Nucleation agents in the glass system BaO/SrO/ZnO/SiO2
This work is dedicated to the search for proper nucleation agents for the base glass in the system BaO/SrO/ZnO/SiO2 from which the Ba1-xSrxZn2Si2O7 phase can crystallize in bulk. The Ba1-xSrxZn2Si2O7 phase exhibits close to zero thermal expansion and can be easily crystallized from appropriate glass compositions. Glass ceramics with negative or zero thermal expansion are suitable candidates for numerous applications, such as cook panels, telescope mirrors and optical applications. Unfortunately, the BaO/SrO/ZnO/SiO2 glass system exhibits sole surface crystallization which leads to the formation of cracks during cooling and finally to the destruction of the produced materials. Finding a proper nucleation agent which enables the crystallization in the volume in a high quantity and small crystallite sizes which can be controlled is a key step for the implementation of the new phase for industrial use. This work is focuses on the effect of different nucleation agents and additives to the base glass BaO/SrO/ZnO/SiO2/N (N = ZrO2, TiO2, Pt, Sb2O3) and the resulting microstructures. In this dissertation also the kinetic parameters such as the activation energy, the Avrami parameter and the characteristic temperatures and their accuracy to predict the crystallization tendency of the certain glass systems are reported.