JPH10120462A - Zirconia refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zirconia refractory excellent in corrosion resistance and foamability, low in staining to the base material, and capable of being produced at a low cost by sintering a mixture of milled monoclinic ZrO2 obtained by resolidifying a high zirconia molten, with alumina powder. SOLUTION: This zirconia refractory is obtained by using a melted and resolidified high zirconia having a structure comprising vaterite crystalline phase surrounded by a small amount of matrix glass phase, and further preferably having chemical composition of about 85-97wt.% ZrO2 and about 2-12wt.% SiO2 , especially >=90% ZrO2 and 1-6% SiO2 . The zirconia refractor is obtained from the melted and resolidified high zirconia of 98-50wt.%, preferably 90-70wt.% and an alumina of 2-50wt.%, preferably 10-30wt.% based on the total amount thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconia refractory suitable mainly as a refractory for a glass melting furnace.

[0002]

2. Description of the Related Art Conventional refractories for glass melting furnaces are roughly classified into sintered (bonded) refractories and molten refractories.

[0003] The former is made by pressing a homogeneously mixed powder raw material and then firing. In this refractory, a gas attached to powder as a raw material and a part of a gas generated during firing remain even after firing, the density of the fired body is low, and the corrosion resistance is poor. Low corrosion resistance indicates that when glass is melted, there is a high probability that defects such as bubbles and gravel will occur.

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 it by cooling, and has a dense and developed crystal structure. Among them, refractories containing a relatively large amount of zirconia have excellent corrosion resistance and are used favorably in glass melting furnaces. Examples of such melt refractories, to ZrO ₂ content is not 33 wt% 41 wt% of Al ₂ O ₃ -ZrO ₂ -
80 wt% to 95 wt% of SiO ₂ refractory and ZrO ₂
There is a high zirconia refractory containing wt%. Since the latter has higher corrosion resistance and lower soil contamination than the former, it has recently become popular as a refractory for high-quality glass melting furnaces.

[0005] Originally, zirconia was used at 900 ° C and 1200 ° C.
Since the phase transition between monoclinic and tetragon occurs between ℃ and
Unless Y ₂ O ₃ or CaO is added to at least partially stabilize zirconia, 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 glass, the stabilizer is selectively eluted due to alkali or the like in the molten glass or glass volatiles, and the corrosion resistance is extremely low.

[0006] The molten refractory comprising zirconia and alumina cracks during cooling and solidification, and it is difficult to obtain an ingot having a size usable as a refractory. The above-mentioned Al was developed to overcome this disadvantage.
₂ O ₃ —ZrO ₂ —SiO ₂ -based molten refractory,
It has a matrix glass phase of about 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 particularly when it comes into contact with molten glass, its corrosion resistance is low. It has not spread yet.

On the other hand, JP-A-7-293851 and JP-A-8-104567 disclose a zirconia material containing a resolidified and crushed product of a molten refractory as a refractory used in a furnace for a waste melting furnace and a glass melting furnace. A refractory is disclosed. Among them, pulverized high zirconia is used as a molten and re-solidified material, but a sintering aid such as clay is used for sintering. When such a substance as a sintering aid is added, the high-temperature strength and corrosion resistance of the refractory itself decrease.

Japanese Patent Application Laid-Open No. 63-103 discloses a method in which a re-solidified and crushed high zirconia refractory is used as an aggregate, and alumina cement, alumina powder and the like are used as a binder.
869, Japanese Patent Publication No. 4-20872, and Japanese Patent Laid-Open No. 5-213.
676, but is limited to irregular shaped refractories.

[0010]

The above-mentioned sintered refractories are:
Due to the high porosity and low corrosion resistance, there is a drawback that it is difficult to use, particularly in a portion in contact with molten glass or glass volatiles.

Further, the high zirconia-based molten refractory contains a large amount of zirconia and is expensive at about 2500 ° C. because it is melted and solidified in a mold. Furthermore, casting cavities (voids) are produced by cooling in manufacturing, and a portion containing many of these cavities may reach half of the volume, resulting in low product yield. There is a method of pulverizing a portion containing a lot of voids and reusing it as a return cullet, but it is difficult to control the components of the product, and the purity decreases due to iron and the like mixed during pulverization. Impairs corrosion resistance and low ground pollution.

[0012] It has been desired to develop a refractory which has both the disadvantages of the refractory brick and the refractory brick as described above and which has the combined performance of the advantages. To date, such refractories have been developed. It has not been. It is an object of the present invention to solve the above-mentioned problems and to provide a refractory which can be manufactured at low cost. If such a refractory can be manufactured, the yield of the melt should be improved by using it as a furnace material for melting glass or the like. Furthermore, it leads to effective use of zirconia resources.

[0013]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and is a refractory mainly used in a glass melting furnace, which is a monoclinic of a high zirconia molten re-solidified material. An object of the present invention is to provide a zirconia refractory obtained by sintering a mixture of a pulverized material mainly composed of crystalline ZrO ₂ and alumina powder.

The high zirconia molten refractory has few pores inside, except for the casting cavity. Since there is a high porosity and uneven distribution of porosity in a portion having a casting cavity, it is hardly used as a refractory. However, the casting cavity can be easily removed by grinding to some extent.
The portion without the casting cavity (the solid phase portion in which pores are removed from the portion having a large number of casting cavity) is only small in size as a refractory, is dense, has a low porosity, and is a product. These properties are not inferior to those of a portion having no or few casting cavities. Furthermore, the degree of oxidation is rather higher than that of a portion that does not include a casting cavity.

It is known that molten refractories having a high degree of oxidation have low resistance to soil pollution, especially low foamability. The refractory of the present invention uses a material having a higher degree of oxidation than a normal molten refractory and is further calcined, so that it is expected that the base material contamination resistance is low. Furthermore, since the site including the casting cavity is used, the cost can be reduced and the resources can be effectively used.

A refractory obtained by sintering a pulverized high zirconia refractory containing monoclinic ZrO ₂ as a main component can be prepared by the following method. JP-B-59-126
19, JP-B-8-18880, and JP-A-3-2189
A portion including a casting cavity generated in the production of a high zirconia-based molten refractory as shown at 80 is pulverized using a pulverizer. Since the casting cavity has a large volume in itself, it can be almost removed by pulverizing it to a particle size of about 5 mm. However, if the size of the pulverized material is too large, it may cause formation of 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 containing monoclinic ZrO ₂ as a main component used in the present invention has a structure in which a small amount of a matrix glass phase surrounds a baddelite crystal phase. As Zr in weight%
O ₂ is 85 to 97% SiO ₂ is preferably made of about 2-12%, in particular ZrO ₂ is 90% or more, Si
O ₂ is desirably 1% or more and 6% or less as described later.

In consideration of the pulverization efficiency and the thermal shock resistance, the particle size of the pulverized material is, for example, 10% by weight to 50% by weight, with the particle size being 1.00 mm or more and less than 4.76 mm (coarse particles). It is preferable that the diameter is 0.15 mm or more and less than 1.00 mm (medium grain) is 10% by weight to 50% by weight, and the particle diameter is less than 0.15mm (fine grain) is 40% by weight or less. Here, the particle size of Xmm or more means particles that do not pass through a sieve having an aperture of Xmm, while the particle size of less than Ymm means that the particle size is at least Ymm.
Particles passing through the sieves of Table 1 below. If coarse or medium grains are contained more than this, sinterability may decrease, and it may be difficult to obtain a desired sintered body.

On the other hand, in consideration of the uniformity of the structure and the reduction in porosity, it is preferable that the particle size is less than 0.15 mm.

When an iron pulverizer is used, it is desirable to remove the contaminating iron by pulverization and then washing with a magnet or an acid such as dilute hydrochloric acid. In this case, the resistance to soil pollution decreases.

Alumina powder can be obtained by re-solidifying an alumina-based 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 cost, it is preferable to use this. Although other aluminas can be used, those having 98% by weight or more as Al ₂ O ₃ are preferable, and those having many impurities are preferably avoided.

Since alumina also plays a role as a sintering aid, the particle size of alumina is preferably smaller than that of the pulverized high zirconia melt-resolidified material. The particle size of alumina is
Preferably less than 0.15 mm, more preferably 0.01
mm.

The pulverized granular or powdery raw material is formed by a die pressing method or a CIP method. In particular, molding is possible without using a binder. This is because firing at a temperature of about 1400 ° C. or more at which mullite is generated is desirable. By the above operation, a sintered body without any cracks can be obtained.

As shown in FIG. 1, the present invention basically has a structure in which a mullite phase 2 (partially including a matrix phase) surrounds a baddelite phase 1 in zirconia particles. . Here, the mullite is formed 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 firmly bonding between 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 with alumina-mullite refractories, the content of ZrO ₂ is remarkably high and the corrosion resistance is excellent. The composition of mullite is 3Al ₂ O _3.
2SiO ₂ (actually, shows a composition between this and Al ₂ O ₃ .SiO ₂ ).
2:28 and 63:37, the SiO _{2 in} the raw material
No more than 100/28 (100/37) of the content is formed. Mullite has a lower corrosion resistance than alumina and zirconia, so that the content of SiO ₂ 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 a high zirconia-based molten refractory which is usually produced, raw materials are easily available, and there is no need for component adjustment.

Mullite or alumina forms a layer rich in alumina at the interface and serves as a protective layer when molten glass or volatiles of the present invention come into contact with the refractory of the present invention, and suppresses elution of baddrite. I do. Therefore, the corrosion resistance is further improved by adding alumina. In addition, alumina has low temperatures (eg, 1300).
Zirconia is more excellent in foaming properties at below ℃.

In consideration of the above, although it depends on the intended use of the refractory, in the present invention, the ratio of the high zirconia melt-resolidified pulverized product to the alumina powder is 9% by weight in the total amount and the former is 9%.
8 to 50%, the latter is preferably 2 to 50%, more preferably the former is 90 to 70%, and the latter is 10 to 30%.

During firing, there is almost no grain growth of baddrite, so there is no segregation of zirconia beyond the state of the raw material particles. This is because high zirconia-based molten refractories have more pores and matrix glass, and are more homogeneous and highly reliable compared to the fact that there are locally inferior parts with poor corrosion resistance and soil pollution resistance. Refractory.

In FIG. 1, reference numeral 3 denotes mainly a matrix glass phase, alumina particles or pores.

The present invention thus comprises the high zirconia melt-resolidified pulverized material and the alumina particles. Other components can be added to such an extent that the purpose and effect are not impaired. It is desirable to keep it as small as possible.

[0031]

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

The following is an example of a method for producing the product of the present invention. First, a predetermined amount of desilicated zircon, Bayer alumina, silica sand, and sodium carbonate are weighed and mixed, and then mixed in a 500 kVA single-phase electric arc furnace using a graphite electrode to 2500.
It melted completely at about ° C. This molten metal is buried in Bayer Alumina with inner dimensions of 160 mm x 200 mm x 350
The molten metal was poured into a graphite mold having a diameter of 2 mm and allowed to cool to room temperature. Next, the ingot was cut to obtain a portion including a casting cavity.

The portion including the casting cavity of the re-solidified product was pulverized with a jaw crusher and then with an iron pot to obtain a pulverized product having a particle size of about 1 cm. Next, this was immersed in a 1 mol / liter hydrochloric acid aqueous solution, washed, dissolved in mixed iron, and dried. In addition, about 0.1 wt% Fe ₂ O
₃ was observed. Furthermore, it was pulverized using alumina balls. For the same casting, the chemical composition was measured for particle sizes less than 0.15 mm. ZrO ₂ content, S
The iO ₂ content and the Al ₂ O ₃ content were quantified by a glass bead method using a fluorescent X-ray analyzer, and the Na ₂ O content was quantified with an atomic absorption spectrophotometer after decomposition with hydrofluoric acid-sulfuric acid ( Table 1).

The obtained high zirconia melt-resolidified and pulverized product contained monoclinic ZrO ₂ as a main component.

Next, the sieved raw materials were blended so as to exhibit a predetermined particle size distribution (Table 2). This was mixed with alumina having a predetermined particle size distribution (Table 2). The alumina used was obtained by the Bayer method, and had an Al ₂ O ₃ content of 99% or more. Table 1 shows Examples 1 to 16.
Next, each mixed raw material was molded and fired as follows.

500 g of the mixed raw material is pressed by a mold
Pressing was performed by the IP method (1500 kg / cm ³ ) to obtain a raw product. This was heated in a resistance heating electric furnace at 1600
C. for 24 hours. Each of the fired bodies was obtained without generating cracks.

The bulk density of the obtained sintered body was measured by the Archimedes method (Table 4).

In order to examine the corrosion resistance, a 15 mm × 15 m
A rectangular parallelepiped sample of m × 50 mm was cut out from the fired body and immersed in a tube panel glass at 1500 ° C. for 48 hours. Then, it was bisected in the vertical direction, and the amount of erosion was measured (Table 4).

Further, in order to examine the foaming property, 40 mm ×
A plate-shaped sample of 40 mm × 5 mm was cut out from the fired body,
A ring made of alumina and having an inner diameter of 30 mm is placed on the
Heat at 00 ° C. for 24 hours. Thereafter, the number of remaining bubbles was measured using an optical microscope (Table 4).

As a control (comparative example), Table 1 Composition V
Shown in Pulverized product of high zirconia melt-resolidification (particle size: 0.
(Less than 15 mm) only (Comparative Example 1), to which 5% and 10% by weight of clay were added and sintered (Comparative Examples 2 and 3), and zircon-mullite-fired The finished product (Comparative Example 4) was 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 as follows:
This is shown as a relative comparison when Comparative Example 1 is set to 100.
In these cases, when the value of the erosion amount is 100 or more, it indicates that the erosion amount is larger than that in Comparative Example 1, and the foaming amount is 100
The above indicates that the foaming amount is large.

When the cross-sectional structure of the structure shown in the example was observed with a microscope, it was found that all of the structure was basically the same as that shown in FIG.
It was confirmed that the organization consisted of the following.

As can be seen from Table 4, the corrosion resistance and especially the foaming property are improved by adding alumina to the pulverized product of the high zirconia melt-resolidification. Furthermore, the product of the present invention is a conventional zircon-mullite sintered product,
Compared to a sintered product obtained by adding clay to a pulverized high zirconia refractory, its corrosion resistance and foaming properties are remarkably excellent.

In Table 4, 1) Examples are theoretical values based on the composition values in Table 1 and the mixing ratios in Table 3, comparative examples are actually measured values, and 2) relative comparison when Comparative Example 1 is 100. value. 100
This is where the amount of erosion is large. NM indicates measurement impossible due to stone. 3) Relative comparison value when Comparative Example 1 is set to 100. 100
This is where the amount of foaming is large.

From the above, the product of the present invention can be used as a refractory for a glass melting furnace regardless of contact or non-contact with molten glass, and causes glass defects such as bubbles and gravel. It is an irresistible refractory. The refractory of the present invention can be used not only for melting glass but also as a refractory used for melting metals, melting incineration ash, and the like.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

The zirconia-based fired refractory of the present invention comprises:
Compared to conventional zirconia refractories, the structure and composition are uniform and they have a strong bond, so they have stable quality and reliability, and have excellent corrosion resistance and foaming properties. In addition, glass defects such as bubbles and gravel are unlikely to occur in the molten glass, the resistance to soil pollution is low, and the yield of glass production is improved.

Further, since the product of the present invention can utilize a portion containing a casting cavity that cannot be used as a product of a high zirconia-based molten refractory, it can be manufactured at low cost, and can contribute to resource recycling, that is, resource saving.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a part of the structure of a zirconia refractory of the present invention.

[Explanation of symbols]

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

Claims (8)

[Claims] 1. A monoclinic Z of a high zirconia re-solidified material.
A zirconia refractory obtained by sintering a mixture of a pulverized material containing rO ₂ as a main component and alumina powder. 2. The high zirconia melt-resolidified pulverized product is Zr.
_2. The refractory according to claim 1, wherein the O ₂ content is 90% by weight or more and the SiO ₂ content is 1% by weight or more and 6% by weight or less. 3. The refractory as claimed in claim 1, wherein the amount of the alumina powder is 2 to 50% by weight based on the total amount of the alumina powder and the pulverized product of the high zirconia melt-resolidification. 4. The method according to claim 1, wherein a part or all of the periphery of the baddelite phase is composed of the mullite phase.
The refractories described in (1). 5. A powder having a particle size of 10 to 50% by weight, from 1.00 mm to less than 4.76 mm, from 0.15 mm to 1.
Less than 00mm 10wt% ~ 50wt%, 0.15m
The mixture according to any one of claims 1 to 4, wherein a mixture comprising a high-zirconia melt-resolidified pulverized material having a particle size of less than 40% by weight and an alumina powder having a particle size of less than 0.15 mm is sintered. Refractory. 6. The method according to claim 1, wherein a mixture comprising a high-zirconia melt-resolidified pulverized material having a particle size of less than 0.15 mm and alumina having a particle size of less than 0.15 mm is sintered. The refractories described in (1). 7. The refractory according to claim 1, wherein the particle size of the alumina is less than 0.01 mm. 8. The refractory according to any one of claims 1 to 7, wherein the refractory is used in a glass melting furnace.