Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2017/105389
PCT/US2015/065532
CA 03008449 2018-06-13
Title: A HIGH CARBON GRADE GRAPHITE BLOCK AND A METHOD TO MAKE IT
Inventors: Gordon Chiu, Teresa Sung, Jay Walter McCloskey, Robert John Hyatt,
Jr.
PRIORITY
This application does not claim priority to any other patent or patent
application.
FIELD OF THE INVENTION
The present invention relates to graphite blocks of high carbon purity having
any chosen
dimensions and a method to make same. The blocks have utility for example as
thick lubrication
blocks, low cost electrode replacements for expensive synthetic graphite
electrodes, neutron ray
filters, furnace liners in addition to other uses.
BACKGROUND OF THE INVENTION
Graphite is a natural form of carbon. It holds an important role as industrial
materials
because of its outstanding heat and chemical resistances, high electric
conductivity. It has
been widely used as electrodes, heating elements, and structural materials.
Due to its spectral
and reflective characteristics it has also been used as X-ray or neutron ray
monochromators,
filters or spectral crystal articles.
Natural graphite may be used for all the aforementioned and other purposes.
However, natural graphite with high quality occurs in an extremely limited
amount and may
be unsuitable for desired use due to its powder or flake form.
There are three principal types of natural graphite, each occurring in
different types of
ore deposit.
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Crystalline flake graphite, also called flake graphite, occurs as isolated,
flat, plate like
particles with hexagonal edges if unbroken and when broken the edges can be
irregular or
angular. Most economic deposits of flake graphite are of the Archean to late
Proterozoic
age. These rocks may contain up to 90% graphite, although 10-15% graphite is a
more
typical ore body grade. Graphite flake ranges in size from 1 to 25 mm, with an
average size
of 2.5 mm. Commercially flake graphite is divided into coarse (150-850 gm in
diameter) and
fine (45 -150 gm in diameter) flake. Fine flake may be further subdivided into
medium flake
(100 to 150 m), fine flake (75 to 100 gm) and powder (less than 75 m).
Impurities include
minerals commonly found in metasegments, such as quartz, mica, or calcite.
Amorphous graphite occurs as fine particles and is the result of thermal
metamorphism of coal and is sometimes called meta-anthracite. Amorphous
graphite is
define as being finer than 40 gm in diameter, but some trade statistics define
the upper limit
at 70 gm. Deposits with grades over 80% carbon are considered to be
economically viable.
Lump graphite which is also called vein graphite occurs in fissure veins or
fractures
and is probably hydrothermal in origin. Vein graphite is the rarest and most
valuable form of
graphite due to its high carbon grade. Vein graphite may come in lumps ranging
from about 8
cm by diameter to as small as 5 gm. The purity of the vein graphite is usually
between 94
and 99%.
The application of graphitic material is constantly evolving due to its unique
chemical, electrical and thermal properties. Graphite maintains its stability
and strength
under temperatures in excess of 3500 C and is very resistant to chemical
corrosion. It is also
one of the lightest of all reinforcing elements and has high natural
lubricating abilities.
Natural graphite has varying levels of quality depending on the type. The
degree of the
purity can vary greatly and the purity is the factor that influences the use
of the material in
applications and the pricing of the material. Carbon purity of natural
graphite ranges generally
between 70 and 99%, as discussed above. High carbon purity is an important
feature for high-
tech applications of graphite, such as semiconductors, photovoltaic, and
nuclear applications
among other.
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However, natural graphite with high quality occurs in an extremely limited
amounts as
discussed above. Usually graphite with very high carbon content (96-99%) has
been achieved by
chemical and thermal treatment to reduce the level of impurities. Therefore,
efforts of producing
synthetic graphite having similar characteristics as natural graphite have
been made.
One of the processes of making synthetic graphite is one which includes
pyrogenic
deposition of hydrocarbons in vapor phase and hot working of gaseous
hydrocarbons. In the
process, re-annealing is effected at a temperature of 3400 C for a long
period of time under high
pressure. The graphite thus obtained is called highly oriented pyrographite
(HOPG) and although
it has almost the same characteristics as natural graphite it does not have
the lubricating character
of natural graphene. Additionally, the process is long, complicated and the
yield is low.
Therefore the productions costs are high.
Synthetic graphite may be a manufactured product made by high temperature
treatment
of calcined petroleum coke and coal tar pitch. The manufacturing process
includes various
mixings, molding and baking operations followed the heat treatment at 2500 to
3000 C. The
morphology of most synthetic graphite varies from flakey in fine powders to
irregular grains and
needles in coarser products. Due to the high temperature treatment volatile
impurities are
vaporized and the purity of the synthetic graphite is usually more than 99%
carbon. Synthetic
graphite is generally available in particle sized from about 2 micrometer
powders to about 2 cm
pieces.
Synthetic graphite producers are faced with escalating energy costs associated
with
turning petroleum coke into graphite. Petroleum coke is the solid waste
remaining after refining
oil. To turn petroleum coke into graphite is extremely energy intensive and
therefore expensive,
but additionally there is are environmental issues. Moreover, the supply of
petroleum coke
derived from low sulfur, sweet crude oil is diminishing.
One solution to the problem of natural graphite being impure and synthetic
graphite being
expensive is to chemically purify natural graphite to achieve natural graphite
with higher purity.
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The commonly used chemical purification methods are hydrofluoric acid leaching
and
hydrochloric acid caustic leach. A high temperature thermal treatment also
allows for
purification of natural graphite. However, these purification methods still do
not give carbon
purity as high as synthetic carbon and therefore other methods to provide high
purity graphite are
needed.
For various purposes, there is also a need for graphite blocks and rods. Due
to graphite's
high thermal conductivity graphite blocks are preferred for example as furnace
linings. Graphite
blocks are also widely used for lubrication purposes. Graphite blocks are
commonly made of
synthetic graphite made of petroleum coke. However, because the price of
synthetic graphite is
high it is not economical to make graphite blocks from synthetic graphite.
Therefore, other
methods for producing graphite blocks are disclosed in the following patent
publications:
U.S. 4,983,244 and EP 0360217 provide a method to produce graphite blocks by
process
where one or more polymer films selected form aromatic polyimides, aromatic
polyamines and
polyoxadiazoles are heat treated to obtain carbonaceous films. A plurality of
the carbonaceous
films are then hot pressured to obtain a thick graphite block.
U.S. 5,449,507 provides a process for producing a graphite block from a
plurality of
graphitizable polymer films or a plurality of carbonaceous films separately
obtained from
graphitizable polymer films. The method comprises superposing the polymer
films or the
carbonaceous films, and thermally treating the films in a substantially
compression pressure-free
condition. The graphite blocks obtained are about 1 cm thick and about 16 cm
in square.
U.S. 7,491,421 provides a method to make a heat sink by grinding a composition
formed
nanometer natural graphite and bonding agent to a ball-like graphite and
treating the ball-like
graphite with high pressure, dipping it in liquid phase asphalt, graphitizing
the mass to a dry
graphite block and coating the block with metal to form the sink.
U.S. 5,236,468 provides a method for producing formed bodies from carbonaceous
substances in which the starting materials are dry synthetic graphite
particles and coal tar pitch
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particles. A mixture of the particles is compressed under pressure and the
result is a compact
carbonaceous body having a volume at least equal to that of a sphere of 1/8
inches in diameter.
Despite the efforts taken to develop synthetic large sized graphite blocks,
synthetic
graphite lacks some features of natural graphite. Purified natural flake
graphite exhibits a much
higher crystalline structure than synthetic and is therefore more electrically
and thermally
conductive. Furthermore, natural graphite has superior lubricating features.
There is currently no
existing procedure to make large blocks from natural flake graphite, although
flake graphite can
be used to make graphite foil. If the foil is 100% graphite, the stress/strain
is insignificant and it
fails to build a block.
Therefore, there is a need to provide a high purity graphite with the
properties of natural
graphite. There is also a need to provide a method to make large graphite
blocks having a high
carbon purity and lubricating characters.
The invention disclosed herein provides solutions to the flaws of the prior
art.
SUMMARY OF THE INVENTION
This invention generally provides a novel composition comprising graphite
flakes and
graphene oxide. In one aspect the composition comprises 1-10% of graphene
oxide and 90-99%
of graphite flakes. In one aspect of the invention the carbon grade of the
composition
embodiment is over 90% and in another aspect the carbon grade is 99%.
In one aspect this invention a graphite block composed of graphite flakes and
graphene
oxide is provided. A graphite block composed of graphite flakes and graphene
oxide. The carbon
grade of the block is preferably over 90% and more preferably the carbon grade
is 99%.
In one aspect of the invention the graphite block has a volume of at least
1cm3.
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In one aspect of the invention the graphite block has a density of at least
1.8g/cm3,
preferably at least 1.9 g/cm3 and most preferably at least 2.0g/cm3.
In one aspect of the invention the graphite block may contain enforcing
fibers.
In one aspect of the invention a process to make a graphite block from
graphite flakes and
graphene oxide, wherein the process comprises the steps of: a) Preparing a
graphene oxide
solution; b) Mixing the graphene oxide solution with graphite flakes to
receive a mixture; c) Heat
treating the mixture of step b) in an increased temperature to remove water
and oxygen from the
mixture; and d) Compressing the heat treated mixture under pressure to obtain
the block.
In one aspect of the invention the graphite block is formed of a mixture
comprising 5-
50% of graphene oxide and 50-95% of graphene flakes. In another aspect the
mixture comprises
the mixture comprises 90-95% of graphene flakes and 5-10% of graphene oxide,
and in a still
another aspect the mixture comprises 95% of graphene flakes and 5% of graphene
oxide.
In one aspect of the invention the graphite block is formed of a mixture of
graphene oxide
and graphite flakes by heat treating the mixture in an elevated temperature
and compressing the
mixture under a high pressure.
It is accordingly an object of this invention to provide a composition for
making
graphite blocks of any size or shape with high carbon purity and high density.
It is another object of this invention to provide high purity graphite blocks
with
characteristics similar to natural graphite.
It is yet another object of this invention to provide an economic and
environmentally
clean method to make high purity graphite blocks with characteristics similar
to natural
graphite.
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It is an object of this invention to provide high purity graphite blocks for
use in
furnace linings, lubrication, and electrodes.
It is an object of this invention to provide a graphite block originating from
graphite
flakes and graphene oxide, where the block has 99% carbon purity and a density
higher than 1.8
g/cm3.
It is an object of this invention to provide a graphite block originating from
graphite
flakes and graphene oxide, where the block may be of any desired size and have
the
characteristics of natural graphite.
It is another object of this invention to provide a graphite block originating
from graphite
flakes and graphene oxide, where the block has a density substantially similar
to natural graphite.
It is another object of this invention to provide a graphite block originating
from graphite
flakes and graphene oxide, where the block has superlubricating
characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a graphite blocks of this invention with dimensions of about
3"x4"x5"
(7.62x10.16x12.17 cm).
Figure 2 shows the compressive testing apparatus for compressed graphite
blocks.
Figure 3A, B, and C show failure modes of cylindrical blocks in compression
tests. In
Figure 3A triplicate of blocks made under 3000 pressure are shown. In Figure
3B triplicates of
blocks made under 7500 psi pressure are shown. In Figure 3C triplicates of
blocks made under
10000 psi are shown.
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Figure 4 shows the modulus of rupture test set up for testing compressed
graphite blocks.
Figure 5 A, B, C show failure modes of cubical blocks in modulus rupture
tests. In
Figure 5A triplicate of blocks made under 3000 pressure are shown. In Figure
5B triplicates of
blocks made under 7500 psi pressure are shown. In Figure 5C triplicates of
blocks made under
10000 psi are shown.
Figure 6 shows stereoscopic photographs of the compressed graphite blocks
compressed
under 3000, 6500 or 10000 psi pressure. Top surface photographs as well as
side surface
photographs are shown. Two different magnifications are shown.
Figure 7A and B show HIROX micrographs of the compressed graphite blocks
compressed under 3000, 6500 and 10,000 psi pressure. Figure 7A shows the top
surface
micrographs and Figure 7B shows the side surface micrographs. Three different
magnifications
are used.
DETAILED DESCRIPTION OF THE INVENTION
Definitions:
By natural graphite it is meant graphite obtained from ore. Natural graphite
may be
flake graphite, amorphous graphite or vein graphite. The term natural graphite
also includes
graphite obtained from ore and purified chemically or thermally to increase
the carbon
purity.
By synthetic graphite it is meant graphite manufactured from coke and coal tar
pitch.
Also highly oriented pyrographite (HOPG) is included into the term synthetic
graphite.
Synthetic graphite also includes graphite made of polymer films.
By superlubricity it is meant a phenomenon where the friction nearly vanishes
between
two solid surfaces.
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Graphene oxide is a compound of carbon, oxygen and hydrogen in variable
rations.
Traditionally graphene oxide is obtained by treating graphite with strong
oxidizers. Maximally
oxidized graphene is yellow solid with carbon: oxygen ratio between 2.1 and
2Ø By the
oxidation of graphite using strong oxidizing agents, oxygenated
functionalities are introduced in
the graphite structure which not only expand the layer separation, but also
makes the material
hydrophilic (meaning that they can be dispersed in water). This property
enables the graphite
oxide to be exfoliated in water using sonication, ultimately producing single
or few layer
graphene, known as graphene oxide (GO). The main difference between graphite
oxide and
graphene oxide is, thus, the number of layers. While graphite oxide is a
multilayer system,
graphene oxide is few layered.
Graphene has been synthesized by many methods including mechanical
exfoliation (Scotch tape method), chemical vapor deposition, epitaxial growth,
and solution
based approaches. Fabrication of large-area graphene has been the challenge
and an average size
of graphene sheets is 0.5-1 pm2. International patent application publication
W02013/089642 for
National University of Singapore which is incorporated herein by reference
discloses a process
for forming expanded hexagonal layered minerals and derivatives from graphite
raw ore using
electrochemical charging. Mesograf Tm is large area few layered graphene
sheets manufactured
by the method disclosed in W02013/089642. These few layered graphene sheets
made in one
step process from graphite ore have an area of 300 -500 pm2 in average.
Graphene oxide is a compound of carbon, oxygen and hydrogen in variable
rations.
Traditionally graphene oxide is obtained by treating graphite with strong
oxidizers. Maximally
oxidized graphene is yellow solid with carbon: oxygen ration between 2.1 and
2Ø Graphene
oxide for use in this invention is preferably made from Mesograf Tm instead of
the process of
oxidizing graphite first to graphite oxide and then via sonication to graphene
oxide. Graphene
oxide made of Mesograf TM is called Amphioxiderm. Amphioxidelm is graphene
oxidized at
least 20%. Amphioxide TM retains the layer structure of Mesograf Tm.
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Graphene oxide, including Amphioxide TM is highly hydrophilic. Amphioxide TM
is the
preferred graphene oxide of this disclosure and it is obtainable from Althean
Limited, Guernsey.
Amphioxide sheets have a lateral size of about 100 micrometers. The sheet may
have lateral
size as large as 200 micrometers. The area of AmphioxideTM sheets is at least
100 lim2, and
preferably at least 2001.1m2. The sheets may have an area as large as 300-500
pm2.
Even if AmphioxideTm graphene oxide sheets is preferred in this invention, the
graphene
oxide may be of other sources as well.
Preferred embodiments of the invention are now described.
According to a preferred embodiment of this invention a mixture of graphite
flakes of any
size and a solution of graphene oxide sheets with area of at least 100 pm2is
provided. According
to a preferred embodiment the mixture contains 5-50 v-% of graphene oxide and
50 -95v-% of
graphite flakes. The graphite flakes used may have coarse, fine or powder
flake size. However,
the flake size is not a determining factor of the process but any flake size
can be used. The
carbon purity of the flakes is preferably 87 to +99%, and more preferably 95
to +99% and most
preferably +99%.The mixture is placed in an elevated temperature for a period
of time that is
required to removal of water and oxygen molecules of the graphene oxide
component. Preferably
the mixture is heat treated at 120-600 C, more preferably at 300- 500 C, and
most preferably at
300- 400 C. Preferably the heat treatment is between 20 minutes to 3 hours,
more preferably
between 30 minutes to 2.5 hours, and most preferably from 60 minutes to 2
hours. After the heat
treatment a pressure of at least 1,000 psi is applied on the mixture. There is
no definite upper
limit for the pressure to be used. According to one preferred embodiment the
pressure may be up
to 50,000 psi. Most preferably the pressure is between 3,000 and 10,000 psi.
Once the pressure
is released a block of graphite is received. The carbon grade of the block is
higher than 99%,
indicating that the heat treatment was efficient to remove water and oxygen
from the mixture.
Preferably the carbon grade is 99.0 to 99.9%. Most preferably the carbon grade
is about 99.9%.
The size of the block depends on the amount of the mixture used; there seems
not to be any limit
to the size of the block. The density and the strength of the block varies
with the pressure used,
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but according to a preferred embodiment the density of the obtained block is
about same as
natural graphite.
According to a preferred embodiment the graphene oxide solution has 5 to 10
g/L of
graphene oxide.
According to one preferred embodiment the graphene oxide is AmphioxideTm.
According to another preferred embodiment the graphite block is enforced by
mixing
fibers, such as fiber glass fibers or basalt fibers into the mixture.
According to a preferred
embodiment the mixture has up to 12 v-% of fibers. The fibers may also include
steel fibers,
synthetic fibers and natural fibers.
The graphite block may also include fillers and extenders, such as but not
limited to
silica, kaolite, micas.
According to one preferred embodiment the resulting block is cubical.
According to
another preferred embodiment the resulting block is cylindrical. According to
yet another
embodiment the block may be of any feasible shape.
According to preferred embodiments the resulting graphite block is used to
replace
synthetic graphite in applications such as but not limited to electrodes,
furnace linings, and
lubrication.
The invention is now described in light of non-limiting examples. A skilled
artisan
understands that various changes and variations may be made to the examples
without diverting
from the spirit of this invention.
EXAMPLE 1. A method to make a graphite block by using 5% of 10g//L graphene
oxide and 95% of graphite flakes
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A mixture containing 5v-% of 10g/L solution (in 3% HC1) of graphene oxide
sheets
with an average area of at least 100 m2 (Amphioxideml) and 95v- % natural
graphite flakes
(Dixon #1 Flake Graphite) was prepared.
The mixture was heat treated in an oven in a temperature of 300 C for 60
minutes.
Amphioxide is provided in water solution and Amphioxide includes approximately
20-
30% oxygen. The heat treatment removes the water and the oxygen from the
mixture. The heat
treated mixture was compressed in a rectangular die at compaction force of
1000ps. In this
experiment the compaction force was applied for a period of 168 hours.
Depending on the
compaction force used and the size of the block, the time of compression may
vary between 100
and 250 hours.
As a result of the treatment a graphite block was obtained. The carbon grade
of
the block was over 99% indicating that the heat treatment was sufficient to
remove water and
oxygen.
The carbon grade may be defined for example spectrophotometrically. The
obtained
block is shown in Figure 1. In this case, the measurements of the block are
3"x4"x5"
(7.62x10.16x12.17 cm)
EXAMPLE 2. A method to make a graphite block by using 10% of 10g//L graphene
and 90% of graphite flakes
A mixture containing 10v-% of 10g/L solution (in 3% HC1) of graphene oxide
sheets
with an average area of at least 100 i_tm2 and 90% natural graphite flakes was
prepared. The
mixture was heat treated in an oven at a temperature of 400 C for 120 minutes.
The heat treated
mixture was compressed in a rectangular die at compaction force of 1000ps.
As a result of the treatment a graphite block is obtained. The carbon purity
of the block is
over 99%.
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EXAMPLE 3. A method to make a graphite block by using 10% of 5g//L graphene
and 90% of graphite flakes
A mixture containing 10v-% of 5g/L solution (3% HC1) of graphene oxide sheets
with an
area of at least 100 vm2 (AmphioxideTm) and 90% natural graphite flakes (Dixon
#1 flake)
was prepared. The mixture was heat treated in an oven at a temperature of 300
C for 120
minutes. The heat treated mixture was compressed in a rectangular die at
compaction force of
1000ps.
As a result of the treatment a graphite block is obtained. The carbon purity
of the block is
over 99%.
EXAMPLE 4. A method to make a graphite block by using 50% of lOgn
graphene and 50% of graphite flakes
A mixture containing 50v-% of 10 g/L solution (3% HC1) of graphene oxide
sheets with
average area of at least 1001.1m2 (AmphioxideTm) and 50v-% natural graphite
flakes (Dixon #1
flake) was prepared. The mixture was heat treated in an oven at a temperature
of 300 C for 60
minutes. The heat treated mixture was compressed in a rectangular die at
compaction force of
1000ps.
As a result of the treatment a graphite block is obtained. The carbon purity
of the block is
over 99%.
EXAMPLE 5. A method to make a graphite block by using 10% of 10g//L graphene
and 80% of graphite flakes and 10% of fiber glass.
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A mixture containing 10v-% of 10g/L solution (3% HC1) of graphene oxide sheets
with
average area at least 100 m2, 80% of natural graphite flakes and 10% of fiber
glass fibers was
prepared. The mixture was heat treated in an oven at a temperature of 300 C
for 120 minutes.
The heat treated mixture was compressed in a rectangular die at compaction
force of 1000ps.
As a result of the treatment a graphite block is obtained.
EXAMPLE 6. A method to make a graphite block by using 10% of 10g//L graphene
and 10% of graphite flakes and 10% of basalt fibers.
A mixture containing 10v-% of 10g/L solution (in 3% HC1) of graphene oxide
sheets
with an area of at least 100 m2, 80 v%of natural graphite flakes and 10 v-%
of basalt fibers
was prepared. The mixture was heat treated in an oven at a temperature of 300
C for 120
minutes. The heat treated mixture was compressed in a rectangular die at
compaction force of
1000ps.
As a result of the treatment a graphite block is obtained.
EXAMPLE 7. Density tests of blocks compressed under different pressures
In this example a number of blocks were prepared by using various compaction
forces to
compress the blocks. The compression time was constant. A mixture containing
5v-% of 10g/L
solution (in 3% HC1) of graphene oxide sheets with an average area of at least
100 iim2
(AmphioxideTM) and 95v-% natural graphite flakes (Dixon #1 Flake Graphite) was
prepared
as described in Example 1. The mixture was heat treated for 120 minutes in 300
C. Samples of
cubical and cylindrical blocks were made in a rectangular or a cylindrical die
using compaction
forces in pounds per square inch (psi) of 3,000, 5,000, 6,500, 7,500 and
10,000. The resulting
blocks were weighted, and the density of the blocks was measured. Table 1
below shows the
results with block type (B) and cylinder type (C) blocks.
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Test number Block type Compression Weight (g) Pressed Density
force PSI x volume (cc) (g/cc)
1000
1 B 10.00 49.73 24.382 2.040
2 B 7.50 49.73 24.990 1.990
3 C 10.00 26.23 12.926 2.029
4 C 7.50 22.62 10.823 2.089
Table 1.
As is seen from Table 1, the density of the blocks is very high, ranging from
1.990 to
2.089 g/cc.
Table 2 below shows another set of tests. In this case only block type (B)
blocks were
tested.
Test number Block type Compression Weight (g) Pressure Density
force PSI x volume ((cc) (g/cc)
1000
1 B 3.00 34.09 18.190 1.874
2 B 3.00 37.42 30.975 1.784
3 B 3.00 35.65 19.664 1.813
4 B 6.50 34.34 17.206 1.996
5 B 6.50 37.84 19.173 1.973
6 B 6.50 35.73 18.190 1.964
7 B 10.00 35.56 17.534 2.028
8 B 10.00 37.71 18.517 2.036
9 B 10.00 29.95 15.076 1.987
B 10.00 35.49 17.534 2.024
11 B 10.00 36.83 17.543 2.100
12 B 10.00 36.10 17.698 2.040
14 B 7.50 36.15 18.190 1.987
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14 B 5.00 36.07 18.517 1.948
Table 2.
Again it can be seen that the density of the blocks is very high, ranging from
1.784 g/cc
in a block compressed under 3000 Psi to 2.2g/cc in a block compressed under
10,000Psi
Table 3 below shows the average densities of blocks compressed at a defined
compression force level.
Compression force (PSI x 1000) Average density (g/cc)
10.00 2.043
7.50 2.002
6.50 1.978
5.00 1.948
3.00 1.824
Table 3.
The data in the Tables 1-3 indicate that the density of the samples is high
and increases as
the compaction force increase. The Dixon #1 Flake Graphite has a density of
approximately
1.051 gram per cubic centimeter (glee). The data shows that the density
increases from an
average of 1.824 g/cc for the blocks compressed at 3,000psi, to 1.984 g/cc for
the blocks
compressed at 5,000 psi, to 1.978 g/cc for the blocks compressed at 6,500 psi,
to 2.002 g/cc for
the blocks compressed at 7,500 psi and finally to 2.043 g/cc for the blocks
compressed at 10,000
psi samples. The literature indicates that the natural density of graphite is
approximately 2.2 g/cc.
Theoretical density of graphite is 2.26 glee. Any value lower than this
indicates that the graphite
material is porous. Maximum values for nonimpregnated manufactured graphites
is 1.90 g/cc.
This means that in the very best case, about 16% of the volume of such bulk
piece is open or
closed pores. The blocks according to this invention compressed under 10,000
psi had an average
density of 2.043g/cc, which means that only about 1.1% of the block volume is
open or closed
pores. Accordingly, the blocks made with the method of this invention have
very low porosity
and a density very close to the theoretical density of natural graphite.
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There is generally a correlation of hardness of graphite material to the
density. As density
increase, a general increase is seen in hardness. This is associated with the
amount of porosity,
which basically lowers the resistance to penetration. The lower the density,
the greater the pore
volume and the less the resistance to the penetrator, and hence, a lower
hardness. Therefore, the
high density of the blocks of this invention indicate low porosity as well as
high hardness.
The density of graphite is also known to relate to electrical resistivity of
graphite. As the
density increases the electrical resistivity is known to decrease. Thus the
high density of the
blocks of this invention indicate lot resistivity or high conductivity,
similar as natural graphite
has. Furthermore, the density is known to relate to thermal conductivity of
graphite. As the
density increases, the thermal conductivity also increases. Upon higher
thermal conductivity the
material has higher thermal shock resistance.
EXAMPLE 7. Compressive strength testing of the compressed graphite blocks
Additional characterization data was developed on both cylinder- and block-
type of
blocks. The Table 4 below summarizes compressive strength testing performed on
triplicate
block samples. The blocks were made as described in Example 1 and compressed
at pressures of
5000, 7500 and 10 000 psi.
The cylinder compression samples were made for compressive strength testing
while the
block samples were made for Modulus of Rupture testing. The average densities
for both the
cylinder and the block samples the three different compaction pressures are
almost identical and
mirror the densities shown in Tables 1-3.
When graphite material is portioned between two flat, parallel platens and a
continually
increasing compressive force is applied, the atomic or molecular bonds cannot
be re-formed
easily and therefore when crystalline planes begin to slip under the pressure,
catastrophic failure
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occurs and the material fractures. The compressive strength of a brittle
material such as graphite,
is expressed as the maximum force per unit area that can be withstood before
failure occurs.
Table 4.Characterization of cylinder (CL) and block (B) type of blocks.
Flake Graphite Compression Sample for Characterization Data
Merle Maws Average
Sumter, Compression Pressed Average Resistivity
Compressive Compressive of Modulus
Force Weight Volume Density Density Olin
Strength Strength Rupture R uptix e
PS1 X 1000 (g) tct) (g/cc) (gfcc) (0) (Psi) (psi)
(ksi) (ksii
0,- la 5 29.75 15.9 1.94 0,002 N,
a- 1 b . 5 29.7 15,55 1,91 0.002 175
a-1 c r
J 79:67 15.58 1,90 1.919 0,C*2 43 :308
.
Cl.s2z 7.5 29.91 14.81 2.02 0.1k2 550.
CL-2b . 7.5 29.8 14.9 1.99 0.002 612
CL-k , 7.5 29.77 14.94 1.99 2902 0.002 461 :542
: .
0.-3a 10 29.84 14,55 2,05 0.002 433
C1.-313 10 29.81 14.62 2.04 0.002 t.t96
C1-3c 10 29,77 14.64 2.03 2.942 0.002 786 706
B-1 a 5 49.71 25.79 1.93 0,002 65
9
B-it) . 5 49.7 25,84 1,92 0.002
68.3
B-1c 5 49.68 25,75 1,93, 1,927 4
002 69.6 ' 67.9
B-2.a 7,5 493 24,97 199 0.1K,12
123.8
. . ..õ ....... ... .
. ..... . ..
- .8-126 . ...1, .... 44:6 : .4:0 ii . OW
114,1
B-2c 7.5 49,65 24,93 199 1.991 0.002 121,3 119,7
,
B-3a 10 49.61 24.40 2.03 0,002
143.9
B-31) 10 49.61 24,37 2,04 0.002
132,3
B-3c 10 4957 2430 2,04 2,036 0.002 129.3 1352
EXAMPLE 8 Compression tests with cylindrical blocks
Dixon #1 Flake Graphite was mixed with graphene oxide as described above in
Example
1. After heat treating the mixture as described in example 1, samples were
labeled as 1, 2 and 3
and the blocks were made in a cylindrical die and compacted at pressures of
5000, 7500 and
10000 psi, respectively. The compression tests were performed in triplicate
and averages were
calculated in pounds per square inch (psi). The results of the compression
test are provided in
Table 5 below.
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Table 5. Compression strength tests for cylindrical blocks
Specimen ID Load (lb) Compressive strength
(psi)
1A 285 284
1B 176 175
1C 462 463
_
Average 308 308
SD 145 145
CV% 47 47
2A 553 550
2B 614 612
2C 465 464
Average 544 542
SD 75 75
CV% 14 14
3A 439 438
3B 897 896
3C 788 786
Average 708 706
SD 239 239
CV% 34 34
The test data indicates that the compressive strength increases from an
average of 308 psi
for the blocks compressed under 5,000 psi, to 542 psi for the blocks
compressed under 7,500 psi
and to 706 psi for the blocks compressed under 10,000 psi.
Figure 2 shows the compressive testing apparatus. Figure 3 shows failure modes
of each
tested triplicate.
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EXAMPLE 9. Modulus of Rupture tests with the cubical blocks
Dixon #1 Flake Graphite was mixed with graphene oxide as described above in
Example
1. After heat treating the mixture as described in example 1, the samples were
labeled as 1, 2
and 3 and the blocks were made in a rectangular die and compacted at pressures
of 5000, 7500
and 10000 psi, respectively. The modulus of rupture (MOR) tests were performed
in triplicate
and averages were calculated in pounds per square inch (psi). The results of
the compression test
are provided in Table 5 below.
Specimen ID Width (in) Thickness (in) Load (lb) MOR (ksi)
lA 0.638 0.959 12.5 65.9
1B 0.638 0.957 12.9 68.3
1C 0.638 0.955 13.1 69.6
Average 12.8 67.9
SD 0.3 1.9
CV% 2 3
2A 0.638 0.924 21.8 123.8
2B 0.638 0.924 20.1 114.1
2C 0.638 0.925 21.4 121.3
Average 21.1 119.7
SD 0.9 5
CV% 4 4
3A 0.638 0.903 24.2 143.9
3B 0.638 0.906 22.4 132.3
3C 0.638 0.902 21.7 129.3
Average 22.8 135.2
SD 1.3 7.7
CV% 6 6
Table 5. Modulus rupture date for cubic blocks
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The results indicate that the MOR increases from an average of 67.9 ksi for
the blocks
made under 5000 psi pressure, to 119.7 ksi for blocks made under 7500 psi
pressure to 135.2 ksi
for blocks made under 10 000 psi pressure.
Figure 4 shows the modulus of rupture test set up. Figure 5 shows failure
modes of each
tested triplicate.
EXAMPLE 10 Photographic illustrations of the dense structure of the blocks
Figure 6 shows stereoscopic photographs of the compressed graphite blocks
compressed
under 3000, 6500 or 10000 psi pressure. Top surface photographs as well as
side surface
photographs are shown. Two different magnifications are shown. The photographs
reveal the
increasing density of the material of blocks compressed under 3000, to blocks
compressed under
6500 and to blocks compressed under 10000 psi.
Figure 7A and B show HIROX micrographs of the compressed graphite blocks
compressed under 3000, 6500 and 10 000 psi pressure. Figure 7A shows the top
surface
micrographs and Figure 7B shows the side surface micrographs. Three different
magnifications
are use. The photographs reveal the increasing density of the material of
blocks compressed
under 3000, to blocks compressed under 6500 and to blocks compressed under
10000 psi.
EXAMPLE 11 Superlubricity character of the blocks
The lubrication characteristics of the blocks were confirmed by Atomic Force
Microscopy. Preliminary results show that the when the block of this invention
as prepared as
described in Example 1 is rubbed on to a glass surface the lubrication effect
is six times higher
than for graphene (results not shown).
Graphite alone applied as a powder or as graphite foil showed 90% less
lubrication than
graphene. Moreover, graphite alone cannot be applied as a block or a brick as
such structure
does not exist.
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When the block of this invention prepared as described in Example 1 was rubbed
on Si02
the lubrication was 2 to 4 times more than rubbing graphene (results not
shown). Again graphite
powder or graphite foil alone did not show any improvement as compared to
graphene's
lubricating characters.
The great advantage of the present invention is that the superlubricator is
provided in a
form of a block. Therefore superlubtication becomes convenient as the block
can simply be run
across a surface that is in need of lubrication. This lubrication method can
be used for example in
making brakes, superlubricating rail guns and machine parts, wheels and so on.
Although this invention has been described with a certain degree of
particularity, it is to
be understood that the present disclosure has been made only by way of
illustration and that
numerous changes in the details of construction and arrangement of parts may
be resorted to
without departing from the spirit and the scope of the invention.
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