JPS61205699A - Production of silicon nitride whisker - Google Patents

Abstract

PURPOSE:Iron or its compound is added to an amorphous powder of silicon nitride at a specific weight ratio and they are roasted to produce silicon nitride whiskers which is suitably used as a material for ceramic composite materials in high yield in a short time. CONSTITUTION:An amorphous powder of silicon nitride is prepared by allowing a silicon halide to react with ammonia in liquid or vapor phase and heat-treating the reaction product. Then, 100pts.wt. of amorphous silicon nitride powder are combined with 0.05-10pts.wt., calculated as elementary iron, of iron or its compound such as iron oxide, iron halide. The mixture is roasted in a nonoxidative atmosphere such as nitrogen or argon to give the objective silicon nitride whiskers.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for manufacturing silicon nitride whiskers.

(Prior art and its problems) Silicon nitride whiskers are defect-free single crystals grown in the form of fibers and have very high tensile strength and elastic modulus, and are used in composite materials, especially at high temperatures. It is expected to be used as a material for metal or ceramic composite materials.

Methods for producing silicon nitride whiskers include a method in which silicon or silicon oxide vapor is generated and whiskers are grown on a substrate under nitrogen or ammonia gas flow, and a method in which silicon tetrachloride and ammonia are reacted at high temperature to grow whiskers on a substrate. Methods to do this have been proposed. These methods may have low whisker yields, require a long time to produce a given amount, or require processing to separate the desired product after whisker growth. It is difficult to say that this method is suitable as an industrial manufacturing method.

(Means for Solving the Problems) The present invention provides a method for producing silicon nitride whiskers free from the above drawbacks, and the gist thereof is that a specific amount of iron and/or iron compounds is added to amorphous silicon nitride powder. The purpose is to sinter the blended mixture in a non-oxidizing gas atmosphere.

The amorphous silicon nitride powder used in the present invention is 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 powder that does not show a clear diffraction phenomenon by ordinary X-ray diffraction.

The iron compound may be one that at least partially decomposes to produce iron during firing, but it is preferable to use one that easily decomposes into iron during firing. Specific examples thereof include iron oxide, iron oxide,
Mention may be made of iron halides, iron oxyhalides and iron alloys.

The amount of iron and/or iron compound used is amorphous silicon nitride powder 1
00 parts by weight, 0.05 to 101i parts in terms of iron,
Preferably it is 0.1 to 2 parts by weight. If the amount of iron and/or iron compound used is out of the above range, the yield of whiskers will decrease.

There are no particular restrictions on the method for producing a mixture of amorphous silicon nitride powder and iron and/or iron compounds, and methods known per se may be used, such as a method of dry mixing the two, or a method of dry mixing the two in an inert liquid. A method of removing an inert liquid after wet mixing can be adopted as appropriate. 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-mentioned mixture is to mix and disperse iron and/or iron compounds into a precursor of amorphous silicon nitride powder, such as silicon diimide or silicon tetraamide, and heat-treat the dispersion. You can also do that. In each of these manufacturing methods, amorphous silicon nitride and its precursors are extremely sensitive to oxygen and water and must be handled under a controlled inert atmosphere.

Specific examples of the non-oxidizing gas constituting the non-oxidizing gas atmosphere during firing include nitrogen, argon, ammonia, or a mixed gas thereof.

As the firing conditions, it is desirable to select such conditions that the temperature of the mixed powder is raised from 100 Ot to the maximum temperature in several seconds to several tens of hours, preferably in 1 to 20 hours. The maximum temperature is usually 1800'C, preferably 1650C.

There are no particular restrictions on the furnace used for firing the mixed powder; for example, a batch furnace using a high-frequency induction heating method or a resistance heating method, a rotary furnace, a fluidized flow furnace, a pusher furnace, etc. can be used. .

(Example) Example 1 50 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200°C and ferric oxide (reagent special grade)
0.1 g was placed in a V-type mixer under nitrogen atmosphere and mixed for 1 hour. The mixture was placed in a graphite crucible having an inner diameter of 128 cm and an inner volume of 450 cc, and the crucible was placed in a high frequency induction furnace. Under a nitrogen atmosphere, from room temperature to 1200°C for 1 hour, 12
The temperature was raised from 00 to 1400°C for 40 hours, from 1400 to 1500°C over 1 hour, and further held at 1500°C for 1 hour.

When the obtained silicon nitride powder was examined by X-ray diffraction, the crystal form was α type, and when observed using a scanning electron microscope, it was found to have a whisker shape with a length of 10 to 100 μm and a diameter of 0.1 to 1 μm.

Example 2 The same method as Example 1 was repeated except that 0.1 g of iron powder passed through a 100 mesh sieve was used instead of ferric oxide.

The obtained silicon nitride powder is an α-type crystal with a length of 20 to 1
It had a whisker shape with a diameter of 0.00μ and a diameter of 0.5 to 1μ.

(Effects of the Invention) According to the present invention, silicon nitride whiskers can be obtained in good yield and in a short time.

Claims (1)

[Claims] A silicon nitride whisker is produced by firing a mixture of 100 parts by weight of amorphous silicon nitride powder and 0.05 to 10 parts by weight of iron and/or iron compounds in a non-oxidizing gas atmosphere. Manufacturing method