JP2004099441A - Zirconia-rich fused refractory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the damage from one-side heating and the damage from heat-cycling, and has a high electric resistance. <P>SOLUTION: Chemical components of a zirconia-rich fused refractory include the contents of 85-96wt.% ZrO<SB>2</SB>, 3-8wt.% SiO<SB>2</SB>, 0.1-2wt.% Al<SB>2</SB>O<SB>3</SB>, >0.05wt.% and ≤3wt.% B<SB>2</SB>O<SB>3</SB>, 0.05-3wt.% sum of BaO, SrO and MgO, ≥0.05wt.% Na<SB>2</SB>O, 0.05-0.6wt.% sum of Na<SB>2</SB>O and K<SB>2</SB>O, and ≤0.3wt.% sum of Fe<SB>2</SB>O<SB>3</SB>and TiO<SB>2</SB>, and do not substantially include P<SB>2</SB>O<SB>5</SB>nor CuO. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a high zirconia molten refractory having high corrosion resistance and no cracks suitable for a glass melting furnace, and particularly to a high zirconia molten refractory having significantly improved thermal spalling properties and electrical properties at 400 to 600 ° C. is there.

As a refractory for a glass melting furnace, a molten refractory containing a large amount of ZrO ₂ (also referred to as zirconia or zirconium oxide) has been frequently used. The reason for this is that ZrO ₂ (zirconia) is a metal oxide having particularly high corrosion resistance to molten glass. For example, as such molten _{refractory, Al 2 O 3 -ZrO 2 -SiO} 2 quality molten refractory containing ZrO ₂ 34 to 41 wt% (hereinafter, referred to as AZS refractory material) and the ZrO ₂ 80 wt% The high zirconia melted refractories including the above are used.

And recently, the use of high zirconia molten refractories has been particularly increasing.

The reason is that the high zirconia molten refractory has excellent characteristics as described below. Since the content of ZrO ₂ (zirconia) is high and the structure is dense, the high zirconia molten refractory has a feature of being excellent in corrosion resistance to all kinds of molten glass. Further, when a contact is made with the molten glass, a reaction layer is not formed at the interface between the refractory and the glass, so that stones and cords are not generated in the glass. Therefore, the glass melted using the high zirconia molten refractory has very few stones and cords.

Regarding the phenomenon that bubbles are generated in the glass due to the state and chemical composition of the high zirconia molten refractory, so-called foaming, the high zirconia molten refractory is brought into a sufficiently oxidized state, or the high zirconia molten refractory is Almost all of them are eliminated by reducing the components such as Fe ₂ O ₃ (diiron trioxide), TiO ₂ (titanium dioxide), and CuO (cupric oxide) contained in the material to a certain amount or less.

改良 Due to such improvements, high zirconia refractories are used as furnace materials for melting glass not only in the field of general-purpose glass but also in the field of very special glass.

高 This high zirconia molten refractory is composed of monoclinic zirconia crystals that occupy the majority and a small amount of glass phase. It is well known that zirconia crystals undergo a reversible transformation between a monoclinic system and a tetragonal system with a rapid change in volume around 1150 ° C.

Therefore, in order to obtain a high zirconia molten refractory without cracks, it is a major issue to absorb the volume change accompanying this transformation into the glass phase.

従 来 Various proposals have been made to solve this problem.

For example, Japanese Patent Application Laid-Open No. 53-12012 discloses that SiO ₂ (also referred to as silica or silicon dioxide) is contained in an amount of 1 to 4% by weight, and Al ₂ O ₃ (alumina or aluminum oxide) with respect to the content of SiO _2. (Al ₂ O ₃ / SiO ₂ ) with a content ratio of 0.5 to 1.0 and a small amount of CaO (calcium oxide) and MgO (magnesium oxide) added. In addition, Japanese Patent Application Laid-Open No. 56-129675 proposes that the glass phase is softened by adding P ₂ O ₅ (diphosphorus pentoxide).

In recent years, the number of electric melting furnaces has increased as relatively small glass furnaces and melting furnaces for glass with special chemical components, and raising the electrical resistance of high zirconia refractory has also become an issue. I have.

In order to solve this problem, JP-A-62-59576 discloses that the content of alkali metal oxide having good conductivity is reduced, and P ₂ O ₅ and B ₂ O ₃ (diboron trioxide) are used. To form a glass phase. In addition, JP-A-63-285173 discloses that K ₂ O (potassium oxide), Rb ₂ O (rubidium oxide), and Cs _{2 having} a large ionic radius without containing Na ₂ O (sodium oxide). A high zirconia molten refractory containing O and the like and containing an alkaline earth metal oxide and having a glass phase and high electric resistance is disclosed. In addition, Japanese Unexamined Patent Publication (Kokai) No. 4-193766 discloses a high zirconia molten refractory having a high electrical resistance and containing an alkaline earth metal oxide to form a glass phase.

In addition, improving the resistance to thermal cycling is also an issue.

To solve this problem, Japanese Patent Laid-Open No. 2-156575, since P ₂ O ₅ has a property to act as zircon forming agent in the glass phase, in order to improve the resistance to thermal cycles, P ₂ It has been proposed that O ₅ should not be contained.

As described above, in the conventional high zirconia molten refractory, it is possible to obtain a high zirconia molten refractory having no crack at the time of manufacturing, to obtain a high zirconia molten refractory having a high electric resistance, and to have excellent properties with respect to a heat cycle. The main object is to obtain a high zirconia molten refractory, and many improvement proposals have been made to achieve each purpose.
JP-A-53-122012 JP-A-56-129675 JP-A-2-156575 JP-A-63-285173 JP-A-4-193766 JP-A-2-156575

However, when a glass melting furnace is built using the above-mentioned conventional high zirconia molten refractory, the corner of the high zirconia molten refractory breaks off during the heating after the furnace is built, and the furnace interior surface is broken. Some of the surfaces of the used high-zirconia molten refractory shell-like and peel off, and more seriously, the high-zirconia molten refractory used as pavement explosively cracks over almost the entire area. Accidents have occurred.

破損 Such a high zirconia molten refractory breakage accident can occur due to failure in furnace design or heating, etc., but also occurs when the furnace design or heating is good.

On the other hand, if a refractory other than a high zirconia molten refractory, for example, AZS refractory, corundum refractory, α-β alumina refractory, or mullite refractory is used, such a damage accident may occur. Does not happen. Therefore, the above-mentioned damage accident is considered to be a phenomenon peculiar to the high zirconia molten refractory.

場合 If such breakage occurs, the corrosion resistance to the molten glass becomes very weak in the broken portion. As a result, defects such as stones and cords are generated in the molten glass, and molten glass enters the cracked gaps in the damaged part to promote erosion and entrap bubbles, causing serious glass defects. Occurs. As described above, conventionally, there is a problem that the advantage of the high zirconia molten refractory described above cannot be maximized.

The present inventors, in order to investigate the cause of such damage, in the same manner as in Examples 1 to 14 described below, a high zirconia molten refractory containing a chemical component according to the above-mentioned conventional proposal (Comparative Example 1). To 14), and the residual stress on the surface, the presence or absence of breakage during single-sided heating, and the presence or absence of cracks due to thermal cycling were examined. Table 1 shows the results.

Referring to Table 1, in the refractories of the chemical components disclosed in the above-mentioned JP-A-56-129675 and JP-A-2-156575, that is, in Comparative Examples 1 and 2, and Comparative Examples 3, 4, and 5, In each case, there was no crack at the time of production, and a compressive force remained as a residual stress on the surface of the refractory, and the magnitude of the compressive force exceeded 50 MPa. Further, in the refractories of chemical components disclosed in JP-A-63-285173 and JP-A-4-193766, that is, in Comparative Examples 6, 7 and Comparative Examples 8 to 11, cracks at the time of production were all low. No tension remained on the surface of the refractory as residual stress, and the magnitude of the tension exceeded 80 MPa. In Comparative Examples 1 to 11, breakage occurred during heating on one side.

In addition, in the refractories having the composition disclosed in JP-A-62-59576, that is, Comparative Examples 12 and 13, the residual stress was small and there was no breakage during single-sided heating. However, cracks occurred due to thermal cycling.

On the other hand, in other types of molten refractories, for example, AZS refractories, corundum refractories, α-β alumina refractories, and mullite refractories, tension remains as residual stress on the surface. Among these refractories, the AZS-based refractory containing 34% by weight of ZrO ₂ has the largest tension remaining, and the magnitude of the tension does not exceed 50 MPa. In addition, these refractories do not break when heated on one side.

に As is clear from comparison of Comparative Examples 1 to 14 with refractories other than such a high zirconia fused refractory, the type and magnitude of residual stress is a factor of breakage during single-sided heating.

This residual stress is generated during the casting and slow cooling process during the manufacturing process. Therefore, it is considered that the residual stress is greatly affected by the type of mold used and the slow cooling rate.

However, the type and magnitude of the residual stress cannot be controlled only by adjusting the type of mold and the slow cooling rate. For example, when the above-mentioned conventional high zirconia molten refractories are manufactured by using the same type of mold and slow cooling rate, some of them have tension as a type of residual stress, while others have a compression force. There is. That is, there are two types of high zirconia fused refractories having completely opposite types of residual stress, and the type of residual stress is not controlled.

(4) Even if the residual stress can be controlled to prevent breakage during one-sided heating, the same problem as described above occurs when there is a crack due to a heat cycle as in Comparative Examples 12 to 14.

As a result of intensive judgment and experiments repeated in consideration of these facts, the present inventors have found that by adjusting the glass phase component of the high zirconia molten refractory, it is possible to control the residual stress by changing the expansion coefficient. Was found.

By the way, according to the measurement by the present inventors, the bending strength of a conventional general high zirconia molten refractory at room temperature is in the range of 90 to 130 MPa. That is, if the tensile or compressive force generated in the high zirconia molten refractory exceeds this range, the refractory is cracked and damaged.

In fact, in other words, when the high zirconia molten refractory used in the glass furnace is heated, its heated surface becomes hot and tends to expand, so the opposite force, compressive force, acts on the refractory surface . Therefore, when the residual stress on the surface of the high zirconia molten refractory is a compressive force, since the combined force of the compressive force and the residual stress by heating acts on the surface of the high zirconia molten refractory, even if the residual stress is relatively small, Breakage such as cracks easily occurs when the temperature rises. On the other hand, when the residual stress is a tension, the compressive force due to heating acts in a direction to release the residual stress, so that even if the residual stress is relatively large, breakage such as a crack is unlikely to occur when the temperature is increased.

Therefore, in order to prevent cracks from being generated on the surface of the refractory at the time of single-sided heating, when the residual stress is a compressive force, it is proposed in the above-mentioned JP-A-56-129675 and JP-A-2-156575. When the residual stress is tension, the tension is slightly smaller than the tension of the refractory proposed in JP-A-63-285173 and JP-A-4-193766. Should.

The AZS-based refractory, corundum-based refractory, α-β alumina-based refractory, and mullite-based refractory do not break when heated in a glass furnace, unlike the high zirconia fused refractory. This is because the residual stress remaining on the surface of each refractory is a tension that does not exceed the mechanical strength of the refractory.

破損 Further, breakage peculiar to the conventional high zirconia molten refractory has all occurred at 400 to 600 ° C. That is, everything happens at a relatively low temperature before the glass phase of the refractory softens.

Therefore, it is clear from this point that the selection of the components constituting the glass phase is extremely important in order to prevent breakage.

It is also desired to have high electrical resistance, to prevent defects such as cracks from occurring in the refractory at the time of fabrication, and to prevent cracks due to thermal cycling. For that purpose, it is necessary to devise a chemical component of the glass phase.

With respect to the electric resistance, Japanese Patent Application Laid-Open No. 62-59576 mentioned above discloses a high zirconia produced without adding an alkali metal oxide such as Na ₂ O or K ₂ O in order to increase the electric resistance. A molten refractory is shown. However, this refractory causes diffusion of ions by contact with the molten glass. As a result, a phenomenon occurs in which the molten glass component and the glass phase component of the refractory are replaced, and the electric resistance of the refractory decreases.

In order to prevent this phenomenon, the above-mentioned Japanese Patent Application Laid-Open No. 63-285173 discloses K ₂ O of an alkali metal oxide having a large ionic radius and hardly causing substitution, BaO of an alkaline earth metal oxide, and the like. Addition of SrO is shown. However, this refractory has a problem that it has a large tension as a residual stress and is easily broken at the time of one-side heating.

In addition, the conventional proposals such as the above-mentioned Comparative Examples 1 to 11 make various efforts on the components of the glass phase so that the refractory obtained at the time of production does not crack. However, a situation that may occur when a glass furnace is actually built and heated up, that is, a situation at the time of one-side heating is not sufficiently considered.

For example, in the above-mentioned Japanese Patent Application Laid-Open No. 2-156575, an extremely small sample is placed in a furnace and the resistance to a heat cycle is examined. However, since the small sample is entirely contained in the furnace, a partial temperature difference is unlikely to appear in the sample, which greatly differs from the actual use conditions of the refractory. Under actual use conditions of the refractory, a partial temperature difference occurs in the refractory as follows. In an actual glass furnace, the temperature inside the furnace is raised after the furnace is built, so that the refractory used as the furnace wall generates a temperature difference between the inside and outside of the furnace. That is, when the temperature is raised, the inner surface of the refractory and the outer surface of the furnace do not reach the same temperature.

The object of the present invention is to prevent the damage specific to the conventional high zirconia molten refractory, that is, the damage at the time of single-sided heating, and to improve the resistance to a heat cycle by controlling the residual stress. Another object is to improve the electric resistance.

解決 The following is an example of the solution of the present invention.

(1) As chemical components, the content of ZrO ₂ is 85 to 96% by weight, the content of SiO ₂ is 3 to 8% by weight, and the content of Al ₂ O ₃ is 0.1 to ₂ % by weight. in _and, B 2 _{O 3} content is less and 3 wt% greater than 0.05% by weight, 0.05 to 3 wt% combined content of BaO, SrO, MgO, _Na 2 O Is 0.05% by weight or more, the total content of Na ₂ O and K ₂ O is 0.05 to 0.6% by weight, and the content of Fe ₂ O ₃ and TiO ₂ is the same. A high zirconia molten refractory, characterized in that the content is not more than 0.3% by weight and that P ₂ O ₅ and CuO are not substantially contained.

(2) The high zirconia molten refractory as described above, wherein the residual stress on the surface is a tension of 80 MPa or less or a compressive force of 50 MPa or less.

(3) The high zirconia molten refractory as described above, wherein the content of K ₂ O is 0.05% by weight or more.

According to the present invention, as a chemical component, the content of ZrO ₂ is 85 to 96% by weight, the content of SiO ₂ is 3 to 8% by weight, and the content of Al ₂ O ₃ is 0.1 to 2% by weight, the content of B ₂ O ₃ is more than 0.05% by weight and not more than 3% by weight, and the total content of BaO, SrO and MgO is 0.05 to 3% by weight, The content of Na ₂ O is 0.05% by weight or more, and the total content of Na ₂ O and K ₂ O is 0.05 to 0.6% by weight, and the content of Fe ₂ O ₃ and TiO ₂ is Since the total content is 0.3% by weight or less, and P ₂ O ₅ and CuO are not substantially contained, residual stress on the surface is controlled to prevent breakage at the time of one-side heating, and furthermore, thermal cycling Can be prevented.

Thereby, the specific damage in conventional high corrosion resistant high zirconia fused refractories, especially those which occur frequently at relatively low temperatures during heating after furnace construction, such as cracks, horns, peeling, explosive splashing For example, the resistance to so-called thermal spalling can be remarkably improved, and breakage during heating can be completely eliminated.

Furthermore, when used in a glass melting furnace, the glass can be colored.

As a result of various studies, the present inventor found that the content of ZrO ₂ as a chemical component was 85 to 96% by weight, the content of SiO ₂ was 3 to 8% by weight, and the content of Al ₂ O ₃ was The content is 0.1 to ₂ % by weight, the content of B ₂ O ₃ is more than 0.05% by weight and 3% by weight or less, and the content of BaO, SrO and MgO is 0.05 a 3% by weight, is not less 0.05 wt% or more Na ₂ O content is 0.05 to 0.6 wt% combined content of Na ₂ O and _{K 2} O, Fe ₂ A high zirconia molten refractory was completed, characterized in that the total content of O ₃ and TiO ₂ was 0.3% by weight or less, and P ₂ O ₅ and CuO were substantially not contained.

(4) In the present invention, substantially not containing means that the content is 0.05% by weight or less, which means that it is not intentionally added.

残留 Further, the residual stress remaining on the surface of the high zirconia molten refractory of the present invention is preferably a tension of 80 MPa or less or a compressive force of 50 MPa or less.

Further, the content of K2O as a chemical component is preferably 0.05 to 0.55% by weight.

The content of ZrO ₂ of a high zirconia fused refractories of the present invention, 85 to 96 wt%, preferably 90-95 wt%. When ZrO ₂ is more than 96% by weight, a refractory without cracks cannot be obtained, and when it is less than 85% by weight, corrosion resistance to molten glass is inferior.

The content of SiO ₂ is 3 to 8% by weight, preferably 3 to 5.5% by weight. SiO ₂ is an essential component for forming a glass phase. If it is less than 3% by weight, a glass phase cannot be formed. If it is more than 8% by weight, the corrosion resistance to the molten glass is inferior.

The content of Al ₂ O ₃ is 0.1 to 2% by weight, preferably 0.1 to 1.5% by weight. Al ₂ O ₃ has the property of reducing the tension of residual stress and improving the flow of the melt. If it is less than 0.1% by weight, such properties cannot be utilized. When the content is more than 2% by weight, the compressive force of the residual stress is increased and a stable glass phase cannot be formed, so that a refractory without cracks cannot be obtained.

The content of B ₂ O ₃ is more than 0.05% by weight and 3% by weight or less, preferably more than 0.05% by weight and 2% by weight or less. B ₂ O ₃ is an essential component for forming borosilicate glass, and plays an important role in the present invention. For example, it plays a large role in suppressing cracking during the production of a high zirconia molten refractory. If the content is less than 0.05% by weight, such a role cannot be fulfilled. When the content is more than 3% by weight, there is a problem that the tension of the residual stress is increased. When added in an excessive amount, the high zirconia molten refractory has a hygroscopic property, whereby H ₃ BO ₄ is formed to cause weathering, which adversely affects the refractory structure.

In the present invention, since an alkali metal oxide such as Na ₂ O or K ₂ O is added as described later, an extremely stable borosilicate glass can be formed, whereby the above-mentioned phenomenon can be prevented. This borosilicate glass is stable as a glass phase. Na ₂ O and K ₂ O are indispensable components for turning B ₂ O ₃ into stable borosilicate glass.

The content of BaO (barium oxide), SrO (strontium oxide), and MgO is 0.05 to 3% by weight in total, and preferably 0.05 to 2% by weight. Thereby, a sufficiently stable glass phase is formed, which is very important for adjusting the glass phase. If the amount is less than 0.05% by weight, a stable glass phase cannot be formed.

BaO, SrO, and MgO are alkaline earth metal oxides and are components of the glass phase. They have a property of forming a stable glass phase because they have little volatilization during melting and easy component adjustment. Therefore, unlike the P ₂ O ₅ , when heating the high zirconia molten refractory, even if part of the alkali metal is volatilized from the high zirconia molten refractory and the glass phase changes, crystals such as zircon are formed. There is an advantage that it is not generated and the resistance to thermal cycling is not extremely reduced.

By the way, electronic glass, for example, photomask, CRT glass, and liquid crystal glass often contain BaO, SrO, and MgO. Therefore, when the high zirconia molten refractory of the present invention is used in a melting furnace for electronic glass, since the same component is contained in both the molten glass and the glass phase of the refractory, diffusion of ions hardly occurs, and the refractory It also has the advantage of slowing down erosion.

As described above, BaO, SrO, and MgO are essential components, but when the total content thereof is more than 3% by weight, it has a function of increasing the tension of residual stress similarly to B ₂ O ₃ .

The present invention may contain at least one of BaO, SrO and MgO, and may contain two or more of them in combination. However, considering their properties and stability in the glass phase, it is preferable to contain at least BaO. That is, when one type is used, BaO is preferentially contained, and when two or more types are contained, BaO and SrO, or BaO and MgO, or BaO, SrO and MgO in combination are effective. It is a target.

The content of Na ₂ O is 0.05% by weight or more, and the total content of Na ₂ O and K ₂ O is 0.05 to 0.6% by weight, preferably 0.05 to 0. 3% by weight. That is, it contains only Na ₂ O or a combination of Na ₂ O and K ₂ O. Thereby, the tension of the residual stress is reduced. However, when the total content of Na ₂ O and K ₂ O is more than 0.6% by weight, the compressive force of the residual stress is increased.

As a component for reducing the tension of the residual stress, there is Al ₂ O ₃ described above in addition to Na ₂ O and K ₂ O. However, since the content is limited, when only Al ₂ O ₃ is contained without Na ₂ O and K ₂ O, the tension generated by B ₂ O ₃ and the alkaline earth metal oxide is reduced. It cannot be relaxed enough. Therefore, Na ₂ O and K ₂ O are components that also have an important effect in this regard.

Further, when only K ₂ O is added without containing Na ₂ O, the tension as the residual stress cannot be reduced as in, for example, Comparative Examples 6 and 7, so that breakage occurs during one-side heating, Moreover, the resistance to thermal cycling is poor, which is not good.

In order to improve the electrical resistance characteristics of the high zirconia molten refractory, that is, to increase the electrical resistance, the content of Na ₂ O and the content of K ₂ O are each 0.05 to 0.55% by weight. Is preferable. That is, it is effective to contain each of Na ₂ O and K ₂ O at 0.05% by weight or more. The greatest effect is to add Na ₂ O and K ₂ O in an equimolar ratio.

As described above, according to the present invention, by containing at least Na ₂ O, breakage during single-sided heating can be prevented, and high electrical resistance can be achieved.

CuO and P ₂ O ₅ have the function of reducing the tension and increasing the compressive force in a conventional high zirconia molten refractory not containing B ₂ O _3, and have a function of reducing the glass phase so that cracks occur during production. Not effective for making refractories. However, when it is added at the same time as B ₂ O ₃ , it has the property of forming a low-melting glass and extremely reducing chemical durability. In addition, P ₂ O ₅ has a property of lowering resistance to thermal cycling and a property of hardly producing a dense refractory due to the hygroscopicity of the raw material. In addition, CuO is effective in reducing cracks, but since the molten glass is colored, the use of refractories containing CuO is limited.

For these reasons, the present invention does not intentionally add CuO or P ₂ O ₅ . That is, the present invention does not substantially contain CuO and P ₂ O ₅ .

TiO ₂ and Fe ₂ O ₃ can be mixed as impurities, but since they affect the occurrence of cracks, their contents must not exceed 0.3% by weight in total.

残留 The residual stress on the surface of the high zirconia molten refractory is a tension of 80 MPa or less or a compressive force of 50 MPa or less. Preferably, the residual stress is a tension of 60 MPa or less, or a compressive force of 30 MPa or less. Thereby, it becomes a high zirconia fusion refractory excellent in various properties. For example, damage due to single-sided heating and damage due to a heat cycle can be prevented.

A description will be given of a high zirconia molten refractory according to a preferred embodiment of the present invention.

This high zirconia molten refractory has, as chemical components, a content of ZrO ₂ of 85 to 96% by weight, a content of SiO ₂ of 3 to 8% by weight, and a content of Al ₂ O ₃ of 0. 1 to 2% by weight, the content of B ₂ O ₃ is more than 0.05% by weight and not more than 3% by weight, and the total content of BaO, SrO and MgO is 0.05 to 3% by weight. The content of Na ₂ O is 0.05% by weight or more, the total content of Na ₂ O and K ₂ O is 0.05 to 0.6% by weight, and the content of Fe ₂ O ₃ and TiO ₂ is not more than 0.3% by weight in total, is substantially free of P ₂ O ₅ and CuO, and has no crack.

High zirconia fused refractories according to another embodiment, the chemical composition, the content of ZrO ₂ is 90 to 95 wt%, the content of SiO ₂ is 3 to 5.5 wt%, _Al 2 _{O 3} Is 0.1 to 1.5% by weight, the content of B ₂ O ₃ is more than 0.05% by weight and 2% by weight or less, and the contents of BaO, SrO and MgO are combined. 0.05 to ₂ % by weight, the content of Na ₂ O is 0.05% by weight or more, and the total content of Na ₂ O and K ₂ O is 0.05 to 0.3% by weight. Yes, the total content of Fe ₂ O ₃ and TiO ₂ is 0.3% by weight or less, P ₂ O ₅ and CuO are not substantially contained, and there is no crack.

Preferably, the residual stress on the surface of the high zirconia molten refractory is a tension of 80 MPa or less, or a compressive force of 50 MPa or less.

Preferably, the content of K ₂ O is 0.05% by weight or more, and the electric resistance is 150 Ω · cm or more.

Examples 1 to 14
Next, Examples 1 to 14 of the present invention will be described.

Table 2 shows the chemical components contained in the high zirconia molten refractory of each example and their contents. The symbol "-" in the column of content in Table 2 indicates a content of less than 0.05% by weight and means that the content is substantially not contained. “≦ 0.3” indicates a content of 0.3% by weight or less. For Fe ₂ O ₃ and TiO ₂ , the total content is shown.

高 The high zirconia molten refractory of each example was manufactured as follows.

An artificial zirconia obtained by desiliconizing zircon is prepared as a starting material, and this artificial zirconia is added to Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Na ₂ O, K ₂ O, BaO, SrO, MgO, etc. Was added as a powder raw material at a predetermined ratio in each example, and after mixing, the mixture was melted in an electric arc furnace, poured into a graphite mold having an internal size of 100 × 150 × 350 mm, and cast to obtain a powder of Bayer alumina. It was buried inside and cooled slowly to room temperature. Thus, the high zirconia molten refractory of each example having the chemical components shown in Table 2 was produced.

(4) In consideration of practical use conditions, each example was tested by the following method in order to check whether or not there was damage during one-sided heating. Using the high zirconia molten refractory as a material, three shrinkage-free samples having a size of 100 × 150 × 350 mm were arranged on the refractory, and their surroundings were surrounded by a heat insulating material. Then, a heating element was provided above the sample, and a 150 × 350 mm surface of the sample was heated. The surface heated in this manner was heated from room temperature to 1000 ° C. at a rate of 0.1 ° C./min. At this time, the presence or absence of damage to the sample, that is, the presence or absence of damage during single-sided heating was observed. Table 2 shows the results.

Further, for each example, the residual stress (also called residual strain) was measured by the following method. Using the high zirconia molten refractory of each example as a sample, residual stress at six locations on the surface of a sample having a size of 100 × 150 × 350 mm without shrinkage cavities was measured by a perforation method using a strain gauge. Table 2 shows the measurement results. However, when the residual stress is a compressive force, the maximum value of the absolute value is shown by adding +, and when the residual stress is a tensile force, the maximum value of the absolute value is shown by adding-. As described above, breakage at the time of temperature rise, which is characteristic of high zirconia molten refractories, is closely related to residual stress on the surface.

明 ら か As is clear from Table 2, since the residual stress is a compression force of 50 MPa or less or a tension of 80 MPa or less, the high zirconia molten refractory does not break in the single-sided heating test.

試 験 In addition, in order to examine the resistance to thermal cycling, a test was performed for each example by the following method. First, a sample having a size of 30 × 40 × 40 mm was cut out from the high zirconia molten refractory of each example. Next, after holding at 1250 ° C. for 60 minutes, it was held at 800 ° C. for 60 minutes. This was repeated once and repeated 20 times. Each material was observed for cracks. Table 2 shows the results.

Furthermore, the electrical resistance at 1500 ° C. was measured for each example. Table 2 shows the results. The symbol "-" described in the column of electric resistance in Table 2 indicates that it could not be measured because it could be easily estimated from chemical components.

The following conclusions were obtained from the results of the above tests.

As is apparent from Examples 1 to 14, high zirconia having excellent properties without cracking if the residual stress is within the range of the chemical components of the present invention and the residual stress is a compression force of 50 MPa or less or a tension of 80 MPa or less. A molten refractory is obtained. For example, damage during single-sided heating can be prevented, and damage due to a heat cycle can be prevented.

Further, when the residual stress is a compression force of 30 MPa or less or a tension of 50 MPa or less, a high zirconia molten refractory having more excellent properties can be obtained.

Further, in order to obtain a high electric resistance, it is effective to add Na ₂ O and K ₂ O at the same time.

In Examples 1, 2, 4, and 8, the content of Na ₂ O was larger than those of the other Examples, and there was no breakage due to single-sided heating. The reason is that the addition of B ₂ O ₃ , BaO, SrO, MgO, etc. suppresses the function of Na ₂ O and reduces the compressive force of the residual stress.

Examples 1 to 14 and Comparative Examples 1 to 14 are compared with reference to Tables 1 and 2 described above before Examples 1 to 14 and Comparative Examples 1 to 14.

Comparative Examples 1 and 2, unlike Example _{1~14, B 2 O 3, BaO} , SrO, does not contain _MgO, containing P 2 _{O 5.} Therefore, the interaction of Na 2 _O operations and Na 2 _O and P ₂ O _5, greater residual compressive force as a residual stress, damage, such as part of the separation of the corner angle deleted and faces in a test of single-sided heating was there.

Comparative Example 3, 4 and 5, unlike Examples _1-14, not containing _{B 2 O 3, BaO, SrO} , and MgO. Therefore, Na ₂ O, Al ₂ O ₃ , and SiO ₂ were the main components of the glass phase, the compressive force remaining as residual stress was large, and there was damage during one-side heating. In particular, Comparative Example 3 was greatly broken around 500 ° C. and scattered.

Comparative Examples 6 and 7, unlike Examples 1 to 14, do not contain Na ₂ O, contain only K ₂ O as an alkali metal oxide, and have a residual tension greater than 80 MPa. Therefore, cracks occur due to single-sided heating. In addition, cracks due to thermal cycling also occur.

Comparative Example 8-11, unlike Examples 1 to _14, not including the alkali metal oxides such as Na ₂ O, _K 2 O. Therefore, a considerably large tension remained as a residual stress. The refractory was subjected to a one-sided heating test. As a result, unlike the case of a large compressive force, the refractory did not scatter and cracked so as to be divided into two in the length direction.

Comparative Examples 8 to 11 have high electrical resistance characteristics by not containing an alkali metal oxide.

On the other hand, according to the present invention, by adding equimolar amounts of Na ₂ O and K ₂ O as alkali metal oxides as described above, it is possible to increase the electric resistance and prevent breakage during single-sided heating. For example, in Example 9, a refractory having high electric resistance was obtained by adding equimolar amounts of Na ₂ O and K ₂ O, and further adding B ₂ O ₃ and BaO, an alkaline earth metal oxide having a large ionic radius. Have gained.

Comparative Examples 12 and 13, unlike Examples 1 to 14, do not contain BaO, SrO, and MgO, but contain P ₂ O ₅ . Therefore, the tension remaining as the residual stress is small. However, since P ₂ O ₅ was contained, a phenomenon in which the surface was peeled off in the thickness direction was observed in the thermal cycle test. This is because the volatilization of P ₂ O ₅ changes the composition of the glass phase between the surface and the inside of the sample and changes the expansion coefficient.

Comparative Example 14 differs from Examples 1 to 14 in that it does not contain Na ₂ O, contains only K ₂ O as an alkali metal oxide, has a small residual compressive force as a residual stress, and has a single-sided heating test. No destruction occurs. However, since it contained only K ₂ O and did not contain Na ₂ O as an alkali metal oxide, its resistance to thermal cycling was weak. Therefore, when adding K ₂ O, it is necessary to add K ₂ O simultaneously with Na ₂ O.

Modifications The present invention is not limited to the embodiments described above.

For example, the surface of the high zirconia molten refractory may be polished or cut. Thereby, the residual stress can be reduced to some extent. However, the residual stress cannot be largely eliminated by such a method.

Claims (3)

As chemical components, the content of ZrO ₂ is 85 to 96% by weight, the content of SiO ₂ is 3 to 8% by weight, the content of Al ₂ O ₃ is 0.1 to ₂ % by weight, The content of B ₂ O ₃ is more than 0.05% by weight and not more than 3% by weight, the content of BaO, SrO and MgO is 0.05 to 3% by weight in total, and the content of Na ₂ O is Is 0.05% by weight or more, the total content of Na ₂ O and K ₂ O is 0.05 to 0.6% by weight, and the total content of Fe ₂ O ₃ and TiO ₂ is 0.1%. A high zirconia molten refractory which is not more than 3% by weight and is substantially free of P ₂ O ₅ and CuO. The high zirconia molten refractory according to claim 1, wherein the residual stress on the surface is a tension of 80 MPa or less or a compressive force of 50 MPa or less. The high zirconia molten refractory according to claim 1 or 2, wherein the content of K ₂ O is 0.05% by weight or more.