- Email: [email protected]
Sodium Benzoate
Rare Metal Materials and Engineering Volume 40, Issue 5, May 2011 Online English edition of the Chinese language journal
Cite this article as: Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772.
ARTICLE
Corrosion Inhibition of LaFe11.6Si1.4 Alloy by BTA/Sodium Benzoate Zhang Enyao,
Chen Yungui,
Tang Yongbai,
Wang Jinwei
Sichuan University, Chengdu 610065, China
Abstract: The corrosion behavior of LaFe11.6Si1.4 alloy was investigated in benzotriazole and sodium benzoate mixed solution. Polarization measurements and electrochemical impendence spectroscopy techniques were used to measure the electrochemical parameters. Experiment results show that the inhibition efficiency is influenced strongly by the concentration of benzotriazole and pH value. The high concentration benzotriazole and high pH value are beneficial to form a compact oxidation layer and thus prevent the dissolution of Fe. Key words: LaFe11.6Si1.4 alloy; corrosion; electrochemical measurement
LaFe13-xSix alloys, as one of the best magnetic refrigeration materials, have attracted much attention due to their large magnetocaloric effect and low raw materials cost. However, they are eroded seriously in water solution. A mass of corrosion precipitate will be produced in a short period of time, which can deteriorate the heat exchange performance of LaFe13-xSix alloys. For this reason, an inhibitor is needed to prevent the occurrence of corrosion. Benzotriazole (BTA) and carboxylates as the excellent inhibitor have been used widely for the protection of copper and mild steel [1, 2]. BTA is one of the best corrosion inhibitors for the pure copper and copper alloys over a wide temperature and pH range if the carboxylate is absent, but the inhibition effect is not good for ferrous metals [3-9]. So, recently, a synergistic effect of BTA and carboxylates has been studied in many compounds [10, 11]. And the mixed inhibitor shows a good inhibition effect via decreasing the contact between electrolyte and materials, and repairing the defects of oxide layer In this paper, the corrosion behavior of LaFe11.6Si1.4 alloy has been studied using BTA/sodium benzoate as the mixed inhibitor to improve the inhibition effect.
1 Experiment The ingots of LaFe11.6Si1.4 alloy were made from high purity
elements in a high vacuum arc melting system. Each ingot of about 40 g was re-melted four times to assure homogeneity. Then, the ingots were heat-treated at high temperature of 1623 K for 3 h and cooled down in the vacuum furnace. The corrosion medium was composed of BTA and sodium benzoate. The concentration of sodium benzoate was 0.05 mol/L, and it was mixed with 0.01, 0.03, 0.05 mol/L BTA respectively. The solution temperature was set at (25±2) ºC. The pH value was adjusted by nitric acid and sodium hydroxide. For the electrochemical study, a conventional three-electrode corrosion cell was carried out to evaluate the corrosion resistance. The working electrode (WE) was taken from the heat-treated LaFe11.6Si1.4 alloy ingot and embedded in resin. Saturated calomel electrode (SCE) and rectangle platinum electrode were used, as reference and auxiliary electrode, respectively. The cross section of the WE (0.875 cm2 areas) was polished with emery paper up to 1200 grit and cleaned with AR grade acetone and ethanol prior to the polarization test. Electrochemical measurements were performed using a PARSTAT 2273 (EG&G, USA) potentiostat controlled through a personal computer. The Tafel curves were recorded by changing the electrode potential automatically from cathode to anode with scan rate of 1 mV/s. EIS measurements were performed by applying a sinusoidal potential perturbation of 10
Received date: May 20, 2010 Foundation item: National Natural Science Foundation of China (50731007); National High Technology Research and Development Program of China (2007AA03Z440) Corresponding author: Zhang Enyao, Ph. D., School of Materials Science and Engineering, Sichuan University, Chengdu 610065, P. R. China, Tel: 0086-28-85405670; Chen Yungui, Professor, E-mail: [email protected] Copyright © 2011, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.
769
Zhang Enyao et al. / Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772
mV at the open circuit potentials. The impedance spectra were measured with frequency sweep from 10 kHz to 10 mHz in logarithmic increment.
Results and Discussion
The polarization measurements of LaFe11.6Si1.4 alloy were performed in 0.05 mol/L sodium benzoate solution with different concentration BTA after 16 h immersion. The values of associated electrochemical parameters such as corrosion potential (Ecorr), corrosion current density (icorr) and the corrosion inhibition efficiency (IE) calculated are presented in Table 1. The IE (%) was calculated according to the following equation [12]: IE (%)=100 ×
j
0 corr
− jcorr
Potential/V
0.0
a 0.05 mol/L
–0.2 0.03 mol/L
–0.4 –0.6
0.01 mol/L
–0.8 –1.0
10-8
10-7
10-6
(1)
0 jcorr
Where j c0o rr and j corr are the values of the corrosion density in the absence and presence of inhibitor, respectively. As can be seen from Fig.1, the decrease of corrosion current density is pronounced with the increase of concentration of BTA. This behavior means that the synergistic effect is stronger in high concentration solution than in the low one. Generally, the BTA is adsorbed on the surface and prevents the diffusion process when the sodium benzoate forms an oxidation layer with Fe[11]. In Table 1, the corrosion potential is -664, -237 and -190 mV respectively for different concentration. This result means, that corrosion is more difficult to happen in the high concentration BTA solution. In Fig.1, the impedance measurements of LaFe11.6Si1.4 alloy were performed after 16 h immersion, and the equivalent circuit was simulated in Fig.2. Two time constant is used to explain the surface condition, where the low frequency represents the oxidation layer and the high frequency describes adsorption process. Various parameters in the equivalent circuit include electrolyte resistance (Re), resistance of oxide layer (Rox), capacitance of oxide layer (Cox), resistance of adsorption layer (Rad), and capacitance of adsorption layer (Cad). Furthermore, the two semi-circle is depressed, which is attributed to the roughness and other inhomogeneity of the electrode surface. So, the two capacitances are replaced by constant phase element CPE (ZCPE= [Q(jω)n]-1)[13]. The fitted data (by Zsimpwin soft) are summarized in Table 2. The inhibition efficiency (IE) obtained from the polarization resistance is calculated by the following equation [14]: R − R p0 (2) IE (% ) = 100 × p Rp
10-5
10-4
i/A·cm-2 120 000
b
90 000 Zim/Ω
2
0.2
0.05 mol/L
60 000 0.03 mol/L 30 000 0.01 mol/L
0 0
30 000
60 000
90 000
120 000
Zre/Ω
Fig.1 Tafel lines (a) and Nyquist plots (b) for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution Cad
Cox
Rad
Rox
Re
Fig.2 Equivalent circuit used to fit the experimental data of EIS for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution Table 2 EIS parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution
Table 1
Tafel parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution
Ecorr -bc ba icorr Inhibitor concenIE/% tration/mol·L-1 /mV(SCE) /μA·cm-2 /m·V-1 /m·V-1 Uninhibited 0.01 BTA 0.03 BTA 0.05 BTA
-696 -664 -237 -190
5.7 3.2 0.54 0.12
396 351 122 150
189 192 289 337
43 90 98
Re Inhibitor concentration /kΩ· /mol·L-1 cm2
Cox /×10-5 F·cm-2
Uninhibited 1.972
28.4
4.4
0.01
BTA 0.062
1.2
0.148
0.03
BTA 0.053
5.3
0.05
BTA 0.023
1.97
Rad Rox Cad/×10-5 IE/% /kΩ·cm2 F·cm-2 /kΩ·cm2
24
7.1
39
438
1.2
14.5
99
660
1.08
10.7
99.3
770
Zhang Enyao et al. / Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772
Where Rp and Rp0 denote the polarization resistance with and without inhibitor respectively, and Rp=Rox+Rad. As above mentioned, the sodium benzoate will form an insoluble compounds with Fe (ΙΙΙ) and avoid the further corrosion of the sample. However, in the low-concentration BTA solution, this process is difficult to complete and leads to a weak inhibition effect. With the increase of BTA, more surface will be covered by the insoluble Fe (ΙΙΙ) compound and the corrosion will be weakened. It is clear to see from the data of Table 2 that the high concentration BTA is beneficial to form a compact oxidation layer on the surface; however, it seems that the adsorption ability has no more change with the oxidation process regularly. This phenomenon indicates that the thickness of the oxidation layer determines the corrosion degree, while the adsorption layer maybe just prevents the dissolution of Fe (ΙΙΙ). Furthermore, this oxidation layer is formed by Fe (ΙΙΙ), and sodium benzoate is easy to corrode in low concentration BTA solution. So, the high BTA solution is necessary to decrease the corrosion. The results of the pH measurements in 0.05 mol/L BTA /0.05 mol/L sodium benzoate solution are shown in Fig.3. The Tafel lines indicate that the corrosion current decreases with the increase of pH value. Comparing pH 8 and pH 6, the difference of the corrosion current density is about fifty times (Table 3). Generally, in a neutral and alkaline solution, the corrosion speed will be controlled by the diffusion process of oxygen,
0.2
Potential/V
0.0 –0.2
a pH=8 pH=7
–0.4 pH=6 –0.6 –0.8
10-9
10-8
10-7
10-6
10-5
b 200 000
Zim/Ω
pH=8
pH=7 pH=6
0
Tafel parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and 0.05 mol/L BTA mixed solution with different pH values
-bc ba IE Inhibitor concentration/ Ecorr icorr mol·L-1 /mV(SCE) /μA·cm-2 /m·V-1 /m·V-1 /% Uninhibited
–696
5.7
396
pH=6
–579
0.34
135 220.6
pH=7
–143
0.14
193
204
97.5
pH=8
–140
0.069
137
240
98.7
Table 4
189
-94
EIS parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and 0.05 mol/L BTA mixed solution with different pH values Cox/ Rox Cad/×10-5 Rad IE ×10-5 2 /kΩ·cm F·cm-2 /kΩ·cm2 /% -2 F·cm
Inhibitor concentration/ mol·L-1
Re /kΩ·cm2
Uninhibited pH=6 pH=7
1.972 0.022 0.051
28.4 8.1 4
4.4 175 275
1.9 3
7.7 9.7
97.6 98.5
pH=8
0.054
1.6
675
2.4
11
99.3
which is determined by the hydrogen evolution reaction in acid solution. So, in 0.05 mol/L BTA/0.05 mol/L sodium benzoate solution with high pH value, the small corrosion current may be attributed to the absent of oxidation. As above mentioned, the high concentration BTA is beneficial to form a compact oxidation layer and increases the Rox values. Similarly, the Rox can also be influenced by the pH value under the same concentration of the mixed solution. In Table.4, the Rox at pH 6, pH 7 and pH 8. is 175, 275 and 675 kΩ, respectively. The increase of Rox means that the oxidation products formed by Fe (ΙΙΙ) is not stable at low pH values and a dissolution will happen. In addition, the EIS measurements show that the adsorption resistance still keeps a constant value. It means that the adsorption ability only depends on the concentration of BTA and sodium benzoate.
3
i/A·cm-2
100 000
Table 3
Conclusion
1) In the high concentration BTA solution, the oxide layer is thicker than that in the low concentration solution, which means that the high concentration BTA can strengthen the oxidation effect. 2) The oxidation layer will also be influenced by the pH value. When pH=8, the inhibition efficiency approaches 99.3%.
References 0
100 000
200 000
Zre/Ω Fig.3 Tafel lines (a) and Nyquist plots (b) for LaFe11.6Si1.4 alloy in
1 Subramanian, R.; Lakshminarayanan, V. Corros. Sci., 2002, 44: 535 2 Vuorinen, E.; Kalman, E.; Focke, W. Surf. Eng., 2004, 20: 281
0.05 mol/L sodium benzoate and 0.05 mol/L BTA mixed so-
3 Popova, A. Corros. Sci., 2007, 49: 2144
lution with different pH values
4 Srikanth, A. P.; Sunitha, T. G.; Raman, V. Mate. Chem. Phys.,
771
Zhang Enyao et al. / Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772
2007, 103: 241 5 Mamas, S.; Kiyak, T.; Kabasakaloğlu, M. Chem. Phys., 2005, 93: 41 6 Tadeja, Kosec; Ingrid, Milošev; Boris, Pihlar. Appl. Surf. Sci., 2007, 253: 8863 7 Nageh, Allam K.; Elsayer, Ashour A. Appl. Surf. Sci., 2008, 254: 5007 8 Tadeja, Kosec; Darja, Kek Merl; Ingrid, Milošev. Corros. Sci., 2008, 50: 1987 9 John, Berchmans L.; Sivan, V.; Venkata, Krishna, Iyer S. Mate.
Chem. Phys., 2006, 98: 395 10 Rammelt, U.; Koehler, S.; Reinhard, G. Corros. Sci., 2008, 53: 1659 11 Rammelt, U.; Köhler, S.; Reinhar, G. Electrochim Acta, 2008, 53: 6968 12 Tebbji, K.; Faska, N.; Tounsi, A. Mater. Chem. Phys., 2007, 106: 260 13 Dong, C. F.; Fu, A. Q.; Li, X. G. Electrochim Acta, 2008, 54: 628 14 Varvara, S.; Liana, Maria Muresan; Kamal, Rahmouni. Corros. Sci., 2008, 50: 2596
772
Cite this article as: Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772.
ARTICLE
Corrosion Inhibition of LaFe11.6Si1.4 Alloy by BTA/Sodium Benzoate Zhang Enyao,
Chen Yungui,
Tang Yongbai,
Wang Jinwei
Sichuan University, Chengdu 610065, China
Abstract: The corrosion behavior of LaFe11.6Si1.4 alloy was investigated in benzotriazole and sodium benzoate mixed solution. Polarization measurements and electrochemical impendence spectroscopy techniques were used to measure the electrochemical parameters. Experiment results show that the inhibition efficiency is influenced strongly by the concentration of benzotriazole and pH value. The high concentration benzotriazole and high pH value are beneficial to form a compact oxidation layer and thus prevent the dissolution of Fe. Key words: LaFe11.6Si1.4 alloy; corrosion; electrochemical measurement
LaFe13-xSix alloys, as one of the best magnetic refrigeration materials, have attracted much attention due to their large magnetocaloric effect and low raw materials cost. However, they are eroded seriously in water solution. A mass of corrosion precipitate will be produced in a short period of time, which can deteriorate the heat exchange performance of LaFe13-xSix alloys. For this reason, an inhibitor is needed to prevent the occurrence of corrosion. Benzotriazole (BTA) and carboxylates as the excellent inhibitor have been used widely for the protection of copper and mild steel [1, 2]. BTA is one of the best corrosion inhibitors for the pure copper and copper alloys over a wide temperature and pH range if the carboxylate is absent, but the inhibition effect is not good for ferrous metals [3-9]. So, recently, a synergistic effect of BTA and carboxylates has been studied in many compounds [10, 11]. And the mixed inhibitor shows a good inhibition effect via decreasing the contact between electrolyte and materials, and repairing the defects of oxide layer In this paper, the corrosion behavior of LaFe11.6Si1.4 alloy has been studied using BTA/sodium benzoate as the mixed inhibitor to improve the inhibition effect.
1 Experiment The ingots of LaFe11.6Si1.4 alloy were made from high purity
elements in a high vacuum arc melting system. Each ingot of about 40 g was re-melted four times to assure homogeneity. Then, the ingots were heat-treated at high temperature of 1623 K for 3 h and cooled down in the vacuum furnace. The corrosion medium was composed of BTA and sodium benzoate. The concentration of sodium benzoate was 0.05 mol/L, and it was mixed with 0.01, 0.03, 0.05 mol/L BTA respectively. The solution temperature was set at (25±2) ºC. The pH value was adjusted by nitric acid and sodium hydroxide. For the electrochemical study, a conventional three-electrode corrosion cell was carried out to evaluate the corrosion resistance. The working electrode (WE) was taken from the heat-treated LaFe11.6Si1.4 alloy ingot and embedded in resin. Saturated calomel electrode (SCE) and rectangle platinum electrode were used, as reference and auxiliary electrode, respectively. The cross section of the WE (0.875 cm2 areas) was polished with emery paper up to 1200 grit and cleaned with AR grade acetone and ethanol prior to the polarization test. Electrochemical measurements were performed using a PARSTAT 2273 (EG&G, USA) potentiostat controlled through a personal computer. The Tafel curves were recorded by changing the electrode potential automatically from cathode to anode with scan rate of 1 mV/s. EIS measurements were performed by applying a sinusoidal potential perturbation of 10
Received date: May 20, 2010 Foundation item: National Natural Science Foundation of China (50731007); National High Technology Research and Development Program of China (2007AA03Z440) Corresponding author: Zhang Enyao, Ph. D., School of Materials Science and Engineering, Sichuan University, Chengdu 610065, P. R. China, Tel: 0086-28-85405670; Chen Yungui, Professor, E-mail: [email protected] Copyright © 2011, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.
769
Zhang Enyao et al. / Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772
mV at the open circuit potentials. The impedance spectra were measured with frequency sweep from 10 kHz to 10 mHz in logarithmic increment.
Results and Discussion
The polarization measurements of LaFe11.6Si1.4 alloy were performed in 0.05 mol/L sodium benzoate solution with different concentration BTA after 16 h immersion. The values of associated electrochemical parameters such as corrosion potential (Ecorr), corrosion current density (icorr) and the corrosion inhibition efficiency (IE) calculated are presented in Table 1. The IE (%) was calculated according to the following equation [12]: IE (%)=100 ×
j
0 corr
− jcorr
Potential/V
0.0
a 0.05 mol/L
–0.2 0.03 mol/L
–0.4 –0.6
0.01 mol/L
–0.8 –1.0
10-8
10-7
10-6
(1)
0 jcorr
Where j c0o rr and j corr are the values of the corrosion density in the absence and presence of inhibitor, respectively. As can be seen from Fig.1, the decrease of corrosion current density is pronounced with the increase of concentration of BTA. This behavior means that the synergistic effect is stronger in high concentration solution than in the low one. Generally, the BTA is adsorbed on the surface and prevents the diffusion process when the sodium benzoate forms an oxidation layer with Fe[11]. In Table 1, the corrosion potential is -664, -237 and -190 mV respectively for different concentration. This result means, that corrosion is more difficult to happen in the high concentration BTA solution. In Fig.1, the impedance measurements of LaFe11.6Si1.4 alloy were performed after 16 h immersion, and the equivalent circuit was simulated in Fig.2. Two time constant is used to explain the surface condition, where the low frequency represents the oxidation layer and the high frequency describes adsorption process. Various parameters in the equivalent circuit include electrolyte resistance (Re), resistance of oxide layer (Rox), capacitance of oxide layer (Cox), resistance of adsorption layer (Rad), and capacitance of adsorption layer (Cad). Furthermore, the two semi-circle is depressed, which is attributed to the roughness and other inhomogeneity of the electrode surface. So, the two capacitances are replaced by constant phase element CPE (ZCPE= [Q(jω)n]-1)[13]. The fitted data (by Zsimpwin soft) are summarized in Table 2. The inhibition efficiency (IE) obtained from the polarization resistance is calculated by the following equation [14]: R − R p0 (2) IE (% ) = 100 × p Rp
10-5
10-4
i/A·cm-2 120 000
b
90 000 Zim/Ω
2
0.2
0.05 mol/L
60 000 0.03 mol/L 30 000 0.01 mol/L
0 0
30 000
60 000
90 000
120 000
Zre/Ω
Fig.1 Tafel lines (a) and Nyquist plots (b) for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution Cad
Cox
Rad
Rox
Re
Fig.2 Equivalent circuit used to fit the experimental data of EIS for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution Table 2 EIS parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution
Table 1
Tafel parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and BTA solution
Ecorr -bc ba icorr Inhibitor concenIE/% tration/mol·L-1 /mV(SCE) /μA·cm-2 /m·V-1 /m·V-1 Uninhibited 0.01 BTA 0.03 BTA 0.05 BTA
-696 -664 -237 -190
5.7 3.2 0.54 0.12
396 351 122 150
189 192 289 337
43 90 98
Re Inhibitor concentration /kΩ· /mol·L-1 cm2
Cox /×10-5 F·cm-2
Uninhibited 1.972
28.4
4.4
0.01
BTA 0.062
1.2
0.148
0.03
BTA 0.053
5.3
0.05
BTA 0.023
1.97
Rad Rox Cad/×10-5 IE/% /kΩ·cm2 F·cm-2 /kΩ·cm2
24
7.1
39
438
1.2
14.5
99
660
1.08
10.7
99.3
770
Zhang Enyao et al. / Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772
Where Rp and Rp0 denote the polarization resistance with and without inhibitor respectively, and Rp=Rox+Rad. As above mentioned, the sodium benzoate will form an insoluble compounds with Fe (ΙΙΙ) and avoid the further corrosion of the sample. However, in the low-concentration BTA solution, this process is difficult to complete and leads to a weak inhibition effect. With the increase of BTA, more surface will be covered by the insoluble Fe (ΙΙΙ) compound and the corrosion will be weakened. It is clear to see from the data of Table 2 that the high concentration BTA is beneficial to form a compact oxidation layer on the surface; however, it seems that the adsorption ability has no more change with the oxidation process regularly. This phenomenon indicates that the thickness of the oxidation layer determines the corrosion degree, while the adsorption layer maybe just prevents the dissolution of Fe (ΙΙΙ). Furthermore, this oxidation layer is formed by Fe (ΙΙΙ), and sodium benzoate is easy to corrode in low concentration BTA solution. So, the high BTA solution is necessary to decrease the corrosion. The results of the pH measurements in 0.05 mol/L BTA /0.05 mol/L sodium benzoate solution are shown in Fig.3. The Tafel lines indicate that the corrosion current decreases with the increase of pH value. Comparing pH 8 and pH 6, the difference of the corrosion current density is about fifty times (Table 3). Generally, in a neutral and alkaline solution, the corrosion speed will be controlled by the diffusion process of oxygen,
0.2
Potential/V
0.0 –0.2
a pH=8 pH=7
–0.4 pH=6 –0.6 –0.8
10-9
10-8
10-7
10-6
10-5
b 200 000
Zim/Ω
pH=8
pH=7 pH=6
0
Tafel parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and 0.05 mol/L BTA mixed solution with different pH values
-bc ba IE Inhibitor concentration/ Ecorr icorr mol·L-1 /mV(SCE) /μA·cm-2 /m·V-1 /m·V-1 /% Uninhibited
–696
5.7
396
pH=6
–579
0.34
135 220.6
pH=7
–143
0.14
193
204
97.5
pH=8
–140
0.069
137
240
98.7
Table 4
189
-94
EIS parameters for LaFe11.6Si1.4 alloy in 0.05 mol/L sodium benzoate and 0.05 mol/L BTA mixed solution with different pH values Cox/ Rox Cad/×10-5 Rad IE ×10-5 2 /kΩ·cm F·cm-2 /kΩ·cm2 /% -2 F·cm
Inhibitor concentration/ mol·L-1
Re /kΩ·cm2
Uninhibited pH=6 pH=7
1.972 0.022 0.051
28.4 8.1 4
4.4 175 275
1.9 3
7.7 9.7
97.6 98.5
pH=8
0.054
1.6
675
2.4
11
99.3
which is determined by the hydrogen evolution reaction in acid solution. So, in 0.05 mol/L BTA/0.05 mol/L sodium benzoate solution with high pH value, the small corrosion current may be attributed to the absent of oxidation. As above mentioned, the high concentration BTA is beneficial to form a compact oxidation layer and increases the Rox values. Similarly, the Rox can also be influenced by the pH value under the same concentration of the mixed solution. In Table.4, the Rox at pH 6, pH 7 and pH 8. is 175, 275 and 675 kΩ, respectively. The increase of Rox means that the oxidation products formed by Fe (ΙΙΙ) is not stable at low pH values and a dissolution will happen. In addition, the EIS measurements show that the adsorption resistance still keeps a constant value. It means that the adsorption ability only depends on the concentration of BTA and sodium benzoate.
3
i/A·cm-2
100 000
Table 3
Conclusion
1) In the high concentration BTA solution, the oxide layer is thicker than that in the low concentration solution, which means that the high concentration BTA can strengthen the oxidation effect. 2) The oxidation layer will also be influenced by the pH value. When pH=8, the inhibition efficiency approaches 99.3%.
References 0
100 000
200 000
Zre/Ω Fig.3 Tafel lines (a) and Nyquist plots (b) for LaFe11.6Si1.4 alloy in
1 Subramanian, R.; Lakshminarayanan, V. Corros. Sci., 2002, 44: 535 2 Vuorinen, E.; Kalman, E.; Focke, W. Surf. Eng., 2004, 20: 281
0.05 mol/L sodium benzoate and 0.05 mol/L BTA mixed so-
3 Popova, A. Corros. Sci., 2007, 49: 2144
lution with different pH values
4 Srikanth, A. P.; Sunitha, T. G.; Raman, V. Mate. Chem. Phys.,
771
Zhang Enyao et al. / Rare Metal Materials and Engineering, 2011, 40(5): 0769-0772
2007, 103: 241 5 Mamas, S.; Kiyak, T.; Kabasakaloğlu, M. Chem. Phys., 2005, 93: 41 6 Tadeja, Kosec; Ingrid, Milošev; Boris, Pihlar. Appl. Surf. Sci., 2007, 253: 8863 7 Nageh, Allam K.; Elsayer, Ashour A. Appl. Surf. Sci., 2008, 254: 5007 8 Tadeja, Kosec; Darja, Kek Merl; Ingrid, Milošev. Corros. Sci., 2008, 50: 1987 9 John, Berchmans L.; Sivan, V.; Venkata, Krishna, Iyer S. Mate.
Chem. Phys., 2006, 98: 395 10 Rammelt, U.; Koehler, S.; Reinhard, G. Corros. Sci., 2008, 53: 1659 11 Rammelt, U.; Köhler, S.; Reinhar, G. Electrochim Acta, 2008, 53: 6968 12 Tebbji, K.; Faska, N.; Tounsi, A. Mater. Chem. Phys., 2007, 106: 260 13 Dong, C. F.; Fu, A. Q.; Li, X. G. Electrochim Acta, 2008, 54: 628 14 Varvara, S.; Liana, Maria Muresan; Kamal, Rahmouni. Corros. Sci., 2008, 50: 2596
772