JPS6363510B2 - - Google Patents

Description

[Detailed description of the invention]

Generally cordierite (2MgO・2Al ₂ O ₃・
5SiO ₂ ) exhibits a very low coefficient of thermal expansion over a wide temperature range, and has excellent resistance to thermal shock caused by rapid temperature changes.
For this reason, cordierite has been widely used as a heat-resistant hot plate, a heat-resistant material for physical and chemical use, and, in recent years, as a material for honeycomb structures in heat exchangers. However, cordierite has a narrow densification temperature range, and due to the expansion of this temperature range, alumina, zircon,
This drawback is eliminated by adding aluminum titanate or the like. For example, zircon has long been considered the best additive to meet the requirements of not having too large a thermal expansion and being thermally strong, but the properties of the sintered body may vary depending on the grain size of the zircon added. Rather than promoting sintering, it actually makes sintering difficult, and a dense sintered body cannot be obtained in many cases. This method allows zircon to coexist in the cordierite sintered body, but by allowing only zircon crystals produced by decomposition from barium zirconate to exist in the matrix, it can be easily densified.
The sintered body is characterized by being mechanically, electrically and thermally excellent. Earlier, we applied for a patent on a method for producing low-expansion cordierite ceramics, which is characterized by the production of zircon by adding 2 to 30% by weight of zirconium and phosphorus (calculated as oxides) (Tokuko Showa). 60-35312). Zircon is generally made by finely pulverizing natural zircon sand, but it contains a lot of iron as an impurity and is hard, making it difficult to crush.Generally, fine pulverization allows impurities to enter easily, and the drawback is that iron spots appear when fired. There is. Synthetic zircon is also expensive and not common. Although zircon flour is a fine powder, it is unsuitable for producing sintered bodies. The present invention relates to the sharing of zircon in cordierite as described above (Japanese Patent Publication No. 60-35312).
No.), but the additive is barium zirconate, and a cordierite sintered body with excellent properties can be obtained. That is, by adding 2.5 to 20% by weight of barium zirconate to synthetic cordierite powder,
Bake at ℃. The commonly used cordierite composition is MgO5-17% by weight, Al ₂ O ₃ 30
~45 wt%, _SiO2 ranging from 43 to 60 wt%,
If the composition does not fall within these ranges, or in the case of raw cordierite, the production of zircon will be hindered. In particular, the composition of raw cordierite produces barium, magnesium, aluminum, silicate (BaMg ₂ Al ₃ (Si ₉ Al ₃ O ₃₀ )), etc., which increases the coefficient of thermal expansion and reduces the thermal shock resistance. When the firing temperature is 1250°C or lower, no zircon is produced, and at 1450°C or higher, it becomes molten, which is not suitable. The feature of the present invention is that the barium zirconate added to the synthetic cordierite decomposes during the sintering process to form zircon and a glassy material, which makes sintering easier than when zircon and barium oxide are added. It is possible to obtain a sintered body that has excellent electrical insulation properties, and has sufficient mechanical strength and thermal shock resistance. Next, an example will be shown. Example 1 Cordierite (2MgO・2Al ₂ O ₃・
5SiO ₂ ) was synthesized at 1350°C. This material was coarsely crushed and ground with water in a pot mill for 24 hours to obtain a dry powder. 0 to 25% by weight of barium zirconate (composite molar ratio 0.990, <325 mesh) was added to this,
The pellets were molded to 750 kg/cm ² and fired at 1250 to 1450° C. for 1 hour in an electric furnace with a SiC heating element. The temperature at which the absorption rate becomes 0.02% or less due to sintering is
It was impossible to achieve temperature higher than 1420℃, but at 25% by weight, 1420
℃, and decreased as the amount added increased, reaching 1315℃ at 25% by weight. When the amount added was 20% by weight or more, it became difficult to maintain the shape. The light transmittance of the sintered body was also particularly excellent when the amount added was 1 to 12.5% by weight. Table 1 shows the coefficient of thermal expansion of these sintered bodies from room temperature to 500℃ and from room temperature to 1000℃, Te value, thermal shock resistance value (crack initiation temperature) when dropped into water at 0℃ from high temperature,
Bending strength and mineral identification by X-rays are shown. Example 2 10.0% by weight of barium zirconate from Example 1 was added to commercially available synthetic cordierite (containing mullite as seen by X-rays), and a small amount of manganese dioxide was added, and the mixture was similarly calcined. Created a body. The results are shown in Table 2. Comparative Example 1 Table 3 shows a comparison of properties when barium zirconate was added to the synthetic cordierite of Example 1 and a raw preparation thereof in an amount of 10% by weight. Comparative Example 2 A case in which 10% by weight of barium zirconate was added to a commercially available high-purity synthetic cordierite powder, and a case in which zirconia and barium carbonate were added to the composition of barium zirconate (raw state) so that it became 10% by weight. A sintered body was produced in the same manner as in the example. The results are shown in Table 4.

【table】

【table】

[Table] When a small amount of manganese dioxide was added as a sintering accelerator, the material turned brown and became denser at lower temperatures, with almost no change in properties.

【table】

【table】

Claims (1)

[Claims] 1. A method for producing a cordierite sintered body, which comprises adding 2.5 to 20% by weight of barium zirconate to synthetic cordierite and firing at 1250 to 1450°C to generate zircon in the matrix.