Coal sample preservation in foil multilaminate bags

An initial 1-year study on a bituminous coal sample indicated that storage under argon in heat-sealed 0.20-mm thick bags of laminated polyethylene, aluminum foil, and fibrous polyethylene preserved initial sample properties better than conventional containers already in use. Continuation of the study over 14 years showed that this storage protocol preserves that sample's initial properties very well. A 2-year comparison to samples in flame-sealed glass ampoules showed comparable ability to preserve thermoplastic behavior. Thirty-three samples in the Penn State Coal Sample Bank, collected since 1989 for the “Department of Energy Coal Sample” (DECS) series, are stored under argon at 3 °C in these bags. Selected samples from this series have been analyzed periodically for up to 13 years; for the majority of the samples, moisture, sulfate sulfur, and calorific value were maintained within ASTM reproducibility limits over the term of the tests. Gieseler fluid behavior (for samples of appropriate rank) was maintained within the more narrow repeatability limits for at least several years. In some cases, trends suggest that the initial properties will be maintained indefinitely. An 8-year comparison of refrigerated to unrefrigerated storage has not yet shown significant differences.