WO2022014613A1

WO2022014613A1 - Exhaust pipe

Info

Publication number: WO2022014613A1
Application number: PCT/JP2021/026360
Authority: WO
Inventors: 裕亮尾下; 崇弘冨田
Original assignee: 日本碍子株式会社
Priority date: 2020-07-13
Filing date: 2021-07-13
Publication date: 2022-01-20
Also published as: JPWO2022014613A1

Abstract

This exhaust pipe comprises a metal pipe and an inorganic porous layer provided in a region on the inner surface of the metal pipe where exhaust gas passes through. In this exhaust pipe, the inorganic porous layer has a porosity of 45 vol% or greater, contains ceramic fibers, and is configured from 15 mass% or more of an alumina component and 45 mass% or more of a titania component. Moreover, at the interface between the inorganic porous layer and the metal pipe, the contact area between a skeleton portion and the metal pipe is 40% or greater.

Description

Exhaust pipe

This application claims priority based on Japanese Patent Application No. 2020-120261 filed on July 13, 2020. The entire contents of that application are incorporated herein by reference. The present specification discloses techniques relating to exhaust pipes.

Japanese Patent Application Laid-Open No. 2018-031346 (hereinafter referred to as Patent Document 1) describes an exhaust pipe of an internal combustion engine in which an inorganic porous layer (heat insulating material) is arranged between a metal inner pipe and a metal outer pipe. It has been disclosed. In Patent Document 1, an inorganic porous layer is provided between the inner pipe and the outer pipe to insulate the space between the inner pipe and the outer pipe, and the temperature of the exhaust gas flowing into the catalyst provided downstream of the exhaust pipe. The decline is suppressed. By suppressing the temperature drop of the exhaust gas flowing into the catalyst, the warm-up of the catalyst is completed at an early stage.

When the inorganic porous layer is arranged between the double tubes as in Patent Document 1, the adhesion between the tubular body (metal tube) and the inorganic porous layer is not particularly required. However, in the case of providing an inorganic porous layer inside the inner pipe of the double pipe or inside the single pipe in order to prevent the metal pipe and the exhaust gas from coming into direct contact with each other and further suppress the temperature drop of the exhaust gas. The adhesion between the metal tube and the inorganic porous layer is important. It is an object of the present specification to provide an exhaust pipe having improved adhesion between a metal pipe and an inorganic porous layer.

The exhaust pipe disclosed in the present specification may include a metal pipe and an inorganic porous layer provided at a portion of the inner surface of the metal pipe through which the exhaust gas passes. In this exhaust pipe, the inorganic porous layer has a porosity of 45% by mass or more, contains ceramic fibers, and may be composed of an alumina component of 15% by mass or more and a titania component of 45% by mass or more. Further, at the interface between the inorganic porous layer and the metal tube, the contact area between the skeleton portion of the inorganic porous layer and the metal tube may be 40% or more.

The perspective view of the exhaust pipe is shown. A partially enlarged view of the exhaust pipe is shown. The sectional view of the exhaust pipe is shown. The figure for demonstrating the measuring method of the contact area between an inorganic porous layer and a metal is shown. The results of the experimental example are shown. The results of the experimental example are shown.

The exhaust pipe disclosed in the present specification includes a metal pipe and an inorganic porous layer provided at a portion of the inner surface of the metal pipe through which the exhaust gas passes. Further, the inorganic porous layer may contain ceramic fibers. The ceramic fiber can absorb the influence of the difference in the coefficient of thermal expansion between the metal tube and the inorganic porous layer. Specifically, since the inorganic porous layer can be deformed following the deformation (heat expansion, heat contraction) of the metal tube, it is possible to prevent the inorganic porous layer from peeling off from the metal tube. That is, the adhesion between the metal tube and the inorganic porous layer is improved. Further, in the exhaust pipe, the inorganic porous layer can suppress the exhaust gas from coming into contact with the metal pipe and prevent the metal pipe from deteriorating. Further, since the inorganic porous layer is composed of 15% by mass or more of an alumina component and 45% by mass or more of a titania component, the melting point of the inorganic porous layer itself is high, and the shape changes due to the heat of the exhaust gas. Can also be suppressed.

At the interface between the inorganic porous layer and the metal tube, the contact area between the skeleton portion of the inorganic porous layer and the metal tube (the surface of the metal tube) may be 40% or more. In other words, the area where the surface of the metal tube is exposed to the void portion of the inorganic porous layer may be less than 60% at the interface between the inorganic porous layer and the metal tube. This further improves the adhesion between the inorganic porous layer and the metal tube. At the interface between the inorganic porous layer and the metal tube, the contact area between the skeleton portion and the metal tube may be 45% or more, 50% or more, 55% or more, and 60% or more. It may be 65% or more, 70% or more, or 75% or more. Further, the contact area between the skeleton portion of the inorganic porous layer and the metal tube may be 80% or less. When the contact area between the skeleton portion and the metal tube exceeds 80%, the Young's modulus of the inorganic porous layer becomes too high in the vicinity of the interface between the inorganic porous layer and the metal tube. If the contact area between the skeleton and the metal tube is 80% or less, Young's modulus is suppressed from becoming too high, and thermal shock immediately after the start of the internal combustion engine (high temperature exhaust gas comes into contact with the inorganic porous material in a low temperature state). This) prevents the inorganic porous layer from being damaged (cracking or the like). The contact area between the skeleton portion and the metal tube may be 80% or less, 75% or less, 70% or less, 60% or less, 55% or less. ..

When the coefficient of thermal expansion of the inorganic porous layer is α1 and the coefficient of thermal expansion of the metal tube is α2, the following equation (1) may be satisfied. The phenomenon that the inorganic porous layer is peeled off from the metal tube can be prevented more reliably.
Equation 1: 0.5 <α1 / α2 <1.2

The inorganic porous layer may contain flat plate-shaped plate-shaped ceramic particles. The plate-shaped ceramic particles may have an aspect ratio of 10 or more and 60 or less when the cross section is observed by SEM. The aspect ratio of the cross section of the plate-shaped ceramic particles contained in the inorganic porous layer can be confirmed by observing the cross section of the inorganic porous layer by SEM. The plate-shaped ceramic particles appear in a rod shape in the SEM. The plate-shaped ceramic particles can suppress a decrease in the strength (mechanical strength) of the inorganic porous layer itself. The plate-shaped ceramic particles having a cross-sectional aspect ratio of 10 or more and 60 or less have an aspect ratio in the manufacturing process of the inorganic porous layer by using, for example, plate-shaped ceramic particles having a cross-sectional aspect ratio of 60 or more and 100 or less as a raw material. The ratio becomes smaller and as a result remains in the inorganic porous material. By using the plate-shaped ceramic particles, a part of the ceramic fiber can be replaced with the plate-shaped ceramic particles. Typically, the length of the plate-like ceramic particles (longitudinal size) is shorter than the length of the ceramic fibers. Therefore, by using the plate-shaped ceramic particles, the heat transfer path in the inorganic porous layer is divided, and heat transfer in the inorganic porous layer is less likely to occur. As a result, the heat insulating performance of the inorganic porous layer is further improved.

The inorganic porous layer may contain granular particles of 0.1 μm or more and 10 μm or less. When the inorganic porous layer is formed (baked), the ceramic fibers are bonded to each other via granular particles to obtain a high-strength inorganic porous layer. Further, the thickness of the inorganic porous layer may be 1 mm or more. As a result, the heat insulating property of the exhaust pipe can be sufficiently exhibited. In the exhaust pipe, since the inorganic porous layer contains ceramic fibers, it is possible to realize an inorganic porous layer of 1 mm or more. That is, since the ceramic fiber that is unlikely to shrink in the process of forming the inorganic porous layer (for example, the firing step) is contained, the inorganic porous layer can be formed to 1 mm or more. For example, when the inorganic porous layer does not contain ceramic fibers, the inorganic porous layer shrinks during the molding process and cracks or the like occur. Therefore, when the inorganic porous layer does not contain ceramic fibers, the inorganic porous layer is inorganic porous. It is difficult to form the quality layer into a thick film of 1 mm or more.

As described above, the inorganic porous layer is composed of an alumina (Al ₂ O ₃ _{) component of 15% by mass or more and 55% by mass or less and a titania (TiO 2} ) component of 45% by mass or more and 85% by mass or less. .. The alumina component contained in the inorganic porous layer may be 25% by mass or more, 30% by mass or more, or 40% by mass or more.

It is preferable that the difference in thermal conductivity between the metal tube and the inorganic porous layer is large. Specifically, the thermal conductivity of the metal tube may be 100 times or more the thermal conductivity of the inorganic porous layer. The thermal conductivity of the metal tube may be 150 times or more the thermal conductivity of the inorganic porous layer, 200 times or more the thermal conductivity of the inorganic porous layer, and the heat of the inorganic porous layer. The conductivity may be 250 times or more, and the thermal conductivity of the inorganic porous layer may be 300 times or more.

The thermal conductivity of the metal tube may be 10 W / mK or more and 400 W / mK or less. The thermal conductivity of the metal tube may be 25 W / mK or more, 50 W / mK or more, 100 W / mK or more, 150 W / mK or more, and 200 W / mK or more. It may be 250 W / mK or more, 300 W / mK or more, or 380 W / mK or more. Further, the thermal conductivity of the metal tube may be 350 W / mK or less, 300 W / mK or less, 250 W / mK or less, 200 W / mK or less, 150 W / mK or less. May be.

The thermal conductivity of the inorganic porous layer may be 0.05 W / mK or more and 3 W / mK or less. The thermal conductivity of the inorganic porous layer may be 0.1 W / mK or more, 0.2 W / mK or more, 0.3 W / mK or more, and 0.5 W / mK or more. It may be 0.7 W / mK or more, 1 W / mK or more, 1.5 W / mK or more, or 2 W / mK or more. The thermal conductivity of the inorganic porous layer may be 2.5 W / mK or less, 2.0 W / mK or less, 1.5 W / mK or less, and 1 W / mK or less. It may be 0.5 W / mK or less, 0.3 W / mK or less, and 0.25 W / mK or less.

Further, the inorganic porous layer may be made of a uniform material in the thickness direction. That is, the inorganic porous layer may be a single layer. Further, the inorganic porous layer may be composed of a plurality of layers having different compositions in the thickness direction. That is, the inorganic porous layer may have a multi-layer structure in which a plurality of layers are laminated. Alternatively, the inorganic porous layer may have an inclined structure in which the composition gradually changes in the thickness direction. When the inorganic porous layer is a single layer, the exhaust pipe can be easily manufactured (the step of forming the inorganic porous layer on the inner surface of the metal pipe). When the inorganic porous layer has a multi-layered or inclined structure, the characteristics of the inorganic porous layer can be changed in the thickness direction. For example, the porosity may be low (high proportion of skeleton) in the vicinity of the interface between the inorganic porous layer and the metal layer, and the porosity may be higher (low proportion of skeleton) in the portion other than the interface. While ensuring a high contact area between the skeleton portion of the inorganic porous layer and the metal tube, it is possible to secure a high porosity of the entire inorganic porous layer. As a result, it is possible to improve the heat insulating property of the inorganic porous layer while improving the adhesion between the inorganic porous layer and the metal tube. The structure of the inorganic porous layer (single layer, multi-layer, inclined structure) can be appropriately selected according to the purpose of use of the exhaust pipe.

The porosity of the inorganic porous layer may be 45% by volume or more and 90% by volume or less. When the porosity is 45% by volume or more, the heat insulating property can be sufficiently exhibited. Further, when the porosity is 90% by volume or less, sufficient strength can be secured. The porosity of the inorganic porous layer may be 55% by volume or more, 60% by volume or more, or 65% by volume or more. Further, the porosity of the inorganic porous layer may be 85% by volume or less, 80% by volume or less, 70% by volume or less, 65% by volume or less, and 60% by volume. It may be as follows. When the inorganic porous layer has a multi-layer structure or an inclined structure, the porosity of the inorganic porous layer may be 45% by volume or more and 90% by volume or less as a whole, and the porosity may differ in the thickness direction. .. In this case, there may be a portion having a porosity of less than 45% by volume or a portion having a porosity of more than 90% by volume.

The thickness of the inorganic porous layer may be 1 mm or more, although it depends on the required performance. When the thickness of the inorganic porous layer is 1 mm or more, the heat insulating property can be sufficiently exhibited. In the case of the inorganic porous layer in which the ceramic fiber is not used, it is difficult to maintain the thickness at 1 mm or more because it shrinks in the manufacturing process (for example, the firing step). Since the inorganic porous layer disclosed in the present specification contains ceramic fibers, shrinkage in the manufacturing process is suppressed, and a thickness of 1 mm or more can be maintained. If the thickness of the inorganic porous layer is too thick, it becomes difficult to obtain an improvement in heat insulating properties commensurate with the cost (manufacturing cost, material cost). Therefore, although not particularly limited, the thickness of the inorganic porous layer may be 30 mm or less, 20 mm or less, 15 mm or less, 10 mm or less, and 5 mm or less.

The inorganic porous layer is composed of one or more materials of ceramic particles (granular particles), plate-shaped ceramic particles, and ceramic fibers. The ceramic particles, the plate-shaped ceramic particles, and the ceramic fibers may contain alumina and / or titania as constituent components. In other words, the ceramic particles, the plate-shaped ceramic particles, and the ceramic fibers may be formed by alumina and / or titania. That is, the inorganic porous layer may contain 15% by mass or more of an alumina component and 45% by mass or more of a titania component in the entire constituent material (constituting substance). However, the inorganic porous layer contains at least ceramic fibers, although the constituent components are arbitrary (alumina component and titania component may or may not be contained).

The ceramic particles may be used as a joining material for joining aggregates (reinforcing materials) such as plate-shaped ceramic particles and ceramic fibers. The ceramic particles may be granular particles of 0.1 μm or more and 10 μm or less. The ceramic particles may have a larger particle size due to sintering or the like in the manufacturing process (for example, firing process). That is, as a raw material for producing the inorganic porous layer, the ceramic particles may be granular particles having a size of 0.1 μm or more and 10 μm or less (average particle size before firing). The ceramic particles may be 0.5 μm or more, and may be 5 μm or less. As the material of the ceramic particles, for example, a metal oxide may be used. An example of a metal oxide, alumina _(Al _{2 O} 3), spinel (MgAl ₂ O _4), titania _(TiO 2), zirconia _(ZrO 2), magnesia (MgO), mullite _{_{_{(Al 6 O 13 Si 2)}}} , cordierite _{_{(MgO · Al 2 O 3 ·}} SiO 2), yttria _(Y _{2 O} 3), steatite (MgO · _SiO 2), forsterite (2MgO · _SiO 2), lanthanum aluminate (LaAlO _3), strontium titanate (SrTiO ₃ ) and the like can be mentioned. These metal oxides have high corrosion resistance and can be suitably applied as a protective layer for an exhaust pipe.

The plate-shaped ceramic can function as an aggregate or a reinforcing material in the inorganic porous layer. That is, the plate-shaped ceramic, like the ceramic fiber, improves the strength of the inorganic porous layer and further suppresses the shrinkage of the inorganic porous layer in the manufacturing process. By using the plate-shaped ceramic particles, the heat transfer path in the inorganic porous layer can be divided. Therefore, the heat insulating property can be improved as compared with the form in which only the ceramic fiber is used as the aggregate.

The surface shape (shape observed from the thickness direction) of the flat plate-shaped ceramic particles is not particularly limited, and is, for example, a polygon such as a rectangle, a substantially circular shape, a curved line, and / or an indefinite shape surrounded by a straight line. The longitudinal size when observing the cross section may be 5 μm or more and 100 μm or less. When the size in the longitudinal direction is 5 μm or more, excessive sintering of the ceramic particles can be suppressed. When the size in the longitudinal direction is 100 μm or less, the effect of dividing the heat transfer path in the inorganic porous layer can be obtained as described above, and it can be suitably applied to an exhaust pipe used in a high temperature environment. Further, the plate-shaped ceramic particles may have an aspect ratio of 10 or more and 60 or less in cross section. When the aspect ratio of the cross section is 10 or more, it is possible to prevent the inorganic porous layer from becoming too hard (the Young's modulus becomes too high) after production (after firing). As a result, it is possible to prevent the inorganic porous layer from being damaged by the thermal shock immediately after the start of the internal combustion engine. Further, when the aspect ratio of the cross section is 60 or less, the decrease in the strength of the plate-shaped ceramic particles themselves is suppressed, and the damage of the inorganic porous layer due to the vibration of the exhaust pipe or the gas flow of the exhaust gas can be suppressed. can. As the material of the plate-shaped ceramic particles, in addition to the metal oxide used as the material of the ceramic particles described above, talc (Mg ₃ Si ₄ O ₁₀ (OH) ₂ ), minerals such as mica and kaolin, clay, glass, etc. Can also be used.

The ceramic fiber can function as an aggregate or a reinforcing material in the inorganic porous layer. That is, the ceramic fiber improves the strength of the inorganic porous layer and further suppresses the shrinkage of the inorganic porous layer in the manufacturing process. The length of the ceramic fiber may be 50 μm or more and 200 μm or less. The diameter (average diameter) of the ceramic fiber may be 1 to 20 μm. The ceramic fiber can also be confirmed by observing the cross section of the inorganic porous layer by SEM. The ceramic fibers are substantially circular in the SEM image. That is, the radial cross section of the ceramic fiber appears in the SEM image. Further, when the material of the ceramic fiber is different from the other materials constituting the inorganic porous layer, the ceramic fiber can be discriminated (confirmed) by performing an analysis. The volume fraction of the ceramic fiber in the raw material for forming the inorganic porous layer may be 5% by volume or more and 25% by volume or less. When the raw material of the inorganic porous layer contains 5% by volume or more of ceramic fibers, the shrinkage of the ceramic particles in the inorganic porous layer can be sufficiently suppressed in the manufacturing process (firing step) of the inorganic porous layer. Further, by setting the volume ratio of the ceramic fibers in the raw material to 25% by volume or less (that is, the volume ratio of the ceramic fibers in the inorganic porous layer is 25% by volume or less), the heat transfer path in the inorganic porous layer is set. It can be divided and heat transfer to the metal tube can be suitably suppressed. When the material of the ceramic fiber is different from other materials constituting the inorganic porous layer, the ratio (volume ratio) of the ceramic fiber in the inorganic porous layer should be measured by image processing the result of EDS analysis. Can be done.

Incidentally, as a material of ceramic fibers, alumina _(Al _{2 O} 3), spinel (MgAl ₂ O _4), titania _(TiO 2), zirconia _(ZrO 2), magnesia (MgO), mullite _(Al ₆ O 13 _Si 2) , cordierite _{_{(MgO · Al 2 O 3 ·}} SiO 2), yttria _(Y _{2 O} 3), steatite (MgO · _SiO 2), forsterite (2MgO · _SiO 2), lanthanum aluminate (LaAlO _3), strontium The same material as the above-mentioned ceramic particles such as titanate (SrTiO _{3) can be used.} Further, the inorganic porous layer may contain one or more kinds of ceramic fibers formed of the above materials.

In addition, the content of aggregates and reinforcing materials (ceramic fibers, plate-shaped ceramic particles, etc., hereinafter simply referred to as aggregates) in the raw materials for forming the inorganic porous layer is 15% by mass or more and 55% by mass or less. May be. When the content of the aggregate in the raw material is 15% by mass or more, the shrinkage of the inorganic porous layer in the firing step can be sufficiently suppressed. Further, when the content of the aggregate in the raw material is 55% by mass or less, the aggregates are satisfactorily bonded to each other by the ceramic particles. The content of the aggregate in the raw material may be 20% by mass or more, 30% by mass or more, 50% by mass or more, or 53% by mass or more. The content of the aggregate in the raw material may be 53% by mass or less, 50% by mass or less, 30% by mass or less, or 20% by mass or less.

As described above, both the ceramic fiber and the plate-shaped ceramic particle can function as an aggregate and a reinforcing material in the inorganic porous layer. However, in order to surely suppress the shrinkage of the inorganic porous layer after the exhaust pipe is manufactured (after firing), even when both the ceramic fiber and the plate-shaped ceramic particles are used as the aggregate, it is contained in the raw material. The content of the ceramic fiber may be at least 5% by mass or more. The content of the ceramic fiber in the raw material may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more. The content of the ceramic fiber in the raw material may be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, and 10% by mass. It may be less than or equal to%.

When both ceramic fibers and plate-shaped ceramic particles are used as the aggregate, the ratio of the plate-shaped ceramic particles to the entire aggregate may be 70% by mass or less. That is, in terms of mass ratio, at least 30% by mass or more of the aggregate may be ceramic fibers. The ratio of the plate-shaped ceramic particles to the entire aggregate may be 67% by mass or less, 64% by mass or less, 63% by mass or less, 60% by mass or less, and 50. It may be mass% or less. The plate-shaped ceramic particles are not always essential as an aggregate. The ratio of the plate-shaped ceramic particles to the entire aggregate may be 40% by mass or more, 50% by mass or more, 60% by mass or more, and 62% by mass or more. , 63% by mass or more, and may be 65% by mass or more.

The content of the plate-shaped ceramic particles in the raw material for forming the inorganic porous layer may be 5% by mass or more and 35% by mass or less. By containing 5% by mass or more of plate-shaped ceramic particles as the raw material of the inorganic porous layer, it is possible to sufficiently suppress the shrinkage of the ceramic particles in the inorganic porous layer in the manufacturing process (firing step) of the inorganic porous layer. can. Further, by setting the content of the plate-shaped ceramic particles in the raw material to 35% by mass or less (that is, the proportion of the plate-shaped ceramic particles in the inorganic porous layer is 35% by mass or less), the transfer in the inorganic porous layer is performed. The heat path can be divided, and heat transfer to the metal tube can be suitably suppressed. The content of the plate-shaped ceramic particles in the raw material may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, and 33% by mass. It may be% or more. The content of the plate-shaped ceramic particles in the raw material may be 35% by mass or less, 33% by mass or less, 30% by mass or less, or 20% by mass or less. It may be 10% by mass or less.

_{The SiO 2} contained in the inorganic porous layer may be 25% by mass or less. The formation of an amorphous layer in the inorganic porous layer is suppressed, and the heat resistance (durability) of the inorganic porous layer is improved.

When forming the inorganic porous layer, a raw material in which a binder, a pore-forming material, and a solvent are mixed may be used in addition to ceramic particles, plate-shaped ceramic particles, and ceramic fibers. As the binder, an inorganic binder may be used. Examples of the inorganic binder include alumina sol, silica sol, titania sol, zirconia sol and the like. These inorganic binders can improve the strength of the inorganic porous layer after firing. As the pore-forming material, a polymer-based pore-forming material, carbon-based powder, or the like may be used. Specific examples thereof include acrylic resin, melamine resin, polyethylene particles, polystyrene particles, carbon black powder, graphite powder and the like. The pore-forming material may have various shapes depending on the purpose, and may be, for example, spherical, plate-shaped, fibrous, or the like. By selecting the addition amount, size, shape, etc. of the pore-forming material, the porosity and pore size of the inorganic porous layer can be adjusted. The solvent may be any solvent as long as the viscosity of the raw material can be adjusted without affecting other raw materials, and for example, water, ethanol, isopropyl alcohol (IPA) or the like can be used.

The above-mentioned inorganic binder is also a constituent material of the inorganic porous layer. Therefore, when alumina sol, titania sol, etc. are used to form the inorganic porous layer, the inorganic porous layer contains 15% by mass or more of the alumina component and 45% by mass or more of the titania component in the entire constituent material including the inorganic binder. It may be included.

The composition and raw material of the inorganic porous layer are adjusted according to the type of the metal tube. The exhaust pipe disclosed in the present specification is not particularly limited, but stainless steel such as SUS430, SUS429, and SUS444 or cast iron can be used as the metal pipe. The composition and raw material of the inorganic porous layer may be adjusted according to the coefficient of thermal expansion of the metal tube used. Specifically, when the coefficient of thermal expansion of the inorganic porous layer is α1 and the coefficient of thermal expansion of the metal tube is α2, the following equation 1 may be adjusted to be satisfied. For example, when the metal tube is SUS430, the coefficient of thermal expansion α1 is 6 × 10 ^-6 / K <α1 <14 × 10 ^-6 / K, and more preferably the coefficient of thermal expansion α1 is 6 × 10 ^-6. The composition and raw materials of the inorganic porous layer may be adjusted so that / K <α1 <11 × ^{10-6 / K.} When the metal tube is copper, the coefficient of thermal expansion α1 is 8.5 × 10 ^-6 / K <α1 <20 × 10 ^-6 / K, and more preferably, the coefficient of thermal expansion α1 is 8.5. The composition and raw materials of the inorganic porous layer may be adjusted so that × ^10-6 / K <α1 <18 × ^{10-6 / K.} The value of "α1 / α2" may be 0.55 or more, 0.6 or more, 0.65 or more, 0.75 or more, and 0.8. It may be the above. Further, the value of "α1 / α2" may be 1.15 or less, 1.1 or less, 1.05 or less, or 1.0 or less.
Equation 1: 0.5 <α1 / α2 <1.2

The metal pipe may be a single pipe or a multiple pipe (for example, a double pipe). The metal tube may be linear, the whole (or a part) may be curved, the intermediate portion may be tapered, or the metal tube may be a branch tube. The inorganic porous layer may be provided on the inner surface of the metal tube in the case of a single tube, or on the inner surface of the metal tube arranged on the innermost side in the case of a multiple tube. Further, the inorganic porous layer may cover the entire inner surface of the metal tube, or may cover a part of the inner surface of the metal tube. For example, the inorganic porous layer may cover a portion other than the end portion (one end or both ends) of the metal tube.

In the exhaust pipe disclosed in the present specification, the above raw material may be applied to the inner surface of the metal pipe, dried and fired to form an inorganic porous layer on the inner surface of the metal pipe. As a method for applying the raw material, dip coating, spin coating, aerosol deposition (AD) method, brush coating, trowel coating, mold cast molding and the like can be used. If the target inorganic porous layer is thick, or if the inorganic porous layer has a multi-layer structure, the application of the raw material and the drying of the raw material are repeated multiple times to adjust the thickness to the target or the multi-layer structure. You may. The above coating method can also be applied as a coating method for forming a coating layer, which will be described later.

Further, in the exhaust pipe disclosed in the present specification, a coating layer may be provided on the surface of the inorganic porous layer (the surface opposite to the metal pipe side). That is, the inorganic porous layer may be sandwiched between the metal tube and the coating layer. The coating layer may be provided on the entire surface of the surface of the inorganic porous layer, or may be provided on a part of the surface of the inorganic porous layer. By providing the coating layer, the inorganic porous layer can be protected (reinforced).

The material of the coating layer may be a porous or dense ceramic. Examples of the porous ceramic used in the coating layer include zirconia (ZrO ₂ ), partially stabilized zirconia, stabilized zirconia and the like. In addition, yttria-stabilized zirconia (ZrO _2- Y ₂ O ₃ : YSZ), a metal oxide obtained by adding _{Gd 2} O ₃ , Yb ₂ O ₃ , Er ₂ O _3, _{etc. to YSZ, ZrO 2-} HfO _2- Y ₂ O ₃ , ZrO _2- Y ₂ O _3- La ₂ O ₃ , ZrO _2- HfO _2- Y ₂ O _3- La ₂ O ₃ , HfO _2- Y ₂ O ₃ , CeO _2- Y ₂ O ₃ , Gd ₂ Zr ₂ O ₇ , Sm ₂ Zr ₂ O ₇ , LaMnAl ₁₁ O ₁₉ , YTa ₃ O ₉ , Y _0.7 La _0.3 Ta ₃ O ₉ , Y _1.08 Ta _2.76 Zr _0.24 O ₉ , Examples thereof include Y ₂ Ti ₂ O ₇ _{, LaTa 3} O ₉ , Yb ₂ Si ₂ O ₇ , Y ₂ Si ₂ O ₇ , and Ti ₃ O ₅ . Examples of the dense ceramic used in the coating layer include alumina, silica, zirconia and the like. Further, by removing the ceramic fibers and the plate-shaped ceramic particles from the constituent materials of the above-mentioned inorganic porous layer, the porosity becomes low (dense), so that it may be used as a coating layer. By using the porous or dense ceramic as the coating layer, the inorganic porous layer can be reinforced and the inorganic porous layer can be prevented from peeling off from the surface of the metal tube. When a dense ceramic is used as the coating layer, for example, it is possible to suppress the permeation of high-temperature gas through the inorganic porous layer and the retention of exhaust gas in the inorganic porous layer. As a result, the effect of suppressing the heat transfer of the exhaust gas to the metal pipe can be expected.

The exhaust pipe 10 will be described with reference to FIGS. 1 to 3. The exhaust pipe 10 is provided with an inorganic porous layer 4 on the inner surface of a metal pipe 2 made of SUS430. The inorganic porous layer 4 is joined to the inner surface of the metal tube 2 (see FIGS. 1 and 2). The exhaust pipe 10 was manufactured by immersing the metal pipe 2 in the raw material slurry, drying and firing the metal pipe 2 with the outer surface of the metal pipe 2 masked. The raw material slurry includes alumina fibers (average fiber length 140 μm), plate-shaped alumina particles (average particle diameter 6 μm), titania particles (average particle diameter 0.25 μm), and alumina sol (alumina amount 1.1% by mass). Acrylic resin (average particle size 8 μm) and ethanol were mixed to prepare the mixture. The raw material slurry was adjusted so that the viscosity was 2000 mPa · s.

After immersing the metal tube 2 in the raw material slurry and applying the raw material to the inner surface of the metal tube 2, the metal tube 2 was put into a dryer and dried at 200 ° C. (atmospheric atmosphere) for 1 hour. As a result, an inorganic porous layer of about 300 μm was formed on the inner surface of the metal tube 2. Then, the step of immersing the metal tube 2 in the raw material slurry and drying it was repeated three times to form a 1.2 mm inorganic porous layer on the inner surface of the metal tube 2. Then, the metal pipe 2 was placed in an electric furnace and fired at 800 ° C. in an atmospheric atmosphere to prepare an exhaust pipe 10. The inorganic porous layer 4 was formed on the entire inner surface of the metal tube 2 (see FIG. 3). In the obtained exhaust pipe 10, the porosity of the inorganic porous layer 4 was 61% by volume, and the coefficient of thermal expansion was 7 × 10 ^-6 K- ¹ . Although not shown, it was confirmed that the titania particles were interposed between the aggregates and joined the aggregates in the exhaust pipe 10. It was also confirmed that the titania particles were interposed between the inner surface of the metal tube 2 and the aggregate (alumina fibers and plate-like alumina particles), and joined the inner surface of the metal tube 2 and the aggregate.

(Experimental example)
As described above, the inorganic porous layer prepares a raw material slurry in which alumina fibers, plate-like alumina particles, titania particles, alumina sol, acrylic resin and ethanol are mixed, and the metal (metal plate and metal tube) is immersed in the raw material slurry. After that, it was dried and fired to prepare it. In this experimental example, in order to confirm the effect of the amounts of the alumina component and the titania component on the characteristics of the inorganic porous layer, the proportions of the alumina fiber, the plate-like alumina particle and the titania particle were changed, and the alumina fiber was changed to the mullite fiber. The plate-like alumina particles were replaced with plate-like mica, and the state of the inorganic porous layer after firing was confirmed.

Specifically, the blending amounts of ceramic fibers (alumina fibers, murite fibers), plate-shaped ceramic particles (plate-shaped alumina particles, plate-shaped mica), titania particles, and zirconia particles are changed as shown in FIGS. 5 and 6. , Alumina fiber, plate-shaped alumina particles, titania particles and zirconia particles are blended so that the total is 100% by mass, and further, 10% by mass of alumina sol (1.1% by mass of alumina contained in the alumina sol) is added. 40% by mass of acrylic resin was added, and the slurry viscosity was adjusted with ethanol to prepare a raw material slurry. Note that sample 9 does not use plate-shaped ceramic particles, and samples 1 to 11, 14 and 15 do not use zirconia particles. Then, the raw material slurry was applied to a metal made of SUS430 (SUS plate, SUS tube), dried in an air atmosphere of 200 ° C. for 1 hour, and then calcined in an air atmosphere of 800 ° C. for 3 hours. The number of times the raw material slurry was applied (the number of times the metal plate and the metal tube were immersed) in each sample was adjusted so that an inorganic porous layer of about 1.2 mm was formed on the metal surface (inner surface in the case of a metal tube). For sample 4, the amount of acrylic resin added to the first raw material slurry to be applied to the metal plate was set to 50% by mass, and for sample 6, the amount of acrylic resin added to the first raw material slurry was set to 30% by mass. For sample 7, the amount of acrylic resin added to the first raw material slurry was 10% by mass, and for sample 8, the amount of acrylic resin added to the first raw material slurry was 5% by mass. For samples 4, 6 to 8, the amount of acrylic resin added to the raw material slurries for the second and subsequent times was set to 40% by mass.

In this experimental example, the influence of the amounts of the alumina component (ceramic fiber, plate-shaped ceramic particles) and the titania component on the appearance of the inorganic porous layer (presence or absence of cracks, peeling, etc.), and the skeleton portion of the inorganic porous layer. The heat insulating property of the inorganic porous layer has not been evaluated for the purpose of confirming the influence of the contact area between the metal plate and the metal plate on the adhesion.

The appearance of the sample after firing was evaluated. The appearance was evaluated with a sample in which an inorganic porous layer was formed on a metal plate. In the appearance evaluation, the presence or absence of cracks and peeling was visually observed. In FIG. 6, "○" is attached to the sample in which crack and peeling did not occur, "△" is attached to the sample in which one of crack and peeling occurred, and "△" was attached to the sample in which both crack and peeling occurred. "X" is attached.

The contact area between the inorganic porous layer and the metal was measured for Samples 1 to 15. The contact area was measured with a sample in which an inorganic porous layer was formed on a metal plate. As shown in FIG. 4, the contact area is measured by observing the interface portion 25 between the inorganic porous layer 20 and the metal plate 30 by SEM, and the contact length between the skeleton 22 of the inorganic porous layer 20 and the surface 32 of the metal plate 30. Was measured and calculated. Specifically, the length L0 of the surface 32 of the metal plate 30 is measured, the total length L1 of the lengths of the portions 24 in which the skeleton 22 is in contact with the surface 32 is calculated, and the contact area is calculated from the following formula (2). S was calculated. The results are shown in FIG.
Equation 2: S (%) = L1 / L0 × 100

For the samples 1 to 15, the ratio (mass%) of the alumina component and the titania component in the inorganic porous layer was measured, and the porosity (volume%) of the inorganic porous layer was measured. The sample for measuring the component ratio and the porosity was prepared by molding the bulk body of the inorganic porous layer into a bulk body using the above-mentioned raw material slurry and then firing the bulk body at 800 ° C. For the alumina and titania components, the amounts of aluminum and titanium were measured using an ICP emission spectrometer (PS3520UV-DD, manufactured by Hitachi High-Tech Science Co., Ltd.). 5 and 6 show the results of converting the amounts of aluminum and titanium into oxides (Al ₂ O ₃ , TiO _2).

^{The porosity is the total pore volume (unit: cm 3} / g) measured in accordance with JIS R1655 (a molded body pore size distribution test method by the mercury intrusion method of fine ceramics) using a mercury porosity, and a gas substitution formula. It was calculated from the following formula (3) using ^{the apparent density (unit: g / cm 3} ) measured by a density measuring meter (Accupic 1330 manufactured by Micromeritix). FIG. 5 shows the result of porosity.
Equation 3: Porosity [%] = total pore volume / {(1 / apparent density) + total pore volume} x 100

For samples 1 to 15, the coefficient of thermal expansion of the inorganic porous layer and the metal (metal plate) was measured. The sample for measuring the coefficient of thermal expansion of the inorganic porous layer was prepared by molding the above-mentioned raw material slurry into a bulk body having a size of 4 mm × 3 mm × 20 mm and then firing the bulk body at 800 ° C. As the sample for measuring the coefficient of thermal expansion of the metal, a sample having a size of 4 mm × 3 mm × 20 mm was used. The measurement sample was measured using a thermal expansion meter in accordance with JIS R1618 (measurement method of thermal expansion by thermomechanical analysis of fine ceramics). FIG. 5 shows the result of the coefficient of thermal expansion.

The thermal conductivity of the inorganic porous layers of Samples 1 to 8 and 15 and the metal plates of Samples 1 to 15 was measured. Thermal conductivity was also measured using separate bulk bodies for the inorganic porous layer and the metal plate. The thermal conductivity was calculated by multiplying the thermal diffusivity, the specific heat capacity and the bulk density. For the heat diffusion rate, a laser flash method heat constant measuring device is used, and for the specific heat capacity, a DSC (differential scanning calorimetry) is used. Method) was measured at room temperature. For the bulk density of the metal plate, the weight of a bulk body having a diameter of 10 mm and a thickness of 1 mm was measured, and the value obtained by dividing the weight by the volume was taken as the bulk density (unit: g / cm ³ ). The bulk density (unit: g / cm ³ ) of the inorganic porous layer was calculated from the following formula (4). The thermal diffusivity is obtained by molding the above-mentioned raw material slurry into a bulk body having a diameter of 10 mm × 1 mm, and the specific heat capacity is obtained by molding the above-mentioned raw material slurry into a bulk body having a diameter of 5 mm × a thickness of 1 mm, and then each bulk body is 800. A sample for measuring thermal diffusivity and specific heat capacity was prepared and measured by firing at ° C. The measurement results are shown in FIG.
Formula 4: Bulk density of the inorganic porous layer = apparent density × (1-porosity [%] / 100)

A heating vibration test was performed on the samples 1 to 15. The heating vibration test was performed on a sample in which an inorganic porous layer was formed on the inner surface of the metal tube. Specifically, the outer surface of a pipe (made by SUS430) having an inner diameter of Φ55 mm, an outer diameter of Φ62 mm (thickness 3.5 mm), and a length of 80 mm is immersed in a raw material slurry while being masked, and an inorganic porous layer is applied to the inner wall of the pipe. did. Then, each sample was prepared by drying at 200 ° C. and calcining at 800 ° C. In the heating vibration test, the sample was attached to the heating vibration test device, and the combustion gas of propane was circulated in the pipe for 5 minutes from the heating vibration test device, and then the normal temperature air gas was circulated for 5 minutes. The combustion gas was adjusted so that the gas temperature at the end face on the inflow side of the pipe was 900 ° C. at the maximum and the gas flow rate was 2.0 Nm ^{3 / min.} Next, while the combustion gas was continuously supplied into the pipe, vibration in the longitudinal direction (longitudinal direction) was applied to the pipe. The vibration conditions were 100 Hz and 30 G, and vibration was applied for 50 hours. The test was conducted under these conditions, and the rate of change in weight before and after the test, the appearance of the inorganic porous layer after the test, and the state of the cross section of the inorganic porous layer were evaluated. In FIG. 6, regarding the appearance of the inorganic porous layer, a sample having a weight change rate of 1% or less and no change in appearance (no cracks and peeling) has “◎”, a weight change rate of 1% or less, and three cracks of less than 3 cm. Below, "○" for the sample without peeling, weight change rate of 1% or less, cracks of 3 cm or more, or 4 or more cracks of less than 3 cm, "△" for the sample without peeling, weight change rate of more than 1%, Alternatively, a sample with cracks and peeling is indicated by an “x”. Regarding the cross-sectional state of the inorganic porous layer, "○" was found in the sample for which no cracks were confirmed, "△" was found in the sample with two or less cracks of less than 500 μm, and there were cracks of 500 μm or more, or less than 500 μm. Samples with 3 or more cracks are indicated by "x".

The adhesion test of the inorganic porous layer was performed on the samples 1 to 15. In the adhesion test, samples similar to the heating vibration test are prepared, and each sample is freely dropped from a height of 1 m with respect to the concrete block, and the presence or absence of peeling of the inorganic porous layer (presence or absence of exposure of the inner surface of the metal tube). Was confirmed and evaluated. Specifically, in the adhesion test, the shaft of the metal pipe is freely dropped from a height of 1 m in a posture parallel to the concrete block in the axial direction (longitudinal direction), and then the shaft of the metal pipe is dropped with respect to the concrete block. One set was a test in which the concrete was freely dropped from a height of 1 m in a vertical direction, and the number of sets from which the inorganic porous layer was peeled off was measured. The test was performed up to 5 sets. The results are shown in FIG. As a result of the adhesion test, it was confirmed that the adhesion (adhesion strength) increases as the contact area between the inorganic porous layer and the metal tube increases (see comparison of samples 4 to 7).

As shown in FIG. 6, in Samples 1 to 12 and 15, no cracks or peeling were confirmed in the inorganic porous layer after firing. On the other hand, in the sample 13, although peeling was not confirmed, the occurrence of cracks was confirmed. In addition, both cracks and peeling were confirmed in the sample 14. This result shows that when the alumina component (ceramic fiber and plate-shaped ceramic particles) in the inorganic porous layer is small (less than 15% by mass) or the titania component is small (less than 45% by mass), the metal- during firing is obtained. It is shown that the force acts between the inorganic porous layers and the characteristics of the inorganic porous layer are deteriorated. Specifically, since the proportion of the alumina component in the sample 13 is less than 15% by mass, it is presumed that the bonding force between the ceramics (particles, fibers) is reduced and cracks are generated in the inorganic porous layer. Further, since the proportion of the titania component in the sample 14 is less than 45% by mass, it is presumed that the bonding force between the ceramics is lowered and cracks are generated in the inorganic porous layer. Further, in the sample 14, the content of the titania component (titania particles) having a high coefficient of thermal expansion is low, and the ratio of the coefficient of thermal expansion to the metal plate (α1 / α2) is small (less than 0.5). It is presumed that the inorganic porous layer was peeled off from the metal plate based on the difference in thermal expansion between the layers. From the above, regardless of the type of ceramic fiber (alumina fiber, mullite fiber) and the type of plate-shaped ceramic particles (plate-shaped alumina particle, plate-shaped mica), 15% by mass or more of alumina component and 45% by mass or more of titania component. It was confirmed that the inorganic porous layer containing the above was less likely to cause deterioration such as cracks and peeling after firing.

As shown in FIG. 6, in Samples 1 to 3, 5 to 7, 10 to 12, and 15, no deterioration was confirmed on the surface and cross section of the inorganic porous layer even after the heating vibration test. On the other hand, in Samples 4 and 9, deterioration was not confirmed after firing, but deterioration was confirmed on the surface of the inorganic porous layer after the heating vibration test. In the samples 13 and 14, deterioration of the inorganic porous layer was confirmed both after firing and after the heating vibration test. Comparing the samples 4 to 8, it is confirmed that the adhesion between the inorganic porous layer and the metal tube is improved as the contact area S between the inorganic porous layer and the metal tube increases. Further, when the contact area S was 40% or more, no surface deterioration of the inorganic porous layer was confirmed after the heating vibration test. On the other hand, in the sample (Sample 4) having a contact area S of less than 40%, deterioration was confirmed on the surface and cross section of the inorganic porous layer after the heating vibration test. As a result, in Sample 4, the adhesion between the inorganic porous layer and the metal tube was low, and a part of the interface between the inorganic porous layer and the metal tube was damaged (cracking occurred) due to thermal shock or vibration impact. It is presumed that the cracks extended to the surface of the inorganic porous layer. Further, in the sample (Sample 8) having a contact area S of more than 80%, no deterioration was confirmed on the surface of the inorganic porous layer after the heating vibration test, but slight cracks were confirmed in the cross section. As a result, the sample 8 has a high Young's modulus (low toughness) of the inorganic porous layer at the interface between the inorganic porous layer and the metal tube, and a part of the interface portion between the inorganic porous layer and the metal tube due to thermal shock. Is presumed to have been damaged. The contact area S of the sample 9 is 40%, which is the same as that of the sample 5, but the inorganic porous layer is not sufficiently reinforced because it does not contain plate-like alumina particles, and when a high-temperature LP gas is circulated. It is presumed that a part of the inorganic porous layer was damaged. From the above results, it was confirmed that the thermal impact resistance and vibration resistance of the exhaust pipe are improved by setting the contact area between the skeleton portion of the inorganic porous layer and the metal pipe to 40% or more and 80% or less.

Although the embodiments of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above. Further, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in the present specification or the drawings achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

2: Metal pipe 4: Inorganic porous layer 10: Exhaust pipe

Claims

An exhaust pipe provided with a metal pipe and an inorganic porous layer provided at a portion of the inner surface of the metal pipe through which exhaust gas passes.
The inorganic porous layer is
Porosity is 45% by volume or more,
It contains ceramic fibers and is composed of 15% by mass or more of alumina component and 45% by mass or more of titania component.
An exhaust pipe in which the contact area between the skeleton portion and the metal pipe is 40% or more at the interface between the inorganic porous layer and the metal pipe.
The exhaust pipe according to claim 1, wherein the thermal conductivity of the metal pipe is 100 times or more the thermal conductivity of the inorganic porous layer.
The exhaust pipe according to claim 2, wherein the inorganic porous layer has a thermal conductivity of 0.05 W / mK or more and 3 W / mK or less.
The exhaust pipe according to claim 2 or 3, wherein the thermal conductivity of the metal pipe is 10 W / mK or more and 400 W / mK or less.
The exhaust pipe according to any one of claims 1 to 4, which satisfies the following formula (1) when the coefficient of thermal expansion of the inorganic porous layer is α1 and the coefficient of thermal expansion of the metal pipe is α2.
0.5 <α1 / α2 <1.2 (1)
The exhaust pipe according to any one of claims 1 to 5, wherein the inorganic porous layer contains plate-shaped ceramic particles.
The exhaust pipe according to any one of claims 1 to 6, wherein the inorganic porous layer contains granular particles of 0.1 μm or more and 10 μm or less.
The exhaust pipe according to any one of claims 1 to 7, wherein the thickness of the inorganic porous layer is 1 mm or more.
The exhaust pipe according to any one of claims 1 to 8, wherein a coating layer is provided on the surface of the inorganic porous layer.