Title of Invention	"AN IMPROVED PROCESS FOR THE PREPARATION OF CERAMIC MATRIX COMPOSITES SUCH AS A12O3-SICWAB COMPOSITE"
Abstract	An improved process for making of ceramic matrix composites: The process of present invention provides a modified SHS technique termed as rapid heating self propagating high temperature synthesis (RH-SHS) for the manufacture of ceramic composites. In this modified technique, the reacting mixture is heated rapidly so that a sharp thermal gradient is established between surface and the core of the samples. A wide range of ceramic matrix composites such as AI203 - TiC, AI2O3 - WC, MoSi2 - SiC, AI2O3 - TiB2, MgO - TiC, AI2O3 -AIN - SiC, AI2O3 - ZrB2, TiB2 - B4C can be synthesized by this modified SHS process. In this present invention aluminium, silica and carbon is used as raw materials for the production of AI2O3 - SiCwin-situ composite.

Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF CERAMIC MATRIX COMPOSITES SUCH AS A12O3-SICWAB COMPOSITE"

Abstract

An improved process for making of ceramic matrix composites: The process of present invention provides a modified SHS technique termed as rapid heating self propagating high temperature synthesis (RH-SHS) for the manufacture of ceramic composites. In this modified technique, the reacting mixture is heated rapidly so that a sharp thermal gradient is established between surface and the core of the samples. A wide range of ceramic matrix composites such as AI203 - TiC, AI2O3 - WC, MoSi2 - SiC, AI2O3 - TiB2, MgO - TiC, AI2O3 -AIN - SiC, AI2O3 - ZrB2, TiB2 - B4C can be synthesized by this modified SHS process. In this present invention aluminium, silica and carbon is used as raw materials for the production of AI2O3 - SiCwin-situ composite.

Full Text	This invention relates to an improved process for the prepara¬tion of ceramic matrix composites. This invention relates to in situ synthesis of ceramic matrix composites by rapid heating self propagating high temperature synthesis (RH SHS). The present invention is useful for the production of ceramic matrix composites having wide range of application in automobile, aero industries, where high temperature proper¬ties under certain extreme atmospheres are important. These products are also likely to find application in making drill bits and wire drawing dies where abrasive resistance and hardness of the composites will be of utmost importance. Hitherto the practiced process for the manufacture of ceramic based composites is by conventional powder process¬ing route. In the conventional synthesis technique of ceramic matrix composites, the powder mixture of compound components which are present in the final product are mixed together and exposed to high temperature sintering for sufficiently long time. The sintering temperature and time of exposure depend upon the type of components under consideration. The high temperature exposure brings about only physical changes in the green compacts and no significant chemical reaction are accom¬plished. Addition of sintering aids helps in bringing down the processing temperature and time. Recently, emphasis has been laid to utilisation of the heat generated due to exothermic chemical reactions during synthesis of compounds. The process is known as combustion synthesis (CS). Combustion synthesis can broadly be classified as self propagating high temperature synthesis (SHS) and thermal explosion synthesis (TES). In the former, the reaction is initiated at one end of the reactant mixture by limited supply of external heat through various means such as, heating coil, laser beam, electric arc etc. Reaction front then propa¬gates from one end to the other, if the heat generated by chemical reactions is sufficient enough to sustain it. Self sustainability of the reactions depend upon compactness of the green mixture. High compactness provides better chance for chemical reaction. On the contrary, low porosity increases the thermal conductivity of the mixture and thus enhanced heat loss. Successful execution of SHS process needs optimum density of the green compacts. Heat generated due to exothermic chemical reactions raises the localised temperature and thus zonewise sintering takes place. In TES, the reacting mixture is heated up slowly in a furnace to the reaction initiation temperature (Ti) so that the whole mixture experiences a more or less same temper¬ature. At Ti, the entire volume of the mixture undergoes exothermic reactions simultaneously. This process is relative¬ly less dependant on the physical properties of the green compacts. The drawbacks of the existing processes are: For the first process: 1) It is a two stage process i.e. first to produce the ingredi¬ ent compounds for green mixture and then the final products. 2) Many of the compounds such as SiC are carcinogenic and thus associated handling problems. 3) Non-utilization of reaction heat and so requires more ener¬ gy- 4) Difficulty in achieving compositional homogeneity due to difference in densities. For the second process (combustion synthesis), 1) Difficulty in processing low melting points components. 2) Dependance of the process on physical properties of the green compact. 3) Incomplete development of high temperature properties due to existence of heat sinks. This in turn may necessitate a sec¬ ondary step for high temperature treatment. The above mentioned drawbacks make the known processes cost intensive. The main object of the present invention is to provide an improved process for the preparation of ceramic matrix composites which obviates the above noted drawbacks. Another object is to provide an improved process for the in - situ production of ceramic mixture composites by rapid heating self propagating high temperature synthesis (RH-SHS) . Still another object of the present invention is to provide an improved process which makes the process inde¬pendent of physical properties of the green compacts. Yet another object of the present invention is to provide an improved process to produce homogeneous ceramic matrix compos¬ites through modified self propagating high temperature single step synthesis route and thereby reducing the processing cost in terms of time and energy. The process of present invention provides a modified SHS technique termed as rapid heating self propagating high temperature synthesis (RH-SHS) for the manufacture of ceramic composites. In this modified technique, the reacting mixture is heated rapidly so that a sharp thermal gradient is established between surface and the core of the samples. Even when the surface temperature or one end of the sample reaches TI, the core or the other end will be at lower temperature and the exothermic SHS reaction will set in. A wide range of ceramic matrix composites such as AI2O3 - TiC, AI2O3 - WC, MoSi2 - SiC, AI2O3 - TiB2, MgO - TiC, AI2O3 - AIM - SiC, AI2O3 - ZrB2, TiB2 - B4C etc. can be synthesized by this modified SHS process. In this present invention aluminium, silica and carbon is used as raw materials for the production of AI2O3 - SiCw in-situ composite. Aluminium reduces silica to produce silicon which in turn reacts with carbon to form silicon carbide. Accordingly the present invention provides, an improved process for the preparation of ceramic matrix composites such as AI2O3 - SiCw composite characterized in that use of Rapid heating self propagating high temperature synthesis (RH - SHS) method, which comprises the steps of: i) mixing silica 22 to 56% (by weight) , Aluminium 13 to 34% (by weight) , Carbon 4 to 12% (by weight), Magnesia 0 to 5% (by weight) in a ball mill for a period of 4 to 5 hours, ii) compacting the resulted green mix after addition of a binder such as herein described in the range of 0.5 to 1.0% form desired shapes by conventional methods, ill) drying of the resultant green compacts in a temperature range of 100 to 200«C for a period of 4 to 5 hours, iv) heating of dried compacts in a furnace by RH - SHS method which comprises heating the compacted dies at 383 K for three hours followed by graphite furnace treatment with heating rates ranging from 100 to 400 K/min upto a temperature in the range of 1523 to 2273K having a soaking time ranging a period of 0 to 30 minutes at this temperature, v) furnace cooling the sintered products to room temperature ( 25 - 30°C) in presence of air or inert gas. In embodiment of the present invention ceramic matrix composices such as Al O - SiCw, Al O -TiC, Al O - WC, MoSi -SiC, Al 0 - 23 23 23 2 23 TiB , MgO-TiC, Al 0 -AlN-SiC, Al O -ZrB , TiB -B C may be 2 23 232 24 prepared. In a particuler embodiment of the present invention Al 0 -SiCw 2 3 composite may be prepared using Silica : 22 to 56 % (by weight) Aluminium : 13 to 34 % (by weight) Carbon : 4 to 12 % (by weight) Magnesia : 0 to 5 % (by weight) In this embodiment of the present invention SiO powder of 95% 2 or above purity with particle size varying between 40 to 70 m is thoroughly mixed with Al powder of 99% purity and 20 to 45 m size and carbon powder with particle size of 40 to 70 m. According to yet another feature of this invention, carbon powder may be chosen from activated carbon, graphite, amorphous carbon and the like individually or in combination of more than one. One of the ingredients in the green mix being silica and in the product being alumina, the ash content of carbon can be varied over a wide range (5-15%). Green compacts of desired shape and size is produced using a forming pressure varyif? between 700 to 1300 Kg/cm2. The binder used may be selected from polyvinyl alcohol, polyvinyl butyryl, polymethyl metha-crylic acid, resins and the like individually or in combination of more than one. By the process of the present invention, ceramic matrix composites are produced through rapid heating self propagating high temperature synthesis route having properties in the range of Properties ' Values Bulk density (gm/cc) 2.0 - 3.0 Proportion of SiC(%) 10.0 - 37.0 Apparent porosity (%) 14.0-45.0 MOH hardness 6-9 The following examples are given by way of illustration and should not be construed to limit the scope of the present inven¬tion. Example - 1 28 gms of Si02 powder is intimately mixed with 5.5 gms of amorphous carbon containing around 10% ash and 17 gms of aluminium to make a mixture of around 50 gms. This mixture presents stoichiometric composition for the reaction. This intimately mixed powders are ball milled for 6 hours. 1.5 c.c. of freshly prepared polyvinyl alcohol is added to the milled mixture and are compacted in the form of one inch diameter pellets at 775 Kg/cm2 pressure. The compacted pellets are heated at 383 K for 3 hours. Pellets thus obtained are treated in a graphite furnace in air atmosphere. Pellets are heated to 1723 K for no soaking time with a heating rate of approximately 400 K/minute. Once the reaction and soaking are over, samples are furnace cooled to room temperature. Example - 2 28 gms of Si02 powder is intimately mixed with 5.5 gms of amorphous carbon -containing around 10% ash and 17 gms of aluminium to make a mixture of around 50 gms. This mixture presents stoichiometric composition for the reaction. This intimately mixed powders are ball milled for 6 hours. 1.5 c.c. of freshly prepared polyvinyl alcohol is added to the milled mixture and are compacted in the form of one inch diameter pellets with a central hole of 1 mm diameter (Die) at 775 Kg/cm2 pressure. The compacted dies are heated at 383 K for 3 hours. Dies thus obtained are treated in a graphite furnace in air atmosphere. Furnace temperature is first raised to 1973 K and the pellet sample is inserted in the hot furnace. Once the reactions are complete, the temperature of the furnace is further raised to 2223 K. Holding the samples at that tempera¬ture for one minute, power supply of the furnace is cut off and the samples are furnace cooled in air atmosphere. Example - 3 34.7 gms of SiO2 powder is intimately mixed with 6.2 gms of amorphous carbon containing around 6.23% ash, 21 gms of aluminium powder and 3.5 gms of MgO powder (as sintering aid) to make a mixture of around 65 gms. This intimately mixed powders are ball milled for 6 hours. 2 c.c. of freshly prepared polyvinyl alcohol is added to the milled mixture and are com- pacted in the form of one inch diameter cylindrical disc at 775 Kg/cm2 pressure. The compacted discs are heated at 383 K for 3 hours. Discs thus obtained are treated in a graphite furnace in argon atmosphere. Discs are heated to 1523 K for a soaking time of 10 minutes with a heating rate of approximately 200 K/minute. Once the reaction and soaking are over, samples are furnace cooled to room temperature in argon atmosphere. Test results of the end products of the above examples are given in Table 1 below : Table - 1 (TableRemoved)Scanning Electron Microscopic (SEM) investigation of the treated samples reveals uniform distribution of silicon carbide in alumina matrix, imparting high strength to the composite. Amount and nature of silicon carbide in the product depends upon the temperature of treatment and its soaking time. Further, the products show excellent capacity to withstand severe thermal shock generated by rapid heating as well as sudden rise in localized temperature. This is evident by crack free and dimensionally stable products achieved after the heat treatment. The properties of the products synthesised by the present invention show the possibility of fabricating a wide range of ceramic composites through rapid heating self propagating high temperature synthesis route. The main advantages of the present invention are: l)In the present invention, any low melting point component can be successfully used for the synthesis of composites whereas the practiced processes do not have much scope for it. 2)The present invention permits the use of green sample of any physical properties whereas the combustion synthesis techniques depend on compact properties. 3)High heating rate in the present invention reduces the proc¬essing time and energy loss, thus reduction in processing cost. 4)The present invention provides flexibility to control the product composition and high temperature properties in compari¬son to other combustion processes. 5)The present invention provides a possibility of near net shape component fabrication by single step processing whereas other known processes involve multiple steps. We Claim: 1. An improved process for the preparation of ceramic matrix composites such as Al2O3 - SiCw composite characterized in that use of Rapid heating self propogating high temperature synthesis (RH - SHS) method, which comprises the steps of: i) mixing silica 22 to 56% (by weight), Aluminium 13 to 34% (by weight), Carbon 4 to 12% (by weight) , Magnesia 0 to 5% (by weight) in a ball mill for a period of 4 to 5 hours to get a green mix , ii) compacting the obtained green mix after addition of a binder such as herein described in the range of 0.5 to 1.0% to form desired shapes by conventional methods, iii) drying of the resultant green compacts in a temperature range of 100 to 200°C for a period of 4 to 5 hours, iv) heating of dried compacts in a furnace by RH - SHS method which comprises heating the compacted dies at 383 K for three hours followed by graphite furnace treatment with heating rates ranging from 100 to 400 K/min upto a temperature in the range of 1523 to 2273K having a soaking time ranging a period of 0 to 30 minutes at this temperature, v) furnace cooling the sintered products to room temperature ( 25 - 30°C) in presence of air or inert gas. 2. An improved process as claimed in claims 1 wherein the binder used is selected from polyvinyl, alcohol, polyvinyl butyryl, polymethyl methacrylic acid and resins. 3. An improved process as claimed in claims 1 - 2 wherein silica and aluminium and Magnesia is of 95% , 99% and 99% purity respectively. 4. An improved process as claimed in claims 1 - 3 wherein the particle size of silica and aluminium are in the range of 40 to 70 urn and 20 to 40 urn respectively. 5. An improved process as claimed in claims 1-4 wherein carbon powder used is selected from activated carbon, graphite and amorphous carbon having ash content in the range of 5 to 15% and particle size in the range of 40 to 70 urn. 6. An improved process for preparation of ceramic matrix composites such as AfeOa - SiCw substantially as herein described with reference to the examples.

Full Text

This invention relates to an improved process for the prepara¬tion of ceramic matrix composites. This invention relates to in situ synthesis of ceramic matrix composites by rapid heating self propagating high temperature synthesis (RH SHS).
The present invention is useful for the production of ceramic matrix composites having wide range of application in automobile, aero industries, where high temperature proper¬ties under certain extreme atmospheres are important. These products are also likely to find application in making drill bits and wire drawing dies where abrasive resistance and hardness of the composites will be of utmost importance.
Hitherto the practiced process for the manufacture of ceramic based composites is by conventional powder process¬ing route. In the conventional synthesis technique of ceramic matrix composites, the powder mixture of compound components which are present in the final product are mixed together and exposed to high temperature sintering for sufficiently long time. The sintering temperature and time of exposure depend upon the type of components under consideration. The high temperature exposure brings about only physical changes in the green compacts and no significant chemical reaction are accom¬plished. Addition of sintering aids helps in bringing down the processing temperature and time.
Recently, emphasis has been laid to utilisation of the heat generated due to exothermic chemical reactions during synthesis of compounds. The process is known as combustion synthesis (CS). Combustion synthesis can broadly be classified as self propagating high temperature synthesis (SHS) and
thermal explosion synthesis (TES). In the former, the reaction is initiated at one end of the reactant mixture by limited supply of external heat through various means such as, heating coil, laser beam, electric arc etc. Reaction front then propa¬gates from one end to the other, if the heat generated by chemical reactions is sufficient enough to sustain it. Self sustainability of the reactions depend upon compactness of the green mixture. High compactness provides better chance for chemical reaction. On the contrary, low porosity increases the thermal conductivity of the mixture and thus enhanced heat loss. Successful execution of SHS process needs optimum density of the green compacts. Heat generated due to exothermic chemical reactions raises the localised temperature and thus zonewise sintering takes place.
In TES, the reacting mixture is heated up slowly in a furnace to the reaction initiation temperature (Ti) so that the whole mixture experiences a more or less same temper¬ature. At Ti, the entire volume of the mixture undergoes exothermic reactions simultaneously. This process is relative¬ly less dependant on the physical properties of the green compacts.
The drawbacks of the existing processes are: For the first process:
1) It is a two stage process i.e. first to produce the ingredi¬
ent compounds for green mixture and then the final products.
2) Many of the compounds such as SiC are carcinogenic and thus
associated handling problems.

3) Non-utilization of reaction heat and so requires more ener¬
gy-
4) Difficulty in achieving compositional homogeneity due to
difference in densities.
For the second process (combustion synthesis),
1) Difficulty in processing low melting points components.
2) Dependance of the process on physical properties of the
green compact.
3) Incomplete development of high temperature properties due to
existence of heat sinks. This in turn may necessitate a sec¬
ondary step for high temperature treatment.
The above mentioned drawbacks make the known processes cost intensive.
The main object of the present invention is to provide an improved process for the preparation of ceramic matrix composites which obviates the above noted drawbacks.
Another object is to provide an improved process for the in - situ production of ceramic mixture composites by rapid heating self propagating high temperature synthesis (RH-SHS) .
Still another object of the present invention is to provide an improved process which makes the process inde¬pendent of physical properties of the green compacts. Yet another object of the present invention is to provide an improved process to produce homogeneous ceramic matrix compos¬ites through modified self propagating high temperature single

step synthesis route and thereby reducing the processing cost in terms of time and energy.
The process of present invention provides a modified SHS technique termed as rapid heating self propagating high temperature synthesis (RH-SHS) for the manufacture of ceramic composites. In this modified technique, the reacting mixture is heated rapidly so that a sharp thermal gradient is established between surface and the core of the samples. Even when the surface temperature or one end of the sample reaches TI, the core or the other end will be at lower temperature and the exothermic SHS reaction will set in. A wide range of ceramic matrix composites such as AI2O3 - TiC, AI2O3 - WC, MoSi2 - SiC, AI2O3 - TiB2, MgO - TiC, AI2O3 - AIM - SiC, AI2O3 - ZrB2, TiB2 - B4C etc. can be synthesized by this modified SHS process. In this present invention aluminium, silica and carbon is used as raw materials for the production of AI2O3 - SiCw in-situ composite. Aluminium reduces silica to produce silicon which in turn reacts with carbon to form silicon carbide.
Accordingly the present invention provides, an improved process for the preparation of ceramic matrix composites such as AI2O3 - SiCw composite characterized in that use of Rapid heating self propagating high temperature synthesis (RH - SHS) method, which comprises the steps of:
i) mixing silica 22 to 56% (by weight) , Aluminium 13 to 34% (by weight) , Carbon 4 to 12% (by weight), Magnesia 0 to 5% (by weight) in a ball mill for a period of 4 to 5 hours,
ii) compacting the resulted green mix after addition of a binder such as herein described in the range of 0.5 to 1.0% form desired shapes by conventional methods,
ill) drying of the resultant green compacts in a temperature range of 100 to 200«C for a period of 4 to 5 hours,
iv) heating of dried compacts in a furnace by RH - SHS method which comprises heating the compacted dies at 383 K for three hours followed by graphite furnace treatment with heating rates ranging from 100 to 400 K/min upto a temperature in the range of 1523 to 2273K having a soaking time ranging a period of 0 to 30 minutes at this temperature,
v) furnace cooling the sintered products to room temperature ( 25 - 30°C) in presence of air or inert gas.
In embodiment of the present invention ceramic matrix composices
such as Al O - SiCw, Al O -TiC, Al O - WC, MoSi -SiC, Al 0 -
23 23 23 2 23
TiB , MgO-TiC, Al 0 -AlN-SiC, Al O -ZrB , TiB -B C may be
2 23 232 24
prepared.
In a particuler embodiment of the present invention Al 0 -SiCw
2 3
composite may be prepared using
Silica : 22 to 56 % (by weight)
Aluminium : 13 to 34 % (by weight)
Carbon : 4 to 12 % (by weight)
Magnesia : 0 to 5 % (by weight)
In this embodiment of the present invention SiO powder of 95%
2
or above purity with particle size varying between 40 to 70 m is thoroughly mixed with Al powder of 99% purity and 20 to 45 m size and carbon powder with particle size of 40 to 70 m. According to yet another feature of this invention, carbon powder may be chosen from activated carbon, graphite, amorphous carbon and the like individually or in combination of more than one. One of the ingredients in the green mix being silica and in the product being alumina, the ash content of carbon can be varied over a wide range (5-15%). Green compacts of desired shape and size is produced using a forming pressure varyif?
between 700 to 1300 Kg/cm2. The binder used may be selected from polyvinyl alcohol, polyvinyl butyryl, polymethyl metha-crylic acid, resins and the like individually or in combination of more than one.
By the process of the present invention, ceramic matrix composites are produced through rapid heating self propagating high temperature synthesis route having properties in the range of
Properties ' Values
Bulk density (gm/cc) 2.0 - 3.0
Proportion of SiC(%) 10.0 - 37.0
Apparent porosity (%) 14.0-45.0
MOH hardness 6-9
The following examples are given by way of illustration and should not be construed to limit the scope of the present inven¬tion.
Example - 1
28 gms of Si02 powder is intimately mixed with 5.5 gms of amorphous carbon containing around 10% ash and 17 gms of aluminium to make a mixture of around 50 gms. This mixture presents stoichiometric composition for the reaction. This intimately mixed powders are ball milled for 6 hours. 1.5 c.c. of freshly prepared polyvinyl alcohol is added to the milled mixture and are compacted in the form of one inch diameter pellets at 775 Kg/cm2 pressure. The compacted pellets are heated at 383 K for 3 hours. Pellets thus obtained are treated in a graphite furnace in air atmosphere. Pellets are heated to
1723 K for no soaking time with a heating rate of approximately 400 K/minute. Once the reaction and soaking are over, samples are furnace cooled to room temperature.
Example - 2
28 gms of Si02 powder is intimately mixed with 5.5 gms of amorphous carbon -containing around 10% ash and 17 gms of aluminium to make a mixture of around 50 gms. This mixture presents stoichiometric composition for the reaction. This intimately mixed powders are ball milled for 6 hours. 1.5 c.c. of freshly prepared polyvinyl alcohol is added to the milled mixture and are compacted in the form of one inch diameter pellets with a central hole of 1 mm diameter (Die) at 775 Kg/cm2 pressure. The compacted dies are heated at 383 K for 3 hours. Dies thus obtained are treated in a graphite furnace in air atmosphere. Furnace temperature is first raised to 1973 K and the pellet sample is inserted in the hot furnace. Once the reactions are complete, the temperature of the furnace is further raised to 2223 K. Holding the samples at that tempera¬ture for one minute, power supply of the furnace is cut off and the samples are furnace cooled in air atmosphere.
Example - 3
34.7 gms of SiO2 powder is intimately mixed with 6.2 gms of amorphous carbon containing around 6.23% ash, 21 gms of aluminium powder and 3.5 gms of MgO powder (as sintering aid) to make a mixture of around 65 gms. This intimately mixed powders are ball milled for 6 hours. 2 c.c. of freshly prepared polyvinyl alcohol is added to the milled mixture and are com-
pacted in the form of one inch diameter cylindrical disc at 775 Kg/cm2 pressure. The compacted discs are heated at 383 K for 3 hours. Discs thus obtained are treated in a graphite furnace in argon atmosphere. Discs are heated to 1523 K for a soaking time of 10 minutes with a heating rate of approximately 200 K/minute. Once the reaction and soaking are over, samples are furnace cooled to room temperature in argon atmosphere. Test results of the end products of the above examples are given in Table 1 below :
Table - 1

(TableRemoved)Scanning Electron Microscopic (SEM) investigation of the treated samples reveals uniform distribution of silicon carbide in alumina matrix, imparting high strength to the composite. Amount and nature of silicon carbide in the product depends upon the temperature of treatment and its soaking time.
Further, the products show excellent capacity to withstand severe thermal shock generated by rapid heating as well as sudden rise in localized temperature. This is evident by crack free and dimensionally stable products achieved after the heat treatment.
The properties of the products synthesised by the present invention show the possibility of fabricating a wide range of ceramic composites through rapid heating self propagating high temperature synthesis route.
The main advantages of the present invention are:
l)In the present invention, any low melting point component can be successfully used for the synthesis of composites whereas the practiced processes do not have much scope for it. 2)The present invention permits the use of green sample of any physical properties whereas the combustion synthesis techniques depend on compact properties.
3)High heating rate in the present invention reduces the proc¬essing time and energy loss, thus reduction in processing cost. 4)The present invention provides flexibility to control the product composition and high temperature properties in compari¬son to other combustion processes.
5)The present invention provides a possibility of near net shape component fabrication by single step processing whereas other known processes involve multiple steps.

We Claim:
1. An improved process for the preparation of ceramic matrix composites such
as Al2O3 - SiCw composite characterized in that use of Rapid heating self
propogating high temperature synthesis (RH - SHS) method, which
comprises the steps of:
i) mixing silica 22 to 56% (by weight), Aluminium 13 to 34% (by weight),
Carbon 4 to 12% (by weight) , Magnesia 0 to 5% (by weight) in a ball mill
for a period of 4 to 5 hours to get a green mix , ii) compacting the obtained green mix after addition of a binder such as
herein described in the range of 0.5 to 1.0% to form desired shapes
by conventional methods, iii) drying of the resultant green compacts in a temperature range of 100
to 200°C for a period of 4 to 5 hours, iv) heating of dried compacts in a furnace by RH - SHS method which
comprises heating the compacted dies at 383 K for three hours
followed by graphite furnace treatment with heating rates ranging
from 100 to 400 K/min upto a temperature in the range of 1523 to
2273K having a soaking time ranging a period of 0 to 30 minutes
at this temperature, v) furnace cooling the sintered products to room temperature ( 25 -
30°C) in presence of air or inert gas.
2. An improved process as claimed in claims 1 wherein the binder used is
selected from polyvinyl, alcohol, polyvinyl butyryl, polymethyl methacrylic
acid and resins.
3. An improved process as claimed in claims 1 - 2 wherein silica and
aluminium and Magnesia is of 95% , 99% and 99% purity respectively.
4. An improved process as claimed in claims 1 - 3 wherein the particle size
of silica and aluminium are in the range of 40 to 70 urn and 20 to 40 urn
respectively.
5. An improved process as claimed in claims 1-4 wherein carbon powder
used is selected from activated carbon, graphite and amorphous carbon
having ash content in the range of 5 to 15% and particle size in the range
of 40 to 70 urn.
6. An improved process for preparation of ceramic matrix composites such
as AfeOa - SiCw substantially as herein described with reference to the
examples.

Documents:

2267-del-1997-abstract.pdf

2267-del-1997-claims.pdf

2267-del-1997-correspondence-others.pdf

2267-del-1997-correspondence-po.pdf

2267-del-1997-description (complete).pdf

2267-del-1997-form-1.pdf

2267-del-1997-form-19.pdf

2267-del-1997-form-2.pdf

2267-DEL-1997-Form-3.pdf

2267-DEL-1997-Petition-138.pdf

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Patent Number

214901

Indian Patent Application Number

2267/DEL/1997

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

18-Feb-2008

Date of Filing

13-Aug-1997

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL, RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	DEBAJYOTI BANDYOPADHYAY	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.
2	LOKESH CHANDRA PATHAK	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.
3	RANJIT GHATAK GANGULY	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.
4	SWAPAN KUMAR DAS	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.
5	PATCHA RAMACHANDRA RAO	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.

PCT International Classification Number

C04B 41/80

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA