zinc electrodeposition from bromide electrolytes …
TRANSCRIPT
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
REFERENCES
1. F A Lownheim (Edn), Modern Eleclropillting, Wiley Inter Science Publications, New York (1974)
2. H G Crentz and S Martin, Plat and Surf Finish, 60 (1 (75) 681
3. T R Anantharaman and J Blliachllndra, ] Electrochem Soc, 100 (1953) 237
4. Goto, Japan patent 75, 110, 940, S ptemher ( (75) 5. R M Krishnan et ai, Met Finish, 89(2) (1991) 15 6. 1 J Duprat, Surfaces, 269 (1997) 14
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
7. W R Pitner llnd (' L Hussey,] Electrochem Soc, U A,I44(9) (1997) 3OQ5
8. A Rllmllchllndrlln and S M Mayannll, Met Finish, 90(2) (1992) 61
9. TV Venkillesha. Bull Electrochem. 12(7/8) (1996) 472 10. Fabio Gilivani and IVllni A Carlos, Metal Finishing, 95(2),
(1997) 70
11. G N K Rameshbapu and R Kumarcsan, Bull Electrochem, 13(4) (1997) 166
12. M C'hllndran, R Lckshmllna Sarm and R M Krishnan, Natl Conf on Emerging Trends in Electrometal and Eighth Nat! Convention of Electrochemists, Abstracts lanullry 28-30 (1998) 26(A)
247