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A Reviewed Turn at of Methods for Determining the Type of Fault in Power Transformers Based on Dissolved Gas Analysis

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ENERGIES 2024年第10期17卷 2331页

作者： Aciu, Ancuta-Mihaela Enache, Sorin Nitu, Maria-Cristina Natl Inst Res Dev & Testing Elect Engn ICMET Craio Res & Dev Dept Craiova 200746 Romania Univ Craiova Fac Elect Engn Craiova 200440 Romania

Since power transformers are the most important pieces of equipment in electricity transmission and distribution systems, special attention must be paid to their maintenance in order to keep them in good condition for a long time. This paper reviews the main steps in the process of diagnosing the health of power transformer insulation, which involves the science of analysing the gases dissolved in power transformer oil for effective identification of faults. An accurate diagnosis of incipient faults is favourable to sustainable development and necessary to maintain a reliable supply of electricity. The methods presented for fault diagnosis in mineral-oil-immersed power transformers are divided into analytical and graphical methods and have been found to be simple, economical and effective. After describing the methods, both their strengths and weaknesses were identified, and over the years, the methods were complemented to provide highly accurate information, validated by field inspections. This paper focuses on practical information and applications to manage maintenance based on accurate and up-to-date data. The contents of this paper will be of particular use to engineers who manufacture, monitor and/or use high-power transformers in the energy sector, as well as to undergraduate, master's and PhD students interested in such applications.

关键词： power transformer faults dissolved gas analysis maintenance

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Synthesis of Thermoresponsive Chitosan-graft-Poly(N-isopropylacrylamide) Hybrid Copolymer and Its Complexation with DNA

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POLYMERS 2024年第10期16卷 1315页

作者： Zaharia, Marius-Mihai Bucatariu, Florin Karayianni, Maria Lotos, Elena-Daniela Mihai, Marcela Pispas, Stergios Petru Poni Inst Macromol Chem 41A Grigore Gh Voda Alley Iasi 700487 Romania Natl Hellen Res Fdn Theoret & Phys Chem Inst 48 Vassileos Constantinou Ave 11635 Athens Greece

A hybrid synthetic-natural, thermoresponsive graft copolymer composed of poly(N-isopropyl acrylamide) (PNIPAM) side chains, prepared via RAFT polymerization, and a chitosan (Chit) polysaccharide backbone, was synthesized via radical addition-fragmentation reactions using the "grafting to" technique, in aqueous solution. ATR-FTIR, TGA, polyelectrolyte titrations and 1H NMR spectroscopy were employed in order to validate the Chit-g-PNIPAM copolymer chemical structure. Additionally, 1H NMR spectra and back conductometric titration were utilized to quantify the content of grafted PNIPAM side chains. The resulting graft copolymer contains dual functionality, namely both pH responsive free amino groups, with electrostatic complexation/coordination properties, and thermoresponsive PNIPAM side chains. Particle size measurements via dynamic light scattering (DLS) were used to study the thermoresponsive behavior of the Chit-g-PNIPAM copolymer. Thermal properties examined by TGA showed that, by the grafting modification with PNIPAM, the Chit structure became more thermally stable. The lower critical solution temperature (LCST) of the copolymer solution was determined by DLS measurements at 25-45 degrees C. Furthermore, dynamic and electrophoretic light scattering measurements demonstrated that the Chit-g-PNIPAM thermoresponsive copolymer is suitable of binding DNA molecules and forms nanosized polyplexes at different amino to phosphate groups ratios, with potential application as gene delivery systems.

关键词： chitosan poly(N-isopropylacrylamide) RAFT polymerization grafting thermal response DNA polyplexes gene delivery systems

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Ensuring Safety and Reliability: An Overview of Lithium-Ion Battery Service Assessment

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BATTERIES-BASEL 2025年第1期11卷

作者： Comanescu, Cezar Natl Inst Mat Phys 405A Atomistilor Str Magurele 77125 Romania Univ Politehn Bucuresti Fac Chem Engn & Biotechnol Dept Inorgan Chem Phys Chem & Electrochem 1 Polizu St Bucharest 011061 Romania Univ Bucharest Fac Phys 405 Atomistilor Str Magurele 77125 Romania

Lithium-ion batteries (LIBs) are fundamental to modern technology, powering everything from portable electronics to electric vehicles and large-scale energy storage systems. As their use expands across various industries, ensuring the reliability and safety of these batteries becomes paramount. This review explores the multifaceted aspects of LIB reliability, highlighting recent advancements and ongoing challenges. The importance of safety has been underscored by numerous incidents, such as the well-known smartphone battery explosions and more than 10,000 fires a year at facilities throughout Australia, both linked to LIB failures. These events emphasize the need for robust reliability and safety measures to ensure consistent performance and longevity. Factors like battery chemistry, design, manufacturing, and operating conditions can all influence the reliability of LIBs. Despite their widespread use, the mechanisms of failure, failure rates, and consequences of LIB failures are still not well understood, raising significant safety concerns. Current reliability assessment techniques include experimental methods, computational models, and data-driven approaches. Emerging trends, such as advanced characterization techniques and standardized testing protocols, advocate for improved practices to enhance the reliability and safety of LIBs across all applications.

关键词： lithium-ion batteries battery safety reliability assessment battery performance electrochemical stability regulatory standards risk management

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Applications of Natural Polymers in the Grapevine Industry: Plant Protection and Value-Added Utilization of Waste

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POLYMERS 2025年第1期17卷 18-18页

作者： Toma (Sardarescu), Daniela-Ionela Manaila-Maximean, Doina Fierascu, Irina Baroi, Anda Maria Matei (Brazdis), Roxana Ioana Fistos, Toma Chican, Irina Elena Fierascu, Radu Claudiu Natl Res & Dev Inst Biotechnol Hort INCDBH 37 Bucuresti Pitesti Str Stefanesti 117715 Romania Natl Univ Sci & Technol Politehn Bucharest Fac Chem Engn & Biotechnol 1-7 Gheorghe Polizu St Bucharest 011061 Romania Natl Univ Sci & Technol POLITEHN Bucharest Fac Appl Sci Bucharest 060042 Romania Acad Romanian Scientists 3 Ilfov Bucharest 050044 Romania Natl Inst Res & Dev Chem & Petrochem ICECHIM Bucha 202 Spl Independentei Bucharest 060021 Romania Univ Agron Sci & Vet Med Bucharest Fac Hort 59 Marasti Blvd Bucharest 011464 Romania

The grapevine industry is confronted with challenges such as plant stress from environmental factors and microbial infections, alongside the need for sustainable waste management practices. Natural polymers offer promising solutions to these issues due to their biocompatibility, biodegradability, and functional versatility. This review explores the dual role of natural polymers in enhancing the grapevine industry: as protective agents against various stressors and as carriers for the delivery of valuable compounds recovered from grapevine wastes. We examine the use of natural polymers such as chitosan, alginate, and cellulose in formulating bio-based protective coatings and treatments that bolster plant resistance to abiotic stress, pathogens, and pests. Additionally, the review delves into the innovative utilization of grapevine residues, including skins, seeds, and stems, as sources of polyphenols and other bioactive compounds. These compounds can be efficiently encapsulated in natural polymer matrices for applications in agriculture, food, and pharmaceuticals. Key topics include the mechanisms of action, benefits, and limitations of natural polymer-based interventions, as well as case studies demonstrating their practical implementation in vineyards. The review also addresses future research directions, emphasizing the need for integrated approaches that enhance sustainability and economic viability in the grapevine industry.

关键词： pathogen resistance grapevine waste valorization biodegradable materials bioactive compound encapsulation

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Hydrothermal Synthesis of Lithium Lanthanum Titanate

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CRYSTALS 2025年第3期15卷

作者： Okos, Alexandru Mocioiu, Ana-Maria Dragut, Dumitru Valentin Matei, Alexandru Cristian Bogdanescu, Cristian Natl Res & Dev Inst Nonferrous & Rare Met INCDMNR IMNR Pantelimon 077145 Romania

Lithium lanthanum titanate (LLTO) is a very promising material due to its ability to conduct lithium ions. It has many potential applications in the field of lithium batteries and sensors. Typical synthesis methods include solid-state reaction and sol-gel synthesis. We report a novel solvothermal synthesis method that produces almost single-phase LLTO samples at significantly reduced costs. The samples thus obtained were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical impedance spectroscopy (EIS), and chemical analysis. The results obtained for the newly synthesized samples were compared with results obtained from samples prepared using the solid-state reaction method. The XRD data show the formation of orthorhombic LLTO for the solvothermal synthesis, tetragonal LLTO for the hydrothermal synthesis, and cubic LLTO for the solid-state reaction. Additionally, XRD showed that the solid-state reaction of LLTO is a multi-stage process in which intermediary compounds such as La2Ti2O7 are formed. The bulk ionic conductivity of the LLTO samples produced through the solvothermal and hydrothermal processes is estimated at 10-4 S/cm, and the grain boundary conductivity is estimated at 10-6 S/cm.

关键词： lithium lanthanum titanate lithium batteries hydrothermal synthesis ionic conductivity perovskite oxides

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Fs Laser Patterning of Amorphous As2S3 Thin Films

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MATERIALS 2024年第4期17卷 798页

作者： Mihai, Claudia Jipa, Florin Socol, Gabriel Kiss, Adrian E. Zamfirescu, Marian Velea, Alin Natl Inst Mat Phys Atomistilor 405A Magurele 077125 Romania Natl Inst Lasers Plasma & Radiat Phys Atomistilor 409 Magurele 077125 Romania Natl Inst Optoelect INOE 2000 Atomistilor 409 Magurele 077125 Romania

This study investigates the morphological changes induced by femtosecond (fs) laser pulses in arsenic trisulfide (As2S3) thin films and gold-arsenic trisulfide (Au\As2S3) heterostructures, grown by pulsed laser deposition (PLD). By means of a direct laser writing experimental setup, the films were systematically irradiated at various laser power and irradiation times to observe their effects on surface modifications. AFM was employed for morphological and topological characterization. Our results reveal a clear transition threshold between photoexpansion and photoevaporation phenomena under different femtosecond laser power regimes, occurring between 1 and 1.5 mW, irrespective of exposure time. Notably, the presence of a gold layer in the heterostructure minimally influenced this threshold. A maximum photoexpansion of 5.2% was obtained in As2S3 films, while the Au\As2S3 heterostructure exhibited a peak photoexpansion of 0.8%. The study also includes a comparative analysis of continuous-wave (cw) laser irradiation, confirming the efficiency of fs laser pulses in inducing photoexpansion effects.

关键词： femtosecond laser pulses arsenic trisulfide (As2S3) photoexpansion and photoevaporation

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Composition and Surface Optical Properties of GaSe:Eu Crystals before and after Heat Treatment

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MATERIALS 2024年第2期17卷 405页

作者： Sprincean, Veaceslav Qiu, Haoyi Tjardts, Tim Lupan, Oleg Untila, Dumitru Aktas, Cenk Adelung, Rainer Leontie, Liviu Carlescu, Aurelian Gurlui, Silviu Caraman, Mihail Moldova State Univ Fac Phys & Engn 60 Alexei Mateev Str MD-2009 Kishinev Moldova Univ Kiel Fac Engn Inst Mat Sci Funct Nanomat Kaiserstr 2 D-24143 Kiel Germany Univ Kiel Inst Mat Sci Multicomponent Mat Kaiserstr 2 D-24143 Kiel Germany Tech Univ Moldova Ctr Nanotechnol & Nanosensors Dept Microelect & Biomed Engn 168 Stefan Cel Mare Av MD-2004 Kishinev Moldova Univ Cent Florida Dept Phys Orlando FL 32816 USA Alexandru Ioan Cuza Univ Fac Phys 11 Carol 1 Iasi 700506 Romania Alexandru Ioan Cuza Univ Inst Interdisciplinary Res Res Ctr Environm Sci North Eastern Romanian Reg CE Sci Res Dept 11 Carol 1 Iasi 700506 Romania

This work studies the technological preparation conditions, morphology, structural characteristics and elemental composition, and optical and photoluminescent properties of GaSe single crystals and Eu-doped beta-Ga2O3 nanoformations on epsilon-GaSe:Eu single crystal substrate, obtained by heat treatment at 750-900 degrees C, with a duration from 30 min to 12 h, in water vapor-enriched atmosphere, of GaSe plates doped with 0.02-3.00 at. % Eu. The defects on the (0001) surface of GaSe:Eu plates serve as nucleation centers of beta-Ga2O3:Eu crystallites. For 0.02 at. % Eu doping, the fundamental absorption edge of GaSe:Eu crystals at room temperature is formed by n = 1 direct excitons, while at 3.00 at. % doping, Eu completely shields the electron-hole bonds. The band gap of nanostructured beta-Ga2O3:Eu layer, determined from diffuse reflectance spectra, depends on the dopant concentration and ranges from 4.64 eV to 4.87 eV, for 3.00 and 0.05 at. % doping, respectively. At 0.02 at. % doping level, the PL spectrum of epsilon-GaSe:Eu single crystals consists of the n = 1 exciton band, together with the impurity band with a maximum intensity at 800 nm. Fabry-Perrot cavities with a width of 9.3 mu m are formed in these single crystals, which determine the interference structure of the impurity PL band. At 1.00-3.00 at. % Eu concentrations, the PL spectra of GaSe:Eu single crystals and beta-Ga2O3:Eu nanowire/nanolamellae layers are determined by electronic transitions of Eu2+ and Eu3+ ions.

关键词： chalcogenides gallium(III) trioxide native oxide Eu doping single crystals layers optical properties photoluminescence

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Electrical and Electro-Thermal Characteristics of (Carbon Black-Graphite)/LLDPE Composites with PTC Effect

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MATERIALS 2024年第5期17卷 1224页

作者： Lungulescu, Eduard-Marius Stancu, Cristina Setnescu, Radu Notingher, Petru V. Badea, Teodor-Adrian Natl Inst Res & Dev Elect Engn ICPE CA 313 Splaiul Unirii Bucharest 030138 Romania Univ POLITEHN Bucuresti Fac Elect Engn 313 Splaiul Independentei Bucharest 060042 Romania Valahia Univ Targovi?te Fac Sci & Arts Dept Adv Technol 13 Aleea Sinaia Targoviste 130004 Romania Romanian Res & Dev Inst Gas Turbines COMOTI 220D Iuliu Maniu Av Bucharest 061126 Romania

Electrical properties and electro-thermal behavior were studied in composites with carbon black (CB) or hybrid filler (CB and graphite) and a matrix of linear low-density polyethylene (LLDPE). LLDPE, a (co)polymer with low crystallinity but with high structural regularity, was less studied for Positive Temperature Coefficient (PTC) applications, but it would be of interest due to its higher flexibility as compared to HDPE. Structural characterization by scanning electron microscopy (SEM) confirmed a segregated structure resulted from preparation by solid state powder mixing followed by hot molding. Direct current (DC) conductivity measurements resulted in a percolation threshold of around 8% (w) for CB/LLDPE composites. Increased filler concentrations resulted in increased alternating current (AC) conductivity, electrical permittivity and loss factor. Resistivity-temperature curves indicate the dependence of the temperature at which the maximum of resistivity is reached (Tmax(R)) on the filler concentration, as well as a differentiation in the Tmax(R) from the crystalline transition temperatures determined by DSC. These results suggest that crystallinity is not the only determining factor of the PTC mechanism in this case. This behavior is different from similar high-crystallinity composites, and suggests a specific interaction between the conductive filler and the polymeric matrix. A strong dependence of the PTC effect on filler concentration and an optimal concentration range between 14 and 19% were also found. Graphite has a beneficial effect not only on conductivity, but also on PTC behavior. Temperature vs. time experiments, revealed good temperature self-regulation properties and current and voltage limitation, and irrespective of the applied voltage and composite type, the equilibrium superficial temperature did not exceed 80 degrees C, while the equilibrium current traversing the sample dropped from 22 mA at 35 V to 5 mA at 150 V, proving the limitation capa

关键词： LLDPE composite PTC conductivity self-regulating temperature carbon filler

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Clam Shell-Derived Hydroxyapatite: A Green Approach for the Photocatalytic Degradation of a Model Pollutant from the Textile Industry

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MATERIALS 2024年第11期17卷 2492页

作者： Matei (Brazdis), Roxana Ioana Baroi, Anda Maria Fistos, Toma Fierascu, Irina Grapin, Maria Raditoiu, Valentin Raduly, Florentina Monica Nicolae, Cristian Andi Fierascu, Radu Claudiu Natl Inst Res & Dev Chem & Petrochem ICECHIM Bucha 202 Spl Independentei Bucharest 060021 Romania Natl Univ Sci & Technol Politehn Bucharest Fac Chem Engn & Biotechnol 1-7 Gh Polizu Str Bucharest 011061 Romania Univ Agron Sci & Vet Med Bucharest Fac Hort 59 Marasti Blvd Bucharest 011464 Romania

This work aims to evaluate the potential use of natural wastes (in particular, clam shells) to synthesize one of the most well-known and versatile materials from the phosphate mineral group, hydroxyapatite (HAP). The obtained material was characterized in terms of morphology and composition using several analytical methods (scanning electron microscopy-SEM, X-ray diffraction-XRD, X-ray fluorescence-XRF, Fourier transform infrared spectroscopy-FTIR, thermal analysis-TGA, and evaluation of the porosity and specific surface characteristics by the Brunauer-Emmett-Teller-BET method) in order to confirm the successful synthesis of the material and to evaluate the presence of potential secondary phases. The developed material was further doped with iron oxide (HAP-Fe) using a microwave-assisted method, and both materials were evaluated in terms of photocatalytic activity determined by the photodecomposition of methylene blue (MB) which served as a contaminant model. The best results (approx. 33% MB degradation efficiency, after 120 min. of exposure) were obtained for the hydroxyapatite material, superior to the HAP-Fe composite (approx. 27%). The utilization of hydroxyapatite obtained from clam shells underscores the importance of sustainable and eco-friendly practices in materials syntheses. By repurposing waste materials from the seafood industry, we not only reduce environmental impact, but also create a valuable resource with diverse applications, contributing to advancements in both healthcare and environmental protection.

关键词： hydroxyapatite clam shells wastes methylene blue degradation photocatalysis environmental remediation

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Restructuring the Basic Design of Several Accelerator-Based Concrete Mixes by Integrating Superplasticizers

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MATERIALS 2024年第22期17卷 5582页

作者： Simedru, Alexandru Florin Cadar, Oana Becze, Anca Simedru, Dorina Tech Univ Cluj Napoca Dept Phys & Chem Bdul Muncii 14 Cluj Napoca 400114 Romania Subsidiary Res Inst Analyt Instrumentat INCDO INOE 2000 67 Donath St Cluj Napoca 400293 Romania

The increasing demand for infrastructure, the need to consolidate aging structures, and the effects of climate change imply the replacement or improvement of traditional concrete. This study investigates three accelerators and their mixtures (Ca(NO3)24H2O, Al2(SO4)318H2O, and Na2S2O35H2O) (series I) and their counterparts with superplasticizers (Dynamon SR41) (series II) as additives in standard concrete to improve its functionality. The standard concrete and new concrete mixes were analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and tests for water absorption, bulk density, and compressive strength. XRD analysis showed that all concrete mixes had similar structures composed of quartz, portlandite, larnite, calcium silicate, ettringite, albite, and muscovite in varying proportions. Their microstructures, as shown by SEM images, revealed the presence of ettringite, portlandite, and C-S-H gel at high magnification (1-5 kx). The addition of the superplasticizer remodeled the surface of the concrete mix, reducing the pore radius and increasing its compaction. These changes helped to reduce its bulk density while increasing the compressive strength. The results showed that all the concrete mixtures are similar to the standard concrete and can replace it for better functionality, but Na2S2O35H2O with superplasticizer concrete mixture had the higher compressive strength, supplying additional benefits.

关键词： concrete accelerator superplasticizer XRD SEM-EDX compressive strength

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