Browsing by Author "Muecklich, Frank"

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    Growth, characterization and thermo-mechanical analysis of Al/Al2O3 core/shell nanoparticles obtained under H2 atmosphere
    (2020) Diaz-Droguett, D. E.; Ramos-Moore, E.; Roble, M.; Muecklich, Frank
    In this work, growth, characterization and thermo-mechanical behavior of Al/Al2O3 core/shell nanoparticles (NP) is performed. The growth was carried out by gas condensation methods using H-2 as carrier gas at a pressure of 100 Pa and with a temperature of the evaporation source of 1315 degrees C. The prepared NP were characterized by Energy Dispersive X-ray Spectroscopy for chemical information, transmission electron microscopy for morphological study, and electron diffraction patterns for structural information. The prepared Al NP exhibit a thin Al2O3 passivating oxide shell due to the air exposure when removed from the preparation vacuum chamber. Afterwards, the growth of the Al2O3 oxide shell of the Al NP and the thermo-mechanical interaction between this growing oxide shell and its Al core was studied by performing in-situ thermal X-ray diffraction from RT up to 505 degrees C. Coefficients of thermal expansion of both Al core and Al2O3 oxide shell were obtained by means of X-ray strain analysis. It was found that the thickness of the Al2O3 shell increases with temperature and the thermal stress induced in the system increases linearly with temperature. Our results highlight that these NP overcome higher values of fracture toughness compared with Al2O3 NP used in micro-nano composites, thus improving their mechanical properties for nanofluid applications.
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    Study of thermally induced phase transformations and microstructural changes in porous MoO3 nanostructures for the design of tribological additives
    (2021) Diaz-Droguett, D. E.; Ramos-Moore, E.; Roble, M.; Muecklich, Frank
    The thermal behavior of MoO3-nanostructures is relevant for the design of tribological additives containing Mo-oxides. We report on thermal behavior of porous MoO3-nanostructures analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The nanostructures were grown by gas condensation under H-2. Our results revealed 3 stages of phases behavior as a function of temperature. We found dehydration of MoO3-0,33 H2O after 180 degrees C followed by the formation of beta-MoO3 after 230 degrees C, then to alpha-MoO3 after 280 degrees C, and finally formation of suboxide gamma-Mo4O11 at similar to 330 degrees C. The formation of the latter is mainly due to the crystallization and reduction of the porous oxide matrix. Our results highlight that both thermal and chemical processes must be taken into account when designing tribological additives that contain MoO3. (C) 2021 Elsevier B.V. All rights reserved.