Thermodynamics of the lanthanum-hydrogen system at 917/sup 0/K

Journal Article · Sat Nov 01 00:00:00 EST 1980 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(80)90460-0· OSTI ID:6863943

Dantzer, P; Kleppa, O J

The binary system lanthanum-hydrogen has been studied at pressures up to 1 atm at 917/sup 0/K by a calorimetric-equilibrium method. From the calorimetric measurements we found the enthalpy of formation of LaH/sub 2/ at 917/sup 0/K to be -45.7 kcal mole/sup -1/ with an estimated uncertainty at +- 0.3 kcal mole/sup -1/. This result is about 4 kcal mole/sup -1/ less negative than the values derived indirectly from plateau pressure equilibrium measurements by Mulford and Halley and by Korst and Warf. A comparison between the calorimetric and equilibrium measurements at 917/sup 0/K provides information on the partial entropy of hydrogen in lanthanum and in the dihydride LaH/sub 2 +- delta/. The excess entropy of hydrogen in lanthanum is about 6 cal K/sup -1/ mole/sup -1/ at 917/sup 0/K; this value is essentially fully accounted for by the estimated vibrational entropy contribution of the hydrogen atoms. In LaH/sub 2 +- delta/ the partial entropy of hydrogen changes from small negative values at X approx. = 1.95 to positive values for X > 2. This entropy change is explained by an assumed intrinsic disorder of hydrogen in LaH/sub 2/ of about 0.02.

• Research Organization: Univ. of Chicago, IL
• OSTI ID: 6863943
• Journal Information: J. Solid State Chem.; (United States), Vol. 35:1
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
08 HYDROGEN
LANTHANUM HYDRIDES
FORMATION HEAT
BINARY ALLOY SYSTEMS
HIGH TEMPERATURE
HYDROGEN
LANTHANUM
THERMODYNAMICS
ALLOY SYSTEMS
ELEMENTS
ENTHALPY
HYDRIDES
HYDROGEN COMPOUNDS
LANTHANUM COMPOUNDS
METALS
NONMETALS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
RARE EARTHS
REACTION HEAT
THERMODYNAMIC PROPERTIES
360105* - Metals & Alloys- Corrosion & Erosion
080201 - Hydrogen- Chemisorption Storage