Method for estimating properties of fired ceramic bodies

Abstract

A method for estimating properties of a fired ceramic body, the method comprising: Producing a fired ceramic body by firing a shaped green body; Measuring a color of the fired ceramic body; and using a correlation between the color and at least one property selected from the group consisting of porosity, pore diameter, and thermal expansion coefficient previously determined for a fired ceramic body having the same composition as that of the fired ceramic body, estimating the at least one property of the fired ceramic body from the color of the fired ceramic body measured in the previous step.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for estimating the properties of a fired ceramic body. BACKGROUND OF THE INVENTION

[0002] Ceramic products are used in various industrial applications such as heat sinks, filters, catalyst supports, sliding parts, nozzles, heat exchangers, electrical insulation elements, and parts for semiconductor manufacturing equipment, utilizing their properties such as high heat resistance, high hardness, high chemical resistance, and high abrasion resistance. Generally, ceramic products are manufactured through steps including mixing and kneading ceramic raw material powder, a dispersion medium, a binder, a pore-forming agent, and the like into a green body, and then molding and firing the green body into a predetermined shape.

[0003] In the industrial production of ceramic products, it is desirable to conduct quality control by checking whether various properties required for ceramic products, such as porosity, pore diameter, and thermal expansion coefficient, meet specified criteria. In recent years, higher quality ceramic products have been demanded, and the importance of quality control to meet the required quality has been further increased.

[0004] However, conducting quality inspection of all test items for all manufactured ceramic products increases costs and delays delivery. Therefore, quality control has traditionally been performed through random sampling in some cases. In addition, there are circumstances where destructive testing is required to measure porosity, pore diameter, and thermal expansion coefficient, making it difficult to inspect all products. Under such circumstances, the prior art proposes a method that can easily conduct quality inspection of ceramic products.

[0005] JP 2005-315861 A (Patent Document 1) proposes an inspection method for a porous structure which can be easily carried out by examining the weight of a molded body processed into a predetermined size after molding and drying, without requiring any special device or technique, and which also enables easy inspection of all products.Specifically, Patent Document 1 discloses a method for inspecting a porous structure, which includes previously measuring a relationship between a pore property of a fired body obtained by firing a molded body having a predetermined shape after molding and drying and the weight of the molded body, setting a standard value for the pore property of the fired body and a standard value for the weight of the molded body, and then inspecting the pore property of the fired body from the weight of the molded body based on each of the standard values.

[0006] JP H11 - 258 148 A relates to a cement-based cured body surface for testing the resistance to acidic water of concrete, mortar, paste, and materials coated on the surface with cement as a curing material. The deterioration of the cement-based cured product by acidic water is analyzed by a color change, which is caused by the change in the balance of the mineral composition on the surface due to the decomposition and leaching of cement hydrate.

[0007] US 2013 / 0 206 601 A1 relates to a method for producing an article having a fine concave-convex structure on a surface thereof, the structure having pores in which a pore spacing is less than or equal to a wavelength of visible light, the method comprising: irradiating a surface of the article having the fine concave-convex structure on the surface with light from an illumination device; capturing an image of reflected light from the surface of the article having the fine concave-convex structure on the surface using an imaging device; capturing color information from an image captured by the imaging device; and inspecting the article having the fine concave-convex structure based on the color information. CITATION LISTPatent literature

[0008] Patent document 1: JP 2005- 315 861 A SUMMARY OF THE INVENTION

[0009] Patent Document 1 focuses on a correlation between the weight and pore property of the ceramic molded body and proposes a method for easily and nondestructively conducting quality inspection of the ceramic product. However, it is believed that it is also useful to provide a method other than weight measurement for easily and nondestructively conducting quality inspection of a ceramic product. The present invention has been made in view of the above circumstances. In one aspect, an object of the present invention is to provide a method for nondestructively estimating the properties of a fired ceramic body without relying on weight measurement.

[0010] As a result of intensive studies to solve the above-mentioned problems, the present inventor found that the color of the fired ceramic body has a significant correlation with the porosity, pore diameter, and thermal expansion coefficient. The present invention was made based on this finding and is illustrated below. [1] A method for estimating the properties of a fired ceramic body, the method comprising: Producing a fired ceramic body by firing a shaped green body; Measuring a color of the fired ceramic body; and using a correlation between the color and at least one property selected from the group consisting of porosity, pore diameter, and thermal expansion coefficient previously determined for a fired ceramic body having the same composition as that of the fired ceramic body, estimating the at least one property of the fired ceramic body from the color of the fired ceramic body measured in the previous step. [2] Method for estimating the properties of a fired ceramic body according to [1], wherein the correlation has a determination factor (R 2 ) of 0.7 or more for a linear regression equation. [3] A method for estimating properties of a fired ceramic body according to [1] or [2], wherein the correlation is a correlation between the at least one property and a Z component in a CIE 1931 XYZ color space. [4] Method for estimating the properties of a fired ceramic body according to [1] or [2], wherein the correlation is a correlation between the at least one property and an L* component in a CIE 1976 (L*, a*, b*) color space. [5] A method for estimating the properties of a fired ceramic body according to any one of [1] to [4], wherein the at least one property is the pore diameter. [6] A method for estimating the properties of a fired ceramic body according to any one of [1] to [5], wherein the fired ceramic body is made of cordierite. [7] A method for estimating the properties of a fired ceramic body according to any one of [1] to [6], wherein the fired ceramic body comprises a columnar honeycomb structure portion, the columnar honeycomb structure portion comprising: an outer peripheral side wall; and partition walls arranged on an inner peripheral side of the outer peripheral side wall, the partition walls defining a plurality of cells, each cell forming a flow path from one end face to another end face for a fluid. [8] A method for estimating properties of a fired ceramic body according to [7], wherein the step of measuring the color comprises measuring a color of the one end face, and wherein a correlation between the at least one property and the color of the one end face is used as the correlation. [9] A method for estimating the properties of a fired ceramic body according to [8], wherein the color of one end face is measured while the other end face is shielded from light by a flat surface of a predetermined material and color.

[10] A method for estimating properties of a fired ceramic body according to [7], wherein the step of measuring the color comprises measuring a color of the outer peripheral sidewall, and wherein a correlation between the at least one property and the color of the outer peripheral sidewall is used as the correlation.

[11] A method for conducting a quality inspection of a fired ceramic body based on at least one property estimated by the method for estimating the properties of a fired ceramic body according to any one of items [1] to

[10] .

[0011] According to the method for estimating the properties of a fired ceramic body according to the present invention, one, preferably two, more preferably three properties selected from the group consisting of porosity, pore diameter, and thermal expansion coefficient of a fired ceramic body can be estimated simply by measuring a color of the fired ceramic body. Therefore, the present invention is useful, for example, as a method for easily conducting a quality inspection for a fired ceramic body. Since it measures the color of the honeycomb fired body, a color tone can be managed collectively.

[0012] Typically, when measuring pore properties such as pore diameter and porosity of a fired ceramic body, as well as a thermal expansion coefficient, destructive testing is performed. Therefore, the sample cannot be subjected to other tests, and the measurement takes time. Furthermore, the measurement sample is wasted, resulting in a reduction in yield. However, according to an embodiment of the method for estimating the properties of the fired ceramic body according to the present invention, it is possible to estimate the pore properties and the thermal expansion coefficient in a short time without wasting the sample. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view schematically showing a wall-through type fired ceramic body. Fig. 2 is a schematic cross-sectional view of a through-wall type ceramic body, viewed from a direction perpendicular to a cell extension direction. Fig. 3 is a perspective view schematically showing a wall flow type ceramic body. Fig. 4 is a schematic cross-sectional view of a wall-flow type fired ceramic body viewed from a direction perpendicular to a cell extension direction. Fig. Figure 5 shows the results of plotting a relationship between an X value in a CIE 1931 XYZ color space and a porosity for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 6 shows the results of plotting a relationship between a Y value in a CIE 1931 XYZ color space and a porosity for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 7 shows the results of plotting a relationship between a Z-value in a CIE 1931 XYZ color space and a porosity for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 8 shows the results of plotting a relationship between an L* value in a CIE 1976 (L*, a*, b*) color space and a porosity for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 9 shows the results of plotting a relationship between an a* value in a CIE 1976 (L*, a*, b*) color space and a porosity for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 10 shows the results of plotting a relationship between a b* value in a CIE 1976 (L*, a*, b*) color space and a porosity for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 11 shows the results of plotting a relationship between an X value in a CIE 1931 XYZ color space and a mean pore diameter for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 12 shows the results of plotting a relationship between a Y value in a CIE 1931 XYZ color space and a mean pore diameter for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 13 shows the results of plotting a relationship between a Z-value in a CIE 1931 XYZ color space and a mean pore diameter for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 14 shows the results of plotting a relationship between an L* value in a CIE 1976 (L*, a*, b*) color space and a mean pore diameter for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 15 shows the results of plotting a relationship between an a* value in a CIE 1976 (L*, a*, b*) color space and a mean pore diameter for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 16 shows the results of plotting a relationship between a b* value in a CIE1976 (L*, a*, b*) color space and a mean pore diameter for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 17 shows the results of plotting a relationship between an X value in a CIE 1931 XYZ color space and a thermal expansion coefficient for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 18 shows the results of plotting a relationship between a Y value in a CIE 1931 XYZ color space and a thermal expansion coefficient for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R2 ). Fig. Figure 19 shows the results of plotting a relationship between a Z-value in a CIE 1931 XYZ color space and a thermal expansion coefficient for each fired honeycomb body, along with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 20 shows the results of plotting a relationship between an L* value in a CIE 1976 (L*, a*, b*) color space and a thermal expansion coefficient for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 21 shows the results of plotting a relationship between an a* value in a CIE 1976 (L*, a*, b*) color space and a thermal expansion coefficient for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). Fig. Figure 22 shows the results of plotting a relationship between a b* value in a CIE 1976 (L*, a*, b*) color space and a thermal expansion coefficient for each fired honeycomb body, together with a linear least squares regression equation and a coefficient of determination (R 2 ). DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments according to the present invention will be specifically described with reference to the drawings. Note that the present invention is not limited to the following embodiments, and various modifications and improvements within the scope of the present invention can be made based on the ordinary knowledge of one skilled in the art without departing from the spirit of the present invention.

[0014] According to a method for estimating the properties of a fired ceramic body of the present invention, the method comprises: Producing a fired ceramic body by firing a shaped green body; Measuring a color of the fired ceramic body; and using a correlation between the color and at least one property selected from the group consisting of porosity, pore diameter, and thermal expansion coefficient previously determined for a fired ceramic body having the same composition as that of the fired ceramic body, estimating the at least one property of the fired ceramic body from the color of the fired ceramic body measured in the previous step. (1st step of producing the fired ceramic body)

[0015] The fired ceramic body can be produced by any known method. Generally, the fired ceramic body can be produced by a step of mixing and kneading ceramic raw material powder, a dispersion medium, a binder, a pore-forming agent, and the like into a green body, and then forming the green body into a predetermined shape and firing it. The type of ceramic produced in this step is not limited. Examples of the ceramic include cordierite, mullite, zircon, aluminum titanate, silicon carbide, a silicon-silicon carbide composite, zirconia, spinel, indialite, sapphirine, corundum, titanium oxide, and the like. These ceramics may be included alone or in combination of two or more.

[0016] However, in view of the easy recognizability of a color change of the fired ceramic body, the fired ceramic body preferably has a relatively light color. In particular, the fired ceramic body to be measured preferably has a value (brightness) of an L* component in a CIE 1976 (L*, a*, b*) color space of preferably 30 or more, and more preferably 40 or more, and even more preferably 50 or more. An upper limit for the brightness is not particularly specified, but it may generally be 90 or less, usually 80 or less. Therefore, for example, white or milky white cordierite can be used as a ceramic when used as an exhaust filter for an automobile and / or as a catalyst support.

[0017] The application of the fired ceramic body is also not limited. For example, a fired ceramic body used for various industrial applications such as heat sinks, filters (e.g., GPFs, DPFs), catalyst supports, sliding parts, nozzles, heat exchangers, electrical insulation elements, and parts for semiconductor manufacturing equipment can be characterized according to the invention.

[0018] Fig. 1 and Fig. 2 show a schematic perspective view and a schematic cross-sectional view, respectively, of a fired ceramic body (100) usable as a through-wall type exhaust gas filter for an automotive vehicle and / or as a catalyst carrier. The fired ceramic body (100) comprises: an outer peripheral sidewall (102); and partition walls (112) arranged on an inner peripheral side of the outer peripheral sidewall (102) and defining a plurality of cells (108) that form flow paths from one end face (104) to the other end face (106) for a fluid. In this fired ceramic body (100), both ends of each cell (108) are open, and an exhaust gas flowing into a cell (108) from one end face (104) is purified as it passes through the cell and flows out from the other end face (106).

[0019] Fig. 3 and Fig. 4 show a schematic perspective view and a cross-sectional view of a fired ceramic body (200) usable as a wall-flow exhaust filter for a motor vehicle and / or as a catalyst carrier. The fired ceramic body (200) comprises: an outer peripheral sidewall (202) and partition walls (212) arranged on an inner peripheral side of the outer peripheral sidewall (202) and defining a plurality of cells (208a, 208b) that form flow paths from one end surface (204) to the other end surface (206) for a fluid.

[0020] In the fired ceramic body (200), a plurality of cells (208a, 208b) can be classified into a plurality of first cells (208a) extending from a first end surface (204) to a second end surface (206), the first end surface (204) being open and the second end surface (206) being closed; and a plurality of second cells (208b) arranged on an inner side of the outer peripheral side wall (202) and extending from the first end surface (204) to the second end surface (206), the first end surface (204) being closed and the second end surface (206) being open. In the fired ceramic body (200), the first cell (208a) and the second cell (208b) are alternately arranged to be adjacent to each other across the partition wall (212).

[0021] When a soot-containing exhaust gas is supplied to the first end face (204) on an upstream side of the fired ceramic body (200), the exhaust gas is introduced into the first cells (208a) and flows downstream through the first cells (208a). Since the first cells (208a) are closed at the second end face (206) on the downstream side, the exhaust gas flows through the porous partition walls (212) defining the first cells (208a) and the second cells (208b) and flows into the second cells (208b). Since the soot cannot penetrate the partition walls (212), it is collected and deposited in the first cells (208a). After the removal of the soot, the purified exhaust gas that has flowed into the second cells (208b) flows downstream in the second cells (208b) and flows out at the second end surface (206) on the downstream side.

[0022] Examples of the end face shape of the fired ceramic body (100, 200) include polygonal and irregular shapes such as circular, elliptical, racetrack, oval, triangular, near-triangular, square, and near-square. The fired ceramic body shown has a circular end face and a circular columnar shape as a whole.

[0023] Preferred examples of the cell shape in a cross-section perpendicular to the flow path direction include a square, a hexagon, an octagon, or a combination thereof. Among these, square and hexagon are preferred. Such a cell shape can lead to reduced pressure loss when a liquid flows through the fired honeycomb body, resulting in improved catalyst purification performance.

[0024] Examples of cell density (a number of cells per unit cross-section) include 6 to 2000 cells / in 2(0.9 to 311 cells / cm 2 ), and more preferably 50 to 1000 cells / in 2 (7.8 to 155 cells / cm 2 ), and more preferably 100 to 600 cells / in 2 (15.5 to 92.0 cells / cm 2 ). Here, the cell density is calculated by dividing an end surface of the fired ceramic body (100, 200), excluding the outer peripheral side wall, by an opening area of the entire cell at the end surface (in the case of sealed cells, the calculation is carried out by determining the cells not to be sealed).

[0025] The partition walls may be porous. The porosity of the partition walls can be adjusted as needed depending on the application. It may preferably be 40% or more, more preferably 50% or more, and even more preferably 60% in terms of suppressing liquid pressure loss. The porosity of the partition walls may preferably be 80% or less, more preferably 75% or less, and even more preferably 70% or less in order to ensure the strength of the fired honeycomb body. The porosity is measured by mercury porosimetry using a mercury porosimeter in accordance with JIS R 1655:2003.

[0026] It is desirable that an average pore diameter of the partition walls be set within an appropriate range depending on the application. For example, when the fired honeycomb body is used as a filter, the average pore diameter of the partition walls is preferably 24 μm or less, more preferably 22 μm or less, and even more preferably 20 μm or less. The average pore diameter of the partition walls in the above range can lead to significantly improved particulate matter removal efficiency. In addition, the average pore diameter of the partition walls is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. The average pore diameter of the partition walls in the above range can suppress a reduction in pressure loss.

[0027] Each of the partition walls preferably has a thickness of 150 μm or more, more preferably 170 μm or more, and even more preferably 190 μm or more, in order to increase the strength of the fired honeycomb body and the separation efficiency when used as a filter. Furthermore, the thickness of each partition wall is preferably 260 μm or less, more preferably 240 μm or less, and even more preferably 220 μm or less in terms of suppressing pressure loss.

[0028] When the fired ceramic body (100, 200) is used as a catalyst support, the surface of the partition walls (112, 212) may be coated with a suitable catalyst depending on the purpose. Examples of the catalyst include an oxidation catalyst (DOC) for oxidizing and burning hydrocarbons (HC) and carbon monoxide (CO) to increase the exhaust gas temperature; a PM combustion catalyst for assisting the combustion of PM such as soot; an SCR catalyst and NSR catalyst for removing nitrogen oxides (NO x ); and a three-way catalyst capable of simultaneously removing hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO x ). The catalyst may contain, for example, noble metals (Pt, Pd, Rh, etc.), alkali metals (Li, Na, K, Cs, etc.), alkaline earth metals (Mg, Ca, Ba, Sr, etc.), rare earths (Ce, Sm, Gd, Nd, Y, La, Pr, etc.), transition metals (Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr, etc.) and the like.

[0029] A fired ceramic body having a columnar honeycomb structural part (hereinafter also referred to as a "fired honeycomb body") such as the fired ceramic body (100, 200) can be manufactured by a known manufacturing method, which will be described below by way of example. First, a raw material composition containing a ceramic raw material, a dispersion medium, a pore former, and a binder is kneaded into a green body, and the green body is then extruded into a desired columnar honeycomb formed body. An additive such as a dispersant can be added to the raw material composition as needed. In extrusion molding, a die having a desired overall shape, cell shape, partition wall thickness, cell density, and the like can be used.

[0030] A ceramic raw material is a material for a part remaining after firing metal oxides, metals, and the like, which, as a ceramic, forms a skeleton of the fired honeycomb body. The ceramic raw material can be provided, for example, in the form of powder. Examples of the ceramic raw material include a raw material for obtaining ceramics, such as cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titanium oxide. Specific examples include silicon dioxide, talc, alumina, kaolin, serpentine, pyroferrite, brucite, boehmite, mullite, magnesite, and aluminum hydroxide. The ceramic raw material can be used alone or in combination with two or more.

[0031] For filter applications such as DPFs and GPFs, cordierite can be used as a ceramic. In this case, cordierite raw material can be used as a ceramic raw material. Cordierite raw material is a raw material that forms cordierite through firing. Cordierite raw material has a chemical composition of 30 to 45 mass% alumina (Al2O3) (including a portion of aluminum hydroxide converted to alumina), 11 to 17 mass% magnesium oxide (MgO), and 42 to 57 mass% silicon dioxide (SiO2).

[0032] The pore-forming agent is not particularly limited as long as it forms pores after firing. Examples of the pore-forming agent include flour, starch, foaming resins, water-absorbent resins, silica gel, carbon (e.g., graphite), ceramic balloon, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resins, phenolic resins, foamed resins, and unfoamed resins. The pore-forming agent can be used alone or in combination with two or more. In view of increasing the porosity of the fired honeycomb body, the content of the pore-forming agent is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, based on 100 parts by mass of the ceramic raw material.In order to ensure the strength of the fired honeycomb body, the content of the pore-forming agent is preferably 10 parts by mass or less, and more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or more, based on 100 parts by mass of the ceramic raw material.

[0033] Examples of the binder include organic binders such as methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. In particular, the use of methylcellulose in combination with hydroxypropylmethylcellulose is preferred. Further, the content of the binder is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 6 parts by mass or more, based on 100 parts by mass of the raw material, from the viewpoint of increasing the strength of the honeycomb formed body. The content of the binder is preferably 9 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7 parts by mass or less, based on 100 parts by mass of the ceramic raw material, from the viewpoint of suppressing cracking due to abnormal heat generation in the firing step.The binder can be used alone or in combination of two or more.

[0034] Dispersants that can be used include ethylene glycol, dextrin, fatty acid soaps, polyether polyol, and the like. The dispersant can be used alone or in combination with two or more. The dispersant content is preferably 0 to 2 parts by mass based on 100 parts by mass of the ceramic raw material.

[0035] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, etc. Specifically, water can be used.

[0036] The water content of the honeycomb formed body before performing the drying step is preferably 20 to 90 parts by mass, more preferably 60 to 85 parts by mass, and even more preferably 70 to 80 parts by mass, based on 100 parts by mass of the ceramic raw material. The water content of the honeycomb formed body of 20 parts by mass or more based on 100 parts by mass of the ceramic raw material can easily provide the advantage of easily stabilizing the quality of the honeycomb formed body. The water content of the honeycomb formed body of 90 parts by mass or less based on 100 parts by mass of the ceramic raw material can lead to reduced shrinkage upon drying and thereby suppress deformation. As used herein, the water content of the honeycomb formed body refers to a value measured by a loss on drying method.

[0037] The columnar honeycomb formed body may be open at both ends of all cells, as in the fired ceramic body (100). Furthermore, the columnar honeycomb formed body may have a cellular structure in which one end of the cells is alternately closed, as in the case of the fired ceramic body (200). The method for closing the end surface of the columnar honeycomb formed body is not particularly limited and can be a known method.

[0038] The sealed parts may be made of any material with respect to strength and heat resistance, such as preferably ceramic. The ceramic includes a ceramic material containing at least one material selected from the group consisting of cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titanium oxide. The sealed parts are preferably made of a material containing 50 mass% or more, and more preferably a material containing 80 mass% or more in total of these ceramics. It is even more preferable that the sealed parts have the same material composition as the main body part of the honeycomb formed body because the expansion coefficient during firing can be the same, resulting in improved durability.

[0039] After drying the honeycomb body, degreasing and firing can be performed to produce a fired honeycomb body. Known conditions can be applied for the drying step, degreasing step, and firing step depending on the material composition of the honeycomb body, and no specific description is required. However, specific examples are given below.

[0040] In the drying step, conventional drying methods such as hot air drying, microwave drying, dielectric drying, negative pressure drying, vacuum drying, and freeze drying can be used. Among them, a combined drying method of hot air drying with microwave drying or dielectric drying is preferable because the entire molded body can be dried quickly and evenly. When forming the plugged parts, plugged parts are formed on both end surfaces of the dried honeycomb molded body, and the plugged parts are then dried to obtain a dried honeycomb body.

[0041] A method for forming plugged parts is described as an example. A plugging slurry is stored in a reservoir. A mask with openings at the positions corresponding to the cells where plugged parts are to be formed is then attached to one end face. The end face to which the mask has been attached is immersed in the reservoir, and the openings are filled with the plugging slurry to form plugged parts. The plugged parts can also be formed on the other end face in the same way.

[0042] Next, the degreasing step is described. The combustion temperature of the binder is approximately 200°C, and the combustion temperature of the pore-forming agent is approximately 300 to 1000°C. Therefore, the degreasing step can be performed by heating the honeycomb formed body at a temperature in the range of approximately 200 to 1000°C. The heating time is not particularly limited, but it is usually about 10 to 100 hours. The honeycomb formed body after the degreasing step is called a calcined body.

[0043] The firing step can be carried out, for example, by heating the calcined body to 1350 to 1600 °C and maintaining the temperature for 3 to 10 hours, depending on the material composition of the honeycomb body. (2nd step of color measurement of the fired ceramic body)

[0044] The step of color measurement of the fired ceramic body can be performed using a known colorimeter, e.g., a colorimeter capable of measuring various parameters of a CIE 1931 XYZ color space and / or a CIE 1976 (L*, a*, b*) color space.

[0045] In the step of color measuring the fired ceramic body, the step is preferably performed so that external light does not enter the color measuring section to improve the accuracy of color measurement. A method for preventing external light from entering the color measuring section includes, for example, a method of covering the color measuring section with a light-shielding member. As the light-shielding member, a hard (rigid) light-shielding member made of a hard plastic, ceramic, hard rubber, wood, metal, or the like can be used, but using a soft (flexible) light-shielding member made of a soft rubber, film, cloth, paper, or the like as the light-shielding member prevents light from entering the color measuring section even if the color measuring section of the fired ceramic body has irregularities or curved surfaces.This prevents external light from entering the color measurement section, ensuring that only light emitted by the colorimeter falls on the color measurement section, eliminating noise and improving color measurement accuracy. Measuring color in a dark room also prevents light other than the light from the colorimeter from falling on the color measurement section.

[0046] The color measuring section of the fired ceramic body is not particularly limited. For example, when the fired ceramic body is a fired honeycomb body, the color of one of the end faces may be measured. In this case, the measurement is preferably performed while covering one end face with the light-shielding member to prevent external light from entering the color measuring section. Furthermore, in the case where both ends of the cells of the fired ceramic body are open, light enters from the other open end face when one end face is measured. Moreover, the light from the color measuring device is incident even if it is shielded so that it does not enter the other end face from the outside. Therefore, it is preferable to measure the color of one end face while protecting the other end face from light by a flat surface made of a predetermined material and having a predetermined color.The light-shielding member with a flat surface can be selected from the light-shielding members described above to suit the intended use. For example, this includes a method in which the fired honeycomb body is placed on a plate made of a specific material and color to shield the lower end surface, and the color of the upper end surface is measured.

[0047] When the fired ceramic body is a honeycomb fired body, the color of the outer peripheral sidewall can be measured. As described above, the color of the outer peripheral sidewall is preferably measured by covering the outer peripheral sidewall with a light-shielding member to prevent external light from entering the color measurement section. (3rd step of estimating the properties of the fired ceramic body)

[0048] The color of the fired ceramic body shows a significant correlation with porosity, pore diameter, and thermal expansion coefficient, particularly porosity and pore diameter. Therefore, after measuring the color of the fired ceramic body, a correlation between the color and at least one property selected from the group consisting of porosity, pore diameter, and thermal expansion coefficient, previously determined for a fired ceramic body with the same composition as the above-mentioned fired ceramic body, can be used to estimate the at least one property of the fired ceramic body from the color of the fired ceramic body measured in the previous step.

[0049] The porosity and pore diameter of the fired ceramic body can be measured using mercury porosimetry, e.g., a mercury porosimeter according to JIS R 1655: 2003. Mercury porosimetry is a method in which a sample is immersed in mercury under vacuum and a uniform pressure is applied. The mercury penetrates into the sample with a gradual increase in pressure. A pore diameter distribution is calculated from the pressure and the volume of mercury that has penetrated into the pores. A typical example of the pore diameter includes an average pore diameter. In mercury porosimetry, as the pressure is gradually increased, mercury successively penetrates from the pores with a larger diameter, and when all pores are finally filled with mercury, the cumulative mercury volume is balanced. The cumulative volume at this time is the total pore volume (cm 3 / g), and the pore diameter at the time when 50% of the total pore volume is penetrated by mercury is the mean pore diameter. Porosity can also be determined from the total pore volume.

[0050] The thermal expansion coefficient includes a linear expansion coefficient and a volumetric expansion coefficient. Known methods for determining the linear expansion coefficient include, but are not limited to, an optical interference method, an X-ray diffraction method, a microscopic telescope method / optical scanning method, a push-rod dilatometer, a mechanical lever method, an optical lever method, an electrical capacitance method, a strain gauge method, and the like. The volumetric expansion coefficient can also be measured using the known method.

[0051] The above-mentioned properties can each be measured using a variety of measurement methods. However, they are preferably measured under the same measurement conditions as those used in the previous determination of the correlation between the properties and color in order to obtain a highly reliable estimate.

[0052] From the point of view of increasing the accuracy of estimating the properties of the fired ceramic body, it is preferable to use, like the above-mentioned correlation, a correlation with a determination factor (R 2 ) of 0.7 or more for a linear regression equation, preferably a correlation with a coefficient of determination (R 2 ) of 0.8 or more, more preferably a correlation with a coefficient of determination (R 2 ) of 0.9 or more. For example, a correlation with a coefficient of determination (R 2 ) from 0.7 to 0.95 can be used.

[0053] The determination factor (R 2 ) is a parameter that is a measure of the accuracy of a regression equation and takes a value from 0 to 1. For a certain property of the fired ceramic body and a certain color parameter, it can be said that a correlation between them is high if a determination factor determined by the regression equation based on the measured data is found close to 1, which makes it possible to estimate the properties from the color with high accuracy.

[0054] The determination factor (R 2 ) is determined by the following equation: R2=∑i=1n(y^i−y¯)2∑i=1n(yi−y¯)2=1−∑i=1n(yi−y^i)2∑i=1n(yi−y¯)2 by: (xi, yi) represents an actually measured data value; (x i ,ŷ i ) represents a data value estimated from the regression equation; (x̅,y̅) represents an average value calculated from the entire data; and n represents the number of data.

[0055] The at least one property has a high correlation with a Z component in the CIE 1931 XYZ color space. Among the properties, porosity and pore diameter have a higher correlation with the Z component in the CIE 1931 XYZ color space, and porosity has an even higher correlation with the Z component in the CIE 1931 XYZ color space. For this reason, in a preferred embodiment, a correlation between the at least one property and the Z component in the CIE 1931 XYZ color space can be used as this correlation. In a further preferred embodiment, a correlation between one or two properties selected from the group consisting of porosity and pore diameter and the Z component in the CIE 1931 XYZ color space can be used as this correlation.In a still further preferred embodiment, a correlation between the porosity property and the Z component in the CIE 1931 XYZ color space may be used as this correlation.

[0056] The at least one property also has a high correlation with an L* component in the CIE 1976 (L*, a*, b*) color space. Among the properties, porosity and pore diameter have a higher correlation with the L* component in the CIE 1976 (L*, a*, b*) color space, and porosity has an even higher correlation with the L* component in the CIE 1976 (L*, a*, b*) color space. For this reason, in a preferred embodiment, a correlation between the at least one property and the L* component in the CIE 1976 (L*, a*, b*) color space can be used as this correlation. In a further preferred embodiment, a correlation between one or two properties selected from the group consisting of porosity and pore diameter and the L* component in the CIE 1976 (L*, a*, b*) color space can be used as this correlation.In a still further preferred embodiment, a correlation between the porosity and the L* component in the CIE 1976 (L*, a*, b*) color space may be used as this correlation.

[0057] An example of the method for previously determining the correlation between the property and the color is a method of establishing a calibration curve or regression equation representing the correlation between each property and the color for a fired ceramic body having the same composition as that of the fired ceramic body in order to estimate the at least one property. From the viewpoint of improving the accuracy of estimating the properties, it is preferable to establish a calibration curve or regression equation representing the correlation between each property and the color for a fired ceramic body having the same composition and dimensions as those of the fired ceramic body in order to estimate the at least one property.Using the created calibration curve or regression equation, each property can be estimated based on the color of the fired honeycomb. Examples of regression equations that can be used include a linear regression equation, an exponential regression equation, a logarithmic regression equation, or a polynomial regression equation, among others. When estimating properties using the regression equation, a regression equation with a coefficient of determination (R) is preferred. 2 ) of 0.7 or more, and more preferably 0.8 or more, and even more preferably 0.9 or more. (4th quality check)

[0058] According to one embodiment of the present invention, a method for performing a quality inspection of a fired ceramic body is provided based on at least one property estimated by the property estimation method described above. That is, whether or not the estimated value of each of the above-mentioned properties satisfies a predetermined criterion can be used as a criterion for quality inspection without actually measuring each of the above-mentioned properties.

[0059] The color of the fired ceramic body can be used to estimate product properties such as dimensions, water absorption, isostatic strength, thermal shock resistance or deposition efficiency or material properties such as crystal quantity, softening temperature or stability at elevated temperature or management of production conditions such as firing temperature or firing shrinkage, although it has not been described in detail here. EXAMPLES (1. Manufacturing the fired honeycomb body)

[0060] To 100 parts by mass of a cordierite-forming raw material, 13 parts by mass of a pore-forming agent, 35 parts by mass of a dispersion medium, 6 parts by mass of an organic binder, and 0.5 parts by mass of a dispersant were added. They were mixed and kneaded to prepare a green body. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite-forming raw material. Water was used as the dispersion medium, coke with an average particle diameter of 1 to 10 µm was used as the pore-forming agent, hydroxypropylmethylcellulose was used as the organic binder, and ethylene glycol was used as the dispersant.

[0061] The green body was placed in an extruder and extruded to obtain a cylindrical honeycomb body. The resulting honeycomb body was dried by dielectric drying and hot air drying, and both end faces were then cut to a predetermined size to obtain the required number of dried honeycomb bodies for subsequent testing.

[0062] The specifications of the dried honeycomb bodies are as follows: Overall shape: cylindrical shape with a diameter of 118 mm and a height of 152 mm; Cell shape in a cross-section perpendicular to a flow path direction of the cells: square; Cell density (the number of cells per unit cross-section): 300 cells / cm 2 ; and Partition thickness: 8 mil (200 µm). Each dried honeycomb body was then fired in an air atmosphere at different firing temperatures to obtain a large number of fired honeycomb bodies. (2. Measuring the color)

[0063] Each fired honeycomb was placed on a plate (color: black, material: soft rubber) to shield the lower end face. Then, using a handheld colorimeter (model: NR-12A) available from NIPPON DENSHOKU INDUSTRIES Co., Ltd., the color of the upper end face of each fired honeycomb was measured based on the CIE 1931 XYZ color space and the CIE 1976 (L*, a*, b*) color space. During color measurement, the color measuring section at the upper end face was protected from light by a cover to prevent external light other than the colorimeter light source from entering the color measuring section at the upper end face. (3. Correlation between porosity and color)

[0064] The porosity of the partition walls of the various fired honeycombs subjected to color measurement was measured by mercury porosimetry using a mercury porosimeter according to JIS R 1655: 2003.

[0065] Fig. Figure 5 shows the results of plotting a relationship between the X-value (x-axis) in the CIE 1931 XYZ color space and the porosity (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0066] Fig. Figure 6 shows the results of plotting a relationship between the Y value (x-axis) in the CIE 1931 XYZ color space and the porosity (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0067] Fig. Figure 7 shows the results of plotting a relationship between the Z-value (x-axis) in the CIE 1931 XYZ color space and the porosity (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0068] Fig. Figure 8 shows the results of plotting a relationship between the L* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the porosity (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0069] Fig. Figure 9 shows the result of plotting a relationship between the a* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the porosity (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R2 ).

[0070] Fig. Figure 10 shows the results of plotting a relationship between the b* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the porosity (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0071] The above results show that porosity can be estimated based on the color of the fired honeycomb body, since porosity and color have a correlation. In particular, the determination factor (R 2 ).between the Z value in the CIE 1931XYZ color space and porosity is 0.9 or more, indicating a higher correlation. (4. Correlation between mean pore diameter and color)

[0072] The average pore diameter of the partition walls of each fired honeycomb subjected to color measurement was measured by mercury porosimetry using a mercury porosimeter according to JIS R 1655: 2003.

[0073] Fig. Figure 11 shows the results of plotting a relationship between the X value (x-axis) in the CIE 1931 XYZ color space and the mean pore diameter (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0074] Fig. Figure 12 shows the results of plotting a relationship between the Y value (x-axis) in the CIE 1931 XYZ color space and the mean pore diameter (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0075] Fig. Figure 13 shows the results of plotting a relationship between the Z-value (x-axis) in the CIE 1931 XYZ color space and the mean pore diameter (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0076] Fig. Figure 14 shows the results of plotting a relationship between the L* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the mean pore diameter (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0077] Fig. Figure 15 shows the results of plotting a relationship between the a* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the mean pore diameter (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0078] Fig. Figure 16 shows the results of plotting a relationship between the b* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the mean pore diameter (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0079] The above results show that the mean pore diameter can be estimated based on the color of the fired honeycomb body, since the mean pore diameter and the color have a correlation. In particular, the determination factor (R2 ) between the Z value in the CIE 1931 XYZ color space and the mean pore diameter is 0.7 or more, indicating a higher correlation. (5. Correlation between the coefficient of thermal expansion and the color)

[0080] The thermal expansion coefficients (linear expansion coefficients) of the partition walls of the various fired honeycomb bodies subjected to color measurement were determined using the following method. Each fired honeycomb body was cut out to prepare a test sample with a height of 5 mm, a width of 5 mm, and a length of 50 mm. The test sample was prepared by cutting it out of the fired honeycomb body so that the expansion direction of the cells of the fired honeycomb body corresponded to the longitudinal direction of the test sample. The average linear expansion coefficient in the longitudinal direction when the prepared test sample was heated from 40 °C to 800 °C was measured using a differential detection thermodilatometer.

[0081] Fig. Figure 17 shows the results of plotting a relationship between the X value (x-axis) in the CIE 1931 XYZ color space and the thermal expansion coefficient (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0082] Fig. Figure 18 shows the results of plotting a relationship between the Y value (x-axis) in the CIE 1931 XYZ color space and the thermal expansion coefficient (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0083] Fig. Figure 19 shows the results of plotting a relationship between the Z value (x-axis) in the CIE 1931 XYZ color space and the thermal expansion coefficient (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0084] Fig. Figure 20 shows the results of plotting a relationship between the L* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the thermal expansion coefficient (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0085] Fig. Figure 21 shows the results of plotting a relationship between the a* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the thermal expansion coefficient (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0086] Fig. Figure 22 shows the results of plotting a relationship between the b* value (x-axis) in the CIE 1976 (L*, a*, b*) color space and the thermal expansion coefficient (y-axis) for each fired honeycomb body, along with the linear regression equation using the least squares method and the coefficient of determination (R 2 ).

[0087] The above results show that the thermal expansion coefficient can be estimated based on the color of the fired honeycomb body because the thermal expansion coefficient and color have a correlation. DESCRIPTION OF REFERENCE SYMBOLS 100, 200 fired ceramic body 102, 202 outer peripheral side wall 104, 204 an end face 106, 206 the other end face 108, 208a, 208b cell 112, 212 partition wall

Claims

[1] A method for estimating properties of a fired ceramic body, the method comprising: Producing a fired ceramic body by firing a shaped green body; Measuring a color of the fired ceramic body; and using a correlation between the color and at least one property selected from the group consisting of porosity, pore diameter, and thermal expansion coefficient previously determined for a fired ceramic body having the same composition as that of the fired ceramic body, estimating the at least one property of the fired ceramic body from the color of the fired ceramic body measured in the previous step. [2] A method for estimating properties of a fired ceramic body according to claim 1, wherein the correlation has a determination factor (R 2) of 0.7 or more for a linear regression equation. [3] A method for estimating properties of a fired ceramic body according to claim 1 or 2, wherein the correlation is a correlation between the at least one property and a Z component in a CIE 1931 XYZ color space. [4] A method for estimating properties of a fired ceramic body according to claim 1 or 2, wherein the correlation is a correlation between the at least one property and an L* component in a CIE 1976 (L*, a*, b*) color space. [5] A method for estimating properties of a fired ceramic body according to any one of claims 1 to 4, wherein the at least one property is the pore diameter. [6] A method for estimating properties of a fired ceramic body according to any one of claims 1 to 5, wherein the fired ceramic body is made of cordierite. [7] A method for estimating properties of a fired ceramic body according to any one of claims 1 to 6, wherein the fired ceramic body comprises a columnar honeycomb structural portion, the columnar honeycomb structural portion comprising: an outer peripheral side wall; and partition walls disposed on an inner peripheral side of the outer peripheral side wall, the partition walls defining a plurality of cells, each cell forming a flow path from one end face to another end face for a fluid. [8] A method for estimating properties of a fired ceramic body according to claim 7, wherein the step of measuring the color comprises measuring a color of the one end face, and wherein a correlation between the at least one property and the color of the one end face is used as the correlation. [9] A method for estimating properties of a fired ceramic body according to claim 8, wherein the color of one end face is measured while the other end face is shielded from light by a flat surface of a predetermined material and having a predetermined color. [10] A method for estimating properties of a fired ceramic body according to claim 7, wherein the step of measuring the color comprises measuring a color of the outer peripheral sidewall, and wherein a correlation between the at least one property and the color of the outer peripheral sidewall is used as the correlation. [11] A method for performing a quality inspection of a fired ceramic body based on at least one property estimated by the method for estimating properties of a fired ceramic body according to any one of claims 1 to 10.

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