Electrolyte Vortex Dynamics in the Vicinity of a Ferromagnetic Surface

Subscriber access provided by MONASH UNIVERSITY

Article

Electrolyte Vortex Dynamics in the Vicinity of Ferromagnetic Surface in a DC Magnetic Field Dmytro Oleksandrovich Derecha, Yury B. Skirta, and Igor V. Gerasimchuk J. Phys. Chem. B, Just Accepted Manuscript • Publication Date (Web): 25 Nov 2014 Downloaded from http://pubs.acs.org on November 26, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry B is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Electrolyte Vortex Dynamics in the Vicinity of Ferromagnetic Surface in a DC Magnetic Field Dmytro O. Derecha, Yury B. Skirta and Igor V. Gerasimchuk* Institute of Magnetism, National Academy of Sciences of Ukraine and Ministry of Education and Science of Ukraine, Vernadsky Blvd. 36-b, 03142 Kyiv, Ukraine AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

ABSTRACT. We propose a new method for determining the frequency characteristics of the rotational motion of an electrolyte flow during electrochemical reactions under the influence of an external magnetic field. The main advantage of the proposed method is the possibility to determine the frequency characteristics without introducing marker particles or other changes in the electrolyte or in the nature of the reaction. The effectiveness of this method is demonstrated by measuring the electrolyte rotation frequencies during the corrosion of the steel ball in an external magnetic field. It is shown that at the chosen experimental conditions the typical electrolyte rotation frequencies during etching of the steel ball are 0.88 Hz and 1.7 Hz. The developed method can be used for determining corrosion areas of metallic compounds via in-situ testing.

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 20

KEYWORDS. Electrolyte, metal surface, electrochemical reaction, magnetic field, rotation frequency, metallic compounds, corrosion.

INTRODUCTION In recent years a considerable attention is paid to the interaction of metal surfaces with electrolytes under the influence of an external magnetic field and, in particular, to the spontaneous formation of spatial structures. A classic example of the formation of such structures is the wave propagation along certain types of metals and alloys [1-3] and the hydrodynamic mixing of electrolyte during their electrochemical treatment in a magnetic field [4-7]. The main reason for the formation of such structures is the nonlinearities in the reaction mechanism, such as catalysis or phase transitions on the surface. These investigations are of great interest both from practical and experimental standpoints because of timeliness of selforganization processes and formation of dissipative structures in physical and chemical interactions of metals with electrolytes. The magnetic field is thus an additional parameter that allows us to modify existing or create new spatiotemporal structures. In a broader sense, its influence greatly alters the electrochemical processes, in particular, the diffusion mechanism of the reaction is often replaced by convection one [6-8]. In addition, from the experimental point of view the solids during their contact with electrolyte are relatively simple objects for investigations. In this regard, they are widely used in experimental approbations of theoretical models. But the better half of such investigations is devoted to the study of changes in the structure of metal surfaces after their magneto-electrochemical treatment [9-11]. The works devoted to the study of changes in the structure and dynamic properties of electrolytes are mainly theoretical that is caused, in the first place, by complexity of the experiment and the impossibility of use of traditional investigation methods. In this regard, the present work is


2

Page 3 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


devoted to the development of the method and to the study of dynamical characteristics of the rotational motion of electrolytes during chemical reactions in a magnetic field.

EXPERIMENTAL METHODS A number of studies [12,13] indicate that during the corrosion of the ferromagnetic ball in an external uniform magnetic field at its equator (the field is applied in the horizontal plane) the spheric electrolyte flows arise. Due to these fluxes the refractive index and the optical clarity of the solution locally change. The characteristic frequencies of these processes were determined. We used the steel ball (AISI 52100 Alloy Steel, manufactured according to GOST 801-78 [14]) of 10.0 mm in diameter. The ball was mounted on a non-conductive holder and placed in a quartz cuvette filled with a 7-percent solution of nitric acid. The external magnetic field of 0.16 Tesla was applied in a horizontal plane. The electrolyte solution was semiconductor laser beamrayed with a wavelength of 650 nm and a power of 1 mW, the beam diameter was 0.5 mm. Outside the cuvette the beam was projected on a white screen where the image appeared. This image changed its shape and intensity simultaneously with the movement of liquid in the cuvette. The image was recorded by SLR camera in the mode of 30 frames per second. The duration of filming was 270 sec with the frame size of 1280 by 720 pixels. The laser beam passed through different parts of the cuvette, but the most strong and regular image changes were observed when the laser beam passed in a very close vicinity of the ball in the region of its equator. In the absence of an external magnetic field the regular changes of the image disappeared.


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 20

Figure 1. Scheme of the experiment: 1 – pole tips of the electromagnet; 2 – cuvette; 3 – steel ball; 4 – screen; 5 – camera; 6 – laser. For treatment of the data obtained the resulting video picture was laid out on the video frames, the resulting sequence of images was processed by the Pattern software. Since the electronic filming was conducted in daylight, for eliminating the backlight and contrast enhancement only the red component was left on all frames. The further processing was carried out following two algorithms of identifying the areas with a maximum intensity variation of an image. In both of them the averaged and differential images were used. The averaged pixel intensity I A is calculated as the sum of pixel intensities I i ( i -th frame pixel intensity) for the entire sequence divided by the total number of frames N :


4

Page 5 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


N

∑I IA =

i

i =1

N

.

(1)

The sum of absolute values difference between the previous and the next frame for the entire sequence divided by the total number of frames represents the pixel intensity variation of the differential image I D : N

∑| I ID =

i −1

i =2

N

− Ii | .

(2)

The averaged and differential images obtained by the first algorithm are presented in Fig.2.

a)

b)

Figure 2. The averaged (a) and differential (b) images obtained by the first algorithm with the help of expressions (1) for I A and (2) for I D , correspondingly. It can be seen from Fig. 2a that the area with a maximum intensity variation of the image is a white spot at the bottom right of the image. It should be noted that in this case the camera noises and the distortions caused by the mpeg-video compression algorithm (rectangular grid) are rather essential. To improve the algorithm the averaged image was built (see Fig. 2a), each pixel of


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 20

which was equal to the sum of all corresponding pixels of the sequence divided by the number of frames. Then the pixels with intensity above a certain threshold value, for both averaged and differential images, were processed, that is, they belonged to the area of the image but not the background, and at the same time changed significantly. Further the map of variations, according to (2), was built. We chose the threshold values as 0.5 of the maximum intensity for the averaged image and 0.67 – for the differential image, and normalized them to the maximum intensity. These values were chosen for convenience in the experiment processing. In the second algorithm, for all pixels of the image the minimum and maximum values in the entire sequence of frames were found, and then the difference between them was determined (Fig. 3a):

I D = I max − I min .

(3)

After this the map with the biggest variations was built. The pixels with intensity above a given threshold value were allocated on this map (see Fig. 3b).

a)

b)

Figure 3. The processing results obtained by the second algorithm: a) differential image; b) map of the area variations.


6

Page 7 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Note that the second algorithm is less sensitive to noises and distortions, so for the further work just this algorithm was selected. The high threshold value of 0.925 for the differential image was chosen in order to simplify further calculations. The area with maximum intensity variations was highlighted on the map; 2480 pixels fall in this area. The averaged image is the same like in the first algorithm (with the threshold value of 0.5) and is not presented in Fig.3. The dependences of the intensity on time for each of these pixels were recorded by our software into separate files. Further for these dependences the Fourier transform was applied, and the frequency dependences for all pixels were summarized and averaged. The phase dependences were not analyzed because between the oscillations of different pixels a significant phase shift was observed. Moreover the frequency distribution map was built on the laser beam image. To reduce the amount of calculations all the frames were scaled up to 320x240 pixels. For each individual pixel the dependence of its intensity on time was obtained, and then to each such dependence the Fourier transform was applied. Three regions, from 0 Hz till 0.6 Hz, from 0.6 Hz till 1.0 Hz, and from 1.0 Hz till 15.0 Hz, were allocated in the frequency dependences. The boundaries were chosen conventionally, i.e., below the main maximum peak, and right boundary was chosen above the maximum value. As a result, three images were obtained, and each pixel was proportional to a maximum intensity for the frequencies in the specified borders. At the same time the normalization for each image was performed separately, i.e., the maximum intensity within the specified range corresponds to the maximum brightness. The resultant color image was also built, the red component of which corresponds to low frequencies, the green one – to medium frequencies, and the blue one – to high frequencies (Fig. 4).


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 20

Figure 4. Frequency distribution over the surface of the laser beam image. Red color corresponds to the frequencies 0.0-0.6 Hz, green color – 0.6-1.0 Hz, blue color – 1.0-15.0 Hz.

RESULTS AND DISCUSSION Let us consider the obtained frequency characteristics of the processed image. As can be seen from Fig. 5, the maximum peaks of the characteristic frequencies are clearly distinguished on the background of noise. The most intensive are the peaks at frequencies 0.88 Hz and 1.7 Hz which correspond to the frequencies of the most notable changes in the optical characteristics of the solution. The steady component is not shown on the graph in order to improve the perception. The comparison of the obtained data with the theoretical and experimental studies [9,12,13,15] shows that the results are in the range of the characteristic frequencies of the magnetohydrodynamic (MHD) electrolyte mixing. The maximum of 1.7 Hz is much lower than the first one of 0.88 Hz and perhaps is the second harmonic. The second harmonic in this case can be generated due to non-uniformity of the rotational motion of electrolyte and to the nonlinearity of the camera CCD matrix.


8

Page 9 of 20

1.0

0.876 Hz

0.8

Intensity, a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.6

0.4

1.698 Hz

0.2

0.0 0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15

Frequency, Hz

Figure 5. Frequency spectrum of the pixels in the selected area excluding the steady component. Note that with the increasing of recording time the signal-noise ratio is greatly improved. Also to avoid additional distortions it is necessary to conduct the recording without compression. It follows from the figure of frequency distribution over the surface of the laser beam image (see Fig. 4) that the obtained characteristic frequencies can be seen to the fullest extent in the region of the maximum intensity variation which has been found earlier. In the hum noise area the low frequencies predominate; in the centre (the brightest) area both the low and high frequencies are presented. At high signal intensity the CCD matrix enters the saturation regime and works with large distortions that lead to a big steady component and the appearance of higher harmonics. The background signal is mostly composed of low frequency noises. This means it is necessary to carefully choose the intensity of a laser beam and the area of the image analysis. The area should be bright enough to provide a sufficient signal-noise ratio, but does not expose the matrix which must operate in the linear mode.


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 20

CONCLUSIONS Finally, the conducted investigations and the developed methods of the results processing show the possibility of determining the dynamic characteristics of the rotational motion of electrolytes during electrochemical reactions in an external magnetic field. The developed technique allows us using the video recording, without introducing the marker particles, i.e. without changing of the electrolyte structure, to determine the characteristic frequencies of its motion. The obtained results show that under the chosen experimental conditions the typical frequencies of the electrolyte motion are 0.88 Hz and 1.70 Hz that is in good agreement with the theoretical data. Furthermore, in the case of video recording of the whole cuvette in a wide laser beam, most likely, we can simultaneously obtain the data on the rotational motion of the electrolyte for different distances from the electrode surface and build the corresponding image. In general, the developed technique, with certain modifications, can be used for the study of frequency characteristics of the motion of fluids, gases and small objects without a direct influence on the medium under investigation and for determining corrosion areas of metallic compounds via in-situ testing.

Notes The authors declare no competing financial interests. REFERENCES (1) Devos, O.; Aogaki, R. Transport of Paramagnetic Liquids under Nonuniform High Magnetic Field. Analytical Chemistry 2000, 72, 2835-2840.


10

Page 11 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(2) Fahidy, T.Z. Magnetic Effects in Electrochemistry, in Electrochemistry Encyclopedia 2008, http://electrochem.cwru.edu/encycl/art-m01-magnetic.htm (3) Hinds, G.; Coey, J.M.D.; Lyons, M.E.G. Influence of Magnetic Forces on Electrochemical Mass Transport. Electrochemistry Communications 2001, 3, 215-218. (4) Waskaas, M.; Kharkats, Y.I. Effect of Magnetic Fields on Convection in Solutions Containing Paramagnetic Ions. Journal of Electroanalytical Chemistry 2001, 502, 51-57. (5) O’Brien, R.N.; Santhanam, K.S.V. Magnetic Field Assisted Convection in an Electrolyte of Nonuniform Magnetic Susceptibility. Journal of Applied Electrochemistry 1997, 27, 573-578. (6) Gorobets, Yu.I.; Gorobets, O.Yu.; Mazur, S.P. Vortex Structure of Electrolyte in a Steady Magnetic Field in the Vicinity of a Metallic Cylinder. Magnetohydrodynamics 2004, 40, 17-23. (7) Grant, K.M.; Hemmert, J.W.; White, H.S. Magnetic Field Driven Convective Transport at Inlaid Disk Microelectrodes: The Dependence of Flow Patterns on Electrode Radius. Journal of Electroanalytical Chemistry 2001, 500, 95-99.

(8) Quraishi, M.S.; Fahidy, T.Z. The Effect of Magnetic Fields on Natural Convective Mass Transport at Inclined Circular Disk Electrodes. Electrochimica Acta 1980, 25, 591-599. (9) Gorobets, O.Yu.; Derecha, D.O. Electronic Structure and Properties: Periodic Potential Distribution Over the Metal-Electrolyte Interface in the Uniform Magnetic Field. Metallofizika i Noveishie Tekhnologii 2010, 32, 1429-1434.

(10)

Coey, J.M.D.; Hinds, G.; Lyons, M.E.G. Magnetic Field Effects on Fractal

Electrodeposits. Europhysics Letters 1999, 47, 267-272. (11)

Gorobets, O.Yu.; Gorobets, V.Yu.; Derecha, D.O.; Brukva, O.M. Nickel

Electrodeposition under Influence of Constant Homogeneous and High-Gradient Magnetic Field. Journal of Physical Chemistry C 2008, 112, 3373-3375.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(12)

Page 12 of 20

Gorobets, O.Yu.; Gorobets, Yu.I.; Bondar, I.A.; Legenkiy, Yu.A. Quasi-

Stationary Heterogeneous States of Electrolyte at Electrodeposition and Etching Process in a Gradient Magnetic Field of a Magnetized Ferromagnetic Ball. Journal of Magnetism and Magnetic Materials 2013, 330, 76-80.

(13)

Ilchenko, M.Yu.; Gorobets, O.Yu.; Bondar, I.A.; Gaponov, A.M. Influence of

External Magnetic Field on the Etching of a Steel Ball in an Aqueous Solution of Nitric Acid. Journal of Magnetism and Magnetic Materials 2010, 322, 2075-2080. (14)

for technical characteristics of AISI 52100 Alloy Steel see, for ex.,

http://www.azom.com/article.aspx?ArticleID=6704 (15)

Landau, L.D.; Lifshitz, E.M. Fluid Mechanics, Vol. 6, 2nd ed. (Course of

Theoretical Physics); Butterworth-Heinemann: 1987.

TOC GRAPHICS


12

Page 13 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


135x101mm (120 x 120 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

146x167mm (120 x 120 DPI)


Page 14 of 20

Page 15 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


270x152mm (120 x 120 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

270x152mm (120 x 120 DPI)


Page 16 of 20

Page 17 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


270x152mm (120 x 120 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

270x152mm (120 x 120 DPI)


Page 18 of 20

Page 19 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


67x50mm (120 x 120 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

296x209mm (300 x 300 DPI)


Page 20 of 20

Electrolyte Vortex Dynamics in the Vicinity of a Ferromagnetic Surface

Recommend Documents