Improvements in the Process of Manufacturing Carbons for Electrical and Electro-chemical and other purposes.
Year: 1899

page_text: Date of Application, 29th Nov., 1899
Complete Specification Left, 23rd July, 1900-Accepted, 8th Sept., 1900
Improvements in the Process of Manufacturing Carbons for Electrical
and Electro-chemical and other purposes.
I, EDUARD POHL, of Kalk, near Cologne, Prussia, Germany, Engineer, do
hereby declare the nature of this invention to be as follows:-
The present invention relates to the manufacture of carbon bodies for elec-
trical and electro-chemical and other purposes, such as pencils for electrical
lamps, contacts for generators, motors, interrupters and the like, microphonic
contacts, electrodes for electrolytical cells etc., and its object is to improve
that step in said manufacture which is commonly understood by the term
“graphitising."
It is well known that carbon bodies in order to be fit for use in electrical and
electro-chemical appliances must combine high density with great strength,
and to obtain this the bodies are subjected to what is called graphitising'
which term means treating the carbon bodies by the action of heat and, filling
up their pores by the deposition therein of carbon.
It has been found a long time ago that the carbon deposit forming on the
inside of the retorts in which coal subjected to the process of destructive dis-
tillation, by virtue of its specific molecular condition answers very well the
requirements as to density and strength. This peculiar condition of the so-
called gas-retort carbon is due to the fact that the incandescent deposit once
formed, is constantly in contact with, and penetrated by part of the hot gases
generated within the retort, which part of the gases by its intimate contact
with the incandescent deposit is caused to dissociate, the carbon molecules thus
set free being deposited in the pores and upon the surface of the deposit
and welded together with the same, so to say. The result is a very dense and
strong carbon having somewhat of the nature of the graphitic modification.
As gas-retort carbon requires a long time for forming and, moreover, is obtain-
able in comparatively small pieces only attempts have been made to imitate
its forming process, so as to produce in a short time. One way is to make a
carbon body, impregnate the same with hydrocarbons, embedding such impreg-
nated body in coal dust and subjecting it to the action of heat with exclusion
of the outer air. Another way is to heat the carbon body in an atmosphere
containing hydrocarbons. The result of either of these processes has proved to
be unsatisfactory, as is clearly evidenced by the fact that at present attempts
are made to improve the strength and density by an admixture of metallic
compounds to the carbon.
I have discovered that in order to obtain a perfect effect as to the filling up
of the pores of the body and its conversion to the desired modification of carbon,
the carbon yielding gas must not be generated within the body itself nor
caused to act on a naked body, but that the body requires to be embedded in
a mass of reduced coal which is impregnated with an atmosphere of said gas,
in other terms, the body has to be enclosed in an intimate mixture of carbon
particles and carbon yielding gas. When, under these conditions, a sufficiently

page_text: high degree of heat is applied from the outside, a very copious transfer or
immigration of carbon molecules is caused to take place from the enclosing
mixture of solid carbon particles and carbon yielding gas into the enclosed
body, the molecules of the latter uniting with the immigrating molecules and
the nature of the body being thoroughly modified. That is to say, the body has
imparted to it such a degree of density, strength, and hardness as are in no
wise obtainable by applying either of the known processes. Carbon bodies
treated according to this improved method will answer with a metallic sound
when struck by means of a hard object; their density is great; their hardness
is such as to withstand the action of the best qualities of emery, and their
colour is by far brighter than that of the best carbons in the market. There is,
however, a serious defect in that the surface of the enclosed body frequently
becomes incrusted with irregular agglomerations of carbon, which, owing to
their extreme mechanical resistance, it is very difficult to remove so that the
product, though admirably well adapted in all other respects, is unfit for use in
such cases where a smooth or even surface is required. Obviously these
agglomerations are due to circumstances such as imperfect contact which allow
depositions of carbon molecules to take place between the enclosing mass and the
enclosed body.
My attempts to prevent these agglomerations from forming have resulted in
the discovery of the very striking fact, that by the interposition between the
body and the enclosing mass, of a thin screen composed of an organic substance
adapted to be readily transformed into coke-like carbon; when heat is applied
the enclosed body is improved as stated without any agglomeration or incrusta-
tion being allowed to form on its surface.
Such screening substances are textile fabrics, sawdust, peat, starch and the
like applied to the body as a thin layer. The best results have been obtained
by closely wrapping the body in a thin sheet of paper. In any case the effect
is striking; the enclosed carbon body is closely encompassed in a thin envelope
of a coke-like nature which adheres in no point to the enclosed body, but can
easily be removed from the same leaving it with a perfectly smooth or even
surface, so that the body can be made use of without further treatment.
The impregnation of the enclosing carbon mass with carbon yielding gas can
be effected by forcing a current of such gas into the same, or by impregnating
the enclosing carbon mass with such substances as give off such gases when heat
is applied. I prefer the first cited mode and moreover, I prefer to heat the
current of gas prior to forcing it into the enclosing carbon mass.
From what has been said it is easily to be understood that the present în-
vention consists in its most perfect form in the combination with a mixture of
solid carbon particles and a carbon yielding gas for enclosing the carbon body
to be treated, of a readily forming non-adhesive screen of coke-like nature, but
that in cases where evenness of surface is of no importance said screen may be
omitted.
"
"
I wish it to be understood that the term carbon is used as comprising any
appropriate description of fossil or artificial carbon in its raw or in a prepared
state; that the term paper is to include any carbonaceous substance capable
of being readily reduced to a coke-like nature by the application of heat, and
that the term "carbon yielding gas" is intended to express any non-oxydising
gas capable of giving off carbon when in contact with incandescent carbon.
In carrying out my invention I prefer to proceed as follows: a carbon body,
shaped as desired, for instance a rod or a plate, is produced in the usual way,
that is to say by mixing powdered coke, charcoal, gas-retort carbon or any other
description of coal or carbon with an appropriate cementing agent such as tar,
oil and the like, and moulding, all as is well known to those skilled in the
art. After drying and burning the body is closely wrapped in a sheet of
paper, and the wrapped body, placed centrally into a receptacle of iron or other
fire proof material which can be airtightly closed and is provided with a gas

page_text: inlet. The space between the body and the walls of the receptacle is filled
with reduced charcoal, coke, peat, or with lamp-black and the like, when the
receptacle is closed and heated up to white heat as readily as possible, and
the current of hot gas admitted. The latter may consist in carbonic oxide,
hydrocarbons, cyanogen or cyanogen-compounds and the like, I prefer to use a
hot current of hydro-carbon gas. After having been exposed for a sufficiently
long period to the action of heat, the receptacle and its contents are allowed
to cool, when the receptacle is opened, the body taken out from the enclosing
mass, and the coke-like envelope removed.
Dated the 20th
1000
W. P. THOMPSON & Co..
322, High Holborn, London, W.C.,
Patent Agents for the Applicant.
Improvements in the Process of Manufacturing Carbons for Electrical
and Electro-chemical and other purposes.
I, EDUARD POHL, of Kalk, near Cologne, Prussia, Germany, 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:—
The present invention relates to the manufacture of carbon bodies for elec-
trical and electro-chemical and other purposes, such as pencils for electrical
lamps, contacts for generators, motors, interrupters and the like, microphonic
contacts, electrodes for electrolytical cells etc., and its object is to improve
that process in said manufacture which is commonly understood by the term
graphitising."
It is well known that carbon bodies in order to be fit for use in electrical and
electrochemical appliances must combine high density with great strength,
and to obtain this the bodies are subjected to what is called " graphitising"
which term means treating the carbon bodies by the action of heat and filling
up their pores by the deposition therein of carbon.
It was found a long time ago that the carbon deposit forming on the
inside of the retorts in which coal is subjected to the process of destructive dis-
tillation, by virtue of its specific molecular condition answers very well the
requirements as to density and strength. This peculiar condition of the so-
called gas-retort carbon is due to the fact that the incandescent deposit once
formed, is constantly, in contact with, and penetrated by part of the hot gases
generated within the retort, which part of the gases by its intimate contact
with the incandescent deposit is caused to dissociate, the carbon molecules thus
set free being deposited in the pores and upon the surface of the deposit
and welded together with the same, so to say. The result is a very dense and
strong carbon having somewhat of the nature of the graphitic modification.
As gas-retort carbon requires a long time for forming and, moreover, is obtain-
able in comparatively small pieces only attempts have been made to imitate
its forming process, so as to produce in a short time. One way is to make a
carbon body, impregnate the same with hydrocarbons, embedding such impreg-
nated body in coal dust and subjecting it to the action of heat with exclusion
of the outer air. Another way is to heat the carbon body in an atmosphere
containing hydrocarbons. The result of either of these processes has proved to

page_text: be unsatisfactory, as is clearly evidenced by the fact that at present attempts
are made to improve the strength and density by an admixture of metallic
compounds to the carbon.
I have discovered that in order to obtain a perfect effect as to the filling up
of the pores of the body and its conversion in the desired modification of carbon,
the carbon-yielding gas must not be generated within the body itself nor
caused to act on a naked body, but that the body requires to be embedded in a
mass of reduced coal which is impregnated with an atmosphere of said gas,
in other terms, the body has to be enclosed in an intimate mixture of carbon
particles and carbon yielding gas. When, under these conditions, a sufficiently
high degree of heat is applied from the outside, a very copious transfer or
immigration of carbon molecules is caused to take place from the enclosing
mixture of solid carbon particles and carbon yielding gas into the enclosed
body, the molecules of the latter uniting with the immigrating molecules and
the nature of the body being thoroughly modified. That is to say, the body has
imparted to it such a degree of density, strength and hardness as are in no
wise obtainable by applying either of the known processes. Carbon bodies
treated according to this improved method will answer with a metallic sound
when struck by means. of a hard object; their specific gravity is up to 17;
their hardness is 'such as to withstand the action of the best qualities of emery,
and their colour is by far brighter than that of the best carbons in the market.
There is, however a serious defect in that the surface of the enclosed body
frequently becomes incrusted with irregular agglomerations of carbon, which,
owing to their extreme mechanical resistance, it is very difficult to remove
so that the product, though admirably well adapted in all other respects, is unfit
for use in such cases where a smooth or even surface is required. Obviously
these agglomerations are due to circumstances such as imperfect contact which
allow depositions of carbon molecules to take place between the enclosing mass
and the enclosed body.
My attempts to prevent these agglomerations from forming have resulted in
the discovery of the very striking fact, that by the interposition between the
body and the enclosing mass, of a thin screen composed of an organic substance
adapted to be readily transformed into coke-like carbon by the action of heat,
the enclosed body is improved as stated without any agglomeration or incrusta-
tion being allowed to form on its surface. Such screening substances are textile
fabrics, saw-dust, peat, starch, and the like applied to the body as a thin layer.
The best results have been obtained by closely wrapping the body in a thin sheet
of paper. In any case the effect is striking; the enclosed carbon body is closely
encompassed in a thin envelope of a coke-like nature which adheres in no
point to the enclosed body, but can easily be removed from the same, leaving it
with a perfectly smooth or even surface, so that the body can be made use
of without further treatment.
The impregnation of the enclosing carbon mass with carbon yielding gas can
be effected by forcing a current of such gas into the same, or by impregnating
the enclosing carbon mass with such substances as give off such gases when heat
is applied. I prefer the first cited mode and, moreover, I prefer to heat the
current of gas prior to forcing it into the enclosing carbon mass.
From what has been said it is easily to be understood that the present in-
vention consists in its most perfect form in the combination with a mixture of
solid carbon particles and a carbon yielding gas for enclosing the carbon body
to be treated, of a readily forming non-adhesive screen of coke-like nature, but
that in cases where evenness of surface is of no importance said screen may be
omitted.
I wish it to be understood that the term "carbon" is used as comprising any
appropriate description of fossil or artificial carbon in its raw or in a prepared
state that the term "paper" is to include any carbonaceous substance capable
of being readily reduced to a coke-like nature by the application, of heat, and

page_text: that the term "carbon yielding gas" is intended to express any non-oxydising
gas capable of giving off carbon when in contact with incandescent carbon.
In carrying out my invention I prefer to proceed as follows: a carbon body,
shaped as desired, for instance a rod or a plate, is produced in the usual way,
that is to say by mixing powdered coke, charcoal, gas retort carbon or any other
description of coal or carbon with an appropriate cementing agent such as tar,
oil and the like, and moulding, all as is well known to those skilled in the
art. After drying and burning the body is closely wrapped in a sheet of
paper, and the wrapped body, placed centrally into a receptacle of iron or other
fire proof materal which can be air-tightly closed and is provided with a gas
inlet. The space between the body and the walls of the receptacle is filled
with reduced charcoal, coke, peat, or with lamp-black and the like, when the
receptacle is closed and heated up to white heat as readily as possible, and
the current of hot gas admitted. The latter may consist in carbonic oxide,
hydrocarbons, cyanogen or cyanogen-compounds and the like, I prefer to use a
hot current of hydro-carbon gas. After having been exposed for a sufficiently
long period to the action of heat, the receptacle and its contents are allowed
to cool, when the receptacle is opened, the body taken out from the enclosing
mass, and the coke-like envelope removed.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:
1. The described improved process of manufacturing so-called “ graphitised
carbon" by treating carbon bodies, while embedded in a mass of reduced carbon,
with a carbon-yielding gas under the action of heat, being characterised by
the fact that the said gas is conducted from the outside into, or produced
within, the said enclosing mass of reduced carbon, substantially as and for the
purpose stated.
2. A modification of the improved process as claimed under head 1, in which
the carbon body to be treated is, previously to being embedded in the enclosing
mass of reduced carbon, tightly covered with a thin layer of a readily cokeable
substance, substantially as and for the purpose described.
Dated the 23rd day of July 1900.
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham.