Title of Invention	CERAMIC BONDED SILICON CARBIDE FILTER AND METHOD OF MAKING THE SAME
Abstract	A porous silicon carbide product having a uniform, unimodal and controlled pore size, sufficient permeability and durability for use in high temperature gas filtration such as removal of particulates from hot flue gases or coal gases. The method of making the product involves selecting the silicon carbide grains of defined particle size, mixing with substantially small part of a mixture of minerals which forms a ceramic bond at low temperature of below 1250°C and shaping into required product. When the product is fired at this temperature, the ceramic phase formed in-situ bridges Silicon carbide grains leaving the defined pores with high pore connectivity resulting in high permeability. The ceramic bond formed at this temperature results in a product with high mechanical strength and sufficient hot strength for use as filters or membrane supports in hot gas filtration and other industrial filtration applications.

Title of Invention

CERAMIC BONDED SILICON CARBIDE FILTER AND METHOD OF MAKING THE SAME

Abstract

A porous silicon carbide product having a uniform, unimodal and controlled pore size, sufficient permeability and durability for use in high temperature gas filtration such as removal of particulates from hot flue gases or coal gases. The method of making the product involves selecting the silicon carbide grains of defined particle size, mixing with substantially small part of a mixture of minerals which forms a ceramic bond at low temperature of below 1250°C and shaping into required product. When the product is fired at this temperature, the ceramic phase formed in-situ bridges Silicon carbide grains leaving the defined pores with high pore connectivity resulting in high permeability. The ceramic bond formed at this temperature results in a product with high mechanical strength and sufficient hot strength for use as filters or membrane supports in hot gas filtration and other industrial filtration applications.

Full Text	2 TITLE: THE MANUFACTURE OF CERAMIC BONDED SILICON CARBIDE FILTER AND METHOD THEREOF FIELD OF INVENTION The invention relates to manufacture of a porous silicon carbide filtes having a uniform, unimodal and controlled pore size, sufficient permeability and durability for use in high temperature gas filtration such as removal of particulates from hot flue gases or coal gases. BACKGROUND OF INVENTION Various porous ceramic materials are used as a filter, a catalyst carrier, a substrate of separation membrane used as a gas separating member or the like. The use of ceramic filters for filtering hot flue gases or coal gas or like is well known and use of such filter elements is known for ex: in US Pat. No 4,713,17*. A method of manufacturing ceramic filter elements in moulding operation is described in US. Pat. No. 4,629,483. Such filter elements perform very well but they are expensive to manufacture, because the firing temperature is above 1400° C. Ceramic filters have been tested in processes such as coal gasification and coal combustion to remove particulates from hot flue gases to protect down stream equipment from corrosion and erosion. Ceramic filters in tubular (candle) form, with one end closed and the other end open have been shown to remove the particulates efficiently (EP1772178). 3 Ceramic hot-gas candle filters must withstand exposure to chemically corrosive gas streams at temperatures in excess of 800°C. In addition they are subjected to significant thermal stresses during back pulse cleaning which can cause catastrophic failure of the ceramic candle filter element. Ceramic hot-gas candle filters known in the art are generally fabricated from either porous monolithic materials or porous fiber-composite materials (ES Pat. No. 5,075,160). Candle filters may have relatively uniform porosity throughout the filter or they may comprise a porous support with a thin layer, or membrane, of fine porosit/ on the outer surface of the support. The membrane layer is typically applied to the filter using a variety of method such as coating from a dispersion containing finer grains than those used in the support for small membrane pore size, bonding randomly arranged chopped ceramic fibers to the support using colloidal (or sol) materials, or forming a ceramic matrix by chemical as given in US Pat. No. 6180054. Materials used to fabricate ceramic hot-gas generally include oxideS such as aluminosilicates, glass, and alumina, and non-oxides such as silicon carbide and silicon nitride. Oxide-based ceramic filters have adequate resistance to flue gas atmospheres and fly-ash for the design life of the filters; however, they generally have thermal shock resistance. Non-oxide ceramics generally have good shock resistance, however they are susceptible to oxidation in the corrosive environment to which they are subjected which results in degradation of mechanical properties. 4 In recent years, non-oxide ceramics having silicon such as silicon nitride and silicon carbide as the main constituents gain attention as a microporous ceramic material used for these applications. For example, in US Patent No. 2004043888 the microporous ceramic materials having silicon nitride as the main constituent have excellent heat resistance and thermal shock resistance, and are suitable for use under a high temperature environment. This uses metal silicon powder and high temperature process. Extensive work has been done in using various types of bonds to make Silicon carbide (SiC) filter. One material which has shown promise in clay bonded silicon carbide which has goon chemical resistance and good physical properties at elevated temperatures. However, this material has limits in that it looses strength at very high temperatures and oxidation produces a glass formation that decreases permeability and can seriously restrict filtration. High temperature creep also deforms and damages these filter tubes. Recrystallized silicon carbide has been extensively used for kiln furniture and structural shapes in high temperature applications. This type of silicon carbide has much higher strength, both at room temperature and elevated temperature, than clay bonded silicon carbide. US Pat. No. 6214078 provides a method of recrystallized silicon carbide restricts both the pore size and the permeability of the material making it unsuitable for a gas filter. US Pat No. 2005158534 provides a method for silicon carbide-based porous material characterized by comprising silicon carbide particles as an aggregate. Metallic silicon and an oxide phase containing Si, Al and an alkaline earth metal; 5 it is high in porosity and strength and superior in oxidation resistance and thermal shock resistance. A silicon carbide ceramics filter for dust collection which has high strength with the addition of alkali metal and alkali earth metal is prepared by firing at 1400°C for 10 hours as claimed in KR 20020069051 In EP 1568669, the above method is used wherein the alkaline earth metal is strontium. In another method in US Pat No. 2005143255 Cordierite phase formed in-situ is used as bond between silicon carbide grains but the temperature of formation of cordierite phase above 1350°C or more All the known arts for producing porous silicon carbide monolithic filter involves heating the product at least 1350°C or more hence the product cost is very high To overcome the above drawbacks i.e. firing the Silicon carbide filter at higher Temperature which is not only increases the cost of production but also deteriorates the silicon carbide grains by oxidizing its surface, it would be desirable to have a ceramic bond which is formed between silicon carbide grains when fired at temperature below 1250°C while providing a stronger and highly permeable filter which is durable at application temperature. 6 OBJECTS OF INVENTION It is therefore, an object of the present invention to propose the manufacture of porous silicon carbide filters for high temperature gas purification applications which eliminates the disadvantages of prior Art. A further object of the present invention is to propose the manufacture of porous silicon filter carbide filters for high temperature gas purification application which contains uniform and unimodal pores for use as filters or as supports for membranes Another object of the present invention is to propose of the manufacture of silicon carbide filter for high temperature gas purification application in which the silicon carbide grains of define particle size are bonded by small amount ceramic phase which forms at temperature below 1250°C, preferably between 1200°C to 1250°C and results in a product with high mechanical strength and sufficient hot strength. Still another object of the present invention is to propose the manufacture of silicon carbide filter candle for high temperatures gas purification which can be effective for hot gas filtration of flue gas or coal gas. BRIEF DEACRIPTION OF INVENTION That is, according to the present invention, there is provided a porous material comprising: a connected structure formed by bonding silicon carbide which is an aggregate by a ceramic phase which is formed in- situ at temperature below 7 1250°C and hold a large number of interconnected pores, characterized in that the material has a porosity of 30 to 50% and a medium pore diameter of 1 to 70 urn. In the present invention, a ratio of a content of silicon carbide to a total content of ceramic bond and silicon carbide is preferable 80 to 90 % by weight. In the present invention, a median particle diameter of silicon carbide is preferably 5 to 300 um is chosen to form the filter with desired pore size in the range of 1 to 70 um. Moreover, according to the present invention, there is provided a method of manufacturing a porous material using silicon carbide which is an aggregate or grain, and a mixture of minerals which forms a ceramic bond when fired below 1250°C, preferably between 1200 to 1250°C. The ceramic bond thus formed contains the phases preferably mullite and quartz which are interlocked in amorphous phase that connects the silicon carbide grains and provides strong bonding. In the present invention, ceramic bond is formed by using a mixture of power which is prepared by grinding mineral sources for Si, Al and alkaline and alkaline earth fluxes preferably Si and Al source is clay which is more than 50% of the total weight of the mixture and total flux preferably consists of more that 2 mineral sources and its weight ratio is not more than 30% of the total weight of the mixture In the present invention, the fine powders of ceramic forming raw material is mixed with silicon carbide grains of selected size along with organic binders, pore forming agents and water and formed into shapes by any one of the known method such pressing, casting, ramming, extrusion, isostatic pressing etc. The 8 amount and type of binders and types of tools and moulds are selected depend on type of products such as filter candles, honeycomb filters, membrane supports, etc. In the present invention the product formed has as optimum, physical, mechanical and thermal properties suitable for hot gas filtration application as shown in Tablel. Moreover, according to the present invention, there is provided a method of manufacturing a porous material where, the porosity, pore size permeability of the product can be varied as shown in Table 2 by selecting the suitable particle size of Silicon carbide grains and varying the amount of ceramic bond which forms at temperature below 1250°C which is economical. TABLE 1: physical, mechanical and thermal properties of hot gas filter candle made as per the invention. Parameters Typical values Material Silicon carbide support & Mullite membrane Diameter OD=60 mm, ID=40mm Length 1000mm Pore Size Support:26 microns Membrane:3.5 microns Material Density 1.85 gm/cc Porosity 38% Specific Permeability 3.9 Darcy Bending Strength (MOR) 39Mpa Young's Modulus (MOE) 57Gpa Thermal expansion (CTE) 4.86X 10"6/°C Thermal Shock Resistance AT=1000 °C 9 Table 2: Porous Properties of Various types of filters prepared by varying the particle size of Silicon carbide (SiC) and the amount of ceramic bond Grain Size Bond% of SiC(microns) Porosity% PORE SIZE (microns) PERMEABIIJTY (Darcy) Example 1 5 18 35 1.8 0.032 Example 2 5 10 49 1.8 0.25 Example 3 15 20 36 9 0.26 Example 4 15 10 44 9 1.01 Example 5 183 20 33 26 2.68 Example 6 183 15 38 26 3.89 Example 7 183 10 40 26 4.87 Example 8 283 15 42 69 4.26 A porous silicon carbide product having a uniform, unimodal and controlled pore size, sufficient permeability and durability for use in high temperature gas filtration such as removal of particulates from hot flue gases or coal gases. The method of making the product involves selecting the silicon carbide grains of defined particle size, mixing with substantially small part of a mixture of minerals which forms a ceramic bond at low temperature of below 1250°C and shaping into required product. When the product is fired at this temperature, the ceramic phase formed in-situ bridges Silicon carbide grains leaving the defined pores with high pore connectivity resulting in high permeability. The ceramic bond formed at this temperature results in a product with high mechanical strength and sufficient hot strength for use as filters or membrane supports in hot gas filtration and other industrial filtration applications.

Full Text

2
TITLE: THE MANUFACTURE OF CERAMIC BONDED SILICON CARBIDE
FILTER AND METHOD THEREOF
FIELD OF INVENTION
The invention relates to manufacture of a porous silicon carbide filtes having a
uniform, unimodal and controlled pore size, sufficient permeability and durability
for use in high temperature gas filtration such as removal of particulates from
hot flue gases or coal gases.
BACKGROUND OF INVENTION
Various porous ceramic materials are used as a filter, a catalyst carrier, a
substrate of separation membrane used as a gas separating member or the like.
The use of ceramic filters for filtering hot flue gases or coal gas or like is well
known and use of such filter elements is known for ex: in US Pat. No 4,713,17*.
A method of manufacturing ceramic filter elements in moulding operation is
described in US. Pat. No. 4,629,483. Such filter elements perform very well but
they are expensive to manufacture, because the firing temperature is above
1400° C. Ceramic filters have been tested in processes such as coal gasification
and coal combustion to remove particulates from hot flue gases to protect down
stream equipment from corrosion and erosion. Ceramic filters in tubular (candle)
form, with one end closed and the other end open have been shown to remove
the particulates efficiently (EP1772178).

3
Ceramic hot-gas candle filters must withstand exposure to chemically corrosive
gas streams at temperatures in excess of 800°C. In addition they are subjected
to significant thermal stresses during back pulse cleaning which can cause
catastrophic failure of the ceramic candle filter element.
Ceramic hot-gas candle filters known in the art are generally fabricated from
either porous monolithic materials or porous fiber-composite materials (ES Pat.
No. 5,075,160).
Candle filters may have relatively uniform porosity throughout the filter or they
may comprise a porous support with a thin layer, or membrane, of fine porosit/
on the outer surface of the support. The membrane layer is typically applied to
the filter using a variety of method such as coating from a dispersion containing
finer grains than those used in the support for small membrane pore size,
bonding randomly arranged chopped ceramic fibers to the support using colloidal
(or sol) materials, or forming a ceramic matrix by chemical as given in US Pat.
No. 6180054.
Materials used to fabricate ceramic hot-gas generally include oxideS such as
aluminosilicates, glass, and alumina, and non-oxides such as silicon carbide and
silicon nitride. Oxide-based ceramic filters have adequate resistance to flue gas
atmospheres and fly-ash for the design life of the filters; however, they generally
have thermal shock resistance. Non-oxide ceramics generally have good shock
resistance, however they are susceptible to oxidation in the corrosive
environment to which they are subjected which results in degradation of
mechanical properties.

4
In recent years, non-oxide ceramics having silicon such as silicon nitride and
silicon carbide as the main constituents gain attention as a microporous ceramic
material used for these applications. For example, in US Patent No. 2004043888
the microporous ceramic materials having silicon nitride as the main constituent
have excellent heat resistance and thermal shock resistance, and are suitable for
use under a high temperature environment. This uses metal silicon powder and
high temperature process.
Extensive work has been done in using various types of bonds to make Silicon
carbide (SiC) filter. One material which has shown promise in clay bonded silicon
carbide which has goon chemical resistance and good physical properties at
elevated temperatures. However, this material has limits in that it looses
strength at very high temperatures and oxidation produces a glass formation
that decreases permeability and can seriously restrict filtration. High
temperature creep also deforms and damages these filter tubes.
Recrystallized silicon carbide has been extensively used for kiln furniture and
structural shapes in high temperature applications. This type of silicon carbide
has much higher strength, both at room temperature and elevated temperature,
than clay bonded silicon carbide. US Pat. No. 6214078 provides a method of
recrystallized silicon carbide restricts both the pore size and the permeability of
the material making it unsuitable for a gas filter.
US Pat No. 2005158534 provides a method for silicon carbide-based porous
material characterized by comprising silicon carbide particles as an aggregate.
Metallic silicon and an oxide phase containing Si, Al and an alkaline earth metal;

5
it is high in porosity and strength and superior in oxidation resistance and
thermal shock resistance.
A silicon carbide ceramics filter for dust collection which has high strength with
the addition of alkali metal and alkali earth metal is prepared by firing at 1400°C
for 10 hours as claimed in KR 20020069051
In EP 1568669, the above method is used wherein the alkaline earth metal is
strontium.
In another method in US Pat No. 2005143255 Cordierite phase formed in-situ is
used as bond between silicon carbide grains but the temperature of formation of
cordierite phase above 1350°C or more
All the known arts for producing porous silicon carbide monolithic filter involves
heating the product at least 1350°C or more hence the product cost is very high
To overcome the above drawbacks i.e. firing the Silicon carbide filter at higher
Temperature which is not only increases the cost of production but also
deteriorates the silicon carbide grains by oxidizing its surface, it would be
desirable to have a ceramic bond which is formed between silicon carbide grains
when fired at temperature below 1250°C while providing a stronger and highly
permeable filter which is durable at application temperature.

6
OBJECTS OF INVENTION
It is therefore, an object of the present invention to propose the manufacture of
porous silicon carbide filters for high temperature gas purification applications
which eliminates the disadvantages of prior Art.
A further object of the present invention is to propose the manufacture of porous
silicon filter carbide filters for high temperature gas purification application which
contains uniform and unimodal pores for use as filters or as supports for
membranes
Another object of the present invention is to propose of the manufacture of
silicon carbide filter for high temperature gas purification application in which the
silicon carbide grains of define particle size are bonded by small amount ceramic
phase which forms at temperature below 1250°C, preferably between 1200°C to
1250°C and results in a product with high mechanical strength and sufficient hot
strength.
Still another object of the present invention is to propose the manufacture of
silicon carbide filter candle for high temperatures gas purification which can be
effective for hot gas filtration of flue gas or coal gas.
BRIEF DEACRIPTION OF INVENTION
That is, according to the present invention, there is provided a porous material
comprising: a connected structure formed by bonding silicon carbide which is an
aggregate by a ceramic phase which is formed in- situ at temperature below

7
1250°C and hold a large number of interconnected pores, characterized in that
the material has a porosity of 30 to 50% and a medium pore diameter of 1 to 70
urn. In the present invention, a ratio of a content of silicon carbide to a total
content of ceramic bond and silicon carbide is preferable 80 to 90 % by weight.
In the present invention, a median particle diameter of silicon carbide is
preferably 5 to 300 um is chosen to form the filter with desired pore size in the
range of 1 to 70 um.
Moreover, according to the present invention, there is provided a method of
manufacturing a porous material using silicon carbide which is an aggregate or
grain, and a mixture of minerals which forms a ceramic bond when fired below
1250°C, preferably between 1200 to 1250°C. The ceramic bond thus formed
contains the phases preferably mullite and quartz which are interlocked in
amorphous phase that connects the silicon carbide grains and provides strong
bonding.
In the present invention, ceramic bond is formed by using a mixture of power
which is prepared by grinding mineral sources for Si, Al and alkaline and alkaline
earth fluxes preferably Si and Al source is clay which is more than 50% of the
total weight of the mixture and total flux preferably consists of more that 2
mineral sources and its weight ratio is not more than 30% of the total weight of
the mixture
In the present invention, the fine powders of ceramic forming raw material is
mixed with silicon carbide grains of selected size along with organic binders, pore
forming agents and water and formed into shapes by any one of the known
method such pressing, casting, ramming, extrusion, isostatic pressing etc. The

8
amount and type of binders and types of tools and moulds are selected depend
on type of products such as filter candles, honeycomb filters, membrane
supports, etc.
In the present invention the product formed has as optimum, physical,
mechanical and thermal properties suitable for hot gas filtration application as
shown in Tablel.
Moreover, according to the present invention, there is provided a method of
manufacturing a porous material where, the porosity, pore size permeability of
the product can be varied as shown in Table 2 by selecting the suitable particle
size of Silicon carbide grains and varying the amount of ceramic bond which
forms at temperature below 1250°C which is economical.
TABLE 1: physical, mechanical and thermal properties of hot gas filter
candle made as per the invention.

Parameters Typical values
Material Silicon carbide support & Mullite membrane
Diameter OD=60 mm, ID=40mm
Length 1000mm
Pore Size Support:26 microns
Membrane:3.5 microns
Material Density 1.85 gm/cc
Porosity 38%
Specific Permeability 3.9 Darcy
Bending Strength (MOR) 39Mpa
Young's Modulus (MOE) 57Gpa
Thermal expansion (CTE) 4.86X 10"6/°C
Thermal Shock Resistance AT=1000 °C

9
Table 2: Porous Properties of Various types of filters prepared by
varying the particle size of Silicon carbide (SiC) and the amount of
ceramic bond

Grain Size Bond%
of SiC(microns)
Porosity% PORE SIZE
(microns) PERMEABIIJTY
(Darcy)
Example 1 5 18 35 1.8 0.032
Example 2 5 10 49 1.8 0.25
Example 3 15 20 36 9 0.26
Example 4 15 10 44 9 1.01
Example 5 183 20 33 26 2.68
Example 6 183 15 38 26 3.89
Example 7 183 10 40 26 4.87
Example 8 283 15 42 69 4.26

A porous silicon carbide product having a uniform, unimodal and controlled pore size, sufficient permeability and durability for use in high temperature gas filtration such as removal of particulates from hot flue gases or coal gases. The method of making the product involves selecting the silicon carbide grains of defined particle size, mixing with substantially small part of a mixture of minerals which forms a ceramic bond at low temperature of below 1250°C and shaping into required product. When the product is fired at this temperature, the ceramic phase formed in-situ bridges Silicon carbide grains leaving the defined pores with high pore connectivity resulting in high permeability. The ceramic bond formed at this temperature results in a product with high mechanical strength and sufficient hot strength for use as filters or membrane supports in hot gas filtration and other industrial filtration applications.

Documents:

00493-kol-2008-correspondence others.pdf

00493-kol-2008-description provisional.pdf

00493-kol-2008-form 1.pdf

00493-kol-2008-form 2.pdf

00493-kol-2008-form 3.pdf

00493-kol-2008-gpa.pdf

493 KOL 2008 Search Report.pdf

493-KOL-2008-(22-09-2011)-AMANDED CLAIMS.pdf

493-KOL-2008-(22-09-2011)-DESCRIPTION (COMPLETE).pdf

493-KOL-2008-(22-09-2011)-EXAMINATION REPORT REPLY RECIEVED.pdf

493-KOL-2008-(22-09-2011)-FORM 1.pdf

493-KOL-2008-(22-09-2011)-FORM 2.pdf

493-KOL-2008-(22-09-2011)-FORM 3.pdf

493-KOL-2008-(22-09-2011)-FORM 5.pdf

493-KOL-2008-(22-09-2011)-OTHERS.pdf

493-KOL-2008-(22-09-2011)-PA.pdf

493-KOL-2008-ABSTRACT.pdf

493-KOL-2008-CLAIMS.pdf

493-KOL-2008-CORRESPONDENCE 1.1.pdf

493-KOL-2008-CORRESPONDENCE.pdf

493-KOL-2008-DESCRIPTION COMPLETE.pdf

493-KOL-2008-EXAMINATION REPORT.pdf

493-KOL-2008-FORM 18 1.1.pdf

493-kol-2008-form 18.pdf

493-KOL-2008-FORM 2.pdf

493-KOL-2008-FORM 3.pdf

493-KOL-2008-FORM 5 1.1.pdf

493-KOL-2008-FORM 5.pdf

493-KOL-2008-GPA.pdf

493-KOL-2008-GRANTED-ABSTRACT.pdf

493-KOL-2008-GRANTED-CLAIMS.pdf

493-KOL-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

493-KOL-2008-GRANTED-FORM 1.pdf

493-KOL-2008-GRANTED-FORM 2.pdf

493-KOL-2008-GRANTED-SPECIFICATION.pdf

493-KOL-2008-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

253303

Indian Patent Application Number

493/KOL/2008

PG Journal Number

28/2012

Publication Date

13-Jul-2012

Grant Date

11-Jul-2012

Date of Filing

11-Mar-2008

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO. : 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI- 110049, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	CHENGALA DAMODARA MADHUSOODANA	CTI, BHEL, BANGALORE-560 012
2	ARUMUGAM ELANGOVAN	CTI, BHEL, BANGALORE-560 012

PCT International Classification Number

C04B35/52;C04B35/56B32B18/00;C04B35/571

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA