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TRITIUM RELEASE CHARACTERISTICS OF Al-Li ALLOYS EXAMINED BY LIQUID SCINTILLATION
TECHNIQUE
H. Saito, Y. Ishida, H. Yoshida
To cite this version:
H. Saito, Y. Ishida, H. Yoshida. TRITIUM RELEASE CHARACTERISTICS OF Al-Li ALLOYS
EXAMINED BY LIQUID SCINTILLATION TECHNIQUE. Journal de Physique Colloques, 1987, 48
(C3), pp.C3-541-C3-545. �10.1051/jphyscol:1987363�. �jpa-00226594�
JOURNAL DE PHYSIQUE
Colloque C3, supplbment
au n"9,Tome
48,septembre 1987
TRITIUM RELEASE CHARACTERISTICS OF A1-Li ALLOYS EXAMINED BY LIQUID SCINTILLATION TECHNIQUE
H ,
SAITO, Y. ISHIDA
andH. YOSHIDA*
University of Tokyo, Institute of Industrial Science, 7-22-1 Roppongi, Minato-ku, Tokyo
106, Japan"sumitorno Light Metals Ind. Ltd, 3-1-12 Sennen, ~ i n a t o - k u , Nagoya-shi 455, J a p a n
A b s t r a c t
Hydrogen release characteristics of A1-Li alloys at room temperature were examined by liquid scintillation analysis of tritium which has been doped
electrolytically in the bulk specimen. The tritium release showed quantitatively that both solubility and mobility of hydrogen in the alloy is strong functions of lithium concentration in the matrix suggesting the nature of tritium trapping micro-structures.
Experimentals
The A1-Li alloys were prepared in the form of a sheet specimen of thickness l.Omm by cold rolling. The specimen was sealed in a silica tube containing Ar and were heat-treated as shown in Table
1.After the heat treatment, the specimen was polished electrolytically in nitric acid and methanol solution of volume ratio 1:3 kept at 313K. After polishing the specimen was washed thoroughly with ethanol.
The bulk specimen was charged cathddically in tritium water as shown in Fig.2.
The electrolysis of tritium was made in 0.002N-Sodium hydroxide aqueous solution.
The specific ratioactivity of the solution was 0.1Gi/cm3. Electric current densi,ty and electrolytical charging time was 0.05-5pA/cm2 at 7.2Ks respectively.
Dudng the electrolytical tritium charging, helium gas was made to flow at a constant rate and the tritium contained in the gas was oxidized to tritium water in an electric furnace containing heated copper oxide. The tritium water was cooled in the spiral copper pipe and absorbed firstly by magnesium perchlorate, and finally in water. The water, however, didn't show any radioactivity
confirming that the tritium leakage to atmosphere was negligible. For safety the whole apparatus was contained in a draft chamber.
After tritium charging the specimen was washed immediately with methanol as shown in Fig.2. The bulk specimen as placed at a hanging platium wire(0.159X?mm) and immersed in dioxane scintillator of 10cc in volume. Radiation (@-ray 18KeV) from tritium either in the specimen or diffused out from the specimen to the dioxane scintillator was measured by a liquid scintillation counter(Parkard TRI-CARB-3255). It was measured for 10-20 times at every 30 seconds. The whole sequence was repeated after changing the dioxane scintillator, the tritium counting rate increased with time due to tritium having diffused out from the specimen. The measurement was repeated for three days each time renewing the dioxane scintillator and changing the measurement time until the increase in the tritium counting rate become immeasurable. Tritium release rate (cpm/min) was estimated from the initial slope of the counting rate increase just after renewing the dioxane scintillator(1).
Results
Tritium release characteristics of an A1-Li alloy was shown Fig.?. Tritium total counting rates increased in time and the increment indicated the release of
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987363
C3-542
JOURNALDE
PHYSIQUEd i f f u s i v e t r i t i u m from t h e specimen. The slope decreased g r a d u a l l y and became zero a f t e r t h r e e days. Primary t r i t i u m counting r a t e s , a s shown i n Fig.3, correspond t o t h e r e l e a s e r a t e o f t r i t i u m upon renewing t h e dioxane s c i n t i l l a t o r ( 1 )
.
1. The e f f e c t of h e a t treatment temperature and l i t h i u m concentration.
Tritium r e l e a s e c h a r a c t e r i s t i c s of A1-Li a l l o y were analyzed a s a f u n c t i o n of h e a t treatment c o n d i t i o n and l i t h i u m concentration a s shown i n Fig.4 and 5 r e s p e c t i v e l y . The case of Al-3.lwt.ZLi was shown i n Fig.4. The t r i t i u m r e l e a s e counting r a t e s were high i n annealed than i n overaged specimens. The v a l u e s d i f f e r e d by an o r d e r of magnitude i n t h e i n i t i a l r e l e a s e c h a r a c t e r i s t i c s , b u t a f t e r t h r e e days, t h e two r e l e a s e r a t e s were almost t h e same.
I n t h e same manner, t r i t i u m r e l e a s e c h a r a c t e r i s t i c s of Al-0.24wt.%Li a l l o y were compared. The t r i t i u m r e l e a s e counting r a t e s of annealed, aged and overaged specimens showed a s i m i l a r c h a r a c t e r i s t i c . The t h r e e l i n e s a r e p a r a l l e l . The specimen was h e a t t r e a t e d a t 823K f o r 7.2Ks and showed h i g h e s t t r i t i u m r e l e a s e counting r a t e s . The lowest values were with a specimen h e a t t r e a t e d a t 723K f o r 3.6Ks and overaged 423K f o r 774Ks.
The e f f e c t of l i t h i u m c o n c e n t r a t i o n t o t h e t r i t i u m r e l e a s e i s shown i n Fig.5.
The specimens were t r e a t e d a t 823K f o r 3.6Ks. The A1-0.24wt.ZLi a l l o y r e l e a s e d most g r a d u a l l y while Al-3.lwt.Li a l l o y showed a n a b r u p t decrease. The specimen aged a t 823K f o r 3.6Ks and overaged a t 423K f o r 7 7 G s charged gradually.
2. The e f f e c t of charging c u r r e n t d e n s i t y , time and t h i c k n e s s of t h e specimen Tritium r e l e a s e i n 3.lwt.ZLi a l l o y was a f f e c t e d by t h e c u r r e n t d e n s i t y a s shown i n Fig.6 and by charging time and t h e t h i c k n e s s of t h e specimen ( f i g . 7 )
r e s p e c t i v e l y .
F i r s t l y , t r i t i u m r e l e a s e s a t e l e c t r i c c u r r e n t d e n s i t i e s 0.025 and 0 . 2 5 ~ ~ / c m ' were compared. When t h e c u r r e n t d e n s i t y was below 0.025p~/cm', t h e s l o p e was n i l . Therefore, t h e t r i t i u m counting r a t e decreased gradually. To compare 0.25 and 0.025pA/cmz, t h e counting i n i t i a l counting r a t e was high by a n o r d e r of magnitude f o r few minutes. Afterwards, t h e s l o p e showed s t e e p decrease r a t e . The t r i t i u m r e l e a s e d i f f e r e d by t h e charging time. A t t h e t r i t i u m charging time of 0.5hr and 1.Ohr n e a r l y t h e same counting r a t e s were found. I n case of 2hrs charging, however, a n i n c r e a s e between 2 t o
3
times was noticed. I n t h e Al-3.lwt.%Li a l l o y t h e e f f e c t of t h e t h i c k n e s s of t h e specimen was evident a s shown i n Fig.7. The specimens were marked a t one s i d e by manicure p a i n t and charged a t 5rA/cmZ f o r 7.2Ks. With i n c r e a s e i n t h e t h i c k n e s s of t h e A1-Li specimen, t r i t i u m r e l e a s e counting r a t e has increased, u n t i l t h e t h i c k n e s s of 0.58mm was reached.Discussion
The t r i t i u m r e l e a s e counting r a t e s were h i g h e s t with a n annealed specimen than aged and overaged specimens. With i n c r e a s e i n t h e l i t h i u m c o n c e n t r a t i o n , t h e t r i t i u m r e l e a s e r a t e increased. I n aged and overaged specimens t h e r e l e a s e c h a r a c t e r i s t i c s seemed t h e same because t h e l i n e s i n Fig.7 a r e p a r a l l e l i n s p i t e of t h e magnitude d i f f e r i n g by a n o r d e r of magnitude.
The c o n c e n t r a t i o n of H t 3 H of t h e specimen(2,3,4) were estimated from t h e i n i t i a l counting r a t e and counting r a t e of a s charged specimen.
I n Table 1 curpent d e n s i t i e s were shown with t h e concentrations of t o t a l H t H.
The e f f e c t on t h e t r i t i u m r e l e a s e . s a t e was f i r s t analysed by comparing t h e i n i t i a l counting r a t e s and t h e slope measured immediately a f t e r t r i t i u m charging. With annealed specimen of 3.lwt.ZLi specimens t h e r e l e a s e r a t e R decreased with time by t h e same exponent nn2/3 where R=R,tn
.
The exponent d i d n ' t charge with 0.24wt.ZLi specimens. Although t h e R , value i t s e l f decreased with i n c r e a s e i n t h e agingtime.
The release rate of 3.lwt.%Li alloy returned basically to that of 0.24wt.%Li alloy upon aging at 423K. It may reflect the decrease in the matrix concentration of lithium by the $ precipitation. The reinaining small effect of aging time in Al-0.24wt.%Li alloy and lithium content in the aged specimen may reflect the amount of trapped hydrogen in the changed specimen, because the release exponent n was the same with the specimens.
Conclusion
The present analysis of the release characteristics showed that the enhancement of both the solid solibility and release rate of hydrogen by lithium concentration in the matrix in annealed and water-quenched alloys. The effect of age
precipitated A1-Li alloys to the release rate is small in present aged alloys.
The zinalysis suggested that the solid solibility and mobility of mobile hydrogen is a idnction of lithium concentration in the matrix. The effect of tritium concentration may be neglected in the range of the present experiment.
References
(1)H.Saito and Y-Ishida: The Japan Institute of Metals,Oct.1986,334.
(2)T.Asaoka,H.Saito,N.Nogawa,N..Morikawa
and Y.Ishida: Seisan-Kenkyuu,4,1985,139- 142.
(3)T.H.Sanders,Jr. and E.A.Starke,Jr.: Aluminum-Lithium Alloys
11,The Metallurgical Society of AIME,1983.
(4)M.Yoshida and Y.Baba: The Japan Institute of Metals,10,1984,65-66.
0.002N NaOH Tritiated Water
Furnace
Perchlorate Water
Fig.1 Electrolytical tritium charging of the bulk specimen.
Dioxane ( I ) Naphthalene ( 1009 ) PPO ( 1 0 9 ) PO POP ( 0.25 g t o c c
Fig.2 Tritium measurement with a dioxide scintillator.
Table 1 Heat treatment condition of A1-Li alloy.
A1-0.24 and 3.1 wt . %Li
823K X 3.6Ks(W.Q.)
JOURNAL
DE
PHYSIQUE..-
Elapsed time ( m i n )
Fig.3 Tritium release measurement by a liquid scintillation counter.
Fig.4 Tritium release characteristics as Fig.5 Tritium release characteristics a functjon of heat treatment in an of alloys with
3.1
and 0.2L,wt.%Li81-3.lwt.ZLi alloy. concentration. It was heat treated at 823K for 3.6Ks.
E l a p s e d T i m e ( in I n ) Fig.7 Tritium r e l e a s e c h a r a c t e r i s t i c s Fig.6 Tritium r e l e a s e a s a f u n c t i o n of t h e
as a f u n c t i o n of t h e thickness oLr che charging c u r r e n t d e n s i t y . I t specimen. The SpeCJIEeII was annsaled was annealed a t 825B f o r 3.6Ks and
overaged a t L23K f o r 0.8MKs. at 823K for 3.6Ks and aged a t 423fi f o r 86.Wis.
Table 2 The t o t a l
H + ~ H
c o n c e n t r a t i o n a s a f u n c t i o n of e l e c t r i c c u r r e n t d e n s i t y i n ppm. F i g u r e s i n t h e p a r e n t h e s i s show t h e t r i t i u m counting r a t e sa f t e r t h r e e days. The specimen were annealed a t 823K f o r 3.6Ks and aged a t 423K f o r 86.4Ks. A l l specimens were charged f o r 7.2Ks.
1 5 n/cm2 10.89 ppm (21.2)
11.3 (37.2)
55.7 (207.0) pure aluminium
A1-0.24 wt.%
A1-3.1 wt.%
b
