Paramagnetic centres in exinite, vitrinite and inertinite

Wiȩckowski, Andrzej; Pilawa, Barbara; Lewandowski, Marek; Wojtowicz, W.; Słowik, Grzegorz

doi:10.1007/bf03162031

Cited by 11 publications

(14 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The performed in this work numerical analysis of multi-component structure of EPR spectra of lignite confirmed our earlier results [13][14][15] about complex shape and strong dependence of paramagnetic centres system on metamorphism of coal.…”

Section: Discussionsupporting

confidence: 89%

“…The fast spin-lattice relaxation processes are characteristic of the multi-ring aromatic structures (narrow Lorentz 3 lines), and relatively slow spin-lattice relaxation processes occur in simple aromatic coal structures (broad Gauss and broad Lorentz 1 lines). The correlations between the coal structures and the spin-lattice relaxation times were confirmed by EPR and FTIR studies earlier [5,6,[13][14][15][16][17]. The influence of microwave power on the three component lines of the EPR spectra of the studied demineralised lignite is shown in Figure 3.…”

Section: Resultssupporting

confidence: 59%

“…The paramagnetic centres of multiring aromatic structures corresponding to the Lorentz 2 lines, which were found in the earlier studied medium-rank coal (85.6 wt% C) [14], did not exist in the coal analysed in this work. The paramagnetic centres located at simple aromatic units of coal are responsible for broad lines [5,6,[13][14][15][16][17]. The paramagnetic centres of multi-ring aromatic units of coal, mainly delocalised π electrons, are responsible for narrow lines [5,6,[13][14][15][16][17].…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Microwave saturation of EPR spectra of oxidised coal

et al. 2007

View full text Add to dashboard Cite

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 (HNO 3 ), peroxyacetic acid (PAA), and in O 2 /Na 2 CO 3 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 HNO 3 , PAA and in O 2 /Na 2 CO 3 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.

show abstract

Section: Discussionsupporting

confidence: 89%

Section: Resultssupporting

confidence: 59%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Microwave saturation of EPR spectra of oxidised coal

et al. 2007

View full text Add to dashboard Cite

show abstract

“…Total intensity of EPR line taking into account the existence of paramagnetic centers in singlet and triplet states is presented in the form [12]: (3) where B and C [K] are constants equal to and aN d /2k, respectively [12]. Accordingly, relative contributions of paramagnetic centers in singlet (S = 0) and triplet (S = 1) states to whole amount of centers in doublet, singlet, and triplet states are given in the form [12]: (4) As mentioned earlier, it was shown [6][7][8][9] that in the total group of paramagnetic centers generating components lines in the form of Lorentzian L1 shape in EPR spectra of coal macerals, exinite, and vitrinite, there is a part of centers in excited triplet state (S = 1). Accordingly, these centers do not fulfi l the Curie law represented by the formula I = C/T.…”

Section: Introductionmentioning

confidence: 97%

“…in temperature T 1 [K] by I 1 = I NC (T 1 ) + C/T 1 (C -Curie constant [K]) and in temperature T 2 by I 2 = I NC (T 2 ) + C/T 2 , respectively, where I NC (T) is a part of total intensity I generated by paramagnetic centers, which do not fulfi l the Curie law, while the paramagnetic centers obeying the Curie law are responsible for the component C/T. The existence of paramagnetic centers in the ground doublet state S = ½, for which the temperature dependence of intensity is described by the Curie law (I = C/T) (and paramagnetic centers in excited triplet states (S = 1) was evidenced in coal and coal macerals [4][5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Determination of the fraction of paramagnetic centers not-fulfilling the Curie law in coal macerals by the two-temperature EPR measurement method

Słowik

Wiȩckowski

2015

Nukleonika

View full text Add to dashboard Cite

Abstract. Two-temperature electron paramagnetic resonance (EPR) measurements, applied to determine the relative contributions of paramagnetic centers -fulfi lling and not-fulfi lling the Curie law, were carried out. The measurements were made on the macerals -exinite and vitrinite, separated from clarain of the Polish medium--rank coal (85.6 wt% C). The two-temperature EPR measurements, presented in this work, were performed respectively, at temperatures: T 1 = 293 K and T 2 = 173 K for exinite, and T 1 = 293 K and T 2 = 153 K for vitrinite. The relative contributions X of spins not-fulfi lling the Curie law present in the studied macerals were calculated. A comparison of different methods of calculating the relative contributions of paramagnetic centers -fulfi lling and not-fulfi lling the Curie law, present in exinite and vitrinite studied by EPR was made.

show abstract