Structure, crystallization mechanism, and properties of glass ceramics from molten blast furnace slag with different B2O3/Al2O3

Abstract

Glass ceramics with different B2O3/Al2O3 from molten blast furnace slag (BF slag) were prepared using traditional melting, annealing, and heat treatment method. According to DSC analysis, the parent glass samples were nucleated at 760 °C for 1 h, and then respectively crystallized at 900 °C, 920 °C, and 940 °C for 1 h. The structure of parent glass was characterized using XRD, Raman spectra, 27Al MAS NMR spectra. The results indicated that with an increasing B2O3/Al2O3, Q2 remained dominant in the glass network, Q0 disappeared and Q4 existed when B2O3/Al2O3 was 0.21. [BO3] and [BO4] were both characterized when B2O3/Al2O3 exceeded 0.09, but the further addition of B2O3 was prior to form [BO3] in glass network. The investigation of crystallization mechanism revealed that the crystallization activation energy Ec strikingly decreased from 403.8 kJ/mol to 277.8 kJ/mol with increasing B2O3, and surface crystallization was determined due to that the crystallization index n was below 3. The results of XRD and SEM-EDS analysis both confirmed the main crystalline in glass ceramics was gehlenite. The flexural strength of glass ceramics reached the minimum when B2O3/Al2O3 was 0.21. Glass ceramics nucleated at 760 °C for 1 h and crystallized at 940 °C for 1 h exhibited the highest flexural strength of 57.61 MPa.