M. Alesiani

Micro-Raman study of copper hydroxychlorides and other corrosion products of bronze samples mimicking archaeological coins

Three bronze samples created by CNR-ISMN (National Research Council—Institute of Nanostructured Materials) to be similar to Punic and Roman coins found in Tharros (OR, Sardinia, Italy) were studied to identify the corrosion products on their surfaces and to evaluate the reliability of the reproduction process. Micro-Raman spectroscopy was chosen to investigate the corroded surfaces because it is a non-destructive technique, it has high spatial resolution, and it gives the opportunity to discriminate between polymorphs and to correlate colour and chemical composition. A significant amount of green copper hydroxychlorides (Cu2(OH)3Cl) was detected on all the coins. Their discrimination by Raman spectroscopy was challenging because the literature on the topic is currently confusing. Thus, it was necessary to determine the characteristic peaks of atacamite, clinoatacamite, and the recently discovered anatacamite by acquiring Raman spectra of comparable natural mineral samples. Clinoatacamite, with different degrees of order in its structure, was the major component identified on the three coins. The most widespread corrosion product, besides hydroxychlorides, was the red copper oxide cuprite (Cu2O). Other corrosion products of the elements of the alloy (laurionite, plumbonacrite, zinc carbonate) and those resulting from burial in the soil (anatase, calcite, hematite) were also found. This study shows that identification of corrosion products, including discrimination of copper hydroxychlorides, could be accomplished by micro-Raman on valuable objects, for example archaeological findings or works of art, avoiding any damage because of extraction of samples or the use of a destructive analytical technique.

13C CPMAS NMR spectroscopic analysis applied to wood characterization

Solid-state nuclear magnetic resonance (NMR) spectroscopic analysis were carried out on recent and archaeological wood. Cross-polarization-magic-angle spinning13C NMR spectra obtained from samples of poplar (Populus sp.), oak (Quercus sp.), and silver fir (Abies alba) were examined in this study. The most relevant peaks were assigned according to the extensive literature in the area, and the differences observed discussed in terms of lignin and cellulose composition: by fixing a lignin reference signal intensity, the cellulose and hemicellulose moieties showed a strong depletion compared to the lignin signals in archaeological wood.

NMR study on the early stages of hydration of a porous carbonate stone

Nuclear Magnetic Resonance was employed to obtain information on the pore filling during the absorption process. A porous carbonate stone, largely employed for buildings and mainly outdoor decorations was studied during water absorption by capillary rise, and filled pores radii were evaluated by comparison between experimental and theoretical parametric magnetization decay curves. Non mono-exponential T2 allowed spin populations to be split among the associated different relaxation times.

NMR applications to low porosity carbonate stones

The purpose of this paper is to investigate NMR applications to porous materials widely employed in artistic and historical monuments and largely studied in the Cultural Heritage conservation field. Carrara marble, Candoglia marble and travertine samples were studied and data from relaxation times measurements were compared. Very interesting results from treated samples are reported and explained under the structure related spin lattice relaxation time point of view. Images of Carrara marble aged sample (XIX century), coming from the Florence Cathedral obtained for short absorption time of water by capillary rise and for relatively small thickness slices together show the fluids spatial distribution within the stone. Comparative images showing untreated sample with the treated ones were obtained suggesting very useful applications for the determination of treatment effectiveness.

Intermolecular double-quantum NMR techniques to probe microstructures on porous media

In heterogeneous systems the amplitude of the intermolecular double-quantum (DQ) signal depends on sample heterogeneity over a correlation distance dc=pi/(gammaGct). In this paper two different CRAZED-type sequences were applied in a porous medium phantom. One of these sequences gives rise to a DQ-T2 weighted signal, while the other one gives rise to a DQ-T2* weighted signal. Experimental results indicate that tuning of the correlation distance dc in a porous medium can alter the DQ signal in a manner which depends on the microstructure. This is evident only using the CRAZED-type sequence which gives rise to a DQ-T2* weighted signal.

Effects induced in marbles by water-repellent compounds: the NMR contribution

The purpose of this paper is to investigate nuclear magnetic resonance (NMR) applications to porous materials widely employed in artistic and historical monuments and largely studied in the Cultural Heritage conservation field, with the aim of studying structural variations induced in the porous matrix by the application of strengthening and water-repellent agents. Carrara marble and Candoglia marble samples, both in the native state and after treatment, were studied and data from relaxation time measurements were compared. Results collected on treated samples are reported and explained in terms of the relation between spin-lattice relaxation time and the structure of the porous materials. Traditional techniques were employed in addition to NMR analysis on marble samples for the evaluation of the preservative performances of three agents generally employed in the restoration yards. Comparative images showing untreated samples with the treated ones were obtained suggesting very useful applications for the determination of treatment effectiveness.

New results in the application of innovative experimental techniques for investigation of stone decay's processes

Publisher Summary Water penetration within the stone porous structure is one of the main reasons for the stone deterioration and superficial degradation. Nuclear Magnetic Resonance Imaging (NMR Imaging) is the only non-destructive technique that allows obtaining high-resolution images of water contained inside the porous sample. This chapter describes the study conducted on samples of marble and travertine by NMR imaging to determine their porosity and decay phenomenon. For analyses, samples from quarries and treated with commercial products, which are employed for the consolidation and protection of degraded stones, were used. The study was performed on 5 * 5 * 2 cm 3 samples that absorbed water by capillary pressure from filter paper. Natural absorption conditions following standard laboratory methods for imbibitions by capillary pressure were used in this study, instead of examining vacuumed samples. The results obtained from NMR imaging showed that the stones under investigation are composed of calcium carbonate and consist of a structured porous matrix characterized by small pores in which water is strongly trapped as shown by the considerable amount of water retained and heterogeneously distributed. The chapter also discusses the preliminary results of decaying mechanism as obtained by scanning electron microscopy (SEM) coupled with an energy dispersive X-ray (EDX) system. The mapping of “element probe” by SEM-EDX system for microanalysis provides information about the distribution of organic resins in the first layers of porous structures.

Multiple quantum coherences: New NMR tools to study materials and living systems

Intermolecular multiple-quantum coherences have been proven in recent years to provide a novel contrast mechanism to study heterogeneity in liquid systems. This subject represents a source of remarkable interest in the fields of physics of matter and biomedicine. Recent results achieved on intermolecular double-quantum signal transverse relaxation decay in confined liquid systems (such as in vivo bone marrow in trabecular bone, and doped water in glass capillary pipes) are reported and discussed in this paper. Correlated two-dimensional spectroscopy revamped by asymmetricz-gradient echo detection-like sequences were implemented in order to perform intermolecular doublequantum transverse relaxationT2DQ andT2DQ* measurements. Our experimental results indicated that the relationshipT2,n*=T2*/n betweenn-quantum transverse relaxation time and the conventional singlequantumT2* only applies for homogeneous systems and fails in the case of highly heterogeneous systems like porous systems.

Evaluation of stone pore size distribution by means of NMR

Publisher Summary Nuclear magnetic resonance (NMR) is a technique that exploits magnetic properties of atomic nuclei with spin quantum number different from zero in an external magnetic field. The energy exchanges between the system and its surroundings is obtained by studying the time length needed for the spin system magnetization to reach the equilibrium value, after a selected perturbation. Therefore, NMR helps in determining the interactions between the pore walls and the hydrogen nuclei of water molecules trapped in the stone porous structure. This further gives information about the chemical-physical properties of the porous matrix. The determination of porous matrix properties in natural porous stones is a very important goal in the Cultural Heritage conservation field. Porous structure of a natural stone depends on its genesis and on its particular history. This chapter describes the application of nondestructive NMR technique to determine pore size distribution function on samples of Carrara marble, Candoglia marble, and travertine. The experiment conducted compares the experimental relaxation data with the data obtained from a simulated porous system. Two marbles and one limestone are compared with samples treated with three different agents: (1) a consolidating, adhesive and binding agent; (2) a hydrophobic protective and preconsolidating agent; and (3) a hydrophobic protective no-film agent. NMR data based analysis is totally non-destructive and is representative of the critical regions where water can be dangerous. It provides useful analysis of the material conservation degree and a pointed conservative treatment. The chapter also provides tables and graphs to illustrate mean values and standard deviations of pore size distribution function in different samples.