MODEL STUDY OF THE 1ST STEPS IN THE DETERIORATION OF CALCAREOUS STONE.2. SULFATE FORMATION ON CALCITE

The crucial role of surface water in the formation of surface sulphite was addressed in a previous study by in-situ Diffuse Reflectance Infr ared Fourier Transform spectrometry (DRIFT). No sulphate was formed, i ndicating O2(g) to be too weak an oxidant to oxidize surface sulphite. The usefulness of DRIFT is further emphasized as it is employed to in vestigate the roles of NO2 and O3 in the formation of gypsum on calcar eous stone at close to normal atmospheric conditions. Sulphate formati on at calcite, employed to model e.g. marble, is shown to progress via a surface sulphite intermediate. NO2 is found to catalyze surface sul phate formation by activating molecular oxygen, while ozone acts to fo rm sulphate by direct oxidation.