Fabrication and Characterization of Borosilicate Glasses Engineered for Enhanced Thermal and Mechanical Performance

A set of glass-ceramics was produced using a ternary mixture of B 2 O 3 , granite-sludge waste, and different amounts of Bi 2 O 3 . The samples were prepared through controlled melting and heat treatment guided by DTA. XRD confirmed that all parent glasses were completely amorphous. Heating at 550 °C triggered the first crystallization stage, forming orthorhombic and tetragonal SiO 2 . At higher Bi 2 O 3 levels, a monoclinic bismite phase also appeared. Increasing the temperature to 600 °C produced the same phases but with sharper and stronger peaks, indicating higher crystallinity. HRSEM images showed hexagonal plates in the undoped sample, while 5 wt% Bi 2 O 3 produced petal-like crystals. EDX verified the elemental composition of the detected phases. Photoluminescence revealed a blue emission at 435 nm, linked to Bi3 3+ centers or defect-related sites. Microhardness decreased with Bi 2 O 3 addition, but the glass-ceramics remained harder than the parent glasses due to crystal formation. These findings demonstrate an effective method for converting granite waste into functional glass-ceramics suitable for structural and optical applications.