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Optical interferometry as electrochemical emission spectroscopy of copper alloys in seawater
DESALINATION ELSEVIER
Desalination 158 (2003) 3-8 www.elsevier.com/locate/desaJ
Optical interferometry as electrochemical emission spectroscopy of copper alloys in seawater Khaled Habib*, Hanna Al-Mazeedi Materials Science Laboratory, Department of Advanced Systems, KIN?, PO Box 24885 Safat, 13109 Kuwait Tel. +96S 543-0238; Fax: +965 543-0239; email:[email protected]
Received 13 January 2003; accepted 20 January 2003
Abstract In the present investigation, holographic interferometry was utilized for the first time to determine the rate change of the number of the liinge evolutions during the corrosion test of a pure copper, 99% Cu, and an aluminium brass, 76% Cu +22% Ni +2%Al, in natural seawater. In other words, the anodic dissolution behaviours (corrosion) of the pure copper and the aluminium brass were determined by holographic interferometry, an electromagnetic method. Thus, the abrupt rate change of the number of the fringe evolutions during corrosion tests of both the copper alloys is called electrochemical emission spectroscopy. The corrosion process of both copper alloys was carried out in the seawater at room temperature. The electrochemical emission spectra of both copper alloys in seawater represent a detailed picture of the rate change of the anodic dissolution of both copper alloys throughout the corrosion processes. Furthermore, the optical interferometry data of the both copper alloys were compared to data obtained from the common methods of electrochemical techniques of corrosion measurements, namely, the linear polarization method and electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data ofthe electrochemical emission spectra of both copper alloys with data of the electrochemical techniques in seawater. In both techniques of electrochemical emission spectroscopy and electrochemical techniques, the corrosion behaviour of the pure copper was observed to be higher than that of alum&m brass. Consequently, holographic interferometty was found very useful for monitoring the anodic dissolution behaviours of metals, in which the number of the fringe evolutions of both copper alloys can be determined in situ. Keywords:
Holographic interferometry; Electrochemical impedance spectroscopy; Electrochemical emission spectroscopy; Linear polarization; Corrosion; Seawater; He Ne laser light
*Corresponding author. Presented at the European Conference on Desalination and the Environment: Fresh Waterfor All, Malta, 4-8 May 2003. European Desalination Society, International Water Association. 001 l-9164/03/$- See front matter 0 2003 Elsevier Science B.V. All rights reserved PII: SO01 1-9 164(03)00425-9
4
K. Habib, H. Al-Mzzeedi /Desalination
1. Introduction In works conducted by the author [l-l 61, an optical transducer was developed for materials testing and evaluation of different electrochemical phenomena. The optical transducer was developed based on incorporating methods of holographic interferometry for measuring microscopic deformations and electrochemical techniques for determining electrochemical parameters of samples in aqueous solutions. In addition, the optical transducer was applied not only as an electrometer for measuring different electrochemical parameters, but also the optical transducer was applied as a 3D-interferometric microscope for detecting different microalterations at a metal surface in aqueous solution at microscopic scale. Initially, the optical transducer was used to determine the mechano-chemical behaviours of metals in aqueous solution, i.e., stress corrosion cracking, corrosion fatigue, and hydrogen embrittlement [l-5]. Determination of the mechanochemical behaviours of metals in aqueous solutions was based on detecting microdeformations and measuring the corresponding current density by the optical transducer. Furthermore, the optical transducer was applied as an optical corrosion meter [6-81 for measuring cathodic deposit and anodic dissolution layers of metals in aqueous solutions. The optical corrosion meter was also used to determine the cathodic and anodic current densities which correspond to the cathodic deposit and anodic dissolution layers, respectively. The cathodic and anodic current densities were measured electromagnetically by the optical transducer rather than electronically by one ofthe classic methods, i.e, an Ammeter, of measuring the flow of the electronic current in a conductor. In addition, the optical transducer was applied to measure uniform corrosion and localized corrosion on metal surfaces and on substrates covered by organic coatings or under crevice assemblies
158 (2003) 3-8
[S-14]. The optical transducer was also used to document adsorption and desorption phenomena of chemical species on metal surfaces in aqueous solutions [ 121.Finally, the optical transducer was applied as an electrometer for measuring doublelayer capacitance, alternating current impedance and corresponding oxide layer thickness of metals in aqueous solution [ 15,161. The objective of the present work was to determine the rate change of the number of the fringe evolutions during the corrosion test of pure copper, 99% Cu, and aluminium brass in natural seawater. In other words, the anodic dissolution behaviours (corrosion) of both copper alloys were determined by holographic interferometry. Thus, the abrupt rate change of the number of fringe evolutions during the corrosion test of both copper alloys is called electrochemical emission spectroscopy. In addition, the optical interferometry data of both copper alloys were compared to data obtained from the common methods of eiectrochemical techniques of corrosion measurement, namely, the linear polarization method and electrochemical impedance (EI) spectroscopy [ 171,which are electronic methods.
2. Theoretical analysis In a mathematical relationship derived by the author elsewhere [7,8], one can measure the corrosion current density (J) of metallic samples in aqueous solutions according to the following mathematical model [7,8]: J= JVIDU MT
(1)
where J is the corrosion current density of the base metal, F is the Faraday constant, 14 is the absolute number of electron charge, M is the atomic weight of the sample material, T is the time of the anodic current, D is the density of the base metal, and Uis the orthogonal displacement
K. Habib, H. Al-Mazeedi / Desalination 158 (2003) 3-8
of metal surface due to corrosion where U=ivL/(sina+sir$)
(2)
where N is the number of fringes, h is the wavelength of the laser light used in the experiment, a is the illumination angle, and p is the viewing angle; both c1 and p can be obtained from the set-up of the experiment. A detailed derivation of Eqs. (1) and (2) is given elsewhere in the literature [7,8]. Eq. (I) describes the relationship between the corrosion current density, J, and the orthogonal displacement of metal surface due to corrosion, U. In other words, one can measure the corrosion current density of the base metal by knowing the thickness of the orthogonal displacement of metal surface due to corrosion. The thickness of the orthogonal displacement , U, can be measured by holographic interferometry from Eq. (2). Therefore, one can correlate the number of the fringe evolutions, N, to the corrosion current density, J. By applying Eq. (l), one can detect the electrochemical emission spectroscopy of the carbon steel in the blank seawater by holographic interferometry. This can be achieved by plotting dN vs. the elapsed time of the experiment where dN is the difference between the number of the fringe evolutions of two subsequent readings of the number of fringe evolutions. By plotting dIV vs. time, this will definitely reflect the abrupt rate change, electrochemical emission spectroscopy, of the anodic dissolution behaviours of the steel samples as a function time of the corrosion test. 3. Experimental Metallic samples of pure copper, 99% Cu, and aluminium brass, 76% Cu +22% Ni +2%Al, were used in this investigation. Samples of both copper alloys were manufactured in two different sizes in a circular shape. The larger size was 9 cm in diameter with a total surface area of 63.6 17 cm2,
5
which was used for the holographic interferometry test. The smaller samples had a dimension of 1.4 cm in diameter and a surface area of 1.54 cm*, and were used in the other electrochemical tests. Then all large samples (9 cm in diameter) were covered by black epoxy (polyamide tar) except for one side. The reason behind covering the samples with black epoxy was to isolate the surface area of the samples from contact with seawater while testing the bare side of the samples to corrosion in seawater. At the beginning of each test, the sample was immersed in an aqueous solution for nearly 45 min. While the sample was in the solution, the corrosion potential was monitored by a potentiometer with respect to the saturated colomel electrode (SCE), a reference electrode, until the steady-state potential was reached. Both copper alloy samples were tested in natural seawater at open circuit potentials of the samples in the seawater (see Table 1 for seawater composition). Then a hologram of the sample was recorded using off-axis holography. In this study, a camera (HC-300 thermoplastic recorder,Newport Corp.) with a thermoplastic film was used to facilitate recordings of the real time-holographic interferometry of the samples during the corrosion test. For more details on the procedures of the experiment, the reader is encouraged to refer to the literature [7,8]. Furthermore, the linear polarization and the EI measurements were recorded for both copper alloys in seawater using the smaller samples. Linear polarization and the AC-impedance measurements were conducted using the ACM Gill 8AC impedance system. The obtained data of the EI measurements were basically Nyquist plots [17], plot of the real alternating current impedance (2’) vs. the imaginary alternating current impedance (z”). By using Nyquist plots, a number of electrochemical parameters of samples of both copper alloys in seawater could be determined. However, the most significant
K. Habib. H. Al-Mazeedi /Desalination
6
Table 1 Chemical composition of the natural seawater Parameter
Max. (ppm)
Min. (ppm)
Normal seawater, ppm
Sodium Magnesium Potassium Calcium Copper Zinc Iron Manganese Chloride Sulfate Bicarbonate Ammonia Nitrate Sulfide TOC Total HC Silica TDS Bromide Fluoride
12,433 1,543 459 404 0.05 0.05 0.5 0.1 22,014 3,272 161 1.13 0.25 0.2 8 0.327 0.09 46,300 80 1.25
11,536 1,490 469 378 co.05 co.05 co.05 co.05 21,933 3,200 156 0.02 0.002 0.005 8 0.204 0.05 44,100 -
11,860 1,340 410 515 20,959 2,650 130 35,840 66 1.3
4. Results and discussion By using data from the obtained interferograms, one can develop a relationship between the difference of the number of the fringe evolutions of two subsequent fringe numbers and the elapsed time of the experiment. Figs. 1 and 2 show plots of the difference between the number of the fringe evolutions of two subsequent fringe numbers and the elapsed time of the experiment of the pure copper and aluminium brass in seawater, respectively. From Figs. 1 and 2, the abrupt rate change of electrochemical emission spectroscopy of both copper alloys in seawater. For instance, Fig. 1 shows the rate change of the difference between the number of the fringe evolutions of the pure copper in seawater. It is obvious from Fig. 1 that the rate change of electrochemical emission spectroscopy of the
t
parameter for this investigation is the polarization
resistance of the samples in seawater. This is because the polarization resistance values from linear polarization or EI measurements, the corrosion current density can be determined [ 181.It is worth mentioning that in each experiment, the holographic interferograms were recorded as a function of time in which each test lasted for 60 min at room temperature. Then, the difference between the number of fringe evolutions of the subsequent numbers of the fringe evolutions, dlv, were plotted as a function time in order to show the abrupt rate change of electrochemical emission spectroscopy of the samples in seawater. The abrupt rate change of electrochemical emission spectroscopy was recorded each consecutive 10 min of elapsed time of the experiment.
158 (2003) 3-8
01.. 0
. 2
4
6
e
lo
12
14
Tfme inlerval (min)
Fig. 1. The electrochemical emission spectra of the pure copper sample in seawater as a function of elapsed time of the experiment.
Time intervals (min)
Fig. 2. The electrochemical emission spectra of the aluminium brass in seawater as a function of elapsed time of the experiment.
K. Habib, H. Al-Mazeedi /Desalination 158 (2003) 3-8
pure copper was observed to decrease initially in a gradual manner from dN = 4 fringes to Cw = 1 fringe per minute, from the beginning of the test to the 20 min of the elapsed time of the experiment. This behaviour of the electrochemical emission spectroscopy of pure cooper in seawater indicates that the corrosion rate of the cooper samples was continuously decreasing as a function of time. In contrast, a sudden change of the fringe evolution (d/V= 2) was observed from 20 to 25 min of elapsed time of the experiment (see Fig. 1). This behaviour can be explained by localized oxidation. Then the electrochemical emission spectroscopy, the fringe evolution, of the copper sample was observed to decrease to a steady-state value (dN = 1) until the end of the test, in which another abrupt change occurred (dN= 3). On the other hand, the rate of change of the electrochemical emission spectroscopy of the aluminium brass in seawater was observed to decrease drastically from dN = 3 fringes to a steady-state value of dN= 1 fringe per minute till the end of the test (see Fig. 2). It obvious from Fig. 2 and the obtained interferograms of aluminium brass in seawater that aluminium brass is more stable, less chemically active, than pure copper in seawater. This is due to the fact that there is no abrupt rate change in the fringe evolution observed in the electrochemical emission spectroscopy (Fig. 2) of aluminium brass in seawater. Also, measurements of the corrosion current density of both copper alloys by linear polarization and EI spectroscopy confirmed that aluminium brass is less active chemically than pure copper in seawater. The corrosion current density of the pure copper was found to be 8.55 @/cm2 and 8.65 PA/cm2 by linear polarization and the EI spectroscopy, respectively. In contrast, the corrosion current density of the aluminium brass was found to be 5.27 PA/cm2 and 7.52 PA/cm2 by linear polarization and EI spectroscopy, respectively.
References PI K. Habib, Holographic interferometry of a polarized and loaded metallic electrodes in aqueous solution, Applied Optics, 29( 13) (1990) 867-869. PI K. Habib, Initial behavior of corrosion fatigue/ hydrogen embrittlement of metallic electrodes in aqueous solutions, Exper. Tech. Physics, 38(5/6) (1990) 535-538. [31 K. Habib, G. Carmichael,R. Lakes and W. S&valley, Noveltechniquefor measuringstress corrosion cracking of metallic electrodes in aqueous solutions: Theory and applications. Corr. J., 49(5) (1993) 354362. [41 K. Habib, Initiation of stress corrosion cracking of Ti 90-A16-V4wire in aqueoussolution:Non- destructive monitoring by holographic interferometry, Optics Lasers Engineer., 20 (1994) 81-85. PI K. Habib, Non-destructive evaluation of metallic electrodes under corrosion fatigue conditions by holographic interferometry, Optics Lasers Engineer., 23 (1995) 65-70. PI K. Habib, Holographic interferometry in predicting cathodic deposition of metals in aqueous solution, Proc. SPIE, 1230 (1990) 293-296. 171 K. Habib, Model of holographic interferometry of anodic dissolution of metals in aqueous solution, Optics Lasers Engineer., 18 (1993) 115-120. PI K. Habib, F. Al Sabti and H. Al- Mazeedi, Optical corrosion-meter, Optics Lasers Engineer., 27(2) (1997) 227-233. K. Habib, Non-destructive evaluation of an epoxy191 based coating by optical interferometry techniques, Optics Lasers Engineer., 23(2) (1995) 213-219. K. Habib and F. Al Sabti, Interferometric sensor for WI electrochemical studies of metallic alloys in aqueous solution, Optical Rev., 4(2) (1997) 324-328. K. Habib and F. Al-Sabti, Monitoring pitting corroillI sion by holographic interferometry, Corr. J., 53(9) (1997) 680-685. PI K. Habib, In-situ monitoring of pitting corrosion of stainless steel by optical interferometry, Electrochemica Acta, 44 (1999) 463511641. [I31 K. Habib, In-situ monitoring pitting corrosion of copper alloys by holographic interferometry, Corr. Sci., 40(8) (1998) 1435-1440.
8
K. Habib, H. AI-Mazeedi /Desalination 158 (2003) 3-B
[ 141 K. Habib, Crevice corrosion of copper alloys by opti-
cal intibrometry, Optics Lasers Engineer.,3 1(1999) 13-20. [ 151 K. Habib, Measurement of the double layer capacitance of aluminium samples by holographic interferometry, Optics Laser Technol., 28(8) (1996) 579584. [16] K. Habib, Measurement of the a.c. impedance of aluminium samples by holographic interferomeby, Optics Lasers Engineer., 28 (1997) 37-46.
[17] Basics of A.C. Impedance Measurements, Applicatian Note-AC-l, Egand G Princeton Applied Research, Electrochemical InstrumentDivision, Princeton, NJ,1982. [ 181 R. Baboian, Electrochemical Techniques for Corrosion, Nate Press, Houston, TX, 1977, p. 58. [19] H. Uhlig, CorrosionControl, Wiley,NewYork, 1971, pp. 322-350.
Desalination 158 (2003) 3-8 www.elsevier.com/locate/desaJ
Optical interferometry as electrochemical emission spectroscopy of copper alloys in seawater Khaled Habib*, Hanna Al-Mazeedi Materials Science Laboratory, Department of Advanced Systems, KIN?, PO Box 24885 Safat, 13109 Kuwait Tel. +96S 543-0238; Fax: +965 543-0239; email:[email protected]
Received 13 January 2003; accepted 20 January 2003
Abstract In the present investigation, holographic interferometry was utilized for the first time to determine the rate change of the number of the liinge evolutions during the corrosion test of a pure copper, 99% Cu, and an aluminium brass, 76% Cu +22% Ni +2%Al, in natural seawater. In other words, the anodic dissolution behaviours (corrosion) of the pure copper and the aluminium brass were determined by holographic interferometry, an electromagnetic method. Thus, the abrupt rate change of the number of the fringe evolutions during corrosion tests of both the copper alloys is called electrochemical emission spectroscopy. The corrosion process of both copper alloys was carried out in the seawater at room temperature. The electrochemical emission spectra of both copper alloys in seawater represent a detailed picture of the rate change of the anodic dissolution of both copper alloys throughout the corrosion processes. Furthermore, the optical interferometry data of the both copper alloys were compared to data obtained from the common methods of electrochemical techniques of corrosion measurements, namely, the linear polarization method and electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data ofthe electrochemical emission spectra of both copper alloys with data of the electrochemical techniques in seawater. In both techniques of electrochemical emission spectroscopy and electrochemical techniques, the corrosion behaviour of the pure copper was observed to be higher than that of alum&m brass. Consequently, holographic interferometty was found very useful for monitoring the anodic dissolution behaviours of metals, in which the number of the fringe evolutions of both copper alloys can be determined in situ. Keywords:
Holographic interferometry; Electrochemical impedance spectroscopy; Electrochemical emission spectroscopy; Linear polarization; Corrosion; Seawater; He Ne laser light
*Corresponding author. Presented at the European Conference on Desalination and the Environment: Fresh Waterfor All, Malta, 4-8 May 2003. European Desalination Society, International Water Association. 001 l-9164/03/$- See front matter 0 2003 Elsevier Science B.V. All rights reserved PII: SO01 1-9 164(03)00425-9
4
K. Habib, H. Al-Mzzeedi /Desalination
1. Introduction In works conducted by the author [l-l 61, an optical transducer was developed for materials testing and evaluation of different electrochemical phenomena. The optical transducer was developed based on incorporating methods of holographic interferometry for measuring microscopic deformations and electrochemical techniques for determining electrochemical parameters of samples in aqueous solutions. In addition, the optical transducer was applied not only as an electrometer for measuring different electrochemical parameters, but also the optical transducer was applied as a 3D-interferometric microscope for detecting different microalterations at a metal surface in aqueous solution at microscopic scale. Initially, the optical transducer was used to determine the mechano-chemical behaviours of metals in aqueous solution, i.e., stress corrosion cracking, corrosion fatigue, and hydrogen embrittlement [l-5]. Determination of the mechanochemical behaviours of metals in aqueous solutions was based on detecting microdeformations and measuring the corresponding current density by the optical transducer. Furthermore, the optical transducer was applied as an optical corrosion meter [6-81 for measuring cathodic deposit and anodic dissolution layers of metals in aqueous solutions. The optical corrosion meter was also used to determine the cathodic and anodic current densities which correspond to the cathodic deposit and anodic dissolution layers, respectively. The cathodic and anodic current densities were measured electromagnetically by the optical transducer rather than electronically by one ofthe classic methods, i.e, an Ammeter, of measuring the flow of the electronic current in a conductor. In addition, the optical transducer was applied to measure uniform corrosion and localized corrosion on metal surfaces and on substrates covered by organic coatings or under crevice assemblies
158 (2003) 3-8
[S-14]. The optical transducer was also used to document adsorption and desorption phenomena of chemical species on metal surfaces in aqueous solutions [ 121.Finally, the optical transducer was applied as an electrometer for measuring doublelayer capacitance, alternating current impedance and corresponding oxide layer thickness of metals in aqueous solution [ 15,161. The objective of the present work was to determine the rate change of the number of the fringe evolutions during the corrosion test of pure copper, 99% Cu, and aluminium brass in natural seawater. In other words, the anodic dissolution behaviours (corrosion) of both copper alloys were determined by holographic interferometry. Thus, the abrupt rate change of the number of fringe evolutions during the corrosion test of both copper alloys is called electrochemical emission spectroscopy. In addition, the optical interferometry data of both copper alloys were compared to data obtained from the common methods of eiectrochemical techniques of corrosion measurement, namely, the linear polarization method and electrochemical impedance (EI) spectroscopy [ 171,which are electronic methods.
2. Theoretical analysis In a mathematical relationship derived by the author elsewhere [7,8], one can measure the corrosion current density (J) of metallic samples in aqueous solutions according to the following mathematical model [7,8]: J= JVIDU MT
(1)
where J is the corrosion current density of the base metal, F is the Faraday constant, 14 is the absolute number of electron charge, M is the atomic weight of the sample material, T is the time of the anodic current, D is the density of the base metal, and Uis the orthogonal displacement
K. Habib, H. Al-Mazeedi / Desalination 158 (2003) 3-8
of metal surface due to corrosion where U=ivL/(sina+sir$)
(2)
where N is the number of fringes, h is the wavelength of the laser light used in the experiment, a is the illumination angle, and p is the viewing angle; both c1 and p can be obtained from the set-up of the experiment. A detailed derivation of Eqs. (1) and (2) is given elsewhere in the literature [7,8]. Eq. (I) describes the relationship between the corrosion current density, J, and the orthogonal displacement of metal surface due to corrosion, U. In other words, one can measure the corrosion current density of the base metal by knowing the thickness of the orthogonal displacement of metal surface due to corrosion. The thickness of the orthogonal displacement , U, can be measured by holographic interferometry from Eq. (2). Therefore, one can correlate the number of the fringe evolutions, N, to the corrosion current density, J. By applying Eq. (l), one can detect the electrochemical emission spectroscopy of the carbon steel in the blank seawater by holographic interferometry. This can be achieved by plotting dN vs. the elapsed time of the experiment where dN is the difference between the number of the fringe evolutions of two subsequent readings of the number of fringe evolutions. By plotting dIV vs. time, this will definitely reflect the abrupt rate change, electrochemical emission spectroscopy, of the anodic dissolution behaviours of the steel samples as a function time of the corrosion test. 3. Experimental Metallic samples of pure copper, 99% Cu, and aluminium brass, 76% Cu +22% Ni +2%Al, were used in this investigation. Samples of both copper alloys were manufactured in two different sizes in a circular shape. The larger size was 9 cm in diameter with a total surface area of 63.6 17 cm2,
5
which was used for the holographic interferometry test. The smaller samples had a dimension of 1.4 cm in diameter and a surface area of 1.54 cm*, and were used in the other electrochemical tests. Then all large samples (9 cm in diameter) were covered by black epoxy (polyamide tar) except for one side. The reason behind covering the samples with black epoxy was to isolate the surface area of the samples from contact with seawater while testing the bare side of the samples to corrosion in seawater. At the beginning of each test, the sample was immersed in an aqueous solution for nearly 45 min. While the sample was in the solution, the corrosion potential was monitored by a potentiometer with respect to the saturated colomel electrode (SCE), a reference electrode, until the steady-state potential was reached. Both copper alloy samples were tested in natural seawater at open circuit potentials of the samples in the seawater (see Table 1 for seawater composition). Then a hologram of the sample was recorded using off-axis holography. In this study, a camera (HC-300 thermoplastic recorder,Newport Corp.) with a thermoplastic film was used to facilitate recordings of the real time-holographic interferometry of the samples during the corrosion test. For more details on the procedures of the experiment, the reader is encouraged to refer to the literature [7,8]. Furthermore, the linear polarization and the EI measurements were recorded for both copper alloys in seawater using the smaller samples. Linear polarization and the AC-impedance measurements were conducted using the ACM Gill 8AC impedance system. The obtained data of the EI measurements were basically Nyquist plots [17], plot of the real alternating current impedance (2’) vs. the imaginary alternating current impedance (z”). By using Nyquist plots, a number of electrochemical parameters of samples of both copper alloys in seawater could be determined. However, the most significant
K. Habib. H. Al-Mazeedi /Desalination
6
Table 1 Chemical composition of the natural seawater Parameter
Max. (ppm)
Min. (ppm)
Normal seawater, ppm
Sodium Magnesium Potassium Calcium Copper Zinc Iron Manganese Chloride Sulfate Bicarbonate Ammonia Nitrate Sulfide TOC Total HC Silica TDS Bromide Fluoride
12,433 1,543 459 404 0.05 0.05 0.5 0.1 22,014 3,272 161 1.13 0.25 0.2 8 0.327 0.09 46,300 80 1.25
11,536 1,490 469 378 co.05 co.05 co.05 co.05 21,933 3,200 156 0.02 0.002 0.005 8 0.204 0.05 44,100 -
11,860 1,340 410 515 20,959 2,650 130 35,840 66 1.3
4. Results and discussion By using data from the obtained interferograms, one can develop a relationship between the difference of the number of the fringe evolutions of two subsequent fringe numbers and the elapsed time of the experiment. Figs. 1 and 2 show plots of the difference between the number of the fringe evolutions of two subsequent fringe numbers and the elapsed time of the experiment of the pure copper and aluminium brass in seawater, respectively. From Figs. 1 and 2, the abrupt rate change of electrochemical emission spectroscopy of both copper alloys in seawater. For instance, Fig. 1 shows the rate change of the difference between the number of the fringe evolutions of the pure copper in seawater. It is obvious from Fig. 1 that the rate change of electrochemical emission spectroscopy of the
t
parameter for this investigation is the polarization
resistance of the samples in seawater. This is because the polarization resistance values from linear polarization or EI measurements, the corrosion current density can be determined [ 181.It is worth mentioning that in each experiment, the holographic interferograms were recorded as a function of time in which each test lasted for 60 min at room temperature. Then, the difference between the number of fringe evolutions of the subsequent numbers of the fringe evolutions, dlv, were plotted as a function time in order to show the abrupt rate change of electrochemical emission spectroscopy of the samples in seawater. The abrupt rate change of electrochemical emission spectroscopy was recorded each consecutive 10 min of elapsed time of the experiment.
158 (2003) 3-8
01.. 0
. 2
4
6
e
lo
12
14
Tfme inlerval (min)
Fig. 1. The electrochemical emission spectra of the pure copper sample in seawater as a function of elapsed time of the experiment.
Time intervals (min)
Fig. 2. The electrochemical emission spectra of the aluminium brass in seawater as a function of elapsed time of the experiment.
K. Habib, H. Al-Mazeedi /Desalination 158 (2003) 3-8
pure copper was observed to decrease initially in a gradual manner from dN = 4 fringes to Cw = 1 fringe per minute, from the beginning of the test to the 20 min of the elapsed time of the experiment. This behaviour of the electrochemical emission spectroscopy of pure cooper in seawater indicates that the corrosion rate of the cooper samples was continuously decreasing as a function of time. In contrast, a sudden change of the fringe evolution (d/V= 2) was observed from 20 to 25 min of elapsed time of the experiment (see Fig. 1). This behaviour can be explained by localized oxidation. Then the electrochemical emission spectroscopy, the fringe evolution, of the copper sample was observed to decrease to a steady-state value (dN = 1) until the end of the test, in which another abrupt change occurred (dN= 3). On the other hand, the rate of change of the electrochemical emission spectroscopy of the aluminium brass in seawater was observed to decrease drastically from dN = 3 fringes to a steady-state value of dN= 1 fringe per minute till the end of the test (see Fig. 2). It obvious from Fig. 2 and the obtained interferograms of aluminium brass in seawater that aluminium brass is more stable, less chemically active, than pure copper in seawater. This is due to the fact that there is no abrupt rate change in the fringe evolution observed in the electrochemical emission spectroscopy (Fig. 2) of aluminium brass in seawater. Also, measurements of the corrosion current density of both copper alloys by linear polarization and EI spectroscopy confirmed that aluminium brass is less active chemically than pure copper in seawater. The corrosion current density of the pure copper was found to be 8.55 @/cm2 and 8.65 PA/cm2 by linear polarization and the EI spectroscopy, respectively. In contrast, the corrosion current density of the aluminium brass was found to be 5.27 PA/cm2 and 7.52 PA/cm2 by linear polarization and EI spectroscopy, respectively.
References PI K. Habib, Holographic interferometry of a polarized and loaded metallic electrodes in aqueous solution, Applied Optics, 29( 13) (1990) 867-869. PI K. Habib, Initial behavior of corrosion fatigue/ hydrogen embrittlement of metallic electrodes in aqueous solutions, Exper. Tech. Physics, 38(5/6) (1990) 535-538. [31 K. Habib, G. Carmichael,R. Lakes and W. S&valley, Noveltechniquefor measuringstress corrosion cracking of metallic electrodes in aqueous solutions: Theory and applications. Corr. J., 49(5) (1993) 354362. [41 K. Habib, Initiation of stress corrosion cracking of Ti 90-A16-V4wire in aqueoussolution:Non- destructive monitoring by holographic interferometry, Optics Lasers Engineer., 20 (1994) 81-85. PI K. Habib, Non-destructive evaluation of metallic electrodes under corrosion fatigue conditions by holographic interferometry, Optics Lasers Engineer., 23 (1995) 65-70. PI K. Habib, Holographic interferometry in predicting cathodic deposition of metals in aqueous solution, Proc. SPIE, 1230 (1990) 293-296. 171 K. Habib, Model of holographic interferometry of anodic dissolution of metals in aqueous solution, Optics Lasers Engineer., 18 (1993) 115-120. PI K. Habib, F. Al Sabti and H. Al- Mazeedi, Optical corrosion-meter, Optics Lasers Engineer., 27(2) (1997) 227-233. K. Habib, Non-destructive evaluation of an epoxy191 based coating by optical interferometry techniques, Optics Lasers Engineer., 23(2) (1995) 213-219. K. Habib and F. Al Sabti, Interferometric sensor for WI electrochemical studies of metallic alloys in aqueous solution, Optical Rev., 4(2) (1997) 324-328. K. Habib and F. Al-Sabti, Monitoring pitting corroillI sion by holographic interferometry, Corr. J., 53(9) (1997) 680-685. PI K. Habib, In-situ monitoring of pitting corrosion of stainless steel by optical interferometry, Electrochemica Acta, 44 (1999) 463511641. [I31 K. Habib, In-situ monitoring pitting corrosion of copper alloys by holographic interferometry, Corr. Sci., 40(8) (1998) 1435-1440.
8
K. Habib, H. AI-Mazeedi /Desalination 158 (2003) 3-B
[ 141 K. Habib, Crevice corrosion of copper alloys by opti-
cal intibrometry, Optics Lasers Engineer.,3 1(1999) 13-20. [ 151 K. Habib, Measurement of the double layer capacitance of aluminium samples by holographic interferometry, Optics Laser Technol., 28(8) (1996) 579584. [16] K. Habib, Measurement of the a.c. impedance of aluminium samples by holographic interferomeby, Optics Lasers Engineer., 28 (1997) 37-46.
[17] Basics of A.C. Impedance Measurements, Applicatian Note-AC-l, Egand G Princeton Applied Research, Electrochemical InstrumentDivision, Princeton, NJ,1982. [ 181 R. Baboian, Electrochemical Techniques for Corrosion, Nate Press, Houston, TX, 1977, p. 58. [19] H. Uhlig, CorrosionControl, Wiley,NewYork, 1971, pp. 322-350.