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Vladimír Danielik and Dominika Szendreiová

Abstract

Temperature dependency of densities of the liquid system magnesium nitrate hexahydrate - zinc nitrate hexahydrate was measured. Densities of liquid mixtures were experimentally measured at different temperatures by a method using submersible corpuscle. Based on the obtained data, temperature dependence on the density was obtained. A model describing the density in the whole concentration range very well was created.

Open access

Vladimír Danielik, Peter Šoška and Katarína Felgerová

Abstract

The paper presents the results of a study on the corrosion behaviour of copper (EN CW004A) in five possible phase change materials (PCMs): magnesium nitrate hexahydrate pure and with an addition of Mg(OH)2 (0.5 wt. %) or Sr(OH)2 (0.5 wt. %) at 90 °C, calcium nitrate tetrahydrate at 50 °C and a mixture of magnesium nitrate hexahydrate and calcium nitrate tetrahydrate (1:1 mass ratio) at 72 °C. The corrosion rate of copper samples is low except for the use of Mg(NO3)2 · 6H2O with/without an addition of Mg(OH)2. The lowest corrosion rate was observed for the mixture Mg(NO3)2 · 6H2O—Ca(NO3)2 · 4H2O (1:1), and it was ca six times lower than that of pure magnesium nitrate hexahydrate.

Open access

Vladimír Danielik, Pavel Fellner, Marián Bobok and Jomar Thonstad

Abstract

Intercalation of sodium into the carbon lining of aluminium electrolysis cells is a common cause of its failure. The effect of sodium on model carbon cathode materials was studied in the system with high activity of sodium (molten NaF–NaCl system). Commercially available carbon materials such as semigraphite and electrographite (Kompozitum, Topol’čany, SK) were chosen as model cathodes. The experiments were carried out at a constant cathode current density of 0.7 A cm−2. A modified Rapoport test was developed and used to study the expansion of the chosen types of carbon materials.

Open access

Vladimír Danielik, Pavel Fellner, Jana Jurišová and Milan Králik

Abstract

Reactivity of energy gypsum was investigated. The method is based on the conversion reaction of aqueous suspension of gypsum with ammonium carbonate solution. Rate of the conversion of all investigated samples, including gypsum originating from flue gas desulphurization (FGD), was high and 80 % conversion was achieved during one hour. It was found that there is a correlation between BET specific surface and the rate of the conversion reaction.

Open access

Marta Ambrová and Vladimír Danielik

Abstract

Corrosion resistance of tungsten and nickel in molten eutectic mixture LiF-NaF-KF was investigated by measurement of polarization resistance and chronopotentiometry. Results obtained by both methods were compared by digital simulation of diffusion of corrosion products. All measurements were carried out at the temperature of 680 °C in inert argon atmosphere and in oxidation air atmosphere. Surface of the metal samples after measurements was investigated by scanning electron microscope and X-ray microanalysis that was, together with X-ray diffraction analysis, used for the identification of corrosion products.

Open access

Kristína Oravcová and Vladimír Danielik

Abstract

Materials used for heat accumulation are substances with the phase change at temperatures below 80 °C. In such substances, a high amount of energy can be stored due the phase change. Because of possible corrosion of the heat container components, it is necessary to know their resistance in the given medium. In this work, the corrosion of aluminum, copper and carbon steel was studied in two liquid media: zinc nitrate hexahydrate and calcium chloride hexahydrate. Corrosion tests have shown that steel is the least resistant to corrosion in both media. Aluminum has been proved as the most durable material in zinc nitrate hexahydrate media. On the other hand, pitting corrosion on aluminum occurred in the calcium chloride hexahydrate making it unsuitable for the use in this media. From the comparison of two studied PCMs follows that zinc nitrate hexahydrate is a more aggressive medium in comparison with calcium chloride hexahydrate. From the point of view of corrosion, zinc nitrate hexahydrate is not suitable for heat accumulation when using the studied metals. When using the calcium chloride hexahydrate as PCM, copper is suitable as a construction material; aluminum and carbon steel show pitting corrosion.

Open access

Emília Kubiňáková, Ján Híveš and Vladimír Danielik

Abstract

Electrical conductivity of NaF-AlF3 melts with an addition of 2 wt % Al2O3 and/or 5 wt % CaF2 was measured using a pyrolytic boron nitride tube-type cell with a constant distance of electrodes. The molar cryolite ratios MR = n(NaF)/n(AlF3) were 1.8 and 1.6, and the temperature was varied from 865 °C to 1005 °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. Experimental data were used to describe the dependence of the electrical conductivity in fluoride melts with lower temperature on the amount of various additions and temperature.

Open access

Marta Ambrová and Vladimír Danielik

Abstract

Corrosion resistance of tungsten and nickel in molten eutectic LiF-NaF was investigated by measurement of polarization resistance and chronopotentiometry. Results obtained by both methods were compared by digital simulation of diffusion of corrosion products. All measurements were carried out at the temperature of 680 °C in two types of atmospheres; in inert argon and oxidation air atmosphere. It was found that presence of air (oxygen) significantly decreases corrosion resistance of used metals. From tested materials, tungsten was more corrosion resistant material than nickel in both types of atmospheres. Obtained results were also compared with those measured in the molten eutectic LiF-NaF-KF earlier.

Open access

Jana Jurišová, Pavel Fellner, Vladimír Danielik, Marek Lencsés, Milan Králik and Rastislav Šípoš

Abstract

Preparation of potassium nitrate from magnesium nitrate and potassium chloride was investigated. Prepared potassium nitrate contains less than 0.5 % chlorides and it can be applied as environmentally friendly fertilizer in hydroponic systems. After filtration out potassium nitrate crystals from the reciprocal system K+, Mg2+//Cl-, NO3 - - H2O, the mother liquor still contains reasonable amount of potassium cations. By evaporation of the mother liquor, carnallite (MgCl2・KCl・6H2O) with admixture of MgCl2・6H2O crystallizes out. Decomposition of carnallite with cold water makes it possible to separate potassium chloride from this compound. When this KCl is returned back to the process of KNO3 making, utilization of potassium as high as 97 % can be achieved.

Open access

Jana Jurišová, Vladimír Danielik, Pavel Fellner, Marek Lencsés and Milan Králik

Abstract

Potassium nitrate as a fertilizer suitable for greenhouse and hydroponic applications can be prepared by the reaction of potassium sulphate with calcium nitrate. However, it may happen that simultaneously with the precipitation of gypsum (CaSO4·2H2O) also two other binary salts, viz. syngenite (K2SO4·CaSO4·H2O) and görgeyite (K2SO4·5CaSO4·H2O) can crystallize. This would lower the yield of KNO3. For minimization of potassium loss we have to determine the conditions under which syngenite and görgeyite crystallize. As a useful tool for the quantitative determination of specific hydrates, simultaneous DTA/TG technique appeared. Each hydrate decomposes at a certain temperature. The loss of water at dehydration can be used for a quantitative determination of the amount of the hydrate in the precipitating solid phase. Based on the experimental data several conclusions can be drawn: (i) excess of calcium cations lowers the concentration of sulphate ions in the liquid phase together with lowering of contents of syngenite and görgeyite in the solid phase; (ii) higher content of water results in a higher solubility of sulphate ions; (iii) joint crystallization of syngenite and gypsum occurs in the composition area interesting from the point of KNO3 production; (iv) area of the primary crystallization of görgeyite does not exist in the phase diagram at 80 °C. However, görgeyite crystallizes at the molar ratio Ca(NO3)2:K2SO4 = 1:1 by ternary crystallization; (v) area of crystallization of pure gypsum is shifted to lower ratio Ca(NO3)2:K2SO4 by the addition of water to the system.