JP2017006828A - Method for producing honeycomb structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a honeycomb structure having oxygen storage capacity while preventing the generation of breakage caused by thermal impact and the scattering of broken pieces.SOLUTION: Raw material grains CZ using a ceria-zirconia composite oxide as the main component and an inorganic binder 4 are mixed, a green body added with a green body control material is subjected to extrusion molding, and thereafter, it is fired into a honeycomb structure 1. The firing step includes: the first stage S1 of performing temperature increase to the first temperature range T1 at which the organic components in the green body control material are thermally decomposed under the first low oxygen atmosphere A1; the second step S2 of performing temperature increase to the second temperature range T2 at which the honeycomb molded body is sintered; the third stage of performing temperature decrease to the third temperature range T3 at which the residual carbon component caused by the organic components are burnt; the fourth stage S4 of gradually increasing the oxygen concentration not exceeding the second low oxygen atmosphere A2 in the third temperature range T3; and the fifth stage of forming the ambient atmosphere after the temperature decrease to the fourth temperature range T4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a honeycomb structure that is composed mainly of a ceria-zirconia composite oxide and has an oxygen storage capacity.

  In order to purify automobile exhaust gas, a catalytic converter that supports a catalyst using a honeycomb structure as a base material and accommodates the catalyst in a case is used. A honeycomb structure is generally configured using a material such as cordierite or SiC, and covers the inner surface of many cells through which exhaust gas flows to form a porous coat layer containing a promoter component and a noble metal catalyst. The In addition, the honeycomb structure is usually fixed in the case in a state where a holding mat for canning is wound around the entire outer peripheral surface.

  On the other hand, it has been studied that the substrate itself made of a honeycomb structure is made of a material mainly composed of a promoter component. For example, a technology is known in which a promoter structure made of ceria-zirconia composite oxide having oxygen storage ability is used, and the promoter particles are bonded together with an inorganic binder to form a honeycomb structure having oxygen storage ability. . However, a material mainly composed of a promoter component has a problem that its mechanical strength is weaker than that of a conventional material. For this reason, it is necessary to take measures against surface pressure, thermal shock, etc. caused by canning.

  Patent Document 1 proposes a honeycomb structure including a honeycomb unit including ceria particles, particles of a ceramic material whose self-sinterability is lower than that of ceria particles, and an inorganic binder. The ceramic material having a low self-sintering property is a material having a relatively high binding reactivity between the secondary particles, for example, alumina, silica, zeolite, and the average particle size thereof is equal to or less than the average particle size of the ceria particles. Blended into the raw material paste to increase the strength of the honeycomb unit. Moreover, a large-diameter honeycomb structure is obtained as a segment structure in which the side surfaces of a plurality of honeycomb units are joined by an adhesive layer.

Japanese Patent No. 518583

  However, in the process of manufacturing a honeycomb structure by forming and firing a raw clay containing a clay adjusting material made of an organic component in order to perform extrusion molding, mainly with a promoter component having oxygen storage capacity, Sudden self-heating occurred, and there was a problem that breakage such as cracks occurred due to thermal shock. This is presumably because of the catalytic function of the promoter component, the organic component contained in the raw material clay self-decomposes in an atmosphere where oxygen is present, and a temperature distribution is generated due to rapid heat generation at the reaction site. Even when firing is performed in a low-oxygen atmosphere, when the honeycomb structure cooled from the firing temperature is taken out, when the firing furnace is opened to the atmosphere, rapid oxygen storage occurs and heat is generated. In this case, the higher the proportion of the cocatalyst component is, and the larger the honeycomb structure is, the larger the heat generation temperature rise is, and there is a high possibility that breakage due to thermal shock and further scattering of broken pieces will occur. .

  The present invention has been made in view of such a background, and an object of the present invention is to produce a honeycomb structure having an oxygen storage capacity while preventing occurrence of damage due to thermal shock and scattering of broken pieces.

One aspect of the present invention is a method for manufacturing a honeycomb structure,
Mixing raw material particles mainly composed of ceria-zirconia composite oxide and an inorganic binder that joins the raw material particles, adding a soil conditioner composed of organic components, and kneading the kneaded material obtained by kneading, Extrusion molding to form a honeycomb molded body,
The resulting honeycomb formed body is dried and then sintered to obtain the honeycomb structure, and
The firing step is
A first step of raising the temperature of the honeycomb formed body to a first temperature range in which the organic component in the clay adjusting material can be thermally decomposed in a first low-oxygen atmosphere having an oxygen concentration lower than that of an air atmosphere;
A second step of raising the temperature from the first temperature range to a second temperature range where the honeycomb formed body can be sintered in the first low oxygen atmosphere;
A third step of lowering the temperature of the residual carbon component resulting from the organic component from the second temperature range to a third temperature range where oxidation combustion is possible under the first low oxygen atmosphere;
While maintaining the third temperature range, the oxygen concentration is gradually increased within a range that does not exceed the second low oxygen atmosphere having a higher oxygen concentration than the first low oxygen atmosphere and a lower oxygen concentration than the air atmosphere. A fourth step;
A fifth step of lowering the temperature to a fourth temperature range lower than the third temperature range, reaching the second low oxygen atmosphere, and then increasing the oxygen concentration to the air atmosphere. In the manufacturing method.

  According to the manufacturing method, the first to third steps are performed in a first low oxygen atmosphere. Therefore, when raising the temperature from the first temperature range to the second temperature range, it is possible to suppress the catalytic activity of the ceria-zirconia composite oxide, while suppressing heat generation due to the self-decomposition of organic components in the clay, Firing can be performed. In addition, after the temperature of the residual carbon component is lowered to the third temperature range where oxidation combustion is possible, in the fourth step, oxygen is gradually introduced in a range not exceeding the second low oxygen atmosphere. Therefore, the residual carbon component can be gradually oxidized and burned, and the oxygen storage can be gradually advanced. Therefore, in the fifth step, when the oxygen concentration is raised to the atmospheric atmosphere after the temperature is lowered to the fourth temperature range, rapid heat generation is suppressed, and occurrence of breakage such as cracks due to thermal shock can be prevented.

  As a result, a honeycomb structure having an oxygen storage capacity can be manufactured while preventing breakage due to thermal shock and scattering of broken pieces. And according to the said manufacturing method, since the stable honeycomb structure of the quality which is not damaged is obtained, the compounding ratio of a promoter component can be made comparatively large, and a promoter function can be improved. Further, even if the aperture is relatively large, the required mechanical strength can be maintained, so that it can be mounted on an automobile catalytic converter as an integral non-segment honeycomb structure.

The firing profile figure for demonstrating the firing process of the honeycomb structure in Embodiment 1. FIG. 1 is an overall perspective view of a honeycomb structure in Embodiment 1. FIG. 1 is an overall schematic cross-sectional view of a catalytic converter including a honeycomb structure according to Embodiment 1. FIG. FIG. 2 is a schematic diagram showing a comparison of structures before and after firing of a honeycomb structure in the first embodiment. FIG. 3 is a schematic diagram for explaining a sintering process of a honeycomb structure in the first embodiment. The typical figure which compares and shows the structure | tissue before and after baking of the conventional honeycomb structure before and behind sintering. The firing profile figure of a honeycomb structure in Example 1. FIG. The figure which shows the relationship of the heat_generation | fever temperature of a honeycomb structure in Example 1, and required reaction time.

(Embodiment 1)
Next, a preferred embodiment of the method for manufacturing a honeycomb structure will be described with reference to the drawings. As shown in FIG. 2, the honeycomb structure 1 has a large number of cells 12 partitioned by cell walls 11 in a cylindrical outer skin. A large number of cells 12 are formed in parallel with each other, with the direction parallel to the axial direction of the honeycomb structure 1 being the cell extension direction indicated by X in the figure, and both ends of the cells 12 are both end faces of the honeycomb structure 1. Open to. The honeycomb structure 1 is made of a material containing a ceria-zirconia composite oxide having oxygen storage capacity, and has a function as a promoter for a noble metal catalyst. The cell wall 11 is porous and suitable for supporting a noble metal catalyst. The honeycomb structure 1 is applied to an automobile catalytic converter 10 shown in FIG.

  Such a honeycomb structure 1 is manufactured through a forming process in which a clay containing a base material is extruded into a honeycomb shape and a firing process in which the honeycomb formed body is fired. In the forming step, raw material particles mainly composed of ceria-zirconia composite oxide (hereinafter referred to as CZ particles) are mixed with an inorganic binder that joins the CZ particles, and a clay conditioner composed of organic components is added. In this step, the kneaded material obtained by kneading is extruded to form a honeycomb formed body. The firing step is a step in which the obtained honeycomb formed body is dried and then sintered in a low oxygen atmosphere to obtain the honeycomb structure 1.

  The CZ particles constitute the base material of the honeycomb structure 1, and the ceria-zirconia composite oxide as the main component has an oxygen storage capacity to enhance the catalyst performance. The CZ particles include ceria-zirconia solid solution particles or solid solution particles in which a rare earth element such as La or Y is further solid-solved. In addition to the CZ particles, particles for reinforcing the cell walls 11 of the honeycomb structure 1, such as alumina particles, can be added to the base material. It is preferable to use θ-alumina particles having a large specific surface area.

  The blending ratio of CZ particles and alumina particles, which are base material materials, can be adjusted to an arbitrary value with respect to the required oxygen storage capacity. From the viewpoint of catalyst performance, in order to maximize the oxygen storage capacity, it is preferable that the addition mass ratio of CZ particles to alumina particles is high. From the viewpoint of ensuring strength, the addition mass ratio of CZ particles to alumina particles is low. Is preferred.

  Further, the CZ particles can be a combination of CZ particles having different average particle diameters. The average particle diameter means a particle diameter at a volume integrated value of 50% in a particle size distribution obtained by a laser diffraction / scattering method. At this time, particles having a relatively small average particle diameter enter between particles having a relatively large average particle diameter, thereby improving the sinterability. Further, when the blending ratio of particles having a relatively small average particle size is increased, the specific surface area of the base material is increased, while the sintering reaction proceeds to decrease the specific surface area after sintering. For this reason, it is good to adjust an average particle diameter and a mixture ratio so that it may become a desired specific surface area after sintering.

  The inorganic binder retains the three-dimensional structure of the cell walls 11 by fixing the particles of the base material material during firing. As the inorganic binder, a sol containing metal oxide or inorganic binder particles that become a metal oxide after sintering, for example, an alumina sol containing sol-like aluminum hydroxide is used. The amount of the inorganic binder added is desirably 5 to 20% by volume with respect to the base material, for example. Within this range, the strength of the honeycomb structure 1 after sintering can be further improved, and the oxygen storage capacity of the honeycomb structure 1 can be sufficiently increased.

  In the molding step, a clay adjusting material is further added and kneaded to a material obtained by mixing these base material particles and an inorganic binder to prepare a clay. The clay adjusting material includes water as a solvent, an organic binder, a lubricant, and the like, and improves the moldability of the clay. Organic binders and lubricants are composed of organic components that can be thermally decomposed or burned off during the heating process during firing. The addition amount of the organic component is desirably 8 to 20% by mass with respect to the base material, for example. Within this range, the shape retention property, fluidity, and adhesiveness of the clay can be further improved, and the clay characteristics suitable for extrusion molding can be maintained well.

  The clay is formed into a honeycomb shape using an extrusion molding machine, and becomes a honeycomb formed body having a desired shape and size. In producing the kneaded material, a known pore former can be added as a pore adjusting material for adjusting the porosity of the honeycomb structure 1.

  As shown in FIG. 1, the firing process includes a first process S1 to a fifth process S5. The first step S1 is a honeycomb formed body degreasing step, in which the organic component in the clay adjusting material is thermally decomposed while adjusting the atmosphere to a predetermined first low oxygen atmosphere A1 having an oxygen concentration lower than that of the air atmosphere. The temperature is raised to a possible first temperature range T1. In the first step, the oxygen concentration in the atmosphere is lowered by substituting the atmosphere of the firing furnace with an inert gas such as nitrogen gas in advance. The first low oxygen atmosphere A1 is, for example, an atmosphere having an oxygen concentration of 0.5% by volume or less, and is preferably an atmosphere having an oxygen concentration below the detection limit, that is, 0.1% by volume or less. Moreover, 1st temperature range T1 is suitably set in the range more than the temperature which the organic component in a clay adjusting material starts thermal decomposition, for example, about 200-500 degreeC, and is about 250 degreeC here.

  The temperature increase rate R1 from the start of temperature increase to the first temperature range T1 may reach the first temperature range T1 while increasing the temperature in two stages, as shown in the figure, or until the first temperature range T1. You may make it hold | maintain for a fixed time after temperature rising in steps or continuously. In the former case, for example, the temperature rising rate R1 is increased up to 150 ° C. (for example, 60 ° C./hour), and thereafter decreased to 250 ° C. (for example, 30 ° C./hour). It is good to degrease, raising temperature toward 1 temperature range T1. In either case, the holding time in the vicinity of the first temperature range T1 is adjusted to be sufficiently long. As described above, the thermal decomposition of the organic component can be favorably controlled by maintaining the extremely low oxygen concentration, suppressing the catalytic activity of the CZ particles, and adjusting the temperature rising rate and the like. Therefore, in the first step S1, it is possible to prevent a temperature distribution due to heat generation from occurring in the honeycomb formed body and damage such as cracks due to thermal shock.

  The second step S2 is a sintering step of the honeycomb formed body, and the temperature is raised from the first temperature range T1 to the second temperature range T2 under the first low oxygen atmosphere A1. Usually, it is held for a predetermined time in the second temperature region T2, but this is not necessarily the case when the time until it reaches the second temperature region T2 is sufficiently long. The second temperature range T2 is appropriately set within a temperature at which the honeycomb formed body can be sintered, for example, in a range of 700 to 1200 ° C., and is about 1050 ° C. here. The temperature increase rate R2 from the first temperature range T1 to the second temperature range T2 can be quickly increased to the vicinity of the second temperature range T2 to shorten the time required for the temperature increase. For example, as shown in the figure, the temperature rising rate R2 is increased up to 800 ° C. (for example, 60 ° C./hour), and is decreased from 800 to 1050 ° C. (for example, 30 ° C./hour). Raise the temperature in stages. The holding time H1 in the second temperature region T2 can be set to a time sufficient for the honeycomb formed body to become a honeycomb sintered body, for example, about 10 hours.

  The third step S3 is a step for cooling the honeycomb sintered body, and the temperature is lowered from the second temperature range T2 to the third temperature range T3 under the first low oxygen atmosphere A1. The third temperature range T3 is equal to or higher than a temperature at which the carbon component remaining due to the organic component in the honeycomb molded body, that is, the carbon component remaining in the honeycomb sintered body can be oxidized and burned, for example, in a range of 500 to 800 ° C. It is set appropriately, and here, it is about 600 ° C. In the third step S3, the rate of temperature decrease R3 from the second temperature range T2 to the third temperature range T3 is, for example, 30 ° C./hour. In the first step S1, the organic components in the honeycomb formed body may remain in a tar-like or carbonized state without being decomposed and burned, and these residual carbon components are removed in the subsequent fourth step S4.

  The fourth step S4 is a decarburization / oxygen storage step of the honeycomb sintered body, and while maintaining the third temperature range T3, the oxygen concentration is gradually increased from the first low oxygen atmosphere A1, and the residual carbon component is removed. While oxidizing and burning, oxygen is stored in the CZ particles of the honeycomb sintered body. This oxygen storage reaction is an exothermic reaction, and a predetermined second low oxygen atmosphere A2 is set in order to avoid excessive heat generation. Then, the oxygen concentration is increased stepwise or continuously so as not to exceed the second low oxygen atmosphere A2. The second low oxygen atmosphere A2 is an atmosphere having an oxygen concentration higher than that of the first low oxygen atmosphere A1 and lower than that of the air atmosphere. Preferably, the low oxygen atmosphere A2 is an atmosphere having a relatively low oxygen concentration, for example, an atmosphere having an oxygen concentration of 5% by volume or less within a range in which oxygen can be stored in the honeycomb sintered body. The atmosphere has a concentration of 2% by volume.

  The timing and rate of increase in the oxygen concentration from the first low oxygen atmosphere A1 to the second low oxygen atmosphere A2 are appropriately adjusted so that excessive heat generation does not occur in the honeycomb sintered body. For example, the calorific value of the honeycomb sintered body per unit time, that is, the sum of the calorific value due to the oxygen storage reaction of the honeycomb sintered body and the calorific value due to the oxidation reaction of the residual carbon component in the honeycomb sintered body is It is preferable that the amount of heat that can be dissipated from the sintered body is approximately equal to or less than that.

  In the fourth step S4, the honeycomb sintered body is decarburized and oxygen occluded while suppressing rapid heat generation by gradually increasing the oxygen concentration and holding it in the third temperature region T3 for a predetermined time. Processing can be performed. At this time, the oxygen concentration in the introduced atmospheric gas is preferably set in advance based on the heat capacity of the honeycomb sintered body, the blending amount of CZ particles, and the like. The holding time H2 in the third temperature region T3 is not less than the time during which the oxygen storage reaction can be completed in the introduction atmosphere, and preferably has a sufficient length with respect to the time during which the oxygen storage reaction can be completed. About 20 hours. Oxygen occlusion of the honeycomb sintered body is almost completed at the holding time H2 in the third temperature region T3, and at this time, the oxygen concentration is increased to the second low oxygen atmosphere A2 during the set holding time H2. You don't have to. In that case, for example, by increasing the oxygen concentration to the second low oxygen atmosphere A2 through the subsequent fifth step S5, the oxygen storage of the honeycomb sintered body is almost completed, and the heat release amount exceeds the heat generation amount. Oxygen can be introduced more safely.

  Specifically, as shown in the figure, after introducing an atmospheric gas having an oxygen concentration of 0.5% by volume at time point a, the oxygen concentration is increased step by step at regular intervals, and at time point b, oxygen concentration is increased. At a concentration of 0.7% by volume and at time point c, an atmospheric gas having an oxygen concentration of 1.0% by volume is introduced. Further, at the time point d in the fifth step S5, an atmosphere gas having an oxygen concentration of 2.0 vol% is introduced to form a second low oxygen atmosphere A2. Thus, the effect of improving the quality of the honeycomb structure 1 is high by keeping the oxygen concentration in the fourth step longer than about 1% by volume and not exceeding 2% by volume.

  The fifth step S5 is a step of releasing the honeycomb sintered body to the atmosphere, and the temperature is further lowered from the third temperature range T3 until the temperature reaches a predetermined fourth temperature range T4 lower than the third temperature range T3. Meanwhile, the oxygen concentration is increased from the second low oxygen atmosphere A2 to the air atmosphere. The fourth temperature range T4 may be a temperature range in which breakage due to rapid cooling does not occur due to a temperature difference from room temperature due to removal of the honeycomb structure, and is, for example, about room temperature to about 100 ° C. In the fifth step S5, the rate of temperature decrease R4 from the third temperature region T3 to the third temperature region T4 is, for example, 60 ° C./hour. Thereafter, when the temperature reaches the fourth temperature range T4, the honeycomb structure is taken out.

  By using the firing profile as described above, degreasing in the first step S1 is performed with good controllability, and in the fourth step S4, the residual carbon component is surely removed and the oxygen storage treatment is completed. it can. In other words, in the fourth step S4, the oxygen concentration is gradually increased to rapidly increase oxygen while suppressing self-heating of the honeycomb sintered body, and then in the fifth step S5, the second low oxygen atmosphere A2 is changed. Since it is allowed to cool to the fourth temperature range T4 while keeping it, even if the air is introduced at a time at this time, rapid oxygen uptake and heat generation associated therewith do not occur. Therefore, after the honeycomb sintered body is cooled, there is little possibility that a rapid temperature rise occurs due to oxygen storage or combustion of residual carbon components, causing damage.

  The honeycomb sintered body thus obtained, that is, the honeycomb structure 1 is then mounted on the catalytic converter 10 shown in FIG. The catalytic converter 10 has a cylindrical case 21 which is connected to a cylindrical tubular exhaust pipe and becomes a part thereof, and the honeycomb structure 1 is accommodated therein. A canning protective mat 22 is interposed between the cylindrical case 21 and the honeycomb structure 1. Here, the left side of the figure is the upstream side of the exhaust gas flow and the right side is the downstream side, and the holding mat 22 is a sheet-like mat made of inorganic fibers such as alumina fibers.

  The honeycomb structure 1 mounted on the catalytic converter 10 carries a noble metal catalyst in advance to form a honeycomb catalyst body. The noble metal catalyst is at least one kind of noble metal selected from, for example, Pt, Rh, and Pd. In the honeycomb structure 1, since the material constituting the cell wall 11 itself has a promoter function, the catalytic performance of the noble metal can be effectively exhibited. At this time, it is possible to change the kind of the precious metal partially supported or change the amount of the precious metal. As an example, when Pd and Rh are supported, first, the honeycomb structure 1 is impregnated with an aqueous solution containing Pd, and then a coat layer containing Rh is formed by wash coating. Further, if necessary, an aqueous solution containing Pd is re-impregnated and dried, followed by baking to obtain a honeycomb catalyst body. Thereafter, canning is performed, and the catalytic converter 10 shown in FIG. 3 can be obtained by press-fitting into the cylindrical case 21 with the holding mat 22 wound around the outer periphery of the obtained honeycomb catalyst body.

  4 and 5, the particle bonding reaction using alumina sol as an inorganic binder and the sintered structure of the honeycomb structure 1 will be described. Here, the clay before firing shown in the left diagram of FIG. 4 is an example including a pore former as a pore adjuster in addition to the clay adjuster. As shown in the left diagram of FIG. 4, the kneaded clay (that is, before firing) is a state in which the CZ particles and alumina particles 3 as the base material, and the pore former 5 are dispersed in the inorganic binder 4. It has become. On the other hand, as shown in FIG. 5, the aluminum hydroxide contained in the alumina sol is aluminized by dehydration condensation during sintering, and the adjacent particles are joined together at that time. That is, a liquid phase is not formed in the transition process to the sintered structure. At this time, when the clay shown in the left diagram of FIG. 4 is fired, the alumina sol that is a grain boundary component gels before the pore former 5 volatilizes, and the three-dimensional configuration in the clay is fixed. Next, aluminization by dehydration condensation proceeds in the sintering process. As a result, as shown in the right figure of FIG. 4, the sintered product is sintered in a compressed state with the particle shape maintained and the fixed grain arrangement as shown in the right figure.

  Thus, in the sintered structure of the honeycomb structure 1, pores are easily formed at the grain boundaries of the base material, and the pores 5 are not used because the intraparticle pores are formed between the primary particles. However, it is possible to relatively increase the porosity. On the other hand, as shown in FIG. 6, conventional base material baking such as cordierite is usually liquid phase sintering. That is, as shown in the left diagram of FIG. 6, the clay before firing includes the raw material particles 71 and 72, the pore former 5, and the liquid phase forming component 6, and as shown in the right diagram of FIG. 6, the pore former 5. After volatilization, a liquid phase is generated at high temperature. At this time, the liquid phase forming component 6 spreads on the surfaces of the raw material particles 71 and 72, and sintering proceeds with the flow and rearrangement of the particles using the space generated by the loss of the pore former. For this reason, the pores between the particles become small, and the pores in the particles tend to decrease due to the wetting of the liquid phase forming component 6.

  Therefore, the honeycomb structure 1 obtained by the above method becomes a porous body mainly composed of a promoter component having an oxygen storage ability, and is excellent in catalyst carrying ability and gas diffusibility. Then, the honeycomb structure 1 having the oxygen storage ability is controlled by controlling the oxygen concentration and the atmospheric temperature in the firing atmosphere of the honeycomb formed body according to the first step S1 to the fifth step S5. Can be manufactured. Therefore, even if the mixture ratio of the ceria-zirconia composite oxide is relatively large and the honeycomb structure 1 has a relatively large diameter, it can be fired without causing rapid heat generation, and prevents breakage such as cracks. Thus, a desired mechanical strength can be maintained. Therefore, the honeycomb structure 1 having an integral non-segment structure can be mounted on an automobile catalytic converter, and the catalytic performance can be improved.

  Specifically, the first step S1 is performed in the first temperature range T1 of 200 to 500 ° C. in the first low oxygen atmosphere A1 having an oxygen concentration of 0.5% by volume or less, so that the thermal decomposition of the organic component is good. To do. In addition, after obtaining the honeycomb sintered body in the second temperature range T2 of 700 to 1200 ° C. in the second step S2, the temperature is lowered to the third temperature range T3 of 500 to 800 ° C. in the third step S3. In the fourth step S4, the oxygen storage reaction is limited by restricting the oxygen concentration to the second low oxygen atmosphere A2 having an oxygen concentration of 0.5 to 2.0% by volume or less, gradually introducing oxygen, and setting the retention time to H2. And the residual carbon component can be removed. And after lowering to 4th temperature range T4 of normal temperature-100 degreeC, it can be set as air atmosphere safely in 5th process S5.

  Further, in the honeycomb structure 1, CZ particles as a base material are secondary particles in which nano-sized primary particles are aggregated, and pores formed between the primary particles are mutually connected to pores formed at the grain boundaries. It communicates and contributes to the diffusion of exhaust gas. At this time, using two types of CZ particles having different average particle diameters is advantageous in improving the specific surface area and sinterability.

Example 1
Next, a material for forming clay was prepared by the above-described method, and the honeycomb structure 1 was manufactured. Here, the honeycomb structure 1 has a cylindrical shape, and has a size of φ103 mm × L105 mm, and a large number of cells 12 having a square cross section are formed therein.

  First, a mixed material was prepared in which two types of CZ particles serving as raw material particles and alumina particles having an average particle diameter of 20 μm were used as a base material, and an alumina sol having an average primary particle diameter of 20 nm was added as an inorganic binder. The two types of CZ particles are CZ particles having an average particle diameter of 14 μm (hereinafter referred to as CZ1) and CZ particles having an average particle diameter of 2 μm (hereinafter referred to as CZ2), and the blending ratio thereof is CZ1: CZ2 = 80: 20 ( (Unit: mass%).

  In the molding step, water as a solvent, an organic binder, and a lubricant are mixed with this material, and the mixture is mixed with a kneader (for example, “MS pressure kneader DS3-10” manufactured by Moriyama Co., Ltd.). A clay was formed by kneading for a minute. Next, the kneaded material was formed into a honeycomb shape by a known extruder. The molding pressure was 10 MPa. Then, it cut | disconnected to predetermined length and obtained the honeycomb molded object.

  Here, the mixing ratio of alumina sol which is an inorganic binder (for example, “AS-520” manufactured by Nissan Chemical Industries, Ltd.) with respect to 100 parts by volume of the base material was 12 parts by volume in solid content. In addition, with respect to 100 parts by mass of the base material, the mixing ratio of water was 37 parts by mass, the mixing ratio of the organic binder was 13.5 parts by mass, and the mixing ratio of the lubricant was 1 part by mass. Methylcellulose (for example, “65MP4000” manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) was used as the organic binder, and “Unilube 50MB26” manufactured by NOF Corporation was used as the lubricant. The raw material particles in this example are CZ particles in which zirconium is solid-dissolved in ceria, but in addition to zirconium, rare earth elements La and Y are also solid-dissolved.

  In the firing step, the honeycomb formed body obtained as described above was sufficiently dried by a microwave dryer and a hot air dryer, and then fired according to the first step S1 to the fifth step S5. As shown in FIG. 7, first, as the first step S1, introduction of nitrogen into the firing furnace is started at time 0 in FIG. 7, so that the oxygen concentration is below the detection limit (ie, 0.1% by volume or less). After the inert atmosphere (that is, the first low oxygen atmosphere A1) was set, the temperature was raised. The temperature rising rate R1 is, for example, 60 ° C./hour from room temperature to 150 ° C., and then slightly lowering the temperature rising rate to reach 250 ° C. (that is, the first temperature range T1) for a certain time (for example, 10 hours), the honeycomb formed body was degreased.

  In the second step S2, in order to sinter the honeycomb formed body, the temperature was raised again and held at 1050 ° C. (that is, the second temperature range T2) for a predetermined time. The temperature rising rate R2 was, for example, 30 to 100 ° C./hour up to 250 to 800 ° C., and then 30 ° C./hour thereafter. The holding time H1 is, for example, 10 hours.

  As 3rd process S3, atmospheric temperature was temperature-fallen to 600 degreeC (namely, 3rd temperature range T3). The temperature lowering rate R3 was set to 30 ° C./hour. Next, as the fourth step S4, the temperature was maintained in the third temperature range T3 and held for a predetermined time. The holding time H2 is 20 hours, for example. Further, the temperature of the atmosphere was lowered to 600 ° C., and when the fourth step S4 was started, the oxygen concentration in the atmosphere to be introduced was increased to 0.5% by volume. Thereafter, the oxygen concentration was gradually increased to 0.7% by volume and 1.0% by volume at regular time intervals. Further, the oxygen concentration in the atmosphere was increased to 2% by volume before the end of the predetermined holding time H2. The increase to 2% by volume was, for example, first increased to about 1.8% by volume, and then gradually introduced by gradually introducing oxygen. In the middle of this, the temperature reduction in the fifth step S5 was started.

  As the fifth step S5, the temperature was lowered to 200 ° C. (that is, the fourth temperature range T4), and then the oxygen concentration was raised from 2% by volume to the air atmosphere. The temperature decrease rate R4 was set to 60 ° C./hour, for example. Here, the setting of the holding time H2 in the fourth step S4 and the oxygen concentration introduced in the fourth and fifth steps S4 and S5 will be described with reference to FIG.

  FIG. 8 shows the honeycomb structure 1 in the fourth step S4 of the firing process, based on the relationship between the amount of heat generated by the occlusion of oxygen in the honeycomb structure 1 manufactured in this example and the amount of heat released based on the heat capacity of the honeycomb structure 1. The result of having investigated the required reaction time with respect to the exothermic temperature of is shown. The exothermic temperature in the figure is the temperature at which oxygen-unoccluded ceria generates heat per unit time due to the oxygen occlusion reaction, based on the ratio of ceria contained in the base material of the honeycomb structure 1. The higher the percentage, the higher the temperature. Further, it can be controlled by the oxygen concentration to be introduced. Therefore, based on the heat capacity calculated from the weight and specific heat of the honeycomb structure 1 (that is, the amount of heat necessary for the temperature to rise by 1 ° C.), the heat consumption rate at which the heat generation temperature = the heat radiation temperature is substantially satisfied. The time required to consume the total amount of heat generated in the honeycomb structure 1 was defined as the required reaction time.

  As shown in the figure, the higher the heat generation temperature, the shorter the required reaction time for storing oxygen in the entire honeycomb structure 1 and the higher the productivity. However, when the heat generation temperature increases, the temperature rise of the honeycomb structure 1 cannot be controlled, and the risk of damage such as cracks due to thermal shock increases. For this reason, preferably, the exothermic temperature is adjusted so that the required reaction time is within an allowable range within a range where the temperature of the honeycomb structure 1 does not greatly deviate from the third temperature range T3 in the fourth step S4. To do. For example, when the oxygen concentration is less than 1.0% by volume and the exothermic temperature is 2.0 K / min, the required reaction time is 10 hours, so this may be set as the holding time H2.

  The honeycomb structure 1 obtained in this way had no damage such as cracks in the outer skin or in the inner part. Further, no discoloration or the like was observed inside. From these results, it was confirmed that the organic component in the honeycomb formed body was decomposed and removed and the residual carbon component was oxidized and removed satisfactorily by the firing step based on the firing profile.

  Thus, according to the method of the present invention, degreasing and decarburization can be performed with good controllability in the firing step of the honeycomb structure 1 having oxygen storage capacity. Therefore, the honeycomb structure 1 with high quality can be obtained without causing breakage of the honeycomb structure 1 or scattering of broken pieces.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the first embodiment and the first embodiment, the outer shape of the honeycomb structure 1 to be manufactured is a cylindrical shape, but may be a polygonal cylinder shape such as a square cylinder. Further, the cell shape of the honeycomb structure 1 may be a polygon such as a triangle, a hexagon, an octagon or the like in addition to the quadrangle, or may be a circle.

  Moreover, the manufacturing method of the honeycomb structure 1 can also change a part, such as a material to be used, a shaping | molding method, and other conditions. For example, the material of the honeycomb structure 1 only needs to include at least raw material particles mainly composed of a ceria-zirconia composite oxide and an inorganic binder, and other ceramic particles such as alumina particles may not necessarily be added. .

DESCRIPTION OF SYMBOLS 1 Honeycomb structure 21 Cylindrical case 22 Holding mat 3 Alumina particle 4 Inorganic binder 10 Automotive catalytic converter 11 Cell wall 12 Cell CZ Ceria-zirconia solid solution particle (namely, raw material particle)

Claims (9)

A method for manufacturing a honeycomb structure (1), comprising:
The raw material particles (CZ) mainly composed of ceria-zirconia composite oxide and the inorganic binder (4) for joining the raw material particles (CZ) are mixed, and a clay adjusting material composed of organic components is added and mixed. The molding process obtained by extruding the clay obtained by smelting into a honeycomb formed body,
The obtained honeycomb formed body is dried and then sintered to obtain the honeycomb structure (1).
The firing step is
The honeycomb formed body is heated to a first temperature region (T1) in which the organic component in the clay adjusting material can be thermally decomposed under a first low oxygen atmosphere (A1) having an oxygen concentration lower than that of the air atmosphere. The first step (S1)
A second step (S2) of raising the temperature from the first temperature range (T1) to the second temperature range (T2) at which the honeycomb formed body can be sintered under the first low oxygen atmosphere (A1);
A third step of lowering the temperature from the second temperature range (T2) to the third temperature range (T3) in which the residual carbon component caused by the organic component can be oxidized and combusted in the first low oxygen atmosphere (A1) ( S3)
A range that does not exceed the second low oxygen atmosphere (A2) having a higher oxygen concentration than the first low oxygen atmosphere (A1) and a lower oxygen concentration than the air atmosphere while maintaining the third temperature range (T3). In the fourth step (S4) of gradually increasing the oxygen concentration,
A fifth step of lowering the temperature to a fourth temperature range (T4) lower than the third temperature range (T3), reaching the second low oxygen atmosphere (A2), and then increasing the oxygen concentration to the air atmosphere ( And (5) a manufacturing method of the honeycomb structure (1).   In the first step (S1), the first low oxygen atmosphere (A1) is a low oxygen atmosphere in which the oxygen concentration in the atmosphere is 0.5% by volume or less, and the first temperature range (T1) is 200%. The method for manufacturing a honeycomb structured body (1) according to claim 1, wherein the temperature is in a predetermined temperature range selected from a range of ~ 500 ° C.   The honeycomb structure (1) according to claim 1 or 2, wherein, in the second step (S2), the second temperature range (T2) is a predetermined temperature range selected from a range of 700 to 1200 ° C. Manufacturing method.   The honeycomb according to any one of claims 1 to 3, wherein in the third step (S3), the third temperature range (T3) is a predetermined temperature range selected from a range of 500 to 800 ° C. Manufacturing method of structure (1).   In the fourth step (S4), the second low-oxygen atmosphere (A2) is a predetermined low-oxygen atmosphere selected from a range where the oxygen concentration in the atmosphere is 0.5 to 2.0% by volume. Item 5. The method for manufacturing a honeycomb structured body (1) according to any one of Items 1 to 4.   In the fourth step (S4), the holding time (H2) in the third temperature range (T3) is equal to or longer than the time when the oxygen storage reaction of the honeycomb structure (1) is completed. A method for manufacturing a honeycomb structured body (1) according to any one of the preceding claims.   The honeycomb according to any one of claims 1 to 6, wherein in the fifth step (S5), the fourth temperature range (T4) is a predetermined temperature range selected from a range of room temperature to 100 ° C. Manufacturing method of structure (1).   The method for manufacturing a honeycomb structured body (1) according to any one of claims 1 to 7, wherein the raw material particles (CZ) in the base material raw material are secondary particles in which primary particles are aggregated.   The method for manufacturing a honeycomb structured body (1) according to any one of claims 1 to 8, wherein in the base material, the raw material particles (CZ) are composed of two kinds of particles having different average particle diameters.

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