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Zinc ferrite/polyaniline composite particles: Pigment applicable as electro-active paint
Lenka Munteanu,Andrei Munteanu,Michal Sedlacik,Erika Kutalkova,Miroslav Kohl,Andrea Kalendova 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.115 No.-
Hybrid conductive paint pigments composed of zinc ferrites (ZF) and polyaniline (PANI) were analysed asboth a potential electro-active and corrosion-protective paint from the electrorheological (ER) point ofview. The particles were characterised using scanning electron microscopy and X-ray diffraction spectroscopy. These hybrid conductive particles are used as pigments suitable for applications in paints whichwas confirmed by determining the consumption of linseed oil, the specific conductivity of aqueousextracts and the density of the tested pigments according to the relevant standardized methods. Thechemical stability of particles was evaluated by means of durability tests in aggressive environmentshowing excellent results for the coated particles. Both ZF/PANI particles and pure ZF were dispersedin silicone oil and their ER behaviour was analysed through controlled shear rate and dynamic oscillatorytests. The ER performance of the pure ZF and the composite ZF/PANI suspensions were compared, showingpromising results and enhanced ER performance and attention-worthy ER efficiency of the later (inparticular, the ER efficiency of the coated particles exceeded 105 % at 0.01 s1). Lastly, the results werefurther validated via dielectric spectroscopy. Thus, the ZF/PANI particles have the potential to be appliedas a hybrid ER fluid and an electro-active paint.
Effect of metakaolin on the properties of conventional and self compacting concrete
Lenka, S.,Panda, K.C. Techno-Press 2017 Advances in concrete construction Vol.5 No.1
Supplementary cementitious materials (SCM) have turned out to be a vital portion of extraordinary strength and performance concrete. Metakaolin (MK) is one of SCM material is acquired by calcinations of kaolinite. Universally utilised as pozzolanic material in concrete to enhance mechanical and durability properties. This study investigates the fresh and hardened properties of conventional concrete (CC) and self compacting concrete (SCC) by partially replacing cement with MK in diverse percentages. In CC and SCC, partial replacement of cement with MK varies from 5-20%. Fresh concrete properties of CC are conducted by slump test and compaction factor tests and for SCC, slump flow, T500, J-Ring, L-Box, V-Funnel and U-Box tests. Hardened concrete characteristics are investigated by compressive, split tensile and flexural strengths at age of 7, 28 and 90 days of curing under water. Carbonation depth, water absorption and density of MK based CC and SCC was also computed. Fresh concrete test results indicated that increase in MK replacement increases workability of concrete in a constant w/b ratio. Also, outcomes reveal that concrete integrating MK had greater compressive, flexural and split tensile strengths. Optimum replacement level of MK for cement was 10%, which increased mechanical properties and robustness properties of concrete.
Nonlinear analyses of steel beams and arches using virtual unit moments and effective rigidity
Lenka Koubova,Petr Janas,Alexandros Markopoulos,Martin Krejsa 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.5
This study examined geometric and physical nonlinear analyses of beams and arches specifically from rolled profiles used in mining and underground constructions. These profiles possess the ability to create plastic hinges owing to their robustness. It was assumed that displacements in beams and arches fabricated from these profiles were comparable with the size of the structure. It also considered changes in the shape of a rod cross-section and the nonlinearities of the structure. The analyses were based on virtual unit moments, effective flexural rigidity of used open sections, and a secant method. The use of the approach led to a solution for the "after-critical" condition in which deformation increased with decreases in loads. The solution was derived for static determinate beams and static indeterminate arches. The results were compared with results obtained in other experimental tests and methods.
Lenka Koubova,Petr Janas,Karel Janas,Martin Krejsa 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.5
Closed steel supports of different shapes are used in mining and underground constructions. The supports are prefabricated from rolled, usually robust, steel profiles. The load carrying capacity of a support is considerably influenced by the active loading and passive forces. The passive forces are induced by interactions between the support and the surrounding rock mass. The analysis herein comprises three parts: The first part consists of structural geometry processing. The second part involves finding the numerical solution of a statically indeterminate structure for a specified load. The third part is calculation of the load carrying capacity and the components of internal forces and deformations. For this, the force method and numerical integration are used. The Winkler model is applied when the support interacts with the surrounding environment. The load carrying capacity is limited by the slip resistance of the connected parts and it is limited by reaching the ultimate state of the profile. This paper serves as a comprehensive reference for the determination of the load carrying capacity of closed steel supports and includes stepwise derivations of the governing formulas.
Rao G. Purnachandra,Lenka Trupti Ranjan,Singh Rajan,Nguyen Hieu Pham Trung 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.9
In this work, a recessed gate AlGaN/AlN/GaN HEMT (high electron mobility transistor) on β-Ga2O3 substrate is proposed using a feld-plate mechanism and compared with a recessed gate structure (recessed depth of 25 nm, 30 nm, and 35 nm) without feld-plate. The device is optimized and analysed to obtain diminished leakage current (10−16A/mm), RON (1.27 Ω-mm), PFOM (power fgure of merit) (4373 MW/cm3 ), breakdown voltage (108 V), and excellent DC characteristics using Atlas TCAD. It is observed that the obtained results are better than those reported in recent studies. These RON and PFOM demonstrate that the suggested device structure on the preferred β-Ga2O3 substrate is an excellent contender for future highpower nanoelectronics applications
STEPANKA KLIMKOVA,MIROSLAV CERNIK,LENKA LACINOVA,JAROSLAV NOSEK 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.4
It is known that the reductive effects of zero-valent iron (Fe0) and the sorptive capability of iron and its oxides can be used for both the dehalogenation of chlorinated hydrocarbons (CHC), especially of chlorinated ethenes (PCE → TCE → DCE → VC → ethene, ethane), and the removing of heavy metals from groundwater by turning them into a less-soluble form through changes of their oxidation state, or by adsorption. These consequences are being exploited in the construction of iron filling permeable reactive barriers for a longer time.1 The advantages of nanoscale zero-valent iron (nanoFe0) over the macroscopic one consist not only in the better reactivity implicit in their greater specific surface area but also in their mobility in rock environment.2,3 Numerous laboratory experiments, especially the batch-agitated experiments, with samples from seven various contaminated localities in Europe have been carried out withthe aim to discover the measurement of the reductive effect of the nanoFe0 on selected contaminants. It was found that the nanoFe0 can be reliably usable as a reductive reactant for in-situ chemical decontamination of sites polluted by chlorinated ethenes (CEs), or hexa-valent chromium (CrVI). The rate of reductive reaction and the optimal concentrations for the real remediation action were determined. On the basis of these laboratory experiments, the methods for pilot application of nanoFe0 have been specified. Subsequently the pilot experiments were accomplished in surveyed localities.
Ultrasonic atomization of magnesium alloy AZ61 based on the TIG melting method
Jan Jaros,Daniel Koutny,Lenka Klakurkova,Stefan Gneiger,Sascha Senck 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11
In the present study, ultrasonic atomization based on the TIG melting method was used to atomize magnesium alloy AZ61. Magnesium alloys have the potential for medical applications due to their biocompatibility and mechanical properties close to human bone. First, the process parameters for atomization of magnesium alloy AZ61 were determined, and atomized powder particles were analyzed by scanning electron microscope and X-ray diffraction analysis. The atomized powder was used for the production of a basic experiment of a single track by laser powder bed fusion technology. The atomized powder particles had a fine round shape and led to the production of continuous single tracks. However, the efficiency of the atomization process was low around 0.22 g/hour which was mainly caused by the oxidation of magnesium alloy.