1,721,117 research outputs found
Design of Magnetic Spinel Oxide Nanoarchitetures
No full textUnderstanding the interplay among chemical, microstructural and physical properties is the key to design new materials.
In this framework the intrinsic versatility of chemical science can give a wide and at the same time deep view, allowing to correlate
synthesis and properties. This contribution focuses on the design of magnetic nanostructured spinel oxides, describing how
to manipulate the matter to realize nanoarchitectures, in order to govern the magnetic properties
Preliminary archaeometric study of menhir statues from Allai (central Sardinia, Italy): source provenance and technological properties
No full textIn the 1990s a number of anthropomorphic sculptures (“menhir statues”) of ignimbritic rock, were found into the walls of the Nuragic tower of Arasseda-Allai (Sardinia, Italy). They had probably belonged to a nearby Aeneolithic sanctuary (III millennium BC) and they
were reused as a building material by the Nuragics during the II millennium BC. Some of these megaliths have been removed
from the protohistoric site and are now exposed at the Archaeological Museum of Laconi. Also an ancient quarry of volcanic blocks, which was probably used in the Prehistoric Age, has been discovered in the same area where the Nuraghe and the sculptures had been found. An autoptic and instrumental multi-technique approach has been carried out on 10 geological samples collected from the local volcanic stone of the Monte Ironi geological unit. On the geological material (two samples from Arasseda quarry and eight from other points of the outcrop) we have used a macroscopic survey and chemical analytical techniques such as ED-XRF by conventional and non-destructive approaches both, ICP-OES, and ICP-MS. This study has allowed us to determine the geochemical intra-source variability of the lithic raw material. Furthermore, the mineralogical investigation by X Ray Diffraction and the ICP data on geological samples have led to a definition of some technological properties of local geo-source. After testing the uniformity between the results of all geochemical techniques, on three sculpturesfrom Arasseda, according to conservative requirements we have achieved only non-destructive fluorescence measurements and autoptic observations. Through the comparison between artifacts and lithological outcrop’s analytical data, we have been able to define the source of origin of the raw materials employed for the Prehistoric megaliths and to establish spatial relationships between the stone sources and the sites where the sculptures had been found
Eneolithic menhirs of Laconi (central Sardinia, Italy): From provenance to technological properties
No full textA multi-technique approach was carried out to investigate the provenance and technological properties of 34 anthropomorphic menhirs from Laconi (central Sardinia, Italy) dated back to the local Copper Age (III millennium BC). After visual inspection, geological materials coming from local ignimbritic outcrops were characterized by elemental and mineralogical analyses: portable X-Ray Fluorescence (pXRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Powder X-Ray Diffraction (PXRD). Conversely, the menhirs were studied only by visual examination and non-destructive pXRF measurements. By means of a comparison between pXRF data collected on the menhirs and the lithological outcrops, it was possible to assign the prehistoric artifacts of Laconi to local geo-sources, taking into account geochemical intra- and inter-source variabilities. pXRF was demonstrated to be a useful tool for provenance studies while mineralogical analysis resulted fundamental for the technological aspects. The latter technique pointed out the main use of hardstones, probably owing to the durability they give to the menhirs.To the best of our knowledge, this is the first archaeometric study on Sardinian menhirs and one of the few recently developed on European megaliths
Geo-materials selection and procurement strategies in Copper Age menhirs production at Allai (central-western Sardinia, Italy)
No full textIn the 1990s a group of anthropomorphic menhirs were found into the walls of the Nuraghe Arasseda, in Allai (central-western Sardinia, Italy). They probably belonged to a Copper Age sanctuary of III millennium BC, and were reused as a building material by nuragic people during the II millennium BC. In modern times three of these megaliths were removed from the Nuraghe Arasseda and exposed at the Sardinian archaeological museum of Laconi.
After testing the reliability of a non-destructive archaeometric approach, a study concerning the source provenance and the technological properties of the raw materials employed for the menhirs production were carried out. On eight geological samples (two of which come from an ancient quarry) collected from the Monte Ironi volcanic outcrop of Allai, visual examination and instrumental measurements were performed. Chemical analyses by portable X-Ray Fluorescence spectrometry (pXRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) were carried out to determine the coherence between the analytical data collected by the different techniques [1], to characterise the stone raw material and to evaluate its chemical intra-source variability. On the three menhirs from Arasseda, in accordance with preservation of archaeological heritage, visual inspection and non-destructive pXRF measurements were achieved only. By means of a comparison between pXRF data collected on artefacts and geological samples, it was possible to indicate the Monte Ironi unit as the geo-source of two out of three Arasseda menhirs.
Powder X-Ray Diffraction (PXRD) measurements were useful to recognize the technological properties of the Monte Ironi stone and to reconstruct the criteria adopted during Copper Age in selecting geo-materials for sculptural purposes.
To the knowledge of the authors, this is the first research study on the Arasseda menhirs by means of chemical and physical methods (the second one on Sardinian menhirs [2]), and one of the few archaeometric studies recently developed on European megaliths.
[1] D. Mitchell, P. Grave, M. Maccheroni, E. Gelman, Geochemical characterisation of north Asian glazed stonewares: a comparative analysis of NAA, ICP-OES and non-destructive Pxrf, Journal of Archaeological Science 39, 2921–2933, 2012.
[2] M. Serra, V. Mameli, C. Cannas, Eneolithic menhirs of Laconi (central Sardinia, Italy): from provenance to technological properties, Journal of Archaeological Science: Reports 5, 197-208, 2016
Structural investigation of Fe2O3-SiO2 nanocomposites through radial distribution functions analysis
No full textTwo Fe2O3-SiO2 nanocomposites containing 50% by weight of iron oxide were prepared by a sol-gel method. By changing the surface to volume ratio of the gelling mass from 0.04 (sample A) to 0.3 cm(-1) (sample B), gelation times changed, resulting in nanoparticles of average size of about 10 and 4 nm, respectively. Accurate X-ray diffraction (XRD) data were collected and used to calculate total structure and correlation functions. The analysis of these functions unequivocally proved that in both samples maghemite is the iron oxide formed. The result demonstrated that decreasing the gelation time gives rise to the formation of smaller and smaller nanoparticles of the same phase. The possibility of interpreting the XRD pattern of sample B in terms of occurrence of 2-line ferrihydrite was discussed
Hydrotalcite-like sulfate minerals as a natural sink for arsenic. Field evidences in an old mine of Sardinia, Italy
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Oxygen evolution on Ti/Co(3)O(4)-coated electrodes in alkaline solution. CHEMICAL PAPERS
No full textThe electrochemical performances of Co(3)O(4) nanopowders, obtained by the sol-gel method, were investigated and compared with those of commercial Co(3)O(4) powders, for oxygen evolution reaction in alkaline solution. The active oxide powder was mixed with teflon and assembled on Ti substrate to form thin catalyst film. Cyclic voltammetry, polarization curves, and electrochemical impedance spectroscopy were used to assess the mechanism of oxygen evolution reaction, chemical structure, and morphology of the catalyst
ZnO-SiO2 nanocomposites obtained by impregnation of mesoporous silica
No full textThe synthesis of ZnO-SiO2 nanocomposites through impregnation of a commercial mesoporous silica with zinc nitrate aqueous or ethanolic solutions is reported. During thermal treatment the samples evolve toward the formation of nanocrystalline ZnO particles (zincite phase) dispersed onto amorphous silica stable up to the temperature of 700 degreesC. The nanoparticle size distribution is affected by the process parameters used in the impregnation. A narrower and more homogeneous distribution is obtained using ethanolic instead of aqueous solutions. At higher temperatures the samples evolve towards the formation of a zinc silicate phase. (C) 2003 Elsevier Science Ltd. All rights reserved
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