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Low density specific heat measurements of para-hydrogen adsorbed on exfoliated graphite

1985; Elsevier BV; Volume: 150; Issue: 1 Linguagem: Inglês

10.1016/0039-6028(85)90212-2

1879-2758

Ferney A. Chaves, M.E.B.P. Cortez, R.E. Rapp, E. Lerner,

Phase Equilibria and Thermodynamics

Heat-capacity measurements of para-hydrogen adsorbed on bare graphite foam for coverages below about the (3× 3) R30° configuration between 0.0126 and 0.0622 Å−2 were made as a function of temperature in the range of 5 to 25 K using a quasiadiabatic method. From the data a phase diagram is suggested having three distinct regions: a pure (3× RCD>3)R30°; phase, a coexistence region between (3× 3)R30° and fluid and a pure fluid region. A tricritical point seems to exist at TTC ⋍ 12.4 K and nTC ⋍ 0.039 Å−2. The critical exponent α = 0.37 ± 0.03 was calculated which, within our experimental measurements, is the theoretical 3-state Potts value of 13. Considering the adatoms behaving as localized Einstein oscillators, for the 0.0636 Å−2 density, an average Einstein temperature of 54.4 ± 4.9 K was obtained. Our results are compared with data obtained by other authors.