Stability of naturally relevant ternary phases in the Cu-Sn-S system in contact with an aqueous solution

A relevant research effort is devoted to the synthesis and characterization of phases belonging to the ternary system Cu–Sn–S, mainly for their possible applications in semiconductor technology. Among all ternary phases, kuramite, Cu3SnS4, mohite, Cu2SnS3, and Cu4Sn7S16 have attracted the highest interest. Numerous studies were carried out claiming for the description of new phases in the ternary compositional field. In this study, we revise the existing literature on this ternary system, with a special focus on the phases stable in a temperature range at 25 °C. The only two ternary phases observed in nature are mohite and kuramite. Their occurrence is described as very rare. A numerical modelling of the stable solid phases in contact with a water solution was underwent to define stability relationships of the relevant phases of the system. The numerical modelling of the Eh-pH diagrams was carried out through the phreeqc software with the lnll.dat thermodynamic database. Owing to the complexity of this task, the subsystems Cu–O–H, Sn–O–H, Cu–S–O–H and Sn–S–O–H were firstly considered. The first Pourbaix diagram for the two naturally relevant ternary phases is then proposed

Thermochemistry of the E-ALD process for the growth of Cu x Zn y S on Ag(111): Interpretation of experimental data

The electrochemical atomic layer deposition (E-ALD) growth of chalcogenides materials enables the deposition of technologically interesting ultra-thin films. However, this method raises some questions about the actual growth mechanism. We addressed one of the more interesting anomalies reported lately: the occurrence of the Zn-deficiency and of the polycrystalline thread-like overgrown structures in the E-ALD growth of CuxZnyS. The present study was developed using a computational speciation approach under the mass balance method. Exploiting a well-established computational approach, but uncommonly applied to the electrochemical science, we calculated the predominance charts and the equilibrium speciation of the solid phases during the electrochemical process. On this basis, we obtained a deep insight into the mechanism underlying the E-ALD process from a thermodynamic standpoint. Thus, we identified the crucial steps of the CuxZnyS growth leading to the anomalies object of this research

Influence of permeability on the hydrothermal system at Vulcano Island (Italy): inferences from numerical simulations

AbstractVolcano-hydrothermal systems are governed by complex interactions between fluid transport, and geochemical and mechanical processes. Evidence of this close interplay has been testified by distinct spatial and temporal correlations in geochemical and geophysical observations at Vulcano Island (Italy). To understand the interaction between fluid circulation and the geochemical and geophysical manifestations, we perform a parametric study to explore different scenarios by implementing a hydro-geophysical model based on the equations for heat and mass transfer in a porous medium and thermo-poroelastic theory. Numerical simulations allow us to define the controlling role of permeability distribution on the different modeled parameters as well as on the geophysical observables. Changes in the permeability within the highly fractured crater area could be responsible for the fluctuations in gas emission and temperature recorded during the crisis periods, which are accompanied by shallow volcano-seismicity in the absence of significant deformation and gravity variations. Despite the general medium permeability of the volcanic edifice, the presence of more highly permeable pathways, which allow the gas to rapidly escape, as testified by the presence of a well-developed fumarolic field, prevents the pressure buildup at shallow depths. Graphic abstrac

Experimental Analysis of the Reaction Rate of Hydrated Class G Cement Powder at 11 bar PCO2 and Ambient Temperature

The aim of this work is to study the alteration of class G Cement at ambient temperature under a relatively high CO2 partial pressure through suitably designed laboratory experiments, in which cement hydration and carbonation are taken into account separately. First, the hydration process was carried out for 28 days to identify and quantify the hydrated solid phases formed. After the completion of hydration, accompanied by partial carbonation under atmospheric conditions, the carbonation process was investigated using a stirred micro-reactor by reacting cement powder with pure CO2(g) (PCO2 = 11 bar) and MilliQ water for different reaction times. The reaction time was varied to constrain the reaction kinetics of the carbonation process and to investigate the evolution of primary and secondary solid phases. Mineralogical analyses (X-ray Powder Diffraction and Scanning Electron Microscope) were carried out to this purpose. Water analyses were also performed by ion chromatography at the end of each experimental run to investigate the chemical effects of cement carbonation on the aqueous solution. The carbonation degree was calculated from the results of Thermo-Gravimetric analysis (TGA). The main results of these experiments is the quick conversion of portlandite and Ca1.60SiO3.6·2.58H2O (C-S-H) to calcite. In fact, the carbonation degree attains 80% after 6 hours of reaction time. Experimental outcomes will be simulated by means of the PHREEQC software package to obtain further indications on cement carbonatio

Operando SXRD study of the structure and growth process of Cu2S ultra-thin films

International audienceElectrochemical Atomic Layer Deposition (E-ALD) technique has demonstrated to be a suitable process for growing compound semiconductors, by alternating the under-potential deposition (UPD) of the metallic element with the UPD of the non-metallic element. The cycle can be repeated several times to build up films with sub-micrometric thickness. We show that it is possible to grow, by E-ALD, Cu2S ultra-thin films on Ag(111) with high structural quality. They show a well ordered layered crystal structure made on alternating pseudohexagonal layers in lower coordination. As reported in literature for minerals in the Cu-S compositional field, these are based on CuS3 triangular groups, with layers occupied by highly mobile Cu ions. This structural model is closely related to the one of the low chalcocite. The domain size of such films is more than 1000 angstrom in lateral size and extends with a high crystallinity in the vertical growth direction up to more than 10 nm. E-ALD process results in the growth of highly ordered and almost unstrained ultra-thin films. This growth can lead to the design of semiconductors with optimal transport proprieties by an appropriate doping of the intra metallic layer. The present study enables E-ALD as an efficient synthetic route for the growth of semiconducting heterostructures with tailored propertie

Green and scalable synthesis of nanocrystalline kuramite

The new generation of solar cells aims to overcome many of the issues created by silicon-based devices (e.g., decommissioning, flexibility and high-energy production costs). Due to the scarcity of the resources involved in the process and the need for the reduction of potential pollution, a greener approach to solar cell material production is required. Among others, the solvothermal approach for the synthesis of nanocrystalline Cu-Sn-S (CTS) materials fulfils all of these requirements. The material constraints must be considered, not only for the final product, but for the whole production process. Most works reporting the successful synthesis of CTS have employed surfactants, high pressure or noxious solvents. In this paper, we demonstrate the synthesis of nanocrystalline kuramite by means of a simpler, greener and scalable solvothermal synthesis. We exploited a multianalytical characterization approach (X-ray diffraction, extended X-ray absorption fine structure, field emission scanning electron microscopy, Raman spectroscopy and electronic microprobe analysis (EMPA) to discriminate kuramite from other closely related polymorphs. Moreover, we confirmed the presence of structural defects due to a relevant antisite population

Origin and Distribution of Thiophenes and Furans in Gas Discharges from Active Volcanoes and Geothermal Systems

The composition of non-methane organic volatile compounds (VOCs) determined in 139 thermal gas discharges from 18 different geothermal and volcanic systems in Italy and Latin America, consists of C2–C20 species pertaining to the alkanes, alkenes, aromatics and O-, S- and N-bearing classes of compounds. Thiophenes and mono-aromatics, especially the methylated species, are strongly enriched in fluids emissions related to hydrothermal systems. Addition of hydrogen sulphide to dienes and electrophilic methylation involving halogenated radicals may be invoked for the formation of these species. On the contrary, the formation of furans, with the only exception of C4H8O, seems to be favoured at oxidizing conditions and relatively high temperatures, although mechanisms similar to those hypothesized for the production of thiophenes can be suggested. Such thermodynamic features are typical of fluid reservoirs feeding high-temperature thermal discharges of volcanoes characterised by strong degassing activity, which are likely affected by conspicuous contribution from a magmatic source. The composition of heteroaromatics in fluids naturally discharged from active volcanoes and geothermal areas can then be considered largely dependent on the interplay between hydrothermal vs. magmatic contributions. This implies that they can be used as useful geochemical tools to be successfully applied in both volcanic monitoring and geothermal prospection

Data integration and conceptual modelling of the Larderello geothermal area, Italy

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