J. Serb. Chem. Soc. 71 (6) 661–668 (2006)
JSCS–3459
UDC 546.811+547.918:54.552+66.087
Original scientific paper
Influence of decyl glucoside on the electrodeposition of tin
MOHAMED CHARROUF*1, SAID BAKKALI1, MOHAMMED CHERKAOUI1 and
MAHASSIN EL AMRANI2
1Laboratoire d'Jlectrochemie et de traitement de surface (LETS), FacultJ des Sciences,
UniversitJ Ibn-Tofail, 14000 KJnitra and 2Laboratoire des procJdés de sJparation, FacultJ des
Sciences, Université Ibn-Tofail, 14000 KJnitra, Morocco (e-mail: [email protected])
(Received 25 April, revised 26 September 2005)
Abstract: The aim of the present study was to improve an electrochemical deposition
bath for tin coating an acidic sulphate medium by addition of decyl glucoside. The effects of this additve on the deposition kinetics were examined by electrochemical methods, namely voltammetry and galvanostatic tin-layer formation, while scanning electron microscopy and X-ray diffraction analysis allowed the determination of the morphological and structural modifications resulting from the addition of this new surface
active agent. The presence of the examined additive induced an increase of the activation energy and of the overvoltage of the reduction of stannous ions. From the morphological point of view, a marked decrease in the grain size of the deposit was achieved in
the presence of the additive. The preferential crystal growth axes was also changed from
Sn (200) without additive to Sn (112) with the additive.
Keywords: tin, electrodeposition, decyl glucoside, voltammetry, X-ray diffraction,
scanning electron microscopy.
INTRODUCTION
Tin coatings have largely been used in industry to improve corrosion resistance or enhance appearance and/or solderability. In acidic solutions, tin is electrodeposited with a small activation overpotential.1,2 Porous or dendritic deposits are
usually obtained. A lead compound is often added to inhibit the reduction of the
stannous species and increase the polarization reaction.3 To avoid pollution problems, organic additives1,4–11, or surfactants2,12–18 are commonly used to improve
the deposit morphology.
A new class of organic compounds, alkylpolyglucosides, are biodegradable
and non toxic. These compounds find application as emulsifying agents, hydrolysing agents of proteins,19 and vectors of medicines.20
In the present work, the effect of decyl glucoside on tin deposition was investigated because of its high solubility in aqueous solutions and excellent biodegra*
To whom correspondence should be addressed.
doi: 10.2298/JSC0606661C
661
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CHARROUF et al.
dability. A kinetic investigation was carried out using cyclic voltammetry and
chronopotentiometry, while structural characterization was performed by X-ray
diffraction and scanning electron microscopy.
EXPERIMENTAL
A classical three-electrode cell was used. The bath temperature was kept at 20 ± 1 oC. The working electrode was a disc of iron or copper, the surface of which was polished with SiC paper down to 1200 grade.
The reference electrode was a saturated calomel electrode and the counter electrode was a platinum wire.
A PG P201 potentiostat connected to a computer was used. The surface trension was measured
by means of a Kruss K12 tensiometer with a precision of 0.1 mN m-1. The morphology was examined using a LEO 1530 FEG-microscope. X-Ray diffraction was performed in q/2q geometry using
a diffractometer with a cobalt anticathode.
The solutions of tin sulfate and sulphuric acid were prepared using analytical grade chemicals.
Their pH was close to 1.1, as in industrial applications. The basic electrolyte, denoted (a), contained
stannous sulfate (0.14 mol dm-3) and sulphuric acid (0.56 mol dm-3). The electrolyte labeled (b)
contained stannous sulfate and sulfuric acid in the same concentrations as electrolyte (a) and 10-3
mol dm-3 of decyl glucoside.
The additive was decyl glucoside with a molar mass of 390 g mol-1. It is a surfactant agent with
a hydrophilic head to glucose and a hydrophobic chain with 8, 10 or 12 carbon atoms (Scheme 1). It
was used as a 50 weight % aqueous solution.
Scheme 1. Structure of decyl glucoside.
RESULTS AND DISCUSSION
Determination of the critical micellar concentration (CMC) of decyl glucoside
The surface tension of the electrolyte was measured as a function of the decyl
glucoside concentration in the range of 1´10–4 to 5´10–3 mol dm–3 (Fig. 1). Two
regimes were observed: in the low concentration range, the surface tension de-
Fig. 1. Variation of the surface tension with the concentration of decyl
glucoside.
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ELECTRODEPOSITION OF TIN
creased strongly. For higher concentrations, the surface tension was nearly constant. The critical micellar concentration is equal to 5.1´10–4 mol dm–3.
For the electrodeposition, electrolytes with concentrations of additive higher
than the CMC were used to induce the formation of micellar aggregates of high
molecular weight which are able to adsorb on the electrode surface and affect the
reduction of the stannous species.
Polarization measurements
Continuous recordings of the cathodic potential versus the duration of the deposition of tin on an iron rotating disc electrode, at 1000 rpm, at a constant current density
of –10 mA cm–2 for plating solutions with and without additive are shown in Fig. 2.
Fig. 2. Time dependence of the
electrode potential during the electrodeposition of tin at –10 mA
cm-2 from electrolyte without decyl glucoside (a) and with decyl
glucoside (b).
According to Fig. 2, in presence of additive, tin is deposited on the iron
substante with a high overpotential. The increase in the polarization in the presence
of the additive is due to the micelles which block the electrode surface.
Voltammetric investigation
The cyclic voltammograms recorded at a scan rate of 500 mV min–1 in
quiescent electrolytes (a) and (b) are shown in Fig. 3. In both cases, a cathodic peak in
the forward scan was observed at –540 mV. During the reverse scan. for bath (a) without additive, the current was much higher than during the direct scan, which indicates
that a non-uniform deposit was formed, which dramatically increased the specific area.
In the anodic scan, in both solutions an oxidation peak was observed at –360 ± 10 mV.
TABLE I. Cathodic and anodic charges calculated from the cyclic voltammogams of tin electrodeposition and dissolution (data taken from Fig. 3).
Qc/C cm-2
Qa/C cm-2
Qa/Qc
Electrolyte (a)
2.17
1.14
0.52
Electrolyte (b)
0.60
0.55
0.92
As shown in Table I, in the absence of additive, the efficiency, estimated by the
664
CHARROUF et al.
Fig. 3. Cyclic voltammograms of
tin electrodeposition from the electrolyte without decyl glucoside (a)
and with decyl glucoside (b). Scan
rate 500 mV min-1.
ratio of the anodic and cathodic charge, was much lower than in bath (b). This indicates that the hydrogen evolution was much more important in bath (a) and also
that some of the tin deposited during the cathodic cycle might not be oxidised during the anodic cycle.
Temperature dependence
The voltammograms recorded at a linear sweep of 500 mV min–1 at various
temperatures in the electrolytes with and without additive are shown in Fig. 4.
As can be seen, at a given potential, the current density increases with increasing temperature.
The lines describing the limiting current density versus the reciprocal temperature, are given in Fig. 5. The energy of activation calculated from the slope of
these lines was found to increase from 18 kJ mol–1 without additive to 30 kJ mol–1
in the presence of additive. This increase confirms the blockage of the surface of
the working electrode by molecules of the additive.
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ELECTRODEPOSITION OF TIN
Fig. 4. Electrodeposition of tin from
the electrolytre without decyl glucoside (a) and with decyl glucoside
(b) recorded at various temperatures. Scan rate 500 mV min-1.
Surface morphology and crystal orientation of the electrodeposited tin
Scanning electtron micrographs (SEM) and X-ray diffraction patterns of the
electrodeposited tin obtained from the electrolytes with and without additive under
galvanostatic conditions (–mA cm–2) on an iron disc rotating at 2000 rpm were recorded. Figure 6 shows that the presence of decyl glucoside in the bath decreases
the grain size of the deposit significantly.
The X-ray diffraction patterns of the tin electrodeposited from electrolytes (a)
and (b) are shown in Fig. 7. Both deposits exhibit a tetragonal structure. The film
deposited from the electrolyte (a) without additive showed a strong (200) preferred
orientation, whereas the layer deposited from the bath with additive (b) exhibited a
strong intensity (112) diffraction peak.
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CHARROUF et al.
Fig. 5. Logarithm of the current density versus T-1 for the electrodeposition of tin at a potential of –600 mV.
Data taken from Fig. 4.
Fig. 6. Scanning electron micrographs of the tin deposited from the electrolyte without decyl
glucoside (i) and with decyl glucoside (ii).
Fig. 7. X-Ray diffraction patterns of the tin deposited from
the electrolyte without decyl glucoside (a) and with decyl glucoside (b).
ELECTRODEPOSITION OF TIN
667
CONCLUSION
This paper presents the results of a study aimed at improving an electrochemical deposition bath for tin coating in acidic sulphate medium by the addition of
decyl glucoside. The effects of this additive on the deposition kinetics were examined by cyclic voltammetry and galvanostatic thin-layer formation, while scanning
electron microscopy (SEM) and X-ray diffraction analysis allowed the determination of the morphological and structural modifications resulting from the addition
of this new surface active agent. It was found that the presence of the additive examined induced an increase of the activation energy and of the overvoltage of the
reaction of stannous. From the morphological point of view, the additive induces a
uniform deposition of tin over the entire surface and a marked improvement of the
deposit was achieved, i.e., a reduction of the grain size. In the presence of additive,
the electrodeposited tin had a preferred orientation with the (112) plan parallel to
the surface.
IZVOD
UTICAJ DECIL-GLUKOZIDA NA ELEKTROHEMIJSKO TALO@EWE
KALAJA
MOHAMED CHARROUF1, SAID BAKKALI1, MOHAMMED CHERKAOUT1 i MAHASSIN EL AMRANI2
1Laboratory d'électrochimie et de traitement de surface (LETS), Faculté des Sciences, Université Ibn-Tofail, 14000 Kénitra i
2Laboratoire des procédés de séparation, Faculté des Sciences, Université Ibn-Tofail, 14000 Kénitra, Morocco
Ciq rada je bio da se poboq{a kiseli sulfatni elektrolit za elektrohemijsko
talo`ewe kalaja dodatkom decil-glukozida. Efekti ovog aditiva na kinetiku talo`ewa kalaja su ispitivani elektrohemijskim metodama cikli~ne voltametrije i
galvanostatskog talo`ewa tankog sloja metala. Uticaj na morfolo{ke i strukturne
karakteristike prevlake kalaja je ispitivan metodama skeniraju}e elektronske mikroskopije i difrakcije X-zraka. Prisustvo aditiva je dovelo do pove}awa energije
aktivacije i prenapetosti za redukciju Sn(II) jona. Sa morfolo{ke ta~ke gledi{ta,
do{lo je do zna~ajnog smawewa veli~ine zrna kalaja u prisustvu aditiva. Tako|e je
promewena i preferencijalna kristalna ravan od Sn(200) bez aditiva na Sn (112) uz
prisustvo aditiva.
(Primqeno 25. aprila, revidirano 26. septembra 2005)
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