Recent advances in coal characterization by 13C and 1H n.m.r.

Solid-state nuclear magnetic resonance (NMR) spectroscopic analysis were carried out on recent and archaeological wood. Cross-polarization-magic-angle spinning ~3C NMR spectra obtained from samples of poplar (Populus sp.), oak (Quercus sp.), and silver fir (Abies alba) were examined in this study. The most relevan t peaks were assigned according to the extensive literature in the area, and the differences observed discussed in terms of lignin and cellulose composition: by fixing a lignin reference signal intensity, the eellulose and hemicellulose moieties showed a strong depletion compared to the lignin signals in archaeological wood.

show abstract

“…Therefore, only a qualitative analysis was performed on the basis of the extensive literature in this field [15][16][17][18]. Fig.…”

Section: Resultsmentioning

confidence: 99%

13C CPMAS NMR spectroscopic analysis applied to wood characterization

et al. 2005

View full text Add to dashboard Cite

show abstract

“…The peak in the aliphatic region at about 2 ppm is broadened. In the C sp 2 region, the signal due to carbodiimide groups is still present, and a broad signal appears around 160 ppm, which is assigned to a free-carbon phase formed during the decomposition of the organic groups . To identify the 2 ppm signal, IRCP experiments with variable inversion times were performed (Figure ).…”

Section: Resultsmentioning

confidence: 99%

Thermal Decomposition of Poly(methylsilsesquicarbodiimide) to Amorphous Si−C−N Ceramics

Gabriel¹,

Riedel²,

Dreßler³

et al. 1999

Chem. Mater.

View full text Add to dashboard Cite

This paper is based on the recent discovery that the thermal decomposition of poly(methylsilsesquicarbodiimide), [CH3Si(NCN)1.5] n , leads to amorphous silicon carbonitride (SiCN) ceramics. In the present study the polymer-to-ceramic transformation is characterized using analytical and spectroscopic methods. In particular, the structural transition from the molecular precursor to the final amorphous SiCN ceramic was studied by solid-state NMR spectroscopy. The coordination of the silicon atoms changes from CH3−Si(−NCN−)3 in the polysilylcarbodiimide precursor at room temperature to Si(−N<)4 in the X-ray amorphous reaction product formed at 1200 °C. This result implies the formation of amorphous silicon nitride (Si3N4). The remaining weight fraction is analyzed to be elemental carbon. According to bulk chemical analysis, the poly(methylsilsesquicarbodiimide)-derived SiCN is comprised of a mixture of 1 mol amorphous Si3N4 with 3 mol amorphous carbon. The molar ratio Si3N4/C = 1/3 is suitable for the formation of stoichiometric silicon carbide, which is expected thermodynamically at temperatures exceeding 1440 °C in 0.1 MPa N2. The pyrolysis behavior of the poly(silylcarbodiimide) and the formation of silicon carbonitride ceramics are compared to those of poly(silazanes).

show abstract

“…To obtain information on the distribution of carbon functionalities, we have measured solid state 13 C NMR with the CP/MAS method in recent studies. Several authors, however, have pointed out that from CP/MAS 13 C NMR quantitative information is difficult to obtain and SPE (single pulse excitation) is better. − Therefore, we decided to use the SPE/MAS method. First, we have examined the effect of a pulse delay (PD, the waiting time for the next acquisition) on carbon aromaticity ( f a ) with 512 scans.…”

Section: Resultsmentioning

confidence: 99%

Structural Evaluation of Zao Zhuang Coal

et al. 1998

View full text Add to dashboard Cite

The structure of Chinese bituminous Zao Zhuang coal was carefully evaluated on the basis of information from NMR, pyrolysis, ruthenium-catalyzed oxidation reaction (RICO), and single coal particle solvent swelling methods. This coal and its SRC liquefaction fractions show good coking property so that the pyrolysis is accompanied by a lot of coke, this being less useful for its structural elucidation than the case of Japanese Akabira coal. The pretreatment of this coal by the ether bond cleavage reaction can increase volatile-comprising molecules that when recognized provide valuable information on molecular constituents of the coal. SPE/MAS 13 C NMR and CP-DD (dipolar dephasing)/MAS 13 C NMR techniques were used to assess carbon distribution. The RICO reaction offered information regarding aliphatic functionalities and bridge types and also suggested the presence of some types of molecular units. Solvent swelling experiments implied that this coal has, on average, relatively low cross-link density and verified the structural heterogeneity of the coal. By using the data from the analytical techniques given above, a model structure of Zao Zhuang coal consisting of one MS, one PS, and two PI structures was constructed. The proposed structure is in keeping with various aspects of its reactivity.

show abstract

Recent advances in coal characterization by 13C and 1H n.m.r.

Cited by 22 publications

References 27 publications

13C CPMAS NMR spectroscopic analysis applied to wood characterization

13C CPMAS NMR spectroscopic analysis applied to wood characterization

Thermal Decomposition of Poly(methylsilsesquicarbodiimide) to Amorphous Si−C−N Ceramics

Structural Evaluation of Zao Zhuang Coal

Contact Info

Product

Resources

About