JPH0469215B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention is a β-type silicon nitride whisker molded article that is effectively used as a reinforcing material for whisker-reinforced plastic materials (FRP), whisker-reinforced metal materials (FRM), or whisker-reinforced ceramic materials (FRC). and its manufacturing method. (Prior art and its problems) Ceramic Industry Association Magazine 91, 559 (1983) describes a method in which yttrium oxide powder is blended with amorphous silicon nitride, and the blend is molded and fired to produce a silicon nitride sintered body. A method of manufacturing is described. This report only discloses a method for producing a sintered body using yttrium oxide as a sintering aid, and does not explicitly describe a method for producing a silicon nitride whisker molded body. JP-A-59-14700 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. The method for producing a β-type silicon nitride whisker molded body is not described at all. In order to use whiskers as preforms for composite materials, it is common to reshape powdered whiskers by an appropriate method. The length of the preformed whiskers obtained in this way is shorter than that at the time of whisker generation, and many complicated and highly technical processes must be performed before forming the preform, so it is necessary to manufacture the preform by the above-mentioned method. is not satisfactory from an economic point of view. Further, even when used as preforms for various composite materials, there is a problem that they do not have sufficient strength and hardness because they rely on the manufacturing method described above. (Summary of the Invention) According to the present invention, the density is 0.15 to 1.1 g/cm ³ , the bending strength is 25 Kg/cm ² or more, the hardness is 45 Kg/cm ² or more, and the compressive strength is
A β-type silicon nitride whisker molded article having a weight of 30 kg/cm ² or more, 90% by weight or more of the molded product is composed of β-type silicon nitride whiskers, and 80% by weight of the whiskers.
The β-type silicon nitride whisker molded article has a diameter of 0.1 to 5 μm and a length of 2 to 100 μm, and the whiskers are in contact with each other at one or more locations per whisker. is provided. Further, according to the present invention, amorphous silicon nitride and/or
Or, 0.1 to 20 parts by weight of rare earth element and/or alkaline earth metal oxide powder or compound powder that can be converted into the above-mentioned oxide during firing is blended with 100 parts by weight of α-type silicon nitride powder. Mixed powder,
Fill a crucible mold with a desired shape with a density in the range of 0.15 to 1.1 g/cm ³ and under a nitrogen-containing non-oxidizing gas atmosphere.
There is provided a method for producing the β-type silicon nitride whisker molded body, characterized in that firing is performed at a maximum temperature of 1600 to 1850°C. (Specific Description of the Invention) The bending strength, hardness, and compressive strength of the β-type silicon nitride whisker molded product of the present invention are JIS
This is a value measured according to Z2113, JIS Z2117 and JIS Z2111. The β-type silicon nitride whisker molded article of the present invention is
It has a density of 0.15 to 1.1 g/cm ³ , a bending strength of 25 Kg/cm ² or more, a hardness of 45 Kg/cm ² or more, and a compressive strength of 30 Kg/cm ² or more. In addition, the above molded body is 90
At least 80% by weight consists of β-type silicon nitride whiskers, and furthermore, 80% of the β-type silicon nitride whiskers
These have a diameter of 0.1-5 μm and a length of 2-100 μm. These β-type silicon nitride whiskers are in contact with each other and fixed to each other at one or more locations per whisker in the molded product, thereby forming a strong molded product. The β-type silicon nitride whisker molded article of the present invention can be prepared by the method described above. Amorphous silicon nitride powder can be prepared by a method known per se,
For example, it can be prepared by heating a reaction product obtained by reacting silicon tetrahalide and ammonia in a liquid or gas phase, and no clear diffraction phenomenon appears in ordinary X-ray diffraction. It is a so-called amorphous powder. In addition to the above-mentioned method of firing 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 0.01~
It is preferably 20 m ² /g, especially 2 to 13 m ² /g. Specific examples of rare earth elements include yztrium,
Lanthanum, cerium, praseodymium, neodymium, samarium, europium, gaddonium,
Examples include lanthanum series elements such as dysprosium and ytterbium, and scandium. Further, specific examples of alkaline earth metals include magnesium, calcium, strontium, barium, and the like. As the compound that can be converted into an oxide of a rare earth element and/or alkaline earth metal 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. Common examples include hydroxides, carbonates, and the like. The blending amount of rare earth element and/or alkaline earth metal compound powder is amorphous silicon nitride and/or α
Per 100 parts by weight of raw material powder selected from silicon nitride,
It is 0.1 to 2.0 parts by weight in terms of oxide. If the blending amount is smaller than the lower limit, whisker formation will be insufficient, and if it is larger than the upper limit, something similar to a densified sintered body will be generated, and it cannot be said to be a molded body with whiskers, but will not be in the form of a composite material preform. As such, I can only do something unsatisfactory. There is no particular restriction on the method for preparing the mixed powder of amorphous silicon nitride and/or α-type silicon nitride powder and rare earth element and/or alkaline earth/rare earth compound powder, and methods known per se, for example, both of them may be used. A method of dry mixing them, a method of wet mixing them in an inert liquid and then removing the inert liquid, etc. can be adopted. 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 mixed powder is to mix and disperse rare earth element or alkaline earth metal compound powder into a precursor of amorphous silicon nitride powder, such as silicon diimide or silicon tetraamide, and then heat-process the dispersion. It is also possible to adopt the method of 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 nitriding non-oxidizing gas include nitrogen,
Examples include argon, ammonia, or a mixture thereof. As for the firing conditions, the mixed powder
It is preferable to set the heating temperature between 1000° C. and the maximum temperature for an average of 0.1 to 40 hours, particularly 4 to 20 hours. The maximum temperature during firing is 1850℃ or less,
Preferably the temperature is within the range of 1600 to 1800°C.
There is no particular restriction on the furnace used for firing the mixed powder, and for example, a batch furnace, rotary furnace, pusher furnace, etc. using a high frequency induction heating method or a resistance heating method can be used. Various composite materials can be prepared using the β-type silicon nitride whisker molded article of the present invention. The whisker-reinforced metal material (FRM) can be manufactured by the method of casting molten metal into the whisker molded body of the present invention under high pressure. As the metal, aluminum, magnesium, titanium, or an alloy based on these is preferably used. In addition, whisker-reinforced ceramic materials (FRC)
A method of infiltrating the whisker molded body of the present invention with a substance that will become a matrix, such as a glass-like substance, a method of filling the space of the molded body with a substance that will become a matrix by a chemical vapor deposition method (CVD method),
Alternatively, it can be manufactured by filling a space in a molded body with a ceramic raw material that will become a matrix and reacting it at a high temperature. The whisker-reinforced plastic material (FRP) can be manufactured by a method in which the whisker molded body of the present invention is impregnated with a polymer melt under high pressure, a method in which polymerization is caused in the space of the molded body to form a polymer, etc. . (Effects of the Invention) The β-type silicon nitride whisker molded article of the present invention has an appropriate porosity and excellent bending strength and hardness, and even when a whisker-reinforced metal material is manufactured by high-pressure casting, for example. , it is possible to stably produce a metal material in a desired shape without losing its shape. Furthermore, according to the method for producing a β-type silicon nitride whisker molded body of the present invention, the whiskers generated during crystallization are not cut, and the whiskers are uniform and tightly intertwined with each other without containing almost any impurities. A molded body can be produced in a desired shape simultaneously with crystallization without going through a molded body manufacturing process. Therefore, the composite material manufacturing process can be shortened,
This not only contributes to cost reduction, but also enables the production of stronger composites. (Example) Examples are shown below. Example 1 100 parts by weight of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200°C and purity 99.9%
and 1 part by weight of yttrium oxide were placed in a vibrating ball mill under a nitrogen gas atmosphere and mixed for 1 hour. Approximately 0.2 of the mixed powder was placed in a cylindrical carbon crucible with an inner diameter of 300 mm and a bottomed carbon crucible in which 7 mm thick carbon plates were placed vertically at 17 mm intervals.
It was filled to a height of about 175 mm with a packing density of g/cm ³ .
This crucible was set in a resistance heating furnace and heated from room temperature to 1200℃ for 1 hour in a nitrogen gas atmosphere.
The temperature was raised to 1400°C for 4 hours, from 1400 to 1750°C over 3.5 hours, and further held at 1750°C for 4 hours. After cooling to room temperature, the carbon plate inside the crucible was removed and found to be 17mm thick and approximately 100mm high.
A yellowish-white plate-like material with the same width as the crucible circumference was obtained. This plate has a density of approximately 0.32g/cm ³ and a density of 40.5Kg/cm ²
It had a flexural strength of , a hardness of 69.5 Kg/cm ² and a compressive strength of 46.2 Kg/cm ² . When this plate-like material was observed with a scanning electron microscope, it was found that the whiskers were mainly 5-100 μm long and 0.2-4 μm in diameter, and each whisker was stuck to each other at one or more points and intertwined in a complicated manner. The statue was recognized. Furthermore, when the powder obtained by pulverizing the plate-like material was examined by X-ray diffraction, almost no diffraction other than that attributable to β-type silicon nitride was observed. Example 2 A mixture of amorphous silicon nitride powder and yttrium oxide powder was placed between a carbon cylindrical tube with an inner diameter of 45 mm and a carbon cylinder with an outer diameter of 25 mm at its center on a carbon plate. Fill it to a height of about 100mm,
Example 1 except that this was heated in a high frequency induction furnace
In the same way as above, the inner diameter is 25 mm, the outer diameter is 45 mm, and the height is approx.
A yellowish-white cylindrical molded product measuring 60 mm and having a density of about 0.32 g/cm ³ was obtained. When the fragments of this compact were observed with a scanning electron microscope, a structure very similar to that of the plate-like material obtained in Example 1 was observed, and X-ray diffraction examination of the crushed material also revealed that the β-type No diffraction other than that attributed to silicon nitride was observed. Example 3 A mixed powder of amorphous silicon nitride powder and yttrium oxide was packed at a packing density of 0.50 g/cm ³ to a height of about 150 mm, and the temperature was raised to 1400 to 1700°C in 3 hours during the heating process. , Example 1 was repeated except that the temperature was further held at 1700°C for 8 hours, and the thickness was 17 mm and the height was about 150 mm.
A yellowish-white plate-like material with the same width as the crucible circumference was obtained. When this plate-like material was observed with a scanning electron microscope, an image of complex intertwining of whiskers, mainly consisting of whiskers 10 to 100 μm in length and 0.2 to 5 μm in diameter, was observed, as shown in Figure 1. Ta. Also,
When the plate-like material was crushed and examined by X-ray diffraction, the crystal form was β-type silicon nitride. Example 4 120 g of α-type silicon nitride powder with a specific surface area of 4.8 m ² /g,
3.6 g of calcium oxide and 600 ml of ethanol were placed in a ball mill, wet-mixed for 10 hours, and then dried under reduced pressure. The resulting lump was ground in a mortar to form a mixed powder. This mixed powder was placed in a bottomed cylindrical carbon crucible with an inner diameter of 300 mm, in which carbon plates each having a thickness of 7 mm were installed vertically at intervals of 17 mm, at a packing density of 0.35 g/cm ³ . It was filled to a height of 150mm. Set this crucible in a resistance heating furnace,
Under a nitrogen gas atmosphere, the temperature was raised from room temperature to 1200°C for 2 hours, from 1200 to 1750°C over 5.5 hours, and further held at 1750°C for 5 hours. When the obtained plate-like material was observed with a scanning electron microscope, it was found that the length was 10 to 100 μm, as shown in Figure 1.
An image consisting mainly of whiskers with a diameter of 0.5 to 0.7 μm, in which the whiskers were intricately intertwined with each other, was observed. Further, when the plate-like material was crushed and examined by X-ray diffraction, its crystal form was found to be β-type silicon nitride. Examples 5-7 Example 3 was repeated except that the compounds listed in Table 1 were used in place of yttrium oxide. The results are shown in Table 1.

[Table] When the plate-like products obtained in Examples 5 to 7 were observed with a scanning electron microscope, an image of whiskers intricately intertwined with each other was observed. Comparative Example 1 Example 1 was repeated except that a mixed powder of amorphous silicon nitride powder and yttrium oxide was filled into a carbon crucible at a packing density of 0.1 g/cm ³ . The bending strength of the plate-like material obtained was 15Kg/cm ² and the hardness was
The compressive strength was 25Kg/cm ² and the compressive strength was 20Kg/cm ² . Comparative Example 2 Example 1 was repeated except that a mixed powder of amorphous silicon nitride powder and yttrium oxide was filled into a carbon crucible at a packing density of 1.3 g/cm ³ . An attempt was made to produce a silicon nitride whisker-reinforced metal composite material by placing the resulting whisker preform in a casting mold and forcing an aluminum alloy into the preform at 800°C.
The preform cracked during the pressing of the aluminum alloy, making it impossible to obtain the desired composite material.

[Brief explanation of the drawing]

FIG. 1 shows the structure of whiskers (fibrous single crystals) constituting the plate-like material obtained in Example 3.

Claims (1)

[Claims] 1. A β-type silicon nitride whisker molded body having a density of 0.15 to 1.1 g/cm ³ , a bending strength of 25 Kg/cm ² or more, a hardness of 45 Kg/cm ² or more, and a compressive strength of 30 Kg/cm ² or more, At least 90% by weight of the molded body consists of β-type silicon nitride whiskers, and at least 80% by weight of the whiskers have a diameter of 0.1 to 5 μm.
1. A β-type silicon nitride whisker molded body, which has a diameter of 2 to 100 μm, and is characterized in that the whiskers are in contact with each other at one or more locations per whisker. 2 Amorphous silicon nitride and/or α-type silicon nitride powder
100 parts by weight of a mixed powder containing 0.1 to 20 parts by weight of rare earth element and/or alkaline earth metal oxide powder or compound powder that can be converted into the above-mentioned oxide upon firing, based on the oxide, is mixed into a desired shape. in the shape of a crucible
Filled with a density in the range of 0.5 to 1.1 g/ ^cm3 , and heated to a maximum temperature of 1600 to 1850° in a nitrogen-containing non-oxidizing gas atmosphere.
Density 0.15~, characterized by firing at a temperature of
1.1g/cm ³ , bending strength 25Kg/cm ² or more, hardness 45Kg/
cm ² or more, and a compressive strength of 30 Kg/cm ² or more, a β-type silicon nitride whisker molded body, in which 90% by weight or more of the molded body consists of β-type silicon nitride whiskers, and 80% by weight or more of the whiskers are 0.1 to 30 kg/cm 2 or more. 5μm diameter, 2~
A method for producing a β-type silicon nitride whisker molded article, which has a length of 100 μm and is characterized in that the whiskers are in contact with each other at one or more locations per whisker.