Isothermal equilibrium hydrogen pressure measurements were carried out as a function of composition for the yttrium-hydrogen system in the temperature ranges 250 to 350" and 650 to 950", up to a pressure of 1 atm. The existence of three solid solution phases in this system is indicated by the data. The primary solid solution range extends to about YH0.55. The other two solid solution phases can be described as yttrium hydride phases deficient in hydrogen with respect to YH2 and YH3. The phase boundaries were evaluated in the temperature ranges 650 to 950" and 250 to 350", respectively. The experimental relative partial molal and integral thermodynamic quantities were calculated.
IntroductionAlthough the position of yttrium metal in the periodic table is significant in regard to the correlation of the properties of the hydrogen compounds with those of the alkaline earth, transitional, and rare earth hydrides, the lack of available high-purity metal has been a hindrance to accurate work on the Y-H system.Lundin and Blackledge2 recently published pressuretemperature-composition curves for the Y-H system in the temperature range 900 to 1350". They reported the existence of a stable hydrogen-deficient yttrium dihydride in this temperature range and determined the solubility limits of hydrogen in yttrium and yttrium dihydride. They also reported the existence of YH3 from 300" down to room temperature but gave no isotherinal equilibrium pressure measurements for this low temperature range. Their findings have been substantiated also by X-ray data of Dialer and Frank.3 Flotow, Osborne, and Otto416 have also reported the preparation of YHs and YHB and the measurement of low-temperature heat capacities.The purpose of the work reported here was the determination of thermodynamic data and the elucidation of the yttrium-hydrogen phase diagram.
pearance potentials are 199 and 201 kcal./mole, respectively. These values are higher than that of 173 kcal./mole,11 but agree with those determined from the ethylene oxide and propylene oxide study2 and the above study of 1,2-epoxy-3-methoxypropane.m/e -42.-C2H20 + is formed from epichlorohydrin with the neutral products CH3 + Cl. ARrf+(C2H20) is calculated to be 191 kcal./mole. This is somewhat lower than values reported in the literature.2'11 m/e = 49.-The only possible ion is CH2C1+, since from Fig. 1 it can be seen that the ratio of ht/hi is about 3. But the energetics do not distinguish between the neutral products CO + CH3 and C2H30. Afff+(CH2C1) is calculated to be 226-256 kcal./mole. For the present, we tend to favor the greater value. The heat of formation for this ion, to our knowledge, has not been reported previously. The corresponding ion in epibromohydrin was not observed.m/e = 57.-This ion is formed by removal of halogen from the parent molecule-ion in both epichlorohydrin and epibromohydrin. Afff+(C3-H5O) are 207 kcal./mole for epichlorohydrin and 216 kcal./mole for epibromohydrin. Although in fair agreement, these values are a little higher than that reported from a study of propylene oxide.2 THERMODYNAMIC PROPERTIES AND PHASE RELATIONS IN THE SYSTEM HYDROGEN-HAFNIUM12
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