TOUGHER GLASSES: INCREASING OXIDE GLASSES RESISTANCE TO STRESS CORROSION CRACKING – ToughGlasses

Our motivation during ToughGlasses was to understand how amorphous-amorphous phase separation alters stress corrosion cracking (SCC) properties of SBN glasses. Hence, we selected a homogenous glass sample (SBN12 [SiO2]=59.6 mol%, [B2O3]=23.9 mol%, and [Na2O]=16.5 mol%) and 2 glass compositions (target chemical compositions: (SBN42 [SiO2]=70 mol%, [B2O3]=23 mol%, and [Na2O]=7 mol% and SBN96 [SiO2]=62.9 mol%, [B2O3]=29.6 mol%, and [Na2O]=7.5 mol%) which fall in the theoretical 3 phase zone of amorphous-amorphous phase separation. The samples were fabricated at IPR (Institut de physique de Rennes) in the University of Rennes. Subsequently, IPR annealed the samples to invoke phase separation. Annealing protocols concern fixed temperatures and for a prescribed annealing time. This procedure invoked phase separation in the samples. As the inherent glass structure scales up to alter other properties beyond SCC properties, a holistic viewpoint was taken and glass samples underwent a battery of tests to probe their structural and physical properties. Lastly, glass samples were underwent SCC tests in a well-controlled environment. Additionally, we conducted simulations to capture the thermos-physical properties of the glasses.

Annealing easily generates APS for glasses falling within the immiscibility area. Both, SBN42 and SBN96 ToughGlasses samples concern spinodal decomposition. NMR structural studies indicated the Na+ ions in SBN46 preferentially stay in the B-rich phase. SCC tests via the Deben machine and DCDC samples were performed on SBN12, SBN42 and SBN96 pristine and annealed samples. The experiments on SBN12 aided in testing the experimental setup developed during ToughGlass. Considering the SCC results for SBN42 and SBN96, APS structure significantly influences the SCC behavior. First, the existence of APS leads to the occurrence of two different slopes in Region I. Secondly, the APS sizes promote shifting in SCC curves. The development of 3-D complex APS network enhances the SCC performances.

It is clear the mid-range structure (ring-structure to phase separated structure) play on the SCC properties of SBN glasses. However, sub-micrometer tests to uncover this mid-range structure remain outside the grasp of researchers today. This lack of comprehension on the microstructure brings difficulties in understanding the local interactions between the crack front and the different phases during SCC. Molecular dynamic (MD) simulations can aid in filling this gap. Additionally, studies on APS kinetics are important.

As this project is mainly fundamental, the impact was through academic publications (3 + 3 in preparation) and oral presentations (> 20) at international conferences, workshops, meetings, and seminars. Towards the end of 2023 or early 2024, we will organize a thematic day on the Mechanics of Glasses in Ile-de-France in conjunction with USTV. This will be in preparation for a school in 2025 or 2026. At this school, we will communicate the main results of ToughGlasses and interact with the rest of the glass / physical / mechanical community. We have also organized a session titled “Strength, Fracture, and the Mechanical Properties” during the 26th International Congress on Glass in Berlin in 2022, which is one of the major conferences in the areas of glass.