1,721,064 research outputs found
Cation migration and structural modification of Co-exchanged ferrierite upon heating: a time-resolved X-ray powder diffraction study
No full textThe in situ time-resolved analysis of Co-exchanged synthetic ferrierite was performed in the range 53-810 degreesC by Rietveld refinements of powder diffraction data. The small contraction of the unit cell volume (-2.35%) confirmed that the ferrierite framework behaves as a noncollapsible framework. Moreover, continuous monitoring of the structural modifications induced by heating showed that cobalt ions migrate to new positions following the dehydration process step by step. Above 500 degreesC, five cation sites were localized; four of these are readily accessible to absorbed molecules and act as Lewis acid sites
In-situ XRPD of hydrating cement with lab instrument: reflection vs. transmission measurements
No full textThe complex system of reactions taking place during cement hydration can be investigated by means of in-situ XRPD. Time-resolved synchrotron XRPD is the optimal source although it is hardly accessible for routine measurements. The present work was aimed to test the feasibility of in situ measurements of hydrating cement pastes using a labo-ratory diffractometer (PANalytical X’Pert PRO) in reflecting and focusing transmission geometries. Ordinary CEM-I 52.5 R paste (w/c = 0.5) was measured using three different instrumental settings: reflection Bragg-Brentano geometry, focusing transmission capillary geometry and focusing transmission flat sample geometry. Semi-quantitative phase analysis were performed using a Rietveld full profile fitting approach. Advantages and disadvantages of the three different experimental configurations are critically discussed
Dehydration-rehydration processes in zeolites A: crystal-chemical characterization and possible application to improve the selectivity of gas sensors
No full textThe efficiency of hydrophilic zeolite A in its Na-, Na,K- and Na,Ca-form (4A, 3A and 5A, respectively) as an absorbing water molecules filter was tested after repeated thermal rigeneration cycles. The zeolite samples were characterized by means of thermogravimetric (TG) and X-ray diffraction (XRD) analyses. Water absorption capacity for all samples remains approximately the same after repeated dehydration-rehydration cycles and even if the process is accelerated. Rietveld structure refinements revealed no significant structural changes as a function of the number of regeneration cycles; slight variations of framework T-O distances and T-O-T angle were only recorded after the thermal activation
X-ray powder diffraction diagram clustering and quantitative phase analysis on historic mortars
No full textThis paper deals with the application of cluster analysis to X-ray powder diffraction patterns to define homogeneous groups of mortar-based materials according to their mineralogical composition. For this purpose, the diffraction patterns of 110 samples of mortars from the Temple of Venus (Pompeii, southern Italy) were used to test this method. Rietveld refinement, for quantitative mineralogical phase analysis, was performed on the most representative sample of each cluster. The mineralogical grouping yielded by the cluster analysis of XRPD data turned out to be consistent with the petrographic groups
The Debated Discovery of Dolomite and the Proposal of a New Geosite at Borcola Pass (Eastern Italian Pre-Alps) in Honor of Giovanni Arduino
Get PDFWithin the Venetian Pre-Alps, the Borcola Pass connects the Posina (Vicenza province) and the Terragnolo (Trento province) valleys. The Posina valley is located north of Schio (Vicenza) within the Italian Southern Alps structural unit. In this area, the injection of Paleogene basaltic dykes along fault/fractures in the late Triassic Dolomia Principale unit has produced a local metamorphism of the dolomite rock into a marble characterized by the presence of brucite veins. This marble was studied in the eighteenth century by the famous Italian scientist Giovanni Arduino, who understood its metamorphic origin. In fact, the marble is always associated with sub-vertical basaltic dykes intruded into the carbonate rocks of the Pre-Alps. Arduino performed also chemical experiments on the marble. The reading of the description of the experiments induced later authors (e.g., Maraschini, von Morlot, Mc Kenzie) to infer that Arduino unknowingly discovered the mineral called dolomite. In this work, we propose that the abandoned Borcola Quarry should be nominated as a geosite, to allow its conservation and popularization and to preserve the memory of a probably minor, yet informative step in the long-lived history of the discovery of dolomite. In addition, this site presents other reasons of interest, such as petrography, mineralogy, structural geology, industrial archeology, and eco-geotourism. The proposed geosite is therefore of great importance in terms of its multidisciplinary scientific value, aesthetic appeal, and educational valu
Over-loaded Cu-ZSM-5 upon heating treatment: A time resolved X-ray diffraction study
No full texthe over-loaded Cu-ZSM-5 under heating treatment (50-910 degrees C) in oxidative conditions exhibits the formation of copper aggregates, which show different oxidation states as a function of temperature (Cu-0, Cu2O and CuO). At room temperature the excess of copper is not detectable by X-ray diffraction (XRD). It is likely present as divalent copper species (Cu-x(OH)(y)) dispersed on the zeolite surface that appear amorphous at XRD. This is confirmed by the UV-Vis diffuse reflectance spectroscopy data. From Rietveld refinement of room temperature and high temperature diffraction data, there are no indications of the presence of copper clusters inside the zeolite cavities. As the heating treatment proceeds, the dispersed copper species transform to metallic copper particles with increasing diffracting domains as a function of temperature. Above 510 degrees C the metallic copper starts to progressively oxidise to Cu2O and finally CuO
Molecular H2O in microporous silicates: Thermodynamic and H-bonding behavior of confined H2O
No full textMolecular H2O in armenite, BaCa2Al6Si9O30 center dot 2H(2)O, and epididymite, Na2Be2Si6O15 center dot H2O: Heat capacity, entropy and local-bonding behavior of confined H2O in microporous
No full textArmenite, ideal formula BaCa(2)Al(6)Si(9)O(30)center dot 2H(2)O, and its dehydrated analog BaCa(2)Al(6)Si(9)O(30) and epididymite, ideal formula Na(2)Be(2)Si(6)O(15)center dot H(2)O, and its dehydrated analog Na(2)Be(2)Si(6)O(15) were studied by low-temperature relaxation calorimetry between 5 and 300 K to determine the heat capacity, C(p), behavior of their confined H(2)O. Differential thermal analysis and thermogravimetry measurements, FTIR spectroscopy, electron microprobe analysis and powder Rietveld refinements were under-taken to characterize the phases and the local environment around the H(2)O molecule
Laboratory in situ X-ray diffraction and isothermal calorimetry: a useful tool to evaluate cement kinetics
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