Advances in Chemical Engi neering and Science , 2011, 1, 118-124
doi:10.4236/aces.2011.13018 Published Online July 2011 (http://www.SciRP.org/journal/aces)
Effect of Sodium Dodecyl Sulphate on the Composition of
Electroless Nickel—Yttria Stabilized Zirconia Coatings
Nkem O. Nwosu, Alan M. Davidson, Colin S. Hindle
School of Engineering and the Built Environment, Edinburgh Napier University, Edinburgh, UK
Received June 1, 2011; revised June 27, 2011; accept ed July 5, 2011
Abstract
The influence of a surfactant on the composition of nickel—yttria stabilised zirconia (YSZ) cermet coatings,
applied by electroless nickel plating technique was examined. The amphiphilic characteristics of anionic
surfactant sodium dodecyl sulphate (SDS), was relied upon for enhanced dispersion of YSZ particles
co-deposited for use as anodes in solid oxide fuel cell technology and potential heat absorbing layers in
thermal barrier coatings. Optical microscopy was employed to study the correlation between the plating
thickness, level of ceramic loading and SDS concentration while the effect of the surfactant and fineness of
YSZ particles on the as-deposited coating’s ceramic to metal ratio, was analysed using energy dispersive
X-ray analysis (EDXA) characterisation technique.
Keywords: Electroless Nickel Composite Coatings, Solid Oxide Fuel Cell Anodes, Coating Composition,
Additives
1. Introduction
Electroless nickel plating (ENP) is a highly desirable
surface coating technique that has the capability of pro-
ducing uniform surface deposits regardless of recesses
and bores [1]. Although Brenner & Riddell are credited
with developing the process [1,2], Odekerken who while
attempting to improve the corrosion resistance of nickel
chromium electrodeposits, applied an intermediate layer
of alumina (Al2O3) and poly vinyl chloride (PVC) within
a metal matrix, is widely acknowledged as the earliest
demonstrator of particulate matter incorporation by ENP
[3,4]. Since then, numerous studies such as those of
Sheela & Pushpavanam [5] who adopted the technique to
synthesise high wear resistant diamond-nickel composite
coatings, have been carried out to establish potential ap-
plications for the technology.
Recently, Davidson & Waugh [6] successfully applied
ENP to the manufacture of nickel-yttria stabilised zirco-
nia cermet coatings for use as solid oxide fuel cell (SOFC)
electrodes. This was called electroless co-deposition (ECD)
of nickel and ceramic. Simply requiring a source of en-
ergy to liberate chelated metal ions maintained in sus-
pension by complexing agents, the technique has been
shown to have a much faster rate of production and low-
er energy consumption than traditional SOFC electrode
manufacturing techniques such as silk screening and tape
casting [7]. It’s non-requirement of a high energy sinter-
ing stage, offers an opportunity for cost reduction and
complete elimination of high temperature induced de-
fects such as cell warpage occasionally associated with
existing processes. In SOFC technology, nickel aids fuel
catalysation and electronic conductivity while YSZ in
addition to preventing nickel from sintering at high
SOFC operating temperatures of about 1000˚C, re- lieves
the coefficient of thermal expansion (CTE) mismatch
between the anode and electrolyte [8,9,10] (nickel –13 ×
10–6/˚C & YSZ –10 × 10–6/˚C). High nickel content pro-
motes cell cracking while too low a content and corre-
spondingly high YSZ presence could compromise cell
efficiency and performance [11]. To avoid unwanted
occurrences such as cell de-lamination which may arise
due to CTE mismatch, an understanding of the structure
of ceramic to metal ratios obtained by ECD or the effect
of additives that may aid achievement of a desired 60 -
40 composition is essential. In fact for use of ECD de-
posits as intermediate layers in thermal barrier coatings
(TBC) where material insulation in high temperature
environments is sought, the required proportion of ce-
ramic to metal is even greater.
Surfactants, non-ionic (steric stabilised) or anionic, ca-
tionic and zwitter ionic (electrostatic interaction) are

N. O. NWOSU ET AL. 119
surface active agents that in addition to lowering the sur-
face tension of a liquid also allow for easy spreading and
less interfacial tension between two liquids. Its inherent
amphiphilic property that arises du e to its molecules dual
lyophobic—lyophilic tendency, has been previously em-
ployed for dispersion of ceramic powders in polymers
[12,13] and polymers in solutions including electroless
nickel [14]. While Wu, et al. [15] used sodium dodecyl
sulphate (SDS) to increase the wettability a nd dispersion
of silicon carbide particles, Elansezhian, et al. [16] per-
formed studies on Ni-P coatings influenced by anionic
and cationic surfactants SDS and cetyltrimethyl ammo-
nium bromide (CTAB). They reported that the concen-
tration of surfactant utilised in the process had an effect
on the surface morphology of the deposits. Hardness of
the coatings was found to progressively increase with
SDS content while surface roughness reduced as the lev-
el of surfactant reached 0.6 g/l. The resultant smooth
surface was attributed to uniform dispersion of fine nick-
el particles. While their observation is in line with the
findings of Tr ipathy, et al. [17] who studied the effect of
sodium lauryl sulphate on zinc electrowinning from
acidic sulfate solutions, Karuppusamy & Anantharam
[18] also reported that addition of 150ppm SDS resulted
in uniform and pit free nickel deposits.
In this work, the influen ce of SDS on the compositio n
of nickel-YSZ coatings applied by ECD process is inves-
tigated. Associated changes in the characteristics of the
coatings such as thickn ess is also assessed and reported.
2. Experimental
2.1. Procedure
Alumina (Al2O3) tiles, 40 × 15 × 1 mm were used as
substrates for the deposition. Overcoming the insulation
posed by such ceramic surfaces was achieved via pre-
treatment processes. Cuprolite X-96 DP (2-Aminoe-
thanols (1% - 4%)) (A lfachimici, Italy), was employed at
60˚C for 15 mins to degrease the substrate’s surface.
Next, to sensitise the surface, the subs trate was immersed
in 100 ml of stannous chloride solution at room tem-
perature for 15 mins. The final step performed for sur-
face activation was carried out in a solution containing
palladium chloride with temperature ranging between
36˚C to 40˚C.
Electroless nickel solution for the deposition process
was made up from proprietary slotonip 18 - 51 starter
and slotonip 18 - 53 replenisher chemicals supplied by
Schloetter company limited. Bath pH and plating tem-
perature were 4.9 and 89˚C respectively. SDS (Fisher
Scientific, UK) and yttria stabilised zirconia (YSZ) (Un-
itec Inc.) were added to the bath prior to the introduction
of the pre-treated alumina tile. A magnetic stirrer was
used to ensure particle dispersion and deposition time
was 1 hr. Governing reactions are as detailed by Gutzeit
[19] in Equations 1-4.


22 223
HPOHOHPO2H 2e
 
  (1)
2
Ni 2eNi

 (2)
2
2H 2eH

 (3)

22 2
HPO2HeP 2HO

 (4)
Electrons from the hypophosphite ion reduce nickel
ions to nickel metal (1) & (2). The nickel metal thereafter
entraps YSZ particles while adsorbing on the activated
alumina substrate.
Unfortunately, phosphorus, a resultant element simul-
taneously produced from the hypophosphite ion (4),
poses a challenge in fuel cell technology. Besides being
noted to have a characteristic property of reducing the
anode/cell performance [20,21], phosphorus has a ten-
dency to form a liquid phase with nickel at temperatures
above 850˚C which thereafter precipitation hardens to
yield an undesired material, nickel phosphide (Ni3P).
Alternatives such as hydrazine (N2H4)—probably with
less deleterious effects—do exist, but have considerable
cost implications.
2.2. Sample Preparation and Characterisation
A Struers Accutom-5 precision cutter was used to cut
cross-sections of the coated substrate. The feed rate was
set at 0.02 mm/s and the utilised diamond tip cutting disc
was maintained at a speed of 3000 rpm. The samples
were thereafter mounted in 40 mm diameter epoxy resin
and grinding and polishing was carried out with the aid
of the TegraForce-5/TegraPol-21. Contact force for both
operations was 50 N with an anti-clockwise rotation of
150 rpm .
The surface structure of the coatings was observed
with a Cambridge Stereoscan 90 Scanning Electron Mi-
croscope (SEM) while an in-situ Oxford Instrument Inca
Energy Dispersive X-ray Analysis system (EDXA) was
relied upon for analysis of its composition. For examina-
tion of the thick ness and characteristics of th e coatings, a
Leitz Aristomet Hi-power light microscope was em-
ployed.
All experiments were repeated twice and an average of
both results is reported.
3. Results and Discussion
3.1. Pre-surfactant Ceramic Loading
Prior to the introduction of SDS, the optimum pre-sur-
factant YSZ concentration for maximum incorporation of

N. O. NWOSU ET AL. 120
the ceramic into the nickel matrix was sought. Evaluation
of ECD coatings for selected YSZ bath loadings of 0 g/l,
10 g/l, 50 g/l and 100 g/l was carried out to estimate this
value.
Light microscopy images revealed that, with increas-
ing YSZ loading in the bath, the uniform surface finish
generally associated with ENP processes, gradually be-
came uneven (Figure 1). Visually, the coatings changed
colour from shiny metallic silver to dark black—an ob-
servation probably due to reduced metal exposure which
resulted in lower light reflection from the surface of the
coating.
On assessment of coating thicknesses achieved, an in-
verse relationship was foun d to exist between the plating
thickness and level of YSZ loading in the bath (Figure
2). As un-activated co-deposited YSZ particles provide
insulating less reactive facets, that do not encourage au-
tocatalytic deposition of nickel metal continuously re-
duced from its ions, increase in YSZ loading may have
resulted in growth retardation of the depo sit layer. In fact,
examination of coatings carried out with 100 g/l YSZ
bath loading, which showed a thickness of only about 2
µm, is evidence that the YSZ powder formed an almost
complete barrier to nickel adsorption on the surface.
Sheela and Pushpavanam [5] who studied electro less nic-
kel-diamond coatings and Balaraju, et al. [22] who in-
vestigated electroless Ni-P composite coatings also ob-
served a similar trend. The latter suggests that the emer-
gent pattern could be ascribed to the possibility of grou-
ping or agglomeration of second phase particles resulting
(a)
(b) (c)
Figure 1. Photo micrographs showing the cross sectional
view of nickel-YSZ coatings (a) No ceramic loading (b) 10
g/l and (c) 50 g/l (×500 mag).
Figure 2. Coating thickness vs 5 µm particle size YSZ bath
loading.
from a decrease in the mean distance between them.
EDXA analysis of the coatings showed that maximum
incorporation of YSZ particles occurred at 50 g/l with a
ceramic to metal ratio of about 40:60 volume% (Figure
3). As this value was found to vary with the maximum
30 volume% ceramic content of electroless nickel com-
posite coatings reported by Baba, et al. [23] and Dini
[24], the resultant higher ceramic ratio may be related to
a different particle size used or bath composition adopted.
Further increases beyond the 50 g/l YSZ loading how-
ever yielded no increased ceramic content.
3.2. SDS Incorporation
Based on the results obtained, 50 g/l YSZ loading was
adopted for the surfactant study. YSZ powders of 1 µm
and 5 µm average particle sizes were utilised with SDS
concentration varied from 0 to 0.9 g/l.
With bath parameters held constant, it was observed
Figure 3. Ceramic (Y, Z, O) and metal (Ni) content of 5 µm
YSZ particle size loading.
Su
b
strate E
p
ox
y
resin
Coatin
g

N. O. NWOSU ET AL. 121
that the coatings became incoherent as SDS concentra-
tion increased. This occurrence which probably indicates
improper or obstructed nick el adherence to the substrate,
may be linked with the findings by Ger & Hwang [14]
who while attempting to improve the mechanical and
tribological properties of Ni-P deposits, employed the
cationic surfactant fluorinated alkyl quaternary ammo-
nium iodides (FC) to aid incorporation of polytetraflou-
roethylene particles into the nickel matrix. The authors
who noted a reduction in nickel’s rate of deposition as
the quantity of surfactant increased suggest that, the be-
haviour can be associated with increased adsorption of
the surfactant on the substrates surface which thereof
acts as a barrier to deposition.
Increase in the level of SDS appeared to have a greater
impact on the characteristics o f platings carried out with 1
µm YSZ particles than the 5 µm sizes. While the latter
maintained almost the same features pre- and post- SDS
(Figures 4(a) and 5(a)), the former witnessed higher in-
corporation of ceramic particles (Figure 4(b)) but at the
expense of coating thickness which experienced a drastic
reduction from about 14 µm to 2 µm (Figure 5(b)). Cor-
responding EDXA spectra (Figure 6) of SDS incorporated
(a)
(b)
Figure 4. Influence of SDS on the ceramic to metal content
of 50g/l (a) 5 µm & (b) 1 µm YSZ particle size coatings.
(a)
(b)
Figure 5. Influence of SDS on the thickness of nickel—(a) 5
µm & (b) 1 µm YSZ particle size coatings.
1 µm YSZ particle coatings, which shows increasing
peaks of Yttrium, Zirconium and Oxygen, and the de-
creasing peaks of nickel, further illustrates the observed
increase in ceramic content. Working with the surfactant
1179 Forafac (trade name for similar FC surfactant used
in [14]), Grosjean, et al. [25] also observed a similar
trend. The authors reported that when 500ppm FC was
added to the bath, incorporation of silicon carbide parti-
cles rose from 19 to 53 volume %.
An inspection of both ceramic to metal ratio plots
(Figure 4) though showed that on addition of 0.3 g/l
SDS, an increase in the nickel content of both 5 µm and
1 µm YSZ particle size coatings occurred. But as the
concentration of SDS in the bath increased, the metal
content of both particle size coatings was found to de-
crease. This behaviour maybe akin to the varying critical
micelle concentration (CMC) of SDS in different solu-
tions. Newberry [26], Muijselaar, et al. [27] and Su, et al.
[28], have all shown via various studies that the CMC of
SDS in divalent metal solutions is far less than its usu al 8
× 10–3 M in pure water being 4 × 10–3 M for nickel and 2
× 10–3 M for copperdepending on concentration. As 4 ×
10–3 M corresponds to 0.6 g/l SDS content, it can be in

N. O. NWOSU ET AL. 122
(a)
(b)
(c)
Figure 6. Energy Dispersive X-ray spectra of (a) 0.3 g/l (b) 0.6 g/l (c) 0.9 g/l SDS incorporated Ni-YSZ coatings.
ferred that the attained CMC enhanced YSZ particle dis-
persion which yielded an increased level of ceramic in-
corporation in the coating.
Examination of SEM micrographs (Figure 7) appear
to suggest that surface roughness of the coatings in-
creased with SDS content—an observation consistent
with the report by Alsari, et al. [29]. While investigating
the effect of SDS solutions as gelation media on the for-
mation of polyethersulfone (PES) membranes, the au-
thors noted that upon SDS attaining its CMC, the conse-
quential increase in pore size resulted in increased rough-
ness of the membranes.
4. Conclusions
The effect of the surfactant SDS on the composition of
keV

N. O. NWOSU ET AL. 123
(a)
(b)
(c)
Figure 7. SEM images of (a) 0.3 g/l (b) 0.6 g/l (c) 0.9 g/l SDS
incorporated 50 g/l YSZ loading/1 µm particle size coatings
× 1,000 mag.
nickel-YSZ ECD composite coatings, has been investi-
gated and reported.
Results obtained show that, by adding SDS to an
elec-troless nickel bath containing a pre-determined op-
timum YSZ loading of 50 g/l, up to 60 volume% YSZ can
be incorporated into cermet coatings applied by ECD. A
trade-off though w as observed w ith increasing SDS con-
tent as plating thickness decrea sed f r om 14 µm to about 2
µm and the coatings became incoherent. Inspection of the
surfaces via micrographs obtained by SEM appeared to
support the fact that surface roughness also increased with
SDS concentration.
Overall, the achievement of 60:40 ceramic to metal ra-
tio may suggest, existence of materials that may be in-
corporated to enhance the ceramic content of SOFC
electrodes synthesised by ECD. However, with a rela-
tively high metal content still present, further optimisa-
tion may be needed to adapt the process to technologies
such as thermal barrier coatings.
5. References
[1] G. O. Mallory and J. B. Hajdu, “Electroless Plating:
Fundamentals and Applications,” William Andrew
Publishing, Burlington, 1990.
[2] A. Brenner and G. Riddel, “Nickel Plating on Steel by
Chemical Reduction,” US Patent 2532282, 1950.
[3] R. C. Agarwala and V. Agarwala, “Electroless Alloy/Com-
posite Coatings: A Review,” Sadhana, Vol. 28, No. 3-4,
2003, pp. 475-493. doi:10.1007/BF02706445
[4] J. M. Odekerken, “Use of Co-deposited Non-conducting
Materials to Improve the Corrosion Resistance of Nickel-
Chromium Electrodeposits,” British Patent 1041753, U.S.
Patent 3644183 and DDR Patent 414061964.
[5] G. Sheela and M. Pushpavanam, “Diamond-Dispersed
Electroless Nickel Coatings,” Journal of Metal finishing,
Vol. 100, No. 1, 2002, pp. 45-47.
[6] A. Davidson and W. Waugh, “Method of Manufacture of
an Electrode for a Fuel Cell,” World intellectual Property
Organisation Patent No. O/2009/044144, 2009.
[7] N. Nwosu, A. Davidson and W. Waugh, “Characterisa-
tion of Solid Oxide Fuel Cell Cathodes Manufactured by
Traditional and Novel (Low Cost) Techniques,” Proceed-
ings of the First International Conference on Materials
for Energy, Karlsruhe, 4-8 July 2010, pp. 81-85.
[8] J. Mizusaki, S. Tsuchiya, K. Waragai, H. Tagawa, A.
Yoshihidi and Y. Kuwayama, “Simple Mathematical
Model for the Electrical Conductivity of Highly Porous
Ceramics,” Journa l of American Ceramic Society, Vol. 79,
No. 1, 1996, pp. 109-113.
doi:10.1111/j.1151-2916.1996.tb07887.x
[9] W. Dees, T. D. Claar, T. E. Easler, D. C. Fee and F. C.
Mrazek, “Conductivity of Porous Ni/ZrO2-Y2O3 Cermets,”
Journal of Electrochemical Society, Vol. 134, No. 9, 1987,
pp. 2141-2146. doi:10.1149/1.2100839
[10] T. Iwata, “Characterization of Ni-YSZ Anode Deg radation
for Substrate-Type Solid Oxide Fuel Cells,” Journal of
Electrochemical So c i e ty, Vol. 143, No. 5, 1996, pp. 1521-
1525. doi:10.1149/1.1836673
[11] R. Bauri, “Development of Ni-YSZ Cermet Anode for
Solid Oxide Fuel Cells by Electroless Ni Coating,” Jour-
nal of Coating Technology and Research, 2009.
doi:10.1007/s11998-009-9223-z
[12] Y. Rao, A. Takahashi and C. P. Wong, “Di-block Co-
polymer Surfactant Study to Optimize F il ler D ispersion in
High Dielectric Constant Polymer-Ceramic Composite,”
Journal of Composites Part A: A pplied Sci ence and Manu -

N. O. NWOSU ET AL. 124
facturing, Vol. 34, No. 11, 2003, pp. 1113-1116.
doi:10.1016/S1359-835X(03)00202-1
[13] L. Gabrieson and M. J. Edirisinghe, “On the Dispersion of
Fine Ceramic Powders in Polymers,” Journal of Materials
Science Letters, Vol. 15, No. 13, 1996, pp. 1105-1107.
doi:10.1007/BF00539950
[14] M.-D. Ger and B. J. Hwang, “Effect of Surfactants on
Co-deposition of PTFE Particles with Electroless Ni-P
Coating,” Materials Chemistry and Physics, Vol. 76, No.
1, 2002, pp. 38-45. doi:10.1016/S0254-0584(01)00513-2
[15] Y. C. Wu, G. H., Li L. Zhang and B. Yan, “Study on
Constitution and Wear Resistance of Nickel Phosphorus
Alloy-Silicon Carbide Composite Coatings,” Materials
Research and Advanced Techniques, Vol. 91, 2000, pp.
788-793.
[16] R. Elansezhian, B. Ramamoorthy and P. K. Nair, “The In-
fluence of SDS and CTAB Surfactants on the Surface
Morphology and Surface Topography of Electroless Ni-P
Deposits,” Journal of Materials Processing Technology,
Vol. 209, No. 1, 2009, pp. 33-240.
doi:10.1016/j.jmatprotec.2008.01.057
[17] B. C. Tripathy, S. C. Das., G. T. Hefter and P. Singh,
“Electro Winning from Acidic Sulphate Solution. Part 1.
Effects of SLS,” Journal of Applied Electrochemistry, Vol.
27, No. 6, 1997, pp. 673-674.
doi:10.1023/A:1018431619595
[18] K. Karuppusamy and R. Anantharam, “Pit-Free Nickel
Electroplating,” Metal finishing , Vol. 90, No. 13, 1992, pp.
15-19.
[19] G. Gutzeit, “Catalytic Nickel Deposition from Aqueous
Solution. I-IV,” Plating surface finishing, Vol. 46, 1959,
pp. 1158-1164, 1275-1278, 1377-1378.
[20] K. Haga, Y. Shiraton, Y. Nojiri, K. Ito and K. Sasaki,
“Phosphorus Poisoning of Ni-Cermet Anodes in Solid
Oxide Fuel Cells,” Journal of Electrochemical Society,
Vol. 157, No. 11, 2010, pp. 1693-1700.
doi:10.1149/1.3489265
[21] A. Tsoga, A. Naoumidis and P. Nikolopoulos, “Wettabil-
ity and Interfacial Reactions in the Systems Ni/YSZ and
Ni/Ti-TiO2/YSZ,” Acta Materialia, Vol. 44, No. 9, 1996,
pp. 3679-3692. doi:10.1016/1359-6454(96)00019-5
[22] J. N. Balaraj u, T. S. N. S. Naraya nan an d S. K. Sesha dri,
“Electroless Ni-P Composite Coatings,” Journal of Ap-
plied Electr ochemistry, Vol. 33 , No. 9, 2003, pp. 807 -816.
doi:10.1016/1359-6454(96)00019-5
[23] N. B. Baba, W. Waugh and A. Davidson, “Manufacture of
Electroless Nickel/YSZ Composite Coatings,” Proceed-
ings of World Academy of Science, Engineering and
Technology, Vol. 49, 2009, pp. 715-720.
[24] J. W. Dini, “Electrodeposition: The Materials Science of
Coatings and Substrates,” William Andrew Publishing,
Noyes, 1993, p. 336.
[25] A. Grosjean, M. Rezrazi and M. Tachez, “Study of the
Surface Charge of Silicon Carbide (SIC) Particles for
Electroless Composite Deposits: Nickel-SIC,” Surface
and Coating technology, Vol. 96, No. 2-3, 1997, pp. 300-
304.
[26] J. E. Newberry, “Surface Interactions of Micelles and
Divalent Metal Ions,” Journal of Colloid and Interface
Science, Vol. 74, No. 2, 1979, pp. 483-488.
doi:10.1016/0021-9797(80)90217-9
[27] P. G. Muijselaar, K. Otsuka and S. Terabe, “Micelles as
Pseudo-Stationary Phases in Micellar Electrokinetic
Chromatography,” Journal of Chromatography, Vol. 780,
No. 1, 1997, pp. 41-61.
doi:10.1016/S0021-9673(97)00632-8
[28] S. Su, Y. L. Chen and C. Y. Mou, “Micelle-Counterion
Interaction, I. Critical Micelle Concentrations of SDS
under the Influence of Copper Counterion,” Journal of
Chinese Chemical Society, Vol. 32, No. 1, 1985, pp. 5-10.
[29] A. M. Alsari, K. C. Khulbe and T. Matsuura, “The Effect
of Sodium Dodecyl Sulfate Solutions as Gelation Media
on the Formation of PES Membranes,” Journal of Mem-
brane Science, Vol. 188, No. 2, 2001, pp. 279-293.
doi:10.1016/S0376-7388(01)00395-7