JP3185340B2 - Method for producing aluminum titanate-based ceramic member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aluminum titanate-based ceramic member. Since the aluminum titanate-based ceramic member obtained in the present invention has high heat insulating properties, it is useful for automobile engine parts and the like.

[0002]

2. Description of the Related Art Aluminum titanate has a low thermal conductivity of about several W / m · K, and applied research utilizing this property has been advanced. For example, in automobiles, it is expected to be applied as an exhaust system cast-in part for various engines, and it has been proposed to use aluminum titanate for a ceramic part cast into a ceramic port head.

However, it is known that a fired aluminum titanate is thermally decomposed at a predetermined temperature or higher. JP-A-2-258670 discloses a low thermal expansion ceramic which suppresses thermal decomposition and exhibits high stability even at high temperatures by coexisting magnesium titanate solid solution and yttrium titanate in aluminum titanate. I have.

[0004]

However, although aluminum titanate has a low thermal conductivity, it does not have sufficient heat insulating properties for use in the exhaust system of an automobile engine, and it is necessary to reduce cold emission and cooling loss. It is necessary to further reduce the thermal conductivity. Further, even in the ceramics disclosed in the above publication, the thermal expansion property is reduced, but the heat insulating property is hardly improved, and further improvement is desired.

[0005] It is known that the low thermal conductivity characteristic of aluminum titanate is caused by microcracks existing between particles. The microcracks occur during cooling from a high temperature to room temperature and are due to thermal anisotropy of the particles. Therefore, when the composition is the same, it is difficult to adjust the degree of occurrence of microcracks by adjusting the cooling conditions and the like, and it is necessary to further reduce the thermal conductivity of the aluminum titanate member which is already low in thermal conductivity. It is difficult.

The present invention has been made in view of such circumstances, and has as its object to easily produce an aluminum titanate-based ceramic member having a lower thermal conductivity than conventional ones.

[0007]

According to the present invention, there is provided a method of manufacturing an aluminum titanate-based ceramic member having uniform fine pores and a relative density of 90 to 96%. A method, comprising: a forming step of forming a shaped body having a predetermined shape from a ceramic powder forming aluminum titanate; a firing step of firing the shaped body at a temperature at which aluminum titanate is formed to form a fired body; After maintaining the body at a temperature at which aluminum titanate decomposes for a predetermined time, aluminum titanate
For a predetermined time at the temperature at which
A heat treatment step of maintaining the aluminum at a temperature at which the aluminum is decomposed for a predetermined time .

[0008]

If the relative density is less than 90%, a problem occurs in the strength surface of the aluminum titanate-based ceramic member, and if it exceeds 96%, it becomes difficult to lower the thermal conductivity. Note that, in the present invention , it is desirable that the heat treatment step is repeated a plurality of times. The thermal conductivity tends to decrease as the number of repetitions increases. When the aluminum alloy is kept at a temperature at which aluminum titanate is formed again for a predetermined time during the heat treatment, it is preferable that the heat treatment be performed under the condition that TiO ₂ and Al ₂ O ₃ which are decomposition products slightly remain. Accordingly, when the temperature is maintained at the decomposition temperature in the next stage of the heat treatment, the decomposition is promoted, and the processing time can be shortened.

[0010]

According to the method for manufacturing an aluminum titanate-based ceramic member of the present invention, the aluminum titanate fired body is maintained at a temperature at which the aluminum titanate is decomposed for a predetermined time in the heat treatment step. As a result, about 80 to 90% of the aluminum titanate is decomposed into TiO ₂ and Al ₂ O _3, and a uniform and fine pore of about 1 to 5 μm is generated due to the volume reduction accompanying this decomposition. 96% relative density due to these pores
As a result, an aluminum titanate-based ceramic member having a low thermal conductivity and an improved heat insulating property can be obtained.

[0011] Further, after holding for a predetermined time at a temperature at which aluminum titanate decomposes, holding at a temperature at which aluminum titanate is formed for a predetermined time, and then performing heat treatment at a temperature at which aluminum titanate decomposes for a predetermined time, An aluminum titanate-based ceramic member having a further reduced relative density and further improved heat insulating properties due to repeated decomposition and generation of aluminum oxide can be obtained.

When the aluminum titanate is again maintained at a temperature at which aluminum titanate is formed for a predetermined time, the decomposition product Ti
If O ₂ and Al ₂ O ₃ are slightly retained, the remaining TiO ₂ and Al ₂ O ₃ are assumed to be nucleation sites for the next decomposition, and the initial decomposition is promoted to shorten the processing time. Can be.

[0013]

The present invention will be described more specifically with reference examples and examples. ( Reference Example ) <Molding Step> Commercially available TiO ₂ powder and Al ₂ O ₃ powder were weighed at an equimolar ratio, and ethanol was added thereto, followed by mixing by a ball mill wet method for 24 hours. After drying, a molded article having a predetermined test piece shape was formed by press molding using a mold. The forming method is not limited to the press forming method, and a forming method used for forming conventional ceramics, such as a slip casting method or an injection molding method, can be used. <Firing Step> The obtained molded body was heated and fired at 1500 ° C. for 2 hours in the air to form a fired body made of aluminum titanate.

Aluminum titanate is generally 1000
TiO ₂ and A by reheating around ~ 1300 ° C
decomposed into l ₂ O _3. However, since the decomposition rate varies depending on the characteristics of the starting materials and the firing conditions, the decomposition behavior of the fired body was first investigated. Put the above sintered body in air 8
Decompose by heating in the range of 00 to 1250 ° C for 6 hours,
With respect to the sample after the treatment, the generated phase was examined by the X-ray powder diffraction method, and the decomposition rate of aluminum titanate was calculated. The results are shown in FIG.

FIG. 5 shows that the fired body of this embodiment is 1050 ° C.
It can be seen that the decomposition rate is maximized in the vicinity. The reason why the treatment time was set to 6 hours was that the decomposition rate was saturated at a treatment time of 6 hours or more, and no difference due to the heating temperature was observed. The higher the decomposition rate, the higher the pore generation rate and the lower the thermal conductivity. Therefore, in this reference example , the heat treatment was performed at 1050 ° C. for 6 hours. <Heat treatment step> Then, after heating the above-mentioned molded body at 1500 ° C for 2 hours, it was cooled to 1050 ° C as shown in FIG.
For 6 hours to obtain a test piece composed of aluminum titanate, TiO ₂ and Al ₂ O ₃ . The relative density and the thermal conductivity of this test piece were measured, and are shown in FIG. 6 and Table 1, respectively. FIG. 8 shows a micrograph thereof. (Example 1) to the firing step is performed in the same manner as in Reference Example, after reference example similar heat treatment step, and heated again, as shown in FIG. 2 1350 ° C.
At 1050 ° C., and again cooled to 1050 ° C.
Hold at 0 ° C. for 3 hours. The relative density and the thermal conductivity of the obtained test piece were measured, and are shown in FIG. 6 and Table 1, respectively. The micrograph is shown in FIG.

It has been clarified that the decomposition rate of aluminum titanate during the decomposition treatment varies depending on the firing temperature. That is, as shown in FIG. 7, when the decomposition treatment is performed at 1050 ° C., the decomposition of aluminum titanate occurs earlier at 1350 ° C. for 10 minutes than when the firing conditions are 1500 ° C. for 2 hours. It became clear. This is because TiO ₂ and Al ₂ O ₃ react almost completely under the firing conditions of 1500 ° C. × 2 hours,
Under firing conditions of 1350 ° C. for 10 minutes, unreacted TiO ₂
And Al ₂ O ₃ remained, and these became nucleation sites for decomposition, which is considered to promote the decomposition.

Therefore, in the present embodiment, the reheating condition is set to 13
The heating was performed at 50 ° C. for 10 minutes, and TiO ₂ and Al ₂ O ₃ generated by decomposition at 1050 ° C. for 6 hours were prevented from completely reacting. Therefore, the subsequent 1050 ° C
The decomposition of aluminum titanate is further promoted in the decomposition treatment for 3 hours, and the thermal conductivity and the relative density are lower than those of the reference example . (Example 2) to the firing step is performed in the same manner as in Reference Example, after similar heat treatment as in Reference Example, and heated again, as shown in FIG. 3 1350 ° C.
At 1050 ° C., and again cooled to 1050 ° C.
The heat treatment maintained at 0 ° C. for 3 hours was repeated three times. The relative density and the thermal conductivity of the obtained test piece were measured, and are shown in FIG. 6 and Table 1, respectively. The micrograph is shown in FIG.
Shown in (Comparative Example) The steps up to the firing step were performed in the same manner as in the Reference Example, and were cooled to room temperature without heat treatment as shown in FIG. The relative density and the thermal conductivity of the obtained test piece were measured.
And Table 1.

[0018]

[Table 1] (Evaluation) From FIG. 6, it can be seen that the relative density decreases as the heat treatment is repeated, and the thermal conductivity decreases as Table 1 shows. 8 to FIG.
It is clear that homogeneous pores of several microns have been formed and the pores have increased as the heat treatment has been repeated, and that these pores have clearly reduced the thermal conductivity.

That is, the aluminum titanate-based ceramic member obtained in the embodiment has a uniform fine pore and 90%.
Since it has a relative density of up to 96%, it has a lower thermal conductivity and higher heat insulation than the aluminum titanate member of the comparative example.

[0020]

According to the method for producing an aluminum titanate-based ceramic member of the present invention, the relative density is 90%.
An aluminum titanate-based ceramic member of up to 96% can be reliably and easily manufactured. The obtained aluminum titanate-based ceramic member exhibits high heat insulating properties due to low thermal conductivity, and is suitable for a cast-in part for an exhaust port of an automobile engine.

[Brief description of the drawings]

FIG. 1 is a time chart showing temperature conditions of a reference example of the present invention.

FIG. 2 is a time chart showing temperature conditions according to the first embodiment of the present invention.

FIG. 3 is a time chart showing temperature conditions according to a second embodiment of the present invention.

FIG. 4 is a time chart showing temperature conditions of a comparative example of the present invention.

FIG. 5 is a graph showing a relationship between a decomposition temperature and a decomposition rate.

FIG. 6 is a graph showing the relationship between the number of heat treatment cycles and the relative density.

FIG. 7 is a graph showing a relationship between a decomposition processing time and a decomposition rate.

FIG. 8 is a micrograph of the particle structure of an aluminum titanate-based ceramic member obtained in a reference example .

FIG. 9 is a micrograph of the particle structure of the aluminum titanate-based ceramic member obtained in Example 1 .

FIG. 10 is a micrograph of the particle structure of the aluminum titanate-based ceramic member obtained in Example 2 .

Claims (2)

(57) [Claims] (1) having a uniform fine pore and a relative density of 90 to
A method for producing a 96% aluminum titanate-based ceramic member, comprising: a forming step of forming a compact having a predetermined shape from ceramic powder forming aluminum titanate; and firing the compact at a temperature at which aluminum titanate is formed. A firing step of forming a fired body by heating the fired body at a temperature at which aluminum titanate is decomposed for a predetermined time, and then forming a fired body at a temperature at which aluminum titanate is formed.
For a predetermined time, after which the aluminum titanate decomposes
And performing a heat treatment step of maintaining the temperature at a predetermined temperature for a predetermined time . 2. The method according to claim 1, wherein the fired body is separated from aluminum titanate.
After holding for a predetermined time at the temperature at which the aluminum
The step of holding at a temperature at which the system is generated for a predetermined time includes TiO ₂
And Al ₂ O ₃ are slightly retained.
2. The aluminum titanate-based ceramic according to claim 1,
Manufacturing method of the member.