- Email: [email protected]
Investigation of the intermediate hydride phase β-LaNi5H3.5 by high pressure and high temperature gravimetry
Joumalofthe
Less-Common
L17
Metals, 171(1991) L17-L21
Letter
Investigation of the intermediate hydride phase /3-LaNi,H,., by high pressure and high temperature gravimetry P. Selvam* and K. Yvon Laboratoire de Cristallographie aux Rayons X, UniversitP de GenPve, 24, Quai E. Anserrnet, CH-1211 Gendve 4 (Switzerland)
(Received January 2,199l)
The intermediate hydride phase /3-LaNi,H,_, reported by Ono et al. [l] and later by Matsumoto and Matsushita [2] has been studied by in situ X-ray powder diffraction [l-4], neutron powder diffraction [4, 51, heat conduction calorimetry [6], volumetric measurements of pressure-composition isotherms (p-c-T) [l, 71, combined p-c-T calorimetry [8] and differential scarming calorimetry [9]. It is considered [2] to be a strain-induced metastable phase that grows at the interface between hydrogen-poor a-LaNi,H,,, and hydrogen-rich y-LaNi,H,,,, previously called /?-LaNi,H,,, [lo], at temperatures above 343 K (absorption) and 367 K (desorption) [3]. Its formation is enhanced by high temperature cycling [2-4, 11, 121. The phase can be stabilized at room temperature by exposing the sample to carbon mono~de f5]. Its existence is of tec~olo~cal importance because it contributes to the sloping of the a-y plateau isotherms in LaNi,H, during cycling [ 131 or leads to a splitting of the plateaux according to the reactions a-LaNi,H,,3
-
/-?-LaNi,H,,s -
#?-LaNi,H,,,
(lower plateau)
y-LaNi,H,,
(upper plateau)
(I)
(2) The exact role of that phase during hydrogen absorption and desorption, however, is not yet clear. Thermodynamic data (enthalpy of desorption, AH, and entropy of desorption, As) of low accuracy have been reported for reactions (1) and (2) from differential thermal analysis [9], heat conduction calorimetry [6] and volumetrically measured p-c isotherms [l, 7] on non-cycled samples. This prompted us to derive more accurate values for both cycled and non-cycled samples from gravimetrically measured p-c isotherms by using our newly installed high pressure, high temperature microbalance. The balance (type M25 D-P, Sartorius G.m.b.H., Glittingen, F.R.G.) is of a type similar to that described in refs. 14 and 15. It has two pans with symmetrical load cells (suspended beam with automatic electromagnetic compensation) with a m~imum weight capacity of 25 g, a sensitivity of 1 pg and operation ranges of 300-873 K and low3 mbar-150 bar. The heating system consists of a high *Present affiliation: Department de Physique de la Matikre Conderke. 0022-5088/91/S3.50
0 Elsevier Sequoia/P~nted
in The Netheriands
Llb
temperature double-tube furnace with a temperature control system (Type 410, Netzsch-Geratebau G.m.b.H., Selb, F.R.G.) that permits operation at constant temperature as well as thermal cycling between preset temperatures at desired heating and cooling rates (0.1-99.9 K mint, steps of 0.1 K min-‘, holding periods in steps down to 1 min). The pressure is measured by using a pressure gauge ( 10m3 mbar-1 bar) and pressure manometers (1-15 bar, l-60 bar). The change in mass of the sample is directly read out from the weighing system. Two types of LaNi, samples were measured. One sample (called “commercial” hereinafter) was obtained from the Ergenics Division of MPD Technology Corporation (Wyckoff, NJ, U.S.A.) with the designation HYSTOR-205. The stated purity was 99.8%. Part of that sample was activated at 300 K and 50 bar H, for 24 h. Thereafter it underwent cycling for about 30 absorption-desorption cycles between 1 and 60 bar H, and 300 and 423 K (10 times at 300 K between 1 and 60 bar, 15 times at 373 K between 1 and 60 bar, five times at 423 K between 1 and 60 bar). The other sample (called “as cast” hereinafter) was prepared at the stoichiometric composition by high frequency induction levitation melting of lanthanum (99.9%, Research Chemicals, Pflatz & Bauer Inc., Stamford, CT, U.S.A.) and nickel 56, 52 -
,
I
,
I
1 I I
,
LaNi5-H, .
(after 30 cycles1
0
46 -
44-
T= s
3632 -
P 5 Lx
26 -
E 24 b = $
zo-
16 -
I
I
I
2
3
4
5
6
7
composition (H/LoNQ
Fig. 1. Pressure-composition desorption.
isotherms for cycled LaNi,-H,
(commercial sample) l, absorption;
0,
Ll9
(99.998O~, Johnson
Matthey Chemicals Ltd., London, U.K.) under argon atmosphere. X-ray powder diffraction analysis (Co Ka radiation, silicon standard) confirmed that the samples were single phase, with refined lattice parameters for the commercial sample of a = 5.0201(4) A, c= 3.9773(5) A (uncycled) and a = 5.027( 1) A, c = 3.997( 1) A (cycled). The samples were charged in the microbalance by using high purity hydrogen (99.9999%, Polygaz, Geneva, Switzerland) and deuterium (99.7%, Polygaz, Geneva, Switzerland) gases. Pressure-composition isotherms for the activated commercial hydride sample are shown in Fig. 1. The plots show plateau splitting at about 3.5 hydrogen atoms per mole of LaNi, which is well defined compared to that observed previously by the volumetric method 11, 71. It is clearest for the 373 and 398 K isotherms, for which it amounts to about 4 and 5 bar Hi, pressure respectively. For the nonactivated hydride and deuteride samples and the as-cast sample (data not shown in Fig. 1) the splittings occur at the same hydrogen concentration. They decrease as the temperature decreases and virtually disappear at room temperature, in agreement with previous reports [ 1, 2,6, 11, 121 and a recently proposed phase diagram [7]. At given temperatures the plateau pressures of the deuteride are always higher than those of the hydride, in agreement with previous reports (see e.g. ref. 16). Those of the as-cast sample differ from those of the commercial sample, as expected from the different metal ratios and heat treatments of the samples. Thermodynamic constants for reactions (1) and (2) were derived for all samples from van? Hoff plots
In PH2=
As
AH
-R+iz
where PHzis the plateau pressure, R is the gas constant, T is the absolute temperature and AS and AH are the changes in entropy and enthalpy per mole of H, (D,) respectively. Examples of such plots are shown in Fig. 2 for the cycled hydride sample. Equilibrium pressures are defined at the middle of the plateau regions (at H : LaNi, = 2.5 and 4.5 for reactions ( 1) and (2) respectively). The results are listed in Table 1. The A,!? and AH values obtained from the present measurements are more accurate than, and differ si~ic~tly from, those reported previously. In particular, they show no significant difference in enthalpy between reactions ( 1) and (2), in contrast to previous work that indicates higher enthalpies for reaction (2) than for reaction (1). As to the entropies (not stated in previous work), our measurements indicate values slightly higher on average for reaction (2) than for reaction (l), at least in the temperature interval investigated. Assuming identical enthalpies for reactions ( 1) and (2), the entropy difference estimated from eqn. (3) amounts to about 6 J K-’ mol-’ H,. This is of the order expected for a possible change in configurational entropy of hydrogen in the meta host structure of LaNi,, as deduced from specific heat [ 171 and neutron diffraction [ 18, 191 measurements for y-LaNi,H,,. Neutron diffraction experiments on @-LaNi,H,., are in progress to test this hypothesis.
L20 TABLE 1 Enthalpy AH(kJ mol-’ H,) and entropy AS(J K-r mol-’ Hz) change for /?-LaNi,H(D),,, during absorption and desorption. Values are derived from linear least-squares fits to the experimental data according to eqn. (3) AHahs
A&es
A%,
A%,
- 31.5(4)
-31.7(4) -28.9(l) - 34.6( 9) - 32.6(4) -30 - 30.7(0.3) - 29.5( 1.0)
-111(l) - lOl( 1) - 106(2) - 117(4)
- 108.9(3) - 103.2(2) - 119(2) -111(2)
- 101.4(5.1)
- 102.0(4.1)
- 32.1(2) - 29.4(2) - 35.5(4) - 32.1(2) -33 -35 -39.5(1.2)
-111.4(g) - 98( 2) -108(l) -119.9(l)
-
- 138.3( 8.3)
- 137.3(6.2)
Lower plateau, reaction P-a Hydride (comm., cycled) Hydride (comm.) Deuteride (comm.) Hydride (cast) Hydride [l] Hydride [6] Hydride [7]
- 27.0( 3) - 27.9( 7) -33(l)
- 28.2( 1.4)
Upper plateau, reaction y-/3 Hydride (comm., cycled) Hydride (comm.) Deuteride (comm.) Hydride (cast) Hydride [l] Hydride [6] Hydride [7]
- 30.7( 1)
- 25.4(6) - 28.3(5) - 33.5(4)
-38.1(2.3)
114.6(8) 106.5(9) 122( 1) 113.1(3)
LaNi,-H, (after 30 cycles1
151 22
n 23
’ 2.4
’ 2.5
’ 26 000/T
’ 2.7
’ 2.8
’ 2.9
(K)
Fig. 2. Equilibrium pressure PCs during absorption (filled circles) and desorption (open circles) as a function of temperature for the upper (a, c) and lower (b, d) plateaux in cycled LaNi,-H, (commercial sample).
LZl
This work was supported by the Swiss National Science Foundation and the Swiss Federal Office of Energy. We thank Professor L. Schlapbach for supplying the “as-cast” sample and Mrs. B. Kiinzler for help with the drawings.
References 1 S. Ono, K. Nomura, E. Akiba and H. Uruno, J. Less-Cummon Met., 113 (1985) 113. ‘I’. Matsumoto and A. Matsushita, 3. Less-Common Met., 123 (1986) 135. E. Akiba, K. Nomura and S. Ono, J. Less-Common Mef., 129 ( 1987) 159. E. Akiba, H. Hayakawa, Y. Ishido, K. Nomura and S. Shin, Z. Whys. Gem. N.F., 163 (1989) 291. H. Hayakawa, K. Nomura, Y. Ishido, E. Akiba, S. Shin, H. Asano, E Izumi and N. Watanabe, J.
2 3 4 5
Less-CommonMet., 143(1988) 315. 6 M. L. Post, J. J. Murray and D. M. Grant, 2. Phys. Chem. N.F., 163 (1989) 135. 7 A. L. Shilov, M. E. Kost and N. T. Kuznetsov, J. Less-Common Met., 144 (1988) 23. 8 P. Dantzer, E. Orgaz and V. K. Sinha, Z. f%ys. Chem. N.F., 163 (1989) 141.
9 1. E. Nemirovskaya,
V. Z. Mordkovich,
Yu. K. Baychtok, A. M. Alekseyev and V. P. Mordovin,
Thermochim.
Actu, 160 (1990) 201. 10 L. Schlapbach (ed.), Topics in Applied Physics? Vol. 63, Hydrogen in Intermetallic Compounds
11 12
13 14 15
16 17
18 19
I,
Springer, Berlin, 1988. P. D. Goodell, J. Less-Common Met., PP( 1984) 1. K. Nomura, H. Uruno, S. Ono, H. Shinozuka and S. Suda, J. Less-Common Met., f07( 1985) 22 1, H. Uchida, K. Terao and Y. C. Huang, 2. Whys. Chem. N.F., 164 (1989) 1275. H. M. Lutz, R. Schmitt and F. Steffens, Thermochim. Acta, 24 (1978) 369. A. S. Pedersen, J. Kjoller, B. Larsen and B. Vigeholm, Int. J. Hydrogen Energy, 8 (1983) 205. A. Biris, R. V. Bucur, P. Ghete, E. Indrea and D. Lupu, J. Less-Common Met., 49( 1976) 477. D. Ohlendorf and H. E. Flotow, J. Chem. Phys., 73 (1980) 2937. W. E. Wallace, H. E. Flotow and D. Ohlendorf, J. Less-Common Met., 79 ( 198 1) 15 7. J. C. Achard, C. Lartigue, A. Percheron-Guegan, J. C. Mathieu, A. Pasture1 and E Tasset, J. LessCommon Met., 79(1981) 161.
Less-Common
L17
Metals, 171(1991) L17-L21
Letter
Investigation of the intermediate hydride phase /3-LaNi,H,., by high pressure and high temperature gravimetry P. Selvam* and K. Yvon Laboratoire de Cristallographie aux Rayons X, UniversitP de GenPve, 24, Quai E. Anserrnet, CH-1211 Gendve 4 (Switzerland)
(Received January 2,199l)
The intermediate hydride phase /3-LaNi,H,_, reported by Ono et al. [l] and later by Matsumoto and Matsushita [2] has been studied by in situ X-ray powder diffraction [l-4], neutron powder diffraction [4, 51, heat conduction calorimetry [6], volumetric measurements of pressure-composition isotherms (p-c-T) [l, 71, combined p-c-T calorimetry [8] and differential scarming calorimetry [9]. It is considered [2] to be a strain-induced metastable phase that grows at the interface between hydrogen-poor a-LaNi,H,,, and hydrogen-rich y-LaNi,H,,,, previously called /?-LaNi,H,,, [lo], at temperatures above 343 K (absorption) and 367 K (desorption) [3]. Its formation is enhanced by high temperature cycling [2-4, 11, 121. The phase can be stabilized at room temperature by exposing the sample to carbon mono~de f5]. Its existence is of tec~olo~cal importance because it contributes to the sloping of the a-y plateau isotherms in LaNi,H, during cycling [ 131 or leads to a splitting of the plateaux according to the reactions a-LaNi,H,,3
-
/-?-LaNi,H,,s -
#?-LaNi,H,,,
(lower plateau)
y-LaNi,H,,
(upper plateau)
(I)
(2) The exact role of that phase during hydrogen absorption and desorption, however, is not yet clear. Thermodynamic data (enthalpy of desorption, AH, and entropy of desorption, As) of low accuracy have been reported for reactions (1) and (2) from differential thermal analysis [9], heat conduction calorimetry [6] and volumetrically measured p-c isotherms [l, 7] on non-cycled samples. This prompted us to derive more accurate values for both cycled and non-cycled samples from gravimetrically measured p-c isotherms by using our newly installed high pressure, high temperature microbalance. The balance (type M25 D-P, Sartorius G.m.b.H., Glittingen, F.R.G.) is of a type similar to that described in refs. 14 and 15. It has two pans with symmetrical load cells (suspended beam with automatic electromagnetic compensation) with a m~imum weight capacity of 25 g, a sensitivity of 1 pg and operation ranges of 300-873 K and low3 mbar-150 bar. The heating system consists of a high *Present affiliation: Department de Physique de la Matikre Conderke. 0022-5088/91/S3.50
0 Elsevier Sequoia/P~nted
in The Netheriands
Llb
temperature double-tube furnace with a temperature control system (Type 410, Netzsch-Geratebau G.m.b.H., Selb, F.R.G.) that permits operation at constant temperature as well as thermal cycling between preset temperatures at desired heating and cooling rates (0.1-99.9 K mint, steps of 0.1 K min-‘, holding periods in steps down to 1 min). The pressure is measured by using a pressure gauge ( 10m3 mbar-1 bar) and pressure manometers (1-15 bar, l-60 bar). The change in mass of the sample is directly read out from the weighing system. Two types of LaNi, samples were measured. One sample (called “commercial” hereinafter) was obtained from the Ergenics Division of MPD Technology Corporation (Wyckoff, NJ, U.S.A.) with the designation HYSTOR-205. The stated purity was 99.8%. Part of that sample was activated at 300 K and 50 bar H, for 24 h. Thereafter it underwent cycling for about 30 absorption-desorption cycles between 1 and 60 bar H, and 300 and 423 K (10 times at 300 K between 1 and 60 bar, 15 times at 373 K between 1 and 60 bar, five times at 423 K between 1 and 60 bar). The other sample (called “as cast” hereinafter) was prepared at the stoichiometric composition by high frequency induction levitation melting of lanthanum (99.9%, Research Chemicals, Pflatz & Bauer Inc., Stamford, CT, U.S.A.) and nickel 56, 52 -
,
I
,
I
1 I I
,
LaNi5-H, .
(after 30 cycles1
0
46 -
44-
T= s
3632 -
P 5 Lx
26 -
E 24 b = $
zo-
16 -
I
I
I
2
3
4
5
6
7
composition (H/LoNQ
Fig. 1. Pressure-composition desorption.
isotherms for cycled LaNi,-H,
(commercial sample) l, absorption;
0,
Ll9
(99.998O~, Johnson
Matthey Chemicals Ltd., London, U.K.) under argon atmosphere. X-ray powder diffraction analysis (Co Ka radiation, silicon standard) confirmed that the samples were single phase, with refined lattice parameters for the commercial sample of a = 5.0201(4) A, c= 3.9773(5) A (uncycled) and a = 5.027( 1) A, c = 3.997( 1) A (cycled). The samples were charged in the microbalance by using high purity hydrogen (99.9999%, Polygaz, Geneva, Switzerland) and deuterium (99.7%, Polygaz, Geneva, Switzerland) gases. Pressure-composition isotherms for the activated commercial hydride sample are shown in Fig. 1. The plots show plateau splitting at about 3.5 hydrogen atoms per mole of LaNi, which is well defined compared to that observed previously by the volumetric method 11, 71. It is clearest for the 373 and 398 K isotherms, for which it amounts to about 4 and 5 bar Hi, pressure respectively. For the nonactivated hydride and deuteride samples and the as-cast sample (data not shown in Fig. 1) the splittings occur at the same hydrogen concentration. They decrease as the temperature decreases and virtually disappear at room temperature, in agreement with previous reports [ 1, 2,6, 11, 121 and a recently proposed phase diagram [7]. At given temperatures the plateau pressures of the deuteride are always higher than those of the hydride, in agreement with previous reports (see e.g. ref. 16). Those of the as-cast sample differ from those of the commercial sample, as expected from the different metal ratios and heat treatments of the samples. Thermodynamic constants for reactions (1) and (2) were derived for all samples from van? Hoff plots
In PH2=
As
AH
-R+iz
where PHzis the plateau pressure, R is the gas constant, T is the absolute temperature and AS and AH are the changes in entropy and enthalpy per mole of H, (D,) respectively. Examples of such plots are shown in Fig. 2 for the cycled hydride sample. Equilibrium pressures are defined at the middle of the plateau regions (at H : LaNi, = 2.5 and 4.5 for reactions ( 1) and (2) respectively). The results are listed in Table 1. The A,!? and AH values obtained from the present measurements are more accurate than, and differ si~ic~tly from, those reported previously. In particular, they show no significant difference in enthalpy between reactions ( 1) and (2), in contrast to previous work that indicates higher enthalpies for reaction (2) than for reaction (1). As to the entropies (not stated in previous work), our measurements indicate values slightly higher on average for reaction (2) than for reaction (l), at least in the temperature interval investigated. Assuming identical enthalpies for reactions ( 1) and (2), the entropy difference estimated from eqn. (3) amounts to about 6 J K-’ mol-’ H,. This is of the order expected for a possible change in configurational entropy of hydrogen in the meta host structure of LaNi,, as deduced from specific heat [ 171 and neutron diffraction [ 18, 191 measurements for y-LaNi,H,,. Neutron diffraction experiments on @-LaNi,H,., are in progress to test this hypothesis.
L20 TABLE 1 Enthalpy AH(kJ mol-’ H,) and entropy AS(J K-r mol-’ Hz) change for /?-LaNi,H(D),,, during absorption and desorption. Values are derived from linear least-squares fits to the experimental data according to eqn. (3) AHahs
A&es
A%,
A%,
- 31.5(4)
-31.7(4) -28.9(l) - 34.6( 9) - 32.6(4) -30 - 30.7(0.3) - 29.5( 1.0)
-111(l) - lOl( 1) - 106(2) - 117(4)
- 108.9(3) - 103.2(2) - 119(2) -111(2)
- 101.4(5.1)
- 102.0(4.1)
- 32.1(2) - 29.4(2) - 35.5(4) - 32.1(2) -33 -35 -39.5(1.2)
-111.4(g) - 98( 2) -108(l) -119.9(l)
-
- 138.3( 8.3)
- 137.3(6.2)
Lower plateau, reaction P-a Hydride (comm., cycled) Hydride (comm.) Deuteride (comm.) Hydride (cast) Hydride [l] Hydride [6] Hydride [7]
- 27.0( 3) - 27.9( 7) -33(l)
- 28.2( 1.4)
Upper plateau, reaction y-/3 Hydride (comm., cycled) Hydride (comm.) Deuteride (comm.) Hydride (cast) Hydride [l] Hydride [6] Hydride [7]
- 30.7( 1)
- 25.4(6) - 28.3(5) - 33.5(4)
-38.1(2.3)
114.6(8) 106.5(9) 122( 1) 113.1(3)
LaNi,-H, (after 30 cycles1
151 22
n 23
’ 2.4
’ 2.5
’ 26 000/T
’ 2.7
’ 2.8
’ 2.9
(K)
Fig. 2. Equilibrium pressure PCs during absorption (filled circles) and desorption (open circles) as a function of temperature for the upper (a, c) and lower (b, d) plateaux in cycled LaNi,-H, (commercial sample).
LZl
This work was supported by the Swiss National Science Foundation and the Swiss Federal Office of Energy. We thank Professor L. Schlapbach for supplying the “as-cast” sample and Mrs. B. Kiinzler for help with the drawings.
References 1 S. Ono, K. Nomura, E. Akiba and H. Uruno, J. Less-Cummon Met., 113 (1985) 113. ‘I’. Matsumoto and A. Matsushita, 3. Less-Common Met., 123 (1986) 135. E. Akiba, K. Nomura and S. Ono, J. Less-Common Mef., 129 ( 1987) 159. E. Akiba, H. Hayakawa, Y. Ishido, K. Nomura and S. Shin, Z. Whys. Gem. N.F., 163 (1989) 291. H. Hayakawa, K. Nomura, Y. Ishido, E. Akiba, S. Shin, H. Asano, E Izumi and N. Watanabe, J.
2 3 4 5
Less-CommonMet., 143(1988) 315. 6 M. L. Post, J. J. Murray and D. M. Grant, 2. Phys. Chem. N.F., 163 (1989) 135. 7 A. L. Shilov, M. E. Kost and N. T. Kuznetsov, J. Less-Common Met., 144 (1988) 23. 8 P. Dantzer, E. Orgaz and V. K. Sinha, Z. f%ys. Chem. N.F., 163 (1989) 141.
9 1. E. Nemirovskaya,
V. Z. Mordkovich,
Yu. K. Baychtok, A. M. Alekseyev and V. P. Mordovin,
Thermochim.
Actu, 160 (1990) 201. 10 L. Schlapbach (ed.), Topics in Applied Physics? Vol. 63, Hydrogen in Intermetallic Compounds
11 12
13 14 15
16 17
18 19
I,
Springer, Berlin, 1988. P. D. Goodell, J. Less-Common Met., PP( 1984) 1. K. Nomura, H. Uruno, S. Ono, H. Shinozuka and S. Suda, J. Less-Common Met., f07( 1985) 22 1, H. Uchida, K. Terao and Y. C. Huang, 2. Whys. Chem. N.F., 164 (1989) 1275. H. M. Lutz, R. Schmitt and F. Steffens, Thermochim. Acta, 24 (1978) 369. A. S. Pedersen, J. Kjoller, B. Larsen and B. Vigeholm, Int. J. Hydrogen Energy, 8 (1983) 205. A. Biris, R. V. Bucur, P. Ghete, E. Indrea and D. Lupu, J. Less-Common Met., 49( 1976) 477. D. Ohlendorf and H. E. Flotow, J. Chem. Phys., 73 (1980) 2937. W. E. Wallace, H. E. Flotow and D. Ohlendorf, J. Less-Common Met., 79 ( 198 1) 15 7. J. C. Achard, C. Lartigue, A. Percheron-Guegan, J. C. Mathieu, A. Pasture1 and E Tasset, J. LessCommon Met., 79(1981) 161.