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Open access

Jana Jurišová, Vladimír Danielik, Pavel Fellner, Milan Králik and Tomáš Foltinovič

Abstract

Reactivity of various calcium carbonate samples for flue gas desulfurization was tested. Two groups of CaCO3 samples were considered; natural limestone containing calcite phase dominantly and samples prepared by the conversion of gypsum with ammonium and carbon dioxide (precipitated CaCO3) containing different amounts of calcite, aragonite and vaterite.

Reactivity of precipitated calcium carbonate depends primarily on the particle size, similarly as in case of industrial samples. The initial reaction rate was comparable with the industrial limestones for samples with the average particle size lower than 15 μm. However, the conversion of laboratory samples was significantly higher after 5 min of the reaction.

Phase composition of the precipitated calcium carbonate has a minor but noticeable impact on the reactivity. The presence of vaterite slightly increased the reactivity, which is in accordance with its lower compact structure in comparison with calcite and aragonite. Unexpected effect of the increased content of aragonite, which is the most compact phase in comparison with calcite and vaterite, was observed. If calcium carbonate contains up to approximately 30 % of aragonite the reactivity increases, which can be explained by the SEM pictures showing agglomerate composition with relatively high specific surface. At higher contents of aragonite, the reactivity decreases. All the obtained results proved the suitability of precipitated CaCO3 prepared from flue gas desulfurization gypsum to be recycled in the flue gas desulfurization process.

Open access

Alžbeta Medveďová and Romana Györiová

Abstract

There is evidence that the transmission of Staphylococcus aureus and methicillin-resistant S. aureus between the community and environmental surfaces still exists. Even the means of this transmission remain uncertain, the public transport system may serve as a potential source of different bacteria, and the contact with contaminated public surfaces may increase the risk for bacterial diseases emergence. This study aimed to investigate S. aureus contamination on Bratislava’s public transport vehicles. Forty samples of hand-touched surfaces were collected during December 2015 and March 2017 by using surface sampling method. S. aureus was detected in all analysed swabs. Simultaneously, antibiotic resistance of S. aureus from swabs was evaluated. Of 40 samples, only 23 % did not contain S. aureus resistant to some of 10 analysed antibiotics. On the other hand, the severe prevalence of highly resistant S. aureus to penicillin, methicillin, ampicillin, and cefoxitin was confirmed. 15 % of isolates displayed resistance to at least three antimicrobial classes. The amount of S. aureus was not significantly influenced by the lines or by the analysed surface (grabs rails or on-board stop buttons). However, there was a statistically significant effect of year period, both between samples from December and March and between samples from the same month but different year. The study confirmed the widespread occurrence of resistant S. aureus in public transport vehicles in Bratislava, Slovakia.

Open access

Blanka Zachariášová, Katarína Haberová, Michal Oravec and Viera Jančovičová

Abstract

Plasma pre-treatment represents the key enabler technology for microfine cleaning, surface activation and plasma coating of almost all types of materials — from plastics, metals and glasses to textiles, composites and photographs. More and more conventional industrial treatment methods are being replaced by plasma technology in order to make processes more effective and environmentally friendly. This study is oriented on the characterization of a photographic image on two types of photographic paper (glossy and matt photographic paper with a barite layer), and monitoring the effects induced by the Atmospheric Discharge with Runaway Electrons (ADRE) plasma in air atmosphere on the photographic image layers. To evaluate their long-term stability before/after plasma treatment, degradation of black and white gelatin photographic components upon accelerated light aging using Q-SUN was investigated and the photoinduced changes were recorded by FTIR spectroscopy, densitometry and colorimetry. The results obtained demonstrated that the plasma discharge had no significant destructive effect on the photographic image as only negligible changes in the structure of the gelatin were detected due to plasma processing. Consequently, it can be concluded that low-temperature ADRE plasma in air atmosphere has the potential for successful applications in microbial decontamination and purification of damaged gelatin photographs.

Open access

Denisa Cagardová, Vladimír Lukeš, Ján Matúška and Peter Poliak

Abstract

A computational study using density functional theory is reported for selected model aza[n]circulenes (n = 6, 7, 8 and 9) and their derivatives consisting of pyrrole and benzene units. Local aromaticity of central rings was discussed and analyzed using theoretical structural indices. Depending on their molecular structures, energies of the highest occupied and lowest unoccupied molecular orbitals change from –5.23 eV to –4.08 eV and from –1.97 eV to –0.41 eV, respectively. Based on B3LYP calculated optimal geometries, electronic structure of molecules and their charge transport properties resulted in the suggestion of three planar molecules containing three or four pyrrole units as potential candidates for p-type semiconductors. Hole drift mobilities for ideal stacked dimers of these potential semiconductors were calculated and they range from 0.94 cm2·V−1·s−1 to 7.33 cm2·V−1·s−1.

Open access

Ján Kruželák, Andrea Kvasničáková, Rastislav Dosoudil and Ivan Hudec

Abstract

Two types of composites based on natural rubber (NR) and strontium ferrite were tested in this study. Composites of the first type were prepared by incorporation of strontium ferrite in the concentration range ranging from 0 to 100 phr (parts per hundred rubber) into pure NR based rubber matrix, while with those of the second type, strontium ferrite was dosed in the same concentration level into NR based rubber batch with constant amount of carbon black — 25 phr. For rubber matrices cross-linking, a standard sulfur based curing system was used. This work is focused on the effect of magnetic filler content on physico-mechanical, magnetic and thermo-physical properties of composite materials. Subsequently, the cross-link density and the structure of the formed sulfidic cross-links were examined. The results showed that the cross-link density of both types of composites increased with the increasing content of magnetic filler, while the structure of the sulfidic cross-links was almost not influenced by the amount of strontium ferrite. Tensile strength of rubber composites with pure rubber matrix was slightly improved by the incorporation of ferrite, while in case of composites based on a carbon black batch, the incorporation of magnetic filler resulted in the decrease of this characteristic. The presence of magnetic filler in both types of composites leads to a significant increase of the remanent magnetic induction.

Open access

Miroslava Mališová, Michal Horňáček, Pavol Hudec, Jozef Mikulec, Vladimír Jorík and Elena Hájeková

Abstract

The aim of the research was to prepare and characterize hydrotalcite synthesized under different preparation conditions. The most common hydrotalcite preparation is the co-precipiaton method. The preparation process strongly influences the catalytic properties of hydrotalcite; therefore, optimal conditions have to be determined. During the study, seven samples of the catalyst were prepared in the pH range from 8 to 12 and the synthesis temperature range from 25 to 55 °C. Based on several catalyst properties, optimal synthesis pH 10 was found. Ideal temperature of the preparation was determined to be 35 °C, but the temperature does not have a significant effect on the catalyst properties.

Open access

Barbora Šopová and Matilda Zemanová

Abstract

The aim of the study was to find parameters of electrolytic colouring on tin basis to form uniform black coatings on anodized aluminium. A two steps electrolytic process consisting of aluminium anodization in a sulphuric acid electrolyte and colouring in tin acidic electrolyte was used. Among parameters influencing the colouring process, AC colouring voltage, composition of the counter electrode and agitation of the colouring electrolyte were studied. Spectrocolorimetry was applied to analyse the quality of the colouring. Thickness of the coloured and sealed anodized specimens was also evaluated. Optimal parameters for uniform colouring of anodized specimens were found. Unfortunately, colouring electrolyte on tin basis is susceptible to oxidation which negatively influences the colouring.

Open access

Emília Kubiňáková, Ján Híveš, Vladimír Danielik, Andrea Červenková and Michaela Benköová

Abstract

Electrical conductivity of NaF-KF-AlF3 melts with different ratios of sodium fluoride and potassium fluoride was measured using a pyrolytic boron nitride tube-type cell with constant distance of electrodes. Molar cryolite ratios MR = (n(NaF) + n(KF))/n(AlF3) varied from 1.5 to 1.2 (with a step 0.1) in the temperature range of (675—900) °C. AC-techniques with a sine wave signal with small amplitude in the high frequency range were applied. Electrolyte resistance was obtained from nonlinear regression analysis according to equivalent circuit. Concentration and temperature dependency of electrical conductivity was described and defined. Experimental data were compared with literary sources and regression equations.

Open access

Simona Matejová, Miroslava Puchoňová, Dominika Hrindová, Vladimír Jorík, Milan Mazúr and Dušan Valigura

Abstract

Blue methylsalicylatocopper(II) complex with picolinamide Cu(3-Mesal)2(pnia)2 has been prepared and characterized by elemental analysis and spectral methods. Based on the infrared spectra, monodentate coordination of 3-methylsalicylate anion has been assumed and the coordination variability of the anion has been shown. By determination and refinement of the unit cell from powder diffraction data, the existence of a monomeric Cu(II) complex can be anticipated. EPR spectrum of the complex is in good agreement with these results. The g-factors fulfil the relation g || > g > 2.0023, which is consistent with the dx2 – y2 ground electronic state and indicates coordination sphere of distorted tetragonal symmetry {CuN2O2O2 ´} for the central copper(II) ions.

Open access

Veronika Hrabovská, Marcela Hricová and Anna Ujhelyiová

Abstract

At the present time, characterised by worsening environmental conditions, the protection of human organism against irreversible damage is necessary. Protective clothing on base of smart textiles represents the future in human clothing. In this article, the effect of photochromic pigments on spinnability, drawability and properties of pigmented polypropylene (PP) fibres is presented.

Mechanical properties (tenacity and elongation at break, Young’s modulus), thermo-mechanical properties and the factor of average orientation of fibres were evaluated and discussed. The obtained results indicate a possibility of fibres preparation with photochromic pigments.