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  • Author: Walerian Arabczyk x
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Walerian Arabczyk, Jacek Zamłynny and Dariusz Moszyński

Kinetics of nanocrystalline iron nitriding

Nitriding of nanocrystalline iron was studied under the atmosphere of pure ammonia and in the mixtures of ammonia - hydrogen - nitrogen at temperatures between 350°C and 500°C using thermogravimetry and x-ray diffraction. Three stages of nitriding were observed and have been ascribed to the following schematic reactions: (1) α-Fe → γ'-Fe4N, (2) γ'- Fe4N → ε - Fe3N and (3) ε - Fe3N → ε - Fe2N. The products of these reactions appeared in the nitrided nanocrystalline iron not sequentially but co-existed at certain reaction ranges. The dependence of a reaction rate for each nitriding stage on partial pressure of ammonia is linear. Moreover, a minimal ammonia partial pressure is required to initiate the nitriding at each stage.

Open access

Ewa Ekiert, Rafał Pelka, Krzysztof Lubkowski and Walerian Arabczyk

The possibility of implementation of spent iron catalyst for ammonia synthesis

An iron catalyst used in the ammonia synthesis is pyrophoric in its reactive, reduced form. Before further use the catalyst has to be passivated. Results of the research on the iron catalyst - its passivation, re-use as a catalyst in other processes and implementation as a substrate to obtain new nanocrystalline materials have been presented in the paper.

Open access

Urszula Narkiewicz, Anna Pietrasz, Iwona Pełech and Walerian Arabczyk

Removal of SO2 from gases on carbon materials

The aim of the work is to describe a capability of the active carbon CARBON L-2-4 (AC) and of the nanocarbon (NC) materials containing iron nanoparticles to continuously remove SO2 from air. The carbon nanomaterials (NC) containing iron nanoparticles were synthesised using a chemical vapor deposition method - through catalytic decomposition of ethylene on nanocrystalline iron.

The process of SO2 removal was carried out on dry and wet with water carbon catalyst (AC or NC) and was studied for inlet SO2 concentration 0.3 vol.% in the presence of O2, N2 and H2O, in the temperature range of 40-80°C.

Open access

Wojciech Konicki, Rafał Pelka and Walerian Arabczyk

Abstract

The removal of Ni2+ from aqueous solution by iron nanoparticles encapsulated by graphitic layers (Fe@G) was investigated. Nanoparticles Fe@G were prepared by chemical vapor deposition CVD process using methane as a carbon source and nanocrystalline iron. The properties of Fe@G were characterized by X-ray Diffraction method (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), Fourier Transform-Infrared Spectroscopy (FTIR), BET surface area and zeta potential measurements. The effects of initial Ni2+ concentration (1–20 mg L−1), pH (4–11) and temperature (20–60°C) on adsorption capacity were studied. The adsorption capacity at equilibrium increased from 2.96 to 8.78 mg g−1, with the increase in the initial concentration of Ni2+ from 1 to 20 mg L−1 at pH 7.0 and 20oC. The experimental results indicated that the maximum Ni2+ removal could be attained at a solution pH of 8.2 and the adsorption capacity obtained was 9.33 mg g−1. The experimental data fitted well with the Langmuir model with a monolayer adsorption capacity of 9.20 mg g−1. The adsorption kinetics was found to follow pseudo-second-order kinetic model. Thermodynamics parameters, ΔHO, ΔGO and ΔSO, were calculated, indicating that the adsorption of Ni2+ onto Fe@G was spontaneous and endothermic in nature.

Open access

Roman Jedrzejewski, Zofia Lendzion-Bieluń and Walerian Arabczyk

Abstract

The iron catalyst precursor promoted with Al2O3, CaO, and Li2O was obtained applying the fusing method. Lithium oxide forms two phases in this iron catalyst: a chemical compound with iron oxide (Li2Fe3O4) and a solid solution with magnetite. The catalyst promoted with lithium oxide was not fully reduced at 773 K, while the catalyst containing potassium was easily reducible at the same conditions. After reduction at 873 K the activity of the catalyst promoted with lithium oxide was 41% higher per surface than the activity of the catalyst promoted with potassium oxide. The concentration of free active sites on the surface of the catalyst containing lithium oxide after full reduction was greater than the concentration of free active sites on the surface of the catalyst promoted with potassium oxide.

Open access

Janusz Typek, Grzegorz Zolnierkiewicz, Rafal Pelka, Karolina Kielbasa, Walerian Arabczyk and Nikos Guskos

Abstract

Nanocrystalline iron was obtained by fusing magnetite and promoters. The oxidized form was reduced with hydrogen and passivated (sample P0). The average nanocrystallite size in sample P0 was d(P0) =16 nm and the width of size distribution was σ(P0) = 18 nm. Samples of nanocrystalline iron with narrower diameter ranges and larger and smaller average crystallite sizes were also synthesized. They were: sample P1 (d(P1) = 28 nm, σ(P1) = 5 nm), sample P2 (d(P2) = 22 nm, σ(P1) = 5 nm), sample P3 (d(P3) = 12 nm, σ(P1) = 9 nm). These four samples were studied at room temperature by dc magnetization measurements and ferromagnetic resonance at microwave frequency. Correlations between samples sizes distributions (average size and width of the sizes) and magnetic parameters (effective magnetization, anisotropy field, anisotropy constant, FMR linewidth) were investigated. It was found that the anisotropy field and effective magnetization determined from FMR spectra scale linearly with nanoparticle sizes, while the effective magnetic anisotropy constant determined from the hysteresis loops decreases with nanoparticle size increase.

Open access

Janusz Typek, Nikos Guskos, Grzegorz Zolnierkiewicz, Aleksander Guskos, Kielbasa Karolina, Rafal Pelka and Walerian Arabczyk

Abstract

Samples obtained by nitriding of promoted nanocrystalline iron and the nitrides reduction at various nitriding potential in terms of thermodynamic parameters were investigated by electron paramagnetic resonance/ferromagnetic resonance (EPR/FMR) method at room temperature. Experimental FMR spectra were fitted by the Dysonian-type resonance lines arising from the presence of different Fe–N phases. The obtained FMR parameters allowed us to identify the component phases and to determine their magnetic properties. In general, the proposed simple method of decomposition of the FMR spectra produced results on the phase content in investigated samples that were consistent with XRD measurements and additionally, magnetic characteristics of the studied nanomagnets.

Open access

Walerian Arabczyk, Urszula Narkiewicz, Zofia Lendzion-Bieluń, Dariusz Moszyński, Iwona Pełech, Ewa Ekiert, Marcin Podsiadły, Rafał Pelka, Roman Jędrzejewski, Izabela Moszyńska and Daniel Sibera

Utilization of spent iron catalyst for ammonia synthesis

Several methods of the utilization of spent iron catalyst for ammonia synthesis have been presented. The formation of iron nitrides of different stoichiometry by direct nitriding in ammonia in the range of temperatures between 350°C and 450°C has been shown. The preparation methods of carbon nanotubes and nanofibers where iron catalyst catalyse the decomposition of hydrocarbons have been described. The formation of magnetite embedded in a carbon material by direct oxidation of carburized iron catalyst has been also presented.