How to protect rocket nozzles from erosion? AGH University scientists want to use CFRC

Technology for the few

The history of developing carbon-carbon composites began in the 1960s and is related to the American Apollo programme, which took humans to the Moon. In the following years, they were used to make the casing for nose cones or wings of space shuttles. During the same time, the military carried out projects related to CFRC materials. Similarly to so many other technologies originally meant for space programmes and military applications, C/C composites had made it to the civilian market. Since then, they have been used to produce brake discs for planes, high-speed trains, and Formula 1 bolides. They are also widely used in the sports, medical, chemical, and metallurgical industries.

Unfortunately, the abundance of applications for C/C composites does not go hand in hand with their availability on the market. The manufacturing methods of CFRC materials is a secret held by only a few European, American, and Asian companies, and the demand still cannot keep up with the supply. ‘The carbon-carbon production technology is a multiphase and energy-consuming process. Their production falls under the scope of large companies that already have their clients. They are much more difficult to get for smaller companies, including those on the Polish market’, says Dr Eng. Maciej Gubernat from the Faculty of Materials Science and Ceramics.

Therefore, Polish companies in the space and arms sectors that want to use CFRC materials in their projects can suffer from this lack of availability. Soon, it can all take a turn due to the work carried out at the aforementioned faculty by the team led by Dr Gubernat, who took it upon himself to develop a competitive technology to produce C/C composites, and then to use them to manufacture a rocket nozzle.

A monolith or a hybrid?

The scientist explains that creating such an element is possible in the form of a monolith or a hybrid. In the latter case, the throat is equipped with a disc made of a material that is the most erosion-resistant, while the walls are made from a less durable material. ‘If we made a nozzle from two different materials that are characterised by different thermal expansion parameters, we would run the risk of weakening the connection point. We would like our nozzle to be made of a single material to eliminate this problem. To achieve this, we plan to lay our carbon fibres in such a way as to protect the matrix from stress, which would lead to its degradation’, declares the AGH University employee.

The nozzle will be tested in rocket engines developed by the SpaceForest company from Gdynia, Poland – the main partner of the project. SpaceForest is the producer of the Perun suborbital rocket, designed for microgravity investigations, which will reach an altitude of 150 kilometres and carry a payload of 50 kilogrammes. The company wants to use the results of this project in its future rocket engine constructions and the thrust vector control (TVC) systems they are developing.

A recipe for Polish CFRC

As part of previously conducted experiments at the faculty laboratories, the scientists managed to create prototype CFRC 2D materials that are very similar, in terms of the parameters, to their selected commercial counterparts. Now, our scientists want to use their experience to produce a material with a more complex architecture, the parameters of which will correspond to the goals of the project. They intend to examine the possibility of forming the composites using various techniques to create the reinforcement – by creating multidirectional preforms from spooled carbon-fibre-reinforced rods, as well as by using multifarious carbon-phase precursors and methods of imbuing the composites with additional substances.

Among other things, they will test the chemical vapour infiltration method (CVI), where the matrix precursor is a carboniferous gas that settles on the preform and, after being subjected to pyrolysis, creates a matrix with a density and microstructure that should yield the expected erosion-resistance. ‘We place our hopes in this method not only to be good quality but also competitive economically compared to the other methods’, says the project leader.

The scientists also intend to add a ceramic layer to their composites, containing silicon compounds and pyrocarbons, to increase their resistance to oxidation and erosion in high-temperature environments.

The work of Professor Chłopek and Professor Błażewicz

Research projects into carbon-carbon composites carried out currently at the Faculty of Materials Science and Ceramics expand the intellectual capital accumulated by the previous generation of scientists. ‘At our faculty, projects concerning implants made of carbon-carbon composites have been implemented since the 1990s. What they studied then was the possibility of adjusting the mechanical properties of the materials to the bone, which would allow them to eliminate the problem of excessive post-implantation stress. For more than ten years, Professor Jan Chłopek and Professor Stanisław Błażewicz have been quite successfully dealing with the issue; the latter was the supervisor of my doctoral dissertation and authored several hundred publications and about 60 patents in the field of synthetic carbon materials’, explains Dr Gubernat.

The scientist is convinced that there is still potential to develop this technology. ‘Within this project, we plan to purchase new equipment that will allow us to manufacture and modify a new generation of such materials. We have many ideas, for instance, in the field of nanoadditive modification. As little as a dozen or so years ago, this would not have been possible’.

The project received funding from the National Centre for Research and Development within the 13^th edition of the LIDER programme.