JPS6236986B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a zircon-chromium oxide refractory containing 10% by weight or more of Cr ₂ O ₃ .

Currently, zircon refractories and chromia refractories (refractories containing Cr ₂ O ₃ as a main component) are manufactured. However, refractories made of zircon and chromium oxide are difficult to sinter, so they are hardly produced. However, in order to improve the erosion resistance of zircon refractories,
There is only one containing about 1 to 5% by weight of Cr ₂ O ₃ . However, in this case as well, it is difficult to perform dense sintering, so although the performance can be improved somewhat, it cannot be said to be sufficient.

The present invention aims to provide a method for producing a refractory material containing 10% by weight or more of Cr ₂ O ₃ in zircon, which is uniformly and densely sintered and has excellent physical properties.

The present inventor has previously developed the ability to obtain dense sintering by firing a molded body of Cr ₂ O ₃ alone in carbon powder (Japanese Patent Laid-Open No. 54-96508).
Further research led to the development of sintering a mixed compact of zircon powder and Cr ₂ O ₃ powder, which was previously considered difficult to sinter. When 10% by weight or more of Cr ₂ O ₃ powder was mixed with zircon powder, this was molded and sintered in carbon powder, it was sintered uniformly and densely, and the resulting sintered body had good physical properties. It was found that this material is an excellent refractory. The present invention was completed based on this knowledge.

The refractories produced by this method have characteristics that mutually reinforce the drawbacks of conventional zircon refractories and chromia refractories.

That is, zircon refractories have the advantage of having a small coefficient of thermal expansion, excellent thermal shock resistance, and further excellent abrasion resistance. However, on the other hand, it is difficult to sinter zircon to make it densified (at temperatures above about 1500°C, zircon dissociates into zirconia and silica, so sintering to densify it by high-temperature firing is not possible), and a considerable amount of pores remain. During use as a refractory, highly reactive substances such as slag melt enter the pores of the zircon, causing it to decompose into zirconia and silica, which react with the intruding components to form low-melting compounds and melt. and removed. Therefore, there is a drawback that the organization becomes weakened and eroded.

On the other hand, chromia refractories have the advantage of being difficult to wet and dissolve in melts such as slag and have excellent corrosion resistance, but have the disadvantages of a high coefficient of thermal expansion and poor thermal shock resistance.

In contrast, the zircon-chromium oxide refractories obtained by the method of the present invention have a high relative density, as shown in Figure 1, and are particularly suitable for refractories containing 20% by weight or more of _{Cr2O3 .} The porosity of is 5% or less. The microstructure is uniform and dense, as shown in the reflection micrograph (Figure 2) and the scanning electron micrograph (Figure 3) of an example of an equivalent sintered body. . Due to this compactness, there is almost no intrusion of foreign components through the pores during use, and
Since the Cr ₂ O ₃ component is difficult to wet with melts such as slag, and dissolves and dissolves, it has superior corrosion resistance against melts of slag compared to zircon refractories.

In addition, as shown in Figure 1, as the proportion of zircon contained increases, the coefficient of thermal expansion decreases, and at the same time, the thermal shock resistance increases, and these points are improved compared to chromia refractories. Ru.

In other words, the refractory manufactured by the method of the present invention has improved thermal shock resistance with almost no reduction in erosion resistance when considered based on chromia refractories. Based on high-quality refractories, it improves corrosion resistance without significantly reducing thermal shock resistance.

In addition, it can be produced easily and at a low temperature of 1400 to 1500℃, so it is low cost, and when used as a refractory for melting long fiber glass, which is currently mainly used as a chromia refractory, it is possible to It is believed that this would provide significant benefits, such as by increasing impact resistance. Furthermore, it is believed that it will bring many benefits, such as superior corrosion resistance, compared to zircon refractories currently used as refractories for steelmaking, such as for ingot making and continuous casting.

Furthermore, the zircon-chromium oxide sintered body produced by the method of the present invention has an extremely dense microstructure, high hardness, and high fire resistance, so it can be used not only as refractories but also as special porcelain. You can also expect

Example: Mix chromic oxide reagent powder and zircon reagent powder in various proportions, perform wet mixing with acetone, and mold this mixed powder into a plate shape with a thickness of 15 to 10 mm in a mold with a width of 45 x 27 mm. It was press-molded at a pressure of 800 kg/cm ² . This was placed in an alumina container, carbon powder was sufficiently filled around the sample, the lid was closed, and the alumina container was placed in an electric furnace and fired at 1500° C. for 2 hours. A reaction layer of 0.1 to 1 mm mainly consisting of chromium carbide was formed around the fired sample, so after removing it, the bulk density was determined, and from that the relative density {(bulk density/true density) x 100 } was calculated.

For comparison, relative densities were also determined for samples fired in an air atmosphere.

The results show that, as shown in Figure 1A, by firing in carbon powder, Cr ₂ O ₃ of 20% or more composition is 95%
In addition to the above relative density, when the composition was 50% Cr ₂ O ₃ or more, it was fired to a density of 98% or more. but
If Cr ₂ O ₃ is less than 20%, densification is difficult to proceed;
For compositions below Cr ₂ O ₃ , the relative density was below 80%. On the other hand, when fired in an air atmosphere, all compositions showed almost no shrinkage when fired at 1500°C.

Furthermore, the thermal expansion curves of samples fired in carbon powder were almost linear for all compositions. The relationship between expansion coefficient and composition decreases with increasing proportion of zircon, as shown in Figure 1B;
While the Cr ₂ O ₃ content is 7 x 10 ^-6 cm/℃, when the zircon content is 50%, it is 5 x 10 ^-6
cm/℃, and when it reached 70%, it decreased to 4.7×10 ^-6 cm/℃.

[Brief explanation of the drawing]

Figure 1 shows the relative densities of samples obtained by mixing zircon (ZrSiO ₄ ) powder and Cr ₂ O ₃ powder in various proportions and firing the mixed powder compacts in carbon powder and in air at 1500°C for 2 hours. (Fig. 1A).
Furthermore, the linear expansion coefficient of the sample fired in carbon powder is shown in relation to the composition (FIG. 1B). 1 indicates the case of firing in carbon powder, and 2 indicates the case of firing in air. Figures 2 and 3 show the microstructure of a sample obtained by mixing equal weights of ZrSiO ₄ powder and Cr ₂ O ₃ powder, and firing this mixed powder compact in carbon powder at 1500°C for 2 hours. FIG. 2 is a reflection micrograph of the polished surface, and FIG. 3 is a scanning electron micrograph of the fractured surface.

Claims (1)

[Claims] 1. A method for producing a zircon-chromium oxide refractory, which comprises firing a compact of a mixture of zircon powder and 10% by weight or more of Cr ₂ O ₃ powder in carbon powder.