João Pedro Veiga

Bluish-grey limestones have been extensively used as ornamental stones for decoration purposes in buildings, as well as in works of art, and accordingly, have been the target of intense exploration. In Portugal, the Jurassic limestone massif known as the Maciço Calcário Estremenho (MCE), has been the source of grey-coloured ornamental stones, namely the Azul Valverde (one of the most well-known bluish-grey limestones) and Atlantic Blue varieties, both of which may undergo colour changes in outdoor environments. In this sense, it is important to understand the sudden colour change from bluish-grey to yellow/beige in the same limestone block in a quarry, or even, what happens to the colour when polished limestone is placed outdoors. This study was undertaken using various techniques, namely XRF (X-ray fluorescence spectrometry), XRD (X-ray diffraction), SEM (scanning electron microscopy), DTA–TG (differential thermal analysis/thermogravimetry) and colourimetry. Synchrotron radiation was also used at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) where XANES (X-ray Absorption Near Edge Structure) spectra at Fe K-edge were collected to ascertain the speciation state of Fe in different coloured zones of the limestone, previously checked by EDXRF (energy dispersive X-ray fluorescence). The presence of Fe2+ and Fe3+ are responsible for the greyish and yellow/brown colour, respectively. On the other hand, the UV radiation from the sun causes a quickened and severe bleaching/fading on the dark blue/grey polished limestone.

Sol-gel production of hybrid materials has, to some extent, revolutionised materials’ engineering and the way science and technology perceive the creation of new materials. Despite that, the method presents some limitations that are circumvented by radiation processing. Electron beam irradiation was used to promote synthesis of hybrid structures while using silanol-terminated PDMS, TEOS and TPOZ as precursors. Evaluation of the method’s performance was executed by gel fraction determination, WDXRF and FTIR-ATR. Results showed that, although there is some pre-irradiation reactivity between precursors, radiolysis induces scission on multiple sites of precursor’s structures, which induces hybrid network formation to a greater extent. Characterisation allowed determining electron beam irradiation to be effective in the creation of Si–O–Zr bonds, resulting in the production of a Class II hybrid material.