Glass-frit size dependence of densification behavior and mechanical properties of zinc aluminum calcium borosilicate glass-ceramics

Glass-ceramic frits of various sizes composed of zinc aluminum calcium borosilicate (CaO-B₂O₃-SiO₂-ZnO-Al₂O₃) were prepared by mechanical milling and subsequent size selection of the glass melt. Glass frits with mean particle sizes of 1.2 ± 0.9 μm, 2.9 ± 2.1 μm, and 4.8 ± 2.3 μm were successfully obtained using a two-step size selection process combined with gravity sedimentation and centrifugation methods. Dilatometry, DTA, XRD, SEM, and high-resolution TEM were utilized to examine densification/crystallization behaviors of the produced materials, while mechanical properties of sintered samples were evaluated using a three-point bending test and micro-indentation method. The obtained results show that densification temperatures of the produced glasses were notably lowered, while bending strength and indentation hardness of the sintered samples increased as the initial frit size decreased to ∼1 μm. The observed enhancement of mechanical properties is attributed to pore reduction, small grain sizes, and formation of nano-sized crystalline phases in the glass matrix.