Production and characterization of ZnO-Al₂O₃-SiO₂ based glass ceramics

In the present study, it was aimed to produce ZnO-Al₂O₃-SiO₂ (ZAS) based transparent glass ceramics using nucleating agents and to investigate the structural and transparent properties of the obtained ZAS based glass ceramics. TiO₂ and ZrO₂ were used as nucleating agents in the study. In addition, transparent ZAS glassceramics, which are high-tech ceramics, are of great importance as optical glassceramics. In this study, a composition was prepared from ZnO, Al₂O₃, SiO₂, B₂O₃, PbO and TiO₂, ZrO₂ powders as nucleating agents in order to produce ZAS based transparent glass-ceramic. While preparing these compositions, composition ratios of ZnO-Al₂O₃-SiO₂ (ZAS) ternary equilibrium diagram were taken into consideration. In the system called ZAS-A, B, C and D, ZAS-A has 36% ZnO, 12% Al₂O₃, 47% SiO₂, 5 %B₂O₃ by weight. 34% ZnO, 11.5% Al₂O₃, 44.5 %SiO₂, 5 %B₂O₃ and nucleating 2.5% TiO₂, 2.5% ZrO₂ were prepared for ZAS-B. ZAS-C contains 36% ZnO, 12% Al₂O₃, 47% SiO₂, 5% PbO by weight, while ZAS-D contains 34% ZnO, 11.5% Al₂O₃, 44.5% SiO₂, 5% PbO and nucleating 2.5% TiO₂, 2.5% ZrO₂. Homogeneous ZAS compositions melted in the electric lift furnace at 1450ºC for 2 hours were poured into a graphite mold and subjected to stress relieving annealing at 600ºC for 1 hour in the annealing furnace to remove thermal stresses. Glass crushing and grinding processes are carried out and the powders obtained after the annealing process; XRD, DTA (10-15-20 ° C / min speed) and kinetic analyzes were performed. Using the DTA analysis, the samples were heat treated at 900 ºC and 950 ºC for ZAS-A and 950 ºC, for ZAS-C at 950 ºC and 1000 ºC, and for ZAS-D at 850 ºC, 900ºC ve and 950 ºC for 4 hours. ZAS coded glass-ceramics produced in XRD analyzes were determined to consist of willemite, gahnit and quartz phases. They were subjected to sintering process at three different temperatures and times (800ºC, 850ºC and 900 ºC for 1, 3 and 5 hours) and their SEM analysis was performed. In kinetic studies, crystallization and viscous flow activation energies for ZAS-coded glasses were 311.775 kJ/mol and 365.816 kJ/mol for ZAS-A, 267.143 kJ/mol and 277.133 kJ/mol for ZAS-B, 271.457 kJ/mol and 290.990 kJ/mol, for ZAS-C 239.758 kJ/mol and 266,745 kJ/mol for ZAS-D. The hardness values measured for ZAS coded glass-ceramics vary between 515-934 HV0.05 values depending on the sintering