Microwave saturation of EPR spectra of oxidised coal

• Authors: Barbara Pilawa , Andrzej Więckowski , Robert Pietrzak , Helena Wachowska
• Languages of publication: EN

Abstracts

EN

Microwave saturation of multi-component EPR spectra of oxidized lignite Mequinenza (Spain) with a carbon content of 65.1 wt % and with a high sulphur content of 10.3 wt % was studied. The coal was oxidized with nitric acid (NHO3), peroxyacetic acid (PAA), and in O2/Na2CO3 system. Three different groups of paramagnetic centres exist in the coal samples analyzed. The EPR spectrum of the demineralised coal was a superposition of broad Gauss (ΔB pp = 0.75 mT), broad Lorentz 1 (ΔB pp = 0.42 mT) and narrow Lorentz 3 lines (ΔB pp = 0.08 mT). The three EPR components with linewidths: 0.58–0.77 mT (Gauss line), 0.30–0.39 mT (Lorentz 1 line) and 0.05–0.06 mT (Lorentz 3 line) were recorded for the oxidized coal. The g-values were obtained for the samples studied in the ranges 2.0043–2.0046 (Gauss lines), 2.0035–2.0038 (Lorentz 1 lines) and 2.0032–2.0034 (Lorentz 3 lines). The broad Gauss and Lorentz 1 lines saturate at low microwave powers. The narrow Lorentz 3 lines of demineralised coal were not saturated at microwave power from the range considered. After the coal oxidation with HNO3, PAA and in O2/Na2CO3 system, the microwave saturation of the narrow Lorentz 3 lines was also observed, which indicated a degradation of the multi-ring aromatic structures upon oxidation. [...]

Keywords

EN

Paramagnetic centres; coal; oxidation; EPR

• Publisher: De Gruyter Open
• Journal: Open Chemistry
• Year: 2007
• Volume: 5
• Issue: 1
• Pages: 330-340

Dates

published

1 - 3 - 2007

online

1 - 3 - 2007

Contributors

author

Barbara Pilawa

• Institute of Coal Chemistry, Polish Academy of Sciences, 44-121, Gliwice, Poland

author

Andrzej Więckowski

• Division of Magnetic Resonance Spectroscopy, Institute of Physics, Faculty of Physics & Astronomy, University of Zielona Góra, 65-516, Zielona Góra, Poland

author

Robert Pietrzak

• Laboratory of Coal Chemistry and Technology, Faculty of Chemistry, Adam Mickiewicz University, 60-780, Poznań, Poland

author

Helena Wachowska

• Laboratory of Coal Chemistry and Technology, Faculty of Chemistry, Adam Mickiewicz University, 60-780, Poznań, Poland

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Identifiers

DOI

10.2478/s11532-006-0056-7