1,720,994 research outputs found
Synthesis of Ca(OH)2 nanoparticles with the addition of Triton X-100. Protective treatments on natural stones: Preliminary results
No full text"Calcium hydroxide is typically used in Cultural Heritage conservation for superficial protective treatments. thanks to its conversion into calcium carbonate. Calcium carbonate is, in fact, compatible with many. carbonate-based architectonic surfaces, because its characteristics are similar to those of the restored. materials. In order to improve calcium hydroxide treatments, Ca(OH)2 particles with sub-micrometric. dimensions (nanolimes), are synthesised by a chemical precipitation process: a sodium hydroxide solution,. used as precipitator, is added, drop by drop, to a calcium chloride one. In this paper, a nanometric. calcium hydroxide, to be used in stones treatment, is produced adding in the initial solutions a surfactant. agent (Triton X-100); the solutions are then mixed together simultaneously, drastically reducing. the time needful for preparation. Different contents of surfactant are employed, and the influence on. particles dimension and carbonatation process is analysed too. The obtained Ca(OH)2 nanoparticles are. characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction. (ED). The Ca(OH)2 nanoparticles are regularly shaped, hexagonally plated and with side dimensions. less than 200 nm: in particular, increasing the surfactant content, the particle dimension reaches values. until 20 nm. Comparing nanolime suspensions obtained without and with the addition of the surfactant. agent, the last ones have comparable, if not better, performances in terms of average particle size. and morphology, crystallinity and reactivity. Afterwards, the alcoholic nanolime suspension obtained by. using Triton X-100 is applied on some natural stones; in fact, the aim of this section is to compare the. obtained results with those achieved using a nanolime synthesised without the surfactant agent. To evaluate. the treatment effectiveness in a preliminary way, standard tests are performed and compared with. the same tests previously obtained by the nanolime synthesised without the surfactant agent: “Scotch. Tape Test” and capillarity test.
Nanolime mixtures with silica fume or natural pozzola. Preliminary investigations
No full textIt is known that hydrated lime (Ca(OH)2) can be activated by reacting with siliceous materials, such as natural pozzolans (P) or silica fume (SF), in presence of water. During the interaction process, the active silica contained in siliceous materials reacts with hydrated lime to form calcium silicate hydrates (C-S-H), according to the pozzolanic reaction. Such reactions, however, could require enough time to complete mainly due to lime particles dimensions. Aim of the present work is to preliminarily study the interaction between commercial silica fume, or natural pozzolan, with nanostructured Ca(OH)2 particles, (nanolime), dispersed in aqueous suspension. The nanolime is synthesized in laboratory by our patented, simple, eco-friendly, time and energy saving and scalable route (RM2011A000370, WO2014020515A1). The interaction is carried out in water, at room temperature, considering a proper water/solid ratio, and different Ca(OH)2/SF(P) ratios in weight. The hydrates phases that forms are investigated at different hydration times by means of several techniques
MgO Nanoparticles Starting from Mg(OH)<sub>2</sub> Colloidal Suspensions Synthesized by a Facile and Scalable Process
No full textIn this paper, MgO nanoparticles are prepared by calcinating Mg(OH)2colloidal suspensions produced through an original, eco-friendly, single step, and scalable method. This method, based on an exchange ion process, is extremely simple and rapid (few minutes); it employs low-cost or renewable reactants, operates at room temperature and does not require intermediate steps, such as washings and purifications. The synthesized Mg(OH)2nanoparticles, as well as the MgO ones, are characterized by means of chemico-physical, microstructural and morphological analyses such as thermal analyses (TG-DTA), X-ray diffraction analysis (XRD), infrared spectroscopy (FTIR), surface area measurements (BET) and transmission electron microscopy (TEM). Pure and crystalline phases are produced, characterized by very small crystals. MgO nanoparticles appear aggregated into large flocks, although maintaining a plate-like shape of the original hydrate phase; these flocks seem to be constituted by a two-dimensional network consisting of well-developed and roughly spherical and monodispersed nanoparticles, with size less than 10 nm
Synthesis of Ca(OH)2 nanoparticles aqueous suspensions and interaction with silica fume
No full text"In this work, interaction at ambient temperature between silica fume and artificially produced Ca(OH)2 nanoparticles by two different methods was analyzed. Initial products and formed hydrated phases were characterized by several investigations including X-ray diffraction, thermal analyses, transmission and scanning electron microscopy. Synthesized Ca(OH)2 nanoparticles appeared regularly shaped and hexagonally plated, with side dimensions from 200nm to less than 20nm. Characterization analyses showed that, by reducing particles dimensions, calcium silicate hydrate phase formation was evident already after 7 day of hydration and a nearly complete consuming of free Ca(OH)2 after 28 days was observed. Besides, formed hydrate phases showed a highly wrinkled layer with marked crumple and rough-edge surfaces.
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A PROCESS FOR THE SYNTHESIS OF CA (OH) 2 NANOPARTICLES BY MEANS OF IONIC EXCHANGE RESINS
No full textSimple and scalable synthesis of earth-alkaline hydroxides nanoparticles in aqueous suspension
No full textIntroduction: Ca-hydroxide nanoparticles are emerging as effective conservation materials for all carbonatic-based substrates and mortars of Cultural Heritage, guaranteeing compatibility, durability, reduced environmental impact and human risk. Parallely, the development of nanoscale Mg-hydroxide, revealed considerable interest in the de-acidification of paper and wood, but also as antibacterial, flame retardant agent, and as MgO nanoparticles precursors. Ca- or Mg- hydroxide nanoparticles are obtained by several methods, generally characterized by some critical drawbacks: high temperature, processes are time and energy consuming, and low specific yield in the production, so determining a limit to their application to particular or restricted fields. In this work we present a facile and scalable method, recently patented (RM2011A000370, WO2014020515A1), to synthesize Ca- and Mg- hydroxide nanoparticles in aqueous suspension. This eco-friendly and time-energy saving route is based on an ion exchange process, operates at room temperature, starts from cheap or renewable reactants, with no intermediate steps (washings/purifications), drastically reduces times of synthesis and has the ability to scale up the nanoparticles production. The produced nanoparticles are pure and crystalline, with dimension generally less than 80 nm.
Materials and methods: To synthesized Ca(OH)2 (or Mg(OH)2) nanoparticles, a CaCl2·H2O (MgCl2) aqueous solution and an ion-exchange resin are mixed together, at room temperature and under moderated stirring. The substitution of hydroxyl groups on the resin substrate with the chlorides ions in solution leads, in supersaturation conditions, to the formation of a white precipitated phase inside the preparation, already after few minutes; maintaining the stirring, the preparation is rapidly separated from the resin by a sieving procedure. Resin can be regenerated to be reused for a scale-up production, according a cyclic procedure. The produced nanoparticles are characterized from structural and morphological point of view, by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermal analyses (TG-DTA), surface area measurements (BET) and transmission electron microscopy (TEM). Carbonatation efficiency of the produced Ca-hydroxides nanoparticles suspension is investigated too.
Results and discussion: From XRD measurements, only pure and crystalline Ca(OH)2 (Mg(OH)2) phases are produced after few minutes, as evidenced by the absence of peaks belonged to other substances in the experimental XRD pattern. The purity of the obtained phases is confirmed by FTIR and TG-DTA measurements. From BET measurements, we have obtained that the synthesized
Mg(OH)2 sample reaches values of surface area up to 155 m2/gr, generally higher than those reported in literature. TEM images referred to Ca(OH)2 and Mg(OH)2) samples, respectively, show nanoparticles characterized by a plate-like morphology, with dimensions generally ranging from 20 to 80 nm. Moreover, observations reveal that nanoparticles are formed by an oriented aggregation of Mg(OH)2 primary hexagonal particles (singlets), crystalline, homodispersed, and with dimensions of about 3 nm.
The analysis of Ca(OH)2 nanoparticles carbonatation process, investigated when the suspension is exposed to air (T = 20°C, RH = 70%), shows a complete transformation of Ca(OH)2 into CaCO3 (calcite), already after 3 h of air exposure time. This result is very interesting for the fast reactivity but also for the formation of pure calcite, that guarantees the perfect compatibility with all the carbonatic substrates
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