TITLE OF THE INVENTION
Aluminum oxycarbide composition, production method therefor, and refractory material
TECHNICAL FIELD
[0001]
The present invention relates to an aluminum oxycarbide composition usable as a ceramic
or refractory material or a raw material therefor, a production method for the aluminum
oxycarbide composition, and a refractory material using the aluminum oxycarbide composition.
BACKGROUND ART
[0002]
As an aluminum oxycarbide, the following two types: Al2OC and Al4O4C, have been known.
In particular, Al4O4C is characterized by high-temperature stability, anti-oxidation effect,
excellent corrosion resistance, and low thermal expansion coefficient. It is expected as a
refractory or ceramic material or a raw material therefor, in the future. Especially, Al4O4C is
expected as a raw material for a carbon-containing refractory material, such as an
alumina-carbon based refractory material or a magnesia-carbon based refractory material, used
as a refractory material for use with molten metal such as molten iron or steel.
[0003]
As a method of producing an aluminum oxycarbide composition containing such Al4O4C
(aluminum oxycarbide), the following Non-Patent Document 1 discloses a method in which
alumina and graphite are subjected to a heat treatment in an argon atmosphere. Specifically,
after adding ethanol to alumina having an average particle size of 0.1µm, and graphite reagent
having a particle size of 45 µm or less, they are mixed together in an agate mortar, and then dried.
A powder (2g) of the mixture is put into a graphite crucible, and burnt at 1700°C in a
preliminarily evacuated electric furnace, while supplying argon gas thereinto. The following
Non-Patent Document 2 discloses a method of producing an aluminum oxycarbide composition
using an arc furnace. However, the Non-Patent Document 2 mentions that, along with an
increase in amount of carbon in the aluminum oxycarbide composition obtained by the disclosed

production method, Al4C3 reactive with water is formed in a larger amount.
[0004]
On the other hand, the following Patent Document 1 discloses a technique for suppressing
the formation of Al4C3, wherein a carbon-based raw material and alumina are homogeneously
mixed together to eliminate a dispersion in C component.
[0005]
However, it is known that in ambient atmosphere, Al4O4C is oxidized at about 850°C and
transformed into alumina. Particularly, in cases where Al4O4C having fine crystal grains is used
as a raw material for a refractory material, it will be oxidized. Thus, it is difficult to maintain
the advantageous effects such as oxidation resistance, corrosion resistance and low thermal
expansion coefficient, for a long time.
LIST OF PRIOR ART DOCUMENTS
[PATENT DOCUMENTS]
[0006]
Patent Document 1: WO 2010/113972 A
[NON-PATENT DOCUMENTS]
[0007]
Non-Patent Document 1: REFRACTORIES, Vol. 59, p 288,2007
Non-Patent Document 2: REFRACTORIES, Vol. 35, p 316,1983
SUMMARY OF THE INVENTION
[TECHNICAL PROBLEM]
[0008]
The technical problem to be solved by the present invention is to provide an aluminum
oxycarbide composition capable of suppressing oxidation of Al4O4C during use to maintain
advantageous effects of Al4O4C for a long time, a production method for the aluminum
oxycarbide composition, and a carbon-containing refractory material using the aluminum
oxycarbide composition.

[SOLUTION TO THE TECHNICAL PROBLEM]
[0009]
The present invention provides an aluminum oxycarbide composition comprising Al4O4C
crystals. The aluminum oxycarbide composition is characterized in that the Al4O4C crystals
have an average diameter of 20 urn or more, based on an assumption that a cross-sectional area
of each Al4O4C crystal during observation of the aluminum oxycarbide composition in an
arbitrary cross-section thereof is converted into a diameter of a circle having the same area as the
cross-sectional area.
[0010]
Preferably, the aluminum oxycarbide composition of the present invention comprises
corundum crystals, in addition to the Al4O4C crystals. More preferably, the corundum crystals
and the Al4O4C crystals alternately lie in layered relationship. In addition to Al4O4C and
corundum, the aluminum oxycarbide composition of the present invention may contain Al2OC,
oxynitride such as AlON, and/or γ-Al2O3, in a small amount. Preferably, the aluminum
oxycarbide composition of the present invention contains carbon in an amount of 3.2 to 6.3
mass%.
[0011]
The present invention also provides a method of producing the above aluminum oxycarbide
composition. The method is characterized in that it comprises subjecting a carbon-based raw
material and an alumina-based raw material to melting in an arc furnace and then cooling within
the arc furnace.
[0012]
Preferably, in the method of the present invention, one or more selected from the group
consisting of silicon carbide, boron carbide, aluminum nitride, boron nitride and a metal are
added to the carbon-based raw material and the alumina-based raw material in an amount of 0.2
to 10.0 mass% with respect to and in addition to a total amount of the carbon-based raw material
and the alumina-based raw material. More preferably, the raw materials, such as the
carbon-based raw material, the alumina-based raw material and the silicon carbide, are

homogeneously mixed together to allow a dispersion in C component to fall within ± 10%.
[EFFECT OF THE INVENTION]
[0013]
In the present invention, the Al4O4C crystals have an average diameter of 20 µm or more,
based on the assumption that a cross-sectional area of each Al4O4C crystal is converted into a
diameter of a circle having the same area as the cross-sectional area. This makes it possible to
suppress oxidation of Al4O4C during use to maintain advantageous effects of Al4O4C for a long
time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
FIG. 1 is a photograph of a microstructure of an aluminum oxycarbide composition
according to the present invention (inventive sample 2 in Table 1).
FIG. 2 is a photograph of a microstructure of a conventional aluminum oxycarbide
composition (comparative sample 1 in Table 1).
DESCRIPTION OF EMBODIMENTS
[0015]
An aluminum oxycarbide composition of the present invention comprises Al4O4C crystals,
and is characterized in that the Al4O4C crystals have an average diameter of 20 µm or more,
based on an assumption that a cross-sectional area of each Al4O4C crystal during observation of
the aluminum oxycarbide composition in an arbitrary cross-section thereof is converted into a
diameter of a circle having the same area as the cross-sectional area.
[0016]
Al4O4C crystals in an aluminum oxycarbide composition belong to the orthorhombic system,
so that they have a columnar or prismatic structure, in many cases. Although a crystal shape in
microscopic observation varies depending on in what cross-section the observation is performed,
each of the Al4O4C crystals in the present invention has a length of about 10 to 2000 µm in a

short-side direction, as measured by observing columnar structures.
[0017]
As used in this specification, the term "average diameter based on the assumption that a
cross-sectional area of each Al4O4C crystal is converted into a diameter of a circle having the
same area as the cross-sectional area" means an average value of diameters based on an
assumption that respective cross-sectional areas of the Al4O4C crystals are cumulatively added in
descending order of cross-sectional area until a cumulative addition value becomes greater than a
half of the entire area of an observation field of view during microscopic observation of the
aluminum oxycarbide composition, and a cross-sectional area of each of a plurality of specific
ones of the Al4O4C crystals subjected to the cumulative addition is converted into a diameter of a
circle having the same area as the cross-sectional area. A cross-sectional area of each Al4O4C
crystal, and a diameter of a circle converted from the cross-sectional area, can be calculated
using image processing software.
[0018]
For example, the aluminum oxycarbide composition comprising Al4O4C crystals having an
average diameter of 20 urn or more can be produced by subjecting a carbon-based raw material
and an alumina-based raw material to melting in an arc furnace, and then cooling within the arc
furnace, i.e., slow cooling.
[0019]
Heretofore, in the field of grinding materials or the like, in a method of producing an
aluminum oxycarbide composition by means of arc melting, a mixture of raw materials is
subjected to melting in an arc furnace, and a resulting molten mixture is cast into a die outside
the arc furnace to form an ingot. However, in this production method, after melting in the arc
furnace, the molten mixture is cast into the die outside the arc furnace. Thus, a cooling rate
after the melting becomes greater than 10°C/min, i.e., the molten mixture is subjected to rapid
cooling, so that resulting Al4O4C crystals are finely formed to have an average diameter of less
than 10 µm.
[0020]
Differently, in the case where a mixture of raw materials is subjected to melting in an arc

furnace and then cooling within the arc furnace without any transfer, the cooling rate becomes
equal to or less than 10°C/min, i.e., a molten mixture is subjected to slow cooling, so that Al4O4C
crystals grow in the course of the slow cooling to have an average diameter of 20 µm or more.
In some cases, in addition to Al4O4C crystals, the aluminum oxycarbide composition comprises
corundum crystals, and further contains Al2OC, oxynitride such as AlON, and/or γ-Al2O3, in a
small amount.
[0021]
As above, the Al4O4C crystals have an average diameter of 20 µm or more. This makes it
possible to suppress oxidation of Al4O4C during use to maintain advantageous effects of Al4O4C
for a long time. In addition, when the aluminum oxycarbide composition contains corundum
crystals, the corundum crystals can function as barrier to suppress the oxidation of Al4O4C, so
that it becomes possible to more reliably maintain the advantageous effects of Al4O4C for a long
time. Although an upper limit of the average diameter of the Al4O4C crystals is not particularly
limited, it is preferably set to 3 mm or less, because a particle size usable as an aggregate raw
material for a refractory material is generally about 3 mm in a coarse particle fraction.
[0022]
Preferably, the aluminum oxycarbide composition of the present invention has a layered
microstructure in which the Al4O4C crystals and the corundum crystals alternately lie in layered
relationship. As mentioned above, it is known that Al4O4C is oxidized in an oxidation
atmosphere at 850°C and transformed into alumina. If Al4O4C is oxidized and transformed into
alumina, it becomes impossible to obtain an anti-oxidation effect, a corrosion resistance
enhancement effect and an effect based on low thermal expansion coefficient, which are innate
features of Al4O4C. In the microstructure where corundum crystals lie in layers, the corundum
crystal layers are effective in protecting Al4O4C crystals from oxidation, and highly effective in
suppressing oxidation of the entire aluminum oxycarbide composition, so that it becomes
possible to maintain the above features of Al4O4C for a long time.
[0023]
Preferably, the aluminum oxycarbide composition of the present invention contains carbon
in an amount of 3.2 to 6.3 mass%. This carbon content gives an indication of an amount of

Al4O4C contained in an aluminum oxycarbide composition. Specifically, a theoretical carbon
content in Al4O4C is 6.52 mass%. When a carbon content in an aluminum oxycarbide
composition is 6.52 mass%, an Al4O4C content in the aluminum oxycarbide composition is 100
mass%. If the carbon content in the aluminum oxycarbide composition is less than 3.2 mass%,
an amount of Al4O4C is reduced, so that it is likely that the advantageous effects of Al4O4C
cannot be sufficiently obtained. On the other hand, if the carbon content is greater than 6.3
mass%, formation of aluminum carbide susceptible to hydration becomes more likely to occur,
resulting in poor microstructural stability. Moreover, an amount of corundum crystal
s becomes reduced or zero, so that an oxidation suppression effect of Al4O4C is deteriorated,
which causes difficulty in maintaining Al4O4C in an oxidation atmosphere for a long time.
[0024]
As mentioned above, the aluminum oxycarbide composition of the present invention may
be produced by subjecting a carbon-based raw material and an alumina-based raw material to
melting in an arc furnace and then cooling (slowly cooling) within the arc furnace.
[0025]
As the carbon-based raw material, it is possible to use a carbon-based raw material which is
commonly used as a raw material for a refractory material. For example, the usable
carbon-based raw material includes pitch, graphite, coke, carbon black and powdered organic
resin. Among them, as graphite, it is possible to use flaky graphite, earthy (amorphous)
graphite, expanded graphite and/or artificial graphite. A content rate of carbon (C content rate)
of the carbon-based raw material may be 90 mass% or more, preferably, 95 mass% or more.
[0026]
As the alumina-based raw material, it is possible to use an alumina-based raw material
which is commonly used as a raw material for a refractory material. For example, the usable
alumina-based raw material includes fused alumina, sintered alumina and/or calcinated alumina,
which are prepared by artificially refining natural bauxite or the like through a Bayer process or
the like, to allow an Al2O3 purity to become 95 mass% or more. It is also possible to use China
bauxite, bauxite, clay and/or brick dust to an extent that an Al2O3 purity in the entire
alumina-based raw material is preferably 90 mass% or more, more preferably, 95 mass% or more

[0027]
In the present invention, a refractory material containing carbon and alumina, such as an
alumina-carbon based or alumina-graphite based refractory material, may be used as the
carbon-based raw material and the alumina-based raw material. In this case, a total content of
carbon and alumina with respect to the entirety of the carbon-based raw material and the
alumina-based raw material is adjusted to 90 mass% or more, preferably, 95 mass% or more.
Further, it is preferable that a mole ratio of carbon to alumina (C/Al2O3) in the entirety of the
carbon-based raw material and the alumina-based raw material is adjusted to a range of 0.8 to
2.0.
[0028]
Al4O4C is formed through the following reaction (1). Thus, ideally, a mole ratio of the
carbon-based raw material to the alumina-based raw material is set to 1.5.
2A1203 + 3C = Al4O4C + 2 CO — (1)
[0029]
The carbon content (Al4O4C content) in the aluminum oxycarbide composition can be
controlled to some extent by adjusting a content of the carbon-based raw material. However, in
typical melting conditions, carbon is oxidized to form a large amount of corundum (Al2O3),
although the reason is not clear. Moreover, local formation of AI4C3 and other problem occur.
[0030]
It is believed that the local formation of AI4O3 is due to an influence of a melting
atmosphere depending on a type of arc furnace, a voltage condition, etc. Considering practical
mass production, it is necessary to use a large arc furnace and perform melting at high voltage or
electric power. In this case, the melting atmosphere becomes an oxidation atmosphere. Thus,
it is considered that Al4O4C is less likely to be formed, and formation of corundum (Al2O3) is
accelerated.
[0031]
Therefore, preferably, one or more selected from the group consisting of silicon carbide,
boron carbide, aluminum nitride, boron nitride and a metal, are added to the carbon-based raw
material and the alumina-based raw material in an amount of 0.2 to 10.0 mass% with respect to

and in addition to a total amount of the carbon-based raw material and the alumina-based raw
material, whereafter the obtained mixture is subjected to melting in the arc furnace.
[0032]
Based on adding an antioxidant such as a metal in the above manner, it becomes possible to
suppress oxidation of the carbon-based raw material due to an atmosphere during melting and
cooling, to efficiently induce reaction between and melting of the carbon-based raw material and
the alumina-based raw material, although details of the mechanism is unclear. A melting point
of Al4O4C is in a high-temperature region of 1850°C or less. On the other hand, it is considered
that formation of Al4O4C occurs at an appropriate temperature ranging from 1000°C (which
would cause sintering reaction) to 1850°C (which causes formation of a liquid phase). Thus,
the metal to be added in the present invention is required to have oxygen affinity stronger than
that of carbon, in a temperature range of 1000°C or more.
[0033]
It is believed that the added metal in the present invention reacts with carbon monoxide
generated by a reaction between alumina and carbon, e.g., an aftermentioned reaction (2), to
immobilized carbon which would otherwise disappear as the carbon monoxide to exert an effect
of increasing the yield of carbon.
[0034]
When silicon is added as the metal, the following reaction (2) occurs.
2CO + Si = Si02 + 2C — (2)
[0035]
The metal to be added in the present invention is used in the form of a metal power or a
solid metal blank, to suppress oxidation of the carbon-based raw material and Al4O4C due to an
atmosphere during melting and cooling (i.e., during production). Therefore, a metal is used
which has oxygen affinity stronger than that of carbon, in a temperature range equal to or greater
than 500°C at which oxidation of carbon starts, preferably, equal to or greater than 1000°C which
would cause formation of Al4O4C. Specifically, for example, it is possible to use one or more
selected from the group consisting of Si, Mn, Al, Ca, Mg, Zr, and Ti. Further, an alloy
containing one or more of the above metals may also be used. Although a purity of the metal or

alloy is not particularly limited, the metal or alloy preferable has a purity of 90% or more.
[0036]
In another embodiment of the present invention, instead of or in addition to a metal, one or
more selected from the group consisting of silicon carbide, boron carbide, aluminum nitride and
boron nitride are added.
[0037]
It is assumed that each of silicon carbide (SiC), boron carbide (B4C), aluminum nitride
(A1N) and boron nitride (BN) exerts a function of suppressing oxidation of the carbon-based raw
material during melting and cooling due to an atmosphere, to efficiently induce reaction between
and melting of the carbon-based raw material and the alumina-based raw material, as with the
metal, although details of the mechanism is unclear. For example, in the case of adding SiC, it
is assumed that carbon is efficiently eluted therefrom into the molten raw materials to contribute
to formation of Al4O4C.
[0038]
As the silicon carbide, boron carbide, aluminum nitride or boron nitride to be added in the
present invention, it is possible to use a type which is commonly used as an antioxidant for
carbon, or. the like, in the technical field of refractory materials. Although a purity thereof is
not particularly limited, it preferable has a purity of 90% or more.
[0039]
Preferably, the raw materials in the present invention, such as the carbon-based raw material,
the alumina-based raw material, the metal and the silicon carbide, are homogeneously mixed
together to allow a dispersion in C component to fall within ± 10%. Based on preliminarily
homogeneously mixing the raw materials, it becomes possible to increase the yield of Al4O4C,
while suppressing formation of AI4C3.
[0040]
As used here, the term "homogeneously mixed (homogeneous mixing)" means a state in
which dispersion is significantly reduced when the mixture of the raw materials is sampled. In
the present invention, an index of the homogeneous mixing is represented by a dispersion in C
component. As used here, the term "dispersion in C component" means a ratio (%) of a

difference between a specific one of a plurality of analysis values, and a preset target value of the
C component, to the preset target value, wherein the plurality of analysis values are obtained by
taking a sample three times from the mixture of the raw materials, and analyzing respective C
components of the sampled mixtures, and the specific analysis value has the largest difference
with the preset target value. The dispersion in C component is set to fall, preferably, within ±
10%, more preferably within ± 5%. In order to achieve the homogeneous mixing, it is
preferable to perform mixing using a commercially available powder mixer. The term "preset
target value (%)" means [a ratio (%) of the carbon-based raw material to the mixture of the raw
materials] x [a content rate (%) of C component in the carbon-based raw material], wherein the
content rate (%) of the C component in the carbon-based raw material is a measurement value
before the mixing.
[0041]
As the arc furnace, it is possible to use a type which is commonly used to melt a refractory
material such as magnesia or alumina so as to produce a refractory material. In the arc furnace,
the mixture of the carbon-based raw material and the alumina-based raw material with other raw
material added thereto according to need, such as the metal, is melted. Specifically, the mixture
is melted at a temperature of about 1850 to 2400°C. After the melting, the molten mixture is
cooled to form an ingot, and the ingot is pulverized to obtain an aluminum oxycarbide
composition.
[0042]
In the present invention, a mole ratio of carbon in the carbon-based raw material to alumina
in the alumina-based raw material (C/Al2O3) may be controlled in a range of 0.8 to 2.0 to control
a content rate of Al4O4C.
[0043]
The aluminum oxycarbide composition of the present invention can be suitably used as a
raw material for a refractory material, particularly, aggregate (particle size: 0.2 mm or more).
When the aluminum oxycarbide composition of the present invention is used as a raw material
for a refractory material, it is preferably contained in an amount of 15 to 95 mass%. If the
content of the aluminum oxycarbide composition is less than 15 mass%, it is likely that the

advantageous effects of the aluminum oxycarbide composition cannot be sufficiently obtained.
On the other hand, if the content is greater than 95 mass%, an amount of carbon to be added in
order to reduce an elastic modulus, an amount of a metal to be added as a anti-oxidation or
sintered material or an antioxidant such as a metal, a carbide, a nitride or a boride, and an amount
of phenolic resin to be added as a binder, are restricted, so that it becomes difficult to obtain
sufficient characteristics as a refractory material, such as strength, elastic modulus and oxidation
resistance.
[EXAMPLES]
[0044]
Aluminum oxycarbide compositions were produced by the method of the present invention
designed to subject a mixture of raw materials to melting in an arc furnace and then cooling
(slow cooling) within the arc furnace, and by the conventional method designed to subject the
mixture to melting in an arc furnace, and then a resulting molten mixture is cast into a die outside
the arc furnace and subjected to rapid cooling, and characteristics thereof were evaluated. A
result of the evaluation is illustrated in the following Table 1.
[0045]
TABLE 1
[0046]
At respective ratios illustrated in Table 1, calcinated alumina (Al2O3 component: 99.9
mass%) and flaky graphite (C component: 99 mass%) were weighted by a total amount of 500
kg. As for the inventive samples 1 to 6, 8 and 9 and the comparative sample 2, Al, Si or SiC
was added thereto with respect to and in addition to a total 100 mass% of the calcinated alumina
and the flaky graphite
[0047]
As for the inventive samples 1 to 5, 8 and 9 and the comparative sample 2, the above raw
materials were blended, and mixed together by a V-Cone mixer for 5 minutes. As for the
inventive samples 6 and 7 and the comparative sample 1, the homogeneous mixing treatment

was not performed. The dispersion in C component of the raw material mixture was evaluated
by the aforementioned method.
[0048]
The raw material mixture was put in a 1000 KVA arc furnace, and subjected to melting.
Then, the molten mixture in each of the inventive samples was subjected to slow cooling without
transfer to the outside, and the molten mixture in each of the comparative samples was cast into a
die outside the arc furnace. In this way, ingots of inventive and comparative aluminum
oxycarbide compositions were produced. A cooling rate in each of the inventive samples was
set to about 0.7°C/min, and a cooling rate in each of the comparative samples was set to about
15°C/min.
[0049]
Each of the produced ingots of the aluminum oxycarbide compositions was subjected to
pulverization and particle size regulation, and then an apparent porosity and an apparent specific
gravity were measured according to JIS-R2205. In regard to a chemical composition, a C
content was measured according to JIS-R2011. The C content was evaluated by a total carbon
amount which is a sum of free carbon described in JIS-R2205, and carbon in silicon carbide.
Specifically, considering that oxidation of Al4O4C starts at a temperature of 820°C or more, the
carbon content was evaluated by a sum of a carbon amount measured at 900°C and a carbon
amount in silicon carbide measured at 1350°C. The theoretical C content in Al4O4C is 6.52
mass%.
[0050]
A mineral phase was quantified by an internal reference method based on X-ray
diffractometry.
[0051]
A microstructure of the aluminum oxycarbide composition was observed by a microscope.
As mentioned above, an average diameter of Al4O4C crystals means an average value of
diameters based on the assumption that respective cross-sectional areas of the Al4O4C crystals
are cumulatively added in descending order of cross-sectional area until a cumulative addition
value becomes greater than a half of the entire area of an observation field of view during

microscopic observation of the aluminum oxycarbide composition, and a cross-sectional area of
each of a plurality of specific ones of the Al4O4C crystals subjected to the cumulative addition is
converted into a diameter of a circle having the same area as the cross-sectional area.
[0052]
A rectangular columnar sample having a size of 8 x 8 x 12 mm was directly cut from each
of the ingots, and a thermal expansion coefficient was measured in an ambient atmosphere up to
1000°C by thermo-mechanical analysis (TMA). Further, in order to evaluate a thermal
expansion coefficient maintenance ratio after oxidation of the aluminum oxycarbide composition,
the rectangular columnar sample of 8 x 8 x 12 mm was subjected to an oxidation treatment
under an ambient atmosphere at 1500°C for 3 hours, and the thermal expansion coefficient was
measured in an ambient atmosphere up to 1000°C by thermo-mechanical analysis (TMA) in the
same manner.
[Formula 1]
Alumina transformation rate = [(Al4O4C amount before oxidation test - Al4O4C amount after
oxidation test) / Al4O4C amount before oxidation test] x 100
[0053]
In view of the fact that when Al4O4C is oxidized, it is transformed to alumina (corundum),
oxidation resistance was evaluated by calculating an alumina transformation rate indicative of an
Al4O4C decrease rate (corundum increase rate). The alumina transformation rate is expressed
as the following formula:
[0054]
Specifically, a sample having a size of 10 x 10 x 10 mm was cut from each of the ingots,
and subjected to an to an oxidation treatment under an ambient atmosphere at a temperature of
1500°C for 3 hours using a rotary furnace. Then, a carbon content was measured, and the
alumina transformation rate was calculated by comparison with a carbon content preliminarily
measured before the oxidation test. The aluminum oxycarbide composition primarily consists
of corundum and Al4O4C, and contains other components in an extremely small amount. Thus,

an Al4O4C content can be calculated by measuring a carbon content. Therefore, carbon
contents before and after the oxidation test were measured to derive Al4O4C contents before and
after the oxidation test, and calculate the alumina transformation rate.
[0055]
As is evident from Table 1, all of the inventive samples in which the average diameter of
Al4O4C is 20 um or more, are excellent in oxidation resistance. On the other hand, the
comparative samples in which the average diameter of Al4O4C is less than 10 um, are inferior in
terms of oxidation resistance.
[0056]
In regard to a thermal expansion coefficient of the aluminum oxycarbide composition
oxidized at 1500°C in an ambient atmosphere, all of the inventive samples 1 to 9 in which the
average diameter of Al4O4C is 20 um or more, maintain a low thermal expansion coefficient.
On the other hand, the comparative samples 1 and 2 in which the average diameter of Al4O4C is
less than 10 um, have an increased thermal expansion coefficient.
[0057]
A comparison between the inventive sample 2 and the inventive sample 6 shows that the
yield (content rate) of Al4O4C is enhanced by preliminarily homogenously mixing the raw
materials. However, from a comparison between the inventive sample 2 and the comparative
sample 2, it is proven that an effect of enhancing the oxidation resistance cannot be obtained
only by the preliminarily homogenous mixing of the raw materials.
[0058]
A comparison between each of the inventive samples 6, 8 and 9 and the inventive sample 7
shows that the yield (content rate) of Al4O4C is enhanced by adding an antioxidant such as a
metal.
[0059]
FIG. 1 illustrates a microstructure of the inventive sample 2, and FIG. 2 illustrates a
microstructure of the comparative sample 1. It is proven that, in the inventive sample 2,
columnar Al4O4C crystals having a short diameter of about 50 to 250 um, and columnar
corundum crystals having a short diameter of about 30 to 300 um or corundum- Al4O4C

co-crystals, grow while alternately lying in layered relationship. On the other hand, in the
comparative sample 1, each of Al4O4C crystals and corundum crystals is finely formed to have
an average diameter of less than 10 um.
[0060]
Then, three types of carbon-containing refractory materials were produced by using the
aluminum oxycarbide compositions of the inventive sample 2 and the comparative samples 1 and
2, and characteristics thereof were evaluated. A result of the evaluation is illustrated in the
following Table 2.
[0061]
TABLE 2
[0062]
The various raw materials were blended at respective ratios illustrated in Table 2, and, after
adding a phenolic resin as a binder thereto in an amount of 5 mass% with respect to and in
addition to a total amount of the raw materials, subjected to mixing and shaping. Then, the
resulting shaped body was heated at a temperature of 300°C to produce a carbon-containing
refractory material.
[0063]
The produced carbon-containing refractory material was evaluated in terms of bulk specific
gravity, apparent porosity, thermal expansion coefficient, corrosion resistance, oxidation
resistance, liquid-phase oxidation resistance and thermal shock resistance.
[0064]
The bulk specific gravity and the apparent porosity were evaluated by the method described
in JIS-R2205. The thermal expansion coefficient was evaluated in a nitrogen atmosphere up to
1000°C by the non-contact method described in JIS-R2207-1.
[0065]
The corrosion resistance was evaluated by melting an SS material and an iron oxide powder
using a high-frequency induction furnace to prepare synthetic slag having a CaO/Al2C>3 ratio of
2.2, and subjecting a sample to a corrosion resistance test in the synthetic slag at 1600°C for 3

hours to measure a wear amount. Then, the obtained measurement value was converted into an
index value on an assumption that a wear amount of the comparative sample 5 in the
aftermentioned Table 3 is 100. A smaller value indicates better corrosion resistance.
[0066]
The liquid-phase oxidation resistance was evaluated by melting an SS material using a
high-frequency induction furnace, and subjecting a sample to a liquid-phase oxidation resistance
test in the molten steel at 1600°C for 5 hours to measure a thickness of an oxide layer on a steel
bath portion. Then, the obtained measurement value was converted into an index value on an
assumption that a thickness of an oxide layer of the comparative sample 5 in the aftermentioned
Table 3 is 100. A smaller value indicates better liquid-phase oxidation resistance.
[0067]
The thermal shock resistance was evaluated by repeating a cycle of immersing a sample in
molten steel at 1600°C for 3 minutes and subjecting the sample to air cooling, to determine
quality based on the number of cycles before occurrence of peeling (spalling). Specifically, the
thermal shock resistance was evaluated by an average cycle number in two samples before the
occurrence of peeling. A larger value indicates better thermal shock resistance.
[0068]
Table 2 shows that the inventive sample 10 using the aluminum oxycarbide composition of
the inventive sample 2 in Table 1 is superior to the comparative samples 3 and 4 using respective
ones of the aluminum oxycarbide compositions of the comparative samples 1 and 2 in Table 1, in
terms of corrosion resistance, liquid-phase oxidation resistance and thermal shock resistance.
In the inventive sample 10, Al4O4C was maintained for a long time without being oxidized even
under the high-temperature testing condition. It is considered that the result comes from
excellent corrosion resistance based on improvement in wettability with slag, which is one
feature of Al4O4C. Further, in view of the fact that Al4O4C is also maintained in the
liquid-phase oxidation test, it is believed that oxidation resistance in a high temperature region is
enhanced. It is considered that the effect of enhancing liquid-phase oxidation resistance comes
from a high oxidation suppression effect based on a dense Al2O3 layer formed through a reaction
between Al4O4C and FeO. Further, in view of the fact that Al4O4C is maintained under the

repetitive high-temperature heat treatments in the thermal shock resistance test, it is believed that
spalling resistance is improved by the low thermal expansion coefficient-based effect. In
contrast, each of the aluminum oxycarbide compositions of the comparative samples 3 and 4
were oxidized and transformed into Al2O3 under the high-temperature testing condition, within a
short period of time. It is considered that the result is due to deterioration in corrosion
resistance caused by deterioration in wettability with slag, deterioration in oxidation resistance,
and deterioration in spalling resistance caused by increase in thermal expansion coefficient.
[0069]
Then, a carbon-containing refractory material using the aluminum oxycarbide composition
of the inventive sample 5 in Table 1 was produced, and characteristics thereof were evaluated.
A result of the evaluation is illustrated in the following Table 3. In Table 3, the comparative
sample 5 is a carbon-containing refractory material using no aluminum oxycarbide composition.
[0070]
TABLE 3
[0071]
Various raw materials were blended at respective ratios illustrated in Table 3, and
carbon-containing refractory materials were produced by the same method as that for the
samples in Table 2. Characteristics of each of the produced carbon-containing refractory
materials were evaluated by the same method as that for the samples in Table 2.
[0072]
All of the inventive samples were superior to the comparative sample 5 in terms of
corrosion resistance, liquid-phase oxidation resistance and thermal shock resistance.

We Claim:
1. An aluminum oxycarbide composition comprising Al4O4C crystals, characterized in that the
Al4O4C crystals have an average diameter of 20 µm or more, based on an assumption that a
cross-sectional area of each Al4O4C crystal during observation of the aluminum oxycarbide
composition in an arbitrary cross-section thereof is converted into a diameter of a circle having
the same area as the cross-sectional area.
2. The aluminum oxycarbide composition as defined in claim 1, which further comprises
corundum crystals.
3. The aluminum oxycarbide composition as defined in claim 2, wherein the Al4O4C crystals
and the corundum crystals alternately lie in layered relationship.
4. The aluminum oxycarbide composition as defined in any one of claims 1 to 3, which
contains carbon in an amount of 3.2 to 6.3 mass%.
5. A method of producing the aluminum oxycarbide composition as defined in any one of
claims 1 to 4, characterized in that it comprises subjecting a carbon-based raw material and an
alumina-based raw material to melting in an arc furnace and then cooling within the arc furnace.
6. The method as defined in claim 5, wherein one or more selected from the group consisting
of silicon carbide, boron carbide, aluminum nitride, boron nitride and a metal are added to the
carbon-based raw material and the alumina-based raw material in an amount of 0.2 to 10.0
mass% with respect to and in addition to a total amount of the carbon-based raw material and the
alumina-based raw material, whereafter the obtained mixture is subjected to melting in the arc
furnace and then cooling within the arc furnace.
7. The method as defined in claim 6, wherein the raw materials are homogeneously mixed

together to allow a dispersion in C component to fall within ± 10%.
8. A refractory material which contains, as aggregate, the aluminum oxycarbide composition
as defined in any one of claims 1 to 4.
9. A refractory material which contains the aluminum oxycarbide composition as defined in
any one of claims 1 to 4, in an amount of 15 to 95 mass%.