Thermal decomposition of perlite concrete under different water vapor pressures

The influence of atmospheric water vapor on the kinetics of the thermal decomposition of perlite concrete, which is used in the construction of sodium-cooled fast reactor (SFR) plants, was investigated. Changes in the overall thermal behavior were systematically tracked using humidity-controlled thermogravimetry (TG) at various heating rates (β) and atmospheric water vapor pressures (p(H2O)). The multistep process, mainly composed of the thermally-induced removal of various types of water molecules in the cement matrix and the thermal decompositions of Ca(OH)2 and CaCO3, was successfully separated into component reaction steps using kinetic deconvolution analysis (KDA) based on a cumulative kinetic equation. During the thermal dehydration steps, three derivative TG peaks became more clearly distinguishable and shifted to higher temperatures with increasing p(H2O). A significant retardation effect of p(H2O) was observed for the thermal decomposition of Ca(OH)2. Conversely, a slight but detectable catalytic effect of p(H2O) was observed for the thermal decomposition of CaCO3. Through isoconversional analysis of the kinetic curves extracted using KDA, universal kinetic descriptions for the thermal decompositions of Ca(OH)2 and CaCO3 over different β and p(H2O) values were achieved by introducing accommodation functions considering the effect of p(H2O) into the fundamental kinetic equation. The achieved universal kinetic descriptions for the thermal decompositions of Ca(OH)2 and CaCO3 can be introduced into the cumulative kinetic equation for the overall thermal decomposition of perlite concrete as a means to improve the kinetic information used in SFR plant simulation systems for safety assessment.