•Iron chalcogenides crystals are recrystallized in molten chlorides at 675 °C.•Hexagonal Fe3(Se0.43Te0.57)4 and Tetragonal Fe1.02Se0.41Te0.59 crystals are grown.•Tetragonal crystals exhibit ...superconductivity at 14 K.
In this work we report the crystallization of iron chalcogenides compounds starting from a Fe(Se0.5Te0.5) solid pellet. The synthesis process is carried out at 675 °C using a molten chloride salts mixture and permitted to obtain well defined and easily separated hexagonal and tetragonal crystals, characterized by Fe3(Se0.43Te0.57)4 and Fe1.02Se0.41Te0.59 compositions respectively. The obtained tetragonal compound exhibits superconductivity at 14 K with critical current density of ~105 A/cm2 at 5 K.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Water thermolysis by means of the sodium manganese ferrite cycle for sustainable hydrogen production is reviewed, with particular focus on known elementary chemical processes taking place on solid ...substrates in the 600–800 °C temperature range. For the purpose, in-situ high temperature x-ray diffraction technique has been utilized to observe structural transformations produced by both temperature and reactive environment. The water-splitting reaction and the regeneration of initial reactants are described as multi-step reactions, in which the role of carbon dioxide, through carbonation and de-carbonation reactions is highlighted. A thermodynamic phase stability diagram is reported for the system MnFe2O4/Na2CO3/CO2.
► Chemistry of Na–Mn ferrite thermochemical cycle for hydrogen production is reviewed. ► H2 generation by reaction of H2O with MnFe2O4/Na2CO3 mixture is a multi-step process. ► Regeneration of initial ferrite/carbonate mixture is influenced by multiple equilibria. ► Carbonation and de-carbonation can occur independently from the oxide redox process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The transient dynamics of interacting biological species extracted from two ecosystems is investigated. We model the environment interaction by a multiplicative noise and the temperature oscillations ...by a periodic forcing. We find noise-induced effects such as enhanced temporal oscillations, spatial patterns and noise delayed extinction for the model of two competing species. We extend our analysis to an ecosystem of three interacting species, namely one predator and two preys. We find spatial patterns induced by the noise.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We analyze the transient dynamics of an ecosystem described by generalized Lotka–Volterra equations in the presence of a multiplicative noise and a random interaction parameter between the species. ...We consider specifically three cases: (i) two competing species, (ii) three interacting species (one predator–two preys), (iii) n-interacting species. The interaction parameter in case (i) is a stochastic process which obeys a stochastic differential equation. We find noise delayed extinction of one of two species, which is akin to the noise-enhanced stability phenomenon. Other two noise-induced effects found are temporal oscillations and spatial patterns of the two competing species. In case (ii) the noise induces correlated spatial patterns of the predator and of the two preys concentrations. Finally, in case (iii) we find the asymptotic behavior of the time average of the ith population when the ecosystem is composed of a great number of interacting species.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The optimization of sintering behaviour of iron chalcogenides superconducting materials is mandatory to enhance their critical current density, in order to pursuit their application in the production ...of superconducting wires. In this context it has been investigated here the effect of oxygen contamination on the material densification, considering the issues related to industrial oxygen-free isolated production lines. Our results show that the densification process is negatively affected by oxygen contamination. However, despite the difference in density, all sintered samples are characterized by similar structural and morphological features, and show comparable electrical and magnetic properties, with low critical current densities (Jc<103 A/cm2). These results suggest that densification is not the key limiting factor in these conditions, and that grain boundary or misorientation factors may play a greater role in limiting the performance of sintered iron chalcogenides superconductors.
The effect was investigated of low H2S concentrations, simulating biogas impurity, on the poisoning behaviour of a Ni-based, molten carbonate fuel cell anode. A conventional Ni–Cr anode was coated ...with ceria using dip coating to form a rare earth metal oxide thin layer on the surface of the anode. Electrochemical studies of the Ni-based samples were performed in symmetric cells under anode atmosphere (H2, CO2, H2O and N2 as balance) with 2, 6, 12, and 24 ppm of H2S by means of electrochemical impedance spectroscopy.
The recorded data showed that the poisoning resistance was enhanced at low coating percentages of ceria; effects depend on H2S concentration and the applied load. These results were confirmed by electrochemical impedance tests where the cerium oxide addition appears through stable polarization behaviour up to 6 ppm of H2S, particularly in the mass transfer region. The protection is explained by the depression of poisoned Ni active sites and formation of a protective layer to the metal surface. The ceria coating layer is a potential solution to reduce H2S poisoning of MCFCs fuelled with biogas.
► Low H2S concentrations was used to simulate biogas impurity. ► Dip coating method was carried out to form a cerium oxide thin layer on the surface of the anode. ► Electrochemical studies was performed in symmetric and button cells under anode atmosphere. ► The cerium oxide addition forms a protective layer to the metal surface. ► The ceria coating layer is a potential solution to reduce H2S poisoning of MCFCs fuelled with biogas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In this paper, the effect of post synthesis annealing treatments on a Fe(Se,Te) polycrystalline material is evaluated and discussed. The samples have been obtained via melting route. The material has ...been subjected to a high-temperature annealing treatment, carried out for 45 h at 680 °C. The role of the cooling step was investigated comparing samples obtained after a controlled cooling or after quenching in liquid nitrogen. From a morpho-structural point of view, the annealing treatment improves homogeneity, with respect to pristine samples, and influences secondary phase precipitate morphology. Regarding superconducting properties, a key role of the cooling procedure is assessed: controlled cooling leads in fact to a significant improvement of high field behaviour with respect to the melted material, while quenched samples are characterized by a worsening of the superconducting properties. Despite the overall worsening, however, the quenched samples show evidence of the presence of superconducting phases characterized by a remarkably high critical temperature (Tc > 18 K), observed for these materials only in films or under pressure.
High-energy ball milling is a material-processing method promoting near-room temperature transformations of powder mixtures. Obtained products possess peculiar properties, otherwise difficult or ...impossible to obtain by using conventional methods. Powder transformation is promoted by energy releases from milling media to trapped powder and the mechanism strongly depends by mechanical characteristics of the milling device. Planetary and horizontal ball mills, attritors, 1D and 3D vibrating apparatus are well-known and utilized in this powder-processing technology. This paper is focused on a ZOZ Simoloyer CM01 horizontal ball milling apparatus; a kinematic model characterizing balls motion and energy released have been found. For the purpose, an experimental setup, based on digital image acquisition, has been constructed and ball trajectories have been caught by using a properly developed software. Using image analysis results, tangential and radial components of balls speed distribution have been assessed and kinetic energies of the impacting balls inside the milling vial have been evaluated. The obtained results permits to evaluate the energy released to the powder during the milling action and to infer some expected consequences on mechanically activated reactions.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Nanocrystalline MnFe
2O
4 particles were synthesized by a high-energy ball milling technique, starting from a manganosite (MnO) and hematite (α-Fe
2O
3) stoichiometric powder mixture. The ...mechanosynthesis process was performed at room temperature both in hardened steel and in tungsten carbide vials. X-ray powder diffraction quantitative phase analysis by the Rietveld method was used to study the chemical transformations promoted by the milling action. The nanocrystalline MnFe
2O
4 spinel phase begins to appear after 10
h of milling and reaches its maximum content (≈0.8 molar fraction) after 35
h of milling. A prolonged milling time induces a dramatic contamination of the powder mixture, when hardened stainless steel was adopted, due to metallic iron originating from vial and balls debris. Ball milling is able to induce a redox reaction between Fe
III and metallic iron, transforming the MnFe
2O
4 spinel phase into a wüstite type (Fe, Mn)O phase. The yield of the hydrogen production reaction on synthetised materials is reported.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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