Monica Fabrizio

Sol–gel synthesis and characterisation of ZnO-based nanosystems

Semiconductor nanoclusters embedded in thin coatings of transparent and homogeneous silica glasses are suitable materials for the development of optical devices. The optical properties of such systems are strongly dependent on the elemental composition and the morphology of the coatings as well as on the nanocluster size distribution, their mutual interactions and the interactions with the host matrix. To achieve a good control over film composition and morphology the sol–gel route was used. The sol–gel synthesis of ZnO nanocrystals embedded in silica has been faced by the study of the gel-derived binary system ZnO–SiO2. The dip-coating procedure from alcoholic solutions containing tetraethoxysilane [Si(OC2H5)4, TEOS] and zinc acetate [Zn(CH3COO)2] was adopted. Zinc oxide nanograins have been generated in silica by hydrolysis of TEOS and the zinc salt and subsequent thermal annealing of the coatings. The system evolution under thermal treatment was studied by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, UV-Vis absorption spectroscopy and secondary-ion mass spectrometry.

High conductivity and chemical stability of BaCe1−x−yZrxYyO3−δ proton conductors prepared by a sol–gel method

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 BaCe1−x−yZrxYyO3−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, BaCe1−x−yZrxYyO3−δ solid solutions having Zr ≈ 20–40% and Y ≈ 15–20% showed good chemical stability and high conductivity.

Electrocatalytic oxidation of hydrazine in acid media on polyaniline-filmed vitreous carbon

0.5 M hydrazine in aqueous H2SO4 for pHs in the range 1.5–3.75 catalytically oxidizes on polyaniline-filmed vitreous carbon, whereas the process is totally inhibited on the bare electrode substrate. The pH dependence of the reducing power of hydrazine accounts for the onset potential of the oxidation, while the currents are under pure kinetic control. A kinetic analysis of the “chemical” reduction of the emeraldine by hydrazine indicates that its rate characterizes the currents. Catalytic oxidation is faster in aprotic medium but the currents are transient owing to progressive deactivation of the polymer electrode.

Exceptional hydrogen permeation of all-ceramic composite robust membranes based on BaCe0.65Zr0.20Y0.15O3−δ and Y- or Gd-doped ceria

Mixed proton and electron conductor ceramic composites were examined as hydrogen separation membranes at moderate temperatures (higher than 500 °C). In particular, dense ceramic composites of BaCe0.65Zr0.20Y0.15O3−δ (BCZ20Y15) and Ce0.85M0.15O2−δ (M = Y and Gd, hereafter referred to as YDC15 and GDC15), as protonic and electronic conducting phases respectively, were successfully prepared and tested as hydrogen separation membranes. The mixture of these oxides improved both chemical and mechanical stability and increased the electronic conductivity in dual-phase ceramic membranes. The synthetic method and sintering conditions were optimized to obtain dense and crack free symmetric membranes. The addition of ZnO as a sintering aid allowed achieving robust and dense composites with homogeneous grain distribution. The chemical compatibility between the precursors and the influence of membrane composition on electrical properties and H2 permeability performances were thoroughly investigated. The highest permeation flux was attained for the 50 : 50 volume ratio BCZ20Y15–GDC15 membrane when the feed and the sweep sides of the membrane were hydrated, reaching values of 0.27 mL min−1 cm−2 at 755 °C on a 0.65 mm thick membrane sample, currently one of the highest H2 fluxes obtained for bulk mixed protonic–electronic membranes. Increasing the temperature to 1040 °C, increased the hydrogen flux up to 2.40 mL min−1 cm−2 when only the sweep side was hydrated. The H2 separation process is attributed to two cooperative mechanisms, i.e. proton transport through the membrane and H2 production via the water splitting reaction coupled with oxygen ion transport. Moreover, these composite systems demonstrated a very good chemical stability under a CO2-rich atmosphere such as catalytic reactors for hydrogen generation.

Sol–gel synthesis and characterization of Ag2S nanocrystallites in silica thin film glasses

Silver sulfide particles embedded in thin coatings of transparent and homogeneous silica glass are promising materials for the development of optical devices. The optical properties are strongly dependent on the elemental composition and morphology of the coatings as well as on the size distribution of the nanoclusters. A sol–gel route has been used to achieve good control over film composition and morphology. The dip-coating procedure from alcoholic solutions containing tetraethoxysilane [Si(OEt)4] and silver diethylthiourea complexes [Ag(EtNHCSNHEt)n]+ has been adopted. The silver sulfide particles were directly generated in silica by decomposition of the silver complexes upon heating the coatings. Annealing was performed in a nitrogen atmosphere in order to prevent sulfide oxidation to sulfate. The sol–gel method has been shown to be a suitable procedure for controlling the size of the metal sulfide particles. Evolution of the system under heating has been studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS) and atomic force microscopy (AFM).

The Synthesis and Effect of Copper Nanoparticles on the Tribological Properties of Lubricant Oils

Cu nanoparticles (NPs) are widely studied to understand how they work in lubricant oils to improve its tribological properties. This paper describes the synthesis and characterization of Cu NPs of different size (φ = 60 and 130 nm) carried out in EG and the dispersion procedure used to prepare nanolubricants containing different amounts of NPs (0.005 vol% -0.01 vol% -0.02 vol%). The base oil was a commercially available lubricant oil for internal combustion engines. In order to study the influence of different parameters such as particles size and concentration on tribological properties of nanolubricants, the Stribeck curves were recorded at 25°C in the three lubrication regions (elasto-hydrodynamic, mixed lubrication, and boundary lubrication) and the results discussed. It was found that Cu NPs with a 130-nm mean diameter were more effective in reducing the coefficient of friction in all the lubrication regimes with respect to smaller ones.

Nanocrystalline Pt thin films obtained via metal organic chemical vapor deposition on quartz and CaF2 substrates: an investigation of their chemico-physical properties

Abstract Nanocrystalline platinum thin films were deposited on quartz and CaF2 substrates using platinum(II)acetylacetonate as a precursor. The depositions were carried out at 420 °C in N2+O2, N2+O2+H2O and N2+H2 atmospheres in order to examine the effect of synthesis conditions on the chemico-physical properties of the layers. Their microstructure, chemical composition and morphology were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and atomic force microscopy. The obtained results revealed the formation of metallic platinum thin films with no preferential orientation. The presence of C and O contamination, as indicated by XPS and SIMS analyses, is discussed in terms of the precursor decomposition pathway.

Molecularly interconnected SiO2–GeO2 thin films: sol–gel synthesis and characterization

SiO2–GeO2 films have been synthesized by the sol–gel method starting from an ethanolic solution of Si(OC2H5)4 and Ge(OCH3)4. The coatings have been annealed in air at temperatures ranging between 300 °C and 900 °C. The compositional and microstructural evolution of the samples under thermal annealing has been investigated by X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), Secondary-Ion Mass Spectrometry (SIMS) and Atomic Force Microscopy (AFM). Pure and molecularly homogeneous films have been obtained after 300 °C thermal treatment. An amorphous network of interconnected SiO4 and GeO4 tetrahedra has been observed up to 700 °C. At higher treatment temperatures the formation of crystalline silica in the cristobalite phase has been detected.

Surface and bulk effects in the extraction of hydrogen from highly loaded Pd sheet electrodes

Abstract It has been shown that hydrogen extraction from highly loaded Pd sheet electrodes takes place under the mixed control of hydrogen diffusion within the solid and kinetic steps at the boundaries. Analysis of the transients of the potentiostatic extraction currents revealed the relevant kinetic and diffusion parameters. The kinetic parameter, which is probably related to the transition H abs → H abs , thus depends on both the history of the Pd sample electrode and the electrolytic environment, whereas the diffusion parameter may depend on the degree of hydrogen loading in the metal.

Surface chemistry of RuO2/IrO2/TiO2 mixed-oxide electrodes: secondary ion mass spectrometric study of the changes induced by electrochemical treatment

The IrO(2)/RuO(2)/TiO(2) ternary system is well known for its electrocatalytic activity towards oxygen- and chlorine-evolution reactions. Electrochemical processing induces noticeable chemical and morphological modifications on these electrodes, depending on the noble metal oxide content. In this work, cathodic/anodic polarization and the oxygen-evolution reaction were studied in order to evaluate the electrocatalytic activity at various noble metal oxide percentages. The best performing electrode (30 mol% noble metal oxides) was analyzed before and after electrochemical tests by means of secondary ion mass spectrometry (SIMS) in order to determine the chemical composition modification which occurred on the surface and in deeper regions of the mixed-oxide film.