Effects of Silica Nanoparticle Co-Deposition on Macrothrowing Power of Zinc-Nickel Alloy Plating from an Acid Sulfate Bath+

Home , Clarke number

Makoto Hino1, Koji Murakami2, Ken Muraoka2, Norihito Nagata3 and Teruto Kanadani4

1Faculty of Engineering, Hiroshima Institute of Technology, Hiroshima 731-5193, Japan 2Industrial Technology Research Institute of Okayama Prefecture, Okayama 701-1296, Japan 3SURTECH NAGATA CO., LTD., Akashi 673-0028, Japan 4Faculty of Engineering, Okayama University of Science, Okayama 700-0005, Japan

ZincnickelSiO2 electrodeposits have been produced from an acid sulfate bath. The co-deposition behavior of SiO2 and the macro throwing power of plating baths were examined. The presence of SiO2 nanoparticles in the plating bath appears to change the alloy deposition behavior. The rate of nickel deposition was considerably decreased by the presence of SiO2 nanoparticles in the bath. The macro throwing power of plating was improved by adding SiO2 nanoparticles to the bath. At an early stage of electrodeposition, it seems that the SiO2 nanoparticles act as a nucleus for the precipitation. The SiO2 nanoparticles did not disperse uniformly in a plating ﬁlm; they distributed only in a SiO2 rich layer (³50 nm thick) that formed beneath the surface. In addition, this SiO2 rich layer can improve anticorrosive performance. Therefore, zincic use can be suppressed because ﬁlm thickness can be reduced compared to zinc and zincnickel alloy electroplating. [doi:10.2320/matertrans.M2014329]

(Received September 17, 2014; Accepted October 23, 2014; Published December 5, 2014)

Keywords: zinc-nickel alloy plating, SiO2 nanoparticle co-deposition, anticorrosive performance, resources depletion problem

1. Introduction reduce film thickness. Consequently, it may be possible to reduce zincic use by the application of zincnickelSiO2 Currently, iron and steel, which are low cost materials with composite plating. In addition, reduced power consumption excellent workability, are the most widely used as basic and reduced manufacturing time can be expected. Although materials world-wide. However, since these materials are the co-deposition behavior of zincnickelSiO2 composite 710) vulnerable to red rust under corrosive environments, per- plating has been reported, the effects of SiO2 co- formance deterioration occurs, particular in relation to deposition on the macro throwing power as well as the mechanical properties. To satisfy long-term reliability, zinc relations between corrosion resistance and film thickness are electroplating is widely used for iron and steel materials due not clear. 1) to its protective ability against corrosion. Zinc plating, In this study, we investigate the effects of SiO2 co- which is a well-known, low cost process, has been applied deposition on macro throwing power and the relations as a rust prevention surface treatment for iron and steel between corrosion resistance and film thickness for zinc 2) materials. nickelSiO2 composite plating from an acid sulfate bath, However, zincic resources are scarce; the Clarke number which has excellent anticorrosive properties. The overall goal of zinc is 0.004%. The global demand for zincic resources of this investigation is to find ways to reduce zincic use and has increased concurrent with the rising demand for iron and power consumption. steel materials. This increase in demand is associated with rapidly expanding economies in Southeast Asia and the 2. Experimental BRIC nations (i.e., Brazil, Russia, India, and China). Given the known anti-corrosive properties of zinc plating and the Experiments were conducted using cold roll steel sheets rising demand for iron and steel materials, it has been (SPCC, JIS G 3141, Standard refining, Bright finish, 50 projected that that zinc resources could be completely mm © 50 mm © 0.6 mm). Zincnickel alloy plating was 3) depleted within 20 years. Therefore, finding ways to reduce obtained from sulfate baths, and zincnickelSiO2 composite the use of zinc is an important undertaking. plating was obtained from sulfate baths with SiO2 sol. Zinc The anticorrosive performance of zinc plating is directly and zincSiO2 composite plating were also undertaken as related to the thickness of the film. However, a thin film is comparison specimens. Table 1 shows the bath composition insufficient to ensure long-term reliability of iron and steel and plating conditions. Colloidal silica (Nissan Chemical materials. To improve anticorrosive performance, zinc-based Industries, Ltd., SNOWTEX-O, specific gravity: 1.12, alloy plating, such as ZnNi and ZnMn plating, as well as average particle size: 20 nm, SiO2 content rate: 20 mass%) Zn-composite plating and zinc-based alloy composite plating was used in this study. A cylindrical glass cell containing 4,5) ¹3 3 have been developed. ZincnickelSiO2 composite plating 2.0 © 10 m of electrolyte, which was stirred constantly, 6) was remarkably improved due to the SiO2 nanoparticles. was used. Prior to plating, the steel cathode was degreased by Compared with zinc plating, the excellent anticorrosive solvent, electrocleaned cathodically for 1 min in an alkaline performance of zincnickelSiO2 plating makes it possible to solution, pickled by 10% hydrochloric acid for 10 s, and washed. An insoluble electrode, which was plated platinum +This Paper was Originally Published in Japanese in J. Japan Inst. Met. on a titanium substrate, was used as the anode electrode. The Mater. 78 (2014) 3136. film thickness ranged from 110 µm. 86 M. Hino, K. Murakami, K. Muraoka, N. Nagata and T. Kanadani

1μm 3μm5μm 10μm Zn Zn-Ni 2 Zn-Ni-SiO

1mm

Fig. 1 Appearance of the each plated specimen for various plating types.

Table 1 Bath compositions and plating conditions. ranging from 110 µm). For zinc plating, the 1 µm deposit Plating type Zinc Zinc-Nickel was white, approximately uniform, and perfectly covered the substrate. As the film thickness increased, the white color ZnSO4·7H2O: 0.3 peculiar to the zinc electroplating resulting from an acid Bath composition ZnSO4·7H2O: 1.0 NiSO4·6H2O: 0.7 fi (mol/L) Na SO : 0.5 Na SO : 0.5 sulfate bath increased, as did the coverage factor of the lm. 2 4 2 4 fi SiO2 colloid: 0, 60 g/L For zinc nickel alloy plating, the lm (thickness less than Bath pH 2 « 0.2 3 µm) was deposited non-uniformly, and the iron substrate was partially exposed. However, at a thickness of 5 µm, Current density 0.5 (kA/m2) the deposits were approximately uniform and covered the « Temperature 323 2 (K) substrate perfectly. The expected silver-white film was obtained. The uniformity was improved with film thickness of 10 µm. As noted, zincnickel alloy plating could not completely The electroplated specimens were subjected to salt spray cover the substrate at a thickness of 3 µm. However, 1 µm tests in accordance with Japanese Industrial Standard Z 2371, thick zincnickelSiO2 composite plating film was uniformly and the corrosion resistance of each specimen was evaluated deposited, and uniform films were obtained at greater by red rust occurrence time. The composition of the thicknesses. It was found that the macro throwing power electroplated film was determined using an X-ray fluores- of the zincnickel alloy plated film at an early stage of cence spectrometer. To examine the effects of SiO2 co- electrodeposition can be improved by adding silica to the deposition on the macro throwing power of deposits, bath. electroplated specimens were studied using field-emission Figure 2 shows the scanning electron images of the plated electron probe microanalysis (FE-EPMA, JEOL, JXA- film (thickness 110 µm) obtained by different plating types. 8500FS), and the crystal structure of the deposit was studied For zinc plating, despite varying film thickness, deposits of with an X-ray diffractometer (Cu-K¡, 40 kV, 200 mA, the hexagon board state depending on the hexagonal close- Rigaku, RINT-1300), transition electron microscopy (TEM, packed structure were observed. These zinc deposits then JEOL, JEM-2100F) observation and energy dispersive X-ray grew as film thickness increased. spectroscopy analysis (JEOL, JED-2300T). For the zincnickel alloy plating, it was observed that the surface morphology of the deposit (1 µm thick) was finely 3. Results and Discussion granular, i.e., approximately 1 µm in diameter, and the surface seemed to be a substrate. As the film thickness 3.1 Effects of SiO2 nanoparticles on deposits increased to 3 µm, a smooth film with fine granularity was Figure 1 shows the appearance of each deposit (thickness formed; however, a partially un-deposited area (broken line, Effects of Silica Nanoparticle Co-Deposition on Macrothrowing Power of Zinc-Nickel Alloy Plating from an Acid Sulfate Bath 87

1μm 3μm 5μm 10μm Zn Zn-Ni 2 Zn-Ni-SiO

10μm

Fig. 2 SEM observation of the each plated specimen for various plating types.

Fig. 2) was observed. For film thickness over 5 µm, fine and cathode during electrolysis. However, Nishimura et al.11) uniform deposits perfectly covered the substrate. have reported that, in zincnickel alloy plating, the nickel The SiO2 nanoparticles were added to the zincnickel alloy ions adsorb preferentially to the SiO2 nanoparticle in the acid plating bath, and, even at a thickness of 1 µm, the obtained sulfate bath, and the SiO2 nanoparticles, which are adsorbed 11) film perfectly covered the substrate, and the fine granular by the nickel ions, act as a cation. Thus, these SiO2 deposits seen in the zincnickel alloy plating were not nanoparticles migrate to the cathode side, and then act as a observed. In addition, fine and uniform films were formed in nucleus of precipitation on the cathode surface. In addition, films of thickness greater than 3 µm. Thus, it was found that large numbers of precipitation nuclei exist because the SiO2 addition of silica sol to the plating bath influenced the particles are nanometer scale particles. Therefore, it seems morphology of the obtained film. likely that the SiO2 particles in the zincnickel alloy plating Figure 3 shows the scanning electron images and X-ray bath enable formation of uniform deposition. The SiO2 maps for zinc, nickel, and iron obtained by FE-EPMA nanoparticles in the bath demonstrate activity that is equal analysis for the surfaces of the zincnickel alloy and zinc to the additives in the plating. nickelSiO2 composite plated films. For the zincnickel alloy To add new functions, such as wear resistance, self- plating, zinc, nickel, and iron in a film (1 µm thick) were lubrication, corrosion resistance, and polymer adhesion to the distributed non-uniformly. Since the granular deposits shown plating film, various composite platings co-deposited with in Fig. 2 corresponded with the zinc and nickel of the element fine particles, such as oxides and carbides, and organic map, the deposits occurred partially at an early stage of substance particles (e.g., PTFE), have been developed.1113) electroplating, and the iron substrate was partially exposed. On the other hand, it was found that the SiO2 nanoparticle The non-uniform deposits of zinc and nickel were observed demonstrated a function that is unlike conventional compo- with 3 µm film thicknesses; however, zinc, nickel, and iron site plating, i.e., the macro throwing power of the plated film were almost distributed uniformly in the films of thickness is improved. greater than 5 µm. These results indicate that the deposits of Figure 4 shows the X-ray diffraction patterns of the zinc- thickness greater than 5 µm covered the substrate perfectly. nickel alloy plating and zincnickelSiO2 composite plating. As SiO2 nanoparticles were added to the zincnickel alloy Each film structure was composed of the £phase (Ni5Zn21) plating bath, zinc and nickel were distributed uniformly, even orientated in the (411) plane; thus, the crystal structures could with 1 µm film thickness. Note that a non-uniform distribu- not be differentiated. The results of Figs. 2 and 3, show that tion was not observed on iron. Thus, the SiO2 nanoparticle the SiO2 nanoparticles in the plating bath facilitated a change composite film was deposited uniformly and covered the in the form of precipitation; specifically, uniform precipita- substrate perfectly at an early stage of electroplating. tion was promoted at an early electrodeposition stage. The SiO2 nanoparticle used in this study has negative However, it was found that the SiO2 nanoparticles in the surface charge; therefore, the repulsive force works for the plating bath did not affect the crystal structure of the obtained 88 M. Hino, K. Murakami, K. Muraoka, N. Nagata and T. Kanadani

SEI Zn-Kα Ni-Kα Fe-Kα m μ 1 Zn-Ni m μ 5 Zn-Ni 2 m μ 1 Zn-Ni-SiO 2 m μ 5 Zn-Ni-SiO

50μm

Fig. 3 Secondary electron images and X-ray maps for zinc, nickel and iron by FE-EPMA analysis for the various specimens.

films. Note that zincnickel alloy plating deposited in only 2.03 mass%. There appears to be little correlation between 14) the £phase shows excellent corrosion resistance. SiO2 content and film thickness. In the case of films of Table 2 shows the zinc, nickel, and SiO2 content of the the same thickness, since the nickel content in the films plating films obtained via different platings using an X-ray decreased, depending on the SiO2 co-deposition, the fluorescence spectrometer. For zincnickel alloy plating, it is abnormal co-deposition was accelerated. In addition, this evident that there is significant nickel content in 1 µm thick tendency became more noticeable as film thickness decreas- films and that nickel content decreased and zinc content ed. With regard to the acceleration mechanism of the increased as the film thickness increased. This result indicates abnormal co-deposition, which is dependent on SiO2 co- that more much nickel is depositing at an early stage of deposition, as previously described, the SiO2 nanoparticles electrodeposition. Zincnickel alloy plating in which zinc that are absorbed by nickel ions migrate to the cathode less noble than nickel, preferentially deposits is well known surface and consequently suppress the reduction of nickel as an abnormal co-deposition type.15) However, from the ions on the cathode surface. On behalf of the reduction of above results, in the acid sulfate bath used for this study, nickel ions, hydrogen ions are reduced, pH near the cathode the abnormal co-deposition is suppressed at an early stage surface rises, and zinc hydroxide is formed. Therefore, it is of electrodeposition, while the abnormal co-deposition is reasonable to assume that zinc precipitation increases.16) promoted as electrodeposition proceeds. These results revealed that the SiO2 nanoparticles in the On the other hand, when the silica sol was added to the bath contributed to the deposition of a uniform film at an zincnickel alloy plating bath, the SiO2 nanoparticles were early stage of electrodeposition and reduced the nickel co-deposited in a film. The SiO2 content, which differed content in the film due to acceleration of the abnormal co- depending on film thickness, was in the range of 1.00 deposition. In addition, the SiO2 nanoparticles suppressed the Effects of Silica Nanoparticle Co-Deposition on Macrothrowing Power of Zinc-Nickel Alloy Plating from an Acid Sulfate Bath 89

8000 Table 2 Chemical compositions of plated ﬁlms obtained via different (411) Zn-Ni : -phase(Ni5Zn21) plating (mass%). 7000 :Iron substrate Plating type Zn-Ni Zn-Ni-SiO2 6000 Element Zn Ni SiO2 Zn Ni SiO2 5000 1 µm 73.8 26.2 ® 81.4 16.9 1.71 3 µm 74.9 25.1 ® 82.0 16.7 1.33 4000 ® 10μm 5 µm 76.2 23.8 84.3 15.7 1.00 3000 10 µm 81.5 18.5 ® 85.3 13.6 2.03 5μm 2000 3μm 1000 Table 3 Red rust occurrence time for various electroplated specimens by 1μm salt spray test. 0 20 30 40 50 60 70 80 90 100 8000 Thickness Zn Zn-Ni Zn-Ni-SiO2 Zn-Ni-SiO2 : -phase(Ni5Zn21) 1 µm 8 h 24 h 48 h 7000 (411) :Iron substrate 3 µm 16 h 120 h 334 h 6000 5 µm 48 h 1440 h 2400 h

5000 10 µm 96 h 1680 h 3600 h

4000 10μm Intensity (arb.unit)3000 Intensity (arb.unit) Compared to zinc plating, the corrosion resistance of the 5μm 2000 zinc nickel SiO2 composite plating improved more than that of zincnickel alloy plating. In particular, the corrosion 3μm 1000 resistance of zincnickelSiO2 composite plating with a 3 µm 1μm thick film improved by approximately three times compared 0 20 30 40 50 60 70 80 90 100 to the corrosion resistance of the zincnickel alloy plating of Diffraction angle, 2 equal film thickness. It is supposed that the uniform film Fig. 4 X-ray diffraction patterns of various plated specimens. deposition and the suppression of nickel content due to the SiO2 nanoparticles result in improved corrosion resistance. Cross-sectional TEM observation and element map results change of nickel content associated with different film for zincnickelSiO2 composite plating for a 10 µm thick film thickness and contributed to homogeneous deposition of are shown in Fig. 5. TEM observation revealed that a SiO2 the composition in the film thickness direction. nanoparticle-rich layer of 50 nm in thickness was formed on the surface of this film. In the acid solution, the dispersive- 3.2 Co-deposition of SiO2 nanoparticles and corrosion ness of the silica sol used in this study is extremely good. resistance However, silica sol aggregates and gels as pH rises to near Table 3 shows the results of red rust occurrence time for neutral.11) The result of accelerating the abnormal co- various plated specimens after a salt spray test. On the zinc deposition by adding the silica sol to the zincnickel alloy plating, at a 1 µm thickness, red rust occurred within 8 h, and plating bath indicates the formation of zinc hydroxide at the an increase in film thickness proportionately increased the electrode surface with increasing pH.16) Increased pH at the red rust occurrence time. Thus, for zinc plating, corrosion electrode surface simultaneously accelerated the aggregation resistance is improved proportional to film thickness. There- and gelation of the SiO2 nanoparticles, which are adsorbed fore, for use in a severely corrosive environment and when by nickel ions, and the formation of the silica-rich layer. long-term corrosion resistance is required, it is difficult to This silica-rich layer may contribute to the improvement in reduce the thickness of the film. anticorrosive performance. On the other hand, the corrosion resistance of zincnickel From these results, because the corrosion resistance of the alloy plating was remarkably improved compared to that of zincnickelSiO2 composite plating where silica sol was zinc plating. The corrosion resistance of zincnickel alloy added to the zinc-nickel alloy plating bath, was significantly plating with a 3 µm thick film was much better than that of better than that of zinc plating and zincnickel alloy plating, zinc plating with a 10 µm thick film. The corrosion resistance it is possible that film thickness can be reduced. Con- of zincnickel alloy plating improved significantly when sequently, zincic use can be reduced. In addition, plating time film thickness was greater than 5 µm. Thus, the corrosion and power consumption may also be reduced. resistance of zincnickel alloy plating was not proportional to film thickness and differed from that of zinc plating. This 4. Conclusion result can be explained by the non-uniform deposition for film thickness up to 3 µm film thickness, as shown in Figs. 2 For the purpose of reducing zincic use, effects of SiO2 co- and 3, and the reduction of the sacrificial protection deposition on the macro throwing power of deposits and the associated with the increase in the nickel content. relations between corrosion resistance and film thickness on 90 M. Hino, K. Murakami, K. Muraoka, N. Nagata and T. Kanadani

TEM image Zn-Kα Ni-Kα

Surface side

Si-Kα O-Kα 50nm

Fig. 5 Cross-sectional TEM images and EDS mapping images of Zn, Ni, Si and O on zinc-nickel-SiO2 composite ﬁlm (Film thickness: 10 µm).

zincnickel alloy plating from an acid sulfate bath were Suga Weathering Technology Foundation Research Grants investigated. The following results were obtained. for promoting this research. (1) The SiO2 nanoparticles, which are adsorbed by nickel ions, in the zincnickel alloy plating bath act as a cation REFERENCES and then migrate to the cathode surface during 1) M. Hiramatsu, M. Hino and T. Omi: Corros. Eng. 45 (1996) 4761. electrolysis. Consequently, these SiO2 nanoparticles act as a nucleus of precipitation and allow the formation 2) Mekki Gyo Bijon 2012, ed. by Federation of Electro Plating Industry Association, Japan, (2012) p. 8 (in Japanese). of a uniform deposit. In addition, the SiO2 nanoparticles 3) Information on http://www.nims.go.jp/publicity/publication/ that migrate to the cathode surface cause the reduction 4) A. Shibuya: Recent Advances in Coated Steels Used for Automobile, of the hydrogen ion, and promote the abnormal co- ed. by K. Yamakawa and H. Fujikawa, (ELSEVIER Press, The Soc. of deposition in which zinc is deposited preferentially Materials Sci. Japan, 1996) pp. 19. 5) M. Hiramatsu, M. Hino, K. Murakami and T. Kanadani: Materia Japan based on the rise in pH near the cathode surface. fi 44 (2005) 917 924 (in Japanese). (2) The lm structure of both the zinc nickel alloy plating 6) M. Hino, M. Hiramatsu, K. Murakami, A. Saijo and T. Kanadani: Acta and the zincnickelSiO2 composite plating was Metall. Sin. 18 (2005) 416422. composed of the £phase (Ni5Zn21), which showed 7) A. Takahashi, Y. Miyoshi and T. Hada: Surf. Technol. 44 (1993) 977. excellent corrosion resistance. The SiO2 nanoparticles 8) L. Jianguo, G. Gaoping and Y. Chuanwei: Surf. Coat. Technol. 200 did not affect the film structure significantly. (2006) 4967 4975. 9) M. Hino, M. Hiramatsu, K. Murakami and T. Kanadani: J. Japan Inst. (3) The corrosion resistance of the zinc nickel SiO2 Metals 69 (2005) 973976 (in Japanese). composite plating was significantly better than that of 10) T. J. Tuaweri and G. D. Wilcox: Trans. Inst. Met. Finish. 85 (2007) the zinc plating and zincnickel alloy plating due to 245253. uniform deposition and the silica-rich layer formed 11) K. Nishimura, Y. Miyoshi and T. Hada: Kinzoku Hyomen Gijutsu 38 (1987) 217222 (in Japanese). beneath the surface. Therefore, zincic use can be 12) T. Hayashi and N. Furukawa: DENKI KAGAKU 53 (1985) 51 55 reduced, because with zinc nickel SiO2 composite (in Japanese). plating it becomes possible to reduce film thickness. 13) M. Hiranmatsu, H. Kawasaki, Y. Nakayama and T. Omi: Plat. Surf. In addition, we might expect reduction of both plating Finish. 74 (1987) 481483. time and power consumption. 14) A. Shibuya, T. Kurimoto, Y. Hoboh and N. Usuki: Trans. ISIJ 23 (1983) 923929. 15) A. Brenner: Electrodeposition of Alloys, (Academic Press, New York Acknowledgment and London, 1963). 16) H. Fukushima, T. Akiyama, K. Higashi, R. Kammel and M. The authors would like to express sincere thanks to the Karimkhani: Metall. 42 (1988) 242246.