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Sujet de stage / Master 2 Internship

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Stress corrosion behavior of mesostructured glass by phase separation

Contact: Rountree Cindy, , cindy.rountree@cea.fr, +33 1 69 08 26 55
Summary:
The objective of this internship is to examine stress corrosion cracking in several different demixed glassy ceramics. Several glass compositions with such a phase separation will be studied. The rate of crack propagation and its variation with applied stress will be measured for each sample to obtain the characteristic stress corrosion resistance curves. Additionally, a post-mortem characterization of the fracture surface of the samples will be carried out by near-field microscopy (AFM, ...) and analyzed with different statistical tools (stochastic modeling, fractal analysis).
Possibility of continuation in PhD: Oui
Deadline for application:29/03/2023

Full description:
Glass is a widely used material due to its many advantagious properties: transparency, hardness, low thermal expansion, high melting point temperature, relative chemical inertia, etc. However, it has one major weakness: its fragility. Relatively moderate stresses can cause it to break suddenly and without any warning. Glass is also sensitive to stress corrosion cracking: sub-crtical cracking aided by environmental conditions (relative humidity, temperature, etc.). In this case, apparently harmless stresses (much lower than those leading to its sudden breakage) can lead to crack propagation at low rates, as observed in the slow cracking of car windscreens. This stress corrosion cracking (SCC) also depends on the intrinsic parameters of the glass: chemical composition, microstructure, etc.

The phenomenon of phase separation in glasses leads to a meso-structured material which can improve mechanical properties such as crush resistance1. It is also at the origin of glass-ceramics, consisting of microcrystals dispersed in a glass matrix, developed to take advantage of the benefits of both components: ceramics and glasses. They are used, for example in optical thermometry applications, kitchen utensils, dental materials, etc. However, the stress corrosion behaviour of this type of material is still poorly understood.

The objective of this internship is to examine stress corrosion cracking in several different glassy ceramics. Samples will concern as fabricated samples and their phased separated counterparts which will be achieved by varying annealing protocols. The candidate will make use of an existing SCC experimental set-up (Figure 1 top). The rate of crack propagation and its variation with applied stress will be measured for each sample to obtain the characteristic stress corrosion resistance curves. Additionally, the candidate will have the opportunity to use a state-of-the-art Atomic Force Microscope (AFM) to characterize post-mortem fracture surfaces. These studies will aid in characterising the size of phase separation and will feed different statistical tools (stochastic modeling, fractal analysis).
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