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Flow-Assisted Corrosion of Carbon Steel in Simulated Nuclear Plant Steam Generator Conditions
Flow-assisted corrosion occurs via increased dissolution and/or mechanical degradation of protective oxide formed on the surface of construction materials in direct contact with coolant liquids. In the present paper, this phenomenon is studied on carbon steel in an ammonia-ethanolamine-hydrazine electrolyte by in situ electrochemical impedance spectroscopy in conditions that closely simulate those that prevail in nuclear plant steam generators. Based on the obtained results, a quantitative kinetic model of the process is proposed and parameterized by nonlinear regression of experimental data to the respective transfer function. On the basis of the experimental and calculational results, it is concluded that flow-assisted corrosion of carbon steel is limited by oxide dissolution and cation ejection processes and the protective layer–coolant interface. Expressions for the film growth and corrosion release processes are proposed and successfully compared to operational data.
Lithium Manganese Sulfates as a New Class of Supercapattery Materials at Elevated Temperatures
To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li2Mn(SO4)2 and orthorhombic Li2Mn2(SO4)3, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20–60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperature. Li2Mn(SO4)2 outperforms Li2Mn2(SO4)3 and displays excellent electrochemical properties at elevated temperatures: at 60 °C, the energy density reaches 280 Wh/kg at a power density of 11,000 W/kg. During cell cycling, there is a transformation of the Li-rich salt, Li2Mn(SO4)2, into a defective Li-poor one, Li2Mn2(SO4)3, which appears to be responsible for the improved storage properties. The data reveals that Li2Mn(SO4)2 is a prospective candidate for supercapacitor electrode materials at elevated temperatures.
Novel Electrospun Composite Membranes Based on Polyhydroxybutyrate and Poly (vinyl formate) Loaded with Protonated Montmorillonite for Organic Dye Removal: Kinetic and Isotherm Studies
The use of biodegradable polyesters derived from green sources and their combination with natural abundantly layered aluminosilicate clay, e.g., natural montmorillonite, meets the requirements for the development of new sustainable, disposable, and biodegradable organic dye sorbent materials. In this regard, novel electrospun composite fibers, based on poly β-hydroxybutyrate (PHB) and in situ synthesized poly(vinyl formate) (PVF), loaded with protonated montmorillonite (MMT-H) were prepared via electrospinning in the presence of formic acid, a volatile solvent for polymers and a protonating agent for the pristine MMT-Na. The morphology and structure of electrospun composite fibers were investigated through SEM, TEM, AFM, FT-IR, and XRD analyses. The contact angle (CA) measurements showed increased hydrophilicity of the composite fibers incorporated with MMT-H. The electrospun fibrous mats were evaluated as membranes for removing cationic (methylene blue) and anionic (Congo red) dyes. PHB/MMT 20% and PVF/MMT 30% showed significant performance in dye removal compared with the other matrices. PHB/MMT 20% was the best electrospun mat for adsorbing Congo red. The PVF/MMT 30% fibrous membrane exhibited the optimum activity for the adsorption of methylene blue and Congo red dyes.
Investigation of Ni- and Co-Based Bifunctional Electrocatalysts for Carbon-Free Air Electrodes Designed for Zinc-Air Batteries
Ni- and Co-oxide materials have promising electrocatalytic properties towards the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), and attract with low cost, availability, and environmental friendliness. The stability of these materials in alkaline media has made them the most studied candidates for practical applications such as a gas diffusion electrode (GDE) for rechargeable metal-air batteries. In this work, we propose a novel concept for a carbon-free gas GDE design. A mixture of catalyst (Co3O4, NiCo2O4) and polytetrafluoroethylene was hot pressed onto a stainless-steel mesh as the current collector. To enhance the electrical conductivity and, thus, increase ORR performances, up to 70 wt.% Ni powder was included. The GDEs produced in this way were examined in a half-cell configuration with a 6 M KOH electrolyte, stainless steel counter electrode, and hydrogen reference electrode at room temperature. Electrochemical tests were performed and coupled with microstructural observations to evaluate the properties of the present oxygen electrodes in terms of their bifunctionality and stability enhancement. The electrochemical behavior of the new types of gas-diffusion electrodes, Ni/Co3O4 and Ni/NiCo2O4, shows acceptable overpotentials for OER and ORR. Better mechanical and chemical stability of electrodes consisting of Ni/NiCo2O4 (70:30 wt.%) was registered.
Thermal behavior of acid phosphate salts Ca2MH7(PO4)4•2H2O (M = K+, NH4+) and CaK3H(PO4)2
New knowledge about various aspects of little-known acid salts is of great scientific and practical importance in view of their potential application in different areas such as proton conductors. For the first time, the thermal behavior of three acid phosphate salts, dicalcium potassium heptahydrogen tetrakis(phosphate) dihydrate (Ca2KH7(PO4)4⋅2H2O), dicalcium ammonium heptahydrogen tetrakis(phosphate) dihydrate (Ca2(NH4) H7(PO4)4⋅2H2O) and calcium tripotassium hydrogenbis(phosphate) (CaK3H(PO4)2), has been investigated. By means of simultaneous thermogravimetry, differential thermal and mass spectrometry analyses (TG/DTA/MS)the schemes of their thermal decomposition have been proposed. The two isostructural compounds Ca2KH7(PO4)4⋅2H2O and Ca2(NH4)H7(PO4)4⋅2H2O are stable up to 90 – 95 ◦C and then undergo multiple-steps thermal decomposition process owing to dehydration of the crystallization water and dehydration-condensation. The anhydrous salt CaK3H(PO4)2 exhibits very high thermal stability up to 530 ◦C. The products of the thermal decomposition have been identified.
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