JPH0365553A - Mullite-based sintered material and production thereof - Google Patents

Abstract

PURPOSE:To inexpensively produce mullite-based sintered materials having excellent characteristics such as high-temperature strength by making a composition consisting of a specific amount of B4C and mullite having a specific particle diameter. CONSTITUTION:(A) Mullite (at least two or more selected from purified clay minerals, Bayer alumina and silica rock having 10-100mum particle diameter and comprising >=90% particles with <=5mum particle diameter are used as main raw material and a composition ratio of Al2O3/SiO2 is prepared into a mullite formation range) is blended with (B) 5-30wt.% based on the component A of B4C (particle diameter: <=30mum), dried, molded and calcined (at >=1,550 deg.C for >=1 hour) to give a mullite-based sintered material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a mullite-based sintered body and a method for producing the same, and particularly to a mullite-based sintered body that has excellent properties such as high-temperature strength and is inexpensively provided. It relates to its manufacturing method.

[Prior art] Mullite is Aj! 203 and SiO2, the chemical composition is theoretically 3AIL203-2S i 02,
Its properties include excellent heat resistance and particularly good creep properties. Also, although the thermal shock properties are good, the electrical properties are not so good.

Mullite ceramics belong to old ceramics.
This research has a long history, and the main raw materials used are kaolin and Bayer alumina as an alumina source, and silica as a silica source. Recently, it has become possible to achieve physical properties comparable to synthetic mullite by modifying natural mullite, but the focus of this research is on preventing the precipitation and vitrification of the SiO2 phase in the mullite composition, and The preparation and sintering conditions were investigated.

On the other hand, there is also a material with a theoretical composition called high-purity mullite using fine ceramics technology, which is produced by a coprecipitation method from metal alkoxides to a theoretical composition.

Mullite ceramics are made by mixing and sintering these raw materials according to the purpose. Mullite ceramics, like alumina ceramics, have relatively high high-temperature strength and are made from natural raw materials. Since it is an inexpensive material, it has been mainly used as a refractory material, such as furnace materials, sheaths, setter materials, heat-resistant materials, and structural materials.

[Problems to be solved by the invention] Among conventional mullite ceramics, in those modified from natural mullite, the A1203Si02 bonding originally contained decomposes during long-term use or high-temperature use, and 5i02 forms at the mullite grain boundaries. Precipitates as a glass phase.

For this reason, the strength was significantly reduced, making it difficult to use continuously or repeatedly.

High-purity mullite produced by the alkoxyquito method was developed to solve the above-mentioned drawbacks, but although high-purity mullite has the effect of greatly improving high-temperature strength and durability, it has not been used conventionally due to its high price. It was disadvantageous in terms of cost for use in the field of industrial materials such as heat-resistant materials.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a mullite-based sintered body that has excellent properties such as high-temperature strength and can be provided at low cost, and a method for producing the same.

[Means for Solving the Problems] The mullite-based sintered body of claim (1) is made of 84C (boron carbide) and mullite, and the 8.4C content is 5 to 30% by weight based on mullite. , mullite particle size is 10~
100 μm, the method for producing a mullite-based sintered body according to claim (2) is characterized in that A 1120 s
/ S I O2 is mixed so that the composition ratio falls within the mullite production range, and after wet-pulverizing the blended raw material so that 90% or more has a particle size of 5 μm or less,
4C is added and mixed in an amount of 5 to 30% by weight with respect to the above-mentioned raw materials, and the resulting mixture is then dried and crushed. After that, it is mixed with an organic binder, and the molded body is heated to a temperature of 1550°C or higher. It is characterized by being fired for more than an hour.

That is, the present invention uses inexpensive raw materials that have been conventionally used as raw materials, and as a means of improving physical properties, high strength is achieved by dispersing specific ceramic particles as a second phase within mullite crystals or at grain boundaries. The aim is to provide a material with properties comparable to that of high-purity synthetic mullite.

The present invention will be explained in detail below.

The mullite-based sintered body according to claim (1) contains 5 to 30% by weight of B4C based on mullite. B4C
If the content of 84C is less than 5% by weight based on mullite, the strength improvement effect of the present invention cannot be obtained, and if it exceeds 30% by weight, the amount of 84C becomes too large and the properties as a mullite-based sintered body are impaired. It will be done. Therefore, in the present invention, B
4C content is 5 to 30% by weight based on mullite. In particular, when the 84C content is 7 to 20% by weight based on mullite, a particularly high-strength mullite-based sintered body can be obtained.

The mullite crystal in the mullite-based sintered body of claim (1) is
The particle size is in the range of 100 μm.

When the grain size of the mullite crystal is larger than 100 μm, the bending strength of the obtained mullite-based sintered body decreases;
If it is smaller than , it becomes difficult to incorporate B4C particles into mullite crystals or grain boundaries. Therefore, the grain size of mullite crystals is 1
0 to 1001.1 m, preferably 10 to 50 m.

On the other hand, if the grain size of the B+C particles incorporated into the mullite crystals or grain boundaries and contained in the mullite-based sintered body is too fine, surface activity will occur and surface oxidation of 84C itself will occur. It is also difficult to mix uniformly with mullite. On the other hand, if the grain size of the 84C grains is too large, B4C will exist only at the mullite grain boundaries, resulting in grain boundary cracks (D
EC cause): )xru. Therefore, “C1 Invention “Hey T’,
B4C particle size I is less than 307z m, special! =: 1
It is preferably 0 μm or less, especially ゎ+-3:q to 1071 m.

Note that the composition of mullite in the mullite-based sintered body is the theoretical composition 0'') A j2 ;!02 / S i O2=
3/2 (mole ratio, i.e. 71.8/28.2C weight %)
It is preferable that it is 1 no. Al1203 with Murai 1 composition
Although there is more than the theoretical composition, there is unevenness in the 7F crystals, and sufficient strength is obtained. On the other hand, if the mullite composition σ') SiO2 is too much than the theoretical composition, the silica phase in the mullite will become a glass phase and a high temperature strength of 1 min will be obtained.
``1.Therefore, the mullite in the mullite-based sintered body is
Theoretical composition Al220s/S i O2 = 3/2
(Molar ratio) It is preferable that the composition is as close as possible.

The mullite-based sintered body of claim (1) is
Method 2) ``It can be manufactured more easily, efficiently, and at low cost.

``Yu 2 I:, ``Method for manufacturing a sintered body based on MURAI'' according to claim (2) will be explained.

In the method of claim (2), first, refined slime mineral, Bayer mineral, or silica is used as a raw material, and the Aj2203/SiO2 composition ratio is within the mullite production range, preferably Aflw. 03 /S i O
2 = 3/2 (molar ratio).

In the case of a special trowel raw material, it is better to use purified kaolin or Bayer alumina and 17 stones. These raw materials require ff
l by a ball mill or an atto lighter, etc.
~ 1 ? using a method such as 1 ? W-type crush. Next, the obtained pulverized material was added with a particle size of 3
04m or less, preferably 1oμn1 or less, especially 3=-
5 to 30% by weight of 10 μm 84C based on the pulverized material,
Preferably, it is added in an amount of 7 to 20%, and further mixed using a ball mill or the like.

The resulting mixture is dried, crushed, and then molded using an organic binder such as polyvinyl alcohol (PVA) at a pressure of 300 kg, f/e m or more. After, 1000 kg f/c +-
It is preferable to carry out three-stage molding by isostatic press molding at nF or higher.

The obtained molded body is fired by hot pressing or pressureless sintering to obtain a mullite-based sintered body. In this case, the heating rate is preferably 50 to 200°C/11r, the firing temperature is 1550°C or higher, preferably 1, and 2< is 1550 to 1
It is preferable to bake at 650°C, 1″1 inch, and for a baking time of 1 hour or more, preferably 1 to 3 hours.If hot press is used, the pressure is 300 to 600 kg/
It is preferable to set it to about c d.

stomach.

[Function] In general, even if raw materials such as refined kaolin, Bayer alumina, or silica stone are pulverized and mixed using a ball mill, it is impossible to mix them to the theoretical composition with a single atom. However, it takes a long time for the company to diffuse it through sintering.

On the other hand, in No. 1, B4C as the second phase in the mullite composition.
When 5 to 30% by weight of particles are added, a mullite-based sintered body having superior high-temperature strength than normal molding and firing (ζ) can be obtained even by pulverizing and mixing using a ball mill or the like.

The details of the mechanism of high-temperature strength improvement due to the addition of B4C are unclear, but the B4C particles incorporated into the mullite crystals or grain boundaries block the movement of 5i02 in the mullite to the glass phase. This is thought to be because B4C particles migrate into mullite crystal grains and grain boundaries, suppressing the growth of mullite crystals.

[Example] The present invention will be described in more detail with reference to Examples and Comparative Examples below.

Examples 1 and 2, Comparative Example 1 Purified Kaolinite K: Composition is Al2O3/Si
Alumina was added so that O203/5iO2=3/2 (molar ratio), and the mixture was pulverized using alcohol in a ball mill (Zr02 ball) for 48 hours. In this case, it is possible to process in 1 to 2 hours using a media stirring type pulverizer (71 to lighter). After pulverizing the raw material so that 90% or more has a particle size of 5 μm or less,
To this was added 84C powder (manufactured by Denka Co., Ltd.: average particle diameter: 5 μm) in the amount shown in Table 1 (no addition was made in Comparative Example 1), and the mixture was further mixed in a ball mill for 5 hours. After drying and crushing this,
5% by weight of an organic binder (PVA) was added and thoroughly kneaded.

The kneaded material was press-molded into a size of 50 mmφ x 5 mm.
kg/c rn" and then further pressurized with a rubber press at f500 kg/c1111 to obtain a green body. This green body was sintered to obtain a mullite-based sintered body. Note that sintering Using a hot press, the temperature increase rate is 150
℃/hr, and the test was carried out at 1550°C for 1 hour at 300 kg/hr.

Table 1 shows various properties of the obtained mullite-based sintered body.

Table 1 It is clear from Table 1 that the mullite-based sintered body to which a predetermined amount of 84C is added can stably provide significantly high strength from room temperature to high temperatures such as 1300°C.

[Effects of the Invention] As detailed above, the mullite-based sintered body of the present invention can be provided at low cost using inexpensive raw materials, and has outstanding properties such as high-temperature strength and durability. . Therefore, the mullite-based sintered body of the present invention can be used extremely effectively for a long period of time as an industrial refractory material.

Therefore, such a mullite-based sintered body of the present invention can be easily and efficiently manufactured at low cost by the method of the present invention.

Claims (2)

[Claims] (1) A mullite-based sintered body consisting of B_4C and mullite, characterized in that the B_4C content is 5 to 30% by weight based on mullite, and the mullite particle size is 10 to 100 μm. (2) Al
_2O_3/SiO_2 is blended so that the composition ratio falls within the mullite production range, and more than 90% of the blended raw materials have a particle size of 5μ.
After wet pulverization to a particle size of 30 μm or less, 5 to 30% by weight of B_4C with a particle size of 30 μm or less is added and mixed to the raw material, and the resulting mixture is dried and crushed. The molded body was molded using 155
A method for producing a mullite-based sintered body, comprising firing at a temperature of 0° C. or higher for 1 hour or more.