The Effects of the Mn/Zn Ratio on the Thermal Stability of MnO-ZnO-B2O3-SiO2 Glass System

Abstract

The focus of this thesis is a relatively overlooked subset of the MnO-doped zinc borosilicate glass system with a goal of investigating the effects of MnO-doping on the thermal stability of crystallite phase formation in the system. A glass system of general composition 55ZnO-20B2O3-25SiO2 with added MnO dopant, which replaces Zn modifier locations with Mn, of ratios 0, 0.005, 0.01, and 0.015 MnO:ZnO were prepared, via batch melting at 1550°C for 1.5 h. The glasses were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS). Thermal analysis, followed by detailed XRD and Rietveld structural refinement, reveal the formation of zinc borate (Zn4O(BO2)6), willemite (Zn2SiO4), and manganese zinc silicate ((ZnMn)SiO4) crystallites after heat-treatment at 875°C for 4 h and no zinc borate crystallite in samples heated to ≈ 955°C at a ramp rate of 10°C/min and held for 4 h. Microstructure and elemental maps confirmed that the zinc borate had become an integral part of a glass phase in the resulting glass-ceramic samples. Low MnO-content influences the formation of the boron-containing glass phase. When heat-treated at the transition point between two crystalline maxima, 875°C, samples exhibited a variety of structures as glass-ceramics of zinc borate and willemite/(Mn,Zn) silicate crystalline phases regardless of Mn:Zn ratio. Samples heat-treated to the Tm, ≈ 955°C, at a rate of 10°C/min showed nucleation of SiO2 inclusions and willemite / manganese zinc silicate crystallites in a zinc borosilicate glass matrix, with increasing zinc borosilicate Mn:Zn ratio.