Optimizing Micro-Wave CVI: Insights and Models from the CEM-WAVE Project

The CEM-WAVE  explores a microwave-assisted CVI process, emphasizing the importance of a strong thermal gradient for successful infiltration. CNRS-LCTS developed theoretical and numerical models to determine optimal conditions, enhancing process efficiency.

By Gerard L. Vignoles (CNRS - Centre National de la Recherche Scientifique)

The micro-wave CVI process put forward in the CEM-WAVE project is a variation of the Thermal-Gradient CVI, in which the thermal gradient is provided by the imbalance between micro-wave internal heating and surface heat losses by radiation. To ensure correct operation of these processes, the fundamental theoretical question is: how strong a thermal gradient has to be so that infiltration proceeds correctly, ie. from the inside to the outside?

The CNRS-LCTS team has worked out some considerations based on previous experiments of CVI with thermal gradients (in which heating was achieved by RF induction or by contact with a hot resistor, instead of micro-waves). Detailed numerical modeling* has been carried out for all those cases and compared to experimental results. Some cases lead to a correct infiltration, others do not. So, an analytical study has also been worked out, to obtain a general criterion which helps understanding why the process works well or fails to do so, depending on the chosen parameters.
Hence, from this double modeling study, it becomes now possible for an engineer to optimize his process and obtain a successful infiltration. 

The results have been published open access in:

• Hal Science (Open repository): https://hal.science/hal-04133547v1/file/taming_gradients_rev.pdf 
• Zenodo (Open repository) - CEM WAVE Community: https://zenodo.org/records/11538517 
• The Journal of the European Ceramic Society: https://www.sciencedirect.com/science/article/pii/S2666539523000470 

DOI: https://doi.org/10.1016/j.jeurceramsoc.2023.12.095 

Related posts: Numerical modelling ''a multiphysics challenge:  https://www.cem-wave.eu/blog/modelling-chemical-vapor-infiltration-microwave-heating-multi-scale-multi-physics-challenge 

The next papers from CNRS-LCTS will discuss the application of these modeling tools to the precise cases of MW-CVI considered in CEM-WAVE.