JPH10245270A - Highly oriented silicon nitride sintered compact and production of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon nitride molding having extremely enhanced strength, toughness and coefficient of thermal conductivity in oriented direction by extrusion molding of a mixture of β-silicon nitride cylindrical particle and α-silicon nitride spherical particle in a specific ratio incorporated with a sintering aid and sintering the molding in which the β-silicon nitride cylindrical particle is uniaxially oriented. SOLUTION: The molding raw material is obtained by adding the sintering aid to the mixture of the β-silicon nitride cylindrical particle and α-silicon nitride spherical particle mixed so that the ratio of α-silicon nitride spherical particle is 5-95wt.%. This material is extrusion molded to afford the molding in which the β-silicon nitride cylindrical particle is uniaxially oriented, and the molding is sintered. High orientation is obtained by carrying out the extrusion using an extrusion molding form having extrusion nozzle thickness of <=3mm, extrusion nozzle length of >=5mm, at an extrusion rate >=5cm/min. A highly oriented sintered compact having more than 70% of orientation degree, 100W/m.K of coefficient of thermal conductivity can be produced in this process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly oriented silicon nitride sintered body and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, silicon nitride (Si ₃ N ₄ ) sintered bodies have been developed as high-temperature structural materials for automobile engine members and the like and heat conductive insulating materials for electronic circuit boards and the like. In such a silicon nitride sintered body as a structural material, strength,
Toughness and thermal conductivity are particularly important properties. First, strength and toughness are basic properties that determine the practicality or range of application as structural materials, and thermal conductivity is a property directly required in applications such as circuit boards that require heat dissipation. It is also an important property in reducing the occurrence of local thermal stress and improving practical strength. Silicon nitride sintered bodies are among the highest toughness classes among ceramic sintered bodies, but still have a fracture toughness (K _IC ) value of 1/10 or less as compared with metal materials. It has been a long-standing issue in the development of structural ceramics. Further, in order to reduce thermal stress or thermal shock as much as possible to compensate for low toughness, it is necessary to increase thermal conductivity as much as possible.

Conventionally, methods for increasing the toughness of a silicon nitride sintered body include a method of dispersing columnar particles in a structure and a method of dispersing SiC particles or the like as second phase particles. These are toughened by utilizing the bridging effect and the drawing effect during crack propagation. However, in these methods, since the added particles also act as defects, the strength is reduced, and it is difficult to realize a sintered body having both high strength and toughness.

In general, a silicon nitride sintered body is formed of a spherical α-Si ₃ N
_The mixture obtained by adding a sintering aid to ₄ is molded and sintered. In this sintering process, α-Si ₃ N ₄ spherical particles are dissolved, precipitated as β-Si ₃ N ₄ columnar particles, grown in various directions, and finally in a state where the columnar particles are three-dimensionally entangled. Become. On the other hand, it has been proposed that β-Si ₃ N ₄ columnar particles are oriented in a specific direction, and high strength and high toughness are simultaneously developed in this orientation direction. That is, Japanese Patent Application Laid-Open No. 8-143400 discloses that a single crystal β-Si ₃ N ₄ columnar particle is added as a seed crystal to a mixture of silicon nitride powder and a sintering aid in an amount of 0.1 to 10 vol% to form a sheet. Alternatively, there has been disclosed a technique in which a molded body in which β-Si ₃ N ₄ columnar particles are oriented in a specific direction by extrusion molding or the like and a sintering technique is performed, whereby the strength is 1100 MPa or more and the fracture toughness (K _IC ) is improved. It is described that a silicon nitride sintered body of 11 MPa · m ^1/2 or more can be obtained. However, only the sheet molding by the doctor blade method is specifically disclosed as a molding method of the molded article, and the extrusion molding merely refers to its name, and there is no specific disclosure.

In the sheet forming by the doctor blade method, which is the only forming method specifically disclosed in the above publication,
By extracting the slurry into a sheet having a thickness of about 100 μm, the columnar particles are two-dimensionally oriented in a plane parallel to the sheet surface, but it is difficult in principle to orientate one-dimensionally, that is, uniaxially. There was a limit to the improvement in strength, toughness and thermal conductivity in the orientation direction.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a highly-oriented silicon nitride sintered body which achieves a high degree of uniaxial orientation, thereby significantly improving strength, toughness and thermal conductivity in the orientation direction, and a method for producing the same. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided, according to the present invention, a mixture of β-silicon nitride columnar particles and α-silicon nitride spherical particles in which the proportion of α-silicon nitride spherical particles is 5 to 95 wt%. A sintering aid is added to the mixture thus mixed to form a forming raw material, and the forming raw material is extruded to produce a formed body in which β-silicon nitride columnar particles are uniaxially oriented, and firing the formed body. This is achieved by a method for producing a highly oriented silicon nitride sintered body characterized by the following.

In the method of the present invention, a mixture of columnar particles of β-silicon nitride and spherical particles of α-silicon nitride to which a sintering aid is added is extruded to form a mixture of β-silicon nitride in a molding process. The columnar particles are uniaxially oriented. When the extruded body in this state was fired under the conditions generally used, the β-silicon nitride columnar particles were uniaxially oriented in the same direction as the molding due to the sintering process including the transition from α-silicon nitride to β-silicon nitride. A highly oriented silicon nitride sintered body is obtained.

As described above, in the present invention, it is very important that β-columnar particles are highly uniaxially oriented at the molding stage by using extrusion molding as the molding means.
Before extrusion, the β-columnar particles are in a non-oriented state in which random directions are oriented inside the forming raw material. When this is extruded, a resistance force from a mold acts on the flow of the molding raw material generated by the extrusion, so that a flow velocity gradient or a flow velocity distribution is generated along the transverse direction of the flow.

[0010] Macroscopically, the flow of the molding material has the lowest flow velocity because the flow of the molding raw material is directly resisted by the molding die at the side edge in contact with the molding die. Since the action of the resistance force from the mold is reduced, the flow velocity is increased. When the action of the resistance force from the mold reaches the center of the flow, the flow velocity distribution in which the flow velocity continuously increases from the side edge of the flow to the center, that is, a mountain-shaped flow distribution with a peak at the center become.

In a flow having such a flow velocity distribution, columnar particles inclined with respect to the direction of flow have a slow progress at the particle end near the side edge of the flow, whereas the center of the flow has The movement of the particle end near the part becomes faster, and eventually the direction of the particle is deflected in the direction of the flow as the flow proceeds.
In this way, the orientation of all columnar particles in the flow is deflected in the direction of the flow. As a result, a state is achieved in which the β-columnar particles are uniaxially oriented in the extrusion direction (flow direction) inside the extruded molded body.

The orientation effect by the extrusion molding used in the present invention is significantly different from the orientation effect by the doctor blade method used in the prior art described in the above publication in the following points.
First, the state of the forming raw material used in the doctor blade method is a slurry, which is not a state capable of maintaining a constant shape against its own weight and being self-sustaining, but a state closer to a liquid rather than a solid. On the other hand, the state of the molding raw material used in the extrusion molding method is, for example, a state in which it is harder than the clay at the time of potter's wheel molding, maintains a certain form against its own weight and can stand alone, and can be said to be almost solid. is there.

As described above, since the state of the forming raw material is largely different, a large difference occurs in the deflection force acting on the columnar particles in the flow of the forming raw material. That is, in the doctor blade method, since the slurry-like raw material in a state close to a liquid is merely applied to the blade in an open state without particularly pressurizing tightly, the resistance force acting on the flow is substantially the thickness of the flow from the blade. Direction, and there is no deflecting force acting in the width direction of the flow.
Although the formed sheet is two-dimensionally oriented along the sheet surface, it is not one-dimensionally or uniaxially oriented to further deflect the inclination of the columnar particles in the plane along the sheet longitudinal direction. This is the biggest difference from the extrusion molding used in the present invention.

Further, since the slurry close to the liquid is merely applied to the blade in the released state as described above, the resistance acting on the flow of the slurry from the blade is small. for that reason,
The flow velocity gradient is generated only in a very thin surface layer that comes into contact with the wall of the blade or the like, and the deflection force based on the flow velocity gradient is rapidly reduced when leaving the surface layer. As a result, the thickness of the sheet must be very small in order to reliably orient it to the center of the thickness of the formed sheet. In the example described in the above-mentioned publication, the formed sheet is as thin as 150 μm.

On the other hand, the extrusion molding used in the present invention is:
A hard molding material in a state close to a solid is placed in a molding die, and a force large enough to extrude the hard material is applied in a state that can be said to be a pseudo-closed state in which the extrusion port is closed with the molding material itself. Therefore, the resistive force from the mold effectively acts not only in the thickness direction of the flow but also in the width direction, and one-dimensional orientation, that is, uniaxial orientation, is achieved along the flow direction.

Further, since the hard molding material is loaded in a pseudo closed state as described above, the resistance acting on the flow of the molding material from the molding die can be greatly increased, and the surface layer of the flow can be increased. The flow velocity gradient can be formed not only at the center but also at the center. As a result, if the thickness is up to 3 mm, a high degree of uniaxial orientation with an orientation degree of 70% or more can be obtained.

As described above, the method of the present invention using extrusion molding can achieve a high degree of orientation as compared with the conventional method using a doctor blade method. Also, in the doctor blade method, it is necessary to control the molding conditions including temperature control, viscosity control, concentration control, etc. of the slurry very strictly, but such complicated control is not required in extrusion molding. This is also a great practical advantage.

In order to realize the uniaxial orientation of β-columnar particles by the extrusion molding of the present invention, the ratio of α-sphere particles in the mixture of β-columnar particles and α-spherical particles should be within the range of 5 to 95% by weight. There is a need to. In extrusion molding raw materials, which are merely mixtures, the β-columnar particles are entangled with one another in random directions. In order for the β-columnar particles to be uniaxially oriented by extrusion, it is necessary to disentangle the β-columnar particles. This entanglement becomes stronger as the density of the β-columnar particles increases, and it becomes difficult to unravel. β-columnar particles mixed with α-spherical particles
By diluting the existing density of the columnar particles to a certain level or less, the entanglement is reduced, and it becomes easy to disentangle.
As described above, in order to facilitate the untangling of the entanglement of the β-columnar particles and to realize the uniaxial orientation by extrusion, the proportion of the α-spherical particles needs to be 5% by weight or more. On the other hand, to the extent that a high degree of uniaxial orientation can be obtained by firing, to perform uniaxial orientation of β-columnar particles in the molding stage,
It is necessary that at least 5 wt% of β-columnar particles be present in the forming raw material, that is, the proportion of α-spherical particles must be at most 95 wt%.

In the present invention, a silicon nitride sintered body having a degree of orientation of 70% or more can be obtained by setting the proportion of α-silicon nitride spherical particles in the forming raw material in the range of 5 to 95% by weight. Further, the ratio of α-silicon nitride spherical particles is 20 to
If it is limited to 80% by weight, an orientation degree of 80% or more can be secured. As for the extrusion conditions, an extrusion mold having an extrusion opening thickness of 3 mm or less and an extrusion opening length of 5 mm or more is used to perform extrusion molding at an extrusion speed of 5 cm / min or more to secure an orientation degree of 70% or more. can do. Furthermore,
If the extrusion speed is limited to 40 cm / min or more, the degree of orientation is 80
% Or more can be secured.

According to the method of the present invention, the β-silicon nitride columnar particles have an orientation degree of 70% or more and a thermal conductivity of 100 W / m ·
A highly oriented silicon nitride sintered body having a temperature of K or more can be manufactured. Heat conduction is realized by conduction electrons in metals, but ceramic sintered bodies are ionic crystals or covalent crystals that have very few conduction electrons.
Heat conduction mainly by lattice vibration (phonon). If impurities, disordered crystal lattices, or pores are present in the ceramics, the scattering of phonons increases, causing a decrease in thermal conductivity. In the case of silicon nitride, in addition to the disorder of the crystal lattice, the amorphous phase in the grain boundary phase is a main factor in lowering the thermal conductivity. Therefore, by performing uniaxial orientation, the influence of the grain boundary phase is reduced particularly in the C-axis direction of the crystal, and the thermal conductivity is also improved.

Hereinafter, the present invention will be described in more detail by way of examples with reference to the accompanying drawings.

[0022]

EXAMPLE According to the present invention, a silicon nitride sintered body was manufactured in the following procedure. (1) Preparation of β-Si ₃ N ₄ columnar particles Si ₃ N ₄ powder (purity 99% or more) produced by the thermal decomposition method of silicon diimide or the nitriding method of metallic silicon,
Y ₂ O ₃ powder (average particle size 0.3 μm, purity 9
(9.9%) was added and mixed and pulverized at 60 rpm for 72 hours in a Si ₃ N ₄ ball mill using ethyl alcohol as a solvent.

After the ethyl alcohol is removed by evaporation in a hot water bath at 90 to 95 ° C., drying is performed at 90 ° C. × 20 hours with a dryer, and then crushed in a mortar made of Al ₂ O ₃ to obtain an opening of 425 μm.
Was adjusted to a particle size that passes through the mesh. This powder was packed in a firing vessel to a thickness of about 1 cm, and 0.93 MPa of N ₂
It was fired at a predetermined temperature in the range of 1600 ° C. to 1850 ° C. for 4 hours in a gas atmosphere to obtain β-Si ₃ N ₄ columnar particles.

Next, individual particles were separated by treatment with hydrofluoric acid. (2) Preparation of forming raw material Commercially available α-Si ₃ N ₄ spherical particles (purity: 99%) were added at various ratios to the above β-Si ₃ N ₄ columnar particles, and further, The same Y ₂ O ₃ powder and Mg ₂ Al ₂ O ₄ powder (average particle size 0.3 μm, purity 99.9%) as above were added, and mixed and mixed using a 5.3 mm Si ₃ N ₄ ball in a polypot. After removing the alcohol, it was dried to obtain a mixed powder. A binder (mainly methylcellulose, 20
wt.) and water (30 wt.%) were added and kneaded with a double-arm kneader to obtain a forming raw material.

(3) Extrusion molding Extrusion was performed using a cylinder type extruder capable of changing the extrusion speed in a wide range. Extrusion speed is 4-490cm
/ Min range. As a molding die, various types of dies having an extrusion port thickness of 0.5 to 4 mm and an extrusion port length of 4 to 300 mm were used, and were extruded into a flat plate as shown in FIG.

(4) Firing The extruded product is laminated to a predetermined thickness and pressure-bonded.
After drying for 12 hours, a degreasing treatment was performed at 500 ° C for 2 hours. In a 0.93 MPa N ₂ gas atmosphere,
40 MPa at a predetermined temperature in the range of 1600 to 1900 ° C.
Hot press sintering was performed by applying pressure.

The degree of orientation, strength,
Fracture toughness (K _IC ) and thermal conductivity were measured. The degree of orientation was determined from the X-ray diffraction result of a plane perpendicular to the C-axis of the sintered body according to the following equation. Degree of orientation = (P−P ₀ ) / (1−P ₀ ) where: P: ratio of X-ray diffraction intensities of (002 plane) and (101) plane of sample; P ₀ : as reference sample not oriented The ratio of the X-ray diffraction intensities of the (002) plane and the (101) plane of the β-Si ₃ N ₄ powder, both of which are defined by the following equations.

P and P ₀ = (I ₍₀₀₂₎ + I ₍₁₀₁₎ ) /
(I ₍₀₀₂₎ + I ₍₂₀₀₎ + I ₍₂₁₀₎ + ₍₂₀₁₎ + I ₍₃₀₁₎ +
I ₍₁₀₁₎ ) The strength and fracture toughness (K _IC ) were measured in the extrusion direction (orientation direction) by a four-point bending test using a test piece of t3 × W4 × L36 cut in parallel with the extrusion direction. .

The thermal conductivity of a sample of φ10 × t3 was used.
The value in the extrusion direction (orientation direction) was measured. Table 1
The composition of the forming material within the specified range of the present invention and the highly oriented sample prepared under the desired extrusion molding conditions, the composition of the molding raw material, the extrusion molding conditions, the sintering temperature, and the above-described measured characteristic values are shown together. .

Table 2 shows the same items for low-orientation samples prepared outside the specified range of the composition of the present invention or outside the range of desirable extrusion molding conditions. The sample No. in Table 2
Nos. 8, 9, and 10 are formed by die press molding instead of extrusion molding.

[0031]

[Table 1]

[0032]

[Table 2]

In the highly oriented sample shown in Table 1, 71% to 9%
A high degree of orientation of 6% was obtained, and a four-point bending strength of 880.
K _IC 12.0-14.
A combination of a high level of strength and toughness of ¹ MPam ^1/2 has been obtained. In particular, as seen in Sample Nos. 9 and 10, strength exceeding 1300 MPa and 12 MPam ^1/2
A silicon nitride sintered body simultaneously exhibiting a toughness exceeding the above has not been reported so far, and has been achieved for the first time by the present invention. The thermal conductivity is also 106 to 154 W / m.
-A high value of K is obtained. This is equivalent to 3 to 4 times the thermal conductivity obtained with the conventional unoriented silicon nitride sintered body. Conventionally, there has been reported an example in which coarse particles are formed by sintering at 2000 ° C. or higher to obtain a thermal conductivity of 120 Wm · K. However, in the present invention, sintering at 1800 to 1900 ° C. is performed by highly uniaxial orientation. Even so, a high thermal conductivity can be obtained as described above.

On the other hand, in the low-orientation sample of Table 2, the composition of the molding raw material is out of the specified range of the present invention, the extrusion molding condition is out of the desirable range of the present invention, or the present invention is not specified. Because of the use of press molding instead of extrusion, the degree of orientation is as low as 40 to 70% and the strength is equivalent to the highly oriented sample, but the toughness is as low as 5.9 to 8.3 MPam ^1/2, and the high strength and high toughness are obtained. Cannot be expressed simultaneously. The thermal conductivity is also a low value of 53 to 88 W / m · K.

FIG. 2 shows that β-Si ₃ N ₄ columnar particles and α-Si ₃ N ₄
The relationship between the mixing ratio (addition amount) of α-Si ₃ N ₄ spherical particles in the mixed powder with the spherical particles and the degree of orientation of the sintered body is shown. The extrusion conditions were as follows: extrusion port thickness 1 mm, extrusion port length 100 mm, and extrusion rate 490 cm / min. As shown in FIG.
-Si ₃ N ₄ without adding spherical particles (mixing ratio = 0) β-Si ₃ N
_In the case of only _four columnar particles, the degree of orientation is as low as 55%,
When 5 wt% of α-Si ₃ N ₄ spherical particles are added, a high degree of orientation of 78% can be obtained. The degree of orientation reaches a maximum of 93% when the mixing ratio of the α-Si ₃ N ₄ spherical particles is 50% by weight, and the degree of orientation decreases as the mixing ratio is further increased. If it exceeds, it decreases rapidly.

From this result, the mixing ratio of α-Si ₃ N ₄ spherical particles most suitable for orientation is 50 wt%. α-
If the mixing ratio of the Si ₃ N ₄ spherical particles is too small, β-Si ₃ N ₄
Since the entanglement between the columnar particles is not sufficiently unraveled and extruded while leaving the entangled state, the degree of orientation is low. Conversely, if the mixing ratio of α-Si ₃ N ₄ spherical particles is too large, β-Si ₃ N
_{(4) The} columnar particles are uniaxially oriented at the time of extrusion, but the amount is too small.Therefore, the influence on the transition and growth of the α-Si ₃ N ₄ spherical particles during firing is small, and the α-Si ₃ N ₄ spherical particles can be oriented in any direction. Therefore, the degree of orientation after sintering becomes low.

Generally, in the sintering process of silicon nitride, α-Si ₃ N
₄ dissolves, after precipitated as β-Si ₃ N _4, are believed to beta-Si ₃ N ₄ grain growth of the particles occurs as a driving force reduction in free energy due to metastasis. Also, the grown β
-Si ₃ N ₄ particles is believed to further grow while absorbing a portion around the α-Si ₃ N ₄ particles. In the present invention,
Β-Si ₃ N ₄ particles present in the molded body surrounding α-Si ₃ N ₄
It is considered that the particles grow while absorbing some of the particles. Other α-Si ₃ N ₄ particles have β-Si ₃ N ₄ on the surrounding β-Si ₃ N ₄ columnar particles.
It is considered that Si ₃ N ₄ precipitates and grows in the same direction while the growth direction is restricted by the β-Si ₃ N ₄ columnar particles. Therefore, if the mixing ratio of α-Si ₃ N ₄ particles is too large, β-Si ₃ N ₄ columnar particles that are present first are small,
It is considered that the influence of restricting the growth direction is small and the degree of orientation is low.

As described above, in order for the columnar particles to be uniaxially oriented by extrusion, it is important to generate an appropriate flow in the molding material and to transmit the resistance to the mold to the center of the flow. is there. Among the molding conditions, the influence of the extrusion speed is particularly strong, and the higher the extrusion speed, the higher the degree of orientation. In addition, the shape of the mold is also important. If the thickness of the extrusion port is too large, the resistance with the mold is not transmitted to the center of the flow, and the degree of orientation decreases. Also, the longer the extrusion opening length, the higher the resistance and the higher the degree of orientation.

FIG. 3 shows the relationship between the extrusion speed and the degree of orientation. α-Si ₃ N ₄ mixing ratio 50wt%, extrusion port thickness 1m
m and the extrusion opening length were 100 mm, respectively, and the extrusion speed was changed in the range of 4 to 490 cm / min. From the results shown in the figure, an orientation degree of 70% or more can be obtained at an extrusion rate of 5 cm / min or more, and an orientation degree of 80% or more can be obtained if the extrusion rate is limited to 40 cm / min.

From the results obtained so far including this example, the optimal extrusion conditions were an extrusion speed of 350 cm / min or more, an extrusion port thickness of 1 mm, and an extrusion port length of 100 mm. The higher the extrusion speed, the higher the degree of orientation improves. However, as can be seen from FIG. 3, at 350 cm / min or more, the improvement in degree of orientation saturates. The degree of orientation increases as the extrusion opening thickness decreases, but if it is too small, the extrusion resistance becomes too large and extrusion itself becomes difficult. In addition, about the extrusion port length, length 300mm
Even if the length was increased, the degree of orientation obtained was equivalent to that of 100 mm.

FIG. 4 shows a typical uniaxially oriented structure of a highly oriented silicon nitride sintered body according to the present invention. (A) in the figure is a cross section perpendicular to the C axis (extrusion direction), and (B) is a cross section parallel to the C axis. It can be seen that the structure is highly uniaxially oriented along the C axis.

[0042]

As described above, according to the present invention,
By providing a high degree of uniaxial orientation, a highly oriented silicon nitride sintered body having significantly improved strength, toughness, and thermal conductivity in the orientation direction and a method for producing the same are provided. In particular, by setting the proportion of the α-silicon nitride spherical particles in the forming raw material in the range of 5 to 95 wt% with respect to the total amount of the β-particles and the α-particles, the silicon nitride sintered body having an orientation degree of 70% or more And a ratio of α-silicon nitride spherical particles of 20 to 8
If it is limited to 0 wt%, an orientation degree of 80% or more can be secured.

The extrusion conditions were as follows: an extrusion mold having an extrusion opening thickness of 3 mm or less and an extrusion opening length of 5 mm or more was used and extrusion was performed at an extrusion speed of 5 cm / min or more to obtain an orientation degree of 70%. The above can be secured. Furthermore,
If the extrusion speed is limited to 40 cm / min or more, the degree of orientation is 80
% Or more can be secured. According to the method of the present invention, the β-silicon nitride columnar particles have an orientation degree of 70% or more and a thermal conductivity of 100%.
A highly oriented silicon nitride sintered body having W / m · K or more can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration of an extruder used for extrusion of the present invention.

Figure 2 shows the relationship between the degree of orientation of β-Si ₃ N ₄ particles and _{α-Si 3 N 4 α-} Si 3 N 4 particles mixing ratio and sintered body of the mixed powder of particles It is a graph.

FIG. 3 is a graph showing a relationship between an extrusion speed and a degree of orientation of a sintered body.

FIGS. 4A and 4B show a typical uniaxially oriented structure of a highly oriented silicon nitride sintered body according to the present invention (A).
It is a micrograph of the cross section perpendicular | vertical to a C-axis and (B) the cross section parallel to a C-axis.

Claims (5)

[Claims] The ratio of α-silicon nitride spherical particles to α-silicon nitride spherical particles is 5 to 95% by weight.
A sintering aid is added to the mixture mixed so as to obtain a molding raw material, and the molding raw material is extruded to form a β-
A method for producing a highly oriented silicon nitride sintered body, characterized in that a molded body in which columnar particles of silicon nitride are uniaxially oriented is produced, and the molded body is fired. 2. The method according to claim 1, wherein the ratio of the α-silicon nitride spherical particles is 20.
2. The method according to claim 1, wherein the amount is about 80% by weight. 3. The extrusion molding according to claim 1, wherein the extrusion molding is performed at an extrusion speed of 5 cm / min or more using an extrusion die having an extrusion opening thickness of 3 mm or less and an extrusion opening length of 5 mm or more. The described method. 4. The method according to claim 3, wherein the extrusion speed is 40 cm / min or more. 5. The highly oriented silicon nitride sintered body produced by the method according to claim 1, wherein the β-silicon nitride columnar particles have an orientation degree of 70% or more and a thermal conductivity of at least 70%. Is 100 W / m · K or more.