FIELD OF THE INVENTION
The present invention generally relates to a method of reducing the sintering
temperature of high alumina based abrasion resistance tiles for use as liners in
thermal power stations. More particularly, the present invention relates to a
method of producing abrasion resistance ceramic liner for transporting of coals in
thermal power plants produced at low sintering temperature with high sintering
range.
BACKGROUND OF THE INVENTION
Ceramic abrasion resistance tiles are used in thermal power station for the
transportation of coal. High Alumina based abrasion resistance materials are
used for lining the pipes, bends and other equipments of coal and ash handling
in power plants and other industries where the erosion is very sever to extend
the life of these equipments or parts. Alumina based abrasion resistance tiles are
most preferred than other raw materials based tiles because of many
advantages, which include : negligible water absorption with high bulk density,
high abrasion and erosion resistance, low thermal expansion, high bending and
compression strength, high hardness and homogenously distributed
microstructure.
The ceramic abrasion resistance tiles have very high wear resistance as
measured by relative abrasion index or jet erosions methods. Generally the tiles
are prepared from ceramic materials containing about 85 to 90 wt.% Al2O3 and
balance being sintering aids or additives. The sintering aid is typically oxides and
aluminosilicate minerals which form the liquid phase during sintering at around

1500 to 1600 °C. These products are made from calcined alumina and
aluminosilicate mineral and other additives which are mixed in dry or wet form
and spray dryed if mixed in wet form and pressed into tiles and fired at 1500 to
1600 °C to get complete densification characterized by zero water absorption
test.
These tiles are manufactured by the industries for more than three decades.
These tiles are sintered at very high temperatures i.e. from 1580-1600 °C
resulting in high energy requirement for processing. The major raw materials
are alumina, a source of aluminosilicate and additives as sintering aid. The
process involved is batch making, mixing , fabrication of shapes by hydraulic
pressing, drying and high temperature sintering. Since, this is a high alumina
composition, the sintering temperature is high in spite of undergoing liquid phase
sintering since the main raw material is relatively coarse in nature. This has
been in practice in order to avoid high cost for fine alumina powder which can
be sintered at a lower temperature. The production cost of these abrasion
resistance products are mainly attributed to energy cost of high temperature
sintering. Accordingly, it is highly desirable to reduce the firing temperature of
these products. Various options have been tried out. One option is to reduce the
Al2O3 to reduce the Al2O3 content and increase the liquid phase, but this results
in poor wear resistance properties of the product. Another way is to reduce the
particle size of the Al2O3 in the range of nanometer. But this makes the raw
material cost very high. Use of very expensive additives such as Y2O3 were
attempted but not preferred.
A common process for densification of high-modulus ceramics suitable for large
scale processing is the sintering of the alumina powder in the presence of a
reactive liquid. For this type of sintering to occur, three criteria must be met.

First, an appreciable amount of liquid must form at the sintering temperature.
Second, the liquid phase must completely be able to wet the solid phase, and
third, the solid phase must be partially soluble in the liquid. Liquid phase
sintering is an effective densification process for most high-alumina ceramics due
to lower sintering temperature and shorter sintering time. These materials
contain 80 to 99 % alumina with alkaline-earth oxides, silica and other additives.
At the sintering temperature, the components react to form a liquid phase within
the compact. On cooling, the liquid may completely crystallize or remain as an
amorphous phase, depending on the cooling rate and the liquid composition.
In the first step, the liquid is formed either by a eutectic reaction between
different phases in the compact or by melting of one of them, and particle
rearrangement takes places under the influence of surface tension to give a
more efficient particle packing. This rearrangement is one reason for the faster
densification in liquid phase sintering as compared with solid state sintering. In
the second step, densification proceeds by a solution of the solid material at
contact points, faster diffusion through the liquid phase, and precipitation at solid
surface sites outside the contact area. In the third step, a solid skeleton forms in
which the liquid phase will not penetrate the grain boundaries. This occurs when
the energy of the solid-state interface becomes less than twice the energy of the
solid-liquid interface. In general, the solid-solid interfacial energy decreases as
the crystallographic mis-orientation of adjacent grains decreases.
The main purpose of sintering is to provide densification without grain growth.
Therefore, in many cases, sintering agents are used to hinder grain boundary
mobility. Additives have been used either as a second phase forming agents or
as a solid solution in alumina ceramics for several purposes. In both the cases,
the aim is to enhance the densification and suppress the grain growth. Formation

of a liquid phase by using an agent within the body provides a rapid diffusion
pathway to enhance densification. Additives as solid solutions not only enhance
the densification but also inhibit the grain growth by lowering the boundary
mobility. Also, they are used to accelerate sintering or shrinkage rate, to reduce
firing temperature, to change pore shape, to change the physical and chemical
properties, and to remove impurities.
US 3,784,388 discloses a strong highly resistant ceramic article comparable to
that of cemented carbides by hot pressing bauxite compositions containing 78-94
% AI2O3, <9 % SiO2, 2-8 % Fe2O3, 2-4 % TiO2 and a total less than 3 % of CaO,
MgO and Na20. US 3,802,893 describes a polycrystalline abrasion resistant
alumina composition consists essentially of 99.5 % - 99.9% of aluminium oxide
of average particle size in the range of 2-5 µm, 0.01- 0.25 % MgO, and 0.01-
0.25 % Sm2O3 and sintered in the temperature exceeding 1500 °C. US
4,331,627 discloses a process for producing alumina sintered product containing
0.01-0.55 % MgO, 0.5-5.5 % Y2O3 resulting in sintered product having porosity
<0.1% , average grain size <2 µm and can be used for high speed cutting. US
4,719,188 and CA 1253176 highlight a method to develop alumina based
abrasion resistant material by adding sintering agents such as 0.5- 4.0 wt.%
each of TiO2 and CuO, and 0.5-4.0 wt. % each of 3 or 4 oxides selected from the
group consisting of Fe2O3, MnO2, ZrO2 and SiO2 to 100 parts of Al2O3 powder and
then sintering the resultant raw batch in a temperature range of 1200-1350 °C.
In JP 2180747, magnesia and silica each having < 0.3 µm average particle size
are added to alpha-alumina powder having 0.05-0.3 micron average particle size
by 0.025-0.12 %, in total, in 2-15 molar ratio of MgO to SiO2, they are pulverized
and mixed and the mixture is moulded and sintered at 1,300-1,550 °C to obtain
wear resistant alumina ceramics. CA 2020486 discloses a wear-resistant alumina
material by liquid phase sintering a mixture of about 70 to 95 wt.% of

crystalline Al2O3 particles and about 30 to 5 wt.% of glass phase-forming
components in a nitrogenising atmosphere sintering is at about 1550 °C. US
5,447, 894 describes a method of sintering alumina for corrosion resistance
applications in a temperature range of 1400-1800 °C using 3-7 % additives
such as La203, and 0.02 0.08% SiO2. US 5658838 discloses a method to use
Ti02, Mn3O4 , SiO2 additives for sintering alumina at 1350 °C for producing
materials with low coefficient of friction for sliding application.
Indian Patent 198068 discloses an improved additive composition useful for the
preparation of 4-5 urn alumina based abrasion resistant material having
improved wear properties when sintered in the temperature range of 1480 to
1500 °C. The process involves wet milling of 90-92% by weight of alpha alumina
with an admixture of sintering agent substantially containing SiO2, MgO, BaO,
CaO, B203. CN 1673173 discloses a method of low temperature liquid-phase
sintering of bimodal alumina with nanocrystalline a-AI203 through wet chemical
process using MgO and SiO2 as sintering aids and sintering at 1420-1500 °c for
3h. US 6,395,214 describes high pressure and low temperature sintering of
nanophase ceramic powders using hot pressing. The inventors have shown that
under appropriate high pressure conditions, a sintered grain size can be realized
that is actually smaller than the original powder particle size. US 6,723,674
discloses a method for developing a multi-component Al2O3 ceramic containing
a combination of ceramic oxide additives including rare earth ceramic oxide
additive, wherein the total of the additives comprise from about 0.1 wt.% to <
50 wt. % based on the total weight the multi-component ceramic composite, and
wherein all of the components are nanostructured. In JP 2009091196, alumina
ceramic of excellent wear resistance was prepared from 99% Al203 and total 0.2
% sintering aid comprising three components SiO2,CaO &. MgO.

All the known arts for producing Alumina ceramics with high abrasion resistance
involve experimental data generated in the laboratory. Such data are not
compatible when demonstrated in large scale in the commercial production
process. Most of the patents have either used many expensive additives like
Sm2O3 or Y2O3 , and used multiple additives making the process difficult to
establish in a commercial scale. Many other reports highlight reduction in
sintering temperature either by using nanostructured materials or by using
expensive and difficult process like hot pressing, which are good in the
laboratory scale for generation of data but difficult to implement in large scale.
Some other report used different atmosphere for processing alumina such as in
N2, which will make the process more expensive for the product. Therefore,
these processes are not economically viable for commercial production of
alumina based abrasion resistance products for power plant applications. Since,
most of the commercially available alumina based compositions are sintered at
very high temperatures using one or two additives, it is essential to modify
such compositions without disturbing the source and quality of raw materials.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a method of producing
abrasion resistance ceramic liner for transporting of coals in thermal power
plants produced at low sintering temperature with high sintering range, in which
the sintering temperature of known alumina based composition is reduced by
modifying minor additive content so as reduce the cost of the product in a mass-
scale production process.

Another object of the present invention is to propose a method of producing
abrasion resistance ceramic liner for transporting of coals in thermal power
plants produced at low sintering temperature with high sintering range, in which
a modified composition having 1 % manganese dioxide added to the alumina -
aluminosilicate additive mixture as the additional high temperature flux which
can be sintered at 1500-1550°C in a kiln furnace to produce high abrasion
resistance components.
A still another object of the present invention is to propose a method of
producing abrasion resistance ceramic liner for transporting of coals in thermal
power plants produced at low sintering temperature with high sintering range, in
which technical parameters of the product in commercial scale such as bulk
density > 3.35 g/cc, water absorption <0.1 %, relative abrasion index (ASTM G-
65 ) >10, can be achieved.
A further object of the present invention is to propose a method of producing
abrasion resistance ceramic liner for transporting of coals in thermal power
plants produced at low sintering temperature with high sintering range, in which
the energy consumption is reduced without substantially altering the
conventional process and the major raw material composition such as alumina
and aluminosilicate-additive mixture.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method of producing abrasion resistance ceramic
liner for transporting of coals in thermal power plants produced at low sintering
temperature with high sintering range. According to the invention, the sintering
temperature of alumina based abrasion resistance products is reduced without

substantially altering the known process and composition of major raw materials.
This allows sintering of alumina composition at low temperature in the range of
1500-1550 °C with a bulk density in the range of 3.38-3.42 g/cc , water
absorption in the range of 0.02-0.05 % and RAI in the range of 22-28 suitable
for lining applications in power plants.
The modified composition allows use of uniform viscous fluid distributed to bind
the alumina particles together when fired at low temperature. The densification
of modified composition can be achieved at a lower temperature than the
present commercial composition. The new composition including the method is
suitable for commercial production because of fuel saving, productivity
improvement, higher refractory life as well as less breakdown time. The method
including the composition is suitable for producing better abrasion resistant tiles
due to homogeneously distributed viscous force among close pores and close
bonding between the alumina and viscous fluid.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING AND TABLE
Table 1 represents the properties of the modified composition and a comparison
with the properties of known composition.
Figure 1 exhibits the microstructure of the modified composition as opposed to
that of one of the known composition used in prior art.
DETAIL DESCRIPTION OF THE INVENTION
The present invention is based on the modification of a commercial alumina
based composition by varying the additive content in the range of 0.5-1.5 %

more without substantially altering the known process and main raw
materials. According to the present invention, the known main raw materials
such as alumina and a source of aluminosilicate are used alongwith other liquid
phase forming additives. The weight fraction of the alumina in the composition
is in excess of 80 % and that of the aluminosilicate and oxide additive is not
exceeding 20 %. The purity of the alumina in alumina powder is >99.5 % and
the alumina content as estimated in the aluminosilicate source is in the range of
20-30% . The purity of MnCh is more than 80%. The average particle size of
the alumina is in the range of 3-6 µm and that of the aluminosilicate in the
range of 2-10 µm and that of the oxide additive less than 100 µm. The method
comprises the steps of :
batch formation with pre-determined amount of the raw materials, mixing the
raw materials in a high speed mixer alongwith an organic binder, forming
shapes of the product in a hydraulic press, natural drying, and sintering at high
temperature. However, the additive content has been increased in the
composition by 0.5 to 1.5 % . This simple change in the development of a
modified composition exhibits a reduction in the sintering temperature of the
original composition by 40-60°C in a kiln furnace which results into low energy
cost and other benefits as discussed hereinabove.
The tiles manufactured by the new composition were sintered in the
temperature range of 1500-1550 °C in a batch kiln which resulted in
homogeneous glassy phase distribution among the pores and close binding with
alumina particles with the outcome of high density material, low water
absorption and high relative abrasion index ( RAI) . The bulk density ( BD) was
in the range of 3.38-3.42 g/cc, water absorption (WA) : 0.02-0.05 %, RAI: 22-
28 and Hardness: >8 as per Mohr's scale against minimum requirement of BD
:3.3 g/cc, WA: <0.1 %, RAI of 10 and hardness of 8 respectively. The sand
erosion volume loss has also been calculated using ASTM G-76 method and

found the modified composition is having lower erosion loss in the range of
0.10-0.15 mm3/g compared to 0.15 - 0.30 mm3/g for the commercial
composition. Further, the Vicker's hardness is found to be not altered in spite of
adding more liquid phase into the composition.
In a composition having insufficient amount of additives, for example, a known
composition, the full densification can not be achieved at low temperature,
since all the crystalline particles are not expected to form liquid phase sintered
bonding. However, by increasing the flux content, the binding of the particles
can be achieved at lower temperature due to excess low temperature melting
phase. Many additives do not facilitate proper bonding of the particles using
excess glassy phase resulting in deterioration of the properties. However, by
optimizing the proper additive content, a low temperature densification of
alumina ceramics is possible and this has been demonstrated in this invention.
The main advantages of the new composition are : increasing the bulk density
and RAI with low water absorption, better microstructures with homogeneously
distributed viscous liquids among the pores along with close binding of alumina
particles. All these advantages translate into low fuel consumption by 5-6 %,
cycle time reduction by 6-8 % , improving the life of refractory kiln furniture and
overall reduction in cost of production in commercial scale by 5-6 % .
Example 1
A batch consisting of alumina of 4000 g, aluminosilicate and additive mixture of
1000g and magnesium carbonate of 75 g was mixed in a high speed dry
mixer for 5 min. followed by addition of organic binder and mixed again for 5
min. The mixed powder was used for fabrication of bend and straight tiles of
approximate dimension 150mm L x 30 mm width and 60 mm height. The tiles

were dried and sintered in the kiln at a sintering temperature of 1530°C . The
firing yielded results as follows: bulk density : 3.40 g/cc, water absorption :
0.04 % and RAI : 17-20.
Example 2 :
A batch consisting of alumina of 4000 g, aluminosilicate and additive mixture of
1000g and barium carbonate of 50 g was mixed in a high speed dry mixer
for 5 min. followed by addition of organic binder and mixed again for 5 min.
The mixed powder was used for fabrication of bend and straight tiles of
approximate dimension 150mm L x 30 mm width and 60 mm height . The tiles
were dried and sintered in the production kiln at a sintering temperature of
1540 °C . The firing yielded results as follows: bulk density : 3.39 g/cc, water
absorption : 0.03 % and RAI : 15-18.
Example 3 :
A batch consisting of alumina of 4000 g, aluminosilicate and additive mixture of
lOOOg and manganese dioxide of 50 g was mixed in a high speed dry mixer
for 5 min. followed by addition of organic binder and mixed again for 5 min.
The mixed powder was used for fabrication of bend and straight tiles of
approximate dimension 150mm L x 30 mm width and 60 mm height. The tiles
were dried and sintered in the production kiln at a sintering temperature of
1530 °C . The firing yielded results as follows: bulk density : 3.38 g/cc, water
absorption : 0.03 %, RAI : 24-26, sand erosion loss: 0.118 mm3/g and Vicker's
hardness (HV1) : 1120. The sand erosion loss (mm3/g) as measured by
following ASTM G76 indicated a value of 0.10-0.15 compared to the value of
0.15-0.30 achieved for the commercial composition.

Example 4:
A batch consisting of alumina of 4000 g, aluminosilicate and additive mixture of
1000g and manganese dioxide of 75 g was mixed in a high speed dry mixer
for 5 min. each followed by addition of organic binder and mixed again for 5
min. The mixed powder was used for fabrication of bend and straight tiles of
approximate dimension 150mm L x 30 mm width and 60 mm height. The tiles
were dried and sintered in the production kiln at a temperature of 1540 °C .
The firing yielded results as follows: bulk density : 3.12 g/cc, water absorption :
0.25 % and RAI : 12-14, sand erosion loss : 0.025% and Vicker's hardness
(HV1): 1050. This result indicated very high amount of such additives is
detrimental to the properties of fired product.
Figure 1 describes the scanning electron micrograph of the modified
composition fired in the temperature range of 1530-1540 deg C and compared
with that of commercial composition fired at the temperature range of 1570-
1590 deg C. Table 1 summarizes the properties of the sintered modified
composition and compared to that with the commercial composition and the
quality requirement of the product. The results confirmed that the modified
composition has the potential to replace the conventional composition for better
energy efficiency by 5-6 % and improvement in productivity by 6-8 % besides
improvement in refractory life and reduction in breakdown time for operating at
lower temperature. Three such cycles were carried out for demonstrating the
product in large scale in actual production kiln. The results indicate good
sinterability at a temperature lower by 40-60 deg C than the conventionally
processed at 1580-1600 deg c .

The above examples are not limited to the invention and are exemplary in
nature. Many experiments have been carried out in the laboratory by varying
the additive content in the composition and sintering at different temperatures.
Further, many large scale trials have been taken in the actual production kiln
using the composition developed in this work and confirmed the suitability of
such product in commercial scale.
While preferred embodiments have been shown and described, it should be
understood that changes and modifications can be made therein without
departing from the invention in its broader aspects. Various features of the
invention are defined in the following claims:

WE CLAIM :
1. A method of producing a abrasion resistant ceramic liner for
transportation of coals in thermal power stations produced at low sintering
temperature with high sintering range consisting of wt. % of alumina
>80%, an aluminosilicate and oxide additive mixture not exceeding 20%,
and manganese oxide additive of 1 % with organic binding adhesive of
10-15% concentration, the method comprising the steps of
a) dry mixing in a high speed mixer said ingredients;
b) pressing the moist powder in the form of tiles of different sizes and
shaping by a hydraulic press;
c) natural drying of the formed tiles;
d) sintering the tiles in a batch kiln furnace at 1500 - 1550°C temperature
to obtain a high abrasion resistant tile of BD : 3.38-3.42 g/cc and
water absorption property of 0.02-0.05 %, RAI of 22-28 with
homogenous dense microstructure.
2. A method of producing ceramic liner as claimed in claim 1 wherein the
batch comprises alumina powder of average particle size in the range of
3-6 micron, with alumina content >99.5% having particle size >10
micron of <20%, and wherein the alumina content in aluminosilicate is in
the range of 20-30%.
3. A method of producing ceramic liner as claimed in claim 1 , wherein
manganese dioxide is used as an extra additive in the range of 0.5 -1.5%
in the form of high temperature flux, the MnO2% being more than 80%
having no particles above 100 µm.

4. A method of producing ceramic liner as claimed in claim 1 , wherein the
BD and WA are 3.38-3.42 g/cc and 0.02-0.05 % respectively.
5. A method of producing ceramic liner as claimed in claim 1 , wherein the
produced ceramic tiles are homogenous and having dense undergoing
liquid phase sintering of alumina with 1 wt. % MnO2 as the additional
liquid forming agent in the composition.
6. A method of producing ceramic liner as claimed in claim 1 , wherein the
produced ceramic liners posses RAI 22-28, compared to that of mild steel
as defined by ASTM G-65 standard.
7. A method of producing ceramic liners as claimed in claim 1, where in the
sand erosion loss (mm3/g) is in the range of 0.10-0.15.
8. A composition for producing abrasion-resistant ceramic liner in a method
as claimed in claim 1, comprising :
alumina in an amount of 80% by weight,
an aluminosilicate and oxide additive mixture in an amount of 20% by
weight; and
an organic binding adhesive of 10 to 15% by weight;
characterized by comprising :
manganese oxide additive of about 1% by weight.

/

The invention relates a method of producing abrasion resistant ceramic
liner for transportation of coals in thermal power stations produced at low
sintering temperature with high sintering range consisting of wt. % of
alumina >80%, an aluminosilicate and oxide additive mixture not
exceeding 20%, and manganese oxide additive of 1 % with organic
binding adhesive of 10-15% concentration, the method comprising the
steps of a)dry mixing in a high speed mixer said ingredients; b)
pressing the moist powder in the form of tiles of different sizes and
shaping by a hydraulic press; c) natural drying of the formed tiles; d)
sintering the tiles in a batch kiln furnace at 1500 - 1550°C temperature
to obtain a high abrasion resistant tile of BD : 3.38-3.42 g/cc and
water absorption property of 0.02-0.05 %, RAI of 22-28 with
homogenous dense microstructure.