KR101277403B1 - High-electric resistivity, high-zirconia fused cast refractories - Google Patents

Abstract

Provided is a high zirconia cast refractory material having stable high electric resistance characteristics with a small change over time at a high temperature, difficult to peel off at a temperature rise, and having thermal cycle stability.

A high zirconia cast refractories in which the properties related to the viscosity near 1000 ° C. in the glass phase and the residual stress on the refractory surface are controlled, wherein the chemical composition includes ZrO ₂ of 87% by weight to 96% by weight and Al ₂ O ₃ of 0.1% by weight to 0.8 Less than 10% by weight, less than or equal to 3% by weight of SiO ₂ and less than or equal to 10% by weight, less than 0.05% by weight of Na ₂ O, 0.01% to 0.2% by weight of K ₂ O, 0.1% to 1.0% by weight of B ₂ O ₃ 0.1% to 0.5% by weight of BaO, 0.05% to 0.05% by weight of SrO, 0.01% to 0.15% by weight of CaO, 0.05% to 0.4% by weight of Y ₂ O ₃ , 0.1% by weight of MgO Hereinafter, the total amount of Fe ₂ O ₃ and TiO ₂ is 0.3 wt% or less, and P ₂ O ₅ and CuO are not substantially contained (less than 0.01 wt%), and the electrical resistance after holding for 12 hours at 1500 ° C. is 200 Ωcm or more.

Description

High resistance and high zirconia casting refractories {HIGH-ELECTRIC RESISTIVITY, HIGH-ZIRCONIA FUSED CAST REFRACTORIES}

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the hot bending strength measurement result of high zirconia casting refractory body. Flexural strength at many measurement temperatures (25-1400 degreeC) is shown compared with the comparative example 4 and this invention.

2 is a view showing a change over time of the electrical resistance of high zirconia cast refractory.

3 is a diagram showing a micrograph after measuring the electrical resistance of Example 4. FIG.

4 is a diagram showing a micrograph after the electrical resistance measurement of Comparative Example 9. FIG.

TECHNICAL FIELD The present invention relates to a high zirconia cast refractory suitable for a glass fusion furnace, and is stable at high temperatures, especially at around 500 ° C., without delamination, and is particularly excellent in thermal cycle stability and having electrical resistance at high temperatures. The present invention relates to a high zirconia casting refractories with remarkable improvement.

Casting refractories containing a large amount of ZrO ₂ (zirconia or zirconium oxide) as refractory materials for glass melting furnaces have been widely used. This is because ZrO ₂ is a metal oxide having particularly high corrosion resistance to the molten glass. For example, high zirconia cast refractory containing 80 wt% or more of ZrO ₂ is used as such cast refractory.

The high zirconia cast refractory has a large corrosion resistance with respect to all kinds of molten glass, in that the content of ZrO ₂ is high and the structure is dense. Moreover, since there exists a property which does not make a reaction layer in the interface with a molten glass, there exists the outstanding characteristic that a defect like a stone and a cord does not generate | occur | produce in a molten glass. For this reason, high zirconia cast refractory is a particularly suitable refractory for producing high quality glass.

Most of the mineral structure of the high zirconia cast refractory material is occupied by monoclinic zirconia crystals, and a small amount of glass phase forms the grain boundary of this zirconia crystal.

On the other hand, zirconia crystals are known to cause reversible transformation of monoclinic and tetragonal systems with a sudden volume change around 1150 ° C. By mitigating the stress caused by the volume change accompanying the zirconia transformation by the glassy flow, the production of high zirconia cast refractory without cracking at the time of manufacture became possible at the production level (level).

However, although the amount of the glass phase occupied in the high zirconia cast refractory is small, the properties of the high zirconia cast refractory are greatly affected by the type and amount of the components constituting the glass phase.

It is also known that in high zirconia cast refractories, glass silica and zirconia react and crystallize as zircon when subjected to a thermal history. The alkali metal oxides, alkaline earth oxides such as Na ₂ O, BaO, etc. may be added to inhibit the crystallization of such a glass phase to a stable glass phase.

In recent years, in alkali free glass, such as liquid crystal panel glass (LCD), in order to improve the characteristic, the glass of the composition with higher electrical resistance is employ | adopted than before. For this reason, high electric resistance products are also required for high zirconia casting refractories, which are furnace materials of the melting furnace of the glass.

However, it has been found that the electrical resistance of a conventional high electric resistance product is a measured value after the temperature rises to a predetermined temperature or after several hours has elapsed at a predetermined temperature, and there is a problem in the stability of the value and the durability.

If the holding time becomes longer, the electrical resistance may increase. Specifically, comparing the electrical resistance immediately after the 1500 ° C. temperature rise and after the 12-hour holding, there may be an increase to 160% of the electrical resistance immediately after the 12-hour holding. This is because zircon precipitates on glass, and electrical resistance increases as zircon precipitates.

As described above, the deposition of zircon is advantageous from the viewpoint of electrical resistance, but in the thermal cycle test described later, it may cause cracking or powdering, and therefore, it is not preferable in high zirconia casting refractory materials.

Therefore, there is a need for a high zirconia cast refractory material that can maintain stable high electric resistance characteristics at high temperatures.

When the glass melting furnace is defrosted using high zirconia cast refractories, a part of the surface of the high zirconia cast refractories used as the furnace inner surface is cracked out when the corner of the high zirconia cast refractory is broken during the temperature increase after the defrosting. May cause an accident such as peeling off.

When breakage of such high zirconia cast refractory occurs, the erosion to molten glass becomes very weak at the broken part. Therefore, there exists a problem of making defects, such as a stone and a cord, in molten glass.

It is known that the peeling at the time of temperature rise is greatly influenced by the residual stress on the surface of the product. There are two types of residual stress, and a product may leave tensile stress as a residual stress and compressive stress at the time of manufacture. A compressive stress is a case where a force is applied in the direction which concentrates on one point in consideration of one point of a refractory. In addition, a tensile stress means the case where a force is applied in the direction diverging to the outer side from the one point.

In general, when the refractory is heated, the surface tries to expand, and thus a new compressive stress, which is the opposite force, is generated. Therefore, when the residual stress on the surface of the high zirconia cast refractory is a compressive stress, the sum of the compressive stress due to heating and the compressive stress which is the residual stress acts on the surface of the high zirconia cast refractory. Therefore, even if the residual stress is relatively small, breakage or peeling tends to occur at the time of temperature rise. It is preferable that residual stress is small, and tensile stress is more preferable than compressive stress.

Japanese Unexamined Patent Application Publication No. 8-48573 discloses that peeling at the temperature rise can be prevented if the residual stress on the surface is 80 MPa or less in tensile stress or 50 MPa or less in compressive stress. However, in many products, small hole defects that occur when casting molten metal into a mold during manufacture exist near the surface. Compared with other dense parts, in the vicinity of small hole defects with weak strength, peeling at the temperature rise cannot be completely prevented even within the above residual stress range. Therefore, examination of the appropriate range rather than the thing of residual stress is needed.

Moreover, in the glass melting furnace where high zirconia casting refractory is used, there are many burner combustion type heating furnaces. Then, the burner is converted every few minutes, and the temperature of the cast refractory surface rises and falls every conversion. Therefore, cast refractory, which is often used for several years, receives a very large number of heating cycles. For this reason, high zirconia casting refractories stable against heat cycles have been demanded.

It is important that the stability to the heat cycle does not change even if the glass phase capable of absorbing the rapid volume change near 1150 ° C. of the zirconia crystal is subjected to the heat cycle. If zircon precipitates on the glass, the volume change of zirconia cannot be absorbed, and the residual volume expansion rate after a thermal cycle test may become large and a crack may arise. The remaining volume expansion ratio after the thermal cycle test and the stability of the glass phase have the following relationship.

When crystals such as zircon precipitate on the glass, the residual volume expansion ratio after the thermal cycle test exceeds 10%. On the other hand, the residual volume expansion ratio when the glass phase is stable is 10% or less. Therefore, the stability of a glass phase can be estimated by measuring a residual volume expansion rate.

Refractories with high electrical resistance are disclosed in Japanese Patent Laid-Open Nos. 63-285173, JP-A-4-193766, JP-A-8-48573, JP-A-8-277162, JP-A 10-59768, WO2005 It is proposed in / 068393.

Thermal cycle stability is proposed by Unexamined-Japanese-Patent No. 4-193766, 8-48573, and 8-277162.

Surface peeling prevention at the time of temperature rise is proposed by Unexamined-Japanese-Patent No. 8-48573 and 8-277162.

Japanese Unexamined Patent Publication No. 63-285173 does not contain Li ₂ O, Na ₂ O, CaO, CuO, MgO, or P ₂ O ₅ having a small ion radius, and is a type of K ₂ O, SrO, BaO, and Cs ₂ O. The high-electromagnetic-resistance high zirconia casting refractories characterized by containing at least 1.5% by weight or more are shown. However, in Japanese Unexamined Patent Publication No. 63-285173, although the electrical resistance is high, it does not contain CaO necessary for stabilization of the glass phase. Moreover, since it does not contain CaO, there existed a fault which is large in tension and will crack at the time of single side heating.

In Japanese Patent Laid-Open No. 4-193766, it contains 1 to 3% by weight of Al ₂ O ₃ , does not contain Na ₂ O, K ₂ O, and 0.3 to 3 weights of BaO, SrO, and CaO by one or more kinds. It has been proposed a high zirconia pole refractories stable to heat cycles with a high electric resistance, characterized by containing 0% to 1.5% by weight of ZnO.

However, in this Unexamined Patent Publication No. 4-193766, the content of Al ₂ O ₃ is high, the electrical resistance is insufficient, neither of Na ₂ O nor K ₂ O is contained, and thermal cycle stability is insufficient.

In Japanese Patent Laid-Open No. 8-48573, Na ₂ O is contained by 0.05% by weight or more, the total amount of BaO, SrO, and MgO is 0.05 to 3% by weight, stable to heat cycle by repeated heating, and surface peeling Small and high electrical resistance zirconia pole refractories are proposed. However, because the Na ₂ O it contains more than 0.05% by weight, a glass phase is stabilized, but the electric resistance was insufficient. Moreover, although alkaline-earth oxides, such as BaO, are contained, the upper limit of the content is too much at 3 weight%. Therefore, when it contains excessively, the residual expansion ratio becomes large and a problem arises in thermal cycling stability.

In addition, Japanese Patent Application Laid-Open No. 8-48573 proposes a tensile stress of 80 MPa or less and a compressive stress of 50 MPa or less as an appropriate range of residual stress, but the stress range is too wide, so that small hole-shaped defects are formed in the surface portion of the refractory. If present, it may lead to peeling at the temperature rise even within the range.

Japanese Patent Laid-Open No. 8-277162 discloses that Na ₂ O is 0.05% by weight or more, and the total amount of Na ₂ O and K ₂ O is 0.1 to 0.65% by weight, and the total amount of BaO, SrO, and MgO is 1.1. and 2.8% by weight in, zirconia and containing more than 0.2% by weight P ₂ O ₅ shows a pole refractory. The high zirconia pole refractories are stable to thermal cycles by repeated heating, have low surface peeling, and have electrical resistance. However, because the Na ₂ O it contains more than 0.05% by weight, a glass phase is stabilized, but the electric resistance was insufficient.

Japanese Unexamined Patent Publication No. 10-59768 proposes a high zirconia pole refractories that are stable to thermal cycles with high electric resistance that contains 0.05 wt% or more of Na ₂ O and K ₂ O and does not contain alkaline earth metal oxides such as BaO. .

However, in the Japanese Patent Application Laid-Open No. 10-59768 discloses, does not contain an alkaline earth metal oxide, it is necessary to be contained in order to stabilize the glass, more than 0.05% by weight of Na ₂ O. Therefore, electrical resistance was insufficient.

In WO2005 / 068393, a high zirconia pole refractories of high electrical resistance containing 0.8 wt% or more of Al ₂ O ₃ , less than 0.04 wt% of Na ₂ O, and less than 0.4 wt% of CaO have been proposed. However, the refractory material, since the Al ₂ O ₃ it contains at least 0.8% by weight, the electric resistance was insufficient.

Moreover, although CaO is a component which stabilizes glass, when it adds excessively, it produces | generates the zircon, and content requires a more careful restriction | limiting.

An object of the present invention is to provide a high zirconia cast refractories having stable high electric resistance characteristics that have little change with time at high temperature, are difficult to peel off at a temperature rise, and have thermal cycle stability.

When the high zirconia casting refractory material of this invention is illustrated, it is the high zirconia casting refractory material of Claims 1-7.

The high zirconia cast refractory of the present invention has an electrical resistance of 200 Ω · cm or more after holding at 1500 ° C. for 12 hours, and does not cause peeling during temperature rise, and is excellent in stability to heat cycle.

In particular, when the high zirconia cast refractory of the present invention is used in the melting furnace of glass, there is no peeling at the time of temperature rise and it has high electric resistance characteristics. Therefore, the glass products produced by this fusion furnace are free from defects, and long-term operation is possible, which is very advantageous industrially.

The present inventors have intensively studied a result, a high control the properties and the residual stress of the refractory surface in relation to the viscosity in the vicinity of 1000 ℃ of vitreous zirconia-cast refractory material, and more than 87% by weight of ZrO ₂ contained in the zirconia-cast refractory material 96 wt. % Or less, SiO ₂ 3 to 10% by weight, Al ₂ O ₃ to 0.1% to 0.8% by weight, Na ₂ O to less than 0.05% by weight, K ₂ O to 0.01% to 0.2% by weight 0.1% to 1.0% by weight of B ₂ O ₃ , 0.1% to 0.5% by weight of BaO, 0.05% to 0.05% by weight of SrO, 0.01% to 0.15% by weight of CaO, 0.05 to ₂ % of Y ₂ O ₃ By weight to 0.4% by weight, MgO by 0.1% by weight, Fe ₂ O ₃ + TiO ₂ by less than 0.3% by weight, by limiting to the range substantially free of (0.01% by weight or less) CuO and P ₂ O ₅ by , 1500 ℃, electrical resistance after holding for 12 hours is 200 Ω · cm or more, no peeling off during temperature rise, stable to heat cycle It was it possible to obtain a zirconia-cast refractory material.

More preferably, the ZrO ₂ contained in the high zirconia cast refractories is 88 wt% or more and 96 wt% or less as a high zirconia cast refractory in which the properties related to the viscosity near 1000 ° C. on the glass phase and the residual stress of the refractory surface are controlled. ₂ to 3% by weight to 9% by weight, Al ₂ O ₃ to 0.1% to 0.8% by weight, Na ₂ O to 0.04% by weight, K ₂ O to 0.01% to 0.15% by weight, B ₂ O ₃ to 0.1% to 0.7% by weight, BaO to 0.1% to 0.5% by weight, SrO to 0.05% by weight, CaO to 0.01% to 0.15% by weight, Y ₂ O ₃ to 0.05% to 0.2% 1500 ° C. by limiting the content to not more than 0.05% by weight, less than 0.05% by weight of MgO, less than 0.3% by weight of Fe ₂ O ₃ + TiO ₂ , and substantially free of (0.01% by weight or less) CuO and P ₂ O ₅ . High zirconia with a resistance of 200 Ω · cm or more after holding for 12 hours, no peeling off during temperature rise, and stable against thermal cycle It was possible to obtain cast refractory.

MEANS TO SOLVE THE PROBLEM In order to satisfy these simultaneously for the thermal cycling stability as a parameter of the long-term stable high electric resistance property at high temperature of high zirconia casting refractory, the stability to the repetition of temperature rise and temperature fall, and the peeling at the time of temperature rise, The content of a wide range of oxides such as alkali metal oxides, alkaline earth oxides, and alumina was examined in detail, and the following findings were obtained.

The amount of the glass phase in the high zirconia cast refractory is small, but the type and amount of the components constituting the glass phase influence each other, and the glass phase has a great influence on the properties of the high zirconia cast refractory.

That is, in the high zirconia cast refractories, it is necessary to significantly reduce Na ₂ O, which is an oxide of Na having a small ion radius, in order to improve the electrical resistance at high temperature. However, simply reducing Na ₂ O cannot satisfy thermal cycle stability and prevention of peeling at the time of temperature rise. Therefore, especially for Al ₂ O ₃ , K ₂ O, BaO, SrO, and CaO, by adding them in an appropriate range, it is possible to simultaneously satisfy long-term stable high electric resistance, high temperature cycle stability, and preventing peeling at elevated temperatures at high temperatures. I found that.

On the other hand, residual stress occurs on the surface of the product of the high zirconia casting refractory in the process of casting and slow cooling of a manufacturing process. Therefore, the residual stress is greatly influenced by the type of mold used and the slow cooling rate.

However, only by adjusting the conditions of casting and slow cooling, the kind and magnitude | size of residual stress cannot be controlled correctly. That is, even if casting conditions and slow cooling conditions are the same, if composition differs, what has a compressive stress as a residual stress and what has a tensile stress exists.

As a result of intensive studies focusing on the residual stress and the thermal properties of the high zirconia cast refractory glass, the temperature of the fracture state (1) and the glass phase of the high zirconia cast refractory The glass transition point (Tg) (2) of the glass of the same composition is closely related to the residual stress, and by controlling these (1) or (2), it is possible to produce a high zirconia cast refractory material that does not cause peeling at the temperature rise. I found it possible.

The high zirconia cast refractory has a different form of fracture in the low temperature range where the flexural strength is almost the same as the room temperature and the high temperature region where the flexural strength is extremely reduced with respect to hot bending strength measurement. In the low temperature region, brittle fracture is remarkable, and a soft wavefront is formed. In the high temperature region, the softening or flow of the grain boundary causes the fracture to change in the form of fracture accompanied by plastic deformation, resulting in a cracked tip. It shows a wavefront. And above the glass transition point of glass form, strength falls rapidly by the destruction with plastic deformation.

[Example]

1 shows the hot bending strength of Example 4 (Table 1) within the scope of the present invention and Comparative Example 4 (Table 2) outside the scope of the present invention. The change point of the breakage accompanied by plastic deformation from the brittle fracture of Example 4 is a bending strength of 60 MPa and a change temperature of 875 ° C, and is included in the scope of the present invention. The intensity | strength of the low temperature area below 600 degreeC of this sample is 122x10 <^-2> MPa, and the intensity | strength of the high temperature area of 1300 degreeC or more is 2x10 <^-2> MPa. These intermediate strengths are (122-2) ÷ 2 = 60 MPa, and the temperature corresponding to the bending strength is 875 ° C, which is almost the same as the measured value.

In addition, the change temperature of the bending strength of the comparative example 4 is 800 degreeC, and is outside the scope of the present invention.

The temperature equivalent to the intermediate intensity of Comparative Example 4, that is, (107-7) ÷ 2 = 50 MPa is 810 ° C, but is almost the same as the measured change temperature.

In this way, the change temperature of the fracture form of hot bending strength is approximately equal to the temperature corresponding to the intermediate strength of the value at the low temperature portion and the value of the high temperature portion of the bending strength, and the change temperature of the fracture form is estimated from the strength measurement. It is also possible.

In addition, the quantitative analysis of the glass phase of the sample shown in FIG. 1 was performed with EPMA (X-ray microanalyzer). Reagents were blended to obtain a glass of the same composition as the obtained analytical value, and the blend was heated and melted in a platinum crucible to prepare a glassy solid. The glass transition point (Tg) of this glass was measured with the thermal expansion meter. As a result, Tg of Example 4 was 890 degreeC, and Tg of Comparative Example 4 was 810 degreeC.

The viscosity of the glass to the glass transition point (Tg) is about 10 ¹³ to 10 ¹⁵ poise, and at a temperature higher than that, the viscosity decreases as the temperature increases, and the glass has fluidity.

Therefore, high glass transition point (Tg) means that the viscosity of glass is high even at high temperature.

In addition, among the oxides contained in the high zirconia cast refractories, Na ₂ O is the most reducing glass transition point of the SiO ₂ glass. Accordingly, it is the glass transition can be estimated viscosity to some extent by the Na ₂ O content.

In the process from the casting to the cooling of the high zirconia cast refractory, the relationship between the residual stress and the glass phase generated is estimated as follows.

The outer layer of the high zirconia cast refractory material considers the case where solidification is completed and an inner layer starts to solidify from now on. When the viscosity of the glass phase is low and there is sufficient fluidity near the transformation temperature (about 1000 ° C) of the zirconia crystal in the cooling process, the stress generated by the transformation of the zirconia crystal is relaxed by the flow of the glass. Therefore, the stress due to the transformation of the zirconia crystal does not affect the residual stress of the ingot. In this case, cooling further advances, and after the inner layer loses fluidity, the thermal stress based on the temperature difference between the outer layer and the inner layer accumulates, thereby generating residual stress. As a result, the residual stress on the surface of the high zirconia cast refractory becomes a compressive stress.

On the other hand, when the glass phase viscosity is high near the transformation temperature of the zirconia crystal in the cooling process and there is not sufficient fluidity, the stress generated by the transformation of the zirconia crystal is not sufficiently relaxed, and compressive stress is generated in the inner layer. In the outer layer, tensile stress occurs. In this case, cooling further advances, and the sum of the thermal stress based on the temperature difference between the inner layer and the outer layer and the stress generated at the transformation of the zirconia crystal described above becomes the residual stress. As a result, the residual stress on the surface of the high zirconia cast refractory becomes smaller compressive stress or tensile stress than when the glassy viscosity is low.

That is, in the hot bending strength measurement, if the change temperature and the glass transition point (Tg) of the form of fracture are about 800 ° C. and about 810 ° C., respectively, the viscosity near the glass phase of the high zirconia cast refractory is 1000 ° C., and the surface of the product is low. The residual stress of becomes a compressive stress and becomes a residual stress outside the appropriate range of the present invention.

On the other hand, when the change point and the glass transition point (Tg) of the form of fracture in hot bending strength measurement are about 875 ° C and 890 ° C, respectively, as is apparent from Tables 1 and 2, which will be published later, in the high zirconia cast refractory body The viscosity near 1000 degreeC of the glassy phase of a glass is high, and the residual stress of the surface of a product turns into tensile stress, and becomes a residual stress within the appropriate range of this invention.

In this way, by controlling the characteristics related to the viscosity of the glass phase (particularly, the viscosity of the glass phase around 1000 ° C.), the residual stress of the high zirconia cast refractory can be controlled.

In the present invention, attention has been paid to the temperature and the glass transition point at which the form of fracture in the hot bending strength measurement changes, but to pay attention to the indicators of other thermal properties, for example, strain points, the scope of the present invention. Included in

The high zirconia cast refractory is a mixture of zirconia crystal and glass phase.

And the electrical resistance of zirconia is remarkably low compared with the silica which is a main component of a glass phase.

Therefore, in order to increase the electrical resistance of the high zirconia cast refractory, it is necessary to increase the amount of the glass phase in the high zirconia cast refractory or approach the glass phase to a high purity silica glass composition having high electrical resistance.

The amount of glass phase is opposite to the amount of zirconia, and the upper limit of SiO ₂ in terms of corrosion resistance is limited to 10% by weight.

In addition, in order to reduce the high electric resistance of the glass phase, alkali ions having a small ion radius, particularly Na ₂ O, are reduced as much as possible. As a result, the glass transition point Tg of the glass phase increases, and the electrical resistance also increases.

For example, the Tg of Na ₂ Si ₂ O ₅ , which is a glass having a molar ratio 1: 2 of Na ₂ O and SiO ₂ , is 732 ° C., but the Tg of SiO ₂ that does not contain Na ₂ O is 1463 ° C., and thus the electrical resistance Also increases significantly.

However, if the Na ₂ O is simply reduced, the glass transition point Tg and the electrical resistance increase, but the increase in the residual volume expansion rate or the thermal increase due to the formation of cracks during the product manufacture or the formation of zircon after the thermal cycle test occurs. Adequacy of residual stress for preventing cracks cannot be satisfied at the same time.

Therefore, the Na ₂ O content, which has a strong effect on the electrical resistance, is limited to the minimum amount, and A1 ₂ O ₃ , BaO, CaO, Y ₂ , which are important for stabilization of B ₂ O ₃ or glass necessary for crack prevention during manufacturing, are required. O _3, it has become possible that high electrical resistance by nine people intensive studies by the appropriate range of the content, such as SrO.

FIG. 2 shows the change over time of the electrical resistance during the holding at 1500 ° C. of Example 4 in Table 1 and Comparative Example 9 in Table 2. FIG.

In FIG. 2, the electrical resistance of Example 4 is stable, but the electrical resistance of Comparative Example 9 increases with time.

3 is a micrograph of Example 4 after holding at 1500 ° C. for 12 hours. A glass phase is observed at the grain boundary of the granular zirconia crystal. The dark, thin, long-looking part is glassy.

4 is a photomicrograph of Comparative Example 9 after holding at 1500 ° C. for 12 hours. It can be seen that a small zircon granular crystal exists as a point on the grain boundary of the granular zirconia crystal.

In Example 4, even after holding at 1500 ° C. for 12 hours, no zircon was produced, and the electrical resistance value was stable.

However, in Comparative Example 9, since the SiO ₂ content is high, the electrical resistance at the time of 1500 degreeC temperature rise is high, and since zircon is produced | generated from a glass phase with time, electrical resistance is further increasing. In Comparative Example 9, the electrical resistance was high, but zircon was easily produced, and the sample was powdered after the thermal cycle test.

In Example 4, the electrical resistance was stable, after the thermal cycle test, the residual volume expansion ratio was small, and no zircon was produced.

Next, each component of the high zirconia casting refractory body of this invention is demonstrated.

The content of ZrO ₂ is not less than 87% by weight to 96% by weight or less. More preferably, they are 88 weight% or more and 96 weight% or less. If the amount of ZrO ₂ is less than 87% by weight, the corrosion resistance is inferior. If the amount of ZrO ₂ is more than 96% by weight, the balance with other components is broken, and cracks are likely to occur in the refractory.

The content of SiO ₂ is not less than 3% by weight of 10% or less. More preferably, they are 3 weight% or more and 9 weight% or less.

Less than 3% by weight makes it difficult to form a sufficient glass phase in the refractory. The more silica, the more the electrical resistance can be improved, but more than 10% by weight of the refractory to the molten glass of the refractory, while at the same time increasing the oozing out of the refractory from the refractory under high temperature.

The content of B ₂ O _3, is at least 0.1% by weight 1.0% by weight or less. More preferably, they are 0.1 weight% or more and 0.7 weight% or less. When B ₂ O ₃ is less than 0.1% by weight, it is not possible to prevent the occurrence of cracking due to tearing when producing the product. If it is more than 1.0% by weight, the residual volume expansion after the thermal cycle test is close to 20%, and the tensile stress increases, and cracking occurs in a one-sided heating test in which one side of the high zirconia cast refractory of 100 × 300 × 300 mm is heated by an electric furnace. .

The content of Al ₂ O ₃ is less than 0.8% by weight 0.1% by weight or more. Al ₂ O ₃ has the effect of improving the fluidity of the melt of the blended composition, making it easier to cast, and suppressing the dissolution of ZrO ₂ in the refractory in the glass phase, thereby not producing zircon in the glass.

If the content of Al ₂ O ₃ is less than 0.1% by weight, the residual volume expansion ratio after the heat cycle test is about 30%, resulting in poor thermal cycle stability of the refractory. At 0.8% by weight or more, the thermal cycle stability is improved, but the electrical resistance is remarkably lowered.

In addition, Al ₂ O ₃ has the effect of increasing the compressive stress of the surface of the high zirconia cast refractory.

The content of Na ₂ O is less than 0.05% by weight. More preferably less than 0.04% by weight. At 0.05% by weight or more, the electrical resistance of the refractory drops rapidly. In addition, Na ₂ O has an effect of rapidly lowering the glass transition point temperature (Tg) of the glass phase and an effect of increasing the compressive stress of the refractory.

The content of K ₂ O is 0.01 wt% or more and 0.2% or less. More preferably, they are 0.01 weight% or more and 0.15 weight% or less. K ₂ O in the case of the present invention limit the Na ₂ O content is, K ₂ O is an essential component. If K ₂ O is less than 0.01% by weight (that is, substantially free), the residual volume expansion rate of the refractory after the heat cycle test is very large, and thermal cycle stability is inferior. When more than 0.2 wt%, the electrical resistance of the refractory becomes insufficient.

In addition, K ₂ O, like Na ₂ O, has an effect of increasing the compressive stress of the refractory.

BaO is a component which stabilizes a glass phase, and is an essential component in this invention.

Content of BaO is 0.1 weight% or more and 0.5 weight% or less. When less than 0.1 weight%, the residual volume expansion rate after the heat cycle of a refractory material is large, and it falls in heat cycle stability. If it exceeds 0.5% by weight, the electrical resistance decreases, and the residual volume expansion ratio after the heat cycle also increases, resulting in poor thermal cycle stability.

Content of SrO is less than 0.05 weight%. SrO has a great effect of preventing cracks in the shape of the refractory, but at 0.05% by weight or more, the electrical resistance of the refractory becomes insufficient.

The content of CaO is 0.01% by weight or more and 0.15% by weight or less. CaO, like BaO, stabilizes the glass phase. CaO exists as an impurity in a zirconia raw material, and is an essential component in this invention.

When CaO is not contained, tensile stress becomes large and peeling arises at the time of single side heating. However, when the CaO contained in the refractory is more than 0.15% by weight, the residual volume expansion ratio after the heat cycle heating of the refractory becomes large, and in extreme cases, the refractory becomes powdered.

The content of Y ₂ O ₃ is at least 0.05% by weight to 0.4% by weight or less. More preferably, they are 0.05 weight% or more and 0.2 weight% or less. Y ₂ O ₃ exists as an impurity in the zirconia raw material. However, if it exceeds 0.4% by weight, the residual volume expansion ratio after the heat cycle heating of the refractory becomes large, and thermal cycling stability falls, and electrical resistance also falls.

Content of MgO is 0.1 weight% or less. More preferably, it is 0.05 weight% or less. MgO exists as an impurity in zirconia raw materials. When it exceeds 0.1 weight%, the residual volume expansion rate after heat cycle test of refractory becomes large, and thermal cycle stability falls.

The content of the total amount of Fe ₂ O ₃ and TiO ₂ is not more than 0.3% by weight. Fe ₂ O ₃ and TiO ₂ are present as impurities in the raw materials, but it affects the cleavage at the time of production, it is preferably not more than 0.3% by weight.

P ₂ O ₅ and CuO are not substantially contained in the present invention. When P ₂ O ₅ and CuO coexist with B ₂ O ₃ , there is a property of forming a low melting glass and extremely reducing chemical durability. In addition, P ₂ O ₅ significantly lowers the stability of the refractory to the heat cycle. Moreover, the hygroscopicity by these raw materials is large, and when used for a raw material, there exists a property which is hard to produce a compact refractory material.

CuO is effective in reducing the fragmentation of the refractory, but is preferably substantially free from the point of coloring the molten glass.

In the present invention, the term "substantially free" means less than 0.01% by weight, depending on the degree of analysis and analytical instruments.

The high zirconia cast refractory material of each Example and the comparative example mentioned above was created by the conventional method.

That is, SiO ₂ , Al ₂ O ₃ , Na ₂ O, B ₂ O ₃ , and other powder raw materials are added to a zirconia raw material obtained by de-silifying zircon sand in a predetermined ratio, and after mixing them, the molten metal is melted in an arc electric furnace, Casting was carried out to the prepared mold, embedded in alumina powder, and cooled slowly to room temperature.

The mold was made of graphite, and the product part had a dimension of 100 × 300 × 350 mm and integrally connected a hot water part having an external dimension of 140 × 235 × 350 mm to the upper portion thereof.

After slow cooling, the product was taken out of the alumina powder, and the product portion was separated from the hot water portion to obtain a desired high zirconia cast refractory body. At that time, the presence or absence of the appearance crack was confirmed.

Table 1 shows the composition and properties of the high zirconia cast refractory of Example 1 to Example 10.

In addition, the composition and the characteristics of the high zirconia cast refractory of 15 in the comparative example 1 are shown in Table 2.

Each component in Table 1 and Table 2 is a weight% unit. For the analysis of the respective components is, K ₂ O, Na ₂ O, for yeomgwang method _{(炎光法), P 2} O 5, for the absorption method, the other components was carried out by ICP. However, the present invention is not limited to this analysis method, and other analysis methods can also be performed.

The measurement of the glass transition point first performed the glass phase analysis of the high zirconia casting refractory body by EPMA. And the glass of the same composition was melt | dissolved and cooled in the platinum crucible. The glass ingot was processed into a sample having a diameter of 8 mm and a length of 20 mm. Then, a load of 5 gf was applied to the sample, the temperature was raised from 5 ° C. to 1100 ° C. per minute, and the change point of the expansion ratio was measured as Tg.

The hot bending strength cuts the high zirconia cast refractory material into thickness 10 x width 20 x length 100 mm, raises the temperature at a heating rate of 5 ° C. per minute in an electric furnace of a silicon carbide heating element, and maintains it for at least 10 minutes after reaching the set temperature. Then, the flexural strength was measured. The number of samples is three each.

Residual stress was measured by the punching method using a strain gauge about the residual stress of 6 measuring points in the surface of a sample of 100x300x300mm.

This measuring method is based on the SOET and VANCROMBURGGE methods described in Komedanimu's book, `` Generation and Countermeasures of Residual Stresses '' issued by Yang Hyundang. First, one surface of 300 x 300 mm of the sample was polished about 3 mm from the surface. The polished surface was observed, and the epoxy resin was filled in pores which interfered with bonding the strain gauge to obtain a smooth surface.

Next, three strain gauges (Kyowa Electric Strain Gages) were attached to this smooth surface with one portion of the measuring point by epoxy resin. The strain gauge uses a self-temperature-guaranteed gauge suitable for the thermal expansion rate of high zirconia casting refractory, and connects a line with a measuring device by a 3-wire connection method. Since the self temperature guarantee type gauge reduces the apparent deformation caused by the temperature change of the measurement sample, the measurement error can be reduced. In addition, the three-wire connection method is preferable because the apparent deformation caused by the temperature change of the lead wire can be removed as compared with the two-wire connection method conventionally used. This strain gauge was rectangular, and affixed so that the center line of this longitudinal direction might be angle | corner of 120 degree mutually. And the strain which arises by making a 25 mm diameter penetrating hole at the position where this centerline crosses is measured with a measuring instrument (UCAM-20A manufactured by Kyowa Electric Co., Ltd.), and a residual stress is computed by rosette analysis using the value. It was. Residual stress is a positive number (integer) in the case of tensile stress, and a negative number in the case of compressive stress. The larger the negative number, the greater the compressive stress.

In the single-sided heating test, a sample of 100 × 300 × 300 mm was installed in an electric furnace so that a surface of 300 × 300 mm was in the furnace and the opposite side was in contact with outside air. The temperature was raised from 100 degreeC to 1000 degreeC every minute, and it measured about the presence or absence of the crack at the time of temperature rise.

The thermal cycle stability cut out the 50x50x50mm sample from the bottom part of the 100x300x300mm sample. The sample is inserted into an electric furnace, and the temperature is raised to 800 ° C. at 3 ° C. per minute and maintained for 1 hour. Thereafter, the temperature is increased to 3 ° C. at 1200 ° C. per minute and maintained for 1 hour. Then, it cools to 3 degreeC every minute to 800 degreeC. Then, this 800 degreeC and 1200 degreeC heat cycles were repeated 45 times, and after slow cooling, the presence or absence of the crack and powdering was observed. Subsequently, the volume change before and after the heat cycle test was measured, and the remaining volume expansion ratio was calculated.

In addition, zircon is produced when the residual volume expansion ratio exceeds 10% in the thermal cycle test. And, the larger the residual volume expansion rate, the larger the amount of zircon produced. In the comparative example of Table 2 in which zircon generated the residual volume expansion ratio exceeding 10% by the thermal cycle test, the electrical resistance measurement value increased with time as in Comparative Example 9 of FIG. 2, and the stability of the change over time was improved. Falling.

Electrical resistance was measured by the 4-terminal method according to JISR1650-2. From the sample, a 19 mm diameter drill core is taken out and cut into lengths of 30 mm. The grooves were carved into the surface of the 5 mm portion from both ends, and then ultrasonically cleaned and dried with a drier. After drying, a platinum plate is installed at both ends of the sample, and a platinum wire is wound around the groove to serve as a terminal, and a constant voltage is generated from a 60 Hz AC function generator to set the sample and the same resistance as the sample. The voltage across one standard resistor was measured, and the electrical resistance value of the sample was obtained from the obtained voltage value. The measurement was performed by raising the temperature to 1500 ° C. at a temperature increase rate of 4 ° C. per minute and maintaining it for 12 hours. The electrical resistance value when it reached 1500 degreeC was measured, and it confirmed that the electrical resistance value after holding for 12 hours was a stable value continuously. And the electrical resistance measurement value after 12-hour hold was calculated | required as electrical resistance value of 1500 degreeC.

Example 1 to Example 10 shown in Table 1 are in the scope of the present invention.

Comparative Example 1 shown in Table 2 corresponds to the examples of the invention described in WO2005 / 068393. In general, the zirconia material, a Y ₂ O ₃ is contained about 0.1% by weight as an impurity. In WO2005 / 068393, the description of BaO and K ₂ O is not clear, but considering the total amount and the Y ₂ O ₃ content of the analytical value of the example of WO2005 / 068393, these products do not contain K ₂ O or BaO. Will not.

In Comparative Example 1, Na ₂ O was small, but Al ₂ O ₃ was large, resulting in insufficient electrical resistance.

Further, Na ₂ O is small, Moreover, since K ₂ O and BaO are not contained, a large residual volume expansion coefficient after the thermal cycle test, it lacks stability with respect to heat cycle.

Comparative Example 2 is an example in which Al ₂ O ₃ and B ₂ O ₃ are few. A crack occurred at the time of manufacture. The electrical resistance was high, but cracks occurred and powdered after the thermal cycle test.

Comparative Example 3 is a case where there are many A1 ₂ O ₃ , Na ₂ O and there are few B ₂ O ₃ . A crack occurred at the time of manufacture. In addition, there is stability of the thermal cycle test, but the electrical resistance is low.

Comparative Example 4 is a case where there are many Na ₂ O and B ₂ O ₃ . The compressive stress was large and a crack occurred after the one-sided heating test. The residual volume expansion ratio after the heat cycle test is also large and the electrical resistance is low.

Comparative example 5 is an example with many K ₂ O. The electrical resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is insufficient.

Comparative Example 6 is an example of many BaO. The electrical resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is insufficient.

Comparative Example 7 is an example in which K ₂ O and Na ₂ O are few. Viscosity was high at the time of manufacture, and the product became the hollow shape. Although the electrical resistance is high, the residual volume expansion ratio after the heat cycle test is also large, and it is powdered, and the stability to the heat cycle is insufficient.

Comparative Example 8 is an example in which there is little BaO and many SrO and Y ₂ O ₅ . Low electrical resistance and lack of stability to heat cycle.

Comparative Example 9 is an example containing less ZrO ₂ , more SiO ₂ , and containing P ₂ O ₅ . High electrical resistance but lack of stability over time. In addition, the residual volume expansion ratio after the thermal cycle test was large and powdered.

Comparative Example 10 is an example corresponding to the example of Japanese Patent Laid-Open No. 8-277162 described above, which contains a lot of Na ₂ O, MgO, and SrO, contains P ₂ O ₅ . The electrical resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is insufficient.

Comparative Example 11 is an example corresponding to Examples of Japanese Patent Application Laid-Open No. 8-48573 having many Na ₂ O and BaO.

Low electrical resistance

In Comparative Example 12, there are many examples of CaO and Fe ₂ O ₃ + TiO ₂ . The electrical resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is insufficient.

Comparative Example 13 is an example that does not contain Na ₂ O and corresponds to the example of Japanese Patent Application Laid-Open No. 63-285173. Although the electrical resistance was high, the tensile stress was large and cracks occurred in one-sided heating. The residual volume expansion ratio after the heat cycle test was also large and powdered.

Comparative Example 14 is an example in which there are many Al ₂ O ₃ , BaO, CaO, and Na ₂ O, K ₂ O is not contained, and it is an example corresponding to the Example of Unexamined-Japanese-Patent No. 4-193766. It has low electrical resistance and lacks stability against heat cycle.

Comparative Example 15 is an example that contains many Na ₂ O and does not contain alkaline earth oxide, and is an example corresponding to the examples of JP-A-10-59768. Low electrical resistance Moreover, the compressive stress was large and the crack generate | occur | produced by single side heating. The remaining volume expansion ratio after the heat cycle test is also large, and the stability to the heat cycle is insufficient.

According to the present invention, there is provided a high zirconia cast refractories which have no peeling at a temperature rise, particularly at around 500 ° C., are stable, particularly have excellent thermal cycle stability, and remarkably improve the electrical resistance characteristics at high temperatures. High zirconia cast refractory is suitable for glass melting furnaces.

Claims (7)

As high control the properties and the residual stress of the refractory surface in relation to the viscosity in the vicinity of 1000 ℃ of vitreous zirconia-cast refractory material, as chemical components, and ZrO ₂ is less than 96 wt% or more and 87% by weight and a Al ₂ O ₃ 0.1% by weight Less than 0.8 wt%, SiO ₂ 3 wt% or more and 10 wt% or less, Na ₂ O less than 0.05 wt%, K ₂ O is 0.01 wt% or more and 0.2 wt% or less, B ₂ O ₃ is 0.1 wt% or more 1.0 0.1 wt% or less, 0.5 wt% or less of BaO, 0.05 wt% or less of SrO, 0.01 wt% or more and 0.15 wt% or less of CaO, 0.05 wt% or more and 0.4 wt% or less of Y ₂ O ₃ , and 0.1 wt% of MgO. Less than 0.01% by weight, the total amount of Fe ₂ O ₃ and TiO ₂ is 0.3% by weight or less, P ₂ O ₅ and CuO is less than 0.01% by weight, high zirconia casting, characterized in that the electrical resistance after holding for 12 hours at 1500 ℃ is 200Ωcm or more Refractory. As high control the properties and the residual stress of the refractory surface in relation to the viscosity in the vicinity of 1000 ℃ of vitreous zirconia-cast refractory material, as chemical components, and ZrO ₂ is less than 96 wt% or more and 88% by weight and a Al ₂ O ₃ 0.1% by weight Not less than 0.8% by weight, more than 3% by weight of SiO ₂ and not more than 9% by weight, less than 0.04% by weight of Na ₂ O, not less than 0.01% and not more than 0.15% by weight of K ₂ O, not less than 0.1% and not less than 0.7% by weight of B ₂ O _3. Less than or equal to 0.1% by weight, less than or equal to 0.5% by weight of BaO, less than 0.05% by weight of SrO, 0.01% to 0.15% by weight of CaO, 0.05% to 0.2% by weight of Y ₂ O ₃ , 0.05% to 0.2% by weight of MgO Less than 0.01% by weight, the total amount of Fe ₂ O ₃ and TiO ₂ is 0.3% by weight or less, P ₂ O ₅ and CuO is less than 0.01% by weight, high zirconia casting, characterized in that the electrical resistance after holding for 12 hours at 1500 ℃ is 200Ωcm or more Refractory. The high zirconia cast refractory according to claim 1 or 2, wherein the residual stress on the surface is a tensile stress of 30 MPa or less and a compressive stress of 20 MPa or less. The high zirconia cast refractory according to claim 1 or 2, wherein the temperature of changing from brittle fracture to fracture involving plastic deformation in the hot bending test is 850 占 폚 to 950 占 폚. The high zirconia cast refractory according to claim 1 or 2, wherein the glass transition point (Tg) in the glass phase in the high zirconia cast refractory is 850 to 950 ° C. The high zirconia cast refractory according to claim 1 or 2, wherein the residual volume expansion ratio after the heat cycle test is 10% or less. The high zirconia cast refractory according to claim 1 or 2, wherein the electrical resistance after holding at 1500 DEG C for 12 hours is 250? Cm or more.

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