JP2012076953A - Silicon carbide honeycomb body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon carbide honeycomb body in which partial variation in strength is suppressed.SOLUTION: The silicon carbide honeycomb body comprises silicon carbide and has a plurality of axially extending divided cells, wherein an oxide film is uniformly formed on the surfaces of silicon carbide particles forming the silicon carbide honeycomb body.

Description

  The present invention relates to a silicon carbide honeycomb body, and more particularly to a silicon carbide honeycomb body in which an oxide film is formed on the surface of silicon carbide particles.

  Due to the recent increase in awareness of environmental issues, vehicles have been required to reduce carbon dioxide emissions. With this demand, the demand for diesel engines is increasing. It is known that exhaust gas containing a large amount of soot (particulate matter, PM) is discharged from a diesel engine. It is required to remove this PM when exhaust gas is discharged into the atmosphere. PM discharged from the diesel engine is collected by a porous ceramic filter called a diesel particulate filter (DPF).

  As a DPF, a honeycomb structure made of a porous ceramic sintered body produced by sintering silicon carbide powder is known. And it is known that the silicon carbide honeycomb body manufactured by sintering silicon carbide forms an oxide film on the surface of silicon carbide particles by heat treatment in an oxidizing atmosphere to improve the strength. Yes. This is disclosed in Patent Documents 1 to 3, for example.

  However, the oxide film of the silicon carbide honeycomb body disclosed in these documents has a variation in the amount of formation (the thickness of the oxide film formed from the surface of the silicon carbide particles toward the inside of the particles). Specifically, in the conventional silicon carbide honeycomb body, the degree of formation of the oxide film in the central part (inside) of the honeycomb body becomes insufficient compared with the outer peripheral part (outside) of the honeycomb body, and the formation thickness of the oxide film is small. It was not uniform. When the amount of oxide film formed varies, the strength of the oxide film and the honeycomb body are partially different. That is, the strength is high in the portion where the thick oxide film is formed, and the strength is relatively low in the portion where the oxide film is thin (or not formed). As a result, the effect of improving the strength by forming an oxide film cannot be obtained sufficiently, and when used as a DPF, cracks are likely to occur due to concentration of thermal stress in a relatively low strength portion. There was a problem.

Japanese Patent No. 40713381 Japanese Patent No. 2731562 Patent No. 4426083

  This invention is made | formed in view of the said actual condition, and makes it a subject to obtain the silicon carbide honeycomb body by which the partial bias | inclination of intensity | strength was suppressed.

  In order to solve the above-mentioned problems, the present inventor has studied the oxide film formed on the surface of the silicon carbide particles in the silicon carbide honeycomb body, and as a result, has reached the present invention.

  That is, the silicon carbide honeycomb body of the present invention is made of silicon carbide, and in the silicon carbide honeycomb body in which a plurality of cells extending in the axial direction are partitioned, on the surface of the silicon carbide particles forming the silicon carbide honeycomb body, The oxide film is formed uniformly.

  The silicon carbide honeycomb body of the present invention has an oxide film formed uniformly. The uniform oxide film improves the strength of the entire honeycomb body, and suppresses partial concentration of thermal stress when the silicon carbide honeycomb body of the present invention is used as a DPF. That is, partial strength bias is suppressed. As a result, the silicon carbide honeycomb body of the present invention exhibits excellent effects in improving mechanical strength and thermal shock resistance.

1 is a diagram schematically showing an arrangement during heat treatment of a silicon carbide honeycomb body of Example 1. FIG. 1 is a diagram schematically showing a state during heat treatment of a silicon carbide honeycomb body of Example 1. FIG. 6 is a view schematically showing a state during heat treatment of a silicon carbide honeycomb body of Example 2. FIG. 6 is a diagram schematically showing a state of the silicon carbide honeycomb body of Comparative Example 1 during heat treatment. FIG. 2 is a photograph showing the results of SEM and elemental analysis of Example 1. It is the photograph which showed the result of SEM of the comparative example 2, and an elemental analysis. It is the figure which showed the test result of the bending test of the sample of an Example and a comparative example.

(Silicon carbide honeycomb body)
The silicon carbide honeycomb body of the present invention is made of silicon carbide, and in the silicon carbide honeycomb body in which a plurality of cells extending in the axial direction are defined, an oxide film is formed on the surface of the silicon carbide particles forming the silicon carbide honeycomb body. Are uniformly formed.

  The silicon carbide honeycomb body of the present invention is made of silicon carbide. Here, being made of silicon carbide includes not only silicon carbide but also a compound having silicon carbide as a main component. Further, a trivalent element or a pentavalent element may be doped.

  In the silicon carbide honeycomb body of the present invention, an oxide film is formed on the surface of the silicon carbide particles. The oxide film is mainly composed of silicon dioxide. This oxide film has a greater strength than silicon carbide. That is, the silicon carbide honeycomb body of the present invention has high strength by forming an oxide film on the surface of the silicon carbide particles.

  In the silicon carbide honeycomb body of the present invention, an oxide film is uniformly formed on the surface of silicon carbide particles. Here, the term “uniform” refers to a state where no partial deviation (variation) occurs in the amount of oxide film formed. By forming the oxide film uniformly, there is no partial variation in improving the strength of the silicon carbide honeycomb body. That is, even when thermal stress or thermal shock is applied using the honeycomb body of the present invention for a DPF or the like, partial concentration of thermal stress does not occur because partial variation in strength is suppressed. Yes. As a result, the silicon carbide honeycomb body of the present invention becomes a honeycomb body having more excellent durability.

  The confirmation that the oxide film is uniformly formed on the surface of the silicon carbide particles is not particularly limited. For example, the formation amount of the partial oxide film of the silicon carbide honeycomb body is obtained. Can be done. More specifically, it can be confirmed by the analysis method used in Examples described later.

  In the silicon carbide honeycomb body of the present invention, a plurality of cells extending in the axial direction are partitioned. That is, like a general honeycomb body, it is formed so as to have a plurality of cells. In a conventional honeycomb body in which a plurality of cells are partitioned, a sufficient oxide film is not formed in the vicinity of the central portion (particularly the central portion in the axial direction). That is, the degree of formation of the oxide film was uneven. On the other hand, the silicon carbide honeycomb body of the present invention has a uniform oxide film formed on the surface of the silicon carbide particles even in the honeycomb body in which the oxide film has not been formed uniformly.

  In particular, when a plurality of cells extending in the axial direction have a relatively long shape, the conventional honeycomb body cannot form a uniform oxide film. In contrast, in the silicon carbide honeycomb body of the present invention, a uniform oxide film is formed even in such a shape. Here, the relatively long shape related to the cell shape indicates a shape in which an oxide film is hardly formed in the vicinity of the center of the cell. For example, the cell has a small cross-sectional area or a cell (honeycomb body). A shape having a long axial length can be given.

  The amount of oxide film formed at the center of the silicon carbide honeycomb body is preferably 95% or more of the amount of oxide film formed at the outer periphery. If the difference in the amount of oxide film formed exceeds 5%, a uniform oxide film is not formed. The smaller the difference in the amount of oxide film formed, the better. That is, it is preferable that the oxide film formation amount in the central portion is closer to the formation amount in the outer peripheral portion.

  In the silicon carbide honeycomb body of the present invention, the amount of oxide film formed is preferably 1 to 15% when the total mass of the honeycomb body is 100. By forming the oxide film at 1 to 15% in the entire silicon carbide honeycomb body of the present invention, the effect of forming the oxide film is sufficiently exhibited. Specifically, when the content is less than 1%, not only a uniform oxide film is hardly formed, but also the effect of improving the strength is lowered. On the other hand, if it exceeds 15%, the improvement in strength due to the formation of the oxide film increases, but it becomes difficult to obtain the characteristics of silicon carbide. Furthermore, peeling at the interface between the oxide film and silicon carbide tends to occur. The formation amount of the oxide film is more preferably 2 to 10% when the mass of the whole honeycomb body is 100.

  The silicon carbide honeycomb body of the present invention can have the same configuration as the conventional silicon carbide honeycomb body except that the oxide film is uniformly formed. That is, the silicon carbide honeycomb body of the present invention may be either a monolith shape or a segment shape using a combination of a plurality of parts. Since a uniform oxide film can exhibit high strength and thermal shock resistance, a monolith shape is more preferable.

  Further, the silicon carbide honeycomb body of the present invention may be either a honeycomb body forming a wall flow type filter catalyst or a straight flow type honeycomb body. Further, it may be a conductive honeycomb body or a non-conductive honeycomb body.

(Manufacture of silicon carbide honeycomb body)
The manufacturing method of the silicon carbide honeycomb body of the present invention is not limited as long as the manufacturing method can form a uniform oxide film.

  The silicon carbide honeycomb body of the present invention is manufactured by manufacturing a honeycomb body mainly composed of silicon carbide and then heat-treating in an oxidizing atmosphere to form an oxide film. An example is a method in which the heat treatment proceeds in a state where the sexual atmosphere is given a flow rate.

  In the conventional silicon carbide honeycomb body, it is considered that the amount of oxide film formed becomes uneven due to the lack of oxidizing atmosphere (oxygen) inside the cell. On the other hand, even if the oxidizing atmosphere (oxygen) forms an oxide film inside the cell and the amount of the oxidizing atmosphere is reduced due to the flow velocity of the oxidizing atmosphere inside the cell, a new oxidizing atmosphere is generated. (Oxygen) is supplied into the cell. As a result, a uniform oxide film can be formed.

  And as a method of giving a flow velocity to the oxidizing atmosphere inside the cell, a method of flowing a gas for forming an oxidizing atmosphere along the cell extending direction (axial direction), the honeycomb body in the oxidizing atmosphere Displacement in the axial direction (reciprocating the honeycomb body), holding the axial direction of the honeycomb body along the vertical direction, placing an oxidizing compound source below it, generating an oxidizing substance from the oxidizing compound source And a method of introducing the generated oxidizing substance into the cells of the honeycomb body and flowing it in.

  According to these methods, even if the oxidizing atmosphere (oxygen) forms an oxide film inside the cell and the amount thereof decreases, a new oxidizing atmosphere (oxygen) is supplied to the inside of the cell. A uniform oxide film can be formed on the surface of the silicon carbide particles.

  Hereinafter, the present invention will be described using examples.

  As an example of the present invention, a silicon carbide honeycomb body was manufactured.

Example 1
First, the raw materials described in Table 1 were weighed in the parts by mass described. Each of SiC (coarse particles), SiC (fine particles), Si ₃ N ₄ , and graphite was mixed for 15 minutes with a pressure kneader (manufactured by Moriyama Seisakusho, DS1-5GHH-E).

  Thereafter, the mixture was added with a dispersant, a binder, and water composed of an equivalent mixture of the dispersant (A) and the dispersant (B) shown in Table 1, and kneaded for 10 minutes to form a clay.

  The obtained clay-like ceramic raw material was formed by extrusion molding into a substantially cylindrical outer peripheral monolith honeycomb body with an extrusion molding apparatus. Extrusion molding was performed by molding into a substantially cylindrical shape having a number of cells extending in the axial direction using a desktop vacuum kneading molding machine (Unix Corporation, UNIX).

  Next, the molded body was dried by holding at 150 ° C. for 8 hours.

  The dried molded body was degreased by heating under an inert gas atmosphere (nitrogen gas atmosphere).

  Then, it was sintered by sintering at 2100 ° C. for 5 hours under an inert gas atmosphere (argon gas atmosphere). The sintered compact is sintered on a mounting table 2 in a state where the axial direction of the compact 1 is along the vertical direction as schematically shown in FIG. Placed. Here, the mounting table 2 is made of a porous silicon carbide sintered body having a honeycomb structure, and the mounting plate 20 with which the end surface of the molded body 1 abuts has air permeability.

  After firing, the furnace atmosphere of the firing furnace performing the sintering was switched to an oxidizing gas atmosphere (air) and fired at 1200 ° C. for 40 hours. The furnace atmosphere of the firing furnace was maintained with air flowing into the furnace and air discharged outside the furnace. Moreover, the atmosphere that flowed into the furnace flowed upward from below the mounting plate 20 of the mounting table 2 as schematically shown in FIG.

  After the heat treatment, it was allowed to cool to produce a silicon carbide honeycomb body of this example.

(Example 2)
In the same manner as in Example 1, a dried molded body was produced from a clay-like ceramic raw material.

  The dried molded body was put into a firing furnace. The firing furnace used in the manufacture of the present example includes a displacement device that holds the formed body and reciprocates the held formed body.

  And in the state which reciprocated the molded object with the displacement apparatus, it baked and stood on the same temperature conditions as the time of Example 1 (FIG. 3).

  Thus, the silicon carbide honeycomb body of this example was manufactured.

(Comparative Example 1)
This comparative example is a silicon carbide honeycomb body manufactured in the same manner as in Example 1 except that the molded body was placed in a state of being collapsed on the mounting table during firing (FIG. 4).

(Comparative Example 2)
This comparative example is a silicon carbide honeycomb body manufactured in the same manner as in Example 1 except that the treatment in an oxidizing gas atmosphere was not performed.

(Evaluation)
As evaluation of the silicon carbide honeycomb bodies of the examples and comparative examples, samples were prepared in the same manner as the respective examples, and the amount of oxide film formed and the bending strength of the samples were measured.

  The samples of Examples and Comparative Examples were manufactured by molding clay-like ceramic raw materials into a cylindrical shape having a square cross section. The molded body was a cylinder having a square section with an outer peripheral shape of 35 mm square on the cross section perpendicular to the axial direction, a wall thickness of 0.5 mm, and an axial length of 310 mm.

(Confirmation of oxide film)
In the samples of Examples and Comparative Examples, the oxide film formed on the surface of fine silicon carbide particles was confirmed.

  For confirmation of the oxide film, a test piece was cut out from the central portion (inside the central portion in the axial direction) and the outer peripheral portion of the manufactured sample, and the amount of oxide was measured by the analysis method described in JIS R1616. The measurement results are shown in Table 2.

  As shown in Table 2, the presence of silicon dioxide (oxygen) was confirmed on the surface of the silicon carbide particles of the sample treated in an oxidizing atmosphere, indicating that an oxide film was formed. And in Examples 1-2 in which oxidizing gas (air) was supplied to the inside of a cell, the amount of oxide films of a central part (inside) and an outer peripheral part was almost the same. On the other hand, in Comparative Example 1 in which the oxidizing gas was not supplied to the inside of the cell, the amount of the oxide film on the outer peripheral portion was considerably larger than that inside.

  As described above, in Comparative Example 1, it was confirmed that a non-uniform oxide film was formed between the outer peripheral portion and the center portion of the sample, and in Examples 1-2, a uniform oxide film was formed. It was confirmed that

  Next, SEM photographs and elemental analysis of the samples of Example 1 and Comparative Example 2 were performed. As SEM photographs, SEI images and BEI images were taken. Elemental analysis was performed using an energy dispersive X-ray analyzer (JED-2200 manufactured by JEOL Ltd.). FIG. 5 shows the results of the sample of Example 1, and FIG. 6 shows the results of the sample of Comparative Example 2. In FIGS. 5 and 6, (a) is an SEI image, (b) is a BEI image, (c) is an analysis result of silicon (Si) in elemental analysis, and (d) is oxygen (O) in elemental analysis. The analysis results were shown respectively.

  Comparing FIG. 5D and FIG. 6D, almost no oxygen was detected in Comparative Example 2, but in Example 1, it was confirmed that oxygen was uniformly present on the entire surface of the particles. From this, it was confirmed that a uniform oxygen film could be formed on the surface of the particles in the examples.

(Bending strength)
The samples of Examples and Comparative Examples were subjected to a bending test, and the bending strength was measured.

  The bending strength was measured by a three-point bending test with a distance between fulcrums of 15 cm using an electronic universal testing machine (CATE, manufactured by Yonekura Seisakusho). The test results are shown in Table 2 and FIG.

  As shown in Table 2 and FIG. 7, it can be seen that forming the oxide film increases the bending strength. And in Examples 1-2 in which oxidizing gas (air) was supplied to the inside of a cell, bending strength is larger than comparative example 1.

  As described above, it was confirmed that Examples 1 and 2 in which a uniform oxide film was formed had high strength.

  That is, the silicon carbide honeycomb bodies of Examples 1 and 2 are formed with a uniform oxide film and have high strength.

1: Molded body 2: Mounting table 20: Mounting plate

Claims (2)

In the silicon carbide honeycomb body made of silicon carbide and having a plurality of cells extending in the axial direction,
A silicon carbide honeycomb body characterized in that an oxide film is uniformly formed on the surface of silicon carbide particles forming the silicon carbide honeycomb body.   2. The silicon carbide honeycomb body according to claim 1, wherein the formation amount of the oxide film in the central portion of the silicon carbide honeycomb body is 95% or more of the formation amount of the oxide film in the outer peripheral portion.