Rate‐determining steps of oxygen surface exchange kinetics on Sr2Fe1.5Mo0.5O6−δ

The oxygen surface kinetics of Sr2Fe1.5Mo0.5O6−δ was determined using the 16O2/18O2 isotope exchange method with gas phase analysis at 600-800 °C. The heterogeneous exchange rates (rH) and the oxygen diffusion coefficients (D) were calculated by processing the concentration dependences of the 18O fraction using Ezin's model. The rates of oxygen dissociative adsorption (ra) and incorporation (ri) were calculated based on a model using the three exchange type rates. It has been established that the rates ra and ri were comparable in this temperature range. Assumptions were made about the effect of the chemical composition of the surface on the rate of oxygen adsorption. It was found that the oxygen exchange coefficient (k) of Sr2Fe1.5Mo0.5O6−δ is comparable to that of La0.6Sr0.4MnO3±δ oxide. High values of the oxygen diffusion coefficient were found for Sr2Fe1.5Mo0.5O6−δ. The values were comparable to those of the double cobaltite praseodymium-barium and exceed by more than an order those of lanthanum‐strontium manganite. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Russian Foundation for Basic Research, RFBR: 00161Government Council on Grants, Russian FederationThe study was partly financially supported by the Russian Foundation for Basic Research (17-08-00161) and the Russian Federation Government, agreement 02.A03.21.0006 (no. 211)

Биоразлагаемые упаковочные материалы на основе полиэтилена низкой плотности, крахмала и моноглицеридов

Objectives. To investigate the production and biological degradation of biodegradable hybrid compositions (BHCs), dispersed-filled with starch-containing products of various origins and distilled monoglycerides, along with the biodegradation of compositions based on low density polyethylene and thermoplastic starch (TPS) of various origins: corn, pea, and rice.Methods. Thermoplastic starch was obtained based on native starches of several types, which were processed in Brabender and MashkPlast (Russia) laboratory extruders. BHCs in the form of strands, granules, and films were obtained by mixing thermoplastic starches with polyethylene in extruders. Structural BHC parameters were studied by optical and electron scanning microscopy. The biodegradability of the composite films was evaluated by placing them in biohumus for six months; during storage, the change in water absorption of the films was determined. Before and after the biodegradation process, tensile fracture stress and elongation at rupture were determined to evaluate BHC performance (physical and mechanical characteristics of films). Changes in the chemical structure during biodegradation were determined by Fourier infrared spectroscopy.Results. The positive effect (acceleration of the biodegradation process) of using a novel type of starch plasticizer—monoglycerides distilled in TPS–polyethylene compositions—was confirmed. After six months, intensive sporulation of active microorganisms was observed on the surface of the samples. At the same time, water absorption by the samples reached 30%. The observed 60% decrease in strength and deformation properties indicates an intensive process of biodegradation.Conclusions. The biodegradation rate was shown to depend on the concentration and even distribution of the natural biodegradable filler in the synthetic polymer composition. Цели. Исследовать процесс производства биоразрушаемых гибридных композиций (БГК), дисперсно-наполненных крахмалсодержащими продуктами различного происхождения и дистиллированными моноглицеридами, и их биологическую деструкцию, а также процесс биоразложения композиций на основе полиэтилена низкой плотности и термопластичного крахмала (ТПК) различного происхождения: кукурузного, горохового и рисового.Методы. Термопластичный крахмал получали на основе нативных крахмалов разных видов путем переработки их в лабораторных экструдерах фирм «Брабендер» и «МашПласт» (Россия). Смешивая в экструдерах термопластичные крахмалы с полиэтиленом, получали БГК в виде стренг, гранул и пленок. Структурные параметры БГК изучали методами оптической и электронной сканирующей микроскопии. Способность к биоразложению композитных пленок оценивали, помещая их на полгода в биогумус, и в процессе хранения определяли изменение водопоглощения пленок. Для оценки эксплуатационных свойств (физико-механических характеристик пленок) БГК определяли разрушающее напряжение при растяжении и относительное удлинение при разрыве до и после процесса биоразложения. Изменения химической структуры в процессе биоразложения определяли методом инфракрасной спектроскопии с преобразованием Фурье.Результаты. Подтвержден положительный эффект (ускорение процесса биоразложения) от использования нового типа пластификатора крахмала – дистиллированных моноглицеридов в композициях ТПК–полиэтилен. По истечении полугода на поверхности образцов наблюдали интенсивное спороношение активных микроорганизмов. При этом водопоглощение образцов достигало 30%, прочностные и деформационные свойства снизились на 60%, что свидетельствует об интенсивном протекании процесса биоразложения.Выводы. Установлено, что скорость процесса биоразложения композиций зависит от концентрационного соотношения вводимого ТПК, а также от его равномерного распределения в синтетическим полимере

Sedimentation of Ultradispersed Diamonds in the Citrate Copper-Plating Electrolyte

Abstract—The aggregation and sedimentation of ultradispersed diamonds (UDDs) in a citrate copper-plating electrolyte (CCPE) used to fabricate composite electrochemical coatings are investigated. The sedimentation and aggregation stability is investigated in order to select the UDD concentration in the CCPE. This is necessary to fabricate composite copper coatings with improved operational characteristics (increased hardness, wear resistance, and corrosion resistance), as well as impart them new properties (antifriction and catalytic). The UDD content in the electrolyte varies in limits from 0.2 to 2.0 g/L. The size distribution of the UDD particles in the electrolyte immediately after the suspension preparation and after the 10-day holding is determined using a Malvern Mastersizer 2000 laser diffraction analyzer. The aggregation and sedimentation stability of the UDD suspension in the CCPE is investigated by the gravimetric method with the continuous weighing of a quartz small cap immersed into this suspension. The quartz cap is associated with a Sartorius R200D analytical balance with the help of a quartz wire. The experimentally determined time dependence of the weight of settling UDD particles is Q = f(t). The relative size distribution of the particles is determined from this dependence. It is established that the sedimentation stability is substantially affected by the aggregation of the particles, the intensity of which increases with an increase in the UDD concentration. The results satisfying the requirements on the aggregation and sedimentation stability are found for the UDD suspension in the CCPE with a concentration of 1.0 g/L. In this case, the high content of the dispersed phase is combined with aggregation and sedimentation stability, which makes it possible to fabricate copper composite coatings with improved operational properties. © 2019, Allerton Press, Inc

Oxygen diffusion and surface exchange kinetics for the mixed-conducting oxide La0.6Sr0.4Co0.8Fe0.2O3–δ

Received: 14.11.2018. Accepted: 11.12.2018. Published: 31.12.2018.Studies of oxygen surface exchange kinetics for La0.6Sr0.4Co0.8Fe0.2O3–δ oxide were performed using the technique of isotopic exchange of molecular oxygen with analysis of gas phase isotopic composition in a static circulation system at the temperatures of 600–800 °С in the oxygen pressure range of 0.27–2.13 kPa. The values of interphase exchange rate and oxygen diffusion coefficient were determined. The effective activation energies for oxygen exchange and diffusion processes as well as the exponents in the dependence of these values versus oxygen pressure in the double logarithmic coordinates were calculated. The process of oxygen dissociative adsorption at the surface of La0.6Sr0.4Co0.8Fe0.2O3–δ oxide was found to be the rate-determining stage.This work is partly supported by the Russian Science Foundation (Project No. 17‑73‑10196) using facilities of shared access center “Composition of Compounds” of IHTE UB RAS

Application of promising electrode materials in contact with a thin-layer ZrO2-based supporting electrolyte for solid oxide fuel cells

The paper presents the results of an investigation into thin single- and triple-layer ZrO2-Sc2O3-based electrolytes prepared using the tape-casting technique in combination with promising electrodes based on La2NiO4+δ and Ni-Ce0.8Sm0.2O2-δ materials. It is shown that pressing and joint sintering of single electrolyte layers allows multilayer structures to be obtained that are free of defects at the layer interface. Electrical conductivity measurements of a triple-layer electrolyte carried out in longitudinal and transverse directions with both direct and alternating current showed resistance of the interface between the layers on the total resistance of the electrolyte to be minimal. Long-term tests have shown that the greatest degradation in resistance over time occurs in the case of an electrolyte with a tetragonal structure. Symmetrical electrochemical cells with electrodes fabricated using a screen-printing method were examined by means of electrochemical impedance spectroscopy. The polarization resistance of the electrodes was 0.45 and 0.16 Ohm∙cm2 at 800 °C for the fuel and oxygen electrodes, respectively. The distribution of relaxation times method was applied for impedance data analysis. During tests of a single solid oxide fuel cell comprising a supporting triple-layer electrolyte having a thickness of 300 microns, a power density of about 160 mW/cm2 at 850 °C was obtained using wet hydrogen as fuel and air as an oxidizing gas. © 2020 by the authors.Russian Foundation for Basic Research, RFBR: 17‐08‐ 01227Government Council on Grants, Russian FederationFunding: The study was partly financially supported by the Russian Foundation for Basic Research (17‐08‐ 01227), Russian Federation Government, agreement 02.A03.21.0006 (No. 211) and “InEnergy” LTD agreement of 2018

Formation of conductive oxide scale on 33NK and 47Nd interconnector alloys for solid oxide fuel cells

Two grades of chromium-free alloys were studied in order to apply them as interconnectors for solid oxide fuel cells. The surface modification methods were proposed for each alloy with the purpose of forming of oxide scales considering the required physicochemical properties. Investigations of the structure and properties of the obtained oxide scales were performed and the efficiency of the chosen surface modification methods was approved. The samples with the surface modification exhibited higher conductivity values in comparison with the nonmodified samples. A compatibility study of samples with surface modification and glass sealant of chosen composition was accomplished. The modified samples demonstrated good adhesion during testing and electrical resistance less than 40 mOhm/cm2 at 850 ◦C in air, which allowed us to recommend these alloys with respective modified oxide scales as interconnectors for SOFC. © 2019 by the authors.Russian Foundation for Basic Research, RFBR: 17-58-10006This research was funded by the Russian Foundation of Basic Research grant number 17-58-10006. The facilities of the shared access center "Composition of Compounds" of IHTE UB RAS were used in this work

H/D Isotopic Exchange and Electrochemical Kinetics of Hydrogen Oxidation on Ni-Cermets with Oxygen-Ionic and Protonic Electrolytes

Ni–Zr0.82Y0.18O1.91 (YSZ) and Ni–La0.90Sr0.10ScO2.95 (LSS) cermets for solid oxide and protonic ceramic electrochemical cells were studied by means of H/D isotope exchange with the gas phase equilibration method for the first time. The experiments were carried out at 2 mbar of dry hydrogen in the temperature range of 400–800 ᵒC. The three parallel channels of hydrogen surface exchange were found to exist in both Ni-YSZ and Ni-LSS cermets. The mechanism of hydrogen isotope exchange for Ni-YSZ was found to be temperature independent, while, in the case of Ni-LSS, the mechanism changed with temperature and was more complicated at lower temperatures (400–600 °C). It was revealed that hydrogen spillover was the rate-determining step for both cermets. The electrochemical kinetics of hydrogen oxidation were studied on symmetric cells with a YSZ supported electrolyte and Ni-YSZ electrodes and with an LSS supported electrolyte and Ni-LSS electrodes in a wet (3 vol % H 2O) hydrogen atmosphere at 1 atm. The mechanism of hydrogen oxidation on the Ni-LSS electrode differs from that of the Ni-YSZ electrode. It changes with temperature and is also more complicated at a lower temperature range. © 2021 Elsevier B.V.This work is supported by the State Assignment of Ministry of Science and Higher Education of the Russian Federation [No. AAAA-A19-119020190078-6 ], and the Act 211 of the Government of the Russian Federation, agreement [No. 02. A03.21.0006 ]. The facilities of the Shared Access Centre “Composition of Compounds” and Unique Scientific Setup “Isotopic Exchange” of IHTE UB RAS were used. The authors are grateful D.M. Solodyankina and A.Yu. Stroeva for support in the preparation of samples

Non-crystallising Glass Sealants for SOFC: Effect of Y2O3 Addition

The joining of ceramic and metal (interconnect) parts is one of the main challenges in the development of solid oxide fuel cells (SOFC). A promising approach to solving this problem is the use of glassy sealants. In this work, we investigated the effect of yttria additions on the properties of SiO2–Al2O3–CaO–Na2O–ZrO2–Y2O3 glass sealants. An increase in the concentration of yttria is shown to reduce the tendency of the glasses under study to crystallisation. A glass containing 4 wt% of Y2O3 is found to be amorphous, even after exposure at 850 °C for 100 h. Moreover, the defectiveness of the glass microstructure, after sealing, is found to decrease along with a growth in the Y2O3 concentration. The developed non-crystallising sealant was successfully applied for joining a YSZ ceramic and an Fe–Ni–Co alloy having the phase transition of around 500 °C. The use of the non-crystallising sealant allows us to join materials with very different thermal expansion coefficients and to avoid cracking under cooling, which might occur due to a large difference in thermal expansion coefficients. © 2019 Elsevier Ltd and Techna Group S.r.l.This study was financially supported by the RFBR project no. 17-58-10006. The research was partially performed using the facilities of the Shared Access Centre “Composition of Compounds” of IHTE UB RAS . The authors are grateful to Dr. S.V. Plaksin for XRD analysis, Dr. N. I. Moskalenko for AES analysis, A. S. Farlenkov for SEM analysis, and A. A. Solodyankin and V. A. Vorotnikov for their assistance in sample preparation