Papers by Keyword: Laser Pyrolysis

Abstract: Ti-Si composite ceramic coating containing SiO₂ particles was prepared on 45 steel substrate by in-situ laser pyrolysis with laser power of 600W and laser wavelength of 980nm. The density and wear resistance of the composite ceramic coating were improved. By means of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), reciprocating friction and wear tester, the element composition, existing forms, surface morphology and friction and wear properties of Ti-Si composite ceramic coatings with different mass fraction of SiO₂ particles were analyzed. The results show that the addition of SiO₂ particles can improve the surface density and inorganic degree of the composite ceramic coating. When the mass fraction of SiO₂ is 1% and the load is 1N, the friction coefficient of the composite ceramic coating is 61% lower than that of 45 steel. When the mass fraction of SiO₂ is 5% and the load is 3N, the friction coefficient of the composite ceramic coating is 51% lower than that of 45 steel. The composite ceramic coatings show good antifriction performance and wear resistance.

Abstract: Laser pyrolysis is one of the most important and emerging techniques used to synthesize thin films, nano-powders and nano-structured materials. The advantages in this technique include: a well defined interaction volume, no interactions with the reactor chamber walls hence less impurities, and the attainment of very fine particles. In this paper we briefly review the development and the current status of laser pyrolysis world wide. However, the main focus is an overview of our efforts to synthesize vanadium and tungsten oxides using this technique since 2006. We discuss the role of the laser pyrolysis parameters: the beam waist, interaction volume, carrier gas flow rates, laser wavelength and power density on the phase, size and shape of the final products obtained.

Abstract: Rare earth doped materials have many familiar applications (TV screens, solid lasers, scintillators…) thanks to their efficient and robust luminescence properties. In recent years, growing interest has been focused on the changes in their optical properties with the size of the host particles. In this work, nanomaterials were produced for the first time by using laser pyrolysis. Y, Gd, and Eu nitrates were dissolved in water and used as precursors. Cubic phases of Y2O3:Eu3+ and Gd2O3:Eu3+ were obtained with sizes ranging from 3 to 40 nm. The spectroscopic properties revealed a new and nanostructure-specific broad band in the excitation spectrum. The emission spectrum was found to be characteristic of nanostructured sesquioxides only when excited in this new band, which was finally assumed to be a new charge transfer band for the smallest nanoparticles in the sample.

Abstract: Laser pyrolysis is a very suitable gas-phase process for the synthesis of a wide range of nanoparticles at laboratory scale. The principle of the method is based on the decomposition of gaseous or liquid reactants by a high power CO2 laser followed by a quenching effect. The literature reports the possibility to produce carbides, nitrides, oxides, metals and composites nanoparticles by this process. This paper reports a study of the effect of the laser intensity (using an innovative optical system) and of the gas flow rates on the characteristics (size and structure) of silicon carbide (SiC) nanoparticles produced at pilot scale (up to 1.13 kg/h) by using a mixture of silane (SiH4) and acetylene (C2H2). It has been shown that the decrease of the gas flow rate favors the increase of the mean grain size of the particles and that the increase of the laser intensity seems to provoke an increase of the mean crystal size and/or crystal number.

Abstract: We present magnetic and morphological characterization of iron- and iron-carbide- based nanopowder obtained by the laser synthesis from sensitized gas phase mixture containing acetylene and iron pentacarbonyl vapors. The analysis was performed on the as-prepared material and the annealed material. The results of TEM, XRD, Mössbauer and magnetic measurements are reported. Phase transformations taking place during annealing of the nanopowder when core-shell nanoparticles appear are discussed.

Abstract: The paper briefly reviews some fundamental and applicative characteristics of the laser pyrolysis technique. Recent developments of this method for the synthesis of iron-based nanostructures are emphasized. By varying the precursor gas mixture, iron/carbon nanocomposites (core-shell structures) and gamma iron oxide nanopowders were obtained and characterized. Novel structural features of the synthesized titanium-doped nano iron oxides are described.