FIELD OF INVENTION
The invention relates to a method of manufacture of porous ceramic products, filters
and candles of complicated shapes or sizes adaptable to high temperature gas filtration
of particulates from the hot flue gases or the coal gases.
BACKGROUND Of THE INYENTION
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 the hot flue gases or the coal gas or like are well known and use of
such filter elements are known for ex: in US Pat. No 4,713,174. The ceramic filters have
been tested in processes such as coal gasification and coal combustion to remove
particulates from the hot flue gases to protect down stream equipment from the
corrosion and erosion. The ceramic filters in tubular (candle) form, with one end closed
and the other end open have been shown to remove the particulates efficiently in
(EP1772178).
The ceramic hot-gas candle filters known in the art are generally fabricated from either
the porous monolithic materials or the porous fiber-compostte materials (US Pat.No,
5,075,160).

The materials used to fabricate the ceramic hot-gas filters are generally include the
oxides such as aluminosiiicates, glass and alumina, and the non-oxides such as silicon
carbide and silicon nitride. The oxide-based ceramic filters have the adequate resistance
to the flue gas atmospheres and the fly-ash for the design life of the filters; however,
they generally have the low thermal shock resistance. The non-oxide ceramics generally
have a good shock resistance, however they are susceptible to the oxidation in the
corrosive environment to which they are subjected which results in a degradation of
mechanical properties.
In recent years, the non-oxide ceramics having silicon such as silicon nitride and silicon
carbide are the main constituents of 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 the
excellent heat resistance and the thermal shock resistance, and they are suitable for
use under a high temperature environment.
In order to suit for a filter to be appropriate for the temperatures above l000°C
encountered in these two applications, it must have a number of fairly unusual
properties. Besides being used at atmospheric pressure and high flow rates, the filter
must be a physically strong to be utilized in applications of the high pressure with
possible pressure differentials up to 400 pounds per square inch.

First of all, it must be a physically strong to withstand sufficient force of the high
volumes of gas which passes through the filter and impose significant mechanical strain
on the filter.
Second, the filter must have a pore structure of effective diameter which can set to a
specific quantity and held to a very narrow range. Every application of the filter would
require a specific affective diameter in order to optimize the results and it is necessary
that the specific diameter be essentially uniform and within very narrow tolerances
across the entire filter. Otherwise, the filter will not efficiently carry out its filtering
function with minimum resistance to flow. Finally all the qualities of filter must be
maintainable even if the filter is exposed to a very high temperature. For instance, in
the normal range of 1000°C and at least as high as 1500°C and in either oxidizing or
reducing or neutral atmospheric conditions.
The ceramic filter elements are generally of a tubular product having a closed rear end
and an open front end with collar. This complicated shape makes the manufacturing
process more difficult and hence conventional extrusion or casting methods cannot be
directly carried out.
A method of manufacturing the ceramic filter elements by moulding operation is
described and disclosed in US Pat. No. 4,629,483 where isostatic pressing is performed.
The casting method using an epoxy resin, gel casting etc. have been tried. The process
of forming silicon carbide bodies is disclosed in US Pat. No. 4,127,629 wherein a

castable slip of a bimodal distribution of silicon carbide particles are prepared, the slip
preferably containing a water miscible curable resin. The casting and the mold are then
heat treated to increase the strength of the green casting. The objective of heating of
the casting is to release the components which is a major disadvantage for
manufacturing of longer products like candle filters.
In the past decade, several consolidation techniques have been investigated with the
aim of forming the ceramic bodies directly from the colloidal suspensions. These
techniques combine advantages such as the microstructural homogeneity and the ability
to form a complex-shaped ceramic parts. Among which, gelcasting is a novel near-net
shaping method, which was first developed at Oak Ridge National Laboratory by Janney
and Omatete. It had been applied to prepare various ceramics and ceramic foams as
well. In this method, polymerization is a free radical reaction process which is inhibited
by the atmospheric oxygen, resulting in the surface-exfoliation phenomenon of green
bodies. Aggravatingly, for the consolidation of ceramic foams, 0.2% oxygen in the
atmosphere was sufficient to inhibit the reaction completely due to a large numbers of
bubbles in suspensions. Hence, the polymerization procedure is usually carried out in a
N2 filled chamber. However, a technical process under nitrogen environment is
complicated, hence increasing the cost of production, especially in the case of industrial
production. To avoid the surface-exfoiiation phenomenon, some polymers were added
to the gelcasting systems [T. Ma, Z.P. Xie, H.Z. Miao, Y. Huang, Y.B. Cheng, Ceram.
Int. 28 (8X2002) 859-86]. But , these means are based on the sticky assistance of
polymer molecules, and do not prevent the oxygen inhibition effect essentially. The

difference between the surface and the inside still eXists, which will lead to defects and
cracks during drying and sintering. On the other hand, some natural polymers, such as
polysaccharides, [AJ. Fanelli, R.D. Silvers, W.S. Frei, J.V. Burlew, G.B.Marsh, J. Am.
Ceram. Soc. 72 (10) (1989) 1833-1836], alginates, [YJia, Y. Kanno, Z.P.Xie,
J.Eur.Ceram.Soc.22(12)(2002) 1911-1916.] and proteins [0. Lyckfeldt, J. Brandt,
S.Lesca, J.Eur.Ceram.Soc.20(2000)2551-2559] which may gel in the atmosphere, have
been reported as gelling agents. However, difficulties regarding the fluidity of slurries
and the insufficient strength for handling the green bodies discourage their further
applications. M. Takehsita and S. Kurita, have developed a self-hardening slip casting
using water soluble resins [J. Eur. Ceram. Soc., 17, 415-9 (1997)]. Similarly a gelcasting
system based on a water-soluble epoxy resin has been developed by XJ. Mao, S.Z.
Shimai, MJ. Dong, S.W. Wang [J.Am.Ceram. Soc. 90 (3) (2007) 986-988]. The
advantage of this system is that it can be carried out in the air atmosphere, for the
polymerization is a nucleophilic addition reaction and not affected by oxygen. The
polymerization of the system and the consolidation of ceramic suspensions are
unacquainted, though the gelcasting procedure and the properties of obtained alumina
ceramics have been studied. The disadvantage of this water based resin is non-
availability of this specialized resins and the proprietary nature of these resins makes
this process costly and nonviable for the commercial applications.
To overcome the above drawbacks, a new composition of binder system is proposed
using commonly available pre-polymers and a curing materials and the method of
casting of long tubes using this optimized casting slurry is invented.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a method for
manufacturing of ceramic based filters, candles and porous products which are of
complicated shapes and sizes adaptable to high temperature gas filtration of
particulates from hot flue gases or coal gases which eliminates the disadvantages of
prior art.
A further object of the present invention is to propose a method for manufacturing of
ceramic based filters, candles and porous products which are of complicated shapes
and sizes adaptable to high temperature gas filtration of particulates from hot flue
gases or coal gases wherein the composition of binders for casting the ceramic based
filters are cured at room temperature and after the heat treatment results in a porous
ceramic product with a sufficient strength and contains a uniform and unimodal pores
for use as filters or as supports for membranes.
A still further object of the present invention is to propose a method for manufacturing
of ceramic based filters, candles and porous products which are of complicated shapes
and sizes adaptable to high temperature gas filtration of particulates from hot flue
gases or coal gases wherein the composition of binders for casting the ceramic based
filters consists of a pre-polymer resin with a diluents, a catalyst system as curing
components so that moulded product can be cured at room temperature.

Another object of the present invention is to propose a method for manufacturing of
ceramic based filters, candles and porous products which are of complicated shapes
and sizes adaptable to high temperature gas filtration of particulates from hot flue
gases or coal gases wherein the casting slurry with optimum fluidity is poured into a
vacuum sealed mould under vibration and allowed to harden inside the mould so that
the green product acquires a high green strength.
BRIEf DESCRIPTION Of INVENTION
According to the present invention, there is provided a method of casting ceramic
powder or aggregates using pre-polymer resin binder system that caused hardening of
the moulded ceramic at room temperature. The binder system comprising: fIrSt
component consisting of room temperature curing low viscous polymer resins; second
component consisting of diluents; third component consisting of a dispensing agent;
fourth component consisting of Curing system.
Moreover, according to the present invention, there is provided a method of
manufacturing a porous ceramic products such as silicon carbide candles by a casting
.method in which the above components are mixed in a systematic way to get uniformly
mixed, flowable casting slurry.
Moreover, according to the present invention, there is provided a casting mould which
comprises of a cavity and core which are made of Polypropylene (PP) or Teflon coated

metal and a provision to pour the casting slurry and a provision to connect to vacuum
pump for de-airing during casting and further a vibration table on which the mould is
mounted for good compaction.
Moreover, according to the present invention, there is provided a manufacturing
method wherein the measured volume of casting slurry is poured in the de-aired mould
as described above continuously while the mould is under vibration. After the pouring is
completed the vibration and vacuum is stopped. The mould is allowed for 3 to 4 hrs to
set and dismantled to remove the cast product. The ceramic cast component is then
dried in an oven for 1 day and fired in the oxidizing atmosphere at a slower rate to
remove the polymer components preferably at l°C/min up to 600°C and then heated to
the final temperature of the sintering to achieve required strength and porosity.
BRIEF AEICRIPTION OF THE ACCOMPANYING DRAWING
Fig.l - shows a schematic of casting mould for filter candle
DETAILED DESCBIPTION OF A PREFERRED EMBODIMENT Of THE
INVENTION
According to the present invention, there is provided a method of casting ceramic
powder or aggregates using pre-polymer resin binder system that caused hardening of
the moulded ceramic at room temperature. The binder system comprising:

First component consisting of room temperature curing low viscous polymer resins such
as Polyester resin, Epoxy resin, Vinyl ester resin.
Second component consisting of a diluents from any of the Acetone, Toluene, Styrene,
acrylic acid, Dimethylformamide or water.
Third component consisting of a dispensing agent such as polyvinyl Pyrrolidone.
Fourth component consisting of any of the Curing system-methyl ketone peroxide +
cobolt soaps, cyclohexanone peroxide + NN dialkyl aryllamines for Polyester, Vinyl ester
resins or any of the Diethylene triamine, Triethylene tetramine, Isopronediamine, 4,4,-
diaminodiphenylmethane, 4,4- dioaminodiphenyl sulfone for epoxy resins.
Moreover, according to the present invention, there is provided a method of
manufacturing a porous ceramic products such as silicon carbide candles by a casting
method in which the above components are mixed in a systematic way to get uniformly
mixed, flowable casting slurry.
In a preferred composition the first component is preferably a polyester resin which is
preferably in the range of 10 to 15 wt% of the powder and second component is
preferably acetone which is preferably in the range of 10 to 15 wt% of powder, third
component is preferably polyvinyl pyrrolidone which is preferably in the range of 0 to
2% and fourth component is a hardener containing a accelerator and catalyst which is
together preferably in the range of 5 to 10% of the first component.

In a more preferred composition, the first component is preferably a commercially
available water soluble epoxy resin which is preferably in the range of 4 to 6 wt% of
the powder and second component is preferably water which is preferably in the range
of 5 to 10 wt% of powder, third component is preferably polyvinyl pyrrolidone which is
preferably in the range of 0 to 1% and fourth component is a hardener which is
preferably in the range of 0.6 to 0.7 times of the first component.
Moreover, according to the present invention, there is provided a casting mould which
comprises of a cavity and core which are made of Polypropylene (PP) or Teflon coated
metal and a provision to pour the casting slurry and a provision to connect to vacuum
pump for de-airing during casting and further a vibration table on which the mould is
mounted for good compaction as shown in Fig 1.
Moreover, according to the present invention, there is provided a manufacturing
method wherein the measured volume of casting slurry is poured in the de-aired mould
as described above continuously while the mould is under vibration. After the pouring is
completed the vibration and vacuum is stopped. The mould is allowed for 3 to 4 hrs to
set and dismantled to remove the cast product. The ceramic cast component is then
dried in a oven for 1 day and fired in the oxidizing atmosphere at a slower rate to
remove the polymer components preferably at l°C/min up to 600°C and then heated to
the final temperature of the sintering to achieve required strength and porosity.
Preferably 1200-1250°C for ceramic bonded silicon carbide filters.

In the present invention, binder system is a pre-polymer which after mixing with the
ceramic powder and curing agents, polymerizes and produce a hard green compact.
The pre-polymer content is preferably in the range of 5 to 15% more preferably 5 to
10% and lower percentage pre-polymer can be added by using appropriate amount of
diluting component depending on the required viscosity of the casting slurry which
depends on the casting shape and size.
The quantity and the type of binders and the types of tools and the moulds are selected
depend on type of the products such as filter candles, tubes, membrane supports, etc.
The ceramic powder or aggregates is any of the materials such as alumina, mullite,
cordierite, silicon carbide depending on the application, more preferably silicon carbide
for hot gas filter candles and the grain size will vary from 1 to 300 microns depending
on the porosity and pore size in the range of 1 to 100 microns. In the present invention
the product formed has an optimum porosity, pore size, permeability and other
physicall mechanical and thermal properties suitable for the hot gas filtration
application.
Example 1;
300 gm of polyester resin is mixed with 250 ml of acetone and then mixed with 2000
gms of silicon carbide powder. To this paste, a 50 ml of mixture of accelerator and
catalyst is added and mixed. The slurry is poured into a closed cavity mould of 60 mm
OD and 40 mm ID and 600 mm long. The mould is allowed to set for 3 hr in air and
then the component is removed. The component is dried and fired in furnace first

soaking at 600°C and then at 12300C. The obtained product is porous silicon carbide
filter tube. The bulk density is 1.9 gmjcc and porosity is 38%.
300 gm of epoxy resin is mixed with 200 gm of hardener then mixed with 550 ml of
water. This paste is mixed with 5800 gms of silicon carbide powder. The obtained slurry
is poured into a closed caVity mould of 60 mm OD and 40 mm ID and 1600 mm long as
shown in Fig.1. The mould is allowed for 4 hr to set in air and then the component is
removed by releasing the mould. The component is dried for a day and fired in furnace
first soaking at 600°C and then at 1230°c. The obtained product is porous silicon
carbide filter candle. The bulk density is 1.82 gm/cc and porosity is 40%. The burst
strength of the candles are more than 50 bars.

KEY fEATURE
Reference Characteristic Figure
Numerals Feature
(1) M16 Bolt 1
(2) Connection to
Feeding funnel 1
(3) Top place 1
(4) Shell 1
(5) Core 1
(6) Screw Rod (MS) 1
(7) Bottom Plate 1
(8) Vibration Table/Plate 1
(9) Connection to
vacuum pump 1

WE CLAIM
1. A method of manufacture of porous ceramic products filters and candles of
complicated shapes and sizes adaptable to high temperature gas filtration of
particulates from hot flue gases or the coal gas comprises:
- a casting mould which comprises a cavity and a core that are made of
polypropylene or teflon coated metal;
- the casting mould having a provision to pour the casting slurry and a provision to
connect vacuum pump for de-airing during casting;
- the casting mould is placed on a vibration table on which the mould is mounted
for good compaction;
- a casting slurry comprises a mixture of ceramic powder and pre-polymer resin
binder 5-15% of ceramic powder;
- the casting slurry of measured amount is poured in the de-aired mould
continuously while the mould is under vibration and vacuum pump is on;
- the mould is allowed for 3 to 4 hrs to set;
- the mould is dismantled to remove casting;
- characterised in that ceramic powder after mixing with pre-polymer binder
produces a hard green compact of ceramic candle which is dried for 1 day and
thereafter the ceramic casting is fired in the oxidizing atmosphere at l°C/min to
600°C and heated to final sintering temperature of the ceramics to achieve
required strength and porosity.

2. The method of manufacture of porous ceramic products filter as claimed in claim
1 wherein the binder comprises:
i) a first component 4 to 15 wt% of the ceramic powder consisting of room
temperature curing low viscous polymer resins such as polyester resin, epoxy
resin, vinyl ester resin;
ii) a second component 5 to 15 wt% of ceramic powder consisting of a diluents
from any of the acetone, toluene, styrene, acrylic acid, dimethyl/formamide
or water;
iii) a third component 0 to 2%of ceramic powder consisting of a dispersing
agent such as polyvinyl pyrrolidone;
iv) a fourth component 8 to 15% of ceramic powder consisting of
any of the Curing system-methyl ketone peroxide + cobolt soaps,
cyclohexanone peroxide + NN dialkyl aryllamines for Polyester, Vinyl
ester resins or any of the Diethylene triamine, Triethylene tetramine,
Isopronediamine, 4,4,- diaminodiphenylmethane, 4,4-
dioaminodiphenyl sulfone for epoxy resins.
3. The method of manufacture of porous ceramic products filter as claimed in claim
1 wherein ceramic powder or aggregates are any of the materials such as
alumina, mullite, cordierite, silicon carbide having grain size of 1 to 300 microns.

4. The method of manufacture of porous ceramic products filter as claimed in claim
1 wherein the silicon carbide filter candle having a bulk density 1.7 to 2.0 gm/cc
and porosity 35 to 55% and pore size 1 to 100 microns.