JPH0262520B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing β-type silicon nitride whiskers useful as a material for composite materials.

(Prior art and its problems) Ceramic Industry Association Magazine 91 , 43 (1983) describes a method in which yttrium oxide powder is blended with amorphous silicon nitride powder, the blend is molded, and then fired to produce a silicon nitride sintered body. A method of manufacturing is disclosed. This report only discloses a method for producing a sintered body using yttrium oxide as a sintering aid, and does not at all describe a method for producing silicon nitride whiskers.

JP-A-59-147000 describes a method for producing β-type silicon nitride whiskers by subjecting a mixture of silica, carbon, and cryolite to a heating reaction in a mixed atmosphere of ammonia and nitrogen. This method requires complicated operations to remove raw materials such as silica and carbon that remain in the β-type silicon nitride whiskers that are produced, and also has the problem that the yield of whiskers is not high. are doing.

(Objective and Summary of the Invention) An object of the present invention is to provide a method for producing β-type silicon nitride whiskers with good yield and efficiency.

The object of the present invention is to use a raw material powder selected from amorphous silicon nitride and α-type silicon nitride, and 0.01 to 20 parts by weight of yttrium oxide in terms of yttrium oxide per 100 parts by weight of the raw material powder, or yttrium oxide powder that is converted into yttrium oxide during firing. This is achieved by firing a mixed powder with a powder of a compound capable of oxidizing (hereinafter both may be collectively referred to as yttrium compound powder) in a non-oxidizing gas atmosphere.

The amorphous silicon nitride powder used in the present invention can be obtained by a method known per se, for example, by heating a reaction product obtained by reacting silicon tetrahalide and ammonia in a liquid phase or a gas phase. It is a so-called amorphous material that does not show a clear diffraction phenomenon by ordinary X-ray diffraction. Note that this amorphous silicon nitride may contain hydrogen atoms in addition to silicon atoms and nitrogen atoms.

In addition to the above-mentioned method of calcining the amorphous silicon nitride powder, α-type silicon nitride powder can be produced using the silica reduction nitriding method.
It can be manufactured by a known method such as direct silicon nitridation. The specific surface area of α-type silicon nitride powder is 0.001
It is preferably 20 m ² /g, especially 2 to 13 m ² /g.

In the present invention, specific examples of compounds that can be converted into yttrium oxide during firing include yttrium carbonate and yttrium hydroxide.

The amount of yttrium compound powder is a raw material powder selected from amorphous silicon nitride and α-type silicon nitride.
Per 100 parts by weight, converted to yttrium oxide,
The amount is 0.01 to 20 parts by weight, preferably 0.5 to 10 parts by weight. If the amount of yttrium compound powder blended is smaller than the lower limit, the yield of whiskers will be lower, and if the blended amount is more than the upper limit, fusion of whiskers will occur.

There are no particular restrictions on the method for preparing the mixed powder of the raw material powder and the yttrium compound powder, and methods known per se, such as a method of dry mixing the two,
A method may be adopted in which both are wet-mixed in an inert liquid and then the inert liquid is removed. As the mixing device, a V-type mixer, a ball mill or a vibrating ball mill is preferably used. Another method for preparing the above mixture may be to mix and disperse yttrium compound powder in a precursor of amorphous silicon nitride powder, such as silicon diimide or silicon tetraamide, and then heat-treat the dispersion. If amorphous silicon nitride or its precursors are used in the above preparation method, they must be handled under a controlled inert atmosphere since they are very sensitive to oxygen or moisture.

Specific examples of the non-oxidizing gas constituting the non-oxidizing gas during firing include nitrogen, argon, ammonia, or a mixed gas thereof. The firing conditions are desirably set so that the mixed powder is heated between 1000° C. and the maximum temperature for an average of 0.1 to 40 hours, preferably 4 to 20 hours. The maximum temperature during firing is 1800℃ or less, preferably 1500-1750
The temperature is within the range of °C.

There is no particular restriction on the furnace used for firing the mixed powder, and for example, a batch type furnace, rotary furnace, pusher furnace, etc. using a high frequency induction heating method or a resistance heating method can be used.

The β-type silicon nitride whiskers obtained in the present invention can be used as a material for reinforcing metals or ceramics, and can be particularly suitably used as a material for reinforcing silicon nitride sintered bodies and sialon sintered bodies.

(Example) Examples are shown below.

Example 1 50 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200° C. and 1.0 g of yttrium oxide with a purity of 99.9% were mixed in a ball mill under a nitrogen gas atmosphere for 1 hour. Mixed powder, inner diameter
It was placed in a graphite crucible with a diameter of 120 mm and an internal volume of 450 ml, set in a high frequency induction furnace, and heated at room temperature to 1200°C for 1 hour and 1200 to 1400°C for 4 hours under a nitrogen gas atmosphere.
Raise the temperature from 1400 to 1650℃ in 2.5 hours, then further to 1650℃
It was held for 8 hours and fired.

When the obtained powder was examined by X-ray diffraction, its crystal morphology was found to be β type, and observation using a scanning electron microscope revealed that it had a length of 10 to 40 μm and a diameter of 0.5 to 0.5 μm, as shown in Figure 1. It was recognized that it was a 1.5 μm whisker. The whisker yield (hereinafter simply referred to as yield) is 91% based on amorphous silicon nitride.
It was hot.

Example 2 50 g of α-type silicon nitride powder with a specific surface area of 5.3 m ² /g and 1.5 g of yttrium oxide powder with a purity of 99.9%,
Mixed in a vibrating ball mill for 2 hours. Mixed powder,
Place it in a graphite crucible with an inner diameter of 120 mm and an internal volume of 450 ml.
Set in a high frequency induction furnace and heat from room temperature to 1200℃ for 1 hour, then from 1200 to 1750℃ under nitrogen gas atmosphere.
The temperature was raised over 5.5 hours, and the temperature was further maintained at 1750°C for 6 hours for firing.

When the obtained powder was examined by X-ray diffraction, its crystal form was β-type, and observation using a scanning electron microscope revealed that it had a length of 25-30 μm and a diameter of 0.7-30 μm.
It was recognized that it was a 1.5 μm whisker. The yield was 93%.

Example 3 200 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200°C and 10 g of yttrium oxide with a purity of 99.9% were heated in a vibrating mill for 2 hours using a nylon ball pot under a nitrogen gas atmosphere. Mixed. The mixed powder was placed in a graphite crucible with an inner diameter of 290 mm and a height of 70 mm, set in a resistance heating high temperature furnace, and heated from room temperature to 1200°C for 1 hour under a nitrogen gas atmosphere.
time, 1200-1400℃ for 4 hours, 1400-1700℃ for 3 hours
The temperature was raised over an hour and then held at 1700℃ for 7 hours.
Fired.

When the obtained powder was examined by X-ray diffraction, the crystal form was β type as shown in Figure 2, and observation by scanning electron microscope revealed that the length was
The whiskers were found to be 10 to 40 μm and 0.5 to 1.5 μm in diameter.

Example 4 150 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200°C and 9.3 g of yttrium hydroxide [Y(OH) ₃ ] were mixed in a nylon ball pot under a nitrogen gas atmosphere. Mixed on a vibratory mill for 2 hours. Mixed powder, inner diameter 290mm, height 70mm
Place it in a graphite crucible with a diameter of
for 1 hour, 1200-1400℃ for 3 hours, 1400-1650℃
The temperature was raised over 2 hours, and the temperature was further maintained at 1650°C for 12 hours for firing.

When the obtained powder was examined by X-ray diffraction, its crystal form was β type, and observation using a scanning electron microscope revealed that it had a length of 15 to 35 μm and a diameter of 0.7 to 0.7 μm.
It was recognized that it was a 1.5 μm whisker. The yield was 89%.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the particle structure of the β-type silicon nitride whiskers obtained in Example 1, and FIG. 2 is an X-ray diffraction diagram of the β-type silicon nitride whiskers obtained in Example 3.

Claims (1)

[Claims] 1 Raw material powder selected from amorphous silicon nitride and α-type silicon nitride, and 0.01 to 20 parts by weight of yttrium oxide in terms of yttrium oxide per 100 parts by weight of the raw material powder, yttrium oxide powder or powder of a compound that can be converted to yttrium oxide during firing. 1. A method for producing β-type silicon nitride whiskers, which comprises firing a mixed powder of β-type silicon nitride whiskers in a non-oxidizing gas atmosphere.