The+Effect+of+Electroplating+Parameters+on+Microstructure+of+Nanocrystalline+Nickel+Coatings

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J. Mater. Sci. Technol., 2010, 26(1), 82-86.

Effect of Electroplating Parameters on Microstructure

of Nanocrystalline Nickel Coatings

A.M. Rashidi1,2) and A. Amadeh2)

1) Faculty of Engineering, Razi University, P.O. Box 67149-67346, Kermanshah, Iran

2) School of Metallurgy & Materials Engineering, University College of Engineering, University of Tehran, Tehran, Iran

[Manuscript received October 16, 2008, in revised form August 6, 2009]

In order to achieve the optimum conditions for electroplating nanocrystalline nickel coating from Watts-typebath, the effect of some process parameters namely, bath temperature, current density, and saccharin additionon grain size and texture coefficient (TC= I(200)/I(111)) of the deposits were investigated by X-ray diffraction(XRD). The results showed that in a bath containing 5 g/L saccharin, by increasing the bath temperature from45C to 55C, the grain size decreased, whereas further increase of bath temperature resulted in a contraryeffect. By increasing the current density from 10 to 75 mA/cm2, both the grain size and TC decreased,while further increase in current density had no significant effect on the grain size. At a given current density,the grain size and TC decreased rapidly by increasing the saccharin content before leveling off at 3 g/L ofsaccharin. Finally, based on the grain refining the optimum conditions for producing nanocrystalline nickelcoating from Watts-type bath have been proposed.

KEY WORDS: Electroplating; Grain size; Nanocrystalline; Coating

1. Introduction

Recently, the development, production and char-acterization of nanocrystalline (NC) materials, withthe grain size typically smaller than 100 nm, have

been the subject of intensive researches both in sci-entific and industrial communities[1]. Among thevarious manufacturing methods, electroplating hasreceived considerable attention as a feasible, inex-pensive and economically viable processing techniquewhich has been used in the synthesis of bulk NC met-als for over twelve years[2]. However, it has beendemonstrated[3,4] that under certain conditions, onlyelectrodeposition can produce NC nickel coatings. Al-though there are numerous studies focused on syn-thesis of NC nickel deposits[311], but determinationof optimum conditions for production NC nickel coat-ing from the reported results is difficult because they

Corresponding author. Prof.; Tel.:+98 831 4274535, Fax: +98831 4274542; E-mail address: [email protected] (A.M.Rashidi).

are, in some cases, inconsistent or different. For in-stance, Dai et al.[8] found that the grain size of nickeldeposits decreased from 50 nm to about 20 nm byincreasing the current density from 50 mA/cm2 to100 mA/cm2 while the effect of current density higher

than 100 mA/cm2

was negligible. Unlike these re-sults, a continuous increasing in grain size vs cur-rent density has also been recognized in direct cur-rent electrodeposition of nickel coating[47]. On theother hand, Aruna et al.[10] reported that the currentdensity had no significant effect on grain size of nickelelectrodeposits. The effect of saccharin concentrationin the electroplating bath on grain size of Ni depositsis another example. The overall behavior observed bydifferent researchers[8,9,11] is similar but the saccha-rin contents corresponding to leveling off in grain sizereduction are different. Moreover, little informationdeals with the effect of bath temperature on grain size

of nickel deposits, whereas in some cases, a deviationmore than 5C from optimum temperature is suffi-cient to harm the coating quality, deposition rate,


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A.M. Rashidi et al.: J. Mater. Sci. Technol., 2010, 26(1), 8286. 83

Table 1 Electroplating conditions of Ni coatings

Parameter Series I Series II Series III

i/(mA/cm2) 10-20-30-50-75-100-150-200 100 100Cs/(g/l) 5 1-2-3-5-7.5-10 5Tem/(C) 55 55 45-50-55-60-65i: Current density, Cs: Saccharin content, Tem: Bath temperature

and other properties[12]. Therefore, more studies inthis field can be useful to manufacturing of compo-nents and devices coated with NC nickel.

The aim of our present work is to provide a con-sistent set of experimental data within a large rangeof process parameters for synthesis of NC nickel coat-ings. Results on the optimization and synthesis con-ditions of NC nickel deposits from Watts-type bathare presented.

2. Experimental

Nickel coating was prepared by using aWatts-type bath containing 300 g/L nickel sul-fate (Ni2SO46H2O), 30 g/L nickel chloride(NiCl26H2O), and 30 g/L boric acid (H3BO3). Anickel sheet of 99.99% purity with dimensions of100 mm50 mm5 mm was used as anode andpure annealed copper plate with dimensions of20 mm15 mm2 mm as cathode (substrate) mate-rials. Prior to deposition, the copper substrates weremechanically polished with silicon carbide papers of400, 600, 800, 1200 grits and alumina suspensions of

8, 1 and 0.25 m, then rinsed with distilled water andactivated in 10% H2SO4 solution at room tempera-ture for 30 s. The deposition time was adjusted toachieve an average thickness of 100 m based on theFaradays law.

During the electroplating process, it was foundthat the pH of the solution play an important role onquality of the deposits and the pH range of 3.5 to 4.5resulted in the deposits with bright appearances andfree of voids and cracks. Hence, the pH of the bathwas kept to 4.00.2. Other electroplating conditionshave been summarized in Table 1.

The structure of the deposits was studied by X-raydiffraction (XRD), and scanning electron microscopy(SEM). The grain size of NC nickel coatings was cal-culated from full width at half maximum (FWHM)intensity of XRD profile using modified Williamson-Hall relation[13,14]. An annealed nickel sample withan average grain size of 30 m was also used for cor-rection of instrumental peak broadening.

The preferred orientations were investigated bycalculating the texture coefficient (TC) using the fol-lowing relation:

T C =I(200)

I111)(1)

where I(200) and I(111) are the peak intensities of scat-tered X-ray radiation from (200) and (111) crystallo-graphic planes of the deposits, respectively.

Fig. 1 SEM micrographs of surface morphology of nickelcoatings deposited from: (a) a saccharin-free bathat i=100 mA/cm2, (b) a bath containing 5 g/Lsaccharin at i=100 mA/cm2, (c) a bath contain-ing 5 g/L saccharin at i=300 mA/cm2

3. Results and Discussion

The typical SEM micrographs of surface morphol-ogy of electrodeposited nickel have been presented inFig. 1. It can be seen that at the current densitieshigher than 75 mA/cm2, in the absence of saccharinthe nickel layer exhibits a pyramidal-like morphology(Fig. 1(a)) while it changes to a colony-like morphol-ogy in presence of saccharin. An increase in current


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84 A.M. Rashidi et al.: J. Mater. Sci. Technol., 2010, 26(1), 8286.

Fig. 2 Variation of grain size of nickel deposits with: (a)bath temperature, (b) current density, (c) saccha-rin content

density results in larger colonies and brighter appear-ance. Panek et al.[15,16], Weil and Cook[17], El-Sherikand Erb[3] reported the formation of colony-like mor-phology similar to that observed in Figs. 1(b) and1(c). El-Sherik and Erb[3] and Nakamura et al.[18] alsoobserved similar morphological transition in nickel

electrodeposited from a Watts bath in presence of sac-charin. This may be ascribed to the inhibition effectof organic additives on nickel ion reduction[1820].

The variations of the grain size of nickel coatingsas a function of bath temperature (T), current den-sity (i), and saccharin concentration (Cs) have beenpresented in Fig. 2. The grain size of deposits de-creases as the plating temperature increased up to55C and then increases by further increasing bathtemperature. As seen in Fig. 2(a), nanostructurednickel deposits with a mean grain size from 24 nmto 32 nm is obtained at all the investigated tempera-

tures. It is also evident that the bath temperature hasa minor effect on the grain size of the coatings com-pared with current density (Fig. 2(b)) and saccharinaddition (Fig. 2(c)).

According to the pattern presented by Dini[21,22],it is generally expected that the grain size of the de-posits increases by increasing the bath temperature.Such behavior has been experimentally observed forother nanocrystalline deposits[2,23]. The present re-sults (Fig. 2(a)) for plating temperatures above 55C

are consistent with above-mentioned idea but at thetemperatures lower than 55C an unexpected behav-ior is observed, that is an increase in bath temperatureleading to grain refining of nickel deposits.

It is well known that the energy of grainnucleus formation depends on the cathodicoverpotential[24,25]. A large cathodic overpotential re-duces the energy of nucleus formation, and thereforeincreases the nucleus densities (the number of nucleusper surface area) and refines the grains of the coat-ing. Consequently, since the cathodic overpotentialdecreases with increasing the bath temperature[2,21],

it is expected that the grain size of the depositsincreases. Nevertheless, it should be noted that in-creasing the bath temperature has two contradictoryeffects; (i) an increase in critical size of nucleus due toa decrease in thermodynamic driving force of crystal-lization process which leads to lower nucleus densities,and (ii) an increase in kinetic driving force that canlead to higher nucleation rate[26,27]. At the bathtemperatures in which the size of critical clustersis in atomic dimension, every active site can act asa critical nucleus. So, the thermodynamic barriersfor nucleus formation are negligible and the grainsize of deposit is controlled by kinetics variables. Insuch conditions, according to Arrhenius equation,the nucleation rate increases by increasing the bathtemperature[27] leading to finer grain in our presentwork.

According to Fig. 2(b), the grain size decreasesby increasing the current density up to 75 mA/cm2,whereas further increase in current density has nosignificant effect on grain refining. This behavior isconsistent with the data presented by Dai, et al.[8].In general, according to the pattern presented byDini[21,22], it is expected that the grain size of thedeposits decreases by increasing the current density,

because an increase in the current density resultsin a higher overpotential that increases the nucle-ation rate. However, several researchers[47,28] havereported an increase of grain size of nickel depositswith increasing the current density and attributed itto a decrease in the concentration of Ni ions[38] and/orthe co-deposition of hydrogen[6] at cathode-electrolyteinterface.

As it has been mentioned above, the grain size ofnickel deposits does not change at the current den-sity beyond 75 mA/cm2, which can be attributed toco-deposition of hydrogen at cathode surface. The co-

deposition of hydrogen changes the surface energy[29]and the growth mechanism[6] and also the distributionof applied currents between the reduction of Ni2+ andH+ ions[30]. In the latter case, despite an increase


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A.M. Rashidi et al.: J. Mater. Sci. Technol., 2010, 26(1), 8286. 85

in applied current density, the pure current densityavailable for nickel deposition does not increase con-siderably.

Figure 2(c) shows that at a given current density,initially the grain size decreased rapidly by increasingthe saccharin content before leveling off at 3 g/L of

saccharin. By addition of 3 g/L or more of saccharinadditive a reduction of the crystallite size by a fac-tor more than 16 is observed. Similar effect has beenreported by El-Sherik and Erb[3], Dai et al.[8] andXuetao, et al.[11]. This phenomenon can be relatedto the combined effects of retarding the surface diffu-sion, blocking the crystalline growth[3133], hydrogenevolution and/or absorption[34,35], and the change inoverpotential[18,35].

Figure 2(c) also indicates that the saccharin con-centration corresponding to the initiation of curveplateau is about 3 g/L. This value confirms the val-

ues reported by Dai et al.[8] and Xuetao et al.[11].As seen in Fig. 2(c), beyond 3 g/L of saccharin, thegrain size of the coating is approximately independentof saccharin concentration. This phenomenon can beattributed to the leveling off in the overpotential[36]

and/or saturation of adsorption sites on the cathodesurface[37] with increasing the saccharin amount in thebath.

Based on the grain size, the optimum conditionsfor producing nanocrystalline nickel coating by di-rect current electroplating from Watts-type bath atpH4, could be proposed as: current density 75

100 mA/cm2

, saccharin concentration 3 g/L andplating temperature 55C. The XRD pattern ofnickel coating produced under optimum conditionshas been presented in Fig. 3. For comparison, theXRD pattern of reference sample (annealed nickel)has also been shown in Fig. 3. It can be observed thatthe crystal structure of the coating is pure fcc nickeland no characteristic peaks of other phases have beenrecorded. The peak broadening of electrodepositedcoatings with respect to reference sample is also ev-ident in this figure indicating the grain refining intonano-scale size.

The effects of plating parameters on the preferred

orientation of the coatings have been presented inFig. 4. The preferred texture of the coating depositedat the current density of 10 mA/cm2 is (200) tex-ture, while at other current densities, the randomtexture is observed. Also by increasing the saccharincontent in the electrolyte, the texture of the coatingchanges from a (200) preferred orientation to randomtexture. Similar observations have been reported byother researchers[3,8,11,18]. Figure 4(a) shows that in-creasing the bath temperature from 45C to 55C,results in an increase in TC (I(200)/I(111)), whereasfurther increase in bath temperature has an opposite

effect.Comparing Figs. 2 with 4 reveals that when ini-

tially increasing current density and saccharin con-tent, both the grain size and TC decrease, whilst fur-

Fig. 3 XRD patterns of nickel (a) electrodeposited un-der optimum conditions, (b) annealed at 700Cfor 24 h

Fig. 4 Variation of crystallographic texture of nickel de-posits with: (a) bath temperature, (b) currentdensity, (c) saccharin content


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86 A.M. Rashidi et al.: J. Mater. Sci. Technol., 2010, 26(1), 8286.

ther enhancement of bath temperature is accompa-nied by grain growth and an increase of TC. This indi-cates that the mechanism of grain size control in lattercase is different from the former ones. These resultsimply that perhaps the mechanism of electrocrystal-lization of nickel changes when the bath temperature

decreases down to 55C. However, more electrochem-ical experiments are still needed to reveal the exactdependence of grain size of the deposits on bath tem-perature and details of the mechanisms which leadsto unusual results.

4. Conclusions

(1) The grain size of the coatings decreased as theplating temperature increased up to 55C and thenincreased by further increasing bath temperature.

(2) An increase in current density up to

75 mA/cm2

as well as addition of saccharin up to3 g/L resulted in a decrease in the average grain sizeand TC of nickel coatings.

(3) Based on the refining of grain size, the opti-mum conditions for producing nanocrystalline nickelcoating could be proposed as: current density 75100 mA/cm2, saccharin concentration 3 g/L andplating temperature 55C.

Acknowledgements

This work was supported by University of Tehran andRazi University. The authors thank them for financial sup-

port of this work. We would also thank Dr. S.F. Kashani-Bozorg for his fruitful helps.

REFERENCES

[1 ] S.C. Tjong and H. Chen: Mater. Sci. Eng, 2004, R45,1.

[2 ] H. Natter and R. Hempelmann: Z. Phys. Chem., 2008,222, 319.

[3 ] A. M.El-Sherik and U. Erb: J. Mater. Sci., 1995, 30,5743.

[4 ] I. Bakonyi, E. Toth-Kadar, L. Pogany, A. Cziraki,I.Gerocs, K. Varga-Josepovits, B. Arnold and K.

Wetig: Surf. Coat. Technol., 1996, 78, 124.[5 ] I. Bakonyi, E. Toth-Kadar, T. Tarnoczi, L.K. Varga,

A. Cziraki, I. Gerocs and B. Fogarassy: Nanostruct.Mater., 1993, 3, 155.

[6 ] F. Ebrahimi and Z. Ahmed: J. Appl. Electrochem.,2003, 33, 733.

[7 ] K.L. Morgan, Z. Ahmed and F. Ebrahimi: MRS Proc.,2001, 634, B3.11.1.

[8 ] P.Q. Dai, Hui Yu and Q. Li: Trans. Mater. HeatTreatment, 2004, 25, 1283. (in Chinese)

[9 ] R.T.C. Choo, J. M. Toguri, A. M. El-Sherik and U.Erb: J. Appl. Electrochem., 1995, 25, 384.

[10] S.T. Aruna, S. Diwakar, A. Jain and K.S. Rajam:Surf. Eng., 2005, 21, 209.

[11] X.T. Yuan, Y. Wang, D.B. Sun and H.Y. Yu: Surf.Coat. Technol., 2008, 202, 1895.

[12] M. Paunovic and M. Schlesinger: Fundamentals ofElectrochemical Deposition, Wiley-Interscience Pub-lication, John Wiley Sons, Inc., 1998, 197.

[13] T. Ungar, J. Gubicza, G. Ribarik and A. Borbely: J.Appl. Cryst., 2001, 34, 298.

[14] T. Ungar, I. Dragomir, A. Revesz and A. Borbely: J.Appl. Cryst., 1999, 32, 992.

[15] J. Panek, A. Budniok and E. Lagiewka: Rev. Adv.Mater. Sci., 2007, 15, 234.

[16] J. Panek and A. Budniok: Surf. Coat. Technol., 2007,201, 6478.

[17] R. Weil and H.C. Cook: J. Electrochem. Soc., 1962,109, 295.

[18] Y. Nakamura, N. Kaneko, M. Watanabe and H. Nezu:J. Appl. Electrochem., 1994, 24, 227.

[19] J.K. Denis and J.J. Fuggle: Electroplat. Metal Fin.,1967, 20, 370.

[20] J.K. Denis and J.J. Fuggle: Electroplat. Metal Fin.,1968, 21, 16.

[21] J.W. Dini: Electrodeposition: The Material Scienceof Coatings and Substrates, Noyes Publications, NewJersey, 1993, 141.

[22] J.W. Dini: Plat. Surf. Finish., 1988, 75, 11.[23] H. Natter and R. Hempelmann: Electrochim. Acta,

2003, 49, 51.[24] A. Milchev: Electrocrystallization, Fundamentals of

Nucleation and Growth, Kluwer Academic Publishers,

2002, 11.[25] E. Budevski, G. Staikov and W.J. Lorenz: Elec-

trochim. Acta, 2000, 45, 2559.[26] J.W.P. Schmelzer: Mater. Phys. Mech., 2003, 6, 21.[27] J. Vazquez-Arenas, R. Cruz and L.H. Mendoza-

Huizar: Electrochim. Acta, 2006, 52, 892.[28] A. Cziraki, B. Fogarassy, I. Gerocs, E. Toth-Kadar

and I. Bakonyi: J. Mater. Sci., 1994, 29, 4771.[29] K. Haug and T. Jenkins: J. Phys. Chem. B, 2000,

104, 10017.[30] A.M. Rashidi and A. Amadeh: Surf. Coat. Technol.,

2008, 202, 3772.[31] J.P. Bonino, P. Pouderoux, C. Rossignol and A. Rous-

set: Plat. Surf. Finish., 1992, 79, 62.[32] T.C. Franklin: Plat. Surf. Finish, 1994, 84, 62.[33] D. Mockute and G. Bernotiene: Surf. Coat. Technol.,

2000, 135, 42.[34] A. Ciszewski, S. Posluszny, G. Milczarek and M. Bara-

niak: Surf. Coat. Technol., 2004, 183, 127.

[35] B. Szeptycka: Russ. J. Electrochem., 2001, 37, 684.[36] C.C. Roth and H. Leidheiser: J. Electrochem. Soc.,

1953, 100, 553.[37] J. Edwards: Trans. Inst. Metal Fin., 1964, 41, 169.

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