Note: Descriptions are shown in the official language in which they were submitted.
CA 02703869 2010-05-12
Attorney Docket No. DN 09-002
CALCIUM ENRICHED REFRACTORY MATERIAL BY THE ADDITION OF
CALCIUM CARBONATE
BACKGROUND OF THE INVENTION
The present invention relates to refractory material for applying to a
refractory structure
and a method of applying the refractory material to a refractory structure or
lining. More
particularly, the invention is directed to preserving or maintaining
refractory structures or linings
from mechanical erosion and/or attack by corrosive materials such as those
produced during
manufacture of metals or metal alloys including acid and basic slags. The
refractory linings also
are exposed to thermal shock which can cause premature failure of the
refractory.
SUMMARY
The present invention is directed to a composition of a refractory material
and a method of
coating a refractory structure, particularly a hot refractory structure using
the refractory material.
The refractory material can be applied to a refractory structure such as a
vessel or ladle. The
composition of the refractory material which applied to the refractory
structure comprises from
about 20 to about 95 weight percent magnesia-based refractory material, from
about 2.0 to about
weight percent calcium carbonate and from about 0.1 to about 6 weight percent
of a binder
such as organic acid, alkali silicate or alkali phosphate.
Heat from the furnace or vessel which contacts the refractory material on the
refractory
structure accelerates the hardening and curing of the refractory material of
the present invention
by transmission of heat to the refractory material so as to form a high
density matrix of refractory
material. The applied refractory material passes from the plastic state to a
non-plastic or
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substantially rigid and non-pliable state in its final form in which the above
mentioned high
density matrix is present. The calcium carbonate in the refractory material is
calcined in place
upon transfer of the heat from the furnace or vessel which is being processed
in the refractory
structure to which the refractory material is applied. Carbon dioxide gas
evolves therefore after
the refractory material is no longer in the plastic state. The refractory
material forms a high
density matrix which protects against penetration of slag and molten metal.
In the present invention the calcium carbonate calcines in place which leaves
a very
reactive source of calcia within the matrix of the refractory mass. In the
present invention the
coarsest calcium carbonate can be ATF-20 which has a particle size
distribution that starts below
0.85 mm. The very fine calcium carbonate of the present invention can be
Vicron 15-15
limestone product which has a particle size distribution that starts below 15
microns (0.015 mm).
In the present invention fine calcium carbonate is added to be reactive with
the magnesia grains
and any infiltrating slag, not as a coarse particle size distribution for
thermal shock resistance.
In other embodiments the magnesia-based refractory material of the composition
of the
refractory material is present in an amount from about 20 to about 95 weight
percent.
In other embodiments the magnesia-based refractory material of the composition
of the
refractory material is present in an amount from about 60 to about 88 weight
percent.
In other embodiments the calcium carbonate of the composition of the
refractory material
is present in at least two different particle size distributions. A fine form
of calcium carbonate is
present in an amount of from about 3.5 to about 4.5 weight percent and a
coarser form calcium
carbonate is present in an amount of from about 3.5 to about 4.5 weight
percent.
In other embodiments the calcium carbonate of the composition of the
refractory material
is present in at least two different particle size distributions. A fine form
of calcium carbonate is
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present in an amount of from about 2.5 to about 3.5 weight percent and a
coarser form of calcium
carbonate is present in an amount of from about 2.5 to about 3.5 weight
percent.
In other embodiments the composition of the refractory material further
comprises from
about 0.2 to about 8.5 weight percent calcium hydroxide.
In other embodiments the composition of the refractory material further
comprises from
about 0.1 to about 2.0 weight percent of a plasticizer such as bentonite.
In other embodiments the composition of the refractory material further
comprises from
about 0.1 to about 1.0 weight percent of a dispersant such as citric acid.
The refractory material can be applied by a gunning system. The refractory
material can
also be applied by spraying, casting, ramming, shotcreting, slurry coating,
troweling, hot pouring
or dry applied materials such as vibratables, or a hybrid of the listed
methods such as gun
casting. Other manual methods with or without tools can be used.
After the high density matrix of the refractory material has been formed, a
layer of the
refractory material protects the refractory structure to which the refractory
material has been
applied against attack by corrosive materials such as molten slags and molten
metals, especially
against attack by acid and basic slags, and steel.
In the method of the invention, application of the refractory material can be
applied to
provide a layer of refractory material of a thickness of about 1 inch to about
12 inches both prior
to exposing as well as after exposing the lining to corrosive materials.
Desirably, application of
the refractory material is performed prior to initial exposure of the
refractory lining to the
corrosive materials, and can be repeated after each exposure of the lining to
those corrosive
materials. Depending on the degree of erosion, corrosion or penetration of
corrosive materials
into the applied refractory material, the refractory material of the present
invention need not be
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reapplied to the refractory material after every contact of corrosive
materials with the refractory
material.
Application of the refractory material can be performed while the refractory
material is at
a temperature of about 32 degrees F to about 2500 degrees F.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. I is a photograph of a cross section of a conventional refractory sample
after being
exposed to slag in a two hour induction furnace test;
FIG. 2 is a photograph of a cross section of a cast refractory sample of an
embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in detail by reference to the following
specification
and non-limiting examples. Unless otherwise specified, all percentages are by
weight and all
temperatures are in degrees Fahrenheit.
The composition applied to the refractory structure comprises from about 20 to
about
97.9 weight percent of a magnesia based refractory material such as magnesia,
doloma or
dolomite. The composition also contains about 2.0 to about 10 weight percent
calcium
carbonate, and from about 0.1 to about 6.0 weight percent of a binder such as
an organic acid,
alkali silicate or alkali phosphate.
When the material is applied hot, heat from the furnace which contacts the
refractory
material on the refractory structure accelerates the hardening and curing of
the refractory
material of the present invention by transmission of heat from the underlying
refractory structure
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to the refractory material so as to form a high density matrix of refractory
material. The applied
refractory material passes from the plastic state to a non-plastic or
substantially rigid and non-
pliable state in its final form in which the above mentioned high density
matrix is present. In the
case of dry applied materials or room temperature cured castable or shotcrete
materials there is
not a transition from a plastic state to a non-plastic state upon heating as
these materials are
already in their final form. The calcium carbonate in the refractory material
is calcined in place
upon transfer of the heat from the refractory structure or vessel. Carbon
dioxide gas evolves
after the refractory material is in its final or hardened form. The refractory
material forms a high
density matrix which protects against penetration of slag and molten metal.
The calcium from
the calcium carbonate forms CaO or calcia which enriches the matrix phase of
the refractory
material which is where initial slag penetration would occur.
The use of calcium carbonate as a source of CaO (calcia) is desirable because
it does not
significantly react with water (hydrate or decompose) or other refractory
constituents during the
mixing with water or subsequent refractory material application. If calcium
oxide were to be
used instead of the calcium carbonate, the calcium oxide would rapidly react
with water and/or
other bond components so as to disrupt the integrity of the applied mass which
would result in
poor durability of the applied refractory. The calcium carbonate in the
present invention calcines
upon exposure to heat to form reactive calcium oxide. When slag comes in
contact with this
calcium oxide the calcium oxide readily reacts with the slag to produce high
melting point
compounds such as dicalcium silicate. These compounds thicken and or solidify
the slag so as to
prevent further penetration of the slag into the body of the refractory. This
mechanism reduces
corrosion of the refractory thereby extending the service life of the
refractory. In other
embodiments of this invention calcium hydroxide or other calcium bearing
compounds that do
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not react to disrupt the refractory structure but do decompose upon heating
can be used to yield
reactive calcium oxide.
The refractory material can be applied through any gunning system or applied
by
spraying, casting, ramming, shotcreting, slurry coating, troweling, hot
pouring or dry applied
materials such as vibratables, or a hybrid of the listed methods such as gun
casting. Other manual
methods with or without tools can be used.
The refractory material has good slag and erosion resistance. The material is
suitable for
use for the maintenance of electric arc furnaces, basic oxygen furnaces, and
other metallurgical
vessels or ladles.
The dispersant or wetting agent for the composition of the magnesia based
refractory
material can be any suitable superplasticizer, anionic, cationic or nonionic
surfactant, the
selection of which for any particular composition would be understood by one
of ordinary skill
in the art of refractories.
Heat which is applied to the refractory composition of the present invention
contributes
to the forming of a high density matrix of refractory material. A magnesia
based refractory
composition results, having improved physical properties, at temperatures from
about 230
degrees F. to about 3200 degrees F. over compositions currently used for
production or repair of
refractory furnace linings.
Without further elaboration, it is believed that one skilled in the art can,
using the
preceding description, utilize the present invention to its fullest extent.
The following
embodiments are, therefore, to be construed as merely illustrative, and not
limitative of the
remainder of the disclosure in any way whatsoever.
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Magnesia, i.e., MgO, for the refractory material of the present invention can
be derived
from sources such as natural, seawater or brine magnesia, or mixtures thereof.
The magnesia
preferably is dead burned magnesia. By "dead burned" magnesia is meant
magnesia fired to high
temperatures to produce refractory grains with reduced reactivity with water
and impart a degree
of hydration resistance to the refractory grains which are formed
substantially completely of
well-sintered, low porosity crystals to distinguish them from reactive lower
temperature calcined
caustic magnesite. Such materials are commercially available in purities of
from about 60 to
about 99 weight percent magnesia. Some or all of the dead-burned magnesia can
be replaced by
dead-burned doloma. This doloma can be produced from naturally occurring
materials or
synthetic materials. Alternatively, naturally occurring dolomite can also be
used.
In some embodiments, plasticizers useful in the refractory compositions
include but are
not limited to clays such as ball clay, kaolinite, or bentonite, aluminum
hydroxide, silica fume
and starch. These materials are commercially available.
In some embodiments, binders useful in the refractory compositions include but
are not
limited to alkali phosphates such as sodium phosphate, potassium phosphate,
ammonium
phosphate, magnesium phosphate, calcium phosphate, and alkali silicates such
as sodium
silicate, potassium silicate, magnesium silicate, calcium silicate, and
sulfates such as sodium
sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, ammonium
sulfate, zirconium
sulfate, aluminum sulfate and sulfamic acid. Preferred binders include sodium
silicate, sodium
phosphate and sulfamic acid. These materials are commercially available.
In the present invention the amount of calcium carbonate present can be from
about 2.0 to
about 10 weight percent of the total refractory blend. Use of weight
percentages of calcium
carbonate of more than about 10 weight percent is limited by the inability of
the calcium
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carbonate to integrate itself into a resultant refractory matrix which is
formed after heat is
applied to the refractory blend. Use of weight percentages of calcium
carbonate of less than
about 2.0 weight percent of calcium carbonate is limited by the inability of
the calcium carbonate
to be a part of a high density matrix in the refractory material which
inhibits penetration of slag
into the matrix.
The calcium carbonate of the present invention can be of two different
particle size
distributions such as a very fine portion and a coarser portion. A coarser
portion of calcium
carbonate can be a calcium carbonate such as ATF-20 screened limestone product
available from
Specialty Minerals Inc. of Bethlehem, Pennsylvania. ATF-20 screened limestone
product has
only a trace amount of particles larger than 20 mesh (0.85 mm), about 15
weight percent larger
than 40 mesh and about 75 weight percent larger than 100 mesh and about 92
weight percent
larger than 200 mesh. A very fine portion of calcium carbonate can be a
calcium carbonate such
as Vicron 15-15 ground limestone product available from Specialty Minerals
Inc. of Bethlehem,
Pennsylvania. Vicron 15-15 ground limestone has only about 0.004 weight
percent of particles
larger than 325 mesh and an average particle size of 3.5 microns.
In another embodiment the calcium carbonate of the composition of the
refractory
material is present as a single particle size distribution. A very fine form
of calcium carbonate is
present in the refractory material in an amount of from about 2.0 to about 7.0
weight percent, or
in some embodiments about 2.0 to about 8.5 weight percent.
In another embodiment the calcium carbonate of the composition of the
refractory
material is present in at least two different particle size distributions. A
very fine form of
calcium carbonate is present in an amount of from about 3.5 to about 4.5
weight percent and a
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coarser form of calcium carbonate is present in an amount of from about 3.5 to
about 4.5 weight
percent.
In another embodiment the calcium carbonate of the composition of the
refractory
material is present in at least two different particle size distributions. A
very fine form of
calcium carbonate is present in an amount of from about 2.5 to about 3.5
weight percent and a
coarser form of calcium carbonate is present in an amount of from about 2.5 to
about 3.5 weight
percent.
In one embodiment, the refractory material has about 3.5 to about 4.5 weight
percent of a
very fine portion of calcium carbonate and about 3.5 to about 4.5 weight
percent of a coarser
portion of calcium carbonate. In addition, the refractory blend can have from
about 0.2 to about
weight percent of sodium hexametaphosphate as a setting agent and high
temperature binder to
provide strength and substrate adherence. Examples of a refractory material of
this embodiment
is set forth in Examples 1, 2 and 3.
In one embodiment, the refractory material has about 2.5 to about 3.5 weight
percent of a
very fine portion of calcium carbonate and about 2.5 to about 3.5 weight
percent of a coarser
portion of calcium carbonate. In addition, the refractory blend can have from
about 0.2 to about
3.0 weight percent of sulfamic acid as a setting agent and high temperature
binder to provide
strength and substrate adherence. An example of a refractory material of this
embodiment is set
forth in Example 4.
In one embodiment, the refractory material comprises from about 0.2 to about
8.5 weight
percent calcium hydroxide and from about 2.0 to about 10 weight percent
calcium carbonate. In
addition, the refractory blend can have from about 0.2 to about 6.0 weight
percent of sulfamic
acid as a setting agent and high temperature binder to provide strength and
substrate adherence
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and FIG. 2 shows a photograph of a cross section of a cast refractory sample
of this embodiment
of the present invention. after being subjected to two hours in an induction
furnace under
exposure to slag. An example of a refractory material of this embodiment is
set forth in Example
5.
FIG. 1 shows a photograph of a cross-section of a conventional refractory
material
sample after being subjected to two hours in an induction furnace under
exposure to slag.
The refractory material of the present invention can be applied to a lining by
gunning,
spraying, casting, ramming, shotcreting, slurry coating, troweling, hot
pouring, manual
application, dry application or a hybrid method.
The compositions were tested in an induction furnace. The compositions met or
exceeded the performance requirements in the areas of density, strength,
drying, resistance to
cracking, and durability.
Unless otherwise identified, all mesh sizes are in U.S. Mesh. As set forth
below, mesh
sizes are shown in a format such as 5 X 8 which means particles smaller than 5
mesh and larger
than 8 mesh are present.
EXAMPLE 1
Table 1 shows a refractory material for applying onto a hot or cold refractory
structure
such as the slag line of a vessel or ladle. The following formulation of
refractory material was
dry mixed for 3 minutes after all ingredients were in the mixer.
TABLE 1
Material Description Wt. Percent
97 grade Magnesia 5 X 8 Mesh 20.00
97 grade Magnesia 8 X 18 Mesh 28.00
97 grade Magnesia -18 Mesh 28.70
97 grade Magnesia Powder 12.00
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Bentonite Powder 0.80
Very Fine Calcium Carbonate Vicrori 15-15 ground limestone 4.00
Coarser Calcium Carbonate ATF-20 4.00
Sodium Silicate Powder 1.00
Citric Acid Powder 0.50
Sodium hexametaphosphate Powder 1.00
EXAMPLE 2
Table 2 shows a refractory material for applying onto a hot or cold refractory
structure
such as the slag line of a vessel or ladle. The following formulation of
refractory material was
dry mixed for 3 minutes after all ingredients were in the mixer.
TABLE 2
Material Description Wt. Percent
90 grade Magnesia 5 X 8 Mesh 20.00
90 grade Magnesia 8 X 18 Mesh 28.00
90 grade Magnesia -18 Mesh 28.70
90 grade Magnesia Powder 12.50
Bentonite Powder 0.80
Very Fine Calcium Carbonate Vicron 15-15 ground limestone 4.00
Coarser Calcium Carbonate ATF-20 limestone 4.00
Sodium Silicate Powder 1.00
Citric Acid Powder 0.50
Sodium hexametaphosphate Powder 0.50
The sodium silicate of the above Example 2 is hydrated sodium silicate Pyramid
P60 having a
SiO2 to Na2O ratio of 3.3.
EXAMPLE 3
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Table 3 shows a refractory material for applying onto a hot or cold refractory
structure
such as the slag line of a vessel or ladle. The following formulation of
refractory material was
dry mixed for 3 minutes after all ingredients were in the mixer.
TABLE 3
Material Description Wt. Percent
90 grade Magnesia 5 X 8 Mesh 20.00
90 grade Magnesia 8 X 18 Mesh 28.00
90 grade Magnesia -18 Mesh 28.70
97 grade Magnesia Powder 12.00
Bentonite Powder 0.80
Very Fine Calcium Carbonate Vicron 15-15 ground limestone 4.00
Coarser Calcium Carbonate ATF-20 limestone 4.00
Sodium Silicate Powder 1.00
Citric Acid Powder 0.50
Sodium hexametaphosphate Powder 1.00
EXAMPLE 4
Table 4 shows a refractory material for applying onto a hot or cold refractory
structure
such as the slag line of a vessel or ladle. The following formulation of
refractory material was
dry mixed for 3 minutes after all ingredients were in the mixer.
TABLE 4
Material Description Wt. Percent
97 grade Magnesia 5 X 8 Mesh 23.80
97 grade Magnesia 8 X 18 Mesh 35.60
97 grade Magnesia -18 Mesh 12.50
97 grade Magnesia Powder 16.30
Bentonite Powder 0.80
Very Fine Calcium Carbonate Vicron 15-15 ground limestone 3.00
Coarser Calcium Carbonate ATF-20 3.00
Calcium Hydroxide Powder 2.50
Citric Acid Powder 0.50
Sulfamic acid Powder 2.00
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EXAMPLE 5
Table 5 shows a refractory material for applying onto a hot or cold refractory
structure
such as the slag line of a vessel or ladle. The following formulation of
refractory material was
dry mixed for 3 minutes after all ingredients were in the mixer.
TABLE 5
Material Description Wt. Percent
97 grade Magnesia 8 X 18 Mesh 18.80
97 grade Magnesia -18 Mesh 31.60
97 grade Magnesia Powder 29.35
Sulfamic Acid Powder 5.00
Very Fine Calcium Carbonate Vicron 15-15 ground limestone 8.00
Calcium Hydroxide Powder 6.00
Silica Fume Powder 1.00
Powdered Sugar 10 X 0.25
Accordingly, it is understood that the above description of the present
invention is
susceptible to considerable modifications, changes and adaptations by those
skilled in the art,
and that such modifications, changes and adaptations are intended to be
considered within the
scope of the present invention.
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