SEM-XRD investigation of deterioratioN morphologies and consolidation prior to restoration: the case of Porta Nuova in Ravenna (Italy)

Identification and sampling of Porta Nuova materials were both based on macroscopic evidence such as colour, grain-size and consistency, and on different alteration products and deterioration degree of the monument. Only removed fragments, small pieces from hidden portions and/or from the monument cracks caused by deterioration, previous restorations and damages were taken during the diagnostic examination prior to restoration. On all samples of ornamental stones, bricks and mortars of the monument the following examinations were carried out: thin section petrographic analyses, SEM-EDX observations and X-Ray diffraction (XRD) analysis. SEM-EDX observations were carried out using a Scanning Electron Microscope (SEM) Philips 515B fitted with an EDAX DX4 microanalytical device. The operating conditions were: accelerating voltage of 15 kV, beam current of 2 nA, spot size of 1µm and counting time of 100s. The analyses were reduced using ZAF correction. Precision is 2% for oxide abundances > 10% and 5% for oxide abundances between 2 and 10 wt%. Mineralogical data of the materials were obtained by X-ray Diffraction (XRD). Analyses were performed by using a computer-controlled Philips PW 1710 diffractometer with the following operative conditions: CuKa radiation, 40kV and 30mA, 0.02° (2q) step size, counting time of 1 s/step. All powder samples were prepared by side loading of an aluminium holder to obtain a quasi-random orientation. The mineralogical identification was based on comparison with JCPDS data