C. Terenzi

Two-dimensional longitudinal and transverse relaxation time correlation as a low-resolution nuclear magnetic resonance characterization of ancient ceramics

Longitudinal and transverse relaxation time correlation (T1-T2) is employed as a nuclear magnetic resonance noninvasive characterization tool for archeological ceramics. This paper is aimed at investigating whether the most relevant firing-induced changes in ceramics, including those involving pore space properties and paramagnetic mineral structures, could be used as markers of the firing process and therefore of ceramics themselves. Ancient ceramics are made up of naturally available clays, often rich in iron impurities, which undergo relevant modifications of pore distribution upon firing. The firing process also assists chemical and physical rearrangement of iron-bearing species, yielding mineral structures with different magnetic properties. That being so, T1-T2 maps are expected to show the interdependence between ceramic structure and firing technology. T1 and T2 distributions are basically proportional to pore-size distribution, but T2, which is also sensitive to magnetic susceptibility effects, m...

The Use of Portable Single-Sided Relaxometry and Laboratory Imaging NMR Devices in Stone Conservation

Abstract Two nuclear magnetic resonance (NMR) devices, a standard imaging apparatus and a portable single-sided relaxometer (with geometry that allows non-destructive in-situ relaxation measurements on samples of any dimensions), were used to assess the hydrophobic performance of an acrylic polymer (Paraloid B-72) applied as a trichloromethane (chloroform) solution on a biocalcarenite (Lecce stone). The NMR images and relaxation time distribution functions of samples characterized by different treatments were acquired for different water absorption and measurement sequences. Samples were analyzed both fully saturated and during the capillary water absorption. The relaxation results have been compared with NMR images of internal sections of the same samples in the same absorption conditions. In spite of the instrumental and physical differences of the two devices (the single-sided device was tuned to detect the signal from a sensitive volume that is only a small portion of the entire sample, located in the first 2 mm below the surface), the experimental results of relaxometry and imaging are in very good agreement. The comparison allows the assertion to be made that the single-sided NMR technique is a powerful tool for in-situ evaluation of water-repellent treatments used for consolidation and/or protection of stone artifacts.

Effects of time and temperature of firing on Fe-rich ceramics studied by Mössbauer spectroscopy and two-dimensional 1H-nuclear magnetic resonance relaxometry

The combined effects of firing temperature and soaking time on the microstructure of iron-rich porous ceramics have been studied by 57Fe-Mossbauer spectroscopy and 2D 1H nuclear magnetic resonance (NMR) relaxometry using a single-sided probe. Examining water-saturated ceramics using the relaxation correlation method, where longitudinal (T1) and transverse (T2) relaxation times are measured concurrently, provides information about firing-induced changes in both porosity (related to T1) and magnetic properties (related to T2). Comparing the information obtained from 1H-NMR analyses with that obtained from Mossbauer spectroscopy (which characterizes changes in iron-bearing species) shows that the T1-T2 NMR correlation technique is very sensitive to even subtle modifications in the magnetic behavior of Fe-bearing species. Moreover, the single-sided NMR approach allows us to perform millimeter-scale depth-resolved measurements, which can be used to non-invasively study the microstructural heterogeneities assoc...

Noninvasive monitoring of moisture uptake in Ca(NO3)2-polluted calcareous stones by 1H-NMR relaxometry†

NMR transverse relaxation time (T2) distribution of 1H nuclei of water has been used to monitor the moisture condensation kinetics in Ca(NO3)2 · 4H2O‐polluted Lecce stone, a calcareous stone with highly regular porous structure often utilized as basic material in Baroque buildings. Polluted samples have been exposed to water vapor adsorption at controlled relative humidity to mimic environmental conditions. In presence of pollutants, the T2 distributions of water in stone exhibit a range of relaxation time values and amplitudes not observed in the unpolluted case. These characteristics could be exploited for in situ noninvasive detection of salt pollution in Lecce stone or as damage precursors in architectural buildings of cultural heritage interest. Copyright