JP4228987B2 - Manufacturing method of silicon nitride honeycomb filter - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon nitride honeycomb filter suitable for removing dust and the like contained in high-temperature exhaust gas.

  Silicon nitride has excellent properties such as heat resistance, corrosion resistance, chemical resistance, mechanical strength, etc., and particulates discharged from dust collection, dust removal filters and diesel engines under high temperature and corrosive environment It is expected as a removal filter (hereinafter referred to as particulate) (hereinafter referred to as DPF). The manufacturing method of such a silicon nitride filter is roughly divided into a starting material (see Patent Document 1) and a manufacturing method using metal silicon particles as a starting material (Patent Document 2). -6)). The production method using metal silicon particles as a starting material and silicon nitride by direct nitriding is generally superior in terms of production cost because the raw material cost is lower than that in the manufacturing method using silicon nitride particles as a starting material. .

  On the other hand, since the method using metal silicon particles as a starting material involves a process of converting metal silicon into silicon nitride (hereinafter referred to as nitriding) in the heat treatment process, the heat treatment control becomes more important. As heat treatment control, it is necessary to sufficiently control the atmosphere together with the temperature. When heat treating a honeycomb molded body containing metal silicon under various conditions, if the heat balance between nitriding of the metal silicon and the heat dissipation is poor, an abnormal temperature rise occurs inside the honeycomb molded body. (Hereinafter referred to as abnormal heat generation) occurs locally, cracks occur inside the honeycomb molded body, and defects such as swelling occur outside the honeycomb molded body. I experienced that it became more noticeable as the size of.

  In Patent Document 2, a honeycomb formed body containing metal silicon is subjected to calcination and removal in an oxidizing atmosphere, followed by nitriding treatment to 1400 to 1450 ° C. in a reducing atmosphere containing nitrogen or a mixed gas of nitrogen and hydrogen, and heating and firing. A method for manufacturing a honeycomb structure mainly composed of silicon nitride is described.

  Patent Document 3 discloses a method for producing a reticulated porous silicon nitride sintered body by heating and nitriding a molded body containing metallic silicon in an atmosphere of nitrogen gas 40 to 95% by volume and hydrogen gas 60 to 5% by volume. Are listed.

  In Patent Document 4, an inert atmosphere (for example, argon, nitrogen) or an oxidizing atmosphere is used up to 20 to 800 ° C., and the porous silicon nitride gold for die casting is treated with industrial nitrogen or ammonia based on nitrogen up to about 1500 ° C. A method for manufacturing the mold is described.

  In Patent Document 5, a compact containing metal silicon is held at 1100 to 1400 ° C. for 4 to 12 hours in a nitrogen atmosphere, and the second stage heat treatment condition is held at 1450 to 1800 ° C. for 1 to 12 hours in a nitrogen atmosphere. And a method for producing a silicon nitride filter is described.

  Patent Document 6 is not a method for producing a silicon nitride filter, but combusts organic matter by flowing a combustible gas up to about 1000 ° C. at a rate of temperature increase of 200 ° C./h to 1000 ° C./h. After removal, from about 1000 ° C. to 1450 ° C. at a rate of temperature increase of about 5 ° C./h to about 50 ° C./h, nitrogen about 40-60 mol%, helium about 40-60 mol% and hydrogen about 1-4 mol% A method for producing silicon nitride in an atmosphere containing nitrogen, helium and hydrogen at a temperature increase rate of about 250 ° C./h to about 1250 ° C./h from about 1450 ° C. to 1850 ° C. is described. Has been.

  However, in the manufacturing methods proposed in Patent Documents 2 to 6, when nitriding using metal silicon as silicon nitride is an exothermic reaction, when the size of the honeycomb formed body is increased, the nitridation rate inside the formed body, etc. The characteristics are likely to be non-uniform, and in the worst case, defects such as cracks may occur in the honeycomb formed body in the nitriding stage due to abnormal heat generation due to nitriding. Therefore, there is a demand for a method for producing a high-quality silicon nitride filter having a large size, high characteristic homogeneity, and low pressure loss (hereinafter abbreviated as pressure loss).

JP 2002-121073 A (pages 1 to 5) Japanese Patent Publication No. 52-19207 (pages 1 and 2) Japanese Patent Publication No. 2-11555 (pages 1 and 2) JP-T 64-500426 (page 6) International Publication No. 01/47833 pamphlet (4, 5, 7 pages) Japanese Patent No. 3321621 (pages 2, 3, 6)

  An object of the present invention is to provide a method for producing a silicon nitride honeycomb filter having no internal defects such as cracks and blisters, high homogeneity of internal characteristics, and low pressure loss even for a large size honeycomb filter.

The present invention is a method for producing a silicon nitride honeycomb filter in which a honeycomb formed body containing metal silicon particles and a pore-forming material is heat-treated mainly for nitriding and sintering to convert the metal silicon particles into silicon nitride particles, The gas atmosphere at the time of the heat treatment is, in order: 1) first (nitriding prevention) stage; from room temperature to the nitrogen gas introduction start temperature, the atmosphere is substantially free of oxygen and nitrogen;
2) Second (nitriding) stage: From the nitrogen gas introduction start temperature to the nitrogen gas introduction amount control end temperature, the nitrogen gas introduction amount is set to 0.05 to 5 L / min. Per 1 kg of metal silicon in the honeycomb formed body. age,
3) Third (sintering) stage: Provided is a method for manufacturing a silicon nitride honeycomb filter, characterized in that heat treatment is performed as an atmosphere substantially composed of nitrogen gas from the temperature at which nitrogen gas introduction amount control ends.

  The method for manufacturing a silicon nitride honeycomb filter of the present invention (hereinafter referred to as the present manufacturing method) facilitates control of the nitriding reaction, which is particularly problematic in large-sized silicon nitride honeycomb filters, so that defects such as cracks and blisters are eliminated. In addition, a high-quality large-sized silicon nitride honeycomb filter with high uniformity of characteristics inside the filter can be provided. Therefore, by adopting the silicon nitride filter obtained by this production method for removing particulates discharged from a diesel engine, a large DPF having high reliability and excellent durability can be provided.

  Further, in this manufacturing method, even if the pore forming material retains its shape during the heat treatment process and easily generates isolated pores, the generation of isolated pores can be suppressed by controlling nitriding, so that pressure loss is reduced. A low silicon nitride honeycomb filter can be provided. Therefore, the present manufacturing method can provide a silicon nitride honeycomb filter suitable for a DPF that requires severe pressure loss.

  When heat-treating a compact containing metallic silicon, it is important to control the atmosphere centering on the temperature conditions of the heat treatment and the nitrogen gas supply amount control so as not to run away the nitriding reaction. This production method mainly controls nitrogen gas supply amount. That is, this manufacturing method is a method for manufacturing a silicon nitride honeycomb filter in which a honeycomb formed body including metal silicon particles and pore forming material is heat-treated mainly for nitriding and sintering to convert the metal silicon particles into silicon nitride particles. Therefore, the nitrogen gas atmosphere during the heat treatment is basically controlled by the amount of nitrogen gas introduced.

  In this manufacturing method, the heat treatment is divided into the following three stages. That is, the first stage mainly for the purpose of preventing nitriding from room temperature to the nitrogen gas introduction start temperature, and the first step mainly for nitriding metal silicon particles from the nitrogen gas introduction start temperature to the nitrogen gas introduction amount control end temperature. The third stage is intended to sinter silicon nitride particles produced mainly by nitriding from the second stage, the nitrogen gas introduction amount control end temperature.

  The nitrogen gas introduction start temperature is a temperature at which introduction of nitrogen gas is started, and the nitrogen gas introduction amount control end temperature is a temperature at which control of the nitrogen gas introduction amount is finished. In general, the nitrogen gas introduction start temperature is near the temperature at which nitriding starts, and the nitrogen gas introduction amount control end temperature is around the temperature at which nitriding ends, but this is only a qualitative measure and is limited to this. is not.

In this manufacturing method, the atmosphere in each stage is controlled in the following order.
1) First (nitridation prevention) stage; an atmosphere substantially free of oxygen and nitrogen;
2) Second (nitriding) stage: the amount of nitrogen gas introduced was set to 0.05 to 5 L / min. Per kg of metal silicon in the honeycomb formed body. age,
3) Third (firing) stage; an atmosphere consisting essentially of nitrogen.

  As for the temperature of the heat treatment, the nitrogen gas introduction start temperature is preferably 1000 to 1380 ° C., and more preferably 1150 to 1350 ° C. Moreover, the nitrogen gas introduction amount control end temperature is preferably 1350 to 1550 ° C, and more preferably 1400 to 1520 ° C.

  In addition, the maximum temperature in the third stage is preferably set to an optimum temperature for sintering the silicon nitride particles, and specifically, 1550 to 1800 ° C. is preferable. The maximum temperature in the third stage is more preferably 1650 to 1780 ° C, and further preferably 1680 to 1760 ° C.

  The atmosphere in the first stage is not particularly limited as long as it is an atmosphere that substantially does not contain oxygen and nitrogen in order to prevent nitriding. In the present specification, substantially free of oxygen and nitrogen means that the oxygen concentration and the nitrogen concentration are about 0.1% or less, respectively. As such an atmosphere, an atmosphere containing Ar and / or He is preferable. Those containing Ar are more preferable from the viewpoints of handleability, availability, and economical efficiency.

  Further, a vacuum (reduced pressure) atmosphere may be used in the temperature range of the first stage. Since it is better to discharge the organic decomposition gas contained in the honeycomb formed body to the outside of the furnace, for example, a vacuum (reduced pressure) atmosphere is used up to 800 ° C., and then Ar is increased while maintaining the temperature at 800 ° C., for example. It is preferable to introduce until atmospheric pressure is reached.

  The nitrogen gas introduction start temperature does not necessarily have to coincide with the temperature at which nitriding actually starts (hereinafter referred to as nitridation start temperature) if nitrogen is present. Rather, the honeycomb filter having a large porosity and the average pore diameter When manufacturing a honeycomb filter having a large size, it is preferable to set the nitrogen gas introduction start temperature to a temperature higher by about 100 to 200 ° C. than the nitridation start temperature.

  If the nitrogen gas introduction start temperature is set higher than the nitridation start temperature, the detailed mechanism of why the honeycomb filter has a large porosity and average pore diameter is unknown. It is presumed that if the temperature is set higher than the nitriding start temperature, the metal silicon particles themselves are sintered before being nitrided and are nitrided at the stage where the metal silicon particle porous body is formed.

  On the other hand, it is preferable to set the nitrogen gas introduction start temperature to the same level as the nitridation start temperature because a honeycomb filter with high homogeneity and a honeycomb filter with high mechanical strength can be manufactured with little difference depending on the location of pore characteristics in the honeycomb filter. . Therefore, according to this production method, a honeycomb filter having desired characteristics can be produced by appropriately selecting the nitrogen gas introduction start temperature.

  As the atmosphere of the second stage, the amount of nitrogen gas introduced per kg of metal silicon in the honeycomb molded body (hereinafter, unless otherwise specified, the amount of nitrogen gas introduced is expressed per kg of metal silicon in the honeycomb molded body. ) 0.05-5 L / min. And The amount of nitrogen gas introduced is 0.05 L / min. If it is less than 1, the progress of nitriding is too slow and it may take too much time for nitriding. On the other hand, the amount of nitrogen gas introduced is 5 L / min. Exceeding this will cause the nitriding reaction to run out of control and cause abnormal heat generation. The amount of nitrogen gas introduced is 0.2 to 3 L / min. Preferably, the amount of nitrogen gas introduced is 0.3-2 L / min. Is more preferable.

  The nitriding reaction does not proceed at a constant rate, and the reaction proceeds rapidly at a temperature of about 1200 to 1450 ° C. Accordingly, when the reaction is suppressed by reducing the amount of nitrogen gas introduced so that the nitriding reaction does not run out of temperature up to a temperature range of about 1200 to 1450 ° C., abnormal heat generation is prevented, and the final nitriding rate depending on the location in the molded body, pores It is preferable because variations in characteristics such as characteristics can be reduced and homogeneity is improved.

  As the atmosphere of the second stage, up to about 1200 ° C., the amount of nitrogen gas introduced was 1 L / min. The following is preferable. In the temperature range of about 1200 to 1450 ° C., the amount of nitrogen gas introduced is 2 L / min. The following is preferable, and 1 L / min. The following is more preferable. In a temperature range of about 1450 to 1550 ° C., 2 to 5 L / min. This is preferable.

The average rate of change in nitridation rate in the second stage is 0.05 to 0.7% / min. It is preferable that the nitriding reaction proceeds in a controlled manner. Nitride index average change rate, the starting temperature of the second stage _{T 1} (° C.), when the completion temperature of the second stage _T 2 _{(> T} 1) and (° C.), nitride ratio -T ₁ at _{(T 2} Nitriding rate at (3) / (time required from T ₁ to T ₂ (min.)).

  The nitriding rate at the end temperature of the second stage is preferably 80% or more, more preferably 90% or more at the end temperature of the second stage, and the nitriding rate at the end temperature of the second stage is Particularly preferred is 95% or more.

  The atmosphere in the third stage is an atmosphere substantially composed of nitrogen. The pressure is not limited as long as the atmosphere is made of nitrogen. However, the atmospheric pressure is preferable in terms of productivity, cost, and the like because the configuration of the heat treatment furnace is simple. Nitrogen may be introduced to atmospheric pressure while maintaining the temperature at the end of the second stage, or nitrogen may be introduced to atmospheric pressure while raising the temperature without maintaining the temperature.

  However, in this specification, the nitridation rate of silicon nitride is calculated from the mass change. That is, in the formation reaction of silicon nitride, 3 moles of metal silicon react with 2 moles of nitrogen to form 1 mole of silicon nitride as shown in Formula 1.

3Si + 2N ₂ → Si ₃ N ₄ ... Formula 1
From Formula 1, when all the metal silicon is silicon nitride, its mass is 1.67 times ((3 × Si + 4 × N) / (3 × Si) = (3 × 28 + 4 × 14) / (3 × 28) = 1.67). If the mass change is α times, the nitriding rate is calculated as (α-1) / (1.67-1) = (α-1) /0.67. For example, if the mass change of metallic silicon is 1.37 times, the nitriding rate is 55% (0.37 / 0.67 × 100 = 55%).

  In the present manufacturing method, the temperature conditions of the first to third steps may be any as long as the metal silicon in the honeycomb formed body is sufficiently nitrided to form silicon nitride, and a desired silicon nitride honeycomb filter can be manufactured. The conditions listed below are examples.

  As the temperature condition from the first stage, that is, from the room temperature to the nitrogen gas introduction start temperature, the rate of temperature increase is preferably 2 to 10 ° C./min, and 3 to 6 ° C./min. Is more preferable. Up to 800 ° C, 3-6 ° C / min. And 800 ° C. or higher is 2 to 4 ° C./min. This is particularly preferable. You may hold | maintain at 1000-1350 degreeC specific temperature before progressing to the following 2nd step. The holding time is preferably 1 to 10 hours.

  As the temperature condition of the second stage, it is preferable that the heating rate is 0.1 to 3 ° C./min. Up to 1300 ° C is 1 to 3 ° C / min. 1300-1450 ° C., 0.2-1 ° C./min. 1450 to 1550 ° C is 1 to 3 ° C / min. Is more preferable.

  As the temperature condition of the third stage, the rate of temperature increase is preferably 2 to 5 ° C./min, and 2 to 3 ° C./min. Is more preferable. The maximum holding temperature is preferably 1550 to 1800 ° C. because the silicon nitride particles are sufficiently sintered, and more preferably 1650 to 1780 ° C. The maximum temperature holding time is preferably 1 to 5 hours, and more preferably 2 to 4 hours. The atmosphere in the third stage is preferably nitrogen at atmospheric pressure.

  In the heat treatment, it is preferable to treat the honeycomb formed body by placing it in a container made of carbon or silicon nitride. In the case of a carbon container, a coating layer containing at least one selected from the group consisting of silicon nitride particles, metal silicon particles, or silicon carbide particles is preferably formed on the inner surface. More preferably, a multi-layer containing at least silicon nitride particles is formed on the inner surface of the carbon container.

  In the present manufacturing method, the honeycomb formed body includes metal silicon particles and a pore forming material. The metal silicon particles are not particularly limited, but those having an average particle diameter (hereinafter referred to as particle diameter) of 1 to 200 μm are preferably used. The purity of the metal silicon is appropriately selected according to the purpose and application.

  The pore forming material is not particularly limited as long as it forms pores. However, the pore forming material is decomposed during heat treatment and scattered to form pores (hereinafter referred to as a scattering type pore forming material) or oxide ceramic hollow particles (hereinafter referred to as “pores”). (It is simply abbreviated as a hollow particle). Examples of the scattering type pore forming material include thermally decomposable organic polymer particles. As the hollow particles, crystalline or amorphous materials are preferably used as long as they form pores during heat treatment and also function as a sintering aid for the silicon nitride particles generated in the heat treatment process. The When the hollow particles are mainly composed of an oxide of one or more metals selected from the group consisting of Al, Si, Ca, Sr, Ba, Mg and Y, an effect as a sintering aid is obtained in addition to pore formation. This is preferable because the strength of the filter can be improved.

  There are no particular restrictions on the amount of the metal silicon particles and pore forming material in the honeycomb formed body, but the metal silicon particles are preferably 40 to 90% by mass and the pore forming material is 10 to 60% by mass. The honeycomb formed body includes silicon nitride particles, silicon carbide particles, solid oxide particles (for example, alumina particles and yttria particles), organic binders such as methylcelluloses, plasticizers, dispersants, viscosity modifiers, and the like. A molding aid may be included.

  In the present manufacturing method, the manufacturing method of the honeycomb formed body is not particularly limited, but extrusion molding or the like is preferable in terms of productivity and the like. Specifically, an organic binder, a molding aid, ion-exchanged water, etc. are appropriately added to the metal silicon particles and pore forming material as necessary, and kneaded with a kneader such as a kneader to form a clay. It is manufactured by extrusion using a mold having a honeycomb cross-sectional shape. A mold, an extrusion molding machine, and the like are appropriately designed and selected according to the size and cross-sectional shape of the honeycomb molded body.

  Examples of the present invention are shown below.

[Molded article production method]
It consists of 65% by mass of Al ₂ O ₃ component and 35% by mass of SiO ₂ component having an average particle size of 75 μm with respect to 100 parts by mass of metal silicon particles having an average particle size of 22 μm (ELKEM, Si purity 99.5% by mass). Add 30 parts by mass of glassy hollow particles (trade name: SL75, manufactured by Taiheiyo Cement Co., Ltd.), add 15 parts by mass of methylcellulose and 70 parts by mass of ion-exchanged water, knead with a kneader to form a clay, and vacuum A honeycomb molded body having a diameter of 150 mm, a length of 180 mm, a cell pitch of 1.8 mm, and a wall thickness of 0.35 mm was obtained by extrusion molding with an extruder.

[Evaluation methods]
Porosity (%): Calculated by Archimedes method.
Average pore diameter (μm): Measured with a mercury porosimeter (manufactured by Yuasa Ionics Co., Ltd., AUTOSCAN-33).
Crystal phase: Identified with an X-ray diffractometer (trade name: Geigerflex RAD-IIA, manufactured by Rigaku Corporation).
Compressive strength (MPa): A test piece having a size of 10 mm × 10 mm × 10 mm was cut out from the sample and measured by the breaking strength when the test piece was compressed in the extrusion direction. The load application speed was 1 mm / min.

Pore diameter distribution ratio: The honeycomb filter was cut at half height, a cylindrical sample having a radius of 25 mm and a height of 50 mm was cut from the center of the cut surface, and the average pore diameter at the center was d ₁ , A ring-shaped sample having a radius of 50 to 75 mm and a height of 50 mm is cut out from the center of the cut surface, and the average pore diameter of the central portion of the fan-shaped body is d _2, and the pore diameter distribution ratio is d ₂ / d ₁ . .
Soot leak check: A honeycomb filter with both ends sealed in a checkered pattern in a 3.6L diesel engine exhaust pipe is set, and the smoke concentration after passing through the honeycomb filter is measured with a smoke meter (AVL). Regardless of the engine operation mode, if the smoke concentration (FSN) was 0.1 or less, no soot leakage occurred.
Nitriding rate average change rate: The value obtained by dividing the difference in the mass of the honeycomb filter at the start and end of the second stage by 0.67 times the mass of metal Si before sintering is defined as the nitriding rate change (%). The value obtained by dividing the rate change by the required time (min.) Was defined as the average rate of change in nitriding rate (% / min.).

[Example 1 (Example)]
The obtained honeycomb formed body was heated from room temperature to 800 ° C. under a vacuum atmosphere (about 100 Pa) at 5 ° C./min. The temperature was raised at 800 ° C., Ar was introduced to atmospheric pressure at 800 ° C., and the temperature was raised from 800 ° C. to 1200 ° C. at 3 ° C./min. The temperature was then increased from 1200 ° C. to 1300 ° C. at 2 ° C./min. The temperature was raised to 1st stage.

  In the second stage, the amount of nitrogen gas introduced is 1 L / min. The rate of temperature increase is 0.5 ° C./min. The temperature was raised from 1300 ° C to 1400 ° C. In the third stage, nitrogen is introduced to atmospheric pressure and then from 1400 ° C. to 1700 ° C. at 2 ° C./min. After heating at 1700 ° C. for 2 hours, the heating was stopped and the mixture was naturally cooled to near room temperature. The characteristics of the obtained honeycomb filter were a porosity of 63 (%), an average pore diameter of 15 μm at the center, a pore size distribution ratio of 0.9, a compressive strength of 10 MPa, and a soot leak: none. The average rate of change in the nitridation rate in the second stage (1300 to 1400 ° C.) is 0.4% / min. Met.

[Example 2 (Example)]
The obtained honeycomb formed body was heated from room temperature to 800 ° C. under a vacuum atmosphere (about 100 Pa) at 5 ° C./min. The temperature was raised at 800 ° C., Ar was introduced to atmospheric pressure at 800 ° C., and the temperature was raised from 800 ° C. to 1150 ° C. at 3 ° C./min. The temperature was raised to 1st stage.

  In the second stage, a nitrogen gas introduction rate of 0.2 L / min. Temperature rising rate 1 ° C./min. At 1250 ° C. to 1500 ° C., the amount of nitrogen gas introduced is 0.5 L / min. Temperature rising rate 1 ° C./min. The temperature was raised. In the third stage, nitrogen is introduced to atmospheric pressure and then from 1500 ° C. to 1700 ° C. at 3 ° C./min. After heating at 1700 ° C. for 3 hours, the heating was stopped and the mixture was naturally cooled to near room temperature. The characteristics of the obtained honeycomb filter were a porosity of 60 (%), an average pore diameter of 11 μm at the center, a pore size distribution ratio of 0.85, a compressive strength of 17 MPa, and a soot leak: none. The average rate of change in the nitriding rate in the second stage (1150 to 1500 ° C.) is 0.26% / min. Met.

[Example 3 (Example)]
The obtained honeycomb formed body was heated at room temperature to 1100 ° C. under a vacuum atmosphere (about 100 Pa) at 3 ° C./min. The temperature was raised at 1100 ° C., and Ar was introduced to atmospheric pressure at 1100 ° C. to form the first stage.

  In the second stage, the nitrogen gas introduction rate is 0.3 L / min. From 1100 ° C. to 1250 ° C. Temperature rising rate 1 ° C./min. At 1250 ° C. to 1400 ° C. with a nitrogen gas introduction rate of 1 L / min. Temperature rising rate 0.3 ° C./min. At 1400 ° C. to 1500 ° C., a nitrogen gas introduction rate of 3 L / min. Temperature rising rate 2 ° C./min. The temperature was raised to 2nd stage.

  In the third stage, nitrogen is introduced to atmospheric pressure and then from 1500 ° C. to 1750 ° C. at 3 ° C./min. The temperature was raised at 1750 ° C. and maintained at 1750 ° C. for 2 hours. The characteristics of the obtained honeycomb filter were a porosity of 58 (%), an average pore diameter of 8 μm at the center, a pore size distribution ratio of 0.95, a compressive strength of 19 MPa, and a soot leakage: none. The average rate of change in the nitriding rate in the second stage (1100 to 1500 ° C.) is 0.14% / min. Met.

[Example 4 (comparative example)]
In Example 1, the amount of nitrogen gas introduced from 1300 ° C. to 1400 ° C. was 1 L / min. To 7 L / min. The procedure was the same as in Example 1 except that the change was made. Cracks occurred in the honeycomb filter.

The silicon nitride honeycomb filter obtained by this production method is suitably used as a large-sized DPF having excellent heat resistance, corrosion resistance, and thermal shock resistance, and high homogeneity in the structure and characteristics inside the molded body.

Claims (7)

A method for producing a silicon nitride honeycomb filter, in which a honeycomb formed body including metal silicon particles and pore forming material is heat-treated mainly for nitriding and sintering to form metal silicon particles as silicon nitride particles, Gas atmosphere in order 1) 1st (anti-nitriding) stage; from room temperature to the nitrogen gas introduction start temperature, the atmosphere is substantially free of oxygen and nitrogen,
2) Second (nitriding) stage: From the nitrogen gas introduction start temperature to the nitrogen gas introduction amount control end temperature, the nitrogen gas introduction amount is set to 0.05 to 5 L / min. Per 1 kg of metal silicon in the honeycomb formed body. age,
3) Third (sintering) step: A method for producing a silicon nitride honeycomb filter, characterized in that heat treatment is performed as an atmosphere substantially composed of nitrogen gas from the temperature at which the nitrogen gas introduction amount control ends.   The method for producing a silicon nitride honeycomb filter according to claim 1, wherein the atmosphere containing no oxygen and nitrogen is an atmosphere containing Ar and / or He.   The method for producing a silicon nitride honeycomb filter according to claim 1 or 2, wherein the nitrogen gas introduction start temperature is 1000 to 1380 ° C.   The method for producing a silicon nitride honeycomb filter according to claim 1, 2, or 3, wherein the nitrogen gas introduction amount control end temperature is 1380 to 1550 ° C.   During the second stage, the average rate of change in nitridation is 0.05 to 0.7% / min. A method for producing a silicon nitride honeycomb filter according to claim 4.   The method for producing a silicon nitride honeycomb filter according to any one of claims 1 to 5, wherein a maximum temperature in the third stage is 1550 to 1800 ° C. The temperature condition of the heat treatment is from 0.5 to 10 ° C./min. The temperature is increased from 0.1 to 3 ° C./min. From the nitrogen gas introduction start temperature to the nitrogen gas introduction amount control end temperature. At a temperature of 2 to 5 ° C./min. The method for producing a silicon nitride honeycomb filter according to any one of claims 1 to 6, wherein the temperature is raised at a temperature of 5 ° C.