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Characteristics of Silver Nanoparticles in Different pH Values

Mražíková A., Velgosová O., Kavuličová J., Matvija M., Čižmárová E., Willner J.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 2

993--998

EN

Stability of silver nanoparticles strongly influences the potential of their application. The literature shows wide possibilities of nanoparticles preparation, which has significantly impact on their properties. Therefore, the improvement of AgNPs preparation plays a key role in the case of their practical use. The pH values of the environment are one of the important factors, which directly influences stability of AgNPs. We present a comparing study of the silver nanoparticles prepared by „bottom-up“ methods over by chemical synthesis and biosynthesis using AgNO3 (0.29 mM) solution. For the biosynthesis of the silver nanoparticles, the green freshwater algae Parachlorella kessleri and Citrus limon extracts were used as reducing and stabilizing agents. Chemically synthesized AgNPs were performed using sodium citrate (0.5%) as a capping agent and 0.01% gelatine as a reducing agent. The formation and long term stability of those silver nanoparticles synthesized either biologically and chemically were clearly observed by solution colour changes and confirmed by UV-vis spectroscopy. The pH values of formed nanoparticle solutions were 3 and 5.8 for biosynthesized AgNPs using extract of Citrus limon and Parachlorella kessleri, respectively and 7.2 for chemically prepared AgNPs solution using citrate. The SEM as a surface imaging method was used for the characterization of nanoparticle shapes, size distribution and also for resolving different particle sizes. These micrographs confirmed the presence of dispersed and aggregated AgNPs with various shapes and sizes.

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Study of the precipitation hardening process in recycled Al-Si-Cu cast alloys

Kuchariková L., Tillová E., Matvija M., Belan J., Chalupová M.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 1

397--403

EN

The formation of extremely small uniformly dispersed particles of a second phase within the original phase matrix during heat treatment changed material properties. Therefore the characterization of precipitation had been investigated using high resolution transmission electron microscopy (TEM) and electron diffraction of thin foils for an AlSi9Cu3 cast alloy. For investigation the hardening effect onto mechanical properties of aluminium cast was used heat treatment, which consisted from solution treatment at 515°C / 4 hours (h), followed by quenching into water with temperature 50°C and artificial aging using different temperatures 170°C and 190°C with different holding time 2, 4, 8, 16, and 32 hours. The observations of microstructure and substructure reveals that precipitation hardening has caused great changes in size, morphology and distributions of structural components, the formation of precipitates of Cu phases, and the change of mechanical properties as well.

3

Evaluation of Cracking Causes of AlSi5Cu3 Alloy Castings

Eperješi Š., Matvija M., Eperješi Ľ., Vojtko M.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 3

1089--1092

EN

Recently, the castings made from aluminum-silicon alloys by pressure die casting are increasingly used in the automotive industry. In practice, on these castings are high demands, mainly demands on quality of their structure, operating life and safety ensuring of their utilization. The AlSi5Cu3 alloy castings are widely used for production of car components. After the prescribed tests, the cracks and low mechanical properties have been identified for several castings of this alloy, which were produced by low pressure casting into a metal mould and subsequent they were heat treated. Therefore, analyses of the castings were realized to determine the causes of these defects. Evaluation of structure of the AlSi5Cu3 alloy and causes of failure were the subjects of investigation presented in this article.

PL

Zastosowanie odlewów ciśnieniowych ze stopów Al-Si ustawicznie wzrasta w przemyśle samochodowym, gdzie stopy te muszą spełniać wysokie wymagania odnośnie do jakości ich struktury, żywotności i bezpiecznego użytkowania. Odlewy ze stopu AlSi5Cu3 są szeroko stosowane w produkcji części samochodów. Wg pracy wady pęknięć wewnętrznych i niskie właściwości mechaniczne posiada część odlewów obrabianych cieplnie, odlanych do form metalowych pod niskim ciśnieniem. Praca poświęcona jest ocenie struktury i przyczynom pękania odlewów ze stopu AlSi5Cu3.