0
.97LiAlH
4
+ 0.03TiCl
0.12LiCl + 0.687Al + 0.03[Ti] + 1.091H
LiAlH + TiCl = 4LiCl + 4Al + [Ti] + 2H
LiAlH + [Ti] = Li AlH + 2Al + [Ti] + 3H —
4
= 0.283Li
3
AlH
6
The Ames Laboratory is operated for the U.S. Department of
Energy (DOE) by Iowa State University under contract No.W-
+
2
—
—
(2)
(3)
(4)
7
405-ENG-82. Different aspects of this work were supported by
4
4
4
2
the Office of Basic Energy Sciences, Materials Sciences
Division of the U.S. DOE and Iowa State University Carver
Trust Grant.
3
4
3
6
2
The formation of lithium chloride, aluminium and a Ti-
containing micro-crystalline phase with unknown composition
during 5 min ball-milling of lithium aluminohydride and
titanium tetrachloride was confirmed by mechanochemical
Notes and references
†
All experiments described in this communication were carried out in a
treatment of stoichiometric amounts (4+1) of LiAlH
4
and TiCl
eqn. (3)].1 No Bragg peaks corresponding to either LiAlH
or
Li AlH were detected from XRD data. Furthermore, the gas-
4
3b
glove box in a purified helium atmosphere and in a hardened-steel vial
sealed under helium. The X-ray diffraction experiments were performed
under helium in a sample holder covered by X-ray transparent polymer film.
The differential thermal analysis was carried out in an argon atmosphere at
ambient pressure using commercially available equipment. The heating rate
during DTA measurements was 10 K min21. The gas-volumetric experi-
[
4
3
6
volumetric analysis of the obtained reaction mixture [eqn. (3)]
did not reveal observable hydrogen gas evolution up to 925
K.
To verify that the titanium catalyzed solid state transforma-
ments were performed using a standard Sievert’s type apparatus.
4 3 6
tion of LiAlH into Li AlH proceeds only during mecha-
1
2
K. Yvon, Chimia, 1998, 52, 613.
nochemical activation, the mixture containing 97 mol% of
lithium aluminohydride and 3 mol% of titanium tetrachloride
was thoroughly ground in a mortar under helium for 10 min.
Although slight changes of the reaction mixture color from
grayish-white to gray were observed, XRD did not indicate the
formation of detectable amounts (i.e. 5 vol% or more) of
G. Sandrock, in Hydrogen Energy Systems, ed. Y. Yürüm, Kluwer
Academic Publishers, Dordrecht and Boston, 1995, p. 135.
B. Bogdanovic and M. J. Schwickardi, J. Alloys Compd., 1997, 253,
3
1
.
4 R. A. Zidan, S. Takara, A. G. Hee and C. M. Jensen, J. Alloys Compd.,
1999, 285, 119.
5 C. M. Jensen, R. A. Zidan, N. Mariels, A. G. Hee and C. Hagen, Int. J.
Hydrogen Energy, 1999, 24, 461.
Li
3
AlH
6
during grinding. Weak Bragg peaks corresponding to
polycrystalline LiCl and Al were found in the X-ray diffraction
pattern of the reaction mixture after grinding, and therefore, the
observed color changes were likely associated with the
6
K. J. Gross, S. Guthrie, S. Takara and G. Thomas, J. Alloys Compd.,
000, 297, 270.
2
7
8
J. A. Dilts and E. C. Ashby, Inorg. Chem., 1972, 11, 1230.
J. P. Bastide, B. M. Bonnetot, J. M. Letoffe and P. Claudy, Mater. Res.
Bull., 1985, 20, 999.
T. N. Dymova, V. N. Konoplev, D. P. Aleksandrov, A. S. Sizareva and
T. A. Silina, Russ. J. Coord. Chem., 1995, 21, 165.
reduction of TiCl
thermore, our experiments with pure LiAlH
4
by LiAlH
4
according to eqn. (3). Fur-
revealed that this
4
complex hydride is stable during ball-milling without TiCl
up to 35 h.
4
for
9
Currently, several different models describing the observed
rapid solid-state rearrangement of LiAlH (i.e. tetrahedral
10 J. C. Bureau, J. P. Bastide, P. Claudy, J. M. Letoffe and Z. Amri, J. Less-
Common Met., 1987, 22, 185.
11 J. C. Bureau, Z. Amri, P. Claudy, J. M. Letoffe, B. Balland and P.
Gonnard, Mater. Res. Bull., 1989, 24, 551.
4
2
32
[
AlH
presence of TiCl
ambient conditions are being considered. One of the most likely
mechanisms explaining the catalytic effect of TiCl can be its
4
] ion) into Li
3
AlH
6
(i.e. octahedral [AlH
6
]
ion) in the
4
during mechanochemical treatment at
1
2 T. N. Dymova, D. P. Aleksandrov, V. N. Konoplev, T. A. Silina and
A. S. Sizareva, Russ. J. Coord. Chem., 1994, 20, 263.
4
1
3 (a) Solvent free Li
mol) LiH and 1.90 g (0.05 mol) LiAlH
Crystal data: for Li AlH monoclinic, space group P2
b = 8.107(2), c = 7.917(2) Å, b = 92.17(1)°, V = 363.5(2) Å
3
AlH
6
was prepared by ball-milling of 0.80 g (0.1
in a helium atmosphere for 5 h.
/c, a = 5.667(1),
, M =
reduction to a highly reactive nanocrystalline or amorphous
titanium phase [eqn. (3)], which subsequently mechanically
4
3
6
1
alloys into the crystal lattice of LiAlH
4
. The following
3
destabilization of the host crystal lattice caused by the presence
of titanium leads to the formation of metastable ‘melt-like’
hydride phases, where the rearrangement of the tetrahedral
53.8, Z = 4, T = 298 K . The obtained lattice parameters are in excellent
agreement with the previously reported data14 for conventionally
prepared Li
and TiCl was carried out in a Spex mill in a hardened-steel vial sealed
under helium. According to XRD, the reaction mixture contains
3 6 4
AlH ; (b) ball-milling of stoichiometric amounts of LiAlH
2
32
4
[
AlH
4
]
ion into the octahedral [AlH
6
]
ion becomes
kinetically possible. Although the nature of intermediate
phase(s) is presently unclear, it is feasible that they are similar
polycrystalline LiCl, Al and an unidentified intermetallic Ti12xAl
x
phase.
to the metastable high-pressure g-LiAlH
4
with hexa-coordi-
and their formation becomes possible
1
4 J. P. Bastide, B. Bonnetot, J. M. Letoffe and P. Claudy, Stud. Inorg.
Chem. (Solid State Chem.), 1983, 3, 785.
3
2
10,15
nated [AlH
6
]
ion,
due to mechanically induced strain in the presence of titanium
catalyst.
15 J. P. Bastide, J. C. Bureau, J. M. Letoffe and P. Claudy, Mater. Res.
Bull., 1987, 22, 185.
1666
Chem. Commun., 2000, 1665–1666