Improvements in Processes for Reducing Aluminium.
Year: 1894

page_text: COMPLETE SPECIFICATION.
Improvements in Processes for Reducing Aluminium.
A communication from abroad by FRANK A. GOOCH, of the City and County of
New Haven, in the State of Connecticut, United States of America, and
LEONARD WALDO, of Bridgeport, Fairfield County, in the State of
Connecticut, United States of America.
I, JOHN CORRY FELL, of the Firm of Fell and Wilding, of 1, Queen Victoria
Street, in the City of London, Chartered Patent Agent, 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 hereindescribed relates to processes for the reduction of
aluminium from its compounds by the electrolysis of a suitable fused mass
containing such compounds. The invention hereindescribed consists, in general
terms, in passing an electric current through a suitable fused bath containing a
suitable halogen compound of aluminium, thereby electrolyzing the bath, and in
supplying to the bath the vapor of water. In practice, I find that the halogen
compounds of aluminium, which are most suitable and best adapted to be used in
our process, are the chloride of aluminium and the fluoride of aluminium.
For convenience I describe this invention with special reference to the reduction
of aluminium from its chloride.
For simplicity I describe this invention with special reference to the use of
steam as the most convenient form of water vapor.
In the accompanying drawings which are hereby made a part of this Specification,
is shown one form of apparatus suitable to the practice of this invention. 1.do
not, however, limit myself to the apparatus shown, since any other suitable apparatus
would answer equally well for the practice of this invention.
Figure 1 represents a sectional diagrammatic view of the apparatus employed
by me.
Figure 2 represents a sectional view of a modified form of apparatus employed
by me.
Similar letters refer to similar parts throughout the drawings.
F is a furnace having a fire-box f, and opening f' in the top of the furnace,
into which is set a tapering crucible A, the same being supported by the sides of
the opening f. The construction of the crucible and the arrangement of the
electrodes and conductors are hereinafter fully described. T is a boiler, steam
chest, or other generator or receiver from which the steam is supplied through the
tube H, the supply being regulated by a cock t. sare binding posts for the
conductors NP. B is the hath contained in the crucible A through which
the electric current is passed:
In the practice of this invention, so far as it relates to the reduction of
aluminium from its chloride, I preferably prepare a bath by fusing in a suitable
tank or crucible A in suitable proportions, the chloride of aluminium and the
chloride of an alkaline metal (preferably sodium) or of an alkaline earth metal,
with the fluoride of aluminium and the fluoride of sodium. A convenient way to
form a suitable bath is to combine the double chloride of aluminium and sodium
(represented by the formula 2 NaCl. Al,C,,) with the mineral cryolite. I find
it of advantage to add to the combination just named an additional amount of

page_text: But with a bath, constituted as last above described, the proportions are
variable serviceably within considerable limits without materially affecting the
operation or functions of the bath, as in fact any proportions which may be found
suitable may be employed.
The crucible A preferably employed by us in the operation of our invention,
consists of a tank of iron lined with compacted carbon. The carbon lining L of
this tank serves as the cathode, the iron of the tank being connected by the con-
ductor N with the negative pole of a dynamo-electrical machine or other suitable
source of electricity O. The anode C is a detached carbon electrode partially
immersed in the bath B and connected in the following manner with the source of
electricity. I preferably suspend the anode C from an iron bar D raised above
the crucible and resting on wooden supports E. E. The bar D is connected by
the conductor P to the positive pole of the source of electricity. If desired, a
number of separate carbons may be used to form the electrodes, as shown in
Figure 2, where C, C1, C2, C3 and C4, all suspended from the bar D, collectively
form the anode, the relative superficial areas of the electrodes in any particular
case being adjusted so as to secure the greatest economy in action. In place of a
carbon anode, an anode of any other suitable material, as of platinum may be
used. The bath may be fused and the fusion may be maintained by the applica-
tion of heat from any suitable source, as from a furuace F. The temperature
required to fuse the baths suggested above is that of a dull red heat. I may also
fuse the ingredients of the bath in a separate apparatus, and introduce the same
in a molten condition into the tank at the beginning of the process, the fusion
being thereafter maintained in any suitable way. When the electric current is
passed through the bath and electrolysis takes place, aluminium is deposited at the
cathode, and the halogens, (chiefly chlorine) are liberated at the anode. It is well
known that these gases, in a free state, are highly noxious to health. On this

page_text: account, and for the further reason that they attack and quickly destroy the positive
electrode in the apparatus used in any process similar to the one described, their
escape in a free state would render such process commercially useless. To obviate
these difficulties, we supply to the bath the vapor of water, preferably in the
form of steam, which 1 preferably deliver at or beneath the surface of the fused
mass in a substantially continuous manner and in uear proximity to, or through,
the anode. In the latter case, a longitudinally perforated carbon rod C is
preferably employed for the anode, and the steam is passed through the same as
through a pipe, the steam being supplied through a tube H connected with the
upper end of the anode C, which may project above the bar D. The steam may
also, if preferred, be conducted through a separate pipe, as the pipe M in
Figure 2. Where the steam is supplied at the surface of the bath, it may be
passed through pipe M' represented in Figure 2 by dotted lines, in which case
pipe M would be dispensed with. I may dispense with the conduction pipe
altogether, and spray water on the surface of the bath. The water will instantly
assume the spheroidal condition and quickly vaporize. I may also produce the
steam by dropping minute fragments of ice on the surface of the bath. I do not
limit this invention to any particular mode of supplying the steam to the bath,
since any suitable mode may be employed without departing from the essential
nature of this invention. The constituents of the steam being dissociated in or
at the surface of the bath during action, the hydrogen required for our process is
supplied in a substantially continuous manner. When the halogen compounds are
liberated by the electrolysis of the bath, they combine instantly with the hydrogen
constituent of the steam, and escape at the anode in the form of hydrochloric acid
or bydrofluoric acid (chiefly the former). These gases, in the quantities evolved
by our process, are easily controlled and disposed of without injury to apparatus or
workmen, by appropriate means external to the bath, as by the use of a flue K,
having a strong draught and provided with a hood projecting over the
crucible A; or cloths or other absorbent media saturated with water may be
suspended over the crucible, the escaping gases being taken up by the water
whose power of acting as a solvent for hydrochloric and hydrofluoric acid is well
known.
I preferably supply the steam or other form of water vapor to the bath only
in an amount sufficient to furnish the hydrogen for the combination with the
halogen elements, or slightly in excess of such amount.
In the practical operation of this invention, where I use any of the suggested
baths I have found that I obtain, at the anode, hydrochloric acid almost
exclusively, with very little trace of fluorine. This shows that the aluminium
deposited at the cathode is derived chiefly from the chloride of aluminium in the
bath; and I have found that, by the addition to the bath from time to time of
chloride of aluminium (Al,Cl) in sufficient quantities, the bath will be replenished
and the process will be a substantially continuous one during a considerable period
of time. An excess of. the chloride of aluminium produces no injurious effect, as
it is gradually utilized in the subsequent operation of the process. I have spoken"
of fluorine being set free, though I am aware that it is considered very difficult to
isolate this element. I, however, use the term "fluorine" merely for convenience,
meaning thereby to include not only free fluorine, if any be liberated, but also any
compound thereof, which might be set free at the anode, if hydrogen, either free
or in combination, were not used in the process.
As before stated, the aluminium is deposited at the cathode, where it melts,
forming globules, which (when one of the suggested baths is employed) gather at
the bottom of the bath, the aluminium having a higher specific gravity than the
fused bath. The aluminium may then be removed in any suitable or convenient
manner, as for example, by means of a ladle lined and covered with carbon, or by
drawing it off through a suitable opening at the bottom. In case a bath should
be used whose specific gravity is higher than that of aluminium, the aluminiiun
would rise to the top, where it could be easily removed.

page_text: In the process hereindescribed, I use an electric current of suitably low electro-
motive force, usually of from four to ten volts, but the voltage of the current
required will depend upon the size and form of the electrodes as well as on the
composition of the bath, it being only necessary to have a voltage sufficient to
decompose electrolytically the compound of aluminium in the bath under all the
existing conditions of resistance and of chemical constitution. The electric
current which we employ in our process, and which is herein referred to as being
passed through the bath, is employed solely for the purposes of electrolysis. The
steam may in the first instance be supplied to the bath before or after the electric
current is passed through the same, or simultaneously therewith, the order of
the operations being unimportant.
The steam used in our process is likely to cause some oxydation of the anode
if the material of the anode is oxydizable; but, unless the material of the anode
is casily oxydizable, the waste of the anode will be usually much less than would
be the case if the anode were exposed to the action of free halogens.
Having now particularly described and ascertained the nature of this 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 passing an electric current through a suitable
fused bath containing a suitable balogen compound of aluminium, thereby
electrolyzing the bath, and in supplying to the bath the vapor of water,
substantially as and for the purposes set forth.
2. As an improvement in the art of manufacturing aluminium, the herein-
described process which consists in passing an electric current through a suitable
fused bath containing the chloride of aluminium and in supplying steam to the
bath, substantially as and for the purposes set forth.
3. As an improvement in the art of manufacturing aluminium, the herein-
described process which consists in passing an electric current through a suitable
fused bath containing the chloride of aluminium and the chloride of an alkaline
metal, and in supplying steam to the bath, substantially as and for the purposes set
forth.
4. As an improvement in the art of manufacturing aluminium, the herein-
described process which consists in forming a bath by fusing the chloride of
aluminium and the chloride of an alkaline metal with the fluoride of aluminium
and the fluoride of sodium, passing an electric current through the fused mass,
thereby electrolyzing the same, and supplying steam to the bath, substantially as
and for the purposes set forth.
5. As an improvement in the manufacture of aluminium, the hereindescribed
process which consists in forming a bath by fusing together the chlorides of
aluminium and sodium and the fluorides of aluminium and sodium, passing an
electric current through the fused mass, thereby electrolyzing the same, and
supplying steam to the bath, substantially as and for the purposes set forth.
6. As an improvement in the art of manufacturing aluminium, the herein-
described process which consists in forming a bath by fusing together the chlorides
of aluminium sodium and potassium, and the fluorides of aluminium and sodium,
passing an electric current through the fused mass, thereby electrolyzing the
same, and supplying steam to the bath, substantially as and for the purposes set
forth.
7. As an improvement in the art of manufacturing aluminium, the herein-
described process, which consists in forming a bath by fusing the chloride of
aluminium and the chloride of an alkaline earth metal with the fluoride of
aluminium and the fluoride of sodium, passing an electric current of suitably low
voltage through the fused mass, thereby electrolyzing the same, and in supplying
steam to the bath, substantially as and for the purposes set forth.
.8. As an improvement in the art of manufacturing aluminium, the herein-

page_text: described process, which consists in forming a bath by fusing together the chlorides
of aluminium and magnesium with the fluorides of aluminium and sodium, passing
an electric current of suitably low voltage through the fused mass, thereby
electrolyzing the same, and in supplying steam to the bath, substantially as and for
the purposes set forth.
9. As an improvement in the art of manufacturing aluminium, the herein-
described process, which consists in forming a bath by fusing together the chloride
of aluminium, the chloride of an alkaline earth metal and the chloride of sodium
with the fluorides of aluminium and sodium, passing an electric current of suitably
low voltage through the fused mass, thereby electrolyzing the same, and in
supplying steam to the bath, substantially as and for the purposes set forth.
Dated this 27th day of October 1894.
FELL & WILDING,
Agents for the Applicant.