JP2936288B2 - Composite ceramic and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite ceramic having reduced thermal conductivity and a method for producing the same.

[0002]

2. Description of the Related Art In order to improve the thermal efficiency of an internal combustion engine, it is desired to reduce the heat dissipated to the outside as much as possible. In addition, materials used for internal combustion engines are exposed to high temperatures, so that high-temperature strength is required and dimensional accuracy is required. Therefore, materials having low thermal expansion are desirable.

[0003] As a material satisfying these conditions, there is a composite ceramic. As this conventional composite ceramic, for example, Japanese Patent Publication No. 56-14635 and Japanese Patent Publication No.
A method of adding a small amount of Ti as a catalyst for the purpose of accelerating the nitridation of Si is disclosed.

[0004]

However, in the above-mentioned composite ceramics, a small amount of Ti is added as a catalyst for the purpose of accelerating the nitridation, so that the thermal conductivity is reduced, and
The effect of obtaining dimensional accuracy cannot be expected, and the fact is that it has not yet been used as a material for internal combustion engines.

[0005] The present invention has been made in view of the above circumstances, and provides a composite ceramic having a low thermal conductivity.

[0006]

A first means according to the present invention for solving the above-mentioned problems is that Si containing 20% of pores,
The second means is a step of forming a mixed powder of a Si powder and a powder containing a Ti element, and forming the mixed powder in an N2 atmosphere. Baking at a temperature of 1200 ° C. or more, and further performing a heat treatment in the air to remove a part or all of the Ti—N compound formed by the baking in the N2 atmosphere.
This is a method for producing a composite ceramic, characterized by changing to a compound represented by Ti-O or Ti-ON. And, as a third means, the second means
Wherein the mixing ratio of the mixed powder of the powder and the powder containing the Ti element is 20% by weight or more with respect to the total weight of the mixed powder.

[0007]

According to the present invention, the thermal conductivity is reduced by forming a composite ceramic containing 20% of pores and containing elements of Si, Ti, O and N. As a method of obtaining this composite ceramics, a mixed powder of a powder of Si and a powder containing a Ti element is formed,
This mixed powder is fired in an N2 atmosphere at 1200 ° C. or higher, and further heat-treated in the air to convert part or all of the Ti—N compound formed by firing in the N2 atmosphere to Ti—O or The above composite ceramics can be obtained by changing to a compound represented by Ti-ON.

Further, when the mixing ratio of the mixed powder of the Si powder and the powder containing the Ti element is 20% by weight or more with respect to the total weight of the mixed powder, a composite ceramic having a low thermal conductivity is obtained.

[0009]

An embodiment of the present invention will be described below.

Example 1 The samples used in the experiment are as follows. Water and a binder were added to Si and a predetermined amount of Ti powder to form a slurry. This was dried and pulverized to obtain a forming raw material. This was press-molded at a pressure of 1 ton / 2 to produce a pellet-shaped molded body of Φ10. And up to 500 ° C
After volatilizing and removing the organic binder in the N2 atmosphere of
Sintered in N2 atmosphere (9.5atm) up to 1400 ℃
A comparative sample was prepared, and the thermal conductivity and the dimensional change in the diameter direction of the comparative sample were measured by changing the mixing ratio of Ti.

Next, the comparative sample is further heat-treated for about 1.5 hours in an air atmosphere at 800 ° C. to measure the thermal conductivity and the dimensional change in the diameter direction by changing the mixing ratio of Ti. Identification was performed. The result is shown in FIG. As is clear from the figure, it can be seen that the thermal conductivity of the sample further heat-treated in the atmosphere at 800 ° C (solid line) is lower than that of N2 only at 1400 ° C (dotted line). . And, as the mixing ratio of Ti increases, the difference in thermal conductivity between the two increases. And this difference in thermal conductivity is Ti
Is relatively gentle when the mixing ratio of is 20% by weight or more.

Comparative Example 1 Using a material obtained by adding TiO2 to Si as a raw material, forming and drying the same process as in Example 1,
It was fired in an N2 atmosphere. In this case, TiO2 is replaced by TiN
Since it changes to n, it was confirmed that the thermal conductivity showed a high value when compared with that of the same compounding ratio (molar ratio), and that the dimensions shrank during the sintering process. This experiment showed that desired results could not be obtained even if TiO2 was added to Si.

Example 2 A mixture of Si and Ti was prepared by preparing a raw material in which Si was 7 Ti and 3 in the form of a slurry, and this was made of a sintered body of Si3N4 placed on gypsum and having a thickness of 5 mm.
The mixture was poured into a cylinder having a height of 50 mm and an outer diameter of 50 mm, solidified by water absorption, removed from gypsum, and measured for dimensional change at an intermediate point. As a result, at this time, there was a gap of 0.6 mm between the filling portion and the outer frame of Si3N4 due to shrinkage during molding. When this was fired in N2 under the same conditions as in Example 1, the gap was small because of N2, but after this was further heat-treated in the air at 1200 ° C., the gap was measured. However, it was confirmed that the gap had completely disappeared. What has been obtained in this experiment is that heat treatment in a high-temperature atmosphere allows dimensional changes to be adjusted by expansion.

[0014]

As described above in detail, according to the present invention, a raw material obtained by mixing a Si powder and a Ti powder is sintered in an N2 atmosphere, and further heat-treated in a high-temperature atmosphere to obtain Si, Ti. ,
A composite ceramic comprising the elements of O and N can be obtained, and this composite ceramic has a low coefficient of thermal expansion,
In addition, the adjustment of the dimensional change can be performed by expansion. By setting the mixing ratio of Ti to 20% by weight or more with respect to the total weight of the raw materials, the above effect can be remarkable.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing characteristics of the present invention.

Claims (3)

(57) [Claims] 1. A composite ceramic comprising 20% of pores and comprising elements of Si, Ti, O and N. 2. A step of forming a mixed powder of a Si powder and a powder containing a Ti element, and forming the mixed powder in an N2 atmosphere.
Baking at a temperature of 00 ° C. or more, and further performing a heat treatment in the air to convert a part or all of the Ti—N compound formed by baking in the N 2 atmosphere to Ti—O or
A method for producing a composite ceramics, which comprises converting the compound to a compound represented by Ti-ON. 3. The mixing ratio of the mixed powder of the Si powder and the powder containing the Ti element according to claim 1 is based on the total weight of the mixed powder.
A method for producing a composite ceramic, wherein Ti is at least 20% by weight.