3,513 research outputs found
Natural and synthetic zeolites, methodologies of synthesis by chemical reagents and natural materials.
No full textThe Solid-state Conversion of Kaolin to Kalsio<sub>4</sub> Minerals: The Effects of Time and Temperature
No full textA phenomenological–mathematical approach in simulating the loss in weight of chlorine during sodalite synthesis
No full textIn a previous paper we described the results of a sodalite synthesis, performed by the mixing of metakaolinite and NaCl within an alumina crucible, heated in an oven at a temperature of 850 C and ambient pressure. During the synthesis process, a loss of weight of the open crucible, attributed to chlorine (Cl) diffusion through the granular material contained inside the crucible, was observed. A very simple model was proposed, aimed at reproducing mathematically the experimental data behavior. Nevertheless, experimental and numerical result comparisons suggested the need for some modeling improvements. Thus, in this paper the already proposed analytical solution, based on the usual "first principles" approach, was modified through a backfitting phenomenological-analytical approach. We explored the assumptions that at the beginning of the experiment, the inventory of chlorine was completely or partially bound in the matrix, and that it was transformed into a gas free to diffuse only gradually over the transient. In addition, we explored the effect of full or partial variability in time of the diffusion coefficient. The apparent delay in the release of chlorine gas through the matrix mixture could be justified by an incomplete heating of the crucible at 850 degrees C and/or by some structure change of the mixture during the synthesis processes, eventually resulting in changes of diffusion coefficient values. The influences of the actual measurement process on the mathematical modeling setting, in particular the removal of some quantity of substance for diffractometer analysis, are also discussed. The final numerical results show an excellent agreement with the experimental data. Finally, it is worth noting that, notwithstanding the proposed methodology is addressed to the specific problem, it could have application in different fields. Published by Elsevier Ltd
Synthesis and characterization of wollastonite-2<i>M</i>by using a diatomite precursor
No full textABSTRACTSolid phase reaction synthesis of wollastonite-2Mby a natural rock precursor as the source of amorphous silica and CaCO3is reported. Chemical treatments were carried out on a diatomitic rock from Crotone (Calabria, Italy) in order to measure its reactive silica and CaCO3contents. Four series of synthesis were performed at 1000°C at ambient pressure by mixing, at different stoichiometry, the diatomitic rock with a natural limestone as a source of additive CaCO3, and sodium carbonate (Na2CO3) as triggering agent.Wollastonite-2Mwas characterized by chemo-physical, crystallographical and morphological-microtextural analyses. All these characterizations, together with infrared and nuclear magnetic resonance (29Si) responses provide values comparable to literature data. Estimation of the amorphous phase in the synthesis powders was performed through quantitative phase analysis using the combined Rietveld and reference intensity ratio methods, resulting in a final product of 96.3% wollastonite-2M.</jats:p
Syntheses and characterization of zeolites K-F and W type using a diatomite precursor
No full textZeolites K-F and W (EDI and MER types) were synthesized hydrothermally using a natural rock as raw material. Chemical treatments were carried out on a diatomitic rock (containing opaline silica) from Crotone (Calabria, Italy) in order to separate/obtain potassium silicate, a reagent necessary for synthesizing zeolites. Synthesis experiments were performed by mixing the obtained siliceous solution with potassium hydroxide and alumina in varying proportions at 150 degrees C and room pressure. Four synthesis series were performed to form zeolite K-F (EDI) and zeolite W (MER).
The chemical-physical and morphological characterization of the zeolite phases were carried out. Cell parameters were calculated using the Rietveld method. Infrared, thermal and nuclear magnetic resonance (Si-29) experiments confirmed the high quality of the zeolite products. The amorphous phase in the synthesis powders was estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods
Synthesis of zeolite Na-A from Halloysite 10 A° and new crystallization kinetic model for the transformation of Na-A into HS zeolite.
No full textThe present work deals with the synthesis of Na-A zeolite using 10 Å halloysite (collected near Grosseto, Italy) as the starting material, instead of the more expensive chemicals currently used in industry (Na aluminates and Na silicates). The process of synthesizing Na-A zeolite from 10 Å halloysite is rather simple as the reaction of halloysite with alkali occurs very readily and is achieved without prior thermal activation at high temperature. The optimal conditions of crystallization of Na-A zeolite from 10 Å halloysite are reached at 80°C. At lower temperatures, transformation of halloysite into an amorphous material requires more time, and the field within which Na-A zeolite exists overlaps that of 7 Å halloysite, G and HS zeolites. The products of synthesis at 80°C were characterized by X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometry and infrared spectroscopy. We also propose a model to study the reaction kinetics of zeolite (Na-A and HS) nucleation and growth by real-time X-ray powder diffraction data. Copyright © 2005, The Clay Minerals Society
Variations on the Author
No full text“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
Risultati sperimentali di un impianto pilota per la rimozione di ammoniaca da acque di scarico superficiale mediante l'uso di una zeolitite vulcanica italiana
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