JPH03153569A - Alumina-silica-based sintered body and its production - Google Patents

Abstract

PURPOSE:To obtain the inexpensive sintered body excellent in high-temp. strength by forming the sintered body consisting of WC, CaO and mullite and in which the contents of WC and CaO are specified with respect to the mullite content and the grain diameter of the mullite is specified. CONSTITUTION:The sintered body consists of WC, CaO and mullite, the content of WC is controlled to 3-40wt.% and that of CaO to 0.1-1wt.% based on the mullite, and the grain diameter of the mullite is controlled to 10-100mum. Such a sintered body is produced by the following method. Namely, at least two kinds selected from a group consisting of a refined clay mineral, Bayer's alumina, aluminum hydroxide and quartzite are used as the main raw materials, the materials are mixed so that the composition ratio of Al2O3/SiO2 is controlled in a mullite forming range. The mixed raw material is wet-crushed so that the grain diameter of >=90% of the material is controlled to <=5mum, the WC having <=50mum grain diameter is added by 3-40wt.% based on the mixture, the CaCO3 having <=0.1mum grain diameter is added by 0.1-1wt.% expressed in terms of CaO, the obtained mixture is dried, disintegrated and then formed using an org. binder, and the formed body is sintered at >=1600 deg.C for >=1hr.

Description

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

[Prior Art] Mullite is composed of Au203 and 5i02, and its chemical composition is theoretically 3AA203-2SiO2, 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 silica 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 synthetic mullite using fine ceramics technology, and this is mainly produced by a coprecipitation method using methods such as metal alkoxides to achieve the theoretical composition.

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

[Problem to be solved by the invention] Among conventional mullite-based ceramics, those made by modifying natural mullite do not exhibit AJ during long-term use or high-temperature use.
2203-3 i 02 bonding decomposes and silica precipitates as a glass phase at the grain boundaries of mullite. For this reason, the strength was significantly reduced, making it difficult to use continuously or repeatedly.

High-purity synthetic mullite using the alkoxyquito method was developed to solve the above-mentioned drawbacks. Although high-purity mullite has the effect of greatly improving high-temperature strength and durability, it is expensive and has not been used in the past. It is disadvantageous in terms of cost for use in the field of industrial materials such as heat-resistant materials.

It is an object of the present invention to solve the above-mentioned conventional problems and to provide an alumina-silica-based sintered body having a mullite composition 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 alumina-silica-based sintered body of claim (1) is made of WC (tungsten carbide), CaO (calcium oxide), and mullite, and the WC and CaO contents are lower than that of mullite. The method for producing an alumina-silica-based sintered body according to claim (2), wherein the mullite grain size is 3 to 40% by weight and 0.1 to 1f[% by weight], and the mullite particle size is 10 to 1100A1. , refined clay mineral, Bayer alumina, aluminum hydroxide, and silica stone are used as main raw materials, and the composition ratio of Al1203/SiO2 is in the mullite production range. %
After wet-pulverizing the above particles to a particle size of 5 μm or less, WC with a particle size of 50 μm or less is added at 3 to 40%
Weight%, CaCO2 (calcium carbonate) with a particle size of 0.1 μm or less is added to the above-mentioned blended raw material by CaOli calculation of 0.1
It is characterized by adding and mixing ~10% by weight, then drying and crushing the resulting mixture, then molding using an organic binder, and baking the molded product 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. Furthermore, the glassy silica liberated by the addition of CaO is fixed as a solid solution, thereby providing a material having properties comparable to high-purity synthetic mullite.

The present invention will be explained in detail below.

The alumina-silica-based sintered body of claim (1) has a ratio of 3 to 40 compared to mullite! ! % by weight of WC and 0.1 to 1% by weight of CaO. 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 401% by weight, the WCO content becomes too large and the characteristics as an alumina-silica sintered body are deteriorated. is damaged.

Therefore, in the present invention, the WC content is 3 to 40Ii% based on mullite. In particular, when the WC content is 5 to 20% by weight based on mullite, an alumina-silica sintered body with particularly high strength can be obtained.

On the other hand, the content of CaO is 0.1% by weight based on mullite.
If it is less than 1% by weight, the glass phase liberated during the formation of mullite, which will be described later, cannot be sufficiently fixed, and the strength improvement effect will not be sufficient, and if it exceeds 1% by weight, the CaO phase will become large, which is not preferable. Therefore, in the present invention, the CaO content is 0.1 to 1% by weight based on mullite. In particular, when the CaO content is 0.5 to 1% by weight based on mullite, an alumina-silica sintered body with particularly high strength can be obtained. Conventionally, in the sintering of mullite, there are reports of using CaO as an additive during sintering, and in this case, 5 to 15 ffi amount % is added. This is normal Ca
This is because the particles of CaC0z and Ca(OH)2 (calcium hydroxide), which are O raw materials, are several μm in size, and it is necessary to add a large amount in order to uniformly disperse them.

On the other hand, in the present invention, by using ultrafine particles of submicron or less CaC0z, a sufficient effect could be obtained with addition of 0.1 to 1% by weight of evening scenery.

The mullite crystals in the alumina-silica sintered body according to claim (1) have a grain size in the range of 100 μm. If the grain size of the mullite crystal is larger than 100 μm, the bending strength of the alumina-silica sintered body obtained will decrease;
When it is smaller than m, it becomes difficult to incorporate WC particles and CaO particles into mullite crystals or grain boundaries. Therefore, the grain size of mullite crystals is 10 to 100 μm, preferably 10 to 50 μm.
Let it be m.

On the other hand, if the particle size of the WC particles incorporated into the mullite crystals or grain boundaries and contained in the alumina-silica sintered body is too fine, surface activity occurs and the surface oxidation of the WC itself occurs. On the other hand, if the grain size of the WC grains is too large, the WC will exist only at the mullite grain boundaries, causing grain boundary cracks to occur. Therefore, in the present invention, the particle size of the WC particles is 50 μm or less, particularly 10 μm or less, especially 3 to 3 μm.
Preferably, the thickness is 10 μm.

In addition, if the particle size of CaCo3 particles is large, the effect cannot be obtained unless a large amount is added, and the reactivity is also poor.
．． The thickness is preferably 1 μm or less, preferably 0.05 μm or less.

In addition, the composition of mullite in the alumina-silica-based sintered body is the theoretical composition Al10s/SiO2-3/
2 (molar ratio), i.e. 71.8/2B, 2 (wt%) is preferable. If the Al2O5 of the mullite composition is too much than the theoretical composition, mullite crystals will be dispersed in Af120z and sufficient strength will not be achieved. I can't get it. On the other hand, if SiO2 in the mullite composition is too much than the theoretical composition, a free silica phase will form in the mullite as a glass phase, making it impossible to obtain sufficient high-temperature strength. Therefore, the mullite in the alumina-silica sintered body has the theoretical composition Aj2203 /S i
It is preferable that the composition be as close as possible to 02 = 3/2 (molar ratio).

As mentioned above, even if we try to prevent the silica glass phase from precipitating as much as possible, there will be some precipitation, and for this reason it will not be possible to sufficiently increase the strength. Since some of the silica glass reacts with CaO produced by the decomposition of CaCO5 and is fixed, it is no longer precipitated as a glass phase at the mullite grain boundaries, resulting in high strength. The amount of CaC0a added is 0.1 to 1% by weight in terms of CaO, more preferably 0.5%.
When the content was 1% by weight, high strength was obtained. As mentioned above, if the amount of CaCO5 added is too large, the CaO phase will become large, which is undesirable. If the amount is too small, the free glass phase cannot be fixed sufficiently, so there is no effect.

The alumina-silica-based sintered body of claim (1) can be easily and efficiently produced at low cost by the method of claim (2).

The method for producing an alumina-silica-based sintered body according to claim (2) will be explained below.

In the method of claim (2), first, refined clay minerals, Bayer alumina, aluminum hydroxide, or silica are used as raw materials, and AIL20s/Si
O2 composition ratio is in the mullite production range, preferably A 11
20 x / S i O2-3/2 (molar ratio). In this case, it is particularly preferable to use purified kaolin and Bayer alumina or aluminum hydroxide, or Bayer alumina or aluminum hydroxide and silica stone as raw materials. Wet pulverize using alcohol or the like so that 90% or more of the particles have a particle size of 5 μm or less. Next, WC with a particle size of 50 μm or less, preferably 10 μm or less, particularly 3 to 10 μm is added to the obtained pulverized material in an amount of 3 to 40% by weight, preferably 5 to 20% by weight based on the pulverized material.
Add CaCO3 of 0.1 μm or less to Ca0li
A total of 0.81 to 1% by weight, preferably 0.5 to 1% by weight is added and 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). It is preferable that the molding is carried out in two stages by pressure molding at 300 kg f/cm' or more and then isostatic press molding at 1000 kg f/cm' or more.

The obtained molded body is fired by hot pressing or pressureless sintering to obtain an alumina-silica-based sintered body.

In this case, the temperature increase rate is preferably 5° to 200°C/hr, and the firing temperature is 1600°C or higher, preferably 1
It is preferable that the temperature is 600 to 1650°C and the firing time is 1 hour or more, preferably 1 to 3 hours. In addition, when using a hot press, the pressure is 300 to 600 kg/Cr.
It is preferable to set it to about n'.

[Function] In general, even if raw materials such as refined kaolin, Bayer alumina, aluminum hydroxide, or silica stone are used and mixed by pulverization using a ball mill, etc., it is impossible to mix them to the theoretical composition at the atomic level. Therefore, it takes a long time to diffuse by sintering.

On the other hand, in the mullite composition, 3 to 40% by weight of WC particles and 0.0% by weight of CaCO3 particles as the second phase are used as the second phase.
When 1 to 1% by weight is added, an alumina-silica-based sintered body with high high-temperature strength can be obtained by ordinary molding and firing, even by pulverizing and mixing using a ball mill or the like.

In the present invention, although the details of the mechanism of high-temperature strength improvement due to the addition of WC are not clear, the WC particles incorporated within the mullite crystals or at the grain interfaces block the movement of SiO2 in the mullite to the glass phase. Furthermore, it is thought that this is because the WC particles are dispersed within the mullite crystal grains and at the grain boundaries, suppressing the growth of the mullite crystals. Also, CaC
0a! For addition, free silica (glass phase) is CaO
This is thought to be due to the fact that the glass phase is not precipitated and the high-temperature strength is high because the glass phase is fixed by reacting with the glass.

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

Example 1.2, Comparative Example 1 Purified kaolinite with composition Al20z/5iO2
Alumina was added so that the molar ratio was 3/2, and the mixture was milled using alcohol in a ball mill (ZR02 ball) for 48 hours. In this case, if a media agitation type pulverizer (attritor) is used, the treatment can be completed in 1 to 2 hours. More than 90% of the raw materials have a particle size of 5 μm
After pulverizing to the following amount, add WC powder (manufactured by Japan Shinkinzoku Co., Ltd.: average particle size 5 μm) and CaCO3 powder (manufactured by Sanni Mining Cement ■: average particle size 0.5 μm) in the amounts shown in Table 1. Comparative Example 1 was not added) and 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/crn” and then further pressurized with a rubber press at 1500 kg/crr to obtain a molded body. This molded body was sintered to form alumina with a mullite composition.
A silica-based sintered body was obtained. Note that sintering was performed using a hot press, with a temperature increase rate of 150°C/hr, and a temperature of 300 k
g/crn' at 1600°C for 1 hour.

Table 1 shows various properties of the obtained sintered body.

Condolence 1 table It can be used for.

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

Claims (2)

[Claims] (1) Consisting of WC, CaO and mullite, the WC content is 3 to 40% by weight relative to mullite, the CaO content is 0.1 to 1% by weight relative to mullite, and the mullite particle size is 10 to 10% by weight. An alumina-silica sintered body characterized by a thickness of 100 μm. (2) At least two selected from the group consisting of purified clay minerals, Bayer alumina, aluminum hydroxide, and silica stone are blended as main raw materials so that the composition ratio of Al_2O_3/SiO_2 falls within the mullite production range, and the blended raw materials are After wet grinding so that 90% or more has a particle size of 5 μm or less, WC with a particle size of 50 μm or less is added to the blended raw material by 3%.
~40% by weight of CaCO_3 with a particle size of 0.1 μm or less
Addition and mixing of 0.1 to 1% by weight with respect to the above-mentioned raw materials in terms of aO is carried out, and the resulting mixture is then dried and crushed, and then molded using an organic binder to form a molded product with a temperature of 160%
A method for producing an alumina-silica-based sintered body, characterized by firing at a temperature of 0° C. or higher for 1 hour or more.