This work aims at developing TEOS-based sols for the consolidation of carbonate stones, following basic catalysis routes, which have been scarcely explored. The influence of the alkaline media in the sol–gel chemistry is a well-known phenomenon and has been considered a drawback. This work demonstrates that under controlled and well-selected conditions, there is high potential on this novel approach and important advantages. Basic catalysts containing NH-goups (ammonia, n-octylamine, diethanolamine and triethanolamine) were used in the production of TEOS-based sols. The role of the different amines on the consolidation efficacy of the final gels was then investigated. The development of new TEOS-based solutions with potential consolidation efficacy has been achieved by tailoring several parameters (e.g. precursor/catalyst and precursor/solvent ratios). Optimisation of parameters and modification of the silica structure with different amines allowed us to produce a set of consolidants for carbonate stones. The morphology and structure of xerogels were characterised, sol behaviour was studied after their blending with calcite powder, as well as after their application on soft limestone samples. Cohesive monoliths of calcite powder were obtained, and significant and uniform drilling resistance increments in treated stones were achieved using sols with different TEOS : ethanol : catalyst ratios.

This study aimed at evaluating the effect of hydroxyapatite (HAp) nanosized structures and nanoparticles of hydrophilic silica as modifiers of both acid- and alkaline-catalysed tetraethoxysilane (TEOS)-based products for the consolidation of carbonate stones. Their initial effectiveness and some compatibility aspects were assessed in a porous limestone (sound and artificially aged Ançã stone samples) and two types of treatment (capillary absorption and brushing). The studied products were examined by scanning electron microscopy (SEM) and micro-Raman spectroscopy. Their depth of penetration and strengthening effect were evaluated through drilling resistance. Their action on the substrate was also further assessed by non-destructive methods based on colour variation and Shore-D hardness. Treated stone samples were dissimilarly affected by the tested treatments and exhibited a significant increase in strength with a low risk of over-strengthening. Adequate in-depth penetration patterns, as well as colour compatibility with the substrate were obtained with some of the prepared formulations through two types of treatment, both in sound and aged stone samples. The potential most effective treatments with the lowest colour change were obtained with the acid-catalysed TEOS-based products modified with HAp nanosized structures.

Findings of Iron Age metallurgical activities related to tin metal and mining are very rare. In the present work, we present a detailed study of the Outeiro de Baltar hillfort, dated to the Late Iron Age/Early Roman period, located in a place where 20th century tin mining work took place. Elemental and microstructural analysis by portable, micro and wavelength dispersive X-ray fluorescence spectrometry (pXRF, micro-XRF and WDXRF) and scanning electron microscopy with energy dispersion spectrometer (SEM-EDS) showed that metallurgical debris found at the archaeological site is related to tin smelting and binary and ternary bronze productions. Analysis of the artefacts of diverse typologies found at the site showed that a variety of metals and alloys were in circulation and use. Samples of tin ores (cassiterite) from the region were analyzed for comparison with an archaeological tin slag from the site. The analytical results point to the production of tin metal using local cassiterite and the production of bronze by directly adding cassiterite into a smelting process. Furthermore, data of remote sensing (airborne Light Detection and Ranging (LiDAR) and historical aerial imagery) and Geographical Information System (GIS) mapping were combined with archival mining documentation and maps to retrieve a landscape context for the site. The study showed that the place of the Outeiro de Baltar hillfort (NW Iberia) was mined periodically over time.