JPH0319163B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is based on silicon aluminum oxynitride (Si
-Al-O-N compound) The present invention relates to a method for producing a powder raw material. Recently, as nitride-based high-temperature materials, silicon nitride-based ceramics and silicon-aluminum oxynitrides, in which part of the silicon in silicon nitride Si ₃ N ₄ is replaced by aluminum and part of the nitrogen is replaced by oxygen, have been developed. Sialon (Si-Al-O-N) ceramics are attracting attention. Silicon nitride has a large bond covalent nature, and it is difficult to densify and sinter silicon nitride alone. Therefore, unique sintering methods such as adding sintering aids are being researched, but adding sintering aids often fails to fully bring out the expected properties of Si ₃ N ₄ . On the other hand, since sialon contains aluminum and oxygen, which have high ionic bonding properties, it is expected to have better sinterability than silicon nitride itself. Therefore,
If a sialon raw material with relatively high sinterability is synthesized, it can be made without the use of secondary additives, or
It is expected that a sintered body can be obtained by adding only a small amount. Incidentally, it is generally preferable that a ceramic sintered body is made of a dense, fine, and uniform structure, excluding porous materials. For this purpose, the adjustment conditions, molding conditions, sintering conditions, etc. of the powder raw material are relevant, but the finer the powder raw material, the easier it is to obtain a suitable ceramic sintered body at a lower temperature and in a shorter time.
Furthermore, in order to produce a sintered body consisting of fine crystal grains, it is better to use as fine a powder as possible as a starting material. Furthermore, it is desired that the powder raw material, which is prepared by chemically synthesizing two or more components, has homogeneous and highly pure characteristics. Thus, the following method has been proposed to produce a sialon-based powder raw material that meets the above objectives. (i) Silica (SiO ₂ ) powder, carbon powder, and AlN (or Al ₂ O ₃ ) powder are mixed, and the silica is reduced with carbon in a nitrogen atmosphere to perform a nitriding reaction. In this method, the smaller the particle size of the silica powder, the smaller the particle size of the raw material powder. Therefore, silica powder with extremely small particle size is desired, but it is still unsatisfactory because the cost of making silica into fine powder is high and impurities are likely to be mixed in. Moreover, since the starting materials are mixed in powder form,
It takes a considerable amount of time to achieve a uniform mixing state. (ii) CVD method... SiCl ₄ , SiH ₄ is often used as a silicon source, NH ₃ is often used as a nitrogen source, AlCl ₃ gas, O ₂
It is synthesized by a gas phase reaction in the coexistence of gas and water vapor. This manufacturing method can be made into a fairly fine powder and can be made into a highly reactive amorphous state, but the raw materials are relatively expensive and the production process is slow. It is not suitable for mass production because the speed is extremely slow. The present invention was developed in view of the above circumstances, and in addition to the characteristics of SiAlON, which is highly reactive compared to silicon nitride, it has the advantage of having a uniform composition and extremely small particle size, resulting in easy sinterability. The present invention aims to provide a method for producing a sialon-based powder having the following properties. Another object of the present invention is to provide a method for producing sialon-based powder raw materials more easily than conventional methods. Hereinafter, the method for producing the sialon-based powder raw material of the present invention will be explained in detail. The structure of the present invention consists of the following steps. First step: Using silica sol, alumina sol, and carbon slurry (preferably carbon black slurry) as starting materials, a mixed solution is prepared to have a desired silicon-aluminum oxynitride composition. Since each starting material has a unique pH (PH = -log [H ⁺ ], [H ⁺ ] represents the molar concentration of hydrogen ions), the difference in pH between each is approximately 4.6 or less. It is necessary to adjust accordingly. For example, when the PH of silica sol is 2.9, the PH of alumina sol is 4.5, and the PH of carbon black slurry is 3.5, each PH
Among the differences, the maximum PH difference was 1.6, and a uniform mixed solution was easily obtained. However, the pH of silica sol =
9.3, when the pH of the alumina sol was 4.5 and the pH of the carbon black slurry was 7.5, the PH difference between the silica sol and the alumina sol was 4.8, and in this case, when they were mixed, they quickly gelled and were difficult to become uniform. Second Step In order to powderize the mixed solution, hot air drying (for example, spray drying) or pulverization treatment after gel hardening is performed. Although various methods can be used for gelation, gelation can be easily achieved simply by heating to nearly 100°C, and cooling and pH adjustment may also be used. When the gel is crushed using a milk bee or a vibrating mill,
Because it is mixed as a solution, it becomes homogeneous and easily becomes a fine powder. The primary particle size of this powder is approximately 0.01~
It was 0.05 micron. Third Step A sialon-based powder raw material was obtained by carrying out a synthesis reaction on the above mixed powder at about 1200 to 1800°C in an atmosphere of non-oxidizing gas containing nitrogen. If the reaction temperature is below 1200℃, the synthesis reaction will take a long time,
There was a risk of partial decomposition reaction at temperatures above 1800°C. Therefore, a temperature of 1200 to 1800°C, preferably 1300 to 1600°C was suitable. Examples of the present invention will be described below. Example 1 90.1 cc of silica sol (48.0 wt% content), 337.3 cc of alumina sol (7.2 wt% content), and 103.9 cc of carbon black slurry (24.0 wt% content) were mixed (at this time, the PH difference between them was 2) The mixed solution was heated to about 80° C. to quickly form a gel, and this gel was crushed with a milk pestle. The pulverized product was subjected to a synthesis reaction at 1400°C for 2 hours in a nitrogen stream (200 s.l/hr). When the thus obtained powder was examined by X-ray diffraction, it was confirmed that it contained 95% sialon represented by Si ₄ Al ₂ O ₂ N ₆ and the average particle size was about 0.3 μm. Example 2 45.2 cc of silica sol (48.2 wt% content), 207.3 cc of alumina sol (20.0 wt% content), and 69.4 cc of carbon black slurry (24.0 wt% content) were mixed (at this time, the PH difference between them was It was around 3). The mixture was heated to about 80° C. to rapidly gel, and the gel was pulverized using a vibration mill. The pulverized product was subjected to a synthesis reaction at 1500° C. for 2 hours in a nitrogen stream (200 s./hr). When the thus obtained powder was examined by X-ray diffraction, it was confirmed that it contained 95% or more of sialon represented by Si ₂ Al ₄ O ₄ N ₄ and the average particle size was about 0.5 μm. Next, in the first step, the present inventor has come to the knowledge that the pH of each starting material is important in order to mix the starting materials as a solution from a sol, and this will be described in detail below. In order to obtain the desired sialon-based powder raw material, there is a limitation that gelation does not occur during solution mixing. It was confirmed that gel formation occurs over time as the pH difference between each starting material increases. Therefore, in order to make sialon powder represented by Si ₄ Al ₂ O ₂ N ₆ , the pH of silica sol was 2.9, 9.1,
Using various starting materials with pH = 4.5, 6.3 for alumina sol and pH = 3.5, 7.5, and 10.5 for carbon black slurry, we repeated experiments to determine the gel formation tendency by changing the mixing ratio, and the results were as shown in Table 1. Ta. In the table, the samples marked with a circle for evaluation were mixed and adjusted as a solution, regardless of the component content of each starting material, mixing order, mixing method such as stirring means, etc. The x mark indicates that even if the mixing method was changed, a gel was formed over time and uniform mixing was no longer possible. In addition, the mark △ indicates that almost uniform mixing has become possible by improving the component content of each starting material, the mixing order, the mixing method such as the stirring means, etc.

[Table] * In the table, volume % represents the volume ratio of the starting materials.
** The maximum pH difference represents the maximum value among the pH differences between each starting material. As shown in Table 1, the maximum pH difference between each starting material is
When it exceeds 4.6, gelation progresses over time and a homogeneous mixed solution cannot be obtained. However, when the maximum PH difference was about 4.6 or less, preferably about 4.2 or less, the starting materials could be sufficiently mixed and a homogeneous solution was obtained. As is clear from Examples 1 and 2 above, according to the production method of the present invention, the starting material is a sol that is relatively inexpensive and easily available, and just by mixing the solution, a uniform mixture can be obtained, and fine particles and To become
Steps such as milling are eliminated. As a result, the operations and costs required for powder mixing have been dramatically reduced. Moreover, the obtained synthetic powder raw material had high purity and small particle size, and as a matter of course, depending on the blending ratio of the starting raw materials, it became a sialon diameter powder raw material having a desired composition. Thus, sintering using the above-mentioned powder raw materials has the advantage of being easy to sinter at relatively low temperatures and in a short time. Expansion is possible.

Claims (1)

[Claims] 1. A method for producing a silicon-aluminum oxynitride-based powder raw material, characterized by comprising the following steps (A), (B), and (C): (A) silica sol, alumina sol, and slurry carbon; A process of preparing a mixed solution using the starting materials so as to have the desired silicon-aluminum oxynitride composition. (B) A step of pulverizing the mixed solution by drying with hot air or by pulverizing the gel after hardening. (C) A step of performing a heating synthesis reaction on the powder at about 1200 to 1800°C in an atmosphere of a non-oxidizing gas containing nitrogen to obtain a silicon aluminum oxynitride powder.