Synchrotron X-ray diffraction


In situ X-ray diffraction were performed on the I15 beamline at the Diamond Light Source, Harwell Oxford, UK. A specially made gas flow capillary cell was constructed in order to be able to perform in situ measurements, which consisted of a 3 mm wide silica capillary mounted vertically in the beam, with gas delivered onto the sample from above, down through the capillary. The whole cell was mounted on a stage which allowed the cell to be moved between two positions: in the beam (during measurement), and in the hot zone of a hot air blower, out of the beam (during reaction). The pelletized sample was inserted in the middle of the capillary, with silica wool below the sample to prevent movement during the reaction. The pellet was made to fit exactly within the diameter of the capillary, with no gaps to either side.

The measurements were performed at 76 keV, with a microfocused beam of size 70 μm. For each of the data collections, 5 dark images were measured for 1 minute each, followed by between 2 and 5 exposures of the sample for 1 minute each. The number of exposures was varied throughout the experiment to save time; the in situ measurements have 2 exposures per depth and reaction time. The pellet was moved in the beam in order to take measurements at different depths throughout the pellet. For these experiments, data were first collected at room-temperature and then the pellet was moved to the hot air blower operating at 973 K under the respective gas flow (CO2 with or without steam) and held to react for 1 minute. Steam was produced through flowing the CO2 gas through a water bubbler prior to the reaction cell. The sample was then moved out from the hot air blower and immediately into the beam, and data were collected at a number of depths (at room temperature). This process was then repeated, and data collected corresponding to a total carbonation reaction time of 2 minutes.”

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