Effect of B<sub>2</sub>O<sub>3</sub> and P<sub>2</sub>O<sub>5</sub> Addition on the Phase Separation and Crystallization of Li<sub>2</sub>O-MgO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2 </sub> Glass-Ceramics

B 2 O 3 - or P 2 O 5 -doped Li 2 O-MgO-Al 2 O 3 -SiO 2 (LMAS) glass-ceramics were prepared by solid state method using Li 2 CO 3 , MgO, Al 2 O 3 and SiO 2 as the raw materials, B 2 O 3 or P 2 O 5 as the additives. The effects of adding B 2 O 3 and P 2 O 5 on the phase separation, crystallization and thermal expansion coefficient were investigated by means of X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and thermal dilatometer, respectively. The results showed that B 2 O 3 or P 2 O 5 addition could promoted phase separation of glass and increased the size of spherical phase separation droplet. With the addition of B 2 O 3 or P 2 O 5 , the crystallization temperatures (Tc) of LMAS system decreased from 764 o C to 726 o C and 764 o C to 750 o C, respectively. However, the crystalline phase compositions did not changed, and β-quartz solid solution (s.s) (Li 2 Al 2 Si 3 O 10 ) was still the main crystalline phase, and lithium silicate (Li 2 SiO 3 ) and forsterite (Mg 2 SiO 4 ) were the minor phases. The thermal expansion coefficient (α) of B 2 O 3 -doped and P 2 O 5 -doped LMAS glass-ceramics in the temperature range 20-600 o C were 5.215×10 -6 / o C and 5.008×10 -6 / o C, respectively, which were higher than that of LMAS glass-ceramics (α=3.790×10 -6 / o C).