G. Prodan

Direct production of a novel iron-based nanocomposite from the laser pyrolysis of Fe(CO) 5 /MMA mixtures: structural and sensing properties

Iron/iron oxide-based nanocomposites were prepared by IR laser sensitized pyrolysis of Fe(CO)5 andmethylmethacrylate (MMA) mixtures. The morphology of nanopowder analyzed by TEM indicated that mainly core-shell structures were obtained. X-ray diffraction techniques evidence the cores as formedmainly by iron/iron oxide crystalline phases. A partially degraded (carbonized) polymeric matrix is suggested for the coverage of the metallic particles. The nanocomposite structure at the variation of the laser density and of the MMA flow was studied. The new materials prepared as thick films were tested for their potential for acting as gas sensors. The temporal variation of the electrical resistance in presence of NO2, CO, and CO2, in dry and humid air was recorded. Preliminary results show that the samples obtained at higher laser power density exhibit rather high sensitivity towards NO2 detection and NO2 selectivity relatively to CO and CO2. An optimum working temperature of 200°C was found.

Biocompatibility and bioactivity enhancement of Ce stabilized ZrO2 doped HA coatings by controlled porosity change of Al2O3 substrates

Al(2) O(3) substrates with controlled porosity were manufactured from nanosized powders obtained by plasma processing. It was observed that when increasing the sintering temperature the overall porosity was decreasing, but the pores got larger. In a second step, Ce stabilized ZrO(2) doped hydroxyapatite coatings were pulsed laser deposited onto the Al(2) O(3) substrates. It was shown that the surface morphology, consisting of aggregates and particulates in micrometric range, was altered by the substrate porosity and interface properties, respectively. TEM studies evidenced that Ce stabilized ZrO(2) doped HA particulates ranged from 10 to 50 nm, strongly depending on the Al(2) O(3) porosity. The coatings consisted of HA nanocrystals embedded in an amorphous matrix quite similar to the bone structure. These findings were congruent with the increased biocompatibility and bioactivity of these layers confirmed by enhanced growing and proliferation of human mesenchymal stem cells.

Evaluation of Mean Diameter values using Scherrer Equation Applied to Electron Diffraction Images

The aim of this work is to determine mean diameter of poly- crystalline samples using the Scherrer equation. These calculations represent a direct connection between the mean diameter, crystal structure and morphology by applying the Bragg angle and shape factor. Two samples are investigated, first a nano-sized particles of MgO and second a CVD (chemical vacuum deposition) obtained polycrystalline aluminum film. First, the shape factor and mean diameter are evaluated using direct measurement of particle morphology from BF-TEM (bright field - transmission electron microscopy) images. The value of mean diameter is determined by assuming a lognormal distribution. Second, the mean diameter values are evaluated using the Scherrer equation applied to SAED (selected area electron diffraction) images. We obtained for MgO nano-sized a mean diameter about 48 nm from the direct measurement, and 70 nm respectively using the Scherrer equation, and for Al film 77 nm and 70 nm, respectively.

Photochemistry Aspects of the Laser Pyrolysis Addressing the Preparation of Oxide Semiconductor Photocatalysts

The laser pyrolysis is a powerful and a versatile tool for the gas-phase synthesis of nanoparticles. In this paper, some fundamental and applicative characteristics of this technique are outlined and recent results obtained in the preparation of gamma iron oxide () and titania () semiconductor nanostructures are illustrated. Nanosized iron oxide particles (4 to 9 nm diameter values) have been directly synthesized by the laser-induced pyrolysis of a mixture containing iron pentacarbonyl/air (as oxidizer)/ethylene (as sensitizer). Temperature-dependent Mossbauer spectroscopy shows that mainly maghemite is present in the sample obtained at higher laser power. The use of selected samples for the preparation of water-dispersed magnetic nanofluids is also discussed. nanoparticles comprising a mixture of anatase and rutile phases were synthesized via the laser pyrolysis of - (vapors) based gas-phase mixtures. High precursor concentration of the oxidizer was found to favor the prevalent anatase phase (about 90%) in the titania nanopowders.

Silicon carbide multilayer protective coating on carbon obtained by thermionic vacuum arc method

Abstract. Thermionic vacuum arc (TVA) method is currently developing, in particular, to work easily with heavy fusible material for the advantage presented by control of directing energy for the elements forming a plasma. The category of heavy fusible material can recall C and W (high-melting point materials), and are difficult to obtain or to control by other means. Carbon is now used in many areas of special mechanical, thermal, and electrical properties. We refer in particular to high-temperature applications where unwanted effects may occur due to oxidation. Changed properties may lead to improper functioning of the item or device. For example, increasing the coefficient of friction may induce additional heat on moving items. One solution is to protect the item in question by coating with proper materials. Silicon carbide (SiC) was chosen mainly due to compatibility with coated carbon substrate. Recently, SiC has been used as conductive transparent window for optical devices, particularly in thin film solar cells. Using the TVA method, SiC coatings were obtained as thin films (multilayer structures), finishing with a thermal treatment up to 1000°C. Structural properties and oxidation behavior of the multilayer films were investigated, and the measurements showed that the third layer acts as a stopping layer for oxygen. Also, the friction coefficient of the protected films is lower relative to unprotected carbon films.

Dependence of ZnO-based dye-sensitized solar cell characteristics on the layer deposition method

The selection of a proper method for the semiconductor layer deposition is an important requirement towards a high efficiency for dye-sensitized solar cells (DSSCs). We compared three techniques for deposition of the semiconductor thin layer in ZnO-based DSSCs, in order to determine the dependence between the deposition method, the ZnO film properties and finally the DSSCs characteristics. For this purpose, we varied the method used for deposition of the semiconductor film and we replaced ZnO with Al-doped ZnO. The nanostructured films morphology was analysed by transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction. The optical properties were examined by UV–visible spectroscopy and the bandgap energies were calculated using the Tauc equation. The higher fill factor value was registered for DSSCs based on the ZnO film obtained by electrochemical method, but the higher efficiency was registered for doctor-blading method.

Silicon Dicarbide Synthesis

A method for the synthesis of the hypothetical silicon dicarbide structure is proposed. This structure with tetragonal symmetry has been synthesized in matrixes of hardened novolac with silicon powder. Thermal treatment up to 1200°C induces in these matrixes spiroconjugation features with subsequent organizing in tetragonal symmetry. XRD, HRTEM patterns and SAED confirmed that the hypothetical structures proposed are synthetically realizable.

ZnO nanoparticles obtained by hydrothermal method at low temperature

The structural properties and morphology of ZnO nanoparticles obtained by hydrothermal method were studied. ZnO samples were obtained by hydrothermal method, in soft synthesis conditions, temperature of solution about 70°C, in presence of a bidentate ligand or a tensioactive agent. The resulted oxides morphologies were compared with the morphologies of ZnO samples obtained in absence of ligands or tensioactive agents. Samples present a hexagonal phase of ZnO with lattice parameters about a=0.32nm and c=0.5nm, values confirmed by XRD measurements. Morphological properties are studied using bright field images, measuring the nanoparticles diameter and nanopellets size.

Iron-carbon nanocomposite obtained by laser-induced gas-phase reactions

Iron-carbon composite nanopowders have been synthesized by the CO2 laser pyrolysis of gas-phase reactants. The experimental device allows for a very low reaction time and a rapid freezing that creates nanoscale-condensed particles. Iron pentacarbonyl and ethylene-acetylene mixtures were used as iron and carbon precursors. In a two-steps experiment, the reaction products may present themselves as iron-based nanoparticles dispersed in a carbon matrix. By a careful control of experimental parameters and radiation geometries we demonstrate the feasibility of an efficient and well-controlled, single-step technique for the production of iron-based nano-cores embedded in carbon layers. Highly dispersed nanoparticles, narrow size distributions and particles with about 4.5 - 6 nm mean diameters were obtained. Electron microscopy and Raman spectroscopy were used in order to analyze the structure and composition of the obtained nanopowders as well as their Soxhlet residue.

DLC Thin Films and Carbon Nanocomposite Growth by Thermionic Vacuum Arc (TVA) Technology

The aim of this chapter is to report the results on synthesis DLC thin films and carbon nanocomposites by the versatile nanofabrication method based on plasma entitled thermionic vacuum Arc (TVA). TVA technology is based on the localized ignition of the arc plasma in vacuum conditions. Among thin film coating methods by vacuum deposition techniques with high purity, low roughness, and good adhesion on the substrates, TVA is one of the major suitable methods to become a powerful coating technology. Two or three different TVA discharges can be ignited simultaneously in the same chamber for multi-material processing using TVA and separate power supplies. These TVA discharges are localized and do not interfere with each other. Simultaneous two or three TVA discharges were already used for the production of alloy/composite of various materi‐ als. This is due to the high versatility concerning the configuration of experimental arrangements, taking into account the number of electron guns, symmetry of the electrodes, relative position of the anode versus cathode, and also the huge opportunity to combine the materials to be deposited: biand multi-layers, nanocomposites, or alloys in order to have specific applications. This chapter presents the comparative results concerning the surface-free energy information processing, the reflective index, the hardness, and the morphology to provide a coherent description of the diamond-like carbon films and carbon nanocomposites synthesized by thermionic vacuum arc (TVA) and related configurations where Me = Ag, Al, Cu, Ni, and Ti: binary composites (CMe, C-Si) and ternary composites (C+Si+Me). The results include reports on the distribution in size, surface, geometry, and dispersion of the nanosized constituents, tailoring and understanding the role of interfaces between structurally or chemically dissimilar phases on bulk properties, as well as the study of physical properties of nanocomposites (structural, chemical, mechanical, tribological). The results presented