Magnetic relaxation -- coal swelling, extraction, pore size. Quarterly technical progress report, October 1, 1993--December 31, 1993

Abstract

During this quarter, the CW (continuous wave) and pulsed EPR (electron paramagnetic resonance) have been examined of the swelled Argonne Premium whole coals and the swelled residues of these coals. The CW EPR spectra will not be of high quality due to the unexpectedly microwave-lossy character of the pyridine used for swelling. Being relatively unaffected by this characteristic, the pulsed EPR measurements of the spin relaxation times of the broad (non-inertinite) and narrow (inertinite) macerals have been completed. Although detailed analyses of these results have not yet been done, marked differences have been found between the relaxation times of the swelled and unswelled coals and residues. The most startling are the less than 200 nsec times T{sub 1} of the spin-lattice relaxation of the inertinite radicals in the swelled samples. The T{sub 1} of this maceral in the unswelled coal were approaching 1 millisecond. The T{sub 1} contrast was much less pronounced between the swelled and non-swelled non-inertinite macerals. The prospects of significant progress in coal pore size measurements with xenon and NMR (nuclear magnetic resonance) have dimmed since the beginning of this project. This assessment is based on the dearth of these types of studies, a paper at amore » contractors` meeting on this subject that did not materialize, and discussions with colleagues with experience with the technique in coals. Instead, the authors have been developing a pulsed EPR technique for the spin probing of molecular motion to be applied to pores in carbonaceous materials. This report contains a copy of a nearly final draft of a paper being prepared on the development of this technique, entitled {open_quotes}Physical Characterization of the State of Motion of the Phenalenyl Spin Probe in Cation-Exchanged Faujasite Zeolite Supercages with Pulsed EPR.{close_quotes}« less