1,720,964 research outputs found
Environmentally Friendly La0.6Sr0.4Ga0.3Fe0.7O3 (LSGF)-Functionalized Fly-Ash Geopolymers for Pollutants Abatement in Industrial Processes
No full textAbstract: A ready-to use, highly sustainable solution for large scale exhausts catalytic abatement was developed: the active bricks. An environmentally-friendly composite was synthesized by depositing La0.6Sr0.4Ga0.3Fe0.7O3, by combustion synthesis, on a fly ash-based geopolymer improved to bear the high temperatures (> 900 °C) required for synthesis. The geopolymer was obtained using by-products and was synthesized at RT: its production is sustainable and cost efficient. Prepared composites have been tested for methane oxidation and show good, durable activity above 400 °C. Thermal stability was also proved. Composites are a good solution for oxidation of fuel residues in industrial processes. Graphic Abstract: [Figure not available: see fulltext.]
High-temperature behaviour of alkali-activated composites based on fly ash and recycled refractory particles
No full textThis study aims to develop innovative and sustainable alkali-activated composites with enhanced performance at high temperatures. To reduce production costs and promote a circular economy model, coal fly ashes are selected as a precursor for the alkali activation and recycled refractory particles are used to develop products with high thermal dimensional stability. Matrices and composites are investigated as a function of two curing conditions (heat curing vs room temperature curing) and amounts of dispersed phase (recycled refractory particles) added to the matrix. Thermal stability is assessed based on thermal exposure in a muffle furnace at 800 and 1000 °C, heating microscope analysis, and dilatometry. In addition, mineralogical quantitative analyses are performed to obtain an insight into phase changing after thermal exposure. Results show that the recycled refractory particles do not hinder the alkali activation process, significantly reduce heat-induced cracking, increase the maximum temperature of dimensional stability of the composites up to 1240 °C, and improve the linear dimensional stability during heating. In addition, the heat curing does not significantly increase the temperature range of dimensional stability, whereas the room temperature curing generates a product less prone to cracking when exposed to high temperature, and therefore it can be preferred
Life cycle assessment of a geopolymer mixture for fireproofing applications
No full textPurpose: Alkali-activated materials, also known as geopolymers, are considered promising assets in the sustainable materials industry. Given the excellent properties in terms of thermal stability and low thermal conductivity, geopolymer-based matrices can effectively substitute cementitious binders in the preparation of passive fire protection (PFP) systems. The present study aims at evaluating the environmental footprint of a newly proposed geopolymer-based fireproofing material. The results are compared to a reference commercial lightweight cement-based coating with equal PFP performance.
Methods: The boundaries of the system assessed were based on a cradle-to-grave life cycle. A preliminary scale-up of the laboratory protocol allowed the evaluation of the industrial production of the geopolymer-based PFP mix. An ancillary life cycle analysis was performed, comparing the environmental footprint of a geopolymer-based concrete block to the relevant literature studies for the same system in order to validate the approach of the present study. The functional unit of the main study was defined, taking into account the material performance in terms of resistance to heat exposure, allowing a functional comparison with lightweight cement-based PFP. The impact assessment phase used the CML-IA methodology as a characterization method.
Results and discussion: The ancillary LCA confirmed the alignment of the assumptions of the current study with previous analyses. The analyzed geopolymer-based fireproofing material exhibited a life cycle impact which is 27% lower than the lightweight concrete reference in terms of the global warming indicator, mainly thanks to the avoided CO2 emissions from the clinker process in cement manufacturing. Therefore, the greenhouse gas reduction described in previous studies on geopolymer application as a strong environmental advantage of the geopolymer technologies is also confirmed in this case. However, the other considered impact categories, such as resource depletion, acidification, eutrophication, and human toxicity, resulted in indicator values higher than the reference, as a consequence of the energy-intensive production process for the alkali activators (in particular, sodium silicate).
Conclusions: Though the reduction of greenhouse gas emissions is confirmed, the overall sustainability of geopolymers for PFP applications is hindered by the relevant environmental footprint of the sodium silicate production process. However, a substantial reduction of the impacts could be achieved by selecting the production process of sodium silicate which takes advantage of renewable energy supplies (e.g., hydrothermal route) or by reducing the amount of sodium silicate in the geopolymer recipe in favor of waste-based alkali activators
Acoustic emission study of heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars
No full textAlkali-activated fly ashes have been proposed for various applications where resistance against high temperatures is required, yet several details regarding the response of these materials to heat-exposure need to be clarified. In the present study, heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars was analyzed by in-situ acoustic emission (AE)detection during complete heating-cooling cycles (up to ∼1100 °C), augmented by thermogravimetry and ex-situ SEM and XRD analyses. The applicability of the lightweight mortars as passive fire protection coatings was assessed by recording temperature-time curves of mortar-coated steel plates. Cracking during heating was limited and associated exclusively with the dehydration of the materials in the temperature range ∼90–360 °C. However, samples heated to temperatures above ∼600 °C exhibited intense cracking on cooling. This was attributed to differential deformations caused by local sintering and partial melting at the glass transition temperature, and subsequent quenching on cooling
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
Use of digital image analysis to determine fracture properties of alkali-activated mortars
No full textResults of three-point bending tests on notched beams cast with three alkali-activated mortars that differ by the type and size of the aggregates are presented. Digital image correlation is used to estimate the size of the fracture process zone. The fracture energy is computed by means of the work-of-fracture method and found to be strongly dependent on the type of aggregate used and does not differ whether the LDVT or DIC load-deflection curves are used. Finally, low values of the fracture energy in alkali-activated mortars might be associated with the presence of unreacted fly ash
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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