Improvements in Processes for Reducing Aluminium.
Year: 1897

page_text: Date of Application, 9th. Mar., 1897-Accepted, 5th June, 1897°.
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COMPLETE SPECIFICATION.
Improvements in Processes for Reducing Aluminium.
I, FRANK AUSTIN GOOCH, of 169, Edwards Street, City of New Haven, in the
County of New Haven, and State of Connecticut, in the United States, of America,
College Professor, do hereby declare the nature of this invention, and in what
manner-the same is to be performed, to be particularly described and ascertained
in and by the following statement:-
The invention herein described relates to processes for the reduction of aluminium
by the electrolysis of a suitable fused bath. In general terms, my invention consists
in fusing together the fluoride of a suitable alkaline metal, the oxide of aluminium and
a suitable hydrous chlorine compound of aluminium, and passing an electric current
I have found that the
through the fused mass, thereby electrolysing the same.
alkaline metals whose fluorides are most suitable for employinent in my process are
sodium and potassium. I preferably employ the fluoride of sodium, but the fluoride
of potassium can also be used with almost equal success.
It is well known that sodium fluoride in a fused condition will not dissolve the
oxide of aluminium, commonly known as alumina. If powdered alumina be placed in
a crucible containing fused sodium fluoride, the alumina will remain in suspension,
whatever the degree of heat in the mixture.
I find, however, when a small amount of the hydrous crystalline chloride of
aluminium (whose formula is Al,C, 12 H,O) is added to the fused sodium fluoride
containing the alumina in suspension, that the chloride dissolves and immediately
thereafter the insoluble alumina dissolves also. Also the other hydrous chlorides
and the various hydrous oxy-chlorides of aluminium (the latter produced by heating
the hydrous chlorides), when added to sodium fluoride in which alumina is held in
suspension, will, when their contents in chlorine are sufficiently great, themselves
dissolve freely and will cause the alumina to dissolve. I use the term hydrous chlorine
compound of aluminium in this specification and in the claims hereto annexed, to
embrace the ordinary hydrous chlorides of aluminium and also the hydrous oxy-
chlorides. Of the various chlorides mentioned, I find the bydrous crystalline chloride
upon the whole the most economical and suitable one to employ, though the other
hydrous chlorine compounds mentioned answer almost equally well for theoretical
purposes.
More particularly, therefore, my invention consists in the improved process herein
described, which consists in fusing together sodium fluoride, alumina and a suitable
hydrous chloride of aluminium, and passing an electric current through the fused
mass, thereby electrolyzing the same.
It is well known that, when ordinary hydrous_crystalline chloride of aluminium is
heated strongly by itself, it is decomposed ultimately into alumina, water and hydro-
chloric acid. It is also known that, when the solution of the chloride in water is
simply evaporated by heat to dryness, only a part of the chlorine is given off, while
a basic chloride or oxy-chloride still retaining water constitutes the residue. When
the heating is so conducted that the loss of chlorine does not exceed one-half the
entire amount of that element contained in the crystalline chloride, the hydrous oxy-
chloride remaining is soluble in hot water, which shows that the decomposition of
the chloride has in this case not gone so far as to produce alumina. I find also that
a hydrous oxy-chloride of aluminium which is soluble in water may also be obtained
by drying the hydrous aluminium chloride taken in crystalline or solid condition

page_text: until it has lost from one-third to one-half of its chlorine together with a portion of its
water. Such a hydrous oxy-chloride of aluminium 1 find dissolves in fused sodium
fluoride. I find also that when the hydrous crystalline aluminium chloride is thrown into
fused sodium fluoride, a similar action takes place. The hydrous chloride completely
dissolves in the fused sodium fluoride, and, if alumina is present in suspension, it also
will be dissolved. It would appear that the high temperature of the bath sets up
chemical interaction before the hydrous chloride or oxy-chloride has had time to
undergo excessive decomposition due to the action of beat alone. When the hydrous
chloride or the hydrous oxy-chloride as the case may be is mixed with cold sodium
fluoride, and the mixture then heated to fusion, the solvent action of the sodium
fluoride is manifested similarly but not quite to the same extent as when the hydrous
chloride or oxy-chloride is brought quickly into contact with the fluoride already in
a state of fusion. Not only the crystalline chloride, but also the other hydrous
chlorides and the various hydrous oxy-chlorides (produced by heating the hydrous
chloride), in like manner, when their contents in chlorine are sufficiently great, will
not only dissolve in fused sodium fluoride but will render the bath thus produced
capable of dissolving alumina.
In the accompanying drawing, which is hereby made a part of this specification,
is shown one form of apparatus suitable for the practice of my invention. I do not,
however, limit myself to the apparatus shown, since any other suitable apparatus
would answer equally well for the practice of my invention.
In the drawings, F is a furnace having a fire-box f, and opening f¹ in the top of
the furnace, into which is set a tapering crucible A, the same being supported by the
sides of the opening'. The crucible A preferably employed in the operation of my
invention consists of a tank of iron lined with compacted carbon. The carbon lining f
of this tank serves as the cathode, the iron of the tank being connected by the
conductor N with the negative pole of a dynamo electric machine or other suitable
source of electricity O. For the anode, I preferably use a number of separate carbon
electrodes, C, C', &, C, C, which are preferably suspended from an iron bar D raised
above the crucible resting on wooden supports E E. These electrodes are partially
immersed in the bath contained in the crucible. The bar D. is connected by the
conductor P to the positive pole of the source of electricity. If desired, the cathode
may also be formed of a detached carbon suspended in a similar way for that just
described for the anode, or otherwise supported and partially immersed in the bath.
A single electrode might also be used in place of the separate carbons shown in the
drawing, which when used collectively form the anode, the relative superficial areas
of the electrodes in any particular case being adjusted so as to secure the greatest
economy of action. In place of a carbon anode, an anode of any other suitable
material as of platinum may be used. S S' are binding posts for the conductors N, P.
B is the bath contained in the crucible A, through which the electric current is
passed.
In the practice of my invention, I preferably prepare a bath by fusing in the
crucible A in proper proportions the fluoride of sodium, alumina and the hydrous
crystalline chloride of aluminium corresponding to the symbol Al,Cl, 12 H₂O.“ These
ingredients are preferably mingled together in the following proportions :
Alumina (Al,O)
8 parts
But these ingredients are variable serviceably within reasonable limits, without
materially affecting the operation or function of the bath, as in fact any 50
proportions which may be found suitable may be employed. If the amount of the
chloride added be insufficient, the result will be that part of the alumina will remain
in suspension. On the other hand, a moderate excess of the chloride will produce
no deleterious effect.
The bath may be fused and the fusion may be maintained by the application of 5

page_text: heat from any suitable source, as externally from the furnace F. The temperature
required to fuse the baths suggested above is that of red heat. The ingredients
of the bath may also be fused together in a separate apparatus and introduced in
a molten condition into the crucible at the beginning of the process, the fusion
being thereafter maintained in any suitable way. If now the electric current is
passed through the bath and electrolysis takes place, aluminium is deposited at the
cathode, whence it may be removed in any suitable and well known manner. By
adding alumina to the bath from time to time in suitable quantities, the process
becomes a substantially continuous one through a considerable period of time. A
moderate excess in the amount of alumina added does no harm.
In the process herein described, an electric current of suitably low electro motive
force, say of from four to ten volts, is used, but the voltage of the current required
will depend on the size and forin of the electrodes, as well as on the condition of
the bath under all the existing circumstances of resistance and of chemical
constitution. The hydrous chlorine compound of aluminium in my. process herein
described may be introduced into the bath before or after the alumina, or may be
mixed with the sodium fluoride in a dry state and the mixture fused, the order of
operations not being of essential importance. 1 find, however, that there is less
evolution of hydrochloric acid from the mixture, and consequently that a given
amount of the hydrous chlorine compound has greater effectiveness, if the hydrous
chlorine compound is added to the mixture of sodium fluoride and alumina when the
former is already in a state of fusion.
If preferred, in place of using alumina as such in the constitution of the original
bath, the hydrous chlorine compound may be used in excess of the amount of the
same which will dissolve in the sodium fluoride. The excess of the hydrous chlorine
compound would be decomposed by the heat of the bath mainly into alumina, water
and a small amount of hydrochloric acid. The alumina necessary to constitute the
bath would thus be supplied indirectly through the excess of the hydrous chlorine
compound. When this method of constituting the bath is employed, I preferably
constitute the bath in the proportion of 100 parts of sodium fluoride to 200 parts of
the hydrous chloride of aluminium. When the current is passed through the bath
thus constituted, aluminium is deposited as before. I then preferably make the bath
continuous by adding alumina from time to time in suitable quantities as before
stated. It would be possible to supply all the alumina necessary for the continuous
process by simply adding additional quantities of the hydrous chloride of aluminium,
bat such a method would be disadvantageous because it would result in the formation
of large quantities of hydrochloric acid, which would have to be disposed of, in order
to prevent danger to the workmen. The conditions as to temperature, voltage and
methods of creating and maintaining fusion are the same whether the alumina is
supplied in the first instance as such or through the excess of the hydrous chlorine
compound in the manner described.
Having now particularly described and ascertained the nature of my said inven-
tion; and in what manner the same is to be performed, I declare that what I
claim is :-
1. As an improvement in the art of manufacturing aluminium, the herein described
process which consists in fusing together sodium fluoride, the oxide of aluminium or
alumina and a suitable hydrous chloride or chlorine compound of aluminium, and
passing an electric current through the fused mass, substantially as described.
2. As an improvement in the art of manufacturing aluminium, the herein described
process which consists in fusing together sodium Huoride, alumina or the oxide of
aluminium and the hydrous crystalline chloride of aluminium, (whose symbol is
AI,Cl, 12 H₂O,) or a suitable hydrous chlorine compound of aluminium and passing
an electric current through the fused mass, adding to the bath from time to time if or as
required suitable quantities of the oxide of aluminium, substantially as described.
3. As an improvement in the art of manufacturing aluminium, the herein described
continuous process which consists in fusing together sodium fluoride, alumina and a

page_text: suitable hydrous chloride of aluminium or the hydrous crystalline chloride of
aluminium, whose symbol is Al,Cl, 12 H,O passing an electric current through the
fused mass, and adding to the bath from time to time if and as required suitable
quantities of alumina, substantially as described.
4. As an improvement in the art of manufacturing aluminium, the herein
described process which consists in fusing together sodium fluoride and the hydrous
crystalline chloride of aluminium in excess of the amount thereof which will
dissolve or fuse in the sodium fluoride used, passing an electric current through
the fused mass and adding to the bath from time to time if or as required suitable
quantities of alumina, substantially as described.
Dated this 9th day of March 1897.
For the Applicant,
J. C. CHAPMAN,
70 Chancery Lane, London, W.C., Chartered Patent Agent.