THE HEAT CAPACITY AND THERMODYNAMIC FUNCTIONS OF /cap beta/-URANIUM HYDRIDE FROM 5 TO 350 K

Journal Article · Mon Jul 20 04:00:00 EDT 1959 · Journal of the American Chemical Society (U.S.)

DOI:https://doi.org/10.1021/ja01523a011· OSTI ID:4241781

Flotow, H E; Lohr, H R; Abraham, B M; Osborne, D W

S>The heat capacity of beta -UH/sub 3/ was measured from 5 to 350 deg K in an adiabatic calorimeter. The enthalpy and entropy at 298.15 deg K calculated from the data are 2155 cal. mole/sup -1/ and 15.24 cal. deg./sup -1/ mole/sup -1/, respectively. The entropy and free energy of formation for UH/sub 3/ at 298.15 deg K as well as the heat of formation at absolute zero were calculated from these data and the previously determined heat of formation and have the values -43.60 cal. deg./sup -1/ mole/sup -1/, -17,353 cal. mole/sup -1/ and -27,945 cal. mole/sup -1/. It was found that the calculated and observed dissociation pressures are not in agreement. The discrepancy is believed due to a particle size effect in the dissociation pressure measurements or to the heat of transition from alpha -UH/sub 3/ to beta -UH/sub 3/. An anomaly is observed in the heat capacity which anises from the transition from the ferromagnetic to the paramagnetic state. The maximum in the heat capacity is 10.72 cal. deg./sup - 1/ mole/sup -1/ and occurs at 170.7 plus or minus 0.5 deg K. It was estimated that 1.01 cal. deg./sup -1/ mole/sup -1/ is the entropy change in the transition which is less than R ln 2 = 1.38 cal. deg./sup -1/ mole/sup -1/ expected from thc Heisenberg theory of ferromagnetism. (auth)

• Research Organization: Argonne National Lab., Lemont, Ill.
• Sponsoring Organization: USDOE
• NSA Number: NSA-13-017882
• OSTI ID: 4241781
• Journal Information: Journal of the American Chemical Society (U.S.), Journal Name: Journal of the American Chemical Society (U.S.) Vol. Vol: 81; ISSN JACSA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

CALORIMETERS
CHEMISTRY
DECOMPOSITION
MAGNETISM
MATHEMATICS
MEASURED VALUES
PRESSURE
SPECIFIC HEAT
THERMODYNAMICS
TRANSIENTS
URANIUM HYDRIDES