Browsing by Author "Kozhukharov V."
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Item Assessment of Nd2-xSrxNIO4-d as a cathodic material for solid oxide fuel cell applications(2013-05-21) Simeonov S.; Kozhukharov S.; Grenier J.; Machkova M.; Kozhukharov V.The features and performance of each device and equipment is directly related to its composing materials. The efficiency and durability of the Solid Oxide Fuel Cells (SOFC) also depend on their composing elements. Other important factors for the SOFC behavior are the working conditions (compositions, and humidity of the fuel and oxidant gaseous mixtures, temperature, pressure, etc.). These facts predetermine the necessity for detailed investigation of the behavior of each composing layer of SOFC. For this reason, the electrical characteristics of Nd2-xSrxNiO4-d as SOFC cathodic material were evaluated by high temperature electrochemical methods, durability tests, and posterior XRD and SEM characterization. As a result, the optimal composition and working conditions for the investigated material in assembled SOFC were determined. The obtained material reveals excellent durability and compatibility with the rest SOFC components.Item Ceramic materials for SOFCs: Current status(2002-01-01) Kozhukharov V.; Brashkova N.; Ivanova M.; Carda J.; Machkova M.It is well known that the main parts of Solid Oxide Fuel Cells (SOFCs) are build from ceramic materials. Namely the ceramic materials and composites, used for SOFCs manufacturing, are objects of the overview in the present work. The analysis carried out covers the last current publications in the field discussed. Special attention and examination in details have been done on patents state-of-the-art. After a background and short classification of the ceramic SOFCs materials the attention is focused on cathode, electrolyte, anode, interconnection and sealing materials. Their requirements, structure, thermal stability, composition control and behavior, processing and performance are the object of overview. A correlation has been made between the phase diagrams oxygen incorporation and transport, and SOFC advantages, generally for materials of lanthanum- base perovskite family. In order to analyze the innovative investigations regarding the patent branch of the SOFCs development and application, an object of review was patents from Japan, USA, Germany and European Union. Some examples of the inventions with accent on the ceramic materials are shown. In addition the tendency regarding R&D activities of SOFCs development materials from the leading companies in the world is analyzed. On the base of the most important technological and economical parameters of cell cathode/electrolyte/anode materials an attempt for evaluation and correlation has been made and innovative conceptions are shown.Item Ceramic materials for SOFCs: Current status(2002-01-01) Kozhukharov V.; Brashkova N.; Ivanova M.; Carda J.; Machkova M.It is well known that the main parts of Solid Oxide Fuel Cells (SOFCs) are build from ceramic materials. Namely the ceramic materials and composites, used for SOFCs manufacturing, are objects of the overview in the present work. The analysis carried out covers the last current publications in the field discussed. Special attention and examination in details have been done on patents state-of-the-art. After a background and short classification of the ceramic SOFCs materials the attention is focused on cathode, electrolyte, anode, interconnection and sealing materials. Their requirements, structure, thermal stability, composition control and behavior, processing and performance are the object of overview. A correlation has been made between the phase diagrams oxygen incorporation and transport, and SOFC advantages, generally for materials of lanthanum- base perovskite family. In order to analyze the innovative investigations regarding the patent branch of the SOFCs development and application, an object of review was patents from Japan, USA, Germany and European Union. Some examples of the inventions with accent on the ceramic materials are shown. In addition the tendency regarding R&D activities of SOFCs development materials from the leading companies in the world is analyzed. On the base of the most important technological and economical parameters of cell cathode/electrolyte/anode materials an attempt for evaluation and correlation has been made and innovative conceptions are shown.Item Ceramic materials for SOFCs: Current status(2002-01-01) Kozhukharov V.; Brashkova N.; Ivanova M.; Carda J.; Machkova M.It is well known that the main parts of Solid Oxide Fuel Cells (SOFCs) are build from ceramic materials. Namely the ceramic materials and composites, used for SOFCs manufacturing, are objects of the overview in the present work. The analysis carried out covers the last current publications in the field discussed. Special attention and examination in details have been done on patents state-of-the-art. After a background and short classification of the ceramic SOFCs materials the attention is focused on cathode, electrolyte, anode, interconnection and sealing materials. Their requirements, structure, thermal stability, composition control and behavior, processing and performance are the object of overview. A correlation has been made between the phase diagrams oxygen incorporation and transport, and SOFC advantages, generally for materials of lanthanum- base perovskite family. In order to analyze the innovative investigations regarding the patent branch of the SOFCs development and application, an object of review was patents from Japan, USA, Germany and European Union. Some examples of the inventions with accent on the ceramic materials are shown. In addition the tendency regarding R&D activities of SOFCs development materials from the leading companies in the world is analyzed. On the base of the most important technological and economical parameters of cell cathode/electrolyte/anode materials an attempt for evaluation and correlation has been made and innovative conceptions are shown.Item Crystal and magnetic structure of substituted lanthanum cobaltites(1997-01-01) Sonntag R.; Neov S.; Kozhukharov V.; Neov D.; Ten Elshof J.The crystal and magnetic structures of the lanthanum cobaltites La0.6Sr0.4CoO3, La0.6,Sr0.4Co0.9Fe0.1O3 and La0.6Ba0.4Co0.9Fe0.1O3 have been studied by neutron powder diffraction at temperatures of 2, 300 and 900 K. All compounds undergo a phase transition from cubic to rhombohedral structure. Below the room temperature La0.6Sr0.4CoO3 becomes ferromagnetic while for the components with 10% Fc substituted for Co, we found an antiferromagnetic order. © 1998 Elsevier Science B.V. All rights reserved.Item In-situ sol-gel synthesis and thin film deposition of Cu(In, Ga)(S, Se)2 solar cells(2013-12-17) Oliveira L.; Lyubenova T.; Martí R.; Fraga D.; Rey A.; Kozhukharov V.; Carda J.Chalcogenide-based solar cells Cu(In, Ga)(S, Se)2 were developed using an in-situ sol-gel method and spin coating thin film deposition. The influence of chemical composition and thermal treatment were studied in detail. It was revealed that these variables are related to band gap changes and final device performance. Increasing in band gap experimental values (1.18-1.67 eV) was observed, due to the formation of solid solution of Ga (III) and S (-II) incorporation in the crystal lattice. Optimal device performance of 3,1 % efficiency of solar energy conversion was achieved for the Cu(In1-xGax)(S, Se)2 solid solution.Item Influence of ce(iii)/ce(iv)-supplements on the characteristics of humidity sensors with tio2 films prepared via a sol-gel method(2013-03-01) Kozhukharov S.; Nenova Z.; Nenov T.; Machkova M.; Kozhukharov V.Humidity sensors have been prepared via a sol-gel method to deposit TiO2 films with additions of Ce-compounds on alumina substrates, with interdigitated silver palladium electrodes. Observations by scanning electron microscopy (SEM) were performed in order to determine the surface morphology of the respective layers. Structural and compositional characterization was done by X-ray diffraction analysis (XRD), and energy dispersive X-ray spectroscopy (EDX) for investigation of the relation between the film structures and the parameters of the respective sensors. The influence of Ce-compounds on the electrical characteristics of the samples as humidity sensing elements has been evaluated by an impedance analyzer.Item Mössbauer effect and X-ray distribution function analysis in complex Na2O-CaO-ZnO-Fe2O3-Al2O 3-SiO2 glasses and glass-ceramics(1999-01-01) Romero M.; Rincón J.; Mûsik S.; Kozhukharov V.Mössbauer spectroscopy at room temperature was carried out to determine the state of iron ions in complex glasses and glass-ceramics in the SiO2-CaO-ZnO-Na2O-Fe2O3-Al 2O3 system. Isomer shift values of the glasses suggest that Fe3+ and Fe2+ are in tetrahedral and octahedral coordination, respectively. The spectrum of the glass-ceramic shows that about 60 wt% total iron is in the magnetite phase. The Fe+3/Fe+2 ratio varies with the total iron oxide content of the glasses, indicating that the vitreous network is more distorted when the iron content is greater. X-ray diffraction measurements were carried out to obtain the radial distribution function (RDF). The interatomic distances for Si-Si and Si-O have been determined. The complex composition of these glasses does not allow the estimation of Al-O and Fe-O distances. © 1999 Elsevier Science Ltd.Item Mössbauer study of iron-based perovskite-type materials as potential catalysts for ethyl acetate oxidation(2010-01-01) Paneva D.; Dimitrov M.; Velinov N.; Kolev H.; Kozhukharov V.; Tsoncheva T.; Mitov I.La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile organic compounds (VOCs) elimination as they possess high conversion ability and selectivity to total oxidation of ethyl acetate. Catalytic performance of LaSr3Fe3O10 is depended on the stability of structure and Fe4+-oxidation state. © 2010 IOP Publishing Ltd.Item Multifunctional smart coatings on novel ceramics and glassceramic substrates in the context of the circular economy(2018-01-01) Lyubenova T.S.; Fraga D.; Castelló J.B.C.; Kozhukharov V.; Machkova M.S.Nowadays is time of products generated by ``smart coatings`` that exhibit multiple functionalities. In particular, the construction industry is reached the point where it is possible to fabricate ``smart and sustainable`` buildings that fulfill the requirements of a growing marketplace of products and devices for ``smart cities`` generation. In addition, if the buildings are ``green``, i.e. in accordance with the today's economic model ``made to be made again`` or so-called ``circular economy`` they are very attractive and viable alternative for future businesses and industrial exploring. In this concept, we report a development sustainable ceramic and glass-ceramic tile substrates made by cheap, easily accessible and recycled materials that are further functionalized by different ``smart coatings`` for specific applications. Devices that generate and save energy, air and pollution cleaning, with anti-slip and phosphorescence properties are some examples of the overview that this publication described.Item Nanomaterials and nanotechnology: European initiatives, status and strategy(review)(2013-05-21) Kozhukharov V.; Machkova M.The aim of the present work is to present a short overview regarding European initiatives, state-of-the-art and RTD strategy in the field of nanomaterials and nanotechnologies. The idea is to mark the national action plans of the leading European countries, to analyse and to discuss their activities, in order to synchronize to the EU nano-initiatives, regarding R&D and social aspects in the field of nanoscience and technoloiesy. Object of discussion are the most important industrial countries in the European Union. Since the field is too broad, some countries are selected and the overview is done by dividing ofEuropean Union relatively in two parts: West Europe (e.g. Germany, UK, France, Italy, Spain, Scandinavian countries, Switzerland, etc.) and East Europe (e.g. Poland, Bulgaria, Russia). Adequate conclusions are extracted.Item Reproducibility of the corrosion parameters for AA2024-T3 aluminium alloy in chloride solution after different preliminary treatment procedures(2015-01-01) Matter E.A.; Kozhukharov S.; Machkova M.; Kozhukharov V.The reproducibility of the superficial morphology and corrosion parameters of AA2024 alloy in 0.6 M NaCl solution under different preliminary treatment procedures have been studied. It was achieved by applying optical metallographic microscopy (OMM), atomic force microscopy (AFM) and electrochemical methods as linear voltammetry (LVA) and electrochemical impedance spectroscopy (EIS). Four different preliminary treatment procedures are investigated. Statistic methods are used for the reproducibility evaluation of each measured parameter. The results revealed that the approach of etching with a slightly alkaline solution after mechanical grinding increases the reproducibility, and the best reproducibility was achieved in the approach of mechanical grinding.Item Rheological effect of different deflocculation mechanisms on a porcelain ceramic composition(2015-01-01) Barrachina E.; Llop J.; Notari M.; Fraga D.; Martí R.; Calvet I.; Rey A.; Lyubenova T.; Kozhukharov S.; Kozhukharov V.; Carda J.The current environmental policy imposes general optimisation of the industrial process. There are two critical steps related to suspensions fluidity in the ceramic spray-drying industry: the emptying of the ball mill and the spray-drying operation. The chemicals producers provide a large number of commercial deflocculants aiming to improve both processes. The present research is focused on the comparison of the rheological effect of four commercial liquid deflocculants on a porcelain ceramic composition in view of different mechanisms of deflocculation. The suspensions prepared have 70 %-solid content and a range of deflocculant concentrations between 0.1 mass % and 0.6 mass %. Each suspension is characterized by measuring its solid content, particle size distribution, pH values, conductivity and rheology, including viscosity at two shear rates and thixotropy calculated from the hysteresis area of the flowability curves. On the basis of the experiments carried out adequate conclusions are presented.Item Surface analysis of doped lanthanide cobalt perovskites by X-ray photoelectron spectroscopy(1996-10-01) Kozhukharov V.; Machkova M.; Ivanov P.; Bouwmeester H.J.M.; Van Doorn R.