JP2855460B2 - Method for producing silicon nitride-based composite powder - Google Patents

Description

The present invention relates to a method for producing a silicon nitride-based composite powder, and more particularly, to a method for producing silicon nitride-based composite sintered material having high strength. The present invention relates to a method for producing a silicon nitride-based composite powder.

[Conventional technology]

Silicon nitride ceramics (silicon nitride, sialon, etc.) have been attracting attention as structural ceramic materials such as various refractory materials and engine members because of their excellent high-temperature strength and wear resistance. Because of its low toughness, attempts have been made to increase the fracture toughness value by combining with silicon carbide, and as a method of combining with silicon carbide, silicon carbide powder and silicon nitride-based powder (for example, nitrided (Silicon powder, sialon powder) and firing the mixture.

[Problems to be solved by the invention]

However, even if the silicon carbide powder and the silicon nitride powder are mixed by a conventional method such as a ball mill, it is difficult to obtain a mixed powder in which both powders are completely and uniformly dispersed. for that reason,
The fracture toughness value of the sintered body using the mixed powder shows only a slight property improvement effect compared to that of a single silicon nitride based sintered body. There was a problem that when it was made into a body, it became a defect, and on the contrary, the strength was reduced.

[Means for solving the problem]

The present inventors have studied various methods for synthesizing silicon carbide powder and silicon nitride powder in the same continuous manufacturing process so that the dispersion of silicon carbide powder and silicon nitride powder becomes uniform. Led to a homogeneously dispersed composite powder, and found that the composite crystal obtained by sintering the composite powder is superior in both fracture toughness and strength to the sintered body according to the prior art, and the present invention It was completed.

That is, the present invention, SiO ₂ quality powder and metal Si powder, or
First baking in which SiO ₂ powder, Al ₂ O ₃ powder and metal Si powder are mixed with carbon powder and a carbonization reaction is mainly carried out with the metal Si powder and carbon powder in a nitrogen-containing inert gas atmosphere. Process, SiO ₂ powder and carbon powder, or SiO ₂ powder
A method for producing a silicon nitride-based composite powder, characterized by continuously performing a second firing step of performing a reduction nitridation reaction with an Al ₂ O ₃ powder and a carbonaceous powder.

 Hereinafter, the present invention will be described in detail.

(Starting Raw Material) As the starting raw materials used in the present invention, conventional metal Si powder, SiO ₂ powder, Al ₂ O ₃ powder and carbonaceous powder can be used.

Metallic Si powder is ordinary metallic silicon, and its purity is 95% or more, preferably 98% or more.

Examples of the SiO ₂ powder include hydrolysates of organic compounds such as white carbon, silica gel, silica powder, and ethyl silicate.

Examples of the Al ₂ O ₃ powder include, in addition to ordinary alumina powder, hydrolysates such as alumina aerosil, aluminum hydroxide, and aluminum alkoxide.

The carbonaceous powder is blended as a carbon source of silicon carbide and a reducing agent in the reductive nitridation reaction. In addition to amorphous carbon such as carbon black, phenol resins and urea resins which decompose and generate carbon by heating are used. Precursors are also included.

The fineness of each of the raw material powders is not particularly limited, but it is preferable to use metal Si having an average particle size of 10 μm or less, and other material powders having an average particle size of 5 μm or less.

(Blending ratio) The raw material blend for synthesizing the silicon nitride-based composite powder using the above-mentioned starting materials is as follows.

(1) In the case of synthesizing a composite powder mainly composed of silicon carbide and silicon nitride, SiO ₂ powder, metal Si powder and carbon powder are used as raw materials, and the compounding ratio is C / (SiO ₂ + Si) ≧ 2.

At this time, there is no upper limit on the amount of carbon compounded. However, if the amount of carbon is more than necessary, it is only economically disadvantageous.
C / (SiO 2 + Si) = 2 to 5 is preferred.

The mixing ratio of Si / (SiO ₂ + Si) is determined by the required amount of silicon carbide. When a high-density, high-strength material is required, the mixing ratio (molar ratio) of Si / (SiO ₂ + Si) is preferably 0.5 or less. Above this, in the case of normal pressure sintering, the density of the sintered body does not increase, resulting in a porous sintered body and reduced strength. However, when pressure sintering such as hot pressing is performed, densification proceeds, so that a good sintered body can be obtained without being particular about the above-mentioned mixing range.

(2) When synthesizing a composite powder mainly composed of silicon carbide and sialon, SiO ₂ powder, Al ₂ O ₃ powder, carbon powder and metal Si powder are used, and SiO ₂ powder and Al ₂ O ₃ powder are used. The mixing ratio of the powder is 0.017 <Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ ) <0.54 in molar ratio. The above molar ratio is based on the general formula of Sialon (Si _{6 −z} Al
_z O _z N ₈ - _z values at _z) is equivalent to the 0.2 to 4.2.

In the present invention, a specific composition value is not limited within the above range, but a preferable range is 0.026 <Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ ) <0.44. When the amount of Al ₂ O ₃ is smaller than the above range, the amount of fixed Al in the sialon powder to be formed is difficult to be uniform, and when the amount is large, by-products such as AlN are easily generated.

The compounding ratio of the SiO ₂ powder, the carbon powder and the metal Si powder is set to Si / (SiO ₂ + Si) ≧ 2 in molar ratio.

(Mixing) In any of the above blending, each raw material is mixed using a conventional apparatus to obtain a blended raw material.

(Firing) Next, a process of reacting the compounding raw materials to synthesize a composite powder will be described.

In the present invention, the apparatus used for reacting the compounding raw materials may be a conventional atmosphere furnace (for example, a rotary kiln, a fluidized-bed firing furnace, a pusher furnace, etc.).

In the present invention, when reacting the blended raw materials in a nitrogen-containing inert gas atmosphere, first, a first firing step at a temperature that mainly carbonizes metal Si and generates silicon carbide;
It is important to continuously perform the second firing step at a temperature at which O ₂ or SiO ₂ and Al ₂ O ₃ are reduced and nitrogenated to generate mainly silicon nitride or sialon.

(1) First sintering step The first sintering step, which mainly produces carbon silicon, is performed using metal.
The carbonization reaction of Si is mainly performed, and nitridation of metal Si and reduction nitridation reaction of SiO ₂ are partially performed.

The firing temperature in this step is usually 1250 to 1420 ° C. If the temperature is higher than this, the metal Si melts, and the desired composite powder cannot be obtained. If the temperature is lower than this, carbonization of the metal Si does not proceed. The temperature is preferably in the range of 1300 to 1400 ° C. in that the reaction easily proceeds and the temperature is easily controlled.

The firing time is determined by the amount of silicon carbide finally combined, but at least one hour or more is required.

(2) Second baking step The second baking step mainly produces silicon nitride or sialon.
The firing step is a step in a temperature range where SiO ₂ or SiO ₂ and Al ₂ O ₃ are converted into silicon nitride or sialon by a reductive nitridation reaction, and is usually at a temperature of 1400 to 1550 ° C. At a temperature higher than this, carbonization of the material increases due to the reduction carbonization reaction, and it becomes difficult to control the amount of silicon carbide in the composite powder. If the temperature is lower than this, the reduction nitridation reaction is slow, which is not preferable as the temperature for producing the composite powder. In order to carry out the reductive nitriding reaction efficiently, a temperature range of 1450 to 1530 ° C. is preferable.

The reaction time varies depending on the firing temperature, but is 2 to 10
The time is a rough standard. If the time is shorter than this range, unreacted oxide tends to remain. Even if the reaction time is longer than this range, the reaction has already been completed, which is economically disadvantageous.

In these firing steps, the formation of silicon carbide, the generation of silicon nitride or sialon may be stepwise increased in the firing step, respectively.As described above, mainly at the temperature at which silicon carbide is generated Continuing from the first firing step, the composite powder obtained by performing the second firing step by raising the temperature to a temperature at which silicon nitride or sialon is mainly produced includes the intended silicon carbide / silicon nitride composite powder or It contains unreacted carbon in addition to the silicon carbide / sialon composite powder. This residual unreacted carbon can be easily removed by performing an oxidation treatment in air, and a desired composite powder can be obtained.

[Action]

As in the present invention, after sintering mainly in a temperature range in which silicon carbide is generated, the temperature is mainly increased to a temperature range in which silicon nitride or sialon is generated, and sintering is performed. Is synthesized by a series of continuous processes, since the carbonization reaction and the nitridation reaction are continuous, a composite powder in which carbides and nitrides are extremely uniformly dispersed is synthesized. In particular, the composite powder synthesized by such a method becomes a so-called nanocomposite having a dispersed phase on the order of nm, and has significantly improved strength and fracture toughness, and improved hardness and wear resistance.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

Examples 1 to 5 silica powder ("SP-3" manufactured by Kyoritsu Ceramics Co., Ltd., average particle size: 0.5 μm), carbon powder ("MA20" manufactured by Mitsubishi Chemical Corporation)
0RB ") and metallic silicon powder (" HiS "manufactured by Yamaishi Metal Co., Ltd.)
i-600S ”, average particle size: 5.5 μm) were mixed as shown in Table 1 and mixed by a pot mill. Then, the carbonizing step and the nitriding step were continuously performed under the firing conditions shown in Table 1.

The obtained powder was subjected to a decarbonizing treatment at 700 ° C. for 6 hours in the air to obtain a silicon carbide / silicon nitride composite powder. It was determined from the diffraction peak ratio of the X-ray diffraction result of the obtained composite powder.
Table 1 shows the SiC: Si ₃ N ₄ generation ratio.

In addition, Y ₃ O ₃ and Al ₂ O are used as sintering aids in the obtained composite powder.
₃ was added in an amount of 5% by weight, and after press molding, the sintered body was pressurized and sintered at 1780 ° C. for 3 hours in nitrogen.
Table 1 shows the results of the bending test strength measured according to 1601 and the fracture toughness measured by the indentation method.

Comparative Examples 1 to 3 After mixing silicon carbide (“Beta Random Ultra Fine” manufactured by Ibiden Co., Ltd.) and silicon nitride powder (“KSN-10M” manufactured by Shinano Chemical Industry Co., Ltd.) using a pot mill, Example 1 was used. In the same manner as in Examples 5 to 5, a sintering aid was blended, molded and sintered, and the measurement results obtained are shown in Table 1.

Examples 6 to 10 SiO ₂ powder (Zeoseal 1100 manufactured by Taki Kagaku Co., Ltd.)
V "), Al ₂ O ₃ powder (" Aluminum "manufactured by Nippon Aerosil Co., Ltd.)
Oxide C "), carbon powder (MA20 manufactured by Mitsubishi Kasei Corporation)
0RB ") and metallic silicon powder (" HiS "manufactured by Yamaishi Metal Co., Ltd.)
i-600S ”, average particle size: 5.5 μm) as shown in Table 2, mixed by a pot mill, and sintered under the conditions shown in Table 2.

The obtained powder was decarbonized at 700 ° C. for 6 hours in the air to obtain a silicon carbide / sialon composite powder. X-ray diffraction results of the obtained composite powder, and Y ₂
Add O ₃ by 3% by weight Table 2 shows the measurement results of the bending test strength and the fracture toughness value obtained in the same manner as in Examples 1 to 5 for the sintered body which was sintered under normal pressure at 1760 ° C. in nitrogen for 3 hours after molding.

Comparative Examples 4 to 6 SiO ₂ powder (Zeoseal 1100 manufactured by Taki Kagaku Co., Ltd.)
V "), Al ₂ O ₃ powder (" Alumiunm "manufactured by Nippon Aerosil Co., Ltd.)
Oxide C "), carbon powder (MA20 manufactured by Mitsubishi Kasei Corporation)
0RB ") sialon general formula _{(Si 6 - z Al z O} z N 8 - z values at _z) is formulated to 0.5, silicon carbide and sialon powder obtained by firing for 6 hours at at 1450 ° C. After mixing with a powder (Ibiden Co., Ltd. Beta Random Ultra Fine) in a pot mill, a sintering aid was blended and sintered in the same manner as in Examples 6 to 10, and the measurement results obtained are shown in Table 2. .

〔The invention's effect〕

The present invention is primarily after the metal Si powder and carbonaceous powder was subjected to the first stage of the firing step to produce a silicon carbide reacts, SiO ₂ quality powder and carbonaceous powder, or SiO ₂ quality powder and
By performing a reductive nitridation reaction between the Al ₂ O ₃ -based powder and the carbonaceous powder and continuously performing a second-stage firing step for producing silicon nitride-based powders such as silicon nitride and sialon, silicon carbide is obtained. The powder and the silicon nitride-based powder are uniformly dispersed in the reaction stage, and a composite powder composited into a nanocomposite can be manufactured.

The silicon carbide / silicon nitride-based composite powder or silicon carbide / sialon-based composite powder synthesized by the method of the present invention is a powder in which silicon carbide is extremely uniformly dispersed, and therefore, is manufactured from the present composite powder. Is a superior engineering ceramic material with significantly improved strength and fracture toughness compared to conventional composite ceramics manufactured from mixed powders.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C01B 31/36 C01B 31/36 A C04B 35/626 C04B 35/58 102Q 35/56 101P (58) Fields surveyed (Int.Cl. . ^6, DB name) C01B 21/068 C04B 35/58 C04B 35/56 C01B 21/082 C01B 31/36

Claims (1)

(57) [Claims] 1. An SiO ₂ material powder and a metal Si powder, or a mixture of an SiO ₂ material powder, an Al ₂ O ₃ material powder and a metal Si powder with a carbon material powder,
A first baking step in which a carbonization reaction is carried out at a temperature of 1225 to 1400 ° C. mainly with a metal Si powder and a carbonaceous powder in a nitrogen-containing inert gas atmosphere, and an SiO ₂ powder and a carbonaceous powder or Si
O ₂ quality powder and Al ₂ O ₃ by the quality powder and carbonaceous powder 1400-155
A method for producing a silicon nitride-based composite powder, comprising continuously performing a second firing step of performing a reduction nitridation reaction at a temperature of 0 ° C.