Effects of pressure, temperature, and coal type on coal plasticity were investigated. Seven coals, from the Argonne premium sample bank ranging from lignite to low volatile bituminous, were studied. Elevated pressures, up to 10 atm of helium, did not affect coal plasticity, but reducing pressure from atmosphere to vacuum resulted in diminished plasticity, i.e. a shorter plastic period and a higher minimum apparent viscosity. It is hypothesized that high pressure inhibits mass transport of metaplast to tar vapors, but also favors metaplast repolymerization into coke and char. Higher holding temperature decreased the coal plastic period. It is hypothesized that higher temperature increases mass transport of liquid metaplast to tar vapors and metaplast repolymerization to coke and char. Heating rate had essentially no effect on the individual softening temperatures of five different plastic coals. Possible explanations are that, depending on coal type, metaplast generation, by chemical bond breaking or physical melting, or both, is not strongly affected by heating rate. In particular, for medium and low volatile bituminous cools, there is evidence that generation of the metaplast responsible for initial softening involves largely chemical bond breaking as opposed to physical melting.
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