JP2681843B2 - Manufacturing method of β-type silicon nitride whiskers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing β-type silicon nitride whiskers useful as a raw material for composite materials, and particularly, the average diameter of whiskers is 2
The present invention relates to a method for producing β-type silicon nitride whiskers having a size of μm or more.

(Prior Art and Problems Thereof) Silicon carbide whiskers and silicon nitride whiskers are known as typical ceramic whiskers.
These are generally expected to be used as a reinforcing material that gives a composite material having good wear resistance and high strength and elastic modulus, and one of these applications is a whisker-reinforced ceramic composite material.

By the way, unlike the α-type silicon nitride whiskers, the β-type silicon nitride whiskers do not change their crystal structure even at a high temperature of 1500 ° C. or higher and a decomposition temperature of silicon nitride (about 1800 ° C.) or lower in a non-oxidizing gas atmosphere. Since it is possible to maintain the excellent characteristics that silicon nitride originally has, it is suitable as a reinforcing material for refractory metals or ceramics.

There are several proposals regarding the manufacturing method of β-type silicon nitride whiskers.

For example, JP-A-59-147000 discloses a method for producing β-type silicon nitride whiskers by heating and reacting a mixture of silica, carbon and cryolite in a mixed atmosphere of ammonia and nitrogen. . Further, in JP-A-1-278500, a silica powder is heated in a mixed gas of ammonia gas and hydrocarbon gas to produce amorphous silicon nitride, and a metal halogen compound is added to the amorphous silicon nitride to make it non-oxidizing. A method for producing β-type silicon nitride whiskers by heat treatment in gas is disclosed.

Furthermore, the applicant of the present invention also discloses that the Japanese Patent Laid-Open No. 63-2900,
63-25299 discloses a method of producing β-type silicon nitride whiskers by adding a rare earth oxide to amorphous silicon nitride or α-type silicon nitride and baking the mixture.

By the way, in recent years, a whisker having a large diameter has been desired in order to strengthen a composite material using ceramics as a matrix.

However, in the above-mentioned conventional manufacturing method, only whisker diameters as small as 0.1 to 1.5 μm are obtained, and the average diameter is 2 μm.
It was difficult to manufacture thick whiskers of m or more.

(Object of the Invention) The object of the present invention is to solve the above-mentioned drawbacks and to have an average diameter of 2 μm.
It is intended to provide a method capable of efficiently producing the thick β-type silicon nitride whiskers described above in a high yield.

(Technical Means for Solving Problems) The present invention provides 100 parts by weight of amorphous silicon nitride and / or α-type silicon nitride powder as an oxide powder or a compound powder that can be converted into an oxide during firing (however, Of the β-type silicon nitride whiskers, characterized in that the mixed powder in which 0.01 to 20 parts by weight of the fluoride powder is added in total is baked at 1550 to 1800 ° C. in a non-oxidizing gas atmosphere. Regarding manufacturing method.

The amorphous silicon nitride powder used in the present invention is prepared by a method known per se, for example, by heat-treating a reaction product obtained by reacting silicon tetrahalide with ammonia in a liquid phase or a gas phase. It is a so-called amorphous powder in which a clear diffraction phenomenon does not appear by ordinary X-ray diffraction. Further, this amorphous silicon nitride powder may contain silicon atoms, hydrogen atoms other than nitrogen atoms, and oxygen atoms.

The α-type silicon nitride powder can be manufactured by a known method such as a reduction nitriding method of silica or a direct nitriding method of silicon, in addition to the method of firing the above-mentioned amorphous silicon nitride powder. The specific surface area of the α-silicon nitride powder is 0.001~20m ² / g, especially 2~13m ² / g
It is preferred that

As the oxide powder in the present invention, at least one powder selected from oxides of rare earth elements and alkaline earth metals is used.

Specific examples of the rare earth element include lanthanum series elements such as yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, dysprosium, and ytterbium, and scandium.

In addition, specific examples of the alkaline earth metal include magnesium, calcium, strontium, barium, and the like.

The compound powder that can be converted into the oxide during firing may be any compound powder that can be partially or wholly converted into the oxide during β-type silicon nitride whisker growth, and examples thereof include carbonate and hydroxide. Can be mentioned. However, fluoride is excluded.

As the fluoride powder in the present invention, at least one powder selected from fluorides of alkali metals, alkaline earth metals and rare earth elements is used. In particular, those having a melting point of 1200 to 1700 ° C. are preferable.

The ratio of the oxide powder or the compound powder that can be converted into an oxide during firing and the fluoride powder is not particularly limited, but the oxide is a weight ratio (however, in the case of a compound that can be converted into an oxide during firing, the oxide is Conversion): Fluoride = 2: 1 to 1:10 is preferable.

The compounding amount of the oxide powder or the compound powder and the fluoride powder that can be converted into the oxide during firing is amorphous silicon nitride and / or
Alternatively, the total amount is 0.01 to 20 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the α-type silicon nitride powder (however, in the case of a compound that can be converted into an oxide during firing, calculated as oxide). If the blending amount of these is less than the lower limit, the formation of whiskers is insufficient and the yield becomes poor, and the diameter of the whiskers becomes thin. On the other hand, if the blending amount is more than the upper limit, whiskers will be fused together and the length of the whiskers will be shortened.

There is no particular limitation on the method for preparing a mixed powder of amorphous silicon nitride and / or α-type silicon nitride powder and an oxide powder or a compound powder and a fluoride powder which can be converted into an oxide during firing, and there are no particular limitations on the method known per se. A method, for example, a method of dry-mixing both of them, a method of wet-mixing both in an inert liquid and then removing the inert liquid, and the like can be adopted. A V-type mixer, a ball mill or a vibrating ball mill is preferably used as the mixing device. As another method of preparing the above mixed powder, a precursor of amorphous silicon nitride powder, for example, silicon diimide or silicon tetraamide is mixed with an oxide powder or a compound powder and a fluoride powder which can be converted into an oxide during firing. It is also possible to employ a method of dispersing and heating the dispersion. If amorphous silicon nitride or its precursor is used in the above method of preparation, it is extremely sensitive to oxygen or moisture and must be handled under a controlled inert atmosphere.

In the present invention, the β-type silicon nitride whiskers are obtained by firing the mixed powder in a powder state without molding in a non-oxidizing gas atmosphere at 1550 to 1800 ° C.

Specific examples of the non-oxidizing gas include nitrogen, argon, ammonia, or a mixed gas thereof. The firing conditions are preferably set so that the mixed powder is heated for 0.1 to 40 hours, particularly 4 to 20 hours on average from 1000 ° C to the maximum temperature. Maximum temperature during firing is 1800
C. or lower, preferably in the range of 1550 to 1750.degree. The furnace used for firing is not particularly limited, and for example, a high frequency induction heating method, a resistance heating method batch furnace, a rotary furnace, a pusher furnace, or the like can be used.

(Effects of the Invention) According to the present invention, thick β-type silicon nitride whiskers having an average diameter of 2 μm or more can be obtained in good yield, and production suitable for mass production has become possible. In particular, since this β-type silicon nitride whisker has a larger diameter than conventional whiskers, when it is used to produce a reinforced composite material of metal, plastic, or ceramic, an excellent strengthening effect can be obtained. In particular, it is possible to provide a sintered body having excellent characteristics, particularly improved toughness, simply by mixing it with various types of ceramic powder as a ceramic reinforcing material and sintering it.

(Example) An example and a comparative example are shown below.

Example 1 50 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200 ° C. and yttrium oxide having a purity of 99.9%
1.0 g and 1.0 g of calcium fluoride having a purity of 99.9% were mixed in a nitriding gas atmosphere in a ball mill for 1 hour.

Then, the mixed powder is put into a graphite crucible having an inner diameter of 120 mm and an inner volume of 450 ml, and set in a high frequency induction furnace, and the temperature is from room temperature to 1200 ° C. for 1 hour and 1200 ° C. to 1400 ° C. under a nitriding gas atmosphere.
The temperature was raised from 1400 ° C. to 1750 ° C. in 2.5 hours, and then held at 1750 ° C. for 6 hours for firing.

When the obtained powder was examined by X-ray diffraction, its crystal form was β type as shown in FIG. 1, and when it was observed with a scanning electron microscope, as shown in FIG.
It was confirmed that the whiskers had a length of 20 to 80 μm and a diameter of 1.5 to 4.0 μm (average diameter of 2.5 μm). Whisker yield based on amorphous silicon nitride (hereinafter simply referred to as yield)
Was 91%.

Example 2 50 g of α-type silicon nitride powder having a specific surface area of 5.3 m ² / g and purity of 99.9%
Yttrium oxide (1.5 g) and cerium fluoride (3.0 g) having a purity of 99.9% were mixed with a vibrating ball mill for 2 hours.

Next, the mixed powder is put into a graphite crucible having 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 and from 1200 ° C. to 1750 in a nitriding gas atmosphere.
The temperature was raised to 5.5 ° C. for 5.5 hours, and the temperature was maintained at 1750 ° C. for 8 hours for firing.

When the obtained powder was examined by X-ray diffraction, its crystal form was β type, and when observed with a scanning electron microscope, the length was 25 to 60 μm, and the diameter was 1.0 to 3.5 μm (average diameter).
It was confirmed that the whiskers were 2.0 μm). The yield of whiskers was 93%.

Comparative Example 1 50 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200 ° C. and yttrium oxide having a purity of 99.9%
2.0 g was mixed with a ball mill for 1 hour in a nitrogen gas atmosphere.

 The obtained mixed powder was fired in the same manner as in Example 1.

When the obtained powder was examined by X-ray diffraction, the crystal form was β type, and when observed with a scanning electron microscope, as shown in FIG. 3, the length was 10 to 30 μm and the diameter was 10 μm.
It was recognized that the whiskers were 0.5 to 1.5 μm (average diameter 0.8 μm). The yield of whiskers was 93%.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of the β-type silicon nitride whiskers obtained in Example 1 of the present invention, and FIGS. 2 and 3 are obtained in Example 1 of the present invention and Comparative Example 1, respectively. It is a scanning electron micrograph which replaces the drawing which shows the particle structure of the obtained β-type silicon nitride whiskers.

Claims (3)

(57) [Claims] 1. 100 parts by weight of amorphous silicon nitride and / or α-type silicon nitride powder, oxide powder or compound powder (excluding fluoride) that can be converted into oxide during firing, and fluoride powder A method for producing β-type silicon nitride whiskers, which comprises firing a mixed powder containing 0.01 to 20 parts by weight in total at 1550 to 1800 ° C in a non-oxidizing gas atmosphere. 2. The method for producing β-type silicon nitride whiskers according to claim 1, wherein the oxide powder is at least one powder selected from oxides of rare earth elements and alkaline earth metals. 3. The β-nitride according to claim 1, wherein the fluoride powder is at least one powder selected from fluorides of alkali metals, alkaline earth metals and rare earth elements. How to make silicon whiskers.