Papers by Oksana Velgosová
High Temperature Materials and Processes, Jun 1, 2005
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Archives of Metallurgy and Materials, Mar 1, 2016
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Polymers, Feb 28, 2023
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Nova Biotechnologica et Chimica, Jun 1, 2015
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Molecular Crystals and Liquid Crystals, Nov 1, 2020
Abstract In the article the green synthesis of silver nanoparticles (AgNPs) by four extracts of P... more Abstract In the article the green synthesis of silver nanoparticles (AgNPs) by four extracts of Parachlorella kessleri the alga: solution A—a mixture of H2O and algae (also used as a stock solution), B—heat treated and centrifuged stock solution, C—heat treated stock solution, and D—centrifuged stock solution is performed. FTIR, UV-vis, TEM, light microscope and image analysis were used for the analysis of the solutions composition, synthesis process, AgNPs size and morphology, and changes caused by the solution type. The impact of extracts treatment on AgNPs synthesis rate, size, stability and amount was proved.
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Nano-Structures and Nano-Objects, Oct 1, 2021
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Metallurgical Research & Technology, 2018
The Al-Al4C3metal matrix composite (MMC) reinforced by Al4C3nanoparticles was produced by a powde... more The Al-Al4C3metal matrix composite (MMC) reinforced by Al4C3nanoparticles was produced by a powder metallurgy route. Well-dispersed coherent Al4C3phase was formed during the fabrication process, which guarantees good interface bonding and thus results in good mechanical properties. Yield strength (YS) for materials strengthened by 1 wt.% of C reached 275 MPa, ultimate tensile strength (UTS) 295 MPa and elongation (A) 14%, which means that this material can compete with Al matrix strengthened by comparable amount of carbon nanotubes (CNTs/Al). To analyse the thermal stability, the Al-Al4C3composite was exposed to a temperature of 250 °C, 500 °C and 620 °C for 5 hours with subsequent gradual furnace cooling to room temperature. The composite exhibits high structural stability (the subgrains size after thermal treatment at 250 °C was ∼0.82 μm and did not change to a temperature of 500 °C) with preserved mechanical properties up to 500 °C. After thermal exposing to 620 °C, the subgrains size increased, by almost twice the initial value (∼1.93 μm) and degradation of substructure was observed, but the material maintained good YS (∼220 MPa) and UTS (∼245 MPa) values. The structural and mechanical properties of the composite, even after thermal treatment, are significantly determined by the Al4C3phase created “in situ”. Thus, we suggest that Al-Al4C3composites might be a good alternative, depending on the application purpose, to CNTs/Al composites.
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Materials Science Forum, Feb 1, 2003
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Materials in engineering, 2006
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Polymers
A biological method was successfully applied to synthesize spherical silver nanoparticles (AgNPs)... more A biological method was successfully applied to synthesize spherical silver nanoparticles (AgNPs) while using the extract of lavender (Ex-L) (lat. Lavandula angustifolia) as the reducing and stabilizing agent. The produced nanoparticles were spherical with an average size of 20 nm. The AgNPs’ synthesis rate confirmed the extract’s excellent ability to reduce silver nanoparticles from the AgNO3 solution. The presence of good stabilizing agents was confirmed by the excellent stability of the extract. Nanoparticles’ shapes and sizes did not change. UV-Vis absorption spectrometry, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize the silver nanoparticles. The silver nanoparticles were incorporated into the PVA polymer matrix by the “ex situ” method. The polymer matrix composite with AgNPs was prepared in two ways: as a composite film and nanofibers (nonwoven textile). The anti-biofilm ...
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Metallic Materials
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International Journal of Applied Physics, Oct 25, 2017
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Molecular Crystals and Liquid Crystals, 2020
In the article the green synthesis of silver nanoparticles (AgNPs) by four extracts of Parachlore... more In the article the green synthesis of silver nanoparticles (AgNPs) by four extracts of Parachlorella kessleri the alga: solution A—a mixture of H2O and algae (also used as a stock solution), B—heat treated and centrifuged stock solution, C—heat treated stock solution, and D—centrifuged stock solution is performed. FTIR, UV-vis, TEM, light microscope and image analysis were used for the analysis of the solutions composition, synthesis process, AgNPs size and morphology, and changes caused by the solution type. The impact of extracts treatment on AgNPs synthesis rate, size, stability and amount was proved.
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The principle of strength enhancement in dispersion strengthened materials lies in introducing hi... more The principle of strength enhancement in dispersion strengthened materials lies in introducing high strength dispersed phase into the matrix. This phase can be introduced into the matrix from outside, or it can be formed „in-situ“ during the milling, which is called the method of mechanical alloying. The change in fracture behaviour for the Al-12Al4C3 system was investigated and analysed at temperatures from 20 to 400°C and strain rates from 2.5·10 -5 to 10 -1 s -1 . At room temperature during tensile testing the strain is controlled by dislocation movement and reactions. For high temperatures in the investigated region the principal mechanism keying the strain is the presence of dynamic recovery processes. Strain rate influences on facture are analysed.
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AIP Conference Proceedings, 2017
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Bulletin of Materials Science, 2021
The aim of this study was to prepare and analyse polymer matrix composite (PMC) thin films and mi... more The aim of this study was to prepare and analyse polymer matrix composite (PMC) thin films and micro-fibres doped with different amounts of silver nanoparticles (AgNPs). AgNPs were synthesized by green method. The process of synthesis was observed and analysed by UV–visible and Fourier transform infrared analyses. The morphology and size of synthesized AgNPs was observed by scanning electron microscopy (SEM), transmission electron microscopy and energy dispersive X-ray techniques. Synthesized nanoparticles were uniform, near spherical, with mean diameter ~20 nm. Polyvinyl alcohol–silver (PVA–AgNPs) composite films (prepared by spin-coating) and micro-fibres (prepared by electrospinning) with different amount of nanoparticles (~6 and ~20% of AgNPs) were prepared. The distribution of AgNPs in composites was observed by the SEM. The observation showed the presence of clusters of AgNPs in polymer matrix. Significant changes in distribution was observed after increasing the amount of AgNPs. The antimicrobial activity of prepared thin films and micro-fibres was tested against one cell algae Parachlorella kesleri and compared to colloidal AgNPs. The toxicity tests showed good toxic effect on both AgNPs colloid and PVA–AgNPs composites.
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Archives of Metallurgy and Materials, 2017
The application of green synthesis in the nano-science and technology is of great importance in t... more The application of green synthesis in the nano-science and technology is of great importance in the area of the preparation of various materials. In this work, three selected algal species Parachlorella kessleri, Dictyosphaerium chlorelloides and Desmodesmus quadricauda were successfully used for the preparation of silver nanoparticles (AgNPs). Presence of AgNPs was confirmed by UV-vis spectroscopy and transmission electron microscopy. AgNPs produced by P. kessleri had narrow size distribution and average sizes of 7.6 nm. However, nanoparticle production lasted for long time. Nanoparticle formation by D. chlorelloides was the fastest, although, their average sizes were 23.4 nm with broad size distribution. Nanoparticles produced by D. quadricauda had average sizes 23.9 nm but they were the least stable, aggregated and precipitated from solutions within 3 days. These results confirmed that the size distribution and mean diameter of the nanoparticles, crucial for various applications,...
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Materials & Design, 2006
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Papers by Oksana Velgosová