1,721,150 research outputs found
Mineralogical-geochemical study of the anionic competition effect on the octacalcium phosphate reaction into fluorapatite
Full text linkThe unstable compound octacalcium phosphate (OCP) is one of the crystalline precursors of the apatite mineral series composed by hydroxyapatite, fluorapatite and chlorapatite. The feature of OCP to react into apatite, depending on the media conditions, has been mainly exploited for biomedical applications as bone and tooth substitute material. Recently, some important applications of OCP have been documented: e.g. as electrode material for supercapacitors and as fluoride remover reagent for environmental purposes. With the aim of deepening the property of OCP to be the crystalline precursor of apatite and assessing if and how the anionic competition can influence the formation of the different apatite end-members, the OCP → apatite reaction has been here investigated placing 0.223 mmol of OCP in 50 mL aqueous solution with 0.368 mmol of dissolved fluoride, chloride, hydroxyl and carbonate anions (fluoride alone, fluoride with each of the other anions, and all the anions together) at room temperature. The post-experiment analyses of solid and liquid phases, conducted by using XRD, ESEM and ICP-OES, show that fluoride is always the main anion removed from solution during the OCP transformation reaction. The precise mineralogical characterization of solid phases formed, performed using the Rietveld algorithm, shows that fluorapatite is always the main resulting apatitic phase, followed by hydroxyapatite. Taking into account the different application fields of OCP, these results could be significant in better defining the OCP → apatite reaction in aqueous solutions where different competing anions are involved
Calcined and uncalcined carbonate layered double hydroxides for possible water defluoridation in rural communities of the East African Rift Valley
No full textHealth risks linked to the regular consumption of water with high fluoride (F − ) content seriously affect rural areas of the East African Rift Valley. The F − removal capacity has been tested on uncalcined and calcined carbonate layered double hydroxides (LDHs), with different cationic compositions (M 2+ = Mg 2+ , Zn 2+ ; M 3+ = Al 3+ , Fe 3+ ) and M 2+ /M 3+ molar ratio (2, 3, 4), taking into account the necessity of a simple defluoridation method. The 3MgAlFe-cal phase derived from calcination of a hydrotalcite-like compound with composition Mg/(Al + Fe) = 3/(0.5 + 0.5) results to be the best F − remover (43 mg/g) and can uptake up to 92.3 mg/g when the interlayer is fully saturated with F − . At the high pH reached during the experiments (up to pH 12 for calcined LDHs), the presence of carbonate species in solution significantly affects the F − removal capacity. The recyclability of the sorbent was tested by regeneration through calcination of the 3MgAlFe-cal phase: under F − unsaturated interlayer conditions, up to 80% of the starting F − removal capacity is still preserved after four regeneration cycles, indicating that LDHs can be reused after regeneration and have a potential use in water defluoridation
Nuovo codice di calcolo per il solar cooling
No full textUn codice di calcolo realizzato
per la simulazione di macchine ad
assorbimento con coppia di lavoro
acqua/bromuro di litio, alimentate
con acqua calda prodotta da collettori
solari termici, del tipo piano selettivi
o a tubi sottovuot
Water defluoridation by carbonate calcined and uncalcined Layered Double Hydroxides (LDHs)
Full text linkCarbonate Layered Double Hydroxides (LDHs) with different cationic composition and M/M3+ molar ratio were tested, both untreated and calcined, for water defluoridation. The defluoridation capacity of calcined LDHs, produced by intercalation during the reconstruction of lamellar structure, is more effective than the anion exchange of untreated LDHs. Among the calcined LDHs tested, that with 3Mg/(0.5Al+0.5Fe) molar ratio yields a maximum fluoride sorption capacity up to 92.3 mg/g, in spite of the high pH value (up to 12) of the experiments. After four cycles of regeneration by calcination and subsequent water defluoridation, this LDH composition maintains more than 80% of its fluoride removal capacity
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
- …
