ACTIVE/PASSIVE BEHAVIOR OF LOW CARBON STEEL IN DEAERATED BICARBONATE SOLUTION
WEN Huailiang1,2, DONG Junhua2(), KE Wei2, CHEN Wenjuan2, YANG Jingfeng2, CHEN Nan2
1 College of Chemical and Materials Science, University of Science and Technology of China, Hefei 230026 2 State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016
Cite this article:
WEN Huailiang, DONG Junhua, KE Wei, CHEN Wenjuan, YANG Jingfeng, CHEN Nan. ACTIVE/PASSIVE BEHAVIOR OF LOW CARBON STEEL IN DEAERATED BICARBONATE SOLUTION. Acta Metall Sin, 2014, 50(3): 275-284.
As a kind of clean, efficient and relatively safe energy, nuclear energy has been widely used around the world. The high-level radioactive waste (HLRW) generated in the nuclear has also become a major risk, so the disposal safety of HLRW will be especially important. The planned concept of China's HLRW disposal program is a shaft-tunnel model located in saturated zones in granite. The metal container for sealing the HLRW is the key because its interaction with the ground water will lead to the leak of the HLRW during the long repository time. Beishan is a selected repository area and the ground water contains a bicarbonate () buffer solution. Therefore, as a candidate material of the container, the active/passive state of low carbon steel in the ground water with is of significance, which determines the container's service life. The active state will ensure that the container achieves the designed life under general corrosion, and moreover the passive state will degrade the container's life under stress corrosion cracking (SCC) caused by pitting corrosion. In this work, the effect of on the corrosion behavior of low carbon steel was examined in deaerated bicarbonate solutions (pH 8.3) over 50 d. The presence of enhanced both the anodic Fe dissolution and cathodic hydrogen evolution reaction. The situ-measurement of corrosion potential revealed that the increased concentration of led to the high corrosion potential. When the concentration of was 0.01 mol/L, the corrosion potential was in the active region. When the concentration of was higher than 0.02 mol/L, the corrosion potential was in the passive region. EIS results showed that the charge transfer resistance, film resistance and the diffusion impedance increased with the increasing concentration. Results of XRD analysis illustrated that the key corrosion products were mainly composed of Fe3O4 and α-FeOOH.
Fund: Supported by National Natural Science Foundation of China (No.51071160)
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Figure 1. Polarization curves of low carbon steel in 0.01 mol/L(a), 0.02 mol/L (b), 0.05 mol/L (c) and 0.1 mol/L (d)deaerated solutions
Figure 2. Evolution of open circuit potential in 0.01 mol/L(a), 0.02 mol/L (b), 0.05 mol/L (c) and 0.1 mol/L (d)deaerated solutions
Figure 3. Measured EIS results of low carbon steel in 0.01 mol/L deaerated solutions (ZIm—imaginative part of electrochemical impedance, ZRe—real part of electrochemical impedance, f—frequency, Z—impedance)
(a) ZIm-ZRe (b) Z-f (c) phase angle-f
Figure 4. Measured EIS results of low carbon steel in 0.02 mol/L deaerated solutions
(a) ZIm-ZRe (b) Z-f (c) phase angle-f
Figure 5. Measured EIS results of low carbon steel in 0.05 mol/L deaerated solutions (Inset in Fig.5a shows the enlarged view)
(a) ZIm-ZRe (b) Z-f (c) phase angle-f
Figure 6. Measured EIS results of low carbon steel in 0.1 mol/L deaerated solutions
(a) ZIm-ZRe (b) Z-f (c) phase angle-f
Figure 7. Equivalent circuit for fitting the EIS data (Qp—capacitance caused by high frequency phse shift, Rs—solution resistance, Qr—rust capacitance, Rr—real part of electrochemical impedance, Qdl—double layer capacitance, Rct—charge transfer resistance, W—Warburg impedance)
Time / d
Yr mS·sn·cm-2
nr
Rr Ω· cm2
Ydl mS·sn·cm-2
ndl
Rct kΩ·cm2
Yw mS·s0.5·cm-2
Initial
-
-
-
0.33
0.7
3.4
-
5
0.28
0.5
2.7×10-5
0.11
1.0
6.7
-
14
0.11
1.0
15
0.33
0.5
6.9
-
27
0.14
1.0
46
0.52
0.5
6.6
-
33
0.66
0.8
62
0.83
0.2
6.9
-
59
1.40
0.9
89
3.60
0.6
7.1
120
Table 1 Fitting results for EIS plots in 0.01 mol/L solution
Time / d
Yr mS·sn·cm-2
nr
Rr Ω·cm2
Ydl mS·sn·cm-2
ndl
Rct kΩ·cm2
Yw mS·s0.5·cm-2
Initial
-
-
-
0.34
0.7
2.2
-
23
0.21
1.0
26
6.00
0.5
1.0
0.60
29
0.13
1.0
31
5.50
0.6
1.6
0.32
35
0.27
1.0
38
5.00
0.6
1.9
1.30
39
1.10
0.7
71
5.50
0.6
1.9
4.0×10-3
Table 2 Fitting results for EIS plots in 0.02 mol/L solution
Time / d
Yr mS·sn·cm-2
nr
Rr Ω·cm2
Ydl mS·sn·cm-2
ndl
Rct kΩ·cm2
Yw mS·s0.5·cm-2
Initial
-
-
-
0.35
0.7
2.4
-
5
0.12
0.9
0.06
0.28
0.6
2.6
-
23
0.43
0.8
5.90
0.60
0.6
2.8
5.6×10-5
39
0.35
0.7
22.0
0.19
0.6
2.4
2.1×10-4
46
0.07
1.0
34.0
0.47
0.6
1.9
1.7×10-4
52
0.07
1.0
48.0
0.72
0.7
1.5
3.4×10-4
Table 3 Fitting results for EIS plots in 0.05 mol/L solution
Time / d
Yr mS·sn·cm-2
nr
Rr Ω·cm2
Ydl mS·sn·cm-2
ndl
Rct kΩ·cm2
Yw mS·s0.5·cm-2
Initial
-
-
-
0.29
0.8
3.90
-
9
0.16
0.5
1
0.34
1.0
4.70
-
23
0.07
1.0
11
1.40
0.6
2.00
4.9×10-7
26
0.13
1.0
22
1.40
0.7
0.15
1.7×10-17
41
0.20
1.0
40
1.20
0.7
0.17
1.0×10-16
48
0.76
0.7
53
0.59
0.7
0.18
1.0×10-17
Table 4 Fitting results for EIS plots in 0.1 mol/L solution
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