Ceramic aerogels of the Si-C-N-O system from pre-ceramic polymer

Research in materials science field is often driven by the necessity to overcome problems in fast, reliable and possibly cost effective ways. Many times the starting point to find a solution is a literature survey, to understand if someone already encountered a similar problem and proposed an answer, or if some authors developed a material that can be used to solve the issue. The work performed within this thesis however fits in another type of approach, i.e. research for the research's sake. In this kind of approach the efforts are not dedicated directly to solve a given, precise and detailed problem, but to invent and develop new types of materials, characterizing them so that other researchers can take benefits from both the synthetic way and the measured properties of the new material produced. In particular, this PhD thesis deals with the combination of two "exotic" class of materials, which are aerogels and polymer derived ceramics. Aerogel is actually a shape, more than a material, from the proper chemical point of view. This kind of shape, anyway, is so peculiar that many of the properties are common to all the aerogels' products, similarly to what happen for other class of materials like conductivity for metals, hardness for ceramics and high specific strength for polymers. These common properties are: low density, high specific surface and predominantly mesoporous microstructure. Polymer derived ceramic (PDC) denotes a family of ceramic materials that can be obtained by a controlled thermolysis of a polymeric precursor. These polymers are usually Si based and contain functional groups that allow to control the final chemistry of the ceramic produced, along with the great advantage that the shape can be set already in the polymeric state. Successfully combining the two techniques, i.e. to produce polymer derived ceramic aerogel, is the core of this thesis. Preference was given to the use of commercially available pre-ceramic polymers so ceramic aerogels belonging to the SiOCN system were produced, starting from polycarbosilane (SMP-10), polysilazane (PSZ-20) and polysiloxane (PMHS). A reliable procedure was set up to produce aerogels with different composition and microstructure, leading to a wide range of properties in terms of density, specific surface, high temperature stability, electrochemical functionality etc., as will be better depicted through the thesis. Additionally, some application of the materials produced were tested, in which the aerogel shape, combined with the proper chemistry, was expected to give interesting results.