Hot new ceramic composites

CMCs have already been used in demanding high-temperature space applications, and the manufacturing, transport and energy sectors are obvious potential beneficiaries. However, these advanced materials are currently difficult and expensive to produce, requiring long processing times and high energy consumption.

Overcoming these challenges to open the door to new materials technologies is the impetus behind the EU-funded project HELM. Scientists are investigating innovative MW heating technologies to be integrated with standard thermal processing routes in the short-term and eventually replace them in the long-term.

They promise to reduce processing time by 60 % or more and energy consumption by 50–60 % for concurrent reductions in costs. The conventional routes under investigation are chemical vapour infiltration (CVI), liquid silicon infiltration (LSI), graphite expansion (GE), and polymer impregnation and pyrolysis (PIP).

An MW-CVI furnace is being produced entirely of graphite for the first time to avoid contamination of the material produced. Models have facilitated careful characterisation of thermal and electromagnetic behaviour of the furnace regarding its graphite walls, and the pilot-scale furnace is now nearing completion.

Tests on an existing small lab-scale MW-LSI furnace produced very promising results. Liquefaction of silicon occurred in only a few minutes compared to several hours for a conventional industrial furnace. A larger lab-scale system and a pilot-scale system are currently under construction for further testing and optimisation. The MW-GE process was also shown to be very rapid and effective. A pilot-scale furnace is currently under development in collaboration among industrial partners.

Building on success with the MW-CVI furnace chamber that does not utilise quartz, MW heating of the PIP process will be done without a quartz cavity. Simulations facilitated a design capable of achieving a uniform MW field.

HELM scientists are well on their way to delivering novel MW heating technology that will significantly reduce processing time and energy consumption compared to standard thermal processes alone. The processing will facilitate more cost-effective and high-quality CMCs and EG, enabling achievement of new microstructures currently not accessible with conventional technology.