MODEL STUDY OF THE 1ST STEPS IN THE DETERIORATION OF CALCAREOUS STONE.1. INITIAL SURFACE SULFITE FORMATION ON CALCITE

An experimental set-up to investigate the reactions at ppm concentrati ons of pollutants with stone surfaces, involving a minimum of sample t ampering, is proposed. In-situ Diffuse Reflectance Infrared Fourier Tr ansform spectrometry (DRIFT) is employed to monitor the time evolution of products formed at a precipitated calcite sample. The powdered sam ple was exposed to a mixture of air and SO,(g) at different humidities . The nature of the initial sulphite formed is discussed in terms of a nhydrous and hemihydrate calcium sulphite and sulphite in solution. In all three cases IR spectra are produced and compared to previous stud ies. The DRIFT spectra reveal the presence of at least two sulphite sp ecies on calcite at humid conditions, one chemisorbed and one dissolve d. The relevance of this study to the understanding of calcareous ston e deterioration is discussed.