refinement method. Differential thermal analysis (DTA), Fourier-transform infrared (FTIR), field emission scanning electron microscopy (FESEM), coefficient of thermal expansion (CTE) and dielectric properties were also performed. Results show that the materials crystallized as a hexagonal structure with space group of P6/mcc and the room temperature lattice parameters are a = 9.743742 (Å) and c = 9.389365 (Å). FTIR analysis on the glass revealed that only silicate species is the only unit that exists in the glass network. DTA also confirmed that α-cordierite completely formed after 13.5 min of isothermal heating at 900 °C. Coefficient of thermal expansion of synthesized α-cordierite is 2.5 × 10−6 °C−1. The dielectric constant is between 5.0 and 5.5 for 1 MHz and 1.8 GHz, respectively, and the dielectric loss is in the range 10−2. FESEM micrographs revealed that the material is fully densified.