US400666A - Process of electro lyzing crude salts of aluminium - Google Patents

Description

(No Mddel.)

C. M. HALL.

PROCESS OF ELEGTROLYZING CRUDE SALTS 0F ALUMINIUM Patented Apr. 2, 1889.

ummwmx UNITED STATE PATENT OFFICE.

CHARLES M. HAIL, OF OllERlilN, ()lllt).

PROCESS'OFWELECTROLYZING CRUDE SALTS OF ALUMINIUM.

SPECIFICATION forming part of Letters Patent No. 400,666, dated April '2, 1889.

Application filed August 17. 1888. $erial No. 282,955. (No specimens.

T0 all-whom it nmy colbccrn:

Be it known that-- I, CHARLES M. llALL, a

citizen of the United States, residing at Oberlin, in the county of Iiorain and State of Ohio, have invented or discovered certain nevi-"and useful Improvements in theManufacture of Aluminium by Electrolysis of itsFused Salts, of which improvements thev followingis a specification.

In applications filed July 9, 1886, and February 2, 1887, and serially numbered 207,601v

and 226,206, respectively, I have described and claimed processes for the reduction of tion of the fiuoride'of lithiunnand in the process described in application, Serial No. 226,206 I employed a bath formed of the fluo rides of potassium and aluminium, (represented by the formula K AI F with or without the addition of the fluoride of lithium; The salts forming "either of the above-mentioned baths are placed in a suitable yessel,

preferably one formed of. metal and-lined with carbon, and then subjected tosu flicient heat to fuse them and .form a homoge-nous bath. Electrodes formed of carbon orany suitablemetal and connected to.oppositc poles of a dynamo-elcctric machine are then placed i'iithe bath, or the conmining-vessel may be employed as thencgativeelectrode. The alumina is now added to the bath, and

being dissolved aluminium is reduced at the negative electrode, and being fused'byihe heat of the bath sinks to the bottom of the vesscl, the oxygen being liberated atthcposiium produced. The formation of the black the form of bauxite, anhydrous oxide of compound, which occurs sooner in the bath composed of the fluorides of sodium and aluminium than in thatcomposcd of the fluorides of potassium and aluminium, necessitates a com paratiwrl y f requent renewal of the bath.

The obj ect of theinventio'u described herein is to provide a bath wherein the objections heretofore mentioned do not obtain, and which can be used continuously without changes or renewal, exceptto supply loss occurring. from evaporation.

In the accompanying drawings forming a part of this specification is shown a construction of apparatus applicable for carrying out my improved process.

In the practice of the present invention I form an electrolyte or'bath of the fluorides of calcium, sodium, and aluminium, the fluorides of calcium and sodium being obtained in the form of fluor-spar and cryolite,respect.-

ively, and the fluoride of aluminium being obtained by saturating hydrated alumina (Alllq with hydrofluoric acid. The compound resulting from the mint ure of the abovementioned fluorides, which is represent-ed approximately by the formula Na Al Ffi erably formed of metal and lined with pure carbon, for the purpose of preventing the admixture of any foreign material with the bath or with the aluminium when reduced. The vessel 1. is placed in a furnace, 2, and sub jected to sufficient heat to fuse the materials placed therein. 'lwo clcctrmles, 3 and 4, of any suitable material, prefi-u'ably carbon ,when pure aluminium is desired, and connected to the positive and negative poles of any suit-, able generator of electricity, preferably a dynamo-electric machine, are placed in thef used bath; or, if desired, the carbon-lined vessel may be employed as the negative electrode, as represented in dotted lines. -Alumina in aluminium, or any othcr suitable form of alumina, preferably the pure anhydrous oxidc A1 0 artificially prepared, is then placed in the bath, and, being dissolved thereby, aluminium is reduced by the action of electric current at the negative electrode and being fused by the heat of the bath sinks down to the bottom of the vessel, the bath being of aless specific gravity than the aluminium.

.CaAl F placed in a suitable vcssel,1, pref- This difference in specific gravityis an important feature of my process, as the superineumbeut bath serves to protect the aluminium from oxidation. The oxygen of the alumina is liberated by the action of the electric current at the positive electrode, and, when the latter is formed of carbon, combines therewith and escapes in the form of carbonic oxide 0) or carbonic acid ((0 As the aluminium is reduced, more alumina is added, so that the bath may be maintained in a saturated condition with the fused alumina. 'lheaddition of more alumina than can be dissolved at one time is not detrimental, provided the bath is not chilled, as such excess will sink to the bottom and be taken up by the bath, as required.

The proportions of the materials employed in forming the bath or electrolyte are approximately as follows: Fluoride of calcium, two hundred and thirty-four parts; cryolite, the double fluoride (Na Al F four hundred and twenty-one parts, and fluoride of aluminium, eight hundred and forty-five parts, by weight. These proportions can, however, be widely varied without materially changing the efficiency of the bath. During the reduction of the aluminium the positive electrode, when formed of carbon, is slowly consumed and must be renewed from time to time; but the bath or electrolyte remains unchanged for a long time. In time, however, a partial clogging occurs, which, however, does not render the bath wholly ineffective, but does necessitate an increase in the electro-motive force of the reducing-current, the resistance of the bath being increased in proportion to the degree to which the bath becomes clogged,

thereby increasing the cost of reduction. In order to entirely prevent any clogging of the bath, I add approximately three or four per cent. (more or less) of calcium chloride to the bath or electrolyte hereinbefore described. As the addition of the calcium chloride prevents, as stated, any clogging or increase of resistance in the bath, it can be used continuously without renewals or any additions, except such as may be needed to replace loss by evaporation, and without increasing the electro-motive force of the reducing-current; and, further, the addition of the calcium chloride enables each atom of carbon of the positive electrode to take up two atoms of oxygen, forming carbonic acid, (C0 thereby reducing the amount of carbon consumed in proportion to the amount'of aluminium produced. The calcium chloride being quite volatile is subject to loss faster than the rest of the bath, and must be renewed occasionally on this account.

In red ucing aluminium; as above described, I prefer to employ an electric current of about six volts electro-motive force; but the electromotive force can be varied within large limits.

I claim herein as my invention-- 1. As an improvement in the art of manufacturing aluminium, the method herein described, which eonsists in fusing a combination of the fluoride of aluminium, the fluoride of calcium, and the fluoride of sodium, adding alumina to the bath so formed, and then passing-a current of electricity through the fused mass, substantially as set forth.

2. As an improvement in the art of manufacturing aluminium, the method herein described, which consists in fusing a combina-,

tion of the fluoride of aluminium, the fluoride of calcium, the fluoride of sodium, and the chloride of calcium, adding alumina to the bath so formed, and then passing a current of electricity through the fused mass, substantially as set forth.

In testimony whereof I have hereunto set. my hand. I

CHARLES M. HALL. \V itnesses:

W. B. CORWIN, DARWIN S. WoLco'rr.

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