JP2001072472A - Jig for burning silicon carbide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a jig for burning silicon carbide, scarcely producing coarse particles of silicon carbide on the surface when burning and capable of repeatedly using. SOLUTION: This jig is a plate-like jig for burning composed of a carbon material used when degreasing columnar silicon carbide forming product in which many through holes are arranged side by side in longitudinal direction at a distance from partition wall and then burning the forming product and the carbon material has 30-60% porosity. In the jig, a processing is preferably applied so as to leave a belt-like or rectangular protruded part 15 when viewed in a plane onto a face placing the silicon carbide forming product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a jig for firing a columnar silicon carbide molded body having a large number of through holes arranged in a longitudinal direction.

[0002]

2. Description of the Related Art Recently, it has become a problem that particulates contained in exhaust gas discharged from internal combustion engines such as vehicles such as buses and trucks and construction machines cause harm to the environment and human bodies. Various ceramic filters have been proposed which purify the exhaust gas by collecting the particulates in the exhaust gas by passing the exhaust gas through a porous ceramic.

In general, a ceramic filter 20 is formed by bundling a plurality of porous ceramic members 30 as shown in FIG. As shown in FIG. 4, the porous ceramic member 30 has a large number of through holes 31 arranged in a longitudinal direction, and a partition wall 33 separating the through holes 31 functions as a filter.

[0004] That is, as shown in FIG. 4B, the through hole 31 formed in the porous ceramic member 30 has a filling material 3 at either the inlet or outlet end of the exhaust gas.
The exhaust gas plugged by 2 and flowing into one through hole 31 always passes through a partition wall 33 separating the through hole 31,
When the exhaust gas passes through the partition wall 33, the particulates are captured at the partition wall 33 and the exhaust gas is purified. Among such porous ceramic members 30, particularly, a silicon carbide porous member is extremely excellent in heat resistance and easy to regenerate, so that it is used for various large vehicles and the like.

Conventionally, when producing such a silicon carbide porous member, first, a ceramic powder, a binder, and a dispersion medium are mixed to prepare a mixed composition for producing a molded body, and then the mixed composition is prepared. By extruding the composition, etc.,
A silicon carbide compact is produced.

Then, the obtained silicon carbide molded body is dried using a heater or the like to obtain a dried silicon carbide molded body 40 shown in FIG. 5 which has a certain strength and can be easily handled. To manufacture. After this drying step, by heating the silicon carbide molded body 40 to 400 to 600 ° C. in an oxygen-containing atmosphere, a solvent in the organic binder component is volatilized, and a degreasing step of decomposing and eliminating the resin component is performed. Subsequently, a firing step of sintering the degreased silicon carbide molded body (hereinafter, referred to as a degreased molded body) was performed to manufacture the silicon carbide porous member 30.

Usually, in the degreasing step, the silicon carbide compact 40
After being placed on a jig such as a plate-shaped body and carried into a degreasing furnace, degreasing is performed.Then, the molded body after the degreasing step is carried as it is to a firing furnace, and in an inert gas atmosphere,
It was fired by heating to 2000 to 2200 ° C. In the above process, the jig used to place the silicon carbide molded body 40 needs to be a material having characteristics that can withstand high temperatures in the firing process. As such a heat-resistant material, A carbon material having a dense structure has been used.

However, the firing process using a jig made of a carbon material having such a dense structure (hereinafter, referred to as a silicon carbide firing jig) has the following problems. That is, about 3% of SiO ₂ is contained in the silicon carbide powder due to the manufacturing conditions.
And the above-mentioned Si
O ₂ is sublimated and released, and the following reaction formula (1) of SiO gas and carbon constituting the jig for firing silicon carbide is used.

SiO + 2C → SiC + CO (1)

The reaction shown in [1] proceeds, and silicon carbide is generated on the surface of the jig for firing silicon carbide. Further, since the silicon carbide firing jig is dense, the SiO gas easily stays at the interface between the molded body and the jig, so that the generated silicon carbide is used as a seed crystal to coarsen the particles. Further, a phenomenon is also observed in which silicon carbide powder partially evaporates due to high temperature and recrystallizes on silicon carbide particles formed on the surface of silicon carbide. as a result,
Coarse particles were generated on the surface of the jig for firing silicon carbide, and the smoothness of the surface was lost. These coarse particles were often found in a portion where the silicon carbide compact and the jig for firing silicon carbide were in contact with each other.

In such a jig for firing silicon carbide having coarse particles of silicon carbide particles on its surface, when the silicon carbide compact is placed and the firing step is performed, the jig is caused by the coarse particles. The surface of the silicon carbide molded body is easily scratched, causing deterioration of the mechanical properties of the silicon carbide molded body. Also, silicon carbide generated on the surface of the silicon carbide firing jig is:
Extremely hard and difficult to remove,
It was difficult to reuse a conventional jig for firing silicon carbide.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in order to solve these problems, and it is difficult to form large particles of silicon carbide on the surface during firing, and it is possible to use silicon carbide for firing repeatedly. It is intended to provide a jig.

[0013]

SUMMARY OF THE INVENTION The present invention provides a jig for sintering silicon carbide in which a plurality of through-holes are degreased and fired after forming a columnar silicon carbide molded body which is juxtaposed in a longitudinal direction across a partition wall. A plate-like firing jig made of a carbon material used for the above, wherein the carbon material has a porosity of 30 to 60%.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a jig for firing silicon carbide of the present invention will be described.

The jig for firing silicon carbide according to the present invention is a plate-shaped firing jig made of a carbon material.
It has a porosity of 0-60%. A carbon material having a porosity in such a range easily passes SiO gas, and by using this carbon material, a SiO gas generated from a degreased molded body during firing and a jig for firing silicon carbide are constituted. It is possible to suppress the generation of coarse particles of silicon carbide on the surface of the jig for firing silicon carbide by reacting with carbon not only on the surface but also inside the surface.

If the porosity of the carbon material is less than 30%,
The generated SiO is difficult to pass through the jig for firing silicon carbide,
Since the silicon carbide firing jig easily stays on the surface, it is impossible to suppress the generation of coarse particles of silicon carbide on the surface of the silicon carbide firing jig. On the other hand, when the porosity exceeds 60%, the strength of the silicon carbide firing jig is reduced. Is reduced, and may not be used as a jig for firing silicon carbide.

The pore diameter of the pores of the carbon material is preferably as large as possible.
Those having a thickness of about 0 to 300 μm are used.

The carbon material constituting the silicon carbide firing jig is not particularly limited as long as it has a porosity in the above range, and examples thereof include porous carbon. Specific examples of the above porous carbon include:
For example, G100 (manufactured by Tokai Carbon Co., Ltd.), PC5060
G (manufactured by Tokai Carbon Co., Ltd.) and the like.

The jig for firing silicon carbide preferably has a groove formed on a surface on which the silicon carbide compact is placed. By performing the groove processing, coarse particles of silicon carbide are likely to be generated inside the groove because the SiO gas passes through the inside of the groove, but coarse particles of silicon carbide are hardly generated on the surface, and The formation of coarse particles on the surface of the silicon firing jig can be prevented.

The above groove processing is performed by forming a groove having a depth of 1.0 to 2.0 mm and a width of 1.0 to 2.0 mm by 0.5 to 1.5 mm.
It is preferable to apply at intervals.

Preferably, the jig for firing silicon carbide is processed so that a band-shaped or rectangular projection in plan view remains on the surface on which the silicon carbide molded body is placed. That is, in the present invention, when performing the groove processing, the groove width may be widened, and the groove processing may be performed such that the area of the protrusion that is not subjected to the groove processing is considerably smaller than the area of the groove. .

As shown in FIGS. 1A and 1B,
Instead of performing the groove processing on the plate-like silicon carbide firing jig 11, the protrusions on the sides (edges) are also cut so that only the band-shaped protrusions 15 in plan view remain in the portions away from the sides. Processing may be performed. The shape of the projection 15 is not limited to a band shape in plan view, and may be a rectangular shape in plan view.

That is, the remaining protrusions are portions on which the degreased molded body is placed. Therefore, the shape is not limited as long as the protrusion is formed in such a shape that they can be placed. To place the degreased molded body,
It is desirable that at least two protrusions are left.

By processing so that such projections remain, the contact area with the degreased molded body is also reduced, so that most of the SiO gas flows through portions other than the projections. Therefore, the surface of the projection is less likely to be roughened, and a decrease in the strength of the porous silicon carbide member to be manufactured can be more effectively prevented.

In sintering, the progress of sintering is considerably affected by the heat conduction by heat transfer at the projections and the heat conduction by radiation from portions other than the projections. Therefore, the thickness and the width (contact area) of the protrusion may be set in consideration of the thermal conductivity of the jig for firing silicon carbide and the firing conditions. A range from 10 to 10 mm is preferred.

Further, as described above, the position of the projection is not limited, and may be at both ends of the silicon carbide firing jig, or both ends may be deleted and other portions may be provided.

The jig for firing silicon carbide is preferably a jig in which a coating layer made of silicon carbide is formed on the surface of a plate made of the carbon material. The thickness of the silicon carbide coating layer is preferably from 20 to 60 μm. By forming the coating layer, even if SiO gas is generated from the silicon carbide molded body at the time of firing, there is no carbon simple substance which easily reacts with the SiO gas on the surface of the jig for firing silicon carbide. Are hardly generated on the surface of the jig for firing silicon carbide.

The thickness of the jig for firing silicon carbide is not particularly limited, but is preferably 5 to 20 mm. The above thickness is 5m
If it is less than m, the mechanical strength is not sufficient because it is too thin, and breakage tends to occur during use. On the other hand, if it exceeds 20 mm, the generated SiO gas becomes difficult to pass through the jig for firing silicon carbide. It is also economically disadvantageous.

Next, a firing method using the jig for firing silicon carbide of the present invention will be described. The silicon carbide molded object to be degreased and fired in the present invention is made of a mixed composition of silicon carbide powder, a binder, and a dispersion medium.

The particle size of the silicon carbide powder is not particularly limited, but preferably has a small shrinkage in the subsequent firing step, for example, 100 parts by weight of a powder having an average particle size of about 0.3 to 50 μm. It is preferable to use a combination of a powder having an average particle diameter of about 0.1 to 1.0 μm and 5 to 65 parts by weight.

The binder is not particularly limited.
For example, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, phenol resin, epoxy resin and the like can be mentioned. Generally, the amount of the binder is preferably about 1 to 10 parts by weight based on 100 parts by weight of the silicon carbide powder.

The dispersion medium is not particularly restricted but includes, for example, organic solvents such as benzene; alcohols such as methanol, and water. The dispersion medium is mixed in an appropriate amount so that the viscosity of the mixed composition falls within a certain range. The silicon carbide powder, the binder, the dispersion medium and the like are mixed with an attritor or the like, and then sufficiently kneaded with a kneader or the like, and a number of through-holes are arranged in the longitudinal direction across the partition by extrusion molding or the like. The provided columnar silicon carbide molded body is manufactured.

When the silicon carbide molded body is heated to 400 to 600 ° C. in an oxygen-containing atmosphere, the binder and the like volatilize, and decompose and disappear, leaving almost only silicon carbide powder. After this step, firing is performed under the following conditions.

FIG. 2 is a cross-sectional view illustrating an example of a method of firing a silicon carbide compact using the silicon carbide firing jig of the present invention.

In this firing step, as shown in FIG. 2, the silicon carbide firing jig 11 on which the silicon carbide molded body 12 is placed is placed in the crucible 13 so as not to adhere to the bottom of the crucible 13. . Thereafter, heating is performed by heater 14 provided around crucible 13, and silicon carbide molded body 12 that has undergone the degreasing step is fired. The firing is performed by heating at 2000 to 2200 ° C. in an atmosphere of an inert gas such as nitrogen or argon.

In the firing step, the SiO gas generated from the silicon carbide compact 12 easily passes through the silicon carbide firing jig 11 because the porosity of the silicon carbide firing jig 11 is high. The amount of SiO which reacts with carbon on the surface is greatly reduced as compared with the conventional case, and the generation of silicon carbide is suppressed and the silicon carbide is hardly coarsened. On the other hand, in a conventional dense carbon material, generated SiO tends to stay near its surface, so that it reacts with carbon and generated silicon carbide tends to be coarse.

In FIG. 2, jig 11 for firing silicon carbide is provided.
However, in the present invention, the silicon carbide firing jig 11 on which the silicon carbide compact 12 is mounted may be directly mounted in a firing furnace. In this case, by fixing a support member around the silicon carbide firing jig 11 so that the silicon carbide firing jig placed above does not come into contact with the silicon carbide molded body 12, silicon carbide The firing jigs may be stacked in several stages.

The silicon carbide firing jig is used as a jig for mounting the silicon carbide molded body not only in the above firing step but also in a degreasing step performed at a lower temperature than the firing step. be able to. Therefore, in the production of the silicon carbide sintered body, a series of steps from the degreasing step to the firing step can be performed without replacing the silicon carbide molded body.

[0039]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 70 parts by weight of α-type silicon carbide powder having an average particle diameter of 30 μm, 30 parts by weight of β-type silicon carbide powder having an average particle diameter of 0.28 μm,
5 parts by weight of methylcellulose, 4 parts by weight of a dispersant, and 20 parts by weight of water were blended and uniformly mixed to prepare a mixed composition of raw materials. This mixed composition was charged into an extruder, and a silicon carbide molded body 40 as shown in FIG. 5 was produced at an extrusion speed of 2 cm / min. This silicon carbide molded body 40 has a size of 33 mm × 33 mm × 300 mm, the number of through holes 41 is 31 / cm ² , and the thickness of partition 43 is 0.35
mm.

Next, after drying the silicon carbide compact 40, it is placed on a silicon carbide firing jig made of G100 (manufactured by Tokai Carbon Co., Ltd.), and air and nitrogen having an oxygen concentration of 5% are mixed. The degreasing step was performed by heating at 450 ° C. in a mixed gas atmosphere. Next, the silicon carbide molded body 40 is carried into the firing apparatus while being placed on the silicon carbide firing jig, and
The silicon carbide molded body was fired by heating to 00 ° C. to obtain a silicon carbide sintered body.

The obtained silicon carbide sintered body was directly used by a bending strength measuring instrument, and a three-point bending test was performed under a span of 135 mm, the bending strength was measured, and the Weibull coefficient was calculated. As a result, the average bending strength was 48 MPa, and the Weibull coefficient m was 19.5. In addition, the said average bending strength and the Weibull coefficient were calculated about the sintered compact obtained by using the same jig for sintering silicon carbide 5 times, and using the 2nd-5th time. After the completion of the five firing steps, the silicon carbide molded body mounting surface of the silicon carbide firing jig was visually observed, and almost no coarse crystals of silicon carbide having a particle size of 50 μm or more were found.

Example 2 1 m of the silicon carbide firing jig made of the same material as that used in Example 1
A silicon carbide sintered body was obtained in the same manner as in Example 1, except that a jig for firing silicon carbide having grooves of 1.0 mm in width and 1.0 mm in depth formed at m intervals was used. The bending strength of the obtained silicon carbide sintered body was measured in the same manner as in Example 1, and the Weibull coefficient was calculated.
MPa and Weibull coefficient m were 18.3. Also, 5
After the completion of the two firing steps, the mounting surface of the silicon carbide molded body of the jig for firing silicon carbide was visually observed, and almost no coarse crystals of silicon carbide having a particle size of 50 μm or more were found.

Example 3 A silicon carbide firing jig made of the same material as the silicon carbide firing jig used in Example 1 had a surface coated with 40 μm of silicon carbide.
A silicon carbide sintered body was obtained in the same manner as in Example 1, except that a jig for firing silicon carbide having a coating layer having a thickness of m was used. The bending strength of the obtained silicon carbide sintered body was measured in the same manner as in Example 1, and the Weibull coefficient was calculated. The average bending strength was 47 MPa and the Weibull coefficient m was 18.9. After the completion of the five firing steps, the silicon carbide molded body mounting surface of the silicon carbide firing jig was visually observed, and almost no coarse crystals of silicon carbide having a particle size of 50 μm or more were found.

Example 4 A silicon carbide firing jig made of the same material as the silicon carbide firing jig used in Example 1 had a 3 mm-thick and 10 mm-wide band-like projection on a surface on which the formed honeycomb body was placed. A silicon carbide sintered body was obtained in the same manner as in Example 1, except that a jig for firing silicon carbide having formed portions was used. The bending strength of the obtained silicon carbide sintered body was measured in the same manner as in Example 1, and the Weibull coefficient was calculated.
a, the Weibull coefficient m was 27.5. After the completion of the five firing steps, the band-shaped projections of the silicon carbide firing jig were visually observed, and almost no coarse crystals of silicon carbide having a particle size of 50 μm or more were found.

Comparative Example 1 A silicon carbide firing jig made of ET-10 (manufactured by IBIDEN, having a porosity of 15%) was used as a silicon carbide firing jig, and firing was performed twice, except that the firing was performed twice. In the same manner as in the above, a silicon carbide sintered body was obtained. The bending strength of the silicon carbide sintered body obtained by the second firing was measured in the same manner as in Example 1, and the Weibull coefficient was calculated. The average bending strength was 41 MPa and the Weibull coefficient m was 9.01. there were. Further, after the two firing steps, the surface of the silicon carbide molded body on which the silicon carbide molded body was placed was visually observed, and the particle size of the silicon carbide molded body was 50 μm or more over the entire surface of the silicon carbide molded body. Crystals of silicon carbide were observed, and in particular, many silicon carbide crystals were observed in portions that were in contact with the silicon carbide compact.

As described above, the silicon carbide sintered bodies prepared in Examples 1 to 4 have the average bending strength of 44 MPa or more and the Weibull coefficient of 15 or more, and have the desired characteristics. On the other hand, the silicon carbide sintered body produced in Comparative Example 1 had a low average bending strength and a low Weibull coefficient,
It did not have enough mechanical strength to be used.

[0048]

According to the jig for firing silicon carbide of the present invention, as described above, coarse particles of silicon carbide are less likely to be generated on the surface during firing, and as a result, it can be used repeatedly.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view schematically showing a jig for firing silicon carbide of the present invention processed so as to leave a projection, and FIG. 1B is a plan view thereof. .

FIG. 2 is a cross-sectional view illustrating an example of a method for firing a silicon carbide molded body using the jig for firing silicon carbide of the present invention.

FIG. 3 is a perspective view schematically showing a ceramic filter.

FIG. 4A is a perspective view schematically showing a porous ceramic member constituting a ceramic filter, and FIG.
Is a longitudinal sectional view parallel to the longitudinal direction.

FIG. 5 is a perspective view schematically showing a silicon carbide molded body fired using the silicon carbide firing jig of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Jig for silicon carbide firing 12, 40 Silicon carbide molded body 13 Crucible 14 Heater 15 Projection 20 Ceramic filter 30 Porous ceramic member 31, 41 Through hole 32 Filler 33, 43 Partition wall

Claims (4)

[Claims] 1. A plate-like firing jig made of a carbon material used for degreasing and firing a columnar silicon carbide molded body in which a large number of through holes are juxtaposed in a longitudinal direction across a partition wall. A jig for firing silicon carbide, wherein the carbon material has a porosity of 30 to 60%. 2. The jig for firing silicon carbide according to claim 1, wherein a groove is formed on a surface on which the silicon carbide compact is placed. 3. The jig for firing silicon carbide according to claim 1, wherein the jig for firing silicon carbide is processed so that a band-shaped or rectangular projection in plan view remains on a surface on which the silicon carbide molded body is placed. 4. The jig for firing silicon carbide according to claim 1, wherein a coating layer made of silicon carbide is formed on the surface.