JPH0543328A - Method for manufacturing silicon nitride-based sintered body - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to obtain a highly reliable silicon nitride sintered body which does not decrease in strength and has small variation in physical properties. [Structure] In this method, an organometallic compound is bonded to the surfaces of the silicon nitride powder and the sintering aid powder, and a mixed powder obtained by dispersing these powders in a solvent is molded and fired. Examples of organometallic compounds are RnSi (OR ') _4-n or RnS
iX _4-n (R ′: alkyl group, aryl group, X: halogen, n = 1 to 3), examples of sintering aids are oxides, nitrides, and oxynitrides of Y, Al, and Mg. Is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a highly reliable silicon nitride-based sintered body having small variations in physical properties such as strength.

[0002]

2. Description of the Related Art A conventional method for manufacturing a silicon nitride sintered body is
Silicon nitride powder and mainly sintering aid powder such as Y ₂ O ₃ and Al ₂ O ₃ are pulverized and mixed in a solvent such as an organic solvent or water using a ball mill or the like, and a molding binder is added thereto. After dry granulation, molding, degreasing and other treatments, firing is performed in a non-oxidizing atmosphere to obtain a sintered body.

[0003]

However, when the silicon nitride powder and the sintering aid powder are mixed with each other, the surface characteristics of each powder, for example, the wettability with respect to the solvent are different from each other, so that the coagulation of the same kind of powder occurs. However, there is a problem that the sintering aid is unevenly distributed in the molded body. In such a compact, the distribution and composition of the liquid phase formed during firing become non-uniform, causing abnormal grain growth and inhomogeneous and non-uniform distribution of the grain boundary phase, leading to a decrease in the strength of the sintered body. As a result, variations in strength are increased and reliability is significantly reduced. On the other hand, measures such as strengthening pulverization and adding a deflocculant such as a surfactant to the solvent have hitherto been taken. However, mechanical crushing has a limit, and strengthening the crushing conversely causes contamination of impurities due to wear of the media. In addition, even when a deflocculating agent is added, due to the difference in the surface characteristics, it results in promoting aggregation rather than depending on the powder type, and it is very difficult to improve the dispersibility for all powders, and it is still effective. At present, no means have been found.

[0004]

In view of the above points, according to the present invention, each raw material powder is uniformly dispersed in a solvent to obtain a molded product having no uneven distribution of a sintering aid, so that variations in strength are small. It is intended to provide a highly reliable method for producing a silicon nitride-based sintered body.

That is, the present invention is characterized in that an organometallic compound is bonded to the surfaces of the silicon nitride powder and the sintering aid powder, and the mixed powder obtained by dispersing these powders in a solvent is molded and fired. It is a method for manufacturing a silicon-based sintered body.

Note that at least the following is included as an embodiment of the present invention.

B. The organometallic compound is RnSi (OR
′) A structure having a structure represented by _4-n or RnSiX _4-n , where R is an organic compound chain, R ′ is an alkyl group or an aryl group, X is halogen, and n = 1 to 3 is used.

B. The sintering aid powder is at least one of Y, Al, and Mg oxides, nitrides, and oxynitrides.

C. The average particle size of the silicon nitride powder and the sintering aid powder is 1 μm or less.

In the present invention, the organosilicon compound among the organometallic compounds is, for example, vinyltrichlorosilane, vinyltris (β-methoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane,
γ-methacryloxypropyltrimethoxysilane, β
(3,4 epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N- β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, n-butyltrichlorosilane, octadecyltrichlorosilane Etc.

In addition, an organometallic compound containing the same metal as the metal compound used as the sintering aid, for example, an organoaluminum compound such as acetoalkoxyaluminum diisopropylate can be used. The method of binding the organometallic compound to the powder surface is not particularly limited, but for example, a solution of the organometallic compound dissolved in a solvent such as alcohol is prepared, and the powder is dispersed and reacted with this solution.
Examples thereof include a method of removing the solvent by drying and the like, a method of directly spraying the solution onto the powder to dry it. Alternatively,
Alternatively, each raw material powder may be treated in a solution in which an organometallic compound is dissolved, and each solution may be mixed as it is to obtain a mixed powder. This method is industrially advantageous because the desolvation step can be omitted. By binding the organometallic compound to the powder surface in this manner, the surface of each raw material powder having different surface characteristics is homogenized and a mixed powder uniformly dispersed in a solvent is obtained.

The amount of the organometallic compound treated with respect to each powder is preferably 0.1 to 5 wt%. If it is less than 0.1 wt%, the surface modification is insufficient and it is difficult to obtain the effect of improving the dispersibility, and if it exceeds 5 wt%, an excessive organometallic compound is produced, which is not preferable.

The average particle size of the silicon nitride powder and the sintering aid used in the present invention is preferably 1 μm or less. When the particle size is large, the coarse particles themselves are equivalent to the agglomerates of the fine particles, and it is difficult to obtain the effect of uniform dispersion.

The respective powders having the organometallic compound bonded to the surface by the above method are mixed in a solvent with stirring. At this time, if the mixed liquid is irradiated with ultrasonic waves, the dispersibility can be further improved. If necessary, an appropriate amount of binder is added to and mixed with the obtained mixed powder solution, and then the amount of solvent is adjusted to form a slurry and molding is performed by a casting method or the like, or dry granulation is performed using a spray dryer to perform molding. In addition,
The molding method is not particularly limited to the above method. The molded body is subjected to degreasing treatment if necessary, and then fired in a non-oxidizing atmosphere such as N ₂ .

[0015]

When fine powder is dispersed in a solvent, interfacial tension γ exists at the interface between the powder surface and the solvent. Interfacial tension γ
Is the interface free energy {gs} existing in the unit boundary area. Now, assuming that the system including 1 g of the entire powder is S and the interfacial area (specific interfacial area m ² · g ⁻¹ ) of the entire particle is S, the total interfacial free energy Gs is Gs = {gs} S = γS { g
Since s} = γ takes a positive value, the value of Gs also becomes positive, and the system including the particles becomes thermodynamically unstable. Therefore, this system tends to reduce the interfacial area S. That is, the powder particles aggregate to try to reduce S. At this time, the aggregation rate varies depending on the powder species due to the characteristics of the surface of the powder particles, for example, the wettability with the solvent (solvation) and the action of the surface potential. Therefore, it is difficult to avoid agglomeration between powders of the same kind by simply mixing each raw material powder in a solvent as in the conventional manufacturing method, and even if mechanical pulverization is strengthened, the thermodynamic stability is improved. Re-aggregation occurs, and as a result, a large effect cannot be obtained for improving the dispersibility of each raw material powder.

On the other hand, the action of the demulsifiers such as surfactants and dispersants is mainly that the surface of the powder is coated by adsorbing a high molecular weight or organic substance which is a demulsifier to the solids to prevent aggregation. There is an obstacle. However, the interaction between these peptizers and the powder is greatly different depending on the surface potential and electric charge of the powder. For example, silicon nitride has a predominantly negative surface potential in a neutral solvent due to the state of silicon oxide formed on its surface by oxidation. On the contrary, Al ₂ O ₃ generally shows a positive surface potential. Therefore, due to the charge of the demulsing agent, when the same demulsing agent is used, a completely opposite interaction occurs between silicon nitride and Al ₂ O _3, and it is very difficult to obtain the effect of improving the dispersibility in each raw material powder. difficult. Further, even for different kinds of powders having the same potential, the optimum amount of the demulcent is different due to the difference in the surface charge amount or the amount of the surface functional group serving as the adsorption site of the demulcent. Insufficient or excessive addition of the amount of the demulcent agent usually results in cross-linking of the demulcent agent between the powders and conversely promotes aggregation.

On the other hand, according to the present invention, the same organometallic compound is strongly chemically bonded to the surfaces of the different powders having different surface characteristics as described above to homogenize the surface characteristics, thereby improving the affinity for the solvent. By homogenizing and imparting effective cohesive repulsion force to the organic substance of the organometallic compound, the dispersibility of the mixed powder can be significantly improved. As a result, it is possible to obtain a molded body in which the sintering aid is uniformly dispersed in a state close to the primary particles, and it is possible to obtain a highly reliable sintered body with small strength variations.

The molded product obtained according to the present invention is roasted in an oxidizing atmosphere to form an oxide of a metal in the organometallic compound bonded to the powder surface, eg, SiO ₂ when an organosilicon compound is bonded. Are generated on the powder surface. These metal oxides act as a sintering aid. Generally, in a silicon nitride-based sintered body, SiO ₂ as a sintering aid is supplied from an oxide layer on the surface of silicon nitride.
Similarly, since the SiO ₂ coating is formed on the surface of the sintering additive, the effect of homogenizing the liquid phase composition can be obtained in addition to the uniform dispersion of the sintering additive powder. The mixing amount of the sintering aid is desirably determined after taking into consideration the amount of metal oxide formed from the organometallic compound bonded to the powder surface. The roasting temperature varies depending on the type of the organometallic compound used, but is preferably in the range of several hundred to 1000 ° C.

[0019]

EXAMPLES The present invention will be described below with reference to examples and comparative examples.

Example 1 Average particle size 0.4 μm, particle size distribution (3σ) 0.3 μm, α
Si ₃ N ₄ powder having a crystallization rate of 96.5% and an oxygen content of 1.4% by weight, and an average particle size of 0.7 μm, 0.4 μm, and 0.
9 μm of Y ₂ O ₃ , Al ₂ O ₃ , and AIN powders were each prepared in ethanol in which 2.0% by weight of each powder was dissolved in an organosilicon compound, γ-aminopropyltriethoxysilane.
After stirring for a time, the powder was reacted with the organosilicon compound and dried to obtain each treated powder. Y ₂ O ₃ , Al ₂ O ₃ , and AIN treated powders were added to 92% by weight of Si ₃ N ₄ treated powders, _{4, 3} , and 1, respectively.
% By weight and in ethanol using a stir mixer 5
After stirring and mixing for an hour, the resulting mixed powder is dried to 300
CIP molding was performed at 0 Kg / cm ² . After roasting this molded body in the air at 800 ° C., it was sintered in N ₂ gas at 1750 ° C. for 5 hours, and the obtained sintered body was heated to 1720 ° C. and 1000 atm N _2.
HIPed for 3 hours.

Thirty test pieces were cut out from this sintered body and a four-point bending test based on JISR1601 was performed (test piece size 3 mm × 4 mm × 40 mm).

As a result, the average strength was 122 kg / mm ² ,
A Weibull coefficient of 20 was obtained.

Example 2 92% by weight of Si ₃ N ₄ powder, ₄ % by weight of Y ₂ O ₃ powder, 3% by weight of Al ₂ O ₃ powder and 1% by weight of AIN powder used in Example 1 were respectively separated. The mixture was transferred to a melting vessel and stirred in ethanol containing 2.0% by weight of γ-aminopropyl-triethoxysilane dissolved in each powder for 3 hours while being irradiated with ultrasonic waves.
The powder was reacted with the organosilicon compound. Next, all the solutions were transferred to the stirring mixer used in Example 1, stirred and mixed for 5 hours, and then dried to obtain a mixed powder. This mixed powder is CIP-molded at 3000 Kg / cm ² and 800 ° C. in air.
After baking at 1,750 ° C. for 5 hours in N ₂ gas, the obtained sintered body is heated at 1720 ° C. and 1000 atm N _{2 for} 3 hours.
HIPed for hours.

Thirty test pieces were cut out from this sintered body and subjected to a four-point bending test in accordance with JIS R1601. As a result, the average strength was 120 kg / mm ² , and the Weibull coefficient was 22.
Met.

Comparative Example 1 92% by weight of Si ₃ N ₄ powder, ₄ % by weight of Y ₂ O ₃ powder, 3% by weight of Al ₂ O ₃ powder and 1% by weight of AIN powder used in Example 1 were used in Example 1. After stirring and mixing in ethanol with the stirring mixer used for 8 hours, it was dried to obtain a mixed powder. This mixed powder was CIP-molded at 3000 Kg / cm ² and then air
After roasting at 00 ° C, it was sintered in N ₂ gas at 1750 ° C for 5 hours, and the obtained sintered body was N ₂ at 1720 ° C and 1000 atm.
HIPed for 3 hours.

From this sintered body, 30 test pieces were cut out and subjected to a four-point bending test in accordance with JIS R1601. The average strength was 100 Kg / mm ² , the Weibull coefficient was 1.
It was 2.

Comparative Example 2 92% by weight of Si ₃ N ₄ powder, ₄ % by weight of Y ₂ O ₃ powder, 3% by weight of Al ₂ O ₃ powder and 1% by weight of AIN powder used in Example 1 were added to the total weight of the powder. On the other hand, the mixture was stirred and mixed in ethanol containing 0.5% by weight of a polycarboxylic acid type demulcer for 8 hours with the stirring mixer used in Example 1 and dried to obtain a mixed powder. This mixed powder was C at 3000 Kg / cm ² .
After IP molding and sintering at 800 ° C in air, in N ₂ gas 17
Sintered for 5 hours at 50 ° C.
HIP treatment was performed in N ₂ at 1000 ° C. for 3 hours.

From this sintered body, 30 test pieces were cut out and subjected to a four-point bending test in accordance with JIS R1601. The average strength was 103 Kg / mm ² , the Weibull coefficient was 1.
It was 4.

Comparative Example 3 In Example 4, an Al ₂ O ₃ ball sill was used instead of the stirrer and mixed at 100 rpm for 100 hours, and 30 test pieces were cut from the sintered body obtained by the same method. JI
When a four-point bending test based on SR1601 was conducted,
The average strength was 112 kg / mm ² , and the Weibull coefficient was 13.

Table 1 shows the average strengths and Weibull coefficients of the sintered bodies obtained in the above Examples and Comparative Examples.

[0031]

[Table 1]

The molded bodies obtained in the respective examples and comparative examples were subjected to surface analysis of Al and Y by EPMA. As a result, in comparative examples 1, 2, and 3, Al of about several μm was obtained.
Aggregation of (Al ₂ O ₃ , AIN) and Y of 3 to several μm (Y ₂
While a large number of O ₃ ) aggregates were observed, in Examples 1 and 2 according to the present invention, no remarkable uneven distribution of Y and Al was observed.

Further, when the fracture starting point after the bending strength evaluation was investigated, an abnormal structure in which Y segregation was detected in Comparative Examples 1, 2 and 3, and an Al segregation in Comparative Example 1 were detected. Foreign matter, in Comparative Example 3, coarse β crystal grains were recognized.

[0034]

According to the production method of the present invention, since a uniform molded body can be obtained in which the sintering aid is not unevenly distributed, the strength of the sintered body does not decrease, and the variation is extremely small and highly reliable. A sintered body can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Yamakawa 1-1-1 Kunyo Kita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (4)

[Claims] 1. A silicon nitride based sintering characterized in that an organometallic compound is bonded to the surfaces of a silicon nitride powder and a sintering aid powder, and a mixed powder obtained by dispersing these powders in a solvent is molded and fired. Body manufacturing method. 2. The organic metal compound is RnSi (OR ').
R has a structure represented by _4-n or RnSiX _4-n , R
Is an organic compound chain, R'is an alkyl group or an aryl group, X is a halogen, and n = 1 to 3. The method for producing a silicon nitride-based sintered body according to claim 1. 3. The method for producing a silicon nitride-based sintered body according to claim 1, wherein the sintering aid powder is at least one of Y, Al, and Mg oxides, nitrides, and oxynitrides. 4. The method for producing a silicon nitride-based sintered body according to claim 1, wherein the silicon nitride powder and the sintering aid powder have an average particle diameter of 1 μm or less.