Changes in free radicals in coal-derived pyrites upon heating in N2, H2, and vacuum: Role of pyrite—pyrrhotite conversion
✍ Scribed by Gopalan Srinivasan; Mohindar S. Seehra
- Publisher
- Elsevier Science
- Year
- 1982
- Tongue
- English
- Weight
- 676 KB
- Volume
- 61
- Category
- Article
- ISSN
- 0016-2361
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✦ Synopsis
Through electron spin resonance (e.s.r.) studies, three different kinds of free radicals have been identified in pyrite samples containing coal impurities. Changes in the e.s.r. parameters (g-value, linewidths, and concentration n) of free radicals have been monitored as the coal-derived pyrites are heated in different atmospheres (vacuum, N, and Hz) from room temperature to 500°C in 50X steps for a residence time of 30 min at each temperature. Changes in n (concentration/g) and other parameters begin to occur at 300°C in vacuum, at 200°C in N,, and at 100°C in H, amtospheres. At these temperatures conversion of pyrite to pyrrhotite is also observed to occur. It is argued that the enhancement of n in these samples is related to the conversion mechanism of pyrite to pyrrhotites. The maximum relativeincreaseinnfollowsthesequencen (vacuum) >n(N,)>n(H,).At hightemperaturen decreases due to recombination of free radicals formed so that at 500°C. all three types of radicals have small but equal concentrations.