JPH0331680B2 - - 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) Silicon nitride whiskers are single crystals grown in the form of fine fibers without defects, and have extremely high tensile strength and
It has a high elastic modulus and is expected to be used as a material for composite materials, especially metal or ceramic composite materials used at high temperatures.

Ceramic Industry Association 91 , 43 (1983) discloses a method of manufacturing a silicon nitride sintered body by blending yttrium oxide powder with amorphous silicon nitride powder, forming a blend, and then firing. 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 combine a raw material powder selected from amorphous silicon nitride and α-type silicon nitride with 0.01 to 20 parts by weight of rare earth elements (excluding yttrium) in terms of oxide per 100 parts by weight of the raw material powder. A mixed powder of an oxide powder or a compound powder of a rare earth element (excluding yttrium) that can be converted into an oxide during firing (hereinafter both may be collectively referred to as a rare earth element compound) is a non-oxidizing powder. This is achieved by firing under a gas atmosphere.

The amorphous silicon nitride powder used in the present invention is obtained by a method known per se, for example, by heat-treating 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.

Specific examples of rare earth elements other than ythtrium include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium,
Examples include lanthanum series elements such as dysprosium and ytterbium, and scandium.

As the compound that can be converted into an oxide of a rare earth element during firing, any compound can be used as long as it can be partially or completely converted into an oxide during silicon nitride whisker growth. Hydroxides and carbonates are conveniently employed. Such examples include lanthanum carbonate and scandium hydroxide.

The blending amount of the rare earth element compound powder is 100% of the raw material powder selected from amorphous silicon nitride and α-type silicon nitride.
Per part by weight, the amount is 0.01 to 20 parts by weight, preferably 0.5 to 10 parts by weight, in terms of oxide. If the amount of rare earth element 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 rare earth element compound powder, and methods known per se can be used, such as dry mixing the two, wet mixing the two in an inert liquid, and then mixing the two in an inert liquid. It is possible to adopt a method of removing . 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 includes mixing and dispersing rare earth element compound powder in a precursor of amorphous silicon nitride powder, such as silicon diimide or silicon tetramide;
It is also possible to adopt a method of heat-treating this 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 set so that the mixed powder is heated from 1000° C. to the maximum temperature in an average of 4 to 20 hours.
The maximum temperature during firing is within the range of 1600-1750°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.

(Effects of the Invention) According to the present invention, highly pure β-type silicon nitride whiskers with no residual raw materials can be produced with good yield. 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 lanthanum oxide (La ₂ O ₃ ) powder with a purity of 99.9% were combined in a ball mill under a nitrogen gas atmosphere. Mixed for an hour. The mixed powder was placed in a graphite crucible with an inner diameter of 120 mm and an inner volume of 450 ml, set in a high frequency induction furnace, and heated from room temperature to 1200°C for 1.5 hours at 1200 to 1400°C under a nitrogen gas atmosphere.
The temperature was raised from 1400 to 1700°C over 3 hours for 4 hours, and the temperature was further maintained at 1700°C for 7 hours for firing.

When the obtained powder was examined by X-ray diffraction, its crystal form was β type as shown in Figure 1, and observation using a scanning electron microscope revealed that it was β type.
As shown in the figure, length 10~30μm, diameter 0.5~1.5μm
It was recognized that it was a whisker. The whisker yield (hereinafter simply referred to as yield) was 91% based on amorphous silicon nitride.

Example 2 50 g of α-type silicon nitride powder with a specific surface area of 4.8 m ² /g and 2.6 g of lanthanum carbonate [La ₂ (CO ₃ ) ₃ ] powder with a purity of 99.9% were mixed in a vibrating ball mill for 1 hour.
The mixed powder was placed in a graphite crucible with an inner diameter of 120 mm and an inner volume of 450 ml, set in a high frequency induction furnace, and heated from room temperature to 1200°C for 1 hour in a nitrogen gas atmosphere.
The temperature was raised to 1750°C over 5.5 hours, and the temperature was further maintained at 1750°C for 4 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 1.0 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 8 g of cerium oxide (CeO ₂ ) powder with a purity of 99.9% were mixed in a nylon ball pot under a nitrogen gas atmosphere. Mixed on a vibratory mill for 1.5 hours. Mixed powder, inner diameter 290mm,
Place it in a graphite crucible with a height of 70 mm, set it in a resistance heating high temperature furnace, and heat it from room temperature under a nitrogen gas atmosphere.
1200℃ for 2 hours, 1200~1400℃ for 4 hours, 1400~
The temperature was raised to 1700°C over 3 hours, and the temperature was further maintained at 1700°C for 8 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 10 to 40 μm and a diameter of 0.3 to 0.3 μm.
It was recognized that it was a 1.4 μm whisker. The yield was 89%.

Example 4 30 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200° C. and 0.6 g of scandium oxide (SC ₂ O ₃ ) powder were mixed for 1 hour in a ball mill under a nitrogen gas atmosphere. . The mixed powder was placed in a graphite crucible with an inner diameter of 120 mm and an inner volume of 450 ml, set in a high frequency induction furnace, and heated under a nitrogen gas atmosphere.
Raise the temperature from room temperature to 1200℃ for 1.5 hours, 1200 to 1450℃ for 5 hours, 1450 to 1650℃ for 2 hours, and then 1650℃ for 2 hours.
It was kept at ℃ for 10 hours and fired.

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 30 μm and a diameter of 0.2 to 0.2 μm.
It was recognized that it was a 1.0 μm whisker. The yield was 92%.

Example 5 50 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200°C and 2.5 g of samarium oxide (Sm ₂ O ₃ ) powder with a purity of 99.9% were placed in a closed mold under a nitrogen gas atmosphere. Mixing was carried out in a V-type mixer for 3 hours. The mixed powder was placed in a graphite crucible with an inner diameter of 120 mm and an inner volume of 450 ml, set in a high frequency induction furnace, and heated from room temperature to 1200°C for 2 hours under a nitrogen gas atmosphere.
The temperature was raised to 1,200 to 1,400°C for 5 hours, to 1,400 to 1,600°C for 2 hours, and then held at 1,600°C for 15 hours for firing.

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 80% of the powder had a crystal shape of 20 to 20 mm in length.
The whiskers are 25 μm in diameter and 1.0 to 1.2 μm in diameter.
20% was found to be β-type granular silicon nitride. The total yield of whisker-like and granular silicon nitride is
It was 87%.

Example 6 250 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200°C and 6.3 g of dysprosium oxide (Dy ₂ O ₃ ) powder with a purity of 99.9%,
The mixture was mixed for 3 hours using a vibrating mill under a nitrogen gas atmosphere.
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 2 hours at 1200°C under a nitrogen gas atmosphere.
The temperature was raised to ~1410°C for 3 hours, then to 1410~1720°C for 3 hours, and then held at 1720°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 5 to 40 μm and a diameter of 0.2 to 0.2 μm.
It was recognized that it was a 1.2 μm whisker. The yield was 89%.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing the X-ray diffraction pattern and particle structure of β-type silicon nitride whiskers obtained in Example 1, respectively.

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 rare earth element (excluding yttrium) oxide powder or at the time of firing, in terms of oxide per 100 parts by weight of the raw material powder. A mixed powder of rare earth elements (excluding yttrium) that can be converted into oxides is heated in a non-oxidizing gas atmosphere from 1000°C to a maximum temperature of 4 to 20 hours until the maximum temperature reaches 1600°C. A method for producing β-type silicon nitride whiskers, which is characterized by firing at a temperature in the range of 1750°C.