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The behaviour of diffusion and permeation of tritium through 316L stainless steel with coating of TiC and TiN + TiC
journal of
nuclear materials
Journal of Nuclear Materials 191-194 (1992) 221-225 North-Holland
The behaviour of diffusion and permeation of tritium through 316L stainless steel with coating of TiC and TiN + TiC Changqi Shan, Aiju Wu, Yongjing Li, Ziqiang Zhao, Oingwang Chen, Qiurong Huang and Suolang Shi Academia Sinica, Institute of Atomic Energy, P.O. Box 275-51, Beijing, People's Republic of China
The diffusion and permeation behaviour of tritium through the films of TiC and TiN + TiC coated on surface of 316L stainless steel by chemical vapour deposition has been described. The permeability of tritium through these two kinds of films is low and is five to six orders of magnitude lower than that in bulk at 200-5000C. The films have good compatibility with the bulk, high resistance to thermal shock and irradiation. They can be used as clad materials of the tritium breeder in the breeder irradiation container in a fusion reactor tritium technology study and as candidate materials of the first wall in a fusion reactor study.
1. Introduction At present, investigations on preventing tritium permeation through metal construction materials is not aimed at the inherent permeability of the metal construction materials themselves, but at the permeability of the coating materials on the surfaces of the metal construction materials. The coatings can be put into two categories: one is the compact oxidation film formed by' oxidation of elements of metal construction materials, and the other is the coated films on the surfaces of the metal construction materials by chemical vapour deposition, ion sputtering, ion implanting, and so on. The purpose of investigating these coatings is to determine the conditions for forming tritium permeation barriers in these coating materials and the barrier stability and to find coating materials with low permeability at high temperature. Alire et al. [1] found a way of forming a compact oxidation film on the aluminium surface by controlled oxidation. The tritium permeability through aluminium is decreased greatly, because the tritium permeation barrier of OT- ions is formed in the process of this kind of diffusion and permeation through the film. Lee et al. [2J investigated the permeation behaviour of tritium in some glasses. The OT- ions are also formed in the process of diffusion and permeation of tritium through glasses above 300·C, making the tritium permeability through glasses decrease. Thus, we think the action of preventing tritium permeation is obvious by forming OT~ ions, making the permeability decrease by several orders of magnitude. The formation and stability of the tritium permeation barrier in the films of TiC and TiN + TiC coated
on the surface of 316L stainless steel are investigated in this work. An investigation of tritium permeation through a TiN + TiC composite film has not been reported previously.
2. Experimental 2.1. Sample preparation
By the chemical vapour deposition method, a titanium film of about 200 A is deposited on the surfaces of the double-cup samples shown in fig. 1. Then TiC films of about 2.5 ILm are formed by leading C 2 H 2 onto the samples. By the same method, titanium of about 200 A is deposited on the sample surfaces, then TiN films of about 1 ILm are formed on the sample surfaces by leading nitrogen gas onto the samples. Finally the TiN + TiC composite films of about 2.5 ILm are formed on the sample surfaces by leading C 2 H 2 onto the samples. The samples are taken out after the films are coated. The test of the film compatibility with bulk and the thermal shock test have been made. The sample shown in fig. 1 is put in a copper radiator, and the radiator is welded on the permeation device with an argon arc weld within 20 s. Finally, a leak detection test is made. The method and the apparatus of permeability measurement are shown in ref. [3J. 2.2. Test procedures
The samples are stripped on a film stripper. The combination strength of the film with the bulk is larger than the bulk strength. The diffusion combination of
0022-3115/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
222
C. Shan et al. / Diffusion and permeation of tritium
Fig. I. Double cup sample.
film with bulk is very good, as shown by electronic probe. Between film and bulk, no crack is found, as shown in fig. 2. After the samples are heated to 611°C and held for 21 h, they are cooled rapidly to room temperature in an argon atmosphere. The above tests were made and no changes in film construction and comhination strength of film with bulk were found. 2.3. Procedure for determining CH4- in films of TiC and TiN + TiC
The samples coated with TiC and TiN + TiC films were annealed in vacuum (6 X 10- 2 mm Hg) in a mix-
ture of deuterium and argon of 500 Pa and in an argon atmosphere (containing 10 ppm oxygen,S ppm hydrogen) at 336°C and in an argon atmosphere (containing 10 ppm oxygen, 5 ppm hydrogen) at 611°C, respectively. The film surface composition analyses were made by secondary ion mass spectroscopy (SIMS) for samples annealed at 336°C for 25 days and at 611 °C for 1 day and for unannealed samples. The analysis results are shown in figs. 3a and 3b. A large number of CH 4 ions are found in the TiC film annealed in the argon atmosphere and in the deuterium atmosphere at 336°C, and some 0+ ions existed simultaneously. Since the binding force between hydrogen and carbon is stronger than that between deuterium and carbon, the CD4ions are seldom found in the SIMS analyses of TiC films [4,5]. The amount of 0- ions in TiC film in the argon atmosphere at 611°C is the same as at 336°C, and the amount of CH 4 ions contained is only one ten thousandth of that at 336°C. The presence of 0 + and CH 4 ions is very rare in the TiC film which is not annealed. It is considered that CH 4 in the film is oxidized at 611 °C and the oxidation reaction (incomplete burn) is
That is, methane is decomposed into carbon and water.
Fig. 2. Electronic probe photographs of cross section of 316L stainless steel coated with TiC and TiN + TiC films on its surface. Ca) TiC films 2000 X; (b) TiN + TiC films 3000 x.
C. Shan et al. I D(ffusion and permeation of tritium
223
b
Cl-I4
O· C, H;
1 •. 0,1, ',1
C~
-
H
lJ~ \
d (1-
C
0; C( ; _ _
~~
/21619 24 32·35'37,
48
~
Mg M
Ilrt
lie
TiC;
60
72
K'
N' I<
c:
Sit
tJ'", o+Lt
3639
485256 60 64 72
I'
I
A~
I
I
U
f 71216202428
r'
j
I
I
t
Fe
2(fI t
4044 48 52566064- 72
Fig. 3. Mass spectra of secondary ions of TiN + TiC films coated on the surface of 316L stainless steel. (a) In argon 610°C for 21 h; (b) in mixture of deuterium and argon at 336°C for 25 d.
Table 1 Diffusivity and permeability of tritium through 316L stainless steel coated with TiN + TiC films on its surface T [K]
480
573
665
720
773
879
A B C
6.74XlO 17 1.00 X 10- 17 9.33x1O-12
2.42 X 10-'16 2.41 X 10- 16 1.07 X 10- 10
6.51X1O 16 2.34x1O-IS 6.l6xlO-1O
7.56X1O 16 6.91XlO- 15 1.41x1O-9
1.69 X 10-- 14 J.69x1O-14 2.81xlQ-9
2.03xIO 12 7.36xlO- 14 8.68xlO- 9
Empirical formula: B '" 3.3 x 10 9 exp( -78281 [J Imol]l RT) [mol(NPT) 1m s MPa1/2]. Note: A - measured values; B - calculated values from empirical formula; C - measured values on clean surface of stainless steel.
Table 2 Diffusivity and permeability of tritium through 316L stainless steel coated with TiC films on its surface T [K]
478
573
674
719
773
878
A B C
3.33xIO 16 4.30xlO- IB 8.76xlO- 12
1.07xlO 16 1.07 x 10- 16 1.07 x 10-10
1.l9xtO 15 1.1lx10- 15 7.12xlO- 1O
5.49 x 10- 14 2.80X10- 15 1.39 x 10- 9
2.31 X 10- 13 6.88xlO- 1S 2.81XlO- 9
6.47x1O 11 2.88x1O-14 8.60xlO- 9
Empirical formula: B'" 1.07 x 10 9 exp( -76788 [J ImolJ/ RT) [mol(NTP)/m s MPa1/2]. Note: A - measured values; B - calculated values from empirical formula; C - measured values on clean surface of stainless steel.
224
C. Shan et at. / Diffusion and permeation of tritium
3. Results and discussion
-13
3.1. Diffusivity and permeability measurements
The results of the measurements diffusivity and permeability of tritium through the films of TiC and TiN + TiC coated on the surface of 316L stainless steel at 200-600°C are shown in tables 1 and 2. It is obvious from tables 1 and 2 that the diffusivity and permeability of tritium through the composite film of TiN + TiC coated on the surface of 316L stainless steel are five to six orders of magnitude lower than that of bulk at 200-500°e. The diffusivity and permeability of tritium through the TiC film coated on the surface of 316L stainless steel are four to six orders of magnitude lower than that of the bulk. The diffusivity and permeability do not change greatly at 200-450°e. The permeability at 200°C is a bit larger than that at 300°e. This can be verified from the SIMS analysis results of the hydrocarbon contained in the TiC film in different atmospheres, different heat treatment states at different temperatures. Since a large amount of CHi ions are formed in the films of TiC and TiN + TiC in the permeation processes at 300°C, the CHi ions in the film lattices resist tritium permeation [6]. It is also obvious from tables 1 and 2 that the permeability of tritium in the TiC film at 450-600°C is two to three orders of magnitude larger than that calculated from the empirical formula. This indicates that a change of mechanism occurs for the diffusion and permeation of tritium through the films of TiC and TiN + TiC in this temperature range. From the SIMS analyses described above, it is clear that the barrier of the large amount of CH 4 formed in the permeation process in the films of TiC and TiN + TiC begins to oxidize and resolve into C and HTO, and this makes the permeability of tritium through films of TiC and TiN + TiC increase greatly. The tritium measured is in the form of HTO, for the most part (> 95%), and in the form of HT in a small amount. It is known from the oxidation experiment of TiC and TiN + TiC that the film begins to oxidize in air at about 390°C, which is visible to the naked eye since the films begin to lose gloss and become grey by oxidation above 450°C. The TiC film begins to scale at 600°C. Although the oxygen content is not large in argon gas, the TiC film has begun to oxidize (the oxidation is invisible to the naked eye). Since TiC is oxidized to form TiO, oxygen enters into the film to oxidize the CHi ions formed earlier and produce carbon and water. The tritium permeation barrier is ruined, and the permeability of tritium through the TiC film increases greatly. It is possible that the tritium permeation barrier could be protected from oxidation if SiC or Al Z0 3 films were coated on the surface of the TiC film. The next step of our work is to coat pyrolytic graphite and silicon on the surface of the TiC film and
. INITIAL x FRESH
-
16
1~-==~;::~~=.=X~:..:_:..:_-:':;--:'i;~'"~==:=':7"===::"-'" i ! ~
o
100
200
300
500
600
l(hr)
Fig. 4. Contrast of initial experiment with fresh experiment of 316L stainless steel coated with TiC films at 300°C.
to make them form a SiC protective film. We will also coat a thin aluminium layer on the surface of the TiC film and oxidize this aluminium layer to Al z0 3 completely by the method of control oxidation. 3.2. Film stability
The experiments show the permeability of tritium through the films of TiC and TiN + TiC is stable in long-term operations at 200-450°C. No change in permeability is found in a continuous experiment of 90 days. After 90 days, this sample was stored for 90 days at room temperature, and then used again for a permeation experiment. The permeability is stable for a 20day experiment at 200-450°C, and there is no process of forming the tritium barrier at the beginning of the fresh experiment, as shown in fig. 4. Experiments also show that the compatibility of the films with the bulk is good and the films resist thermal shock and irradiation [7]. 3.3. Mechanism analysis
The SIMS analysis results of the hydrocarbon formed in TiC films in different atmospheres and different heat treatment states at different temperatures and the experimental results in tables 1 and 2 show the diffusion and permeation of tritium through the films of TiC and TiN + TiC below 300°C are molecular diffusion. This follows because a large amount of CHi ions have not been formed in the lattice of the TiC film to resist tritium diffusion. At 300-450°C, since a large amount of CHi ions are formed in the permeation process, the tritium permeation barrier is formed. Because the CH i ions are in the rest state in the TiC lattices, the dominant form of transport of tritium in this kind of film is migration of the T+ ion from one carbon site to a neighboring carbon site in the basic lattices. Immediately after transport, T 2 (or HT) is formed on the surface of the film, then leaves the film surface. At 450-600°C, since the TiC film is oxidized, the CH 4 tritium permeation barrier resolves into carbon and water. The tritium permeation barrier is ru-
C. Shan et al. / Diffusion and permeation of tritium
ined, and the diffusion of tritium through the TiC film is changed into molecular (T 2 and HT) diffusion.
225
breeder in a breeder irradiation container in a tritium technology study of a fusion reactor and as first wall materials in a fusion reactor study.
4. Summary References
The results show that a tritium permeation barrier is formed in the process of tritium permeation through the films of TiC and TiN + TiC coated on the surface of 316L stainless steel above 300°C. At 200-500°C, the permeability of tritium through the film of TiC coated on the surface of 316L stainless stcel is four to six orders of magnitude lower than that in bulk, while the permeability of tritium through the films of TiN + TiC coated on the surface of 316L stainless steel is five to six orders of magnitude lower than that in bulk. These films can be used as clad materials for the tritium
[I) R.M. Alire, in: Tritium Proceeding, Tritium Technology in Fusion, Fusion and Isotopic Applications, April 29-May 1 (1980) 98-01. [2) R. Lee et aI., J. Chern. Phys. 36 (4) (962) 1062. [3) Shan Changqi et al., J. Nue!. Mater. 179-181 (] 991) 322. [4) C.B. Kwok et al., J. Nuel. Mater. 170 (J 990) 57. [5) c. Ferro et aI., J. Nue!. Mater. 101 (1981) 224. [6) M. Saeki and N.M. Masaki, Radiochimica Aeta 46 (1989) 163. [7) Y. Weiguo et aI., Nue!. Fusion and Plasma Phys. 7 (4) (1987) 176.
nuclear materials
Journal of Nuclear Materials 191-194 (1992) 221-225 North-Holland
The behaviour of diffusion and permeation of tritium through 316L stainless steel with coating of TiC and TiN + TiC Changqi Shan, Aiju Wu, Yongjing Li, Ziqiang Zhao, Oingwang Chen, Qiurong Huang and Suolang Shi Academia Sinica, Institute of Atomic Energy, P.O. Box 275-51, Beijing, People's Republic of China
The diffusion and permeation behaviour of tritium through the films of TiC and TiN + TiC coated on surface of 316L stainless steel by chemical vapour deposition has been described. The permeability of tritium through these two kinds of films is low and is five to six orders of magnitude lower than that in bulk at 200-5000C. The films have good compatibility with the bulk, high resistance to thermal shock and irradiation. They can be used as clad materials of the tritium breeder in the breeder irradiation container in a fusion reactor tritium technology study and as candidate materials of the first wall in a fusion reactor study.
1. Introduction At present, investigations on preventing tritium permeation through metal construction materials is not aimed at the inherent permeability of the metal construction materials themselves, but at the permeability of the coating materials on the surfaces of the metal construction materials. The coatings can be put into two categories: one is the compact oxidation film formed by' oxidation of elements of metal construction materials, and the other is the coated films on the surfaces of the metal construction materials by chemical vapour deposition, ion sputtering, ion implanting, and so on. The purpose of investigating these coatings is to determine the conditions for forming tritium permeation barriers in these coating materials and the barrier stability and to find coating materials with low permeability at high temperature. Alire et al. [1] found a way of forming a compact oxidation film on the aluminium surface by controlled oxidation. The tritium permeability through aluminium is decreased greatly, because the tritium permeation barrier of OT- ions is formed in the process of this kind of diffusion and permeation through the film. Lee et al. [2J investigated the permeation behaviour of tritium in some glasses. The OT- ions are also formed in the process of diffusion and permeation of tritium through glasses above 300·C, making the tritium permeability through glasses decrease. Thus, we think the action of preventing tritium permeation is obvious by forming OT~ ions, making the permeability decrease by several orders of magnitude. The formation and stability of the tritium permeation barrier in the films of TiC and TiN + TiC coated
on the surface of 316L stainless steel are investigated in this work. An investigation of tritium permeation through a TiN + TiC composite film has not been reported previously.
2. Experimental 2.1. Sample preparation
By the chemical vapour deposition method, a titanium film of about 200 A is deposited on the surfaces of the double-cup samples shown in fig. 1. Then TiC films of about 2.5 ILm are formed by leading C 2 H 2 onto the samples. By the same method, titanium of about 200 A is deposited on the sample surfaces, then TiN films of about 1 ILm are formed on the sample surfaces by leading nitrogen gas onto the samples. Finally the TiN + TiC composite films of about 2.5 ILm are formed on the sample surfaces by leading C 2 H 2 onto the samples. The samples are taken out after the films are coated. The test of the film compatibility with bulk and the thermal shock test have been made. The sample shown in fig. 1 is put in a copper radiator, and the radiator is welded on the permeation device with an argon arc weld within 20 s. Finally, a leak detection test is made. The method and the apparatus of permeability measurement are shown in ref. [3J. 2.2. Test procedures
The samples are stripped on a film stripper. The combination strength of the film with the bulk is larger than the bulk strength. The diffusion combination of
0022-3115/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
222
C. Shan et al. / Diffusion and permeation of tritium
Fig. I. Double cup sample.
film with bulk is very good, as shown by electronic probe. Between film and bulk, no crack is found, as shown in fig. 2. After the samples are heated to 611°C and held for 21 h, they are cooled rapidly to room temperature in an argon atmosphere. The above tests were made and no changes in film construction and comhination strength of film with bulk were found. 2.3. Procedure for determining CH4- in films of TiC and TiN + TiC
The samples coated with TiC and TiN + TiC films were annealed in vacuum (6 X 10- 2 mm Hg) in a mix-
ture of deuterium and argon of 500 Pa and in an argon atmosphere (containing 10 ppm oxygen,S ppm hydrogen) at 336°C and in an argon atmosphere (containing 10 ppm oxygen, 5 ppm hydrogen) at 611°C, respectively. The film surface composition analyses were made by secondary ion mass spectroscopy (SIMS) for samples annealed at 336°C for 25 days and at 611 °C for 1 day and for unannealed samples. The analysis results are shown in figs. 3a and 3b. A large number of CH 4 ions are found in the TiC film annealed in the argon atmosphere and in the deuterium atmosphere at 336°C, and some 0+ ions existed simultaneously. Since the binding force between hydrogen and carbon is stronger than that between deuterium and carbon, the CD4ions are seldom found in the SIMS analyses of TiC films [4,5]. The amount of 0- ions in TiC film in the argon atmosphere at 611°C is the same as at 336°C, and the amount of CH 4 ions contained is only one ten thousandth of that at 336°C. The presence of 0 + and CH 4 ions is very rare in the TiC film which is not annealed. It is considered that CH 4 in the film is oxidized at 611 °C and the oxidation reaction (incomplete burn) is
That is, methane is decomposed into carbon and water.
Fig. 2. Electronic probe photographs of cross section of 316L stainless steel coated with TiC and TiN + TiC films on its surface. Ca) TiC films 2000 X; (b) TiN + TiC films 3000 x.
C. Shan et al. I D(ffusion and permeation of tritium
223
b
Cl-I4
O· C, H;
1 •. 0,1, ',1
C~
-
H
lJ~ \
d (1-
C
0; C( ; _ _
~~
/21619 24 32·35'37,
48
~
Mg M
Ilrt
lie
TiC;
60
72
K'
N' I<
c:
Sit
tJ'", o+Lt
3639
485256 60 64 72
I'
I
A~
I
I
U
f 71216202428
r'
j
I
I
t
Fe
2(fI t
4044 48 52566064- 72
Fig. 3. Mass spectra of secondary ions of TiN + TiC films coated on the surface of 316L stainless steel. (a) In argon 610°C for 21 h; (b) in mixture of deuterium and argon at 336°C for 25 d.
Table 1 Diffusivity and permeability of tritium through 316L stainless steel coated with TiN + TiC films on its surface T [K]
480
573
665
720
773
879
A B C
6.74XlO 17 1.00 X 10- 17 9.33x1O-12
2.42 X 10-'16 2.41 X 10- 16 1.07 X 10- 10
6.51X1O 16 2.34x1O-IS 6.l6xlO-1O
7.56X1O 16 6.91XlO- 15 1.41x1O-9
1.69 X 10-- 14 J.69x1O-14 2.81xlQ-9
2.03xIO 12 7.36xlO- 14 8.68xlO- 9
Empirical formula: B '" 3.3 x 10 9 exp( -78281 [J Imol]l RT) [mol(NPT) 1m s MPa1/2]. Note: A - measured values; B - calculated values from empirical formula; C - measured values on clean surface of stainless steel.
Table 2 Diffusivity and permeability of tritium through 316L stainless steel coated with TiC films on its surface T [K]
478
573
674
719
773
878
A B C
3.33xIO 16 4.30xlO- IB 8.76xlO- 12
1.07xlO 16 1.07 x 10- 16 1.07 x 10-10
1.l9xtO 15 1.1lx10- 15 7.12xlO- 1O
5.49 x 10- 14 2.80X10- 15 1.39 x 10- 9
2.31 X 10- 13 6.88xlO- 1S 2.81XlO- 9
6.47x1O 11 2.88x1O-14 8.60xlO- 9
Empirical formula: B'" 1.07 x 10 9 exp( -76788 [J ImolJ/ RT) [mol(NTP)/m s MPa1/2]. Note: A - measured values; B - calculated values from empirical formula; C - measured values on clean surface of stainless steel.
224
C. Shan et at. / Diffusion and permeation of tritium
3. Results and discussion
-13
3.1. Diffusivity and permeability measurements
The results of the measurements diffusivity and permeability of tritium through the films of TiC and TiN + TiC coated on the surface of 316L stainless steel at 200-600°C are shown in tables 1 and 2. It is obvious from tables 1 and 2 that the diffusivity and permeability of tritium through the composite film of TiN + TiC coated on the surface of 316L stainless steel are five to six orders of magnitude lower than that of bulk at 200-500°e. The diffusivity and permeability of tritium through the TiC film coated on the surface of 316L stainless steel are four to six orders of magnitude lower than that of the bulk. The diffusivity and permeability do not change greatly at 200-450°e. The permeability at 200°C is a bit larger than that at 300°e. This can be verified from the SIMS analysis results of the hydrocarbon contained in the TiC film in different atmospheres, different heat treatment states at different temperatures. Since a large amount of CHi ions are formed in the films of TiC and TiN + TiC in the permeation processes at 300°C, the CHi ions in the film lattices resist tritium permeation [6]. It is also obvious from tables 1 and 2 that the permeability of tritium in the TiC film at 450-600°C is two to three orders of magnitude larger than that calculated from the empirical formula. This indicates that a change of mechanism occurs for the diffusion and permeation of tritium through the films of TiC and TiN + TiC in this temperature range. From the SIMS analyses described above, it is clear that the barrier of the large amount of CH 4 formed in the permeation process in the films of TiC and TiN + TiC begins to oxidize and resolve into C and HTO, and this makes the permeability of tritium through films of TiC and TiN + TiC increase greatly. The tritium measured is in the form of HTO, for the most part (> 95%), and in the form of HT in a small amount. It is known from the oxidation experiment of TiC and TiN + TiC that the film begins to oxidize in air at about 390°C, which is visible to the naked eye since the films begin to lose gloss and become grey by oxidation above 450°C. The TiC film begins to scale at 600°C. Although the oxygen content is not large in argon gas, the TiC film has begun to oxidize (the oxidation is invisible to the naked eye). Since TiC is oxidized to form TiO, oxygen enters into the film to oxidize the CHi ions formed earlier and produce carbon and water. The tritium permeation barrier is ruined, and the permeability of tritium through the TiC film increases greatly. It is possible that the tritium permeation barrier could be protected from oxidation if SiC or Al Z0 3 films were coated on the surface of the TiC film. The next step of our work is to coat pyrolytic graphite and silicon on the surface of the TiC film and
. INITIAL x FRESH
-
16
1~-==~;::~~=.=X~:..:_:..:_-:':;--:'i;~'"~==:=':7"===::"-'" i ! ~
o
100
200
300
500
600
l(hr)
Fig. 4. Contrast of initial experiment with fresh experiment of 316L stainless steel coated with TiC films at 300°C.
to make them form a SiC protective film. We will also coat a thin aluminium layer on the surface of the TiC film and oxidize this aluminium layer to Al z0 3 completely by the method of control oxidation. 3.2. Film stability
The experiments show the permeability of tritium through the films of TiC and TiN + TiC is stable in long-term operations at 200-450°C. No change in permeability is found in a continuous experiment of 90 days. After 90 days, this sample was stored for 90 days at room temperature, and then used again for a permeation experiment. The permeability is stable for a 20day experiment at 200-450°C, and there is no process of forming the tritium barrier at the beginning of the fresh experiment, as shown in fig. 4. Experiments also show that the compatibility of the films with the bulk is good and the films resist thermal shock and irradiation [7]. 3.3. Mechanism analysis
The SIMS analysis results of the hydrocarbon formed in TiC films in different atmospheres and different heat treatment states at different temperatures and the experimental results in tables 1 and 2 show the diffusion and permeation of tritium through the films of TiC and TiN + TiC below 300°C are molecular diffusion. This follows because a large amount of CHi ions have not been formed in the lattice of the TiC film to resist tritium diffusion. At 300-450°C, since a large amount of CHi ions are formed in the permeation process, the tritium permeation barrier is formed. Because the CH i ions are in the rest state in the TiC lattices, the dominant form of transport of tritium in this kind of film is migration of the T+ ion from one carbon site to a neighboring carbon site in the basic lattices. Immediately after transport, T 2 (or HT) is formed on the surface of the film, then leaves the film surface. At 450-600°C, since the TiC film is oxidized, the CH 4 tritium permeation barrier resolves into carbon and water. The tritium permeation barrier is ru-
C. Shan et al. / Diffusion and permeation of tritium
ined, and the diffusion of tritium through the TiC film is changed into molecular (T 2 and HT) diffusion.
225
breeder in a breeder irradiation container in a tritium technology study of a fusion reactor and as first wall materials in a fusion reactor study.
4. Summary References
The results show that a tritium permeation barrier is formed in the process of tritium permeation through the films of TiC and TiN + TiC coated on the surface of 316L stainless steel above 300°C. At 200-500°C, the permeability of tritium through the film of TiC coated on the surface of 316L stainless stcel is four to six orders of magnitude lower than that in bulk, while the permeability of tritium through the films of TiN + TiC coated on the surface of 316L stainless steel is five to six orders of magnitude lower than that in bulk. These films can be used as clad materials for the tritium
[I) R.M. Alire, in: Tritium Proceeding, Tritium Technology in Fusion, Fusion and Isotopic Applications, April 29-May 1 (1980) 98-01. [2) R. Lee et aI., J. Chern. Phys. 36 (4) (962) 1062. [3) Shan Changqi et al., J. Nue!. Mater. 179-181 (] 991) 322. [4) C.B. Kwok et al., J. Nuel. Mater. 170 (J 990) 57. [5) c. Ferro et aI., J. Nue!. Mater. 101 (1981) 224. [6) M. Saeki and N.M. Masaki, Radiochimica Aeta 46 (1989) 163. [7) Y. Weiguo et aI., Nue!. Fusion and Plasma Phys. 7 (4) (1987) 176.