Institute of Fundamental Technological Research

The synthesis of magnetically-active nickel-yttrium oxide (Ni-Y2O3) nanocomposite particles is described in this work. The investigated material is produced with a modified ultrasound spray pyrolysis (USP) device which differs from a common USP setup in terms of use of three independently heating zones. They provide a direct feed of H2 to the second reaction zone and allow controlling the formation of the nanocomposite particles and facilitating their post-reaction stabilization with polyvinylpyrrolidone (PVP). According to the morphological and structural studies, the Ni-Y2O3 material takes a form of nanoparticles whose sizes are not homogeneously distributed as well as shapes are not smooth due to the successful formation of composite material with two interpenetrating phases. Moreover, the organic layer is detected on the surface of the nanoparticles which confirms the presence of PVP stabilizer. The magnetic investigations confirm that the Ni-Y2O3 nanocomposite reveals a spin glass-like behavior in which a collective freezing of magnetic moments might occur due to the interparticle interactions between Ni nanocrystallites presented in the sample.

A coupled process of ultrasonic spray pyrolysis and lyophilisation was used for the synthesis of dried gold nanoparticles. Two methods were applied for determining their melting temperature: uniaxial microcompression and differential scanning calorimetry (DSC) analysis. Uniaxial microcompression resulted in sintering of the dried gold nanoparticles at room temperature with an activation energy of 26–32.5 J/g, which made it impossible to evaluate their melting point. Using DSC, the melting point of the dried gold nanoparticles was measured to be around 1064.3°C, which is close to pure gold. The reason for the absence of a melting point depression in dried gold nanoparticles was their exothermic sintering between 712 and 908.1°C.

gold nanoparticles, melting point, ultrasonic spray pyrolysis, characterisation