In-situ XRD for limestone decomposition

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

“Sintering induced deactivation is a major drawback in CaO-based sorbents; and the underlying sintering process and identification of the key parameters controlling its rate remain under investigation. Sintering can be assessed by following the CaO crystallite size (e. g., under realistic calcination conditions under high partial pressures of CO₂).^14, 24, 39 For example, Valverde et al.^40, 41 studied the calcination of limestone in CO₂ partial pressures (0.05–0.9 bar) and temperature conditions near equilibrium (P/P_eq≲1) by in-situ XRD. They found that at low conversions, an intermediate metastable CaO* phase is present, which forms during the desorption of CO₂ and is characterized by a preferred orientation of CaO in the [110] direction.⁴² The proposed exothermicity of the CaO* to CaO transformation and the high CO₂ partial pressure were suggested to delay the nucleation of CaO. As the calcination temperature is well below the Tamman temperature (T_T; an indication for the onset of sintering) of CaO (T_T=1310 °C),¹² the authors concluded that the observed CaO crystallite growth during calcination in CO₂ is mainly a consequence of the sintering of the metastable CaO* phase rather than that of the final CaO.”