Inspection methods for monolithic structures

Abstract

To provide a method for inspecting monolithic structures that can smoothly and accurately inspect defects in monolithic structures. [Solution] A method for inspecting a monolithic structure according to one embodiment of the present invention includes a visualization step and a location identification step. In the visualization step, an inspection gas having a different density from 25°C air is supplied to the side and / or second end face of the monolithic structure, and the density distribution of the gas in the space adjacent to the first end face is visualized by the background Schlieren method. In the location identification step, the location of a defect in the monolithic structure is identified three-dimensionally based on the visualized gas density distribution.

Description

Technical Field

[0001] The present invention relates to a method for inspecting a monolithic structure.

Background Art

[0002] Monolithic structures having a plurality of flow paths are used in various industrial products. Examples of industrial products using monolithic structures include separation membrane composites that separate specific components from mixtures containing a plurality of components, and particulate filters (PF) that capture fine particles in fluids. Such monolithic structures may contain internal defects generated during manufacturing. Therefore, it is required to inspect for the presence or absence of internal defects in the monolithic structure. Conventionally, as a method for inspecting defects in a monolithic structure, a foaming inspection using water has been carried out. However, in order to subject a monolithic structure to a foaming inspection, it is necessary to make the monolithic structure permeable to water before the inspection and to dry the monolithic structure after the inspection. Therefore, there is a problem that the inspection efficiency of the monolithic structure is reduced. Therefore, various methods for inspecting defects in a monolithic structure without using water have been studied. For example, a method for inspecting defects in a green honeycomb formed body having a plurality of flow paths, including a step of applying a gas pressure to one end of the plurality of flow paths and a step of visualizing the gas refractive index distribution near the other end of the plurality of flow paths, and visualizing the refractive index distribution by any of the shadowgraph method, Mach-Zehnder method, and schlieren method has been proposed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003] [[ID=3))

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the method for inspecting defects in green honeycomb molded bodies described in Patent Document 1 involves a complicated process of visualizing the gas refractive index distribution, and there is room for improvement in the accuracy of detecting defects in green honeycomb molded bodies. The main objective of the present invention is to provide a method for inspecting monolithic structures that can smoothly and accurately inspect defects in the monolithic structure. [Means for solving the problem]

[0005] [1] A method for inspecting a monolithic structure according to one embodiment of the present invention is a method for inspecting a monolithic structure having a plurality of flow channels. The monolithic structure has a first end face, a second end face, and a side surface. The second end face is located away from the first end face. The side surface is located between the first end face and the second end face. Each of the plurality of flow channels extends in the monolithic structure from the first end face to the second end face. The inspection method for the monolithic structure includes a visualization step and a location identification step. In the visualization step, an inspection gas having a density different from that of 25°C air is supplied to the side surface and / or the second end surface of the monolithic structure, and the density distribution of the gas in the space adjacent to the first end surface is visualized using a background Schlieren method. In the location identification step, the location of a defect in the monolithic structure is identified in three dimensions based on the visualized gas density distribution. [2] In the visualization step of the inspection method for the monolithic structure described in [1] above, the density distribution of gas in the space adjacent to the first end face may be visualized using three or more optical units. Each of the three or more optical units described above may include a background image and an imaging unit. The background image is positioned away from the adjacent space of the first end face in a direction intersecting the normal direction of the first end face. The imaging unit is positioned on the opposite side of the adjacent space of the first end face from the background image. [3] In the visualization step of the inspection method for the monolithic structure described in [1] or [2] above, the steps of: placing a sealing plate on the first end face to expose a portion of the end of the plurality of flow channels on the first end face side and sealing the remainder to visualize the gas density distribution in the space adjacent to the first end face; and moving the sealing plate by a predetermined amount along the first end face; may be repeated in order. [4] In the visualization step of the inspection method for a monolithic structure described in any of [1] to [3] above, the steps of: visualizing the gas density distribution in the space adjacent to the first end face; and rotating the monolithic structure by a predetermined amount with the normal direction at the center of the first end face as the axis of rotation; may be repeated in order. [5] In the method for inspecting a monolithic structure described in any of [1] to [4] above, the monolithic structure may comprise a porous substrate and a separation membrane. The porous substrate has a plurality of through holes. The separation membrane is provided on the inner surface of each of the plurality of through holes in the porous substrate. Each of the plurality of flow channels is formed in the portion of each of the plurality of through holes where the separation membrane is not provided. The inspection method for the monolithic structure described above may further include a sealing step of sealing the ends on the second end face side of the plurality of flow channels before the visualization step. In this case, the inspection gas may be supplied to the side surface of the monolithic structure during the visualization step. [6] In the method for inspecting a monolithic structure described in any of [1] to [4] above, the monolithic structure may comprise a porous substrate, a first eye seal portion, and a second eye seal portion. The porous substrate has a honeycomb shape that divides the plurality of channels. The first eye seal portion is provided on one of the plurality of adjacent channels. The first eye seal portion seals the end on the first end face side of the one channel. The second eye seal portion is provided on the other of the plurality of adjacent channels. The second eye seal portion seals the end on the second end face side of the other channel. In this case, the inspection gas may be supplied to the second end face of the monolithic structure during the visualization step. [Effects of the Invention]

[0006] According to embodiments of the present invention, defects in monolithic structures can be inspected smoothly and accurately. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram illustrating a method for inspecting a monolithic structure according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic plan view illustrating the visualization process included in the inspection method for the monolithic structure shown in Figure 1. [Figure 3] Figure 3 is a schematic plan view illustrating a method for inspecting a monolithic structure according to another embodiment of the present invention. [Figure 4] Figure 4 is a schematic plan view illustrating a method for inspecting a monolithic structure according to yet another embodiment of the present invention. [Figure 5] Figure 5 is a schematic cross-sectional view illustrating a modified example of the monolithic structure shown in Figure 1. [Figure 6] Figure 6 is a schematic diagram illustrating the adjustment of the detection amount in the inspection method for the monolithic structure shown in Figure 1. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Furthermore, in order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments; however, these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overview of Inspection Methods for Monolithic Structures Figure 1 is a schematic diagram illustrating a method for inspecting a monolithic structure according to one embodiment of the present invention. In one embodiment, the inspection method of the monolithic structure is an inspection method of the monolithic structure 1 having a plurality of flow channels 10, and it is possible to inspect the presence or absence of defects in the monolithic structure 1. The monolithic structure 1 typically has a columnar shape extending in a predetermined direction. The monolithic structure 1 has a first end face E1, a second end face E2, and a side face S. The first end face E1 and the second end face E2 are end faces in the axial direction of the monolithic structure 1. The second end face E2 is located away from the first end face E1. The side face S is located between the first end face E1 and the second end face E2. Each of the plurality of flow channels 10 extends from the first end face E1 to the second end face E2 in the monolithic structure 1. Such an inspection method of the monolithic structure 1 includes a visualization step and a position identification step. In the visualization step, an inspection gas having a density different from that of air at 25°C is supplied to the side face S and / or the second end face E2 of the monolithic structure 1, and the density distribution of the gas in the adjacent space of the first end face E1 of the monolithic structure 1 is visualized by the background schlieren method. In the position identification step, based on the visualized gas density distribution, the position of the defect in the monolithic structure 1 is identified three-dimensionally. According to such a method, an inspection gas having a density different from that of air at 25°C is supplied to the monolithic structure, and the density distribution of the gas in the adjacent space of the first end face of the monolithic structure is visualized. Therefore, compared with an inspection method using particles such as the laser smoke method, the influence on the quality of the monolithic structure can be reduced, and the detection accuracy of fine defects of several tens of μm or less can be improved. Also, since the background schlieren method is adopted in the visualization step, optical members such as a collimating lens can be omitted compared with other optical inspection methods such as the schlieren method. Therefore, the inspection unit can be miniaturized, and the adjustment of optical members such as a collimating lens can be omitted. As a result, the number of man-hours for optical adjustment can be shortened, and the defects of the monolithic structure can be inspected smoothly and accurately.

[0010] The visualization process is typically carried out at normal temperature and pressure (25°C, 0.1 MPa). The inspection gas used in the visualization process is arbitrarily and appropriately selected as long as it has a density different from that of air at 25°C. Examples of the inspection gas used in the visualization process include air at 50°C or higher (warm air), air at 0°C or lower (cold air), carbon dioxide, dimethyl ether, helium, and argon. The inspection gas can be used alone or in combination. Among the inspection gases, warm air and cold air are preferably used, and warm air is more preferably used.

[0011] In the visualization process, the pressure of the inspection gas supplied to the side surface S and / or the second end surface E2 of the monolith structure 1 is appropriately adjusted according to the size of the defects that the monolith structure 1 may have. The pressure of the inspection gas is, for example, 5 kPa to 20 kPa, preferably 10 kPa to 15 kPa. If the pressure of the inspection gas is within such a range, the density distribution of the gas in the adjacent space of the first end surface of the monolith structure can be stably visualized.

[0012] In the visualization process, typically, an optical unit 2 capable of imaging local refractive index changes of the gas visualizes the density distribution of the gas in the adjacent space of the first end surface E1 of the monolith structure 1. The optical unit 2 includes a background image 21 and an imaging unit 22. The background image 21 is located away from the adjacent space of the first end surface E1 of the monolith structure 1 in a direction intersecting the normal direction of the first end surface E1. Typically, the background image 21 is located away from the monolith structure 1 in a direction orthogonal to the axial direction of the monolith structure 1. In the direction orthogonal to the axial direction of the monolith structure 1, the distance between the monolith structure 1 and the background image 21 is, for example, 500 mm to 1100 mm, preferably 700 mm to 900 mm, and more preferably 750 mm to 850 mm.

[0013] The imaging unit 22 is configured to capture the density distribution (optical distortion) of the gas against the background image 21. The imaging unit 22 is located on the opposite side of the background image 21 from the space adjacent to the first end face E1 of the monolithic structure 1. Typically, the imaging unit 22 is located on the opposite side of the background image 21 from the monolithic structure 1 in a direction perpendicular to the axial direction of the monolithic structure 1. The distance between the imaging unit 22 and the monolithic structure 1 is adjusted arbitrarily and appropriately. In a direction perpendicular to the axial direction of the monolithic structure 1, the distance between the imaging unit 22 and the monolithic structure 1 is typically greater than the distance between the monolithic structure 1 and the background image 21. In a direction perpendicular to the axial direction of the monolithic structure 1, the distance between the imaging unit 22 and the monolithic structure 1 is, for example, 1.00 to 1.50 times, preferably 1.20 to 1.30 times, the distance between the monolithic structure 1 and the background image 21. In a direction perpendicular to the axial direction of the monolithic structure 1, the distance between the imaging unit 22 and the monolithic structure 1 is, for example, 700 mm to 1300 mm, preferably 900 mm to 1100 mm, and more preferably 950 mm to 1050 mm. If the imaging unit, the monolithic structure, and the background image are in this positional relationship, defects in the monolithic structure can be inspected with greater accuracy, and the size of the defects in the monolithic structure can be estimated.

[0014] Viewed from the axial direction of the monolithic structure 1, the imaging area of ​​the imaging unit 22 includes at least a portion of the multiple flow channels 10 of the monolithic structure 1 (see Figure 2). In the illustrated example, all of the multiple flow channels 10 of the monolithic structure 1 are included in the imaging area of ​​the imaging unit 22. In one embodiment, the imaging unit 22 is equipped with a fixed-focus macro lens. With this configuration, the imaging unit can be easily adjusted, and the optical adjustment time can be further reduced. Furthermore, when performing wide-field measurements, this can be addressed by adjusting the relative distance of the imaging unit to the first end face of the monolithic structure, and / or by replacing the imaging unit with a wide-angle lens.

[0015] As shown in Figure 6, in the visualization process, the detection amount X by the background Schlieren method can be appropriately adjusted by changing the inspection gas. This allows for stable visualization of the gas density distribution in the space adjacent to the first end face of the monolithic structure. Note that, for convenience, the multiple flow channels 10 provided by the monolithic structure 1 are omitted in Figure 6. When a test gas is present in the space adjacent to the first end face E1 of the monolithic structure 1, light is refracted as it passes through the test gas. At this time, the angle of refraction ε of the light satisfies equation (1) below. Angle of refraction of light ε = arcsin(n 空気 / n 検査ガス )···(1) (In formula (1), n 空気 represents the refractive index of air at 25°C; n 検査ガス (This represents the refractive index of the test gas at 25°C.) Therefore, the amount detected by the background Schlieren method, X, is observed as a displacement from the case where no inspection gas is present in the space adjacent to the first end face E1 of the monolithic structure 1 in the background image 21 (dotted line in Figure 6). More specifically, the detection amount X in the background Schlieren method is calculated from the product of the distance L between the location of the test gas and the background image 21, and tanε. In other words, since the detection amount X in the background Schlieren method correlates with tanε, it can be adjusted by changing the test gas and thus changing the angle of refraction ε of light. The adjustable range of detection amount X in the background Schlieren method is, for example, 0.4 to 3.8 times that when carbon dioxide is used as the test gas.

[0016] Furthermore, the detection amount X of the background-type Schlieren method may be adjusted by changing the distance between the monolithic structure 1 and the background image 21, thereby varying the distance L from the location of the test gas to the background image 21. In adjusting the detection amount X of the background-type Schlieren method, both the test gas and the distance between the monolithic structure 1 and the background image 21 may be changed, or only one of them may be changed. Since there are practical limitations such as "depth of field" and / or "degrees of freedom of geometric arrangement" when changing the distance between the monolithic structure 1 and the background image 21, it is preferable to prioritize changing the inspection gas.

[0017] As shown in Figure 2, the number of optical units 2 used in the visualization process is, for example, 1 or more, preferably 3 or more. On the other hand, the upper limit of the number of optical units 2 used in the visualization process is typically 12.

[0018] In one embodiment, three or more optical units 2 visualize the gas density distribution in the space adjacent to the first end face E1 of the monolithic structure 1. This method can suppress the false detection of defects that do not actually exist in the monolithic structure, and can accurately pinpoint the location of defects in three dimensions during the location identification process. Alternatively, a calibration pattern may be used to recognize the position of each of the three or more optical units 2. This allows for flexible setting of the position of each optical unit, as calculations can be performed using the position information of each optical unit.

[0019] Furthermore, as shown in Figure 3, the visualization process may involve repeating, in order, an imaging process in which one or more optical units 2 visualize the gas density distribution in the space adjacent to the first end face E1 of the monolithic structure 1; and a rotation process in which the monolithic structure 1 is rotated by a predetermined amount with the normal direction at the center of the first end face E1 of the monolithic structure 1 as the axis of rotation. Typically, the imaging process and the rotation process are repeated until the monolithic structure 1 completes one rotation (2π rad). This method can suppress false detection of defects that do not exist in the monolithic structure, even if the number of optical units is less than three, and can accurately pinpoint the location of defects in three dimensions during the location identification process. The amount of rotation of the monolithic structure 1 in each rotation process is set arbitrarily and appropriately. For example, the amount of rotation of the monolithic structure 1 in each rotation process is less than 2πrad. The product vt of the rotation speed v (m / s) of the outer circumference of the monolithic structure 1 and the exposure time t (s) is preferably 1 / 1000 m or less. When converted to a 300 mm equivalent, it is 6.0 × 10 e-5π ÷ t. If the number of imaging cycles is small, the total imaging time can be shortened by repeating a method of stationary and imaging. The rotational speed v of the outer circumference of the monolithic structure 1 is, for example, 0.05 m / s to 100 m / s, and preferably 0.2 m / s to 10 m / s. The exposure time t is, for example, 0.01 ms to 20 ms, preferably 0 lms to 5 ms.

[0020] Furthermore, as shown in Figure 4, the visualization process may involve an imaging step in which a sealing plate 3 is placed on the first end face E1 of the monolithic structure 1 to expose a portion of the ends of the multiple flow channels 10 on the first end face side, and the remaining portion is sealed, thereby visualizing the gas density distribution in the space adjacent to the first end face E1; and a moving step in which the sealing plate 3 is moved by a predetermined amount along the first end face E1; these steps may be repeated in sequence. Typically, the imaging step and the moving step are repeated until the sealing plate 3 exposes all of the flow channels 10 that are open at the first end face E1 of the monolithic structure 1 at least once. This method can suppress false detection of defects that do not exist in the monolithic structure, even if the number of optical units is less than three, and can accurately pinpoint the location of defects in three dimensions during the location identification process. The sealing plate 3 is configured to be substantially impermeable to fluid. The sealing plate 3 has any suitable shape when viewed in the thickness direction. The sealing plate 3 is made of any suitable material. Examples of materials for the sealing plate 3 include rubber materials such as ethylene propylene rubber. The materials for the sealing plate 3 can be used individually or in combination. In the illustrated example, the sealing plate 3 has a slit 31. The slit 31 is configured to expose the end on the first end face side of the flow channel 10 during the imaging process. The slit 31 extends inward in the planar direction from the edge of the sealing plate 3. The width of the slit 31 is typically greater than that of the flow channel 10.

[0021] In one embodiment, a plurality of rows 10a, each containing the ends of a plurality of flow channels 10 aligned linearly in a predetermined direction, are arranged on the first end face E1 of the monolithic structure 1 in a direction perpendicular to the predetermined direction. The predetermined direction in which the rows 10a extend is, for example, substantially perpendicular to a virtual line segment connecting the center of the first end face E1 of the monolithic structure 1 and the center of the macro lens of the imaging unit 22. In each imaging step, the slit 31 of the sealing plate 3 typically exposes one of the multiple rows 10a. During the movement process, the sealing plate 3 typically moves in a direction perpendicular to the predetermined direction in which the rows 10a extend. As a result, the slit 31 of the sealing plate 3 exposes the row 10a adjacent to the row 10a exposed in the preceding imaging process, in the direction of movement of the sealing plate 3. In the illustrated example, the direction of movement of the sealing plate 3 is substantially parallel to the imaginary line segment connecting the center of the first end face E1 of the monolith structure 1 and the center of the macro lens of the imaging unit 22.

[0022] In the visualization process described above, it is preferable to capture multiple two-dimensional images (Schlieren images). The number of two-dimensional images captured in the visualization process is, for example, 1 to 1000, and preferably 50 to 200. As shown in Figure 1, in the location identification step, the location of defects in the monolithic structure 1 is typically identified in three dimensions by analyzing the two-dimensional image (i.e., the gas density distribution) captured in the visualization step using the control unit 5. Examples of analysis methods performed by the control unit 5 include the application of the tomographic background Schlieren method, algebraic geometric 3D estimation (Algebra reconstruction technique), and the application of a physical neural network. The control unit 5 may be capable of performing a single analysis method, or it may be capable of performing multiple analysis methods. In one embodiment, the control unit 5 averages multiple two-dimensional images (Schlieren images) and performs numerical analysis. This can further improve the accuracy of defect detection in monolithic structures. The control unit 5 is typically connected to the imaging unit 22 in a communication manner. The control unit 5 includes, for example, a central processing unit (CPU), ROM, and RAM. The control unit 5 stores a program capable of performing the analysis method described above.

[0023] B. Details of Monolithic Structures Next, we will describe the details of the monolithic structure 1 with reference to Figures 1 and 5. The monolithic structure 1 has a monolithic shape with multiple channels 10. The monolithic shape refers to a columnar shape with multiple through-holes, and is a concept that includes a honeycomb shape in which each of the multiple through-holes is defined by a cell. The axial direction of the monolithic structure 1 and the direction in which the flow path 10 extends are typically substantially parallel.

[0024] Each of the multiple channels 10 has an arbitrary suitable shape in a cross-section perpendicular to the axial direction of the monolithic structure 1. Examples of cross-sectional shapes of the channels 10 include triangles, quadrilaterals, pentagons, polygons with hexagons or more, circles, and ellipses. Among these cross-sectional shapes of the channels 10, circular and rectangular shapes are preferred, and circular shapes are more preferred.

[0025] The cross-sectional shapes and sizes of the flow channels 10 may all be identical, or at least some of them may differ. If the cross-sectional shape of the flow path 10 is circular, the inner diameter of the flow path 10 is, for example, 1 mm to 5 mm. The distance between the centers of adjacent channels 10 among the multiple channels 10 is set arbitrarily and appropriately according to the application of the monolithic structure 1. The distance between the centers of adjacent channels is measured, for example, as the length of the line segment connecting the centers of adjacent channels in the cross-section of the monolithic structure.

[0026] The density of the channel 10 in the monolithic structure 1 is, for example, 20 cpsi to 500 cpsi. In this specification, "density of flow channels in a monolithic structure" refers to the density of flow channels in a cross-section perpendicular to the axial direction (direction in which the flow channels extend) of the monolithic structure, and "cpsi" refers to 6.4516 cm² of that cross-section. 2 This refers to the number of flow channels per square inch.

[0027] Examples of such monolithic structures 1 include a separation membrane assembly 1a and a particulate filter 1b.

[0028] B-1. Details of the separation membrane assembly In one embodiment, the monolithic structure 1 is a separation membrane assembly 1a. The separation membrane assembly 1a typically comprises a porous substrate 11 having a monolithic shape and a separation membrane 12.

[0029] B-1-1. Porous base material The porous substrate 11 has multiple through holes 11a corresponding to multiple flow channels 10. Each of the multiple through holes 11a extends from the first end face E1 to the second end face E2 of the monolithic structure 1. Each of the multiple through-holes 11a has an arbitrary appropriate shape in a cross-section perpendicular to the axial direction of the monolithic structure 1. An example of the cross-sectional shape of the through-holes 11a is the same as that of the flow channel 10 described above.

[0030] The porous substrate 11 typically has a columnar shape (overall shape). Examples of the overall shape of the porous substrate 11 include a cylindrical shape with a circular base, an elliptical columnar shape with an elliptical base, a prismatic columnar shape with a polygonal base, and a columnar shape with an irregular base. The outer diameter and length of the porous substrate 11 can be appropriately set depending on the purpose.

[0031] The porous substrate 11 typically comprises a three-dimensional, continuous network structure and interconnected pores partitioned by this structure. The framework of the porous substrate 11 is composed of any suitable material. Typical materials for the porous substrate include ceramic materials. Examples of ceramic materials include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide, and cordierite. Ceramic materials can be used individually or in combination. Among ceramic materials, alumina is a preferred choice.

[0032] The average pore size of the porous substrate 11 is, for example, 0.01 μm to 70 μm, and preferably 0.05 μm to 25 μm. Regarding the distribution of pore sizes in the porous substrate 11, D5 is, for example, 0.01 μm to 50 μm, D50 is, for example, 0.05 μm to 70 μm, and D95 ​​is, for example, 0.1 μm to 2000 μm. The average pore size of porous substrates is measured, for example, by a mercury porosimeter, palm porometer, or nanopalm porometer.

[0033] Such a porous substrate 11 is prepared by any suitable method. In one embodiment, first, the raw material powder containing the ceramic material described above is molded into a desired shape by any suitable molding method (e.g., vacuum extrusion). This typically yields an unfired molded body having a monolithic shape. Next, the unfired molded body is fired by any suitable method. The firing temperature is, for example, 900°C to 1800°C, preferably 1200°C to 1450°C. The firing time is, for example, 1 hour to 20 hours. This process prepares a porous substrate 11 having a monolithic shape.

[0034] B-1-2. Separation membrane Typically, the separation membrane 12 is provided on the inner surface of each of the multiple through-holes 11a in the porous substrate 11. In the illustrated example, a channel 10 is formed inside the through-holes 11a. More specifically, in a cross-section obtained by cutting the monolithic structure 1 in a direction perpendicular to the axial direction, the channel 10 is formed in the portion of the through-holes 11a where the separation membrane 12 is not provided (typically the central portion). The separation membrane 12 may be formed over the entire inner surface of the through-hole 11a (i.e., surrounding the flow path 10), as shown in the illustrated example, or it may be formed on a part of the inner surface of the through-hole 11a.

[0035] The separation membrane 12 typically has micropores. The separation membrane 12 separates specific components from a mixture by permeating them, for example, by utilizing differences in molecular size and / or differences in adsorption properties.

[0036] The separation membrane 12 is composed of any suitable material. Examples of materials for the separation membrane 12 include zeolite, alumina, titania, silica, zirconia, mullite, and carbon. The materials for the separation membrane 12 can be used individually or in combination.

[0037] In one embodiment, the separation membrane 12 is a zeolite membrane 12a. The zeolite membrane 12a is prepared by forming a zeolite in a film-like manner on the surface of a porous substrate 11. The zeolite membrane 12a may contain a single zeolite, or it may contain two or more zeolites that have different structures and / or compositions.

[0038] Examples of zeolites that make up a zeolite film include those in which the central atom (T atom) of the oxygen tetrahedron (TO4) constituting the zeolite is solely Si, or composed of Si and Al; AlPO-type zeolites in which the T atom is composed of Al and P; SAPO-type zeolites in which the T atom is composed of Si, Al and P; MAPSO-type zeolites in which the T atom is composed of magnesium (Mg), Si, Al and P; and ZnAPSO-type zeolites in which the T atom is composed of zinc (Zn), Si, Al and P. Some of the T atoms may be substituted with other elements.

[0039] Examples of the above-mentioned zeolites include AEI type, AEN type, AFN type, AFV type, AFX type, BEA type, CHA type, DDR type, ERI type, ETL type, FAU type (X type, Y type), GIS type, LEV type, LTA type, MEL type, MFI type, MOR type, PAU type, RHO type, SAT type, and SOD type zeolites. Among such zeolites, DDR-type zeolites are preferred.

[0040] The maximum number of rings in a zeolite is, for example, 12 or less, preferably 10 or less, and more preferably 8 or less. On the other hand, the lower limit of the maximum number of rings in a zeolite is typically 6.

[0041] The zeolite film contains SiO2 and Al2O3. The zeolite film may further contain alkali metals. Examples of alkali metals include sodium (Na) and potassium (K).

[0042] The molar ratio of SiO2 / Al2O3 in the zeolite film is, for example, 100 or less, preferably 10 or less, more preferably less than 5, and even more preferably 4 or less. The lower limit of the molar ratio of SiO2 / Al2O3 in the zeolite film is typically 2. When the molar ratio of SiO2 / Al2O3 in the zeolite film is within this range, the damage to the zeolite film can be reliably suppressed. The molar ratio of SiO2 / Al2O3 can be measured, for example, by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX; X-ray acceleration voltage 10kV).

[0043] The average pore size of the separation membrane 12 can be arbitrarily and appropriately selected depending on the object to be separated. The average pore size of the separation membrane 12 is, for example, 0.2 nm to 1 nm, preferably 0.3 nm to 0.5 nm. Reducing the average pore size of the separation membrane 12 increases selectivity. The average pore diameter of the separation membrane 12 is smaller than the average pore diameter of the porous substrate 11. If the separation membrane 12 is a zeolite membrane 12a, the average pore diameter is defined as the arithmetic mean of the short and long axes of the n-membered ring pores, with n being the maximum number of member rings in the zeolite. An n-membered ring pore is a pore in which the number of oxygen atoms in the ring structure formed by the bonding of oxygen atoms with T atoms is n. If there are multiple n-membered ring pores with equal n, the arithmetic mean of the short and long axes of all n-membered ring pores is taken as the average pore diameter of the zeolite. The average pore diameter of a zeolite film is determined by the skeletal structure of the zeolite, and can be found, for example, in the International Zeolite Society's "Database of Zeolite Structures" [online], or via the internet.<URL:http: / / www.iza-structure.org / databases / > It can be determined from the values ​​disclosed.

[0044] The thickness of the separation membrane 12 is, for example, 0.05 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.5 μm to 10 μm. When the thickness of the separation membrane is within this range, a good balance between selectivity and transmission velocity can be achieved.

[0045] The separation membrane 12 is formed by any appropriate method depending on the material that constitutes the membrane. For example, a zeolite film 12a can be obtained by coating a zeolite seed crystal onto a porous substrate 11, immersing the porous substrate 11 with the attached seed crystal in a raw material solution, and growing the zeolite using the seed crystal as a nucleus by hydrothermal synthesis. The raw material solution includes, for example, a silica source, an alumina source, organic matter, an alkali source, and water. The heating temperature in hydrothermal synthesis is, for example, between 60°C and 200°C. The heating time is, for example, between 1 hour and 240 hours. Furthermore, a separation membrane can also be formed using a raw material slurry obtained by mixing an organic binder, ceramic raw materials, and a solvent.

[0046] B-1-3. Inspection method for separation membrane assemblies If the monolithic structure 1 is a separation membrane assembly 1a, the inspection method for the monolithic structure 1 (separation membrane assembly 1a) typically includes a sealing step before the visualization step described above. In the sealing process, the ends on the second end face side of the multiple flow channels 10 provided by the monolithic structure 1 (separation membrane assembly 1a) are sealed. In the illustrated example, a lid 4 that is substantially impermeable to fluid is placed on the second end face E2 of the monolithic structure 1 (separation membrane assembly 1a). This seals the ends on the second end face side of the multiple flow channels 10 all at once. In this case, during the visualization process, the inspection gas described above is supplied to the side surface S of the monolithic structure 1 (separation membrane assembly 1a). Therefore, if the monolithic structure 1 (separation membrane assembly 1a) has an internal defect, the inspection gas flows into the flow path 10 through the defective portion. Subsequently, the inspection gas that has flowed into the flow path 10 is discharged from the end of the flow path 10 on the first end face side into the space adjacent to the first end face. As a result, a distribution of gas density occurs in the space adjacent to the first end face, and the imaging unit of the optical unit can image this gas density distribution as optical distortion.

[0047] B-2. Particulate Filter As shown in Figure 5, in one embodiment, the monolithic structure 1 is a particulate filter 1b. A particulate filter 1b typically comprises a porous substrate 11, a first sealing portion 13, and a second sealing portion 14.

[0048] B-2-1. Porous base material The porous substrate 11 of the particulate filter 1b has a honeycomb shape that divides multiple flow channels 10. The porous substrate 11 of the particulate filter 1b will be described in the same way as the porous substrate 11 of the separation membrane assembly 1a described above. Therefore, a detailed description of the porous substrate 11 will be omitted.

[0049] B-2-2. First sealing section and second sealing section The first sealing portion 13 is provided in one of the adjacent flow paths 10 among the multiple flow paths 10, and seals the end on the first end face side of that flow path 10. The second sealing portion 14 is provided on the other of two adjacent flow paths 10 among the multiple flow paths 10, and seals the end on the second end face side of the other flow path 10. In the illustrated example, all of the multiple flow channels 10 are provided with either a first sealing portion 13 or a second sealing portion 14. Each of the first and second sealing portions 13 and 14 is configured to be substantially impermeable to fluid. Each of the first and second sealing portions 13 and 14 is typically fixed to the porous substrate 11. Each of the first eye seal portion 13 and the second eye seal portion 14 is made of any suitable material. Examples of materials for the eye seal portions include the ceramic materials described above. The ceramic materials can be used alone or in combination. The material constituting the first sealing portion 13 and the material constituting the second sealing portion 14 may be the same as or different from each other.

[0050] B-2-3. Inspection Method for Particulate Filters If the monolithic structure 1 is a particulate filter 1b, the visualization step of the inspection method for the monolithic structure 1 (particulate filter 1b) is to supply the inspection gas described above to the second end face E2 and / or side face S of the monolithic structure 1 (particulate filter 1b). In one embodiment, the inspection gas described above is supplied to the second end face E2 of the monolithic structure 1 (particulate filter 1b). In this case, if the monolithic structure 1 (particulate filter 1b) has an internal defect, the inspection gas flows into the flow path 10 through the defective portion. Subsequently, the inspection gas that has flowed into the flow path 10 is discharged from the end of the flow path 10 on the first end face side, which is not sealed by the first sealing portion 13, into the space adjacent to the first end face. As a result, a distribution of gas density occurs in the space adjacent to the first end face, and the imaging unit of the optical unit can image this gas density distribution as optical distortion. [Industrial applicability]

[0051] The method for inspecting monolithic structures according to embodiments of the present invention can be used in the manufacture of monolithic structures, and is particularly suitable for the manufacture of separation membrane assemblies and particulate filters. [Explanation of Symbols]

[0052] 1 Monolithic Structure 1a Separation membrane assembly 1b Particulate filter 11 Porous substrate 11a Through hole 12 Separation membrane 13. First sealing section 14. Second sealing section 2 Optical Units 21 Background Images 22 Imaging Department 3. Sealing plate 31 slits

Claims

1. A method for inspecting a monolithic structure having multiple flow channels, The monolithic structure has a first end face, a second end face located away from the first end face, and a side surface located between the first end face and the second end face. Each of the aforementioned plurality of flow channels extends from the first end face to the second end face in the monolithic structure. The inspection method for the aforementioned monolithic structure is: A visualization step is performed by supplying an inspection gas having a density different from that of 25°C air to the side surface and / or second end surface of the monolithic structure, and visualizing the gas density distribution in the space adjacent to the first end surface using a background Schlieren method. A method for inspecting a monolithic structure, comprising a positioning step of three-dimensionally identifying the location of defects in the monolithic structure based on a visualized gas density distribution.

2. In the visualization step, the density distribution of gas in the space adjacent to the first end face is visualized using three or more optical units. Each of the three or more optical units is A background image located at a distance from the adjacent space of the first end face in a direction intersecting the normal direction of the first end face, A method for inspecting a monolithic structure according to claim 1, comprising: an imaging unit located on the opposite side of the background image with respect to the space adjacent to the first end face.

3. In the visualization process, A step of placing a sealing plate on the first end face to expose a portion of the end portion on the first end face side of the plurality of flow paths, and sealing the remainder, thereby visualizing the gas density distribution in the space adjacent to the first end face, A method for inspecting a monolithic structure according to claim 1, comprising the steps of sequentially repeating the step of moving the sealing plate by a predetermined amount along the first end face.

4. In the visualization process, A step of visualizing the gas density distribution in the space adjacent to the first end face, A method for inspecting a monolithic structure according to claim 1, comprising the steps of: rotating the monolithic structure by a predetermined amount with respect to the direction normal to the center of the first end face as the axis of rotation; and repeating these steps in sequence.

5. The aforementioned monolithic structure is A porous substrate having multiple through holes, The porous substrate comprises a separation membrane provided on the inner surface of each of the plurality of through holes, Each of the plurality of flow paths is formed in the portion of each of the plurality of through holes where the separation membrane is not provided. The inspection method for the monolithic structure further includes, prior to the visualization step, a sealing step of sealing the end on the second end face side of the plurality of flow channels, A method for inspecting a monolithic structure according to any one of claims 1 to 4, wherein in the visualization step, the inspection gas is supplied to the side surface of the monolithic structure.

6. The aforementioned monolithic structure is A porous substrate having a honeycomb shape that partitions the plurality of channels, A first sealing portion provided in one of the adjacent flow paths among the plurality of flow paths, the first sealing portion sealing the end on the first end face side of the one flow path, A second sealing portion provided in the other of the adjacent channels among the plurality of channels, the second sealing portion sealing the end on the second end face side of the other channel, A method for inspecting a monolithic structure according to any one of claims 1 to 4, wherein in the visualization step, the inspection gas is supplied to the second end face of the monolithic structure.

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