TWI403487B - High-electric resistivity, high-zirconia fused cast refractories - Google Patents

Abstract

This invention provides a high zirconia cast refractory having a stable high electric resistance with less change in aging at a high temperature and a heat cycle stability with difficulty in being peeled off in raising a temperature. The high zirconia cast refractory whose property relating to the viscosity of a glass phase at a temperature of around 1,000 DEG C and residual stress at the surface of the refractory are controlled contains ZrO2 of 87-96 wt.%, Al2O3 of ≥ 0.1 and < 0.8 wt.%, SiO2 of 3-10 wt.%, Na2O of < 0.05 wt.%, K2O of 0.01-0.2 wt.%, B2O3 of 0.1-1.0 wt.%, BaO of 0.1-0.5 wt.%, SrO of < 0.05 wt.%, CaO of 0.01-0.15 wt.%, Y2O3 of 0.05-0.4 wt.%, MgO of ≤ 0.1 wt.%, and Fe2O3 and TiO2 in total of ≤ 0.3 wt.%, but substantially does not contain P2O5 and CuO. Its electric resistance after being kept at 1,500 DEG C for 12 h is 200 &OHgr;cm or above.

Description

High resistance and high zirconia cast refractory

The present invention relates to a high zirconia cast refractory suitable for a glass melting furnace, which is characterized in that it does not cause peeling at a temperature rise especially at around 500 ° C, and is stable, particularly excellent in thermal cycle stability, and resistance characteristics at high temperatures. A significantly improved high zirconia cast refractory is obtained.

Previously, a large amount of cast refractories containing ZrO ₂ (zirconia or zirconia) has been used as a refractory for glass melting furnaces. The reason for this is that ZrO ₂ is a metal oxide having particularly high corrosion resistance to molten glass. For example, a high zirconia cast refractory containing 80% by weight or more of ZrO ₂ is used as such a cast refractory.

In the high zirconia cast refractory, the content of ZrO ₂ is high and the structure is dense, so that it has a large corrosion resistance with respect to all kinds of molten glass. Further, it has an excellent feature that it does not cause defects such as stones or ribs in the molten glass because it has a property of not forming a reaction layer at the interface with the molten glass. Therefore, high zirconia cast refractory systems are particularly suitable for the manufacture of high quality glass refractories.

The mineral structure of the high zirconia cast refractory is constructed in such a manner that monoclinic zirconia crystals occupy most of it, and a small amount of glass phase fills the grain boundaries of the zirconia crystal.

On the other hand, it is known that zirconia crystals cause reversible transformation of monoclinic and orthorhombic systems with a sharp volume change at around 1150 °C. By the flow of the glass phase, the stress generated by the volume change caused by the transformation of the zirconia is alleviated, whereby the high zirconia cast refractory which does not cause cracking at the time of manufacture can be produced in a production grade.

However, the amount of the glass phase in the high zirconia cast refractory is small, but the characteristics of the high zirconia cast refractory are greatly affected depending on the kind or amount of the components constituting the glass phase.

Further, it can be seen that if the high zirconia cast refractory is subjected to a thermal history, the cerium oxide of the glass phase reacts with zirconia to form zircon. An alkali metal oxide such as Na ₂ O or BaO or an alkaline earth oxide is added to suppress the glass phase to be a stable glass phase.

Recently, in the case of an alkali-free glass such as a liquid crystal display (LCD), in order to improve the characteristics, a glass having a higher electric resistance than the previous composition is used. Therefore, it is also required that the high zirconia cast refractory as the material in the furnace of the glass melting kiln is a high-resistance product.

However, it has been clarified that the resistance of the previous high-resistance product is raised to a specific temperature or measured at a specific temperature for several hours, and the stability or sustainability of the value is problematic.

There is also a case where the resistance increases as the holding time becomes longer. Specifically, there is a case where the electric resistance immediately after the temperature rise to 1500 ° C and after 12 hours is maintained, the electric resistance after 12 hours is increased to 160% of the electric resistance immediately after the temperature rise. The reason for this is that zircon precipitates into the glass phase, and the electric resistance increases as zircon precipitates.

As such, the precipitation of zircon is advantageous in terms of electric resistance. However, it is a cause of cracking or chalking in the heat cycle test described later, and therefore it is not preferable for the high zirconia cast refractory.

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

Moreover, when a glass melting furnace is built using a high zirconia cast refractory, the following accident may occur: the corner portion of the high zirconia cast refractory is broken and flew out during the heating process after the furnace is built, or One part of the surface of the high zirconia cast refractory which is the inner surface of the furnace is a shell-like peeling.

When such a high zirconia cast refractory is damaged, the damaged portion becomes very weak to the molten glass. Therefore, there is a problem that defects such as stones or ribs are generated in the molten glass.

Regarding the peeling at the time of temperature rise, it is known that it is largely affected by the residual stress on the surface of the product. There are two kinds of residual stresses, and in the case of a product, as a residual stress, there are cases of residual tensile stress and residual compressive stress. The term "compressive stress" refers to a situation in which a force is applied in a direction concentrated at a point of the refractory. Further, the term "tensile stress" refers to a case where a force is applied in a direction in which it is diverged outward from the point.

In general, when the refractory is heated, since the surface expands, a force opposite thereto, that is, a compressive stress is newly generated. Therefore, when the residual stress on the surface of the high zirconia cast refractory is a compressive stress, the resultant force of the compressive stress due to heating and the compressive stress as the residual stress acts on the surface of the high zirconia cast refractory. Thereby, even if the residual stress is relatively small, it is easy to cause cracking or peeling at the time of temperature rise. It is preferred that the residual stress is small and the residual stress is a compressive stress rather than a tensile stress.

Japanese Patent Publication No. 8-48573 discloses that if the residual stress on the surface is a tensile stress of 80 MPa or less or a compressive stress of 50 MPa or less, peeling at the time of temperature rise can be prevented. However, for most articles, small hole-like defects generated during the casting of the molten metal in the mold for casting are present near the surface at the time of manufacture. Compared with other dense portions, in the vicinity of the small-pore defects having weak strength, even in the range of the above residual stress, peeling at the time of temperature rise cannot be completely prevented. Therefore, a more appropriate range of residual stress must be studied.

Further, in the case of a glass melting furnace using a high zirconia cast refractory, a burner-type heating furnace is often used. Moreover, the burner is switched every few tens of minutes, and the temperature of the surface of the cast refractory fluctuates up and down each time it is switched. Therefore, most of the cast refractories used for several years will be subjected to a very many heating cycles. Therefore, there is a need for high zirconia cast refractories that are relatively stable to thermal cycling.

As far as the stability of the thermal cycle is concerned, it is important that the glass phase which can absorb the sharp volume change of the zirconia crystal at around 1150 ° C does not change even if it is subjected to thermal cycling. When zircon is precipitated in the glass phase, the volume change of zirconia cannot be absorbed, and the residual volume expansion ratio after the heat cycle test becomes large, and cracks occur. Further, there is the following relationship between the residual volume expansion ratio after the heat cycle test and the stability of the glass phase.

When the crystal of zircon or the like is precipitated into the glass phase, the residual volume expansion ratio after the heat cycle test exceeds 10%. On the other hand, when the glass phase is relatively stable, the residual volume expansion ratio is 10% or less. Therefore, the stability of the glass phase can be inferred by measuring the residual volume expansion ratio.

A refractory having a high electric resistance is disclosed in Japanese Laid-Open Patent Publication No. SHO63-285173, Japanese Patent Application Laid-Open No. Hei No. Hei No. Hei No. Hei No. Hei No. Hei. It is disclosed in Japanese Laid-Open Patent Publication No. Hei 10-59768, No. WO 2005/068393.

The thermal cycle stability is disclosed in Japanese Patent Laid-Open No. Hei 4-193766, Japanese Patent Application Laid-Open No. Hei No. 8-48573, and Japanese Patent Application No. Hei 8-277162.

The surface peeling at the time of the temperature rise is disclosed in Japanese Laid-Open Patent Publication No. Hei 8-48573, and Japanese Patent Application Laid-Open No. Hei 8-277162.

Japanese Patent Publication No. Sho 63-285173 discloses a high-resistance high-zirconia cast refractory characterized in that it does not contain Li ₂ O, Na ₂ O, CaO, CuO, MgO, P ₂ having a small ionic radius. In the case of O ₅ , one or more of K ₂ O, SrO, BaO, and Cs ₂ O are contained in an amount of 1.5% by weight or less. However, in the disclosure of Japanese Laid-Open Patent Publication No. SHO63-285173, although the electric resistance is high, CaO which is necessary for stabilization of the glass phase is not contained. Further, since CaO is not contained, there is a disadvantage that the tension is large and cracking occurs upon heating on one side.

A high-zirconia electroformed refractory having high electrical resistance and stable to thermal cycling is disclosed in Japanese Laid-Open Patent Publication No. Hei-4-193766, which is characterized in that it contains 1 to 3% by weight of Al ₂ O ₃ , It contains Na ₂ O and K ₂ O, and contains 0.3 or more by weight of one or more of BaO, SrO, and CaO, and contains 0 to 1.5% by weight of ZnO.

However, in the disclosure of Japanese Laid-Open Patent Publication No. Hei-4-193766, the content of Al ₂ O ₃ is high, the electric resistance is not sufficient, and it does not contain any of Na ₂ O and K ₂ O, so the thermal cycle Stability is not sufficient.

Japanese Laid-Open Patent Publication No. Hei 8-48573 discloses a high zirconia electroformed refractory containing 0.05% by weight or more of Na ₂ O, and a total amount of BaO, SrO, and MgO is 0.05 to 3% by weight. Moreover, the thermal cycle for repeated heating is relatively stable, and thus the surface peeling is small and has high electrical resistance. However, since it contains 0.05% by weight or more of Na ₂ O, although the glass phase becomes stable, the electrical resistance is not sufficient. Further, although an alkaline earth oxide such as BaO is contained, the upper limit of the content is too large and is 3% by weight. Therefore, when it is contained in excess, the residual expansion ratio becomes large, and there is a problem in thermal cycle stability.

Further, in Japanese Laid-Open Patent Publication No. Hei 8-48573, it is proposed that the tensile stress is 80 MPa or less and the compressive stress is 50 MPa or less as an appropriate range of residual stress. However, if the range of stress is too wide, there are the following cases: If a small hole-like defect is present on the surface portion of the refractory, peeling at the time of temperature rise occurs even in the range.

Japanese Laid-Open Patent Publication No. Hei 8-277162 discloses a high zirconia electroformed refractory containing 0.05% by weight or more of Na ₂ O and a total content of Na ₂ O and K ₂ O of 0.1 to 0.65 by weight. %, the total amount of BaO, SrO, and MgO is 1.1 to 2.8% by weight, and contains 0.2% by weight or less of P ₂ O ₅ . The high zirconia electroformed refractory is relatively stable to the thermal cycle of repeated heating, and further, has less surface peeling and high electrical resistance. However, since it contains 0.05% by weight or more of Na ₂ O, although the glass phase becomes stable, the electrical resistance is not sufficient.

Japanese Laid-Open Patent Publication No. Hei 10-59768 discloses a high-zirconia electroformed refractory having high electrical resistance and stable to thermal cycle, which contains 0.05% by weight or more of Na ₂ O and K ₂ O, Contains an alkaline earth metal oxide such as BaO.

However, in the disclosure of Japanese Laid-Open Patent Publication No. Hei 10-59768, since the alkaline earth metal oxide is not contained, the content of Na ₂ O must be 0.05% by weight or more in order to stabilize the glass. Therefore, the resistance is insufficient.

In WO 2005/068393, there is disclosed a high zirconia electroformed refractory having a high electrical resistance comprising 0.8% by weight or more of Al ₂ O ₃ , containing less than 0.04% by weight of Na ₂ O, and containing less than 0.4 weight. % CaO. However, since the content of Al ₂ O ₃ in the refractory is 0.8% by weight or more, the electric resistance is insufficient.

Further, CaO is a component which stabilizes the glass. However, if it is excessively added, it promotes the formation of zircon, and therefore it is necessary to more precisely limit the content.

An object of the present invention is to provide a high zirconia cast refractory having high resistance characteristics which are less stable at a high temperature and stable, which is difficult to peel off at the time of temperature rise and which has thermal cycle stability.

If the high zirconia cast refractory of the present invention is exemplified, it is a high zirconia cast refractory according to claims 1-7.

The high zirconia cast refractory of the present invention has a resistance of 200 Ω cm or more after being kept at 1500 ° C for 12 hours, does not cause peeling during heating, and is excellent in stability against thermal cycling.

In particular, when the high zirconia cast refractory of the present invention is used in a glass melting furnace, peeling does not occur at the time of temperature rise, and high resistance characteristics are obtained. Therefore, the glass product produced by the melting furnace has no defects and can be used for a long period of time, which is very advantageous in the industry.

As a result of intensive research by the inventors of the present invention, a high zirconia cast refractory having properties relating to the viscosity of the glass phase at around 1000 ° C and residual stress on the surface of the refractory is provided, and the high zirconia is cast and fire resistant. each of the components contained in the composition is limited to the following range, i.e., ZrO ₂ less than 87 wt%, 96 wt%, SiO ₂ less than 3 wt%, 10 wt% or less, Al ₂ O ₃ is 0.1 wt% or more Less than 0.8% by weight, Na ₂ O is less than 0.05% by weight, K ₂ O is 0.01% by weight or more, 0.2% by weight or less, B ₂ O ₃ is 0.1% by weight or more, 1.0% by weight or less, and BaO is 0.1% by weight or more. 0.5% by weight or less, SrO is less than 0.05% by weight, CaO is 0.01% by weight or more, 0.15% by weight or less, Y ₂ O ₃ is 0.05% by weight or more, 0.4% by weight or less, and MgO is 0.1% by weight or less, and Fe ₂ O ₃ + TiO ₂ is less than 0.3% by weight, and substantially does not contain CuO and P ₂ O ₅ (0.01% by weight or less), and the electric resistance after holding at 1500 ° C for 12 hours is 200 Ω cm or more, and does not increase when heated. A high zirconia cast refractory that is stripped and is relatively stable to thermal cycling.

Further preferably, a high zirconia cast refractory having properties relating to the viscosity of the glass phase in the vicinity of 1000 ° C and residual stress on the surface of the refractory is obtained by casting each of the high zirconia cast refractories component is limited to the following range, i.e., ZrO ₂ less than 88 wt%, 96 wt%, SiO ₂ is more than 3 wt%, 9 wt% or less, Al ₂ O ₃ less than 0.1 wt%, less than 0.8 wt%, Na ₂ O is less than 0.04% by weight, K ₂ O is 0.01% by weight or more, 0.15% by weight or less, B ₂ O ₃ is 0.1% by weight or more, 0.7% by weight or less, and BaO is 0.1% by weight or more and 0.5% by weight or less. SrO is less than 0.05% by weight, CaO is 0.01% by weight or more, 0.15% by weight or less, Y ₂ O ₃ is 0.05% by weight or more, 0.2% by weight or less, MgO is 0.05% by weight or less, and Fe ₂ O ₃ + TiO ₂ is less than 0.3. The weight % does not substantially contain CuO and P ₂ O ₅ (0.01% by weight or less), so that the electric resistance after holding at 1500 ° C for 12 hours is 200 Ω. Above hm, high zirconia cast refractory which does not peel off at the time of temperature rise and is stable to thermal cycle.

The present inventors have been able to satisfy the high-resistance characteristics of the high-zirconia-cast refractory at a high temperature for a long period of time, the thermal cycle stability as a parameter for the stability of the temperature rise and the temperature drop, and the prevention of peeling at the time of temperature rise. As a result of detailed investigation of the contents of a wide range of oxides such as an alkali metal oxide, an alkaline earth oxide, and an alumina, the following findings were obtained.

Although the content of the glass phase in the high zirconia cast refractory is small, the kind or amount of the components constituting the glass phase may affect each other, resulting in a very large influence of the characteristics of the glass relative to the high zirconia cast refractory.

That is, in the high zirconia cast refractory, in order to increase the electric resistance at a high temperature, it is necessary to make Na ₂ O which is an oxide of Na having a small ionic radius significantly smaller than the former. However, if only Na ₂ O is reduced, the thermal cycle stability cannot be satisfied, and peeling at the time of temperature rise can be prevented. Therefore, it has been found that, in particular, in terms of Al ₂ O ₃ , K ₂ O, BaO, SrO, and CaO, by adding these components within an appropriate range, it is possible to simultaneously satisfy a high resistance which is stable for a long period of time at a high temperature, Thermal cycle stability and prevention of peeling during temperature rise.

On the other hand, on the surface of the article of high zirconia cast refractory, the residual stress is generated during the casting and gradual cooling of the manufacturing step. Therefore, the residual stress is greatly affected depending on the type of the mold used or the gradual cooling rate.

However, if only the conditions of casting or gradual cooling are adjusted, the kind or size of the residual stress cannot be precisely controlled. That is, even if the casting conditions or the gradual cooling conditions are the same, if the composition is different, there are cases where residual compressive stress is used as residual stress and residual tensile stress is used as residual stress.

Moreover, focusing on the thermal stress characteristics of the residual stress and the glass phase of the high zirconia cast refractory, it was found that the temperature at the time of failure in the state of failure in determining the thermal bending strength of the high zirconia cast refractory (1) And the glass transition point (Tg) (2) of the same glass composition as the high zirconia cast refractory glass, which is closely related to the residual stress, can be manufactured by controlling the (1) or (2) A high zirconia cast refractory that does not cause peeling when heated.

In the high zirconia cast refractory, in the hot bending strength measurement, the fracture mode is different in a low temperature region in which the bending strength is substantially equal to room temperature and a high temperature region in which the bending strength is extremely lowered. In the low temperature region, the brittle fracture is remarkable, forming a smooth cross section; in the high temperature region, due to the softening or flow of the glass phase at the grain boundary, the fracture becomes a failure mode accompanied by plastic deformation, thereby presenting a burr section. . Further, when the glass phase is at or above the glass transition point, the strength is drastically lowered due to the destruction of the plastic deformation.

Example

Fig. 1 shows the thermal 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 from the brittle fracture to the destruction accompanying the plastic deformation in Example 4 was such that the bending strength was 60 MPa and the temperature was 875 ° C, which was included in the scope of the present invention. The strength of the sample in the low temperature region of 600 ° C or lower is 122 × 10 ^-2 MPa, and the strength in the high temperature region of 1300 ° C or higher is 2 × 10 ^-2 MPa. The intermediate strength is (122-2) ÷ 2 = 60 MPa, and the temperature corresponding to the bending strength is 875 ° C, which is substantially equal to the measured value.

Further, the change temperature of the bending strength of Comparative Example 4 was 800 ° C, which was outside the scope of the present invention.

The intermediate strength of Comparative Example 4, that is, (107-7) ÷ 2 = 50 MPa, was 810 ° C, which was approximately equal to the measured temperature.

Thus, the temperature at which the fracture form of the thermal bending strength changes is approximately equal to the temperature corresponding to the intermediate value of the value at the low temperature portion of the bending strength and the value at the high temperature portion, and the temperature at which the failure mode is changed can also be inferred from the intensity measurement value.

Further, quantitative analysis of the glass phase of the sample shown in Fig. 1 was carried out by using an EPMA (Electron Probe X-ray Micro Analyzer, X-ray microanalyzer). The reagent was prepared to obtain a glass having the same composition as that obtained, and the formulation was heated and melted in a platinum crucible to obtain a glassy cured product. The glass transition point (Tg) of the glass was measured using a thermal expansion meter. As a result, the Tg of Example 4 was 890 ° C, and the Tg of Comparative Example 4 was 810 ° C.

The viscosity of the glass at the glass transition point (Tg) is about 10 ¹³ to 10 ¹⁵ poise. At a temperature higher than the glass transition point (Tg), the viscosity decreases with an increase in temperature, so that the glass has fluidity.

Therefore, the glass transition point (Tg) is higher, meaning that the viscosity of the glass is higher even at high temperatures.

Further, among the oxides contained in the high zirconia cast refractory, the glass transition point of the SiO ₂ glass is most reduced to Na ₂ O. Therefore, depending on the content of Na ₂ O, the glass transition point can also be inferred to some extent.

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

Consider the case where the inner layer of the high zirconia cast refractory is solidified after the solidification of the outer layer is completed. When the viscosity of the glass phase is low and the fluidity is low in the vicinity of the morphological change temperature (about 1000 ° C) of the zirconia crystal during the cooling process, the stress generated by the morphological change of the zirconia crystal is by the glass. Flow and ease. Therefore, the stress generated by the morphological change of the zirconia crystal does not affect the residual stress of the ingot. In this case, further cooling is performed, and after the fluidity is lost from the inner layer, thermal stress based on the temperature difference between the outer layer and the inner layer is accumulated, 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 viscosity of the glass phase is high and there is no sufficient fluidity in the vicinity of the morphological change temperature of the zirconia crystal during cooling, the stress generated by the morphological change of the zirconia crystal is not sufficiently alleviated. Thereby, a compressive stress is generated in the inner layer, and a tensile stress is generated in the outer layer. In this case, further cooling is performed, and the total of the thermal stress based on the temperature difference between the inner layer and the outer layer and the stress generated when the zirconia crystal is changed as described above becomes a residual stress. As a result, the residual stress on the surface of the high zirconia cast refractory becomes a smaller compressive stress or tensile stress than in the case where the viscosity of the glass phase is low.

That is, if the temperature at which the fracture mode is changed and the glass transition point (Tg) in the measurement of the thermal bending strength are about 800 ° C and 810 ° C, respectively, the glass phase of the high zirconia cast refractory has a low viscosity at around 1000 ° C, and the product is low. The residual stress of the surface is a compressive stress which becomes a residual stress outside the proper range of the present invention.

On the other hand, if the temperature at which the fracture mode is changed and the glass transition point (Tg) in the measurement of the thermal bending strength are about 875 ° C and 890 ° C, respectively, the following Tables 1 and 2 can also show that the high zirconia cast refractory The viscosity of the glass phase in the vicinity of 1000 ° C is high, and the residual stress on the surface of the product is tensile stress, which becomes a residual stress in an appropriate range of the present invention.

Thus, by controlling the properties associated with the viscosity of the glass phase (especially the viscosity of the glass phase near 1000 ° C), the residual stress of the high zirconia cast refractory can be controlled.

In the present invention, attention is paid to the temperature at which the failure mode is changed in the measurement of the thermal bending strength and the glass transition point. However, it is also within the scope of the present invention to pay attention to other thermal characteristics such as strain points.

Further, the high zirconia cast refractory is a mixture of zirconia crystals and a glass phase. Moreover, the resistance of zirconia is significantly lower than that of ruthenium dioxide which is a main component of the glass phase.

Therefore, in order to increase the electric 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 to make the composition of the glass phase close to the high-purity high-purity ceria glass.

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

Further, in order to increase the resistance of the glass phase, it is only possible to reduce alkali ions having a small ionic radius, especially Na ₂ O. As a result, the glass transition point (Tg) of the glass phase is increased, and the electric resistance is also increased.

For example, a T2 of a glass having a molar ratio of Na ₂ O to SiO ₂ of 1:2, that is, Na ₂ Si ₂ O ₅ is 732 ° C, whereas a Tg of SiO ₂ not containing Na ₂ O is 1463 ° C, and the electric resistance is also remarkably increased. .

However, when Na ₂ O is simply reduced, although the glass transition point Tg and electric resistance increase, it is not possible to simultaneously satisfy the suitability for preventing residual stress in the following conditions, that is, cracking when manufacturing a product, or heat cycle test. An increase in the residual volume expansion ratio caused by the formation of zircon or a crack generated at the time of temperature rise.

Therefore, by limiting the content of Na ₂ O which has a large influence on electrical resistance to a minimum amount, and focusing on research and finding out B ₂ O ₃ necessary for preventing cracking at the time of manufacture or Al which is important for glass stabilization. An appropriate range of the contents of ₂ O ₃ , BaO, CaO, Y ₂ O ₃ , SrO, etc., can achieve high resistance.

Fig. 2 is a graph showing changes with time in the resistance of Example 4 of Table 1 and Comparative Example 9 of Table 2 at 1500 °C.

In Fig. 2, the electric resistance of Example 4 was relatively stable, and the electric resistance of Comparative Example 9 increased with the passage of time.

Figure 3 is a photomicrograph of Example 4 after 12 hours at 1500 °C. The glass phase was observed at the grain boundaries of the granular zirconia crystals. The part that is thicker in color and looks slender is a glass phase.

Figure 4 is a photomicrograph of Comparative Example 9 after 12 hours at 1500 °C. It can be seen that the smaller granular crystal of zircon is dispersed in the glass phase of the grain boundary of the granular zirconia crystal.

In Example 4, zircon was not formed after 12 hours at 1500 ° C, so the resistance value was relatively stable.

However, in Comparative Example 9, since the SiO ₂ content was large, the electric resistance when the temperature was raised to 1500 ° C was high, and zircon was formed from the glass phase with the passage of time, so that the electric resistance was further increased. In Comparative Example 9, although the electric resistance was high, zircon was easily formed, and the sample was powdered after the heat cycle test.

In Example 4, the electrical resistance was stable, and after the thermal cycle test, the residual volume expansion ratio was also small, and zircon was not formed.

Next, the components of the high zirconia cast refractory of the present invention will be described.

The content of ZrO ₂ is 87% by weight or more and 96% by weight or less. More preferably, the content of ZrO ₂ is 88% by weight or more and 96% by weight or less. When ZrO _{2 is} less than 87% by weight, the corrosion resistance is inferior, and if it is more than 96% by weight, it is unbalanced with other components, and cracks are likely to occur in the refractory.

The content of SiO ₂ is 3% by weight or more and 10% by weight or less. More preferably, the content of SiO ₂ is 3% by weight or more and 9% by weight or less.

If the content of SiO ₂ is less than 3% by weight, it is difficult to form a sufficient glass phase in the refractory. Although the electric resistance is increased as the amount of cerium oxide is increased, if it is more than 10% by weight, the corrosion resistance of the refractory to the molten glass is deteriorated, and the leaching of the glass phase from the refractory increases at a high temperature.

The content of B ₂ O ₃ is 0.1% by weight or more and 1.0% by weight or less. More preferably, the content of B ₂ O ₃ is 0.1% by weight or more and 0.7% by weight or less. If B ₂ O _{3 is} less than 0.1% by weight, the occurrence of tear-type cracking cannot be prevented when the product is formed. If it is more than 1.0% by weight, the residual volume expansion after the heat cycle test is close to 20%, and the tensile stress becomes large, and one side of the high zirconia cast refractory of 100×300×300 mm is heated using an electric furnace. Cracking occurs in the one-sided heating test.

The content of Al ₂ O ₃ is 0.1% by weight or more and less than 0.8% by weight. Al ₂ O ₃ has an effect of improving the fluidity of the melt of the additive component, facilitating the casting, and suppressing the dissolution of ZrO ₂ in the refractory in the glass phase, so that zircon is not formed in the glass. .

When the content of Al ₂ O ₃ is less than 0.1% by weight, the residual volume expansion ratio after the heat cycle test becomes about 30%, and the thermal cycle stability of the refractory is deteriorated. When the content of Al ₂ O ₃ is 0.8% by weight or more, the thermal cycle stability can be improved, but the electric resistance is remarkably lowered.

Further, Al ₂ O ₃ has an effect of increasing the compressive stress on the surface of the high zirconia cast refractory.

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

The content of K ₂ O is 0.01% by weight or more and 0.2% by weight or less. More preferably, the content of K ₂ O is 0.01% by weight or more and 0.15% by weight or less. K ₂ O is an essential component in the case of the present invention in which the content of Na ₂ O is limited. If K ₂ O is less than 0.01% by weight (that is, substantially not contained), the residual volume expansion ratio of the refractory after the heat cycle test is very large, and the thermal cycle stability is deteriorated. If it is more than 0.2% by weight, the electrical resistance of the refractory becomes insufficient.

Further, K ₂ O also has an effect of increasing the compressive stress of the refractory material similarly to Na ₂ O.

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

The content of BaO is 0.1% by weight or more and 0.5% by weight or less. When the content of BaO is less than 0.1% by weight, the residual volume expansion ratio after the thermal cycle of the refractory is large, and the thermal cycle stability is deteriorated. When the content of BaO exceeds 0.5% by weight, the electric resistance decreases, and the residual volume expansion ratio after the heat cycle also increases, and the thermal cycle stability deteriorates.

The content of SrO is less than 0.05% by weight. In the case of SrO, the effect of preventing cracking when drilling a refractory is large, but if it is 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 the zirconia raw material, and is an essential component in the present invention.

When CaO is not contained, the tensile stress becomes large, and peeling occurs upon heating on one side. However, if the CaO contained in the refractory is more than 0.15% by weight, the residual volume expansion ratio of the refractory after the heat cycle heating is increased, and in the extreme case, the refractory is pulverized.

The content of Y ₂ O ₃ is 0.05% by weight or more and 0.4% by weight or less. Further, it is preferred that the content of Y ₂ O ₃ is 0.05% by weight or more and 0.2% by weight or less. Y ₂ O ₃ is present as an impurity in the zirconia raw material. However, when it exceeds 0.4% by weight, the residual volume expansion ratio after heat cycle heating of the refractory becomes large, the thermal cycle stability is poor, and the electric resistance is also lowered.

The content of MgO is 0.1% by weight or less. Further, it is preferred that the content of MgO is 0.05% by weight or less. MgO exists as an impurity in the zirconia raw material. When it exceeds 0.1% by weight, the residual volume expansion ratio after the heat cycle test of the refractory becomes large, and the thermal cycle stability is inferior.

The total content of Fe ₂ O ₃ and TiO ₂ is 0.3% by weight or less. Fe ₂ O ₃ and TiO ₂ are present as impurities in the raw material, but since it affects cracking at the time of production, it is preferably 0.3% by weight or less.

In the present invention, substantially no P ₂ O ₅ and CuO are contained. In the case where P ₂ O ₅ and CuO and B ₂ O ₃ coexist, a low-melting point glass is formed, and the chemical durability is extremely lowered. Moreover, P ₂ O ₅ significantly reduces the stability of the refractory to thermal cycling. Further, these raw materials have a large hygroscopic property, and when used as a raw material, they have a property of being difficult to form a dense refractory.

CuO is effective in reducing the rupture of the refractory, however, since it causes the molten glass to be colored, it is preferable that CuO is substantially not contained.

In the present invention, the finger is not substantially contained, and although it is accurate by an analytical method or an analytical instrument, it is still less than 0.01% by weight.

The high zirconia cast refractories of the respective examples and comparative examples described above were produced by a usual method.

That is, SiO ₂ , Al ₂ O ₃ , Na ₂ O, B ₂ O ₃ , and other powder raw materials are added to the zirconia raw material obtained by decarburizing the zircon sand, and these are mixed, and then The electric arc furnace was melted and cast in a prepared mold, which was buried in an alumina powder and gradually cooled to room temperature.

For the mold, a black lead was used, and the product portion had a size of 100 × 300 × 350 mm, and a riser portion having an inner size of 140 × 235 × 350 mm was integrally joined to the upper portion thereof.

After cooling, the product was taken out from the alumina powder, and the product portion was cut away from the riser portion to obtain a desired high zirconia cast refractory. At this time, confirm the appearance of cracks.

The compositions and characteristics of the high zirconia cast refractories of Examples 1 to 10 are shown in Table 1.

Further, the compositions and characteristics of the high zirconia cast refractories of Comparative Examples 1 to 15 are shown in Table 2.

The components in Tables 1 and 2 are based on units by weight. The analysis of each component was carried out by using the luminescence method for K ₂ O and Na ₂ O, the absorption method for P ₂ O ₅ , and the ICP for other components. However, the present invention is not limited to the analysis methods, and may be carried out by other analysis methods.

The measurement of the glass transition point is first, using EPMA, the analysis of the glass phase of the high zirconia cast refractory. Then, it was melted in a platinum crucible and cooled to prepare a glass of the same composition. The glass block was processed to produce 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, and the temperature was raised to 1,100 ° C at a temperature increase rate of 5 ° C in 毎 minutes, and the change point of the expansion ratio was measured as Tg.

The thermal bending strength is such that the high zirconia cast refractory is cut into a thickness of 10×width 20×length 100 mm, and is heated in an electric furnace of a niobium carbide heating element at a temperature increase rate of 5° C., and is maintained at a set temperature for 10 minutes or more. Then, the bending strength was measured. The number of samples is 3 each.

The residual stress was measured by measuring the residual stress at six measurement points of the sample surface of 100 × 300 × 300 mm by using a perforation method with a strain gauge.

This measurement method is carried out in accordance with the SOET and VANCROMBURGGE methods described in "Generation of Residual Stress and Countermeasures" by Mi Gumao. First, for a sample of 300 × 300 mm, the surface is ground by about 3 mm. Observe the ground surface and fill the pores that will cause obstacles to the strain gage to fill the epoxy to make it smooth.

Then, on the smooth surface, three strain gauges (strain gauges) were attached to the measurement points by epoxy resin. The strain gauge is a self-temperature-guaranteed strain gauge that conforms to the thermal expansion rate of the high zirconia cast refractory and is connected to the tester by a 3-wire wiring method. The self-temperature-guaranteed strain gauge reduces the apparent strain caused by the temperature change of the measured sample, thus reducing the measurement error. Further, the 3-wire type wiring method is preferable to the 2-wire type wiring method previously used, since the apparent strain due to the temperature change of the wire can be removed. The strain gauges have a rectangular shape and are adhered so that the center lines of the longitudinal directions thereof are at an angle of 120 degrees to each other. Then, at the position where the center line intersects, the strain generated by the opening of the through hole having a diameter of 25 mm is measured by a measuring device (UCAM-20A manufactured by Gonghe Electric Co., Ltd.), and the value is calculated by the three-direction strain analysis using this value. Residual stress. The residual stress is expressed as a positive number for tensile stress and as a negative number for compressive stress. When it is negative, the larger the number, the greater the compressive stress.

For the one-sided heating test, a sample of 100 × 300 × 300 mm was placed in an electric furnace so that the surface of 300 × 300 mm was in the furnace, and the opposite side was in contact with the outside air. The sample was heated to 1000 ° C at a temperature increase rate of 100 ° C in 毎 minutes, and the presence or absence of cracking at the time of temperature rise was measured.

Thermal cycling stability was performed by cutting a 50 x 50 x 50 mm sample from the bottom of a 100 x 300 x 300 mm sample. The sample was inserted into an electric furnace and heated up to 800 ° C at a temperature increase rate of 3 ° C for 1 hour. Thereafter, the temperature was raised to 1200 ° C at a temperature increase rate of 3 ° C for 1 hour and held for 1 hour. Thereafter, it was cooled to 800 ° C at a cooling rate of 3 ° C at 毎 minute. Thereafter, the thermal cycle of 800 ° C and 1200 ° C was repeated 45 times, and after cooling, the presence or absence of cracking or chalking was observed. Further, the volume change before and after the heat cycle test was measured, and the residual volume expansion ratio was calculated.

Further, if the residual volume expansion ratio in the thermal cycle test exceeds 10%, zircon is formed. Further, the larger the residual volume expansion ratio, the larger the amount of zircon formation. In the comparative example in Table 2 in which the residual volume expansion ratio was more than 10% in the thermal cycle test, the resistance measurement value was increased with time as in Comparative Example 9 of Fig. 2, and the stability over time was poor.

The resistance was measured by a four-terminal method based on JISR1650-2. A 19 mm diameter core was used to cut a 30 mm sample from the sample. The surface was cut at a distance of 5 mm from both ends, and then ultrasonically cleaned and dried by a dryer. After drying, a platinum plate is placed at both ends of the sample, and a platinum wire is wound as a terminal in the groove portion, and a fixed voltage is generated by an AC 60 Hz function wave generator, and the measurement is applied to the sample and the resistance is set to be the same as the sample. The voltage of the standard resistor is obtained from the obtained voltage value to determine the resistance value of the sample. The measurement was carried out by heating to 1500 ° C at a temperature increase rate of 4 ° C at 毎 minute and holding for 12 hours. The resistance value at the time of reaching 1500 ° C was measured, and further, it was confirmed that the resistance value after holding for 12 hours was a stable value. Then, the measured value of the resistance after 12 hours was obtained as a resistance value of 1500 °C.

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

Comparative Example 1 shown in Table 2 corresponds to the embodiment of the invention disclosed in WO 2005/068393. Usually, about 0.1% by weight of Y ₂ O _{3 is} contained as an impurity in the zirconia raw material. In WO 2005/068393, the disclosure of BaO and K ₂ O is not clear, but if the total amount of analytical values and the Y ₂ O ₃ content of the examples in WO 2005/068393 are taken into consideration, it is clear that These products do not contain K ₂ O or BaO.

In Comparative Example 1, Na ₂ O was small, but there were many Al ₂ O ₃ , and thus the electric resistance was insufficient.

Further, since Na ₂ O is small and does not contain K ₂ O and BaO, the residual volume expansion ratio after the heat cycle test is large, and the stability against thermal cycling is lacking.

Comparative Example 2 is an example in which Al ₂ O ₃ and B ₂ O _{3 are} small. Cracks were generated during manufacture.

The resistance is high, but cracks are generated after the thermal cycle test.

Comparative Example 3 is a case where there are many Al ₂ O ₃ and Na ₂ O and B ₂ O _{3 is} small. Cracks were generated during manufacture. Moreover, although it has thermal cycle test stability, the resistance is low.

Comparative Example 4 is a case where Na ₂ O and B ₂ O ₃ are large. The compressive stress is large, and cracks are generated after the single-sided heating test. After the thermal cycle test, the residual volume expansion rate is also large, and the resistance is also low.

Comparative Example 5 is an example in which K ₂ O is more. The resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is lacking.

Comparative Example 6 is an example in which BaO is more. The resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is lacking.

Comparative Example 7 is an example in which K ₂ O and Na ₂ O are small. The viscosity is high during manufacture, and the product becomes a concave shape. As the resistance is higher, the residual volume expansion rate after the thermal cycle test is also larger and chalky, lacking stability to the thermal cycle.

Comparative Example 8 is an example in which BaO is less and SrO and Y ₂ O ₅ are more. Low resistance and lack of stability to thermal cycling.

Comparative Example 9 is an example in which ZrO ₂ and SiO ₂ are many and P ₂ O ₅ is contained. Although the resistance is high, it lacks stability over time. Moreover, the residual volume expansion ratio after the heat cycle test was large and powdered.

In the comparative example 10, Na ₂ O, MgO, and SrO are many and contain P ₂ O ₅ , which corresponds to an example of the embodiment of the above-mentioned Japanese Patent Laid-Open No. Hei 8-277162. The resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is lacking.

In Comparative Example 11, there are many examples of Na ₂ O and BaO, and it corresponds to an example of the embodiment of the above-mentioned Japanese Patent Publication No. Hei 8-48573. The resistance is low.

Comparative Example 12 is an example in which CaO and Fe ₂ O ₃ +TiO ₂ are abundant. The resistance is low, the residual volume expansion rate after the thermal cycle test is large, and the stability to the thermal cycle is lacking.

Comparative Example 13 is an example which does not contain Na ₂ O and corresponds to an embodiment of the above-mentioned Japanese Patent Laid-Open Publication No. SHO63-285173. Although the electric resistance is high, the tensile stress is large, and cracking occurs on one side heating. The residual volume expansion rate after the thermal cycle test was also large and pulverized.

Comparative Example 14 is an example in which Al ₂ O ₃ , BaO, and CaO are many and does not contain Na ₂ O or K ₂ O, and is an example equivalent to the embodiment of the above-mentioned Japanese Patent Laid-Open No. Hei-4-193766. The resistance is also low, lacking stability to thermal cycling.

Comparative Example 15 is an example in which the Na ₂ O is large and does not contain an alkaline earth oxide, and is an example corresponding to the embodiment of the above-mentioned Japanese Patent Laid-Open No. Hei 10-59768. The resistance is low. Further, the compressive stress is large and cracking occurs upon heating on one side. The residual volume expansion rate after the thermal cycle test is also large, and the stability to the thermal cycle is lacking.

Fig. 1 is a view showing the results of measurement of thermal bending strength of a high zirconia cast refractory. The bending strength at a majority of the measured temperatures (25 to 1400 ° C) is shown in comparison with Comparative Example 4 and the present invention.

Fig. 2 is a graph showing the temporal change of the electric resistance of the high zirconia cast refractory.

Fig. 3 is a view showing a photomicrograph of the electric resistance measurement of Example 4.

Fig. 4 is a view showing a photomicrograph of the electric resistance measurement of Example 9.

Claims (7)

A high zirconia cast refractory characterized in that it has a viscosity-related property near the glass phase at 1000 ° C and a residual stress on the surface of the refractory, and the chemical composition thereof is: ZrO ₂ is 87% by weight or more. 96% by weight or less, Al ₂ O ₃ is 0.1% by weight or more and less than 0.8% by weight, SiO ₂ is 3% by weight or more, 10% by weight or less, Na ₂ O is less than 0.05% by weight, and K ₂ O is 0.01% by weight or more. 0.2% by weight or less, B ₂ O ₃ is 0.1% by weight or more and 1.0% by weight or less, BaO is 0.1% by weight or more, 0.5% by weight or less, SrO is less than 0.05% by weight, and CaO is 0.01% by weight or more and 0.15% by weight. Hereinafter, Y ₂ O ₃ is 0.05% by weight or more and 0.4% by weight or less, MgO is 0.1% by weight or less, and the total amount of Fe ₂ O ₃ and TiO ₂ is 0.3% by weight or less, and substantially does not contain P ₂ O ₅ and CuO. (less than 0.01% by weight), and the electric resistance of the high zirconia cast refractory after maintaining at 1500 ° C for 12 hours is 200 Ω cm or more. A high zirconia cast refractory characterized in that it is controlled by a viscosity-related property of a glass phase near 1000 ° C and a residual stress of a refractory surface, and the chemical composition thereof is: ZrO ₂ is 88% by weight or more, 96% by weight or less, Al ₂ O ₃ is 0.1% by weight or more and less than 0.8% by weight, SiO ₂ is 3% by weight or more and 9% by weight or less, Na ₂ O is less than 0.04% by weight, and K ₂ O is 0.01% by weight or more. 0.15 wt% or less, B ₂ O ₃ is 0.1% by weight or more and 0.7% by weight or less, BaO is 0.1% by weight or more and 0.5% by weight or less, SrO is less than 0.05% by weight, and CaO is 0.01% by weight or more and 0.15% by weight. Hereinafter, Y ₂ O ₃ is 0.05% by weight or more and 0.2% by weight or less, MgO is 0.05% by weight or less, and the total amount of Fe ₂ O ₃ and TiO ₂ is 0.3% by weight or less, and substantially does not contain P ₂ O ₅ and CuO. (less than 0.01% by weight), and the electric resistance of the high zirconia cast refractory after maintaining at 1500 ° C for 12 hours is 200 Ω cm or more. The high zirconia cast refractory of claim 1 or 2 has a residual stress on the surface of 30 MPa or less and a compressive stress of 20 MPa or less. The high zirconia cast refractory according to any one of claims 1 to 3, wherein the temperature from the brittle failure to the destruction with plastic deformation in the hot bending test is 850 ° C to 950 ° C. The high zirconia cast refractory according to any one of claims 1 to 4, wherein the glass transition point (Tg) of the glass phase in the high zirconia cast refractory is from 850 ° C to 950 ° C. The high zirconia cast refractory according to any one of claims 1 to 5, which has a residual volume expansion ratio of 10% or less after the heat cycle test. The high zirconia cast refractory according to any one of claims 1 to 6, which has a resistance of 250 Ω cm or more after being maintained at 1500 ° C for 12 hours.