Nuclear magnetic proton relaxation studies of oxidized coals

✍ Scribed by Tetsuro Yokono; Kunio Miyazawa; Yuzo Sanada; Harry Marsh

• Publisher: Elsevier Science
• Year: 1981
• Tongue: English
• Weight: 651 KB
• Volume: 60
• Category: Article
• ISSN: 0016-2361
• DOI: 10.1016/0016-2361(81)90159-9

✦ Synopsis

Coals of NCB rank 301 a (coking), 502 (caking) and 802 (very weakly caking) are oxidized in air at 373 K or 383 K for up to 42 days. Spin-lattice and spin-spin relaxation times, 7, and T2 respectively, of oxidized coals are measured using a Bruker SXP 4-l 00 and FT spectrometer. Free radical concentrations in the coals are obtained using a JES PE e.s.r. spectrometer. Infrared spectra of oxidized coals are obtained and optical textures of cokes from fresh and oxidized coals are assessed by optical microscopy. For two coking coals, decreasing values of 7, and increasing concentration of free radicals occurred with oxidation at 383 K to 16 and 28 days. Thereupon values of 7, increased and free radical concentrations decreased with further progressive oxidation. At the point of inflexion in properties, resultant cokes from the coals ceased to shown any anisotropy in their optical textures and became isotropic resembling cokes from low-rank coals. For the caking coals, 7, increased at all stages of oxidation to 42 days with decreasing concentrations of free radicals. Two values of T2 were found in each coal corresponding to a rigid and mobile component ((f,),< ( 72)m). The rigid component (Tz),was not affected by oxidation but values of ( T2)m decreased with increasing duration of oxidation. It is considered that coking and caking coals exhibit different effects of oxidation with perhaps phenols andquinones in caking coals acting as inhibitors to the growth of stable free radicals. Oxidized coking coal may behave like fresh caking coal.