In the recent years, great interest has been devoted to the unique properties of nanofluids. The dispersion process and the nanoparticle suspension stability have been found to be critical points in the development of these new fluids. For this reason, an experimental study on the stability of water-based dispersions containing different nanoparticles, i.e. single wall carbon nanohorns (SWCNHs), titanium dioxide (TiO₂) and copper oxide (CuO), has been developed in this study. The aim of this study is to provide stable nanofluids for selecting suitable fluids with enhanced thermal characteristics. Different dispersion techniques were considered in this study, including sonication, ball milling and high-pressure homogenization. Both the dispersion process and the use of some dispersants were investigated as a function of the nanoparticle concentration. The high-pressure homogenization was found to be the best method, and the addition of n-dodecyl sulphate and polyethylene glycol as dispersants, respectively in SWCNHs-water and TiO₂-water nanofluids, improved the nanofluid stability.

The optimization of the poor heat transfer characteristics of fluids conventionally employed in solar devices are at present one of the main topics for system efficiency and compactness. In the present work we investigated the optical and thermal properties of nanofluids consisting in aqueous suspensions of single wall carbon nanohorns. The characteristics of these nanofluids were evaluated in view of their use as sunlight absorber fluids in a solar device. The observed nanoparticle-induced differences in optical properties appeared promising, leading to a considerably higher sunlight absorption. We found that the thermal conductivity of the nanofluids was higher than pure water. Both these effects, together with the possible chemical functionalization of carbon nanohorns, make this new kind of nanofluids very interesting for increasing the overall efficiency of the sunlight exploiting device.

High-temperature proton conductors are promising as electrolytes for intermediate-temperature solid oxide fuel cells. Among them, BaCeO₃-based materials have high proton conductivity but rather poor chemical stability. In contrast, barium zirconates are rather stable, but have poorly reproducible densities and conductivities. In this study, the investigation of BaCe_1−x−yZr_xY_yO_3−δ solid solutions (x = 0, 0.10, 0.20, 0.30, 0.40; y = 0.15, 0.20) was undertaken, with the final aim of finding a composition having both high conductivity and good stability. The influence of the modified sol–gel Pechini synthetic approach on the powder morphology, and of a barium excess on the densification were demonstrated. Single-phase perovskite powders were prepared and high density pellets were obtained at temperatures lower than those commonly employed. Stability tests demonstrated that the Zr introduction into doped barium cerate greatly enhanced the chemical stability, particularly for Zr ≥ 20%. The proton conductivities, measured in a humidified H₂/Ar atmosphere by impedance spectroscopy, were only slightly influenced by the Zr amount. Overall, BaCe_1−x−yZr_xY_yO_3−δ solid solutions having Zr ≈ 20–40% and Y ≈ 15–20% showed good chemical stability and high conductivity.