Josu Trebolazabala

Nature and origin of white efflorescence on bricks, artificial stones, and joint mortars of modern houses evaluated by portable Raman spectroscopy and laboratory analyses.

Bricks and mortar currently constitute one of the most important building materials used in the construction of most modern facades. The deterioration of these materials is caused primarily by the impact of numerous external stressors, while poor manufacturing quality, particularly of mortars, can also contribute to this process. In this work, the non-invasive Raman spectroscopy technique was used to identify the recently formed deterioration compounds (primarily sulfates and nitrates) in bricks, artificial stones, and joint mortars from detached houses in the Bilbao metropolitan area (Basque Country, North of Spain), as well as to investigate the deterioration processes taking place in these materials. Additionally, to confirm and in some cases complement the results obtained with Raman spectroscopy, SEM-EDS and XRD measurements were also carried out.

Use of portable devices and confocal Raman spectrometers at different wavelength to obtain the spectral information of the main organic components in tomato (Solanum lycopersicum) fruits

Tomato (Solanum lycopersicum) fruit samples, in two ripening stages, ripe (red) and unripe (green), collected from a cultivar in the North of Spain (Barrika, Basque Country), were analyzed directly, without any sample pretreatment, with two different Raman instruments (portable spectrometer coupled to a micro-videocamera and a confocal Raman microscope), using two different laser excitation wavelengths (514 and 785 nm, only for the confocal microscope). The combined use of these laser excitation wavelengths allows obtaining, in a short period of time, the maximum spectral information about the main organic compounds present in this fruit. The major identified components of unripe tomatoes were cutin and cuticular waxes. On the other hand, the main components on ripe tomatoes were carotenes, polyphenoles and polysaccharides. Among the carotenes, it was possible to distinguish the presence of lycopene from β-carotene with the help of both excitation wavelengths, but specially using the 514 nm one, which revealed specific overtones and combination tones of this type of carotene.

Multianalytical approach to explain the darkening process of hematite pigment in paintings from ancient Pompeii after accelerated weathering experiments

In this paper, recently excavated fresco painting fragments from the House of Marcus Lucretius (Pompeii) and not exposed to the atmosphere since the eruption of the Mount Vesuvius were subjected to a controlled SO2 atmosphere and high relative humidity. These experiments were conducted in order to simulate under accelerated conditions the possible deterioration of the hematite pigment and plaster. The mineralogical transformation of the polychromy and plaster was monitored using mainly Raman spectroscopy, a non-destructive technique, but also infrared spectroscopy (FT-IR) and scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDS). After different exposure cycles to SO2, it was confirmed that hematite red pigment (Fe2O3) can be reduced into magnetite (Fe3O4), which provides the darkened colour to the pigment. While Fe(III) from hematite is reduced into Fe(II) or mixed Fe(III) and Fe(II), the SO2 can be oxidized (SO3) and hydrated to experience a subsequent wet deposition (H2SO4 aerosol) causing also the transformation of calcite into gypsum. Finally, it was assessed that high concentrations of SO2 can also cause the sulphation of hematite pigment promoting its transformation into paracoquimbite/coquimbite (Fe2(SO4)3·9H2O). Moreover, in some areas of the deteriorated painting fragments, non-expected iron(II) sulphate and sulphite species were also identified.

Portable Raman spectroscopy for an in-situ monitoring the ripening of tomato (Solanum lycopersicum) fruits

Ripening is one of the most important transformations that fruits and vegetables suffer, from an unripe to a ripe stage. In this study, it was followed up and analyzed the variations in the composition of tomato fruits at different ripening stages (green or unripe, orange or middle ripe, red or ripe and brown or overripe). The results obtained from the Raman measurements carried out showed a change in the composition of tomato fruits in the transit from green to brown. The analysis confirmed an increase of carotenoids from an unripe to a ripe stage of these fruits, being lycopene the characteristic carotenoid of the optimum ripe stage. The presence of chlorophyll and cuticular waxes decrease from the unripe to the ripe stage. Moreover, the relative intensity of phytofluene, a transition compound in the carotenoid biosynthetic pathway, is higher in the orange or middle ripening stage. The results obtained in-situ, without cutting and handling the tomato fruits, by means of a portable Raman spectrometer offered the same information that can be achieved using a more expensive and sophisticated confocal Raman microscope.