STUDIES OF RARE-EARTH HYDROGEN SYSTEMS. Final Report, Parts 1 and 2
; : 8 ? 8 ; ressure line with a gage that permitted the measurement of pressures up to 65 atmospheres was built and the hydrides of lanthanum, cerium, and ytterbium investigated. The lanthanum- and ceriumhydrogen systems were studied and equilibrium dissociation pressure-temperature- composition data obtained. The results were compared with the low-pressure data of other authors and with the high-pressure results on the ceriumhydrogen system by Streck and Dialer. Lines of constant composition were drawn through plots of the log P versus reciprocal absolute temperature data. From the slopes of these lines values for the heats of dissociation were obtained for the following reaction. RH/sub 3-x/ yields RH/sub 2-y/, + (1 + y -- x)/(2) H/sub 2/, where R represents the rare-earth metal and x and y depend essentially upon the temperature and presx and y depend essentialiy upon the temperature and pressure. Heats of dissociation of LaH/sup 2.70/ and LaH/sup 2.80/ are 6.6 and 6.8 kcal/ mole H/sub 2/ respectively, while those for CeH/sub 2.80/ and CeH/sub 2.90/ are 6.5 and 6.8 kcal/mole H/sub 2/ respectively. The lattice constant for a specimen of CeH/sub 2.97/ was determined to be 5.539 plus or minus 0.001 A. A higher hydride of ytterbium was prepared. Absorption of hydrogen at approximately 20 atmospheres and several hundred degrees by ytterbium samples resulted in the formation of hydrides having the compositions YbH/sup 2.55/, YbH/ sup 2.2/, and YbH/sup 2.56/. X-ray diffraction photographs of these hydrides showed the presence of a new face-centered cubic phase. The value of the lattice constant of this phase was determined to be 5.1921 plus or minus 0.0012 A. Thermally decomposed and quenched samples of YbH- 55 having the compositions of YbH/sup 2.42/ and Yb/sup 2.84/ were examined by X-ray diffraction techniques and found to contain an additional f.c.c. phase. The unit-cell constant of this phase was determined to be 5.2532 plus or minus 0.0009 A. Annealing the sample of YbH/sub 2.04/ effected conversion of this metastastable substance to orthorhombic ytterbium dihydride and to the f.c.c. ( a = 5.192 A) higher ytterbium hydride. Measurements of the magnetlc susceptibility of samples with 1.88 < H/Yb < 2.55 were carried out, using the Gouy Method. The data could be interpreted in terms of mixtures of various amounts of virtually diamagnetic ytterbium dihydride and a strongly paramagnetic higher hydride of ytterbium containing Yb/sup 3+/ ions. Infrared absorption spectra for several ytterbium hydrides were obtained and compared with the spectrum for a sample of CaH2. lsotherms of dissociation pressure versus composition for the region l.9 < H/Yb < 2.6 consisted of two parts. Below approximately 13 atmospheres and 320 deg C plateaus were observed which indicated a two-solid-phase equilibrium, ytterbium dihydride and the higher ytterbium hydride, while above these critical conditions only one solid phase existed. The investigations indicate that a solid with the composition YbH/sup 2.5/is a stable phase in the YbH2--YbH/sub 3/ system, and that the composition is dependent upon the pressure and temperature. From a van't Hoff plot of the plateau pressures versus reciprocal absolute temperature, the value for the heat of dissociation of YbH/sub 2.5/ was calculated to be 3.3 kcal/mole H/sub 2/. Attempts to prepare higher hydrides of europium and scandium by the reaction of the metals with hydrogen at several atmospheres and high temperatures were unsuccessful. Resistivity measurements on compressed, powder specimens of LaH/sub 2,9/, CeH/sub 2.7/, PrH/sub 2.7,/ and YbH/sub 1.9/ showed respectively 10,000 plus or minus 2000; 27,000 plus or minus 4000; 20,000 plus or minus 2000; and 30,000 plus or minus 4000 ohms/cm. The temperature coefflcient of resistivity, alpha , was determined for LaH/sub 2.88/ to be -- 0.006/ deg C. Examination of a specimen of LaH/sub 2.8/ using nuclear magnetic resonance techniques showed that the proton resonance absorption line width was extremely narrow for solids, approximately 40 milligauss, which indicated rapid movement of the protons in the metal lattice. The line width increased as the sample was cooled, and at --190 deg C was broadened
- Research Organization:
- University of Southern California, Los Angeles
- DOE Contract Number:
- NONR 228(15)
- NSA Number:
- NSA-16-005307
- OSTI ID:
- 4805767
- Report Number(s):
- NP-11180
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- United States
- Language:
- English
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ABSORPTION
ADSORPTION
ANNEALING
CALCIUM HYDRIDES
CERIUM HYDRIDES
CHEMICAL REACTIONS
CONVERSION
COOLING
DECOMPOSITION
DIAGRAMS
DIFFRACTION
ELECTRIC CONDUCTIVITY
EUROPIUM HYDRIDES
GOUY METHOD
HEAT TREATMENTS
HIGH TEMPERATURE
HYDRIDES
HYDROGEN
INFRARED RADIATION
IONS
LABORATORY EQUIPMENT
LANTHANUM HYDRIDES
LATTICES
LOW TEMPERATURE
LUTETIUM HYDRIDES
MAGNETIC MATERIALS
MEASURED VALUES
METALS
MIXING
MOLECULES
NUCLEAR MAGNETIC RESONANCE
NUMERICALS
PERFORMANCE
PHASE DIAGRAMS
PHOTOGRAPHY
POWDERS
PRASEODYMIUM HYDRIDES
PRESSURE
PROTONS
QUALITATIVE ANALYSIS
QUANTITATIVE ANALYSIS
RARE EARTHS
SAMPLING
SCANDIUM HYD