Mesophase formation investigation in pitches by NMR relaxometry

Lima, Alexandre A. B.; Pinto, Ângelo C.; Gil, Rosane A. S. San; Tavares, Maria Inês B.

doi:10.1590/s0103-50532007000200002

Cited by 3 publications

(3 citation statements)

References 8 publications

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“…The relaxometry measures by 1 H NMR were performed in a Maran Ultra 23 NMR analyzer operating at 23.4 MHz (for protons) and equipped with a variable temperature probe of 18 mm as described by Lima et al 42 The longitudinal relaxation time (T 1 H) was measured with the pulse sequence of inversion-recovery (D 1 -p-t-p/2 -acquisition), using a recycle time value greater than 5T 1 (e.g. D 1 of 10 s) and pulse of p/2 of 4.5 µs, automatically calibrated by the software of the equipment.…”

Section: Nmrmentioning

confidence: 99%

Mesophase evolution in heat-treated solid petroleum pitches

Lima¹,

Lima²,

França³

et al. 2012

J. Braz. Chem. Soc.

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Uma combinação de técnicas analíticas foi utilizada para acompanhar a evolução da mesofase em pixes de petróleo em fase sólida. As amostras foram caracterizadas por dessorção a laser assistida por matriz, seguida de espectrometria de massas por tempo de vôo (MALDI-TOF-MS), ressonância magnética nuclear de 13 C ( 13 C NMR) de alto campo, 1 H NMR de baixo campo, ressonância eletrônica de spin (EPR), microscopia ótica polarizada e análise termogravimétrica (TGA). A análise por MALDI-TOF-MS revelou uma distribuição oligomérica de pesos moleculares no pixe: monomérica (m/z 200 a 400), dimérica (m/z 400 a 650), trimérica (m/z 650 a 950) e tetramérica (m/z 950 a 1600), fator essential para a produção de fibras de carbono, bem como outros compósitos de carbono. Estudos de tempo de relaxação (T 1 ) permitiram a observação de duas grandes áreas: a dos aromáticos e a de mesofase. Estes resultados também mostraram que o tempo de aquecimento aumenta a área de mesofase. Através de medidas não destrutivas de 13 C NMR, foram obtidos os conteúdos de carbonos aromáticos e alifáticos, e também o grau de protonação desses carbonos. A microscopia ótica com luz polarizada mostrou as interfaces entre as regiões anisotrópicas e isotrópicas, bem como o processo de coalescência da mesofase. Os resultados obtidos pelas outras técnicas corroboram com os resultados de MALDI-TOF-MS e NMR.A combination of analytical techniques was used to follow the mesophase evolution of petroleum pitches in the solid phase. The samples were characterized by matrix assisted laser desorption and time of flight analysis by mass spectrometry (MALDI-TOF-MS), high field 13 C nuclear magnetic resonance ( 13 C NMR), low field 1 H NMR, electron spin resonance (EPR), polarized optical microscopy and thermogravimetric analysis (TGA). MALDI-TOF-MS revealed an oligomeric distribution of molecular weights in the pitch: monomeric (m/z 200 to 400), dimeric (m/z 400 to 650), trimeric (m/z 650 to 950) and tetrameric (m/z 950 to 1600), an essential factor for the production of carbon fibers, among other advanced composite of carbon. Relaxation time (T 1 ) studies permitted to observe two large areas: the aromatics and the mesophases. These results also showed that the heating time increases the mesophasic area. Also through direct and non-destructive 13 C NMR measurements, we obtained the content of aromatic and aliphatic carbons, as well as the degree of protonation of these carbons. Optical microscopy with polarized light showed the interfaces between the anisotropic and isotropic regions as well as the process of coalescence of mesophase. The results obtained by the other techniques corroborate the MALDI-TOF-MS and NMR results.

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Section: Nmrmentioning

confidence: 99%

Mesophase evolution in heat-treated solid petroleum pitches

Lima¹,

Lima²,

França³

et al. 2012

J. Braz. Chem. Soc.

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“…Several conventional techniques are normally used to characterize the filler dispersion, such as: electronic microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analyses (DSC and TG). More recently solid-state nuclear magnetic resonance has been employed, with success, to better understand the nanostructure formed in the polymeric nanocomposite [7][8][9][10][11][12]. The success comes to the fact that solid-state NMR spectroscopy allows obtaining information on chemical molecular structure; components interaction and filler homogeneity dispersion at molecular level [7][8][9][10][11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

The Evaluation of Polyethylene/Clay Composite from Solid State NMR

Nogueira¹,

Tavares²,

Gil³

et al. 2011

MSA

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“…There is not yet an analytical procedure that can accurately quantify the mesophase in a pitch, i.e. the anisotropic fraction, although there are promising results in NMR [5,6]. The relative amount between the isotropic and anisotropic phases can be determined with some approximation by extraction with hot quinoline or N-methyl-pyrrolidinone (NMP).…”

Section: Introductionmentioning

confidence: 99%

Low Field Nuclear Magnetic Resonance of Structural Alterations in Coal Tar Pitch Subjected to Heat Treatment

Freitas¹,

Tavares²,

Michel³

2011

ChChT

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Development of anisotropy in tar pitches under heat treatment was measured by hot centrifugation and by low field NMR technique through the spin-lattice relaxation time of the hydrogen nucleus (T 1 H). By using a double exponential model for T 1 H calculations it was possible to quantify the size of the isotropic and anisotropic domains, suggesting that low field NMR is a suitable technique to address anisotropy in pitches.

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Mesophase formation investigation in pitches by NMR relaxometry

Cited by 3 publications

References 8 publications

Mesophase evolution in heat-treated solid petroleum pitches

Mesophase evolution in heat-treated solid petroleum pitches

The Evaluation of Polyethylene/Clay Composite from Solid State NMR

Low Field Nuclear Magnetic Resonance of Structural Alterations in Coal Tar Pitch Subjected to Heat Treatment

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