In situ IR study on the initial sulphition and carbonation of Ca(OH)2 and CaO by SO2 polluted air

Absorptions of SO2 and CO2 to fresh and aged forms of CaO and Ca(OH)2 are investigated at dry and humid conditions. Sulphite formation on Ca(OH)2 is found to be fairly independent of the relative humidity, while surface water is found to be a necessary condition for the corresponding carbonation reaction. Results supportive of Ca(OH)2 sulphition to be strongly preferred before carbonation at humid conditions are produced. Marked improvements in SO2 adsorption are seen for the fresh substrates. The observations are put in perspective of an on-going effort to understand the roles of SO2 in the deterioration of calcareous stone monuments, and are relevant to the chemistry of building materials.