JPH03164465A - Sintered body of alumina silica system and production thereof - Google Patents

Abstract

PURPOSE:To provide the sintered body which has excellent characteristics, such as high-temp. strength, and is inexpensive by constituting the sintered body of B4C, CaO and mullite and specifying the ratio of the mullite to the B4C, CaO and the grain size of the mullite. CONSTITUTION:This sintered body of the alumina silica system consists of the mullite having 10 to 100mu grain size, the B4C of 5 to 30% by the weight of the mullite and the CaO of 0.1 to 1% by the same weight. The production of the sintered body is executed by using >=2 kinds of refined clay ore, Bayer alumina, aluminum hydroxide, and silica stone and admixing these materials in such a manner that the compsn. ratio of Al2O3/SiO2 attains a mullite forming range. After the admixed raw materials are ground by a wet process until >=90% attains <=5mu, the B4C of <=30mu grain size is added and mixed to and with the admixed raw materials mentioned above at 5 to 30% and the CaCO3 of <=0.1mu grain size likewise at 0.1 to 1% in terms of CaO. After the mixture is dried and crushed, the mixture is molded by using an org. binder and is calcined for >=1 hours at >=1600 deg.C.

Description

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

[Conventional technology] Mullite is AJ! The chemical composition is theoretically 3AJ2203-2Si02, and its properties include excellent heat resistance and particularly good creep properties. In addition, although the thermal shock characteristics are good, the electrical Is
Majesty is not very 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 to prevent the precipitation and vitrification of the silica phase in the mullite composition. , the preparation of raw materials and sintering conditions were studied.

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.

The mixture of these raw materials according to the purpose and sintering is called mullite-based ceramic material.Mullite-based ceramic material has relatively high high-temperature strength like aluminum ceramics, and is made from natural raw materials. 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 B to be solved by the invention] Among conventional mullite-based ceramics, those made by modifying natural mullite have problems with Af during long-term use or high-temperature use.
The l20z-S i 02 bonding decomposes and silica precipitates as a glass phase at the grain boundaries of mullite. As a result, the strength decreased significantly, making it difficult to use continuously or repeatedly. High-purity mullite produced by the alkoxide process was developed to solve the above-mentioned drawbacks, but although high-purity mullite has a significant improvement effect on high-temperature strength and durability, it is expensive and cannot be used with conventional methods. It is disadvantageous in terms of cost for use in the field of industrial materials such as heat-resistant materials, which are more commonly used.

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) has 84C
(Boron carbide), CaO (calcium oxide) and mullite, and the 84C and CaO contents are 5 to 30% by weight and 0.1 to 1% by weight, respectively, relative to mullite,
The 4.1 characteristic is that the mullite particle size is 10 to 100 μm.

The method for producing an alumina-silica-based sintered body according to claim (2) uses A 11 2 0 3 as main raw materials at least two selected from the group consisting of purified clay mineral, Bayer alumina, aluminum hydroxide, and silica stone. /SiO2 composition ratio is 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, 84C with a particle size of 30tim or less is added to the blended raw material. 5-30% by weight, CaCO3 with a particle size of 0.1 μm or less
Calcium carbonate (calcium carbonate) is added and mixed in an amount of 0.1 to 1% by weight with respect to the above-mentioned raw materials, and then the resulting mixture is dried and crushed, and then an organic binder is used. Molded and molded at a temperature of 1600℃ 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. In addition, the glassy silica liberated by the addition of CaO is fixed as a solid solution, thereby providing a material with #h content comparable to that of high-purity synthetic mullite. The present invention will be explained in detail below. The alumina-silica-based sintered body of claim (1) contains B4C in an amount of 5 to 30% by weight and 0.1 to 1% by weight based on mullite.
of CaO. If the content of 84C is less than 5% by weight based on mullite, the strength improvement effect according to the present invention cannot be obtained, and if it exceeds 30% by weight, the amount of 84C becomes too large, resulting in Al-based silica-based sintering. The characteristics of the body are lost. Therefore, in the present invention, the 84C content is set to 5 to 30% by weight based on mullite. In particular, 8
When the 4C content is 7 to 20% by weight based on mullite, an alumina-silica-based baked viscous material having 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 set to 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, there have been reports of using CaO as an additive during sintering of mullite, and in this case, 5 to 15% by weight is added. This is because the particles of CaCO3 and Ca(OH)2 (calcium hydroxide), which are common CaO raw materials, are several micrometers 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 CaCOz, which is a submicron or smaller particle, a sufficient effect could be obtained with addition of a small amount of 0.1 to 1% by weight.

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 resulting Alyona-silica sintered body will decrease;
When it is smaller than m, it becomes difficult to incorporate 84C 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 μm. On the other hand, if the particle size of the 84C 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 84C itself occurs. On the other hand, if the grain size of the 84C grains is too large, 84C will exist only at the mullite grain boundaries, causing grain boundary cracks. Therefore, in the present invention, 8
The particle size of the 4C particles is preferably 30 μm or less, particularly 10 μm or less, especially 3 to 10 μm.

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

In addition, the composition of the mullite in the Alyona silica-based sintered body is the theoretical composition A It 2 O z / S i O
2 = 3/2 (molar ratio), i.e. 71.8/28.2 (
% by weight). AIL with mullite composition
If the amount of 203 is too much than the theoretical composition, mullite crystals will be dispersed in Au203, and sufficient strength will not be obtained.

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 A j2
2 0 z / S i O 2 = 3 7 2 (
It is preferable that the composition be as close as possible to the molar ratio).

As described above, even if the silica glass phase is prevented from precipitating as much as possible, some precipitation still occurs, and therefore the strength cannot be sufficiently increased. When CaCO3 is added here, some silica glass liberated during mullite formation reacts with CaO generated by the decomposition of CaCO3 and is fixed, so it no longer precipitates as a glass phase at the mullite grain boundaries, resulting in high It becomes strong. The amount of CaCOa added is O. High strength was obtained when the content was 1 to 1% by weight, more preferably 0.5 to 1% by weight. As mentioned above, if the amount of CaC03 added is too large, the CaO phase will become large, which is not preferable. On the other hand, if the amount is too small, the free glass phase cannot be sufficiently fixed, resulting in 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, purified clay mineral, Bayer alumina, aluminum hydroxide, or silica is used as a raw material, and
i O2 composition ratio is within the mullite production range, preferably A
fl 2 0 3 / S i O 2 = 3 /
2 (molar ratio). In this case, it is particularly preferable to use purified kaolin, Peyer alumina or aluminum hydroxide, or Bayer alumina or aluminum hydroxide and silica stone as raw materials. The required amount of these raw materials is wet-milled using alcohol or the like using a ball mill or attritor so that 90% or more of the powder has a particle size of 5 μm or less. Next, the obtained pulverized material was
0 μm or less, preferably 10 μm or less, especially 3 to 10 μm
5 to 30% by weight, preferably 7 to 20% by weight of 84C of
0.1 to 1% by weight of COa calculated by Cadi, preferably 0
．． Add 5 to 1% by weight and mix 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). The substitute model is I O O O kgf / c after pressure molding at 300 kgf / crn' or more.
It is preferable to carry out two-stage molding by isostatic press molding at rd or higher.

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 50~Zoo℃/hr, the firing temperature is 1600℃ or higher, preferably 1600-1650℃, and the firing time is 1 hour or longer.
Preferably, the time is 1 to 3 hours. In addition, when using a hot press, the pressure is 300 to 600 kg/
It is preferable to set it to about "crn".

[Function] In general, even if raw materials such as refined kaolin, Peyer alkuna, aluminum hydroxide, or silica stone are used and mixed by finely pulverizing them with a ball mill, etc., it is impossible to mix them to the theoretical composition at the atomic level. Therefore, C requires a long time to be diffused by sintering.

On the other hand, 5 to 30% by weight of 84C particles as the second phase in the mullite composition and O
．． When added in an amount of 1 to 1% by weight, an alumina-silica sintered body with excellent 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 84C are not clear, the B4C particles incorporated within the mullite crystals or at the grain interfaces block the movement of Si02 in the mullite to the glass phase. Furthermore, 84
This is thought to be because the C particles separate into the mullite crystal grains and grain boundaries, suppressing the length of the mullite crystals. Also,
The reason for the addition of CaCO3 is thought to be that free silica (glass phase) reacts with CaO and is fixed, eliminating precipitation of the glass phase and resulting in high high-temperature strength.

[Example] The present invention will be explained in more detail by giving examples and comparative examples below. Examples 1 and 2, Comparative Example 1 Purified kaolinite with a composition of Ad203/S i O
Alumina was added so that the molar ratio of 2 = 3/2 was obtained, and the mixture was ground using alcohol in a ball mill (ZR02 ball) for 48 hours. ), it is possible to process the raw material in 1 to 2 hours.
After grinding so that % or more has a particle size of 5 μm or less, B4C powder (manufactured by Denriki Co., Ltd., average particle size 5 μm) and Ca
CO3 powder (manufactured by Mitsubishi Mining Cement ■: average particle size 0.5μ
m) was added in the amount shown in Table 1 (comparative example 1 was not added),
The mixture was further mixed in a ball mill for 5 hours. After drying and crushing this, 5% by weight of organic trade binder (PVA) was added and thoroughly kneaded at °C.

The kneaded material was press-formed into 50 mmφ x 5 mm by press molding C.
After molding at 0 kg/c n/, the molded body was further pressurized at 1500 kg/cm" using a rubber press to obtain a rod-shaped body. This molded body was sintered to form alumina with a mullite composition.
A silica-based sintered body was obtained. For sintering, a hot press was used, the heating rate was 150℃/hr, and the temperature was 300kg/hr.
The test was carried out at 1600°C for 1 hour at Ctrl'. Table 1 shows various properties of the obtained sintered body.

Audience Table 1 It is clear from Table 1 that the alumina-silica sintered body of mullite composition to which B4C and CaCOs of the specified i are added can stably provide extremely high strength from room temperature to high temperatures such as 1300°C. [Effects of the Invention] As detailed above, the alumina-silica m-concrete of the present invention can be provided at low cost using inexpensive raw materials, and has excellent properties such as high-temperature strength and durability. Remarkably excellent. Therefore, the present sintered body can be used extremely effectively over a long period of time as an industrial fireproof material.

Therefore, such a sintered body of the present invention can be produced in a challenging and efficient manner at low cost by the method of the present invention.

Claims (2)

[Claims] (1) Consisting of B_4C, CaO and mullite, B_4
Alumina/silica having a C content of 5 to 30% by weight based on mullite, a CaO content of 0.1 to 1% by weight based on mullite, and a mullite particle size of 10 to 100 μm. system sintered body. (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, 5 to 30% by weight of B_4C with a particle size of 30 μm or less based on the blended raw material, CaCO_3 with a particle size of 0.1 μm or less
0.1 to 1% by weight of the above-mentioned blended raw materials in terms of CaO
addition and mixing, then drying and crushing the resulting mixture,
After that, it is molded using an organic binder, and the molded product is made into 1
A method for producing an alumina-silica-based sintered body, which comprises firing at a temperature of 600°C or more for 1 hour or more.