TITLE OF THE INVENTION
Refractory material
TECHNICAL FIELD
[0001]
The present invention relates to a refractory material for use in
an industrial kiln, particularly, in a pig-iron/steel making process
for the iron and steel industry.
BACKGROUND ART
[0002]
Generally, a lining of a vessel for holding a molten metal such as
molten iron in an industrial kiln, particularly, in a pig-iron/steel
making process, or a nozzle or plate for use in a continuous casting
process, is formed using a refractory material. Through usage, a
refractory material will become worn or damaged. Thus, when expiration
of a usable life thereof is determined, it is necessary to demolish or
disassemble a used refractory portion or member, and then install a new
refractory material to form a lining, or perform replacement with a new
refractory member. Along with an increasing need for productivity
enhancement, there is an increasing need for extending a durable period
of a refractory material so as to shorten a time necessary for
demolition/disassembly or lining installation, or a shutdown time during
the replacement,
[0003]
Meanwhile, as a technique for improving durability of a refractory
material, it is widely known to mix aluminum in a refractory raw material.
While aluminum itself has a melting point of about 660°C, i.e., is melted
at a temperature far lower than a usage environmental temperature of

1200 to 1800°C in a pig-iron/steel making process, it reacts with oxygen
or nitrogen in an atmosphere to form alumina (Al2O3) , aluminum nitride
(A1N), aluminum oxynitride (A1QN) , etc, so that the melting point
becomes higher, thereby providing enhanced corrosion resistance, and
a strong bonding structure is formed in a matrix, thereby providing
improvement in strength and thus improvement in abrasion resistance.
For example, the following Patent Document 1 discloses a carbon brick
for blast furnace produced by preparing a mixture mixed with a metal
aluminum powder having an average particle diameter of 25 urn or less,
and subjecting the mixture to kneading, shape forming and firing, The
following Patent Document 2 discloses a technique of using a composition
comprising a refractory powder and additives including a carbon fiber
and Si and/or Al, to form a compound of Si and/or Al on the carbon fiber.
[0004]
An aluminum powder includes two types: a granular atomized powder
and a scaly flake powder. As described in upper right column, page 3
in the following Patent Document 3, the flake powder is excellent in
reactivity, so that it is more likely to form strong bonds through a
reaction with an atmosphere gas or other refractory raw material. On
the other hand, the flake powder is poor in kneadability and formability.
Thus, although there are some cases where it actually enhance strength
of a refractory material, there are quite a lot of cases where it
conversely gives rise to a problem such as a growing deterioration or
variation in the strength.
LIST OF PRIOR ART DOCUMENTS
[PATENT DOCUMENTS]
[0005]
Patent Document 1: JP 08-143361A

Patent Document 2: JP 05-07gi§SA
Patent Document 3: JP 57-027968A
SUMMARY OF THE INVENTIOK
[TECHNICAL PROBLEM]
[0006]
The present invention addresses a technical problem of reducing a
variation in strength of a refractory material which is obtained by
incorporating a scaly flake powder made of aluminum and/or aluminum alloy
(hereinafter referred to as "aluminum flakes") into a refractory raw
material, and suitable for use in an industrial kiln, particularly, in
a pig-iron/steel making process for the iron and steel industry,
[SOLUTION TO THE TECHNICAL PROBLEM]
[0007]
Although aluminum flakes are excellent in reactivity, and therefore
expected to contribute to enhancement in strength of a refractory
material, there have heretofore been quite a lot of cases where it
conversely gives rise to a problem, such as decrease or variation in
the strength, as mentioned above. The inventors of this application
conducted studies on the causes. As a result, it was found that a scaly
shape of an aluminum flake causes difficulty in allowing aluminum flakes
to be uniformly dispersed during kneading of a refractory raw material
mixture, and thus, when a shaped body of the mixture is subjected to
a heat treatment, a reaction of the aluminum flakes during the heat
treatment is non-uniformly produced. The inventor also found that,
during the heat treatment, aluminum undergoes volumetric expansion
during a reaction with an atmosphere gas, and thus the shaped body is
locally expanded, thereby causing micro-cracks thereinside, which leads
to decrease or variation in strength.

[0008]
As a result of earnest studies on solutions to the above problems,
the inventors found that the problems can be solved by using non-leafing
type of aluminum flakes, and have accomplished the present invention,
[0009]
Specifically, according to one aspect of the present invention, there
is provided a refractory material which is obtained by incorporating,
into a refractory raw material, scaly non-leafing aluminum flakes made
of non-leafing type aluminum and/or aluminum alloy.
[0.010]
When the non-leafing aluminum flakes are incorporated into the
refractory raw material, needle-like crystals consisting of an aluminum
compound and having a length of 2 urn or less are formed on aggregate
surfaces (surfaces of aggregate grains) and/or fill a space between
neighboring aggregates (voids between aggregate grains). That is,
according to another aspect of the present invention, there is provided
a refractory material which comprises needle-like crystals consisting
of an aluminum compound and having a length of 2 urn or less, and a
refractory material which is capable of forming therein needle-like
crystals consisting of an aluminum compound and having a length of 2
urn or less, when heated during usage.
[0011]
The present invention will be described in detail below,
[0012]
As defined in JIS K5 906, as aluminum flakes for paints, there are
leafing type and non-leafing type. The leafing type means a powder
obtained by subjecting surfaces of aluminum flakes to a treatment using
a stearic acid or the like, and has a property of, in a solvent, floating
up toward the surface and staying parallel to each other with respect

to the surface. On the other hand, the non-leafing type means a powder
obtained by subjecting surfaces of aluminum flakes to a treatment using
an oleic acid or the like, and has a property of maintaining a
uniformly-dispersed state in a solvent.
[0013]
In an operation for kneading a refractory raw material mixture, it
is common practice to add a binder containing a solvent to various types
of refractory raw materials, and subject the obtained mixture to kneading.
In the present invention, non-leafing type aluminum flakes are kneaded
together with a given refractory raw material and a binder containing
a solvent. This makes it possible to allow the aluminum flakes to be
uniformly dispersed in the solvent and thus more uniformly dispersed
in the mixture. Then, the mixture obtained in this manner is subjected
to shape forming and heat treatment, so that a homogeneous refractory
material having a small variation in strength can be obtained,
[0014]
A refractory material can be roughly classified into: a so-called
fired refractory material obtained by firing refractory raw material
particles together through a heat treatment, or by firing refractory
raw material so as to form carbon bonds based on a carbon residue of
a resin; and a so-called unfired refractory material which is subjected
to a heat treatment at a relatively low temperature of about 100 to 400°C
in its product stage in order to harden a resin and remove a solvent
used during kneading. In the present invention, with regard to the fired
refractory material, a reaction between each non-leafing aluminum flake
and an atmosphere during firing is uniformly produced in the entire shaped
body, so that a homogeneous refractory material with a small variation
in strength is obtained in its product stage, as mentioned above. On
the other hand, with regard to the unfired refractory material, in its

product stage, aluminum is in an unreacted state. However, during usage,
the refractory material is inevitably heated by a contact with molten
metal or a high-temperature atmosphere, so that a reaction between the
non-leafing aluminum flakes and an internal atmosphere of the refractory
material is produced in the same manner as that in the fired refractory-
material . Therefore, the present invention can achieve its advantageous
effects, irrespective of whether a refractory material is a fired type
or an unfired type.
[0015]
The refractory material of the present invention has a feature that
a variation in strength is small, A refractory material obtained, by
subjecting an aluminum-added mixture to shape forming and heat treatment
is increased in strength as compared to a refractory material obtained
from a mixture without addition of aluminum. Although this tendency
becomes prominent particularly when aluminum flakes are used, there is
a disadvantage of causing a growing variation in strength, as mentioned
above. It is believed that this is because, when using a mixture in which
aluminum is non-uniformly dispersed, micro-cracks/defects locally occur
during the heat treatment. Such a refractory material having a large
variation in strength has a problem that durability thereof become
deteriorated or unstable, because, when it is actually used, the
micro-cracks/defects are likely to be developed due to thermal stress
and mechanical stress during usage, and integrated together to form a
large crack, which becomes a factor for flaking, breaking, drop-out,
etc. In contrast, in the refractory material of the present invention,
aluminum flakes are uniformly dispersed therein, so that the variation
in strength becomes smaller, and the durability is stably maintained
at a high levol.
[0016]

As non-leafing aluminum flakes usable in the present invention, it
is possible to use any commercially available product for paints. As
a form, the non-leafing aluminum flakes can be used in both a paste form
in which the non-leafing aluminum flakes are preliminarily dispersed
in a solvent, and a solvent-free dry form. A chemical composition of
the non-leafing aluminum flakes is not particularly limited. For
example, in addition to pure aluminum, it is possible to use Al-Si alloy,
Al-Mg alloy, Al-Mg-Si alloy and Al-Mg-Ca alloy. Further, a flake size
is not particularly limited. However, in view of uniform dispersion,
it is preferable to use non-leafing aluminum flakes in which 70 mass!
or more thereof have a size passing through a sieve with a mesh opening
size of 0,1 mm, which is defined in JIS Z8801, It is more preferable
to use non-leafing aluminum flakes in which 70 mass% or more thereof
have a size passing through a sieve with a mesh opening size of 44 jam.
A thickness is not particularly limited. For example, it is possible
to use a type having a thickness of about 0.1 to 5 urn.
[0017]
Regarding aluminum for use as a refractory raw material, while it
is most preferable that it totally consists of non-leafing aluminum
flakes, it may consist of any combination of non-leafing aluminum flakes
and other type of aluminum or aluminum flakes. However, in view of
dominantly achieving the effects of the present invention, it is
preferable that the non-leafing aluminum flakes account for 50 mass%
or more of the total of aluminum and/or aluminum alloy in the refractory
raw material. In the case where aluminum is mixed in a relatively large
amount for a refractory material, in such a manner that a total amount
of aluminum to be mixed becomes 5 mass% or more, it is preferable to
increase the ratio of the non-leafing aluminum flakes.
[0018]

Any refractory raw material other than, aluminum and. a binder are not
particularly limited. For example, various refractory raw materials and
binders commonly used for refractory materials may be used in combination,
In one example, the refractory raw material other than aluminum may
include alumina, magnesia, mullite, zirconia, spinel, silica and silicon
carbide. The binder may include phenolic resin, furan resin, silicone
resin, starch and molasses. It is to be noted that, as used in this
specification, the term "aluminum" is encompassed within a concept of
"refractory raw material", although aluminum has a low melting point
and low refractoriness as compared to the aforementioned refractory raw
materials such as alumina.
[0019]
The kneading, shape forming and heat treatment can be performed by
facilities and methods commonly used in production of a refractory
material. According to need, after the heat treatment, other process
such as impregnation treatment and/or (mechanical, chemical or
electrical) processing may be performed.
[0020]
When the shaped body is subjected to firing, the firing may be
performed in ambient air, in a reducing atmosphere while embedding the
shaped body in coke so as to prevent oxidation of a carbon raw material,
or in a nitrogen atmosphere, i.e., in a nitrogen gas. In the reducing
atmosphere or nitrogen atmosphere, it is preferable to perform the heat
treatment at a temperature of 700°C or more causing aluminum to start
a reaction with the atmosphere, in order to allow the non-leafing aluminum
flakes to be transformed into nitride or oxynitride, such as AIM or A10N,
and form strong bonds. It is particularly preferable to perform the heat
treatment at a temperature of 1000°C or more, because, in this case,
the reaction of aluminum is particularly promoted.

[0021]
The present invention more dominantly achieves the effects,
particularly, in a thick refractory material. This is because the
reaction of aluminum is more likely to become non-uniform along with
an increase in thickness of a refractory material. The present invention
is effective, particularly, in a refractory material having a thickness
of 8 0 mm or more. One example of the refractory material having a
thickness of 80 mm or more is a refractory material for a lining of a
blast furnace.
[0022]
A refractory material using non-leafing type aluminum flakes as in
the present invention is characterized in that, when observing a fracture
surface thereof by a scanning electron microscope (SEM), needle-like
crystals consisting of an aluminum compound and each having a. length
of 2 μm or less as indicated by FIG. 1 are formed on aggregate surfaces
(surfaces of aggregate grains) and/or fill a space between neighboring
aggregates (voids between aggregate grains) . On the other hand, in a
refractory material using leafing type aluminum flakes, needle-like or
fiber-like crystals each having a length of about 5 urn are formed as
presented in FIG. 2. It is believed that the formation of needle-like
crystals each having a relatively short length as in FIG. 1 allows
inter-aggregate bonds (bonds between aggregate grains) to become uniform,
thereby reducing a variation in strength.
[0023]
The needle-like crystals are changed in chemical composition
depending on an atmosphere for the firing. In this regard, it is
preferable to perform the firing in a nitrogen atmosphere, because, in
this case, needle-like crystals having a primary mineral phase
consisting of AIM are formed, thereby particularly reducing the

variation in strength and increasing the strength.
[0024]
In the case where non-leafing type aluminum flakes and leafing type
aluminum flakes are used as a refractory raw material in combination,
a microstructure is formed in which needle-like crystals each having
a length of 2 μm or less and those of about 5 μm are mixed. In view of
achieving the effects of the present invention, it is preferable that
the needle-like crystals each having a length of 2 μm or less account
for 50 mass% or more of the entire needle-like crystals.
[0025]
The needle-like crystals can be formed by: kneading a refractory raw
material including non-leafing aluminum flakes to obtain a mixture;
forming the mixture into a given shape; and subjecting the resulting
shaped body to a heat treatment at 700°C or more. On the other hand,
with regard to a so-called unfired refractory material, in its production
stage, no needle-like crystal is formed. However, when heated during
usage, the same needle-like crystals as in the fired refractory material
are formed. Thus, a refractory material capable of forming therein
needle-like crystals having a length of 2 μm or less when heated during
usage is also encompassed within the scope of the present invention.
[EFFECT OF THE INVENTION]
[0026]
The refractory material of the present invention can significantly
reduce the variation in strength, so that it becomes possible to obtain
a refractory material for an industrial kiln with stable and high-level
durability.
BRIEF DESCRIPTION OF THE DRAWINGS

[0027]
FIG. 1 presents a result of SEM observation on a fracture surface
of a refractory material of the present invention using non-leafing type
aluminusn flakes.
FIG. 2 presents a result of SEM observation on a fracture surface
of a refractory material in Comparative Example using leafing type
aluminum flakes.
DESCRIPTION OF EMBODIMENTS
[0028]
An embodiment of the present invention will now be described based
on various examples.
[EXAMPLES]
[0029]
As presented in the "Composition Ratio" in Table 1, various types
of aluminum flakes were used to check influences of the type and a size
of aluminum flakes on a variation of strength of a refractory material.
[0030]
TABLE 1

[0031]
As non-leafing type aluminum flakes (non-leafing aluminum flakes),
a dry type in which the aluminum flakes are not dispersed in a solvent
was used, and the following three kinds of dry types were prepared: a
first dry type having a size of under 0.2 mm; a second dry type having
a size of under 0.15 mm: and a third dry type having a size of under
0.074 mm. For example, in the non-leafing aluminum flakes having a size
of under 0.15 mm, a ratio of non-leafing type aluminum flakes having
a size passing through a sieve with a mesh opening size of 0,1 mm is
about 70 mass%. In the non-leafing aluminum flakes having a. size of under
0.07 4 mm, a ratio of non-leafing type aluminum flakes having a size
passing through a sieve with a mesh opening size of 0.044 mm is about
70 mass%. As non-leafing aluminum flakes, a paste type in which the
aluminum flakes are dispersed in a solvent was also used. The paste type
aluminum flakes were obtained by dispersing the above dry type having
a size of under 0.15 mm in the ratio of two to one solvent. As leafing
type aluminum flakes (leafing aluminum flakes) , a dry type having a size
of under 0.15 mm, and a paste type prepared using this dry type, As a
binder, in addition to a phenolic resin, a silicone resin or molasses
was used in a part of the compositions.
[0032]
The above-mentioned raw materials were weighted according to the
composition ratios in Table 1, and, after adding an appropriate amount
of solvent thereto, uniformly kneaded by a mixer to obtain a mixture.
In Table 1, each competition ratio of the paste type aluminum flakss
indicates a solid content. The mixture was formed into a given shape
using a hydraulic press at a pressure of 98 MPa to form a shaped body
having a thickness of 150 mm. The shaped body was dried at 250°C for

5 hours, and then subjected to firing in a nitrogen atmosphere at a maximum
temperature of 1400°C to prepare a refractory material under test.
[0033]
In order to check a variation of strength of a refractory material,
ten cubic samples each 60 mm on a side were cut out from the refractory
material under test, and subjected to measurement of compressive
strength based on JIS R2206. Based on the resulting data on compressive
strength for the samples (n = 10), the variation in strength was
calculated using the following formula: (maximum value - minimum value)
/ average value x 100. A smaller calculated value means a smaller
(better) variation.
[0034]
Comparing Inventive Examples 1 to 9 with Comparative Examples 1 and
2, it is apparent that each sample of the Inventive Examples has a
significantly small variation in strength. It is assumed that, in both
of the Comparative Examples, crack occurs in the fired body, and thereby
the variation in strength becomes significantly large.
[0035]
Comparing Inventive Examples 1 to 3 with each other, as the size of
the non-leafing aluminum flakes becomes smaller, the variation in
strength becomes smaller (better). Table 1 also shows that, even when
the non-leafing aluminum flakes are added in a paste form as in Inventive
Example 4, a good result can be obtained. In Inventive Examples 5 and
6 as an example in which the binder is changed to a different type, a
good result could also be obtained. In Inventive Examples 7 to 9 as an
example using a combination of non-leafing type and leafing type, as
a ratio of the non-leafing type becomes higher, the variation in strength
becomes better, and, particularly when the ratio becomes less than 50
mass%, the effects of the present invention becomes insufficient. Thus,

when the combination is used, it is preferable that the non-leafing type
is set. to account for 50 rnass% or more of the combination,
[0036]
As presented in Table 2, a thickness of the shaped body was changed
to check influences of the thickness of the shaped body and a type of
aluminum flakes on the variation of strength, A production method for
a refractory material under test was fundamentally the same as that in
the aforementioned Examples, except for the thickness of the shaped body
during shape forming. An evaluation method for the variation in strength
was also fundamentally the same as that in the aforementioned Examples,
except that when the thickness of the shaped body was set to 50 mm and
30 mm, a length of one side of each cubic sample to be subjected to
measurement of compressive strength was set to 50mm and 30mm,
respectively.
[0037]

[0038]
As is evident from Table 2, each sample of Inventive Examples 10 to
13 using non-leafing aluminum flakes has a small variation in strength,
irrespective of the thickness of the shaped body. In contrast, each
sample of Comparative Examples 3 to 6 using leafing aluminum flakes has
a large variation in strength. Particularly when the thickness of the
shaped body is 80 mm or more, the variation in strength become
significantly large, and there is a large difference from that of
Inventive Example which is identical in terms of the thickness of the
shaped body. Thus, it is apparent that the present invention achieves
a remarkable improvement effect when it is applied to a shaped body having
a thickness of 80 mm or more.
[0039]
As presented in Table 3, an aluminum alloy was used while using a
magnesia-graphite based material as a base raw material, to check
influences of the changes on the variation of strength. A production
method for a refractory material under test was fundamentally the same
as that in the aforementioned Examples, except that the heat treatment
was performed in atmospheric air at 250°C. Each of an Al-Mg alloy and
an Al-Si alloy used as the aluminum alloy contains aluminum in an amount
of about 80 mass%. An evaluation method for the variation in strength
was also fundamentally the same as that in the Aforementioned Examples,
except that, taking into account a relatively low heat treatment
temperature for a refractory material under test, the measurement of
strength was performed after subjecting the refractory material to a
heat treatment in a reducing atmosphere at 1400°C for 5 hours, on an
assumption that the refractory material is heated during usage,
[0040]

TABLE 3

[0041]
As is evident from Table 3, it is apparent that, as long as the aluminum
flakes are the non-leafing type, the- variation in strength is
significantly small, irrespective of whether the aluminum flakes are
made of simple aluminum or an aluminum alloy.
[0042]
As presented in Table 4, an addition amount of aluminum was reduced
while using an alumina-silica-graphite based material as a base raw
material, to check influences of the changes on the variation of strength,
A production method for a refractory material under test was
fundamentally the sa,me as that in the aforementioned Examples, except
that the heat treatment was performed in a reducing atmosphere at 1000°C
An evaluation method for the variation in strength was the same as that
described in connection with Table 1.
[0043]
TABLE 4

[0044]
As is evident from Table 4, as the addition amount of aluminum become
smaller, the variation of strength becomes smaller in both of the case
where the non-leafing type aluminum flakes are used and the case where
the leafing type aluminum flakes are used, and a difference between the
two cases becomes smaller. However, in two samples of Inventive and
Comparative Examples each containing the non-leafing type and the
leafing type at the same amount, it is apparent that the sample of the
inventive Example exhibits a superior improvement effect. While, in a
practical sense, the addition amount of aluminum is appropriately
adjusted depending on enquired properties, the present invention
achieves excellent effects in any addition amount.
[0045]
A fracture surface of each sample after measurement of compressive
strength for Inventive Examples 2 and 14 and Comparative Examples 1 and
7 was subjected to SEM observation. Among them,.each sample of Inventive
Example 14 and Comparative Example 7 was subjected to a heat treatment
in a reducing atmosphere at 1400°C for 5 hours, as mentioned above.
Consequently, a large number of needle-like crystals mostly having a
length of 2 urn or less as presented in FIG, 1 were formed on the fracture
surface of each sample of Inventive Examples 2 and 14. On the other hand,
in each sample of Comparative Examples 1 and 7, a number of needle-like
or fiber-like crystals each having a length of about 5 um were formed
as presented in FIG. 2.

What is claimed is:
1. A refractory material obtained by incorporating, into a refractory
raw material, scaly non-leafing aluminum flakes made of non-leafing type
aluminum and/or aluminum alloy.
2 . The refractory material as defined in claim 1, wherein the non-leafing
aluminum flakes account for 50 mass% or more of a total of aluminum and/or
aluminum alloy in the refractory raw material.
3. The refractory material as defined in claim 1 or 2, wherein 70 mass%
or more of the non-leafing aluminum flakes have a size passing through
a sieve with a mesh opening size of 0.1 mm.
4 . The refractory material as defined in any one of claims 1 to 3, wherein
the non-leafing aluminum flakes are incorporated in the refractory
material in the form of a paste obtained by dispersing the non-leafing
aluminum flakes in an organic solvent.
5. The refractory material as defined in any one of claims 1 to 4, which
has been subjected to a heat treatment in a reducing atmosphere or
nitrogen atmosphere at 700°C or over.
6. The refractory material as defined in any one of claims 1 to 5, which
has a thickness of 80 mm or more.
7. The refractory material as defined in any one of claims 1 to 6, which
is a refractory material for a lining of a blast furnace.
8. The refractory material as defined in any one of claims 1 to 7, which

comprises needle-like crystals consisting of an aluminum compound and
having a length of 2 urn or less.
9. The refractory material as defined in any one of claims 1 to 7, which
is capable of forming therein needle-like crystals consisting of an
aluminum compound and having a length of 2 urn or less, when heated during
usage.
10. The refractory material as defined in claim 8 or 9, wherein each of
the needle-like crystals has a primary mineral phase consisting of A1N.
11. The refractory material as defined in any one of claims 8 to 10,
wherein the needle-like crystals each have a length of 2 urn or less account
for 50 mass% or more of the entire needle-like crystals.
12. A refractory material comprising needle-like crystals consisting of
an aluminum compound and having a length of 2 μm or less,
13. A refractory material which is capable of forming therein needle-like
crystals consisting of an aluminum compound and having a length of 2
μm or less, when heated during usage.