ISSN 20702051, Protection of Metals and Physical Chemistry of Surfaces, 2013, Vol. 49, No. 5, pp. 548–553. © Pleiades Publishing, Ltd., 2013.
NANOSCALE AND NANOSTRUCTURED MATERIALS AND COATINGS
Synthesis, Characterization and Optimization of Nanostructured Fe–Ni Coatings by Electrodeposition Method1 M. Karbasi, F. Tavangarian, S. Vardak, and A. Saidi Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran email:
[email protected] Received February 14, 2012
Abstract—In this paper, nanostructured Fe–Ni coatings were successfully coated onto steel substrates by electrodeposition method. Xray diffraction (XRD), scanning electron microscopy (SEM) and energydis persive Xray spectroscopy (EDS) were all employed to characterize nanostructured coatings. Our results showed that with increasing the Ni content in various coatings more homogeneous structures were obtained. Coatings with a higher Fe content had brilliant surfaces and tightly bonded to the substrates. Furthermore, utilizing argon gas during the coating procedure reduced the amount of cavities on the surface of coatings. The coatings had different morphologies depending on the current density and Ni content of the solutions. With optimizing the coating procedure parameters, a coating with starlike morphology and crystallite size of about 16 nm was obtained. DOI: 10.1134/S2070205113050134 1
1. INTRODUCTION Study of nanoscale particles influences recently become a very important field in materials science. Such ultrafine metal powders often exhibit very inter esting electronic, magnetic, optical, and chemical properties. Their unique features depend on particle size, shape, surface composition, and surface atomic arrangement [1–5]. The Fe–Ni alloys are of a worldwide economic interest because of their usage in a great variety of products [6]. Due to their magnetic and mechanical properties these alloys have many applications in the area of memory devices for computers. They are also resistant to corrosion, receptive to chrome, etc. [6, 7]. Various methods have been developed to synthesize Fe–Ni alloy particles including mechanical alloying, the chemical methods, spray pyrolysis, film deposi tion, levitation melting in liquid nitrogen and elec trodeposition procedure [1, 8, 9]. Electrodeposition is an advantageous method to produce nanostructure alloys. The electrodeposition technique allows the possibility of deposition under normal conditions of temperature and pressure and requires relatively inex pensive equipments [10]. Alloy electrodeposition is strongly dependent on experimental parameters such as bath composition, temperature, deposition poten tial, pH, etc. [11]. The purpose of the present study was to synthesize nanostructured Fe–Ni coatings onto steel substrate by electrodeposition method. The influences of various
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The article is published in the original.
parameters such as Fe/Ni ion ratio, current density, and argon gas on the coating properties were studied. A procedure will be proposed to obtain a coating with optimum properties. 2. EXPERIMENTAL PROCEDURE 2.1. Preparation of Coating Bath Ferrous chloride tetrahydrate (FeCl2 ⋅ 4H2O) (99% purity, Merck), nickel chloride hexahydrate (NiCl2 ⋅ 6H2O) (98% purity, Merck) and boric acid (H3BO3) (97% purity, Merck) were used as the initial materials. Hydrochloric acid (HCl) 36.5% was uti lized to regulate the pH of coating solutions. Various baths with different Ni/Fe ion ratios were prepared. For this purpose, an appropriate amount of the initial materials was solved in distilled water. Table 1 shows the composition of different baths and the Ni/Fe ion ratios. In order to achieve stable solutions, each solu tion was kept for 2 days. 2.2. Preparation of substrates Stainless steel plates with 2 cm2 surface area were used as substrates. In order to conduct electricity, cop per wires were attached to the plates. The substrates were mechanically polished up to 2400 grit abrasive paper. Before soaking the plates in different baths, sul furic acid solution (H2SO4) was utilized to active the substrates. The activated substrates were then washed with deionized water and soaked in the electrodeposi tion baths.
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2.4. Characterization of Samples In order to determine the phase composition of dif ferent samples Xray diffractometry (XRD) was used, utilizing a Philips X’PERT MPD diffractometer with Cu Kα radiation (λ = 0.154056 nm). The XRD pat terns were recorded in the 2θ range of 20–90° (step size of 0.05° and time per step of 1 s). The crystallite size of the synthesized coatings was measured by the Scherrer’s formula [12]. The morphology and the thickness of different coatings were studied by scan ning electron microscopy (SEM) in a Philips XL30 at an acceleration voltage of 40 kV. Energy dispersive Xray spectroscopy (EDS) was employed to quantify the composition of the coating surfaces. 3. RESULTS AND DISCUSSION 3.1. XRD Analysis Figure 1 shows the XRD patterns of different sam ples. In the XRD pattern of sample B, FeNi (XRD JCPDS data file No. 031049) and Ni (XRD JCPDS data file No. 011266) phases were observed. With increasing the Ni/Fe ion ratio in various solutions (Table 1), the main peaks shifted toward lower angles which correspond to the main peaks of FeNi3 (XRD JCPDS data file No. 380419) and Ni (XRD JCPDS data file No. 031043) structures. With dissolving Ni in the FeNi structure, the main peaks of FeNi shifted toward lower angels due to an increase in the unitcell parameters and the formation of FeNi3 structure. As can be seen, the intensity of FeNi3 peaks increased with increasing the Ni/Fe ion ratio from sample C to D. This could be ascribed to the higher amount and better crystallization of FeNi3 and Ni phases in sample D. No other phase was observed in the XRD patterns. The crystallite size of obtained coatings was calcu lated by the Scherrer’s formula [12]. The Bragg reflec
Table 1. The composition of different baths and the Ni/Fe ion ratios Solution 1 Solution 2 Solution 3 FeCl2 ⋅ 4H2O (mol/Lit)
0.4
0.09
0.04
NiCl2 ⋅ 6H2O (mol/Lit)
0.6
0.91
0.96
H3BO3 (mol/Lit)
0.5
0.5
0.5
Ni/Fe ion ratio
1.5
10.1
24
Table 2. Designation and deposition process of different sam ples Designation
A
Solution 1 Current density, 50 mA/cm2 Stirring the solution Magnetic stirrer
B
C
D
1 30
2 27
3 27
Argon gas
Argon gas
Argon gas
tions at (110) plane of FeNi and (111) plane of FeNi3 were considered to calculate the crystallite size. The crystallite size of FeNi in sample B and FeNi3 in sam ple C and D was about 8, 16, and 12 nm, respectively. 3.2. EDS Analysis The results of EDS analyses performed on different samples are shown in Fig. 2. As can be seen, the Ni content of deposits increased with rising Ni/Fe ion ratio of baths and reached to about 80% in sample D, (111)
Intensity, arb. units
2.3. Electrodeposition Procedure The steel plate was used as a cathode. On the other hand, Ni with a surface area of about 20 cm2 was set as an anode. Deposition process was carried out using a digital Calometer (model BHP 2520). To produce coating layers, pulse current was used. Three baths with different Ni/Fe ion ratios were prepared (Table 1). Table 2 shows the designation and deposi tion process parameters of various samples. The depo sition was performed in a 500 mL graduated glass bea ker. During the deposition process the temperature of different baths was maintained at 40 ± 2°C. The pH was measured every 10 min and kept constant at 1.5 ± 0.1 for all the experiments using hydrochloric acid. In some experiments argon gas was utilized for the dehy drogenation and to create turbulence in the system. A lid was used to prevent the solution evaporation. The experimental parameters were adjusted in order to achieve a thickness higher than 150 μm.
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FeNi Ni FeNi3
(200) (200)
(220) (220) D
C (110) (200) 20
30
40
50 60 2θ, deg
(211) (220) 70
80
B 90
Fig. 1. Xray diffraction patterns of the surface of various samples after coating procedures.
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ode could be attributed to the acid solution and the high temperature of coating procedure needed to dis solve ferrous chloride tetrahydrate. Therefore, in order to improve the coating adhesion to the substrate the produced hydrogen should be kept away from the sur face. The surface brightness could be observed in Fig. 3h.
100 Fe
80
Ni
60 40 20 0 B
C Sample
D
Fig. 2. EDS analyses results obtained from the surface of different samples.
which is consistent with previous studies [13–15]. The highest Ni/Fe ion ratio of 24 resulted in a deposit con taining 20%Fe which is a permalloy that has been widely studied by others [16–19]. As can be seen in Fig. 2, the relationship between Fe content of different coatings and Ni/Fe ion ratio of various baths is not lin ear. Such a behavior is mentioned for an anomalous codeposition [19, 20]. It is believed that Fe–Ni elec trodeposition proceeds via an anomalous procedure which enables higher rate of deposition for more active ions, i.e. Fe2+ [19–23]. 3.3. SEM micrographs Figure 3 shows the SEM micrographs of sample A. As can be seen in Fig. 3a and 3b, the obtained coating was not homogeneous and had a lot of cracks and a brittle structure. Moreover, the coating of sample A had not the required adhesion to the substrate. This could be ascribed to the presence of acid solution and the high current density. In high current densities the speed of hydrogen release is high and consequently the deposition process is very difficult. In this sample some cavities were formed after coating procedure (Fig. 3c). As can be seen in the higher magnification (Fig. 3d), coating had a mean particle size of about 75 nm. The thickness of coating can be determined by SEM micrographs obtained from crosssection of sample A (Fig. 3e–3g). It was found that the coating had a columnar structure with thickness of about 50 μm. As can be seen in Fig. 3g, the growth directions were random due to the high thickness of coating layer. The thickness of grown columns was in the range of 3 to 6 μm. The columnar growth could be ascribed to the high current density (50 mA) [24]. According to the coating procedure parameters a higher coating thick ness was expected. The lower thickness of coating could be attributed to the release of hydrogen ions on the surface of cathode. This, in turn, prevents the dep osition of Fe and Ni ions on the cathode surface. The reason of the hydrogen release on the surface of cath
Figure 4 shows the SEM micrographs of sample B. As can be seen in Fig. 4a, the surface of sample B con tained lots of cavities due to the higher coating thick ness of this sample in comparison with sample A and the using of argon gas to stir the solution. Argon gas released more hydrogen which was trapped in the coating structure and therefore the amount of cavities increased. On the other hand, no crack was observed on the surface of this sample. The coating surface had a homogeneous structure and the adhesion of coating to the substrate was better than sample A. This could be attributed to the lower current density utilized for coating procedure. Figure 4b shows the crosssection of sample B. As can be seen, the coating with thickness of 150 μm was firmly. In this sample two parameters were changed in order to obtain better coating. Firstly, the current density was decreased and consequently a more homogeneous structure was obtained. Secondly, argon gas was utilized to stir the solution bath and con sequently due to the dehydrogenation the better adhe sion of coating layer to the substrate was achieved. Fig ure 4c and 4d shows the coating surface of sample B. As can be seen, the coating had a uniform structure with an average particle size of about 200 nm. Figure 5 shows the SEM micrographs of sample C. No cavity could be observed in this sample (Fig. 5a) due to the presence of argon gas and lower current density in comparison with sample A and B. As can be seen in Fig. 5b and C, the coating surface consisted of a uniform structure with a star like morphology and a mean particle size of about 1 μm. Figure 5e and 5f illustrates the cross section of sample C. It is obvious that the coating was tightly bonded to the substrate. The coating thickness was about 75 μm. This could be ascribed to the presence of hydrogen on the coating surface. Hydrogen prevents the deposition of Fe and Ni ions on the cathode surface and consequently the thickness of coating was reduced. The SEM micrographs of sample D is shown in Fig. 6. As can be seen in Fig. 6a, the surface consisted of very little and small cavities. The surface morphol ogy was not homogeneous and uniform (Fig. 6b and 6c) and contained of small and large particles. The coating had a columnar structure with thickness of 150 μm and inappropriate adhesion to the substrate (Fig. 6d). In comparison with sample C, sample D was less homogeneous.
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SYNTHESIS, CHARACTERIZATION AND OPTIMIZATION
(a)
1 mm (b)
50 μm
(c)
200 μm
(d)
(e)
50 μm
(f)
40 μm
2 μm (h)
2 μm
(g)
200 nm
Fig. 3. SEM micrographs obtained from Sample A.
(a)
(c)
1 mm (b)
2 μm
(d)
200 μm
200 nm
Fig. 4. SEMmicrographs obtained from Sample B. PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES Vol. 49, No. 5 2013
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100 μm
(a)
2 μm
(c)
50 μm
(e)
(b)
(d)
(f)
20 μm
500 nm
10 μm
Fig. 5. SEMmicrographs obtained from Sample C.
(a)
100 μm
(b)
(c)
2 μm
(d)
10 μm
50 μm
Fig. 6. SEMmicrographs obtained from Sample D.
4. CONCLUSION This paper reports the successful synthesis of nano structured Fe–Ni coatings onto the steel substrates by electrodeposition method. The effects of various parameters on the coating structure were studied. It was found that high current density could produce lots
of cracks on the coating surface. Argon gas increased the coating thickness by preventing the presence of the high amount of hydrogen on the coating surface. Besides, with increasing the coating thickness more cavities were observed in the SEM micrographs due to the trapping of hydrogen gas in the coating structure. An optimum coating with uniform and homogeneous
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structure and mean crystallite size of about 16 nm was obtained in sample C. REFERENCES 1. Gurmen, S., Ebin, B., Stopic, S. et al., J. Alloys Compd., 2009, vol. 480, p. 529. 2. Gusev, A.I. and Rempel, A.A., Nanocrystalline Materi als, Cambridge: International Science Publ., 2004. 3. Duan, H., Lin, X., Liu, G., et al., J. Mater. Process. Technol., 2008, vol. 208, p. 494. 4. Jokanovic, V., Surfact. Sci. Ser., 2006, vol. 130, p. 513. 5. Wei, X.W., Zhu, G.X., Zhou, J.H., et al., Mater. Chem. Phys., 2006, vol. 100, p. 481. 6. Andricacos, P.C. and Romankiw, L.T., in Advances in Electrochemical Science and Engineering, Gerischer, H. and Tobias, C.W., Eds., N.Y.: John Wiley & Sons Inc., 1994. 7. Lacnjevac, U., Jovic, B.M., and Jovic, V.D., Electro chim. Acta, 2009, vol. 55, p. 535. 8. Moustafa, S.F. and Daoush, W.M., J. Mater. Process. Technol., 2007, vol. 181, p. 59. 9. Qin, X.Y., Lee, J.S., Nam, J.G., et al., Nanostruct. Mater., 1999, vol. 11, p. 383. 10. Gómez, E., Labarta, A., Llorente, A., et al., J. Electroa nal. Chem., 2001, vol. 517, p. 63. 11. Bento, F.R. and Mascaro, L.H., Surf. Coat. Tech., 2006, vol. 201, p. 1752.
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