Improved Process for the Production of Pure Aluminium.
Year: 1890

page_text: Date of Application, 27th Aug., 1890
Complete Specification Left, 28th Oct., 1890-Accepted, 28th Mar., 1891
PROVISIONAL SPECIFICATION.
Improved Process for the Production of Pure Aluminium.
We, AUGUST SCHNELLER and ALFRED ASTFALCK, both of Cologne on the
Rhine, Germany, Engineers, do hereby declare the nature of this invention to be
as follows:-
This invention relates to the production of pure aluminium on a manufacturing
scale from natural or artificially prepared aluminium compounds.
The requisite heat for the reduction of the aluminium compounds is produced
by means of high tension electrical energy derived from secondary generators.
The high tension electrical energy is requisite because the compounds to be
reduced possess a very high electrical resistance and also in order to offer to the
reducing gases the greatest possible extent of surface of the material when heated
to the reducing temperature.
The reduction of the metal is effected by means of hydrogen, or gases containing
hydrogen, which, as they expand with considerable force at the high temperature
employed, are forced by suitable known means with sufficient pressure into the
reducing chamber of the furnace.
The vapours passing off at a high temperature can be utilised for the preliminary
heating of the reducing gases in order,that these may not lower the temperature
of the furnace to a detrimental extent on entering.
Dated this 27th day of August 1890
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Improved Process for the Production of Pure Aluminium.
We, AUGUST SCHNELLER and ALFRED ASTFALCK, both of Cologne on the
Rhine, Germany, Engineers, do hereby declare the nature of this invention, and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement :-
This invention relates to the production of pure aluminium on a manufacturing
scale from natural or artificially prepared aluminium compounds.
The processes heretofore employed for the production of aluminium have the
defect that no pure aluminium is obtained directly in the reduction furnace, and
that the capability of production in a single furnace is very limited.
The present invention has for its object to obviate these defects.
Pure aluminium can be obtained according to the formulae :
if the raw materials Al₂ O₂, Al, S, Al, Cl, and Al, Fl, are reasonably pure, as all the
substances combined with aluminium in these compounds, combine with hydrogen
to form compounds which do not render the aluminium obtained impure.
For the purpose of reducing compounds containing aluminium by means of
hydrogen, or gases containing hydrogen, the reducing gas must be affordedá
sufficiently large surface of the material to be acted upon, heated to the reduction
5 temperature. This temperature is, with nearly all aluminium compounds, higher

page_text: than that which can be obtained by means of carbon; but also, in the reduction of
Al, S, by means of H or gases containing H, the vessels if heated externally, will very
soon be destroyed, so that a manufacture on a large scale by this means is not
practicable.
If electrical energy of comparatively low tension be used for the production of
the reduction temperature, the aluminium compounds which have a very high
resistance to conduction, must be mixed with a conducting material, such as carbon,
which can then serve as reducing medium. In this case however the aluminium
which melts out will be rendered largely impure, partly by the carbon, partly by
foreign constituents of the aluminium compounds or of the carbon, such as silicon,
and additional operations must be resorted to for purifying the metal.
In order to obviate these defects, that is to say, in order to obtain the necessary
reduction temperature within the furnace, to afford the reducing gases a sufficiently
extended acting surface, and to obtain the melting aluminium in a pure state, we,
according to our present invention employ electrical energy of high tension, such
as from ten to twenty thousand volts, or even higher, which can hardly be produced
by primary generators, and which are therefore most suitably obtained from the
secondary circuits of transformers or induction apparatus.
On the accompanying drawing is shewn by way of example a diagrammatic
vertical section of a construction of apparatus for carrying out our invention.
r. s. is the furnace, a a the conductors for producing the electric arc b; c is the
primary generator, d the transformer, e the secondary circuit thereof in which a
current of from 20,000 to 30,000 volts is passed to the conductors a a.
For preventing the metal from being rendered impure by the melting away of
the current conductors a, these are made of bars of aluminium. If these bars a
be moved towards each other while the above high tension current is passing, a
direct passage of the current from the one pole to the other will occur already,
when these are at some distance from each other. By the degree of resistance of
the resulting are a direct short circuiting is prevented.
The furnace having been filled from the top of the shafts with the aluminium
compound to be treated, the said electric current is passed through the conductors a a.
By means of the heat thus produced the material in contact with the arc will be
melted or even vaporised and will thus be brought to the reduction temperature.
The electrical energy will pass more readily through the aluminium compounds
thus heated, as the melted or vaporised materials will have a less electrical
resistance, so that the aluminium bars a can be moved farther apart, but only so
far as will allow of the reduction temperature being maintained; this can be
effected by hand or by any suitable known mechanism, such as by toothed pinions t
gearing with racks on the holders of the bars a.
It is not necessary to employ a flux; it would form a slag, and have a prejudicial
effect. If now hydrogen, or reducing gases containing hydrogen be forced into
the reducing chamber from h, aluminium will be separated by melting, and as it is
lighter than or hardly as heavy as the aluminium compounds, it will collect with
these on the bottom of the chamber or in the front chamber.
When reducing pure aluminium compounds by means of hydrogen, only molten
aluminium will flow into the chamber v (the slide m being open) while the other
constituents will be vaporised and pass away with the excess of the reducing
gases containing hydrogen through the shaft s.
If on the other hand the heat of the electric arc should cause a certain portion of
the aluminium compounds to be melted down without being at the same time
reduced these would collect in the form of slag in the chamber v, together with the
aluminium, and would have to be removed either through the same opening
through which the aluminium is run off, or if, owing to the lower temperature of the
chamber, the said unreduced compounds should solidify, they would have to be
removed from time to time through a side door.
The aluminium would still remain liquid at such temperature and would be run
off through the opening n as before. If the aluminium passes in the form of vapour

page_text: from the reducing chamber r as is probable, it will condense in the upper colder
layers in the shaft s, and will flow down again, as there is sufficient room for this
purpose in the reducing chamber r. At the same time a purification of the
aluminium can be effected by the hydrogen either within or without the reducing
chamber, for example in the front chamber v, on closing the slide m, and opening
the escape orifice K, as the silicon contained in nearly all aluminium compounds
can escape in the form of vapour as Si H., simultaneously with the other escaping
vapours passing off through the shafts, and which, according to the material
operated upon, will be H Cl, S H₂, Fl H or H, O; the Si H, will pass off with
excess of H.
These gases and vapours heat the still unreduced material in the furnace shaft s
and then escape through the chimney flue.
Outside the furnace the escaping gases can be separated from excess of hydrogen
by washing, condensing, treating with alkali, or other suitable means, so that the
excess of H can be again used.
The aluminium that collects at the bottom of the reducing chamber r or of the
front chamber v is withdrawn from time to time through the opening n.
Having thus described the nature of this invention, and in what manner the
same is to be performed, we declare that what we claim is :-
For the production of pure aluminium from natural or artificial aluminium
compounds, the herein described process, in which the heat necessary for reduction
of the compounds is obtained by electrical energy of high tension derived from the
secondary circuit of induction apparatus, while at the same time the reduction of
the compounds is effected by hydrogen or gases containing hydrogen.
Dated this 28th day of October 1890.
ABEL & IMRAY,
Agents for the Applicants.