Nano-structured hybrid sheets for electrotechnical high-power insulating applications: The sol-gel route

Among the new insulating materials to be used in high-voltage insulation, hybrid organic/inorganic nanocomposites have received a great attention. Indeed, these materials are gaining in popularity as an effective dielectric insulator with high temperature resistance. This research route is a part of the ANASTASIA consortium, which is made up of a balanced team of academic and industrial partners, and set out to address the wider topic of the reliable production of high performance nanodielectrics. Inorganic micro/nanofillers can be exploited for improving the breakdown strength, the dielectric permittivity and thermal conductivity of polymeric materials, using a sol-gel approach. Literature surveys identified some fillers as potential candidates for insulation applications. These sol-gel techniques show that all the hybrid systems present a structure based on amorphous metal-oxo nanodomains embedded within the polymer network. We further observed a strong influence of the cross-linking metal nature on the size of the metal-oxo nanoparticles and on the extent of the interface between inorganic domains and the polymer phase. Spectroscopic measurements revealed an important nanophase separation for the polymer systems incorporating for example Si(IV), Al(III), Ti(IV), or Zr(IV) alkoxides as cross-linking agents. Preliminary characterization has shown enhanced thermal conductivity and electrical performance for these nanostructured materials, compared with performance of current thermosets. Another advantage brought by this sol-gel technology is the wide choice of fillers and matrix compositions in order to design the mechanical, thermal and dielectric properties of the resulting nanocomposite. This paper will discuss the processes by which inorganic fillers are introduced and how the dielectric and thermal properties are thus improved.