JP3125331B2 - Method for producing highly heat-insulating aluminum titanate sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum titanate sintered body, and more particularly to a method for producing a highly heat-insulating aluminum titanate sintered body having a large number of air bubbles therein.

[0002]

2. Description of the Related Art In order to prevent environmental pollution due to exhaust gas, an exhaust gas purifying catalyst is disposed in an exhaust system of an automobile. An oxidation catalyst such as platinum is mainly used as the exhaust gas purifying catalyst, and oxidatively decomposes and purifies HC and CO in the exhaust gas. Incidentally, the oxidation reaction rate largely depends on the temperature, and the higher the temperature at the time of the reaction, the more efficient the purification. Therefore, for example,
As disclosed in, for example, Japanese Patent Application Laid-Open No. 4 (1994) -212, it has been proposed to dispose a ceramic port liner on the inner surface of an exhaust port of an automobile engine and prevent the temperature of exhaust gas at the exhaust port from lowering by its heat insulating action.

[0003] The ceramic port liner is formed from ceramic powder by a slip casting method or the like, dried and sintered. As a method of arranging the ceramic port liner in the exhaust port, for example, as shown in Japanese Patent Publication No. 62-32155, a method of integrally casting the ceramic port liner when casting the exhaust port is generally used. is there.

[0004]

However, even for ceramics, since the sintered body has a dense structure, the rate of heat transfer by conduction is relatively large, and the heat insulating effect is insufficient. Therefore, it has been proposed to provide a heat insulating layer such as a ceramic fiber between the cast-in metal and the ceramic sintered body, but this is not preferable because it increases the number of steps and increases the cost.

[0005] The present invention has been made in view of such circumstances, and has as its object to produce a ceramic sintered body having heat insulating properties.

[0006]

SUMMARY OF THE INVENTION The method for producing a highly heat-insulating aluminum titanate sintered body of the present invention, which solves the above-mentioned problems, is a method for producing a mixed powder of Al ₂ O ₃ and TiO ₂ and an aluminum titanate powder. 80 to 90% by weight of a base powder composed of at least one, and 5 to 10% by weight of Fe ₂ O ₃ powder
And 5 to 10% by weight of SiO ₂ powder, and after molding,
By sintering at 1500 ° C. or higher, a large number of bubbles are formed inside the sintered body.

The base powder is a sintered body of aluminum titanate by sintering, and is a mixed powder of Al ₂ O ₃ and TiO ₂ or aluminum titanate (Al ₂ TiO
₅ ) Powder is used. Either one of them may be used, or both may be mixed. Incidentally, TiO ₂ to Al ₂ O ₃ 50 to 60 in an oxide weight basis is 40 to 5
It may be used in a ratio of about 0, preferably in an equimolar amount.

The greatest feature of the present invention is that the base powder is
e ₂ O ₃ powder and SiO ₂ powder are mixed and used. That is, Fe ₂ O ₃ powder and SiO ₂
It is molded using a mixed powder of both powders,
Sintered at 00 ° C to form a sintered body. Here, FIGS. 1 and 2
₂ shows a phase diagram of the Fe ₂ O ₃ —SiO ₂ system and a phase diagram of Fe ₂ O ₃ alone. This indicates that the following reaction occurs.

[0009]

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[0010]

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That is, at a temperature of 1420 ° C. or more, Fe ₂ O ₃
O ₂ gas is generated by the decomposition reaction of, and a liquid phase appears at 1455 ° C. or higher. Therefore, by sintering at 1500 ° C. or more, an appropriate liquid phase and gas are generated, so that a large number of air bubbles of microbubbles remain in the sintered body. This gives the sintered body heat insulation. Sintering temperature 1455
When the temperature is 〜1500 ° C., the liquid phase is insufficient in quantity, the remaining bubbles are reduced, and the heat insulating property is hardly improved. Of course, since the liquid phase does not appear below 1455 ° C., the generated gas is released from the grain boundary and does not remain.

The Fe ₂ O ₃ powder and the SiO ₂ powder are 5 to 10%, respectively, when the whole mixed powder is 100% by weight.
% By weight. If each is less than 5% by weight, the amount of liquid phase and gas generated is small, and the heat insulating property is hardly improved. If more than 10% by weight is added,
The ratio of aluminum titanate in the crystal phase in the sintered body relatively decreases, and the thermal conductivity increases. Further, since a large amount of liquid phase or gas is generated, distortion occurs during sintering, and the accuracy of the shape is reduced.

[0013] A compact can be formed from the above powder by a conventionally known molding method such as a slip casting method or an injection molding method. After demolding, sintering is performed at 1500 ° C. or higher as described above.

[0014]

According to the method for producing a highly heat-insulating aluminum titanate sintered body of the present invention, a sintered body containing a large number of air bubbles can be easily produced with almost no increase in man-hours. The obtained sintered body has excellent heat insulating properties and high heat resistance, so that it is most suitable as a port liner and can be cast without any additional heat insulating layer. Therefore, the number of steps can be significantly reduced, and the cost can be reduced.

[0015]

The present invention will be specifically described below with reference to examples. (Example 1) Commercially available synthetic aluminum titanate powder 86
A slip composed of 80% by weight of a mixed powder composed of 6% by weight of Fe ₂ O ₃ powder, 8% by weight of SiO ₂ powder and 20% by weight of water was poured into a gypsum mold and put on. Meat.

After the meat was laid for a predetermined time, the excess slip was discharged, and the molded product was removed from the mold. Then, the molded body was placed in a drying furnace and kept at a maximum temperature of 60 ° C. for 48 hours to dry the water. After that, the dried molded body is 155
The resultant was held at 0 ° C. for 4 hours and sintered to obtain a port liner made of aluminum titanate. The obtained port liner was visually inspected for the presence or absence of air bubbles in the cross section. The thermal conductivity (W / mK) was measured by a laser flash method. Table 1 shows the results. (Example 2) Except that an aluminum titanate powder formed by mixing 56 parts by weight of Al ₂ O ₃ powder and 44 parts by weight of TiO ₂ powder, firing at 1400 ° C. for 4 hours, and then pulverizing was used. Manufactured a port liner in the same manner as in Example 1. Table 1 shows the measurement results. Comparative Example 1 A port liner was manufactured in the same manner as in Example 1, except that 2% by weight of Fe ₂ O ₃ powder and ₃ % by weight of SiO ₂ powder were used. Table 1 shows the measurement results. Comparative Example 2 A port liner was manufactured in the same manner as in Example 1 except that 15% by weight of Fe ₂ O ₃ powder and 15% by weight of SiO ₂ powder were used. Table 1 shows the measurement results. (Comparative Example 3) A port liner was manufactured in the same manner as in Example 1 except that the dried compact was held at 1350 ° C for 4 hours and sintered. Table 1 shows the measurement results. (Comparative Example 4) A port liner was manufactured in the same manner as in Example 1 except that the amount of aluminum titanate powder was increased without using Fe ₂ O ₃ powder. Table 1 shows the measurement results. (Comparative Example 5) A port liner was manufactured in the same manner as in Example 1 except that the amount of aluminum titanate powder was increased accordingly without using SiO ₂ powder. Table 1 shows the measurement results. (Comparative Example 6) During the synthesis of aluminum titanate, Fe ₂
Except that 6% by weight of O ₃ powder and 8% by weight of SiO ₂ powder were simultaneously added, and molded, dried and sintered with the obtained powder,
A port liner was manufactured in the same manner as in Example 2. Table 1 shows the measurement results. (Comparative Example 7) During the synthesis of aluminum titanate, Fe ₂
Except that ₂ % by weight of O ₃ powder and 3% by weight of SiO ₂ powder were simultaneously added and molded, dried and sintered with the obtained powder.
A port liner was manufactured in the same manner as in Example 2. Table 1 shows the measurement results.

[0017]

[Table 1] (Evaluation) From Table 1, in the port liner obtained by the method of the example,
It is clear that the presence of air bubbles provides excellent heat insulation. On the other hand, as in Comparative Example 1, Fe ₂ O ₃ powder and SiO ₂
When the amount of the powder added is small, no air bubbles are generated and the heat insulating property is poor.

If the amounts of the Fe ₂ O ₃ powder and the SiO ₂ powder are too large as in Comparative Example 2, bubbles are generated but phases other than the aluminum titanate phase are increased, and the thermal conductivity does not decrease. Further, since a large amount of liquid phase is generated, distortion occurs during firing. Further, from the results of Comparative Example 3, it is understood that no bubbles are formed even when the sintering temperature is lowered. And, from the results of Comparative Examples 4 and 5, it is necessary to use F
It is clear that both e ₂ O ₃ powder and SiO ₂ powder are needed.

Further, it is understood that it is meaningless to add Fe ₂ O ₃ powder and SiO ₂ powder during the synthesis of aluminum titanate as in Comparative Examples 6 and 7. Progresses, and no gas is generated during the important sintering. And even if bubbles exist in the aluminum titanate synthesized by the gas generated at the time of synthesis, most of the air bubbles are destroyed by the pulverization after the synthesis, and the effect cannot be obtained.

[Brief description of the drawings]

FIG. 1 is a phase diagram of an Fe ₂ O ₃ —SiO ₂ system.

FIG. 2 is a phase diagram of Fe ₂ O ₃ .

Claims (1)

(57) [Claims] 1. A base powder composed of at least one of a mixed powder of Al ₂ O ₃ and TiO ₂ and an aluminum titanate powder in an amount of 80 to 90% by weight, a Fe ₂ O ₃ powder in an amount of 5 to 10% by weight, SiO ₂ 5 to 10% by weight of a powder, and after molding, sintering at 1500 ° C. or more to form a large number of air bubbles inside the sintered body. Production method.