ELECTRODEPOSITIOIK O F NICKEL BY C. W. BENNETT, C. C. ROSE AKD L. G. TINKLER
I n the discussion of the electrodeposition of nickel, it was shown that the apparently mysterious results obtained by Calhane and Gammage? could be explained satisfactorily on the basis of the electrochemical series. I n a solution of nickel ammonium sulphate, there are present hydrogen, nickel, and ammonium ions. Of these the hydrogen ions are liberated most easily. When the electrolysis is started for the deposition of nickel, hydrogen ions, being present, are liberated first, and the efficiency of nickel deposition is, therefore, low. If the electrolyte and cathode be stationary, there is an impoverishment of hydrogen with a subsequent deposition of nickel with an efficiency which depends upon the impoverishment of hydrogen or upon the rate of bringing up of hydrogen ions to the cathode. This rate of bringing up hydrogen ions to the cathode may be effected in two ways: First, the electrolyte or the cathode may be rapidly moved and, therefore, diffusion aided. Second, the concentration of hydrogen ions may be increased, and, therefore, the rate of bringing up hydrogen ions increased, because more are present to be brought up. In the previous work on the deposition of nickel, the latter condition was studied, the concentration of hydrogen ions was changed by adding ammonium hydroxide to the solution, tending to make it alkaline. Under these conditions it was found that starting with straight nickel ammonium sulphate and measuring the efficiency every fifteen minutes, the efficiency of deposition began a t about 87 percent and increased to the fairly definite maximum represented by about 96 percent. The conditions of such electrolysis were stationary cathode and stationary electrolyte. When varying quantities ~
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Jour P h > s Chem , 18, 373 (1914), Trans Am Electrochem SOC, 25, 335 (1914) 2
Jour Am Chem SOC, 29, 1268 (1907)
Electrodeposition of AYickel
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of ammonium hydroxide were added to the solution, the efficiency began higher and reached finally a higher state. The results obtained by Calhane and Gammage referred to above showed that the efficiency of nickel deposition with the rotating cathode was much lower than with a stationary one, and the efficiency decreased as the speed of rotation of the cathode increases. In the previous work it was shown that the surface film a t the cathode could be disturbed by stirring the solution as well as by rotating the cathode, and experiments were given to show that the efficiency of deposition is less the more rapidly the solution is agitated. With reference to the rotating cathode, with which this investigation is interested, the same methods have been used for changing the concentration of hydrogen ions as were used in the previous work. If small quantities of ammonium hydroxide be added to the solution with a rotating cathode, the efficiency should be affected in a way analogous tothat with a stationary cathode. I n other words, it may be expected that the addition of ammonium hydroxide would tend to raise the efficiency of deposition on the rotating cathode as well as on the stationary one, i . e., the efficiency should start higher and approach the same point or perhaps reach a higher one. Experiments were accordingly made with stationary and rotating cathodes with varying amounts of ammonium hydroxide. I cc, 5 cc, and I O cc of I : I O ammonium hydroxide were added t o 1 2 0 cc of the nickel ammonium sulphate solution. This, the same as in the previous work contained 8 grams of nickel ammonium sulphate with one gram of nickel chloride per IOO cc of water. The anodes were all electrolytic nickel containing 0.14 percent iron. The current density was approximately 1 . 2 5 to I . j o amperes per square decimeter. The results of one set of experiments are shown in the curves of Fig. I and Fig. 2 . Curve A, Fig. I , represents a series of efficiency measurements taken every thirty minutes with
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C. W. Bennett, C. C.Rose a?id L. G. TiTtkler
a cathode rotating 1000 revolutions per minute. This cell had I cc of I : I O ammonium hydroxide. Curve B shows a cell with a stationary cathode run under the same conditions in series with the first one. Curve C and D, Fig. 2 , show, respectively, curves for the rotating and stationary /oo 90 80
70
60 50
40 0
2 3 Tme in hours
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4
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90 80 70 / 00
90 f
2
Zms in Hours Fig. 2
3
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electrodes with 5 cc of I : I O ammonium hydroxide. Curves E and F show, respectively, rotating and stationary electrodes with I O cc of I : I O ammonium hydroxide. From these curves i t is evident that if the solution is of the proper alkalinity, the efficiency begins high and is maintained a t fairly high value when the cathode is rotated. This is best shown in Curve C.
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Having shown that it is possible t o increase the efficiency b y decreasing the concentration of hydrogen ions, i t is only a step theoretically to the extreme condition, where the concentration of hydrogen ions is practically zero. If nickel could be deposited from a strongly alkaline solution or from a solution of nickel in a strong base, the hydrogen ion concentration in this solution would be practically zero. Being practically zero, the agitation of the solution would practically not affect the electrolysis in so far as the hydrogen is concerned. If a solution could be obtained, which had a high concentration of hydrogen ions, agitation of the solution should practically not affect the efficiency. If, on the other hand, the ion concentration is low, agitation of the solution or rotation of the cathode should increase the efficiency over that obtained with a stationary electrode. IT7e are, therefore, in a position to say that a solution of nickel in a strong base will yield nickel upon electrolysis with the same efficiency or a higher one if the electrode be rotated. I n other words, the conditions will be just reversed from those obtained from the nickel ammonium sulphate solution. A number of solutions were tried before a satisfactory one was obtained. A solution of nickel cyanide was finally used, the solution containing approximately j percent nickel cyanide and 7 percent potassium cyanide. The experiments were made with a stationary electrode and a rotating electrode in series with a copper coulometer. The runs lasted for one hour and the current density was j amperes per square decimeter. The solution, which was red a t the start, became dark red in the case of the stationary electrode, and nickel hydroxide or cyanide precipitated. I n the case of the rotating cathode, the solution changed from a red to a lemon-yellow and yielded less of the green precipitate than the stationary one. The efficiency of deposition from this solution is very low and has been found by Watts as 0.05 percent. This is due to the very low concentration of nickel ions in the solution. It would accordingly be expected that rotation of the cathode would increase the efficiency over that of the stationary electrode.
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C.W . Bennett, C. C.Rose and L. G. Tinkler The results obtained are tabulated in the following table:
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R.P. M.
500 500 1000 I000 2 000
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Efficiency rotating
Efficiency stationary
0.13 0.13 0.4' 0 .j 8 I .65
0.033 0.048 0.022
0.000
0.057
These values are shown in the curves in Fig. 3 . The efficiency increases with increased rotation according to the prediction, and the efficiency of the rotating cathode is higher than that for-the stationary. ~
Ucvo/uhons per
2,000 minuh
Fig. 3
In conclusion it may be said, that in the nickel ammonium sulphate solution the efficiency of the deposition of nickel-on the rotating cathode, as well as the stationary one, may'be - changed by changing the concentration of hydrogen ions. When the concentration of hydrogen ions is practically zero, as in the case of a strongly alkaline solution, nickel is deposited more easily than the other ions, so that the lower-efficiency would be occasioned by impoverishment of nickel. The rotation of the electrode prevents this impoverishment,' and, therefore, increases the efficiency, while in the case of solutions where hydrogen ions are precipitated, the rotation of the cathode tends to prevent hydrogen ion impoverishment and, therefore, tends to decreases the efficiency. Electrochemzcal Labovatory Cornel1 Cnzrersity
