Sustainable Synthesis and Characterization of Bi2O3 Doped Borate Glass-Ceramics from Granite Sludge Waste with Emphasis on Structure, Luminescence and Mechanical Properties

Abstract A series of glass-ceramics was synthesized from a ternary system comprising the glass-forming oxide B 2 O 3 , granite sludge waste, and varying amounts of the heavy metal oxide (HMO) Bi 2 O 3 , using a controlled heat-treatment process guided by differential thermal analysis (DTA). The crystallization behavior was optimized based on DTA results, while X-ray diffraction (XRD) and high-resolution scanning electron microscopy (HRSEM) were used to characterize the crystalline phases and microstructure. XRD analysis confirmed the amorphous nature of the parent glasses. Upon heat treatment at 600 °C, crystallization was initiated with the formation of crystalline SiO 2 in both orthorhombic and tetragonal forms. At higher Bi 2 O 3 concentrations, a monoclinic bismite phase also emerged. Further heating to 650 °C led to the development of the same crystalline phases, but with significantly sharper and more intense diffraction peaks, indicating improved crystallinity. HRSEM imaging revealed hexagonal plate-like crystals in undoped samples, which transformed into petal-shaped morphologies as the Bi 2 O 3 content increased to 10 wt%. Energy-dispersive X-ray (EDX) spectroscopy confirmed the elemental compositions corresponding to the crystalline phases identified by XRD. Photoluminescence measurements showed blue emission at 448 nm in both glass and glass-ceramic samples, attributed to radiative transitions of excited Bi³⁺ ions or defect-related luminescent centers. Microhardness testing indicated a reduction in hardness with increasing Bi 2 O 3 content; however, the glass-ceramics exhibited significantly higher hardness than their amorphous counterparts, due to crystallization during heat treatment. This study demonstrates a sustainable method for recycling solid waste into functional glass-ceramics and highlights their potential applications in structural materials and optoelectronics.