Studies on the use of microwave for enhanced properties of glass-ceramics produced from sewage sludge pyrolysis residues (SSPR)

• Production of glass-ceramics using SSPR was feasible.
• The utilization of SSPR was up to 80%.
• The M-GC possessed better properties than C-GC.
• The crystallization apparent activation energy was reduced by microwave radiation.
• Microwave radiation converted the crystallization mechanism.

SSPR (sewage sludge pyrolysis residues) were reused as main raw materials (up to 80%) for glass-ceramics. In the present work, glass-ceramics were synthesized by microwave and conventional processes with an objective of investigating the function of microwave radiation on enhancement in the properties and crystallization mechanisms of the two heating styles. The heat treatment schedule of the microwave glass (M-G) and conventional glass (C-G) was decided on the basis of differential scanning calorimetry (DSC) results. A control study of microwave glass (CM-G) was carried out following identical heat treatment schedule as was adopted by M-G under conventional heating process. X-ray diffraction (XRD) analysis revealed that the main crystalline phase of microwave glass-ceramics (M-GC) was anorthite (CaAl2Si2O8), and the main crystalline phases of both conventional glass-ceramics (C-GC) and control microwave glass-ceramics (CM-GC) were wollastonite (CaSiO3) and anorthite (CaAl2Si2O8). The difference of the main crystalline phase between the two heating styles was attributed to the improved ionic interdiffusion caused by microwave radiation. Scanning electron microscopy (SEM) analysis clearly indicated that M-GC possess finer and uniform microstructure. M-GC exhibited excellent properties in comparison to C-GC and CM-GC. The kinetics study indicates that microwave radiation decreased Ea about 76 kJ mol−1. The n values of M-G and C-G were in the range of 3.03–3.43 and 1.73–1.95, representing the crystallization mechanism of bulk nucleation and surface nucleation, respectively.