ElectrochimicaActa, 1967,Vol. 12.PP. 553to 555. PergamonPress tird. Printed in NorthernIreland
NOTE ON THE STRUCTURE OF NICKEL DEPOSITED FROM SULPHAMATE SOLUTIONS* M. SALEEM, P. A. BROOK and J. W. CUTHBERTSON Department
of Metallurgy, University of Nottingham,
Abstract-Earlier work on the structure of deposits from the Watts nickel solution has been extended to an examination of the structure of deposits from the nickel sulphamate bath, which can be operated at very high cathode current density and overpotential. Even at overpotentials > 1 V, very short deposition times produced structures very similar to those found in Watts nickel deposits formed at much lower overpotentials. R&stun&Extension dune precedente etude sur la structure des depots provenant d’une solution de Nickel de Watts I l’examen de la structure de depots provenant d’un bain de sulfamate de nickel, pouvant Ctre utilise a tres hautes densites de courant et surtension. MCme a des surtensions cathodiques > 1 V, des temps de deposition tres courts produisent des structures exactement semblables g celles trouvees sur les depots de nickel de Watts engendres a des surtensions beaucoup plus basses. IN AN earlier
rlz=nnoitpA 111 in thP nf UUYlLlYll arlditinn “~.,I”” aopntp “‘y”““‘” LLlC nr,=c,=r~r~ y”“““’ “I
of the structure
,UPTP rpnnrtprl 1 .,_A_ ‘.+y’“‘CIU.
With nnp pyrmtinn , , *..** v.l_ .u.“wy”““,
of these deposits were obtained from a Watts type of bath. The success recently achieved in the high-speed deposition of nickel from sulphamate solutions2 prompted an extension of these structural studies, and the authors now present some preliminary results obtained from straight solutions of this type, and a comparison with those previously obtained from straight Watts nickel solutions. A feature of the nickel sulphamate bath is that it can be operated up to very high current densities. The upper limit was not reached in this investigation but current densities up to 600 asft have been employed in practice. EXPERIMENTAL nenositinn waq __T_-___-__ ..__i from
th_c followin!alto i_-. solution: .~.~~.
Before use the solution was purified as suggested by Kendrick.2 It was operated at pH 4.0 and 6092, with stirring. The anodes were of commercial purity nickel sheet Polished polycrystalline sheet copper cathodes were used; they bagged in nylon. were degreased in an electrolytic alkaline bath and etched in a phosphoric-aceticnitric acid mixture. flnrhnn rn~l;~~o nf TXTPYP canA thin ILyll~~.l “I the L.llb Aennr;tc “‘y”““” . . ..I_ mgrlp lllU..V hxr “, rnnxrpntinncal V”ll. ~IICIVIAUI terhninner L”“““y”‘u L&ALU Clllll bcu
films by the method described previously. Steady state potentials were measured against see. Deposits were made at current densities from 80 asf and for times from 5 s upwards. * Manuscript received 9 July 1966. + Amperes per square foot. 1 asf - 1.076
1O-3 A./cm3 (Ed.). 553
M. SALEEM, P. A. BROOK and .J. W. CIJT~BERTSON
RESULTS All the deposits were matt except those produced at short times and low current densities, which were moderately lustrous. At 80 asf In the early stages, what appeared to be isolated growth centres deposited on the cathode and spread laterally until after about 30 s the whole surface was covered by block growths, similar in appearance to those Ipreviously reported for Watts nickel. However, a notable difference is that whereas ,the deposits obtained from the latter bath after about 5 min developed into pyramids, those from the sulphamate bath appeared to change with time of deposition, and hence with increasing thickness, into a degenerate pyramid type of structure leading to the formation of a smooth surface with few asperities. The sequence of this change is revealed in Figs. 1, 2 and 3. Extension of the plating time beyond 5 min did not produce any significant change in structure. At 200 asf The structures were similar to those obtained at 80 asf but the rate of deposition was now so high that even for the shortest time, 5 s, there was no evidence of the growth centres detected at 80 asf. The deposits were of the block type and developed in much the same way as those obtained at the lower current density (Figs. 4, 5 and 6). The illustrations represent the normal growth sequence, but deposits of 5 s duration were sometimes much coarser and very nodular, as shown in Fig. 7. This type of structure is reminiscent of that previously reported for nickel sulphate solutions containing thiosulphate additions, and will be referred to later. Somewhat similar nodular growths have been observed in deposits made at 400 and at 600 asf but at these higher current densities the growths were dimensionally much larger. At 400 and 600 asf The deposits were rough and nodular, irreslpective of plating time at 600 asf, but decreasing slightly in roughness with plating tirne at 400 asf (Figs. 8 and 9). The grain size of the deposits, as revealed by thin films, was not markediy dependent on current density, and was about one-,quarter that of Watts nickel deposited at 40 asf. As with Watts nickel, there was extensive evidence of twinning (Fig. 10). The overpotentials measured at 80 and 200 asf were 1200 and 2000 mV respectively. The deposits obtained from these solutions and from the straight Watts bath show some general similarities but the resemblance diminishes with plating time, probably because the sulphamate bath can be operated at much higher deposition rates. DISCUSSIC)N The morphology of copper and nickel deposits has been discussed in terms of overpotentials of a few tens of mV. 3 The overpotent.ials reported here are so large that the ,,,...,+l. “I . ..callr n..-r nr.mm;~ D“I I\,. hlm.L-o ha ~vn~,.twl tn rnmnldelxr ;nh;hitd un.rr_ gl”wLu J.Jj,la,ll,lli) “l”UR”m,,c+ lllL&LIC “ti CZXP”“‘” C”he “1 ‘V”‘~““‘] IIlIII”I&tiU. I%“.,_ ever, at the shorter deposition times deposits made at 80 asf do show some structural characteristics, which would not be expected from the effects of overpotential alone. Henstock and Spencer-Timms4 have shown that during the deposition of nickel-iron alloys the composition varies with thickness and not until the deposit is 1000-3000 8, thick does the deposition reach steady-state conditions. In the present work the time
FIcj. FIG. FIG. FIG. FIG. FIG.
I. 2. 3. 4. 5. 6.
Carbon Carbon Carbon Carbon Carbon Carbon
replica replica replica replica replica replica
of of of of of of
deposit. deposit. deposit. deposit. deposit. deposit.
80 180 80 200 200 200
asf. asf, asf, asf. asf. asf.
plating plating plating plating plating plating
time time time time time time
5 min. 60 s. 30 s. 5 s. I5 s. 30 s.
.\ 6400. 4000. 6400. 8000. 640. 5200. 51i4
FIG. FIG. FIG. FIG.
7. Carbon replica of deposit. 8. Carbon replica of deposit. 9. Carbon replica of deposit. IO. Transmission micrograph
200 asf, plating time 5 s. 400 asf, plating time 30 s. 600 asf, plating time 30 s. of deposit. 400 asf.
Structure of nickel deposited from sulphamate
before the morphology subsequently shows no further changes is of the same order as that reported earlier. It appears that sulphamate nickel when plated for very short times can show structures characteristic of lower overpotentials in Watts nickel. Tknonitc --r-----
at 4Nl -*--
2nd aaf .&I., wx Y”lll”..llUC cnmPxuhat I__._. nt Y. hnll ““V UUI
&-dl~~ tn “AlllllUI L” thncP Cll”Yl
from Watts nickel solutions containing thiosulphate ion. Products from the breakdown of the sulphamate ions can probably become incorporated in the nickel deposit under certain specific conditions. If this is indleed the case, one is led to conjecture whether the structural similarity between the sulphamate ion and the thiosulphate ion, depicted below, is significant:
/’ \ 0
At present there is no evidence that the marked differences in deposit morphology, a function of current density, has any effect on brightness. Further investigation called for; the work is continuing.
Acknowledgements-This work forms part of a research project being undertaken by one of us (M. S.} later to be submitted for consideration for the award ofa higher degree of the University of Nottingham. Its pursuance is being presently undertaken through the aid of a grant received by M. S. from the Electrochemical Engineering Company Ltd., which is most gratefully acknowledged. Our indebtedness is recorded to the Science Research Council, who kindly provided the funds for the purchase of the electron microscope used in this and in the preceding work on the structure of electrodeposits, and our sincere thanks for this generous: benefaction are expressed.
1. 2. 3. 4.
REFERENCES J. A. CROSSLEY,P. A. BRINK and J. W. CUTHBERTSON, Electrochim. Actu (1964). R. J. RENDRICK, Trans. Inst. Metal Finish. 41,235 (1’964). A. DAMJANOVIC,Plating 52,1017 (1965). M. E. HENSTOCKand E. S. SPENCER-TIMMS,Trans. Inst. Metal Finish. 40, 179 (1963).