From in Situ HT-ESEM Observations to Simulation: How Does Polycrystallinity Affects the Sintering of CeO2 Microspheres?

In situ observation of the first stage of sintering of cerium dioxide microspheres performed using an environmental scanning electron microscope at high temperature (HT-ESEM).

The in situ observation of the first stage of sintering of cerium dioxide microspheres was performed using an environmental scanning electron microscope at high temperature (HT-ESEM). The associated morphological modifications were described quantitatively for systems constituted by two single crystal grains, on the one hand, and by two polycrystalline particles, on the other hand. Particularly, the in situ HT-ESEM observations, and subsequent image analysis with homemade image process software, led to assess the evolution of several parameters of interest during isothermal heat treatments, such as neck size, particles radii, dihedral angles between the spheres, and distance between the grains centers. It was then possible to evaluate the activation energies associated with the neck formation for both systems studied, then to identify the different mechanisms involved. The diffusion process operating during the first stage of sintering was also pointed out.

Furthermore, the comparison of the results obtained from polycrystalline particles and single crystals, and their confrontation with data coming from numerical computation, led to assess the influence of polycrystallinity on the sintering kinetics. For all the conditions tested, sintering degree was found to be enhanced for polycrystalline particles, mainly because of the contribution of the mechanical rearrangement of crystallites during the neck’s elaboration and of the existence of diffusion paths within the particles. On this basis, polycrystallinity should be considered during numerical computations in order to provide predictive models for the first step of sintering.

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G. I. Nkou Bouala, N. Clavier, S. Martin, J. Léchelle, J. Favrichon, H. P. Brau, N. Dacheux and R. Podor. J. Phys. Chem. C 120 (1) 386 (2016)