Bulletin of Electrochemistry 15 (7-8) 1uly-August 1999, pp 242-247 0256-1654/99/$ 3-50 © 1999 CECRI

ZINC ELECTRODEPOSITION FROM BROMIDE ELECTROLYTES ­EFFECT OF ADDITIVES

M CHANDRAN", R LEKSHMANA SARMA"" AND RM KRISHNAN

Central Electrochemical Research Institute, Karaikudi 630 006. INDIA

* N I ColJege of Enggineering, Kumaracoil 629 175. INDIA

** Vivekananda College, Agasteeswaram 629701. INDIA

Bright zinc electrodeposition can be obtained by the addition of brighteners in the plating bath. Bdght deposits improve the appearance of the article, besides offering good corrosion resistance. In this paper, the effects of different additives in the zinc bromide plating baths using Hull Cell technique are explained. Among the different additives studied, vanillin gives bright deposits.

Keywords: Electrodeposltlon, zinc, bromide electrolytes.

INTRODUCTION Plating experiments were carried out using mechanically buffed cold-rolled steel specimens subjected to the usual pretreatments like dcgreasing, alkaline electrocleaning and Zinc electrodeposits offer very good corrosion resistance to acid dip. ferrous metal parts because of its sacrificial action [1]. Zinc

electrodcposits can be obtained from different types of 'J!le nature of zinc deposit over a wide range of current

c1ec.trolytes namely, acid, cyanide and non-cyanide alkaline density was ascertained from the Hull Cell experiments using

'[2-8]. The matte white nature of zinc deposits can be a standard 267 ml cell. The Hull Cell experiments were

improved to bright by the addition of brighteners in the carried out at 1 A cell current for a duration of 5 minutes

plating bath (9- tIl. These types' of bright deposits improve at 303 K. The additives used are given ill Table n. the appearance of the article, besides offering good corrosion

RESULTS AND DISCUSSION resistance. The authors have earlier studied the

electrodeposition of zinc from bromide based electrolytes The results obtained from Hull Cell experiments are [121. In the present work the effect of different additives in summarised in Figs. 1 to 15. bromide electrolytes from the Hull Cell experiments are

Effect of vanillindiscussed. The concentration of vanillin was varied from 0.5 to 5.0 gil

EXPER1MENTAL in the low concentrated zinc plating bath and the results are given in Fig. 2. From the Hull Cell patterns, it may be seen

Laboratory grade chemicals were used to prepare the plating

baths. The bath compositions shown in Table I were used to TABLE II: Additives used study the effect of brighteners.

Additive Concentration TABLE I: Bath fonnulation

Vanillin 0.5 - 5.0 gilLow concentration High concentrated Thiourea 0.5 - 2.5 gilzinc plating bath zinc plating bath Glycine 0.5 - 5.0 gil

Zinc bromide 160 gil Zinc bromide 290 gil Dextrin 0.5 - 5.0 gil Boric acid 80 gil Boric acid 80 gil Gelatin 0.5 - 2.5 gil

Potassium bromide 50 gil Potassium bromide 80 gil Furfural 0.5 - 5.0 mIll

Aluminium sulphate 40 gil Aluminium sulphate 20 gil Triethanolamine 0.5 - 5.0 mIll

242

CHANDRAN, LEKSHMANA SARMA AND KRISHNAN - Zinc electrodeposition from bromide electrolytes. Effe t of additive

0 IoIIllIlOA iIRIllHT

g BRXlHT

Cd sao, IlRlClHT

SEN' _ l'lUCYfEE EJ SAtlN

~ GREY

"'TTE WHITE

...rr GREY -0 GREY f'OWGERY

MATTE WHITE ~Y & WHITE POWDERYWiij YEllOWISH~ SUG.". IlI.ACl<1m!

I:-~~-I POOALY COVERED

EJ .....FUTED

SEMI IRK)HT YELlOW QD)E LAYER

S'TNON(V ClIlEY[jiiLJ -[illITI STREAKV YaLOW

Fig. I: Legend used for Hull Cell studies

v....... gil

_~o.o

0.5

1.0

1.5~------2.0

3.0

5.0

I

5.1 3.5 2.6 2.0 1.• 1.0 0.6 0.3 0.1

A I elm'

0 2 e 10• HCO an lCD

Fig. 2: Effed of change of vanillin concentration in low concentrated zinc plating bath at 303 K and at IA cell current

10

HCD an o

LCD

Fig. 3: Effect of change of vanillin concentration in high concentrated zinc plating bath at 303 K and at 1A cell current

tbat tbe increase in concentration of vanillin improves the nature of deposit and at a vanillin concentration of 1.5 gil, a mirror bright deposit was noted between a current density range of 0.05- 4.68 A/dm2

• Further increa e in concentration produced semi bright and grey powdery deposits. Tbe

. optimum concentration of vanillin has been fixed as t.5 gil.

Experimenl'; were also done witb varying concentration of vanillin in tbe higb concentrated zinc plating batb and the

Thiolne. gil o .0'.n 0.0

0.5f:< ·:;::J_----'l'""-.----J'0 1.0~ en 1.5WJ==:;a ./ 1::J::B 2.0~:.,' '1 v c=o

I~ 2.5

'---..l.--L--I.---.JL--'---...L--L~_LI-.J 5.1 3.5 2.6 2.0 l.4 1.0

A I am' 0.6 0.3 O. I

o HCD

• an

10 LCD

Fig. 4: Effect of thio urea concentration in low concentrated zinc plating balh at 303 K and at IA cell current

243

CHANDRAN, LEKSHMANA SARMA AND KRISHNAN - Zinc electrodeposition from bromide electrolytes - Effect of additives

Thiourea, g II

g~2.0

~2.5

! I

5.\ 3.5 2.6 2.0 1.4 1.0 0.6 0.3 0.1

A./ci'nl.

o 2 10

He 0 ern LCD

Fig. 5: Effect of change of thio urea concentration in high concentrated zinc plating bath at 303 K and at lA cell current

results are given in Fig. 3. When the concentration of vanillin was 0.5 g/l, a bright deposit was observed between a current density range of 0.05-1.4 A/dm2 and at 1.5 g/l, a semi bright

Glydne. g/l

~FW.,;;, '~;~;j{ <::'11 0.0

~··:·V.·I,,%%,jh;M'//"; %' "'L j 0.5M:%<:k~:fP!!&-'///1& ;:f" ."l ­

'1- 1 1.0

1.5

2.0

2.5[fLU'. ·'·.,,~~E~

3.0@:f .•. i,,~~t i~~~~-I

rmT' i.~~i;EFJ '.0

5.0

J J ! I I I I I ! t

S.I 3.5 2.6 2.0 1.4 1.0 0.6 0.3 0.1

A I m. 2

o 10

HCD LCD

Fig. 6: Effect of change of glycine concentration in low concentrated zinc platin!{ bath at 303 K and at 1A cell current

deposit was obtained over a wide current density range of 0.05-6.68 A/dm 2

• When the concentration of vanilin was furtber increased, grey deposit region increases. Hence, the optimum concentration of vanillin has been fIXed as 0.5 to 1.5 g/l.

Effect of thiourea

The concentration of thiourea was varird from 0.5 to 2.5 g/l in both low and high concentrated zinc plating baths and the results are given in Figs. 4 and 5 rrspectively. From thr Hull Cell patterns obtained, it may be seen that the introduction of thiourea has no effect in producing hright deposit.

Effect of glycine

The effect of change of concentration of glycine (0.5 to 5.0 gil) in both low and high concentrated zinc plating baths are shown in Figs. 6 and 7 respectively. From the figures, it may be seen that glycine gives matte white or grey powdery deposit.

Effect of dextrin

The concentration of dextrin was varied from 0.5 to 5.0 gil in the low concentrated zinc plating bath and the results are

0.0

0.5

1.0

1.5

2.0

2.5

3.0

•.0

5.0

I I I I I

5.1 3.5 2.6 2.0 U 1.0 0.6 0.3 0.1

A/ am'

o 2 4 8 8 10

HCD ." LCD

Fig. 7: Effect of change of glycine concentration in high concentrated zinc plating bath at 303 K and at 1A cell current

244

CH:\NDRAN, LEKSHMANA SARMA AND KRISHNAN - Zinc electrodeposition from hromide electrolytes - Effect of additives

Dextrln, gil

Do>trin. g II

0.0

0.5

1.0~r ,\'\ .~

~OOO()) UGJ.)oc_o~," 0 0 C I) 0 (: v 0 0 '... .' 2.0~f <;:, 1.5 Q Q Q ;'l 9 n 0 0 " _,Q Q

2.0

2.5~')k" .. /;..- ... :..-:::" ~

3.0~

4.0 I I!r:=J

5,1 3.5 2,6 2.0 1.4 1.0 0,6 0,3 0,1

A I <M'I 4.5c::L]

2

o 10

HCD an LCD

5.1 3.5 2.6 2.0 1.4 1.0 0.6 0.3 0.1

A I dm'

Fig. Q: Effect of change of dextrin concentration in high a 10 concentrated zinc I'latin~ hath at 303 K and at 1A cell current

HCD an LCD

Fig. 8: Effect of change of dextrin concentration in low concentrated zinc platin~ bath at 303 K and at ]A cell current

Gelatln, gilpresented in Fig. 8. It is clear from the Hull Cell patterns tbat the grey matt deposit is ohtained to a greater extent.

Experiments were also carried out by varying the

concentration of dextrin in tbe high conccntratt"d zinc plating

bath. From Fig. 9, it may be seen that matte white powdery

deposit is obtained to a greatt"r extent in the Hull Cell plate.

Effect of ~e1atiD

The effect of gelatin in the low concentrated zinc plating

bath is shown in Fig. 10. Gelatin produces slight black and

streaky grey deposits ill the high current density region. From

Fig. 11, it may be seen tbat the addition of gelatin in the

high C'oncentrated zinc plating bath does not produce zinc

deposit of improved quality.

0,5

1.0

1.5

2,0

2,5

I I I I 5,1 3,5 2.6 2,0 1.4 1.0 0,6 0,3 0.1

Effect of furfural i\ I dm'

The concentration of furfural was varied from 0.5 to 5.0 mill a 2 4 6 8 10

in both low and high conccntrated zinc plating baths and the HCD em LC D

results are prese.nted in Figs. 12 and 13 respectively. It may

be noted that the introduction of furfural produces grey Fig, 10: Effect of change of gelatin concentration in low

powdery or streaky yellow deposit. concentrated zinc plating bath at 303 K and at ] A cell current

~~o,o

0,5

1.0

1.5

3,0

'.0

5.0

245

CHANDRAN, LEKSHMA A SARMA AND KRISHNAN - Zinc electrod position from bromide electrolytes - Effect of additives

Gelatin. gil

D~_o.o

~~~~~ 0.5

Cfr:~ 1.0

_~15

~~~2.0

~L' ~'~~a~~-I 2.5

I I

5.1 3.5 2.6 2.0 1.4 1.00.6 0.3 0.1

A/ckn z

o 2 4 6 8 10

HCD em .LCD

Fig 11: Effect of change of gelatin concentration in high concentrated zinc plaling oulh al 303 K and al ] A cell currenl

Flrtnl. mill

o 0.0

0.5rr=J. 1.0CICI

~[] 1.5

2.0~

2.51_---'[·!ljfl_~

3.0~ 4.0

5. t 3.5 2.6 2.0 1.4 1.0

A I dm2.

0.6 0.3 0.'

o HCD em

10

LCD

Fig. 12: Effect of change of furfural concenlration in low concentraled zinc plating oath at 303 K and at ] A cell current

Effect of triethannlamine

From Figs. 14 and IS, it may be seen that the addition of triethanolamine (0.5 to 5.0 mIll) in to the low and high concentrated zinc plating baths gives grey or white powdery deposit to a larger extent in the Hull Cell plate.

CONcurSION

From the experiments c<lrricd out it may be concluded that bath of the following composition is suitable for producing mirror bright zinc deposit.

Bath compositinn

Zinc bromide 160 gil; horic acid 80 gil; potassium bromide 50 gil; aluminium sulphate 50 gil; vanillin 1.5 gil; te.mperature 303 K and current density 0.05-4.68 A/dm2

•

Acknowledgement: One of the iluthors (M. Chilndriln) expresses his sincere thilnks tn the Director, CECRI, Karilikudi, for hilving grilnted permission tn milke use of the filcilities of the Institute. He illso expresses his grillitude to the Chilirman and the Principil! of N.r. College of Fngincning, KUOlilrilcoil, for their patronage.

........... /1 ­0.5.mmmmmmn 1

1.0~~~ii~ii~i~J I

~Hmmmmmn~

2.0~HlHHlll!inlBB1~

~Hlfil!lHi!lim!!!l!E3

3.0-.mlHWmmmm=:3 4.0~~mlIH$li;l!~i:!iE3

!i.0

I I

5.1 3.5 2.6 2.0 1.4 1.0 0.6 0.3 0.1

A I elm Z

I I

0 2 4 6 8 10

HCD ern LCD

Fig. 13: Effect of change of furfural concen/ration in high concentrated zinc plating oath at 303 K and alIA cell current

246

CHANDRAN, LEKSHMANA SARMA AND KRISHNAN - Zinc electrodeposition from hromide electrolytes - Effect of adJitives

TMw...... '1

0.0

1.0

2.0

3.0

4.0

5.0

I

5.1 I

U I

2.8 I t

2.0 1.4.1.0

A I ch'

0.8 D.3 I

0.1

o 2 4 8 8 10

KCO ClIO LCD

Fig. 14: Effed of change of triethanolamine concentration in /ow concentrated zinc pwting bath at

303 K and at ] A cell current

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0_.............. 0.0

n 0.5

1.0

1.5

2.0

~~

~~ '<"~J~"lj

~~:~. J. .r~

2.5

3.0

4.0

5.1 3.5 2.6 2.0 1.4 1.0 0.8 0.3 0.1

A I ch'

o 2 4 8 8 10 HCO LCD

Fig. 15: Effect of chanKe of triethanolamine concentration in hi,::h concentrated zinc plating bath at

303 K and at 1 A cell current

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247