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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.

2

The Effect of Specific Conditions on Cu, Ni, Zn and Al Recovery from PCBS Waste Using Acidophilic Bacterial Strains

Mrážiková A., Kaduková J., Marcinčáková R., Velgosová O., Willner J., Fornalczyk A., Saternus M.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 1

261--264

EN

The objective of this work was to evaluate the influence of static, stirring and shaking conditions on copper, zinc, nickel and aluminium dissolution from printed circuit boards (PCBs) using the mixed acidophilic bacterial culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The results revealed that static conditions were the most effective in zinc and aluminium dissolution. Zinc was removed almost completely under static conditions, whereas maximum of nickel dissolution was reached under the stirring conditions. The highest copper recovery (36%) was reached under stirring conditions. The shaking conditions appeared to be the least suitable. The relative importance of these systems for the bioleaching of copper and nickel decreased in the order: stirring, static conditions, shaking.

3

Dissolution of Metal Supported Spent Auto Catalysts in Acids

Fornalczyk A., Kraszewski M., Willner J., Kaduková J., Mrážiková A., Marcinčáková R., Velgosová O.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 1

233--236

EN

Metal supported auto catalysts, have been used in sports and racing cars initially, but nowadays their application systematically increases. In Metal Substrate (supported) Converters (MSC), catalytic functions are performed by the Platinum Group Metals (PGM): Pt, Pd, Rh, similarly to the catalysts on ceramic carriers. The contents of these metals make that spent catalytic converters are valuable source of precious metals. All over the world there are many methods for the metals recovery from the ceramic carriers, however, the issue of platinum recovery from metal supported catalysts has not been studied sufficiently yet. The paper presents preliminary results of dissolution of spent automotive catalyst on a metal carrier by means of acids: H2SO4, HCl, HNO3, H3PO4. The main assumption of the research was the dissolution of base metals (Fe, Cr, Al) from metallic carrier of catalyst, avoiding dissolution of PGMs. Dissolution was the most effective when concentrated hydrochloric acid, and 2M sulfuric acid (VI) was used. It was observed that the dust, remaining after leaching, contained platinum in the level of 0.8% and 0.7%, respectively.

4

Models of damage mechanism of glidcop Cu-Al2O3 micro and nanomaterials

Besterci M., Sülleiová K., Ballóková B., Velgosová O.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 69, nr 2

79--85

EN

Purpose:of this paper was to analyze the fracture mechanism before and after ECAP in the Glidcop AL-60 grade (with 1.1 wt. % of Al2O3) system and to propose damage and/or fracture mechanisms models by means of the method “in situ tensile test in SEM”. Design/methodology/approach: The method of “in-situ tensile testing in SEM” was used for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, thank to which the initiation and development of plastic deformation and fracture can be reliably described. Analyses of microstructure and fracture surfaces were carried out by means of the scanning electrone microscope JEM 100 C. Findings: The deformation and fracture mechanisms of Glidcop AL-60 grade with 1.1 wt. % of Al2O3 phase (1.62 vol. % of Al2O3) were analyzed before and after ECAP (Equal Channel Angular Pressing). Before ECAP it was shown that the deformation process causes increasing of pores and formation of cracks. Decohesion of small Al2O3 particles and clusters occurs and the final fracture path is influenced by coalescence of cracks originated in such. The principal crack propagates towards the sample exterior surface. After ECAP initial cracks were formed in the middle of the specimen first of all in the triple junctions of nanograins and together with decohesion of Al2O3 particles and clusters at small strains lead to the failure. Research limitations/implications: To develop more complex knowledge about the objective material further studies are necessary to focus also on the other factors which besides the secondary phase amount can influence the failure mechanism, e.g. strain rate, temperature and others. Complex analysis allows better understanding of material behavior at different conditions and possibilities of application of products from these materials will be thereby improved. Practical implications: This article completes knowledge about damage/fracture mechanisms and processes of the material with 1.1 wt. % of Al2O3 phase. Some materials with the different volume fraction of a secondary phase have been studied. This concrete one with 1.1% clarifies the fracture process of Glidcop AL-60 material not only after mechanical alloying process but also after ECAP treatment. An effect of the ECAP process on the final material was crucial because not only microstructure but also failure mechanism have been changed. Originality/value: Based on the experimental observations original models of damage and/or fracture mechanisms were proposed.

5

Possibilities of Metals Extracton From Spent Metallic Automotive Catalytic Converters by Using Biometallurgical Method

Willner J., Kaduková J., Fornalczyk A., Mrážiková A., Marcinčáková R., Velgosová O.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 3A

1877--1880

EN

he main task of automotive catalytic converters is reducing the amount of harmful components of exhaust gases. Metallic catalytic converters are an alternative to standard ceramic catalytic converters. Metallic carriers are usually made from FeCrAl steel, which is covered by a layer of Precious Group Metals (PGMs) acting as a catalyst. There are many methods used for recovery of platinum from ceramic carriers in the world, but the issue of platinum and other metals recovery from metallic carriers is poorly described. The article presents results of preliminary experiments of metals biooxidation (Fe, Cr and Al) from spent catalytic converters with metallic carrier, using bacteria of the Acidithiobacillus genus.

PL

Głównym zadaniem katalizatorów samochodowych jest zmniejszenie ilości szkodliwych składników spalin. Katalizatory na nośniku metalowym są alternatywą dla standardowych katalizatorów na nośniku ceramicznym. Nośniki metalowe najczęściej wykonuje się ze stali FeCrAl, na którą nieniesiona jest warstwa platynowców, pełniących funkcje katalityczne. W pracy przedstawiono wyniki wstępnych prób bioutleniania metali ze zużytych katalizatorów na nośniku metalowym (Fe, Cr, Al.), z udziałem bakterii z rodzaju Acidithiobacillus.