The hydration reaction of MgO to amorphous Mg(OH)2 is a model hydration reaction and is important to diverse research fields, ranging from catalysis to Earth Sciences. Although the bulk thermodynamics and surface energies of these phases are well studied,[1,2] real time and real space analysis of the reaction at ambient pressure is lacking. In this study, the hydration of MgO nanocrystals is studied at the single particle level, both in real space and in diffraction space using in-situ Transmission Electron Microscopy (TEM) at near-ambient pressure and temperature. Upon exposure to water vapor and the electron beam, the MgO nanocrystals react with H2O and convert to amorphous Mg(OH)2.
Real-time recordings of the hydration reaction reveal that the reaction starts at the MgO nanocrystal surface and proceeds inwards at a constant rate while the Mg(OH)2 shell expands outwards. The growth rate is found to be constant throughout the reaction. Furthermore, as the applied dose rate is increased, the growth rate increases accordingly. Possible mechanisms for the beam-promoted transformation are discussed, including the role of defect formation and migration at the interior and at the surface of the MgO nanocrystals, H2O diffusion towards the MgO surface, and the possible influence of beam-generated H2O dissociation products. Assemblies of converting MgO/Mg(OH)2 nanocrystals exhibited a reorganization of the assembly framework due to the solid volume increase (~100%) of each individual nanocrystal.
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To cite this abstract:Wessel Vlug, Oliver Plümper, Michael Kandianis, Alfons van Blaaderen, Marijn van Huis; In-Situ Hydration of MgO Nanocrystals to amorphous Mg(OH)2 using Liquid Cell Transmission Electron Microscopy. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/in-situ-hydration-of-mgo-nanocrystals-to-amorphous-mgoh2-using-liquid-cell-transmission-electron-microscopy/. Accessed: December 12, 2018
EMC Abstracts - https://emc-proceedings.com/abstract/in-situ-hydration-of-mgo-nanocrystals-to-amorphous-mgoh2-using-liquid-cell-transmission-electron-microscopy/