Evaluation of the initial weathering rate of Istria stone exposed to rain action, in Venice, with X-ray photoelectron spectroscopy

Samples of Istria stone were exposed in rain-washed conditions for 6 and 18 months, in the industrial and marine environment of Venice. To assess the initial stages of weathering, the exposed samples were analyzed by using X-ray photoelectron spectroscopy (XPS) and other analytical techniques, such as Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM–EDS). Within a 6-month period, XPS revealed the deposition of sulfates, calcium silicates, carbonaceous particles, nitrogen compounds and organic compounds of lead, fluorine and chlorine. After an 18-month exposure period, the exposed surface exhibited pollutant compounds of sulfates, fluorine and nitrogen along with new-formed pollutant compounds of phosphorus and zinc. The appearance of silicon, aluminum and iron compounds indicates either dissolution of the argillaceous inclusions of the carbonate matrix or deposition of air-borne particles. The other applied analytical techniques evidence alteration features related more to morphological modification and less to chemical changes. Therefore, XPS revealing deposition of typical components of atmospheric pollution, as well as either deposition or dissolution of soil-derived and intrinsic elements evidences the initial weathering rate of exposed Istria stone to rain action.