THE ELECTROLYTIC PRECIPITATION O F N I C K E L ON N I C K E L BY RALPH C. SIXOWDON
It has been noticed in many books on technical electroplating that nickeled work which is to be replated must be entirely freed from the previous deposit of nickel or the subsequent plating will be in vain. McMillan says in regard to this : ‘ ( I t is even more important in nickeling than in silvering or gilding that an existing film of nickel be entirely removed, or the new deposit will most certainly lack adhesive properties.”l He2 also mentions that suspending wires should be used but once because the subsequent deposits of nickel will peel off and give trouble in the bath. This peeling also causes thick deposits of nickel to be rather unde~irable.~ Burgess and Hambuechen4 have noticed this peeling and non-adherence in the case of other deposits, and they say : (‘A peculiarity, the reason for which does not seem to have been explained, is that a metal, by contact with the plating electrolyte itself, may change the character of its surface to such an extent that a coating subsequently deposited will not adhere firmly to it. We have observed during an investigation on the electrodeposition of iron, that if the iron cathodes are allowed to remain for a few hours in the solution without the flow of current, a subsequent deposition of iron will take place, but the layer thus deposited may be readily separated from the previous layer. . , . T h e same phenomenon has previously been pointed out in the electrolytic separation of nickel.” T h e real reason why the deposit curls up any more than the same metal would, if it were not electrolytically prepared seems to be due to the metal being deposited in a state of strain which is undoubtedly caused by absorbed hydrogen5 or uneven McMillan : “ A Treatise on Electrometallurgy,JJand ed., p. 243.
Ibid., p. 245. Ibid., p. 246. Jour. Phys. Chern., 7, 409 (1903). W.McA. Johnson : Trans. Am. Electrochem. SOC.,3, 255 (1903).
deposition of the metal.‘ There is no evidence that a hydride of nickel is formed. This would hardly account for the fact that the original metal and the deposit do not adhere. Prof. Bancroft suggested that the first metal had become covered with a film of some oxide which could not be removed by ordinary methods of cleaning, or, in other words, the surface was made passive. ” T h e reaction undoubtedly takes place with great readiness in the case of nickel, iron and aluminum, according to Burgess and Hambuechen.z Therefore, if this surface be treated with some strong reducing agent, we should have a metal free from oxide which would take an adherent deposit if it were transferred immediately to a plating bath through which current is flowing. The most convenient way in which to do this is by making the passive metal cathode in an acid solution and passing a fairly large current for a short time. This will cause a heavy evolution of hydrogen, part of which will be taken LIP by the metal and the oxide will be reduced. Quick washing and transferring to the plating bath should give us a metallic surface upon which an adherent deposit could be plated. For the preliminary treatment of the nickel cathodes, we prepared a 3-normal solution of hydrochloric acid and used a current density of 8 amperes per square decimeter. T h e electrodes were both of nickel and were placed about 4.25 cm. apart. T h e run lasted four minutes. Hydrogen was evolved copiously at the cathode. As soon as sufficient treatment had been given the cathode it was washed in clean water and plunged into the regular plating solution which was made LIP: ((
(NH,),SO,. NiSO,. 6H,O Water T h e other conditions : Area cathode Cur rent density Voltage Temperature Ti me
80 g I
114 dmz amp/dm2 3.8 volts 2.0
I8O
I/2
D. H. Browne: Electrochemical Industry,
Jour. Phys. Chem., 7,409 (1903)
liter
I,
hour. 348 (1903).
Electyodytic Prec@itatioiz of N i c k e l
oft
Nickel
401
I n case a rolled nickel anode is used, the solution must be kept neutral or only very slightly acid by means of ammonium hydroxide. Too great acidity causes the precipitation of a spongy deposit. I n our case the deposit came out perfectly smooth and so adherent that it could be burnished and scratch-brushed with impunity. I n order to demonstrate the difference between a prepared or “active” cathode and one ordinarily cleaned we performed another experiment under precisely the same conditions as before, but simply scratch-brushed and cleaned the nickel plate before making it cathode. On removing from the plating solution about half the precipitated nickel had curled up, a slight rubbing causing it to fall off. Therefore the conclusions to be drawn from this paper are: I. Nickel can be precipitated upon the ‘(active)’nickel cathode and caused to adhere without difficulty. 2. Nickel cannot be successfully plated on other nickel because of the presence of a thin film of oxide which cannot be removed except by vigorous reduction. 3. T h e “active” state is very instable. This work was suggested by Prof. Bancroft and carried out under his direction. Cornell University.
