1,721,004 research outputs found
Crystal structure of a potassium-rich natural gmelinite and comparison with the other refined gmelinite samples
No full textA complete crystallochem. characterization of a gmelinite sample from Fara Vicentina (Vicenza, Italy) is given. The mineral is anomalous for the prevalence of K (2.72 atoms per unit cell) among the exchangeable cations. The lattice consts. are a = 13.621(3) and c = 10.254(1) Å. Its crystal structure was refined down to Rw = 5.92% and compared with the structures reported for Na-, Ca- and K-rich gmelinites in the literature; the sample studied is characterized by a very low occupancy (3%) of 1 (C2) of the 2 exchangeable cation sites and by water mols. distributed among 8 partially occupied sites. A correlation involving the C2 site and the geometry of the tetrahedral framework was found between the bond strengths: with decrease in the bond strength, the shape of the 8-ring of the gmelinite cage becomes more circular, the double 6-ring becomes more hexagonal and, consequently, the c parameter increases and the a parameter decreases. Post-crystn. cation exchanges explain the present chem. compn. of the mineral
Crystal chemistry of the zeolites erionite and offretite
No full textMany known occurrences of the zeolites erionite and offretite have been characterized by electron probe microanalysis, X-ray powder diffraction, and optical microscopy. For the first time, a substantial amount of experimentally consistent and homogeneous chemical and crystallographic data have been evaluated for these natural zeolites. Systematic analysis of the data, performed by statistical multivariate analysis, leads to the following conclusions: (1) the two zeolites have well-defined compositional fields in the chemical space describing the extraframework cation content, best illustrated in a Mg-Ca(+Na)-K(+Sr+Ba) diagram; (2) no discrimination is possible on the basis of the framework Si/Al ratio because of the extensive compositional overlap between the two species, however the SI-AI content in the framework tetrahedra is the major control on the unit-cell volume dimensions, particularly in erionite; (3) the crystal chemistry of the Mg cations is a major factor in controlling the crystallization of the mineral species; (4) cation compositions at the boundary of the recognized compositional fields might be due to chemical averaging of two-phase intergrowths, although these mixed-phase occurrences are much less common than previously thought; (5) the sign of optical elongation is not a distinctive character of the two phases, it is related to the Si/Al ratio in the framework tetrahedra of each zeolite type and cannot be used for identification purposes; (6) the zeolite mineral species epitaxially overgrown on levyne in all cases is identified as erionite; in a few cases offretite was found to be overgrown on chabazite; (7) erionite samples epitaxially overgrown on levyne are substantially more Al-rich and Mg-poor than the erionite samples associated with other zeolites
Release of agronomical nutrient from zeolitite substrate containing phosphatic waste
No full textThe principal plant nutrients are phosphorous, nitrogen and potassium. Among these compounds, phosphorous is the most critical: it reacts rapidly, becoming an insoluble compound. The combination of zeolitites with phosphate materials (zeoponic substrate) agrees to a gradual and controlled phosphorous release in soils: phosphorous for plant uptake is released by the combination of dissolution and ionexchange reactions. Animal bone ashes, rich in phosphorous and leached alone, release little amounts of soluble phosphorous and a great deal of alkaline sodium and potassium. Concerning chabazitic-zeolitite, it encourages a both gradual and growing soluble phosphorous release from animal bone ashes, in accordance with clinoptilolitic- and phillipsiticzeolitite abilities; in particular, that release increases, thanks to both a higher zeolitite/bone ash ratio and ammonium enrichment of zeolitite. The use of zeolitite is environmentally sustainable in Italy because large amounts of deposits of zeolitite were present in Italy
Diagenetic Mordenite From Ponza, Italy
No full textDiagenetically altered rhyolitic rocks consisting of major mordenite and minor cristobalite and smectite occur beneath a thick (about 90 m) smectite-rich layer in an abandoned quarry at Cala Fontana, in the northwestern part of the Ponza Island (Thyrrenian Sea, Gulf of Gaeta). The structure of the mordenite was refined by full-profile Rietveld analysis on X-ray powder diffraction data. Quantitative mineralogical analysis of the specimen having the highest zeolite content from the Rietveld-refined phase-scale factors yield: mordenite 72.8%, smectite 2.0%, cristobalite 5.9%, illite 3.0%, sanidine 13.9%, augite 2.4%. The chemical composition of the mordenite from electron microprobe analysis resulted in a content of tetrahedral atoms [Si/(Si + Al) = 0.83] in agreement with the range (0.80-0.85) known for this zeolite. Both the chemical analysis and the structure refinement showed a high K content among the extraframework cations. The assemblage of the authigenic minerals is interpreted as the result of diagenetic alteration of the rhyolitic glass by meteoric or ground water in an hydrologically open system, and the crystallization of mordenite instead of the most common smectite is interpreted as due to locally high pH conditions
Features of Graft Copolymer Formation Through Reaction of Functionalized Polyolefins with Poly-e-Caprolactam"
No full textThe reaction in the melt of polyolefins containing 2-diethylsuccinate groups (DES) with poly-epsilon-caprolactam (PA6) to give a graft copolymer was investigated under different conditions. Even using a large excess of DES groups os-er the PA6 terminal amino groups the graft copolymer yield resulted only partial thus suggesting a kinetic control of the reaction. The effect of various catalysts was then examined taking into account results obtained in a model reaction between a low molecular weight amine and diethylsuccinate. The results are discussed in terms of side reactions and miscibility of the pristine polymers
Theoretical study of the conformational and optical properties of a fluorescent sensor grafted on apolar polymer structures
No full textAn anomalous phillipsite from Saint-Jean-le-Centenaire, Ardeche
No full textPhillipsite [12174-18-4] occurs as clear transparent spheroids, colorless to yellow to reddish-orange in color, in the vugs of a basalt at Saint-Jean-le-Centenaire, Ardeche, France. The fibrous radial nature of the spheroids can be obsd. under the microscope only between crossed polars. It has a higher content of Si than the normal hydrothermal (i.e. those occurring in vugs of massive rocks) phillipsites. The powder pattern lacks all those peaks which make the distinction between phillipsite and merlinoite possible. The peak broadening in the powder pattern indicates a crystallite size of ∼350 Å. This anomalous zeolite is more similar to phillipsite than to merlinoite; its features are near those of some sedimentary and some synthetic phillipsites
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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