US1833425A - Electrolytic process for the manufacture of magnesium and the alkaline earth metals, such as calcium by the electrolysis of molten chlorides, and apparatus for carrying the said process into effect - Google Patents

Description

Nov. 24, 1931. A. JESSUP A 1,833,425

ELECTROLYTIC PROCESS FOR THE MANUFACTURE OF MAGNESIUM AND THE ALKALINE CALCIUM BY' THE ELECTROLYSIS OF MOLTEN CHLORIDES,

EARTH METALS, SUCH AS TO EFFECT AND APPARATUS FOR CARRYING THE SAID PROCESS IN Filed April 2, 1926 Fig i FUSED PRo-rEc-i w: LAYER USED MgCATHoDz EFHA CTOFPY HNopE Fuszo ELECTROLYTE 75% MgClg ZOZBQCM "F- 1' q v LTE M9 PR -I-Ec-HNGLAYER ksonl ANOUE FRAc oRY MATERIEL- Patented Nov; '24, 1931 UNITED STATES -PATENT OFFICE ALFRED 'JESSUP, or PARIS, FRANCE ELECTROLYTIC PROCESS roa THE MANUFACTURE or MAGNESIUM AND THE ALKALINE EARTH METALS, SUCH AS CALCIUM BY THE ELECTROLYSIS OE MO-LTEN CHIORIDES,

AND APPARATUS FOR CARRYING THE SAID PROCESS INTO EFFECT Application filed April 2, I926, Serial No. 99,410, and in France August 5,

bath is markedly higher than In the known methods for the manufacture of magnesium the electrolyte consists of salts which when molten form a bath whose density is greater than that of magnesium. The magnesium as it is produced floats upon the surface of the bath in the shape of molten globules which become oxidized with great ease and which move over the surface of the bath while burning, so that a part of'the magnesium is necessarily lost by oxidation and chloridization, and it also becomes a difficult matter to collect the metal.

My invention relates to a process of manufacture wherein'the electrolyte consists of a mixture of salts whose density exceeds that of the resulting metal at the working temperature, but wherein I obviate all formation of oxide or chloride, and am enabled to collect the metal with facility.

The said process consists essentially in collecting the said metal at the surfaceof the 1' bath in the form of a liquid layer which itself serves as the active cathodic surface.

In order'to form the said layer of molten metal serving as cathode at the surface of the bath, I may employ as the cathodic device a receptacle of refractory material of any suitable shape, disposed at the surface of the bath, and containing the requisite means for conducting the current, for instance a metal ring or cylinder.

The metal which is formed within the said receptacle will unite with the layer of liquid metal preliminarily placed therein and will float upon the surface of the electrolytic bath I in the form ofa liquid layer of a certain thickness which constitutes the active surface of the cathode.

By way of example and for the proper understanding of my said invention, I have set forth hereunder a particular method by which the same is carried into effect. The apl pended drawingstshow three constructional forms of the device employed for this purpose. T In the particular case of the manufacture of magnesium, the electrolyte consists preferabl of magnesium chloride, optionally mixed with alkali metal chlorides earth metal chlorides,fiand if necessar with fluorides, in such a manner that the density or alkaline of the molten that of molten magnesium at the working temperature. I may for instance employ the following percentage composition:

. Per cent MgCl BaCl 20 CaF 5 the bath, and may be variously arranged; but 65 in all cases the active part of the cathode consists of a layer of liquid magnesium. The cathodic device shown in Fig. 1 consists of a cylinder-of sheet iron coated interiorly with with magnesium a metal clilficultly miscible or with a very thin layer of a metal easily miscible with magnesium, and is coated on the external periphery with a refractory substance c or with a part of the chloride bath solidified by a cooling worm, the whole serving as a retainer for a continuous layer 6 of liquid magnesium which floats upon the surface of the bath g. This layer of metal is preserved on its upper surface from all contact with air, by a layer 7 of a melted mixture of chlorides which is *so proportioned that it will be lighter than the liquid magnesium, for instance 5KCl, MgCl or KCLNaCl.

The magnesium produced by the electrolysis will collect below '(and of course v quickly mix with, the layer of liquid magnesium which must preliminarily be present in ,order to start the electrolysis, and the densities is so balanced that the metal will not escape from the ring serving as cathodic support. The magnesium as collected is taken out through the top layer f of molten chlorides.

equilibrium of the In another modification as shown in Fig.

2-, I employ a cathode device of sheet iron having the shape of an inverted basin of large diameter and small height; the said'device is laced face downwards and touches the sur ace of the bath. The device in question is preliminarily filled with liquid magnesium, and during the electrolysis the mag-- nesium, which deposits on the layer of liquid magnesium overflows the lower edge of the 5 device, and collects in the annular space It be:

tween the latter and a suitable external cylinder c consisting'of refractory material used alone or covered with sheet metal on its internal surface, or in place of the refractory W cylinder 0 I may use a cylinder of sheet metal surrounded by a coating of chloride which is solidified by a cooling Worm immersed in I the bath in'proximity to said cylinder, or

, simply of solidified chloride.

The magnesium which collects in the said annular space may be withdrawn from the bath as it is formed, or it may be united in a single layer and covered with a light mixture of molten chlorides in order to avoid oxidation, as in the preceding case.

The apparatus according to my invention may further comprise either a ring of refractory material optionally covered with a suitable metal on its internal surface, or a ring of sheet metal having a coating of chloride which is solidified by a cooling worm, or simply a ring of solidified chloride within which is disposed the conducting part of the cathode; the latter may consist of a grid or af perforated plate, or of an inverted basin, and is made of a metal which in infusibleand only slightly miscible with magnesium, such as chromium, molybdenum, tungsten, man ganese, vanadium, titanium, silicon and their alloys, or of an infusible non-miscible metalemployed either alone or covered with one of the above mentioned metals or with a fusible metal which is difficultly miscible with magnesium such as antimony, bismuth or tin, or with a thin layer of a miscible metal such as copper, zinc or aluminum.

By the use of the aforesaid metals, I am enabled to form upon their surface a layer ofalloys saturated with magnesium or a layer of adherent magnesium upon which the molten magnesium is deposited, which will then act as cathode. Incertain cases,'I may dispense with the preliminary use of the layer 50 of molten magnesium. It'should be noted that in this latter case the protecting layer of light chlorides is added only after the formation of a layer of molten magnesium covering the whole surface and thus obviating all mixture of the light chlorides with the electrolyte.

In the second example of the invention, I may again replace the usual sheet metal cathode device of Fig. 2 by one consisting of a metal as above mentioned in connection with 6Q the third example. I When the said metal or alloy is infusible at the workingtemperature, said device can be made of one of the aforesaid m et ls.

al is fusible a t the'working temperature, I prefer to construct the said receptacle of iron But when the selected metwhich is covered with one of the aforesaid metals. T

Obviously, my said invention is not limited to the special constructions shown in the drawings. In particular, the cathode may consist of any suitable combinations of parts forming the aforesaid cathodes, thus comprising rings, inverted or the like. In this case, the term ring 1s not intended to restrict the same to a cylindrical or round body, but the ring may be of any desired shape.

One can also use this cell as a secondary instead of primary, by substituting as anodean alloy of magnesium heavier than the electrolyte for the anodes of graphite or hard carbon.

I claim:

1. In aprocess for the electrolytic prepara tion of light metals such as fused magnesium basins, plates, grids,

and fused calcium, starting with a fused electrolyte heavier than the fused metal-forming at the cathode, the step of applying a protective layer'of fused salts inert to said fused metal, above the said layer of fused metal in order to isolate'the metal from contact with the atmosphere, such layer of fused salts being of lower specific gravity thanthe fused light metal formed.

' 2. A process of obtaining magnesium and calcium, which comprises the step of forming three superposed layers arranged in the order of the relative densities; first-at the bottom, a relatively heavy layer containing the chloride of the metal which is to be obtained which layer constitutes the electrolyte, secondabove the electrolyte, a layer of the metal to be obtained, serving as the cathode, and third-upon said metal, a layer of moltensalts having a composition difierent from the first mentioned. layer and which is free from action on the obtained metal, and which third layer isolates the said metal from contact with the ambient atmosphere, such third layer being of lower specific gravitythan the second layer, every part of the cathode being out of vertical alignment with the anode.

3. A cell for the electrolytic preparation of light metals such as magnesium and calcium, comprising at the upper part of the cell, at near and partly-below the normal liquid level, a ring of electrically insulating material, in the interior of this ring a piece formed of a conducting material and capable of being wetted by which latter whereby the metal produced at the cathode during the normal operation is confined vby said ring of insulating refractory material,

the molten metal to be obtainedforms the cathode element,

rial from said cell durmg normal operation no I only slightly alloyable' with the metal to be obtamed, such metallic piece being wholl submerged in the fused contents of the cel and an electrical connection to said metallic piece, from above.

In testimony whereof I haveaflixed my signature. .v ALFRED J ESSUP.

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