Analytical assessment to develop innovative nanostructured BPA-free epoxy-silica resins as multifunctional stone conservation materials.

Bisphenol A (BPA)-free epoxy resins, synthesized from low molecular weight cycloaliphatic compounds, may represents promising materials for stone conservation due to their very appealing and tunable physico-chemical properties, such as viscosity, curing rate and penetration ability, being also easy to apply and handle. Furthermore, alkoxysilanes have been widely employed as inorganic strengtheners since they are easily hydrolysed inside lithic substrates affording SiO linkages with the stone matrix. Taking into account the advantages of these two classes of materials, this work has been focused on the development of innovative conservation materials, based on hybrid epoxy-silica BPA-free resins obtained by reaction of 1,4-cycloexanedimethanol diglycidylether (CHDM-DGE) with various siloxane precursors, i.e. glycidoxypropylmethyldiethoxysilane (GPTMS), tetraethyl orthosilicate (TEOS) and isobutyltrimethoxysilane (iBuTMS), using the 1,8-diaminooctane (DAO) as epoxy hardener. Thanks to Raman spectroscopy the synthesis processes have been successfully monitored, allowing the identification of oxirane rings opening as well as the formation of the cross-linked organic-inorganic networks. In accordance with the spectroscopic data, the thermal studies carried out by TGA and DSC techniques have pointed that GPTMS is a suitable siloxane precursor to synthesize the most stable samples against temperature degradation. GPTMS-containing resins have also shown good performances in the dynamic mechanical analysis (DMA) and in contact angle investigations, with values indicating considerable hydrophobic properties. SEM analyses have highlighted a great homogeneity over the entire observed areas, without formations of clusters and/or aggregates bigger than 45 µm, for the cited materials, confirming the efficiency of GPTMS as coupling agent to enhance the organic/inorganic interphase bonding. The variations provided by the incorporation of nanostructured titania, specifically synthesized, inside the epoxy-silica hybrids have been also evaluated. According to all the collected results, the hybrid materials here reported have proven to be promising multifunctional products for potential application in the field of stone conservation.

Multi-analytical methodology to diagnose the environmental impact suffered by building materials in coastal areas.

This work is focused on the development of an innovative multi-analytical methodology to estimate the impact suffered by building materials in coastal environments. With the aim of improving the in situ spectroscopic assessment, which is often based on XRF and Raman spectrometers, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was implemented in the diagnosis study. In this way, the additional benefits from DRIFT were compared to the usual in situ analyses of building materials, which often have interferences from fluorescence and reststrahlen effects. The studies were extended to the laboratory scale by µ-X-ray fluorescence (µ-XRF) cross-section mapping and ion chromatography (IC), and the IC quantitative data were employed to develop thermodynamic models using the ECOS-RUNSALT program, with the aim of rationalizing the behavior of soluble salts with variations in the temperature and the relative humidity (RH). The multi-analytical methodology allowed identification of the most significant weathering agents and classification of the severity of degradation according to the salt content. The suitability of a DRIFT portable device to analyze these types of matrices was verified. Although the Kramers-Kronig algorithm correction proved to be inadequate to decrease the expected spectral distortions, the assignment was successfully performed based on the secondary bands and intensification of the overtones and decreased the time needed for in situ data collection. In addition, the pollutants' distribution in the samples and the possible presence of dangerous compounds, which were not detected during the in situ analysis campaigns, provided valuable information to clarify weathering phenomena.

Characterization of ferruginous cements related with weathering of slag in a temperate anthropogenic beachrock.

This work outlines a temperate latitude beachrock occurrence, which represents the legacy of heavy anthropogenic environmental disturbance. The units contain high amounts of slag and iron-rich wastes derived from metallurgical activities that attest the impact of the past industrial development on such coastal systems. The exposition of the anthropogenic wastes to weathering processes, such as the influence of marine aerosols and the chemical attack of acid gases like the SOx coming from the nearby urban-industrial atmosphere, gave rise to the formation of early diagenetic ferruginous cements. A new analytical methodology based on the combination of micro-Raman spectroscopy (MRS), Raman chemical imaging, SEM-EDS and the Structural and Chemical Analyzer (SCA, an emerging system that hyphenates micro-Raman and SEM-EDS), was applied for the first time to characterize the ferruginous cements. The MRS analyses revealed Fe2+/Fe3+ oxides and oxyhydroxides, CaCO3 polymorphs and less frequently silicates. The Fe mineral species detected were hydrated goethite, hematite, magnetite, magnesioferrite, lepidocrocite and goethite. Complementary Raman imaging, SEM-EDS and SCA analyses unraveled the preferential distribution of hydrated goethite. The identified iron mineral phases are weathering sub-products of hematite commonly derived from atmospheric/aqueous leaching processes triggered by the chemical attack of the acid gases. EDS showed the existence of other elements such as Si, Mg, Cl, Na, Al, K and sporadically S that indicated the importance of permeability, atmospheric deposition and the acid attack. Additionally, calcite and gypsum minerals also evidenced the action of meteoric waters, dry deposition processes or the attack of SOx acid gases. The presence of such compounds is modifying the cement stratigraphy and suggests that the dissolution of carbonates is currently taking place. Those facts influence the erosive susceptibility and the release of the anthropogenic materials trapped originally in the beachrocks, which could act as potential secondary sources of contaminants to the coastal environment.

In situ DRIFT, Raman, and XRF implementation in a multianalytical methodology to diagnose the impact suffered by built heritage in urban atmospheres.

This work addresses the evaluation of an innovative mutianalytical method to assess the conservation state of a fifteenth century palace house. With the goal of reducing the handicaps of field analysis, the in situ spectroscopic assessment, often based on the use of X-ray fluorescence and Raman spectrometers, was complemented by the use of diffuse reflectance infrared Fourier transform spectroscopy. In this manner, its usefulness as a diagnostic tool to discover the origin and mechanisms of the damage caused by atmospheric and infiltration water attacks were thoroughly examined. Moreover, the study was extended in the laboratory to increase the information obtained by nondestructive techniques. The results revealed a severe material loss caused by soluble salts. Thus, a noninvasive sampling method using cellulose patches was tested to study the amount and mobility of salts by means of ion chromatography. Finally, to establish the chemical degradation processes that are occurring in the palace, a chemometric analysis of the quantitative data as well as the construction of thermodynamic models was done to advise on the required restorative actions. Graphical Abstract The different phases of the multianalytical method to assess the conservation state of built heritage.

Raman spectra of the different phases in the CaSO4-H2O system.

Although it is known that the CaSO4/H2O system is formed by at least five different phases, this fact is not correctly documented in Raman spectroscopy studies. The main problem detected in the literature was the incorrect definition of the anhydrite, which produced the assignation of different spectra for a single compound. In this sense, two different spectra were clearly identified from the bibliography, which showed different main Raman bands at 1017 or 1025 cm(-1), although anhydrite could be present even as three different polymorphous species with different structures. A better understanding of the whole system obtained from a review of the literature allowed new conclusions to be established. Thanks to that revision and the development of different thermodynamical experiments by Raman spectroscopy, the Raman spectra of each phase were successfully identified for the first time. In this way, the main Raman bands of gypsum, bassanite, anhydrite III, anhydrite II and anhydrite I were identified at 1008, 1015, 1025, 1017 and 1017 cm(-1), respectively. To conclude this work, the contradictions found in literature were critically summarized.

Relevance of cross-section analysis in correct diagnosis of the state of conservation of building materials as evidenced by spectroscopic imaging.

In the present work the need to use cross-section analysis as a routine procedure to characterize physiochemical damage on building materials was evaluated using a combination of spectroscopic imaging techniques based on Raman spectroscopy, X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). First, samples for cross-section analysis required special preparation to avoid the loss of soluble and weakly anchored compounds and thereby ensure the representativeness of the analysis. To this end, samples were dry drilled and fractured with a single blow rather than cut to avoid friction. Cross-section analysis allowed surface deposition (crusts and patinas) to be differentiated from penetrating pollution and the affected depth to be determined. Elemental and molecular distributions were obtained to establish the origin of the compounds/elements found. Moreover, establishing the depth reached by the pollutant, which depends on the material porosity, can help to determine the physicochemical form of the pollutant. Finally, SEM-EDX images allowed surface and internal cracks, as well as the causes of these physical stresses, to be identified. As a result, surface analysis alone was shown to lead to incomplete or even incorrect conclusions that can be avoided by using cross-section analysis as a routine procedure when assessing the state of conservation of building materials.