Description du sujet de thèse

This PhD. thesis focuses on understanding and optimizing the thermochemical and thermomechanical behavior under high-temperature ablative conditions under an oxidizing atmosphere of based on SiO2, Si3N4 or Si2N2O ceramics with and without additives. The studied materials may be commercial or produced by sintering. This work will be based on a coupling between experimental and theoretical studies, in particular through plasma torch tests and thermodynamic calculations. The aims of this thesis are:
- the development of Si-N-O matrices with and without additives
- high temperature tests in oxidative/ablative conditions
- understanding the ablation mechanisms as a function of the composition of the matrix
Work program
- Development of matrices by sintering
- Thermal tests, in particular resistance under high flux
- Physicochemical characterizations before and after tests
- Thermodynamic and kinetic studies
Techniques implemented:
- Preparation and characterization of powder mixtures with sintering additives
- SPS and HIP sintering
- Plasma torch tests
- Optical and electronic microscopies, Raman, XRD, EPMA, XPS…
- Thermomechanical tests (CTE, TMA, diffusivity)
- Thermodynamic calculations (ThermoCalc)

Contexte de travail

Ceramic matrix composites with silicon oxide, nitride or oxynitride reinforcements and matrices are prime candidates for certain high-temperature aeronautics and aerospace applications due to their low thermal conductivity, high thermal resistance, and high temperature mechanical strength. Oxide (SiO2), nitride (Si3N4), or oxynitride (Si2N2O) matrices therefore appear to be attractive candidates for use at high temperatures (1500°C) in an oxidizing atmosphere and under thermal fluxes for short periods. The development and optimization of a new generation of Si-N-O matrices, which perform better than traditional aluminosilicate-based matrices, requires extensive work. In particular, this involves understanding the influence of the nature of the phases constituting the matrix and its additives on the performance under ablative conditions, to be employed as thermal protection for space vehicles.

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