CaCO3 product layer formation

https://doi.org/10.1002/cssc.202002078

“A crucial aspect of the kinetics of the carbonation reaction is the growth mechanism of the CaCO₃ product on the CaO surface. Hypothetically, CaCO₃ can grow on CaO as a uniform layer, in the form of islands or in a combination of both modes.^34, 43 A study by Li et al.,³⁴ in which CaO single crystals were carbonated at different temperatures and subsequently analyzed by AFM, tentatively indicates that CaCO₃ starts to grow in the form of islands, which eventually merge. As displayed in Figure 4a, the size and distribution of the CaCO₃ islands depends on the carbonation temperature. Higher carbonation temperatures result in larger islands and lower island densities. At high conversions, the islands have merged into a CaCO₃ layer that fully covers the CaO surface as visualized by FIB-TEM (Figure 4c).⁴⁴ Figure 4c shows a CaO particle covered by a CaCO₃ layer with a thickness of about 90 nm. A visualization of the morphology of the product layer at the end of the kinetically-controlled reaction regime has not been reported yet, due to the difficulty to ‘freeze’ the reaction exactly at the transition from the kinetically-controlled to the diffusion-controlled reaction regime.”

“Figure 4 AFM graphs of CaO single crystals after treatment in CO₂ at (a) 500 °C and (b) 600 °C. Adapted with permission from [34]; copyright American Chemical Society, 2012 (c) FIB-TEM image showing the CaCO₃ product layer. Adapted with permission from Ref. [44]; copyright Royal Society of Chemistry, 2019.”