Title of Invention	A PROCESS FOR MAKING SINTERED SILICON CARBIDE-PRASEODYMIUM OXIDE-ALUMINUM OXIDE COMPOSITES USEFUL AS ENGINEERING CERAMICS
Abstract	The present invention relates to a process for making sintered silicon carbide-praseodymium oxide-a aluminum oxide composites. The process steps are: preparing a suspension of a mixture of SiC & A12O3 in praseodymium nitrate solution wherein praseodymium oxide equivalent to praseodymium nitrate solution and alumina used are 5 to 25 percent by wt. of SiC, maintaining a pH in the range of 7.35 to 8.00, pouring this suspension in ammonium hydroxide solution to obtain a gel-like mass, ageing the gel-like mass for a period in the range of 8-24 hours, filtering and washing the aged gel-like mass, drying the material at a temperature in the range of 100± 5°C for 8-12 hours, grinding the dried mass to pass through 100 mesh B.S., pelletizing by known methods the ground mass isostatically under 180-250 MPa, sintering the pressed pellets so obtained at a temperature in the range of 1750-1950°C for a period in the range of 0.25 hour to 1 hour in an inert atmosphere, the said process characterized in that in using praseodymium oxide and sintering at a temperature range of 1750-1950°C.

Title of Invention

A PROCESS FOR MAKING SINTERED SILICON CARBIDE-PRASEODYMIUM OXIDE-ALUMINUM OXIDE COMPOSITES USEFUL AS ENGINEERING CERAMICS

Abstract

The present invention relates to a process for making sintered silicon carbide-praseodymium oxide-a aluminum oxide composites. The process steps are: preparing a suspension of a mixture of SiC & A12O3 in praseodymium nitrate solution wherein praseodymium oxide equivalent to praseodymium nitrate solution and alumina used are 5 to 25 percent by wt. of SiC, maintaining a pH in the range of 7.35 to 8.00, pouring this suspension in ammonium hydroxide solution to obtain a gel-like mass, ageing the gel-like mass for a period in the range of 8-24 hours, filtering and washing the aged gel-like mass, drying the material at a temperature in the range of 100± 5°C for 8-12 hours, grinding the dried mass to pass through 100 mesh B.S., pelletizing by known methods the ground mass isostatically under 180-250 MPa, sintering the pressed pellets so obtained at a temperature in the range of 1750-1950°C for a period in the range of 0.25 hour to 1 hour in an inert atmosphere, the said process characterized in that in using praseodymium oxide and sintering at a temperature range of 1750-1950°C.

Full Text	The present invention relates to a process for making sintered silicon carbide-praseodymium oxide-aluminium oxide composites. The main application of the silicon carbide-praseodymium oxide-aluminium oxide composites are in the field of engineering ceramics for making component parts in the field of automobile industries, fluid transportation systems, space shuttle and in various other applications where superior thermo-mechanical properties are specified. The said material may also be used as special refractory material where thermal shock, abrasion, erosion, oxidative corrosion etc. are to be encountered. Several methods are available for making silicon carbide based composites containing aluminium oxide in combination with rare earth oxides like La2O3, Sm2O3, HoO2, Gd2O3, & Y2O3 which essentially consists of using powder rare earth oxides and aluminium oxides for which references may be made to Zhao Chen, "Pressureless Sintering of SiC with Additives of Samarium Oxide & Alumina, Materials Letters, 17 (1993), pp-27-30, Zhao Chen & Lingfang Zeng , "Pressureless sintering of Silicon Carbide with additives of HoO2 and alumina", Mat. Res. Bull, vol. 30, No. 3, pp-265-70, (1995), Zhao Chen, "Effects of Gadolinia & Alumina Addition on The Densification & Toughening Behaviour of Silicon Carbide", J. Am. Ceram. Soc., & 79 (2), pp-530-32, (1996), M. Omorie & H. Takei, "Pressureless Sintering of SiC", J. Am. Ceram. Soc., 65, C-92 (1982), leading to a product formed at much higher temperature and with considerable inhomogeneity. In all the above processes the main drawbacks may be listed as below: 1. Homogeneous mixing of solid ingredients like silicon carbide, rare earth oxide, aluminium oxide etc. require special processing techniques and expensive equipments. 2. Many of the processes require hot pressing, the technique has several techno-economic problems. 3. All of the above processes require sintering temperature in the viscinity of 2000°C, too high a temperature for normal industrial operation. 4. High rigidity in fixing compositions, which are normally in a narrow range. 5. High level of stringency in process conditions making the process less flexible. 6. Reproducibility is lower. The main objective of the present invention is to provide a process for making sintered silicon carbide composites useful as engineering ceramics which obviates the drawbacks as detailed above. Another object of the present invention is to provide a silicon carbide composite containing praseodymium oxide and aluminium oxide in the starting raw materials. Yet another object of the present invention is to use gel-derived praseodymium oxide as additive for making the material. Still another object of the present invention is to use only pressureless sintering technique for making the material. Yet another object of the present invention is to lower down the sintering temperature from 2000 to 1750°C. Still another object of the present invention is to provide a process wherein a wide range of composition of ingredients allows increase in process flexibility. Yet another object of the present invention is to provide a process for making sintered shapes using the composite prepared by the process of the present invention. Accordingly, the present invention provides a process for making sintered silicon carbide-praseodymium oxide-aluminum oxide composites useful as engineering ceramics which comprises; preparing a suspension of a mixture of SiC & A12O3 in praseodymium nitrate solution wherein praseodymium oxide equivalent to praseodymium nitrate solution and alumina used are 5 to 25 percent by wt of SiC, maintaining a pH in the range of 7.35 to 8.00, pouring this suspension in ammonium hydroxide solution to obtain a gel-like mass, ageing the gel-like mass for a period in the range of 8-24 hours, filtering and washing the aged gel-like mass, drying the material at a temperature in the range of 100± 5°C for 8-12 hours, grinding the dried mass to pass through 100 mesh B.S., pelletizing by known methods the ground mass isostatically under 180-250 MPa, sintering the pressed pellets so obtained at a temperature in the range of 1750-1950°C for a period in the range of 0.25 hour to 1 hour in an inert atmosphere, the said process characterized in that in using praseodymium oxide and sintering at a temperature range of 1750-1950°C. In an embodiment of the present invention the weight ratio of praseodymium nitrate to alumina may be in the range of 0.45 to 4.25. In another embodiment of the present invention the praseodymium oxide and alumina used may be 5 to 25 percent of SiC. In still another embodiment of the present invention the inert atmosphere provided may be such as N2, Ar, He. In yet another embodiment of the present invention the inert atmosphere provided may preferably be N2. The details of the process of the invention are given below: 1. Silicon carbide and aluminium oxide is mixed with praseodymium nitrate solution by constant stirring to prepare a suspension. 2. The entire suspension is poured in concentrated ammonia solution the pH of which is maintained at in the range of 7.35 to 8.00 by addition of ammonia. 3.The gel-like mass is aged for 8-24 hours. 4. The gel-like mass is flletred, washed and dried at a temperature in the range of a period of 110±5°C for a period in the range of 8-12 hours. 5. The dried mass is ground and passed through 100 mesh B. S. 6. The ground mass is pelletised isostatically under a pressure in the range of 180-250 MPa. 7. The pellets are fired at 1750-1950°C for 0.25-1 hour in argon /nitrogen/ helium atmosphere, preferably in nitrogen atmosphere. The process of the present invention can be used to produce sintered silicon carbide-praseodymium oxide-aluminium oxide composites of various shapes and sizes required for application as engineering as well as refractory material. Silicon carbide is difficult to sinter due to its high covalency factor. For effective densification, volume or grain boundary diffusivity needs to be activated. Some rare earth oxides including that of praseodymium are anticipated to be effective sintering aid for silicon carbide, as suggested from thermodynamic point of view. Aluminium oxide is well established as effective sintering aids for silicon carbide. However the use of aluminium oxide require very stringent process control otherwise reaction between silicon carbide and aluminium oxide will lead to excessive loss of material due to the formation of several volatile material at the sintering temperature resulting into a porous product. As regard to praseodymium oxide, though a theoretically recommended material, no record of its ability to act as sintering aid for silicon carbide is found. When praseodymium oxide and aluminium oxide mixture is used in the viscinity of the the eutectic zone, it is expected that both oxide will react to form aluminate of various Pr3+/Pr4+ : A13+ ratio. In this way reactivity of A12O3 is reduced to a large extent in relation to its reaction towards silicon carbide at sintering temperature. In the present system, sintering or densification of compacts are much faster which competes with dissociation reaction as a result of which compact mass with no measurable open porosity forms. Microstructural evaluation reveals the presence of praseodymium aluminate at the grain boundary. An well distributed praseodymium aluminate phase, which is formed during heat treatment, increases fracture toughness of the material. Hydrogel derived praseodymium oxide helps in the formation of praseodymium aluminate at lower temperature, far below the sintering temperature of the material. The following examples are given by the way of illustration of the process of the present invention and should not be construed to limit the scope of the present invention. EXAMPLE 1 19.86 ml. of praseodymium nitrate solution = 5.68 gm. of Pr2O3, 19.32 gm. of A12O3 & 75 gm. of β-SiC powder was taken & to which 18 ml. of NH3 & 32 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1800°C for a soaking time of 1.0 hour in nitrogen atmosphere. EXAMPLE 2 32 ml. of praseodymium nitrate solution = 9.152 gm. of Pr2O3, 10.848 gm. of A12O3 & 80 gm. of β-SiC powder was taken & to which 25 ml. of NH3 & 25 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1850°C for a soaking time of 0.5 hour in nitrogen atmosphere. EXAMPLE 3 50.76 ml. of praseodymium nitrate solution =14.52 gm. of Pr2O3, 10.48 gm. of A12O3 & 75 gm. of p-SiC powder was taken & to which 40.0 ml. of NH3 & 10.0 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1850°C for a soaking time of 1.0 hour in nitrogen atmosphere. EXAMPLE 4 15.89 ml. of praseodymium nitrate solution = 4.546 gm. of Pr2O3, 15.454 gm. of A12O3 & 80 gm. of β-SiC powder was taken & to which 15 ml. of NH3 & 35 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1950°C for a soaking time of 0.5 hour in nitrogen atmosphere. EXAMPLE 5 40 ml. of praseodymium nitrate solution =11.44 gm. of Pr2O3, 13.56 gm. of A12O3 & 75 gm. of p-SiC powder was taken & to which 35 ml. of NH3 & 10 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1900°C for a soaking time of 0.5 hour in argon atmosphere. The results obtained by the process of present invention are given below by way of illustration. TABLE: Sintering Data of SiC Samples (As Referred in Examples): (Table Removed) The main advantages of the present invention are: 1. Production of fully dense material by a simple processing technique, 2. Reduction of firing temperature to 1750°C from above 2000°C, 3. Wide ranging compositional tolerances making the process more flexible, 4. Sintering without going for hot pressing, 5. Imparting homogeneity to the product formed. We Claim: 1. A process for making sintered silicon carbide-praseodymium oxide-alum' oxide composites useful as engineering ceramics which comprises; preparing a suspension of a mixture of SiC & A12O3 in praseodymium nitrate solution wherein praseodymium oxide equivalent to praseodymium nitrate solution and alumina used are 5 to 25 percent by wt. of SiC, maintaining a pH in the range of 7.35 to 8.00, pouring this suspension in ammonium hydroxide solution to obtain a gel- like mass, ageing the gel-like mass for a period in the range of 8-24 hours, filtering and washing the aged gel-like mass, drying the material at a temperature in the range of 100± 5°C for 8-12 hours, grinding the dried mass to pass through 100 mesh B.S., pelletizing by known methods the ground mass isostatically under 180-250 MPa, sintering the pressed pellets so obtained at a temperature in the range of 1750-1950 C for a period in the range of 0.25 hour to 1 hour in an inert atmosphere, the said process characterized in that in using praseodymium oxide and sintering at a temperature range of 1750-1950°C. 2. A process as claimed in claim 1-1 wherein the weight of praseodymium nitrate to alumina are in the range of 0.45 to 4.25. 3. A process as claimed in claims 1&2 wherein the inert atmosphere is provided by as N2, Ar, He. 4. A process as claimed in claims 1-3 wherein the inert atmosphere is provided preferably by N2. 5. A process for making sintered silicon carbide-praseodymium oxide-aluminum oxide composites useful as engineering ceramics substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for making sintered silicon carbide-praseodymium oxide-aluminium oxide composites. The main application of the silicon carbide-praseodymium oxide-aluminium oxide composites are in the field of engineering ceramics for making component parts in the field of automobile industries, fluid transportation systems, space shuttle and in various other applications where superior thermo-mechanical properties are specified. The said material may also be used as special refractory material where thermal shock, abrasion, erosion, oxidative corrosion etc. are to be encountered.
Several methods are available for making silicon carbide based composites containing aluminium oxide in combination with rare earth oxides like La2O3, Sm2O3, HoO2, Gd2O3, & Y2O3 which essentially consists of using powder rare earth oxides and aluminium oxides for which references may be made to Zhao Chen, "Pressureless Sintering of SiC with Additives of Samarium Oxide & Alumina, Materials Letters, 17 (1993), pp-27-30, Zhao Chen & Lingfang Zeng , "Pressureless sintering of Silicon Carbide with additives of HoO2 and alumina", Mat. Res. Bull, vol. 30, No. 3, pp-265-70, (1995), Zhao Chen, "Effects of Gadolinia & Alumina Addition on The Densification & Toughening Behaviour of Silicon Carbide", J. Am. Ceram.

Soc., & 79 (2), pp-530-32, (1996), M. Omorie & H. Takei, "Pressureless
Sintering of SiC", J. Am. Ceram. Soc., 65, C-92 (1982), leading to a
product formed at much higher temperature and with considerable
inhomogeneity.
In all the above processes the main drawbacks may be listed as below:
1. Homogeneous mixing of solid ingredients like silicon carbide, rare earth
oxide, aluminium oxide etc. require special processing techniques and
expensive equipments.
2. Many of the processes require hot pressing, the technique has several
techno-economic problems.
3. All of the above processes require sintering temperature in the viscinity
of 2000°C, too high a temperature for normal industrial operation.
4. High rigidity in fixing compositions, which are normally in a narrow
range.
5. High level of stringency in process conditions making the process less
flexible.
6. Reproducibility is lower.

The main objective of the present invention is to provide a process for
making sintered silicon carbide composites useful as engineering ceramics
which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a silicon carbide
composite containing praseodymium oxide and aluminium oxide in the
starting raw materials.
Yet another object of the present invention is to use gel-derived
praseodymium oxide as additive for making the material.
Still another object of the present invention is to use only pressureless
sintering technique for making the material.
Yet another object of the present invention is to lower down the sintering
temperature from 2000 to 1750°C.
Still another object of the present invention is to provide a process wherein
a wide range of composition of ingredients allows increase in process
flexibility.
Yet another object of the present invention is to provide a process for
making sintered shapes using the composite prepared by the process of the
present invention.

Accordingly, the present invention provides a process for making sintered silicon carbide-praseodymium oxide-aluminum oxide composites useful as engineering ceramics which comprises; preparing a suspension of a mixture of SiC & A12O3 in praseodymium nitrate solution wherein praseodymium oxide equivalent to praseodymium nitrate solution and alumina used are 5 to 25 percent by wt of SiC, maintaining a pH in the range of 7.35 to 8.00, pouring this suspension in ammonium hydroxide solution to obtain a gel-like mass, ageing the gel-like mass for a period in the range of 8-24 hours, filtering and washing the aged gel-like mass, drying the material at a temperature in the range of 100± 5°C for 8-12 hours, grinding the dried mass to pass through 100 mesh B.S., pelletizing by known methods the ground mass isostatically under 180-250 MPa, sintering the pressed pellets so obtained at a temperature in the range of 1750-1950°C for a period in the range of 0.25 hour to 1 hour in an inert atmosphere, the said process characterized in that in using praseodymium oxide and sintering at a temperature range of 1750-1950°C.
In an embodiment of the present invention the weight ratio of praseodymium nitrate to alumina may be in the range of 0.45 to 4.25.
In another embodiment of the present invention the praseodymium oxide and alumina used may be 5 to 25 percent of SiC.
In still another embodiment of the present invention the inert atmosphere provided may be such as N2, Ar, He.

In yet another embodiment of the present invention the inert atmosphere
provided may preferably be N2.
The details of the process of the invention are given below:
1. Silicon carbide and aluminium oxide is mixed with praseodymium nitrate
solution by constant stirring to prepare a suspension.
2. The entire suspension is poured in concentrated ammonia solution the pH
of which is maintained at in the range of 7.35 to 8.00 by addition of
ammonia.
3.The gel-like mass is aged for 8-24 hours.
4. The gel-like mass is flletred, washed and dried at a temperature in the
range of a period of 110±5°C for a period in the range of 8-12 hours.
5. The dried mass is ground and passed through 100 mesh B. S.
6. The ground mass is pelletised isostatically under a pressure in the range
of 180-250 MPa.
7. The pellets are fired at 1750-1950°C for 0.25-1 hour in argon /nitrogen/
helium atmosphere, preferably in nitrogen atmosphere.
The process of the present invention can be used to produce sintered silicon carbide-praseodymium oxide-aluminium oxide composites of various shapes and sizes required for application as engineering as well as refractory

material. Silicon carbide is difficult to sinter due to its high covalency factor. For effective densification, volume or grain boundary diffusivity needs to be activated. Some rare earth oxides including that of praseodymium are anticipated to be effective sintering aid for silicon carbide, as suggested from thermodynamic point of view. Aluminium oxide is well established as effective sintering aids for silicon carbide. However the use of aluminium oxide require very stringent process control otherwise reaction between silicon carbide and aluminium oxide will lead to excessive loss of material due to the formation of several volatile material at the sintering temperature resulting into a porous product. As regard to praseodymium oxide, though a theoretically recommended material, no record of its ability to act as sintering aid for silicon carbide is found. When praseodymium oxide and aluminium oxide mixture is used in the viscinity of the the eutectic zone, it is expected that both oxide will react to form aluminate of various Pr3+/Pr4+ : A13+ ratio. In this way reactivity of A12O3 is reduced to a large extent in relation to its reaction towards silicon carbide at sintering temperature. In the present system, sintering or densification of compacts are much faster which competes with dissociation reaction as a result of which compact mass with no measurable open porosity forms.

Microstructural evaluation reveals the presence of praseodymium aluminate at the grain boundary. An well distributed praseodymium aluminate phase, which is formed during heat treatment, increases fracture toughness of the material. Hydrogel derived praseodymium oxide helps in the formation of praseodymium aluminate at lower temperature, far below the sintering temperature of the material.
The following examples are given by the way of illustration of the process of the present invention and should not be construed to limit the scope of the present invention.
EXAMPLE 1
19.86 ml. of praseodymium nitrate solution = 5.68 gm. of Pr2O3, 19.32 gm. of A12O3 & 75 gm. of β-SiC powder was taken & to which 18 ml. of NH3 & 32 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1800°C for a soaking time of 1.0 hour in nitrogen atmosphere.

EXAMPLE 2
32 ml. of praseodymium nitrate solution = 9.152 gm. of Pr2O3, 10.848 gm. of A12O3 & 80 gm. of β-SiC powder was taken & to which 25 ml. of NH3 & 25 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1850°C for a soaking time of 0.5 hour in nitrogen atmosphere. EXAMPLE 3
50.76 ml. of praseodymium nitrate solution =14.52 gm. of Pr2O3, 10.48 gm. of A12O3 & 75 gm. of p-SiC powder was taken & to which 40.0 ml. of NH3 & 10.0 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1850°C for a soaking time of 1.0 hour in nitrogen atmosphere.

EXAMPLE 4
15.89 ml. of praseodymium nitrate solution = 4.546 gm. of Pr2O3, 15.454 gm. of A12O3 & 80 gm. of β-SiC powder was taken & to which 15 ml. of NH3 & 35 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium & pelletised under a pressure of 200 MPa. The pellets are sintered at 1950°C for a soaking time of 0.5 hour in nitrogen atmosphere.
EXAMPLE 5
40 ml. of praseodymium nitrate solution =11.44 gm. of Pr2O3, 13.56 gm. of A12O3 & 75 gm. of p-SiC powder was taken & to which 35 ml. of NH3 & 10 ml. of distilled water was added & stirred vigorously. The whole mixture was kept for 24 hours. It is then dried at 110°C. The dried mass was ground in acetone medium & calcined at 900°C to drive-off the chemically bonded water. The calcined mass is ground again in acetone medium &

pelletised under a pressure of 200 MPa. The pellets are sintered at 1900°C for a soaking time of 0.5 hour in argon atmosphere.
The results obtained by the process of present invention are given below by
way of illustration.
TABLE: Sintering Data of SiC Samples (As Referred in Examples):
(Table Removed)

The main advantages of the present invention are:
1. Production of fully dense material by a simple processing technique,
2. Reduction of firing temperature to 1750°C from above 2000°C,
3. Wide ranging compositional tolerances making the process more flexible,
4. Sintering without going for hot pressing,
5. Imparting homogeneity to the product formed.

We Claim:
1. A process for making sintered silicon carbide-praseodymium oxide-alum'
oxide composites useful as engineering ceramics which comprises; preparing a
suspension of a mixture of SiC & A12O3 in praseodymium nitrate solution wherein
praseodymium oxide equivalent to praseodymium nitrate solution and alumina
used are 5 to 25 percent by wt. of SiC, maintaining a pH in the range of 7.35 to
8.00, pouring this suspension in ammonium hydroxide solution to obtain a gel-
like mass, ageing the gel-like mass for a period in the range of 8-24 hours,
filtering and washing the aged gel-like mass, drying the material at a temperature
in the range of 100± 5°C for 8-12 hours, grinding the dried mass to pass through
100 mesh B.S., pelletizing by known methods the ground mass isostatically
under 180-250 MPa, sintering the pressed pellets so obtained at a temperature in
the range of 1750-1950 C for a period in the range of 0.25 hour to 1 hour in an
inert atmosphere, the said process characterized in that in using praseodymium
oxide and sintering at a temperature range of 1750-1950°C.
2. A process as claimed in claim 1-1 wherein the weight of praseodymium nitrate to
alumina are in the range of 0.45 to 4.25.
3. A process as claimed in claims 1&2 wherein the inert atmosphere is provided by
as N2, Ar, He.
4. A process as claimed in claims 1-3 wherein the inert atmosphere is provided
preferably by N2.
5. A process for making sintered silicon carbide-praseodymium oxide-aluminum
oxide composites useful as engineering ceramics substantially as herein described
with reference to the examples.

Documents:

1453-del-1999-abstract.pdf

1453-del-1999-claims.pdf

1453-del-1999-correspondence-others.pdf

1453-del-1999-correspondence-po.pdf

1453-del-1999-description (complete).pdf

1453-del-1999-form-1.pdf

1453-del-1999-form-19.pdf

1453-del-1999-form-2.pdf

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Patent Number

215618

Indian Patent Application Number

1453/DEL/1999

PG Journal Number

11/2008

Publication Date

14-Mar-2008

Grant Date

28-Feb-2008

Date of Filing

05-Nov-1999

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001

Inventors:

#	Inventor's Name	Inventor's Address
1	SANKAR GHATAK	CENTRAL GLASS & CERAMIC RESERCH INSTITUTE, CALCUTTA 700032, INDIA.
2	SANTANU MANDAL	CENTRAL GLASS & CERAMIC RESERCH INSTITUTE, CALCUTTA 700032, INDIA.
3	KAJAL KUMAR DHARGUPTA	CENTRAL GLASS & CERAMIC RESERCH INSTITUTE, CALCUTTA 700032, INDIA.

PCT International Classification Number

C04B 35/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA