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Direct mechanochemical synthesis of SrMoO4: structural and luminescence properties
In this study, the effects of ball milling conditions on the phase formation, symmetry of structural units and photoluminescence features of SrMoO4 were investigated. A stoichiometric mixture of SrCO3 and MoO3 in a molar ratio of 1 : 1 was subjected to intense mechanical treatment in air using a planetary ball mill by applying two milling speeds: 500 and 850 rpm. The obtained samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Raman spectroscopy, infrared (IR) spectroscopy, UV-vis (UV-vis) diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. The fast synthesis (1 h milling time) of tetragonal SrMoO4 occurred at the higher milling speed of 850 rpm. A longer milling time (5 h) was needed to synthesize SrMoO4 at a lower milling speed of 500 rpm. The average crystallite sizes of the as-prepared samples were 25 and 20 nm at 500 and 850 rpm, respectively. SEM analysis revealed that the mechanochemically produced SrMoO4 sample contained a variety of particle shapes including hexagonal and polyhedral ones. Raman and IR spectroscopy results confirmed the formation of tetragonal SrMoO4. UV-vis absorption spectra showed one peak at 230 nm, and the calculated optical band gaps of SrMoO4 were 4.27 eV (5 h/500 rpm) and 4.34 eV (1 h/850 rpm). Photoluminescence (PL) spectra of both the samples exhibited blue emissions with a peak maximum at 400 (405) nm upon excitation at 325 nm wavelength. CIE coordinates of this mechanochemically synthesized SrMoO4 were located in the blue region with different positions.
Influence of temperature and flow rate on erosion-corrosion of low-alloy steel in simulated steam generator conditions
The erosion–corrosion mechanism of low-alloy steel in high-ammonia steam generator’s chemistry is studied by in situ impedance spectroscopy coupled with an in-depth analysis of formed oxides using glow discharge optical emission spectroscopy. A novel electrode setup that ensures turbulent conditions in the vicinity of the steel sample is used. The effect of temperature (130–230 °C) and flow rate (2–10 dm3 h−1) is investigated. The energy of adsorption of ammonia depends on temperature and is estimated using molecular dynamic simulations. The kinetic and transport parameters of the corrosion process are estimated via the regression of the experimental impedance spectra to the transfer function of the Mixed-Conduction Model for oxide films. Conclusions are drawn about the effect of Cr in the alloy, and the temperature and flow rate on the corrosion mechanism.
Carbon Dioxide Recycling into Fuels and Valuable Chemicals
The present review proposes an approach for remediation of atmosphere pollution by carbon dioxide. The global economic growth nowadays requires extensive energy consumption. Energy is produced traditionally by combustion of carbon containing fuels, resulting in the release of large amounts of carbon dioxide in the atmosphere. These emissions of released CO2 lead to the greenhouse effect on the atmosphere with subsequent impact on the global climate. Remediation of this harmful effect requires reduction in CO2 emissions. In addition to improving the efficiency of energy consumption, this reduction can be also accomplished by the recycling of carbon dioxide into fuels and useful commodities. This conversion of CO2 into fuels and commercial products leads to multiple benefits such as reduction in carbon emissions and greenhouse gases, production of value-added goods, thus reducing oil consumption and associated pollutions of the environment. This review summarizes the efforts to remove, or at least to remediate, the release of carbon dioxide in the atmosphere by its conversion to value-added products prior to discharging. Some of these products are urea, methanol, formic acid, some polymers of practical importance, light hydrocarbons and methane. The recent achievements in chemical catalysis, electrochemistry, bioelectrochemistry and photocatalysis are considered. Discussion on the feasibility of the considered methods compared to the traditional technologies is made. It is concluded that although production of value-added chemicals by carbon dioxide recycling is not yet competitive, it seems promising in the future when its economic feasibility will become a reality.
Corrosion of Low-Alloy Steel in Ethanolamine Steam Generator Chemistry—The Effect of Temperature and Flow Rate
The corrosion of low-alloy steel in ethanolamine solution, simulating steam generator chemistry, is studied by in situ chronopotentiometry and electrochemical impedance spectroscopy combined with ex situ analysis of the obtained oxide films and model calculations. Hydrodynamic calculations of the proposed setup to study flow-assisted corrosion demonstrate that turbulent conditions are achieved. Quantum chemical calculations indicate the adsorption orientation of ethanolamine on the oxide surface. Interpretation of impedance spectra with a kinetic approach based on the mixed-conduction model enabled estimating the rate constants of oxidation at the alloy–oxide interface, as well as charge transfer and ionic transport resistances of the corrosion process. In turbulent conditions, the dissolution of Fe oxide and ejection of Fe cations are enhanced, leading to Cr enrichment in the oxide and alteration of its electronic and electrochemical properties that influence the corrosion rate.
Influence of Synthesis Conditions on the Capacitance Performance of Hydrothermally Prepared MnO2 for Carbon Xerogel-Based Solid-State Supercapacitors
In this study, the potential to modify the phase structure and morphology of manganese dioxide synthesized via the hydrothermal route was explored. A series of samples were prepared at different synthesis temperatures (100, 120, 140, and 160 ◦C) using KMnO4 and MnSO4·H2O as precursors. The phase composition and morphology of the materials were analyzed using various physicochemical methods. The results showed that, at the lowest synthesis temperature (100 ◦C), an intercalation compound with composition K1.39Mn3O6 and a very small amount of α-MnO2 was formed. At higher temperatures (120–160 ◦C), the amount of α-MnO2 increased, indicating the formation of two clearly distinguished crystal structures. The sample obtained at 160 ◦C exhibited the highest specific surface area (approximately 157 m2/g). These two-phase (α-MnO2/ K1.39Mn3O6)materials, synthesized at the lowest and highest temperatures, respectively, and containing an appropriate amount of carbon xerogel, were tested as active mass for positive electrodes in a solid-state supercapacitor, using a Na+-form Aquivion® membrane as the polymer electrolyte. The electrochemical evaluation showed that the composite with the higher specific surface area, containing 75% manganese dioxide, demonstrated improved characteristics, including 96% capacitance retention after 5000 charge/discharge cycles and high energy efficiency (approximately 99%). These properties highlight its potential for application in solid-state supercapacitors.