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Amorphous metal-hydrogen alloys prepared by mechano-chemical reaction
J O U R N A L OF
Journal of Non-Crystalline Solids 150 (1992) 452-455
North-.o.and
ml"t
Igl
Amorphous metal-hydrogen alloys prepared by mechano-chemical reaction Kazuto Tokumitsu Department of Materials Science, Unicersityof Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan
The mechano-chemical formation of crystalline and amorphous hydrides is described. Niobium transformed into 13-Nb hydride by milling with liquid normal-heptane. Chromium and manganese were transformed into amorphous hydrides. The hydrocarbon served as the source of hydrogen atoms through a dehydrogenation reaction.
1. Introduction
2. Experimental procedure
Metal hydrides are classified into three categories [1]. The first category is the saline hydride, the second is the covalent hydride and the third is the metallic hydride. The binding force between metal and hydrogen atoms is weak compared with that in saline and covalent hydrides and so these hydrides have large non-stoichiometric regions, even if indicated as M H or MH2. Metal hydrides have usually been prepared by the H 2 gas charging method. This method is based on the adsorption and the dissociation of hydrogen gas, but high temperatures and pressures [2] or a complicated activation treatment are needed [3]. However, the supply of hydrogen is not necessarily restricted to hydrogen molecules but is possible through the dehydrogenation of hydrocarlaons. Paraffins and naphthenes are preferred as the source of hydrogen for the reason that they are saturated and contain no oxygen atoms. This p a p e r presents the formation of crystalline and amorphous metal hydrides by the mechano-chemical reaction between metals and hydrocarbons.
2.1. Sample preparation
Correspondence to: Dr K. Tokumitsu, Department of Materials Science, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan. Tel: +81-338 12 2111. Telefax: +81-338 15 8363.
Milling was carried out using a rotating ballmilling apparatus. The vial containing a sample was cylindrical, 120 mm in diameter and 70 mm in height. It was made of SUS304 alloy. The balls were made of hard alloy ( W C - C o ) and their diameter was 10 mm. The purity of the metal powders used was 99.9 at.% and their particle size was about 50 I~m. Normal heptane (C6H14) , which is a saturated chain-like hydrocarbon, was used as the source of hydrogen. The metal powders were put into the vial with the liquid hydrocarbon and balls. The sample was removed after a constant milling time and the milling was carried out at room temperature. A little alkyl-naphthalene oil was added to prevent the oxidation of the powders and the ignition of the hydrocarbon. 2.2. Characterization Changes in the structures of the metal powders were measured by X-ray diffraction analysis (Mo K s ) and their morphology by scanning electron microscopy. The composition of the powders was measured by inductively coupled plasma spectroscopy (ICP) and the transformation of the hydrocarbon by high performance liquid chromatography (HPLC).
0022-3093/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
K. Tokumitsu / Amorphous metal-hydrogen alloys
453
3. Results 1
3.1. Formation of a crystalline hydride: N b / heptane system Figure 1 shows the change in the X-ray diffraction pattern of niobium with milling time. The structure of niobium is body centered cubic and the (110), (100) and (211) planes are observed. However, the shoulders appeared on the low angle sides of each peak after milling for 300 h and grew with increasing milling time. The peaks for pure niobium disappeared after 1000 h. The new diffraction peaks were identified as being due to [3-Nb and hydride (NbH089) [4]. It has been reported that 13-Nb hydride is stable at room temperature [5]. An impurity of 1.80 at.% Fe was contained in the powders, as shown by ICP measurements. This impurity originates from the SUS304 vial.
3.2. Formation of amorphous hydrides: Cr,Mn / heptane system Figure 2 shows the change in the X-ray diffraction pattern of chromium with milling time. The peaks became broad by contrast with the result
[ - - ~
Nb
_~ "~ ~1 >
10h 300h
_ r~,.___~_~ 400h
Cr
i 700h
lmh
2 0 / deg.
Fig. 2. Change in the X-ray diffraction pattern of Cr powder with milling time.
for niobium. A halo pattern was obtained after milling for 1000 h, which is characteristic of an amorphous phase. The impurity from the vial may have some effect on the amorphization, but chromium forms a solid solution with iron [6]. The hydrogen content was determined as CrHoA 7 by the inert gas fusion method, but it was difficult to obtain the precise value. Figure 3 shows the results of SEM observations and EDX measurements. The particle size decreased from about 50 I~m to about 2 p~m and iron was detected in the milled powders. Figure 4 shows the change in the X-ray diffraction pattern of manganese with milling time. The peaks became broad as in the case of chromium. An halo pattern was obtained after milling for 1000 h.
c
oo,,
[--F---I
NbH
5"~___j,__~
1000h
i 20
i 30
i 40
2 e / deg.
Fig. 1. Change in the X-ray diffraction pattern of Nb powder with milling time.
4. Discussion
The surface of metals is usually covered with their oxide. It is known that the fresh surface of metals is active. If the milling repeatedly creates such surfaces, various reactions may occur. Nheptane is saturated and so dehydrogenation is mainly expected. We suggest that hydrogen atoms
454
K. Tokumitsu / Amorphous metal-hydrogen alloys
~h
>ti (n zuJ i--
zI
ENERGY / KeV
: : : : : : : : : : : : : : : : : : : : : :
~h
w
ENERGY / KeV
700h
>Cr
lO00h . . . . . .
ENERGY / KeV Fig. 3. Change in the SEM images and the EDX spectra of Cr powder with milling time.
from the dehydrogenation of n-heptane are taken into niobium and then niobium hydride is produced, which is stable at room temperature. Trzeciak et al. [7] have reported that crystalline hydrides ranging from CrH0. 8 to CrH1. 6
can be formed and then irreversibly decomposed at room temperature. In the C r - H system, the existence of the gaseous diatomic hydride (CrH) has been reported [8]. Krukowski and Baranowski [9] have reported that a crystalline hydride
K. Tokumitsu / Amorphous metal-hydrogen alloys
455
5. Conclusion I Mn
; +;t
.~
20h
=. ¢g
_
~
IOOh
>. .'¢
The author is grateful to Drs. Yoichi Ishida, Itaru Yasui, Shinji Takai, Hideki Ichinose and Daisuke Fujita for useful discussions.
200h
§OOh
l~10h i
i
zo ~ 20 / ~ .
Metal hydrides, both crystalline and amorphous, can be prepared by a mechano-chemical reaction between metals and liquid hydrocarbons. It is suggested that these hydrides are formed via the dehydrogenation of the hydrocarbons.
References i
4o
Fig. 4. Change in the X-ray diffraction pattern of Mn powder with milling time.
(MnHo.82) was obtained using a high pressure hydrogen technique because of the difficulties in obtaining the hydride at room temperature. However, it has also been reported that the gaseous diatomic hydride (MnH) is stable [10]. So, in these two systems it can be said that the stability of the hydride crystal lattice is weak but the bonding between metal and hydrogen is stable. The stability of crystal lattice reflects the longrange ordering and is not directly dependent on the strength of bonding between constituent atoms. We suggest that the amorphous metal-hydrogen phase is easily formed when the stability of hydride crystal lattice is weak but the bonding between metal and hydrogen is stable.
[1] J.P. Blackledge, in: Metal Hydrides, ed. W.M. Mueller, J.P. Blackledge and G.G. Libowitz (Academic Press, New York, 1968) p. 2. [2] J.F. Stampfer, C.E. Holley and J.F. Shuttle, J. Am. Chem. Soc. 82 (1960) 3504. [3] J.J. Reilly and R.H. Wiswall Jr, Inorg. Chem. 9 (1970) 1678. [4] G. Brauer and R. Herman, Z. Anorg. Chem. 274 (1953) 11. [5] J.F. Smith, Bull. Alloy Phase Diagrams 4 (1983) 39; in: Binary Alloy Phase Diagrams, ed. T.B. Massalski (ASM, Metals Park, OH, 1986) p. 1274. [6] M.V. Rao, in: Binary Alloy Diagrams, ed. T.B. Massalski (ASM, Metals Park, OH, 1986) p. 822. [7] M.J. Trzeciak, D. Dilthey and M. Mallett, US Atomic Energy Commision Report, BMI-1112 (1956) 32 pp. [8] B. Kleman and U. Uhler, Can. J. Phys. 37 (1959) 537. [9] M. Krukowski and B. Baranowski, J. Less-Common Met. 49 (1976) 385. [10] T.E. Nevin, Proc. Irish Acad. Sect. A50 (1945) 123.
Journal of Non-Crystalline Solids 150 (1992) 452-455
North-.o.and
ml"t
Igl
Amorphous metal-hydrogen alloys prepared by mechano-chemical reaction Kazuto Tokumitsu Department of Materials Science, Unicersityof Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan
The mechano-chemical formation of crystalline and amorphous hydrides is described. Niobium transformed into 13-Nb hydride by milling with liquid normal-heptane. Chromium and manganese were transformed into amorphous hydrides. The hydrocarbon served as the source of hydrogen atoms through a dehydrogenation reaction.
1. Introduction
2. Experimental procedure
Metal hydrides are classified into three categories [1]. The first category is the saline hydride, the second is the covalent hydride and the third is the metallic hydride. The binding force between metal and hydrogen atoms is weak compared with that in saline and covalent hydrides and so these hydrides have large non-stoichiometric regions, even if indicated as M H or MH2. Metal hydrides have usually been prepared by the H 2 gas charging method. This method is based on the adsorption and the dissociation of hydrogen gas, but high temperatures and pressures [2] or a complicated activation treatment are needed [3]. However, the supply of hydrogen is not necessarily restricted to hydrogen molecules but is possible through the dehydrogenation of hydrocarlaons. Paraffins and naphthenes are preferred as the source of hydrogen for the reason that they are saturated and contain no oxygen atoms. This p a p e r presents the formation of crystalline and amorphous metal hydrides by the mechano-chemical reaction between metals and hydrocarbons.
2.1. Sample preparation
Correspondence to: Dr K. Tokumitsu, Department of Materials Science, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan. Tel: +81-338 12 2111. Telefax: +81-338 15 8363.
Milling was carried out using a rotating ballmilling apparatus. The vial containing a sample was cylindrical, 120 mm in diameter and 70 mm in height. It was made of SUS304 alloy. The balls were made of hard alloy ( W C - C o ) and their diameter was 10 mm. The purity of the metal powders used was 99.9 at.% and their particle size was about 50 I~m. Normal heptane (C6H14) , which is a saturated chain-like hydrocarbon, was used as the source of hydrogen. The metal powders were put into the vial with the liquid hydrocarbon and balls. The sample was removed after a constant milling time and the milling was carried out at room temperature. A little alkyl-naphthalene oil was added to prevent the oxidation of the powders and the ignition of the hydrocarbon. 2.2. Characterization Changes in the structures of the metal powders were measured by X-ray diffraction analysis (Mo K s ) and their morphology by scanning electron microscopy. The composition of the powders was measured by inductively coupled plasma spectroscopy (ICP) and the transformation of the hydrocarbon by high performance liquid chromatography (HPLC).
0022-3093/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
K. Tokumitsu / Amorphous metal-hydrogen alloys
453
3. Results 1
3.1. Formation of a crystalline hydride: N b / heptane system Figure 1 shows the change in the X-ray diffraction pattern of niobium with milling time. The structure of niobium is body centered cubic and the (110), (100) and (211) planes are observed. However, the shoulders appeared on the low angle sides of each peak after milling for 300 h and grew with increasing milling time. The peaks for pure niobium disappeared after 1000 h. The new diffraction peaks were identified as being due to [3-Nb and hydride (NbH089) [4]. It has been reported that 13-Nb hydride is stable at room temperature [5]. An impurity of 1.80 at.% Fe was contained in the powders, as shown by ICP measurements. This impurity originates from the SUS304 vial.
3.2. Formation of amorphous hydrides: Cr,Mn / heptane system Figure 2 shows the change in the X-ray diffraction pattern of chromium with milling time. The peaks became broad by contrast with the result
[ - - ~
Nb
_~ "~ ~1 >
10h 300h
_ r~,.___~_~ 400h
Cr
i 700h
lmh
2 0 / deg.
Fig. 2. Change in the X-ray diffraction pattern of Cr powder with milling time.
for niobium. A halo pattern was obtained after milling for 1000 h, which is characteristic of an amorphous phase. The impurity from the vial may have some effect on the amorphization, but chromium forms a solid solution with iron [6]. The hydrogen content was determined as CrHoA 7 by the inert gas fusion method, but it was difficult to obtain the precise value. Figure 3 shows the results of SEM observations and EDX measurements. The particle size decreased from about 50 I~m to about 2 p~m and iron was detected in the milled powders. Figure 4 shows the change in the X-ray diffraction pattern of manganese with milling time. The peaks became broad as in the case of chromium. An halo pattern was obtained after milling for 1000 h.
c
oo,,
[--F---I
NbH
5"~___j,__~
1000h
i 20
i 30
i 40
2 e / deg.
Fig. 1. Change in the X-ray diffraction pattern of Nb powder with milling time.
4. Discussion
The surface of metals is usually covered with their oxide. It is known that the fresh surface of metals is active. If the milling repeatedly creates such surfaces, various reactions may occur. Nheptane is saturated and so dehydrogenation is mainly expected. We suggest that hydrogen atoms
454
K. Tokumitsu / Amorphous metal-hydrogen alloys
~h
>ti (n zuJ i--
zI
ENERGY / KeV
: : : : : : : : : : : : : : : : : : : : : :
~h
w
ENERGY / KeV
700h
>Cr
lO00h . . . . . .
ENERGY / KeV Fig. 3. Change in the SEM images and the EDX spectra of Cr powder with milling time.
from the dehydrogenation of n-heptane are taken into niobium and then niobium hydride is produced, which is stable at room temperature. Trzeciak et al. [7] have reported that crystalline hydrides ranging from CrH0. 8 to CrH1. 6
can be formed and then irreversibly decomposed at room temperature. In the C r - H system, the existence of the gaseous diatomic hydride (CrH) has been reported [8]. Krukowski and Baranowski [9] have reported that a crystalline hydride
K. Tokumitsu / Amorphous metal-hydrogen alloys
455
5. Conclusion I Mn
; +;t
.~
20h
=. ¢g
_
~
IOOh
>. .'¢
The author is grateful to Drs. Yoichi Ishida, Itaru Yasui, Shinji Takai, Hideki Ichinose and Daisuke Fujita for useful discussions.
200h
§OOh
l~10h i
i
zo ~ 20 / ~ .
Metal hydrides, both crystalline and amorphous, can be prepared by a mechano-chemical reaction between metals and liquid hydrocarbons. It is suggested that these hydrides are formed via the dehydrogenation of the hydrocarbons.
References i
4o
Fig. 4. Change in the X-ray diffraction pattern of Mn powder with milling time.
(MnHo.82) was obtained using a high pressure hydrogen technique because of the difficulties in obtaining the hydride at room temperature. However, it has also been reported that the gaseous diatomic hydride (MnH) is stable [10]. So, in these two systems it can be said that the stability of the hydride crystal lattice is weak but the bonding between metal and hydrogen is stable. The stability of crystal lattice reflects the longrange ordering and is not directly dependent on the strength of bonding between constituent atoms. We suggest that the amorphous metal-hydrogen phase is easily formed when the stability of hydride crystal lattice is weak but the bonding between metal and hydrogen is stable.
[1] J.P. Blackledge, in: Metal Hydrides, ed. W.M. Mueller, J.P. Blackledge and G.G. Libowitz (Academic Press, New York, 1968) p. 2. [2] J.F. Stampfer, C.E. Holley and J.F. Shuttle, J. Am. Chem. Soc. 82 (1960) 3504. [3] J.J. Reilly and R.H. Wiswall Jr, Inorg. Chem. 9 (1970) 1678. [4] G. Brauer and R. Herman, Z. Anorg. Chem. 274 (1953) 11. [5] J.F. Smith, Bull. Alloy Phase Diagrams 4 (1983) 39; in: Binary Alloy Phase Diagrams, ed. T.B. Massalski (ASM, Metals Park, OH, 1986) p. 1274. [6] M.V. Rao, in: Binary Alloy Diagrams, ed. T.B. Massalski (ASM, Metals Park, OH, 1986) p. 822. [7] M.J. Trzeciak, D. Dilthey and M. Mallett, US Atomic Energy Commision Report, BMI-1112 (1956) 32 pp. [8] B. Kleman and U. Uhler, Can. J. Phys. 37 (1959) 537. [9] M. Krukowski and B. Baranowski, J. Less-Common Met. 49 (1976) 385. [10] T.E. Nevin, Proc. Irish Acad. Sect. A50 (1945) 123.