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Specific heat and increases of entropy and enthalpy of the synthetic rubber GR-S from 0 degrees to 330 degrees K

1944; US government; Volume: 33; Issue: 1 Linguagem: Inglês

10.6028/jres.033.029

2376-5305

R. D. Rands, William Ferguson, J.L. Prather,

Polymer crystallization and properties

Specific heat measurements were made over the range 12° to 330° K on a sample of synthetic rubber GR-S (Buna S) by means of a n adiabat ic vacuum-ty pe calorimeter.A D ebye specific he["t function was used to calculate values below 15 0 K .At about -61 0 C the material undergoes a transition of the second order, the specific heat increasing rapidly by about 40 percent.From -50 0 to +60 0 C, the specific heat values can be calculated to within 0.1 percent by the equation C. = 0,4346 + 7.029 X lO-' t+ 1.156 X 10-a t2 in calories gram-I degree Kelvin -I.At 25 0 C the specific heat is 1.894 internat ional joules gram-1 degree Kelvin-I (0.4528 calorie gram-1 degree K elvin -I).The increase in entropy from 0° to 298.16 0 K is calculated to be 1.824 internations.ljoules gram -I degree Kelvin -I (0.4359 caloriE' gram -I degree K elvin -I).Values of specific heat, and increases of entropy, enthalpy , and free energy are tabuls.tedat 5-degree intervals.The experimental data indicate that values below the transition are dependent upon the thermal history of the ~ample .This phenomenon, as well as the temperature drifts observed, ca n be explained on the theory that the transition results from an increasingly slow s.pproach to the equilibrium state at temperatures in the transition region and below.