JP3072877B2 - Zirconia-alumina electroformed refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconia-alumina electroformed refractory having particularly excellent spall resistance.

[0002]

2. Description of the Related Art Electroformed refractories containing alumina or zirconia as a main component generally include high alumina electroformed refractories, alumina / zirconia / silica electroformed refractories (hereinafter referred to as AZS electroformed refractories), Classified as zirconia electroformed refractories. These electroformed refractories have been conventionally used in glass melting furnaces and the like.

[0003] High-alumina electroformed refractories have a high erosion resistance to glass and have a feature that defects such as bubbles and cords are not generated in glass. Further, it is stable against alkali vapor and has a large load resistance.

As AZS refractories, for example, Japanese Unexamined Patent Publication No. Sho 62
There is a refractory disclosed in Japanese Patent No. 65981. This A
ZS refractories contain a large amount of zirconia and have high corrosion resistance to molten glass.

Japanese Patent Application Laid-Open No. 3-28175 discloses a high zirconia electroformed refractory containing 90% or more zirconia. In general, high-zirconia electroformed refractories have very high corrosion resistance to molten glass and scattered raw batches, and there is no problem in terms of corrosion resistance even when used in a portion that directly contacts molten glass. For this reason, electrocast refractories of high zirconia tend to be used more frequently.

[0006]

However, each of the conventional electroformed refractories has the following disadvantages. That is, the high-alumina electroformed refractory is inferior in spall resistance and is unsuitable for a place where temperature conditions are severe such as an upper structural member of a glass melting furnace. In addition, when the AZS refractory is used as a glass melting furnace, there is a risk that a glassy material may flow down from the surface of the refractory during operation and cause defects in the molten glass. On the other hand, the high zirconia electroformed refractories were poor in spall resistance because the structure was dense and the zirconia undergoes crystal transformation. For this reason, high zirconia electroformed refractories have been restricted in use temperature and place of use.

The present invention has been made to solve the above-mentioned drawbacks of the conventional alumina and zirconia electroformed refractories.
Maintaining the content of Al ₂ O ₃ at 80% or more, without greatly changing the specific gravity and porosity of the conventional electroformed refractory,
High corrosion resistance to molten glass and alkali vapor,
An object of the present invention is to provide a zirconia-alumina electroformed refractory which is less foamed when in contact with molten glass and has excellent spall resistance.

[0008]

The present inventors have conducted various studies on the mineral composition of a high alumina electroformed refractory in order to achieve the above object, and as a result, have reduced the glass phase which is considered to be the cause of foaming. By crystallizing badelite at the grain boundaries, which is considered to relieve stress during thermal shock, it has high corrosion resistance to molten glass and alkali vapor without significantly changing specific gravity and porosity. It has been found that a zirconia-alumina cast refractory with less foaming and excellent spall resistance can be produced when the refractory is in contact with a refractory.

The first invention is a zirconia-alumina electroformed refractory containing Al ₂ O ₃ as a main component, wherein the content of ZrO ₂ is 3 to 10% by weight, and Na ₂ O / Al ₂ O ₃
Weight ratio is 0.02 to 0.05, and the crystal structure exhibits a cross structure of corundum and β-alumina, and at least badelite is present at a grain boundary between corundum and β-alumina and at a grain boundary between β-alumina and β-alumina. A zirconia-alumina electroformed refractory characterized by the following.

A second invention relates to a zirconia-alumina electroformed refractory containing Al ₂ O ₃ as a main component, wherein the content of ZrO ₂ is 10 to 15% by weight, and Na ₂ O / Al ₂ O
The weight ratio of ₃ is 0.03 to 0.05, and the crystal structure exhibits a cross structure of corundum and β-alumina, and at least the badelite is present at the grain boundary between corundum and β-alumina and at the grain boundary between β-alumina and β-alumina. A zirconia-alumina electroformed refractory, which is characterized by the above, is summarized.

[0011]

Since the refractory of the present invention has the above-mentioned structure, it does not greatly change the specific gravity and the porosity.
While maintaining low foaming properties with respect to the molten glass, it has extremely excellent spall resistance as compared with conventional high alumina electroformed refractories as well as AZS refractories and high zirconia electroformed refractories.

The reason why the electroformed refractory of the present invention exhibits such excellent spall resistance is considered as follows.

In the crystal structure of the electroformed refractory of the present invention, badelite is widely distributed at the grain boundaries of corundum and β-alumina, which are the main constituent phases. If this refractory is subjected to a large thermal shock, the badderite will undergo a transformation. The transformation of baddelite involves a change in volume, but the change in volume causes many fine cracks at the grain boundaries of corundum and β-alumina, and the many fine cracks reduce thermal stress. Fine cracks at the grain boundaries promote intergranular fracture rather than intragranular fracture. That is, cracks do not occur in the corundum and β alumina particles themselves, but cracks occur between the particles.

Furthermore, since corundum and β-alumina, which are the main constituent phases, form an intersecting structure, their crystal grain boundaries have complicated uneven surfaces. Therefore, the energy at the time of the fracture is consumed as friction energy at the uneven surface between the crystal grains by promoting the grain boundary fracture. It is considered that the spall resistance is greatly improved for the above reasons.

[0015]

The reasons for limiting the range of each composition will be described.

If the ZrO ₂ content is less than 3%, ZrO 2
Insufficient corrosion resistance due to ₂ . That is, the corrosion resistance to molten glass or the like is insufficient. Conversely, when the ZrO ₂ content exceeds 15% (but 10% when the weight ratio of Na ₂ O / Al ₂ O ₃ is 0.02 to 0.03), the spall resistance and the foaming property are reduced. Insufficient. Note that, in Japanese Patent Application No. 4-150023 filed by the present applicant in the past, ZrO ₂
Although the content of was 1.5 to 15%, the reason for increasing the content to 3% or more in the present invention is that if ZrO ₂ is less than 3%, the amount of baddelite crystallized at the grain boundary decreases. This is because sufficient spall resistance cannot be obtained.

The content of Na ₂ O, Na ₂ O / Al ₂ O
The weight ratio of ₃ is set to be 0.02 to 0.05. N
Most of the a ₂ O is a component of β-alumina,
_{If the amount of 2} O is larger than the above range, the corrosion resistance is deteriorated.

Hereinafter, preferred embodiments of the present invention will be described.

In Examples 1 to 18, the main component was Al ₂ O ₃ , the content of ZrO ₂ was 3 to 10% by weight, and Na ₂
O / Al ₂ O ₃ weight ratio of 0.02 to 0.05, or
When the content of ZrO ₂ is 10 to 15% and Na ₂ O / Al ₂
A zirconia-alumina electroformed refractory having an O ₃ weight ratio of 0.03 to 0.05 and a composition shown in Table 1 was produced. As Comparative Examples 1 to 9, Al ₂ O ₃ was used as a main component, the content of ZrO ₂ was 0 to 20% by weight, and Na ₂ O /
The weight ratio of Al ₂ O ₃ is 0.01 to 0.06, and Table 1
A zirconia-alumina electroformed refractory having the composition shown in Table 1 was produced.

[0020]

[Table 1] After the raw materials were melted using an open-top arc furnace, the melt was poured into a carbon mold having an inner size of 100 × 200 × 300 mm. After about 1 minute, the carbon mold was removed and cooled in alumina fine particles. With respect to the refractory obtained in this manner, the crystal structure was observed, and physical properties tests such as spall resistance, corrosion resistance, and foaming property were performed. The results are shown in FIG. FIG. 1 is a sectional view schematically showing a crystal structure of an electroformed refractory according to the present invention. Table 2 shows the results of the physical property tests of the examples and the comparative examples.

[0021]

[Table 2] As shown in FIG. 1, the crystal of the electroformed refractory according to the present invention is mainly composed of corundum 1 and β-alumina 2, and contains a small amount of budelite 3. Corundum and β-alumina are the main constituent phases, and many of these grain boundaries exhibit a complex structure with complex irregularities. Budderite is a grain boundary of corundum and β-alumina and / or
Alternatively, it is elongated or thin at the grain boundary between β alumina and β alumina. Further, badelite may be eutectic 4 with β-alumina. Reference numeral 5 indicates a pore. ZrO
_{As the number of 2} increases, the budderite at the grain boundaries increases, approaches a sphere, and forms a shape that bites into β-alumina. When ZrO ₂ is further increased, the budderite separates β-alumina, and the spall resistance decreases. N
When the content of a ₂ O is small, β-alumina is small, and the density of the paddleite with respect to the β-alumina is increased.

The above three types of crystals show that when the melt solidifies, corundum is first crystallized, then β-alumina is crystallized, and badelite is crystallized before β-alumina is crystallized. It can be inferred from 1.

Next, various physical property test methods will be described.

A spall resistance test A test piece having a size of 25 × 30 × 50 mm was cut out from each refractory, placed in a furnace at 1200 ° C., held for 30 minutes, taken out of the furnace, and then taken out of the furnace. At 30
The operation of cooling for one minute was repeated. And the number of cycles until peeling occurs is obtained as the number of spalling,
The spall resistance was evaluated.

Corrosion resistance test A test piece having a diameter of 20 mm and a length of 80 mm was cut out from each refractory, and the test piece was placed in a crucible having an inner size of 150 × 120 × 80 mm filled with soda lime glass, and the entire test piece was cut. Soak in glass
C. in a furnace for 168 hours. After heating, the test piece was cut in half and the amount of erosion (depth) was measured with a caliper to evaluate the corrosion resistance.

Foamability test A test piece having a diameter of 50 mm and a thickness of 20 mm is cut out from each refractory, the test surface is polished smoothly, washed and dried. This test piece was placed in a furnace at 1200 ° C.
After holding for 1 hour, the inside diameter 35 mm, thickness 15
The test glass was placed on the center of a 2 mm alumina ring, and held for 2 hours. After cooling, the bubbles present in the glass were counted using a magnifying glass to evaluate the foamability.

Looking at the results of the physical property tests shown in Table 2,
Examples 1 to 18 in erosion rate is decreased with increasing amount of ZrO _2. Examples 1 to 18 are comparative examples 1
The erosion rate is small and the corrosion resistance is large as compared with a conventional high alumina electrocast refractory containing no ZrO _{2 of 0} to 12. Further, the number of times of spalling in Examples 1 to 18 was 27 or more, and the spalling resistance was superior to Comparative Examples 1 to 17. Further, the foaming properties of Examples 1 to 18 are as shown in Comparative Examples 1 to 1.
It can be seen that it is generally small and good as compared with No. 7.

Comparative Examples 10 to 13 are conventional high alumina and AZS electroformed refractories. Comparative Examples 14 to 17 are fired refractories which are generally considered to have better spall resistance than electroformed refractories. But,
Even in these refractories, as shown in Table 2, the spall resistance was equivalent to each of the examples of the present invention. Needless to say, the corrosion resistance and fire resistance of these refractories
It was significantly inferior to that of the example.

[0029]

As described above, the zirconia of the present invention is used.
In the electroformed alumina refractory, the spall resistance can be remarkably improved while maintaining the corrosion resistance and the foaming property without largely changing the specific gravity and the porosity as compared with the conventional product.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a crystal structure of an electroformed refractory according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 corundum 2 β-alumina 3 badelite 4 eutectic of β-alumina and badelite 5 pore

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeo Endo 4-4 Nihonbashi Hisamatsucho, Chuo-ku, Tokyo Itoshige Building Inside Toshiba Monoflux Co., Ltd. (56) References JP-B 26-1571 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/657 C04B 35/10

Claims (2)

(57) [Claims] 1. A zirconia containing Al ₂ O ₃ as a main component.
In an alumina electroformed refractory, the content of ZrO ₂ is 3
-10% by weight, the weight ratio of Na ₂ O / Al ₂ O ₃ is 0.02-0.05, and the crystal structures are corundum and β.
It shows a cross structure of alumina, at least corundum and β
A zirconia-alumina electroformed refractory, characterized in that badelite is present at a grain boundary of alumina and a grain boundary of β-alumina and β-alumina. _2. A zirconia containing Al ₂ O ₃ as a main component.
In an alumina electrocast refractory, the content of ZrO ₂ is 1
0 to 15% by weight, the weight ratio of Na ₂ O / Al ₂ O ₃ is 0.03 to 0.05, and the crystal structure shows a cross structure of corundum and β-alumina. A zirconia-alumina electroformed refractory, characterized in that badelite is present at the boundaries and at the grain boundaries of β alumina and β alumina.