JPS6229365B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ceramic powder made of a Si--Al--O--N compound.

Silicon nitride (Si ₃ N ₄ )-based ceramic sintered materials are attracting attention as structural materials used in extremely high-temperature and highly corrosive environments. However, in the case of a pure Si ₃ N ₄ based sintered body of this type of ceramic sintered material, the sinterability is poor and it is difficult to obtain a high density material. As a solution to this problem, there is interest in a so-called sialon (SiAlON) compound in which aluminum (Al) and acid (O) are dissolved in solid solution. In other words, this SiAlON compound has excellent corrosion resistance and can be easily made into a high-density sintered body, so the sintered body made as it is or with rare earth oxide added can be used for structures that require corrosion resistance and mechanical properties. Attempts are being made to use it as a material.
However, the above-mentioned SiAlON-based sintered body can be obtained by sintering a mixture of silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), and alumina (Al ₂ O ₃ ) or silica (SiO ₂ ). However, because it uses expensive Si ₃ N ₄ as a direct raw material, its applications are limited due to cost considerations. Also silica (SiO ₂ ), aluminum (Al)
and silicon (Si) as raw materials, and SiO ₂
There is also a method in which after reduction with Al, the Si produced by the reduction is nitrided and then sintered. However, in this case, it is difficult to control the reaction process, and a high level of skill is required to obtain the desired sintered body, resulting in a lack of mass productivity.

The inventors of the present invention proceeded with their studies in response to the above points, and found that when AlN and Al ₂ O ₃ are co-present during the reduction of SiO ₂ with carbon (C) and the nitridation of the reduced Si, It has been found that a desired silicon-aluminum oxynitride-based compound powder can be synthesized.

That is, the present invention is expressed by the following formula.

3SiO ₂ +6C+2N ₂ →Si ₃ N ₄ +6CO When synthesizing silicon nitride (Si ₃ N ₄ ) powder by the oxide reduction method using silica (SiO ₂ ) and carbon (C) as starting materials, the desired sialon (Si-Al -O-N) compound or rare earth oxide-Sialon (R ₂ O _3.Si -Al-O-N) compound, SiO ₂ , carbon, AlN or Al ₂ O ₃ , and R ₂ if necessary. The main idea is to use a mixture of O ₃ in a predetermined composition ratio as a starting material.
However, according to the present invention, the required sialon compound powder can be synthesized in conjunction with the reduction of SiO ₂ by the carbon in the starting raw material mixed powder and the nitriding reaction of the reduced Si, and this reduction, nitriding Generally, a reaction time of about 2 to 10 hours at 1300 to 1550°C is sufficient.

In the present invention, sialon compounds have the general formula: Si ₆ - _Z Al _Z N ₈ - _Z O _Z , SiAl ₄ N ₄ O ₂ ,
SiAl ₅ N ₅ O, SiAl ₆ N ₆ O ₂ , or SiAl ₆ N ₃ O ₂ or R ₂ O ₃・Si ₆ ― _Z Al _Z ― N ₈ ― _Z O _Z , R ₂ O ₃・
SiAl ₄ N ₄ O ₂ , R ₂ O ₃・SiAl ₅ N ₅ O・R ₂ O ₃・
SiAl ₆ N ₆ O ₂ or R ₂ O ₃・SiAl ₆ N ₃ O ₂ (However, Z
is a number satisfying 0<Z≦4, and R is one or more of Y, Ce, La, and Sc). Therefore, the composition ratio of SiO ₂ and carbon and AlN or Al ₂ O ₃ and R ₂ O ₃ as starting materials is selected depending on (corresponding to) the type of the target sialon compound.
Of course, the amount of carbon contributing to the reduction can also be reduced as appropriate so that SiO ₂ remains as appropriate in the finally obtained sialon compound powder.

As mentioned above, SiO ₂ , carbon, AlN, Al ₂ O ₃ ,
According to the present invention, which uses a selective mixture of R ₂ O ₃ powders in a desired composition ratio as a starting material, first, in the reductive nitriding reaction of SiO ₂ , AlN and other substances are added to the reaction system.
Because other raw material powders such as Al ₂ O ₃ coexist, these
The AlN powder and the like serve as reaction nuclei, and the above reduction and nitridation reactions are easily promoted. On the other hand, as the SiO ₂ reduction and nitriding reaction progresses, residual AlN and Al ₂ O ₃
Reactions between silica and the like easily occur, and the desired fine powder of the sialon compound can be obtained. The fine particle size of the sialon-based compound powder thus obtained greatly affects the sinterability after molding, and has the advantage that a dense sintered body can be easily obtained in the end. Thus, the method of the present invention allows the desired sialon compound powder to be easily obtained without requiring complicated operations, and furthermore, the obtained sialon compound powder is a ceramic sintered body that is dense, has high strength at high temperatures, and has excellent corrosion resistance. It can be said that it is highly evaluated in practical terms because it has reached the point where it can be manufactured.

Next, examples of the present invention will be described.

Example 1 240 g (4 mol) of SiO ₂ powder with an average particle size of 0.013 μ, 72 g (6 mol) of carbon powder with an average particle size of 0.029 μ, and 82 g (2 mol) of AlN powder with an average particle size of 0.95 μ were ball milled. A raw material powder was first prepared. Next, this raw material powder was reduced and nitrided at 1450°C in an _N2 atmosphere for 5 hours, and then heated at 700°C in an air atmosphere for 3 hours.
The remaining carbon was removed by heat treatment for a period of time.

As a result of the above, the yield of the product is approximately 98% and the average particle size is 1.
A gray powder of μm size was obtained, and X-ray diffraction of this powder revealed that it was a sialon compound represented by the following formula, Si ₄ Al ₂ N ₆ O ₂ . The purity was about 99%, and the main impurity was residual carbon, which was about 0.7%.

Example 2 Yttrium oxide (Y ₂ O ₃ ) powder with an average particle size of 0.72μ was added to the raw material powder having the composition in Example 1.
The mixed powder to which 24.5 g (0.11 mol) was added was subjected to reduction, nitriding reaction, and carbon treatment under the same conditions as in Example 1 to obtain a gray powder with an average particle size of 1.1 μm. The yield and purity were the same as in Example-1. When the thus obtained gray powder was examined by X-ray diffraction, it was found to be a sialon compound represented by the following formula: 8wt%Y ₂ O ₃ -92wt%Si ₄ Al ₂ N ₆ O ₂ .

Claims (1)

[Claims] 1 Si _6-Z Al _Z N _8-Z O _Z (0<Z≦4),
SiAl ₄ N ₄ O ₂ , SiAl ₅ N ₅ O ₂ , SiAl ₆ N ₆ O ₂ and
SiAl ₆ N ₃ O ₂ silicon aluminum oxynitride (Si-Al-O-N compound) is mixed at a composition ratio that provides the constituent elements shown in the general formula.
A mixed powder of SiO ₂ , AlN or Al ₂ O ₃ , and C as a reducing agent in an amount necessary to achieve the composition ratio of the above general formula during the nitridation reduction reaction is used as a starting material, and the mixture is heated in a nitrogen-containing atmosphere. By firing with
A method for producing ceramic powder, which comprises synthesizing an O--N compound powder. 2 R ₂ O ₃・Si _6-Z Al _Z N _8-Z O _Z (0<Z≦4),
R ₂ O ₃・SiAl ₄ N ₄ O ₂ , R ₂ O ₃・SiAl ₅ N ₅ O ₂ , R ₂ O ₃・
_{Rare earth oxides and silicon -} aluminum _{oxynitrides (} SiO ₂ mixed in _a composition ratio that provides the constituent elements _{shown in the} general formula of
By using a mixed powder of Al ₂ O ₃ and C as a reducing agent in an amount necessary to achieve the composition ratio of the above general formula during the nitridation reduction reaction as a starting material, and firing it in a nitrogen-containing atmosphere, A method for producing ceramic powder, which comprises synthesizing R ₂ O ₃ .Si-Al-O-N compound powder.