JPH01320264A - Production of alumina-series ceramic - Google Patents

Abstract

PURPOSE:To improve bending strength and thermal shock resistance by blending zircon having prescribed particle diameter, TiO2, silicate flux consisting of SiO2, CaO and MgO, etc., and the balance alumina and molding the compound and thereafter sintering it. CONSTITUTION:100pts.wt. compounded raw material is obtained by blending 1-4pts.wt. ZrSiO4 having 0.1-5mum mean particle diameter, 1-5pts.wt. TiO2, 1-14pts. wt. silicate flux (e.g. compound incorporating >=50wt.% SiO2 and SiO2:MgO:CaO =7:2:1) consisting of composition having 40-95wt.% SiO2, 5-60wt.% CaO, 0-55wt.% MgO and 0-5wt.% one or more kinds selected from the group of B2O3, BaO, SrO, NiO, CdO, ZnO, MnO and CrO and the balance alumina. Then this raw material is molded and thereafter the molded body is sintered at 1,325-1,450 deg.C for 1-3 hours and alumina-series ceramic being a sintered body wherein tetragonal zirconia is dispersed in the vitreous binding phase of grain boundary of alumina is produced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing alumina ceramics, and particularly relates to a method for producing alumina ceramics, which has excellent mechanical strength, thermal shock resistance, and can be fired at low temperatures. Relating to a method of manufacturing.

[Prior Art] Alumina-based ceramics have excellent mechanical properties, electrical properties, etc., and are therefore widely applied as constituent materials of various industrial products by taking advantage of these properties. Conventionally, various additives have been used to improve strength, thermal shock resistance, reduce firing temperature, etc., and research has been conducted on additives for improving properties.

One example of these studies is the improvement of the strength, toughness, and thermal shock resistance of alumina ceramics by adding zirconia. For example, Japanese Patent Application Laid-open No. 52-86413 describes that the addition of zirconia improves the heat resistance. It is shown. Furthermore, in JP-A-55-158173 and JP-A-61-26558, zircon (Zrs) is used as a zirconia-containing oxide for alumina.
It is disclosed that the thermal shock resistance is improved by adding 50 + It is said that this is due to the large amount of monoclinic crystals, which causes micro-cranks. Further, Japanese Patent Publication No. 59-24751 discloses adding zirconia to improve toughness and bending strength. Furthermore, JP-A-53-1
No. 26008 discloses adding flux and a zircon compound.

[Problems to be Solved by the Invention] As described above, it is a known technique to improve the properties of alumina by adding zirconia or zircon, but none of the above methods can satisfy all the required properties. Alumina ceramics have not been obtained.

That is, the method described in JP-A-52-86413 is as follows:
Specifically, about 15% of unstabilized zirconia is added to alumina to improve fracture toughness due to fine microcracks, but the microcracks reduce bending strength.

The method described in JP-A-55-158173 is as follows:
Specifically, 45 to 60% by weight of zircon is mixed with 55 to 60% by weight of alumina, and the method described in JP-A-61-26558 uses 5 to 25% by weight of zircon. It is to be blended. All of these contain a large amount of zircon, so 16
High temperature firing at 00°C or higher or pressure firing is required. Therefore, strength deterioration occurs due to grain growth of alumina and sinter due to high-temperature firing, and further strength deterioration occurs due to monoclinic zirconia produced. Moreover, using a large amount of zircon is disadvantageous from a cost standpoint. In particular, JP-A-55-158173
In the method of the publication, mullite (2AJ220s, 2
A large amount of S t 02 ) is generated, and the characteristics as an alumina ceramic cannot be obtained.

In the sintered body described in JP-A-59-24751, the firing temperature is high (16
00°C or higher).

Further, in the method described in Japanese Patent Application Laid-open No. 53-126008, specifically, Cab is added to alumina.

This method also mixes 4 to 6% by weight of flux of MgO, SiO2, and 1 to 151i% of zirconia, zirconium acid chloride, zirconium hydroxide, etc. as a zircon compound in terms of ZrO2.
rO2 remains as a monoclinic crystal in the sintered body, and compressive stress remains inside. That is, ZrO2 undergoes a phase transition to form microcracks and becomes monoclinic ZrO2, thereby imparting thermal shock resistance, but there is a problem of a decrease in bending strength due to the formation of microcracks.

The present invention aims to solve the above-mentioned conventional problems and provide a method for producing alumina-based ceramics that has excellent mechanical strength and thermal shock resistance and can be sintered at a low firing temperature. .

[Means for Solving the Problems] The method for producing alumina ceramics of the present invention includes 1 to 4 parts by weight of zircon with an average particle size of 0.1 to 5 μm, TiO21
~5 parts by weight, 1 to 14 parts by weight of a silicate flux having the following composition, and the remainder being substantially alumina, by sintering a raw material that is formed by molding and sintering. The method is characterized by obtaining a sintered body in which tetragonal zirconia is dispersed in a binder phase at grain boundaries.

SiO2: 40-95% by weight Cao: 5-60% by weight MgO: 0-55rL amount 1 fffi or 2 or more selected from the group consisting of B2O2, BaO, SrO, NiO, CdO, ZnO, MnO and CrO ~5% by weight The present invention will be described in detail below.

In the present invention, the blending amount of zircon (ZrSiO+) is 1 to 4 parts by weight, and the average particle size is 0.1 to 5 μm.
Use the one.

If the amount of zircon added is less than 1 part by weight, sufficient improvement effects such as strength and toughness cannot be obtained by adding zircon. If the blending amount of zircon exceeds 4 parts by weight, high temperatures are required to decompose zircon, so the firing temperature increases and the properties of the resulting alumina ceramics deteriorate. Therefore, the amount of zircon blended is 1 to 4 parts by weight.

Moreover, when the average particle size of zircon exceeds 5 μm, the zirconia in the obtained alumina-based ceramic will not be tetragonal zirconia, and the monoclinic component will increase, resulting in a decrease in strength. Zircon with an average particle size of less than 0.1 μm has no difference in its properties improvement effect, and is poor in price and handling due to fine particle size. Therefore, the average particle size of the zircon used is 0
．． The thickness is 1 to 5 μm.

Further, the amount of TiO2 added is 1 to 5% by weight. TiO
If 2 is less than 1% by weight, the sintering temperature will not be lowered sufficiently.

If TiO2 exceeds 5ffi%, the sinterability will be significantly reduced and other properties of the resulting alumina ceramics may be deteriorated. Therefore, TiO2 is 1-5% by weight.
shall be.

The silicate flux used in the present invention is SiO2. Mg
In the ternary composition diagram shown in FIG. 1, the ratio of O and CaO is
A (95,0,5).

It is preferable that it be in the area surrounded by the points B (40, 55, 5) and C (40, 0, 60) (both IX amount %). Particularly preferred is a SiO2 content of 50% by weight or more, for example Sio2:MgO:Ca0=7:2:l
SiO2:MgO:CaO-6:3:IS io2:M
Examples include a formulation where gO:Ca0=6:2:2.

Such a silicate flux forms a bonding layer of glass phase at the alumina grain boundaries and improves the strength of the resulting alumina-based ceramic. If the composition of each component of the silicate flux used is outside the range specified by the present invention, a good glass phase having an excellent strength-improving effect cannot be formed.

If the amount of silicate flux is less than 1 part by weight, too little bonding layer of glass phase will be formed, and sufficient strength will not be obtained. On the other hand, if the amount of silicate flux exceeds 14 parts by weight, the amount of alumina will be relatively small and the properties as alumina will be impaired. Therefore, the amount of silicate flux blended is 1 to 14 parts by weight.

In the present invention, there is no particular restriction on the addition form of the silicate flux, and it may be added in the form of a reagent such as SiO:+, CaCO3゜MgCO3, or silicate flux such as talc, kaolin, lime, etc. It may be added in the form of natural raw materials containing the following ingredients.

In manufacturing the alumina ceramics of the present invention,
Zircon, TiO2, silicate flux, and alumina are mixed in predetermined amounts with water and, if necessary, an organic binder such as polyvinyl alcohol, and then molded and fired in accordance with a conventional method. For molding, first, the slurry obtained by mixing the raw materials is spray granulated. Spray granulation improves the fluidity of raw materials,
The filling property into the mold is improved. This raw material powder,
A molded body (powder compact) is obtained using a mold press or the like.

In the present invention, the molded body is fired at 1325 to 1450
It can be carried out at a relatively low temperature of ℃, and the firing time is 1~
About 3 hours is fine. If the firing temperature is less than 1325°C, the sintering reaction will be insufficient, which is not preferable. Also, 1450℃
Firing at a high temperature exceeding 100 mL is not only unnecessary, but also undesirable because it leads to a decline in properties such as strength and toughness due to growth and coarsening of crystal grains.

[Function] The zircon-added alumina ceramics of the present invention have much better properties than conventional products, even though the amount added is very small compared to conventional zircon-added alumina ceramics. Moreover, firing can be performed at a lower firing temperature than in conventional methods.

If zircon is used in excess as in the conventional method, sinterability is poor because sintering proceeds through a solid phase reaction in which mullite crystallizes due to the reaction between alumina and zircon. In addition, due to poor sinterability, high temperature firing at 1600°C or higher is required, resulting in coarse crystal grains and insufficient properties corresponding to the amount of zircon added. Most of the monoclinic zirconia exists as a monoclinic crystal, and although this monoclinic zirconia contributes to improving impact resistance, it causes a decrease in bending strength.

On the other hand, in the present invention, zircon decomposes into zirconia and silica during the firing process, which is the same as in conventional products, but the silica produced does not react with alumina, but with silicate added separately. A glass phase is formed together with the flux to firmly bond the alumina particles. That is,
The sintering in this case is liquid phase sintering, which makes it possible to significantly reduce the firing temperature. Then, the zirconia produced by the decomposition of zircon is uniformly dispersed as very fine zirconia particles in the glass phase formed by the reaction between silica and silicate flux, which strengthens the glass phase. The effect of further improving strength and toughness can be obtained.

Moreover, in the present invention, the zirconia produced by decomposition of zircon is mostly metastable tetragonal zirconia (
It exists as partially stabilized zirconia) and is restrained by the glass layer, so it does not undergo phase transition (although some parts may become monoclinic) and does not cause microcracks. Therefore, its strength is also extremely high. In addition, some of the generated zirconia reacts with T i O2 to form Z r T i
O4 is generated, and this low thermal expansion material X (Z r T i
O4) generation improves thermal shock resistance.

Furthermore, in the present invention, by adding a specific amount of TiO2, a further improvement in sinterability can be obtained, and 1
An alumina-based sintered body having extremely excellent properties is provided at a firing temperature of 500° C. or lower, which is significantly lower than conventional methods.

The effect of improving such properties in the present invention is due to the specific amount of silicate flux of specific composition as well as the specific amount of TiO
2 and extremely fine zircon with an average particle size of 0.1 to 5 μm to 1 to 4! This is achieved by adding a small amount of i parts.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Examples 1 to 3, Comparative Example 1.2 The raw materials were mixed so that the amounts of zircon, TiO2, silicate flux, and alumina were as shown in Table 1. In Comparative Example 1, TiO2 was not added. (Also, in Comparative Example 2, TiO2 and zircon were not added), too much water was added to 1000 g of raw material powder, and polyvinyl alcohol (manufactured by Shin-Etsu Chemical Co., Ltd., 10% by weight aqueous solution) was added as an organic binder by solid weight. 20g was added and mixed by ball milling for 70 hours to obtain a slurry. Note that the average particle size of the zircon powder used was 1.0 μm. As silicic acid flux, SiO2, CaCO5 and Mg
A mixture of CO3 and SiO2: 60% by weight, MgO: 25% by weight, and Cab: 15% by weight was used.

The obtained slurry was spray granulated to obtain a raw material powder, and this raw material powder was sized by a mold press of 100100 O/crn' to a size of 5. Ox5. It was molded to OX40 mm and fired in an electric furnace at the firing temperature shown in Table 1 for 2 hours.

Various properties of the obtained alumina-based sintered body were investigated,
The results are shown in Table 1.

As is clear from Table 1, according to the method of the present invention, a dense sintered body can be obtained at a very low firing temperature, and the resulting alumina ceramics have extremely high bending strength.
It also has excellent thermal shock resistance.

[Effects of the Invention] As detailed above, according to the method for producing alumina ceramics of the present invention, the bending strength is high at a low firing temperature,
Moreover, alumina ceramics with excellent thermal shock resistance can be produced.

[Brief explanation of the drawing]

FIG. 1 is a ternary composition diagram showing the composition of the silicate flux used in the present invention. Patent applicant: Inax Co., Ltd. Attorney: Tsuyoshi Shigeno Figure 1

Claims (1)

[Claims] (1) Zircon with an average particle size of 0.1 to 5 μm 1 to 4 parts by weight TiO_21 to 5 parts by weight Silicate flux having the following composition 1 to 14 parts by weight SiO_
2: 40-95% by weight CaO: 5-60% by weight MgO: 0-55% by weight One or more selected from the group consisting of B_2O_3, BaO, SrO, NiO, CdO, ZnO, MnO and CrO: 0 ~5% by weight and the balance being substantially alumina for a total of 100 parts by weight. By molding and sintering the raw materials, tetragonal crystals are formed in the glassy binder phase at the grain boundaries of alumina. A method for producing alumina ceramics characterized by obtaining a sintered body in which zirconia is dispersed.