U.S. patent application number 11/442637 was filed with the patent office on 2006-12-21 for process for the production of graphite powders of increased bulk density.
This patent application is currently assigned to TIMCAL AG. Invention is credited to Davide Cattaneo, Michael Spahr, Klaus Streb.
Application Number | 20060286025 11/442637 |
Document ID | / |
Family ID | 4227408 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060286025 |
Kind Code |
A1 |
Spahr; Michael ; et
al. |
December 21, 2006 |
Process for the production of graphite powders of increased bulk
density
Abstract
The invention relates to a method for increasing the Scott
density of synthetic and/or natural graphite powders of any
particle size distribution, preferably of highly-pure graphite, by
subjecting the graphite powder to an autogenous surface treatment.
The inventive powder is used, in particular, for producing
dispersions, coatings with an increased graphite/binder ratio and
increased electric and thermal conductivity, gas and liquid-tight
coatings on metal substrates, thermoplastic or duroplastic
graphite-polymer composites, or for producing metallic, non-ferrous
sintering materials.
Inventors: |
Spahr; Michael; (Cham,
CH) ; Cattaneo; Davide; (Arbedo, CH) ; Streb;
Klaus; (Sins, CH) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
TIMCAL AG
|
Family ID: |
4227408 |
Appl. No.: |
11/442637 |
Filed: |
May 26, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10130261 |
Jul 15, 2002 |
7115221 |
|
|
PCT/CH00/00514 |
Sep 22, 2000 |
|
|
|
11442637 |
May 26, 2006 |
|
|
|
Current U.S.
Class: |
423/448 ;
429/231.8 |
Current CPC
Class: |
Y02E 60/50 20130101;
H01B 1/24 20130101; H01M 4/587 20130101; H01M 8/0213 20130101; H01M
8/0226 20130101; Y02P 70/50 20151101; C01B 32/21 20170801; H01M
4/133 20130101; C08K 9/00 20130101; H01M 8/0206 20130101; H01M
8/0228 20130101; C09C 1/46 20130101; C01P 2006/11 20130101; H01M
4/1393 20130101; Y02E 60/10 20130101; C01P 2004/61 20130101; C08K
3/04 20130101; C01B 32/20 20170801 |
Class at
Publication: |
423/448 ;
429/231.8 |
International
Class: |
H01M 4/58 20060101
H01M004/58; C01B 31/04 20060101 C01B031/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 1999 |
CH |
2165/99 |
Claims
1-15. (canceled)
16. A process for increasing the pressed density of a starting
graphite powder of any particle size distribution, the starting
graphite powder chosen from synthetic graphitic carbon and natural
graphitic carbon wherein the starting graphite powder has a high
graphite content in the particle, comprising subjecting the
starting graphite powder to an autogenous surface treatment in
which individual graphite powder particles are allowed to impact
with one another at a measured speed so that their surface
structure changes while substantially retaining graphite particle
shape without a substantial grinding effect occurring and wherein
said autogenous surface treatment is carried out until the pressed
density of the starting material has increased by at least about
0.5% to 10%
17. The process according to claim 16 wherein the graphite powder
is high-purity graphite.
18. The process according to claim 16 wherein the graphite powder
has a xylene density ranging from 1.80 to 2.27 g/cm.sup.3, a
crystal structure characterized by a c/2 value of 0.3354 to 0.3360,
and an L.sub.c value of more than 40nm (L.sub.c>40nm).
19. The process according to claim 16 wherein the graphite powder
has a particle size of up to 150 .mu.m.
20. The process according to claim 19 wherein the graphite powder
has a particle size of 1 pm to 50 .mu.m.
21. The process according to claim 16 wherein the autogenous
surface treatment is carried out until the pressed density of the
starting graphite powder has increased by about 1% to 8%.
22. The process according to claim 16 wherein the autogenous
surface treatment is carried out by fluidizing or dispersing
graphite powder particles with sizes of <100 .mu.m in an inert
carrier gas with the aid of a carrier gas.
23. The process according to claim 16 wherein the autogenous
surface treatment is carried out by dispersing graphite powder
particles with sizes of <300 .mu.m by means of a rotating
mechanical tool.
24. The process according to claim 23 wherein the rotating
mechanical tool is a turbine.
25. A process for decreasing the absorption capacity of a starting
graphite powder of any particle size distribution, the starting
graphite powder chosen from synthetic graphitic carbon and natural
graphitic carbon wherein the starting graphite powder has a high
graphite content in the particle, comprising subjecting the
starting graphite powder to an autogenous surface treatment in
which individual graphite powder particles are allowed to impact
with one another at a measured speed so that their surface
structure changes while substantially retaining graphite particle
shape without a substantial grinding effect occurring and wherein
said autogenous surface treatment is carried out until the
absorption capacity of the starting material has decreased by at
least about 10% to 50%.
26. The process according to claim 25 wherein the graphite powder
is high-purity graphite.
27. The process according to claim 25 wherein the graphite powder
has a xylene density ranging from 1.80 to 2.27 g/cm.sup.3, a
crystal structure characterized by a c/2 value of 0.3354 to 0.3360,
and an L.sub.c value of more than 40 nm (L.sub.c>40 nm).
28. The process according to claim 25 wherein the graphite powder
has an average particle size of up to about 150 .mu.m.
29. The process according to claim 28 wherein the graphite powder
has an average particle size of about 1 .mu.m to 50 .mu.m.
30. The process according to claim 25 wherein the autogenous
surface treatment is carried out until the absorption capacity of
the starting graphite powder has increased by about 20% to 45%.
31. The process according to claim 25 wherein the autogenous
surface treatment is carried out by fluidizing or dispersing
graphite powder particles with sizes of <100 .mu.m in an inert
carrier gas with the aid of a carrier gas.
32. The process according to claim 25 wherein the autogenous
surface treatment is carried out by dispersing graphite powder
particles with sizes of <300 .mu.m by means of a rotating
mechanical tool.
33. The process according to claim 32 wherein the rotating
mechanical tool is a turbine.
34. An apparatus for treating graphite particles comprising a
cylindrical chamber comprising a base and a curved face, the
cylindrical chamber further comprising a first aperture for
graphite particles exiting the cylindrical chamber; a second
aperture for graphite particles entering the cylindrical chamber;
an internal disk for accelerating the graphite particles, having a
diameter less than the inner diameter of the cylindrical chamber
wherein the disk further comprises one or more impact pins and a
rim; a motor for rotating the internal disk; a shaft for connecting
the motor and the internal disk; and a tube for circulating
graphite particles from the first aperture to the second aperture,
further comprising an external input for adding graphite particles
to the tube and an external output for removing graphite particles
from the tube.
35. The apparatus of claim 34 wherein the first aperture is located
on the curved face of the cylindrical chamber.
36. The apparatus of claim 34 wherein the second aperture located
on the base of the cylindrical chamber.
37. The apparatus of claim 36 wherein the second aperture is
located at about the center of the base of the cylindrical
chamber.
38. The apparatus of claim 34 wherein the impact pins are mounted
flush with the rim of the internal disk and extend towards the
center of the internal disk.
39. The apparatus of claim 38 wherein the length of the impact pins
are less than the radius of the internal disk.
40. The apparatus of claim 39 wherein the impact pins are located
on a single face of the internal disk.
41. The apparatus of claim 40 wherein the impact pins are located
on the face of the internal disk nearest to the second
aperture.
42. The apparatus of claim 41 wherein the internal disk has a
periphery of about 0.75m.
43. The apparatus of claim 34 wherein the motor rotates the
internal disk at about 4800 rpm.
44. The apparatus of claim 34 wherein the graphite particles are
added to the tube through the external input and removed from the
circulation tube through the external output continuously.
45. A graphite powder subjected to the process of claim 16 or 25,
having at least one property chosen from increased bulk density,
decreased absorption capacity, and increased pressed density.
46. A graphite material with an average particle size of about 14
micron having a Scott density of about 0.30 g.cm.sup.-3; a tamped
density of about 0.674 g.cm.sup.-3; a dibutyl phthalate (DBP) oil
absorption of about 64 g DBP/100 g graphite; and a pressed density
of about 1.957 g.cm.sup.-3.
47. A graphite material with an average particle size of about 20
micron having a Scott density of about 0.38 g.cm.sup.-3; a tamped
density of about 0.778 g.cm.sup.-3; a dibutyl phthalate (DBP) oil
absorption of about 73 g DBP/100 g graphite; and a pressed density
of about 2.051 g.cm.sup.-3.
48. A graphite material with an average particle size of about 14
micron having a Scott density of about 0.34 g.cm.sup.-3; a tamped
density of about 0.738 g.cm.sup.-3; a dibutyl phthalate (DBP) oil
absorption of about 75.0 g DBP/100 g graphite; and a pressed
density of about 2.036 g.cm.sup.-3.
49. A graphite material with an average particle size of about 15
micron having a Scott density of about 0.36 g.cm.sup.-3; a tamped
density of about 0.766 g.cm.sup.-3; a dibutyl phthalate (DBP) oil
absorption of about 81.8 g DBP/100 g graphite; and a pressed
density of about 2.036 g.cm.sup.-3.
50. A graphite material with an average particle size of about 14
micron having a Scott density of about 0.42 g.cm.sup.-3; a tamped
density of about 0.862 g.cm.sup.-3; a dibutyl phthalate (DBP) oil
absorption of about 58.9 g DBP/100 g graphite; and a pressed
density of about 2.064 g.cm.sup.-3.
51. A graphite material with an average particle size of about 38
micron having a Scott density of about 0.46 g cm.sup.-3; a tamped
density of about 0.902 g.cm.sup.-3; a dibutyl phthalate (DBP) oil
absorption of about 54.7 g DBP/100 g graphite; and a pressed
density of about 1.972 g.cm.sup.-3.
52. A graphite material having a Scott density of about 0.45
g/cm.sup.3 or greater.
53. A graphite material having a tamped density of about 0.90
g/cm.sup.3 or greater.
54. A liquid dispersion comprising a detectable amount of at least
one graphite material of any one of claims 46 to 53 and a
liquid.
55. The liquid dispersion of claim 54, having an increased solids
content.
56. The liquid dispersion of claim 55, wherein the solids content
is increased by about 5% to about 30%.
57. A coating on a metallic substrate, the coating comprising a
detectable amount of at least one graphite material of claim 45 and
a polymeric binder.
58. A negative electrode of a lithium ion battery comprising the
coating of claim 57.
59. A lithium ion battery comprising the negative electrode of
claim 58.
60. A composite comprising a thermoplastic or thermosetting polymer
and a detectable amount of at least one graphite material of claim
45.
61. The composite of claim 60, compressed to provide a graphite
plate of high electrical conductivity.
62. An electrolyte fuel cell, comprising the graphite plate of
claim 61 as a bipolar plate.
63. A metallic sintered material comprising a detectable amount of
at least one graphite material of claim 45 wherein the metallic
sintered material is substantially free of iron.
Description
[0001] This is a continuation of application Ser. No. 10/130,261,
which was accepted as a filing under 35 U.S.C. 371 on Jul. 15, 2002
and which is a 371 filing of PCT Application No. PCT/CH00/00514,
filed Sep. 22, 2000, which claims priority to Swiss Application
2165/99, filed Nov. 26, 1999. All of these applications are
incorporated herein by reference in their entirety.
[0002] The present invention relates to a process for the
production of graphite powders of increased bulk density. The
present invention relates in particular to an autogenous surface
treatment of any pulverulent graphitic materials, their bulk
density and tamped density being markedly increased and other
important material properties being advantageously modified as a
result of the mutual physical-mechanical action of the individual
powder particles.
[0003] Graphitic materials, especially those with a high graphite
content, are known per se and are used in industry in a variety of
ways. High-purity graphitic carbons have xylene densities (also
called single-crystal densities or real densities) ranging from
1.80 to 2.27 g.cm.sup.-3 and a crystal structure which can be
characterized by a c/2 value of 0.3354 to 0.3360 nm and an L.sub.c
value of more than 40 nm (L.sub.c>40 nm). These materials are
obtained from natural sources, enriched and purified or produced
synthetically from amorphous carbon products in a high temperature
process. Subsequent grinding processes produce pulverulent
materials with different mean particle sizes in each case. A given
particle size for a powder is normally always a mean value of a
specific particle size distribution. The particle size distribution
to be used for a particular purpose depends especially on the
composition of the graphitic material and the associated
properties, as well as on the intended use.
[0004] The particle shape is always platelet-like, the anisotropy
of the particles being the more pronounced the higher the xylene
density and L.sub.c values. The Scott density (also referred to as
bulk density) of such materials, for example with particle sizes
smaller than 100 micron (particle size <100 .mu.m, determined by
laser diffraction analysis), is normally below 0.25 g.cm.sup.-3,
the Scott density being the lower the smaller the particle size.
Comminution of the particles by grinding generally results in a
lowering of the Scott density. The Scott density can be somewhat
increased by an optimized particle size distribution. Thus, for
example, Scott densities up to max. 0.3 g.cm.sup.-3 are achieved by
an optimized composition of fine and coarse fractions for such
materials with particle sizes below 100 micron.
[0005] The tamped density, the compressibility and the absorption
capacity for polymeric binder materials and liquids such as oils,
and for organic solvents and aqueous systems, are equally important
properties of graphite powders. These properties correlate with the
composition of the graphite powders and especially with the
particle size distribution. It has now been found that,
surprisingly, the values of the Scott density for a particular
graphite powder of any particle size distribution is considerably
increased when the graphite powder is subjected to an autogenous
surface treatment in which the particles impact with one another at
an appropriate speed and for a sufficient length of time. The
impacts and the associated mutual physical-mechanical action change
the structure or surface of the graphite particle in such a way as
to result in a considerable increase in the Scott density. The
other properties mentioned above are also modified to a
considerable extent.
[0006] Under the electron microscope, the crude, ground,
platelet-like graphite particle has an irregular shape and sharp
edges. The irregular particle contours are abraded and the edges
rounded off by the treatment according to the invention. If the
energy dose is appropriately optimized, the grinding effect which
occurs with other mechanical treatments, leading to a noticeable
lowering of the bulk density, is considerably reduced or minimized.
Although the abrasion of the particles creates dust, which,
together with a minimal grinding effect, leads to a slight
reduction in particle size and Scott density (bulk density), this
particle size effect is far outweighed by the surprisingly large
total increase in Scott density, and the change in the other
properties, caused by the treatment according to the invention. The
present invention can be at least partly explained by the observed
changes in the particle contours, but the invention is not bound to
this explanation.
[0007] The present invention is defined in the Claims. In
particular, the present invention relates to a process for
increasing the Scott density of graphite powders of any particle
size distribution, characterized in that the graphite powder is
subjected to an autogenous surface treatment.
BRIEF DESCRIPTION OF THE DRAWING
[0008] FIG. 1A is a diagram of an apparatus for treating graphite
particles.
[0009] FIG. 1B is an alternative view of the apparatus in FIG.
1A.
[0010] The process of autogenous surface treatment consists in
allowing the individual powder particles to impact with one another
at a measured speed so that, as a result of the associated mutual
physical-mechanical action of the individual particles, their
surface structure changes but the individual particle remains
substantially unbroken, i.e. no substantial grinding effect occurs.
This change in the particle contour or surface structure of the
individual particle gives rise to the increase in Scott density
according to the invention. The autogenous surface treatment is
carried out, and the individual particles are allowed to act on one
another, until the desired Scott density is achieved. The measured
speed means that the speed or energy with which the individual
particles are charged is adjusted so that the particles do not
disintegrate on impact or collision, thereby practically avoiding a
grinding effect. This adjustment is a question of process
optimization and does not present a problem to those skilled in the
art.
[0011] The Scott density achievable by means of the optimized
grinding effect for a graphite powder of any particle size
distribution can be increased in each case by at least about 10% to
about 100%, preferably by about 20% to 80%, by the autogenous
surface treatment according to the invention. Hitherto unattained
Scott densities of 0.45 g/cm.sup.3 or more are thus achieved for
graphitic materials.
[0012] The tamped density achievable by means of the optimized
grinding effect for a graphite powder of any particle size
distribution can also be increased by at least about 10% to 100%,
preferably by about 20% to 80%, by the process according to the
invention. Hitherto unattained tamped densities of at least 0.90
g/cm.sup.3 are thus achieved for graphite powders.
[0013] In the case of particle sizes of <100 .mu.m, the
autogenous surface treatment according to the invention is
preferably carried out by fluidizing or dispersing the graphite
powder particles in an inert carrier gas and accelerating the
particles with the aid of the carrier gas, as described below. The
intensity of this treatment is determined by the carbon type and
the mass of the particles, their speed and the amount of material
used per treatment, i.e. the concentration of the fluidized
particles dispersed in the gas. The intensity of the treatment
increases with the softness of the graphitic carbon used, the mass
of the particles, their speed and the amount used. For particle
sizes of <300 .mu.m, the dispersion and acceleration of the
particles are preferably effected by means of rotating mechanical
tools, for example in the present process by means of a turbine or
directly by means of a rotating disk.
[0014] However, the grinding effect which occurs also increases
simultaneously with increasing intensity of the treatment. Thus, to
achieve the maximum bulk density of a material, there is a maximum
intensity which results from the optimized parameters of particle
speed, particle mass and amount used. The formation of agglomerates
due to the agglutination of smaller particles, which would also
lead to a sustained increase in the Scott density, has not been
observed. Treated particles larger than the untreated particles
used did not appear in any of the experiments performed. Analyses
of the treated materials by scanning electron microscopy also
showed no such agglomeration.
[0015] The treatment according to the invention not only increases
the Scott density but also improves the compressibility properties
of the graphite powders and reduces their absorption capacity for
polymeric binder materials and liquids such as oils, organic
solvents and aqueous systems. The crystallinity of the graphitic
carbon particles, on the other hand, remains unaffected by the
mechanical surface treatment. The structural parameters and the
xylene density also remain unchanged compared with the untreated
particles.
[0016] The process according to the invention also increases the
pressed density achievable by the optimized grinding effect for a
graphite powder of any particle size distribution by at least about
0.5% to 10%, preferably by about 1% to 8%. If the powders treated
according to the invention are used to produce mouldings by
compression under a pressure of 2.5 to/cm.sup.2, markedly higher
pressed densities can be achieved compared with the untreated
materials.
[0017] Furthermore, the powders treated according to the invention
exhibit a markedly reduced oil absorption capacity and binder
uptake ranging from about 10% to 50% and especially from an average
of about 20% to 45%, values in excess of 50% also being obtainable.
This effect is achieved by the treatment according to the invention
because the porosity (pore structure) of the particles is not
affected by the treatment, as can be demonstrated by the fact that
the nitrogen adsorption properties and xylene densities hardly
change.
[0018] Said markedly reduced absorption properties also result in
markedly lower viscosities of dispersions of the graphite powders
treated according to the invention in liquid media, so dispersions
with a correspondingly increased solids content can be prepared
with the graphite powders treated according to the invention. The
solids content of liquid carbon dispersions can be increased by
more than 5% to over 30% by using graphite powders treated
according to the invention.
[0019] Graphite powders suitable for the use according to the
invention are especially those with a high graphite content in the
particle, and particularly so-called high-purity graphites,
preferably with xylene densities ranging from 1.80 to 2.27
g.cm.sup.-3 and a crystal structure characterized by a c/2 value of
0.3354 to 0.3360 nm and an L.sub.c value of more than 40 nm
(L.sub.c>40 nr). The powders can be obtained from natural
sources or prepared synthetically from amorphous carbon products
and can have any mean particle size and particle size distribution.
Preferred pulverulent graphitic materials are those with a mean
particle size of up to 150 .mu.m, preferably of 1 .mu.m to 50
.mu.m, and especially high-purity pulverulent graphites. Such
graphites are known per se.
[0020] The process according to the invention is preferably carried
out in such a way that the graphite powder particles to be treated
are dispersed and fluidized in a gas. This can be done using any
method of fluidization technology known per se in which the
particles impact with one another in the fluidized state and
thereby change their surface contours and surface structures, as is
the case e.g. in a fluidized bed. However, to carry out the process
according to the invention, the fluidized particles are preferably
provided with higher speeds so that the particles fluidized in this
way are accelerated with higher energies. Preferably, the fluidized
particles are continuously concentrated and diluted again in the
gaseous environment. The resulting collisions between the particles
set in rotation, and the friction between them, result in surface
abrasion of the particles, the energy transferred to the particles
being adjusted so that the collisions and friction cause
substantially no disintegration of the particles.
[0021] The process according to the invention can be put into
optimum effect e.g. in the device shown in FIGS. 1A and 1B. This
device consists specifically of a circular disk 100 with radial
impact pins 101 flush-mounted on the rim, said disk being sheathed
by a cylindrical treatment chamber 110 closed to the outside
(turbine with associated turbine effect). The dimensions of the
cylindrical treatment chamber 110 are adjusted so that it encloses
the disk 100 and can allow some space between its inner wall and
the rotating disk 100. The disk 100 is connected to a motor 160,
located outside the treatment chamber 110, by means of a shaft 150
through the wall of the treatment chamber and can be set in
rotation by this motor 160. The cylindrical treatment chamber is
provided with a radial aperture 111 (hole). An additional aperture
112 (hole) is provided in the cylinder jacket of the treatment
chamber 110, perpendicular to the disk and disk axis. Apertures 111
and 112 are connected by a tube 120 located outside the treatment
chamber. Thus tube 120 running outside the treatment chamber 110
and attached to the wall of the treatment chamber 110, connects the
periphery of the treatment chamber 110 to its centre. The gas
(fluid) containing the fluidized particles, accelerated
centrifugally by the rotating disk 100, circulates through this
external treatment tube 120, exiting through the tube at the
periphery of the treatment chamber 110 as a result of the
centrifugal force and flowing back through the other end of this
tube into the centre of the treatment chamber 110, where it is
accelerated again. The particles of material are accelerated by the
impact pins 101 of the rotating disk 100 and driven away in a
peripheral direction by the centrifugal forces produced by the
high-speed rotor. The particles dispersed and accelerated into the
gas in this way circulate in the machine along the inside of the
cylinder jacket. The particles reaching the inlet of the
circulation tube, input 130 enter the tube and return to the
treatment chamber in the region of the centre of the machine. This
results in a continuous concentration and dilution of the particles
in the surrounding gaseous medium. A fraction of the treated
particles is continuously fed into input 130 or withdrawn from an
attached tube, output 140, but the process can also be carried out
as a batch process. The graphite powders treated according to the
invention can advantageously be used as pigments in aqueous or
solvent-based dispersions, thereby achieving higher solids contents
than with untreated powders. The viscosity of liquid dispersions of
materials treated according to the invention is markedly lower for
the same solids content. Also, when dispersions according to the
invention are applied to substrates and dried, coatings with
markedly lower porosity values are obtained because the content of
liquid phase is markedly lower. The higher solids content also
means that smaller binder/carbon ratios are needed to stabilize a
dried carbon coating on a substrate. The low polymeric binder
contents result in a marked increase in the electrical and thermal
conductivities of such carbon layers.
[0022] Dispersions containing mixtures of synthetic and/or natural
graphitic carbons treated according to the invention and a
polymeric binder in an aqueous or solvent-based medium can be
applied to metal foils and dried to give stable coatings (for
thicknesses of 10 to 5000 .mu.m) with an increased graphite/binder
ratio and hence also increased electrical and thermal
conductivities. The porosities of the dried films are normally
below 50% and are thus appreciably lower than those of films formed
of conventional graphites. Such dispersions can therefore
advantageously also be used for gas-tight and liquid-tight coatings
on metal substrates, which can be used as electrically conducting
anticorrosive films on metal foils and plates.
[0023] The dried coatings formed by the graphites treated according
to the invention can be compressed by a calender without the
graphite film delaminating from the metal foil. This delamination
from the metal foil is frequently observed with untreated
graphites. The calendering of graphite films produced from graphite
powders treated according to the invention affords coatings with
porosities below 30% without altering the texture or particle
structure of the graphite powders used. Such film coatings on metal
foils, characterized by porosities below 30% and stabilized with
lower binder/carbon ratios, can be used in lithium ion batteries as
negative electrodes with charge densities above 550 Ah/l. The
current-carrying capacity of such electrodes is markedly higher
than that of electrodes made of conventional graphite powders. Such
negative electrodes can thus be used very advantageously for
lithium ion cells with a high power density.
[0024] The high packing density of the synthetic or natural
graphites treated according to the invention, combined with the
relatively low polymeric binder absorption capacity, is
advantageous in the production of graphite/polymer composites which
can be compressed to gas-tight graphite plates of high electrical
conductivity. Such plates are advantageously used as bipolar plates
in polymer electrolyte fuel cell technology.
[0025] Mixtures of polymers with synthetic or natural graphites or
graphitic carbons treated according to the invention form
thermoplastic or thermosetting composites with a higher proportion
of carbon filler and a lower processing viscosity: Thermoplastic
polymer/graphite composite materials with graphites treated
according to the invention have higher (and hence improved) values
in respect of their isotropic, mechanical, thermal and electrical
properties and behave more isotropically than composites with
untreated graphitic carbons.
[0026] Metallic non-ferrous sintered materials which have been
produced with synthetic or natural graphitic carbons treated
according to the invention, or contain such carbons, have improved
isotropic, mechanical and tribological properties.
[0027] The Examples which follow describe the invention.
[0028] Examples 1 to 6 show the material properties of various
graphites before and after the autogenous surface treatment
according to the invention. The experiments were performed in the
device described in the above section. The rotating disk used had a
periphery of 0.75 m and a speed of rotation of 4800 rpm.
[0029] Examples 1-6 were carried out under the experimental
conditions given in Table 1. TABLE-US-00001 TABLE 1 Type of Speed
of Example graphite Amount used Treatment time rotating disk 1
TIMREX .RTM. 150 g 5 min 4800 rpm KS-graphite 2 TIMREX .RTM. 150 g
5 min 4200 rpm SLX-graphite 3 TIMREX .RTM. 150 g 5 min 4800 rpm
SLM-graphite 4 TIMREX .RTM. 200 g 5 min 4800 rpm SFG-graphite 5
TIMREX .RTM. 200 g 7 min 4800 rpm NP-graphite 6 TIMREX .RTM. 200 g
5 min 4800 rpm KS 5-75 TT TIMREX .RTM. KS-graphite = TIMREX .RTM.
KS 5-25 from TIMCAL AG TIMREX .RTM. SLX-graphite = TIMREX .RTM. SLX
50 from TIMCAL AG TIMREX .RTM. SLM-graphite = TIMREX .RTM. SLM 44
from TIMCAL AG TIMREX .RTM. SFG-graphite = TIMREX .RTM. SFG 44 from
TIMCAL AG TIMREX .RTM. NP-graphite = TIMREX .RTM. NP 44 from TIMCAL
AG
[0030] Examples 1 to 6 show a marked increase in Scott density
(bulk density) and tamped density for the powders treated according
to the invention. The treated powders exhibited no agglomerates
whatsoever. The resulting change in particle size distribution is
indicative of a small grinding effect. The slight lowering of d
values, however, is caused especially by the dust produced by the
abrasion of the particles. The pore structure of the treated
particles is not affected by the surface treatment. It is assumed
that the dust produced by the treatment and the slight decrease in
particle size distribution are the main reason for the slight
lowering of the L.sub.c values and the xylene densities. The
elastic recovery of the compressed treated materials drops sharply.
The pressed density of mouldings produced from the treated
materials under a pressure of 2.5 to/cm.sup.2 increases sharply.
Although the BET values are increased somewhat, the oil absorption
and binder absorption of the particles treated according to the
invention decrease markedly. Dispersions of treated carbon
particles in liquid media exhibit markedly lower viscosities than
dispersions of untreated carbon particles. The solids content of
liquid carbon dispersions can be increased by more than 5% by using
carbon particles according to the invention. The electrical
resistance of the carbons treated according to the invention
increases. The changes in surface contours of the individual
particles which result from the treatment of powders according to
the invention can be clearly seen from scanning electron
micrographs.
Experimental Section
[0031] The particle size distribution of the materials was
determined by laser diffraction analysis using a MALVERN
Mastersizer. The structural parameters were obtained from X-ray
diffraction experiments based on the CuK.sub..alpha.1 line. The
crystallographic cell constant in the c direction (c/2) was
determined from the relative position of the (002) or (004)
diffraction reflex. The maximum height of the single-crystal
domains in a particle in the crystallographic c direction, L.sub.c,
and the resulting number of ideally stacked graphite planes were
obtained from the (002) or (004) diffraction reflex according to
the model of Scherrer and Jones (P. Scherrer, Gottinger Nachrichten
2 (1918) p. 98; F. W. Jones, Proc. Roy. Soc. (London) 166 A (1938)
p. 16). The xylene density was determined according to DIN 51 901.
Determination of the Scott density was based on ASTM B 329. The
tamped density was determined according to AKK-19. The specific
surface areas were determined by the method of Brunauer, Emmett and
Teller using a Micromeritics ASAP 2010. To determine the elastic
recovery, the material was placed under a pressure of 0.5
to/cm.sup.2. The recovery was obtained from the height of the
moulding with and without applied pressure and is given in percent.
The electrical resistance was measured according to DIN 51 911
using a moulding produced under a pressure of 2.5 to/cm.sup.2. The
pressed density of this moulding is also given. The oil absorption
was measured on the basis of DIN ISO 787 with initial weights of
0.5 g of material and 1.5 g of oil. The mixture was centrifuged in
a Sigma 6-10 centrifuge for 90 min at a speed of 1500 rpm.
EXAMPLE 1
[0032] TABLE-US-00002 TIMREX .RTM. KS synthetic graphite TIMREX
.RTM. KS synthetic graphite Untreated After treatment Particle size
Particle size d.sub.10 = 7.0 micron d.sub.10 = 5.9 micron d.sub.50
= 15.2 micron d.sub.50 = 13.5 micron d.sub.90 = 30.2 micron
d.sub.90 = 27.4 micron L.sub.c(002)/L.sub.c(004)
L.sub.c(002)/L.sub.c(004) 120 nm/68 nm 101 nm/64 nm c/2 (002)/c/2
(004) c/2 (002)/c/2 (004) 0.3355 nm/0.3355 nm 0.3355 nm/0.3355 nm
Xylene density Xylene density 2.254 g cm.sup.-3 2.248 g cm.sup.-3
Scott density Scott density 0.23 g cm.sup.-3 0.30 g cm.sup.-3
Tamped density Tamped density 0.539 g cm.sup.-3 0.674 g cm.sup.-3
BET specific surface area BET specific surface area 8.6 m.sup.2
g.sup.-1 9.3 m.sup.2 g.sup.-1 Elastic recovery Elastic recovery 17%
12.3% Electrical resistance Electrical resistance 1.911 m.OMEGA. cm
2.085 m.OMEGA. cm Oil absorption Oil absorption 113.5% .+-. 1.3%
64.3% .+-. 0.2% Pressed density (2.5 to/cm.sup.2) Pressed density
(2.5 to/cm.sup.2) 1.863 g cm.sup.-3 1.957 g cm.sup.-3
EXAMPLE 2
[0033] TABLE-US-00003 TIMREX .RTM. SLX synthetic graphite TIMREX
.RTM. SLX synthetic Untreated graphite After treatment Particle
size Particle size d.sub.10 = 11.6 micron d.sub.10 = 7.4 micron
d.sub.50 = 27.3 micron d.sub.50 = 20.4 micron d.sub.90 = 52.5
micron d.sub.90 = 40.8 micron L.sub.c(002)/L.sub.c(004)
L.sub.c(002)/L.sub.c(004) >500 nm/232 nm 368 nm/158 nm c/2
(002)/c/2 (004) c/2 (002)/c/2 (004) 0.3354 nm/0.3354 nm 0.3354
nm/0.3354 nm Xylene density Xylene density 2.261 g cm.sup.-3 2.258
g cm.sup.-3 Scott density Scott density 0.30 g cm.sup.-3 0.38 g
cm.sup.-3 Tamped density Tamped density 0.641 g cm.sup.-3 0.778 g
cm.sup.-3 BET specific surface area BET specific surface area 4.0
m.sup.2 g.sup.-1 5.9 m.sup.2 g.sup.-1 Elastic recovery Elastic
recovery 7.7% 4.6% Electrical resistance Electrical resistance
0.986 m.OMEGA. cm 1.166 m.OMEGA. cm Oil absorption Oil absorption
94.7% .+-. 11.9% 73.3% .+-. 1.9% Pressed density (2.5 to/cm.sup.2)
Pressed density (2.5 to/cm.sup.2) 2.036 g cm.sup.-3 2.051 g
cm.sup.-3
EXAMPLE 3
[0034] TABLE-US-00004 TIMREX .RTM. SLM synthetic TIMREX .RTM. SLM
synthetic graphite Untreated graphite After treatment Particle size
Particle size d.sub.10 = 7.3 micron d.sub.10 = 4.3 micron d.sub.50
= 23.2 micron d.sub.50 = 13.9 micron d.sub.90 = 49.4 micron
d.sub.90 = 35.0 micron L.sub.c(002)/L.sub.c(004)
L.sub.c(002)/L.sub.c(004) 241 nm/139 nm 196 nm/116 nm c/2 (002)/c/2
(004) c/2 (002)/c/2 (004) 0.3354 nm/0.3354 nm 0.3354 nm/0.3354 nm
Xylene density Xylene density 2.254 g cm.sup.-3 2.252 g cm.sup.-3
Scott density Scott density 0.19 g cm.sup.-3 0.34 g cm.sup.-3
Tamped density Tamped density 0.408 g cm.sup.-3 0.738 g cm.sup.-3
BET specific surface area BET specific surface area 4.9 m.sup.2
g.sup.-1 7.7 m.sup.2 g.sup.-1 Elastic recovery Elastic recovery
14.0% 8.6% Electrical resistance Electrical resistance 1.278
m.OMEGA. cm 1.741 m.OMEGA. cm Oil absorption Oil absorption 109.5%
.+-. 2.7% 75.0% .+-. 5.3% Pressed density (2.5 to/cm.sup.2) Pressed
density (2.5 to/cm.sup.2) 1.930 g cm.sup.-3 2.036 g cm.sup.-3
EXAMPLE 4
[0035] TABLE-US-00005 TIMREX .RTM. SFG synthetic TIMREX .RTM. SFG
synthetic graphite Untreated graphite After treatment Particle size
Particle size d.sub.10 = 7.5 micron d.sub.10 = 4.4 micron d.sub.50
= 24.1 micron d.sub.50 = 15.0 micron d.sub.90 = 49.2 micron
d.sub.90 = 35.5 micron L.sub.c(002)/L.sub.c(004)
L.sub.c(002)/L.sub.c(004) 320 nm/138 nm 283 nm/199 nm c/2 (002)/c/2
(004) c/2 (002)/c/2 (004) 0.3354 nm/0.3354 nm 0.3354 nm/0.3354 nm
Xylene density Xylene density 2.262 g cm.sup.-3 2.258 g cm.sup.-3
Scott density Scott density 0.20 g cm.sup.-3 0.36 g cm.sup.-3
Tamped density Tamped density 0.420 g cm.sup.-3 0.766 g cm.sup.-3
BET specific surface area BET specific surface area 5.9 m.sup.2
g.sup.-1 7.4 m.sup.2 g.sup.-1 Elastic recovery Elastic recovery
9.2% 5.6% Electrical resistance Electrical resistance 0.925
m.OMEGA. cm 0.986 m.OMEGA. cm Oil absorption Oil absorption 110.2%
.+-. 6.4% 81.8% .+-. 6.9% Pressed density (2.5 to/cm.sup.2) Pressed
density (2.5 to/cm.sup.2) 2.005 g cm.sup.-3 2.036 g cm.sup.-3
EXAMPLE 5
[0036] TABLE-US-00006 TIMREX .RTM. NP TIMREX .RTM. NP purified
natural graphite purified natural graphite Untreated After
treatment Particle size Particle size d.sub.10 = 6.6 micron
d.sub.10 = 3.7 micron d.sub.50 = 23.0 micron d.sub.50 = 13.8 micron
d.sub.90 = 49.5 micron d.sub.90 = 36.9 micron
L.sub.c(002)/L.sub.c(004) L.sub.c(002)/L.sub.c(004) 364 nm/166 nm
255 nm/103 nm c/2 (002)/c/2 (004) c/2 (002)/c/2 (004) 0.3354
nm/0.3354 nm 0.3354 nm/0.3354 nm Xylene density Xylene density
2.263 g cm.sup.-3 2.258 g cm.sup.-3 Scott density Scott density
0.24 g cm.sup.-3 0.42 g cm.sup.-3 Tamped density Tamped density
0.495 g cm.sup.-3 0.862 g cm.sup.-3 BET specific surface area BET
specific surface area 5.0 m.sup.2 g.sup.-1 7.9 m.sup.2 g.sup.-1
Elastic recovery Elastic recovery 4.9% 3.8% Electrical resistance
Electrical resistance 0.910 m.OMEGA. cm 1.359 m.OMEGA. cm Oil
absorption Oil absorption 107.2% .+-. 3.6% 58.9% .+-. 0.6% Pressed
density (2.5 to/cm.sup.2) Pressed density (2.5 to/cm.sup.2) 2.066 g
cm.sup.-3 2.064 g cm.sup.-3
EXAMPLE 6
[0037] TABLE-US-00007 TIMREX .RTM. KS TIMREX .RTM. KS purified
natural graphite purified natural graphite Untreated After
treatment Particle size Particle size d.sub.10 = 8.3 micron
d.sub.10 = 3.1 micron d.sub.50 = 38.4 micron d.sub.50 = 38.4 micron
d.sub.90 = 68.4 micron d.sub.90 = 68.4 micron
L.sub.c(002)/L.sub.c(004) L.sub.c(002)/L.sub.c(004) 142 nm/62 nm
105 nm/52 nm c/2 (002)/c/2 (004) c/2 (002)/c/2 (004) 0.3355
nm/0.3355 nm 0.3356 nm/0.3356 nm Xylene density Xylene density
2.227 g cm.sup.-3 2.225 g cm.sup.-3 Scott density Scott density
0.44 g cm.sup.-3 0.46 g cm.sup.-3 Tamped density Tamped density
0.84 g cm.sup.-3 0.902 g cm.sup.-3 BET specific surface area BET
specific surface area 4.1 m.sup.2 g.sup.-1 8.0 m.sup.2 g.sup.-1
Elastic recovery Elastic recovery 25% 14.68% Electrical resistance
Electrical resistance 2.109 m.OMEGA. cm 2.311 m.OMEGA. cm Oil
absorption Oil absorption 97.2% .+-. 1.6% 54.7% .+-. 0.8% Pressed
density (2.5 to/cm.sup.2) Pressed density (2.5 to/cm.sup.2) 1.912 g
cm.sup.-3 1.972 g cm.sup.-3
* * * * *