359 research outputs found
Stepwise dehydration of thomsonite (THO) with disordered Si/Al distribution: A new partially hydrated phase
No full textThe structural transformations occurring as a function of increasing temperature in zeolites are of interest because the porous structure, and therefore the physical properties, can significantly change.
Zeolites with THO framework type are small-pore materials, which received attention because of their applications in catalytic processes. The majority of THO zeolites (synthetic and natural) are characterized by an ordered distribution of the cations at the tetrahedral sites. To date, few cases of disordered thomsonite have been reported. In this study, we investigated the dehydration behavior of a natural thomsonite with disordered Si/Al distribution and chemical composition Ca3.34Na2.66Si11Al9O40∙12H2O. The structure was determined from room temperature (RT) to 698 K in order to compare the thermal behavior with that reported for the ordered variety. Accurate structural analysis was performed by in situ single crystal X-ray diffraction. The dehydration starts at 348 K. Up to 498 K, thomsonite gradually releases four H2O. From 498 to 573 K, additional four H2O are lost and the space group changes from orthorhombic (Pbmn) to monoclinic (P21/n). This partially hydrated phase is characterized by a unit-cell volume contraction of -3% with respect to the RT phase and by a rearrangement of the extraframework cations in the zeolitic pores. The thermally treated thomsonite is able to reabsorb 50% of the lost H2O and transform to the orthorhombic phase, equivalent to that observed at lower temperatures. However, the diffraction pattern analysis indicated a high degree of mosaicity, most probably due to the residual stress accumulated during the phase transformation
Mineralogical study of the fibrous zeolites erionite and offretite and hazard assessment
No full textThe exposure of erionite fibres to humans has been unambiguously linked to malignant mesothelio-ma, and in vivo studies have demonstrated that, at present, erionite is the most carcinogenic mineral in the world. Recently, a growing concern has developed regarding the potential risks associated with environmental and occupational exposures to erionite in different Countries, such as Turkey, U.S.A., Mexico and Iran. Despite of the great number of researches, the relationships among miner-alogical features and biological activity of erionite have not been fully understood and there are no systematic studies on the distribution of erionite or other similar fibrous zeolites in the environment. Moreover, there is another zeolite, named offretite, which is closely related both structurally and chemically to erionite. Despite commonly occurring as prisms, offretite has also been found under asbestiform habit, meaning that the morphology of its crystals has not yet been fully known and many mineralogical aspects are still to be discovered. Due to these similarities and to the possible in-tergrowth, the distinction between erionite and offretite can be hampered. To date, there are no studies regarding a potentially hazard of offretite fibers and it is unclear whether the mineralogical distinction between erionite and offretite has any health implications. The gap of knowledge of the fibrous zeolites erionite and offretite has been the starting point for the development of the present PhD project.
A multi-methodological approach, based on field investigation, morphological characterization, SEM/EDS chemical analysis and structure refinement through X-ray powder diffraction was ap-plied to different samples of potentially carcinogenic erionite and offretite from Italy. These investi-gations were performed on representative samples with variable morphologies, ranging from pris-matic, through acicular and fibrous, to extremely fibrous asbestiform habits. In the investigated samples, fibrils of inhalable size are present. Considering that the toxicity and the carcinogenic po-tential of erionite are associated with its size parameters, together with its in vivo durability and very high surface area, most of the investigated fibers may also be potentially carcinogenic. Despite of the lack of epidemiological information on populations exposed to natural asbestiform minerals oth-er than asbestos and erionite, results acquired in the present investigation suggest that other mineral fibres of similar size, habit, and biopersistence may carry a risk for humans.
Successively, morpho-chemical characterization and surface properties determinations were per-formed on a selection of different asbestiform zeolite fibers: two erionite samples (from USA and Turkey), one offretite sample (Italy) and, for comparison, one scolecite sample (India). These sam-ples have been used to carry out in-vitro experiments to assess the level of reactivity and transfor-mation that such fibers may induce to micelles and membranes in contact with them, and therefore, indirectly the possibility of leading to asbestos-related lung diseases. With this aim, specific surface area determinations coupled with EPR analysis and TEM images in the presence of model mem-branes are performed. This type of study has allowed me to obtain informations on the fiber inter-nalization in the membranes and the interactions occurring at a molecular level that mimicked the at-tack of the fibers at the cell membrane. The carcinogenicity of the zeolites may be nicely related to the structural modifications of the model membranes when interacting with these zeolite fibers. These results helped to clarify the chemical properties and the surface interacting ability of these ze-olite fibres which may be related to their carcinogenicity
Il codice 770 della Biblioteca Oliveriana di Pesaro: alcuni canti della «Liberata» e un discorso sul poema di Pier Matteo Giordani
No full textThe essay analyzes the content of the manuscript 770 of the Biblioteca Oliveriana Pesaro, which hands down some cantos of Torquato Tasso’s «Gerusalemme Liberata» and, a copy of an academic lecture by Pier Matteo Giordani on the poem. The contribution pinpoints the thematic cores of the lecture, a testimony of a blind spot in the literary debate about the poem, and contextualizes it within the framework of the great interest in Pesaro for the literary activity of Tasso and the ties of the author with the Giordani family. Furthermore the essay details the results of an analysis of the text of the poem’s cantos, which clarifies its textual position in relation to the redactional history of the «Liberata». The Appendix contains the transcription of Pier Matteo Giordani’s unpublished lecture
Real-time observation of fibrous zeolites reactivity in contact with simulated lung fluids (SLFs) obtained by Atomic Force Microscope (AFM)
No full textEnvironmental exposure of erionite fibres to humans has been linked to malignant mesothelioma and at present is classified as the most carcinogenic mineral. In opposite, there are no studies regarding a potential hazard of offretite fibres, closely related to erionite both structurally and chemically. In this paper, the interactions of erionite and offretite surfaces with SLFs were investigated by means of in situ AFM. To simulate different environments in the lungs, Artificial Lysosomal Fluid (ALF) and Gamble’s solution were used. In ALF (4.15 < pH < 4.31) the dissolution of erionite and offretite surfaces was detected, as well as an evident removal of particles (mainly attributed to impurities) from the crystal faces. Instead, the growing of a layer of an unknown phase on the surface of both zeolites, was observed during the interaction with Gamble’s solution (7.4 < pH < 8.48). The thickness of this layer reached few tens on nanometers and covered all the observed areas. The understanding of the observed processes is of paramount importance, since they could be potentially involved in the mechanisms triggering the toxicological effects of erionite fibres
Humidity- and temperature-dependent study of YUG type zeolite. A new dehydrated topology
No full textMetasomatic to Hydrothermal Genesis of Natural Calcium Silicate Hydrates (C-S-H): Evidence from Lessini Mountains, Veneto Volcanic Province, Italy
No full textWe report the occurrence of natural calcium silicate hydrates (C-S-H) from the Grolla quarry in the Lessini Mountains of Northern Italy. These minerals are formed by basic and ultrabasic magma interacting with carbonate rocks. The mineral assemblage includes thaumasite, xonotlite, tobermorite, and plombierite, often intergrown with other silicates, as well as minor amounts of carbonates and sulfates. Common zeolites in this area include chabazite, phillipsite/harmotome, natrolite, and thomsonite. Although less abundant, these zeolites are typically associated with calcite, fluoroapophyllite, and barite. The Grolla quarry outcrop allows for the study of the in situ complex crystalline overgrowths and specific crystal chemistry of rare natural mineral phases, such as C-S-H minerals, formed under metasomatic to hydrothermal conditions
Uso del fino di cava per la produzione di componenti a matrice cementizia rinforzati con fibre
No full textCeramic covering of prefabricated reinforced concrete panels: microstructurals, mechanics and technical asptects
No full textChrysotile within calcite veins from Northern Apennines
No full textIn the Northern Apennines several olistoliths made up of serpentinites, calpionelle limestones and ophiolitic breccias
have been recognized within the Porcellara Complex, Monte Cassio Unit. These olistoliths are frequently crossed by a
dense network of centimeter to decimeter veins generally filled by carbonate minerals (e.g. La Costa, Berceto, PR).
Morphological and compositional data (SEM-EDS and XRPD) have revealed that these carbonate minerals consist
mainly of well-formed, white to milky calcite crystals, strictly associated with chrysotile. This mineral is found as white
thin fibers (< 1 micron), grew up in intimate association with calcite crystals. These fibers may be very rare and
randomly scattered within the crystals of calcite, or can be grouped into bundles of millimeter to centimeter size. At
times, the chrysotile can get to completely fill the vein. Chrysotile fibers are well-formed and euhedral at all scales from
hand specimen to electron microscope images. In some cases, individual fibers of chrysotile are not visible in hand
specimen or under the petrographic microscope; however, SEM images show the characteristic elongate crystal
morphology. The fibers are also characteristically curved at the millimeter scale.
It is important to note that the fibers of chrysotile appear, frequently, as a physical extension of calcite crystals, without
any evident morphological discontinuity in the transition from a massive (calcite) to a fibrous (chrysotile) appearence.
The results of detailed SEM-EDS elemental analyses carried out in various segments of the contact areas between
calcite and chrysotile crystals seem to show a gradual transition in chemical composition from pure calcite to pure
chrysotile phases, passing through various intermediate arrangements
Generalizing Deontic Action Logic
No full textWe introduce a multimodal framework of deontic action logic which encodes
the interaction between two fundamental procedures in normative reasoning: conceptual
classification and deontic classification. The expressive power of the framework is noteworthy,
since it combines insights from agency logic and dynamic logic, allowing for a
representation of many kinds of normative conflicts. We provide a semantic characterization
for three axiomatic systems of increasing strength, showing how our approach can
be modularly extended in order to get different levels of analysis of normative reasoning.
Finally, we discuss ways in which the framework can be used to capture other formalisms
proposed in the literature, as well as to model searching problems in Artificial Intelligence
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