Investigation of electrical and magnetic properties of nanoparticles and nanofibers with the aim to tailor material properties of nanocomposites

Licentiatavhandling, 2008

Nanocomposites are the subject of interest in this study which can be explained by the factum that using building blocks with dimensions in the nanosize range makes it possible to design and create new materials which can satisfy several functions at the same time for many applications. The applications of interest in this study belong to the microwave frequency region and for that reason a number of materials were investigated to define their microwave absorbing properties. The aim is to tailor material properties of nanocomposites by using fillers with different electromagnetic properties. Two types of filler were investigated during the study: fillers with electrical- and magnetic-field losses. Among fillers with electrical-field losses SiC nanowires were investigated together with SiC microcrystalline particles. The results presented in this study show that fillers in form of particles and fibers of nanometer size introduce higher level of energy loss in comparison with micrometer sized particles and fibers. It has also been found that in the case of SiC nanowires the higher carbon content introduces higher level of electrical-field losses. Among fillers with magnetic-field losses manganese-ferrite (soft) and cobalt-ferrite (hard) nanoparticles were investigated. The results show that soft and hard magnetic ferrites have absorbing properties in different frequency regions. Thus, manganese- and cobalt-ferrite nanoparticles can be used together to achieve absorption in a wide frequency band. To achieve higher magnetic-field losses in the composite, the nanoparticles with higher initial permeability and lower coercivity are preferable as filler. To connect microwave properties of nanoparticles/nanofibers and nanocomposites to their microstructure two types of materials characterization were always performed: microstructural characterization by applying optical and electron microscopy and characterization in microwave region using an Automatic Network Analyzer (ANA).