JP4394080B2 - Zirconia refractories - Google Patents

Description

  The present invention relates to a zirconia refractory suitable mainly as a refractory for a glass melting furnace.

  Conventional refractories for glass melting kilns are roughly classified into sintered (bonded) refractories and molten refractories.

  The former is made by pressing and firing a homogeneously mixed powder raw material. In this refractory, the gas adhering to the powder as a raw material and part of the gas generated during firing remain after firing, the density of the fired body is low, and the corrosion resistance is poor. Low corrosion resistance indicates that there is a high probability that defects such as bubbles and gravel will occur when glass is melted.

On the other hand, the latter is obtained by melting a homogeneously mixed raw material in a melting furnace, pouring it into a mold and solidifying by cooling, and has a dense and developed crystal structure. Among these, in particular, a refractory containing a relatively large amount of zirconia is excellent in corrosion resistance and is preferably used in a glass melting kiln. As such a molten refractory, an Al ₂ O ₃ —ZrO ₂ —SiO ₂ refractory having a ZrO ₂ content of 33 wt% to 41 wt%, a high zirconia refractory containing ZrO ₂ of 80 wt% to 95 wt%, and There is. Since the latter has higher corrosion resistance and lower substrate contamination than the former, in recent years it has come to be widely used as a refractory for high-quality glass melting kilns.

Originally, zirconia causes a phase transition between a monoclinic crystal and a tetragonal crystal between 900 ° C. and 1200 ° C. Therefore, unless Y ₂ O ₃ or CaO is added and zirconia is at least partially stabilized, A sintered body cannot be obtained. The same applies when alumina is added to zirconia. Even when partially stabilized or stabilized zirconia is used as a refractory for melting a glass, the stabilizer is selectively eluted by alkali or the like in the molten glass or glass volatiles, and the corrosion resistance is remarkably low.

In addition, a molten refractory composed of zirconia and alumina is cracked during cooling and solidification, and it is difficult to obtain an ingot having a size that can be used as a refractory. The above-described Al ₂ O ₃ —ZrO ₂ —SiO ₂ molten refractory has been developed to recover from this defect, and has a matrix glass phase of about 10 to 20 wt%.

  Conventionally, as a refractory containing zirconia and alumina, there is an alumina-mullite-based molten refractory or a zircon-mullite-based sintered refractory, but the corrosion resistance is low, especially when it comes into contact with molten glass. It ’s not there.

  On the other hand, in Japanese Patent Laid-Open Nos. 7-293851 and 8-104567, there is a zirconia refractory containing a resolidified pulverized product of a molten refractory as a refractory used for the bottom of a furnace for melting a waste and a furnace for a glass melting. It is disclosed. Among them, a high zirconia pulverized product is used as a melt resolidified product, but a sintering aid such as clay is used for sintering. When such a substance such as a sintering aid is added, the high temperature strength and corrosion resistance of the refractory itself are lowered.

In addition, re-solidified pulverized high zirconia molten refractory is used as an aggregate, alumina cement,
A method of using alumina powder or the like as a binder has been proposed in Japanese Patent Laid-Open No. 63-103869, Japanese Patent Publication No. 4-20872, and Japanese Patent Laid-Open No. 5-213676, but is limited to an amorphous refractory.

  The sintered refractories described above have a drawback that they are difficult to use, particularly in the portions that come into contact with molten glass or glass volatiles, because of their high porosity and low corrosion resistance.

  Further, the high zirconia molten refractory contains a large amount of zirconia, is melted at about 2500 ° C., and is solidified in the mold, so that it is expensive. Furthermore, casting voids are generated due to cooling in production, and a portion containing a large amount of the void may reach half as much as the volume, resulting in a low product yield. There is a method to pulverize the part that contains a lot of voids and reuse it as a return cullet. However, it is difficult to control the components of the product, and the purity decreases due to the iron content mixed during pulverization, which is an advantage of this refractory. Impairs corrosion resistance and low substrate contamination.

  It was desired to develop a refractory with performance that combines the advantages of both refractory bricks and refractory bricks, but no such refractories have been developed to date. . An object of the present invention is to provide a refractory that can be manufactured at a low cost in order to solve the above-described problems. If such a refractory can be produced, the yield of the melt should be improved by using it as a furnace material for melting glass. Furthermore, it leads to the effective use of zirconia resources.

The present invention has been made to achieve the aforementioned problems, primarily a refractory used for glass melting furnace, the monoclinic ZrO ₂ as a main component, chemical composition ZrO _2; 80 _{.5~95.5%, SiO 2; 3.03~15.1%} , Al 2 O 3; 0.80~2.61%, Na 2 O; 0.38~1.33% high zirconia A mixture of the pulverized melt-resolidified product and 98% by weight or more of Al ₂ O ₃ alumina powder is sintered, and a part or all of the periphery of the monoclinic (badelite) phase is mullite phase The present invention provides a zirconia refractory characterized by comprising.

  Compared to conventional zirconia refractories, the zirconia fired refractories of the present invention have a uniform structure and composition, and have a strong bond, so they have stable quality and reliability. In addition, since it is excellent in corrosion resistance and foamability, it is difficult to cause glass defects such as bubbles and gravel with respect to molten glass, and the substrate contamination resistance is low, so that the yield of glass production is improved.

  In addition, since the product of the present invention can use a portion including a casting cavity that cannot be made of a high zirconia molten refractory product, it can be manufactured at low cost and can contribute to resource recycling, that is, resource saving.

  High zirconia molten refractories have almost no pores inside, except for the casting cavity. Since the porosity is high and the pores are unevenly distributed, the portion with the casting nest is rarely used as a refractory. However, the cast nest can be easily removed by a certain amount of grinding. The part without the casting nest (the solid phase part from which the pores have been removed from the part where there are many casting nests) is not enough in size to be used as a refractory, is dense, has a low porosity, and is a product. These physical properties are not inferior to those with no or few casting voids. In addition, the degree of oxidation is higher than that of the portion not including the casting cavity.

  It is known that a molten refractory having a high degree of oxidation has a low resistance to substrate contamination, in particular, foamability. Since the refractory of the present invention uses a material having a higher degree of oxidation than a normal molten refractory and is further fired, it is expected to have a low resistance to substrate contamination. Furthermore, since the site | part containing a casting nest is utilized, cost can be reduced and it is effective utilization of resources.

A refractory obtained by sintering a pulverized product of a high zirconia molten refractory mainly composed of monoclinic ZrO ₂ can be produced by the following method. Using a pulverizer, pulverize the portion containing the cast nest that is produced in the production of high zirconia molten refractories as disclosed in JP-B-59-12619, JP-B-8-18880, and JP-A-3-218980. To do. Since the casting nest itself has a large volume, it can be almost removed by grinding to a particle size of about 5 mm. However, if the size of the pulverized product is too large, it may cause pores in the sintered body, or the uniformity of the structure may be reduced, and the corrosion resistance may be reduced.

The high zirconia melt-resolidified material mainly composed of monoclinic ZrO ₂ used in the present invention is composed of a structure in which a small amount of matrix glass phase surrounds the badelite crystal phase. % in _{ZrO 2; 80.5~95.5%, SiO 2} ; 3.03~15.1%, Al 2 O 3; 0.80~2.61%, Na 2 O; 0.38~1. 33%.

  As for the particle size of the pulverized product, in consideration of the pulverization efficiency and the thermal shock resistance, the particle size of 1.00 mm to less than 4.76 mm (coarse particles) is 10% to 50% by weight, and the particle size of 0.1%. A configuration in which the particle size is 15% to less than 1.00 mm (medium particles) is 10 to 50% by weight and the particle size is less than 0.15 mm (fine particles) is preferably 40% by weight or less. Here, the particle size of X mm or more indicates particles that do not pass through a sieve having an opening of X mm, and the particle size of less than Y mm indicates particles that pass through a sieve having an opening of Y mm. When coarse grains or medium grains are contained more than this, the sinterability is lowered, and it may be difficult to obtain a desired sintered body.

  Another is that the particle size is preferably less than 0.15 mm, considering the uniformity of the structure and the reduction in porosity.

  When using an iron pulverizer, it is desirable to remove the mixed iron after pulverization by washing with a magnet or acid such as dilute hydrochloric acid. If it does in this way, substrate pollution resistance will fall.

The alumina powder can be obtained by re-solidifying the alumina molten refractory in the same manner as described above, but is not preferable because it contains a large amount of Na ₂ O. Since alumina produced by the Bayer method is commercially available at a low price, it may be used. Other aluminas can also be used, but it is preferable to avoid the use of a material having a large amount of impurities, so that a material containing Al ₂ O _{3 of} 98% by weight or more is used.

  Since alumina also serves as a sintering aid, the particle size of the alumina should be smaller than that of the high zirconia melt resolidified pulverized product. The particle size of alumina is preferably less than 0.15 mm, more preferably less than 0.01 mm.

  The pulverized granular or powdery raw material is molded by a die press method or a CIP method. In particular, molding is possible without using a binder. This is because firing is preferably performed at a temperature of about 1400 ° C. or higher where mullite is generated. By the above operation, a sintered body having no cracks can be obtained.

As shown in FIG. 1, the present invention basically has a structure in which a mullite phase 2 (including part of a matrix phase) is surrounded around a badelite phase 1 in zirconia particles. Here, mullite is produced by the reaction of silica and alumina in the matrix glass phase surrounding the badelite phase of the high zirconia melt resolidified pulverized product. Therefore, mullite plays a role of tightly bonding the badelite particles and does not exist as free crystals. This point is considered to be excellent in corrosion resistance unlike zircon-mullite refractories. Further, compared to alumina-mullite refractories, the ZrO ₂ content is remarkably high and the corrosion resistance is excellent. The composition of _{mullite, 3Al 2 O 3 · 2SiO 2} (. In practice, indicating the composition between the _{Al 2 O} 3 · SiO 2 about this), and 72:28 and 63 in this order in a weight ratio: Since it is 37, 100/28 (100/37) or more of the SiO ₂ content in the raw material is not generated. Since mullite is inferior in corrosion resistance compared to alumina and zirconia, the SiO ₂ content is preferably 1% by weight or more and 6% by weight or less so as not to generate much.

This SiO ₂ content is almost the same as that of the normally produced high zirconia molten refractory, and the raw materials are easily available, and there is no need to adjust the components.

  In addition, mullite or alumina forms a layer rich in alumina at the interface when molten glass or glass volatiles come into contact with the refractory of the present invention, and serves as a protective layer to suppress elution of badellite. Therefore, the corrosion resistance is further improved by adding alumina. Furthermore, alumina is superior to zirconia in foaming properties at a low temperature (for example, 1300 ° C. or lower).

  Considering these, although depending on the purpose of use of the refractory, in the present invention, the ratio of the high zirconia melted resolidified pulverized product to the alumina powder is 98% to 50% for the former in the total weight and 2 to 2 for the latter. 50% is preferable, more desirably, the former is 90 to 70%, and the latter is 10 to 30%.

  During firing, there is almost no grain growth of badellite, so there is no segregation of zirconia beyond the raw material particle state. This is because the high zirconia molten refractory has more pores and matrix glass, and there are parts that are locally inferior in corrosion resistance and substrate contamination resistance. Refractory.

  In FIG. 1, 3 is mainly a matrix glass phase, alumina particles or pores.

  The present invention substantially consists of a high-zirconia melt-resolidified pulverized product and alumina particles as described above, but other components can be added to the extent that they do not impair the purpose and effect. It is desirable to keep it small.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  An example of a method for producing the product of the present invention is shown below. First, a predetermined amount of desilicated zircon, Bayer alumina, silica sand, and sodium carbonate were weighed and mixed, and then completely melted at about 2500 ° C. in a 500 kVA single-phase arc electric furnace using a graphite electrode. The molten metal was poured out into a graphite mold having an inner size of 160 mm × 200 mm × 350 mm embedded in buyer alumina and allowed to cool to room temperature. Next, the ingot was cut to obtain a portion including a casting cavity.

The part including the cast nest of the melted and re-solidified product was pulverized with a jaw crusher and then with an iron bowl to obtain a pulverized product having a particle size of about 1 cm. Next, this was immersed in 1 mol / liter hydrochloric acid aqueous solution, washed, mixed iron was dissolved and dried. In addition, about 0.1 wt% Fe ₂ O ₃ was found to be mixed by pulverization. Furthermore, it grind | pulverized using the alumina ball | bowl. For the same cast product, the chemical composition was measured for a particle size of less than 0.15 mm. The ZrO ₂ content, the SiO ₂ content, and the Al ₂ O ₃ content are quantified by a glass bead method using a fluorescent X-ray analyzer, and the Na ₂ O content is decomposed with hydrofluoric acid-sulfuric acid and then an atomic absorption photometer. (Table 1).

The obtained high-zirconia melt-resolidified pulverized product was mainly composed of monoclinic ZrO ₂ .

Next, the sieved raw materials were prepared so as to exhibit a predetermined particle size distribution (Table 2). This and alumina showing a predetermined particle size distribution (Table 2) were mixed. The alumina used was obtained by the Bayer method and is Al ₂ O ₃ 99% or more. Examples 1 to 16 are shown in Table 3. Subsequently, each mixed raw material was shape | molded and baked as follows.

500 g of the mixed raw material was pressed by a die press and further by a CIP method (1500 kg / cm ³ ) to obtain a raw processed product. This was fired at 1600 ° C. for 24 hours in a resistance heating electric furnace. All the fired bodies were obtained without generating cracks.

About the obtained sintered compact, the bulk density was measured by Archimedes method (Table 4).
In order to investigate the corrosion resistance, a 15 mm × 15 mm × 50 mm rectangular parallelepiped sample was cut from the fired body and immersed in a tube panel glass at 1500 ° C. for 48 hours. Then, it was divided into two equal parts in the vertical direction and the amount of erosion was measured (Table 4).

Moreover, in order to investigate foamability, a plate-like sample of 40 mm × 40 mm × 5 mm was cut out from the fired body, and a ring made of alumina having an inner diameter of 30 mm was placed thereon and heated at 1500 ° C. for 24 hours. Thereafter, the number of remaining bubbles was measured using an optical microscope (Table 4).
In addition, it shows in Table 1 composition V as a control | contrast (comparative example). Sintered high zirconia melt re-solidified pulverized product (particle size less than 0.15 mm) (Comparative Example 1), and added 5% by weight and 10% by weight of clay to this and sintered ( Comparative Example 2 and Comparative Example 3) and a zircon-mullite sintered product (Comparative Example 4) were used. Table 4 shows the results of the chemical composition, bulk specific gravity, erosion amount, and foaming amount of these comparative examples. The test methods are the same as in the examples.

  The amount of erosion and the amount of foaming in Examples and Comparative Examples are shown as relative comparisons when Comparative Example 1 is taken as 100. In these, if the value of erosion amount is 100 or more, it shows that there is much erosion amount compared with the comparative example 1, and if the amount of foaming is 100 or more, it shows that the amount of foaming is also large.

  In addition, when the cross-sectional structure | tissue of what was shown in the Example was observed with the microscope, it was confirmed that all consist of a structure | tissue as shown in FIG. 1 fundamentally.

  As can be seen from Table 4, the addition of alumina to the pulverized product of high zirconia melt resolidification improves the corrosion resistance and particularly the foamability. Furthermore, the product of the present invention is remarkably superior in corrosion resistance and foamability compared to conventional zircon mullite sintered products and sintered products obtained by adding clay to a pulverized product of high zirconia molten refractory.

In Table 4,
1) Examples are theoretical values based on composition values in Table 1 and mixing ratios in Table 3, comparative examples are actually measured values,
2) Relative comparison value when Comparative Example 1 is 100. It shows that there is much erosion amount at 100 or more. NM indicates that it cannot be measured due to stone,
3) Relative comparison value when Comparative Example 1 is 100. A value of 100 or more indicates a large amount of foaming.
From the above, the product of the present invention can be used as a refractory used in a glass melting kiln regardless of contact or non-contact with molten glass, and hardly causes glass defects such as foam and gravel. Refractory. The refractory of the present invention can be used not only for melting glass but also for refractory used for melting metals, melting incinerated ash, and the like.

The present invention has been made to achieve the above-mentioned problems, and is a refractory mainly used in a glass melting furnace, which is mainly composed of monoclinic ZrO ₂ which is a high zirconia melt resolidification product. The present invention provides a zirconia refractory characterized by sintering a mixture of a pulverized product and alumina powder.

Explanatory drawing which showed a part of structure | tissue of the zirconia refractory of this invention roughly.

Explanation of symbols

1: Badelite phase 2: Mullite phase (partially matrix glass phase)
3: Matrix glass phase, alumina phase or pores

Claims (2)

The monoclinic ZrO ₂ as a main component, chemical composition _{ZrO 2; 80.5~95.5%, SiO 2} ; 3.03~15.1%, Al 2 O 3; 0.80~2. Sintering a mixture of 61%, Na ₂ O; 0.38 to 1.33% high zirconia melt resolidified pulverized product and Al ₂ O ₃ 98% by weight alumina powder, A zirconia refractory characterized in that part or all of the periphery of the monoclinic (badelite) phase is composed of a mullite phase.   The zirconia refractory according to claim 1, wherein the zirconia refractory is used in a glass melting furnace.

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