US3502561A - Alkali-chlorine cell having a horizontal mercury cathode - Google Patents

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March 24, 1970 w. RASCHE ETAL 3,502,561

ALKALI-CHLORINE CELL HAVING A HORIZONTAL MERCURY CATHODE Filed Aug. 30. 1967 INVENTORS WILHELM RASCHE EWALD WYGASCH GOTTHARD CSIZI United States Patent Office 3,502,561 Patented Mar. 24, 1970 3,502,561 ALKALI-CHLORINE CELL HAVING A HORIZONTAL MERCURY CATHODE Wilhelm Rasche and Ewald Wygasch, Ludwigshafen (Rhine), and Gotthard Csizi, Bad Duerkheim, Germany, assignors to Badische Anilin- & Soda-Fabrrk Aktiengesellschaft, Ludwigshafen (Rhine), Germany Filed Aug. 30, 1967, Ser. No. 664,349 Claims priority, application Germany, Sept. 5, 1966, 1,567,910 Int. Cl. C22d 1/04 3 Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell having a horizontal mercury cathode for the electrolysis of aqueous solutions of alakli metal chlorides by the amalgam method consists of aluminum onto which a thin layer of steel has been applied and then onto that a chemically resistant, electrically insulating material. Current is supplied by means of mushroomshaped members extending through the bottom of the cell, said members being distributed over the bottom of the electrolytic cell in a definite number and arrangement.

The cells conventionally used for the electrolysis of aqueous alkali metal chloride solutions having horizontal mercury cathode are made of steel, the inner surfaces being lined with a chemically resistant, electrically insulating material, for example hard rubber, in order to protect the walls and bottom of the cell from corrosive influences.- Supply of current to the mercury cathode is effected through mushroom-shaped steel contacts to which the current is fed either through the steel bottom of the cell itself or through bars or cables located beneath the cell bottom. The last mentioned arrangement is not favorable because of its intricate construction. When the current is supplied to the mushroom-shaped contacts through the steel bottom, the latter must be designed so that the current is passed without appreciable drop in potential from the point of connection to the individual contacts. This offers no difliculty, particularly in the case of low current densities of up to about 6000. amperes per square meter. With the present tendency to use considerably higher current densities, the cross-section of the steel bottom has to be increased considerably to keep the potential drop within tolerable limits. This increase in the cross-section of the bottom to satisfy the necessary condition of a small potential drop has to be considerable owing to the low specific conductivity of steel, so that capital costs for a plant are greatly increased owing to the increase in the weight of the cell. It would therefore be desirable to replace the steel hitherto used for the construction of the cell bottom by a material of higher specific conductivity and lower specific gravity. Aluminum is such a material, but it has the disadvantage that it is attacked by chlorine far more readily than steel and that it is not resistant to mercury. Protecting the aluminum cell by a lining of a chemically resistant material, for example hard rubber, is not sufficient because such a protective layer is damaged fairly easily and then the cell is destroyed in a very short time owing to the low resistance of aluminum.

It is therefore necessary to protect the aluminum surface by applying a layer of a corrosion-resistant and mechanically stable material, for example steel, but owing to the different coefficients of expansion of the two metals considerable difiiculty is encountered because the provision of butt joints and the like is precluded for obvious reasons, for example impairment of the stability of the cell. Cells consisting wholly or to a considerable extent of aluminum are therefore unknown hitherto.

The object of the present invention is to provide electrolytic cells which consist essentially of aluminum so that the favorable properties of aluminum (i.e. higher specific conductivity and lower specific gravity than steel) are fully utilized without the above-mentioned disadvantages occurring.

This is achieved according to this invention in an electrolytic cell made of a metallic material and having a horizontal mercury cathode for the electrolysis of aqueous solutions of alkali metal chlorides by the amalgam method, the Walls and bottom of the cell being lined with a chemically resistant, electrically insulating material and mushroom-shaped members extending through the bottom of the cell for the supply of current to the mercury cathode, by applying to the aluminum cell a thin layer of steel and by making the number of mushroom-shaped members per square meter of bottom surface, in dependence on the desired current density i (ka./ sq. m.) and the diameter d (m) of the shaft of the mushroom, at least correspond to the value calculated from the formula the mushrooms being uniformly distributed in parallel rows and staggered in adjacent rows by an amount of 0.5 to 1 times the diameter of the shaft of a mushroom, and the diameter of the mushroom shaft satisfying the condition:

in dependence on the current density.

The aluminum is effectively protected from attack by chlorine and mercury by the steel layer and the lining of chemically resistant material applied to the steel layer. Even if the hard rubber lining which is in contact with chlorine and mercury is damaged, the layer of steel can withstand these two reagents at least until the defect is detected and the cell is shut off. It is entirely adequate to apply the steel layer to the aluminum in a thickness of 0.1 to 0.5 mm., preferably 0.2 to 0.3 mm.

The layer of steel may be applied to the aluminum by any known procedure. Thus for example a deep-drawing steel foil having the abovementioned thickness may be firmly bonded with the aluminum trough by an adhesive. This bond is not loosened in the operation of the cell provided the other feature of the present invention relating to the distribution of the mushroom-shaped members serving to supply current is fulfilled. It is known that temperatures up to about 60 C. occur in the operation of an electrolytic cell. At these temperatures, stresses attributable to the different coefficients of expansion of steel and aluminum are fairly high and, without the distribution of the current supply members in accordance with this invention would destroy the combination of the two metal-s.

Two condtiions have to be fulfilled in the distribution of the current-supplying members. First it is necessary that the number (11) thereof per square meter, which is dependent on their diameter, is chosen so that it is large enough to prevent too marked a potential drop in the cell. This quantity size is determined by the formula: (1) n= g i where d is the diameter of the mushroom shaft in meters and is the current density in ka. per sq. meter.

Since the mushrooms according to the invention are ara fanged in rows parallel to each other, it follows that n nushrooms are arranged in each row, according to Z 1/n14 t The number of mushrooms per square meter; of the treaof the cell base and their distribution over the base are calculated from these equations in combination with he other features of the invention.

The diameter of themushrooms moreover has to satisfy :he equation: 7

for a given current density. a

.These relationships will be illustrated by the following numerical examples:

At a mushroom diameter of 40 mm. and a current density of 10 ka./sq. m. it is necessary, using Formula 1, to use 35 mushrooms per square meter which, according to Formula 2, are arranged in six rows of 6 mushrooms each. By inserting the values for d=0.04 and i=l kaJisq. m. in Equation 4, a value of 0.24 is obtained for the left side of the equation and a Value of 0.166 for the right side of theequation; thus the condition is fulfilled.

At a mushroom diameter of 40 mm. and a current density ef'S ka./ sq. m. it is foundthat this equation is not satisfied (0.17 as against 0.2 on the right side). It is only at a mushroom diameter of 1 30 mm. that the required by bonding. This steel sheet is covered in known manner with a lining 1 of hard nlbber having a thicknessaof to 8 mm. Current supply from the: aluminum trough 3 to the mercury cathode 6 efiected by means of known mushroom-shaped steel contacts 4 whichare firmly secured to the trough by the screw'connection 5 and ensure with projections which are pressed into the protective layer and effect a kind of labyrinth packing,

We claim:

1. An electrolytic cell made of metallic material and having a horizontal mercury cathode for the electrolysis of aqueous solutions of alkali metal chlorides by the amalgam method, the. walls and the bottom of the cell being provided with a lining of chemically resistant, electrically insulating material and mushrobm-shaped mem-" bers, extending through the bottom of the cell, being provided for the supply of current, wherein the electrolytici cell consists of aluminum onto which a thin layer of steel has been applied and the number of mushroom-shaped members per square meter of the area of the bottom corresponds at' 'least to the value calculated from the formula in dependence on'the desired current density t tka. per square meter) and the diameter d (meters; of the shaft of said mushroom-shaped members, said mushroomshaped members being uniformly'distributed in parallel rows and arranged in adjacent rows progressively otfset by an amount of half to one diameter of the mushroom shaft, and the diameter of said mushroom shaft satisfying the condition: a

in dependence on the current density concerned.

2. An electrolytic cell as claimed in claim 1 wherein the layer of steel is 0.1 to 0.5 mm. in thickness.

3, An electrolytic cell as claimed in claim 1 wherein the layer of steel has a thickness of 0T2 to 0.3mm.

References Cited UNITED STATES PATENTS 7 7/1962 De Nora 204-250 in HOWARD s. WILLIAMS? Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. xii. 204420, 250

22 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. },502 56l Dated March 2 L, 19YQ Inventor(s) Wilhelm Rasche et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Co1umn 1, line 17, "alakli" should read --a1kali-.

Column 2, line 34, should read line 60, "condtiions" should read --conditions--; line 71, "and is" should read --and i is--.

SIGNED AN'u SEALED JUL 2 11970 ISEAL) Attest:

E WILLIAM E. suHuYLER dwurd M. Fletcher, 1:. issioner of Patents

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