Structural cast glass-ceramic components

Abstract

This master's graduation project researches the potential of upcycling waste glass into glass-ceramic components through casting techniques and thermal treatments. To explore its potential and possibilities, the process of crystallization, the material glass-ceramic and influencing parameters are studied at first. A glass-ceramic is a glassy yet crystalline material consisting of inorganic and non-metallic compounds. A glass-ceramic can be produced through different controlled crystallization methods, whereas in this research heat treatment of casted components is applied. Upon heat treatment, crystallization occurs when the right temperatures are applied for the two-steps in crystallization; nucleation and crystal growth. Crystallization may occur spontaneously or along preferential sites, whereas this research makes use of the latter. Many parameters affect the crystallization process, whereas this research only focusses on glass composition, temperature and dwell time. The parameters are set through literature study and trial and error of melting experiments. This research focusses on the crystallization of soda-lime-silica bottle glass, the results of each melting experiment show the effect of the parameters. Each glass from another manufacturing has another glass composition. The amounts of glass formers, modifiers and fluxes are various, resulting in diverse temperature curves and thus diverse melting temperatures and crystallization temperatures. Through the melting experiments are noticeable that the applied melting temperature were of bigger influence than the crystallization temperature. A melting temperature too low resulted in an undesired fused sample, while a too high melting temperature resulted in no or little preferential sites for crystallization to occur. Through the results of the splitting experiment the mechanical characteristics could be observed, which are fracture toughness and fracture behaviour in this research. The fracture toughness seems better of samples with a higher quality crystal polymorph or with a higher amount of crystallinity or high amounts of glassy phases, whereby the material acts as one material upon loading rather than as a composite. While for samples with little and unconnected crystallization it does not seem to benefit its fracture toughness. The fracture propagation through glassy and crystalline phases is very different. A fracture propagation through a glassy phase is conchoidal, while the fracture propagation in the crystalline phase follows the crystalline structure, reaching its extremities or can be conchoidal, depending on the crystal polymorph. Observable from the fracture propagation from glassy to crystalline and from crystalline back to glassy is the discontinuity. The crystal or crystalline surface acts like an obstacle once the failure propagation reaches from the glassy phase. The failure does propagate but once it continues over to the glassy phase again, a change in energy and direction is noticeable. All by all, there do is potential in upcycling waste glass into structural cast glass-ceramic components. Crystallization does influence the fracture toughness and fracture behaviour in a cast glass-ceramic component, but the effect is highly dependent on the amount and distribution of glassy and crystalline phases.