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Phase Separation in soda-lime-silica glasses: From microstructure control to the relationships with optical and mechanical properties

par Przepiora, Kevin
Président du jury Delplancke, Marie-Paule
Promoteur Godet, Stéphane
Publication Non publié, 2024-06-24

Thèse de doctorat

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Résumé :

This thesis aims to investigate the properties of phase-separated glasses from an industrial point of view and establish a connection between the nanoscale heterogeneous glass structures and resulting macroscopic properties. A soda-lime-silica glass (Glass80) was chosen as basis for this study because it is part of the most widely produced family of consumer glasses and occupies a favorable position in the immiscibility dome, intersecting both the binodal and spinodal region.Chapter II provides a detailed investigation of microstructure morphologies at various treatment temperatures and a wide range of treatment times. The results reveal that the distribution of secondary particles within the microstructure is not random. The calculated R-index indicates that particles are arranged at greater distance from each other than expected from a random Poisson distribution. Possible causes for the spatial ordering could be periodic arrangements of the secondary phase during spinodal decomposition or the presence of depletion or diffusion zones around droplets during nucleation and growth. The inhibiting effect of diffusion fields between particles becomes more pronounced as the particle fraction increases. However, we also identified a threshold between 5% and 10% particle fraction, below which this effect lacks the strength to significantly deviate the microstructure from randomness. Despite significant morphological changes during coarsening through both coalescence and Ostwald ripening, the particle ordering remains remarkably constant over time. Building upon the understanding of the microstructure morphologies established in Chapter II, Chapter III investigates the optical properties of phase-separated glasses across a range of microstructure morphologies from fine-scale interconnected to large, dilute droplet structures. The observed light scattering on the heterogeneous nanostructures does not follow common, independent scattering laws. This type of scattering, also known as anomalous scattering, is characterized by a higher transparency and stronger wavelength dependency than predicted by theories for independent scatterers, as well as an increasing backward scattering with larger particle sizes. The likely reason for this anomalous scattering is that particles in phase-separated microstructures do not act as independent scatterers, but rather as dependent ones, leading to constructive interferences between scattered waves. Furthermore, the experiments demonstrate that small-scale microstructures do not significantly impact visible light transmission, which opens up avenues for exploring other physical properties relevant to practical consumer applications.Thus, encouraged by the potential to maintain transparency in phase-separated glasses, the focus in Chapter IV shifts to the mechanical properties and underlying deformation mechanisms. The results demonstrate the significance of microstructure morphology on macroscopic mechanical properties. Interconnected structures exhibit significantly higher indentation fracture toughness and flexural strength compared to their droplet counterparts. However, the difference in indentation fracture toughness between morphologies disappears at higher loads, where all samples converge into the same value. The indentation recovery data indicates that densification contributes the most to the deformation at low loads, but its contribution decreases as the load increases, while shear flow becomes more prominent. Additionally, the Raman spectra reveal that droplet structures have larger deformation zones than interconnected structures under low loads. When combined, these findings suggest that the secondary phase in interconnected structures allows for a higher degree of densification. As a result, the remaining energy that has to be dissipated through shear flow is reduced. Consequently, leading to less residual stresses and a smaller crack opening force. However, when larger loads are applied, shear flow becomes more prominent, rendering the increased densification contribution of interconnected structures insignificant in terms of indentation fracture toughness. Therefore, interconnected microstructures could provide enhanced protection against small gravel impacts on windows or windshields. This is because the compressive stresses caused by the impact can be dissipated to a higher degree through densification, lowering the likelihood of opening cracks of critical size that would result in the catastrophic failure of the glass.In summary, this thesis provides a comprehensive analysis of the processes that govern the microstructure morphologies of phase-separated glasses and establishes a crucial connection between these nanoscale heterogeneities and the resulting macroscopic properties. This connection enables us to exert greater control over desired mechanical and optical properties of these glasses. Moreover, this thesis highlights the fact that although glass has been utilized by human society for thousands of years, many unresolved questions remain in all areas of glass research, ranging from the nano- to the macroscale. Each experimental chapter in this manuscript offers avenues for further research. The identified spatial ordering between the nanoscale particles requires further investigation to determine if it is dependent on chemical composition, phase separation mechanism or purely geometric in nature. This is particularly interesting as it is likely to impact both the anomalous scattering character and mechanical properties of phase-separated glasses. It will be necessary to establish descriptive and, consecutively, predictive models for the dependent scattering of phase-separated glasses in order to refine and supplement the current trial and error approach used to reach desired optical properties in these glasses. Additionally, improving the mechanical properties of materials will always be of great interest. The promising observations for fine-scale interconnected structures that seem to enhance strength and toughness while also maintaining glass transparency warrant further research. Consequently, this not only presents us with the ample opportunity to gain a better understanding of the fundamental mechanisms that govern glasses but also enables us to enhance and innovate existing glass products even further.