Study of thermally induced phase transformations and microstructural changes in porous MoO<sub>3</sub> nanostructures for the design of tribological additives
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Date
2021
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Abstract
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.
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Porous MoO3, Thermal X-ray diffraction, Electron irradiation, Phase transformations, Crystallization process, Reduction process