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The effects of CaO/SiO 2 ratio (basicity) and CaCl 2 addition amount on the properties of CaO–MgO–Al 2 O 3 –SiO 2 –CaCl 2 glass-ceramics (GC) were investigated. When sintered at 825 °C, the increase in basicity from 0.35 to 0.75 reduced the porosity of GCs from 1.1 to 0.8 vol%, but the increase of CaCl 2 addition amount from 5 to 10 wt% increased the porosity from 0.8 to 7.0 vol%. The main crystalline phase of GC changed from augite (Ca(Mg 0 · 7 Al 0.3) (Si 1 · 7 Al 0.3)O 6) to Ca 10 Al 12 Cl 2 Si 5 O 37 by increasing the CaCl 2 addition amount to 7.5 wt%. The increase in CaCl 2 addition had adverse effects on the bending strength and Vickers hardness, while the rise in basicity deteriorated the bending strength but had little impact on the Vickers hardness. This study may have a guiding significance for preparing slag-based GCs and treating CaCl 2 -containing wastes. [ABSTRACT FROM AUTHOR]

CaCl 2 can dissolve in the silicate glasses, and thus, using the CaCl 2 -bearing glass for the preparation of glass-ceramic could be a potential method for treating CaCl 2 -bearing wastes. In this work, two kinds of glass powders, CaO-MgO-Al 2 O 3 -SiO 2 and CaO-MgO-Al 2 O 3 -SiO 2 -CaCl 2 , were sintered at 825–850 ℃ to prepare the glass-ceramic. Besides, a low-pressure (19.1kPa) hot-pressing sintering technology was applied to reduce the porosity and pore size of the glass-ceramic. The addition of CaCl 2 (5 wt%) reduced the polymerization degree, glass transition temperature, crystallization peak temperature, and crystallization activation energy of the glass. Augite was the main crystalline phase of the glass-ceramic, and the addition of CaCl 2 promoted the precipitation of anorthite. The glass-ceramic prepared from the Cl-containing glass always exhibited a higher bending strength than that obtained from the Cl-free glass. When sintered at 825 ℃ for 8 h, the glass-ceramic showed the highest bending strength of 171 MPa. [ABSTRACT FROM AUTHOR]

• CaO-MgO-Al 2 O 3 -SiO 2 glass-ceramic with high contents of Cr2O 3 was investigated. • The glass-ceramic was prepared by SPS and showed bulk crystallization behavior. • Coarse spinel crystals resulted in intergranular fracture and effectively hindered crack propagation. • The glass-ceramic showed high bending strength and vickers hardness of 214 MPa and 8.2 GPa, respectively. 2, 6, or 10 wt% of Cr 2 O 3 was added into the CaO-MgO-Al 2 O 3 -SiO 2 precursor glasses (PG), aiming to investigate the effects of high contents of Cr 2 O 3 on the crystallization behavior and mechanical properties of glass-ceramics (GCs). The PGs were milled into powder and then sintered by spark plasma sintering (SPS) technology at 750∼850 °C under the pressure of 10 MPa. It was found that Cr 2 O 3 induced the precipitation of spinel nuclei in the PGs, which served as the heterogeneous nucleation sites for the augite crystals. Augite and spinel were the main phases of the GCs, and the crystallinity increased by increasing the Cr 2 O 3 addition amount and sintering temperature. The GC prepared at 850 °C with 6 wt% Cr 2 O 3 addition showed excellent bending strength, with Vickers hardness, and fracture toughness of 214 MPa, 8.2 GPa, and 1.3 MPa·m1/2, respectively. [ABSTRACT FROM AUTHOR]

• Glass-ceramic was prepared from biomass fly ash by using a powder sintering method. • The crystallization behavior was dominated by surface crystallization. • Fine diopside grains (0.2–1 μm) were observed in the glass-ceramic. • The highest bending strength of glass-ceramic reached 212 MPa when sintered at 920 ℃ for 1 h. In this work, diopside-based CaO-MgO-Al 2 O 3 -SiO 2 glass-ceramic was prepared from biomass fly ash (BFA) by powder sintering method. The parent glass powder was prepared by melting 76%BFA-9%CaO-6%Al 2 O 3 –9%MgO (in mass) at 1450 ℃ followed by water quenching and ball milling. The glass powder was sintered at 830, 850 and 920 ℃ for 1–16 h to obtain the glass-ceramic. It was found that the crystallization behavior was controlled by surface crystallization, and diopside was the major crystalline phase. The mechanical properties of glass-ceramic were improved by prolonging the sintering time from 4 to 16 h at 830 ℃. However, the sizes of pores in glass-ceramic increased as increasing the sintering time at 850 ℃, which deteriorated the properties of the glass-ceramic. The glass-ceramic sintered at 920 ℃ for 1 h has a high crystallinity and fine grains, and showed the highest bending strength of 212 MPa. [ABSTRACT FROM AUTHOR]