Size effect on properties of varistors made from zinc oxide nanoparticles through low temperature spark plasma sintering

Conditions for the elaboration of nanostructured varistors by spark plasma sintering (SPS) are investigated, using 8-nm zinc oxide nanoparticles synthesized following an organometallic approach. A binary system constituted of zinc oxide and bismuth oxide nanoparticles is used for this purpose. It is synthesized at roomtemperature in an organic solution through the hydrolysis of dicyclohexylzinc and bismuth acetate precursors. Sintering of this material is performed by SPS at various temperatures and dwell times. The determination of the microstructure and the chemical composition of the as-prepared ceramics are based on scanning electron microscopy and X-ray diffraction analysis. The nonlinear electrical characteristics are evidenced by current–voltage measurements. The breakdown voltage of these nanostructured varistors strongly depends on grain sizes. The results show that nanostructured varistors are obtained by SPS at sintering temperatures ranging from 550 to 600 8C

Hierarchical Growth of ZnO Particles by a Hydrothermal Route

The crystallization of ZnO microrods by hydrothermal treatment of a suspension formed from reaction of zinc acetate and sodium hydroxide has been examined using scanning and transmission electron microscopy. Polycrystalline hexagonal ZnO microrods first appeared after 0.5 h reaction time at 120°C. These early stage rods were composed of stacks of hexagonal layers, each ~50 nm in thickness containing closely aligned assemblies of nanocrystallites <20 nm in size. Further growth of the microrods involved columns of nanoparticles extending from the basal layers of the preformed hexagonal stacks. Re-crystallization produced single-crystal microrods, many of which existed as twin particles

Synthesis of Chitosan-Coated Co_0.5Zn_0.5Fe₂O₄ Nanoparticles for Contrast Enhancement in Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is an imaging technique that is widely used for the identification of internal organs, and for the medical diagnosis of tumors and cancer in the body. In general, gadolinium is used as a contrast agent to enhance image contrasting in MRI. In this study, chitosan-coated Co0.5Zn0.5Fe2O4 nanoparticles were synthesized using a co-precipitation method with a calcination temperature of 500 °C. The nanoparticles were then coated with chitosan and treated under an external magnetic field of 400 mT. X-ray diffractometer results showed that the chitosan-coated Co0.5Zn0.5Fe2O4 nanoparticles had a pure phase of Co0.5Zn0.5Fe2O4 at the (3 1 1) plane, with an average particle size of 26 nm. The presence of chitosan on the Co0.5Zn0.5Fe2O4 nanoparticles was confirmed by Fourier transform infrared spectroscopy, which showed the primary amine and secondary amine functional groups of chitosan. Here, coating the nanoparticle with chitosan not only prevented nanoparticle agglomeration, but also improved the particle surface charge and reduced the particle toxicity for in vivo testing. Vibrating sample magnetometer results showed that the maximum magnetization value of the magnetic field-assisted process was increased to 8.85 emu/g. Finally, chitosan-coated Co0.5Zn0.5Fe2O4 nanoparticles with 400 mT of magnetic field assistance increased the average brightness in MRI of mouse liver by 21% compared to using gadolinium

Fluidized-Bed MOCVD of Bi2O3 Thin Films from Bismuth Triphenyl under Atmospheric Pressure

Bismuth oxide thin films are of great interest due to their significant band gap, high refractive index, and dielectric permittivity, as well as marked photoconductivity and photoluminescence.[1] These properties make Bi2O3 films well suited for many applications such as microelectronics,[2] sensor technology,[3] optical coatings,[4] and ceramic glass manufacturing.[5] In this work, we report the synthesis of Bi2O3 films on alumina particles using fluidized bed (FB) CVD under atmospheric pressure. Bismuth triphenyl (Bi(Ph)3) was used as a metal-organic (MO) CVD precursor