JP2020083689A - Protective structure of zirconia-carbon based refractory - Google Patents

Abstract

To provide a protective structure of a zirconia-carbon based refractory which prevents a disintegration phenomenon of zirconia particles contained in the zirconia-carbon based refractory, protects the surface of the zirconia-carbon based refractory, thereby preventing degradation of the zirconia-carbon based refractory.SOLUTION: In a zirconia-carbon based refractory as an aspect of the present invention, a protective structure 10 is formed by depositing a resistant protective layer 11 which is not eroded by an acidic oxide and a basic oxide, and an antioxidant 20 containing one or both of an acidic oxide and a basic oxide in layers on the surface of a zirconia-graphite (ZG) material 15 containing a plurality of particulate zirconia particles in graphite. When the antioxidant is melted under a high-temperature environment, the antioxidant cannot be brought into contact with the ZG material due to the resistant protective layer, so that disintegration of the zirconia particles on the surface of the ZG material can be prevented, and thus degradation of the ZG material can be prevented.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a structure for protecting a zirconia-carbonaceous refractory containing zirconia and carbon.

Conventionally, a zirconia-carbonaceous refractory containing zirconia (ZrO ₂ ) and carbon (C) has been known. Among such zirconia-carbonaceous refractories, for example, a zirconia-graphite material composed of zirconia and graphite (hereinafter referred to as "ZG material") is used for a nozzle for continuous casting as shown in FIG. Has been done. The continuous casting nozzle has a meniscus portion which is exposed to a substance having a high erosion property such as mold powder or slag in the middle of the nozzle body. By disposing a ZG material exhibiting high corrosion resistance in the meniscus portion, it is possible to prevent the erosion of mold powder and the like, and the continuous casting nozzle can extend the product life as compared with a nozzle that does not use the ZG material.

On the other hand, the continuous casting nozzle may be preheated in a high temperature environment of 1000° C. or higher before use. Under the high temperature environment, the carbonaceous component contained in the entire continuous casting nozzle and the carbonaceous component of the ZG material disposed in the meniscus portion are strongly oxidized. Therefore, the nozzle for continuous casting is generally coated with an antioxidant having oxidation resistance. The antioxidant is melted during preheating to form a glass film, and protects the continuous casting nozzle from a strong oxidizing atmosphere under a high temperature environment.
However, it has been conventionally confirmed that the meniscus portion on which the ZG material is arranged has a remarkable breakage or disappearance of the antioxidant, that is, the glass film after melting, after preheating, as compared with other portions of the nozzle for continuous casting. ..

The nozzle for continuous casting disclosed in Japanese Unexamined Patent Publication No. 10-263764 applies a coating material containing more than 82% by weight of alumina (Al ₂ O ₃ ) on the surface of a zirconia-carbon refractory, and further At least one layer of glass-based coating material is coated on the top. In this way, if the conventional glass-based coating is layered on the first layer coating made of alumina, the oxidation resistance of the entire coating material becomes high, so the zirconia-carbon refractory is coated with a strong oxidizing atmosphere in the high temperature environment during preheating. It says that the glass coating that remains does not disappear and remains, preventing damage to the coating material.

Japanese Patent Laid-Open No. 10-263764

Here, the inventors not only protect the surface of the zirconia-carbonaceous refractory by simply increasing the oxidation resistance as in the inventions disclosed in the above documents, but also the high temperature environment for a long time. Below, what was happening on the surface of the zirconia-carbonaceous refractory was observed, and in order to investigate the cause of breakage and disappearance of the glass coating, a sample as shown in FIG. 4 was prepared and repeated experiments. A detailed description of the experiment will be given later.

According to these experiments, when taken out from a high temperature environment, the zirconia-carbonaceous refractory coated with an antioxidant should have been coated with the antioxidant as well as the tear and disappearance of the antioxidant. It was revealed that an embrittlement phenomenon occurred in which the surface of the zirconia-carbon refractory material became brittle.
Furthermore, when the embrittlement phenomenon was investigated in detail, it was found that the zirconia particles on the surface of the refractory were collapsed as shown in FIG. 5(b). Note that FIG. 5 is an explanatory diagram schematically showing the surface micrograph obtained in the above experiment.
The inventors presumed that the collapse phenomenon of the zirconia particles causes the surface of the zirconia-carbon refractory to become brittle.

Therefore, the problem to be solved by the present invention is to prevent the collapse phenomenon of the zirconia particles contained in the zirconia-carbon refractory, to protect the surface of the zirconia-carbon refractory, thereby zirconia-carbon An object of the present invention is to provide a protective structure for zirconia-carbonaceous refractory which prevents deterioration of the refractory refractory.

The protective structure for a zirconia-carbonaceous refractory according to claim 1, wherein the surface of the zirconia-carbonaceous refractory contains a plurality of zirconia particles aggregated in a particulate form in the carbonaceous material,
Shows resistance not eroded by both oxidizing oxides and basic oxides, and forms a resistant protective layer capable of protecting the zirconia-carbonaceous refractory,
On the resistance protective layer, an antioxidant containing either or both of the oxidizing oxide and the basic oxide and capable of preventing oxidation of the zirconia-carbonaceous refractory is applied in a layered manner. hand,
When the antioxidant is melted in a high temperature environment, the resistant protective layer prevents the molten antioxidant from contacting the surface of the zirconia-carbonaceous refractory,
The resistant protective layer is adapted to prevent the zirconia particles from collapsing.

The protective structure for a zirconia-carbonaceous refractory according to claim 2 is characterized in that, in the invention according to claim 1, the resistant protective layer is silicon or a silicon-based compound containing at least silicon.

The zirconia-carbonaceous refractory protection structure according to claim 3 is characterized in that, in the invention according to claim 2, the silicon compound is silicon carbide.

The protective structure for a zirconia-carbonaceous refractory according to claim 4 is characterized in that, in the invention according to claim 1, the resistant protective layer is alumina or an alumina refractory containing at least alumina. ..

The zirconia-carbon refractory protection structure according to claim 5 is characterized in that, in the invention according to claim 4, the alumina refractory is a mullite refractory.

The zirconia-carbonaceous refractory protection structure according to claim 6 is characterized in that, in the invention according to claim 1, the resistant protection layer is formed to have a thickness of at least 0.1 mm.

According to the protective structure of the zirconia-carbonaceous refractory according to the present invention, an acidic oxide and a basic oxide are formed between the zirconia-carbonaceous refractory and the antioxidant for preventing the oxidation of the zirconia-carbonaceous refractory. A resistant protective layer was provided that was resistant to both materials and could protect zirconia-carbon refractory materials.
By providing the resistance protective layer in this manner, either or both of the acidic oxide and the basic oxide contained in the antioxidant are retained inside the resistance protective layer. As a result, the resistance protection layer not only enhances the oxidation resistance of the zirconia-carbonaceous refractory in a high temperature environment with the antioxidant, but also protects the molten antioxidant from penetrating into the zirconia-carbonaceous refractory. can do. Therefore, it is possible to prevent the particles of zirconia contained in the zirconia-carbon refractory from collapsing and prevent the deterioration of the zirconia-carbon refractory.

It is explanatory drawing which shows the outline of a structure of the protection structure of the zirconia carbonaceous refractory material which concerns on 1st Example. It is explanatory drawing which shows the example which applied the protection structure of the zirconia-carbonaceous refractory material which concerns on 1st Example. It is explanatory drawing which shows the outline of a structure of the protection structure of the zirconia carbonaceous refractory material which concerns on 2nd Example. It is explanatory drawing which shows the outline of the experiment conducted about the protective structure of the zirconia-carbonaceous refractory material which concerns on a present Example. FIG. 3 is an explanatory diagram showing an outline based on a micrograph of a sample surface showing a result of an experiment of a comparison target performed on a protective structure of a zirconia-carbonaceous refractory according to this example. It is explanatory drawing which showed the outline based on the micrograph of the sample surface which shows the experimental result performed about the protective structure of the zirconia-carbonaceous refractory material which concerns on a present Example. It is an explanatory view showing an outline based on a microscope picture of a sample section showing a result of a comparative experiment conducted about a protective structure of a zirconia-carbonaceous refractory according to this example.

Embodiments according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is an explanatory diagram showing an enlarged view of the vicinity of the surface of a zirconia-carbon refractory material.

As shown in FIG. 1, a protective structure 10 for a zirconia-carbonaceous refractory according to this embodiment includes a zirconia-graphite material 15, a resistant protective layer 11 provided on the surface of the ZG material 1, and a resistant protective layer. And an antioxidant 20 provided on the upper surface of 11.

The zirconia-graphite material (ZG material) 15 is made of zirconia and graphite and is one mode of the zirconia-carbonaceous refractory material.
Here, the zirconia-carbonaceous refractory material refers to a refractory material composed of zirconia (ZrO ₂ ) and carbon (C). Since the carbonaceous material also includes graphite (graphite) which is an allotrope of carbon, the ZG material 15 according to the present embodiment is a zirconia-graphite refractory material, and further a zirconia-carbonaceous refractory material. Since it is one of them, it can be said that the protective structure 10 of the zirconia-carbon refractory is the protective structure 10 of the ZG material 15. The ZG material 15 has corrosion resistance, wettability, or thermal shock resistance depending on the application site, for example, the meniscus portion 51 of the continuous casting nozzle 50 as shown in FIG. In order to satisfy necessary performances such as properties, it is manufactured by appropriately adjusting the proportion of zirconia or graphite contained.

The zirconia constituting the ZG material 15 is not pure zirconia but stabilized zirconia.
The stabilized zirconia is a solid solution of a stabilizer in zirconia. The stabilizer is a substance which is solid-dissolved in order to suppress the phase transition phenomenon of zirconia, and calcium oxide (CaO), magnesium oxide (MgO), or yttrium oxide (Y ₂ O ₃ ) is known. In terms of ease of use and cost, calcium oxide is often used. Therefore, the stabilized zirconia in the present example refers to CaO-stabilized zirconia in which a predetermined amount of calcium oxide is solid-dissolved and stabilized.
The phase transition phenomenon generally means that the crystal system of a substance changes to a different phase due to a change in temperature or pressure. Zirconia in a pure state undergoes a phase transition phenomenon at about 1000° C. and reversibly changes the crystal shape. For example, as in the case of the continuous casting nozzle 50 shown in FIG. 2, when heating to 1000° C. or higher during preheating or use and cooling after use are repeated, the crystal shape of zirconia changes, and with that, As a result, the thermal characteristics also change and become unstable. In such an unstable state, in the case of the ZG material 15, the entire material becomes brittle and may be damaged or chipped. In order to prevent such a situation, the zirconia contained in the ZG material 15 stabilizes calcium oxide as a solid solution.

The graphite that constitutes the ZG material 15 has a large thermal shock resistance, is difficult to be wet with mold powder or slag, and has strong corrosion resistance with respect to the mold powder and the like. The ZG material 15 formed by mixing the graphite with zirconia having strong corrosion resistance can have stronger corrosion resistance than graphite alone. Such a ZG material 15 is used, for example, as shown in FIG. 2, in a meniscus portion 51 that comes into contact with mold powder or slag with a continuous casting nozzle 50.
Since carbonaceous refractories containing graphite and carbon and graphite refractories are strongly oxidized in a high temperature environment such as a preheating furnace of the nozzle 50 for continuous casting, it is easy to apply the antioxidant 20 on the surface. It is treated so as not to be oxidized.

The antioxidant 20 is made of a glaze containing a large amount of silica (SiO ₂ ) component.
Generally, the glaze is formed by appropriately mixing an acidic oxide, a basic oxide, and an amphoteric oxide. As a result, the glaze and antioxidant 20 are melted at a predetermined temperature to form a glass film, and the glass film is easily oxidized. By doing so, it is possible to prevent oxidation of the refractory material in a high temperature environment.
Silica is a typical acidic oxide containing a non-metal element silicon (Si) and reacting with a base to form a salt. Further, since silica has a high melting point, by including a large amount of silica component, the strength and fire resistance of the antioxidant can be improved and the glass coating can be made difficult to flow.
On the other hand, it is necessary that the melting point of the silica is lowered to a predetermined temperature by mixing a predetermined compound with silica so that the antioxidant 20 melts in a predetermined temperature band and coats the refractory. The compound mixed at this time is called a solvent. A typical solvent is calcium oxide (CaO), which is also used as a stabilizer for zirconia. The calcium oxide is a typical basic oxide that contains calcium (Ca) as a metal element and reacts with an acid to form a salt. By mixing the medium solvent with the antioxidant 20, the melting point of the antioxidant 20 can be adjusted to facilitate the formation of the glass film in a high temperature environment.
Thus, the antioxidant 20 is formed by melting silica at a predetermined temperature with silica belonging to an acidic oxide and calcium oxide belonging to a basic oxide to form a glass film, and further adding an amphoteric oxide. The glass coating is formed so as to stably adhere to the surface of the ZG material 15.

The resistance protection layer 11 is formed of a material having resistance to both acidic oxides and basic oxides. In this embodiment, the resistance protection layer 11 is made of silicon (Si) or a compound containing the silicon. The silicon compound is preferably silicon carbide.
Silicon (Si) and silicon carbide (SiC) have a melting point higher than that of the temperature range of 1000° C. to 1400° C. in which the ZG material 15 is used for preheating the nozzle 50 for continuous casting shown in FIG. It has the property that it does not react with other elements below and is not attacked by acid. As a result, even when the acidic oxide or basic oxide contained in the antioxidant 20 is melted in a high temperature environment, they can be prevented from penetrating into the surface of the ZG material 15. ..
The resistance protection layer 11 is formed to have a thickness of at least 0.1 mm. The thickness of at least 0.1 mm is within the range of 0.1 mm to several mm depending on the application location of the ZG material 15, and is within the range common to those skilled in the art together with the antioxidant 20. That's fine.
When the resistance protection layer 11 is thinner than 0.1 mm, the resistance protection layer 11 may be dissolved in the acidic oxide or the basic oxide that is dissolved from the antioxidant 20, and it may not be possible to maintain sufficient resistance. is there.

When the ZG material 15 having the above structure is applied to the continuous casting nozzle 50 as shown in FIG. 2, for example, the resistance protection layer 11 can protect the surface of the ZG material 15 as follows.
The continuous casting nozzle 50 has a nozzle body 50a made of carbonaceous refractory and a ZG material 15 arranged in the meniscus portion 51. As shown in FIG. 1, a resistance protection layer 11 is provided on the surface of the ZG material 15, and the antioxidant 20 is uniformly applied to the entire nozzle including the nozzle body 50a and the meniscus portion 51.
Prior to use, the continuous casting nozzle 50 is placed in a preheating furnace and heated at about 1000°C to about 1400°C for a predetermined time. At this time, the antioxidant 20 is melted, and the contained silica is a main component to form a glass coating on the surface of the continuous casting nozzle 50. On the other hand, the calcium oxide contained in the antioxidant 20 dissolves out of the antioxidant 20 and tries to permeate the resistant protective layer 11 together with the fused silica.

Here, the zirconia (ZrO) particles contained in the ZG material 15 are stabilized by the basic oxide calcium oxide. Therefore, when there is no resistance protection layer 11 and the silica of the acidic oxide is in direct contact with the surface of the ZG material 15, a reaction occurs between the silica and the calcium oxide contained in the ZG material 15, It is considered that the calcium oxide in the ZG material 15 disappears and the zirconia destabilizes and collapses.
On the other hand, the resistance protection layer 11 is made of silicon or silicon carbide having resistance to both silica, which is an acidic oxide, and calcium oxide, which is a basic oxide, and is resistant to both silica and calcium oxide. There is no. As a result, both silica and calcium oxide are blocked by the resistant protective layer made of silicon or silicon carbide, and cannot penetrate to the surface of the ZG material 15.
As described above, in the present example, the resistance protective layer 11 is oxidized in addition to the acidic oxide, as opposed to the conventional example which was considered to improve the oxidation resistance only to silica which is an acidic oxide. It is also made resistant to basic oxides such as calcium. Therefore, the resistance protection layer 11 can effectively protect the ZG material 15 from the antioxidant 20. On the surface of the protected ZG material 15, it is possible to prevent the zirconia particles from collapsing, so that it is possible to prevent the deterioration of the ZG material 15.

Next, another embodiment different from the first embodiment will be described with reference to the accompanying drawings. FIG. 3 is an explanatory view showing an enlarged model near the surface of the zirconia-carbon refractory material according to the present embodiment.

The zirconia-carbonaceous refractory protection structure 10A according to the present embodiment, as shown in FIG. 3, includes a ZG material 15, a resistance protection layer 11A provided on the surface of the ZG material 15, and a resistance protection layer 11A. It consists of an antioxidant 20 provided on the upper surface. Since the ZG material 15 and the antioxidant 20 are the same as those described in the first embodiment, the description thereof will be omitted in this embodiment.

The resistant protective layer 11A is mainly made of an alumina refractory containing alumina (Al ₂ O ₃ ), and the alumina refractory contains, for example, an alumina refractory containing alumina as a main component or a large amount of alumina. A mullite refractory containing mullite (Al ₂ O ₃ —SiO ₂ ) as a main component is included.
When the ZG material 15 having the above structure is applied to the continuous casting nozzle 50 as shown in FIG. 2, for example, the durability protection layer 11A protects the surface of the ZG material 15 as in Example 1. The description is omitted because it is the same.

The following experiments were conducted on the protective structures 10 and 10A of the ZG material 15 according to the first and second embodiments described above. The experiment is an experiment for confirming whether or not the resistance protection layers 11 and 11A can prevent the zirconia particles contained in the ZG material 15 from collapsing.
FIG. 4 is an explanatory diagram for explaining the outline of the experimental configuration. 5A and 5B are schematic model diagrams based on a surface micrograph of a comparative sample in which the resistance protection layer 11A is not provided. On the other hand, FIG. 6 is a model diagram schematically showing a surface micrograph of a sample provided with the resistance protection layer 11A.

As shown in FIG. 4, the base ZG material 15 is composed of 90% zirconia and 10% graphite. The samples according to the present experiment were sample 1 in which nothing was applied to the ZG material 15 shown in FIG. 4A, and antioxidant 20 was applied to the ZG material 15 shown in FIG. 4B in a thickness of 0.1 mm. Sample 2 and a sample in which a resistance protective layer 11A made of alumina (Al ₂ O ₃ ) having a thickness of 0.1 mm was provided between the ZG material 15 shown in FIG. 4(c) and an antioxidant having a thickness of 0.1 mm. It consists of three.
The above Samples 1 to 3 were heated in an electric furnace kept at 1300° C. for 6 hours, and changes in the surface of the ZG material 15 were observed before and after being exposed to a high temperature environment.

FIG. 5A is an explanatory diagram showing an outline based on a micrograph of the surface of the sample 1 after the experiment. In sample 1, oxidation of graphite 120 occurred, but collapse of zirconia particles 100 was not observed.
FIG. 5B is an explanatory diagram showing an outline based on a micrograph of the surface of the sample 2 after the experiment. In sample 2, oxidation of graphite 120 was suppressed, but large zirconia particles 100 as seen in sample 1 collapsed and changed into finer fine particles, and a plurality of zirconia collapsed particles 110 were observed. We were able to.
FIG. 6 is an explanatory diagram showing an outline based on a micrograph of the surface of the sample 3 after the experiment. In sample 3, oxidization of graphite 120 was suppressed, and it was possible to observe zirconia particles 100 that were cracked or scratched but were not completely collapsed.

FIG. 7( a) is a cross-sectional view schematically showing the sample 2 in which the zirconia disintegrated particles 110 are observed on the surface in FIG. 5( b), based on a micrograph of a cross section thereof. 7(b) is a cross-sectional view schematically showing Sample 3 in which the collapse of the zirconia particles 100 shown in FIG. 6 is suppressed, based on a micrograph of a cross section thereof.
As shown in FIGS. 7A and 7B, a glass coating formed by melting the antioxidant 20 and the resistance protection layer 11A could be confirmed near the surface of the ZG material 15.
According to these cross-sectional views, in the case of Sample 2, the presence of the zirconia disintegration particles 110 can be confirmed up to a depth of 0.5 mm and the ZG material 15, whereas in the case of Sample 3, the zirconia disintegration particles 110 are present. It can be confirmed that the presence of γ is suppressed to 0.05 mm near the surface of the ZG material.
Accordingly, the ZG material 15 can significantly suppress the collapse of the zirconia particles 100 by the antioxidant 20 by providing the resistance protective layer 11A between the ZG material 15 and the antioxidant 20 applied on the surface. I was able to confirm.

Similar to the above experiment, the second to fourth experiments according to the first and second examples were continuously performed.
The second experiment is an experiment conducted under the above-mentioned conditions, in which the resistant protective layer 11A made of alumina (Al ₂ O ₃ ) of Sample 3 in the above experiment is a mullite refractory.
The third experiment is an experiment carried out under the above conditions with the resistance protection layer 11 made of silicon.
The fourth experiment is an experiment conducted under the above-mentioned conditions with the resistance protective layer 11 made of silicon carbide.
As a result of each experiment, the same result as that of the sample 3 of the first experiment could be obtained in any of the experiments (not shown). That is, it can be confirmed that in the sample provided with the resistance protection layers 11 and 11A, the collapse of the zirconia particles 110 can be suppressed, and the progress of the collapse phenomenon can also be suppressed in the shallow portion of the ZG material 15. It was

From the above experiments, according to the protective structures 10 and 10A of the ZG material 15 according to the first and second embodiments, the resistance protective layers 11 and 11A are provided between the ZG material 15 and the antioxidant 20. Thereby, it is possible to minimize the infiltration of the antioxidant 20 into the ZG material 15 and the collapse of the zirconia particles 110. Therefore, it is possible to prevent embrittlement in which the surface of the ZG material 15 is brittle and easily collapses, and it is possible to prevent the ZG material 15 from being deteriorated and easily cracked or chipped due to the progress of the embrittlement. For example, the product life of the continuous casting nozzle 50 using the material 15 as shown in FIG. 2 can be extended.

In addition, although the present embodiment describes the ZG material made of zirconia-graphite refractory, the present invention is not limited to this, and the zirconia-carbon refractory containing zirconia-carbon refractory containing allotrope of graphite is used. Even if it is a carbon material, the protection structures 10 and 10A are effective.
Further, the resistance protective layers 11 and 11A are not limited to silicon, silicon carbide, alumina refractory, or mullite refractory as described above, but may be oxides, particularly acidic oxides and basic oxides. Any material may be used as long as it has resistance to both.

The protective structures 10 and 10A of the zirconia-carbonaceous refractory according to the present invention are, as shown in the above-mentioned first embodiment, second embodiment, and experiment, zirconia-carbon even after being heated in a high temperature environment. Since the quality of the refractory material can be kept good, it can be applied to the meniscus portion 51 of the continuous casting nozzle 50 as shown in FIG. 2, for example.
Accordingly, when the continuous casting nozzle 50 is preheated before use, it is possible to prevent the meniscus portion 51 from peeling off or being damaged, and since the characteristics of zirconia are maintained even after repeated use, the product life is improved. It can be postponed.
Further, the protective structures 10 and 10A according to the present invention are not limited to the use in the continuous casting nozzle 50, but include zirconia-carbonaceous refractory or graphite which is an allotrope of carbon. It can also be used when any of the refractory materials is used in a strong oxidizing atmosphere such as in a high temperature environment, for example, when it is used as an inner coating in a furnace.

10, 10A... Protective structure of ZG material,
11, 11A... Resistance protection layer,
15... ZG material, 20... Antioxidant,
50... Nozzle for continuous casting, 50a... Nozzle body, 51... Meniscus portion,
100... Zirconia particles, 110... Zirconia disintegration particles, 120... Graphite

Claims (6)

On the surface of the zirconia-carbonaceous refractory containing a plurality of zirconia particles aggregated in the form of particles in the carbonaceous material,
Shows resistance not eroded by both oxidizing oxides and basic oxides, and forms a resistant protective layer capable of protecting the zirconia-carbonaceous refractory,
On the resistance protective layer, an antioxidant containing either or both of the oxidizing oxide and the basic oxide and capable of preventing oxidation of the zirconia-carbonaceous refractory is applied in a layered manner. hand,
When the antioxidant is melted in a high temperature environment, the resistant protective layer prevents the molten antioxidant from contacting the surface of the zirconia-carbonaceous refractory,
A protective structure for a zirconia-carbonaceous refractory material, wherein the resistant protective layer prevents the zirconia particles from collapsing. The protective structure for zirconia-carbonaceous refractory according to claim 1, wherein the resistant protective layer is silicon or a silicon-based compound containing at least silicon. The protective structure for a zirconia-carbonaceous refractory according to claim 2, wherein the silicon-based compound is silicon carbide. The protective structure for zirconia-carbonaceous refractory according to claim 1, wherein the resistant protective layer is alumina or an alumina-based refractory containing at least alumina. The zirconia-carbon refractory protection structure according to claim 4, wherein the alumina refractory is a mullite refractory. The zirconia-carbonaceous refractory protection structure according to claim 1, wherein the resistant protection layer is formed to have a thickness of at least 0.1 mm.

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