196,023 research outputs found
From HPC to HPSS: The use of superplasticizers for the improvement of S/S technology
No full textThis paper presents an S/S treatment which is based on the principles of High Performance Concrete (HPC). By using superplasticizers and hydrophobic additives, the proposed process allows the transformation of contaminated soils and sediments into low water to cement ratio (W/C) granular materials. These grains are characterized by lower porosity,
lower leaching rate of inorganic contaminants and lower water absorption as well as higher mechanical properties and improved durability compared to solidified products obtained without additives. Moreover, the mixing water may be reduced more than 25%. The results of X-ray microtomography and mercury intrusion porosimetry measurements carried out on samples prepared with and without additives are illustrated here. Volatile and/or semi-volatile organic pollutants, if present, can be removed from the granular material by a steam distillation step, at relatively low temperature (max 250°C) and under vacuum (P < 0.1 bar) in excellent yield. The resulting aggregates are suitable for the re-utilization as backfilling, concrete aggregates or may be employed for covering landfills and in other civil engineering projects
The pigments of the frigidarium in the Sarno Baths, Pompeii: Identification, stratigraphy and weathering
No full textIn the present research is used a multi-analytical approach to study the wall paintings from the Sarno Baths, located in the southern part of Pompeii. In particular the investigation is focused on the frescos of the frigidarium, though a few samples from other rooms were also analysed. Twenty wallpaintings fragments were analysed by laser scanning confocal microscopy (LSCM), optical microscopy (OM), micro-Raman, scanning electron microscope with energy dispersive spectrometry (SEM-EDS), portable X-ray fluorescence spectrometry (p-XRF) and X-ray powder diffraction (XRPD). The XRPD data were used for the mineralogical semi-quantitative phase analyses (SQPA) and the estimation of the hematite crystals size. The obtained data allow the identification of the pigments and the techniques used, and address new question such as whether talc and aragonite were used routinely in the formulation of pigments. The chemical composition of red and yellow pigments is also discussed and compared with data available from the recent literature. The wall paintings are badly preserved and weathering products occur on the pictorial surface. Eight samples of efflorescence salts and patinas were analysed by XRPD: all the samples are composed mainly by alkali sulphates. The systematic difference between the salts present on the northern and the western walls is likely related to the materials inserted during the 19th century restauration
Effects of non-stoichiometry on the spinel structure at high pressure
No full textA non-stoichiometric sample of spinel with composition T(Mg0.4Al0.6)M(Al1.8h0.2)O4 was investigated by single-crystal
X-ray diffraction in situ up to about 8.7 GPa using a diamond anvil cell. The P(V) data were fitted using a third-order
Birch–Murnaghan equation of state and the unit-cell volume V0, the bulk modulus KT0 and its first pressure derivative K0
were refined simultaneously providing the following coefficients: V0 = 510.34(6) A ̊ 3, KT0 = 171(2) GPa, K0 = 7.3(6). This
KT0 value represents the lowest ever found for spinel crystal structures. Comparing our data with a stoichiometric and natural
MgAl2O4 (pure composition) we observe a decrease in KT0 by about 11.5% and a strong increase in K0 by about 33%. These
results demonstrate how an excess of Al accompanied by the formation of significant cation vacancies at octahedral site
strongly affects the thermodynamic properties of spinel structure. If we consider that the estimated mantle composition is
characterized by 3–5% of Al2O3 this could imply an Mg/Al substitution with possible formation of cation vacancies. The
results of our study indicate that geodynamic models should take into account the potential effect of Mg/Al substitution
on the incompressibility of the main mantle-forming minerals (olivine, wadsleyite, ringwoodite, Mg-perovskite).
2008 Elsevier Ltd. All rights reserved
Three-dimensional distribution of anatectic melt inclusions in garnets by X-ray micro-tomography
No full text
Mineralogical interpretation of multispectral images: The case study of the pigments in the frigidarium of the Sarno Baths, Pompeii
No full textWall paintings are invaluable archives of pigments, techniques, and artistic expressions of past civilizations, and Pompeii is an excellent example of such archives for Roman art from mid-first century AD. Assessing wall paintings’ state of preservation requires characterizing the pigments on a large scale and documenting alteration processes which will influence conservation interventions. The problem is that large scale characterization requires delicate high resolution chemical and spectral instrumentation that is limited to the museum environment. Here, we present a new methodology for non-invasive characterization of wall paintings on-site, based on analyzing stacked photos as multi-spectral data. The photos were imaged using a portable modified digital camera that registers the ultraviolet, visible, and infrared spectral regions through external band-pass filters. Combined with portable X-ray fluorescence and fiber optic reflectance spectrometers, predetermined mineral-specific band ratios were developed on fragments found below the wall paintings, and large scale mineralogical maps were constructed. The mineralogical maps show the distribution of hematite, goethite and Egyptian blue in a wall painting of the frigidarium of the Sarno Baths complex of Pompeii, documenting iconographic figurines of plants, pygmy people, and animals from a degraded depiction of a river scene. The applications are in conservation and archaeological sciences, showing the ancient technology of the wall paintings using non-invasive measurements, and developing restoration strategies that are matching the ancient materials
Non-invasive assessment of the formation of tourmaline nodules by X-ray microtomography and computer modeling
No full textTourmaline nodules occurring in the Capo Bianco (Elba Island, Italy) aplitic rocks are here investigated by X‐ray microtomography 3D imaging. This non-invasive technique provides 3D images of the tourmaline nodules, revealing an irregular morphology consisting of branches that extend radially from the cores. The nodules present scale-invariant features that can be described by a box-counting fractal dimension. The value of the fractal dimension is proportional to the size of the nodules and tends asymptotically to a value of 2.5, in agreement with the results obtained from the simulation of virtual nodules, by means of a diffusion-limited aggregation model based on a Monte Carlo Metropolis algorithm, in which the growth probability at the tips of the nodule is an inverse function of the diffusion coefficient. The results support the hypothesis that tourmaline formed by a disequilibrium magmatic process, in which diffusion represents the rate-limiting step, inducing the formation of nodules with irregular shapes. This study shows the potential of X‐ray microtomography, in combination with numerical modeling, as a probe for accessing the 3D microstructural information of complex mineral morphologies with a non-invasive approach. The combination of numerical and experimental, non-invasive, 3D techniques represents a fundamental step forward in bridging the gap between the observation of microstructures and the interpretation of the associated processes
In situ analysis of garnet inclusion in diamond using single-crystal X-ray diffraction and X-ray micro-tomography
No full textA single crystal of garnet enclosed in a diamond from the Jericho kimberlite (Slave Craton, Canada) has been investigated using X-ray diffraction and X-ray micro-tomography. The novel experimental approach allowed us to determine the crystal structure of the garnet. The unit-cell edge a and fractional atomic coordinates of oxygen were used to determine the composition via an updated Margules model for garnets. The composition is Pyr(0.41(5))Alm(0.36(7))Gro(0.22(1))Uva(0.01(1)), which is indistinguishable from the eclogitic garnets found in other Jericho diamonds. We also demonstrated that residual pressures on the inclusion of up to 1 GPa do not affect significantly the determination of the garnet composition by structure refinement
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