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Electrical resistance variations with content of hydrogen in bulk MmNi4.5Al0.5
International Journal of Hydrogen Energy 27 (2002) 85–90
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Electrical resistance variations with content of hydrogen in bulk MmNi4:5Al0:5 I.P. Jain ∗ , Y.K. Vijay, Mohammed I.S. Abu Dakka Centre for Non-Conventional Energy Resources, University of Rajasthan, 14-Vigyyan Bhavan, Jaipur-302004, India.
Abstract Hydrogen absorption mechanism in bulk MmNi4:5 Al0:5 (having a composition La 9.17%, Ce 17.43%, Pr 1.86%, Nd 5.34%, Ni 62.92% and Al 3.28%) was investigated by measuring in situ electrical resistance under atmospheric pressure of hydrogen. It was observed that the resistance increases with an increase in hydrogen pressure. The e9ect of the number of cycles of hydrogen absorption on electrical properties of MmNi4:5 Al0:5 was also studied and P–C–T isotherms gave the hydrogen to metal ratio (H=M) value of 1.0 at 2:06 × 105 Pa hydrogen pressure. In the attempts made to relate the content of hydrogen with changes in resistance, it was found that resistances of MmNi4:5 Al0:5 increases with increasing the hydrogen content. ? 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. Keywords: Hydrogen content; Thin ;lm hydride; Hydrogen storage; P–C–T isotherms; Metal hydride
1. Introduction Hydrogen storage properties of MmNi5 have been extensively studied and has already found valuable technological applications because of its excellent hydrogen storage ability under moderate conditions. Introduction of interstitial hydrogen into a metallic lattice produces several consequences with respect to electrical resistance [1–8], and Krukowski [9] studied the change in relative electrical resistance of two Ni–Mn alloys as a function of hydrogen pressure. Baranowski et al. [10] have studied the electrical resistance measurements in Ni–Fe alloys, and found that hydrogen absorption activity starts above 20 k bar of hydrogen pressure, for Ni–Fe alloy with 0.23 and 0.50 at% of iron; it was found that changes in electrical resistances observed during hydride formation was mainly related to an increase in residual resistivity.
In the case of pure palladium, formation of the hydride phase is accompanied by a large increase in electrical resistance [6,11,7]. The electrical conductivity of the rare earth dihydrides has been studied by Stalinski [12,13] in granular form and by Heckman [14,15] in bar form and by Libowitz et al. [16] in single crystal form in CeH2 . As the hydrogen content of the rare earth hydride increases towards RH3 not only does the resistance increase drastically but even the temperature coeHcient changes its sign. For RH3 , the resistivity decreases with increasing temperature but with RH2 there is an increase in resistivity as temperature is increased according to Stalinski [12,13]. The above discussion deals with the variations in electrical resistance in various materials due to hydrogen absorption. However, studies related to electrical resistance variations in MmNi4:5 Al0:5 materials with the hydrogen content in the specimen have not been carried out so far. In the present work, P–C–T isotherms of MmNi4:5 Al0:5 have been studied in granular form and attempts have been made to relate changes in electrical resistance with respect to hydrogen content.
∗ Corresponding author. Tel.: +0091-141-701-602; fax: +0091141-510-880. E-mail address: [email protected] (I.P. Jain).
0360-3199/02/$ 20.00 ? 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. PII: S 0 3 6 0 - 3 1 9 9 ( 0 1 ) 0 0 0 6 0 - X
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Fig. 1. Schematic diagram to measure the electrical resistance and content of hydrogen in the specimen.
2. Experimental techniques 2.1. Fabrication of equipment for resistance measurements In the present work, an experimental technique has been developed for studying the change in resistance due to hydrogen absorption in the MmNi4:5 Al0:5 system. A schematic diagram of the experimental set-up is shown in Fig. 1. A special type of experimental set-up is required in the present study, because most of the experiments described in the literature have used metal wire or foil since rare earth metal hydrides have normally been found to be very brittle and diHcult to fabricate in pellet form for measurements of resistivity. A modi;ed reactor vessel has been designed for containing the material by providing an electrode with ceramic insulation for in situ electrical resistance measurements with changes in hydrogen pressure in order to give information on the hydriding process. Hydrogen can be introduced at high pressure to the material kept in reactor via a valve. A water displacement method has been used to measure contents of hydrogen in the alloy from which H=M and changes in resistance could be measured. 2.2. Activation of MmNi4:5 Al0:5 samples In the present study, 20 gm sample of MmNi4:5 Al0:5 alloy as obtained from Japan Metals and Chemical Co. Ltd., Tokyo, Japan, where the company had already characterised the material for composition and homogeneity. Samples were ;rst evacuated to 1:33×10−1 Pa in vacuo, then Kushed with 99.95% of pure hydrogen at 1:01 × 105 Pa pressure and again evacuated to 1:33 × 10−1 Pa in vacuo and then heated to 403 K for 2 h; hydrogen was introduced after cooling and again heated to 403 K for 2 h in a hydrogen environment before evacuating to 1:33 × 10−1 Pa in vacuo. Series of introducing hydrogen, heating and evacuating were carried out for 4 cycles before activation processes were completed.
In order to calculate hydrogen to metal ratio (H=M) and wt% of hydrogen in MmNi4:5 Al0:5 alloy, the required temperature for hydrogen absorption was 333 K and for desorption it was 403 K. Hence, each point in Figs. 3– 6 is calculated accordingly.
3. Results and discussions 3.1. Resistance of MmNi4:5 Al0:5 with hydrogen pressure Fig. 2, shows an example of the variation of resistance with equilibrium hydrogen pressure and illustrates that there are decreases in resistance with introductions of hydrogen pressure ranging from 2:06 × 105 Pa to 3:4 × 105 Pa. At 3:4 × 105 Pa hydrogen pressure, values of resistance start increasing gradually. Each point in Fig. 2 represents a consecutive number of hydrogen absorption cycles, i.e. the ;rst point shows the ;rst cycle of hydrogen absorption, and the second represents the second cycle of hydrogen absorption and so on. The initial decrease in resistance can be explained on a basis of compression of the specimen due to hydrogen pressure as initially the material was in powder form and the application of pressure compression results in decreasing inter-particle distance, which is responsible for the decrease in resistance. After 16 cycles, the material becomes stabilised and at this point the resistance of the specimen increases with an increase in hydrogen pressure which can be attributed to the transfer of electron to hydrogen from the conduction band of MmNi4:5 Al0:5 similar to the results of Adachi et al. [17–19] for LaNi5 ;lms where in the absorption cycles the hydrogen atoms that dissolved in LaNi5 also accept electrons from LaNi5 and become hydrogen anions (H− ) resulting in the decrease of the number of electrons in the conduction band thereby increasing the resistivity of LaNi5 ;lm. In the hydrogen pressure range 3:4 × 105 –4:1 × 105 Pa, the resistance becomes almost constant; this Kat constant pressure part of the ;gure, called the “plateau” region represents the pressure of hydrogen in equilibrium with metal.
I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
87
Fig. 2. Variation of resistance with hydrogen pressure on MmNi4:5 Al0:5 specimen, for the activation processes of the specimen.
Fig. 3. Variation of hydrogen to metal (H=M) ratio with the resistance of MmNi4:5 Al0:5 .
In the hydrogen desorption process, the dissolved hydrogen anions are removed as hydrogen molecules and they leave their electrons in the conduction band of the LaNi5 . Since the number of electrons in the conduction band of the alloy increases, the resistivity of the ;lm decreases. 3.2. H=M for MmNi4:5 Al0:5 Fig. 3 shows the variation of the H=M ratio with the resistance of MmNi4:5 Al0:5 specimen, according to the increase in the resistance of the material with the increase in the H=M ratio, where H is hydrogen
and M is MmNi4:5 Al0:5 . The H=M ratio shown in Fig. 3 has been studied with hydrogen pressure in the region 3:4 × 105 – 4:8 × 105 Pa, which represents the -phase region of the P–C–T isotherm of the material. In the -phase region, the pressure of hydrogen remains in equilibrium with the metal under study, and hence it is the most important region of the specimen. 3.3. Variations of wt% of hydrogen in MmNi4:5 Al0:5 Fig. 4 relates the variation of resistance at room temperature with wt% hydrogen in MmNi4:5 Al0:5 . It is clear from
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I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
Fig. 4. Resistance as a function of wt% of hydrogen in MmNi4:5 Al0:5 .
Fig. 5. Variation in the resistance of MmNi4:5 Al0:5 with the number of hydrogen absorption–desorption cycles at (2.06 and 1.03) ×106 Pa hydrogen pressure.
Fig. 4 that the wt% of hydrogen in the material increases with hydrogen pressure over the range (3.4 – 4:8) × 105 Pa and corresponds to increase in the resistance of the material and to the content of hydrogen in the material. Such a type of investigation of variations of electrical properties on hydrogen content has been carried out by Adachi et al. [17–19] on LaNi5 thin ;lms and by Sakaguchi et al. [20] in LaCo5 ;lms. Recently, Jain, et al. [21] have studied the hydrogen absorption in Al doped MmNi5 alloy with di9erent misch metal compositions. Hydrogen content in the material has been measured by a water displacement method. Hence, changes of resistance of the material due to hydrogen absorption are known at high pressure, contents of
hydrogen in the material at a particular value of resistance can be known. 3.4. Resistance of MmNi4:5 Al0:5 with number of cycles Fig. 5 shows variations of the resistance of MmNi4:5 Al0:5 with the number of hydrogen absorption—desorption cycles at 300 and 150 psi hydrogen pressure, respectively. This ;gure gives an idea that, with constant hydrogen pressure that the resistance increases with a number of hydrogen absorption cycles, and that it increases further with an increase of the hydrogen pressure, due to a further increase in the content of hydrogen in the specimen.
I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
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Fig. 6. H=M vs. hydrogen pressure for MmNi4:5 Al0:5 at room temperature.
3.5. Variations of H=M ratio with hydrogen pressure Fig. 6, illustrates variations of H=M ratio with hydrogen pressure for MmNi4:5 Al0:5 . It is clear from Fig. 6 that the H=M ratio initially increases slowly with the introduction of hydrogen of (0 –2:06) × 105 Pa pressure. Then, at 2:06 × 105 Pa equilibrium hydrogen pressure, a plateau region appears which corresponds to an increase of H=M concentration without a corresponding change in pressure. The maximum value for this increase of H=M was found to be 1.0 at 2:06 × 105 Pa which represents the corresponding equilibrium pressure of hydrogen. Above 2:06 × 105 Pa, the purely -phase region appears and the H=M concentration again increases with the increasing hydrogen pressure. In this highest pressure region as discussed above, it follows that the resistance of MmNi4:5 Al0:5 also increases with increasing pressure in the -phase region as illustrated in Fig. 3. Conclusions 1. The resistance of powdered MmNi4:5 Al0:5 decreases due to hydrogen absorption in the pressure region (2.06 – 3:4) × 105 Pa, and then increases in the pressure region (3.4 – 4:8) × 105 Pa. 2. The H=M value increases with the increase in the resistance of the material in the hydrogen pressure region (3.4 – 4:8) × 105 Pa. 3. The wt% of the hydrogen in the material increases with the increase in the resistance of the material due to hydrogen absorption. 4. The change in the resistance of the material is a measure of the hydrogen content in the material.
5. The resistance of MmNi4:5 Al0:5 increases with the number of hydrogen absorption cycle at ;xed hydrogen pressures. Acknowledgements The authors are grateful to the Ministry of NonConventional Energy Sources, Government of India for providing ;nancial support for this work. One of us, Mohammed I.S. Abu Dakka is thankful to Al-Azhar, University of Gaza, Palestine for ;nancial support to carry out this research work at the University of Rajasthan, Jaipur, India. References [1] Alefeld G, Volkl J. (eds). Topics in Applied Physics, vol. 29. New York: Springer Verlag, 1978. [2] Baranowski B, Wisniewski R. Bull Acad Pol Sci 1966;14:273. [3] Baranowski B, Bochanska K, Majchrzak S. Rocz Chem 1967;41:2071. [4] Stroka A, Freilich A. Rocz Chem 1970;44:2271. [5] Szafranski AW, Baranowski B. Phys Status Solidi A 1972;9:425. [6] Baranowski B, Lewis FA, Majuhrzaks S, Wisniewski R. J Chem Soc Farady Trans 1972;168:653. [7] Szafranski A. Electrical and thermal conductivity of some alloys Pol + H, Pd + Ag+H, Pd+Au+H. Thesis, Warsaw, 1976 (in polish). [8] Baranowski B, Majchrzak S, Flanagan TB. J Phys Chem 1970;74:4299. [9] Krukowski M, Baranowski B. J Less-Common Met 1976;49:385. [10] Baranowski B, Filipek S. Rocz Chem 1973;47:2165. [11] Lewis FA. The palladium hydrogen system. New York, London: Academic Press, p. 1967. [12] Stalinski B. Bull Acad Sci (Poland) 1957;5:100. [13] Stalinski B. Bull Acad Sci (Poland) 1959;7:269.
90 [14] [15] [16] [17]
I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
Heckman R. J Chem Phys 1964;40:2958. Heckman R. J Chem Phys 1967;46:2158. Libowitz GG, Pack JG. J Phys Chem 1969;50:3557. Adachi G, Niki K, Shiokawa J. J Less-Common Met 1981;81:345. [18] Adachi G, Niki K, Nagai H, Shiokawa J. J Less-Common Met 1982;88:213.
[19] Adachi G, Sakaguchi H, Niki K, Nagai H, Shiokawa J. J Less-Common Met 1985;108:107. [20] Sakaguchi H, Yagi Y, Taniguchi N, Adachi G, Shiokawa J. J Less-Common Met 1987;135:137– 46. [21] Jain IP, Abu Dakka MIS, Vijay YK. Int J Hydrogen Energy 2000;25:663.
www.elsevier.com/locate/ijhydene
Electrical resistance variations with content of hydrogen in bulk MmNi4:5Al0:5 I.P. Jain ∗ , Y.K. Vijay, Mohammed I.S. Abu Dakka Centre for Non-Conventional Energy Resources, University of Rajasthan, 14-Vigyyan Bhavan, Jaipur-302004, India.
Abstract Hydrogen absorption mechanism in bulk MmNi4:5 Al0:5 (having a composition La 9.17%, Ce 17.43%, Pr 1.86%, Nd 5.34%, Ni 62.92% and Al 3.28%) was investigated by measuring in situ electrical resistance under atmospheric pressure of hydrogen. It was observed that the resistance increases with an increase in hydrogen pressure. The e9ect of the number of cycles of hydrogen absorption on electrical properties of MmNi4:5 Al0:5 was also studied and P–C–T isotherms gave the hydrogen to metal ratio (H=M) value of 1.0 at 2:06 × 105 Pa hydrogen pressure. In the attempts made to relate the content of hydrogen with changes in resistance, it was found that resistances of MmNi4:5 Al0:5 increases with increasing the hydrogen content. ? 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. Keywords: Hydrogen content; Thin ;lm hydride; Hydrogen storage; P–C–T isotherms; Metal hydride
1. Introduction Hydrogen storage properties of MmNi5 have been extensively studied and has already found valuable technological applications because of its excellent hydrogen storage ability under moderate conditions. Introduction of interstitial hydrogen into a metallic lattice produces several consequences with respect to electrical resistance [1–8], and Krukowski [9] studied the change in relative electrical resistance of two Ni–Mn alloys as a function of hydrogen pressure. Baranowski et al. [10] have studied the electrical resistance measurements in Ni–Fe alloys, and found that hydrogen absorption activity starts above 20 k bar of hydrogen pressure, for Ni–Fe alloy with 0.23 and 0.50 at% of iron; it was found that changes in electrical resistances observed during hydride formation was mainly related to an increase in residual resistivity.
In the case of pure palladium, formation of the hydride phase is accompanied by a large increase in electrical resistance [6,11,7]. The electrical conductivity of the rare earth dihydrides has been studied by Stalinski [12,13] in granular form and by Heckman [14,15] in bar form and by Libowitz et al. [16] in single crystal form in CeH2 . As the hydrogen content of the rare earth hydride increases towards RH3 not only does the resistance increase drastically but even the temperature coeHcient changes its sign. For RH3 , the resistivity decreases with increasing temperature but with RH2 there is an increase in resistivity as temperature is increased according to Stalinski [12,13]. The above discussion deals with the variations in electrical resistance in various materials due to hydrogen absorption. However, studies related to electrical resistance variations in MmNi4:5 Al0:5 materials with the hydrogen content in the specimen have not been carried out so far. In the present work, P–C–T isotherms of MmNi4:5 Al0:5 have been studied in granular form and attempts have been made to relate changes in electrical resistance with respect to hydrogen content.
∗ Corresponding author. Tel.: +0091-141-701-602; fax: +0091141-510-880. E-mail address: [email protected] (I.P. Jain).
0360-3199/02/$ 20.00 ? 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. PII: S 0 3 6 0 - 3 1 9 9 ( 0 1 ) 0 0 0 6 0 - X
86
I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
Fig. 1. Schematic diagram to measure the electrical resistance and content of hydrogen in the specimen.
2. Experimental techniques 2.1. Fabrication of equipment for resistance measurements In the present work, an experimental technique has been developed for studying the change in resistance due to hydrogen absorption in the MmNi4:5 Al0:5 system. A schematic diagram of the experimental set-up is shown in Fig. 1. A special type of experimental set-up is required in the present study, because most of the experiments described in the literature have used metal wire or foil since rare earth metal hydrides have normally been found to be very brittle and diHcult to fabricate in pellet form for measurements of resistivity. A modi;ed reactor vessel has been designed for containing the material by providing an electrode with ceramic insulation for in situ electrical resistance measurements with changes in hydrogen pressure in order to give information on the hydriding process. Hydrogen can be introduced at high pressure to the material kept in reactor via a valve. A water displacement method has been used to measure contents of hydrogen in the alloy from which H=M and changes in resistance could be measured. 2.2. Activation of MmNi4:5 Al0:5 samples In the present study, 20 gm sample of MmNi4:5 Al0:5 alloy as obtained from Japan Metals and Chemical Co. Ltd., Tokyo, Japan, where the company had already characterised the material for composition and homogeneity. Samples were ;rst evacuated to 1:33×10−1 Pa in vacuo, then Kushed with 99.95% of pure hydrogen at 1:01 × 105 Pa pressure and again evacuated to 1:33 × 10−1 Pa in vacuo and then heated to 403 K for 2 h; hydrogen was introduced after cooling and again heated to 403 K for 2 h in a hydrogen environment before evacuating to 1:33 × 10−1 Pa in vacuo. Series of introducing hydrogen, heating and evacuating were carried out for 4 cycles before activation processes were completed.
In order to calculate hydrogen to metal ratio (H=M) and wt% of hydrogen in MmNi4:5 Al0:5 alloy, the required temperature for hydrogen absorption was 333 K and for desorption it was 403 K. Hence, each point in Figs. 3– 6 is calculated accordingly.
3. Results and discussions 3.1. Resistance of MmNi4:5 Al0:5 with hydrogen pressure Fig. 2, shows an example of the variation of resistance with equilibrium hydrogen pressure and illustrates that there are decreases in resistance with introductions of hydrogen pressure ranging from 2:06 × 105 Pa to 3:4 × 105 Pa. At 3:4 × 105 Pa hydrogen pressure, values of resistance start increasing gradually. Each point in Fig. 2 represents a consecutive number of hydrogen absorption cycles, i.e. the ;rst point shows the ;rst cycle of hydrogen absorption, and the second represents the second cycle of hydrogen absorption and so on. The initial decrease in resistance can be explained on a basis of compression of the specimen due to hydrogen pressure as initially the material was in powder form and the application of pressure compression results in decreasing inter-particle distance, which is responsible for the decrease in resistance. After 16 cycles, the material becomes stabilised and at this point the resistance of the specimen increases with an increase in hydrogen pressure which can be attributed to the transfer of electron to hydrogen from the conduction band of MmNi4:5 Al0:5 similar to the results of Adachi et al. [17–19] for LaNi5 ;lms where in the absorption cycles the hydrogen atoms that dissolved in LaNi5 also accept electrons from LaNi5 and become hydrogen anions (H− ) resulting in the decrease of the number of electrons in the conduction band thereby increasing the resistivity of LaNi5 ;lm. In the hydrogen pressure range 3:4 × 105 –4:1 × 105 Pa, the resistance becomes almost constant; this Kat constant pressure part of the ;gure, called the “plateau” region represents the pressure of hydrogen in equilibrium with metal.
I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
87
Fig. 2. Variation of resistance with hydrogen pressure on MmNi4:5 Al0:5 specimen, for the activation processes of the specimen.
Fig. 3. Variation of hydrogen to metal (H=M) ratio with the resistance of MmNi4:5 Al0:5 .
In the hydrogen desorption process, the dissolved hydrogen anions are removed as hydrogen molecules and they leave their electrons in the conduction band of the LaNi5 . Since the number of electrons in the conduction band of the alloy increases, the resistivity of the ;lm decreases. 3.2. H=M for MmNi4:5 Al0:5 Fig. 3 shows the variation of the H=M ratio with the resistance of MmNi4:5 Al0:5 specimen, according to the increase in the resistance of the material with the increase in the H=M ratio, where H is hydrogen
and M is MmNi4:5 Al0:5 . The H=M ratio shown in Fig. 3 has been studied with hydrogen pressure in the region 3:4 × 105 – 4:8 × 105 Pa, which represents the -phase region of the P–C–T isotherm of the material. In the -phase region, the pressure of hydrogen remains in equilibrium with the metal under study, and hence it is the most important region of the specimen. 3.3. Variations of wt% of hydrogen in MmNi4:5 Al0:5 Fig. 4 relates the variation of resistance at room temperature with wt% hydrogen in MmNi4:5 Al0:5 . It is clear from
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I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
Fig. 4. Resistance as a function of wt% of hydrogen in MmNi4:5 Al0:5 .
Fig. 5. Variation in the resistance of MmNi4:5 Al0:5 with the number of hydrogen absorption–desorption cycles at (2.06 and 1.03) ×106 Pa hydrogen pressure.
Fig. 4 that the wt% of hydrogen in the material increases with hydrogen pressure over the range (3.4 – 4:8) × 105 Pa and corresponds to increase in the resistance of the material and to the content of hydrogen in the material. Such a type of investigation of variations of electrical properties on hydrogen content has been carried out by Adachi et al. [17–19] on LaNi5 thin ;lms and by Sakaguchi et al. [20] in LaCo5 ;lms. Recently, Jain, et al. [21] have studied the hydrogen absorption in Al doped MmNi5 alloy with di9erent misch metal compositions. Hydrogen content in the material has been measured by a water displacement method. Hence, changes of resistance of the material due to hydrogen absorption are known at high pressure, contents of
hydrogen in the material at a particular value of resistance can be known. 3.4. Resistance of MmNi4:5 Al0:5 with number of cycles Fig. 5 shows variations of the resistance of MmNi4:5 Al0:5 with the number of hydrogen absorption—desorption cycles at 300 and 150 psi hydrogen pressure, respectively. This ;gure gives an idea that, with constant hydrogen pressure that the resistance increases with a number of hydrogen absorption cycles, and that it increases further with an increase of the hydrogen pressure, due to a further increase in the content of hydrogen in the specimen.
I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
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Fig. 6. H=M vs. hydrogen pressure for MmNi4:5 Al0:5 at room temperature.
3.5. Variations of H=M ratio with hydrogen pressure Fig. 6, illustrates variations of H=M ratio with hydrogen pressure for MmNi4:5 Al0:5 . It is clear from Fig. 6 that the H=M ratio initially increases slowly with the introduction of hydrogen of (0 –2:06) × 105 Pa pressure. Then, at 2:06 × 105 Pa equilibrium hydrogen pressure, a plateau region appears which corresponds to an increase of H=M concentration without a corresponding change in pressure. The maximum value for this increase of H=M was found to be 1.0 at 2:06 × 105 Pa which represents the corresponding equilibrium pressure of hydrogen. Above 2:06 × 105 Pa, the purely -phase region appears and the H=M concentration again increases with the increasing hydrogen pressure. In this highest pressure region as discussed above, it follows that the resistance of MmNi4:5 Al0:5 also increases with increasing pressure in the -phase region as illustrated in Fig. 3. Conclusions 1. The resistance of powdered MmNi4:5 Al0:5 decreases due to hydrogen absorption in the pressure region (2.06 – 3:4) × 105 Pa, and then increases in the pressure region (3.4 – 4:8) × 105 Pa. 2. The H=M value increases with the increase in the resistance of the material in the hydrogen pressure region (3.4 – 4:8) × 105 Pa. 3. The wt% of the hydrogen in the material increases with the increase in the resistance of the material due to hydrogen absorption. 4. The change in the resistance of the material is a measure of the hydrogen content in the material.
5. The resistance of MmNi4:5 Al0:5 increases with the number of hydrogen absorption cycle at ;xed hydrogen pressures. Acknowledgements The authors are grateful to the Ministry of NonConventional Energy Sources, Government of India for providing ;nancial support for this work. One of us, Mohammed I.S. Abu Dakka is thankful to Al-Azhar, University of Gaza, Palestine for ;nancial support to carry out this research work at the University of Rajasthan, Jaipur, India. References [1] Alefeld G, Volkl J. (eds). Topics in Applied Physics, vol. 29. New York: Springer Verlag, 1978. [2] Baranowski B, Wisniewski R. Bull Acad Pol Sci 1966;14:273. [3] Baranowski B, Bochanska K, Majchrzak S. Rocz Chem 1967;41:2071. [4] Stroka A, Freilich A. Rocz Chem 1970;44:2271. [5] Szafranski AW, Baranowski B. Phys Status Solidi A 1972;9:425. [6] Baranowski B, Lewis FA, Majuhrzaks S, Wisniewski R. J Chem Soc Farady Trans 1972;168:653. [7] Szafranski A. Electrical and thermal conductivity of some alloys Pol + H, Pd + Ag+H, Pd+Au+H. Thesis, Warsaw, 1976 (in polish). [8] Baranowski B, Majchrzak S, Flanagan TB. J Phys Chem 1970;74:4299. [9] Krukowski M, Baranowski B. J Less-Common Met 1976;49:385. [10] Baranowski B, Filipek S. Rocz Chem 1973;47:2165. [11] Lewis FA. The palladium hydrogen system. New York, London: Academic Press, p. 1967. [12] Stalinski B. Bull Acad Sci (Poland) 1957;5:100. [13] Stalinski B. Bull Acad Sci (Poland) 1959;7:269.
90 [14] [15] [16] [17]
I.P. Jain et al. / International Journal of Hydrogen Energy 27 (2002) 85–90
Heckman R. J Chem Phys 1964;40:2958. Heckman R. J Chem Phys 1967;46:2158. Libowitz GG, Pack JG. J Phys Chem 1969;50:3557. Adachi G, Niki K, Shiokawa J. J Less-Common Met 1981;81:345. [18] Adachi G, Niki K, Nagai H, Shiokawa J. J Less-Common Met 1982;88:213.
[19] Adachi G, Sakaguchi H, Niki K, Nagai H, Shiokawa J. J Less-Common Met 1985;108:107. [20] Sakaguchi H, Yagi Y, Taniguchi N, Adachi G, Shiokawa J. J Less-Common Met 1987;135:137– 46. [21] Jain IP, Abu Dakka MIS, Vijay YK. Int J Hydrogen Energy 2000;25:663.