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Effect of the microstructure in the optimization of geopolymeric membrane supports for microfiltration of wastewaters
No full textAlkali activated materials and geopolymers have attracted a lot of research interests in the last 20 years
thanks to their excellent performances in terms of mechanical, thermal and durability properties. In
addition, these materials show promising properties in terms of sustainability when compared to
traditional binders commonly used in the building sector (i.e., ordinary Portland cement) and to
traditional and advanced ceramics (i.e., membranes, adsorbents, and catalysts). Sustainability in
geopolymers can be reached by using a broad variety of industrial by-products as raw materials and
by ambient or low temperatures (< 100 °C) consolidation.
The aim of the present study was the optimization of microstructural properties of one-part
geopolymers, based on flash-sintered metakaolin and anhydrous sodium silicate, for microfiltration
membrane support in wastewater treatments. Investigated geopolymers were shaped by uniaxial
pressing and cured at 70 °C for 24 h. Several parameters in terms of mix design optimization (i.e., alkali
concentration and water content) and pressing pressure were investigated to obtain a microstructure
suitable for the preparation of the support of flat asymmetric membranes. Assessment of the total
open porosity and the pore size distribution was carried out by mercury intrusion porosimetry, while
microstructural observations were performed by field emission gun-scanning electron microscopy
(FEG-SEM) coupled with energy dispersive spectroscopy (EDS). It was found that pressing is a
particularly suitable shaping method for one-part geopolymers thanks to the use of low water amount
for the activation of the mix. In addition, increasing the water content (up to 15 wt%) and pressing
pressure (up to 20 MPa) allowed the formation of a dense geopolymeric gel, while alkalis
concentration, ranging between Na/Al = 0.7 and 1.1, did not strongly influence the microstructure.
Finally, the optimized parameters for producing flat support for microfiltration membranes are a Na/Al
molar ratio equal to 1.0, 12 wt% water content and 2 MPa of pressing pressure. These conditions
allowed to obtain the same range of open porosity and pore size distribution characteristic of ceramic
membrane support used for the same purpose
Novel geopolymeric support for microfiltration membranes applied in wastewater treatment
No full textMicrofiltration membranes are widely used in wastewater treatment and are typically made of ceramic
or polymer materials. Despite the great durability of ceramic membranes, polymeric membranes are
very often preferred due to production costs. By using geopolymers, however, it is possible to obtain
microfiltration membranes with durability characteristics similar to those of ceramic materials, but
with considerably reduced production costs since geopolymers do not require a sintering treatment.
In this study, a geopolymer support for asymmetric microfiltration membranes is characterized in
terms of porosity and hydraulic permeability. The support was obtained by uniaxially pressing a dry
mixed powder consisting of metakaolin and anhydrous sodium silicate, sprayed with 12 wt% of water.
Curing was carried out at 70 °C for 24 hours and 6 more days at room temperature. The porosity of
samples pressed using 2 MPa (total open porosity of 39 % and a modal pore size of 23 μm) are
comparable to those of ceramic membranes for microfiltration [1]. The support permeability was
measured in a dead-end apparatus at a trans-membrane pressure varying from 0.2 to 0.5 bar, with
pure water and ethanol-water solutions. Hydraulic permeability of 30500 ± 3090 L/(h·m2·bar) was
obtained with 4 samples, whereas the use of 100 and 200 g/L ethanol-water solutions showed a
reduction in permeability to 26140 ± 2640 and 20820 ± 1430 L/(h·m2·bar) respectively. Further tests
performed on less porous samples obtained by pressing the powder at 5 MPa (total open porosity and
modal pore size of 27% and 15 μm, respectively) led to similar results. These initial characterizations
highlight the potential of this new material in the treatment of wastewater by membrane separation.
Future studies are ongoing to develop geopolymer selectives layer by dip coating to be applied on
geopolymer supports
Development of metakaolin-based geopolymeric asymmetric membrane for oil-in-water emulsion microfiltration
Full text linkThe authors would acknowledge the Italian Ministry of University and Research (MUR) for awarding the doctoral and the “Marco Polo” scholarship, which allowed Dr. Alessandro Filipponi to carried out this research in Spain
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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