Reversible reactions between hydrogen and such materials as iron/titanium and magnesium/ nickel alloy may provide a means for storing hydrogen fuel. A demonstration model of an iron/titanium hydride storage bed is described. Hydrogen from the hydride storage bed powers a converted gasoline electric generator

Santana, C. C.

Santos, S. C.

Zwanziger, M. G.

English

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NASA TECHNICAL MEMORANDUM
	
NASA TM-77453
HYDROGEN STORAGE IN THE ^CRM OF METAL HYDRIDES
(NASA-Td-77453) HYD80GEN STCSAGE IN THE 	 N84-29356
IORM OF LIETA.. dYDEIDES (National Aeronautics
and Space Administration) 9 p HC A02/M F A01
CSCL 10C G	 Unclas/44 20038
M.G. Zwanziger, C.C. Santana, S.C. Santos
Translation of "Armazenamento de hidrogenio
na forma de hidretos metalicos", Brazilian
Conference on Energy, lst, Rio de Janeiro,
Brazil, December 12-14, 1978, Proceeding-s,
Vol. B. Rio de Janeiro, ilniversidade Federal
do Rio de Janeiro, 1979, PP. 542-543.
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON D.C. 20546	 MAy 1984
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HYDROGEN STORAGE IN THE FORM OF
METAL HYDRIDES
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M.G. Zwanziger, C.C. Santana,
S.C. Santos
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Translation of "Armazenamento de hidrogenio na forma de
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hidretos metalicos", Brazilian Conference on Energy, lst, Rio
de Janeiro, Brazil, December 12-14, 1978, Proceedings, Vol. B.
Rio de Janeiro, Universidade Federal do Rio de Janeiro, 1979,
pp. 542-548. (A79-33251).
1♦ Abe~ *
R;.versible reactions between hydrogen and such materials
as iron/titanium and magnesium/ nickel alloy may provide
a means for storing hydrogen fuel. In this paper, .a
demonstration model of an iron/titanium hydride storage bed
is described. Hydrogen from the hydride storage bed powers
a converted gasoline electric generator.
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HYDROGEN STORAGE IN THE FORM OF METAL HYDRIDES 	 /542**	
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By M. G. Zwanziger, C. C. Santana and S. C. Santos, UNICAMP
[Universidade Estadual Campinas = State University at
Campinas], Grupo de Energia, C. P. 1170, 13100 Campinas,
,^P (Brazil)
SUMMARY	 One of the critical aspects of hydro-
gen technology is the storage of this raw mate-
rial for later use.	 The reversible chemical
reactions between hydrogen and metallic alloys
are a promissing avenue of research.	 The	 i.dea
i
has been tested in practical applications by seyeral
laboratories with iron/titanium, magnesium/nickel and lanthanum/
nickel systems,	 to mention a few. 	 We demonstrate
an iron/titanium hydride bed that feeds hydrogen
to a converted gasoline motoelectric generator. ^^!
(Authors'
	
summary)
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1.	 INTRODUCTION	 /543a
Currently there are various research centers,	 world-wide,	 that
are studying the feasibility of hydrogen storage in the form
of hydrides,	 whose energies of formation and dissociation are
reversible,
	
with kinetic and	 thermodynamic characteristics	 (in
addition to energy density and cost) 	 suitable	 for practical
applications.
i
Paper No. B-16, pp. 542-548 of the Proceedings of the CBE [I
Congresso Brasileiro de Energia = 1st Brazilian Conference on
Energy], Rio de Janeiro (Brazil), December 1978)
* Numbers in the right margin indicate foreign pagination
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Considerable progress was achieved during the last decade and
the technical feasibility of fuel tanka for automobiles has
already been shown by various companies, such as Billings, in
the US and Daimler-Benz, in West Germany.
In Brazil there is the possibility and hope of producing elec-
trolytic hydrogen from the still fairly abundant hydroelectric
power reserves. As a traditional market technology, the cost of
energy to the consumer - in the form of electrolytic hydrogen -
is comparable to petroleum-based fuel costs, at current price
schedules. Under these conditions it is reasonable to consider
hydrogen operation for fleets of heavy freight transports,
traveling between certain destinations, to minimize supply
problems. The basic point of the entire matter is the storage,
and here metal hydride tanks are a practical and safe alternative.
2. PHYSICOCHEMICAL ASPECTS
Metal hydrides are compounds formed by the reaction be-ween
metals and metal alloys and hydrogen. The metal hydride forma-
tion reactions of interest are exothermal, with the heat removed
providing a measure of the quantity of hydrogen absorbed. At a
given temperature, each system is in equilibrium with a certain
hydrogen pressure, called the equilibrium pressure. The reac-
tion is reversible, which made these systems attractive as
possible hydrogen storage devices. The pressures involved are
moderate (a few Kgf/cm 2 ) and the process is safe, since it is
necessary to supply thermal energy to obtain hydrogen. Hydrogen
de.l^ities in terms of hydrogen atoms per unit volume are higher
even than those for liquid hydrogen, as shown in Table 2 of
reference 2.
The equilibrium pressure is a function of the temperature and
of the 'ydrogen concentration in the solid phase. Figure 1, 	 /544
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KEY: (.Hydrogen pressure 2.Hydrogen/metal ratio
Figure 1. Pressure isotherms as a function of composition
for ideal metal-hydrogen systems
above, shows the typical behavior of metal-hydrogen systems.
As hydrogen is absorbed at constant temperature T 1 and the
hydrogen/metal ratio increases, the equilibrium pressure rises
sharply, to point A. During this period the solid consists of
a solution of hydrogen atoms in the metal, but not a different
compoun3. From point A on, the increase in hydrogen concentra-
tion causes no further increase in the equilibrium pressure;
X-ray analysis shows that the solid consists of a mixture of
metal + metal hydride, with the proportion of the latter in-
creasing until all the metal has become metal hydride, a state
described by point B, in Figure 1. From point B on, we have a
solution of hydrogen in the metal hydride, with a typical
increase in pressure as a function of the composition. In some
systems (for instance, in the iron-titanium alloy), yet a second
plateau can be observed, at a higher pressure level.
The curves marked T2 and T 3 show the effect of temperature
(T 1 <T2 <T 3 ). Figure 2, below, shows the dissociation pressures
as a function of temperature, for sc;me systems.
One system of practical interest, despite its high density, is
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Figure 2. Dissociation pressures for hydrides of
some metals and alloys
that of the iron-titanium alloys, due to its low costs and
moderate equilibrium pressure [1].
The equiatomic intermetallic compound FeTi (46.4% Ti by weight, /545
53.6% by weight iron) reacts reversibly with hydrogen to form
hydrides according to the reactions
	
FeTi + 112 H 2	 FeTiH	 AH=-6,7 kcal/mol
	
FeTi + 112 " 2	 FeTiH2	 &Hc-0,3 kcal/mol
The reaction products are solids of metallic appearance, gray,
fragile, readily reduced to powder, not pyrophoric and
release hydrogen only slowly to the air.
The variation of the equilibrium pressure as a function of the
hydrogen content is shown in Figure 3 (from [11), for various
temperatures. The FeTiH system has a3so a characteristic
hysteresis effect in the absorption/desorption process.
Some advances in the physical chemistry of hydrate formation,
including the effect of additional chemical elements to the
alloys, are described in [ 3 -61.
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KEY;	 I.Dissociation pressure 2.Atomic ratio
Figure 3. Pressure as a function of composition
isotherms for stoichiometric FeTi
hydrates
3 STORAGE TANKS FOR H 2 IN HYDRIDE FORM
In order to test the utilization of hydride tanks for energy-
generation purposes, a demonstration unit was built. A FeTi
alloy was used, prepared at UNICAMP in an electron beam furnace
and activated in the storage tank itself. A quantity of 2.7 kg
of the alloy were placed in a storage tank formed by two steel
cylinders with a combined capacity of 0.8 :, connected to a
Montgomery generator group of 3.6 V mechanical power with the
carburetor removed. Hydrogen was injected directly into the
admission tube. The storage capacity achieved was 250 normal
liters o f hydrogen at an equilibrium pressure of 15 kgf/cm2.
This quantity is half the ideal quantity because a non-stoichio-
metric alloy was used.
The power is regulated by means of a needle valve on the hydro-
gen line. The motor was not modified in any other way. Under
these conditions, the thermodynamic energy conversion yield is
necessarily rather poor, but the device functioned normally and /547
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ORIGINAL PAGE 19
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KEY: I-Vacuum and H2 admission 2-H2 exit 3-Regulator valve 4-Bed
loading window 5-Needle valve 6- FeTi bed 7-Flow meter 8-To
the carburetor of an internal combustion engine 9 - Steel cyli-Aers
Figure 4. 'iydride tank — &emonstration unit
without problems.
Figure 4, above, shows a schematic of the assembly.
REFERENCES
	
/548
1- Reilly, J. J. and Wiswall, R. H., Formation and properties
of iron-titanium hydrides, Inorg.Chem.,13, 218 (1974)
2- Hoffman, K. C. et al., Metal hydride storage for mobile
and stationary applications, Intern.J. Hydrogen Energy,
1, 133 (1976)
3- Reilly, J. J. and Wiswall, R. H., Reaction of hydrogen
with alloys of magnesium and copper, Inorg.Chem.,6, 2220
(1967)
	
f
,
6
4. Reilly, J. J. and Wiswall, R. H., The reaction of hydrogen 	 14
with alloys of magnesium and nickel and the formation of
M92NiH 49 Inorg.Chem., 1968 , 2254
5. Van Mal, H. H., Buschow, K. H. J. and Miedma, A. R.,
Hydrogen absorption in LaNi S and related compounds: Ex-^
perimental observations and their explanationj, J.Less-
t	 Common Metals, 1975 , 65, 163
1	 ^
6•	 Shaltiel, D., Jacob, I. and Davidov, D., Hydrogen absorp-
tion and desorption properties of AB 21 Lab-Phase pseudo-
binary compounds, J. Less-Common Metals, 1977 , 53, 117
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Hydrogen storage in the form of metal hydrides

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