JPH0454608B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing α-type silicon nitride fine powder, and in particular, it is an object of the present invention to provide an industrially advantageous method for producing fine powder α-type silicon nitride with extremely few secondary particles. . The Ministry of International Trade and Industry's research and development of next-generation industrial infrastructure technology is also focusing on ceramics for high-temperature structural materials, with high expectations for their application to high-temperature systems such as gas turbines and engine parts. As ceramics for high-temperature structural materials, strength,
Active research is being conducted on silicon nitride, silicon carbide, and zirconia, which have excellent toughness. Silicon nitride has α-type (α−Si ₃ N ₄ ) and β-type (β
There are two crystal forms of -Si ₃ N ₄ ), and in order to obtain a high-strength, dense sintered body, the α type is preferable from the viewpoint of sinterability, and it is a fine powder with a uniform particle size without secondary particles. is desired, and various studies have been made in the past. In order to facilitate understanding, three typical silicon nitride manufacturing methods that have been studied in the past will be explained as follows. (1) Direct nitriding of metallic silicon (Si) in a nitrogen-containing atmosphere (2) Synthesis using a silane compound such as silicon tetrachloride (SiCl ₄ ) and ammonia (NH ₃ ) (3) Silica raw material ( There are three methods of carbon reduction and nitriding of SiO ₂ ) in an atmosphere containing nitrogen, and method (1) has been studied extensively and has already been adopted as a mass production method. However, the reaction rate is slow, making it difficult to control the α-type and β-type, and since the product becomes lumpy, a long pulverization process is required, which poses problems in terms of contamination and particle size control. Method (2) can produce high-purity, fine silicon nitride powder, but it is not suitable for mass production of silicon nitride for high-temperature structural materials due to its low productivity and large number of steps relative to the scale of the manufacturing equipment. is inappropriate. Method (3) is a method for producing silicon nitride by reducing and nitriding the silica raw material with carbon in a non-oxidizing atmosphere containing nitrogen.The raw material is inexpensive and the reaction operation is relatively easy, making it suitable for mass production. ing. However, in conventional methods, by-products such as silicon carbide (SiC) and silicon oxynitride (Si ₂ ON ₂ ) and β-
There are problems such as easy generation of Si ₃ N ₄ . Production methods using extremely high-purity silica raw materials are being considered, but this not only increases the cost of the raw materials, but also slows down the reaction rate and requires a long reaction time, resulting in low energy efficiency and high costs. Moreover, the silicon nitride produced tends to be a coarse powder of approximately 4 to 10 μm. A method of adding fine particles such as Si ₃ N ₄ as a nucleus has been proposed as a method of increasing the reaction rate and making the produced particles finer using high-purity silica raw materials, but it is expensive in terms of cost and is not essential. Not only is this not a complete solution, it also leaves major problems such as the tendency for the generated fine particles to form secondary particles. In particular, the formation of secondary particles is a serious drawback in the forming and sintering processes involved in producing a good sintered body. In view of this, the present inventors conducted various studies regarding the manufacturing method described in (3) above, which is suitable for mass production and has the possibility of synthesizing fine particles. According to this manufacturing method, a method for manufacturing fine α-Si ₃ N ₄ with a uniform particle size and very little secondary particle formation in a short reaction time, ZrO, which is extremely suitable for high toughness, is added to the silicon nitride fine powder. _Two phases can be uniformly dispersed and generated as required. The present invention will be described in detail below. In the present invention, a siliceous raw material containing trace components can be used, and carbonaceous powder and zirconium oxide powder or compound powder that becomes ZrO ₂ by heating and yttrium, calcium, magnesium oxide powder or by heating Y ₂ O ₃ ,
Adding one or more compound powders that become CaO and MgO,
This method of producing silicon nitride is characterized by firing in a non-oxidizing atmosphere containing nitrogen with a carbon monoxide concentration suppressed to 30% by volume or less. ZrO ₂ can also be added as zircon sand (ZrSiO ₄ ), and the amount added depends on the SiO ₂ in the raw material.
It is desired that the amount is 0.1 to 40% by weight. Next, the effects revealed by the present inventors regarding the addition of zirconium oxide powder and compound powder that generates ZrO ₂ upon heating will be explained. (1) Increasing the reaction rate and shortening the reaction time (2) By reducing the carbon monoxide concentration to an appropriate concentration of 30% by volume or less, SiO, Si ₂ ON ₂ and β
-Suppresses the production of Si ₃ N ₄ and promotes the production of α-Si ₃ N ₄ . (3) Reduce the surface energy of the generated silicon nitride powder particles to promote micronization and suppress the formation of secondary particles.Furthermore, in order to make the above effects even more effective, zirconium oxide powder or heating is used.
The compound powder that becomes ZrO ₂ is preferably 10 μm or less.
It is desirable to disperse the particles with a particle size of 5 μm or less and to set the flow rate of the nitrogen gas in the firing atmosphere in the range of 0.1 m/min to 10 m/min. According to the present invention described above, it is possible to obtain a powder with a high content of α-Si ₃ N ₄ , extremely few secondary particles, and uniform particle size compared to conventional silicon nitride powder using inexpensive raw materials and a short reaction time. be able to. In addition, any amount of _ZrO2 phase can be uniformly dispersed by changing the way and amount of zirconium element added.
Further, the generated ZrO ₂ phase is formed by adding Y ₂ O ₃ , CaO,
It can be easily stabilized into a tetragonal crystal by MgO, etc., and is useful for strengthening the toughness of silicon nitride sintered bodies. Next, examples according to the present invention will be shown. <Example 1> A siliceous raw material with the chemical components shown in Table 1 prepared by crushing and classification to a particle size of 0.5 to 7 μm was
_ZrO2 powder A below and _ZrO2 powder B below 5μm
is added in an amount of 1 to 30% by weight based on SiO ₂ to further improve the purity.
A mixture of 99% carbon powder added and a C/SiO ₂ molar ratio of 10 was fired at 1480° C. in an N ₂ gas flow of 0.4 to 1.5/min. The results of Example 1 are shown in Table 2, and the comparative examples are shown in Table 3.

【table】

【table】

[Table] ** Observation using a scanning electron microscope *** Submicron particle size analyzer "Microtrack"
50% particle size by “SPA”

【table】

[Table] ** Observation using a scanning electron microscope *** Submicron particle size analyzer "Microtrack"
50% particle size by "SPA" Regarding the silicon nitride powders of Examples, Comparative Examples, and commercially available products, we used a 0.2% aqueous solution of sodium hexametaphosphate as a dispersant and dispersed them for 5 minutes using a powerful ultrasonic generator to obtain samples with submicron particle size. Figure 1 shows the results of measuring the particle size distribution using the analyzer “Microtrack SPA.” Conventional silicon nitride powder has a primary particle size of 0.5.
~1.5μm, but as is clear from Figure 1, due to the formation of secondary particles, the particle size distribution is wide and 30% to 50% of the particles are 3μm or more. %, which is extremely low. <Example 2> Powder containing ZrO ₂ and Y ₂ O ₃ components of 5 μm or less was added to the siliceous raw material of approximately 5 μm or less, which has the chemical components shown in Table 4, and the carbonaceous powder and C/SiO ₂ molar ratio were 10 and was fired at 1480°C in an atmosphere with a flow rate of N ₂ gas of 1.5/min.

【table】 The results of Example 2 are shown in Table 5.

【table】

[Table] ** Observation by scanning electron microscope *** 50% particle size by submicron particle size analyzer "Microtrac SPA"

[Brief explanation of the drawing]

FIG. 1 is a particle size distribution diagram of silicon nitride powder produced by the conventional method and products produced by the present invention.

Claims (1)

[Claims] 1. Siliceous powder raw materials, carbonaceous powder, zirconium oxide powder or compound powder that becomes ZrO ₂ when heated, and yttrium, calcium, magnesium oxide powder or Y ₂ when heated.
α-type silicon nitride, which is characterized by adding one or more types of compound powders such as O ₃ , CaO, and MgO, and firing in a non-oxidizing atmosphere containing nitrogen and suppressing the carbon monoxide concentration to 30% by volume or less. Method for producing fine powder. 2 The amount of zirconium oxide powder or compound powder that becomes ZrO ₂ when heated is
The method for producing α-type silicon nitride fine powder according to claim 1, wherein the amount of ZrO ₂ is 0.1 to 40% by weight based on the amount of SiO ₂ .