Influence of atmospheric CO2 on the thermal decomposition of perlite concrete

The thermal behavior of perlite concrete, which is used in sodium-cooled fast reactor plants, was subjected to kinetic modeling to gather the fundamental data for establishing a reliable safety assessment system. In this study, the influence of atmospheric CO2 on the multistep kinetic behavior of perlite concrete was investigated in detail by separating the component reaction steps using kinetic deconvolution analysis (KDA) based on a cumulative kinetic equation. The carbonation of Ca(OH)2 during its thermal decomposition was identified as a specific process observed in the presence of atmospheric CO2. The process was characterized by KDA as the successive thermal decomposition of Ca(OH)2 to form CaO and the subsequent carbonation of CaO. A shift in the temperature range of the overall carbonation process to higher temperatures with increase in partial pressure of CO2 (p(CO2)) was also identified as a specific phenomenon. The thermal decomposition of CaCO3 was separated from the multistep thermal decomposition of the perlite concrete using KDA and analyzed kinetically considering the influence of p(CO2). A universal kinetic description over different temperatures and p(CO2) values was achieved by introducing an accommodation function composed of p(CO2) and the equilibrium CO2 pressure for the reaction. Introduction of the modified kinetic equation with the accommodation function into the corresponding reaction step of the cumulative kinetic equation enables a universal kinetic description of the overall thermal decomposition of perlite concrete over different temperature and p(CO2) conditions.