Preparation and crystallization action of SiO2 -Al2O3 -CaO-ZnO-R2O porous glass-ceramics

Using powder-sintering method, SiO2-Al2O3-CaO-ZnO-R2O porous glass-ceramics were produced for analysis. Five samples with different SiO2/CaO ratios were used in the research. The mechanical properties, microstructures and textures of porous glass-ceramics are investigated by using differential thermogravimetric a-nalysis/differential thermal analysis (TGA/SDTA) , X-ray diffraction (XRD) , and scanning electron microscopy (SEM). The activity energy of crystallization (E) and crystallization kinetics parameter (k) were calculated based on the modified JMA equation. The Avrami parameter n was obtained according to Augis-Bennett function. The results show that the k value of No. 1 sample (SiO2/CaO =61: 18) is the largest among all samples, which tends to crystallize more easily, and crystallization processes of all samples are observed bulk crystallization. The main crystal phase observed is parawollastonite (clinorhombic system) with puncheon shape. Pore-forming agents decomposed at 100 -500 ℃ form a large number of closed pores with micron dimension and several semi-open pores distribute uniformly in the glass-ceramics matrix. This work may be expected to be favorable for industrial scale applications of porous glass-ceramics in the field of building thermal insulation.