The addition of inorganic spherical nanoparticles to polymers allows the modification of the polymers physical properties as well as the implementation of new features in the polymer matrix. This review article covers considerations on special features of inorganic nanoparticles, the most important synthesis methods for ceramic nanoparticles and nanocomposites, nanoparticle surface modification, and composite formation, including drawbacks. Classical nanocomposite properties, as thermomechanical, dielectric, conductive, magnetic, as well as optical properties, will be summarized. Finally, typical existing and potential applications will be shown with the focus on new and innovative applications, like in energy storage systems.

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Nanocrystalline maghemite, γ–Fe2O3, can be synthesized in a microwave plasma using FeCl3 or Fe3(CO)12 as the precursor. Electron microscopy revealed particle sizes in the range of 5 to 10 nm. In general, this material is superparamagnetic. The magnetic properties are strongly dependent on the precursor. In both cases the production process leads to a highly disordered material with the consequence of a low magnetization. The assumption of a disordered structure is also supported by electron energy loss (EEL) and Mössbauer spectroscopy. The structure of this material shows a nearly identical number of cations on tetrahedral and octahedral lattice sites.

The microwave plasma process inherently produces nanoparticulate powders with very narrow particle size distribution. During synthesis, the particles carry electric charges of equal sign. Therefore, by electrostatic repulsion, particle growth is reduced and agglomeration thwarted. This is shown by gas kinetic considerations and experimental results. Furthermore, this process allows coating of the particles with organic or inorganic phases, reducing interaction of different particles. This makes it possible to technically exploit properties, characteristic for isolated particles. Additionally, the coating process allows the combination of different properties such as superparamagnetism and luminescence, as it is demonstrated in different examples.

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