Improvements in the Reduction or Treatment of Refractory Metallic Compounds by Electric Smelting.
Year: 1892

page_text: Date of Application, 28th Nov., 1892
Complete Specification Left, 24th Aug., 1893-Accepted, 30th Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Reduction or Treatment of Refractory Metallic
Compounds by Electric Smelting.
I, THOMAS LEOPOLD WILLSON, of Leaksville, in the County of Rockingham,
and State of North Carolina, United States of America, Electrician, do hereby
declare the nature of the said invention for "IMPROVEMENTS IN THE REDUCTION
OR TREATMENT OF REFRACTORY METALLIC COMPOUNDS BY ELECTRIC
SMELTING to be as follows:-
33
This invention relates to the reduction of aluminium and other difficultly
reducible metals from refractory ores or compounds thereof by means of electric
smelting.
Electric smelting, or metallurgical reduction by means of electrically generated
heat, has heretofore been performed in two ways, namely, by an incandescent
furnace heated by the passage of an electric current through a mass of broken
carbon, the heat being generated by the resistance which this poor conductor
presents to the passage of the electric current; and in an arc furnace wherein
the heat is generated by the passage of an electric current across an arc between
two separated electrodes. In the former or incandescent furnace, the current is
passed horizontally between two carbon bars or electrodes, the space between
them being filled with a mixture of broken carbon and the ore to be reduced,
and with a base metal, as copper. Such furnaces are subject to the practical
disadvantage that as the base metal fuses a pool or bath is formed extending
between the electrodes and serving to short-circuit them around the mass of
material to be reduced, which necessitates the continual drawing apart of the
electrodes in order to maintain the necessary resistance in the furnace. This
difficulty is in great measure overcome by the use of an arc furnace in which
the current passes vertically between two electrodes, one of which consists of a
carbon or graphite crucible or hearth, and the other a carbon bar or pencil above
and entering the hollow of the crucible or hearth. The pencil being lowered
into contact with the crucible or an intervening conducting material, is raised
out of contact therewith to produce an arc, the heat of which performs the
reduction of the material placed in the crucible. As reduction in an arc furnace
was practiced prior to my present invention, the alumina or other refractory ore
is fused by the heat of the arc and covers the bottom of the crucible in a molten
pool or bath. In the direct manufacture of bronzes or other alloys the base
metal thereof forms a pool at the bottom of the crucible, and the molten alumina
or other ore lies in a bath superposed thereupon. The carbon pencil is kept
elevated out of direct contact with the bath of alumina in order to maintain the
A reducing agent being present in the furnace, either by introducing a
reducing atmosphere therein, or by the utilization of the carbon of the electrodes
as such agent, the reduction of the alumina or other metallic compound is effected
by the combined action of the electric arc and the reducing agent.
When a
base metal is present it combines with the reduced metal forming an alloy.
arc.
In the operation of such an electric arc furnace, considerable practical difficulty
is experienced by reason of the sudden and violent fluctuations in the resistance
of the furnace, which occur by reason of the ebullition of the fused bath. The
fused alumina or other ore or metallic compound, being a much better electric
conductor than the vaporous medium of the arc, must be kept out of contact.
with the carbon pencil in order to maintain an arc. By the ebullition of this
fused bath, the liquid alumina or other ore is caused to spatter, or spout, or
foam, upwardly at frequent irregular intervals, into contact with the carbon

page_text: pencil, thereby to a great extent short-circuiting the arc and lowering the resis-
tance of the furnace. In practice, it is found that this boiling up of the alumina
produces a short-circuit of such very low resistance as to seriously affect the
operation of the dynamo by which the current is generated.
The object of my present invention is to overcome the practical difficulties
arising from the presence in the furnace of a fused bath of the ore or compound
under treatment. In the course of numerous experiments that I have made, and
the use of various reducing agents, I have discovered that finely subdivided or
pulverized carbon when commingled with the alumina or other metallic compound
to be reduced, and in sufficient proportions, has the effect of preventing the
formation of a bath of the fused metallic compound.
My present invention
therefore consists in subjecting alumina or other refractory metallic compound to
the continued heat of an electric arc while commingled with subdivided carbon
in sufficient proportion to prevent the formation of a bath of the fused compound.
The violent fluctuations in the resistance of the arc due to the ebullition of such
a bath are consequently avoided, and the resistance of the arc is rendered so
nearly uniform as to render the smelting process of practical operation in
connection with existing means for generating the requisite heavy electrical
currents.
No
In the practice of my process I may use for example such an electric furnace as
that shown in the drawing of my British Patent No. 4757 dated March 17, 1891.
After first preferably heating up the furnace by passing the electric current
through it to form an arc, some alumina (or other refractory metallic compound
to be reduced) thoroughly commingled or intermixed with finely divided or
pulverized carbon, is introduced into the furnace. The carbon pencil is kept
elevated sufficiently to maintain the arc. The reduction then proceeds.
fused bath is formed, and consequently no ebullition occurs within the crucible.
The presence of the subdivided carbon appears to have the effect of maintaining
the subdivision of the alumina as the latter becomes fused, and perhaps to some
extent of absorbing it, the alumina being thus held by the carbon until the
intense heat of the arc effects the dissociation of its oxygen, which is taken up
by the carbon, forming carbon monoxide or dioxide, which flows out of the
furnace, leaving the aluminium free. Upon the interruption of the process while
the reduction is at its height, and the immediate cooling down of the furnace,
no cake of solidified alumina is found such as would result from the presence of
a molten bath; but on the contrary the material in the furnace is found in
apparently the same condition as before its introduction into the furnace, being
a powdered or granulated alumina interniixed or impregnated with carbon, and
ordinarily not even agglomerated by the heat.
In the reduction of aluminium by this method, the aluminium freed within the
furnace must be recovered in some way before it can escape into contact with
the air and be oxidized. The particular means for recovering the aluminium
forms no essential part of my present invention, but there are two methods which
as I believe may be used for this purpose. Of these, the first is to introduce a
base metal into the furnace to instantly alloy with the nascent aluminium as it
is freed, this being the method commonly heretofore employed. The second
method is to have an excess of carbon in the crucible sufficient to combine with
the nascent aluminium, forming an aluminium carbide, from which the metal may
be subsequently extracted.
The result of suppressing the fused bath and consequent ebullition will not be
attained unless the carbon commingled with the ore or compound under treat-
ment be in sufficient proportion. The proportion required will vary according
to the condition of the cre and carbon, varying with their fineness and the
degree of intimacy of their admixture. When alumina is used in the form of
a fine powder, and the carbon is combined with it with the utmost intimacy by
impregnating the alumina with the carbon, I have found that an amount of
carbon equal by weight to fifteen per cent. of the mixture, is sufficient to prevent

page_text: the formation of a fused bath. If the material is in coarser form, and less
intimately commingled, a larger percentage of carbon may be required. I prefer
to use alumina or other ore or compound impregnated with coal tar or other
suitable heavy hydro-carbon, by stirring powdered or granulated alumina or other
metallic compound into the tar or other hydro-carbon while the latter is main-
tained in the liquid state, preferably by being heated, until the alumina etc. is
thoroughly impregnated with the hydro-carbon, and thereupon driving off the
hydrogen and lighter hydro-carbons by heat until the whole is reduced to a dry
powder.
In practicing my process for the production of aluminium bronze, I find it
preferable after initially heating up the furnace, to first introduce the copper,
which instantly fuses and forms a pool of molten base metal in the bottom of the
crucible, and thereafter to introduce the tar impregnated alumina, or intermixed
alumina and powdered carbon as the case may be, lifting the carbon pencil
sufficiently to maintain the arc. The copper, and the alumina and carbon, are
preferably introduced in small quantities or charges and at frequent intervals,
and preferably in alternation.
I contemplate applying my invention in connection with the reduction of other
metals than aluminium. I believe it to be applicable to the reduction of the
following metals among others, namely, barium, calcium, manganese, strontium,
imagnesium, titanium, tungsten, and zirconium. In the manufacture of bronzes, I
propose to apply it to the manufacture of bronzes containing silicon and boron.
My invention is applicable to other chemical reactions than those included by
the word "reduction" used merely in its metallurgical sense; for example, I
propose to apply it for the treatment of refractory compounds or ores of metals, not
necessarily for the production of the metals themselves, but for the production of
other compounds thereof.
Dated this 28th day of November 1892.
J. C. MEWBURN,
55 & 56, Chancery Lane, London, Chartered Patent Agent.
COMPLETE SPECIFICATION.
Improvements in the Reduction or Treatment of Refractory Metallic
Compounds by Electric Smelting.
I, THOMAS LEOPOLD WILLSON, of Leaksville, in the County of Rockingham,
and State of North Carolina, United States of America, Electrical Engineer, 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 :-
This invention relates to the reduction of aluminium and other difficultly
reducible metals from refractory ores or compounds thereof by means of electric
smelting.
Electric smelting, or metallurgical reduction by means of electrically generated
heat, has heretofore been performed in two ways, namely, by an incandescent
furnace heated by the passage of an electric current through a mass of broken
carbon, the heat being generated by the resistance which this poor conductor
presents to the passage of the electric current ; and in an arc furnace wherein the
heat is generated by the passage of an electric current across an arc between two
separated electrodes. In the former or incandescent furnace, the current is passed
horizontally between two carbon bars or electrodes, the space between them being
filled with a mixture of broken carbon and the ore to be reduced, and with a base
metal, as copper. Such furnaces are subject to the practical disadvantage that as
the base metal fuses a pool or bath is formed extending between the electrodes and
serving to short-circuit them around the mass of material to be reduced, which

page_text: necessitates the continual drawing apart of the electrodes in order to maintain the
necessary resistance in the furnace.
This difficulty is in great measure overcome by the use of an arc furnace in which
the current passes vertically between two electrodes, one of which consists of a
carbon or graphite crucible or hearth, and the other a carbon bar or pencil above
and entering the hollow of the crucible or hearth. The pencil being lowered into
contact with the crucible or an intervening conducting material, is raised out of
contact therewith to produce an arc, the heat of which performs the reduction of
the material placed in the crucible. As reduction in an are furnace was practiced
prior to my present invention, the alumina or other refractory ore is fused by the
heat of the arc and covers the bottom of the crucible in a molten pool or bath.
In the direct manufacture of bronzes or other alloys the base metal thereof forms
a pool at the bottom of the crucible, and the molten alumina or other ore lies in a
bath superposed thereupon. The carbon pencil is kept elevated out of direct
contact with the bath of alumina in order to maintain the arc. A reducing agent
being present in the furnace, either by introducing a reducing atmosphere therein,
or by the utilization of the carbon of the electrodes as such agent, the reduction of
the alumina or other metallic compound is effected by the combined action of the
electric arc and the reducing agent. When a base metal is present it combines
with the reduced metal forming an alloy.
In the operation of such an electric arc furnace, considerable practical difficulty
is experienced by reason of the sudden and violent fluctuations in the resistance of
the furnace, which occur by reason of the ebullition of the fused bath. The fused
alumina or other ore or metallic compound, being a much better electric conductor
than the vaporous medium of the arc, must be kept out of contact with the carbon
pencil in order to maintain an arc. By the ebullition of this fused bath, the liquid
alumina or other ore is caused to spatter, or spout, or foam, upwardly at frequent
irregular intervals, into contact with the carbon pencil, thereby to a great extent
short-circuiting the arc and lowering the resistance of the furnace. In practice,
it is found that this boiling up of the alumina produces a short-circuit of such very
low resistance as to seriously affect the operation of the dynamo by which the
current is generated. Whenever such a short-circuit is formed, the quantity of the
current is increased in proportion as the resistance is lowered, thereby throwing a
greatly increased load or work upon the dynamo, the practical effect of which is to
tend to instantly stop its rotation, thereby subjecting the dynamo and the motive
power which drives it, as well as the belt or other intermediary through which the
power is transmitted, to a severe shock, these shocks following each other in such
rapid and irregular succession as to be extremely injurious and detrimental to the
machinery. There is furthermore great liability of burning out the armature of
the dynamo by reason of the excessive current, even in the case of dynamos whose
armatures are constructed to carry currents of extraordinary volume such as must
be used for electro-metallurgical work. This short-circuiting of the arc is perhaps
partly due to the boiling up of the copper or other base metal through the bath of
alumina or other ore when, as in the making of aluminium bronze, such a base metal
is present in the furnace; but the same difficulty is experienced, and to nearly or
quite the same degree, when no base metal is present in the furnace, and when
consequently the only fluid bath is that of the alumina or other ore under
treatment.
The object of my present invention is to overcome the practical difficulties
arising from the presence in the furnace of a fused bath of the ore or compound
under treatment. In the course of numerous experiments that I have made, and
the use of various reducing agents, I have discovered that finely subdivided or
pulverized carbon when commingled with the alumina or other metallic compound
to be reduced, and in sufficient proportions, has the effect of preventing the
formation of a bath of the fused metallic compound. My present invention
therefore consists in subjecting alumina or other refractory metallic compound
to the continued heat of an electric arc while commingled with subdivided carbon

page_text: in sufficient proportion to prevent the formation of a bath of the fused compound..
The violent fluctuations in the resistance of the arc due to the ebullition of such a
bath are consequently avoided, and the resistance of the arc is rendered so nearly
uniform as to render the smelting process of practical operation in connection with
existing means for generating the requisite heavy electrical currents. Such
fluctuations as occur are so trifling in extent, and so gradual, that the machinery
is subjected to no injurious strains. The smelting process is also rendered more
economical because it is conducted more regularly and progressively, is subject
to less interruption by reason of the slowing down of the dynamo, such as results
from the occurrence of a serious short-circuit, and is consequently effected by the
maximum current that the dynamo can generate under the requisite resistance of
the furnace.
In the practice of my process I may use for example such an electric furnace
as that shown in the drawing of my British Patent No. 4757 dated March 17, 1891.
The preferred construction and proportions of such furnace are those shown in
the accompanying drawing, which is a vertical mid-section, the electric connections
and the dynamo being shown diagrammatically.
Let A designate the outer masonry shell or bench of the furnace, B the carbon
or graphite crucible or hearth, C the carbon bar or pencil constituting the movable
electrode, and D the dynamo for generating the currents. From the terminal
brushes of this dynamo, one wire w leads to and communicates with the crucible B,
while the other wire w¹ leads to and communicates with the carbon pencil C. The
connections are preferably made in the manner shown, the wire w being connected
through a fastening bar a to an iron plate 6 underlying the crucible B, and
the wire w¹ being connected to a metal socket c embracing the upper end of the
carbon pencil C. The bench A is made preferably of firebrick, which is a non-
conductor of electricity, and the furnace is covered over with a plate, or preferably
two plates E E of carbon, having a central hole through which the carbon pencil Č
projects down into the crucible.
For tapping out the resulting product, a tap-hole d is formed which in operation
is closed by a plug e of alumina, clay, or other suitable refractory material. The
carbon plates E E rest on the top of the firebrick walls A, which project above
the top of the crucible, forming an intervening space for insulating purposes to
prevent the short-circuiting of the furnace between B and E.
For the vertical adjustment of the carbon pencil, a screw-threaded shaft g is
provided which may be propelled up and down by the engagement therewith of a
suitably mounted rotative nut h. The details shown, however, are not essential to
my invention, which may be applied in connection with furnaces widely different
from that shown.
After first preferably heating up the furnace by passing the electric current
through it to form an arc, some alumina (or other refractory metallic compound to
be reduced) thoroughly commingled or intermixed with finely divided or pulverized
carbon, is introduced into the furnace through a top opening i. The carbon pencil
is kept elevated sufficiently to maintain the arc. The reduction then proceeds.
No fused bath is formed, and consequently no ebullition occurs within the crucible.
The presence of the subdivided carbon appears to have the effect of maintaining
the subdivision of the alumina as the latter becomes fused, and perhaps to some
extent of absorbing it, the alumina being thus held by the carbon until the intense
heat of the arc effects the dissociation of its oxygen, which is taken up by the
carbon, forming carbon monoxide or dioxide, which flows out of the furnace,
leaving the aluminium free. Upon the interruption of the process while the
reduction is at its height, and the immediate cooling down of the furnace, no cake
of solidified alumina is found such as would result from the presence of a molten
bath; but on the contrary the material in the furnace is found in apparently the
same condition as before its introduction into the furnace, being a powdered or
granulated alumina intermixed or impregnated with carbon, and ordinarily not even
agglomerated by the heat.

page_text: :
In the reduction of aluminium by this method, the aluminium freed within the
furnace must be recovered in some way before it can escape into contact with the
air and be oxidized. The particular means for recovering the aluminium forms no
essential part of my present invention, but there are two methods which as I
believe may be used for this purpose. Of these, the first is to introduce a base
metal into the furnace to instantly alloy with the nascent aluminium as it is freed,
this being the method commonly heretofore employed. The second method is to
have an excess of carbon in the crucible sufficient to combine with the nascent
aluminium, forming au aluminium carbide, from which the metal may be subsequently
extracted.
The result of suppressing the fused bath and consequent ebullition will not be
attained unless the carbon commingled with the ore or compound under treatment
be in sufficient proportion. The proportion required will vary according to the
condition of the ore and carbon, varying with their fineness and the degree of
intimacy of their admixture. When alumina is used in the form of a fine powder,
and the carbon is combined with it with the utmost intimacy by impregnating the
alumina with the carbon, I have found that an amount of carbon equal by weight
to fifteen per cent. of the mixture, is sufficient to prevent the formation of a fused
bath. If the material is in coarser form, and less intimately commingled, a larger
percentage of carbon may be required. I prefer to use alumina or other ore or
compound impregnated with coal tar or other suitable heavy hydro-carbon, by
stirring powdered or granulated alumina or other metallic compound into the tar or
other hydrc-carbon while the latter is maintained in the liquid state, preferably by
being heated, until the alumina, etc. is thoroughly impregnated with the hydro-
carbon, and thereupon driving off the hydrogen and lighter hydro-carbons by heat
- until the whole is reduced to a dry powder. This tar-impregnated alumina is the
subject of my application for Patent No. 21,696, dated November 28, 1892.
lieu thereof, however, comminuted alumina or other metallic compound to be
reduced, and powdered or comminuted carbon may be mechanically mixed and
introduced together into the furnace.
In
In practising my process for the production of aluminium bronze, I find it
preferable after initially heating up the furnace, to first introduce the copper,
which instantly fuses and forms a pool of molten base metal in the bottom of the
crucible, and thereafter to introduce the tar impregnated alumina, or intermixed
alumina and powdered carbon as the case may be, lifting the carbon pencil
sufficiently to maintain the arc. The copper, and the alumina and carbon, are
preferably introduced in small quantities or charges and at frequent intervals, and
preferably in alternation.
My present invention is not applicable to incandescent furnaces, that is to say,
those in which the heat is generated by passing a current through a broken
resistance material, such as retort carbon, and I specifically disclaim its application
to such furnaces. My invention is applicable only where the heat is derived from
the electric are. The conditions essential to the maintenance of such an arc, in an
electric furnace, are well understood in the art. The arc is caused by the separation
of the electrodes, thereby forming an interruption in the circuit, and to maintain
the arc, at least one of the electrodes must be maintained out of contact with any
conducting material in the furnace of such low resistance as to shunt sufficient
current around the arc to extinguish the arc. In any case the arc is formed and
maintained close over the material under treatment, or at least close over such
portion of the material as is immediately under treatment. The best arrangement
for producing an arc is that shown, wherein the current passes in vertical direction
through a furnace, the crucible constituting one electrode, and a carbon pencil
thrust into it constituting the other. Other arrangements, however, are admissible,
although believed to be inferior.
I contemplate applying my invention in connection with the reduction of other
metals than aluminium. I believe it to be applicable to the reduction of the
following metals among others, namely, barium, calcium, magnesium, strontium,

page_text: manganese, titanium, tungsten, and zirconium. In the manufacture of bronzes, I
propose to apply it to the manufacture of bronzes containing silicon and boron. My
invention is applicable to other chemical reactions than those included by the word
"reduction" used merely in its metallurgical sense; for example, I propose to
apply it for the treatment of refractory compounds or ores of metals, not necessarily
for the production of the metals themselves, but for the production of other
compounds thereof.
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. The process of reducing or treating refractory metallic compounds, which
consists in subjecting the compound to the continued heat of an electric arc
maintained above the material immediately under treatment, while the compound is
commingled with subdivided carbon in sufficient proportion to prevent the formation
of a bath of fused compound, in substantially the manner specified, whereby during
the operation the fluctuations in the resistance of the arc which would be due to
the presence and ebullition of such bath are avoided.
2. The process of reducing refractory metallic compounds which consists in
subjecting the compound, while commingled with subdivided carbon in sufficient
proportion to prevent the formation of a bath of fused compound, to the continued
heat of an electric arc produced by passing a current in approximately vertical
direction between separated electrodes, one of which is above the material
immediately under treatment substantially as herein before described so that the
arc is maintained close above such material, whereby during the reduction the
fluctuations in the resistance of the arc which would be due to the presence and
ebullition of such bath are avoided.
3. The process of reducing alumina which consists in subjecting it, while
commingled with subdivided carbon in sufficient proportion to prevent the formation
of a bath of fused alumina, to the continued heat of an electric arc between
separated electrodes one above the other, so that the arc is maintained close above
the material immediately under treatment, substantially as herein before described
whereby during the reduction the fluctuations in the resistance of the arc which
would be due to the presence of such bath are avoided.
4. The process of reducing a refractory metallic compound which consists in
commingling therewith a sufficient proportion of finely subdivided carbon as
described, feeding the mixture into an electric arc, maintained between vertically
separated electrodes, and maintaining it subject to the continued heat of such arc,
and so that the arc is maintained close above the material immediately under
treatment, whereby the formation of a bath of the fused compound is avoided,
substantially as set forth.
Dd this 1 dove of August 1802
J. C. MEWBURN,
55, Chancery Lane, London, Chartered Patent Agent.