JPH0365554A - 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 WC 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 and a composition ratio of Al2O3/SiO2 is prepared into a mullite formation range) is blended with (B) 3-40wt.% based on the component A of WC (particle diameter: <=50mum), dried, molded and calcined (at >=1,600 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 composed of Au203 and SiO2, and its chemical composition is theoretically 3AJ2203-2S i 02, and 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.

The mixture of these raw materials according to the purpose and sintering is called mullite-based ceramics material.Mullite-based ceramics has relatively high high-temperature strength and is a natural raw material, just like aluminum ceramics. Because it is an inexpensive material, it has been used mainly as a fireproof material, such as furnace materials, sheaths, setter materials, heat-resistant materials, and structural materials.

[Problem to be solved by the invention] Among conventional mullite ceramics, in those modified from natural mullite, the Al2O3-3iO2 bonding originally contained decomposes during long-term use or high-temperature use, and 5i02 becomes mullite grains. It precipitates as a glass phase in the field. 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 Problem] The mullite-based sintered body of claim (1) is made of WC (tungsten carbide) and mullite, and has a WC content of 3 to 40% by weight based on mullite, and Particle size is 10
The method for producing a mullite-based sintered body according to claim (2), wherein the mullite-based sintered body has a particle diameter of 100 μm, uses A It 203 as main raw materials at least two selected from the group consisting of purified clay mineral, Bayer alumina, and silica stone.
/ S i O2 is blended so that the composition ratio is in the mullite production range, and the blended raw material is wet-pulverized so that 90% or more has a particle size of 5 μm or less, and then W with a particle size of 50 μm or less is mixed.
C is added and mixed in an amount of 3 to 40% by weight with respect to the blended raw materials,
Next, the resulting mixture is dried and crushed, then molded using an organic binder, and the molded product is fired at a temperature of 1600° C. or higher for 1 hour or more.

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 WC in an amount of 3 to 40% by weight based on mullite. If the WC content is less than 3% by weight based on mullite, the strength improvement effect of the present invention cannot be obtained, and if it exceeds 40% by weight, the WC
If the amount becomes too large, the properties of the mullite-based sintered body will be impaired. Therefore, in the present invention, the WC content is 3 to 40% by weight based on mullite. In particular, W.C.
When the content is 5 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 the particle diameter is smaller than 1, it becomes difficult to incorporate the WC particles into the mullite crystal or at the grain interface. Therefore, the grain size of mullite crystals is 10
~100 μm, preferably 10 to 50 μm.

On the other hand, if the particle size of the WC 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 the surface oxidation of the WC itself will occur. In addition, it is difficult to mix uniformly with mullite, and conversely, WC
If the particle size is too large, WC will form only at the mullite grain boundaries.
comes to exist, causing the occurrence of grain boundary cranks. Therefore, in the present invention, the particle size of the WC particles is 50 μm.
Below, especially 1ζ10 /4 m or less, especially 3...10
Preferably, the value is μm.

The composition of mullite in the mullite-based sintered body is the theoretical composition Af! It is preferable that the ratio is 71.8/28.2 (weight %). Mullite/composition A, f220-1
However, the theoretical composition 9): There are too many crystals, and the 71-crystals are dispersed in the Au20i, making it impossible to obtain sufficient strength. On the other hand, if 5 iOz of the mullite composition is too much than the engineering composition, the free silica phase in the mullite becomes a glass phase and forms 4 iOz, making it impossible to obtain a high temperature strength of 1-min. Therefore, it is preferable that the mullite in the mullite-based sintered body has a composition that is close to the theoretical composition Aj220s/5iO2=3/2 (molar ratio).

The mullite-based sintered body of claim (1) is
By the method 2), it can be easily and efficiently manufactured at a low T-strength.

The method for producing a mullite-based sintered body according to claim (2) will be explained below.

In the method of claim (2), the raw materials are
τ: Refined clay - mineral, Bayer - alumina, or silica (
silica) using Afl, 20:3/Si
O21ifl composition ratio is within the mullite production range, preferably A
Blend so that A203/5i02=-3/2 (fl-le ratio). In this case, it is particularly preferable to use purified kaolin and Bayer Al spring or Bayer alumina L silica as raw materials. These raw materials are wet-pulverized in a ball mill or an attritor using aluminum or the like so that 90% or more of the raw materials have a particle size of 5 μm or less. Next, the obtained pulverized product V particle size is 50 μm or less, preferably 1, or 10 μm or less, especially 15
3 = 3 to 40% by weight of 10 μm WC based on the crushed remains
Preferably, add 5-20% in a heavy plate, and then mix in a bowl or the like.

The resulting mixture is dried, crushed, and then molded using an organic binder such as polyvinyl alcohol (PVA). Molding is 300 kg, f/cm. After pressure molding at 2", 1000 kg f/c.
It is preferable to carry out two-step molding using isostatic press molding at n'1" or higher.

The obtained molded body is fired by hot pressing or conventional sintering E, and in the case of 66r to obtain a mullite-based sintered body, the heating rate is preferably 50 to 200°C/11r, and the firing temperature is 1600°C. ℃ or above, 1600 ” 1
Heat at 650°C and bake for at least 1 hour, preferably from 1 hour to
It is preferable to set it as 3 hours. In addition, when using hot press, the pressure is 300-600 kg/cm
``It is preferable to have a moderate amount of heat.

[Function] In general, even if raw materials such as refined kaolin, Bayer mineral springs, or silica stone are used and mixed by pulverizing them with a ball or the like, it is impossible to mix them to the theoretical composition at the atomic level. However, it takes a long time to diffuse by sintering.

On the other hand, in the mullite composition, the second phase and 1.WC
When particles are added in an amount of 3 to 40% by weight, a mullite-based sintered body having better high-temperature strength than ordinary molding and firing can be obtained even by pulverizing and mixing using a ball mill or the like.

The details of the mechanism of this improvement in high-temperature strength due to the addition of WC are not clear (because the WC particles are incorporated into the mullite crystals or at the grain boundaries and block the movement of 5i02 into the glass phase in the mullite). Furthermore, it is said that the WC particles are dispersed within the mullite crystal grains and at the grain boundaries, suppressing the growth of the mullite crystals.

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

Example 1゜2.1.1; Comparative Example 1 Purified kaolinite has a composition of Aj2203/SiO
Add 3″ of aluminum so that the ratio is 2τ3/2 (molar ratio)1
The material was milled using alcohol for 48 hours using a Bo-Rumill (ZrOz ball). In addition, if you use a media agitation type pulverizer (Attritor), 1=2
It is possible to process in hours. After pulverizing the raw material so that 90% or more has a particle size of 5 μm or less, first
Powder (manufactured by Nihon Shinkinzoku Co., Ltd., average particle diameter 5 μm) was added 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.
After molding at kg/crd, it was further pressurized at 1500 kg/crn' using a rubber press to obtain a green body. This green body was sintered to obtain a mullite-based sintered body. Note that sintering uses a hot press, and the temperature increase rate is 150℃/
hr and 300 kg/c rr? At 160
The test was carried out at 0°C for 1 hour.

The properties of the obtained mullite-based sintered body are shown in Table 1.

Table 1 It is clear from Table 1 that the mullite-based sintered body to which a predetermined amount of WC has been 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 is provided at low cost using inexpensive raw materials, and moreover, it 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) Consisting of WC and mullite, the WC content is 3 to 40% by weight based on mullite, and the mullite particle size is 1
A mullite-based sintered body having a diameter of 0 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 50 μm or less, 3 to 40% by weight of WC with a particle size of 50 μm or less is added and mixed to the raw material, and the resulting mixture is dried and crushed.
Molded using an organic binder and heated to 1600℃
A method for producing a mullite-based sintered body, which comprises firing at a temperature above 1 hour or more.