PSI - Issue 5

Vanessa Antunes et al. / Procedia Structural Integrity 5 (2017) 1078–1085 Vanessa Antunes/ Structural Integrity Procedia 00 (2017) 000 – 000

1080

3

Diffraction Data Powder Diffraction Files (ICDD PDF) was used for the identification of crystalline phases using the Bruker EVA software. Samples were analyzed unmounted. Raman analyses were undertaken using a Horiba-JobinYvonXploRA confocal spectrometer, using a 785 nm excitation wavelength, with a maximum incident power of 0.2 mW. Using a 100× magnification objective with a pinhole of 300 μm and an entrance slit of 100 μm, the scattered light collected by the objective was dispersed onto the aircoole d CCD array of an AndoriDus detector by a 1200 lines/mm grating. Raman spectroscopy was performed in a range of 100 – 3000 cm -1 . Spectra deconvolution was performed using LabSpec (V5.78). The identification of pigments was made with Spectral IDTM. Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), was used to perform scanning electron microscopy imaging (Backscattering mode) and elemental composition of the samples cross sections. Hitachi S-3700N scanning electron microscope with a coupled BrukerXFlash 5010 SDD energy dispersive detector were used. Samples were analyzed in variable pressure mode at 40 Pa without carbon coating to be further analyzed by other analytical methods. The operating conditions for EDS analysis were 20 kV accelerating voltage and 10-12 mm working distance. For the analysis of organic binder in ground layers a pyrolysis gas chromatography mass spectrometry (PY-GC/MS) system with a Pyrolyzer Frontier Lab PY-3030D double-shotwas used. Each sample (< 200 μg) was separated (chromatic and ground layers) under a stereomicroscope. The samples, previously derivatized in a 50 μL Eco -cup capsule, were placed in the double-shot pyrolizere, followed by a 2-minute helium purge. Samples were pyrolyzed using a single-shot method at 500°C during 12 seconds. The interface was maintained at a temperature of 280 °C. The pyrolizer was coupled to a Shimadzu GC2010 gas chromatographer, also coupled to a Shimadzu GCMS-QP2010 Plus mass spectrometer. A capillary column Phenomenex Zebron-ZB-5HT (30 m length, 0.25 mm internal diameter, 0.50 μm film thickness) was used for separation, with helium as carrier gas, adjusted to a flow of 1.5 mL min -1. The splitless injector was operated at a temperature of 250 °C. GC temperature programme was the following: 40°C during 5 minutes, ramp until 300 °C at 5 °C min -1 , and then an isothermal period of 3 minutes. Source temperature was placed at 240 °C and the interface temperature was maintained at 280 °C. The mass spectrometer was programmed to acquire data between 40 and 850 m/ɀ .Compound identification was done with software AMDIS, according to NIST and Wiley databases. Fourier Transform Infrared spectroscopy (µ-FTIR) analysis was performed in the samples in order to identify binders in ground layers. Using a Bruker spectrometer Tensor 27 model at medium infrared region (MIR), in transmission mode , using a 15x objective and a diamond compression microcell EX’Press 1.6 mm, STJ-0169. AMercury Cadmium Telluride detector and a microscope Hyperion 3000 controlled by software OPUS 7.2 from Bruker, are used in the spectrometer. For each spectrum 64 scans were recorded with a spectral resolution of 4 cm -1 (working range: 4000 600 cm -1 ). 3. Results The studied group of paintings is a composite structure of wood, ground, paint and varnish layers. These materials are responsive to fluctuations in relative humidity (RH), Mecklenburg (1998) .Results brought by visual observation and material analysis clarified the type of materials used in this group structure: oak wood, probably animal glue sizing, calcium sulfate and organic binder ground layers and oil in emulsion with pigments in paint layers. Four big windows that allow daily fluctuations of light and RH since they are permanently open and have no curtains.Measuring was performed in few days of the months of January/February in the sacristy of Goa Cathedral.Considering that the relative humidity should not oscillate above 10% in the 24 hours we can find in Table 1, with relative humidity and luminosity, oscillations of 11% between the morning and the night in the few days measured. The possibility of degradation of wood and polychrome layers with oscillations greater than ± 10% relative humidity and temperature oscillations above ± 10 ° C can cause physical deterioration in the chromatic layers and varnishes, Herráez (2014) .Ratio between the external conditions and the exhibition space of the works of art cannot be rigid, Casanovas (2006),Thomson (1986) .It should be considered from 50% to maximum value to 70% relative humidity in a tropical region such as India (Tropical rain and dry season) , Casanovas (2006),Thomson (1986) .This is the value from which it is agreed that the various objects of organic structure, especially painting, start to change its dimensions, lose its original cohesion, changing its structure and becoming more vulnerable to the formation of fungi and condensation, Herráez (2014) . Considering previous studies, the temperature should always be below 30ºC, since from this value the probability of deterioration of the materials constituting the works (glues and adhesives) is greater, Herráez (2014) . Temperature