Crystallization behavior and properties of cordierite synthesized by sol-gel technique and hydrothermal treatment

Cordierite gels have been synthesized by sol-gel and hydrothermal treatment starting from silicon tetrachloride (SiCl4), aluminum hydroxide (Al(OH)(3)), and magnesium chloride (MgCl2-6H(2)O). The phase transformation occurring in the temperature range 900-1300 degrees C was characterized by the differential thermal and thermogravimetric analysis (DTA, TGA), X-ray diffraction technique (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and laser granulometry. The properties of uniaxial pressed and sintered specimens as porosity, density, and mechanical strength were measured. The results show that metastable -cordierite was crystallized in the temperature range 900-1200 degrees C and then transformed into -cordierite at 1300 degrees C for both methods. The crystallization of -cordierite took place with a small amount of cristobalite, enstatite, and spinel. The particle size distribution of the powders obtained by both methods progressed as a function of formed phases. The mechanical properties and the density of sintered materials for both methods increased as a function of sintering temperature up to 1200 degrees C and decreased at 1300 degrees C due to high porosity generated by -cordierite crystallization. The sol-gel method has demonstrated better advantages comparing with hydrothermal treatment in terms of phase transformations and the properties of sintered specimens.