Functional Surfaces Obtained by Thermal Spray Techniques PDF Download

Author: Marco Robotti
Publisher:
ISBN:
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Languages : en
Pages : 126

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Book Description
The main subject of this PhD Thesis is the manufacturing of titanium dioxide multifunctional coatings by means of two spraying technologies: Cold Gas Spray (CGS) and Atmospheric Plasma Spray (APS). The characteristics of each spraying technique are a key factor to be able to understand the behaviour of the deposited material. Moreover, the process conditions strongly affect the functional response and activity of the metal oxide layers in different application sectors. The starting scope of the PhD thesis consisted in developing nanostructured TiO2 anatase coatings by LP-CGS technique. Using this method, no melting of material feedstock is needed for being deposited and this fact is fundamental because it is possible to preserve this metastable active anatase phase at room temperature. The large specific surface of this nanometric feedstock is useful for applying it in the field of heterogeneous photocatalysis and degradation of contaminants. In order to avoid clogging phenomena of the nanometric powder and not suitable deposition of only ceramic particles, mechanical blends were prepared with ductile materials which flow properly in the pipelines. The presence of anatase phase on the top surface of the final coatings determines their photocatalytic behaviour. Samples successfully degraded NOx gases in less than half an hour (FEAM Grupo de Fotocatálisis y Espectroscopia Aplicada al Medioambiente, Universidad de Las Palmas de Gran Canaria). A second research topic regarded different TiO2 materials with the objective to test them in photoelectrocatalysis. Three commercial powders (TiO2 rutile, TiO2 anatase and TiO2-x) onto Inconel alloy and carbon steel substrates were studied. The influence of APS thermally-activating technique is explained towards the non-stoichiometric secondary phases that are formed. The performance of the coatings as photoanodes in the solar photoelectrocatalysis (SPEC) treatment of a model azo dye was explored (Group LE03A Laboratori d'Electroquímica de Materials i del Medi Ambient, Universitat de Barcelona). The functional role of these materials has an important added value in the environmental field because of the possibility to achieve cleaner waters in the smart cities of the future. The third purpose of this research was to deposit metal oxides based on titanium dioxide by APS for being applied as electrodes in real batteries. Hydrogen contained in the plasma jet of APS is able to reduce TiO2 metal oxide feedstock, create oxygen vacancies and non stoichiometric compounds such as titanium sub-oxides (TiO2-x) or Magnéli phases (TinO2n-1) during the in-flight interaction of the particles with the jet stream. This lack of oxygen in the crystal structure of TiO2 powder leads to a donor level to the conduction band; therefore a corrosion-resistance ceramic material with an enhanced conductivity was obtained. Coatings were manufactured onto stainless steel, aluminium films, carbon-polymer composite and nickel foam. Four TiO2-x plates onto aluminium substrates were applied as electrodes in a laboratory scale battery. Cyclic voltammograms curves and charge/discharge cycle of the lead acid battery were carried out and gave excellent results (Faculty of Engineering and the Environment, University of Southampton). The fourth objective of this doctorate consisted in developing new functional gas sensors by means of APS technology. It was determined to build-up the sensing layer on a thin ceramic substrate. This fact permits to increase the working temperature respect to polymeric or metallic substrates. Spraying conditions were accurately selected to reach good deposition and not to damage the brittle substrate. The APS process offered also the advantage to increase the quantity of oxygen vacancies in titanium dioxide powder in order to enhance its conductivity and sensing function. Satisfactory performances were obtained testing the response of the device in front of various target gases and sensing efficiency was deeply studied (Group MIND Micro-nanotecnologías y nanoscopias para dispositivos electrónicos y fotónicos, Universitat de Barcelona).