U.S. patent application number 10/255377 was filed with the patent office on 2003-01-30 for fluid permeable flexible graphite fuel cell electrode with enhanced electrical and thermal conductivity.
Invention is credited to Mercuri, Robert Angelo, Warddrip, Michael Lee, Weber, Thomas William.
Application Number | 20030022056 10/255377 |
Document ID | / |
Family ID | 23947062 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030022056 |
Kind Code |
A1 |
Mercuri, Robert Angelo ; et
al. |
January 30, 2003 |
Fluid permeable flexible graphite fuel cell electrode with enhanced
electrical and thermal conductivity
Abstract
A membrane electrode assembly is provided comprising a pair of
electrodes and an ion exchange membrane positioned between the
electrodes, at least one of the electrodes being formed of a sheet
of a compressed mass of expanded graphite particles having a
plurality of transverse fluid channels passing through the sheet
between first and second opposed surfaces of the sheet, one of
opposed surfaces abutting said ion exchange membrane, said
transverse fluid channels being formed by mechanically impacting an
opposed surface of the sheet to displace graphite within the sheet
at predetermined locations.
Inventors: |
Mercuri, Robert Angelo;
(Seven Hills, OH) ; Weber, Thomas William;
(Cleveland, OH) ; Warddrip, Michael Lee; (Parma,
OH) |
Correspondence
Address: |
James R. Cartiglia
Waddey & Patterson
Suite 2020
414 Union Street
Nashville
TN
37219
US
|
Family ID: |
23947062 |
Appl. No.: |
10/255377 |
Filed: |
September 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10255377 |
Sep 26, 2002 |
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09490210 |
Jan 24, 2000 |
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6468686 |
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Current U.S.
Class: |
429/483 ;
429/513; 429/532 |
Current CPC
Class: |
Y10T 428/30 20150115;
Y02E 60/50 20130101; H01M 4/96 20130101; H01M 8/1007 20160201; Y10T
428/24273 20150115; Y10T 428/24322 20150115; C04B 35/536 20130101;
H01M 4/8605 20130101 |
Class at
Publication: |
429/44 ; 429/38;
429/30 |
International
Class: |
H01M 004/96; H01M
008/10 |
Claims
What is claimed is:
1) A membrane electrode assembly comprising a pair of electrodes
and an ion exchange membrane positioned between said electrodes, at
least one of said electrodes being formed of a sheet of a
compressed mass of expanded graphite particles having a plurality
of transverse fluid channels passing through said sheet between
first and second parallel, opposed surfaces of said sheet, one of
said opposed surfaces abutting said ion exchange membrane, said
transverse fluid channels being formed by mechanically impacting an
opposed surface of said sheet to displace graphite within said
sheet at a plurality of predetermined locations.
2) Assembly in accordance with claim 1 wherein said compressed mass
of expanded graphite particles is characterized by expanded
graphite particles adjacent said channels extending obliquely with
respect to said parallel opposed surfaces.
3) Assembly in accordance with claim 1 wherein the channel openings
at said second surface of said sheet are surrounded by a smooth
graphite surface.
4) Assembly in accordance with claim 1 wherein the channel openings
at said first surface are larger than the channel openings at said
second surface.
5) Assembly in accordance with claim 1 wherein the channel openings
at said first surface are from 50 to 150 times larger in area than
the channel openings at said second surface.
6) Assembly in accordance with claim 1 wherein 1000 to 3000
channels per square inch are present in said sheet.
7) Assembly in accordance with claim 1 wherein said graphite sheet
has a thickness of 0.003 inch to 0.015 inch adjacent said channels
and a density of 0.5 to 1.5 grams per cubic centimeter.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an electrode assembly for an
electro-chemical fuel cell which includes an article formed of
flexible graphite sheet which is fluid permeable and has enhanced
isotropy with respect to thermal and electrical conductivity.
BACKGROUND OF THE INVENTION
[0002] Graphites are made up of layer planes of hexagonal arrays or
networks of carbon atoms. These layer planes of hexagonally
arranged carbon atoms are substantially flat and are oriented or
ordered so as to be substantially parallel and equidistant to one
another. The substantially flat, parallel equidistant sheets or
layers of carbon atoms, usually referred to as basal planes, are
linked or bonded together and groups thereof are arranged in
crystallites. Highly ordered graphites consist of crystallites of
considerable size: the crystallites being highly aligned or
oriented with respect to each other and having well ordered carbon
layers. In other words, highly ordered graphites have a high degree
of preferred crystallite orientation. It should be noted that
graphites possess anisotropic structures and thus exhibit or
possess many properties which are highly directional e.g. thermal
and electrical conductivity and fluid diffusion. Briefly, graphites
may be characterized as laminated structures of carbon, that is,
structures consisting of superposed layers or laminae of carbon
atoms joined together by weak van der Waals forces. In considering
the graphite structure, two axes or directions are usually noted,
to wit, the "c" axis or direction and the "a" axes or directions.
For simplicity, the "c" axis or direction may be considered as the
direction perpendicular to the carbon layers. The "a" axes or
directions may be considered as the directions parallel to the
carbon layers or the directions perpendicular to the "c" direction.
The natural graphites suitable for manufacturing flexible graphite
possess a very high degree of orientation.
[0003] As noted above, the bonding forces holding the parallel
layers of carbon atoms together are only weak van der Waals forces.
Natural graphites can be treated so that the spacing between the
superposed carbon layers or laminae can be appreciably opened up so
as to provide a marked expansion in the direction perpendicular to
the layers, that is, in the "c" direction and thus form an expanded
or intumesced graphite structure in which the laminar character of
the carbon layers is substantially retained.
[0004] Natural graphite flake which has been greatly expanded and
more particularly expanded so as to have a final thickness or "c"
direction dimension which is at least 80 or more times the original
"c" direction dimension can be formed without the use of a binder
into cohesive or integrated flexible graphite sheets of expanded
graphite, e.g. webs, papers, strips, tapes, or the like. The
formation of graphite particles which have been expanded to have a
final thickness or "c" dimension which is at least 80 times the
original "c" direction dimension into integrated flexible sheets by
compression, without the use of any binding material is believed to
be possible due to the excellent mechanical interlocking, or
cohesion which is achieved between the voluminously expanded
graphite particles.
[0005] In addition to flexibility, the sheet material, as noted
above, has also been found to possess a high degree of anisotropy
with respect to thermal and electrical conductivity and fluid
diffusion, comparable to the natural graphite starting material due
to orientation of the expanded graphite particles substantially
parallel to the opposed faces of the sheet resulting from very high
compression, e.g. roll pressing. Sheet material thus produced has
excellent flexibility, good strength and a very high degree of
orientation.
[0006] Briefly, the process of producing flexible, binderless
anisotropic graphite sheet material, e.g. web, paper, strip, tape,
foil, mat, or the like, comprises compressing or compacting under a
predetermined load and in the absence of a binder, expanded
graphite particles which have a "c" direction dimension which is at
least 80 times that of the original particles so as to form a
substantially flat, flexible, integrated graphite sheet. The
expanded graphite particles which generally are worm-like or
vermiform in appearance, once compressed, will maintain the
compression set and alignment with the opposed major surfaces of
the sheet. The density and thickness of the sheet material can be
varied by controlling the degree of compression. The density of the
sheet material can be within the range of from about 5 pounds per
cubic foot to about 125 pounds per cubic foot. The flexible
graphite sheet material exhibits an appreciable degree of
anisotropy due to the alignment of graphite particles parallel to
the major opposed, parallel surfaces of the sheet, with the degree
of anisotropy increasing upon roll pressing of the sheet material
to increased density. In roll pressed anisotropic sheet material,
the thickness, i.e. the direction perpendicular to the opposed,
parallel sheet surfaces comprises the "c" direction and the
directions ranging along the length and width, i.e. along or
parallel to the opposed, major surfaces comprises the "a"
directions and the thermal, electrical and fluid diffusion
properties of the sheet are very different, by orders of magnitude,
for the "c" and "a" directions.
[0007] This very considerable difference in properties, i.e.
anisotropy, which is directionally dependent, can be
disadvantageous in some applications. For example, in gasket
applications where flexible graphite sheet is used as the gasket
material and in use is held tightly between metal surfaces, the
diffusion of fluid, e.g. gases or liquids, occurs more readily
parallel to and between the major surfaces of the flexible graphite
sheet. It would, in most instances, provide for greater gasket
performance, if the resistance to fluid flow parallel to the major
surfaces of the graphite sheet ("a" direction) were increased, even
at the expense of reduced resistance to fluid diffusion flow
transverse to the major faces of the graphite sheet ("c"
direction). With respect to electrical properties, the resistivity
of anisotropic flexible graphite sheet is high in the direction
transverse to the major surfaces ("c" direction) of the flexible
graphite sheet, and very substantially less in the direction
parallel to and between the major faces of the flexible graphite
sheet ("a" direction). In applications such as fluid flow field
plates for fuel cells and seals for fuel cells, it would be of
advantage if the electrical resistance transverse to the major
surfaces of the flexible graphite sheet ("c" direction) were
decreased, even at the expense of an increase in electrical
resistivity in the direction parallel to the major faces of the
flexible graphite sheet ("a" direction).
[0008] With respect to thermal properties, the thermal conductivity
of a flexible graphite sheet in a direction parallel to the upper
and lower surfaces of the flexible graphite sheet is relatively
high, while it is relatively very low in the "c" direction
transverse to the upper and lower surfaces.
[0009] The foregoing situations are accommodated by the present
invention.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, a membrane
electrode assembly for an electro-chemical fuel cell is provided
comprising a pair of electrodes and an ion exchange membrane
positioned between the electrodes, at least one of the electrodes
being formed of a sheet of a compressed mass of expanded graphite
particles having a plurality of transverse fluid channels passing
through the sheet between first and second opposed surfaces of the
sheet, one of the opposed surfaces abutting said ion exchange
membrane, said transverse fluid channels being formed by
mechanically impacting an opposed surface of the sheet to displace
graphite within the sheet at predetermined locations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a plan view of a transversely permeable sheet of
flexible graphite having transverse channels in accordance with the
present invention;
[0012] FIG. 1(A) shows a flat-ended protrusion element used in
making the channels in the perforated sheet of FIG. 1;
[0013] FIG. 2 is a side elevation view in section of the sheet of
FIG. 1;
[0014] FIGS. 2(A), (B), (C) show various suitable flat-ended
configurations for transverse channels in accordance with the
present invention;
[0015] FIGS. 3, 3(A) shows a mechanism for making the article of
FIG. 1;
[0016] FIG. 4 shows an enlarged sketch of an elevation view of the
oriented expanded graphite particles of prior art flexible graphite
sheet material;
[0017] FIG. 5 is a sketch of an enlarged elevation view of an
article formed of flexible graphite sheet in accordance with the
present invention;
[0018] FIG. 5, 6, 7 and 7(A) show a fluid permeable electrode
assembly which includes a transversely permeable article in
accordance with the present invention; and
[0019] FIG. 8 is a photograph at 100.times. (original
magnification) corresponding to a portion of the side elevation
view sketch of FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Graphite is a crystalline form of carbon comprising atoms
covalently bonded in flat layered planes with weaker bonds between
the planes. By treating particles of graphite, such as natural
graphite flake, with an intercalant of, e.g. a solution of sulfuric
and nitric acid, the crystal structure of the graphite reacts to
form a compound of graphite and the intercalant. The treated
particles of graphite are hereafter referred to as "particles of
intercalated graphite". Upon exposure to high temperature, the
particles of intercalated graphite expand in dimension as much as
80 or more times its original volume in an accordion-like fashion
in the "c" direction, i.e. in the direction perpendicular to the
crystalline planes of the graphite. The exfoliated graphite
particles are vermiform in appearance, and are therefore commonly
referred to as worms. The worms may be compressed together into
flexible sheets which, unlike the original graphite flakes, can be
formed and cut into various shapes and provided with small
transverse openings by deforming mechanical impact.
[0021] A common method for manufacturing graphite sheet, e.g. foil
from flexible graphite is described by Shane et al in U.S. Pat. No.
3,404,061 the disclosure of which is incorporated herein by
reference. In the typical practice of the Shane et al method,
natural graphite flakes are intercalated by dispersing the flakes
in a solution containing an oxidizing agent of, e.g. a mixture of
nitric and sulfuric acid. The intercalation solution contains
oxidizing and other intercalating agents known in the art. Examples
include those containing oxidizing agents and oxidizing mixtures,
such as solutions containing nitric acid, potassium chlorate,
chromic acid, potassium permanganate, potassium chromate, potassium
dichromate, perchloric acid, and the like, or mixtures, such as for
example, concentrated nitric acid and chlorate, chromic acid and
phosphoric acid, sulfuric acid and nitric acid, or mixtures of a
strong organic acid, e.g. trifluoroacetic acid, and a strong
oxidizing agent soluble in the organic acid.
[0022] In a preferred embodiment, the intercalating agent is a
solution of a mixture of sulfuric acid, or sulfuric acid and
phosphoric acid, and an oxidizing agent, i.e. nitric acid,
perchloric acid, chromic acid, potassium permanganate, hydrogen
peroxide, iodic or periodic acids, or the like. Although less
preferred, the intercalation solutions may contain metal halides
such as ferric chloride, and ferric chloride mixed with sulfuric
acid, or a halide, such as bromine as a solution of bromine and
sulfuric acid or bromine in an organic solvent.
[0023] After the flakes are intercalated, any excess solution is
drained from the flakes and the flakes are water-washed. The
quantity of intercalation solution retained on the flakes after
draining may range from 20 to 150 parts of solution by weight per
100 parts by weight of graphite flakes (pph) and more typically
about 50 to 120 pph. Alternatively, the quantity of the
intercalation solution may be limited to between 10 to 50 parts of
solution per hundred parts of graphite by weight (pph) which
permits the washing step to be eliminated as taught and described
in U.S. Pat. No. 4,895,713 the disclosure of which is also herein
incorporated by reference. The thus treated particles of graphite
are sometimes referred to as "particles of intercalated graphite".
Upon exposure to high temperature, e.g. 700.degree. C. to
1000.degree. C. and higher, the particles of intercalated graphite
expand as much as 80 to 1000 or more times its original volume in
an accordion-like fashion in the c-direction, i.e. in the direction
perpendicular to the crystalline planes of the constituent graphite
particles. The expanded, i.e. exfoliated graphite particles are
vermiform in appearance, and are therefore commonly referred to as
worms. The worms may be compressed together into flexible sheets
which, unlike the original graphite flakes, can be formed and cut
into various shapes and provided with small transverse openings by
deforming mechanical impact as hereinafter described.
[0024] Flexible graphite sheet and foil are coherent, with good
handling strength, and are suitably compressed, e.g. by
roll-pressing, to a thickness of 0.003 to 0.15 inch and a density
of 0.1 to 1.5 grams per cubic centimeter. From about 1.5-30% by
weight of ceramic additives, can be blended with the intercalated
graphite flakes as described in U.S. Pat. No. 5,902,762 (which is
incorporated herein by reference) to provide enhanced resin
impregnation in the final flexible graphite product. The additives
include ceramic fiber particles having a length of 0.15 to 1.5
millimeters. The width of the particles is suitably from 0.04 to
0.004 mm. The ceramic fiber particles are non-reactive and
non-adhering to graphite and are stable at temperatures up to
2000.degree. F., preferably 2500.degree. F. Suitable ceramic fiber
particles are formed of macerated quartz glass fibers, carbon and
graphite fibers, zirconia, boron nitride, silicon carbide and
magnesia fibers, naturally occurring mineral fibers such as calcium
metasilicate fibers, calcium aluminum silicate fibers, aluminum
oxide fibers and the like.
[0025] With reference to FIG. 1 and FIG. 2, a compressed mass of
expanded graphite particles, in the form of a flexible graphite
sheet is shown at 10. The flexible graphite sheet 10 is provided
with channels 20, which are preferably smooth-sided as indicated at
67 in FIGS. 5 and 8, and which pass between the parallel, opposed
surfaces 30, 40 of flexible graphite sheet 10. The channels 20
preferably have openings 50 on one of the opposed surfaces 30 which
are larger than the openings 60 in the other opposed surface 40.
The channels 20 can have different configurations as shown at
20'-20"" in FIGS. 2(A), 2(B), 2(C) which are formed using
flat-ended protrusion elements of different shapes as shown at 75,
175, 275, 375 in FIGS. 1(A) and 2(A), 2(B), 2(C), 2(D), suitably
formed of metal, e.g. steel and integral with and extending from
the pressing roller 70 of the impacting device shown in FIG. 3. The
smooth flat-ends of the protrusion elements, shown at 77, 177, 277,
377, and the smooth bearing surface 73, of roller 70, and the
smooth bearing surface 78 of roller 72 (or alternatively flat metal
plate 79), ensure deformation and complete displacement of graphite
within the flexible graphite sheet, i.e. there are no rough or
ragged edges or debris resulting from the channel-forming impact.
Preferred protrusion elements have decreasing cross-section in the
direction away from the pressing roller 70 to provide larger
channel openings on the side of the sheet which is initially
impacted. The development of smooth, unobstructed surfaces 63
surrounding channel openings 60, enables the free flow of fluid
into and through smooth-sided (at 67) channels 20. In a preferred
embodiment, openings one of the opposed surfaces are larger than
the channel openings in the other opposed surface, e.g. from 1 to
200 times greater in area, and result from the use of protrusion
elements having converging sides such as shown at 76, 276, 376. The
channels 20 are formed in the flexible graphite sheet 10 at a
plurality of pre-determined locations by mechanical impact at the
predetermined locations in sheet 10 using a mechanism such as shown
in FIG. 3 comprising a pair of steel rollers 70, 72 with one of the
rollers having truncated, i.e. flat-ended, prism-shaped protrusions
75 which impact surface 30 of flexible graphite sheet 10 to
displace graphite and penetrate sheet 10 to form open channels 20.
In practice, both rollers 70, 72 can be provided with
"out-of-register" protrusions, and a flat metal plate indicated at
79, can be used in place of smooth-surfaced roller 72. FIG. 4 is an
enlarged sketch of a sheet of flexible graphite 110 which shows a
typical prior art orientation of compressed expanded graphite
particles 80 substantially parallel to the opposed surfaces 130,
140. This orientation of the expanded graphite particles 80 results
in anisotropic properties in flexible graphite sheets; i.e. the
electrical conductivity and thermal conductivity of the sheet being
substantially lower in the direction transverse to opposed surfaces
130, 140 ("c" direction) than in the direction ("a" direction)
parallel to opposed surfaces 130, 140. In the course of impacting
flexible graphite sheet 10 to form channels 20, as illustrated in
FIG. 3, graphite is displaced within flexible graphite sheet 10 by
flat-ended (at 77) protrusions 75 to push aside graphite as it
travels to and bears against smooth surface 73 of roller 70 to
disrupt and deform the parallel orientation of expanded graphite
particles 80 as shown at 800 in FIG. 5. This region of 800,
adjacent channels 20, shows disruption of the parallel orientation
into an oblique, non-parallel orientation is optically observable
at magnifications of 100.times. and higher. In effect the displaced
graphite is being "die-molded" by the sides 76 of adjacent
protrusions 75 and the smooth surface 73 of roller 70 as
illustrated in FIG. 5. This reduces the anisotropy in flexible
graphite sheet 10 and thus increases the electrical and thermal
conductivity of sheet 10 in the direction transverse to the opposed
surfaces 30, 40. A similar effect is achieved with frusto-conical
and parallel-sided peg-shaped flat-ended protrusions 275 and 175.
The perforated gas permeable flexible graphite sheet 10 of FIG. 1
can be used as an electrode in an electrochemical fuel cell 500
shown schematically in FIGS. 6, 7 and 7(A).
[0026] FIG. 6, FIG. 7 and FIG. 7(A) show, schematically, the basic
elements of an electrochemical Fuel Cell, more complete details of
which are disclosed in U.S. Pat. Nos. 4,988,583 and 5,300,370 and
PCT WO 95/16287 (Jun. 15, 1995) and each of which is incorporated
herein by reference.
[0027] With reference to FIG. 6, FIG. 7 and FIG. 7(A), the Fuel
Cell indicated generally at 500, comprises electrolyte in the form
of a plastic e.g. a solid polymer ion exchange membrane 550
catalyst coated at surfaces 601, 603, e.g. coated with platinum 600
as shown in FIG. 7(A); perforated flexible graphite sheet
electrodes 10 in accordance with the present invention; and flow
field plates 1000, 1100 which respectively abut electrodes 10.
Pressurized fuel is circulated through grooves 1400 of fuel flow
field pate 1100 and pressurized oxidant is circulated through
grooves 1200. In operation, the fuel flow field plate 1100 becomes
an anode, and the oxidant flow field plate 1000 becomes a cathode
with the result that an electric potential, i.e. voltage is
developed between the fuel flow field plate 1000 and the oxidant
flow field plate 1100. The above described electrochemical fuel
cell is combined with others in a fuel cell stack to provide the
desired level of electric power as described in the above-noted
U.S. Pat. No. 5,300,370.
[0028] The operation of Fuel Cell 500 requires that the electrodes
10 be porous to the fuel and oxidant fluids, e.g. hydrogen and
oxygen, to permit these components to readily pass from the grooves
1400, 1200 through electrodes 10 to contact the catalyst 600, as
shown in FIG. 7(A), and enable protons derived from hydrogen to
migrate through ion exchange membrane 550. In the electrode 10 of
the present invention, channels 20 are positioned to adjacently
cover grooves 1400, 1200 of the flow field plates so that the
pressurized gas from the grooves passes through the smaller
openings 60 of channels 20 and exits the larger openings 50 of
channels 20. The initial velocity of the gas at the smaller
openings 60 is higher than the gas flow at the larger openings 50
with the result that the gas is slowed down when it contacts the
catalyst 600 and the residence time of gas-catalyst contact is
increased and the area of gas exposure at the membrane 550 is
maximized. This feature, together with the increased electrical
conductivity of the flexible graphite electrode of the present
invention enables more efficient fuel cell operation.
[0029] FIG. 8 is a photograph (original magnification 100.times.)
of a body of flexible graphite corresponding to a portion of the
sketch of FIG. 5.
[0030] The articles of FIGS. 1 and 5 and the material shown in the
photograph (100.times.) of FIG. 8 can be shown to have increased
thermal and electrical conductivity in the direction transverse to
opposed parallel, planar surfaces 30, 40 as compared to the thermal
and electrical conductivity in the direction transverse to surfaces
130, 140 of prior art material of FIG. 4 in which particles of
expanded natural graphite unaligned with the opposed planar
surfaces are not optically detectable.
[0031] A sample of a sheet of flexible graphite 0.01 inch thick
having a density of 0.3 grams/cc, representative of FIG. 4, was
mechanically impacted by a device similar to that of FIG. 3 to
provide channels of different size in the flexible graphite sheet.
The transverse ("c" direction) electrical resistance of the sheet
material samples was measured and the results are shown in the
table below.
[0032] Also, the transverse gas permeability of channeled flexible
graphite sheet samples, in accordance with the present invention,
was measured, using a Gurley Model 4118 for Gas Permeability
Measurement.
[0033] Samples of channeled flexible graphite sheet in accordance
with the present invention were placed at the bottom opening (3/8
in. diam.) of a vertical cylinder (3 inch diameter cross-section).
The cylinder was filled with 300 cc of air and a weighted piston (5
oz.) was set in place at the top of the cylinder. The rate of gas
flow through the channeled samples was measured as a function of
the time of descent of the piston and the results are shown in the
table below.
1 Flexible Graphite Sheet (0.01 inch thick; density = 0.3 gms/cc)
1600 channels per square inch - 0.020 250 channels per inch wide
square inch - 0.020 at top; 0.005 inch wide at top; No inch wide
0.007 inch wide at Channels at bottom bottom Transverse Electrical
80 8 0.3 Resistance (micro ohms) Diffusion Rate - -- 8 seconds 30
seconds Seconds
[0034] In the present invention, for a flexible graphite sheet
having a thickness of 0.003 inch to 0.015 inch adjacent the
channels and a density of 0.5 to 1.5 grams per cubic centimeter,
the preferred channel density is from 1000 to 3000 channels per
square inch and the preferred channel size is a channel in which
the ratio of the area of larger channel opening to the smaller is
from 50:1 to 150:1.
[0035] In the practice of the present invention, the flexible
graphite sheet can, at times, be advantageously treated with resin
and the absorbed resin, after curing, enhances the moisture
resistance and handling strength, i.e. stiffness of the flexible
graphite sheet. Suitable resin content is preferably 20 to 30% by
weight, suitably up 60% by weight.
[0036] The article of the present invention can be used as
electrical and thermal coupling elements for integrated circuits in
computer applications, as conformal electrical contact pads and as
electrically energized grids in de-icing equipment.
[0037] The above description is intended to enable the person
skilled in the art to practice the invention. It is not intended to
detail all of the possible variations and modifications which will
become apparent to the skilled worker upon reading the description.
It is intended, however, that all such modifications and variations
be included within the scope of the invention which is defined by
the following claims. The claims are intended to cover the
indicated elements and steps in any arrangement or sequence which
is effective to meet the objectives intended for the invention,
unless the context specifically indicates the contrary.
* * * * *