In Situ Bragg Coherent Diffraction Imaging Study of
a Cement Phase Microcrystal during Hydration
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Abstract
Results of Bragg coherent diffraction
imaging (BCDI) confirm that
ion migration and consumption occur during hydration of calcium monoaluminate
(CA). The chemical phase transformation promotes the hydration process
and the formation of new hydrates. There is a potential for the formation
of hydrates near where the active ions accumulate. BCDI has been used
to study the in situ hydration process of CA over a 3 day period.
The evolution of three-dimensional (3D) Bragg diffraction electron
density, the “Bragg density”, and strain fields present
on the nanoscale within the crystal was measured and visualized. Initial
Bragg densities and strains in CA crystal derived from sintering evolve
into various degrees during hydration. The variation of Bragg density
within the crystal is attributed to the change of the degree of crystal
ordering, which could occur through ion transfer during hydration.
The observed strain, coming from the interfacial mismatch effect between
high Bragg density and low Bragg density parts in the crystal, remained
throughout the experiment. The first Bragg density change during the
hydration process is due to a big loss of Bragg density as seen in
the image amplitude but not its phase. This work provides new evidence
supporting the through-solution reaction mechanism of CA