JPH0361006A - Molding method of polysilazane - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a method for manufacturing thin-walled hollow articles of polysilazane, which is a precursor of silicon nitride or silicon nitride and silicon carbide mixed ceramics.

[Conventional technology]

Polysilazane is a polymeric compound consisting of silicon, nitrogen and hydrogen, and in some cases further containing carbon, and is generally obtained as a liquid with a molecular weight of 200 to 800 immediately after exposure. This liquid polysilazane becomes solid when heated.

For example, in the case of inorganic polysilazane (IlzSiNII)n, when solid polysilazane is heated while increasing the temperature, thermal decomposition begins at around 150°C and usually ends at around 600°C. What is obtained by this thermal decomposition is amorphous silicon nitride, which is
A sintered body made of α-silicon nitride and metallic silicon can be obtained by heat treatment at a temperature of 1800° C or higher. If the process is carried out in a nitrogen gas atmosphere, a sintered body having a single phase of α-nitrogen silicon can be obtained.

On the other hand, from (CH:+5illNH)n, a sintered body made of silicon nitride and silicon carbide can be obtained by the same treatment.

By the way, it is relatively recently that polysilazane has started to attract attention as a raw material for Ceralinks, and as far as the present inventors know, there is no literature regarding a method for molding polysilazane.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for obtaining a molded article of relatively uniform thickness from liquid polysilazane.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the inventors of the present invention found that
It has been found that when polysilazane is held at a temperature of 100''C or higher, polymerization proceeds and a viscous liquid is obtained, allowing plastic molding.

The present invention has been made based on this knowledge, and is made by heating a liquid polysilazane tube containing ceramic powder or ceramic precursor in an amount of 30% or less by weight to obtain a soft material having a viscosity coefficient of 104 poise or more and 106 poise or less. The soft tube is made into a tube, the diameter of the soft tube is expanded, the soft tube is brought into close contact with a mold, and the soft tube is hardened by heating.

Liquid polysilazane is H2S1C1, Ih5iCI, R5
It can be manufactured from a silane compound such as 1llCIz. R in the above organic silane compound is a methyl group, an ethyl group, a vinyl group, a phenyl group, or the like. Polysilazane is produced by diluting the above-mentioned silane compounds alone or as a mixture in a solvent such as benzene, diethyl ether, dichloromethane, tetrahydrofuran, pyridine, etc. and contacting this solution with liquid or gaseous ammonia. Liquid polysilazane is obtained by filtering off the by-product ammonium chloride and distilling off the solvent.

There are many types of liquid polysilazane produced in this way, and even if the starting materials are the same, the substances produced differ depending on the solvent, temperature, pressure of ammonia, etc.

As a typical polysilazane (Hz SiN H)
xC(Hz S i ) + , s N ) y, (
CH3(CH3NH)Si (CH3N))X, (CH
3Si (CH3N)+, s ))'-(CH3SiH
NH)X (C)iasiHNCH3) V (CH3
S i N ) z and the like.

The liquid polysilazane may be used alone, or it may be mixed with a ceramic powder or a ceramic precursor other than polysilazane up to a maximum of 30% by weight. The purpose of mixing is to accelerate sintering, improve the properties of the ceramic sintered body, improve dimensional accuracy by reducing shrinkage during thermal decomposition and sintering. The ceramics added for the above purpose are oxide powders such as ittria, alumina, magnesia, ceria, scandia, and zirconia as sintering aids, and nitrides such as aluminum nitride to improve the high-temperature strength of the sintered body. These include powder and carbide powder such as silicon carbide, silicon carbide whiskers for improving toughness, and conductive ceramic powder such as titanium carbide and titanium nitride for imparting conductivity. These may be added in the form of precursors that are converted into ceramics by pyrolysis. For example, silicon carbide precursors include polysilastyrene and polycarbosilane, alumina precursors include boehmite and argos nitrate, yttrium precursors include yttrium nitrate, and carbon precursors include sinter. There are phenolic resins that sometimes react with silicon nitride and convert it into silicon carbide.

If the content of these additives exceeds 30% by weight, the deformability of the compound decreases, and cracks are likely to occur in the polysilazane soft tube during molding, which will be described later.

First, such a liquid polysilazane is coated with a thickness of 0.1 mm or more.
Cast into a tube shape with a thickness of approximately 0 mm or less. 0.1
If it is less than mm, cracks are likely to occur in the soft tube during molding, which will be described later. On the other hand, if it exceeds 30 mm, the deformation resistance of the tube is too large, resulting in insufficient adhesion to the mold and poor transferability. .

Polysilazane cast into a tube-shaped mold does not have sufficient shape retention as it is, so if it is released from the mold as it is, it will drip and change the thickness of the tube. To avoid this, the tube is heated to advance polymerization, and the viscosity coefficient is 104.
After adjusting the poise to 106 poise or less, the mold is released to obtain a gelatinous soft tube. If it is less than 104 poise, dripping cannot be sufficiently prevented. On the other hand, if it exceeds 106 poise, the deformation resistance increases and adhesion to the mold becomes insufficient. The heating time to achieve the above-mentioned viscosity is longer as the temperature is lower, and needs to be shortened as the temperature is raised, and also varies depending on the thickness of the soft tube. That is, the thinner the film, the shorter the time required, and the thicker the film, the longer the time required. Therefore, although it cannot be determined unambiguously, the heating temperature 6, which is set according to the thickness so that the heating time is within one hour, preferably within five minutes, is suitably in the range of 100 to 300'C. If the heating temperature is less than 100°C, it will take too long. On the other hand, 300
'C is exceeded, thermal decomposition of polysilazane increases. As a result, air bubbles form on the surface and inside of the soft tube.
This creates pores on the surface and inside of the sintered body as a final product.

The mold having a bottom shaped like a soft tube may be a cavity with one end open and the other end closed, or may be a cavity with both ends open. Each mold consists of an inner mold and an outer mold. In the former case, a test tube-shaped soft tube is obtained, and in the latter case, a soft tube with both ends open is obtained. The mold shall be equipped with a heating device. It may be a heater for electric heating, or a tube or jacket for circulating the heat medium.

Insert the soft tube between molds and make the internal pressure of the soft tube 0.1 kg/cm2 or more 10 kg/cm higher than the external pressure.
Increase the value to 2 or less and expand the tube by internal pressure.

If the differential pressure between the inner and outer surfaces of the tube is less than 0.1 kg/cm2, the tube will not adhere sufficiently to the mold, and as a result,
Transferability deteriorates. The larger the differential pressure between the inner and outer surfaces of the tube, the shorter the time required for the tube to adhere, which increases productivity by 1. Close contact ends instantly.

Although the external pressure may remain at atmospheric pressure, it is more effective to evacuate the inside of the mold.

The temperature of the mold is maintained at a certain temperature of 100°C or more and 300°C or less. If it is less than 100"C, it will take too long for the polysilazane that adheres to the mold to harden. On the other hand, if it is heated at 300"C
If the temperature exceeds this value, the thermal decomposition of the polysilazane increases and bubbles are generated on the surface and inside of the tube, which remain as pores on the surface of the sintered body as a final product.

The means for heating the mold is not particularly limited. Electric heating may be performed by embedding or attaching an electric heater in the mold, or heating by a heating medium may be performed by embedding a tube through which a heating medium is passed in the mold or attaching a jacket. The heating time is until the soft tube is thermally hardened to a predetermined degree.

It goes without saying that the mold may have a complex shape with unevenness or the like.

The materials of molds and molds are mild steel, aluminum alloy,
Zinc alloy, cast iron, beryllium steel, stainless steel, high-speed steel, die m': γ metal, silicone rubber, heat-resistant rubber such as fluororubber, plastic such as phenol resin, plaster, or wood may also be used.

Provide vent holes to allow air to escape if necessary.

Alternatively, the mold may be made of porous material. Gypsum can be used for this purpose, but since it has low strength and is easily chipped, other materials such as porous resin, porous sintered metal, porous ceramics, etc.
Stronger materials may also be used.

A sintered body can be obtained from the thermoset tube by, for example, sintering it under the above-mentioned known conditions.

[Function] Liquid polysilazane alone or containing 30% by weight or less of ceramic powder or ceramic precursor is formed into a tube and heated to advance polymerization of the polysilazane to increase viscosity and ensure shape retention. If the number of viscous bodies in the resulting soft tube is less than 104 poise, the shape retention will be insufficient, while if it exceeds 106 poise, the deformation resistance will be large and the moldability of the soft tube will be insufficient to allow it to adhere tightly to the mold.

Therefore, the heating temperature and time of the tube cast into the mold are adjusted so that the viscosity coefficient falls within the above range. After molding with a mold, a polysilazane molded article of a predetermined shape can be obtained by heating to further advance polymerization.

〔Example〕

Example 1 A tube mold with one end open and the other end closed, consisting of an inner mold 1 and an outer mold 3 divided into two, as shown in FIG. 1, was used.

The inner mold 1 is made of porous alumina with an average pore diameter of 25 μm and a porosity of 35%, and has a cylindrical shape with an inner diameter of 20 mm, an outer diameter of 40 mm, and a length of 150 m with the upper end closed in a substantially hemispherical shape.
On the other hand, the outer mold 3 is made of aluminum and has a cylindrical shape with a similar-shaped hole that is one size larger than the inner mold 1, and has an electric heater built therein. The distance between inner mold 1 and outer mold 3 is 12TffI
11, which is cavity 4. This mold was attached to a machine stand 5, and the outer mold 3 was heated to 200°C using an electric heater 2.

The mold 8 is a two-part mold made of aluminum and has a built-in electric heater. The cavity has a substantially round bottle shape, with a total length of 170 mm and a diameter of the large diameter portion of 150 mm. This mold 8 was also heated in advance to 200° C. by energizing the electric heater.

First, liquid inorganic polysilazane (H2SiC1□ and NH,
(reaction product) was injected into the mold through the injection port 6 shown in FIG. After heating and holding for 5 minutes to form a soft tube, the outer mold 3 was immediately removed and a mold 7 was attached. This state is shown in FIG. Next, from the press inlet 9 to the inside of the inner mold 1 6
The diameter of the soft tube was expanded by introducing compressed air of Kg/cm2, and the soft tube was brought into close contact with the mold 7, and heated and held for 10 minutes to harden it. After the supply of compressed air was stopped and the pressure returned to atmospheric pressure, the mold 8 was removed, and a hardened molded body 12 was obtained as shown in FIG.

This molded body 12 was placed in a sintering furnace, and the pressure was 9.5Kg/cm.
20'C/20°C from room temperature to 200°C in a nitrogen atmosphere of 2.
min, 2° from 200°C to 60°C (:/min
When the temperature was raised from 600°C to 1750°C at a rate of 20°C/min and allowed to cool, a silicon nitride sintered body whose outer diameter had uniformly shrunk to 108 mm was obtained. The density of this sintered body was 89.5% of the theoretical density.

Example 2 Liquid inorganic polysilazane (Hz S i Cl□ and N 1
-13 reaction product) Average particle size 0.1 per 100 parts
2.1 parts of 5μm alumina powder, average particle size 0.12μm
6.2 parts of ittria powder were stirred and mixed for 5 hours and defoamed under vacuum to obtain a liquid polysilazane mainly composed of inorganic polysilazane oil.

As shown in FIG. 4, a split mold 10 having a cylindrical cavity 4 with an inner diameter of 40 mm, a thickness of 12 mm, and an open bottom end and an electric heater 2 is installed in the mold installation space on the upper part of a machine stand 5 having a nozzle 11. I opened it and installed it.

This mold IO was heated and maintained at 160°C. The mold 8 shown in FIG. 5 had a cylindrical cavity with an inner diameter of 150 mm, a total length of 120 mm, and a bowl-like shape with a flat ceiling and a shallow bottom. This mold 8 is a two-part mold made of aluminum and has an electric heater 7 built therein. The mold 8 was also heated to 200°C in advance.

First, the inorganic polysilazane was injected into the mold through the injection port 6 shown in FIG. The mixture was heated and held for 10 minutes to form a soft tube, and the subsequent liquid inorganic polysilazane was supplied from the injection port 6 to extrude the previous jelly-like inorganic polysilazane soft tube 12. Next, the nozzle 11 is raised, the mold 8 is attached to seal the upper part of the soft tube 12, and the nozzle 11 is immediately removed.
Compressed air of 6 Kg/cm" was introduced and held for 10 minutes. Next, the supply of compressed air was stopped and the pressure was returned to atmospheric pressure. After that, the nozzle 11 was lowered and the mold 8 was removed.
As shown in FIG. 6, a cured molded body 13 was obtained.

The upper part of the molded body was cut and placed in a sintering furnace under a pressure of 9.5 kg.
/cm2 nitrogen atmosphere from room temperature to 200°C.
°C/min, 2°C/min from 200°C to 600″C
min, 20°C/m from 600°C to 1750°C
When the temperature was raised at a rate of in and left to cool, the outer diameter was 105 mm.
A silicon nitride 3 sintered body which had uniformly shrunk was obtained. The density of this sintered body is 97% of the theoretical density.
．． It was 0%.

〔Effect of the invention〕

As described above, according to the present invention, liquid polysilazane is poured into a heated mold and heated to form a highly viscous soft tube, which is then brought into close contact with the heated mold, so that it is relatively uniform. It is possible to easily obtain a molded article made of a transfer material having a uniform thickness, which is homogeneous, and has few defects.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the state in which a soft tube is being manufactured in an embodiment of the present invention, and Fig. 2 shows the state in which the outer mold of the mold is removed and the mold is attached to begin diameter expansion and heat curing. It is a sectional view showing the state just before. FIG. 3 is a sectional view showing a state in which thermosetting has been completed. Fig. 4 is a cross-sectional view showing the soft tube being produced in another example, and Fig. 5 shows the soft tube being extruded from the mold and the mold being attached, just before diameter expansion and heat curing. It is a sectional view showing a state. FIG. 6 is a sectional view showing the fourth state after thermosetting.

Claims (1)

[Claims] A liquid polysilazane tube containing a single substance or 30% by weight or less of ceramic powder or ceramic precursor is heated to form a soft tube with a viscosity coefficient of 10^4 poise or more and 10^6 poise or less, and the soft tube is expanded in diameter and formed. A method for molding polysilazane, characterized by adhering it to a mold and curing it by heating.