U.S. patent application number 12/478792 was filed with the patent office on 2009-10-01 for flexible, high purity expanded graphite sheet, method of producing same, and carbon crucible lining using said sheet.
This patent application is currently assigned to TOYO TANSO CO., LTD.. Invention is credited to Yoshiaki HIROSE, Hideki Inomoto.
Application Number | 20090246493 12/478792 |
Document ID | / |
Family ID | 31972367 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090246493 |
Kind Code |
A1 |
HIROSE; Yoshiaki ; et
al. |
October 1, 2009 |
FLEXIBLE, HIGH PURITY EXPANDED GRAPHITE SHEET, METHOD OF PRODUCING
SAME, AND CARBON CRUCIBLE LINING USING SAID SHEET
Abstract
The invention provides a flexible, highly pure expanded graphite
sheet characterized by having an impurity content of 10 ppm or less
and such a degree of flexibility that a sample thereof,
10.times.100 mm in size can withstand at least 10 times of bending
in flexibility test comprising repeatedly bending the sample, with
a 50-g weight suspended from one end thereof, by means of bending
bodies with a diameter of 6 mm.
Inventors: |
HIROSE; Yoshiaki;
(Kan-onji-shi, JP) ; Inomoto; Hideki;
(Kan-onji-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOYO TANSO CO., LTD.
Osaka-shi
JP
|
Family ID: |
31972367 |
Appl. No.: |
12/478792 |
Filed: |
June 5, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10462663 |
Jun 17, 2003 |
|
|
|
12478792 |
|
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Current U.S.
Class: |
428/219 |
Current CPC
Class: |
C04B 2237/363 20130101;
B32B 2315/02 20130101; C04B 2235/604 20130101; C04B 35/536
20130101; Y10T 428/30 20150115; C04B 2235/65 20130101; C04B 2235/72
20130101; C04B 2235/77 20130101; C30B 35/00 20130101; C04B 2235/94
20130101 |
Class at
Publication: |
428/219 |
International
Class: |
B32B 9/00 20060101
B32B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 18, 2002 |
JP |
2002-214564 |
Claims
1. A method of producing flexible, high-purity expanded graphite
sheets which comprises forming an expanded graphite sheet having a
bulk density of 0.7 to 1.3 g/cm.sup.3 into a desired shape and then
subjecting the shaped sheet to treatment for attaining high
purity.
2. A method of producing flexible, high-purity expanded graphite
sheets which comprises forming a plurality of expanded graphite
sheets each having a bulk density of 0.7 to 1.3 g/cm.sup.3 into one
and the same desired shape simultaneously in a laminate form,
followed by treatment for attaining high purity.
3. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 1, wherein the shaping of expanded
graphite sheets is carried out by at least one method selected from
the group consisting of working on a slitting machine, punching
using a Thomson die, water jet working, and laser working.
4. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 2, wherein the shaping of expanded
graphite sheets is carried out by at least one method selected from
the group consisting of working on a slitting machine, punching
using a Thomson die, water jet working, and laser working.
5. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 1, wherein the expanded graphite sheet
before purification treatment has a thickness of 0.2 to 1.0 mm.
6. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 2, wherein the expanded graphite sheet
before purification treatment has a thickness of 0.2 to 1.0 mm.
7. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 1, wherein the expanded graphite sheet
after purification treatment has an impurity content not exceeding
10 ppm.
8. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 2, wherein the expanded graphite sheet
after purification treatment has an impurity content not exceeding
10 ppm.
9. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 5, wherein the expanded graphite sheet
after purification treatment has an impurity content not exceeding
10 ppm.
10. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 6, wherein the expanded graphite sheet
after purification treatment has an impurity content not exceeding
10 ppm.
11. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 5, wherein the thickness is 0.3 to 0.9
mm.
12. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 6, wherein the thickness is 0.3 to 0.9
mm.
13. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 5, wherein the thickness is 0.5 to 0.8
mm.
14. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 6, wherein the thickness is 0.5 to 0.8
mm.
15. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 1, wherein the bulk density is 0.8 to
1.3 g/cm.sup.3.
16. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 2, wherein the bulk density is 0.8 to
1.3 g/cm.sup.3.
17. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 1, wherein the bulk density is 0.9 to
1.3 g/cm.sup.3.
18. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 2, wherein the bulk density is 0.9 to
1.3 g/cm.sup.3.
19. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 1, wherein said purification treatment
comprises heating the sheet at 2,000.degree. C. or above in a
halogen atmosphere.
20. The method of producing flexible, high-purity expanded graphite
sheets as defined in claim 2, wherein said purification treatment
comprises heating the sheet at 2,000.degree. C. or above in a
halogen atmosphere.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a flexible, high-purity
expanded graphite sheet, and to a method of producing the same.
[0003] 2. Description of the Prior Art
[0004] Expanded graphite sheets are generally produced by treating
natural graphite, pyrolytic graphite, kish graphite or the like
with a mixed solution containing sulfuric acid and nitric acid, for
instance, then washing the same with water, drying the same,
treating the same for expansion in an expansion oven at about
1,000.degree. C., and firming the same into sheets using a rolling
machine, for instance. Expanded graphite sheets are excellent in
heat resistance and in gas and liquid in impermeability and
therefore are used as packing materials, valve sheets, gaskets, and
fuel cell separators, among others.
[0005] Japanese Patent No. 2,620,606 discloses that highly pure
expanded graphite sheets having an impurity content of not more
than 15 ppm can be obtained by treating such expanded graphite
sheets for increased purity in a halogen gas atmosphere at
2,000.degree. C. or above. Such sheets are used in the process of
semiconductor production.
[0006] Hereinafter, a detailed description is given of a
high-purity expanded graphite sheet for use in semiconductor
production, which is taken as an example. Such a high-purity
expanded graphite sheet is also used in the Czochralski
(hereinafter referred to as "CZ" for short) process, which is a
representative single crystal pulling technique. A sectional view
of the main parts of a CZ apparatus is shown in FIG. 1. The CZ
apparatus comprises such parts as a carbon crucible 5 supporting a
quarts crucible 1, a heater 2, an upper ring 6, and an inner shield
7, among others. In the CZ apparatus, polycrystalline silicon
placed in the quartz crucible 1 is heated to a high temperature to
give a silicon melt 3, and the tip of a seed crystal held by a seed
chuck is brought into contact with the raw material melt 3 and then
pulled up while maintaining the contact to thereby pull up a
silicon single crystal 4.
[0007] As shown in FIG. 1, the carbon crucible 5 made of graphite
or a carbon fiber-reinforced carbon composite material (such
crucible is hereafter referred to as "carbon crucible") is in
direct contact with the quartz crucible 1 and, therefore, the
surface of the carbon crucible 5 is gradually converted to silicon
carbide (hereinafter referred to as "SiC") as a result of the
reaction between the quartz crucible 1 and carbon crucible 5 and/or
the reaction between vaporized silicon and the graphite crucible.
The difference in coefficient of thermal expansion between carbon
and SiC is conducive to cracking of the carbon crucible, for
instance. Furthermore, the quartz crucible 1 becomes firmly
sticking to the carbon crucible 5, making it difficult to take out
the quartz crucible 1.
[0008] Japanese Patent No. 2,528,285 discloses, as a means for
solving such problems, the use of a high-purity expanded graphite
sheet as a liner intervening between the quartz crucible 1 and
carbon crucible 5.
[0009] When an expanded graphite sheet is treated for improving the
purity thereof, the flexibility of the expanded graphite sheet is
generally impaired, so that it can no loner be used as a member
which is required to have flexibility. Therefore, Japanese Patent
No. 2,620,606 discloses a method of restoring flexibility which
comprises compression molding. However, the method has other
problems; the purity of the high-purity expanded graphite sheet is
decreased upon compression molding and, when a complicated shape is
given to the high-purity expanded graphite sheet insufficient in
flexibility restoration by working with a cutter, for instance, the
peripheral parts of the sheet are subject to cracking and/or
chipping.
[0010] When the whole inside surface (if the carbon crucible is
covered with an expanded graphite sheet, the efficiency of heating
of the quartz crucible 1 decreases. Therefore, in recent years,
various complicated liner shapes have been proposed so that the
quartz crucible heating efficiency may be improved. Basically, each
single crystal production operation consumes one intervening liner
and, therefore, it is important to provide a method of producing
high-purity expanded graphite sheets which is excellent in mass
productivity.
[0011] Accordingly, it is an object of the present invention to
provide a high-purity expanded graphite sheet having flexibility
and a method of producing the same. Another object of the invention
is to provide a method of manufacturing expanded graphite sheets
which is suited for mass production as well.
SUMMARY OF THE INVENTION
[0012] The present inventors made intensive investigations in an
attempt to accomplish the above objects and, as a result, found
that when an expanded graphite sheet whose bulk density is within a
certain specific range is treated for attaining high purity, a
high-purity expanded graphite sheet can be obtained without
deterioration in flexibility even after the treatment for attaining
high purity. This and other findings have now led to completion of
the present invention. Thus, in a first aspect (Claim 1), the
invention provides a flexible, high-purity expanded graphite sheet
characterized in that it has an impurity content not exceeding 10
ppm and has such a degree of flexibility that a sample thereof can
withstand at least 10 times of bending on a testing apparatus such
as shown in FIG. 4. In a second aspect (Claim 2), the invention
provides a flexible, high-purity expanded graphite sheet which has
the above characteristics and is further characterized by its bulk
density being 0.5 to 1.3 g/cm.sup.3. In a third aspect (Claim 3),
the invention provides a flexible, high-purity expanded graphite
sheet as defined in Claim 1 or 2 which is further characterized by
its thickness being 0.2 to 1.0 mm.
[0013] For obtaining the flexible, high-purity expanded graphite
sheet according to Claim 1, it is necessary to use scaly graphite,
kish graphite, pyrolytic graphite or the like as a filler, subject
this to oxidation treatment by immersing the same in a mixed acid
supplemented with concentrated sulfuric acid, concentrated nitric
acid, etc., wash the immersed filler with water and, after drying,
treat the same for expansion by heating to give expanded graphite,
and adjust the bulk density thereof to about 0.7 to 1.3 g/cm.sup.3
by compression molding using a press or rolling machine. Expanded
graphite sheets having a bulk density lower than 0.7 g/cm.sup.3
cannot acquire, even after purification treatment, such a degree of
flexibility as to withstand at least 10 times of bending, hence are
unfavorable. Expanded graphite sheets having a bulk density
exceeding, 1.3 g/cm.sup.3 are also undesirable, since the impurity
content therein cannot be reduced to 10 ppm or below even by
purification treatment. In a preferred embodiment of the invention,
expanded graphite sheets with a bulk density adjusted to 0.8 to 1.3
g/cm.sup.3, more preferably to 0.9 to 1.3 g/cm.sup.3, are subjected
to treatment for attaining high purity. The method of purification
treatment itself may be any of those known in the art. For example,
flexible, high-purity expanded graphite sheets having an impurity
content of not more than 10 ppm and a degree of flexibility as to
withstand at least 10 times of bending can be obtained by heating
expanded graphite sheets at 2,000.degree. C. or above in a halogen
gas atmosphere to thereby convert metals in the sheets to metal
halide compounds showing a high vapor pressure and allow them to
vaporize. The bulk density and sheet thickness of expanded graphite
sheets after purification treatment show little changes and remain
almost equal to those before treatment. A flexibility measuring
apparatus is schematically shown in FIG. 3. A 50-g weight 22 is
attached to one end of a 10 mm.times.100 mm sample 21 of a
high-purity expanded graphite sheet and subjected to repeated
bending by means of bending bodies 24 with a diameter of 6 mm. The
number of times of bending until breakage is counted and recorded
as the flexibility in the longitudinal direction.
[0014] In a fourth aspect (Claim 4), the invention provides a
method of producing flexible, high-purity expanded graphite sheets
which comprises forming an expanded graphite sheet having a bulk
density of 0.7 to 1.3 g/cm.sup.3 into a desired shape and then
subjecting the shaped sheet to purification treatment. Expanded
graphite sheets having a bulk density less than 0.7 g/cm.sup.3 are
undesirable since any purification treatment cannot improve their
flexibility to a level of at least 10 times, as mentioned above.
Expanded graphite sheets having a bulk density exceeding 1.3
g/cm.sup.3 are also unfavorable since their impurity content cannot
be reduced to 10 ppm or less by purification treatment. Preferably,
the expanded graphite sheet to be treated for purification has a
thickness of 0.2 to 1.0 mm. When the expanded graphite sheet before
purification treatment is less than 0.2 mm in thickness, the sheet
after purification treatment tends to show marked decreases in
flexibility and strength, hence are susceptible to cracking, for
instance. When the expanded graphite sheet is thicker than 1.0 mm,
the impurity content cannot be reduced to a satisfactory extent by
purification treatment. More preferably, the expanded graphite
sheet to be subjected to purification treatment has a thickness of
0.3 to 0.9 mm. Most preferably, 0.5 to 0.8-mm-thick expanded
graphite sheets are subjected to purification treatment. As the
"desired shape" so referred to herein, there may be mentioned, for
example, the shape shown in FIG. 2 or FIG. 3 and, further, figures
of line symmetry, such as ellipses, stars and the Imperial crest of
chrysanthemum, and asymmetric figures.
[0015] In a fifth aspect (Claim 5), the invention provides a
modification of the method specified above which modification
comprises forming a plurality of expanded graphite sheets each into
one and the same desired shape simultaneously in a laminate form,
followed by purification treatment. This modification is preferred
since the mass productivity in manufacturing expanded graphite
sheets having one and the same desired, complicated shape can be
improved by laying a plurality of expanded graphite sheets one upon
another and working them simultaneously in one operation according
to the method mentioned above. Preferably, a plurality of expanded
graphite sheets each having a thickness of 0.2 to 1.0 mm are laid
one upon another. When each expanded graphite sheet is less than
0.2 mm in thickness, the expanded graphite sheet cannot acquire
flexibility or strength but becomes susceptible to cracking, for
instance. When each sheet is thicker than 1.0 mm, the impurity
content cannot be reduced to a satisfactory extent by purification
treatment; this is unfavorable. It is desirable that the bulk
density of expanded graphite sheets prior to purification treatment
be 0.7 to 1.3 g/cm.sup.3.
[0016] In a sixth aspect (Claim 6), the invention provides a method
of producing such expanded graphite sheets as mentioned above in
which the shaping of expanded graphite sheets is carried out by at
least one method selected from among such methods as slitting,
punching using a Thomson die, water jet working, and laser working.
From the mass productivity viewpoint, however, punching with a
Thomson die and water jet working are preferred since they can
reduce the working time, are less likely to decrease the purity of
expanded graphite sheets and, further, are excellent in mass
productivity. It is to be added that when expanded graphite sheets
are shaped by punching using a Thomson die, the purification
treatment should preferably be carried out after removing working
dust from the worked surface (cut surface) by ultrasonic cleaning
in a state immersed in water, alcohol or the like and the
subsequent drying for evaporation of the moisture.
[0017] In a seventh aspect (Claim 7), the invention provides the
use of the flexible, high-purity expanded graphite sheet as defined
in any one of Claims 1 to 3 as a carbon crucible liner. When such a
high-purity expanded graphite sheet having flexibility and a low
impurity content is used as a carbon crucible liner, the stability
of the quartz crucible is good and the intrusion of silicon
monoxide gas can be prevented, so that the carbon crucible can be
inhibited from beg converted to silicon carbide and the life of the
expensive carbon crucible can be prolonged.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic sectional view of a single crystal
puller.
[0019] FIG. 2 is an illustration of shaping of a high-purity
expanded graphite sheet suited for use as an intervening liner in a
single crystal pulling apparatus.
[0020] FIG. 3 is an illustration of shaping of another high-purity
expanded graphite sheet suited for use as a liner in a single
crystal puller.
[0021] FIG. 4 is a schematic representation of a flexibility
measuring apparatus.
[0022] In FIGS. 1 and 4, the numerical symbols respectively denote
the following: 1--quartz crucible, 2--heater, 3--silicon melt,
4--silicon single crystal, 5--carbon crucible, 6--upper ring,
7--inner shield, 8--lower ring, 9--bottom heater, 10--heat
insulator, 11--spill tray, 21--sample (of high-purity expanded
graphite sheet), 22--weight, 23--directions of bending,
24--benders
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] The following examples illustrate the present invention more
specifically. These examples are, however, by no means limitative
of the scope of the present invention.
Example 1
[0024] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-50, size: 1,000.times.1,000.times.0.5 (mm), bulk
density: 1.3 g/cm.sup.3, ash content: 0.2% by mass) was obtained.
This sheet was formed into the shape shown in FIG. 2 by punching
using a hydraulic press and a Thomson die at a pressure of 10 MPa.
The shaped article was then treated for purification; thus, it was
maintained at 2,000.degree. C. for 10 hours while gaseous chlorine
was fed.
Example 2
[0025] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 1. This laminate was formed
into the shape shown in FIG. 2 by punching using a hydraulic press
and a Thomson die at a pressure of 50 MPa. The shaped article was
then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 3
[0026] An expanded graphite sheet made by Toyo Tanso Co. Ltd. grade
name: PF-40, thickness 0.4 mm, bulk density: 1.0 g/cm.sup.3, ash
content: 0.2% by mass) was obtained. This sheet was formed into the
shape shown in FIG. 2 by punching using a hydraulic press and a
Thomson die at a pressure of 10 MPa. The shaped article was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
Example 4
[0027] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 3. This laminate was formed
into the shape shown in FIG. 2 by punching using a hydraulic press
and a Thomson die at a pressure of 50 MPa. The shaped article was
then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 5
[0028] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-40, thickness: 0.4 mm, bulk density: 0.7
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by punching using a hydraulic
press and a Thomson die at a pressure of 10 MPa. The shaped article
was then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 6
[0029] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 5. This laminate was formed
into the shape shown in FIG. 2 by punching using a hydraulic press
and a Thomson die at a pressure of 50 MPa. The shaped article was
then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 7
[0030] An expanded graphite sheet made of the same material and
having the same size as that used in Example 1 was obtained. This
sheet was formed into the shape shown in FIG. 2 by subjecting to
water jet working using a nozzle having an orifice diameter of 0.1
mm at a water pressure of 3,000 kg/cm.sup.2. The shaped article was
then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 8
[0031] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 1. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was maintained at 2,000.degree. C. for
10 hours while gaseous chlorine was fed.
Example 9
[0032] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-40, thickness: 0.4 mm, bulk density: 1.0
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by subjecting to water jet
working using a nozzle having an orifice diameter of 0.1 mm at a
water pressure of 3,000 kg/cm.sup.2. The shaped article was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
Example 10
[0033] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 5. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was heated to and maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 11
[0034] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-40, thickness: 0.4 mm, bulk density: 0.7
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by subjecting to water jet
working using a nozzle having an orifice diameter of 0.1 mm at a
water pressure of 3,000 kg/cm.sup.2. The shaped article was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
Example 12
[0035] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 5. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was maintained at 2,000.degree. C. for
10 hours while gaseous chlorine was fed.
Example 13
[0036] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-20, size: 1,000.times.1,000.times.0.2 (mm), bulk
density: 1.3 g/cm.sup.3, ash content: 0.2% by mass) was obtained.
This sheet was formed into the shape shown in FIG. 2 by punching
using a hydraulic press and a Thomson die at a pressure of 10 MPa.
The shaped article was then treated for purification; thus, it was
maintained at 2,000.degree. C. for 10 hours while gaseous chlorine
was fed.
Example 14
[0037] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 13. This laminate was formed
into the shape shown in FIG. 2 by punching using a hydraulic press
and a Thomson die at a pressure of 50 MPa. The shaped article was
then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 15
[0038] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-20, thickness: 0.2 mm, bulk density: 1.0
g/cm.sup.3, ash content 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by punching using a hydraulic
press and a Thomson die at a pressure of 10 MPa. The shaped article
was then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 16
[0039] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 15. This laminate was formed
into the shape shown in FIG. 2 by punching using a hydraulic press
and a Thomson die at a pressure of 50 MPa. The shaped article was
then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 17
[0040] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-20, thickness: 0.2 mm, bulk density: 0.7
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by punching using a hydraulic
press and a Thomson die at a pressure of 10 MPa. The shaped article
was then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 18
[0041] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 17. This laminate was formed
into the shape shown in FIG. 2 by punching using a hydraulic press
and a Thomson die at a pressure of 50 MPa. The shaped article was
then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 19
[0042] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-100, size: 1,000.times.1,000.times.1.0 (mm), bulk
density: 1.3 g/cm.sup.3, ash content: 0.2% by mass) was obtained.
This sheet was formed into the shape shown in FIG. 2 by subjecting
to water jet working using a nozzle having an orifice diameter of
0.1 mm at a water pressure of 3,000 kg/cm.sup.2. The shaped article
was then treated for purification; thus, it was maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 20
[0043] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 19. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was heated to and maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 21
[0044] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-100, thickness: 1.0 mm, bulk density: 1.0
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by subjecting to water jet
working using a nozzle having an orifice diameter of 0.1 mm at a
water pressure of 3,000 kg/cm.sup.2. The shaped article was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
Example 22
[0045] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 21. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was heated to and maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 23
[0046] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-100, thickness: 1.0 mm, bulk density: 0.7
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by subjecting to water jet
working using a nozzle having an orifice diameter of 0.1 mm at a
water pressure of 3,000 kg/cm.sup.2. The shaped article was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
Example 24
[0047] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 23. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was heated to and maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 25
[0048] A laminate was prepared by laying, one upon another, 5
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 1. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice
[0049] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-100, thickness: 1.0 mm, bulk density: 1.0
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by subjecting to water jet
working using a nozzle having an orifice diameter of 0.1 mm at a
water pressure of 3,000 kg/cm.sup.2. The shaped articled was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
Example 22
[0050] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 21. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an ode diameter of 0.1 mm at a water pressure
of 3,000 kg/cm.sup.2. The shaped article was then treated for
purification; thus, it was heated to and maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 23
[0051] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-100, thickness: 1.0 mm, bulk density: 0.7
g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet was
formed into the shape shown in FIG. 2 by subjecting to water jet
working using a nozzle having an orifice diameter of 0.1 mm at a
water pressure of 3,000 kg/cm.sup.2. The shaped article was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
Example 24
[0052] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 23. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was heated to and maintained at
2,000.degree. C. for 10 hours while gaseous chlorine was fed.
Example 25
[0053] A laminate was prepared by laying, one upon another, 5
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 1. This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice die at a pressure of 50 MPa. The
shaped article was then treated for purification; thus, it was
maintained at 2,000.degree. C. for 10 hours while gaseous chlorine
was fed.
Comparative Example 5
[0054] An expanded graphite sheet made by Toyo Tanso Co. Ltd.
(grade name: PF-120, size: 1,000.times.1,000.times.1.2 (mm), bulk
density: 1.3 g/cm.sup.3, ash content: 0.2% by mass) was obtained.
This sheet was formed into the shape shown in FIG. 2 by punching
using a hydraulic press and a Thomson die at a pressure of 10 MPa.
The shaped article was then treated for purification; thus, it was
maintained at 2,000.degree. C. for 10 hours while gaseous chlorine
was fed.
Comparative Example 6
[0055] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made of the same material and having the
same size as the sheet used in Comparative Example 5. This laminate
was formed into the shape shown in FIG. 2 by punching using a
hydraulic press and a Thomson die at a pressure of 50 MPa. The
shaped article was then treated for purification; thus, it was
maintained at 2,000.degree. C. for 10 hours while gaseous chlorine
was fed.
Comparative Example 7
[0056] A laminate was prepared by laying, one upon another, 5
expanded graphite sheets made of the same material and having the
same size as the sheet used in Example 1. This laminate was formed
into the shape shown in FIG. 2 by manual working using a cutter.
The time required for the shaping was 1 hour. The shaped article
was subjected to 3 minutes of ultrasonic cleaning at 43 kHz to
thereby remove cut dust derived from the expanded graphite
laminate. Then, the shaped article was dried at 100.degree. C. for
30 minutes to evaporate the moisture and then treated for
purification; thus, it was maintained at 2,000.degree. C. for 10
hours while gaseous chlorine was fed.
Comparative Example 8
[0057] A laminate was prepared by laying, one upon another 10
expanded graphite sheets made by Toyo Tanso Co. Ltd. (grade name:
PF-40, size: 1,000.times.1,000.times.0.4 (mm), bulk density: 0.6
g/cm.sup.3, ash content: 0.2% by mass). This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was maintained at; 2,000.degree. C. for
10 hours while gaseous chlorine was fed.
Comparative Example 9
[0058] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made by Toyo Tanso Co. Ltd. (grade name:
PF-40, size: 1,000.times.1,000.times.0.4 (mm), bulk density: 0.3
g/cm.sup.3, ash content: 0.2% by mass). This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was maintained at 2,000.degree. C. for
10 hours while gaseous chlorine was fed.
Comparative Example 10
[0059] A laminate was prepared by laying, one upon another, 10
expanded graphite sheets made by Toyo Tanso Co. Ltd. (grade name:
PF-40, size: 1,000.times.1,000.times.0.4 (mm), bulk density: 0.2
g/cm.sup.3, ash content: 0.2% by mass). This laminate was formed
into the shape shown in FIG. 2 by subjecting to water jet working
using a nozzle having an orifice diameter of 0.1 mm at a water
pressure of 3,000 kg/cm.sup.2. The shaped article was then treated
for purification; thus, it was maintained at 2,000.degree. C. for
10 hours while gaseous chlorine was fed.
Comparative Example 11
[0060] An expanded graphite sheet made by Toyo Tanso Co. Ltd. grade
name: PF-40, size: 1,000.times.1,000.times.0.4 (mm), bulk density:
0.6 g/cm.sup.3, ash content: 0.2% by mass) was obtained. This sheet
was formed into the shape shown in FIG. 2 by subjecting to water
jet working using a nozzle having an orifice diameter of 0.1 mm at
a water pressure of 3,000 kg/cm.sup.2. The shaped article was then
treated for purification; thus, it was maintained at 2,000.degree.
C. for 10 hours while gaseous chlorine was fed.
[0061] For each of Examples 1 to 25 and Comparative Examples 1 to
11, the bulk density of the expanded graphite sheet, the thickness
per sheet, the number of sheets in the laminate, the method of
shaping, the flexibility in the longitudinal direction, and the
purity after purification treatment are summarized in Table 1. The
expanded graphite sheets after purification treatment showed little
changes in bulk density or in sheet thickness and thus were
comparable in these respects to the sheets before purification
treatment.
[0062] The impurity content of each expanded graphite sheet after
purification treatment was determined by weighing at least 15 g of
the high-purity expanded graphite sheet in a porcelain crucible,
placing the crucible in an electric furnace, heating it at
850.degree. C. for 48 hours, and calculating the impurity content
from the mass before heating and the mass after heating.
TABLE-US-00001 TABLE 1 Number Bulk Sheet of sheets Impurity density
thickness in Shaping Flexibility content (g/cm.sup.3) (mm/sheet)
laminate method (times) (ppm) Example 1 1.3 0.5 1 Thomson die 12 4
Example 2 1.3 0.5 10 Thomson die 12 4 Example 3 1.0 0.4 1 Thomson
die 10 3 Example 4 1.0 0.4 10 Thomson die 10 3 Example 5 0.7 0.4 1
Thomson die 10 2 Example 6 0.7 0.4 10 Thomson die 10 2 Example 7
1.3 0.5 1 Water jet 12 3 Example 8 1.3 0.5 10 Water jet 12 3
Example 9 1.0 0.4 1 Water jet 10 2 Example 10 1.0 0.4 10 Water jet
10 2 Example 11 0.7 0.4 1 Water jet 10 1 Example 12 0.7 0.4 10
Water jet 10 1 Example 13 1.3 0.2 1 Thomson die 20 3 Example 14 1.3
0.2 10 Thomson die 20 3 Example 15 1.0 0.2 1 Thomson die 18 2
Example 16 1.0 0.2 10 Thomson die 18 2 Example 17 0.7 0.2 1 Thomson
die 10 1 Example 18 0.7 0.2 10 Thomson die 10 1 Example 19 1.3 1.0
1 Water jet 10 5 Example 20 1.3 1.0 10 Water jet 10 5 Example 21
1.0 1.0 1 Water jet 10 4 Example 22 1.0 1.0 10 Water jet 10 4
Example 23 0.7 1.0 1 Water jet 10 2 Example 24 0.7 1.0 10 Water jet
10 2 Example 25 1.3 0.5 5 Water jet 12 1 Compar. Ex. 1 1.5 0.5 1
Thomson die 30 50 Compar. Ex. 2 1.5 0.5 10 Thomson die 30 50
Compar. Ex. 3 1.3 0.1 1 Thomson die 1 1 Compar. Ex. 4 1.3 0.1 10
Thomson die 1 1 Compar. Ex. 5 1.3 1.2 1 Thomson die 5 30 Compar.
Ex. 6 1.3 1.2 10 Thomson die 5 30 Compar. Ex. 7 1.3 0.5 5 Cutter 12
30 Compar. Ex. 8 0.6 0.4 10 Water jet 1 2 Compar. Ex. 9 0.3 0.4 10
Water jet 1 1 Compar. Ex. 10 0.2 0.4 10 Water jet 1 1 Compar. Ex.
11 0.6 0.4 1 Water jet 1 2
[0063] As is evident from Table 1, those expanded graphite sheets
having a bulk density of 0.7 to 1.3 g/cm.sup.3 and a thickness of
0.2 to 1.0 mm per sheet showed only slight decreases in flexibility
after purification treatment and could be prevented from decreasing
in purity.
[0064] A silicon single crystal growth experiment was carried out
using the high-purity expanded graphite sheet obtained in Example
25 and Comparative Example 3 each as an intervening liner in a CZ
apparatus. When the liner produced in Example 25 was used, it was
confirmed by the eye that the area of yellowed portions suggesting
the formation of silicon carbide was smaller as compared with the
case of the liner produced in Comparative Example 3. This resulted
from cracking of the high-purity expanded graphite sheet of
Comparative Example 3 due to lack of flexibility.
[0065] When a plurality of expanded graphite sheets having a bulk
density of 0.7 to 1.3 g/cm.sup.3 and a thickness of 0.2 to 1.0 mm
per sheet are formed into a laminate and the late is worked into a
desired shape, no impairment in flexibility is found after
treatment for attaining high purity. In addition, when the laminate
is shaped by water jet working, the working time can be reduced to
1/10 or shorter as compared with that in the prior art and the
impurity content can also be reduced to 1/10 or below. Therefore,
the products are useful in the semiconductor-related industries as
those carbon crucible liners for use in CZ apparatus, CVD ovens and
the like which are required to have high purity and flexibility
and, in the nuclear industry-related fields, as in-core or in-pile
parts required to be flexile and highly pure.
* * * * *