Preparation and characterisation of joints with preceramic polymers with the aim of energy efficiency and savings

The energy sector is responsible for a significant amount of pollutant emissions associated with the entire production-to-consumption chain, so the need for efficiency measures to reduce production costs, energy use and consumption, and pollutant emissions is of primary interest. Obviously, this would not be possible without continuous developments and improvements in the materials field. The strong synergy between these two sectors, focused on innovation, is the key to this thesis. This thesis work develops a preliminary technical feasibility project for the joining of ceramic materials by means of polymer-derived ceramics (PDCs). In particular, ceramics are of great interest because of their exceptional properties of mechanical, thermal and chemical stability, corrosion resistance and environmental inertness, but high production costs and energy expenditure, combined with the complexity of obtaining large assemblies of complex shapes, limit the field and effective applications. Joints and preceramic polymers fit into this picture as solutions to these problems. The starting point is the current state-of-the-art: once the parameters useful for the realisation of the processes had been identified, it was possible to proceed with the experimental tests. The parallel realisation of a coating and a joint made it possible to understand the real behaviour of the precursor. Analyses such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterise the components obtained. Then, tensile mechanical tests were realised to measure the strength of the joints. Three different preceramic polymers were used, including two silica precursors, one organic and one inorganic, and a silicon carbide precursor, and three different substrates, including a metallic one with a ceramic coating (alumina-coated aluminium substrate), a composite one (CMC of alumina-zirconia matrix reinforced with alumina fibers), and a ceramic one (monolithic SiC). Most of the work has focused on the organic silica precursor, with an initial study carried out on Al-Al2O3 substrates, firstly with the polymer alone and then with the polymer filled with silica nanoparticles. As this type of substrate could not be heated to high temperatures, the curing behaviour of the polymer was investigated. The addition of fillers improved the results already obtained for the polymer in all respects. Therefore, it was possible to extend the study to CMC substrates after they had undergone a surface modification with plasma to improve the adhesion between the filled polymer and the substrates. This treatment made it possible to obtain a joint and to study the pyrolysis step in which the conversion from polymer-to-ceramic takes place. The junction plane was then analysed by CT-scan. On the other hand, the inorganic silica precursor was used to carry out a single preliminary test, leaving the possibility to evaluate its behaviour in the future. Similarly, the work involving silicon carbide was an early stage investigation of the precursor behaviour and the adhesion on the specific substrate, with the aim of being able to realise nuclear grade 'total-SiC' junctions.