An Improved Process for the Preparation of Aluminium by Electrolysis.
Year: 1887

page_text: This Print is in accordance with the Original Specification as it stands after
Amendment (under Section 18 of the Patents, &c. Act, 1883), as allowed by
the decision of the Chief Examiner of the 18th day of August 1898.
An Improved Process for the Preparation of Aluminium by
Electrolysis.
. I, ARTHUR CHARLES HENDERSON, of 46, Southampton Buildings, Holborn, in
the County of Middlesex, and of 31, Lincoln Place, Leinster Street, Dublin,
Patent Agent, do hereby declare the nature of the said invention for An improved
process for the preparation of aluminium, aluminium bronze, and alloys of
aluminium by electrolysis, (a communication to me from abroad by Paul Louis
Toussaint Heroult, Metallurgist, of the City of Paris, in the Republic of France),
to be as follows:-
The principle on which my improved process for the preparation of aluminium
is based, consists in decomposing alumina in solution in a bath of molten cryolite
by means of an electric current reaching the bath, on the one hand, through
the medium of an electrode, in contact with the crucible of agglomerated carbon,
containing the cryolite, and on the other hand, by means of another electrode,
also made of agglomerated carbon like the first, and dipping into the bath. This
combination causes the decomposition of alumina, when a current of low tension
is employed; the oxygen passes to the anode with which it is burnt; while alu-
minium settles upon the walls of the crucible forming the cathode, and precipi-
tates on the bottom of the saine as a inetallic form or mass.
The bath remains constant and may be used again indefinitely provided it is
sufficiently fed with alumina.
The positive electrode or anode must be replaced after its combustion; however
such coinbustion prevents polarization and thereby secures a constant energy and
a uniform action of the electric current. The drawing accompanying this specifi-
cation is intended merely as explanatory of my invention and represents a
vertical section of an apparatus fitted up according to the above principle.
The crucible a, containing the bath of cryolite (natural fluoride of aluminium
and sodium) is a very dense and well conducting agglomerated carbon. It is
placed within another crucible 6, made of graphite or plumbago, and resting upon
a circular or other base plate or support, of any suitable kind e, interposed between
it and the furnace grate.
The electrodes e, e' are pencil shaped agglomerated carbon pieces.
The anode e, is situated along the axis of the crucible a, so as to dip into the
bath; while the cathode el, is in direct contact with the crucible itself. The elec

page_text: trodes rise above just the arch of the furnace, and are insulated. by stone ware
tubes d, d, both from contact with the air, and from the action of the fire.
A conductor f is wound upon the positive electrode e, while a conductor f¹ is
attached to the negative electrode e¹ these conductors f, f¹ are connected with a
dynamo-electric machine of a suitable power and low tension.
The crucible a, is closed by a lid g, made of calcined magnesia or of clay and
through which the anode e, passes.
Over this cover I place a layer of grout of fire-clay h, which I finally cover with
a stratum of mortar, of either vegetable mould or loam k.
The furnace has its chimney at i, and its inlet at c. When the cryolite is in
a molten state, the bath is electrolyzed an electric current being for the purpose
conveyed into the electrodes e, e¹. Oxygen is then evolved upon the anode e,
which being brought to a high temperature, burns with such oxygen, and gene-
rates oxide of carbon, which issues through the central tube d, the tube d¹, being
kept closed so as to avoid the action of the current of air. On the other hand,
the aluminium passes on to the cathode, that is to say on the internal walls of the
crucible a, where it first settles and then falls to the bottom of the crucible where
it finally forms a metallic form or mass.
The cryolite always remains. To render the production of metal continuous,
it will suffice to add thereto a fresh supply of aluinina, to replace that previously
decomposed.
I deem a current of three volts sufficient for the successful and practical per-
formance of this process and is a very considerable saving compared with what
the cost now is with the processes at present employed, and which invariably
require currents of at least ten times greater tension. The reason of this is, that
in my improved process, the carbon of the positive electrode e, while it burns,
yields an amount of heat, which is not necessary to be supplied by the electric
current.
The anode is burnt down in each operation, for three equivalents of burnt
carbon, two equivalents of aluminium are obtained. The same method also applies
to the treatment of borate and silicate of alumina; alumina being always added
in excess so as to restore the initial or original composition of the cryolite bath.
Manufacture of aluminium bronze. This manufacture consists in the electro-
Jysis of alumina melted in presence of copper. The crucible a, is then placed
on a carbon conducting plate p, which conducts the negative pole of the current
to the crucible and the positive carbon c, (which is movable in a vertical direction,
by aid of a screw or otherwise) is plunged in the centre of the crucible.
The crucible is surrounded with powdered retort charcoal 7 which insulates it
from contact with the air and prevents its becoming cold.
b, b', are bricks serving as cover to the crucible and guide to the vertical car-
bon e, m is the brick coffer in which the crucible with its case of powdered retort
charcoal is held. The melted copper is at c, the molten alumina at A and the un-
melted at A¹ this latter forms a cover which resists cooling. If an electric
current of great intensity is passed through this, the aluminium produced is
borne to the copper. The operation lasts as long as aluminium is added and the
metal obtained does not become lighter than the molten alumina.
The electric current produces sufficient heat to keep the alumina in fusion,
the quantity of cryolite can then be reduced and even do without it, the tem-
perature being sufficient to keep the alumina in a partially liquid state without
absolutely melting.
In the same manner aluminium is alloyed with iron or silicium or silicon.
Aluminium and silicium are alloyed by the decomposition of silicate of alumina
in place of pure alumina.

page_text: COMPLETE SPECIFICATION (AMENDED).
An Improved Process for the Preparation of Aluminium by
Electrolysis.
I, ARTHUR CHARLES HENDERSON, of 46, Southampton Buildings, Holborn, in
the County of Middlesex, and of 31, Lincoln Place, Leinster Street, Dublin,
Patent Agent, do hereby declare the nature of this invention (which has been
communicated to me from abroad by Paul Louis Toussiant Heroult, Metallurgist,
of the City of Paris, in the Republic of France) and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement :-
According to this invention aluminium is produced from alumina by electro-
lysis as I will hereinafter describe, cryolite being used as a flux in fusing the
alumina to be electrolysed.
In connection with a crucible of agglomerated carbon a positive electrode or
anode is provided the crucible itself forming a negative electrode or cathode;
cryolite in the crucible forms a bath into which dips the positive electrode which
is of carbon.
With this combination alumina being placed in the crucible and a current of
low tension being employed the alumina is decomposed; the oxygen passes to
the positive electrode or anode with which it is burnt while aluminium settles
upon the walls of the crucible forming the negative electrode or cathode and
settles on the bottom of the same in a metallic form or mass.
The bath of cryolite remains constant and may be used in a continuous manner
alumina being fed in as required; combustion will take place of the positive
electrode or anode whereby polarization will be prevented, and a constant energy
and uniform action of the electric current will result, care being taken to renew
the said electrode from time to time as required. The combustion of the positive
electrode by the oxygen disengaged from the reduced oxide diminishes the quantity
of electrical energy required to heat the bath and causes the production of an
electric current in the same direction as
the principal electrolysing current
thereby further economizing electrical energy.
For the purpose of enabling this part of the invention to be clearly understood
reference is had to Fig. 1 of the drawings filed with my Provisional Specification,
which it is to be understood is intended merely as explanatory of the invention
and represents a vertical section of au apparatus adapted for the production of
aluminium according to my invention.
a is a crucible containing the bath of cryolite (natural fluoride of aluminium
and sodium); it is formed of very dense and well conducting agglomerated carbon.
It is placed within another crucible b made of graphite or plumbago and resting
upon a circular or other base plate or support c of any suitable material inter-
posed between it and the furnace grate. e e¹ are pencil shaped agglomerated
carbon rods of which e serves as the positive electrode or anode. This positive
electrode is arranged centrally within the crucible a and dips into the bath. The
carbon rod e¹ is in direct contact with the crucible which serves as the negative
electrode or cathode. The carbon rods e c¹ which are insulated from each other
rise above the arch of the furnace and are protected from the action of air and
fire by stone-ware tubes d d'.
A conductor is connected to the positive electrode or anode e and a con-
ductor is attached to the carbon e¹; these conductors ff are connected with
an electric generator of suitable power and low tension.
The crucible a is closed by a lid g made of refractory material such as calcined
magnesia or of clay, and through which the positive electrode or anode e passes.

page_text: Over this cover is placed a layer of grout of fire clay h which is finally covered
with a mass of suitable material such as vegetable mould or loam.
i is the flue and the the charging door of the furnace by which the crucibles a
and bare heated.
When the cryolite to which alumina has been previously added, is in a molten
state an electric current is sent through it and the alumina electrolysed.
The oxygen evolved from the alumina unites with the positive electrode or
anode e, which being brought to a high temperature combines with the oxygen
and forms oxide of carbon which escapes through the tube d. The tube d¹ is kept
closed to prevent the entrance of air. The aluminium reduced from the alumina
passes to the cathode, that is to say to the internal walls of the crucible a, where
it first settles and then falls to the bottom of the crucible where it finally forms a
metallic mass.
The cryolite remains unchanged. To render the production of metal continuous
alumina must be added from time to time as required to replace that previously
decomposed.
For the successful and practical carrying out of this part of the invention a
current of three volts has been found sufficient; this results in a considerable
saving of electrical energy as compared with the processes at present in use and
which invariably require currents of at least ten times greater tension. T'he
reason for this is that in my improved process the carbon of the positive electrode e
while it burns, yields an amount of heat which is not necessary to be supplied by
the electric current. For three equivalents of positive carbon electrode consumed
two equivalents of aluminium are obtained.
For the purpose of enabling the operator to know the condition of matters with
respect to the distance apart of the electrodes an ampere meter is inserted in the
circuit and by watching it the operator can tell whether the proper distance
between the electrodes is being maintained, as if not the needle of the meter will
.be affected.
If the needle has slight oscillations or deflections alumina must be added, and
the positive electrode must be slightly raised until such indications cease to be
given by the meter.
For the treatment of alumina by electrolysis on a commercial scale according
to this invention it will usually be more advantageous to use apparatus such as
described in the Specification of an application for Letters Patent No. 10853,
dated 7th December 1887, by William Lloyd Wise, for an invention of "Improve-
ments in Apparatus for Producing Aluminium and other Metals and their Alloys
and operating the same communicated to him from abroad by The Schweize-
rische Metallurgische Gesellschaft; but it is to be noted that the said invention
is not claimed herein as forming any part of the invention, the subject matter of
the application for Letters Patent to which the present specification relates.
Having now particularly described the nature of this invention and in what
manner the same is to be performed, I hereby declare that I am aware metal has
been melted in vessels by electricity without the application of external heat, the
metal so melted serving as one pole of the electric circuit; also that cryolite has
been melted and electrolytically decomposed for the production of aluminium by
the passage of an electric current therethrough and between positive and negative
carbon electrodes without the application of external heat; also that it has been
proposed to produce alloys of aluminium by the electrolytical decomposition of an
aluminium compound rendered fusible by the use of a flux, the said aluminium
compound and flux and also the metal intended to be alloyed with the reduced
aluminium being intended to be melted by the application of external heat to
the vessel containing them. I am likewise aware that it has been proposed to
employ carbon lined crucibles in the production of aluminium. And I desire to
have it noted that I do not claim broadly the melting and electrolytical decom-
position of metallic compounds by the aid of electricity without the application

page_text: of external heat for the production of metallic alloys or compounds, neither do
I claim broadly the use of a molten metal negative electrode formed of one of the
alloying metals or the use of a carbon metal crucible, but what I do claim is :-
1. The production of aluminium from alumina by the herein before described
electrolytic process using cryolite as a flux in fusing the alumina to be electrolysed.
51
C Manch 1000
A. C. HENDERSON