Olivia Gómez-Laserna

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.

Buildings as repositories of hazardous pollutants of anthropogenic origin.

In the present work the pollutant content of diverse building materials was evaluated by the combination of spectrometric and chromatographic techniques. A first non-destructive analysis carried out by μ-XRF and Raman spectroscopy revealed a high impact of pollutants, which reached depths higher than 6mm. The quantitative analyses pointed out that black crust as accumulation nucleus where concentration values up to 3408 mg/kg of lead, 752 mg/kg of chromium or 220 mg/kg of arsenic, high amounts of diverse sulphates and nitrates as well as substantial amounts of polycyclic aromatic hydrocarbons (PAHs) of a clear pyrolytic source were determined. On the other hand, samples without black crust showed also a surprising soluble salt content up to 5%. Polychlorinated biphenyls (PCB) were found to be absent in all material types. The chemometric analysis of the quantitative results revealed that the accumulation capacity and the subsequent pollutant content depends on the type of construction materials, being mortars the most susceptible.

Applicability of a Diffuse Reflectance Infrared Fourier Transform handheld spectrometer to perform in situ analyses on Cultural Heritage materials

This work studies the applicability of a Diffuse Reflectance Infrared Fourier Transform handheld device to perform in situ analyses on Cultural Heritage assets. This portable diffuse reflectance spectrometer has been used to characterise and diagnose the conservation state of (a) building materials of the Guevara Palace (15th century, Segura, Basque Country, Spain) and (b) different 19th century wallpapers manufactured by the Santa Isabel factory (Vitoria-Gasteiz, Basque Country, Spain) and by the well known Dufour and Leroy manufacturers (Paris, France), all of them belonging to the Torre de los Varona Castle (Villanañe, Basque Country, Spain). In all cases, in situ measurements were carried out and also a few samples were collected and measured in the laboratory by diffuse reflectance spectroscopy (DRIFT) in order to validate the information obtained by the handheld instrument. In the analyses performed in situ, distortions in the diffuse reflectance spectra can be observed due to the presence of specular reflection, showing the inverted bands caused by the Reststrahlen effect, in particular on those IR bands with the highest absorption coefficients. This paper concludes that the results obtained in situ by a diffuse reflectance handheld device are comparable to those obtained with laboratory diffuse reflectance spectroscopy equipment and proposes a few guidelines to acquire good spectra in the field, minimising the influence caused by the specular reflection.

Optimization of two methods based on ultrasound energy as alternative to European standards for soluble salts extraction from building materials.

The Italian recommendation NORMAL 13/83, later replaced by the UNI 11087/2003 norm, were used as standard for soluble salts extraction from construction materials. These standards are based on long-time stirring (72 and 2h, respectively) of the sample in deionized water. In this work two ultrasound based methods were optimized in order to reduce the extraction time while efficiency is improved. The instrumental variables involved in the extraction assisted by ultrasound bath and focused ultrasounds were optimized by experimental design. As long as it was possible, the same non-instrumental parameters values as those of standard methods were used in order to compare the results obtained on a mortar sample showing a black crust by the standards and the optimized methods. The optimal extraction time for the ultrasounds bath was found to be of two hours. Although the extraction time was equal to the standard UNI 11087/2003, the obtained extraction recovery was improved up to 119%. The focused ultrasound system achieved also better recoveries (up to 106%) depending on the analyte in 1h treatment time. The repeatabilities of the proposed ultrasound based methods were comparables to those of the standards. Therefore, the selection of one or the other of the ultrasound based methods will depend on topics such as laboratory facilities or number of samples, and not in aspects related with their quality parameters.

Determination of the pigments present in a wallpaper of the middle nineteenth century: the combination of mid-diffuse reflectance and far infrared spectroscopies.

In this work the determination of the pigments present in a decorative wallpaper of the middle nineteenth century from the Santa Isabel factory (Vitoria-Gasteiz, Basque Country, Spain) has been performed by a combination of mid-Diffuse Reflectance Infrared Spectroscopy (DRIFT) and Far Infrared Spectroscopy (FIR) in transmission mode. The DRIFT is a powerful infrared technique that is not widely used in the analyses of artworks in spite of being especially adequate for powdered samples. In this mode, sample pretreatment is not required and the obtained spectra are easier to solve than those obtained in transmittance mode. Those pigments which are not active in the mid-infrared region may be determined easily by FIR. In the last decade, in the field of painted materials very few studies performed by far infrared spectroscopy and mid infrared spectroscopy in diffuse reflectance mode can be found. In most of them the researchers have used one of these techniques, but in no case the combination of both. As we demonstrate in this work, combining these two techniques a complete characterization of the wallpaper can be carried out. Small samples were collected from the wallpaper for the analysis of the rose, brown, yellow and blue colours. In this way, minium (Pb3O4), calcite (CaCO3), barium sulphate (BaSO4), prussian blue (Fe7C18N18), iron oxide yellow (α-FeOOH), vermillion (HgS) and carbon black pigment from organic origen were detected. Finally, the validation was carried out by XRF and Raman spectroscopy getting the same results as with the combination of diffuse reflectance infrared spectroscopy and far infrared spectroscopy.

Diffuse reflectance FTIR database for the interpretation of the spectra obtained with a handheld device on built heritage materials

FTIR handheld devices, working in the diffuse reflectance mode (DRIFT), are promising analytical instruments to perform in situ analyses on cultural heritage materials. However, in the analyses performed in situ with such DRIFT handheld devices, distortions in the DRIFT spectra can be observed in the measurements due to the presence of specular reflection, showing inverted bands in those IR bands with the highest absorption index. These distortions present in the spectra obtained with handheld devices make their resolution very difficult unless the working mode of the devices is well known and a suitable DRIFT database is available. With the aim of getting the most suitable tools to perform analyses in the field, this work has been developed considering two important aspects. In the first one, the differences between the spectra obtained in transmittance, attenuated total reflectance and diffuse reflectance modes of some compounds (nitrates, sulphates and carbonates) that could show the inverted bands when measured with a FTIR handheld device have been studied. In the second one, a preliminary database of several compounds that can be found as original (bulk) compounds or as efflorescence in affected built heritage materials, obtained in the laboratory in diffuse reflectance mode, is presented. Finally, the usefulness of the presented database has been tested using the spectra obtained in situ in the Fishermens association building (San Sebastian, Basque Country, north of Spain) on areas presenting several decaying processes.

Analytical study to evaluate the origin and severity of damage caused by salt weathering in a historical Palace House: the attack of infiltration water

The attack of acid infiltration water on a historical building was thoroughly studied by a combination of ion chromatography, chemometric and thermodynamic chemical modelling. The treatment of the quantitative data points out the formation and damage mechanisms of degradation compounds (salts of nitrates, sulfates and chlorides). The soluble salts content was evaluated by comparison with current guides in order to advise on the required actions of restoration. The results also revealed that the salts followed the Arnold and Zehnders model distribution, by capillarity effect. Using this multianalytical methodology, the principal mechanisms of decay were established.

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

AbstractThis 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 AbstractThe different phases of the multianalytical method to assess the conservation state of built heritage

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.

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.