JPH0686291B2 - Spinel powder and method for producing the same - Google Patents

Description

The present invention relates to a novel spinel powder and a method for producing the same.

[Prior Art] Spinel is a complex oxide that has been known for a long time, but its use has not been sufficiently developed compared to other oxides such as alumina and magnesia. The main reason why spinel has been delayed in application development as compared with other oxides is that powder having excellent moldability and sinterability has not been obtained.

However, since spinel can be sintered at a lower temperature than alumina, ceramics can be easily manufactured, and since infrared absorption is smaller than that of alumina, an excellent light-transmitting body can be obtained, and the crystal structure is cubic. This is one of the ceramics that is expected to be researched and developed in the future because it is possible to obtain isotropic ceramics because of the crystal.

The conditions that are problematic in the industrial production of ceramics are the formability and sinterability of the powder. The powder characteristics required as an ideal ceramic powder having excellent formability and sinterability are as follows.

(1) As small as possible (2) Narrow particle size distribution (3) Not aggregated (4) Nearly spherical (5) Uniform chemical composition and high purity, but such characteristics It is extremely difficult to synthesize a powder having all of the above.

There are three typical conventional methods for synthesizing spinel (MgAl ₂ O ₄ ) powder: solid phase reaction method, coprecipitation method, and alkoxide method.

The solid phase reaction method is the most general method as a ceramic powder synthesis method because of its simple operation, and there have been many reports so far. For example, spinel powder (molded body density 60%) synthesized by adding 1.5 wt% of AlF ₃ as a mineralizer to a mixture of Al (OH) ₃ and Mg (OH) ₂ and calcining at 1100 to 1400 ℃ 1600 After firing at ℃ for 1 hour, a sintered body with a relative density of 95-97% was obtained [WTBA
KKER and JGLINDSAY, Ceramic Bulletin, 46 [11] 1094
-1097, (1967)].

The coprecipitation method and the alkoxide method produce fine powder with high sinterability and high purity, but the operation is complicated and the resulting salt and alkoxide are expensive, so the spinel powder obtained is also expensive. Become. Further, it is difficult to obtain monodisperse particles because it is difficult to control the particle size by calcining the generated hydroxide. And, although fine particles can be obtained by this method, on the other hand, fine particles obtained by this method have a low density of the compact, and therefore, shrinkage during firing is large, which is not preferable for industrial ceramic production.

Next, the solid phase method is simpler in operation than other methods, but it is difficult to obtain fine and monodisperse particles. Therefore, since the formability and sinterability are low, operations such as hot pressing and addition of a sintering aid are required to obtain a dense sintered body. However, those manufactured by a method of adding a sintering aid or an additive such as AlF ₃ as in the above-mentioned documents are not preferable because they may deteriorate the physical properties of the sintered body, particularly the electrical characteristics.

[Problems to be Solved by the Invention] The present invention is intended to provide spherical and monodisperse particles having less of the above-mentioned drawbacks, and particularly to obtain such particles by a solid-phase method which is simple in operation. To do. That is,
An object of the present invention is to provide a spinel powder of spherical monodisperse particles excellent in moldability and sinterability, and a method for producing the same.

[Means for Solving Problems] Based on the situation of spinel, the present inventors have searched for a method for industrially producing spinel powder excellent in formability and sinterability at the same time. In the phase method, a hydroxide was used as a raw material, and by adjusting the composition and particle size of the raw material, a method for producing spinel powder having excellent formability and sinterability was found, and the present invention was accomplished. The structure is as described in the claims.

Generally, high-purity ceramics are desirable, and spinel also has electrical characteristics when MgO + Al ₂ O ₃ is less than 99.5% by weight.
Translucency is reduced. Therefore, the purity of the spinel of the present invention is 9
9.5 wt% or more. The balance is mixed in during manufacture and is composed of impurities of the raw material, but it is preferable that it is smaller in terms of physical properties of the sintered body.

The MgO / Al ₂ O ₃ molar ratio is 0.90 to 1.36, that is, MgO / (MgO + Al ₂ O
₃ ) A weight ratio of 25.5 to 35.0% by weight is required, and in terms of sinterability, the MgO / Al ₂ O ₃ molar ratio is 0.90 to 1.10, that is, MgO / (MgO + Al
₂ O ₃₎ ratio by weight is 25.5 to 31.2% by weight. MgO / Al ₂ O ₃
If the molar ratio is less than 0.90, abnormal grain growth occurs during sintering, and it is difficult to obtain a dense sintered body, and physical properties such as strength are deteriorated even if the sintered body is densified. When the MgO / Al ₂ O ₃ molar ratio is larger than 1.36, sintering is difficult and densification does not occur. On the other hand, if the molar ratio is out of this range, the second phase such as MgO or Al ₂ O ₃ will increase and the original properties of spinel will be lost, which is not preferable.

The spinel powder of the present invention has an average particle size of 0.6 to 1.5 μm,
The particles having a particle size distribution of 0.5 to 2.0 μm are 60% by weight or more, preferably the particles having 0.5 to 2.0 μm are 70% by weight or more, more preferably 80% by weight or more. Here, the sinterability of the powder having an average particle size larger than 0.6 μm sharply decreases, the sinterability of the powder having an average particle size larger than 1.5 μm sharply decreases, and the particle size distribution is wider than that of the powder of the present invention. In that case, the structure of the sintered body becomes non-uniform, and the sinterability decreases.

The apparent apparent specific gravity is one measure of formability, but 1.
If it is less than 1 g / cm ³ , the formability is lowered and it is difficult to obtain a dense sintered body. The apparent apparent specific gravity depends not only on the particle size but also on the shape of the particles, and tends to increase as the spherical shape approaches. The spinel powder of the present invention has a very great feature that the particles are spherical, as is clear from the SEM photograph (scanning microscope photograph) described later. It is presumed that high moldability can be obtained due to such particle shape and narrow particle size distribution. Further, the spinel powder obtained in the present invention is measured by the present inventors.
It is preferable that the specific surface area obtained by the BET method is 2.0 to 7.0 m ² / g, and the ratio of the average particle diameter to the particle diameter calculated from the specific surface area is less than 5. As a result, the particles are spherical, and the dispersibility is improved, and it is considered that the particles are more excellent in moldability and sinterability.

Next, the method for producing the spinel powder in the present invention will be described. The Mg (OH) ₂ powder used as a raw material in the present invention is 98.5% by weight or more of MgO on the basis of burning, SiO ₂ , CaO, and B ₂ O ₃ in a total amount.
Must contain 0.5-1.2% by weight. Mg (OH) ₂ , Si
Impurities other than O ₂ , CaO, and B ₂ O ₃ are unavoidably mixed in during manufacturing, and the smaller the amount, the better. When the total amount of SiO ₂ , CaO, and B ₂ O ₃ is less than 0.5% by weight, the reactivity of spinelization decreases, and unreacted MgO and Al ₂ O ₃ remain in a large amount, or more than 1.2% by weight. Although the reaction proceeds sufficiently, the large particles are likely to be generated and the particle diameter becomes non-uniform, which is not preferable because the sinterability is deteriorated. Further, it is not preferable that the amount is large in terms of purity. The particle size of the Mg (OH) ₂ powder is preferably 20 μm or less in terms of agglomerated particles in order to facilitate the spinelization reaction and to produce a spinel powder having a uniform composition. Such Mg (OH) ₂ powder of the present invention reacts alkali with seawater,
It is obtained by purification by classification and washing.

Further, with regard to Al (OH) ₃ which is another raw material, a spinel powder having a narrow particle size distribution such that the average particle size in the present invention is 0.6 to 1.5 μm and the particles having 0.5 to 2.0 μm are 80% by weight or more. To produce Al ₂ O
_It should be 39.0% by weight, preferably 99.7% by weight or more, and the higher purity is more preferable. And particles of 0.5 to 2.0 μm occupy 80% by weight or more, preferably 95% by weight or more,
The average particle size must be 1.2-1.5 μm. According to the inventors, the particle size of spinel is Mg (OH) ₂ , Al (O
It was revealed that the grain size of Al (OH) ₃ out of H) ₃ is dominated. Therefore, in the present invention, it is important to control the particle size of Al (OH) ₃ powder. When the average particle size of Al (OH) ₃ powder is smaller than 1.2 μm, the average particle size of spinel is smaller than 0.6 μm, and when the average particle size of Al (OH) ₃ powder is larger than 1.5 μm, the average of spinel. Particle size is larger than 1.2 μm, and also A
If the particle size distribution of l (OH) ₃ is wide, the particle size distribution of spinel becomes wide, which is not preferable. The Al (OH) ₃ used in the present invention is synthesized, for example, by the usual Bayer method.

In the present invention, Mg (OH) ₂ and Al (OH) ₃ are desirably mixed uniformly, preferably in water. The Mg (OH) ₂ and Al (OH) ₃ mixed cake thus obtained is calcined and spinel is synthesized by a spinelization reaction. The calcination temperature at this time is 1100 to 1500 ° C, preferably 12
It is from 00 to 1400 ° C. The powder obtained by calcination may consist of weak agglomerates of spinel particles. If necessary, the powder may be crushed with, for example, a ball mill to easily obtain the particle size distribution and the average particle size according to claim (1). A spinel powder is obtained.

As described above, the characteristic of the synthesis method of the present invention is that the raw material
It is to adjust the total amount of SiO ₂ , CaO, B ₂ O ₃ in Mg (OH) ₂ and the particle size and particle size distribution of the raw material Al (OH) ₃ , resulting in excellent formability and sinterability. Spinel powder can be synthesized.

Next, the invention will be specifically described with reference to Examples and Comparative Examples.

[Example] In the present invention, the spinel powder is molded by using a cemented carbide metal mold to obtain a molded body having a size of 9 x 5 x 5 mm ³ and 1 ton.
It was carried out by uniaxial pressing at / cm ² , and the compact density was determined from the diameter and weight of the compact. The density of the sintered body of spinel was determined by the Archimedes method using kerosene as a solvent.

In the measured values of the present invention, the average particle size and the particle size distribution are the light transmission type particle size distribution measuring device (micron.
Fort Sizer, Model: SKA-5000) was subjected to ultrasonic precipitation for 5 minutes by a 0.2% aqueous solution of sodium hexametaphosphate as a dispersion medium by a sedimentation method, and the 50% by weight diameter was determined as the average particle diameter. The apparent apparent specific gravity is a value measured by tapping 180 times with a powder tester manufactured by Hosokawa Iron Works. The shape of the particles was observed with a scanning electron microscope.

Example 1 Magnesium hydroxide having a composition of 28.3% by weight was prepared from magnesium hydroxide synthesized from seawater as shown in Table 1 and commercially available aluminum hydroxide shown in Table 2 (Hijilite H-42 manufactured by Showa Denko KK).
The mixture was stirred and mixed in water so that (MgO / Al ₂ O ₃ molar ratio = 1.00), then filtered and dried. Next, this mixed powder was calcined at 1300 ° C. for 2 hours to form a spinel, which was then crushed by a ball mill. The physical properties of the obtained spinel powder are shown in Table 3, the electron micrograph is shown in FIG. 1, and the particle size distribution is shown in FIG. Thus, the particles were spherical and had good dispersibility.

This powder was pressure-molded and then fired in an electric furnace. Table 4 shows the density of the molded body and the sintered body. Sintering with a theoretical density of 3.58 g / cm ³ was obtained by sintering at 1700 ° C in H ₂ . Further, FIG. 3 shows the relationship between the molding pressure and the density of the molded body. This spinel powder is molded into a sea shape by the doctor blade method,
When baked at 1600 ° C in air, a considerably transparent thin plate was obtained as shown in the photograph in Fig. 5. The size of the thin plate in the photograph was 16.5 cm × 4 cm × 0.6 mm, and the surface was fairly smooth and had no warpage.

Example 2 The same magnesium hydroxide and aluminum hydroxide as in Example 1 were used, and the MgO / (MgO + Al ₂ O ₃ ) weight ratio was 29.3% by weight (MgO /
Al ₂ O ₃ molar ratio = 1.05) was mixed and spinel powder was synthesized in exactly the same manner as in Example 1. The physical properties of the obtained spinel powder are shown in Table 3. This spinel powder was molded and fired in the same manner as in Example 1. The densities of the molded body and the sintered body are shown in Table 4.

Example 3 A spinel powder was produced in the same manner as in Example 1 by using magnesium hydroxide synthesized from seawater and having the composition shown in Table 1 and the same aluminum hydroxide as in Example 1. Table 3 shows the physical properties of the obtained spinel powder. This powder was molded and fired in the same manner as in Example 1. The densities of the molded body and the sintered body are shown in Table 4.

Comparative Example 1 Commercially available magnesium hydroxide having a composition shown in Table 1 (standard product # 200 manufactured by Asahi Glass Co., Ltd.) was crushed and passed through a 15 μm sieve, and the same aluminum hydroxide as in Example 1 was used. A spinel powder was produced in the same manner as in. An electron micrograph of the obtained powder is shown in FIG. 4, and a powder product is shown in Table 3. Unreacted MgO and α-Al ₂ O ₃ remain in this powder, and they are fine particles and often aggregate. This powder was molded and fired in the same manner as in Example 1. The densities of the molded body and the sintered body are shown in Table 4. Also, abnormal grain growth was observed in the sintered body.

Comparative Example 2 Spinel powder was produced in the same manner as in Example 1 from the same magnesium hydroxide as in Example 1 and the coarse-grained aluminum hydroxide shown in Table 2. The physical properties of the obtained powder are shown in Table 3. This powder was molded and fired in the same manner as in Example 1.
Table 4 shows the densities of the molded body and the sintered body.

[Effects of the Invention] As described above, the spinel powder of the present invention has good moldability,
It is a monodisperse powder with excellent sinterability, especially by adjusting the total amount of SiO ₂ , CaO, B ₂ O _{3 in} the raw material magnesium hydroxide and the particle size of aluminum hydroxide. ,
An excellent spinel powder can be obtained.

In addition, as the application, the powder has a narrow particle size distribution, good dispersibility, and has a spherical shape, so that it is used as an abrasive. The molded body is suitable for ceramic substrates and translucent bodies.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle structure of the spinel powder obtained in Example 1, FIG. 2 is a graph showing the particle size distribution of the powder, and FIG. 3 is the relationship between molding pressure and molding density. 4 is an electron micrograph showing the particle structure of the spinel powder obtained in Comparative Example 1, and FIG. 5 is a graph showing the powder obtained in Example 1 formed in the air by the doctor blade method. 2 is a photograph showing the grain structure of a light-transmissive thin plate fired at 1700 ° C.

Front Page Continuation (72) Inventor Koichi Sarugaku 4-2, Onahama Nagisa, Iwaki City, Fukushima Prefecture Asahi Kasei Corporation (56) References JP-A-62-72556 (JP, A) JP-A-63-185803 (JP) , A) JP 62-273044 (JP, A) JP 62-23441 (JP, A) JP 46-7321 (JP, A) JP 59-131570 (JP, A) JP 57-67074 (JP, A) Ceramic Bull. 46 [1], P. 1094-7

Claims (2)

[Claims] 1. Composition of MgO + Al ₂ O ₃ 99.5 wt% or more, MgO 2
5.5 to 35.0% by weight, 0.5 to 2.0 μm particles are 60% by weight or more, the average particle size is 0.6 to 1.5 μm, and the apparent apparent specific gravity is 1.1 g / cm ³ or more. Spinel powder to be. 2. Composition of MgO 98.5% by weight expressed on a burning basis
Or more, and SiO ₂ , CaO, B ₂ O ₃ is a total of 0.5 to 1.2 wt% magnesium hydroxide powder and composition is Al ₂ O ₃ 99.0 wt% or more on a burning standard, and 0.5 ~ 2.0 μm
Particles occupy 80% by weight or more, and the average particle size is 1.2 to 1.5
A method for producing spinel powder, which comprises calcination after mixing aluminum hydroxide powder having a size of μm.