Gas derived graphite fibers are generated by the decomposition of an organic gas. These fibers when joined with a suitable binder are used to make a high thermal conductivity composite material. The fibers may be intercalated. The intercalate can be halogen or halide salt, alkaline metal, or any other species which contributes to the electrical conductivity improvement of the graphite fiber. The heat transfer device may also be made of intercalated highly oriented pyrolytic graphite and machined, rather than made of fibers

Banks, Bruce A.

Gaier, James R.

English

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National Aeronautics and
Space Administration
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Reply to Altn of:
NASA Case No. L_/q/62-4 /
Print Figure I
NOTICE
The invention disclosed in this document resulted from research in
aeronautical and space activities performed under programs of the
National Aeronautics and Space Administration. The invention is
owned by NASA and is, therefore, available for licensing in
accordance with the NASA Patent Licensing Regulation (14 Code of
Federal Regulation 1245.2).
To storage commercial utilization of NASA-owned inventions, it is
NASA policy to grant licenses to commercial concerns. Although
NASA encourage nonexclusive licensing to promote competition and
achieve the widest possible utilization, NASA will consider the
granting of a limited exclusive license, pursuant to the NASA
Patent Licensing Regulations, when such a license will provide the
necessary incentive to the licensee to achieve early practical
application of the invention.
Address inquires and all applications for license for this
invention to Office of P&tent Coun_ (LE-LAW}
NASA/Le_ _ Gem_
Cleveland. ObJ_ 441_
Approved NASA forms for application for nonexclusive or exclusive
license are available from the above address.
(NASA-C_se-LEW-I_I_2-1) HEAT TRANSFER
OFVICF AN_ METHO0 OF MAKING [HE S_MF Patent
Application (NASA) ti p CSCL 20D
Nqi-13o68
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https://ntrs.nasa.gov/search.jsp?R=19910004355 2020-03-19T20:56:36+00:00Z
AWARDS ABSTRACT
HEAT TRANSFER DEVICE AND
METHOD OF MAKING THE SAME
Gas derived graphite fibers are generated by the decomposition
of an organic gas. These fibers when joined with a suitable
binder are used to make a high thermal conductivity composite
material.
The fibers may be intercalated. The intercalate can be
halogen or halide salt, alkaline metal, or any other species
which contributes to the electrical conductivity improvement of
the graphite fiber. The heat transfer device may also be made
of intercalated highly oriented pyrolytic graphite and machined,
rather than made of fibers.
INVENTORS:
EMPLOYER:
EVALUATOR:
SERIAL NO.:
Bruce A. Banks
James R. Gaier
NASA Lewis Research Center
Dr. J. Stuart Fordyce
501,893
FILING DATE: March 30, 1990
NASA Case No. LEW-14,162-1 PATENT
HEAT TRANSFER DEVICE AND
METHOD OF MAKING THE SAME
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Origin of the Invention
The invention described herein was made by employees of the
United States Government and may be manufactured and used by or
for the Government for governmental purposes without the payment
of any royalties thereon or therefor.
Technical Field
This invention is concerned with providing an improved heat
transfer device. The invention is particularly directed to a
material which will transfer heat more efficiently.
Previous methods of transferring heat relied on high thermal
conductivity materials. Some of these devices use class II A
diamond which conducts heat approximately five times the rate of
copper at room temperature. However, such high thermal conduc-
tivity materials, such as class II A diamond, are suitable only
for short distance heat transport because of the expense of the
high quality diamond. Only a short distance transport, on the
order of 5mm, is practical with such materials.
Heat transfer devices of copper, aluminum, silver, and
beryllium oxide have been proposed. While these materials can
be used to transport heat over larger distances, their poor
thermal conductivity requires high temperature gradients to
transport the same power per unit area as diamond.
Heat pipes can be very effective transporters of heat with
low temperature gradients. However, they rely on some active
working fluid and usually have a rather limited temperature range
of operation. Heat pipes are not readily constructed in
arbitrarily small or complex shapes.
It is, therefor, an object of the present invention to provide
a heat transfer device which conducts heat substantially better
than conventional devices, yet is lightweight and strong.
Another object of the invention is to provide a heat conduct-
ing material which can be used instead of more complex heat pipes
and thus, be mechanically supportive, lightweight, and have no
NASA Case No. LEW-14,162-1
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active working fluid to be concerned about. However, the
material would efficiently transfer heat from one place to
another.
Backqround Art
U.S. patent No. 2,542,637 to De Poy is concerned with a method
of rectifying a neutral salt heat-treating bath. A solid
graphite or carbon rod is immersed in the bath to reduce metal
oxides and scavenge for metals in solution. The rod may be
periodically removed, cleansed, and replaced.
U.S. patent No. 4,424,145 to Sara relates to a pitch derived
carbon fiber which has been boronated and intercalated with
calcium. U.S. patent No. 4,435,375 to Tamura is directed to a
graphite filament which has been formed by heating a
purified graphite material in a plasma and then intercalated with
an alkali metal.
U.S. patent No. 3,531,249 to Turkat describes pyrolytic
graphite compositions which are formed by co-depositing refrac-
tory metals and graphite on a mandrel to form a filament which
is in essence pyrolytic graphite. U.S. patent No. 3,294,880
which is also to Turkat describes a continuous method of
manufacturing ablative and refractory materials. The invention
is particularly concerned with a method and apparatus for
manufacturing ablative and refractory filaments in which
hydrocarbon gases are cracked in a vacuum furnace. The decom-
position products are deposited on a rotating mandrel and then
continuously peeled therefrom in the form of a continuous
filament. U.S. patent No. 3,375,308 which is likewise issued to
Turkat is concerned with the making of high purity and non-
melting filaments. High temperature, high strength ablative
refractory materials, such as pyrolytic graphite, are produced
by vapor decomposition and hydrocarbon gas cracking techniques
to provide pure crystalline refractory metals, carbides,
silicides and borides in free standing shapes, coatings and in
compositions to form shapes and structures for space age
applications.
NASA Case No. LEW-14,162-1
Disclosure of the Invention
Gas derived graphite fibers joined with a suitable binder are
used to make a high thermal conductivity composite material
5 device. The fiber is generated by the decomposition of an
organic gas.
The fibers may or may not be intercalated. The intercalate
can be a halogen or halide salt, alkaline metal, or any other
species which contributes to the electrical conductivity
i0 improvement of the graphite fiber. The heat transfer device may
also be made of intercalated highly oriented pyrolytic graphite
and machined, rather than made of fibers.
Brief Description of the Drawings
The objects, advantages, and novel features of the invention
15 will be more fully apparent from the following detailed descrip-
tion when read in connection with the accompanying drawings in
which
FIG. i is an elevation view showing a heat transfer device
constructed in accordance with the present invention;
20 FIG. 2 is a section view taken along the line 2-2 in FIG. 1;
FIG. 3 is an enlarged cross-section view of one of the fibers
shown in FIG. 2;
FIG. 4 is a vertical cross-section view showing an alternate
embodiment of the invention;
25 FIG. 5 is a plan view of still another alternate embodiment
of the invention; and
FIG. 6 is a vertical cross-section view taken along the line
6-6 in FIG. 5.
Best Mode for Carrying Out the Invention
30 Referring now to the drawing, there is shown in FIG. 1 a heat
transfer device i0 constructed in accordance with the present
invention. This apparatus is used to conduct heat from heat
source 12 to a heat sink 14. The source 12 and the sink 14 are
constructed of highly conductive materials while the heat
35 transfer device 10 is a graphite fiber composite composed of
either intercalated or heat treated fibers.
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NASA Case No. LEW-14,162-1
As best shown in FIG. 2 the heat transfer device i0 is made
up of highly oriented graphite fibers 16 which may in addition
have been intercalated. As shown in FIG. 3, each fiber is a
coaxial layered graphite structure which is intercalated with
either electron accepter or donor intercalate species. These
fibers 16 are constructed into composite material in a form
suitable for the specific heat transport application.
The graphite fibers 16 are fabricated by the high temperature
decomposition of an inorganic gas, such as natural gas, benzene,
etc. to produce concentric layers 18 of graphite along the fiber
axis. The organic gas used to generate the fiber and the
conditions under which it is grown can be any number of tech-
niques which produce highly oriented fibers.
These organic gas derived fibers 16 are then heated to
3000°C to further graphitize and orient them. As a result of
this heating, the thermal conductivity of the fibers is in-
creased to about three times that of copper. The high tempera-
ture heat treatment and duration can be varied.
The fibers 16 may also be intercalated with a suitable
electron donor or acceptor material to further increase the
electrical conductivity if enhancement of electrical transport
is desired. Intercalation is achieved by the insertion of ions
or molecules between the planes or layers 18 of graphite. This
is accomplished by surrounding the fibers 16 by vapor of the
intercalant at a suitable elevated temperature. The inter-
calant can be a halogen or halide salt, alkaline metal or any
other species which contributes to the thermal conductivity
improvement of the graphite fiber.
The pristine or intercalated graphite fibers 16 are then
bundled and joined with a suitable binder 20 to produce a high
thermal conductivity composite material device i0. While the
binder 20 is preferably epoxy or other polymer, it is contem-
plated that an electrodeposited metal or low-temperature alloy
could be used.
NASA Case No. LEW-14,162-1
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ALTERNATE EMBODIMENTS OF THE INVENTION
The geometry of the high thermal conductivity composite can
be varied as needed to fit specific applications. Referring now
to FIG. 4 there is shown an intercalated graphite fiber composite
thermal transfer device 22 that is used to cool apparatus which
uses a semiconductor 24. More particularly, the heat transfer
device 22 is tapered and potted into a tapered slot in a heat
sink 26. It is contemplated that the heat sink 26 may be of
copper or other highly conductive material. If required, a thin
film electrical isolator 28 may be interposed between the
semiconductor 24 and the heat sink 26.
The graphite fibers can be sputter vapor, electroless, or
electrodeposited with a thin film of metal to allow electrical
and/or solder bonding of the fibers to heat sinks. Such a
structure is shown in FIGS. 5 and 6 wherein a semiconductor
device 30 is cooled by a radial array of intercalated graphite
fibers 32 which are in contact with a heat sink 34. If required,
a thin film electrical isolator 36 may be interposed between the
semiconductor 30 and the heat sink 34. It will be appreciated
this configuration facilitates the spreading of semiconductor
waste heat by utilizing the intercalated graphite fiber.
The geometry of the high thermal conductivity composite can
be varied as needed to fit the specific application. In addi-
tion, the heat transfer device may be simply made of inter-
calated highly oriented pyrolytic graphite and suitably machined
rather than being made of fibers.
The intercalated graphite fiber composite material devices
shown in the drawings are stronger, lighter and less expensive
than other materials of the prior art. Also, these devices have
the capability of transferring more heat for the same temperature
differential than prior art devices.
Another important advantage of the invention is that the
material operates passively. This does not require any trans-
port of a gravitational environment.
While several embodiments of this invention have been shown
and described it will be appreciated that various modifications
may be made to the disclosed invention without departing from
the spirit thereof or the scope of the subjoined claims.
ABSTRACTOF THE DISCLOSURE
HEAT TRANSFERDEVICE AND
METHODOF MAKING THE SAME
Gas derived graphite fibers are generated by the decomposition
-_ of an organic gas. These fibers when joined with a suitable
binder are used to make a high thermal conductivity composite
material.
The fibers may be intercalated. The intercalate can be
halogen or halide salt, alkaline metal, or any other species
r_
"i_' which contributes to the electrical conductivity improvement of
%
the graphite fiber. The heat transfer device may also be made
of intercalated highly oriented pyrolytic graphite and machined,
rather than made of fibers.
210
/
FIG. 1
10
16
16
18
FIG. 3
FIG. 2
26
22
FIG. 4
-6
t
30
32
6
f
FIG. 5
30
14
FIG. 6


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