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Diffusion of hydrogen in solid aluminium
Scripta METALLURGICA
Vol, II, pp, 921~923, 1977 Printed in the United States
Pergamon Press, Inc
DIFFUSION OF HYDROGEN IN SOLID ALUMINIUM
Researeh,
K. P a p p a n d E . K o v d c s - C s e t ~ n y i Engineering and Prime Contracting Centre of the Hungarian Corporation~ H-1389 Budapest, P.O.B. 12S. Hungary.
Aluminium
(Received July I, 1977) (Revised September 19, 1977)
Introduetion To o b t a i n diffusion data of hydrogen in metals different methods are in general applied: absorption, desorption, NNR o r G o r s k y e f f e c t /1/. In the literature the diffusion of hydrogen is investigated mainly in bee metals and only a few papers deal with fee metals /1/. The r e s u l t s on t h e d i f f u s i o n of hydrogen in a]uminium measured by desorption in the solid or liquid state are inconsistent with each other which is presumably in connection with impurities and/or the oxidelayer covering the s a m p l e /2,3,4,5,6/. The r e m o v i n g o f t h i s layer is very difficult and its presence can influenee the exit velocity of the hydrogen from the metals /2/, w h i c h l e a d s ¢o a c h a n g e o f t h e b u l k d i f f u s i o n as well. This paper deals with the investigation of the diffusion solid aluminium by the desorption m e t h o d . The s u r f a c e of the g a t e d was c o v e r e d only by natural amorphous oxidelayer which the minimal disturbing effect during the measurements.
of hydrogen in samples investiseemed to cause
3The s a m p l e s e a s t a t a t m o s p h e r i c pressure were heat treated in vacuum at 10Pa. AcCording to Sieverts law, the hydrogen releases from metals, until the equilibrium hydrogen concentration corresponding to the partial pressure o f h y d r o g e n a t 10 - 3 Pa i s a p p r o a c h e d asymptotically. Experimental To m e a s u r e t h e e x i t v e l o c i t y of hydrogen from solid aluminium a Mettler thermoanalyser coupled by a Balzers QMG 311 q u a d r u p o l mass,spectrometer was u s e d . The p a r t i a l pressure of hydrogen released in the reaction chamber was measured using a freezing trap. The h e a t x n g r a t e w a s 25 C / m l n w h i c h i s h i g h enough to prevent the hydrogen exit during the heating process. •
The l e a s t spectrometer was estimated
detectable ~artial pressure i s a b o u t 1~ - ~ P ~ . T h e p a r t i a l to be 10-~-10 --' Pa.
The s a m p l e s w e r e m a d e f r o m a l u m i n i u m p h e r e a t 7 2 0 ° C t o r o d s o f 12 mm d i a m e t e r . is due therefore to the equilibrium value momentary humidity of the air. The s u r f a c e ned and cleaned ehemieally. The s a m p l e o f was heated up t o t h e t e m p e r a t u r e of heat cible. Results
O
using the pressure
.
.
.
.
QMG 311 q u a d r u p o l masschange in our measurements
o f 99,S % p u r i t y cast in air atmosThe h y d r o g e n c o n t e n t of the samples between the liquid metal and the of the samples was carefully tur10 mm d i a m e t e r a n d 10 nun l e n g t h treatment in an aluminiumoxide cru-
and Discussion
The h y d r o g e n c o n t e n t of the samples was controlled by Balzers EA I . E x halograph a n d w a s f o u n d t o b e 0 , 5 e m S / l O 0 g A1 / 7 / . This hydrogen content is due first of all to solute hydrogen. The p a r t b o u n d e d t o i m p u r i t i e s is assumed
921
922
to is
D I F F U S I O N OF H Y D R O G E N
be stable at able to take
IN A L U M I N I U M
the temperatures investigated part in the diffusion process.
and
only
Vol.
the
dissolved
II, No.
hydrogen
The m a s s s p e c t r o m e t e r records the partial pressure of hydrogen developing from the sample during an unit time as a function of time. Fig.1. shows the relative values of hydrogen obtained by integration over the time region investigated at different temperatures. It can be seen that the curves above 5OOVC i n t e r s e c t each other which can be a consequence of the hydrogen loss during the heating up p r o c e s s . The e t ~ r v e s c a n be c h a r a c t e r i z e d by the beginning slope which depends on the temperature. The r e l a t i v e change of the hydrogen content of the sample as a function of time can be described by a linear connection as follows /3/:
F[t}- Lo9 et°ot.-f where e,O i is the total h y d r o g e n content releasing from the sample, e is the m o m e n t a r y value of the desorbed h y d r o g e n eontent. F r o m the eurves on Fig.2. the D d i f f u s i v i t y can be obtained. A p p l y i n g the formula of E i e h e n a u e r and
Markopolous /3/
D=2,]x~H2 g[t)/t
where H is the length of sample, D can fusivity as a function of temperature. connection between logD and l/T, which valid in this ease and the activation determined. The a c t i v a t i o n energy was
be determined. Fig.3. shows the D difOne c a n s e e t h a t t h e r e is a linear means that the Arrhenius equation is energy, Q a n d t h e DO e £ n s t a n t can be f o u n d t o b e 90 k J m o 1 - 1 / T a b l e 1./.
To d e t e r m i n e the activation energy of the process independently from its kinetics we h a v e a p p l i e d the cross-cut method, as well. The c r o s s - c u t s used in the calculation are shown in Fig.1. In Fig.4. it can be seen that the points belonging to the different cuts lie along parallel straight lines. This proves that the process has a single activation e n e r g y w h i c h i s now f o u n d t o b e 92 k J m o 1 - 1 i n g o o d a g r e e m e n t with the previous results. Table The v a l u e s Authors
o f DO d i f f u s i o n material
1.
constant
and
Q activation
Do/m2see-1/
energy Q/kJ
mol-1/
Eiehenauer
99,999
% A1
1,1x10-5
Ransley
99,99
% A1
1,2x10 -9
140
41
Present work diff. kin eross-eut
99,8
% A1
2,5xi0 -6 -
90 92
Table 1. contains the data obtained from our measurements as well as the data measured by Eichenauer /3/ and Ransley /4/ in solid aluminium. The d e v i a tion of the different measured values is high which can be explained by the different surface films covering the samples and by the different impurity contents of the aluminium used. This factors can result in an increased activation energy and decreased diffusion constant. Considering our measurements the latter effect seems to be probable. It was shown recently that if the exit through the surface is the rate determining then an Arrhenius type temperature dependence of the D diffusibility cannot be obtained. In this ease the rate constant of the process d o e s n o t d e p e n d on t h e t e m p e r a t u r e /8/. We c a n c o n clude from our results therefore, that the desorption of the hydrogen is controlled by its bulk diffusion and not by its exit through the surface. In high purity a l u m i n i u m we h a v e o b s e r v e d , however, that the oxide film plays a more important role in the desorption process of hydrogen. This result will be published soon.
ii
Vol,
Ii, No.
Ii
D I F F U S I O N OF H Y D R O G E N
IN A L U M I N I U M
923
Acknowledgement Thanks
are
due
to Dr.
D.Beke
for
valuable
di>'eussions.
References I.
H.K.Birnbaum
and
2.
D.Altenpohl, 1965.
Aluminium
~.
W.Eichenaucr
q.
C.E+Ransley
and and
5. W.Eichenauer, 6.
C.A.Wert,
Berichte
und
J.Markopolous~ D.E.Talbot,
B.Selmeezi~
~.
E.Hidw~gi
K.Hattenbaeh
to
be
and
Bunsen-Gesellschaft,
and
A.Rebler,
G.A.Remisov
65, ~6~
649,
326,
S06,/1972/.
Verlag,Berlin,
/197~/.
/1955/.
Z.Metallkunde and
76,
Springer
Z.Metallkunde Z.Metallkunde,
K.J.Vashenko, D.F.Cherenga, Met. No.l. ,I1972/.
7.
der
Aluminiumlegierungen,
52,
O.M.Bjalik,
6S2,
Izv.
/1961/.
Vuz.
Cvetn.
published.
E.Kov~cs-Cset~nyi,
Mat.Sci.
and
~.
27,
39,
/1977/.
m~e
o,I o.i o.+, o.e
~]/
~
,, i/l/_,s lilt/
o,1
Fig.l. content
The as
released relative hydrogen a function of time.
Fi~.2. The relative hydrogen content of function of time.
change of the the sample as
a
/,
16 3
,
,
i
Fig.3: The D diffusivity of temperature.
t
+
_ p
as
a function
Fi~.~. Relationship between temperature obtained by the cuts indicated in Fig.l.
time and cross-
Vol, II, pp, 921~923, 1977 Printed in the United States
Pergamon Press, Inc
DIFFUSION OF HYDROGEN IN SOLID ALUMINIUM
Researeh,
K. P a p p a n d E . K o v d c s - C s e t ~ n y i Engineering and Prime Contracting Centre of the Hungarian Corporation~ H-1389 Budapest, P.O.B. 12S. Hungary.
Aluminium
(Received July I, 1977) (Revised September 19, 1977)
Introduetion To o b t a i n diffusion data of hydrogen in metals different methods are in general applied: absorption, desorption, NNR o r G o r s k y e f f e c t /1/. In the literature the diffusion of hydrogen is investigated mainly in bee metals and only a few papers deal with fee metals /1/. The r e s u l t s on t h e d i f f u s i o n of hydrogen in a]uminium measured by desorption in the solid or liquid state are inconsistent with each other which is presumably in connection with impurities and/or the oxidelayer covering the s a m p l e /2,3,4,5,6/. The r e m o v i n g o f t h i s layer is very difficult and its presence can influenee the exit velocity of the hydrogen from the metals /2/, w h i c h l e a d s ¢o a c h a n g e o f t h e b u l k d i f f u s i o n as well. This paper deals with the investigation of the diffusion solid aluminium by the desorption m e t h o d . The s u r f a c e of the g a t e d was c o v e r e d only by natural amorphous oxidelayer which the minimal disturbing effect during the measurements.
of hydrogen in samples investiseemed to cause
3The s a m p l e s e a s t a t a t m o s p h e r i c pressure were heat treated in vacuum at 10Pa. AcCording to Sieverts law, the hydrogen releases from metals, until the equilibrium hydrogen concentration corresponding to the partial pressure o f h y d r o g e n a t 10 - 3 Pa i s a p p r o a c h e d asymptotically. Experimental To m e a s u r e t h e e x i t v e l o c i t y of hydrogen from solid aluminium a Mettler thermoanalyser coupled by a Balzers QMG 311 q u a d r u p o l mass,spectrometer was u s e d . The p a r t i a l pressure of hydrogen released in the reaction chamber was measured using a freezing trap. The h e a t x n g r a t e w a s 25 C / m l n w h i c h i s h i g h enough to prevent the hydrogen exit during the heating process. •
The l e a s t spectrometer was estimated
detectable ~artial pressure i s a b o u t 1~ - ~ P ~ . T h e p a r t i a l to be 10-~-10 --' Pa.
The s a m p l e s w e r e m a d e f r o m a l u m i n i u m p h e r e a t 7 2 0 ° C t o r o d s o f 12 mm d i a m e t e r . is due therefore to the equilibrium value momentary humidity of the air. The s u r f a c e ned and cleaned ehemieally. The s a m p l e o f was heated up t o t h e t e m p e r a t u r e of heat cible. Results
O
using the pressure
.
.
.
.
QMG 311 q u a d r u p o l masschange in our measurements
o f 99,S % p u r i t y cast in air atmosThe h y d r o g e n c o n t e n t of the samples between the liquid metal and the of the samples was carefully tur10 mm d i a m e t e r a n d 10 nun l e n g t h treatment in an aluminiumoxide cru-
and Discussion
The h y d r o g e n c o n t e n t of the samples was controlled by Balzers EA I . E x halograph a n d w a s f o u n d t o b e 0 , 5 e m S / l O 0 g A1 / 7 / . This hydrogen content is due first of all to solute hydrogen. The p a r t b o u n d e d t o i m p u r i t i e s is assumed
921
922
to is
D I F F U S I O N OF H Y D R O G E N
be stable at able to take
IN A L U M I N I U M
the temperatures investigated part in the diffusion process.
and
only
Vol.
the
dissolved
II, No.
hydrogen
The m a s s s p e c t r o m e t e r records the partial pressure of hydrogen developing from the sample during an unit time as a function of time. Fig.1. shows the relative values of hydrogen obtained by integration over the time region investigated at different temperatures. It can be seen that the curves above 5OOVC i n t e r s e c t each other which can be a consequence of the hydrogen loss during the heating up p r o c e s s . The e t ~ r v e s c a n be c h a r a c t e r i z e d by the beginning slope which depends on the temperature. The r e l a t i v e change of the hydrogen content of the sample as a function of time can be described by a linear connection as follows /3/:
F[t}- Lo9 et°ot.-f where e,O i is the total h y d r o g e n content releasing from the sample, e is the m o m e n t a r y value of the desorbed h y d r o g e n eontent. F r o m the eurves on Fig.2. the D d i f f u s i v i t y can be obtained. A p p l y i n g the formula of E i e h e n a u e r and
Markopolous /3/
D=2,]x~H2 g[t)/t
where H is the length of sample, D can fusivity as a function of temperature. connection between logD and l/T, which valid in this ease and the activation determined. The a c t i v a t i o n energy was
be determined. Fig.3. shows the D difOne c a n s e e t h a t t h e r e is a linear means that the Arrhenius equation is energy, Q a n d t h e DO e £ n s t a n t can be f o u n d t o b e 90 k J m o 1 - 1 / T a b l e 1./.
To d e t e r m i n e the activation energy of the process independently from its kinetics we h a v e a p p l i e d the cross-cut method, as well. The c r o s s - c u t s used in the calculation are shown in Fig.1. In Fig.4. it can be seen that the points belonging to the different cuts lie along parallel straight lines. This proves that the process has a single activation e n e r g y w h i c h i s now f o u n d t o b e 92 k J m o 1 - 1 i n g o o d a g r e e m e n t with the previous results. Table The v a l u e s Authors
o f DO d i f f u s i o n material
1.
constant
and
Q activation
Do/m2see-1/
energy Q/kJ
mol-1/
Eiehenauer
99,999
% A1
1,1x10-5
Ransley
99,99
% A1
1,2x10 -9
140
41
Present work diff. kin eross-eut
99,8
% A1
2,5xi0 -6 -
90 92
Table 1. contains the data obtained from our measurements as well as the data measured by Eichenauer /3/ and Ransley /4/ in solid aluminium. The d e v i a tion of the different measured values is high which can be explained by the different surface films covering the samples and by the different impurity contents of the aluminium used. This factors can result in an increased activation energy and decreased diffusion constant. Considering our measurements the latter effect seems to be probable. It was shown recently that if the exit through the surface is the rate determining then an Arrhenius type temperature dependence of the D diffusibility cannot be obtained. In this ease the rate constant of the process d o e s n o t d e p e n d on t h e t e m p e r a t u r e /8/. We c a n c o n clude from our results therefore, that the desorption of the hydrogen is controlled by its bulk diffusion and not by its exit through the surface. In high purity a l u m i n i u m we h a v e o b s e r v e d , however, that the oxide film plays a more important role in the desorption process of hydrogen. This result will be published soon.
ii
Vol,
Ii, No.
Ii
D I F F U S I O N OF H Y D R O G E N
IN A L U M I N I U M
923
Acknowledgement Thanks
are
due
to Dr.
D.Beke
for
valuable
di>'eussions.
References I.
H.K.Birnbaum
and
2.
D.Altenpohl, 1965.
Aluminium
~.
W.Eichenaucr
q.
C.E+Ransley
and and
5. W.Eichenauer, 6.
C.A.Wert,
Berichte
und
J.Markopolous~ D.E.Talbot,
B.Selmeezi~
~.
E.Hidw~gi
K.Hattenbaeh
to
be
and
Bunsen-Gesellschaft,
and
A.Rebler,
G.A.Remisov
65, ~6~
649,
326,
S06,/1972/.
Verlag,Berlin,
/197~/.
/1955/.
Z.Metallkunde and
76,
Springer
Z.Metallkunde Z.Metallkunde,
K.J.Vashenko, D.F.Cherenga, Met. No.l. ,I1972/.
7.
der
Aluminiumlegierungen,
52,
O.M.Bjalik,
6S2,
Izv.
/1961/.
Vuz.
Cvetn.
published.
E.Kov~cs-Cset~nyi,
Mat.Sci.
and
~.
27,
39,
/1977/.
m~e
o,I o.i o.+, o.e
~]/
~
,, i/l/_,s lilt/
o,1
Fig.l. content
The as
released relative hydrogen a function of time.
Fi~.2. The relative hydrogen content of function of time.
change of the the sample as
a
/,
16 3
,
,
i
Fig.3: The D diffusivity of temperature.
t
+
_ p
as
a function
Fi~.~. Relationship between temperature obtained by the cuts indicated in Fig.l.
time and cross-