Effect of V2O5 colorant on the optical properties and crystallization behaviors of lithium disilicate glass-ceramics

Abstract

To understand the coloration in glass-ceramics for dental application, the effect of V2O5 colorant on the optical properties and crystallization behaviors of lithium disilicate (LS2) glass-ceramics (GCs) has been investigated for two different systems of SiO2-Li2O-P2O5-K2O-ZnO and SiO2-Li2O-P2O5-K2O-Al2O3. For this study, the amount of V2O5, SiO2 + Li2O, and P2O5 were fixed to have 0.5, 93.5, and 1.5 mol%, respectively, while the ratios of both ZnO/K2O (Zn/K) and Al2O3/K2O (Al/K) were varied from 0.5 to 2. The GC samples were prepared by two-stage heat treatments of 500 °C for 1 h as a nucleation stage and 600, 700, and 800 °C for 2 h as a growth stage in air. The light green glass samples having only V5+ ion continuously changed to violet, blue, green, and brown for GC samples due to its reduction into V4+ and V3+ ions with progressing crystallization. TEM-EDS analyses revealed that a small amount of V5+ ion was incorporated into both LS2 and SiO2 crystalline phases, causing greenish fluorescence, while most of vanadium ions remained in a residual glassy matrix. At the growth temperature of 800 °C, while the growth rate of LS2 was increased by lowering the viscosity of the glass matrix, and thus the LS2 crystal size of the GVZ1.5 and GVZ3 samples became larger (∼1 μm) compared with its size below 500 nm for the samples without V2O5 colorant. The GVAl1.5 and GVAl3 samples exhibited the smaller size (<1 μm) than GVZ1.5 and GVZ3 samples because of higher nucleation rate and lower growth rate, leading to undesirable high translucency for the dental application.