JPS61132513A - Alpha-alumina powder and its production - Google Patents

Abstract

PURPOSE:Amorphous aluminum hydroxide is heated at a specific temperature, then crushed to make an alpha-alumina powder with moldability, sintering properties and high performance of sintered products. CONSTITUTION:A solution of sodium aluminate is brought into contact with carbon dioxide gas then rinsed and dried to give amorphous aluminum hydroxide. Then, the aluminum hydroxide is heated over 1,100 deg.C into alpha-alumina, which is crushed to give an alpha-alumina powder which has a specific surface area of 3-15m<2>/g, average particle size of 0.6-1.4mu and a particle size distribution where, when particle sizes are fractionated every 0.2mu, the maximal distribution fraction ranges within 0.1-0.6 time the average particle size and the distribution is more than 1.5 times than the other fractions, respectively.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an α-alumina powder and a method for producing the same. The present invention relates to high-purity α-alumina powder and its manufacturing method.

High-purity α-alumina sintered bodies are used as electronic materials, carriers for fluorescent materials,
It is used in a wide variety of fields, including transparent tubes for sodium lamps.

(Prior Art) The high-purity α-alumina powder used as a raw material for these sintered bodies has a high compact density at the time of compaction, good sinterability, and good performance as a sintered body, such as: It is required to have excellent smoothness, translucency, strength, etc.

However, it is very difficult to satisfy these demands simultaneously. Generally speaking, it is said that α-alumina powder has good sinterability when the particle size is fine, but on the other hand, when the particle size becomes fine, the density of the compact decreases, and as a result, shrinkage during sintering becomes large. A drawback arises that adversely affects dimensional accuracy. On the other hand, powders with large particle sizes have the advantage of increasing the density of the compact, but the sinterability decreases and the performance of the sintered compact is poor.

The high-purity α-alumina powders known so far are satisfactory in terms of chemical purity, but are unsatisfactory in terms of formability, sinterability, and sintered compact performance. to
For example, high-purity alumina obtained by underwater spark discharge of metal aluminum has irregular grain shapes and sizes, making it difficult to obtain a uniform, high-density sintered body. Although high-purity alumina obtained from organic aluminum as a raw material has fine particles, it tends to darken when it is sintered, and there is a need for improved translucency.

Formability, sinterability, and sintered body performance are supposed to be related to the chemical and physical properties of the powder, but the relationship is not sufficiently clear at this stage. .

(Problems to be Solved by the Invention) As mentioned above, conventional high-purity α-alumina powders are unsatisfactory in terms of formability, sinterability, and sintered body performance. It is difficult to be a friend.

(Next technical means to solve the problem) The present inventors have pursued a high-purity alumina powder with excellent formability, sinterability, and sintered body performance, and as a result, have achieved a value line and a unique The discovery of alumina powder with a sharp particle size distribution led to the completion of the present invention.

That is, the present invention has a specific surface area of 5 to 15 rrt/f,
The average particle size is 0.6 to 1.4μ, and the division that accounts for the largest proportion is in the range of 0.1 to 0.6 times the average particle size according to the t$2 degree distribution divided into 0.2μ increments. Yes, the proportion is higher than that of other b
In producing the α-alumina powder, the amorphous aluminum hydroxide 111
This is a method for producing α-alumina powder, which is characterized by heating it to 00C or higher to convert it into α-alumina, and then pulverizing it.

In the present invention, the average particle size and particle size distribution of particles are values measured by the following method using a particle size distribution measuring device using a centrifugal sedimentation method (for example, Horiba Yosakusho Co., Ltd., CAPA-500, etc.). . That is, alumina powder was dispersed in a dispersion medium of isobutyl alcohol by ultrasonic vibration treatment (5 hours), and the resulting charcoal dispersion was heated at a rotational speed of 300 rpm.
The particle size distribution is measured using a particle size distribution analyzer under the condition that the measurement division is every 0.2 μm.

In the present invention, the specific surface area is measured by a gas adsorption specific surface area measuring device, for example, Micromeritics Specific Surface Area Automatic Measuring Device Model 2200 manufactured by Shimadzu Corporation.

In the known alumina powder, the peak of the particle size distribution almost coincides with the average particle size, and the height gradually decreases around that peak, which is a so-called Yamanashi particle size distribution, whereas the alumina powder of the present invention shows a so-called Yamanashi particle size distribution. The peak of the particle size distribution is smaller than the average particle size, and the average particle size is r1.1 to 0. b times range ICI
), and moreover, it has an extremely high ratio of peaks, more than 1.5 times that of other categories, and has a sharp particle size distribution with a so-called single peak.

Among them, in the particle size distribution divided into 0.2 μ increments, 0
．． The alumina powder with a particle size distribution in which the peak in the 2-0.4 μ range is the maximum has % better performance.

The particle size distributions of the alumina powders obtained in Example 1, Comparative Example 1, Comparative Example 2, and Example 2 described later are shown in FIGS. 1 to 4.

In Figures 1 to 4, the vertical axis represents the particle size classification; for example, the number 0.2 means the 0 to 0.2μ division, and the number 0.4 means the 0.2 to 0.4μ division. do. The horizontal axis shows the proportion of that category.

The alumina powder of the present invention can be easily obtained by converting amorphous aluminum hydroxide, which is obtained by contacting a sodium aluminate solution with carbon dioxide gas, into α-alumina by heating it to 1100C or more, and then pulverizing it. It will be done. Here, the pulverization treatment means treatment with commonly known pulverization equipment such as a ball mill, a vibrating ball mill, and a jet mill. Since alumina is known to be difficult to pulverize, it is presumed that by this treatment, the alumina powder will mainly be deagglomerated rather than pulverized, resulting in a monodisperse distribution. Incidentally, such an effect is not obtained when the crystalline aluminum hydroxide is used, and the distribution remains a normal distribution type.

In the present invention, if the specific surface area is large, the surface roughness tends to increase, so it is preferable to set the specific surface area to 15% or less, and if the specific surface area is too small, the low temperature sinterability will deteriorate, so 3% /? The above is good.

(Effect of the invention) The alumina powder of the present invention has good moldability.

When alumina powder is dry-molded at a pressure of t-2 tons/-, a conventional product with a chevron-shaped distribution, for example, high-purity alumina obtained by thermal decomposition of ammonium light bread, has a compact density of 1.9~ However, the alumina powder of the present invention exhibits 2.0 to 2.4 r/dt-, and shrinkage during sintering is small. Furthermore, the alumina powder of the present invention has excellent sinterability. In particular, it has excellent low-temperature sinterability at 1,400 to 1,500 C, and grain growth is less likely to occur during sintering at temperatures near tsooC, which is advantageous for the smoothness and strength of the sintered body. Then, by sintering at high temperature in a hydrogen atmosphere, a solid sintered body with excellent translucency is obtained.

(Example) Examples of the present invention, applied examples, comparative examples, and comparative applied examples will be given and explained.

Example 1 Produced by the Bayer method, aluminum hydroxide was dissolved in caustic soda to form a solid aluminum/sodium acid solution (A40m:
30? / L, Na, O/A40B = 1
．． 3) Hold at 1000r'110G, 500 rp
A slurry containing 45 ff of aluminum hydroxide was reacted for 75 minutes at 200 Mt of carbon dioxide per minute while stirring at m.
This precipitate was then filtered, washed, and dried by spray drying. This aluminum hydroxide was identified by powder X-ray diffraction and was found to be amorphous. Missing, is this 'i11? After firing in OC for 2 hours, it was processed in a vibrating ball mill for 5 minutes to obtain α-alumina powder.

The specific surface area of this alumina powder is 10.5 μm/1, the average particle size is 87 μm, and the particle size distribution is as shown in Figure 1, with a ratio of 0.2 to 0.4 μm being 25 μm. .7
It was a distribution with a single peak showing a price more than three times that of other categories.

Comparative Example 1 A sodium aluminate solution (A40s: 60 t/l-%NatO/
0s = 1.3) 1000 f was held in soC and hydrolysis was carried out under the same conditions as in Example 1 to obtain 70ft1'' of aluminum hydroxide. Of this, 45? was fractionated and used in Example 1. Washed and dried under the same conditions as above.The nine aluminum oxides obtained were identified by powder X-ray diffraction, and the results showed that they were crystalline aluminum hydroxide (
Bayerite) atatsubun. Next K, this at 1230C 2
After 9 hours of firing, it was processed in a vibrating ball mill for 5 minutes to obtain α-alumina powder.

This α-alumina powder has a specific surface area of 10.21re/l,
The average particle size is 0.77 μm, the particle size distribution is shown in Figure 2, the ratio of the 0°2 to 0.4 μm division is 17 chips, and the distribution is a gentle mountain shape with 6 t0 comparative examples. 2 The experiment was conducted in the same manner as in Example 1, except that the vibrating ball mill treatment was omitted.

The obtained nine-α alumina powder has a specific surface area of 9.4 m2/g,
The average particle diameter was 1.3 μm, and the particle size distribution was a mountain-shaped distribution with a ratio of 2% in the 0.2 to 0.4 μm category as shown in Figure 3.

Example 2 A sodium subaluminate solution (A40.: 75 S'/L, Nan
o /Am03=1.3) 1000 f to 100
While stirring at 500 rpm, carbon dioxide was reacted at 400 rpm for 900 minutes, and aluminum hydroxide 9
21 is my friend. This is washed and freeze-dried. The resulting aluminum hydroxide was identified by powder X-ray diffraction and was found to be amorphous and hot. This is 1f! :1230C, calcined for 5.5 hours, and then treated in a ball mill for 3 hours to obtain α-alumina powder. The specific surface area of α-alumina powder is 5.5Trt/f
, average particle diameter 1.064 m, particle size distribution Fi as shown in Figure 4, 6-order distribution with a single peak showing the maximum proportion (20 inches) divided into 0.2 to 0.4 μm.

Application Example 1 and Comparisons IR Application Examples 1 and 2 The tα alumina obtained in Example 1 and Comparative Examples 1 and 2 was applied to a disk with a diameter of 15 mm and a thickness of 2 to 3 mm at a rate of 1.9 tons/d. Molded with pressure.

Density ft of the obtained compacted body - Table 1 (shown t).

Table 1 Application Example 2 and Comparative Application Example 5 After adding 0.1 weight St of magnesium oxide as a sintering aid to the α-alumina obtained in Example 1 and Comparative Example 1, 1? Take a disk with a diameter of 15 and a molding pressure of 1.9.
A friend molded in tons/d. This was heated to 5aQc in a hydrogen atmosphere.
The sample was heated at a temperature increase rate of 1/2 hour and kept at a predetermined temperature for 2 hours, and then its density was measured.

The results are shown in Table 2. It was confirmed that the α-alumina of the present invention has excellent low-temperature sinterability.

Table 2

[Brief explanation of drawings]

Figure 1 is a chart showing the particle size distribution of α alumina obtained in Example 1, Figure 2 is a chart showing the particle size distribution of tα alumina obtained in Comparative Example 1, and Figure S is a chart showing the particle size distribution of α alumina obtained in Comparative Example 2. Obtained α
FIG. 4 is a graph showing the particle size distribution of alumina obtained in Example 2. # Mother (0 Sumida (0) Sumida (0)

Claims (3)

[Claims] (1) Specific surface area is 3-15m^2/g, average particle size is 0.
In the particle size distribution divided into 6-1.4μ and 0.2μ increments, the division that accounts for the largest proportion is the average particle size of 0.1-0.
α-alumina powder, which is in the range of 6 times, and whose ratio is 1.5 times or more compared to any other classification. (2) Specific surface area is 3-15m^3/g, average particle size is 0.
In the particle size distribution divided into 6-1.4μ and 0.2μ increments, the division that accounts for the largest proportion is the average particle size of 0.1-0.
In order to produce α-alumina powder, which has a ratio of 6 times higher than that of any other category, amorphous aluminum hydroxide is heated to 1100°C or higher to produce α-alumina powder. A method for producing α-alumina powder, which is characterized by converting it into alumina and then pulverizing it. (3) The method for producing α-alumina according to claim 2, wherein the amorphous aluminum hydroxide is obtained by washing and drying amorphous aluminum hydroxide obtained by contacting a sodium aluminate solution with carbon dioxide gas.