JPS593435B2 - spherical ceramic material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spherical ceramic material directly obtained from an A1203-8 i 02 series melt useful as an aggregate for ceramic porous bodies and a high temperature refractory material.

Currently, the following materials are used as aggregates for ceramic porous bodies such as various ceramic filters and porous plugs and nozzles for steel manufacturing.

(1) Those using particles obtained by crushing and pulverizing electrofused or sintered corundum lumps.

(2) Use fused mullite beads.

(3) Using fused spinel beads.

However, each has the following drawbacks.

(1) The method using crushed particles of fused corundum or sintered alumina lump is the most common, and the material price is also relatively low.
They are irregularly shaped crushed particles obtained by pulverization.

Such crushed aggregates have not only irregular grain shapes but also acute-angled or flat shapes, and furthermore, they contain minute racks due to the impact of crushing.

Therefore, when a porous body is molded using this aggregate, the filling properties are poor, and if the molding pressure is increased in an attempt to increase the aggregate volume ratio, aggregate destruction may occur, and the aggregate distribution may become uneven, resulting in pores. Since the presence of pores in the porous body is also non-uniform, it is difficult to finely adjust the pores of the porous body, and there are drawbacks such as difficulty in controlling the amount of ventilation.

To address these problems, bead-shaped ceramic aggregates have recently begun to be used.

The bead-shaped ceramic aggregate has a spherical shape, so it has good filling properties, and has a certain degree of strength, so the aggregate does not break during pressure molding.

Furthermore, since the aggregates in the molded product come into contact with each other at points, the pores can be made more uniform and finer, and the amount of ventilation can be easily controlled.

However, each of the conventional bead-shaped ceramic aggregates has the following drawbacks.

The fused mullite beads used in (2) have a lower melting point and inferior fire resistance than corundum. However, there are problems such as large erosion due to corrosion, which limits its use.

(3) uses fused spinel beads, (2)
Compared to fused mullite beads, spinel has a higher melting point and superior fire resistance, but on the other hand, spinel has the disadvantage of poor thermal shock resistance (spalling resistance) due to its large thermal expansion, so it has a limited service life. The disadvantage is that it is extremely bad.

The present inventors conducted various studies in view of the above-mentioned problems in the conventional technology, and as a result, they discovered a spherical ceramic material that has the characteristics required as an aggregate for fire-resistant porous bodies.

That is, the present invention has high fire resistance close to that of fused corundum,
The present invention provides a spherical ceramic material that has a true spherical shape equivalent to various spherical aggregates, and has strength and thermal shock resistance comparable to that of fused mullite beads.

Next, the present invention will be specifically explained.

The present inventors have developed conventional fused mullite beads (3A12
We conducted research to obtain a spherical ceramic material with a higher refractory resistance than the conventional one by transferring 03.2Si02) to the Al2O3 side.

However, if the amount of SiO□ is gradually reduced (and shifted to the Al2O3 side, the fire resistance will gradually increase,
If the amount of O3 is increased, the structure of the spherical objects will gradually become hollow and the strength will drop rapidly. It has been a common concept in the prior art that something with sufficient strength cannot be obtained.

However, the present inventors have conducted further research on the spherical molten quenched material of the Az2o3-SiO2 binary system.
By changing the blended weight of SiO2 and Al2O3, we investigated the relationship between various properties of spherical objects and the weight ratio of SiO2 and Al2O3 (hereinafter referred to as SiO□/ASi03), and found that the single grain crushing strength About S i 0
2/A#203 was found to have singular points at 0.21 and 0.16.

The relationship is shown in FIG. In Figure 1, the horizontal axis shows SiO□ (gravimetric gravimetric analysis value) and SiO□/Al2O
3 and the single grain crushing strength on the vertical axis, SiO□ is 1
This figure schematically explains the relationship between changes in SiO□ and single grain crushing strength, and the crystal structure at the relevant composition point in the range of 0 to 25 weight ratio.

In addition, the single grain crushing strength shown in Figure 1 refers to the average particle diameter of 20 samples taken at random from three types of samples adjusted to 3095μ, 1840μ, and 920μ, respectively.
A load is applied to each sample individually, and the weight at which the sample is crushed (
K7) divided by the maximum area (O4) of the sample.

When these relationships were investigated in terms of macrostructure and microstructure using X-ray diffraction, an electron microscope, and a polarizing microscope, the following was found.

The results will be explained based on FIG.

It is understood that the mullite composition of (A) is composed of radially developed mullite crystals intertwined with each other and has high strength.

As SiO2 decreases, the glass phase that connects the radial mullite crystals begins to decrease, and a corundum phase appears and gradually increases. In (B), the mullite crystals become larger and large partings appear in the crystals. The intensity decreases as it appears.

However, when SiO□/Al2O3 becomes 0.21 or less, a part of the mullite phase comes to surround the corundum crystals, and the strength increases.
3 becomes 0.16 (s:,)f, the corundum microcrystals become dense, and the grain boundaries are filled with a small amount of mullite phase, leaving only small pores, so that the strength is maximum.

Moreover, when the value of SiO2/Al2O3 becomes even smaller than that, the strength begins to decrease rapidly due to the synergistic effect of the decrease in the mullite phase, which is the binder phase, and the increase in pores, and (D)
In this case, the corundum crystal grain size has increased, and the strength has decreased due to the presence of large pores.

This can be fully understood from the X-ray diffraction results shown in FIG.

As is clear from the above description, the present invention is made substantially of corundum crystals or corundum crystals and mullite crystals, and the value of S i 02/AA20s is 0.1.
Despite having a high Al2O8 content, the spherical particles in the range of A120.
-3 i O□ system phase diagram clearly shows that (, Al2O
3 content is high (the higher the fire resistance).

Next, in order to investigate the thermal shock resistance of the spherical ceramic material according to the present invention, a comparative test with conventional products such as fused mullite beads and fused spinel beads was conducted in the following manner.

As a test method, 100 grams of each sample adjusted to a particle size of 3360 to 2830μ was collected and heated to 1400℃.
After heating for 10 minutes in the Elema furnace, which was heated to a temperature of

Next, after drying the sample, pass it through a 2830μ sieve and measure the weight under the sieve.

This operation was repeated 5 times. The results are shown in FIG.

FIG. 4 shows the ratio of the weight under the sieve (cumulative) of 2830μ to 100 duram of the original sample.

As is clear from the results, it was confirmed that the spherical ceramic material according to the present invention exhibits much higher thermal shock resistance than fused spinel beads, and has almost the same thermal shock resistance as fused mullite beads.

As described above, the product of the present invention improves each of the drawbacks of conventional spherical ceramic aggregates, and is highly useful as a strong aggregate for porous bodies with excellent fire resistance and thermal shock resistance. I can say that.

Next, an example of the method for manufacturing the spherical ceramic material of the present invention will be described.

High-purity alumina and silica sand shown in Table 1 are used as raw materials, and the molten S i 02/A12os is 0.
Blend to be in the range of 13 to 0.19, 1500kV
Melting was carried out using an A tilting single-phase electric furnace under the following conditions.

Voltage: 200V Current: 1800A Average load: 353kW Average blowing air pressure: 5Kii/ctA While sufficiently melting the melt, blowing was performed using compressed air at an average rate of 5~/c4.

As a result, a dense spherical ceramic material with a particle size range of about 5000μ to 20μ was produced.

Table 2 shows the main chemical components and properties of the obtained spherical ceramic material.

Incidentally, the particle size of the product depends on the blowing air pressure, and the sieve fraction is used as appropriate depending on the purpose.

Next, in order to further clarify the characteristics of the spherical ceramic material according to the present invention, a comparison was made with various conventional aggregates for porous bodies.

Porous plugs for steelmaking were prepared under the same conditions, and the performance of each was compared by blowing argon gas during ladle refining.

The results are shown in Table 3. As shown in Table 3, (the porous plug made using the spherical ceramic material according to the present invention as an aggregate has nearly double the durability at high temperatures compared to the plug using the conventional aggregate) It shows.

In addition, because uniform and extremely fine pores are obtained, not only can fine gas bubbles be obtained (it was also confirmed that molten steel is less likely to penetrate into the base metal).

The present invention is based on the conventional method that in AA203-8 i 02 two-component system spherical molten quenched material, if the amount of Al2O3 is increased beyond a certain level, the structure of the spherical material becomes hollow and the strength decreases. This eliminates the fixed concept, and according to the present invention substantially consists of corundum crystals or corundum crystals and mullite crystals, and the weight ratio of silica and alumina (SiO2/A1203) is 0.13 to 0.13.
A spherical ceramic material characterized by a range of 0.19 & It has a thermal shock resistance equal to or higher than that of 1, and has great industrial value as an aggregate for ceramic porous bodies and as a high-temperature refractory material.

The scope of the claims defined by the present invention is based on the single grain crushing strength (4.1 Ky/air at 3095μ, 6.1Ky/air at 1840μ) of fused mullite beads, which have been conventionally used in large amounts.
2 Kf//crA, 9.0 Kg/cri at 920μ
i), and if the composition is outside this range, the strength will be extremely low and the aggregate will not be suitable for use as an aggregate for porous bodies.

As described above, the spherical ceramic material of the present invention, like conventional fused mullite beads and fused spinel beads, can be melted in an electric furnace or other melting equipment using air, gas,
It is produced by blowing with water or steam, but the present invention is made by extremely restricting the composition of the melt, with a weight ratio of silica to alumina (SiO2/A1203) of 0.
．． 13 to 0.19, and the effect is achieved by preparing the purity to be substantially composed of corundum crystals or corundum crystals and mullite crystals, and preferably S i 02 /AA203 is 0.14 to 0.19.
Even better characteristics can be exhibited within the range of 18.

[Brief explanation of drawings]

Figure 1 schematically shows the relationship between single grain crushing strength due to compositional changes of Al2O8 and SiO□ in the A1203-S i 02 binary spherical molten quenched product, and the crystal structure at the relevant composition point. be. FIG. 2 shows the relationship shown in FIG. 1 using the peak heights of corundum and mullite as determined by X-ray diffraction. FIG. 3 is a phase diagram of the AA203-8i02 binary system. FIG. 4 shows the results of a thermal shock resistance comparison test between the product of the present invention and conventional products such as fused mullite beads and fused spinel beads.

Claims (1)

[Claims] I AA20B-8i A spherical body directly obtained from a 02-based melt, consisting essentially of corundum crystals or corundum crystals and mullite crystals, and having a weight ratio of silica to alumina (Sio□/A1203) of 0. 1
A spherical ceramic material characterized in that the particle diameter is in the range of 3 to 0.19.