Development and Characterization of a Novel Graphite-matrix Composite Material for Thermal Management Applications

The present Master Thesis has been carried out at CERN, the European Organization for Nuclear Research. CERN is located in Geneva (Switzerland), but some facilities cross the Swiss-French border. At CERN the deepest structure and physics of matter are studied with the aid of high energy particle beams. The beam energy of the world biggest particle accelerator “Large Hadron Collider” (LHC) at CERN is equivalent to that needed for melting one ton of copper in few µs and it is concentrated in a diameter of less than 2mm. Beam control and protection devices, in particular collimators, are required for using these high energy particle beams, and their materials have to withstand one of the hardest man-made environments. This calls for the development of novel advanced materials, as no existing combination of physical, thermal, electrical and mechanical properties withstands the collimators extreme working conditions. Diamond and graphite based composites are the main material families investigated for this application. The research program which is being carried out on these materials at CERN with collaborating partners is mainly focused on the theoretical investigation, manufacturing process, material characterisation and material validation. Besides “High Energy Physics”, these materials are of particular interest for demanding thermal management applications such as high power density electronic packaging, avionics and aerospace systems, nuclear power plants, microwave and radio-frequency devices, turbine engine components, or advanced automotive and aeronautical braking systems. The interest that CERN has to transfer the internally developed knowledge towards society accounts for the motivation of this Master Thesis. The achievements from the materials for “Beam Intercepting Devices” at CERN, led to this Master Thesis research with the aim of designing an outstanding material in thermal management applications and economically viable in the external market. Several graphite-matrix composite materials, which were being developed for collimators, were used as a starting point for this research. They have been used as a reference all along this work. Amongst these composite materials one could also find some made of boron compounds, but those were discarded from the start as boron forms a substitutional solution in graphite which significantly degrades its original thermal and electrical properties. During the course of this Master Thesis, a detailed study of catalytic graphitization was performed. This enabled the selection of the most appropriate compound which would then lead to the formation of a highly oriented and well connected graphite matrix. The survey concluded that nickel was the most appropriate element mainly due to its ability to dissolve, diffuse and precipitate carbon in molten state. Once the composite, named Nickel-Graphite (NiGr), was chosen, its composition and processing were designed. This was followed by its thermo-mechanical, electrical and micro-structural characterization. Finally, two different grades were tested, and one of them showed properties which are very useful for many thermal management applications.