US1984745A - Electrodeposition of zinc - Google Patents

Description

Dec. 18, 1934. K KA|Z|K 1,984,745

ELECTRODEPOSITION OF ZINC Filed Aug. 8, 1932 2 Sheets-Sheet l Fig.1 Fig.6

W. 1434:; i K

Patented fies. E8, 1934 Karl KaizilnBreslau, Germany,

firm Georg Von Glesches Erben,

many I assignor to the Breslau, Ger- Application August 8, 1932, Serial No. 627,961

I In Germany April 21, 1931 8 Claims.

In the electrolysis of aqueous zinc solutions there are disadvantages which are removed by the present invention. I

In order to attract suflicient zinc ions to the cathodes, large distances of about 5 cm. between the electrodes were first used so that the volume of the bath became large. If smaller distances, down to 2 cm. were used, it was necessary to mix the liquid by pumping, which required a considerable expenditure of energy. In the first case there is also the disadvantage of high current consumption. In both cases when zinc lyes containing manganese salts were used, a loose deposit of manganese dioxide was formed on the anodes, which constantly dropped off, thereby leading to short circuits and makingit impossible -to protect the anode against being eaten away as its surface was continually exposed again.

All these drawbacks-are avoided according to the invention by adopting in the electrolysis of aqueous zinc lyes a step whichhas already been employed in the electrolytic decomposition of water and in making bleaching lyes, in' which cases, in contradistinotion to zinc electrolysis, no electrolyte is added or removed and it is not necessary to lift the cathodes out regularly. This step consists in providing the cells with insertions running at right angles 'tothe surfaces of the electrodes.

electrodes being in the middle chamber. The gas bubbles rising from the electrodes draw the electrolyte from the two side chambers so that it passes-under the insertions into the electrode chamber, rises between the electrodes and flows back to the side chambers over the insertions. It has already been proposed to provide these insertions with grooves for securing the bipolar able shape which are secured to the anodes, 'or

of suitable insertions, in the bath in which the electrodes are pushed. Its upper. end is below the surface of the bath so that the electrolyte which becomes specifically lighter on account of gas bub- With two such insertions'in a, cell the latter is divided into three chambers, the

- addition of the neutral lye to each bath is eifected bles and heating is constrained to rise between the electrodes and can only pass over into the free bath chambers at the sides at these points. This invention thus uses the upward drive due to heating and gas bubbles for obtaining a uniform and intensive mixing of the whole content of-the bath and this causes a constant zinc and acid concentration ,to 'be maintained inall parts of the bath. This circulation is assisted by the cooling devices being arranged between lateral limitation of the electrode chamber and bath wall, whereby the electrolyte arriving. there is cooled and becomes specifically heavier and therefore sinks.

I In carrying out this method of operation, since fluctuations in concentration are avoided, a more compact, more adherent and harder manganese dioxide coating is obtained which makes the anode "to a large extent passive and prevents the lead anodes dissolving, so that the lead content of the cathode zinc remains considerably lower than that in an ordinary bath. The adhering manganese dioxide coating gives the further advantage that the distances between the electrodes can be reduced to a minimum without fear of short circuiting. The strong circulation of lye obtained according to the invention and the use of smaller distances between the electrodes makes the volume of the bath much smaller and enables the amount of energy required per unit zinc deposit to be considerably reduced. In addition, the precipitation of manganese dioxide from the electrolyte, after a smoothand solid covering of manganese dioxide has been obtained on the anode, is reduced to a fraction of that'in baths with an electrode chamber which is open at the sides.

Further, the invention allows of the electrodes being drawn out very conveniently, if necessary in groups, it being possible to reduce the distance between the electrodes over the whole surface to 1 cm. This causes a uniform distribution of current and a further saving in current.

A further important advantage of this method of operation liesin the elimination of pumping work when-high current densities are employed. While'with the usual methods, when high current densities are used, the electrolyte has to be; mixed within the bath by continually pumping round the same electrolyte, when using the present invention the pumping is-unnecessary.- The by gravity from a common raised container for several series of baths.

It has also been found that the manganese coating is caused'to adhere still more firmly if,

when using the above-described arrangements,

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