Effects of Saccharin and Quaternary Ammonium Chlorides on t

Surface and Coatings Technology 183(2004) 127–133

0257-8972/04/$ - see front matter� 2003 Elsevier B.V. All rights reserved.doi:10.1016/j.surfcoat.2003.09.054

Effects of saccharin and quaternary ammonium chlorides on theelectrodeposition of nickel from a Watts-type electrolyte

Aleksander Ciszewski*, Szymon Posluszny, Grzegorz Milczarek, Marek Baraniak

Institute of Chemistry and Applied Electrochemistry, Poznan University of Technology, Piotrowo 3, Poznan 60-965, Poland

Received 10 February 2003; accepted in revised form 19 September 2003

Abstract

The effect of the presence of quaternary ammonium chlorides(QACl) and saccharin on various electrodeposition parametersfor nickel deposition on a stainless steel cathode from a Watts-type plating bath was investigated. The parameters includedcathodic current efficiency, throwing power of the bath, cathodic polarization, crystal orientation, and quality of the deposit. Thefollowing additives were investigated: saccharin, 1-alkyloxymethyl 3-benzyl imidazolium chlorideswalkyl RsC , C , C x, 1-2 6 10

decyloxymethyl 3-alkyl imidazolium chlorideswalkyl RsC , C , C x, 1-cycloheksyloxymethyl 3-alkyl imidazolium chlorides2 6 10

walkyl RsC , C , C x, benzyl-dimethyl-alkyl ammonium chloridewalkyl RsC , C , C x, benzyloxymethyl-dimethyl-alkyl2 6 10 2 4 8

ammonium chlorideswalkyl RsC , C , C x, benzyl-dimethyl-alkyloxymethyl ammonium chlorideswRsC , C , C x. The results2 4 8 2 4 8

indicated that only one type of QACl fulfilled all requirements to be acceptable, namely: benzyl-dimethyl-alkyloxymethylchlorides, and especially benzyl-dimethyl-buthyloxymethyl chloride. The mechanism of the action of this additive has also beendiscussed.� 2003 Elsevier B.V. All rights reserved.

Keywords: Nickel electrodeposition; Saccharin; Quaternary ammonium chlorides; Additives; Ion-pairing catalysis

1. Introduction

Electrodeposition of nickel is a commercially impor-tant and versatile surface finishing process. Its applica-tions fall into three main categories: decorative,functional, and electroforming. Nickel is generally elec-trodeposited from sulfate or sulfamate electrolytes withor without additives, and also from a Watts-type electro-lyte containing nickel sulfate, nickel chloride and boricacid. However, the plating baths contain not only themetal to be plated but also additional agents. Additiveshave more of an influence on deposit properties thanany other plating variables. When used at controlled,limited concentrations, organic additives refine the grainstructure, provide desired tensile and ductility properties,impart leveling characteristics to the plating solution,and act as brightenersw1x.It has been found that for nickel plating from a Watts-

type bath two types of organic additives must be used

*Corresponding author. Tel.:q48-61-66-52-152; fax:q48-61-66-52-571.

E-mail address:[email protected](A. Ciszewski).

to obtain commercially acceptable deposit: for examplesaccharin and 2-butyne-1,4-diol which according to clas-sification of additives are also named ‘carrier’ and‘brightener’ or ‘the first class additive’ and ‘the secondclass additive’, respectivelyw1,2x.The effects of the addition of relatively small amounts

of selected organic additives in the plating baths on thecurrent efficiency, deposit morphology and polarizationbehavior of the cathode during nickel deposition arewell documented in the literature. Costavaras et al.w3xstudied the effect of some acetylenic and aryl–sulfoniccompounds and found that the texture of nickel depositis related to the nature of unsaturation present in theaddition agent molecule. Gao et al.w4x studied the effectof 2-butyne-1,4-diol and three other compounds ofdifferent oxidation state of sulfur on the electroreductionof nickel from the Watts bath. Miluskinw5x demonstratedthat thiosemicarbazide derivatives significantlyimproved the quality of the electrodeposited nickel.Kaneko and co-workersw6x reported on the electrochem-ical behavior of saccharin and three kinds of diolcompounds, namely butanediol, butenediol and butyne-

128 A. Ciszewski et al. / Surface and Coatings Technology 183 (2004) 127–133

Table 1Plating electrolyte composition

Compounds Concentrations(g dm )y3

NiSO 7 H O4 2 350NiCl 6 H O2 2 60H BO3 3 40Saccharin 5QACl 1

diol on the electrocrystalization of nickel from the Wattsbath. They also showedw7x the effect of three kinds ofaliphatic alcohols(n-propyl, allyl and propagyl alcohol)and the effect of both saccharin and aliphatic alcoholson the surface morphology and crystal orientation ofelectrodeposited nickel. Many nickel brighteners of the‘second class additive’ contain in their structure anitrogen atom in the form of pyrimidines, pyrazoles orimidazoles derivatives. Shimuzu et al.w8x observed thatbright nickel deposit could be obtained from the solu-tions containing substituted pyridines together with sac-charin. Singh and co-workersw9,10x presented the effectof pyridine and its derivatives on current efficiency,surface quality, and crystallographic orientation of elec-trodeposited nickel from sulfate solutions. Also Gao etal. investigated the electrochemical reactions occurringduring deposition of nickel from the Watts bath in thepresence of pyridinum-1-propane-3-sulfonatew11x.Thus, clear information on the effect of additives with

nitrogen in their structure on the nickel electrodepositioncurrent efficiency and deposit quality is lacking in theliterature. In view of this, the present paper reports theeffect of a few kinds of quaternary ammonium chlorides(QACl) as additives on the nickel plating from theWatts-type electrolyte, in terms of properties of platingbath (cathodic polarization, current efficiency, throwingpower) and deposit quality (brightness, hardness,roughness).

2. Experimental

The influence of additives on the nickel electrodepos-iting was investigated in the Watts-type electrolyte(Table 1). The following additives were investigated:saccharin, 1-alkyloxymethyl 3 benzyl imidazolium chlo-rides walkylsC , C , C x, 1-decyloxymethyl 3-alkyl2 6 10

imidazolium chlorideswalkyl RsC , C , C x, 1-cyclo-2 6 10

heksyloxymethyl 3-alkyl imidazolium chlorideswalkylRsC , C , C x, benzyl-dimethyl-alkyl ammonium chlo-2 6 10

rideswalkyl RsC , C , C x, benzyloksymethyl-dimethyl-2 4 8

alkyl ammonium chlorideswalkyl RsC , C , C x,2 4 8

bemzyl-dimethyl-alkyloxymethyl ammonium chlorideswalkyl RsC , C , C x. The chemical structures of these2 4 8

additives are also presented in Table 2. Saccharin,inorganic salts and boric acid were of analytical grade.

Ammonium and imidazolium derivatives were synthe-sizedw12x.All experiments for studying the polarization behavior

on nickel electrodeposition were carried out in a glasscell with 25 cm electrolyte at 50"1 8C. A stainless3

steel disc electrode of 3-mm diameter and platinum wireof 0.5-mm diameter were used as working and auxiliaryelectrodes respectively. A saturated calomel electrodewas used as the reference electrode through a Luggincapillary and all the potentials were reported as such.Prior to each experiment, the electrode surface waspolished with 600 and 1200 grade silicon carbide paperto a mirror finish and then washed with 1 M HClfollowed by ultrapure water. A linear sweep voltammetrytechnique was used to elucidate the influence of QAClon the reduction of the nickel ion. The cathode potentialwas scanned fromy700 mV in the negative directionat the rate of 1 mV s using a BAS(Model 100W)y1

potentiostat. High purity nitrogen was used to spargeout dissolved oxygen and to maintain an inert atmos-phere throughout the polarization studies. The nucleationpotential(E ) of nickel electrodeposition defined as then

intersection point on the ‘X’ axis when the ascendingportion of the cathodic scan is extrapolated was deter-mined from the polarization data.All the electrodeposition experiments were conducted

in a rectangular electrolytic cell at a current density of500 A m by applying current from a regulated powery2

supplier. A precision voltmeter and an ammeter wereplaced in the cell circuit to record the potentials andcurrent and a thermostat was used for maintaining theelectrolyte temperature at 50"1 8C. The pH of theelectrolyte was maintained at 4.5"0.1. Stainless steeland nickel plates of 1N grade were used as a cathodeand an anode, respectively. The current efficiency wascalculated by weight. Three deposits were plated fromeach bath to a thickness of approximately 20mm.Deposit quality examination was done using a Philips

(PW 1050) X-ray diffractometer to determine the nickelpreferred crystal orientation, Glossmeter 8510-1 forbrightness measurements of electroplated surfaces(withglass mirror as a standard), Taylor–Hobson profilographto describe the roughness of deposit, and Epitop-2 deviceto determine the hardness of plated nickel layers(with50 g applied load).

3. Results and discussion

The effect of the examined QACl on the propertiesof nickel-plating bath and deposited nickel quality ispresented in Tables 2 and 3. Analyzing these data andtaking into account the usefulness of the examined bathsin practical nickel-plating process, it is clear that theonly type of QACl, which fulfils all requirements is thatdescribed as type VI. The rest of the studied additivescaused unacceptable properties of the plating bath(cur-

129A. Ciszewski et al. / Surface and Coatings Technology 183 (2004) 127–133


Table 3Effect of benzyl-dimethyl-butyloxymethyl ammonium chloride oncurrent efficiency, nucleation potential and crystallographic orientationof nickel electrodeposited from the Watts-type electrolyte

Additive CE En Crystallographic orientation(hkl)(g dm# )3 (%) (mV)Relative peak intensities(IyI )%max

(111) (200) (220)

0 92 862 10 100 –0.2 94 912 21 100 –0.4 96 980 39 100 10.6 98 992 71 100 20.8 97 1101 95 100 –1.0 98 1143 100 92 –

rent efficiency, throwing power) or inefficient nickeldeposit quality(brightness, hardness, roughness); forthese reasons the role of these types of additives willnot be discussed here.It is well known that the role of additives in electro-

chemical process is connected with the fact that theseprocesses involve competitive reactions. The electro-chemical deposition of metals in aqueous systemsinvolves at least the evolution of hydrogen from thereduction of water or hydronium ions and the electro-deposition of metal from the reduction of some com-plexes of the metal ion. Additives presented in such asystem can be viewed as inhibitors or catalysts of thesecompetitive processes. These general rules also operatein the case of nickel deposition from the Watts-typebath.The combined effect of saccharin and the studied

QACl of type VI on the nickel plating process has beeninvestigated with good care. Saccharin concentration inthe plating bath was maintained at 5 g dm(accordingy3

to most of the technological protocols) and the examinedadditive concentration was varied between 0.1 and 1 gdm .y3

The mechanism of saccharin action during nickelelectrodeposition has been presented many times in theliterature. This ‘carrier’, a principal source of sulfurdeposited with nickel, is the most effective internalstress reducer and often helps to decrease or eliminatehazes of the depositw6,7,13–16x. The investigated ben-zyl-alkyloxymethyl-dimethyl ammonium chlorides havenot been described as brighteners for nickel-plating fromthe Watts-type electrolytes yet. However, the data pre-sented in this paper(Table 2) clearly show their highadsorptivity onto the electrode surface. This phenome-non may be realized by electrostatic interaction with anegative charged electrode or by chemisorption, mostlikely via the unsaturated benzene ring. As a result, aremarkable shift of nucleation potential of nickel depo-sition towards more negative potentials can be observed.

The most interesting case in our studies is the bathcontaining saccharin and benzyl-butyloxymethyl-di-methyl ammonium chloride. Scanning electron micro-graphs(SEM) of electrodeposited nickel from the Wattsbathqsaccharin in the absence or presence of the abovementioned QACl under galvanostatic condition(500 Am ), are shown in Figs. 1 and 2. It can be seen thaty2

in the absence of QACl(Fig. 1) large granular crystals(1–3mm) were observed on the whole surface and thesurface roughness was relatively large. Consequently, itbecame apparent that smooth, fine-grained and brightnickel deposit could not be obtained when plating bathcontains saccharin only. However, when ammoniumadditive of interest was added, the size of crystalsbecame smaller and fine-grained and compact depositswere obtained(Fig. 2). This may be ascribed to theinhibitory and synergistic effect of the two kinds ofadsorbed species(saccharinqQACl) on the reductionof the nickel ion. The nucleation potential in this casewas shifted to more negative value(Table 2) andconsequently, the nucleation dependent growth of nickelmay occur preferentially and the crystals grain size may,therefore, be smaller.The results of X-ray analysis of the electrodeposited

nickel for this case are given in Table 3 and some ofthem are presented in Fig. 3. When nickel was depositedfrom a bath containing saccharin only, the crystallitesgrew predominantly in the direction of the(200) and(111) planes. The(200) plane was found to be the mostpreferred plane; the intensity of this peak was more than10 times higher than the second one. Thus the order ofthe preferred crystal orientation of the electrodepositednickel in the absence of ammonium salt, was(200))(111).The presence of both saccharin and benzyl-butyloxy-

methyl-dimethyl ammonium chloride in the electrolytepromoted the crystal growth still in direction of the(200) and(111) planes as in the former case. However,the (200) diffraction peak intensity decreased signifi-cantly when concentration of ammonium salt in the bathincreased. An increase in the examined ammonium saltconcentration to 0.8 g dm results in a dramaticallyy3

different XRD spectrum. The(200) and (111) diffrac-tion peak intensities were almost equal; the intensity of(200) peak decreased approximately 10 times and theintensity of (111) peak increased almost two times,compared to the spectrum of nickel deposit obtainedfrom the Watts bath containing saccharin only. Furtherincrease in ammonium salt concentration does notchange the order of the preferred crystal planes signifi-cantly but either(200) or (111) plane becomes a littlebit more preferred. Such changes were reflected in thedeposit quality(brightness, roughness), current efficien-cy and also in power consumption.The second, very interesting feature of the exam-

ined bath (saccharinqbenzyl-butyloxymethyl-dimethyl


Fig. 1. SEM of nickel electrodeposits from the Wattsqsaccharin plating bath.

ammonium salt) was an extremely high cathodic currentefficiency of the process in question. It oscillated in thevicinity of 97.5% ("0.5%) and was decidedly higherthan that offered by commercially approachable a Watts-type baths which according to technological protocolsare characterized by cathodic current efficiency in therange 90–94%w1x. This several percentages’ increaseof current efficiency is very important from both theor-etical and practical point of view. To explain theobserved phenomenon, the working hypothesis has beenassumed that the examined ammonium cations operatein the plating bath not only as a brightener but also asa catalyst for the nickel deposition process. It meansthat this additive is capable of changing the kinetics ofcompetitive reactions: nickel deposition and hydrogenevolution, with preference for the first one.It is well known that in some cases quaternary

ammonium ions can operate as ion-paring phase transfercatalysts for the reduction of metals present as negativelycharged complex ions. In these applications, the reac-tions are accelerated by extracting an ion from a highdielectric constant medium(an aqueous electrolyte) toa low dielectric constant medium(an electrode interface)by the formation of an ion-pair that is more stable inthe low dielectric constant medium. The literature data

show a few very interesting examples where the use ofion-paring method allows controlling the compositionof electrodeposited metal alloysw17–20x.The case of nickel deposition from a Watts-type bath

can also be seen as a system where nickel, at leastpartly, is presented in the form of a negative boratecomplex; therefore, the positive quaternary salt cancreate an ion pair with negative ion and reduce therepulsation between the negative ion and the negativecathode, which may form a new road for nickel electro-deposition. This idea is supported by literature data thatdocument the existence of negative nickel borate com-plexes in the Watts-type nickel-plating bathw21x, andgives the explanation for high cathodic current efficiencyobserved. The scheme presented below shows the pos-sible mechanism that operates in this particular case:

y qw x { w x }Ni(H BO ) qQA l Ni(H BO ) QA2 3 n 2 3 n ads

q y{ w x }Ni(H BO ) QA ™NiqQA H BO2 3 n ads 2 3

4. Conclusions

On the basis of the present studies the followingconclusions may be drawn:


Fig. 2. SEM of nickel electrodeposits from the Wattsqsaccharinqbenzyl-dimethyl-buthyloxymethyl ammonium chloride(0.08 g dm ) platingy3

bath.

Fig. 3. X-Ray diffractogram of electrodeposited nickel sample from the Wattsqsaccharin plating bath.


i. The influence of the examined quaternary ammoniumsalts on the nickel electrodeposition process dependson the structure of additives used.

ii. The nucleation potential values indicate that all theexamined quaternary ammonium salts are cathodedepolarizers for nickel electrodeposition. Imidazoliumsalts are the strongest depolarizers of all investigatedadditives.

iii.The most useful type of the examined additives isbenzyl-alkyloxymethyl-dimethyl ammonium salts andbutyl derivative turned out to be the best.

iv.Combining saccharin and chosen ammonium saltsresulted in a good quality of deposited nickel andhigh current efficiency.

v. The ion-paring catalysis model is useful to explainthe observed phenomenon.

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Effects of Saccharin and Quaternary Ammonium Chlorides on t