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

摘要

Cordierite body with the formulation of 2.8MgO centre dot 1.5Al_2O_3 centre dot 5SiO_2 was prepared from talc and kaolin as the basic raw materials. Following glass crystallization technique the glass powder was successfully heat treated at 900 deg C for 2 h to form a single-phase alpha-cordierite. The crystal structure of alpha-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 (A) and c = 9.389365 (A). FTIR analysis on the glass revealed that only silicate species is the only unit that exists in the glass network. DTA also confirmed that a-cordierite completely formed after 13.5 min of isothermal heating at 900 deg C. Coefficient of thermal expansion of synthesized alpha-cordierite is 2.5 X 10~(-6) deg 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.