JPH03187973A - Alumina-silica-based sintered material and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject alumina silica-based sintered material having a mullite composition, excellent in properties such as high temperature strength and capable of provision at a low cost by specifying the respective contents of TiN and CaO based on mullite. CONSTITUTION:The above mentioned alumina.silica-based sintered material is composed of TiN having <=30mum particle size, CaO having <=0.1mum particle size and mullite having 10-100mum particle size. TiN content and CaO content are respectively 5-30wt.% and 0.1-1wt.% based on mullite. In the above- mentioned sintered material, more economical raw materials than the conventional ones are used and specified ceramic particles as the second phase are dispersed in the mullite crystalline or on the grain boundary surface as a method for improvement of its physical properties to contrive improvement of the strength thereof. In addition, free glassy silica is occluded as a solid solution by addition of CaO, thus providing the objective material having characteristics equal to those of a high-purity synthetic mullite.

Description

[Detailed Description of the Invention] [Industrial Application] 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 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 producing the same.

[Prior Art] Mullite consists of AJl*Ox and 5iOa, and its chemical composition is theoretically 3Aj! aos-2SiOs+,
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 obtain the physical properties of synthetic mullite groups by modifying natural mullite, but the main focus of this research is to prevent 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.

The mixture of these raw materials according to the purpose and sintering is called mullite-based ceramic material ζ, and mullite-based ceramics, like alumina ceramics,
Because it has relatively high high-temperature strength and is an inexpensive material made from natural raw materials, it has been mainly used as a refractory material for furnace materials, sheaths, setter materials, heat-resistant materials, structural materials, etc.

[Problem to be solved by the invention] Among conventional mullite-based ceramics, those modified from natural mullite do not exhibit AA resistance during long-term use or high-temperature use.
The aOs-S i 02 ponding decomposes and silica precipitates as a glass phase at the grain boundaries of mullite. As a result, 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 was 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 TiN
(titanium nitride), CaO (calcium oxide), and mullite, the TiN and CaO contents are 5 to 30% by weight and 0.1 to 1% by weight, respectively, based on mullite, and the mullite particle size is 10 to 100 μm. The method for producing an alumina-silica sintered body according to claim (2), characterized in that 4+t
, using at least two poles selected from the group consisting of clay mineral, Peyer alumina, aluminum hydroxide, and silica stone as main raw materials, and blending the composition ratio of 'Aj220g/SiO2 within the mullite production range, and using the blended raw materials. 90
After wet grinding so that % or more has a particle size of 5 μm or less, 5% of TiN with a particle size of 30 μm or less is added to the raw material mixture.
~30% by weight of CaCO5 (calcium carbonate) with a particle size of 0.1 μm or less, calculated as CaO, relative to the above-mentioned blended raw material.
．． Adding and mixing 1 to 1% 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. It is characterized by

That is, the present invention uses inexpensive raw materials that have been conventionally used as raw materials, and disperses specific ceramic particles as a second phase within the mullite crystals or at the grain boundaries as a means of improving physical properties. In order to strengthen the
The glassy silica liberated by the addition of is fixed as a solid solution, thereby providing a material with properties comparable to high-purity synthetic mullite.

The present invention will be explained in detail below.

The alumina-silica-based sintered body according to claim (1) is a mixture of 5 to 30% by weight of TiN and 0.1 to 1% by weight of CaO based on mullite. If the TiN content 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 TiN becomes too large and the alumina-silica sintered body The characteristics as such are lost. Therefore, in the present invention, the TiN content is 5 to 30% by weight based on mullite. especially,'
When the TiN content is 7 to 15% by weight based on mullite, an alumina-silica sintered body with particularly high strength can be obtained.

゛On the other hand, if the content of CaO is less than 0.1% by weight based on mullite, it will not be possible to sufficiently fix the glass phase released during mullite formation, which will be described later, and the strength improvement effect will not be sufficient. If it exceeds this, 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, CaO
When the content is 0.5 to 1% by weight based on mullite,
Particularly high-strength alumina-silica-based sintered bodies 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 normal CaO
This is because the raw materials CaC0a and Ca(OH)2 (calcium hydroxide) have particles of several μm in size, and it is necessary to add a large amount to uniformly disperse them.

On the other hand, in the present invention, by using CaCO2 in the form of ultrafine particles of submicron size or less, 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 alumina-silica sintered body obtained will decrease;
When it is smaller than m, it becomes difficult to incorporate TiN 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 TiN particles is too fine, it is difficult to mix them uniformly with mullite. On the other hand, if the grain size of the TiN particles is too large, TiN will exist only at the mullite crystal grain boundaries, causing grain boundary cracks to occur. Therefore, in the present invention, the particle size of the TiN particles is preferably 30 μm or less, particularly 10 μm or less, particularly 3 to 10 μm.

In addition, if the particle size of CaCO5 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.

Note that the mullite composition in the alumina-silica sintered body is the theoretical composition (DA1203/S i 02 = 3/2
(molar ratio), i.e., 71.8728.2 (wt%).If the Al2O2 of the mullite composition is too large than the theoretical composition, mullite crystals will be dispersed in Alt20s, and sufficient strength will not be obtained. . On the other hand, if the mullite composition contains too much 5i02 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 jL 20 a /
It is preferable that the composition be as close as possible to S i O2 = 3/2 (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 CaC0a is added here, some silica glass liberated during mullite formation reacts with CaO generated by the decomposition of CaCO5 and is fixed, so it no longer precipitates as a glass phase at the mullite grain boundaries, resulting in high strength. Become something. The amount of CaCO5 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 Ca C, O-a added is too large, Ca
This is not preferable because the O phase becomes large. On the other hand, if the amount is too small, the free glass phase cannot be sufficiently fixed, resulting in no effect.

Such an alumina-silica-based sintered body can be easily and efficiently manufactured 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 A 11202 / Si
O2 composition ratio is in the mullite production range, preferably Al10s
/S i 02 =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. These raw materials are processed by ball milling,
Or 90% using alcohol etc. with attritor etc.
The above is wet-pulverized to a particle size of 5 μm or less, and then the resulting pulverized product is crushed to a particle size of 30 μm or less, preferably 10 μm or less.
5 to 30% by weight, preferably 7 to 15% by weight of TiN of 3 to 10 μm or less is added to the pulverized material,
Furthermore, CaCO5 of 0.1 μm or less is converted to 0.1 as CaO.
~1% by weight, preferably 0.5~1% 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 kgf/crd or higher and then hydrostatic press molding at 100,100 O/crn' 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, it is preferable that the temperature increase rate is 50 to 50°C, the firing temperature is 1600°C or higher, preferably 1600 to 1650°C, and the firing time is 1 hour or more.
Preferably, the time is 1 to 3 hours. If hot press is used, the pressure is 300 to 600 k.
It is preferable to set it to about g/crd.

[Function] In general, even if raw materials such as refined kaolin, Bayer alumina, 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. However, it takes a long time to diffuse through sintering.

On the other hand, 5 to 30% by weight of TiN particles as the second phase in the mullite composition and 0% by weight in terms of CaO as CaCO3 particles.
．． When 1 to 1% by weight is added, an alumina-silica-based 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 TiN are not clear, the TiN particles incorporated into the mullite crystals or grain boundaries block the migration of 5iOa in the mullite to the glass phase1. Furthermore, it is thought that this is because the TiN particles are dispersed within the mullite crystal grains and at the grain boundaries, suppressing the growth of the mullite crystals. Furthermore, with regard to CaC05m addition, it is thought that free silica (glass phase) reacts with CaO and is fixed, so there is no precipitation of glass phase and the high temperature strength is increased.

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

Example 1, Comparative Example 1 Purified kaolinite with a composition of AlI30s/S i
Alumina was added so that the solubility ratio was 02-3/2, and the mixture was pulverized for 48 hours using alcohol in a ball mill (ZrO2 Pole). In this case, if a media agitation type pulverizer (attritor) is used, the treatment can be completed in 1 to 2 hours. After pulverizing the raw material so that 90% or more has a particle size of 5 μm or less, TiN powder (manufactured by Japan Shinkinzoku Co., Ltd.) and CaCO5 powder (manufactured by Mitsubishi Mining Cement ■, average particle size 0.5 μm) are added to it. The amounts shown in Table 1 were added (in Comparative Example 1, no addition was made), and the mixture was further mixed in a ball mill for 5 hours. After drying and crushing this, organic binder (
PVA) was added in an amount of 5% by weight and thoroughly kneaded.

The mixed wire was press-molded to 50 mmφ x 5 mm.
After molding at kg/crd, it was further pressed at 1500 kg/Cnf using a rubber press to obtain a molded body. This compact was sintered to obtain an alumina-silica sintered body having a mullite composition. In addition, sintering is done using a hot press.
The heating rate was 150℃/hr, and the weight was 300 kg.
/cnf at 1600°C for 1 hour.

Table 1 shows the properties of the obtained sintered body.

From Table 1, Table 1A1, it is clear that an alumina-silica-based sintered body with a mullite composition to which a predetermined amount of TiN and CaCO3 are added can stably obtain significantly high strength from room temperature to high temperatures such as 1300°C. .

[Effects of the Invention] As detailed above, the alumina-silica-based sintered body of the present invention is provided at low cost using inexpensive raw materials, and has excellent properties such as high-temperature strength and durability. Remarkably superior. 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 manufactured easily, efficiently, and at low cost by the method of the present invention.

Claims (2)

[Claims] (1) Consisting of TiN, CaO and mullite, the TiN content is 5 to 30% 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 30% 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, 5 to 30% by weight of TiN with a particle size of 30 μm or less based on the blended raw materials, and CaCO_3 with a particle size of 0.1 μm or less in terms of CaO, 0.1 to 1% by weight is added to the raw materials and mixed, then the resulting mixture is dried and crushed, and then molded using an organic binder to form a molded product at 16% by weight.
A method for producing an alumina-silica sintered body, which comprises firing at a temperature of 00°C or higher for 1 hour or more.