Microstructure-mechanical properties of Ag⁰/Au⁰ doped K-Mg-Al-Si-O-F glass-ceramics

In understanding the catalytic efficacy of silver (Ag⁰) and gold (Au⁰) nanoparticles (NPs) on glass-ceramic (GC) crystallization, the microstructure-machinability correlation of a SiO₂-MgO-Al₂O₃-B₂O₃-K₂O-MgF₂ system is studied. The thermal parameters viz., glass transition temperature (T _g) and crystallization temperature (T _c) were extensively changed by varying NPs (in situ or ex situ). Tc was found to be increased (T _c = 870-875 °C) by 90-110 °C when ex situ NPs were present in the glass system. Under controlled heat-treatment at 950 ± 10 °C, the glasses were converted into glass-ceramics with the predominant presence of crystalline phase (XRD) fluorophlogopite mica, [KMg₃(AlSi₃O₁₀)F₂]. Along with the secondary phase enstatite (MgSiO₃), the presence of Ag and Au particles (FCC system) were identified by XRD. A microstructure containing spherical crystallite precipitates (∼50-400 nm) has been observed through FESEM in in situ doped GCs. An ex situ Ag doped GC matrix composed of rock-like and plate-like crystallites mostly of size 1-3 μm ensured its superior machinability. Vicker's and Knoop microhardness of in situ doped GCs were estimated within the range 4.45-4.61 GPa which is reduced to 4.21-4.34 GPa in the ex situ Ag system. Machinability of GCs was found to be in the order, ex situ Ag > ex situ Au ∼ in situ Ag > in situ Au. Thus, the ex situ Ag/Au doped SiO₂-MgO-Al₂O₃-B₂O₃-K₂O-MgF₂ GC has potential for use as a machinable glass-ceramic.