- Email: [email protected]
The solubility of hydrogen in tantalum at high temperatures
Journal of the Less-Common Metals, 55 (1977) 143 - 147 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
143
Short Communication
The solubility of hydrogen in tantalum at high temperatures
H. F. FRANZEN,
A. S. KHAN and D. T. PETERSON
Ames Laboratory-ERDA Engineering, Iowa State
and Departments of Chemistry and Materials Science and University, Ames, Iowa 50011 (U.S.A.)
(Received January l&1977)
Introduction In recent years many investigations of pressure-composition isotherms for solid solutions of hydrogen in vanadium, niobium and tantalum have been reported [l - 131. The results of these studies have been used to obtain thermodynamic quantities for the solution of hydrogen in the Group V transition metals. In the case of the tantalum-hydrogen system, equilibrium hydrogen pressures at temperatures above 973 K have not previously been investigated. Mallet and Koehl [ 31 measured pressure-composition isotherms in the temperature range 573 - 973 K and Kleppa et al. [S] and others [l, 5,6] studied the tantalum-hydrogen system at lower temperatures. Recently a paper by Hosseini [14] on the tantalum-hydrogen system appeared, covering the temperature range 293 - 1273 K. However, equilibrium hydrogen pressures reported in that paper, particularly at higher temperatures, differ significantly from those found by the present authors and from those in the literature measured at comparable temperatures. There were also significant differences between the hydrogen pressures during absorption and desorption. The present authors have found that tantalum could be used, as a crucible material readily permeable to hydrogen, for the hydrogenation of alkaline earth metals at temperatures in the range 900 - 1213 K. Since tantalum crucibles offer special advantages for synthesis and equilibrium hydrogen pressure measurements in the alkaline earth hydrogen systems, it was decided to determine the equilibrium hydrogen pressures in the tantalumhydrogen system in the relevant high temperature range up to 1213 K. Temperatures above 1213 K were not investigated because of the loss of hydrogen by permeation through the quartz tube at higher temperatures. Knowledge of the thermodynamics of solid solutions of hydrogen in tantalum at these higher temperatures will permit comparison with thermodynamic quantities reported in the literature measured at lower temperatures.
144
Experimera tal
High purity 1.27 cm tantalum tubing with walls 0.46 mm thick was obtained from Fansteel Corporation. Specimens were prepared by closing the ends of 6 cm lengths of this tubing with tantalum caps by arc welding in an argon atmosphere. Before sealing, the tantalum tube and the caps were chemically polished and then outgassed at 1700 “C in a vacuum induction furnace under a pressure of 10 -6 Torr. Measurements were carried out with sealed tantalum tubes to check the rate of the solution reaction in this configuration, because the large surface-to-mass ratio promised shorter reaction times. The reaction of hydrogen with these sealed tantalum tubes was found to be rapid; equilibrium, as indicated by constant hydrogen pressures, was reached in about 10 h at 917 K and within one hour at 1213 K. The tantalum sample, which weighed about 35 g, was placed in a quartz reaction tube in a conventional Sievert’s apparatus. The hydrogen pressures were measured with a mercury manometer and the temperature with a chromelalumel thermocouple. The temperature of the furnace was controlled to within *3 “C. The system could be pumped to a residual pressure of less than 5 X 10W6Torr. The effective volume of the furnace section of the apparatus was calibrated with helium in the system at various temperatures with the tantalum sample in position. The composition of the solid phase was calculated from the measured amount of hydrogen in the system and the measured equilibrium hydrogen pressure. High purity cylinder hydrogen was used for hydrogenation. Results and discussion
Equilibrium hydrogen pressures for seven different temperatures in the range 917 - 1213 K were determined for the tantalum-hydrogen system. Experimental hydrogen pressures plotted as P$, (mm) uersus Nn (where NH is the atomic fraction of hydrogen) are shown in Fig. 1. Equilibrium was obtained by both absorption and desorption of hydrogen. An examination
Y II 1.25 9
0
0.01
002 0.03 0.04 0.05 0.06 NH Atom Fraction Hydrogen
0.07
I .oo
a0
Fig. 1. Pressure composition isotherms for tantalum-hydrogen
9.0 104/T’K
system.
Fig. 2. Lvgarithm of Sievert’s law constants us. reciprocal temperature.
IO.0
II 0
145
of the plots in Fig. 1 obtained for different temperatures shows that the observed equilibrium hydrogen pressures are consistent with Sieve&s law. Similar conclusions as to the validity of Sievert’s law at 773 K and above have also been reported by Mallet and Koehl [3] and by Veleckis and Edwards [ 51. At lower temperatures the isotherms show curvature [ 3, 5, 61 which becomes increasingly marked with a decrease in temperature. At each temperature the value of the Sievert’s law equilibrium constant was calculated by a least squares treatment of the measured pressures and compositions. These equilibrium constants are given in Table 1 and are plotted as log K uersus l/T in Fig. 2. In this equilibrium constant, the hydrogen pressure was in atmospheres and the hydrogen concentration was given as an atomic fraction. The equilibrium constant at a given temperature can be calculated from the expression 1781 log K = 2.98 - T Hence, the atomic fraction of hydrogen in tantalum can be calculated for a given temperature and hydrogen pressure within the specified temperature range. The value of A@ for the reaction H(s.s.) = % H2 (g) obtained from the Arrhenius plot in Fig. 2 was found to be 8.2 f 0.3 kcal (mol H)-l. The Ap value obtained in this study is in reasonable agreement with the value of 8.5 kcal (mol H)-l obtained by Kleppa et al. [8] by calorimetric methods and with the value of 8.0 kcal (mol H)-l reported by Veleckis and Edwards [5] from equilibrium hydrogen pressure determinations. However, the values of A@ given by Mallet and Koehl [3] and Kofstad et al. [l] are about 1 kcal higher than_ the value reported by the present authors. Entropies of dissolved hydrogen 5$n(s.s.) have been calculated from data obtained in this study and are presented in Table 1 with those calculated from the available literature data [3, 51. A comparison shows that at 917 K the value of $!u (s.s.) obtained in this study is in reasonable agreement with_ the value reported by Veleckis and Edwards [ 51. At 973 K the value of s”n (s.s.) reported in this study is about one entropy unit larger than the value reported by Mallett and Koehl. Conclusions The reaction of hydrogen with sealed tantalum tube specimens was rapid; equilibrium was achieved in a relatively short time during both absorption and desorption. No measurable difference in hydrogen pressure was found between absorption and desorption cycles. Hydrogen dissolved in tantalum obeyed Sievert’s law in the temperature range 917 - 1213 K. The value of AHe for the hydrogen solution reaction was similar to that reported by Kleppa et aZ. [ 81 and others [ 51; this study essentially confirms the entropy values previously reported.
28.7 34.0
1173 1213
aAt 903 K.
11.1 14.1 17.0 21.0 24.0
constant K
Equilibrium
917 973 1023 1068 1113
T(K)
-7830 -8500
-4390 -5100 -5760 -6460 -7030
(g atom H)-l)
6: 0
8200 + 200 -
-
(cal (g atom H)-l)
AH0
0
13.6 13.7
13.7 13.6 13.6 13.7 13.6
c:
K-l mol-“)
Standard thermodynamic functions for the reaction H(s.s.) -+ */zHz(g) for the tantalum-hydrogen
TABLE 1
6.9 6.8
6.5 6.6
5.7 6.2
(cal K-l moT1)
So,(s.s.)
solid solution
-
5.5a(5) 5.1(3)
(cal K-l mol-l)
So,(s.s.)
z 01
147
Acknowledgment This work was performed for the U.S. Energy Research and Development Administration, W-7405-eng-82.
Division of Physical Research, under contract No.
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
P. Kofstad, W. E. Wallace and L. J. Hyv&en, J. Am. Chem. Sot., 81 (1959) 5016. P. Kofstad and W. E. Wallace, J. Am. Chem. Sot., 81 (1969) 6019. M. W. Mallett and B. G. Koehl, J. Electrochem. Sot., 109 (1962) 611. M. AIbrecht, W. D. Goode and M. W. Mahett, J. Electrochem. Sot., 106 (1969) 981. E. Veleckis and R. K. Edwards, J. Phys. Chem., 73 (1969) 683. J. A. Pryde and I. S. T. Tsong, Trans. Faraday Sot., 65 (1969) 2766. J. A. Pryde and C. G. Titcomb, J. Phys. C, 5 (1972) 1293,130l. 0. J. Kleppa, M. E. Melnichak and T. V. Charlu, J. Chem. Thermodyn., 5 (1973) 596. 0. J. Kleppa, P. Dantzer and M. E. Melnichak, J. Chem. Phys., 61 (1974) 4048. S. Komjathy, J. Less-Common Met., 2 (1960) 466. R. Burch and N. B. Francis, Acta Metail., 23 (1975) 1129. M. A. Pick, Ber. Bunsenges. Phys. Chem., 76 (1972) 767. J. Mareche, J. Rat and A. Herold, J. Chim. Phys. Phys. Chem. Biol., 73 (1976) 1. S. M. Hosseini, Z. MetaIlkd., 67 (1976) 123. H. F. Fransen, A. S. Khan and D. T. Peterson, J. Solid State Chem., 17 (1976) 283. D. R. Stull and G. C. Sinke, Thermodynamic Properties of the Elements, Advances in Chemistry, Ser. 18, American Chemical Society, 1956, p. 113.
143
Short Communication
The solubility of hydrogen in tantalum at high temperatures
H. F. FRANZEN,
A. S. KHAN and D. T. PETERSON
Ames Laboratory-ERDA Engineering, Iowa State
and Departments of Chemistry and Materials Science and University, Ames, Iowa 50011 (U.S.A.)
(Received January l&1977)
Introduction In recent years many investigations of pressure-composition isotherms for solid solutions of hydrogen in vanadium, niobium and tantalum have been reported [l - 131. The results of these studies have been used to obtain thermodynamic quantities for the solution of hydrogen in the Group V transition metals. In the case of the tantalum-hydrogen system, equilibrium hydrogen pressures at temperatures above 973 K have not previously been investigated. Mallet and Koehl [ 31 measured pressure-composition isotherms in the temperature range 573 - 973 K and Kleppa et al. [S] and others [l, 5,6] studied the tantalum-hydrogen system at lower temperatures. Recently a paper by Hosseini [14] on the tantalum-hydrogen system appeared, covering the temperature range 293 - 1273 K. However, equilibrium hydrogen pressures reported in that paper, particularly at higher temperatures, differ significantly from those found by the present authors and from those in the literature measured at comparable temperatures. There were also significant differences between the hydrogen pressures during absorption and desorption. The present authors have found that tantalum could be used, as a crucible material readily permeable to hydrogen, for the hydrogenation of alkaline earth metals at temperatures in the range 900 - 1213 K. Since tantalum crucibles offer special advantages for synthesis and equilibrium hydrogen pressure measurements in the alkaline earth hydrogen systems, it was decided to determine the equilibrium hydrogen pressures in the tantalumhydrogen system in the relevant high temperature range up to 1213 K. Temperatures above 1213 K were not investigated because of the loss of hydrogen by permeation through the quartz tube at higher temperatures. Knowledge of the thermodynamics of solid solutions of hydrogen in tantalum at these higher temperatures will permit comparison with thermodynamic quantities reported in the literature measured at lower temperatures.
144
Experimera tal
High purity 1.27 cm tantalum tubing with walls 0.46 mm thick was obtained from Fansteel Corporation. Specimens were prepared by closing the ends of 6 cm lengths of this tubing with tantalum caps by arc welding in an argon atmosphere. Before sealing, the tantalum tube and the caps were chemically polished and then outgassed at 1700 “C in a vacuum induction furnace under a pressure of 10 -6 Torr. Measurements were carried out with sealed tantalum tubes to check the rate of the solution reaction in this configuration, because the large surface-to-mass ratio promised shorter reaction times. The reaction of hydrogen with these sealed tantalum tubes was found to be rapid; equilibrium, as indicated by constant hydrogen pressures, was reached in about 10 h at 917 K and within one hour at 1213 K. The tantalum sample, which weighed about 35 g, was placed in a quartz reaction tube in a conventional Sievert’s apparatus. The hydrogen pressures were measured with a mercury manometer and the temperature with a chromelalumel thermocouple. The temperature of the furnace was controlled to within *3 “C. The system could be pumped to a residual pressure of less than 5 X 10W6Torr. The effective volume of the furnace section of the apparatus was calibrated with helium in the system at various temperatures with the tantalum sample in position. The composition of the solid phase was calculated from the measured amount of hydrogen in the system and the measured equilibrium hydrogen pressure. High purity cylinder hydrogen was used for hydrogenation. Results and discussion
Equilibrium hydrogen pressures for seven different temperatures in the range 917 - 1213 K were determined for the tantalum-hydrogen system. Experimental hydrogen pressures plotted as P$, (mm) uersus Nn (where NH is the atomic fraction of hydrogen) are shown in Fig. 1. Equilibrium was obtained by both absorption and desorption of hydrogen. An examination
Y II 1.25 9
0
0.01
002 0.03 0.04 0.05 0.06 NH Atom Fraction Hydrogen
0.07
I .oo
a0
Fig. 1. Pressure composition isotherms for tantalum-hydrogen
9.0 104/T’K
system.
Fig. 2. Lvgarithm of Sievert’s law constants us. reciprocal temperature.
IO.0
II 0
145
of the plots in Fig. 1 obtained for different temperatures shows that the observed equilibrium hydrogen pressures are consistent with Sieve&s law. Similar conclusions as to the validity of Sievert’s law at 773 K and above have also been reported by Mallet and Koehl [3] and by Veleckis and Edwards [ 51. At lower temperatures the isotherms show curvature [ 3, 5, 61 which becomes increasingly marked with a decrease in temperature. At each temperature the value of the Sievert’s law equilibrium constant was calculated by a least squares treatment of the measured pressures and compositions. These equilibrium constants are given in Table 1 and are plotted as log K uersus l/T in Fig. 2. In this equilibrium constant, the hydrogen pressure was in atmospheres and the hydrogen concentration was given as an atomic fraction. The equilibrium constant at a given temperature can be calculated from the expression 1781 log K = 2.98 - T Hence, the atomic fraction of hydrogen in tantalum can be calculated for a given temperature and hydrogen pressure within the specified temperature range. The value of A@ for the reaction H(s.s.) = % H2 (g) obtained from the Arrhenius plot in Fig. 2 was found to be 8.2 f 0.3 kcal (mol H)-l. The Ap value obtained in this study is in reasonable agreement with the value of 8.5 kcal (mol H)-l obtained by Kleppa et al. [8] by calorimetric methods and with the value of 8.0 kcal (mol H)-l reported by Veleckis and Edwards [5] from equilibrium hydrogen pressure determinations. However, the values of A@ given by Mallet and Koehl [3] and Kofstad et al. [l] are about 1 kcal higher than_ the value reported by the present authors. Entropies of dissolved hydrogen 5$n(s.s.) have been calculated from data obtained in this study and are presented in Table 1 with those calculated from the available literature data [3, 51. A comparison shows that at 917 K the value of $!u (s.s.) obtained in this study is in reasonable agreement with_ the value reported by Veleckis and Edwards [ 51. At 973 K the value of s”n (s.s.) reported in this study is about one entropy unit larger than the value reported by Mallett and Koehl. Conclusions The reaction of hydrogen with sealed tantalum tube specimens was rapid; equilibrium was achieved in a relatively short time during both absorption and desorption. No measurable difference in hydrogen pressure was found between absorption and desorption cycles. Hydrogen dissolved in tantalum obeyed Sievert’s law in the temperature range 917 - 1213 K. The value of AHe for the hydrogen solution reaction was similar to that reported by Kleppa et aZ. [ 81 and others [ 51; this study essentially confirms the entropy values previously reported.
28.7 34.0
1173 1213
aAt 903 K.
11.1 14.1 17.0 21.0 24.0
constant K
Equilibrium
917 973 1023 1068 1113
T(K)
-7830 -8500
-4390 -5100 -5760 -6460 -7030
(g atom H)-l)
6: 0
8200 + 200 -
-
(cal (g atom H)-l)
AH0
0
13.6 13.7
13.7 13.6 13.6 13.7 13.6
c:
K-l mol-“)
Standard thermodynamic functions for the reaction H(s.s.) -+ */zHz(g) for the tantalum-hydrogen
TABLE 1
6.9 6.8
6.5 6.6
5.7 6.2
(cal K-l moT1)
So,(s.s.)
solid solution
-
5.5a(5) 5.1(3)
(cal K-l mol-l)
So,(s.s.)
z 01
147
Acknowledgment This work was performed for the U.S. Energy Research and Development Administration, W-7405-eng-82.
Division of Physical Research, under contract No.
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
P. Kofstad, W. E. Wallace and L. J. Hyv&en, J. Am. Chem. Sot., 81 (1959) 5016. P. Kofstad and W. E. Wallace, J. Am. Chem. Sot., 81 (1969) 6019. M. W. Mallett and B. G. Koehl, J. Electrochem. Sot., 109 (1962) 611. M. AIbrecht, W. D. Goode and M. W. Mahett, J. Electrochem. Sot., 106 (1969) 981. E. Veleckis and R. K. Edwards, J. Phys. Chem., 73 (1969) 683. J. A. Pryde and I. S. T. Tsong, Trans. Faraday Sot., 65 (1969) 2766. J. A. Pryde and C. G. Titcomb, J. Phys. C, 5 (1972) 1293,130l. 0. J. Kleppa, M. E. Melnichak and T. V. Charlu, J. Chem. Thermodyn., 5 (1973) 596. 0. J. Kleppa, P. Dantzer and M. E. Melnichak, J. Chem. Phys., 61 (1974) 4048. S. Komjathy, J. Less-Common Met., 2 (1960) 466. R. Burch and N. B. Francis, Acta Metail., 23 (1975) 1129. M. A. Pick, Ber. Bunsenges. Phys. Chem., 76 (1972) 767. J. Mareche, J. Rat and A. Herold, J. Chim. Phys. Phys. Chem. Biol., 73 (1976) 1. S. M. Hosseini, Z. MetaIlkd., 67 (1976) 123. H. F. Fransen, A. S. Khan and D. T. Peterson, J. Solid State Chem., 17 (1976) 283. D. R. Stull and G. C. Sinke, Thermodynamic Properties of the Elements, Advances in Chemistry, Ser. 18, American Chemical Society, 1956, p. 113.