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LaNi5 film for hydrogen separation
Journal
of the Less-Common
Metals,
97(1984)
L9
L9-LlO
Letter
LaNi, film for hydrogen separation
GIN-YA ADACHI,
HIROSHI NAGAI and JIRO SHIOKAWA
Department of Applied Osaka 565 (Japan)
Chemistry,
Faculty of Engineering,
Osaka University,
Yamadaoka,
Suita,
(Received October 26,1983)
Palladium thin films are considered to be excetlent membranes for the separation of hydrogen. However, such films are costly and require a high operating temperature. Replacement of the palladium by a cheaper metal or alloy would be very beneficial for the hydrogen industries. Therefore we have investigated the deposition of LaNi, thin films on porous stainless steel substrates and have succeeded in obtaining a suitable module for hydrogen separation. The preparation of LaNi, thin films on quartz substrates and the effects of hydrogen absorption-desorption cycles on the electrical properties of such films have been reported in previous publications [l, 21. It was found that the films did not become pulverized even after 150 cycles. Therefore LaNi, thin films can be used as hydrogen separators. Porous stainless steel discs 3 mm thick and 5 mm in diameter, which were made by sintering fine (1 pm in diameter) stainless steel powder (SW 304), were employed as substrates. The flash evaporation technique was used to deposit the LaNi, films on the substrates [l, 21. The evaporation process was repeated until the substrate pores were completely blocked. The final film thicknesses were about 10 pm. Figure 1 is a typical scanning electron micrograph of the film surface. The disc was inserted into the apparatus shown in Fig. 2. The film, which was able to resist a pressure of more than 9 atm, was activated by performing ten hydrogenation-dehydrogenation cycles at 90 “C. An I-I,-Ar gas mixture was then passed through the apparatus and was collected in gas samplers at the outlet. The gas samples were analysed using a Hitachi RMU-GE mass spectrometer. The rates of permeation of the gas through the film are shown in Table 1. Pinholes or small cracks are unlikely to be present in the films during hydrogen permeation because the hydrogen flow stopped immediately on increasing the temperature of the film to 90 “C. The tendency of the rate of permeation to decrease with increasing temperature is the reverse of what is observed with palladium [S]. This is probably because the permeation mechanism in LaNi, is related to the hydrogenation-dehydrogenation process, whereas in palladium films hydrogen permeates through the lattice interstices. oozz-5088/84/$3.00
$21Elsevier Sequoia/Printed
in The Netherlands
LlO
Pressure
Gas inlet
Bourdon Vacuum
Gauge
Gauge
-B
,
-
I
Vacuum
60 w
Gas Sampler
vacuum
LaNi5 deposited on metal filter
Fig. 1. Scanning electron micrograph of an LaNi, film on a stainless steel filter. Fig. 2. Apparatus for investigating
gas permeation.
TABLE 1 Performance
of the LaNi, films
Gas composition
Primary pressure
(mol.%)
(atm)
of film (“C)
50.OH,-50.OAr
3
55b
0.91
80.OH,-20.OAr
3
9
60 40b 25 85 60 47b 40 50b
0 6.5 188 0 0 1.43 252 0.47
2 3 9
39 39 50b
17.1 55.3 1.45
7
8O.OH,-20.ON,
Temperature
-
Rate of permeation” (x10-6m3h-‘)
Hydrogen content after treatment (mol.%) 52.6
80.8 80.1
80.8 80.1 80.8 81.6 81.9 81.6
“Reduced to standard temperature and pressure. bTemperature at which hydrogen starts to penetrate the film.
The film can withstand more than 42 hydrogen pressurization-evacuation cycles. Hydrogen does not permeate the film at temperatures of 60 “C or above. The hydrogen flow through the film can therefore be controlled by increasing and decreasing the temperature. The applicability of LaNi, films to the purification of hydrogen and the separation of hydrogen from gaseous mixtures such as HZ-N,, H,-CH,, H,C,H, and HZ-CO is now being investigated. 1 2 3
G.-Y. Adachi, K.-I. Niki and J. Shiokawa, J. Less-Common Met., 81(1981) 345. G. Adachi, K. Niki, H. Nagai and J. Shiokawa, J. Less-Common Met., 88(1982) 213. M. Taguma, M. Tada and Y. C. Huang, Proc. Fuc. Eng. Tokai Univ., (1) (1969) 53.
of the Less-Common
Metals,
97(1984)
L9
L9-LlO
Letter
LaNi, film for hydrogen separation
GIN-YA ADACHI,
HIROSHI NAGAI and JIRO SHIOKAWA
Department of Applied Osaka 565 (Japan)
Chemistry,
Faculty of Engineering,
Osaka University,
Yamadaoka,
Suita,
(Received October 26,1983)
Palladium thin films are considered to be excetlent membranes for the separation of hydrogen. However, such films are costly and require a high operating temperature. Replacement of the palladium by a cheaper metal or alloy would be very beneficial for the hydrogen industries. Therefore we have investigated the deposition of LaNi, thin films on porous stainless steel substrates and have succeeded in obtaining a suitable module for hydrogen separation. The preparation of LaNi, thin films on quartz substrates and the effects of hydrogen absorption-desorption cycles on the electrical properties of such films have been reported in previous publications [l, 21. It was found that the films did not become pulverized even after 150 cycles. Therefore LaNi, thin films can be used as hydrogen separators. Porous stainless steel discs 3 mm thick and 5 mm in diameter, which were made by sintering fine (1 pm in diameter) stainless steel powder (SW 304), were employed as substrates. The flash evaporation technique was used to deposit the LaNi, films on the substrates [l, 21. The evaporation process was repeated until the substrate pores were completely blocked. The final film thicknesses were about 10 pm. Figure 1 is a typical scanning electron micrograph of the film surface. The disc was inserted into the apparatus shown in Fig. 2. The film, which was able to resist a pressure of more than 9 atm, was activated by performing ten hydrogenation-dehydrogenation cycles at 90 “C. An I-I,-Ar gas mixture was then passed through the apparatus and was collected in gas samplers at the outlet. The gas samples were analysed using a Hitachi RMU-GE mass spectrometer. The rates of permeation of the gas through the film are shown in Table 1. Pinholes or small cracks are unlikely to be present in the films during hydrogen permeation because the hydrogen flow stopped immediately on increasing the temperature of the film to 90 “C. The tendency of the rate of permeation to decrease with increasing temperature is the reverse of what is observed with palladium [S]. This is probably because the permeation mechanism in LaNi, is related to the hydrogenation-dehydrogenation process, whereas in palladium films hydrogen permeates through the lattice interstices. oozz-5088/84/$3.00
$21Elsevier Sequoia/Printed
in The Netherlands
LlO
Pressure
Gas inlet
Bourdon Vacuum
Gauge
Gauge
-B
,
-
I
Vacuum
60 w
Gas Sampler
vacuum
LaNi5 deposited on metal filter
Fig. 1. Scanning electron micrograph of an LaNi, film on a stainless steel filter. Fig. 2. Apparatus for investigating
gas permeation.
TABLE 1 Performance
of the LaNi, films
Gas composition
Primary pressure
(mol.%)
(atm)
of film (“C)
50.OH,-50.OAr
3
55b
0.91
80.OH,-20.OAr
3
9
60 40b 25 85 60 47b 40 50b
0 6.5 188 0 0 1.43 252 0.47
2 3 9
39 39 50b
17.1 55.3 1.45
7
8O.OH,-20.ON,
Temperature
-
Rate of permeation” (x10-6m3h-‘)
Hydrogen content after treatment (mol.%) 52.6
80.8 80.1
80.8 80.1 80.8 81.6 81.9 81.6
“Reduced to standard temperature and pressure. bTemperature at which hydrogen starts to penetrate the film.
The film can withstand more than 42 hydrogen pressurization-evacuation cycles. Hydrogen does not permeate the film at temperatures of 60 “C or above. The hydrogen flow through the film can therefore be controlled by increasing and decreasing the temperature. The applicability of LaNi, films to the purification of hydrogen and the separation of hydrogen from gaseous mixtures such as HZ-N,, H,-CH,, H,C,H, and HZ-CO is now being investigated. 1 2 3
G.-Y. Adachi, K.-I. Niki and J. Shiokawa, J. Less-Common Met., 81(1981) 345. G. Adachi, K. Niki, H. Nagai and J. Shiokawa, J. Less-Common Met., 88(1982) 213. M. Taguma, M. Tada and Y. C. Huang, Proc. Fuc. Eng. Tokai Univ., (1) (1969) 53.