JP2018199609A - Porous material, honeycomb structure, and manufacturing method of porous material - Google Patents

Abstract

To provide a high-strength porous material.SOLUTION: A porous material 1 includes aggregates 2, and a bonding material 3 used to bind between the aggregates 2 and including cordierite as a main component, where surfaces of three-phase interfaces A in which the aggregates 2, the bonding material 3, and the pores 4 are intersected smoothly bond. Furthermore, in the porous material 1, the bonding material 3 may include at least one additive component 5 selected from among strontium, yttrium, and zirconium, and a bending strength of the porous material is 5.5 MPa or more, or a honeycomb bending strength of a honeycomb structure using the porous material 1 may be 4.0 MPa or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a porous material, a honeycomb structure, and a method for manufacturing a porous material. More specifically, the present invention relates to a high-strength porous material, a honeycomb structure, and a method for producing a porous material for producing the porous material.

  A porous material having a plurality of pores in which an aggregate such as silicon carbide particles (SiC particles) is bonded using an oxide phase binder such as cordierite has excellent characteristics such as thermal shock resistance. ing. Using these porous materials, a honeycomb structure having a plurality of cells partitioned by partition walls is formed, and the honeycomb structure is used as a catalyst carrier or DPF (diesel particulate filter) to purify exhaust gas. Etc. (see, for example, Patent Documents 1 and 2).

Japanese Patent No. 411439 Japanese Patent No. 4227347

  In recent years, a catalyst carrier or DPF using the porous material has been required to have a large size depending on the intended use. Therefore, a large honeycomb structure having a wide honeycomb diameter and a long axial length (honeycomb length) is manufactured. On the other hand, a honeycomb structure other than a large honeycomb structure with a complicated cell structure for high functionality and high performance, and a thin wall for partitioning cells to suppress pressure loss. Structures are also manufactured.

  A large thermal load or mechanical load is applied to these honeycomb structures during use. Therefore, a honeycomb structure formed of a porous material is required to have sufficient strength against mechanical load (mechanical strength) in addition to thermal shock resistance.

  In view of the above circumstances, an object of the present invention is to provide a high-strength porous material, a honeycomb structure using the porous material, and a method for manufacturing the porous material.

  In order to solve the above-described problems, the present invention provides the following porous material, honeycomb structure, and method for producing the porous material.

[1] A porous material comprising an aggregate and a binder mainly composed of cordierite that bonds between the aggregate and the aggregate, and the aggregate, the binder, and the fine material A porous material in which the surfaces of the three-phase interface where pores intersect are smoothly bonded.

[2] The porous material according to [1], wherein the binder contains at least one component of strontium, yttrium, and zirconium.

[3] The porous material according to [1] or [2], wherein the bending strength is 5.5 MPa or more.

[4] The porous material according to any one of [1] to [3], wherein at least a part of the aggregate is covered with the binder.

[5] The total content of each component of the strontium, the yttrium, and the zirconium contained in the porous material after firing is 0.2% by mass to 3.0% by mass. 4]. The porous material according to any one of [4].

[6] The porous material according to any one of [1] to [5], wherein the aggregate contains at least one of silicon carbide particles and silicon nitride particles.

[7] The porous content according to any one of [1] to [6], wherein the total content of alkali components including sodium and potassium contained in the porous material after firing is 0.05% by mass or less. material.

[8] A boundary line between the binder and the pores appearing in a cross-sectional image obtained by mirror-polishing a sample for microscopic observation including the porous material and observing a cross section of the sample where the porous material is exposed under a microscope. The representative value of the rising angle of the edge is 0 ° or more and 25 ° or less with respect to the tangential direction of the position where the curvature is locally maximum at the edge shown in any one of [1] to [7]. The porous material described.

[9] A honeycomb structure including a partition wall that is formed of the porous material according to any one of [1] to [8] and that partitions a plurality of cells extending from one end face to the other end face.

[10] The honeycomb structure according to [9], wherein the honeycomb bending strength is 4.0 MPa or more.

[11] The above [9] or [10], comprising a plurality of plugged portions disposed in the opening of the predetermined cell on the one end face and the remaining opening of the cell on the other end face. The honeycomb structure according to 1.

[12] A method for producing a porous material for producing the porous material according to any one of [1] to [8], comprising an aggregate, a binder, a pore former, and a binder. A molded body forming step of extruding a molding raw material to form a molded body, and a firing step of firing the extruded molded body at a predetermined firing temperature in an inert gas atmosphere to form a porous material. And a method for producing a porous material, wherein the binder contains at least one component of strontium, yttrium, and zirconium.

[13] The above [12], wherein the total addition rate of each component of the strontium, the yttrium, and the zirconium contained in the porous material after firing includes an additive having a content of 0.2% by mass to 3.0% by mass. The manufacturing method of the porous material as described in 2.

[14] The method for producing a porous material according to [12] or [13], wherein the strontium is strontium carbonate.

  According to the porous material of the present invention, the surface of the three-phase interface where the aggregate, the binder, and the pore intersect smoothly has a cross-sectional microstructure, so that the aggregate-binder material near the three-phase interface is between The bonding force of can be reinforced. Thereby, the strength (bending strength or honeycomb bending strength) of the porous material and the honeycomb structure using the porous material can be improved. In particular, by including various components such as strontium in the binder, the above-described “smoothly joined” cross-sectional microstructure can be relatively easily configured.

  Furthermore, according to the honeycomb structure of the present invention, it is possible to easily form the above-described high-strength porous material, and it is possible to manufacture a catalyst carrier or a DPF that resists a strong mechanical load. Moreover, according to the method for producing a porous material of the present invention, a porous material having the above-described excellent effects can be produced stably.

It is explanatory drawing which shows typically the cross-sectional microstructure of the porous material of one Embodiment of this invention. It is explanatory drawing which shows the measurement position in explanatory drawing which shows the cross-sectional microstructure of FIG. 1 typically. It is explanatory drawing which expanded the measurement position vicinity of FIG. 2, which shows a measurement position, a reference line, a rising line, and a rising angle. 4 is a graph showing the correlation between the open porosity of a honeycomb structure using the porous material of the present embodiment and the honeycomb bending strength. It is explanatory drawing which shows typically the cross-sectional microstructure of the conventional porous material.

  Hereinafter, embodiments of a porous material, a honeycomb structure, and a porous material manufacturing method according to an embodiment of the present invention will be described with reference to the drawings. The porous material, the honeycomb structure, and the method for manufacturing the porous material of the present invention are not limited to the following embodiments, and various design changes are possible without departing from the gist of the present invention. Modifications, improvements, etc. can be added.

(1) Porous material:
The porous material 1 of this embodiment is a ceramic mainly composed of an aggregate 2 and a binder 3 mainly composed of cordierite that bonds the aggregate 2 and the aggregate 2 together. Material. As shown in the cross-sectional microstructure schematically shown in FIG. 1, the surface of the three-phase interface where the aggregate 2, the binder 3, and the pores 4 intersect is formed in a “smoothly coupled” state.

  Here, the surface of the three-phase interface is “smoothly bonded” means that the bonding material 3 that bonds between the aggregates 2 is a three-phase where one aggregate 2, the bonding material 3 and the pores 4 intersect. Formed from the vicinity of the interface (for example, the three-phase interface A (see arrow) in FIG. 1), extending smoothly toward the other aggregate 2 while changing smoothly or gently into a curved shape (or curved shape). It is what has been. Although one three-phase interface A is shown in FIG. 1, the present invention is not limited to this, and other three-phase interfaces where the aggregate 2, the binder 3, and the pores 4 intersect are also plural in FIG. 1. Existing.

  In the porous material 1 of the present embodiment, strictly speaking, the “three-phase interface” means, as shown in FIG. 1, a place where the aggregate 2 a, the aggregate 2 b, the binder 3, and the pores 4 intersect. Although it is limited, in this specification, the surface of the aggregate 2 is thinly covered with the binding material 3 and includes the state in which the surface of the aggregate 2 and the pores 4 are close to each other.

  In the case of the porous material 1 of the present embodiment, assuming that the aggregate 2 is solid and at least a part of the binder 3 at the time of high-temperature firing is in a liquid state, the surface of the solid aggregate 2 (solid surface) On the other hand, the liquid binding material 3 adheres in a state where the contact angle is small, and firing is completed and cooled while maintaining such a state, so that the cross-sectional microstructure as shown in FIG. 1 can be obtained. .

  Thereby, a part (or most part) of the aggregate 2 is covered with the binder 3. As a result, the angular edge portion of the aggregate 2 is covered with the binding material 3 so that the overall shape is somewhat rounded. Furthermore, the edge shape of the pores 4 with which the aggregate 2 and the binding material 3 are in contact is also curvilinear. As described above, in this specification, a structure in which many curved portions are included at the three-phase interface where the aggregate 2, the binder 3, and the pore 4 intersect is expressed as a “smoothly bonded” state. Shall.

  On the other hand, for example, in the case of the cross-sectional microstructure of the conventional porous material 10 schematically shown in FIG. 5, the angulated aggregate 11 having straight sharp edges is observed as it is, and the aggregates 11 are The bonding material 12 to be bonded extends toward the other aggregate 11 in a linear shape near the three-phase interface B where the aggregate 11, the bonding material 12, and the pores 13 intersect (see the arrow in FIG. 5). . Therefore, it is not in a “smoothly coupled” state as defined above. Further, most of the surface of the aggregate 11 (for example, 50% or more) is in contact with the pores 13, and the surface of the aggregate 2 is increased by the binder 3 as in the porous material 1 of the present embodiment. A portion (for example, 50% or more) is covered, and the pores 4 and the binder 3 are not in contact with each other.

  That is, in the case of the conventional porous material 10, the bonding material 12 does not exhibit a curved shape near the interface of the aggregate 11 as compared with the porous material 1 of the present embodiment. The shape of the pores 13 is not rounded, but is often configured as an angular portion, a straight line, or an irregular shape. The porous material 1 of this embodiment is greatly different from the conventional porous material 10 in terms of the cross-sectional microstructure.

  Here, quantification of the cross-sectional microstructure of the porous material 1 will be described mainly based on FIGS. In the porous material 1 of the present embodiment, the sample cross section of the sample for microscope observation with the porous material 1 exposed is observed under an operating electron microscope, and appears in the obtained cross-sectional image (see a schematic diagram such as FIG. 2). The edge indicating the boundary line between the binding material 3 and the pores 4 (hereinafter referred to as “binding material edge E”) has a rounded shape. As a result, as an example of a method for quantifying the cross-sectional microstructure of the porous material 1 described above, the roundness of the edge E of these binders is quantified (corresponding to “rise angle θ” to be described later) to obtain a fine cross-section. The structure can be quantified.

  A specific example of quantification will be described. First, the porous material 1 is included in a resin material such as an epoxy resin, and the resin is cured to prepare a sample for microscope observation. Next, the sample for microscopic observation including the obtained porous material 1 is mirror-polished, and the sample cross section is smoothed so that the porous material 1 is exposed. Then, the sample cross-section that has been smoothed by mirror polishing and exposed at least a part of the porous material 1 is observed using a scanning electron microscope. Here, the scanning electron microscope, for example, performs observation at a magnification of 1500 times and captures a cross-sectional image that is a reflected electron image under the microscope observation. Here, the magnification for capturing the cross-sectional image is not particularly limited to 1500, and can be changed to an arbitrary magnification according to the sample for microscope observation. The microscope that captures the cross-sectional image is not limited to the scanning electron microscope, and may be an image obtained by an optical microscope, a transmission electron image obtained by a transmission electron microscope, or the like. In that case, the preparation of the sample for microscopic observation is different from the above.

  Next, an analysis process based on the cross-sectional image obtained by the scanning electron microscope is performed. First, the measurement position P1 on “the edge E of the binding material” is specified from the obtained cross-sectional image (see FIG. 2). Here, the measurement position P1 is specified by specifying “a position where the curvature is locally maximized” at the edge E of the binder. In addition, in the cross-sectional microstructure of the porous material 1 of the present embodiment, the edge E of the binding material that connects the two aggregates 2 is near the three-phase interface in one aggregate 2 and in the other aggregate 2. It becomes concave between the vicinity of the three-phase interface.

  Therefore, as the most typical example, the inclination of the edge E of the binder continuously changes between these three-phase interfaces, and the angular portion is hardly observed (FIG. 1 or FIG. 2 etc.). reference). Therefore, at the edge E of the binder, the position of the maximum curvature between these three-phase interfaces is the position where the curvature is locally maximum (measurement position P1). In the case of the porous materials of Comparative Examples 1 to 3 to be described later, since the edge of the binding material does not have a rounded shape, the top of the recessed portion is specified as the measurement position on the edge of the binding material (not shown) ).

  Next, a straight line indicating a tangential direction with respect to the edge E of the binding material at the measurement position P1 is set on the cross-sectional image as a reference line L1 (see a solid line in FIG. 3). The reference line L1 can be set by drawing the reference line L1 directly after printing the cross-sectional image on a paper medium, or any point from the measurement position P1 of the cross-sectional image displayed on the display. May be set by virtually connecting (the same applies to a rising line L2 described later).

  Next, in the vicinity of the measurement position P1 on the set reference line L1, a straight line rising toward the one side along the edge E of the binder from the measurement position P1 is referred to as a rising line L2 (see the one-dot chain line in FIG. 3). ). Here, the rising line L2 is, for example, a straight line connecting the measurement position P1 and a position separated from the measurement position P1 by a predetermined minute distance (for example, 1 to 5 μm) at the edge E of the binder. Equivalent to. This minute distance can be calculated based on the magnification under the microscope observation and the actual distance in the cross-sectional image.

  As a result, two lines (reference line L1 and rising line L2) that pass through the measurement position P1 are obtained, and the angle formed between the reference line L1 and the rising line L2 can be obtained. Here, in the present invention, the angle formed is defined as “rise angle θ” (see FIG. 3). The rising angle θ is determined by the edge E of the binder with respect to the tangential direction (reference line L1) at the measurement position P1 where the curvature is locally maximum at the edge E of the binder in an arbitrary cross section of the porous material 1. The angle between a straight line rising from the measurement position P1 (rising line L2) is shown. Here, in FIG. 3, in order to simplify the illustration, the portion of the binding material 3 that is not hatched is shown.

  In this way, using the measurement method for measuring the rising angle θ from the cross-sectional image, the plurality of measurement positions P1 are specified from the cross-sectional image of the porous material 1, and the rising angle θ at each measurement position P1 is calculated. . Further, an “average value” is obtained from the calculated values of the plurality of rising angles θ, and the obtained value is determined as a “representative value” of the rising angle θ of the porous material 1. When the porous material 1 of the present embodiment has a fine structure, the representative value of the rising angle θ is defined in the range of 0 ° to 25 °. When the representative value is within this range, in the cross-sectional microstructure of the porous material 1 of the present embodiment, the surface of the three-phase interface where the aggregate, the binder, and the pores intersect is smoothly bonded.

  On the other hand, in the porous material (see FIG. 5) as shown in Comparative Examples 1 to 3 to be described later, the edge of the binding material does not have a rounded shape, and the top of the recessed portion at the edge of the binding material is measured. Must be specified as Therefore, there is a high possibility that the representative value of the rising angle θ is larger than 25 °. Therefore, unlike the porous material 1 of the present embodiment, the surface of the three-phase interface where the aggregate, the binder, and the pores are not smoothly bonded is not obtained.

  Here, the representative value of the rising angle θ described above is not limited to the average value calculated from the values obtained from the plurality of measurement positions P1 described above. For example, it may be a median value or a mode value. The average value is not limited to the so-called “arithmetic average”, and may be a geometric average or the like. When calculating the representative value of the rising angle θ, the number of measurement positions P1 specified on the cross-sectional image is not particularly limited, and is preferably at least 5 or more. More preferably, it may be 5 or more and 100 or less.

  In the porous material 1 of the present embodiment, it is expected that the three-phase interface where the aggregate 2, the binder 3, and the pores 4 are smoothly joined and the contact area between the aggregate 2 and the binder 3 is increased. The As a result, the bonding force between the aggregate 2 and the bonding material 3 can be increased, and the bonding force at each interface between the aggregate 2 and the bonding material 3 in the porous material 1 is increased. The strength of the quality material 1 as a whole is increased.

  As shown in FIG. 1, the porous material 1 having a “smoothly bonded” cross-sectional microstructure is compared with the porous material 10 (see FIG. 5) having a cross-sectional microstructure composed of sharp edges. The stress concentration applied to can be relaxed by a curved shape. Therefore, the strength of the entire porous material 1 is increased.

  The porous material 1 of the present embodiment is made of strontium, yttrium, and yttrium on the binder 3 mainly composed of cordierite, which is used to bond the aggregates 2 together in order to obtain the cross-sectional microstructure described above. Those containing at least one component (hereinafter referred to as “additive component 5”) are used. Here, the present invention is "a porous material comprising an aggregate, and a binder mainly composed of cordierite that bonds between the aggregate and the aggregate. It may be a “porous material containing at least one component of strontium, yttrium, and zirconium”. That is, even if the surface of the three-phase interface where the aggregate, the binder, and the pores are not smoothly bonded, the porous material having a certain strength as long as the additive 5 is included in the binder. It can be.

Examples of the strontium source used for the additive component 5 include various oxides such as strontium carbonate (SrCO ₃ ), strontium oxide (SrO), or strontium hydroxide (Sr (OH) ₂ ), and other strontium salts. Can be used. Similarly, as the yttrium and zirconium used for the additive component 5, various oxides (Y ₂ O ₃ , ZrO _2, etc.), various yttrium salts, zirconium salts, and the like can be used. By including these additive components 5 in the binder 3 in a predetermined ratio, the surface of the three-phase interface can be smoothly bonded. As a result, a high-strength porous material 1 having a cross-sectional microstructure as described above can be obtained.

  The total content of additives (additive component 5) contained in the binder 3 is set in a range of 0.2% by mass to 3.0% by mass with respect to the porous material 1 after firing. When the total content is lower than 0.2% by mass, the effect of the additive component 5 is poor, and the three-phase interface between the aggregate 2 and the binder 3 cannot be “smoothly joined”.

  On the other hand, when the total amount of added components is 3.0% by mass or more, it is expected that the amount of the binder 3 to be liquefied increases during firing. As described above, it is assumed that a part of the binder 3 exposed to a high firing temperature during firing is liquefied. Therefore, a part of the binding material 3 may be liquefied, and a part thereof may be foamed. Thereby, bubbles due to foaming are likely to be generated in the bonding material 3, and a plurality of voids (not shown) may be generated in the bonding material 3 by cooling and solidifying. As a result, due to the gap generated between the aggregate 2 and the binding material 3, the binding force between the aggregate 2 and the binding material 3 is weakened, and the strength of the porous material 1 may be reduced. Therefore, the total content rate of the additive component 5 (strontium etc.) contained in the binder 3 is set within the above numerical range.

  Here, in the porous material 1 of the present embodiment, the strontium or the like as the additive component 5 contained in the binder 3 is not limited to one component, and a plurality of components of two or more components are mixed at a predetermined mixing ratio. It may be added in For example, the binder 3 may be one in which strontium carbonate and zirconium oxide are mixed at a mass ratio of 3: 7, or three components of strontium, yttrium, and zirconium are included in the binder 3. Furthermore, it may contain a plurality of components of the same element. Even in this case, the sum of the content ratios of the respective components may be in the numerical range defined as the total content ratio. By setting it within such a numerical range, the porous material 1 having a unique cross-sectional microstructure can be obtained.

In addition, components other than strontium, yttrium, and zirconium may be included in the binder 3. For example, cerium dioxide (CeO ₂ ) can be used. In this case, the content of cerium dioxide may or may not be added to the total content of each component such as strontium.

  As described above, the porous material 1 of the present embodiment includes the additive component 5 such as strontium in the binder 3 so that the aggregate 2 and the binder 3 have the above-described cross-sectional microstructure. The overall strength of 1 is improved. The bending strength is at least 5.5 MPa or more. Thereby, when producing other products, such as a catalyst support | carrier, using the porous material 1, it has sufficient intensity | strength practically. The bending strength can be measured and evaluated by, for example, producing test pieces of 0.3 mm × 4 mm × 20 to 40 mm and performing a three-point bending test in accordance with JIS R1601.

  In the porous material 1 of the present invention, the lower limit value of the average pore diameter is preferably 10 μm, and more preferably 15 μm. Further, the upper limit value of the average pore diameter is preferably 40 μm, and more preferably 30 μm. When the average pore diameter is less than 10 μm, the pressure loss may increase. When the average pore diameter exceeds 40 μm, when the porous material of the present invention is used as a DPF or the like, a part of the particulate matter in the exhaust gas may pass through the DPF or the like without being collected. In the present specification, the average pore diameter is a value measured by a mercury intrusion method (based on JIS R1655).

  In the porous material 1 of the present invention, pores having a pore diameter of less than 10 μm are 20% or less of the whole pores, and pores having a pore diameter of more than 40 μm are preferably 10% or less of the whole pores. If the pores having a pore diameter of less than 10 μm exceed 20% of the whole pores, the pores having a pore diameter of less than 10 μm are likely to be clogged when the catalyst is supported, and the pressure loss may be easily increased. When the pores with a pore diameter of less than 40 μm exceed 10% of the whole pores, the pores with a pore diameter of less than 40 μm can easily pass through the particulate matter, so that it may be difficult to sufficiently exert a filter function such as DPF. .

  When a honeycomb-shaped honeycomb structure (not shown) is manufactured using the porous material 1, the honeycomb structure has a strength (honeycomb bending strength) of at least 4.0 MPa. Is desirable. Thereby, a product such as a catalyst carrier and a DPF can be constructed using a honeycomb structure having a sufficient strength, and can be used in a harsh environment such as a large mechanical load. Furthermore, it is possible to meet the demand for increasing the size of the honeycomb structure.

The aggregate 2 of the porous material 1 of the present embodiment includes silicon carbide particles (SiC particles) or silicon nitride particles (Si ₃ N ₄ particles), or a mixture of these silicon carbide particles and silicon nitride particles at a predetermined ratio. Can be used. In the following description, an example in which silicon carbide particles are mainly used as the aggregate 2 for the porous material 1 of the present embodiment and the honeycomb structure (not shown) formed using the porous material 1 will be described. However, the type of aggregate 2 and the ratio when using a plurality of types are not particularly limited. Moreover, even if the aggregate 2 is composed of silicon nitride particles or the like, various conditions of the porous material 1 and the honeycomb structure can be made the same.

  In addition, in the porous material of the present embodiment, the total content of alkali components including sodium and potassium contained in the fired porous material 1 is set to 0.05% by mass or less. In the aggregate raw material for forming the aggregate 2 and the binder raw material for forming the binder 3, a trace amount of alkali components such as sodium are present.

  It is known that alkali components such as sodium are generally a factor that reduces the long-term durability of porous materials. For this reason, attempts have been made to suppress alkali components contained in the porous material as much as possible. Therefore, also in the porous material 1 of the present embodiment, the total content of alkali components such as sodium contained in the fired porous material 1 is set to the upper limit value or less. Thereby, the long-term durability of the porous material 1 can be improved.

  Here, it is generally known that the bending strength of the porous material 1 and the honeycomb bending strength of the honeycomb structure are affected by the porosity (open porosity) of the porous material 1 itself. Therefore, the lower limit value of the open porosity of the porous material 1 and the honeycomb structure formed from the porous material 1 is preferably 40%, and more preferably the lower limit value is 50%. It is. On the other hand, the upper limit value of the open porosity is preferably 90%, and the upper limit value is preferably 70%. Here, when the open porosity is less than 40%, the pressure loss increases, and the influence on the product performance when used as a product such as DPF is large. On the other hand, when the open porosity is 50% or more, the use of DPF or the like has low pressure loss characteristics that are particularly suitable.

  Furthermore, when the open porosity exceeds 90%, the strength of the porous material 1 decreases, and a practically sufficient strength when used as a product such as DPF cannot be secured. On the other hand, if the open porosity is 70% or less, it is particularly suitable for use in products such as DPF. Details of the method for calculating the open porosity will be described later.

(2) Honeycomb structure:
A honeycomb structure (not shown) of the present invention is configured using the porous material 1 of the above-described embodiment, and includes partition walls that define and form “a plurality of cells extending from one end surface to the other end surface”. The cell functions as a fluid flow path. The structure, shape, and the like of the honeycomb structure are already well known, and can be constructed with an arbitrary structure and size using the porous material 1 of the present embodiment. For example, a structure having an outer peripheral wall on the outermost periphery It may be. Further, the lower limit of the partition wall thickness is preferably, for example, 30 μm, and more preferably 50 μm. The upper limit of the partition wall thickness is preferably 1000 μm, more preferably 500 μm, and particularly preferably 350 μm. The lower limit of the cell density is preferably 10 cells / cm ^2, more preferably 20 cells / cm ² , and particularly preferably 50 cells / cm ² . The upper limit of the cell density is preferably 200 cells / cm ^{2 and} more preferably 150 cells / cm ² .

  Furthermore, the shape of the honeycomb structure is not particularly limited, and examples thereof include a conventionally known columnar shape and a prismatic shape having a polygonal bottom (triangle, quadrangle, pentagon, hexagon, etc.). In addition, the shape of the cells of the honeycomb structure is not particularly limited. For example, the cell shape in the cross section perpendicular to the cell extending direction (axial direction) may be a polygon (triangle, quadrangle, pentagon, hexagon, heptagon, octagon, etc.), circle, or a combination thereof. Can do.

In addition, the size of the honeycomb structure can be appropriately determined according to the application. Since the honeycomb structure of the present embodiment is configured using the porous material 1 of the present embodiment having high strength characteristics, the honeycomb structure is particularly resistant to mechanical loads. Therefore, a large honeycomb structure for constructing a large DPF or the like can be configured. For example, a honeycomb structure having a volume of about 10 cm ^{3 to} 2.0 × 10 ⁴ cm ³ can be assumed.

  As already described, the honeycomb structure of the present embodiment can be used as a DPF or a catalyst carrier. It is also a preferred embodiment that a catalyst is supported on the DPF. When the honeycomb structure of the present embodiment is used as a DPF or the like, the following structure is preferable. That is, it is preferable to include a plugging portion disposed in an opening of a predetermined cell on one end face and an opening of a remaining cell on the other end face. On both end faces, it is preferable that cells having plugged portions and cells not having plugged portions are alternately arranged to form a checkered pattern.

(3) Production method of porous material (honeycomb structure):
The method for producing the porous material of the present invention will be described below. Note that the method for manufacturing a porous material described below is also a method for manufacturing a honeycomb structure for manufacturing a honeycomb structure having a honeycomb shape made of a porous material.

  First, powdered silicon carbide used as a raw material for the aggregate 2 and a powdery raw material for a binder produced by the binder 3 by firing are mixed, and if necessary, a binder, a surfactant, a pore-forming material are mixed. A molding raw material is prepared by adding a material, water, etc. (molding raw material preparation step). At this time, powdered strontium (for example, strontium carbonate) prepared to a predetermined content rate (total addition rate is 0.2 mass% to 3.0 mass%) is added to the water to be added. Added as component 5 in the forming raw material. Note that the method of adding the additive component 5 is not limited to the above-described method. For example, as with other components such as a binder, the additive component 5 is directly charged into silicon carbide or a raw material for a binder in a powder state. May be.

  In addition, by firing the above-described raw material for the binder, “cordierite” that is the main component of the binder 3 is generated. Alternatively, a well-known cordierite forming raw material may be used instead of the above powdery raw material for a binder, and directly mixed with silicon carbide.

  Furthermore, examples of the binder include well-known organic binders such as methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. In particular, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. For example, the binder content is preferably 2 to 10% by mass with respect to the entire forming raw material.

  As the surfactant, ethylene glycol, dextrin, fatty acid soap, polyalcohol and the like can be used. These may use only one type of surfactant or may be used in combination of two or more types of surfactant. The content of the surfactant is preferably, for example, 2% by mass or less with respect to the entire forming raw material.

  The pore former is not particularly limited as long as it becomes pores after firing, and examples thereof include graphite, starch, foamed resin, water absorbent resin, and silica gel. The pore former content is preferably, for example, 10% by mass or less with respect to the entire forming raw material. The lower limit of the average particle diameter of the pore former is preferably 10 μm, and the upper limit of the average particle diameter of the pore former is particularly preferably 30 μm. Here, when the average particle diameter of the pore former is smaller than 10 μm, the pores (pores 4) in the porous material 1 may not be sufficiently formed. On the other hand, if the average particle diameter of the pore former is larger than 30 μm, there is a possibility that the forming raw material (clay) is clogged in the die for performing extrusion molding. The average particle diameter of the pore former can be measured by a laser diffraction method or the like. When a water absorbent resin is used as the pore former, the average particle diameter is a value obtained by measuring the water absorbent resin after water absorption.

  The water added to the forming raw material can be appropriately adjusted so as to have a clay hardness that facilitates a forming process such as extrusion. For example, it is preferable to add 20 to 80% by mass of water with respect to the entire forming raw material.

  Next, the above-mentioned forming raw material obtained by adding a specified amount of each component is kneaded to form a clay. At this time, a kneader, a vacuum kneader or the like can be used to form the clay.

  Thereafter, the kneaded clay is extruded to form a honeycomb formed body (formed body forming step). Here, in order to extrude the kneaded clay, an extruder having a base having a desired overall shape, cell shape, partition wall thickness, cell density and the like is mainly used. Here, the material of the die is preferably a cemented carbide that does not easily wear. The honeycomb formed body has a structure having porous partition walls that define and form a plurality of cells serving as fluid flow paths and an outer peripheral wall located at the outermost periphery. The partition wall thickness, cell density, outer peripheral wall thickness, and the like of the honeycomb formed body can be appropriately determined according to the structure of the honeycomb structure to be manufactured in consideration of shrinkage during drying and firing.

  The honeycomb formed body thus obtained is preferably dried before the firing step (drying step). Here, the drying method is not particularly limited, and examples thereof include an electromagnetic heating method such as microwave heating drying and high-frequency dielectric heating drying, and an external heating method such as hot air drying and superheated steam drying. Further, an electromagnetic heating method and an external heating method may be used in combination. For example, in order to dry the entire honeycomb molded body quickly and uniformly without cracks, first a certain amount of moisture is dried by an electromagnetic heating method, and then the remaining moisture is dried by an external heating method. Two-stage drying may be performed. In this case, as a drying condition, after removing 30 to 99% by mass of moisture with respect to the amount of moisture before drying using an electromagnetic heating method, moisture is used until it becomes 3% by mass or less using an external heating method. May be removed. In addition, dielectric heating drying is suitable as the electromagnetic heating method, while hot air drying is suitable as the external heating method.

  Furthermore, when the length (honeycomb length) in the cell extending direction (axial direction) of the honeycomb molded body after drying is not a desired length, both end faces (both ends) are provided. It may be cut to a desired length (cutting step). The cutting method is not particularly limited, and examples thereof include a method using a known circular saw cutting machine.

  Next, the honeycomb formed body is fired to produce a honeycomb structure (corresponding to a porous material). Before firing, it is preferable to perform calcination in order to remove the binder and the like (firing step). The calcination is preferably performed at 200 to 600 ° C. for 0.5 to 20 hours in an air atmosphere (degreasing step). Firing is preferably performed in a non-oxidizing atmosphere such as nitrogen or argon (oxygen partial pressure is 10-4 atm or less) (main firing step). The lower limit of the firing temperature is preferably 1300 ° C. The upper limit of the firing temperature is preferably 1600 ° C. The pressure during firing is preferably normal pressure. The lower limit of the firing time is preferably 1 hour. The upper limit of the firing time is preferably 20 hours. Moreover, after baking, in order to improve durability, you may perform an oxidation process in the air | atmosphere (it may contain water vapor | steam) (oxidation baking process). The lower limit of the oxidation treatment temperature is preferably 1100 ° C. The upper limit of the temperature of the oxidation treatment is preferably 1400 ° C. The lower limit of the oxidation treatment time is preferably 1 hour. The upper limit of the oxidation treatment time is preferably 20 hours. In addition, calcination and baking can be performed using an electric furnace, a gas furnace, etc., for example.

  Hereinafter, the honeycomb structure using the porous material of the present invention will be described more specifically based on the following examples. However, the porous material and the honeycomb structure of the present invention are limited to such examples. is not.

(Examples 1-8)
A “base powder” was prepared by mixing powder silicon carbide as an aggregate raw material and powdered binder raw material as a binder raw material in a predetermined ratio. The base powder contains 78.8% by mass of aggregate silicon carbide, 7.7% by mass of talc, 9.6% by mass of aluminum oxide (Al ₂ O ₃ ), and silica (SiO _2). ) Is added to the binder material containing 3.9% by mass. Thereby, it adjusts so that the total mass of base powder may be 100 mass%. That is, the total mass of the above-described aggregate and binder is set to 100% by mass.

  Furthermore, cerium dioxide, a water-absorbing resin and starch as a pore former, hydroxypropyl methylcellulose as a binder, strontium carbonate as an additive, and water were added to the prepared base powder as a “molding raw material”.

  The pore former, binder, and water were cerium dioxide: 0.75% by mass, water-absorbing resin: 5.0% by mass, starch: 28% by mass, and hydroxy when the base powder was 100% by mass. Propylmethylcellulose: 7.0% by mass is added.

Further, the “components” of strontium carbonate (SrCO ₃ ), yttrium oxide (Y ₂ O ₃ ), and zirconium dioxide (ZrO ₂ ) are weighed so that the contents contained in the fired honeycomb structure are within a specified range. (Refer to Table 1 below) and put into 70.0% by mass of water. Further, water containing a component such as strontium carbonate is applied to an ultrasonic vibrator and dispersed for 60 seconds. Thereafter, water in which the component was dispersed was added to each mixed powder. Thereby, the "mixed powder" of Examples 1-8 is obtained. Thereafter, the mixture was kneaded for 45 minutes using a kneader to obtain a plastic clay (molding raw material).

  Here, Example 1 contains 1.0% by mass of strontium carbonate as a component, and Example 2 contains 2.0% by mass of strontium carbonate (see Table 1, hereinafter the same).

  Example 3 contains 0.5% by mass of yttrium oxide as a component, and Example 4 contains 2.0% by mass of yttrium oxide.

  Example 5 contains 2.0% by mass of zirconium dioxide as a component, and Example 6 contains two components of strontium carbonate and zirconium dioxide in a ratio of 0.6% by mass to 1.4% by mass. .

  Example 7 contains 2.0% by mass of strontium carbonate as a component.

  Next, the obtained clay (molding raw material) is formed into a cylindrical shape (cylindrical shape) using a vacuum kneader, and the obtained cylindrical clay is put into an extrusion molding machine to form a honeycomb. A honeycomb formed body was obtained by extrusion molding. The obtained honeycomb formed body was microwave-dried, and further subjected to two-stage drying at 80 ° C. for 12 hours using a hot air dryer to obtain an unfired honeycomb dried body.

  Thereafter, both ends of the obtained honeycomb dried body are cut and adjusted to a predetermined length (honeycomb length), and then degreased by degreasing at a heating temperature of 450 ° C. in an air atmosphere (preliminary firing). Step), and further, fired at a firing temperature of 1350 ° C. to 1500 ° C. (see Table 1) in an inert gas atmosphere (argon gas atmosphere) (main firing step: firing step), and further in the atmosphere from 1100 ° C. to 1350 ° C. An oxidation treatment was performed at a heat treatment temperature of 0 ° C. (oxidation firing step). Thereby, the porous material (honeycomb structure) of the honeycomb structure of Examples 1 to 7 was obtained.

  Example 8 has substantially the same conditions as in Example 7 described above, and does not include cerium dioxide that is previously added together with the raw material of the aggregate.

(Comparative Examples 1-3)
Comparative Examples 1 to 3 are for comparing and examining the effects of the porous material of the present invention, and do not contain components such as strontium carbonate, yttrium oxide, or zirconium dioxide. Example 7 is the same as Example 7 except that these components such as strontium carbonate are not included.

(Measurement of open porosity)
The open porosity (%) was obtained by cutting a plate piece of 20 mm long × 20 mm wide × 0.3 mm high from each of the honeycomb structures of Examples 1 to 8 and Comparative Examples 1 to 3 obtained as described above. Was measured by the Archimedes method using pure water as a medium.

(Evaluation of honeycomb bending strength (strength))
Using a test piece (3 cells × 5 cells × 30 to 40 mm) whose longitudinal direction is the direction in which the honeycomb structure penetrates the cells, a four-point bending test was performed perpendicularly to the cell direction in accordance with JIS R1601, Bending strength was evaluated.

(Measurement method of rising angle)
Since the method for measuring the rising angle has been described above, a detailed description thereof will be omitted. In addition, the details of the measurement conditions and the like will be described together with the measurement results described later.

(Quantification of Na content)
The Na content (content) was determined by analyzing the Na content contained in the fired honeycomb structure by ICP (Inductive Coupled Plasma) emission spectroscopy.

(Quantification of Sr content (content), etc.)
The strontium, yttrium, and zirconium contents (Sr content, Y content, and Zr content) were quantified by ICP (Inductive Coupled Plasma) emission spectroscopy, and the respective Sr, Y, and Zr contents were determined. analyzed. Here, each Sr content rate etc. is strontium in the said honeycomb structure when the whole honeycomb structure (porous material) of Examples 1 to 8 to be measured and Comparative Examples 1 to 3 is 100%. The weight ratio of etc. is shown.

  Table 1 below summarizes the contents of each component such as mass% of the aggregates and binders of Examples 1 to 8 and Comparative Examples 1 to 3, and strontium. Further, Table 1 shows the results of the Sr content, Y content, Zr content, Na content, open porosity, honeycomb bending strength, and calculated rise angle θ measured or calculated by the above measurement method and the like. It is shown. FIG. 4 shows the correlation between the open porosity and the honeycomb bending strength of the honeycomb structure formed using the porous material formed in Examples 1 to 8 and Comparative Examples 1 to 3.

  As shown in Table 1, Examples 1 to 8 containing components such as strontium carbonate in the binder have at least a honeycomb bending strength of 4.0 MPa or more and have a practically sufficient strength (mechanical strength). It has been shown. In contrast, Comparative Examples 1 to 3 that do not contain a component such as strontium carbonate in the binder have a honeycomb bending strength of less than 4.0 MPa. Therefore, it is confirmed that there is a sufficient effect of including a component such as strontium carbonate in the binder.

  Furthermore, as shown in FIG. 4, the honeycomb structures of Examples 1 to 8 show a tendency of a correlation between the open porosity (%) and the honeycomb bending strength that substantially pass through the honeycomb structures of Comparative Examples 1 to 3. It is plotted at a position on the right side of the slope line L, that is, at a position where the open porosity is large. In general, when the open porosity (%) increases, voids increase in the partition walls and the like constituting the honeycomb structure, and the honeycomb bending strength tends to be weakened. However, Examples 1 to 8 show high honeycomb bending strength even when the open porosity increases.

  Furthermore, as a general tendency, it was shown that the honeycomb bending strength tends to be higher when the total content is higher than 3.0% by mass unless the total content exceeds 3.0% by mass (implementation). Comparison between Example 1 and Example 7 or Example 3 and Example 4).

  Furthermore, it is shown that honeycomb bending strength is 4.0 MPa or more even when using yttrium oxide or zirconium dioxide other than strontium carbonate (Examples 3 to 5). Even when two components are included (Example 6), honeycomb bending strength is also shown. Was confirmed to be 4.0 MPa or more. Furthermore, even when cerium dioxide was not included, it was confirmed that the honeycomb bending strength was lower than in the other examples, but the strength was practically sufficient.

  Furthermore, in Table 1, the calculation result is shown for the rising angle θ of the edge of the binder with respect to the porous materials of Examples 1 to 8 and Comparative Examples 1 to 3. Here, the rising angle θ was obtained by imaging a sample cross section after mirror polishing of a sample for microscope observation prepared using the porous material of each example and comparative example with a scanning electron microscope at a magnification of 1500 times. Arbitrary ten measurement positions P1 (see FIGS. 2 and 3) are specified from the cross-sectional image, and an average value is obtained from the values of the ten rising angles θ at the ten measurement positions P1, and this is expressed as “representative value”. "(See Table 1).

  According to this, it was confirmed that the representative value (= average value) of the rising angle θ is 25 ° or less in the porous materials of Examples 1 to 8 in which the binder includes the Sr component, the Zr component, and the Y component. It was. That is, the surface of the three-phase interface in the present invention was shown to be “smoothly bonded”. On the other hand, in the case of the porous materials of Comparative Examples 1 to 3 that do not contain the Sr component, the Zr component, and the Y component, it was shown that the representative value (= average value) of the rising angle θ is higher than 25 °. Thereby, it was shown that the porous materials of Comparative Examples 1 to 3 have “smoothly bonded” surfaces at the three-phase interface. Further, the honeycomb bending strength was less than 4.0 MPa as compared with Examples 1 to 8, and there was a high possibility that practically sufficient strength was not exhibited.

  The porous material of the present invention can be used as a catalyst carrier material, a DPF material, or the like. The honeycomb structure of the present invention can be used as a catalyst carrier, DPF, or the like. Furthermore, the method for producing a porous material of the present invention can be used for producing the porous material.

1: porous material, 2, 2a, 2b, 11: aggregate, 3, 12: binder, 4, 13: pore, 5: additive component, 10: conventional porous material, A, B: three-phase Interface, E: Edge of binding material (boundary line between binding material and pore), L1: Reference line (tangential direction), L2: Rising line, P1: Measurement position (position where curvature is locally maximum), θ: rising angle.

Claims (14)

Aggregate,
A porous material comprising a binder mainly composed of cordierite that bonds between the aggregate and the aggregate,
A porous material in which a surface of a three-phase interface where pores intersect with the aggregate and the binder is smoothly bonded.   The porous material according to claim 1, wherein the binder contains at least one component of strontium, yttrium, and zirconium.   The porous material according to claim 1 or 2, wherein the bending strength is 5.5 MPa or more. The aggregate is
The porous material according to claim 1, wherein at least a part of the porous material is covered with the binder. The total content of each component of the strontium, the yttrium, and the zirconium contained in the porous material after firing is
It is 0.2 mass%-3.0 mass%, The porous material as described in any one of Claims 2-4. The aggregate is
The porous material according to claim 1, comprising at least one of silicon carbide particles and silicon nitride particles. The total content of alkali components including sodium and potassium contained in the porous material after firing is
It is 0.05 mass% or less, The porous material as described in any one of Claims 1-6. At the edge showing the boundary line between the binding material and the pores appearing in a cross-sectional image obtained by mirror-polishing the sample for microscopic observation including the porous material and observing the cross section of the sample exposed to the porous material under a microscope ,
The porous material according to any one of claims 1 to 7, wherein a representative value of the rising angle of the edge is 0 ° or more and 25 ° or less with respect to a tangential direction at a position where the curvature is locally maximum. . It is comprised with the porous material as described in any one of Claims 1-8,
A honeycomb structure including partition walls that partition and form a plurality of cells extending from one end face to the other end face.   The honeycomb structure according to claim 9, wherein the honeycomb bending strength is 4.0 MPa or more.   The honeycomb structure according to claim 9 or 10, further comprising a plurality of plugged portions disposed in the opening of the predetermined cell on the one end face and the remaining opening of the cell on the other end face. . A method for producing a porous material for producing the porous material according to any one of claims 1 to 8,
A molded body forming step of forming a molded body by extruding a molding raw material containing an aggregate, a binder, a pore former, and a binder;
A fired step of firing the extruded molded body at a predetermined firing temperature in an inert gas atmosphere to form a porous material;
The said binding material is a manufacturing method of the porous material containing at least 1 component of strontium, yttrium, and a zirconium.   The porous material according to claim 12, comprising an additive having a total addition rate of 0.2% by mass to 3.0% by mass of each component of the strontium, the yttrium, and the zirconium contained in the porous material after firing. A method for producing quality materials. The strontium is
The method for producing a porous material according to claim 12 or 13, which is strontium carbonate.