Title of Invention	"A SINGLE STEP PROCESS FOR THE PREPARATION OF HIGH DENSITY CARBON-CARBON COMPOSITE MATERIAL"
Abstract	The present invention describes a single step process for the preparation of high density carbon-carbon composite material. The process of developing carbon/carbon composites having high density of 1.8 - 1.85g/cc utilizes a special processing technique, in which a special type of the sample holder (hydraulic press) was designed for heat treatment of polymer composite material up to 1000°C. In this sample holder, green composites are placed and are covered from both the sides by two other plates and heated in a furnace in an inert atmosphere keeping the desired heating rates. These, carbon - carbon composites were further heat treated to 2600 °C in a furnace in inert atmosphere at the desired heating rates, the density of carbon - carbon composites comes out to be in the range of 1.8 - 1.85 g/cc, which is suitable for various structural applications.

Title of Invention

"A SINGLE STEP PROCESS FOR THE PREPARATION OF HIGH DENSITY CARBON-CARBON COMPOSITE MATERIAL"

Abstract

The present invention describes a single step process for the preparation of high density carbon-carbon composite material. The process of developing carbon/carbon composites having high density of 1.8 - 1.85g/cc utilizes a special processing technique, in which a special type of the sample holder (hydraulic press) was designed for heat treatment of polymer composite material up to 1000°C. In this sample holder, green composites are placed and are covered from both the sides by two other plates and heated in a furnace in an inert atmosphere keeping the desired heating rates. These, carbon - carbon composites were further heat treated to 2600 °C in a furnace in inert atmosphere at the desired heating rates, the density of carbon - carbon composites comes out to be in the range of 1.8 - 1.85 g/cc, which is suitable for various structural applications.

Full Text	The present invention relates to a single step process for the preparation of high density carbon-carbon composite material. The process of achieving high density carbon -carbon composite materials is without any impregnation or infiltration whatsoever thus bringing down the cost of material. Carbon/carbon composites are widely used in a number of applications in defense as reentry vehicles , in aircraft and spacecraft as structural parts and brake pad etc, due to their superior thermo-mechanical properties compared to those of conventional materials. However the high cost of these composites prohibits their use in many other cases. The present invention of obtaining high density carbon/carbon composites in a single step without any impregnation will reduce the cost of material thus making this material economically viable for a number of engineering applications. Several types of carbon - carbon composite materials are fabricated in a porous form and thereafter densified to a completely or partially dense final state. This porous form usually has a density of 1.0 - 1.2 g/cc, which can not be used because of its poor thermo mechanical properties. A composite material having highly desirable properties for the use in various elevated temperature applications has a density of 1.7 - 1.9 g/cc is usually formed by densifying the initially formed porous structure. Densification is generally accomplished by introducing a suitable matrix material to the porous carbon -carbon composites. Carbon/carbon composites are fabricated, in general, using a process in which a carbon fiber perform is assembled by a variety of textile processes that either directly yield useful shapes or produces bulk materials that are subsequently shaped(after densification). Thereafter, the carbon matrix is deposited/introduced into the preform either by repeated cycles of liquid impregnation with a suitable resin and pyrolysing the effects of metal carbonyl additions on the cross-linking efficiency of pre-ceramic silicon polymers used for the rapid and cost effective densification .They could achieve FS of 125 MPa with 63% fiber volume content for 2D C/C composites. Some of the more patents related to the above subject are reported below: U.S.Patent No. 5,993,905 describes a process of low temperature densification of carbon fibre preforms by colloidal graphite impregnation and mechanical consolidation to reduce the cost of carbon - carbon composite fabrication.The bulk density of C/C composites varied between lg/cc to 2g/cc which contained from about 5 vol.% to about 50 vol.% fiber and from about 20 vol.% to about 80 vol.% matrix. U.S.Patent No. 5,733,611 describes the process in which a carbon fibre porous perform is densified by heating while immersed in a precursor liquid. Heating is achieved by passing a current through perform or by an induction coil immersed in the liquid. In this way the total cost of the densification is reduced. Final Bulk density achieved in case of 1.5" tubular and 6" long preform was 1.83g/cc and the porosity was 6.2%. The main objective of the present invention is to provide a single step process for the preparation of high density carbon-carbon composite material. Another objective of the present invention is to provide a process of getting high density carbon-carbon composites in a single step of processing without any impregnation or infiltration Yet another objective of the present invention is to reduce the cost of processing of high density carbon-carbon composites. Still another objective of the present invention is to provide a process for getting high density carbon-carbon composites using lower volumes of carbon fibers. In the drawing accompanying this specification, Fig. 1 shows the schematic view of sample holder wherein (1) represents three SS plates, lower, middle and upper of the special sample holder. (2) are the spaces in the middle plate for keeping the green samples The present invention of developing carbon/carbon composites having high density of 1.8 - 1.85g/cc utilizes a special processing technique, in which a special type of the sample holder was designed for heat treatment of polymer composite material up to 1000°C. In this sample holder, green composites are placed and are covered from both the sides by two other plates. Finally, these three plates were sandwiched; keeping plate containing composite samples in the center. Now this sample holder was kept for carbonization upto 1000°C in an inert atmosphere keeping the desired heating rates. Now these, carbon - carbon composites were further heat treated to 2600 °C in a furnace in inert atmosphere at the desired heating rates. After graphitization i.e. heat treatment to 2600 °C, the density of carbon - carbon composites comes out to be in the range of 1.8 -1.85 g/cc, which is suitable for various structural applications. Accordingly, the present invention provides a single step process for the preparation of high density carbon - carbon composite material which comprises: a) mouldig a green polymer composite consisting of 20-30% carbon fiber and a matrix of carbon generating polymer selected from thermosetting resin and thermoplastic resin in a specially designed hydraulic press consisting of three plates, the middle plate having appropriate space for the samples, placing the moulded green polymer composite in middle plate of a press and sandwiching the above said composite sample in between the other two plates of the above said press, gradually heating the above said sample in the presence of an inert atmosphere by soaking the press containing the composite sample in a furnace to a temperature range of 200 to 1000°C and heating it at the same temperature for a period of 1-1.5 hrs, followed by a gradual cooling in the presence of an inert atmosphere to a temperature of 20-25°C, b) placing the above said composite sample obtained from step a) on a graphite plate and gradually heating in the presence of inert atmosphere to a temperature of 2600°C, at a heating rate of 600-1500°C/hr to a temperature of 1500°C and at the rate of 200 to 800°C/hr to a temperature of 2600° C in the furnace and soaking it at the same temperature for a period of 1-1.5 hrs, followed by cooling at the rate of 500°C/hr to 1000°C/hr in the presence of an inert atmosphere to a room temperature of 20-25 C to obtain the carbon-carbon composite having density in the range of 1.8-1.85 gram per C-C of composite.. In an embodiment of the present invention, the carbon fiber used in green polymer composite is selected from pitch based carbon fiber and vapour green carbon fiber. In yet another embodiment of the present invention, carbon fiber used are in chopped form. In yet another embodiment of the present invention , the thermosetting resin used a selected from the group consisting of phenolic resin, polyfurfuryl alcohol resin. Poly aryl acetylene resin and polyester resin. In yet another embodiment of the present invention the thermoplastic resin used is selected from coal tar pitch and petroleum pitch. The main advantages of the present invention are: 1. In the present process, densification of carbon-carbon composite is extremely rapid as compared with all other existing conventional techniques and it involves only a single step processing instead of repeated cycles of impregnation and carbonization. 2. High density 1.8 - 1.85 g /cc could be achieved without any impregnation / infiltration by this invention. 3. n normal processing, it usually takes 4-5 impregnation - carbonization -graphitization cycles to achieve the density of 1.8 g / cc. Because of this the processing cost becomes extremely high, time consuming and repeated heating / cooling cycles deteriorate the mechanical properties of the final product. 4. Usually carbon/carbon composites are manufactured using carbon fibre with volume 50-60 %. In the present invention carbon fibre volume has been used to the extent of 20-25% only to achieve the same bulk density of 1.8-1.85 g/cc. This invented processing technique, overcomes all these three drawbacks. We Claim: 1. A single step process for the preparation of high density carbon - carbon composite material which comprises: a ) mouldig a green polymer composite consisting of 20-30% carbon fiber and a matrix of carbon generating polymer selected from thermosetting resin and thermoplastic resin in a specially designed hydraulic press consisting of three plates, the middle plate having appropriate space for the samples, placing the moulded green polymer composite in middle plate of a press and sandwiching the above said composite sample in between the other two plates of the above said press, gradually heating the above said sample in the presence of an inert atmosphere by soaking the press containing the composite sample in a furnace to a temperature range of 200 to 1000°C and heating it at the same temperature for a period of 1-1.5 hrs, followed by a gradual cooling in the presence of an inert atmosphere to a temperature of 20-25°C, b) placing the above said composite sample obtained from step a) on a graphite plate and gradually heating in the presence of inert atmosphere to a temperature of 2600°C, at a heating rate of 600-1500°C/hr to a temperature of 1500°C and at the rate of 200°Cto 800°C/hr to a temperature of 2600° C in the furnace and soaking it at the same temperature for a period of 1-1.5 hrs, followed by cooling at the rate of 500°C/hrto 1000°C/hr in the presence of an inert atmosphere to a room temperature of 20-25°C to obtain the carbon-carbon composite having density in the range of 1.8-1.85 gram per C-C of composite.. 2. A process as claimed in claim 1, wherein the carbon fiber in green polymer composite is selected from pitch based carbon fiber and vapour green carbon fiber. 3. A process as claimed in claims 1&2, wherein the carbon fiber are in chopped form. 4. A process as claimed in claims 1-3, wherein the thermosetting resin is selected from the group consisting of phenolic resin, polyfurfuryl alcohol resin. Poly aryl acetylene resin and polyester resin. 5. A process as claimed in claims 1-4, wherein the thermoplastic resin is selected from coal tar pitch and petroleum pitch. 6. A process as claimed in claims 1-5, wherein the length of chopped carbon fiber is in the range of 30-5000µm, preferably ranging between 30 µm to 1000 µm. 7. A process as claimed in claims 1-6, wherein the softening point of carbon fiber is in the range of 100-350°C, preferably in the range of 200-225°C. 8. A process as claimed in claims 1-7, wherein the composite sample in step a) is gradually heated first up to a temperature of 200°C, followed by successive heating from 200-600°C and 600-1000°C, respectively. 9. A process as claimed in claim 8, wherein the rate of heating composite sample in step a)is at the rate of 100-600°C/hr up to a temperature of 200°C, preferably in the range of 200-350°C. 10. A process as claimed in claim 8, wherein the rate of heating of composite sample in step a) is at the rate of l-10°C/hr for a temperature from 200-600°C, preferably at the rate of 3-7°C/hr. 11. A process as claimed in claim 8, wherein the rate of heating composite sample in step a) is at the rate of 40-60°C/hr for a temperature from 600-1000°C. 12. A process as claimed in claims 1-11, wherein the rate of flow of inert gas during heating and cooling of the sample is in the range of 50-500 cc/min., preferably ranging between 100-200 cc/min. 13. A process as claimed in claims 1-12, wherein the inert gas in the furnace is selected from the group consisting of nitrogen, helium and argon gas.

Full Text

The present invention relates to a single step process for the preparation of high density carbon-carbon composite material. The process of achieving high density carbon -carbon composite materials is without any impregnation or infiltration whatsoever thus bringing down the cost of material. Carbon/carbon composites are widely used in a number of applications in defense as reentry vehicles , in aircraft and spacecraft as structural parts and brake pad etc, due to their superior thermo-mechanical properties compared to those of conventional materials. However the high cost of these composites prohibits their use in many other cases. The present invention of obtaining high density carbon/carbon composites in a single step without any impregnation will reduce the cost of material thus making this material economically viable for a number of engineering applications.
Several types of carbon - carbon composite materials are fabricated in a porous form and thereafter densified to a completely or partially dense final state. This porous form usually has a density of 1.0 - 1.2 g/cc, which can not be used because of its poor thermo mechanical properties. A composite material having highly desirable properties for the use in various elevated temperature applications has a density of 1.7 - 1.9 g/cc is usually formed by densifying the initially formed porous structure. Densification is generally accomplished by introducing a suitable matrix material to the porous carbon -carbon composites.
Carbon/carbon composites are fabricated, in general, using a process in which a carbon fiber perform is assembled by a variety of textile processes that either directly yield useful shapes or produces bulk materials that are subsequently shaped(after densification). Thereafter, the carbon matrix is deposited/introduced into the preform either by repeated cycles of liquid impregnation with a suitable resin and pyrolysing the
effects of metal carbonyl additions on the cross-linking efficiency of pre-ceramic silicon polymers used for the rapid and cost effective densification .They could achieve FS of 125 MPa with 63% fiber volume content for 2D C/C composites.
Some of the more patents related to the above subject are reported below: U.S.Patent No. 5,993,905 describes a process of low temperature densification of carbon fibre preforms by colloidal graphite impregnation and mechanical consolidation to reduce the cost of carbon - carbon composite fabrication.The bulk density of C/C composites varied between lg/cc to 2g/cc which contained from about 5 vol.% to about 50 vol.% fiber and from about 20 vol.% to about 80 vol.% matrix.
U.S.Patent No. 5,733,611 describes the process in which a carbon fibre porous perform is densified by heating while immersed in a precursor liquid. Heating is achieved by passing a current through perform or by an induction coil immersed in the liquid. In this way the total cost of the densification is reduced. Final Bulk density achieved in case of 1.5" tubular and 6" long preform was 1.83g/cc and the porosity was 6.2%.
The main objective of the present invention is to provide a single step process for the preparation of high density carbon-carbon composite material.
Another objective of the present invention is to provide a process of getting high density carbon-carbon composites in a single step of processing without any impregnation or infiltration
Yet another objective of the present invention is to reduce the cost of processing of high density carbon-carbon composites.
Still another objective of the present invention is to provide a process for getting high density carbon-carbon composites using lower volumes of carbon fibers.
In the drawing accompanying this specification, Fig. 1 shows the schematic view of sample holder wherein (1) represents three SS plates, lower, middle and upper of the special sample holder. (2) are the spaces in the middle plate for keeping the green samples
The present invention of developing carbon/carbon composites having high density of 1.8 - 1.85g/cc utilizes a special processing technique, in which a special type of the sample holder was designed for heat treatment of polymer composite material up to 1000°C. In this sample holder, green composites are placed and are covered from both the sides by two other plates. Finally, these three plates were sandwiched; keeping plate containing composite samples in the center. Now this sample holder was kept for carbonization upto 1000°C in an inert atmosphere keeping the desired heating rates. Now these, carbon - carbon composites were further heat treated to 2600 °C in a furnace in inert atmosphere at the desired heating rates. After graphitization i.e. heat treatment to 2600 °C, the density of carbon - carbon composites comes out to be in the range of 1.8 -1.85 g/cc, which is suitable for various structural applications.
Accordingly, the present invention provides a single step process for the preparation of high density carbon - carbon composite material which comprises:
a) mouldig a green polymer composite consisting of 20-30% carbon fiber and a matrix of carbon generating polymer selected from thermosetting resin and thermoplastic resin in a specially designed hydraulic press consisting of three plates, the middle plate having appropriate space for the samples, placing the

moulded green polymer composite in middle plate of a press and sandwiching the above said composite sample in between the other two plates of the above said press, gradually heating the above said sample in the presence of an inert atmosphere by soaking the press containing the composite sample in a furnace to a temperature range of 200 to 1000°C and heating it at the same temperature for a period of 1-1.5 hrs, followed by a gradual cooling in the presence of an inert atmosphere to a temperature of 20-25°C,
b) placing the above said composite sample obtained from step a) on a graphite plate and gradually heating in the presence of inert atmosphere to a temperature of 2600°C, at a heating rate of 600-1500°C/hr to a temperature of 1500°C and at the rate of 200 to 800°C/hr to a temperature of 2600° C in the furnace and soaking it at the same temperature for a period of 1-1.5 hrs, followed by cooling at the rate of 500°C/hr to 1000°C/hr in the presence of an inert atmosphere to a room temperature of 20-25 C to obtain the carbon-carbon composite having density in the range of 1.8-1.85 gram per C-C of composite..
In an embodiment of the present invention, the carbon fiber used in green polymer composite is selected from pitch based carbon fiber and vapour green carbon fiber.
In yet another embodiment of the present invention, carbon fiber used are in
chopped form. In yet another embodiment of the present invention , the thermosetting resin used a selected from the group consisting of phenolic resin, polyfurfuryl alcohol resin. Poly aryl acetylene resin and polyester resin.
In yet another embodiment of the present invention the thermoplastic resin used
is selected from coal tar pitch and petroleum pitch.
The main advantages of the present invention are:
1. In the present process, densification of carbon-carbon composite is extremely rapid as compared with all other existing conventional techniques and it involves only a single step processing instead of repeated cycles of impregnation and carbonization.
2. High density 1.8 - 1.85 g /cc could be achieved without any impregnation / infiltration by this invention.
3. n normal processing, it usually takes 4-5 impregnation - carbonization -graphitization cycles to achieve the density of 1.8 g / cc. Because of this the processing cost becomes extremely high, time consuming and repeated heating / cooling cycles deteriorate the mechanical properties of the final product.
4. Usually carbon/carbon composites are manufactured using carbon fibre with volume 50-60 %. In the present invention carbon fibre volume has been used to the extent of 20-25% only to achieve the same bulk density of 1.8-1.85 g/cc. This invented processing technique, overcomes all these three drawbacks.

We Claim:
1. A single step process for the preparation of high density carbon - carbon
composite material which comprises:
a ) mouldig a green polymer composite consisting of 20-30% carbon fiber and a matrix of carbon generating polymer selected from thermosetting resin and thermoplastic resin in a specially designed hydraulic press consisting of three plates, the middle plate having appropriate space for the samples, placing the moulded green polymer composite in middle plate of a press and sandwiching the above said composite sample in between the other two plates of the above said press, gradually heating the above said sample in the presence of an inert atmosphere by soaking the press containing the composite sample in a furnace to a temperature range of 200 to 1000°C and heating it at the same temperature for a period of 1-1.5 hrs, followed by a gradual cooling in the presence of an inert atmosphere to a temperature of 20-25°C, b) placing the above said composite sample obtained from step a) on a graphite plate and gradually heating in the presence of inert atmosphere to a temperature of 2600°C, at a heating rate of 600-1500°C/hr to a temperature of 1500°C and at the rate of 200°Cto 800°C/hr to a temperature of 2600° C in the furnace and soaking it at the same temperature for a period of 1-1.5 hrs, followed by cooling at the rate of 500°C/hrto 1000°C/hr in the presence of an inert atmosphere to a room temperature of 20-25°C to obtain the carbon-carbon composite having density in the range of 1.8-1.85 gram per C-C of composite..
2. A process as claimed in claim 1, wherein the carbon fiber in green polymer composite is selected from pitch based carbon fiber and vapour green carbon fiber.
3. A process as claimed in claims 1&2, wherein the carbon fiber are in chopped form.
4. A process as claimed in claims 1-3, wherein the thermosetting resin is selected from the group consisting of phenolic resin, polyfurfuryl alcohol resin. Poly aryl acetylene resin and polyester resin.
5. A process as claimed in claims 1-4, wherein the thermoplastic resin is selected from coal tar pitch and petroleum pitch.

6. A process as claimed in claims 1-5, wherein the length of chopped carbon fiber is
in the range of 30-5000µm, preferably ranging between 30 µm to 1000 µm.
7. A process as claimed in claims 1-6, wherein the softening point of carbon fiber is
in the range of 100-350°C, preferably in the range of 200-225°C.
8. A process as claimed in claims 1-7, wherein the composite sample in step a) is
gradually heated first up to a temperature of 200°C, followed by successive
heating from 200-600°C and 600-1000°C, respectively.
9. A process as claimed in claim 8, wherein the rate of heating composite sample in
step a)is at the rate of 100-600°C/hr up to a temperature of 200°C, preferably in
the range of 200-350°C.
10. A process as claimed in claim 8, wherein the rate of heating of composite sample in step a) is at the rate of l-10°C/hr for a temperature from 200-600°C, preferably at the rate of 3-7°C/hr.
11. A process as claimed in claim 8, wherein the rate of heating composite sample in step a) is at the rate of 40-60°C/hr for a temperature from 600-1000°C.
12. A process as claimed in claims 1-11, wherein the rate of flow of inert gas during
heating and cooling of the sample is in the range of 50-500 cc/min., preferably
ranging between 100-200 cc/min.
13. A process as claimed in claims 1-12, wherein the inert gas in the furnace is selected from the group consisting of nitrogen, helium and argon gas.

Documents:

567-DEL-2005-Abstract-(18-03-2011).pdf

567-DEL-2005-Claims-(18-03-2011).pdf

567-DEL-2005-Claims-(25-01-2012).pdf

567-DEL-2005-Correspondence Others-(19-01-2012).pdf

567-DEL-2005-Correspondence Others-(25-01-2012).pdf

567-DEL-2005-Correspondence-Others-(18-03-2011).pdf

567-DEL-2005-Description (Complete)-(18-03-2011).pdf

567-DEL-2005-Description (Complete)-(25-01-2012).pdf

567-DEL-2005-Form-1-(18-03-2011).pdf

567-DEL-2005-Form-3-(18-03-2011).pdf

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Patent Number

251233

Indian Patent Application Number

567/DEL/2005

PG Journal Number

10/2012

Publication Date

09-Mar-2012

Grant Date

02-Mar-2012

Date of Filing

16-Mar-2005

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	O P BAHL	NPL, NEW DELHI, INDIA.
2	R B MATHUR	NPL, NEW DELHI, INDIA.
3	T L DHAMI	NPL, NEW DELHI, INDIA.
4	S.K. CHAUHAN	NPL, NEW DELHI, INDIA.

PCT International Classification Number

C22C 47/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA