Effects of CaO/SiO2 ratio and heat treatment parameters on the crystallization behavior, microstructure and properties of SiO2-CaO-Al2O3-Na2O glass ceramics.

• SiO 2 -CaO-Al 2 O 3 -Na 2 O typed glass ceramics were synthesized. • Hardness of sample gradually decreased with the increase of temperature. • Flexural strength of sample first increased and then decreased with temperature. • Hardness and flexural strength have maximum values as prolonging sintering time. • CaO/SiO 2 ratio has a significant effect on the composition of crystalline phase. The SiO 2 -CaO-Al 2 O 3 -Na 2 O glass ceramics were prepared by the melting-sintering method. For samples with a CaO/SiO 2 ratio of 0.23, wollastonite was the only crystal phase after heat treatment for 2h in the temperature range of 800–1000 °C, and a maximum flexural strength of 99.39 MPa can be achieved at 900 °C. When the sintering time was extended from 2 h to 40 h at 800 °C, the metastable phase Na 2 CaSiO 4 first appeared, but then disappeared as the heat treatment continued. The maximum hardness and flexural strength were achieved at the sintering time of 20 h in this case. Furthermore, when the CaO/SiO 2 ratio was increased from 0.23 to 0.45 under the same heat treatment conditions (800 °C for 20 h), the main crystalline phase transformed from wollastonite to Na 2 CaSiO 4 , besides nepheline (NaAlSiO 4) and SiO 2. The existence of the nepheline enhanced the mechanical properties of glass ceramics. [ABSTRACT FROM AUTHOR]