Resistance to hydrogen of Al-Sc alloys

Article abstract of DOI:10.1023/A:1012720906417

The behavior of aluminum scandium alloys in hydrogen at an equilibrium pressure of 0.1 MPa was studied on a Sieverts apparatus.

Full text of DOI:10.1023/A:1012720906417

Russian Journal of Applied Chemistry, Vol. 74, No. 3, 2001, pp. 396 399. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 3,
001, pp. 389 392.
Original Russian Text Copyright
2
2001 by Antonova, Chernogorenko.
PHYSICOCHEMICAL STUDIES
OF SYSTEMS AND PROCESSES
Resistance to Hydrogen of Al Sc Alloys
M. M. Antonova and V. B. Chernogorenko
Institute of Materials Science Problems, Ukrainian National Academy of Sciences, Kiev, Ukraine
Received August 24, 2000
Abstract The behavior of aluminum scandium alloys in hydrogen at an equilibrium pressure of 0.1 MPa
was studied on a Sieverts apparatus.
The most efficient modifier of aluminum is scandi-
um [1]. Addition of 1% Sc to AV000 aluminum yields
the maximal number of grains (1090 per 1 cm ) com-
pared to other modifiers. Aluminum and aluminum
alloys modified with scandium have the improved
strength, plasticity, corrosion resistance, and other
operation characteristics [2]. Scandium-doped alumi-
num has found application as structural material for
aircrafts. Electrodes made of aluminum wire doped
with 1% Sc facilitate welding of aluminum parts [3,
alloys containing up to 30% Sc at their various mech-
anical and thermal treatments. The behavior of these
alloys in hydrogen-containing media was not studied
previously.
2
EXPERIMENTAL
The alloys under study were obtained from alumi-
num (A999 ultrapure grade) and SkM-2 grade scandi-
3
um containing (wt %) 99.88 Sc, 9 10 Fe, less than
4], which allows fabrication of compact light articles.
0
0
.001 Cu, 0.0051 Al, 0.05 Ca, 0.02 Mg, less than
.001 Y, less than 0.0005 Yb, less than 0.005 Zr, less
However, the strength of these materials, when operat-
ing for a long time under conditions of sharp tempera-
ture gradients, depends on their resistance to the en-
vironment in which they are exploited, in particular,
air and hydrogen plasma.
than 0.005 Ti, and 0.016 Si. The starting materials
were smelted in an electric arc furnace with a per-
manent tungsten electrode under purified argon. Each
sample was melted sixfold. The content of the ele-
ments in the alloys was determined by X-ray flu-
orescence analysis on a VRA-30 device. In some tests,
chemical analysis was also used.
In this work we studied the hydrogen absorption
capacity of Al Sc alloys. As known, compact alumi-
num does not interact with hydrogen. Aluminum hy-
dride (AlH ) as a white amorphous mass can be pre-
3
The alloys were hydrogenated at a 0.1 MPa hydro-
gen pressure on the improved quartz apparatus of the
Sieverts type [6]. The volume of the reaction chamber
pared solely by the chemical method from the ether
solution [5]. Scandium absorbs hydrogen in the ele-
mental state, forming the hydride ScH [6], and also
2
3
was 60 cm . The pressure was measured with a mer-
as a component of intermetallic compounds with met-
als that are not hydrogenated. For example, the inter-
metallic compound ScMn yields hydrides ScMn H
cury manometer. The hydrogen uptake was monitored
by the pressure change in the system. The pressure
was adjusted to the initial value every 5 min. Hydro-
gen was obtained by decomposing titanium hydride or
2
2 3.8
[
7]; ScFe , ScFe H ; and ScCo , ScCo H [8].
2 2 4 2 2 4
In the Al Sc system, four intermetallic compounds
are formed: Al Sc, Al Sc, AlSc, and AlSc [9, 10].
LaNi hydride in a reactor connected to the reaction
5
3
2
2
chamber. Owing to plasticity, aluminum alloys con-
taining up to 2% Sc were used as powder, which was
prepared from finely disperse cuttings washed with
ethyl alcohol and sieved. The other alloys were used
as crushed ingots. Metallic scandium was hydro-
genated without crushing.
The solubility of Al in Sc reaches about 6.25%. The
limiting solubility of Al in Sc is 0.30%. At high crys-
tallization rates the solubility of Sc can reach 5.1%.
The data on the crystal structure of the phases in the
Al Sc system are given in Table 1. The crystal struc-
tures and the unit cell parameters of aluminum and the
nearest intermetallic Al Sc are close. Therefore, as
We measured the sorption isobars at 0.1 MPa hy-
3
was shown by practical experience, cracks resulting drogen pressure. Before hydrogenation, the alloys
from internal stresses do not appear in aluminum
were activated by heating to 600 800 C at 13 Pa.
1
070-4272/01/7403-0396$25.00 2001 MAIK Nauka/Interperiodica

RESISTANCE TO HYDROGEN OF Al Sc ALLOYS
Table 1. Crystal structure of phases in the Al Sc system [9, 11]
397
Lattice parameters, nm
Structure
Phase
Al
Prototype
Pearson’s symbol
Space group
designation
a
b
c
Cu
AuCu3
cF4
cF4
cF24
cP2
hP6
cI2
Fm3m
Pm3m
Fd3m
Pm3m
Al
0.4041
0.4105
0.758
0.5030
0.488
Al Sc
Ll2
Cl5
B2
B82
A2
A3
3
Al Sc
Cu Mg
2
2
AlSc
AlSc2
CsCl
InNi2
Cu
0.9895
0.3126
0.6166
P6 /mmc
3
-Sc
Fm3m
0.454
0.3309
-Sc
Mg
hP2
P6 /mmc
0.5273
3
Table 2. Sorption characteristics of scandium aluminum solid solutions after activation at 600 C for 1 h
3
1
H2 content, cm g , at indicated temperature,
C
H2 content
in alloy, %
Sample
600
500
400
300
200
100
20
Al + 0.3% Sc:
compact
0
1.1
1.4
1.3
2.0
18.1
4.3
18.5
5.3
24.2
7.1
27.5
8.9
39.3
0.08
0.35
powder
Al + 2% Sc:
compact
0.4
6.0
2.0
6.0
3.5
7.5
4.0
10.9
7.1
15.0
13.1
25.1
13.9
58.8
0.14
0.52
powder
After activation, hydrogen was fed into the reactor,
where the sample preheated to the maximal tempera- tures (the temperature of the -Sc
of the -Sc
-Sc transition toward lower tempera-
-Sc transition
ture was located, and the hydrogen sorption was ob-
served and recorded at constant temperature till the
saturation was complete. After that, the temperature
was decreased by 100 C. The sorption process was
resumed till the saturation was observed at the given
temperature. The test was performed at stepwise de-
crease in the temperature to room temperature. The
incubation period was observed in none of the cases.
The total time of the experiment reached 3 5 days.
in air is 1337 C). In this case, as in the majority of
studies, no scandium hydride of the composition ScH2
was obtained. The hydrogen content in the hydride
obtained corresponds to the composition ScH1.39
.
The hydrogen content in solid solution and scandi-
um aluminum alloys depends on dispersity (Table 2).
Hydrogen absorption is stronger for powders owing
to developed surface. On heating Al + 0.3% Sc and
Al + 2% Sc samples to 600 C in a vacuum, about 7
3
We found that all the compositions studied are
hydrogenated reversibly and after decomposition in a
vacuum and subsequent hydrogenation the final con-
tent of hydrogen in them is similar to the results of
the first hydrogenation. The exception was metallic
scandium. In the course of the first hydrogenation it
10 cm of adsorbed hydrogen per gram of the alloy
is released, with most of hydrogen remaining in the
alloy lattice. Concerning the effect of hydrogen on
aluminum alloys, Dobatkin et al. [14] report that
3
.
..hydrogen content exceeding 0.2 cm per 100 g
drastically deteriorates impermeability of ingots. Also,
it can affect impermeability of deformed semifinished
products. Unfortunately, study of this effect, which is
so important for estimating the potential of metals in
spacecrafts, is given little attention yet.
3
took up only 86.6 cm of H per 1 g and disintegrated
2
by cracking. No hydrogen was released in a vacuum at
9
00 C, and only at 1000 C it started decomposing.
The results of the second hydrogenation are given in
Table 2. Heating it in a vacuum was accompanied by
intense cracking, indicative of transformation of the
hydride structure. It can be presumed that, as in the
Ti H system [12, 13], hydrogen shifts the temperature
The data on hydrogenation of the intermetallic
compounds are given in Table 3. Before interaction
with hydrogen, the alloys were activated in a vacuum
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 3 2001

398
ANTONOVA, CHERNOGORENKO
Table 3. Data on hydrogenation of intermetallic compounds of the Al Sc system and scandium after the first cycle
of hydrogenation dehydrogenation
3
1
Activation
T, C , h
H2 content, cm g , at indicated temperature,
C
Sam-
ple
PH2,
MPa
H , %**
2
800
700
600
500
400
300
200
100
20
Al Sc
600
900
900
800
1.0
0.7
0.5
0.5
0.5
0.5
0.1
0.1
0.1
0.1
2.5
0.1
0
17.7
41.1
2.5
25.5
50.9
24.5
32.5
66.7
24.5
38.4
72.1
25.6
41.4
75.5
42.5
69.5
86.5
44.6
75.6
98.0
0.40
0.67
0.87
1.15
2.16
3.0
3
Al Sc
7.6
20.7
14.3
32.2
2
AlSc
AlSc2
AlSc2* 200
Sc
104.0 105.9 106.6 107.1 126.9 129.4 131.4 150.2 189.5
10.0 241.9
320.9 321.0 321.0 321.0 322.0 326.0 327.0 338.0 338.0
900
*
After the third cycle.
*
* Maximal H content at 20 C.
2
at 800 900 C. The exception was Al Sc, which was
activated at 600 C to prevent possible partial peri-
tectic decomposition at 660 C. The maximum amount
less steel installation. Additional activation of the
alloy grains was performed by repeated hydrogena-
tion dehydrogenation cycles without removing the
sample from the reaction chamber (Table 3).
3
of hydrogen absorbed by AlSc was smaller compared
2
to similar AB alloys (e.g., NiMg and NiTi : 404
2
2
2
We studied the influence of activation temperature
and number of activation cycles on hydrogenation.
After the third cycle the amount of sorbed hydrogen
3
1
and 298 cm g , respectively). As known [15], the
solubility of hydrogen in aluminum and scandium and
the diffusion rate of hydrogen in these metals grow
with increasing pressure. It is presumed that the hy-
drogen pressure of 0.1 MPa is insufficient for com-
3
reached 241.9 cm H per gram of the alloy. Only
2
3
minor amount of hydrogen (9.9 cm H per gram) was
revealed by chemical analysis of the material hydro-
2
plete saturation of AlSc . Therefore, the intermetallic
2
genated at 200 C and 2.5 MPa. Thus, the hydride of
compounds were hydrogenated at 2.5 MPa in a stain-
AlSc is extremely unstable, instantaneously decom-
2
posing at room temperature as the hydrogen pressure
is quickly relieved from 2.5 to 0.1 MPa. For its stor-
age the special stabilization procedures are necessary.
Many hydrides, including LaNi5 hydride, behave
similarly. To stabilize them, the surface is saturated
with oxygen or carbon dioxide at the temperature of
liquid nitrogen.
wt %
T, C
(a)
The sorption capacity for hydrogen as a function of
composition of the Al Sc system is plotted in Fig. 1.
All alloys of the system, especially intermetallic com-
pounds, absorb hydrogen. If during fabrication of
scandium-doped aluminum, namely, in the stage
when aluminum scandium charge is introduced into
aluminum melt, the homogenization of the melt was
not attained and scandium segregated in the course of
subsequent crystallization, then, for example, in space-
craft articles and liquid-hydrogen cylinders, especially
on warming them from the sun side, Al ScH or
3
A, cm g 1
(b)
3
x
Al ScH can be formed with high probability. Scandi-
2
x
um can segregate into intermetallic compounds in
the course of rolling ingot and during welding with a
scandium-containing wire owing to crystallization of
a weld material. The resulting hydrides decompose
with hydrogen evolution, resulting in the formation
at. %
Fig. 1. (a) Phase diagram of the Al Sc system and
b) maximal sorption capacity for hydrogen of the system
alloys vs. alloy composition. (T) temperature and (A) sorp-
tion capacity at P = 0.1 MPa and 20 C.
(
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 3 2001

RESISTANCE TO HYDROGEN OF Al Sc ALLOYS
399
of pores during diffusion. The hydrogen accumulation Tekhnol. Legk. Splavov, 1997, no. 5, pp. 8 10.
in a spacecraft in the presence of oxygen can cause
explosion and fire.
4
5
. Ishchenko, A.Ya., Lozovskaya, A.V., Poklyats-
kii, A.G., et al, Avtom. Svarka, 1993, no. 4, pp. 19 25.
. Nekrasov, B.V., Kurs obshchei khimii (Course of
General Chemistry), Moscow: Khimiya, 1967, part 2.
In this work, the influence of the other components
of traditional aluminum alloys, for example, magnesi-
um and lithium alloys, on their resistance to molecular
hydrogen was not studied. Presumably, the presence
6. Antonova, M.M. and Morozova, R.A., Preparativnaya
khimiya gidridov (Preparative Chemistry of Hydrides),
Kiev: Naukova Dumka, 1976.
7. Kost, M.E., Raevskaya, M.V., Shilov, A.L., et al,
Zh. Neorg. Khim., 1979, vol. 24, no. 12, pp. 3239
of these elements easily forming hydrides MgH and
2
LiH would deteriorate the hydrogen resistance of
aluminum scandium alloys.
3
242.
8
9
. Semenenko, K.N. and Burnasheva, V.V., Dokl. Akad.
Nauk SSSR, 1976, vol. 231, no. 2, pp. 356 358.
. Diagrammy sostoyaniya dvoinykh metallicheskikh
sistem: Spravochnik (Phase Diagrams of Binary Metal
Systems: Reference Book), Lyakishev, N.P., Ed.,
Moscow: Mashinostroenie, 1996.
CONCLUSION
(
1) All alloys of the Al Sc system interact with
hydrogen. The intermetallic compounds Al Sc, Al Sc,
AlSc, and AlSc form hydrides.
3
2
2
(
2) The amount of sorbed hydrogen grows with
1
0. Naumkin, O.P., Terekhova, V.T., and Savitskii, E.M.,
increasing hydrogen pressure.
Izv. Akad. Nauk SSSR, Metally, 1965, no. 4, pp. 176
1
82.
(
3) The AlSc -based alloy can be used for prepar-
2
1
1
1. Gschneidner, K.A., Jr., and Calterwood, F.M., Bull.
Alloy Phase Diagr., 1989, vol. 10, no. 1, pp. 34 36.
2. Svoistva elementov: Spravochnik (Element Properties:
The Reference Book), Samsonov, G.V., Ed., Moscow:
Metallurgiya, 1976.
ing hydrogen-accumulating materials.
(4) The aluminum alloys containing scandium can
be recommended for aerospace technology only after
testing them for hydrogen resistance.
1
1
3. Metal Hydrides, Mueller, W.M., Blackledge, J.P., and
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