EPR characteristics of separated fractions of mesophase pitches
Carbonaceous pitches are complex mixtures of aromatic hydrocarbons with wide distributions of molecular weight and structure. The solid materials are isotropic or nematic glasses which contain neutral odd-alternate doublet free radicals with radical concentrations of 10/sup 18/-10/sup 19/ spins/g. The spin-spin and spin-lattice relaxation properties span the range between inhomogeneous and homogeneous behavior. Studies are presented of the EPR CW saturation and spin-echo of several molecular weight fractions of pitches derived from naphthalene, petroleum, and coal tar. The EPR saturation and line shapes and the spin-echo T/sub 1/ ((1-6) x 10/sup -4/ s) and T/sub 2/ ((2-7) x 10/sup -6/ s) values are compared with one another. The CW and pulsed EPR indicate the detailed nature of the spin relaxation and of the transition from heterogeneous to homogeneous behavior as the samples increase in molecular weight and aromatic character. Comparison of the pulsed and CW EPR saturation parameters indicates that, whereas the EPR results give the average parameters over a wide distribution of molecular species, the pulsed EPR selects out the species with particular spin-spin relaxation times within the time response of the instrument.
- Research Organization:
- Union Carbide Corp., Cleveland, OH
- OSTI ID:
- 6559282
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 91:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
01 COAL, LIGNITE, AND PEAT
PITCHES
ELECTRON SPIN RESONANCE
SEPARATION PROCESSES
COAL TAR
EXPERIMENTAL DATA
NAPHTHALENE
PETROLEUM RESIDUES
SPIN-LATTICE RELAXATION
SPIN-SPIN RELAXATION
AROMATICS
CONDENSED AROMATICS
DATA
ENERGY SOURCES
FOSSIL FUELS
FUELS
HYDROCARBONS
INFORMATION
MAGNETIC RESONANCE
NUMERICAL DATA
ORGANIC COMPOUNDS
OTHER ORGANIC COMPOUNDS
PETROLEUM
PETROLEUM FRACTIONS
RELAXATION
RESONANCE
TAR
400201* - Chemical & Physicochemical Properties
020800 - Petroleum- Waste Management
010800 - Coal
Lignite
& Peat- Waste Management