Effects of Ferromagnetic Inclusions on 13C MAS NMR Spectra of Heat-Treated Peat Samples
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- 作者：Jair C. C. Freitas ; Edson C. Passamani ; Marcos T. D. Orlando ; Francisco G. Emmerich ; Flá ; vio Garcia ; Luiz C. Sampaio ; and Tito J. Bonagamba
- 刊名：Energy & Fuels
- 出版年：2002
- 出版时间：September 2002
- 年：2002
- 卷：16
- 期：5
- 页码：1068 - 1075
- 全文大小：166K
- 年卷期：v.16,no.5(September 2002)
- ISSN：1520-5029
文摘
Peat char samples produced by heat treatments under inert atmosphere were characterizedthrough 13C solid-state NMR, Mössbauer spectroscopy, and magnetization measurements. Forsamples prepared above 700 
C a set of strong spinning sidebands (SSB) were detected in NMRspectra acquired with direct polarization (DP) and magic-angle spinning (MAS), an effect thatwas shown to be consequence of the presence of ferromagnetic impurities associated with themineral content of the studied peat samples. A detailed investigation on the nature and thermaltransformations of the magnetic particles present in the natural and heat-treated peat sampleswas carried out by using magnetization measurements and Mössbauer spectroscopy. A pronouncedincrease in the ferromagnetic character of the heat-treated samples was verified from 600 Cupward, with the development of Fe3+ compounds, Fe3C, and Fe clusters. The effect of theseferromagnetic inclusions was the creation of magnetic field inhomogeneities throughout thesample, which lead to the production of an anisotropic broadening of the NMR lines. A simplifiedmodel is presented to explain the influence of these particles on the 13C DP-MAS NMR spectraof the heat-treated peat samples, showing their capability to generate SSB much stronger thanthe ordinary SSB due to chemical shift anisotropy in pure carbon materials.
C a set of strong spinning sidebands (SSB) were detected in NMRspectra acquired with direct polarization (DP) and magic-angle spinning (MAS), an effect thatwas shown to be consequence of the presence of ferromagnetic impurities associated with themineral content of the studied peat samples. A detailed investigation on the nature and thermaltransformations of the magnetic particles present in the natural and heat-treated peat sampleswas carried out by using magnetization measurements and Mössbauer spectroscopy. A pronouncedincrease in the ferromagnetic character of the heat-treated samples was verified from 600 Cupward, with the development of Fe3+ compounds, Fe3C, and Fe clusters. The effect of theseferromagnetic inclusions was the creation of magnetic field inhomogeneities throughout thesample, which lead to the production of an anisotropic broadening of the NMR lines. A simplifiedmodel is presented to explain the influence of these particles on the 13C DP-MAS NMR spectraof the heat-treated peat samples, showing their capability to generate SSB much stronger thanthe ordinary SSB due to chemical shift anisotropy in pure carbon materials.