THERMODYKAMIC PROPERTIES IN THE SYSTEMS V-H, Nb-H, has an open hydronium hydrogen, and so Ccl4 can solvate this complex better than can isooctane. This enhanced solvation by CC1, just about compensates for the effect of the enhanced interaction of CC14 with TBP itself, and so the values of Kza are almost alike in the two diluents. The diluent 1,2-dichloroethane also must interact with TBP more strongly than does isooctane, thus hindering formation of the acid complex,17 but its most important property is its relatively high dielectric constant, which favors extraction and leads to dissociated ions in the extracted species. KO evidence for a 2 :1species was found in this system in the concentration range studied, and we believe that the loss of interaction with the anion in the dissociated species requires a more complete solvation of the cation by the TBP, thus favoring the 3 : l complex.
AND
683
Ta-H
I n this paper we have shown that the hydronium ion-TBP complex can have lower complexes than the saturated 3:l species, and that the nature of the diluent employed affects both the magnitude of the extraction and the nature of the extracted complex in a reasonable way. Several other studies of HC10419J0or H R e O P extraction by TBP or TBP-diluent systems have been made. These studies, however, are either a t higher concentrations of TBP than used in this study or use a different diluent, so that comparisons with the present work are difficult. In the next paper, this type of study will be extended to chloroform and to aromatic diluents. (19) See ref 1-9 in D . C. Whitney and R . M. Diamond, J.Phys. Chem., 67, 209 (1963). (20) K. Naito and T. Suzuki, ibid., 66, 983 (1962). (21) R. Colton, U.K.A.E.A.Report AE!RE-R3823 (Sept 1961).
Thermodynamic Properties in the Systems Vanadium-Hydrogen, Niobium-Hydrogen, and Tantalum-Hydrogen’
by Ewald Veleckis2 and Russell K. Edwards Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
(Received July 89,1968)
Comprehensive thermodynamic studies have been conducted for the systems V-H (246-554’), Nb-H (352671°), and Ta-H (350-631’) in the pressure range 1-800 Torr by measuring the equilibrium hydrogen pressure as a function of composition. Each of these system is comprised of a single solid phase in the temperature and pressure ranges studied. For each system a semiempirical equation, based on the statistical formulation of the simple interstitial solid solution model, is presented. The equations not only adequately reproduce the P-C-T data within the ranges of study but appear to be reliable to much lower temperatures. For example, they have been used to predict the T-C boundaries of immiscibility regions; for one system (Nb-H), for which comparison with an experimentally derived diagram is possible, agreement is very good. Calculated critical compositions, temperatures, and pressures are given. The partial and integral entropies and enthalpies of formation were calculated for the single-phase regions a t 1 atom % intervals up to the maximum compositions of 34 (V-H), 39 (Nb-H), and 27 (Ta-H) atom 7 0 H. The results are compared in detail with those of other
work.
Introduction Like palladium, the group Vb transition metals, vanadium, niobium, and tantalum, form with hydrogen wide ranges of solid solutions which, a t lower temperatures, are interrupted by miscibility gaps. For the palladium-hydrogen system the pressure-compositiontemperature (P-C-T) data have been obtained both above and below the critical temperature. For the V-H, Nb-H, and Ta-H systems such data below the critical temperature are difficult to obtain because of the slowness of achieving equilibrium ; nonetheless, these systems afford the opportunity of obtaining extensive P-C-T data above the critical temperatures to contribute to the advance of theoretical models.
The reported P-C-T work from which useful thermodynamic data have been or may be calculated consists principally of the following studies.s Kofstad and Wallace4 obtained data for the system V-H in the range 165 to 456’. The Nb-H system, which received considerable attention because of the use of niobium in nuclear reactors, was investigated by Albrecht, (1) Abstracted from the P b D . Thesis of E. Veleckis, Illinois Institute of Technology, 1960. (2) Address correspondence to the authors at Argonne National Laboratory, Chemical Engineering Division, Argonne, Ill. 60439. (3) For more complete literature references refer to H. J. GoldSchmidt, “Interstitial Alloys,” Butterworth and Co., Ltd., London, 1967, Chapter 9. (4) P. Kofstad and W. E. Wallace, J. Amer. Chem Soc., 81, 6019 (1959). Volume 7S,Number 9 March 1060
EWALD VELECKISAND RUSSELL K. EDWARDS
684
3-
rli
II
A (11
11
''4
TO VACUUM PUMPS
I
TO McLEOD GAUGE
S
+ TO HYDROGEN OR HELIUM
Figure 1. Schematic diagram of hydrogen-metal equilibration apparatus: A, porcelain specimen container; B, Vycor tube; C, porcelain protection tube; D, liquid metal bath; E, gas displacement rod; FL,purification and storage furnace for hydrogen; F1, gettering furnace for helium purification; G, calibrated bulb for gas measurements; MI, mercury manometer; N2, Ma, oil manometers; TI, Tg,cold traps.
et aL6 (100-900°), I
