JP6360402B2 - Method for producing porous ceramics - Google Patents

Description

  The disclosed embodiment relates to a method for producing porous ceramics.

  2. Description of the Related Art Conventionally, porous ceramics in which many pores are formed in ceramics, such as filters and adsorbents for removing impurities from gas or liquid, and support materials for automobile exhaust gas purification catalysts, have been used in various applications.

  As a method for producing such porous ceramics, a method of applying a gelation freezing method in which a suspension (slurry) in which ceramic particles are dispersed in an aqueous solution of a water-soluble polymer is gelled and then frozen is known. (For example, refer to Patent Document 1).

Japanese Patent No. 5176198

  However, the method for producing porous ceramics described in Patent Document 1 has room for improvement in reducing the lead time and the equipment cost.

  One aspect of the embodiment has been made in view of the above, and an object of the present invention is to provide a method for manufacturing a porous ceramic capable of realizing a reduction in lead time and a reduction in equipment cost.

The method for producing porous ceramics according to the embodiment includes a step of producing a suspension in which ceramic particles having a weight average molecular weight of 500 to 2,000,000 and water and having an average particle diameter of 0.05 μm to 100 μm are dispersed. And a freezing process, a drying process, a degreasing process, and a baking process. In the freezing step, the suspension is frozen within a predetermined time to generate a frozen body. In the degreasing step, the compound is removed from the frozen body from which the ice has been removed. In the drying step, the ice grown on the frozen body is removed to generate pores. In the firing step, the product formed by removing the compound is fired to produce a fired body. The predetermined time is a time during which the viscosity of the suspension is 50% to 150% with respect to the viscosity immediately after the preparation of the suspension.

  According to one aspect of the embodiment, it is possible to provide a method for producing porous ceramics that can realize a reduction in lead time and a reduction in equipment costs.

Drawing 1 is an explanatory view explaining an outline of a manufacturing method of porous ceramics concerning an embodiment. FIG. 2 is a flowchart showing an example of a method for producing a porous ceramic according to the embodiment. FIG. 3 is a partial cross-sectional view of the porous ceramic produced according to Example 1.

  Hereinafter, with reference to an accompanying drawing, an embodiment of a manufacturing method of porous ceramics indicated by this application is described in detail. In addition, this invention is not limited by embodiment shown below.

  A conventional method for producing porous ceramics includes steps of mixing, gelation, freezing, drying, degreasing and firing. On the other hand, in the porous ceramic manufacturing method according to the embodiment, the gelation step is omitted from the conventional manufacturing method described above by changing the composition of the suspension prepared in the mixing step. Thus, even if the gelling step is omitted, a porous ceramic having the same physical properties as the conventional one is formed. Below, the manufacturing method of the porous ceramics which concern on embodiment is demonstrated using FIG.

  Drawing 1 is an explanatory view explaining an outline of a manufacturing method of porous ceramics concerning an embodiment. In addition, in FIG. 1, each process of mixing, freezing, and baking is illustrated in order from the left among the manufacturing processes described above, and illustrations corresponding to the respective processes of drying and degreasing are omitted.

  First, the mixing process will be described. The mixing step is a step of preparing a suspension 4 that includes the ceramic particles 1, the dispersion stabilizing component 2, and the water 3. By containing the dispersion stabilizing component 2, the ceramic particles 1 are homogeneously dispersed in the water 3. Details of the dispersion stabilizing component 2 will be described later.

  Next, the freezing process will be described. The freezing step is a step of generating the frozen body 6 by cooling the suspension 4. When the suspension 4 is cooled, the water 3 separated from the suspension 4 containing the ceramic particles 1 and the dispersion stabilizing component 2 changes to ice 5 and grows while forming a crystal structure. As a result, the freeze including ceramic particles 1, a portion (not shown) formed around the ceramic particles 1 in which the dispersion stabilizing component 2 is concentrated in water 3, and a portion of crystallized ice 5. A body 6 is obtained.

  Here, when the cooling device 12 is disposed on the lower surface 7 side of the suspension body 4 and the suspension body 4 is cooled, the water 3 in the suspension body 4 is frozen from the lower surface 7 side and changes to a state of ice 5. The crystal of the ice 5 tries to grow from the lower surface 7 side toward the upper surface 8 side. When the ice 5 crystal grows, a pressing force sufficient to move the ceramic particles 1 acts. For this reason, when the ceramic particles 1 are present in the direction in which the crystal of the ice 5 tends to grow, the ceramic particles 1 stably dispersed by the dispersion stabilizing component 2 are excluded around the crystal of the growing ice 5. To move.

  Thus, in the method for producing porous ceramics according to the embodiment, even if the suspension 4 is cooled without going through a conventional gelation step, ice grown in a columnar shape from one direction to the other direction. The ceramic particles 1 are rearranged so as to surround the crystal 4, thereby generating a frozen body 6 in which the distribution of the ceramic particles 1 is coarse.

  Next, the drying process will be described. The drying step is a step of generating pores 10 by removing the ice 5 grown on the frozen body 6. When the frozen body 6 on which the ice 5 has grown is dried, for example, by vacuum drying, the crystals of the ice 5 sublimate and disappear, and the pores 10 are formed instead. That is, the drying process is a process of replacing the ice 5 with the pores 10.

  Next, the degreasing process will be described. A degreasing process is a process of removing an organic component from the frozen body 6 which produced | generated the pore 10 in the drying process. Specifically, a process for decomposing and removing organic components under a predetermined temperature condition is executed according to the type of ceramic particles 1. As will be described later, the dispersion stabilizing component 2 may be included in the organic component removed in the degreasing step.

  Finally, the firing process will be described. The firing step is a step of producing a fired body (porous ceramic) 11 by firing the frozen body 6 from which the organic component and ice 5 are removed and the pores 10 are formed. The porous ceramic 11 obtained by firing has pores 10 formed in the drying step described above and a ceramic skeleton 9 in which the ceramic particles 1 are bonded and densified so as to surround the pores 10.

  As described above, according to the method for manufacturing the porous ceramic 11 according to the embodiment, from the lower surface 7 side toward the upper surface 8 side based on the shape of the ice 5 generated in the frozen body 6 by using the cooling device 12. A porous ceramic 11 having a ceramic skeleton 9 formed around a cylindrical pore 10 oriented in one direction is generated. Here, “the pores 10 are“ oriented in one direction ”” means that the average aspect ratio of the pores 10 is 1.5 or more. The average aspect ratio of the pores 10 is measured by the method described in the examples described later.

  As described above, the suspension 4 prepared in the mixing step includes the ceramic particles 1, the dispersion stabilizing component 2, and the water 3. Below, each component which comprises the suspension body 4 is demonstrated in detail.

  First, the ceramic particles 1 will be described. The ceramic particles 1 contained in the suspension 4 are not particularly limited as long as they can be appropriately fired in the firing step. Specifically, for example, zirconia, alumina, silica, titania, silicon carbide, boron carbide, silicon nitride, boron nitride, cordierite, sialon, zircon, aluminum titanate, and mullite can be applied as the ceramic particles 1. However, it is not limited to these. Further, in order to appropriately fire the ceramic particles 1, the suspension 4 may be blended with a firing aid corresponding to the type of the ceramic particles 1.

  Moreover, the compounding quantity of the ceramic particle 1 in the suspension 4 has the preferable range of 1-50 vol%, More preferably, it is 1-30 vol%. If the blending amount of the ceramic particles 1 is less than 1 vol%, for example, the shape may not be maintained in the drying process, and it becomes difficult to produce the porous ceramic 11 having a desired strength. Moreover, when the compounding quantity of the ceramic particle 1 exceeds 50 vol%, the porosity of the porous ceramic 11 obtained will be less than about 50 vol%. For this reason, the necessity to apply the manufacturing method of the porous ceramics 11 which concerns on embodiment which can produce the porous ceramics 11 with a high porosity stably becomes low. Here, the “porosity” is a value obtained by the Archimedes method based on the method defined in JIS R1634: 2008. In such a measurement, closed pores are not taken into account and are also referred to as “apparent porosity”. In the present embodiment, since closed pores are hardly formed, this “apparent porosity” can be handled as “porosity”.

  Moreover, the ceramic particles 1 preferably have an average particle diameter of 0.05 μm to 100 μm for practical use. If the average particle size of the ceramic particles 1 exceeds 100 μm, it may be difficult to appropriately fire the ceramic particles 1 depending on the desired shape and size of the porous ceramics 12. Here, the “average particle size” is obtained based on a volume-based particle size distribution converted into a sphere equivalent diameter in a laser diffraction particle size distribution measuring apparatus (wet method) such as Nikkiso Microtrack X-100. The obtained median diameter (d50). There is no limitation on the measurement method as long as the same result can be obtained.

  By the way, the behavior of the ceramic particles 1 in the water 3 is different between the case where the average particle diameter of the ceramic particles 1 is 1 μm or less and the case where it exceeds 1 μm. Below, the behavior of the ceramic particles 1 in the water 3 according to the average particle diameter of the ceramic particles 1 will be described.

  First, the behavior change of the suspension 4 in which ceramic particles 1 having an average particle size of 1 μm or less are dispersed in water 3 will be described. Ceramic particles 1 having a relatively small average particle size of 1 μm or less tend to aggregate in water 3 to increase the apparent particle size. When the ceramic particles 1 aggregate in the water 3, the water 3 that can move freely is relatively reduced by the water 3 being held in the gaps between the aggregated ceramic particles 1, and the viscosity of the suspension 4 is reduced. Rises over time. When such ceramic particles 1 are dispersed in water 3, the viscosity of the suspension 4 increases with time, but the sedimentation rate of the ceramic particles 1 increases as the apparent particle diameter increases due to aggregation. . For this reason, the aggregated ceramic particles 1 eventually settle in the water 3 and the distribution of the ceramic particles 1 is uneven.

  Next, the behavior of the suspension 4 in which the ceramic particles 1 having an average particle size of more than 1 μm and 100 μm or less are dispersed in the water 3 will be described. The relatively large ceramic particles 1 having an average particle size exceeding 1 μm are settled by their own weight, and the distribution of the ceramic particles 1 is uneven, and the viscosity of the suspension 4 is lowered.

  As described above, if the distribution of the ceramic particles 1 in the suspension 4 is uneven, the fired fired body 11 is cracked or deformed, or the handleability of the molded body after the drying process is lowered. Therefore, the dispersion of the ceramic particles 1 is further stabilized by preparing a suspension 4 in which the dispersion stabilizing component 2 is mixed with the ceramic particles 1 in the water 3.

  As described above, the behavior of the ceramic particles 1 in the water 3 differs depending on the average particle diameter. For this reason, the dispersion stabilizing component 2 contained in the suspension 4 is required to have a different action depending on the average particle diameter of the ceramic particles 1.

  First, the case where the average particle diameter of the ceramic particles 1 is 1 μm or less will be described. In such a case, a polymer dispersant is included as the dispersion stabilizing component 2. The polymer dispersant is a substance that assists the uniform dispersion of the ceramic particles 1 in the suspension 4. When an appropriate amount of the polymer dispersant is blended, the aggregation of the ceramic particles 1 is suppressed and the sedimentation of the ceramic particles 1 is suppressed, and the viscosity of the suspension 4 is prevented from increasing. In particular, the use of the dispersion stabilizing component 2 reduces the fluctuation range of viscosity in the time from the start of cooling of the suspension 4 in the freezing step to the completion of freezing, thereby suppressing the occurrence of cracks and deformation. .

  In other words, the presence or absence of cracking or deformation of the porous ceramics 11 due to the change in the viscosity of the suspension 4 depends on the viscosity of the suspension 4 immediately after the preparation and the time required for generating the frozen body 6 has elapsed. It can be estimated by the dispersion stability defined as the ratio of the viscosity of the suspension 4. In an embodiment, the dispersion stability of such a suspension 4 is in the range of 50% to 150%, preferably 70% to 130%, more preferably 90% to 110%.

  If the dispersion stability of the suspension 4 is less than 50%, for example, the sedimentation of the ceramic particles 1 in the suspension 4 proceeds during the freezing step, and deformation or cracking such as warping of the porous ceramic 11 occurs. It becomes easy to do. Further, when the dispersion stability of the suspension 4 exceeds 150%, the aggregation and sedimentation of the particles proceeds, so that a difference occurs in the filling rate of the ceramic particles 1 in the thickness direction, thereby forming a heterogeneous structure. . For this reason, in the drying and firing steps, the contraction rate varies depending on the portion of the frozen body 6, and the deformation and cracking of the porous ceramics 11 are likely to occur.

  Here, “the time required for the production of the frozen body 6” means the total time required for producing the frozen body 6 by freezing the suspension 4 after the suspension 4 is prepared. That is, the “time required for producing the frozen body 6” is individually set according to various conditions such as the amount of the suspended body 4, the cooling method, and the cooling temperature. For example, it can be 10 minutes, 30 minutes, 60 minutes, 12 hours, etc., but is not limited thereto.

  The “viscosity of the suspension 4 after the time required for the production of the frozen body 6” is obtained by placing the suspension 4 immediately after the preparation into a thermostat set at 25 ° C. This is a value obtained by measuring the viscosity of the suspension 4 using a B-type viscometer after the "required time" has elapsed. As the B-type viscometer, a digital viscometer manufactured by Brookfield, model (DV1, PRIME) was used. It measured by SC4-34, rotation speed 20rpm (less than 600mPa * s) or 100rpm (600mPa * s or more). However, there is no limitation on the measurement apparatus and the measurement method as long as the same result can be obtained.

  The “viscosity immediately after the preparation of the suspension 4” is the same as the “viscosity of the suspension 4 after the time required for the formation of the frozen body 6” within one minute after the preparation of the suspension 4. It is the value measured by.

  The dispersion stabilizing component 2 preferably contains a compound having a weight average molecular weight of 500 to 2,000,000, and a polymer dispersant or binder described below is preferable. Examples of such preferred polymer dispersants include polycarboxylates or acrylates, copolymers based on these, or mixtures thereof. It is not limited to this as long as it is a substance that exhibits. Moreover, you may mix | blend 1 or more types among ammonia, sodium hydroxide, and potassium hydroxide as needed, or a mixture thereof as a pH adjuster. By mix | blending a pH adjuster, the fluctuation | variation of the viscosity of the suspension body 4 accompanying the change of pH is suppressed.

  The weight average molecular weight of such a polymer dispersant is preferably in the range of 1000 to 40000, more preferably 5000 to 30000, and still more preferably 8000 to 30000. If the weight average molecular weight of the polymer dispersant is less than 1000, a large amount of the polymer dispersant may be required to adjust the viscosity of the suspension 4, which is not preferable. Moreover, when the weight average molecular weight of a polymer dispersing agent exceeds 40000, since fine adjustment of the viscosity of the suspension body 4 may become difficult, it is not so preferable.

  The suspension 4 is composed of an N-alkylamide polymer, an N-isopropylacrylamide polymer, a sulfomethylated acrylamide polymer, an N-dimethylaminopropyl methacrylamide polymer, a polyalkylacrylamide polymer, alginic acid. , Sodium alginate, Ammonium alginate, Polyethyleneimine, Cellulose derivative, Polyacrylate, Polyethylene glycol, Polyethylene oxide, Polyvinyl alcohol, Polyvinylpyrrolidone, Carboxyvinyl polymer, Starch, Gelatin, Agar, Pectin, Glucomannan, Xanthan gum, Locust bean Gum, carrageenan gum, guar gum, gellan gum, lignin sulfonate, polyacrylamide, polyvinyl ester, isobutylene-maleic anhydride Copolymers, vinyl acetate, epoxy resins, one or more of the phenolic resins and urethane resins, or may further comprise a mixture thereof as a binder. The binder is a substance that bonds the ceramic particles 1 in the suspension 4 to each other. For this reason, the suspension 4 can disperse the ceramic particles 1 more stably by containing such a binder as the dispersion stabilizing component 2.

  The weight average molecular weight of these binders is preferably 500 to 2,000,000, more preferably 2000 to 1500,000, and still more preferably 4000 to 1,000,000. When the weight average molecular weight of the binder is less than 500, a large amount of binder may be required to adjust the viscosity of the suspension 4, which is not preferable. Moreover, when the weight average molecular weight of a binder exceeds 2000000, since fine adjustment of the viscosity of the suspension body 4 may become difficult, it is not so preferable.

  Next, the case where the average particle diameter of the ceramic particles 1 is more than 1 μm and 100 μm or less will be described. In such a case, the dispersion stabilizing component 2 includes, for example, cellulose derivatives such as hydroxypropylmethylcellulose and carboxymethylcellulose, acrylic polymers such as polyacrylic acid and polyacrylamide, and thickening polysaccharides such as alginic acid, starch and xanthan gum. Of these, one or more thickeners are included. By blending an appropriate amount of the thickener, sedimentation of the ceramic particles 1 is suppressed, and a decrease in the viscosity of the suspension 4 is suppressed. Note that the thickener is not limited to these as long as the substance exhibits the above-described action on the suspension 4.

  The weight average molecular weight of these thickeners is preferably in the range of 500 to 2,000,000, more preferably 100,000 to 2,000,000, and even more preferably 750000 to 2,000,000. If the weight average molecular weight of the thickener is less than 500, a large amount of thickener may be required to adjust the viscosity of the suspension 4, which is not preferable. Moreover, when the weight average molecular weight of a thickener exceeds 2000000, since fine adjustment of the viscosity of the suspension body 4 may become difficult, it is not so preferable.

  The blending amount of the dispersion stabilizing component 2 is as follows: the time required from the preparation of the suspension 4 to the completion of freezing, the type of ceramic particles 1, the average particle size and blending amount, and the dispersion stabilizing component 2 to be selected. It is determined based on the type. Specifically, when the ratio of the viscosity of the suspension 4 after the time required for producing the frozen body 6 to the viscosity immediately after the preparation of the suspension 4 is defined as dispersion stability, this dispersion stability value is obtained. Is 50 to 150%, preferably 70% to 130%, more preferably 90% to 110%. Thus, by appropriately blending the dispersion stabilizing component 2 according to the average particle diameter of the ceramic particles 1, the aggregation and sedimentation of the ceramic particles 1 dispersed in the suspension 4 are suppressed until the freezing step is completed. can do. For this reason, even if a gelling process is omitted, cracking and deformation of the porous ceramics 11 due to poor dispersion due to sedimentation of the ceramic particles 1 can be appropriately suppressed.

  Finally, the water 3 will be described. As the water 3, tap water, distilled water or the like may be used, but deionized water containing less impurities, particularly inorganic components, is more preferable.

  In addition, although the crack and deformation | transformation of the porous ceramic 11 appear notably in a baking process, depending on the case, it may occur also in a drying process. Here, cracks and deformation of the porous ceramic (fired body) 11 accompanying the sedimentation of the ceramic particles 1 can be easily confirmed visually. In addition, when it is necessary to determine a defect that cannot be visually confirmed depending on the application of the porous ceramic 11, it is possible to evaluate the presence or absence of cracks or deformation of the porous ceramic 11 using a known measuring device. As such a measuring instrument, for example, a method in which a fired body is infiltrated with dye and a crack is confirmed, a method in which light is irradiated on the fired body and a crack is found based on a difference in light transmittance, and a microscope is used. Examples include, but are not limited to, observation methods, X-ray computed tomography (CT), non-destructive inspection using ultrasonic waves, and the like.

  Moreover, it is possible to utilize the well-known cooling device 12 in the freezing process mentioned above. Specifically, the cooling device 12 to which various cooling methods are applied, such as bringing the lower surface 7 of the suspension 4 placed in the mold into contact with a solid such as a cooled metal plate or immersing the mold in a cooled liquid. Is mentioned. Also, for example, the temperature near the liquid level can be obtained by circulating ethanol cooled to a predetermined temperature from one side to the other side so that it flows without stagnation or undulation near the liquid level of ethanol. An ethanol cooling device that keeps the pressure constant may be applied as the cooling device 12. By applying the ethanol cooling device having such a configuration, the bottom surface of the mold containing the suspension 4 is held in contact with or immersed in the cooled ethanol liquid surface, and the frozen body 6 is generated. Porous ceramics 11 with little variation can be produced.

  The freezing temperature of the suspension 4 in the freezing step is not limited as long as the water 3 in the suspension 4 can be frozen to produce the ice 5. Depending on the type of the dispersion stabilizing component 2, the suspension 4 may not freeze at −10 ° C. or higher due to the interaction with the water 3, so that a freezing temperature of −10 ° C. or lower is preferable.

  Further, in the drying process, it is possible to use a drying technique for preventing cracks by gradually replacing the ice 5 with the pores 10 while suppressing the difference in the drying speed inside and outside the frozen body 6. Specifically, the ice 5 can be replaced with the pores 10 by freeze-drying the frozen body 6 or immersing in a water-soluble organic solvent or a water-soluble organic solvent aqueous solution and air-drying.

  For example, when the frozen body 6 is immersed in a water-soluble organic solvent or a water-soluble organic solvent aqueous solution, the ice 5 in the frozen body 6 is melted and mixed with the water-soluble organic solvent. By performing this operation once or a plurality of times, first, the portion that was ice 5 in the frozen body 6 is replaced with a water-soluble organic solvent. Thereafter, when the frozen body 6 in which the inside of the frozen body 6 has been replaced with a water-soluble organic solvent is dried in the air or under reduced pressure conditions, the portion that was ice 5 in the freezing step is replaced with pores 10.

  In the drying step using a water-soluble organic solvent, a water-soluble organic solvent that does not erode the dispersion stabilizing component 2 and has higher volatility than the water 3 is applied. Specific examples include, but are not limited to, methanol, ethanol, isopropyl alcohol, acetone, and ethyl acetate. By performing drying using these water-soluble organic solvents alone or in combination of a plurality of types once or a plurality of times, pores 10 are formed in the portions that were ice 5 in the frozen body 6.

  In the degreasing step, for example, a degreasing temperature of 300 ° C. to 900 ° C. is applied. At this time, for example, when degreasing non-oxide ceramics such as silicon carbide and silicon nitride, it is preferable to degrease in an inert gas atmosphere such as argon or nitrogen. On the other hand, for example, when using oxide ceramics such as alumina or zirconia as a raw material, it is preferable to degrease in an air atmosphere.

  In the firing step, the pores 10 oriented in one direction are formed by appropriately adjusting the firing temperature, firing time, and firing atmosphere according to the type and blending amount of the ceramic particles 1 to be used, the target hardness, and the like. A porous ceramic 11 having the same is produced.

  The porosity of the porous ceramic 11 thus obtained is preferably in the range of 50% to 99%, more preferably 70% to 99%. When the porosity of the ceramic particles 1 is less than 50%, the necessity of using the method for manufacturing the porous ceramic 11 according to the embodiment is reduced. Further, if the porosity of the ceramic particles 1 exceeds 99%, for example, the shape may not be maintained in the drying process, and it becomes difficult to produce the porous ceramics 11 having a desired strength.

  Moreover, it is preferable practically that the porous ceramic 11 has a communicating hole with an average pore diameter of 10 μm to 300 μm, and more preferably 10 μm to 100 μm. Here, the “average pore diameter” refers to the median diameter (d50) obtained based on the pore distribution when the pore 10 is approximated to a cylinder, measured using a mercury intrusion method at a contact angle of 140 degrees.

  The volume of the porous ceramic 11 is preferably fired so as to shrink to 78% or less, more preferably 72% or less of the volume of the frozen body 6. When the volume of the porous ceramic 11 exceeds 78% of the volume of the frozen body 6, the firing property of the raw material is poor, and thus the strength does not show sufficient, and a tendency to easily occur, ie, partial collapse of the molded body. There is.

  Next, a method for manufacturing the porous ceramic 11 according to the embodiment will be described in detail with reference to FIG. FIG. 2 is a flowchart showing a processing procedure for manufacturing the porous ceramic 11 according to the embodiment.

  As shown in FIG. 2, first, a suspension 4 in which ceramic particles 1 are dispersed in water 3 is prepared (step S101). Additives such as the dispersion stabilizing component 2 and the firing aid may be added at this timing. There is no restriction | limiting in the order which mixes the ceramic particle 1, the dispersion stabilization component 2, and the water 3, According to the addition amount, property, etc. of the dispersion stabilization component 2, it can set suitably.

  Subsequently, the suspension 4 prepared in step S101 is frozen to generate a frozen body 6 (step S102). Subsequently, the frozen body 6 is dried to remove the ice 7 that has grown on the frozen body 6, thereby generating pores 10 (step S103).

  Further, degreasing is performed to remove organic components such as the dispersion stabilizing component 2 from the frozen body 6 from which the ice 5 is removed and the pores 10 are generated (step S104), followed by baking (step S105). Through the above steps, the production of a series of porous ceramics 11 according to the embodiment is completed.

  As described above, the method for producing porous ceramics according to the embodiment includes a step of generating a suspension in which ceramic particles are dispersed in water, a freezing step, a drying step, and a firing step. In the freezing step, the suspension is frozen to produce a frozen body. In the drying step, the ice grown on the frozen body is removed to generate pores. In the firing step, the frozen body from which the ice has been removed is fired to produce a fired body. The viscosity of the suspension after the time required for producing the frozen body is 50 to 150% of the viscosity immediately after preparation of the suspension.

  Therefore, according to the method for manufacturing a porous ceramic according to the embodiment, even if the gelling step of the suspension is omitted, the porous ceramic having pores oriented in one direction and having no cracks or deformation is produced. It is possible to reduce the lead time and the equipment cost.

  In the above-described embodiment, the type of the dispersion stabilizing component 2 is changed according to the average particle size of the ceramic particles. However, the viscosity of the suspension 4 immediately after the preparation and after a predetermined time has elapsed since the preparation. As long as the value can be within the predetermined range, there is no limitation on the type, blending amount and combination of the dispersion stabilizing component 2.

  In the above-described embodiment, the ethanol cooling device is described as an example of the cooling device 12. However, if the component has a low coagulation temperature and is liquid to a desired temperature for freezing the suspension 4, ethanol is used. Other than that may be applied. Specific examples of such components include, but are not limited to, methanol, isopropyl alcohol, acetone, ethylene glycol, and the like. In addition, these components can be used alone or in combination of a plurality of kinds and, if necessary, mixed with water.

  Moreover, although the degreasing process (step S104) was demonstrated as an essential process in embodiment mentioned above, you may abbreviate | omit depending on the kind and compounding quantity of the organic component which can contain the dispersion stabilization component 2 grade | etc.,. In such a case, the organic component in the frozen body 6 is decomposed and removed in the firing step (step S105).

Example 1
Alumina particles having an average particle size of 0.5 μm (corresponding to ceramic particles 1) 10 vol% and deionized water (corresponding to water 3) 90.0 vol% were mixed. Polycarboxylic acid ammonium salt (weight average molecular weight (Mw) 30000) (corresponding to dispersion stabilizing component 2 (polymer dispersant)) 1.5% by mass and gelatin (corresponding to dispersion stabilizing component 2 (binder)) Suspension 4 was prepared by adding 3% by mass (both based on 100% by mass of water 3) and placed in a mold. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 6.5 mPa · s.

  Next, the mold containing the suspension 4 was cooled in a freezer set to −10 ° C. for 60 minutes to produce a plate-like frozen body 6 having a thickness of 10 mm. The viscosity (25 ° C.) after 60 minutes of the suspension 4 was 8.5 mPa · s.

  Subsequently, the frozen body 6 was taken out of the mold and dried with a vacuum drying device for 24 hours. Further, after degreasing at 600 ° C. for 2 hours in an electric furnace in an air atmosphere, the firing shrinkage (linear shrinkage accompanying firing) is 21% at a firing temperature of 1600 ° C., that is, 49.3 in volume shrinkage. The porous ceramics 11 were obtained by firing so as to be%.

(Example 2)
10 vol% of alumina particles having an average particle diameter of 2.0 μm and 90.0 vol% of deionized water were mixed. Polycarboxylic acid ammonium salt (weight average molecular weight 30000) 1.5% by mass and polyvinyl alcohol (corresponding to dispersion stabilizing component 2 (binder)) 4% by mass (both based on 100% by mass of water 3) Suspension 4 was prepared by addition and placed in a mold. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 3.5 mPa · s.

  Next, the mold containing the suspension 4 was cooled in a freezer set to −10 ° C. for 50 minutes to produce a plate-like frozen body 6 having a thickness of 10 mm. The viscosity (25 ° C.) after 50 minutes of the suspension 4 was 4.0 mPa · s.

  Subsequently, the frozen body 6 was taken out of the mold and dried with a vacuum drying device for 24 hours. Furthermore, after degreasing at 600 ° C. for 2 hours in an electric furnace in an air atmosphere, firing was performed at a firing temperature of 1600 ° C. for 2 hours so that the firing shrinkage rate was 8%, that is, the volume shrinkage rate was 77.9%. A porous ceramic 11 was obtained.

(Example 3)
Except that it was changed to hydroxypropylmethylcellulose (weight average molecular weight 750000) (corresponding to dispersion stabilizing component 2 (thickener)) 3% by mass (relative to 100% by mass of water 3) instead of the polymer dispersant A porous ceramic 11 was produced in the same manner as in Example 2. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 1130 mPa · s, and the viscosity (25 ° C.) after 50 minutes of the suspension 4 was 1050 mPa · s.

Example 4
20 vol% of zirconia particles having an average particle diameter of 9 μm and 80.0 vol% of deionized water were mixed. This corresponds to 1.5% by mass of polycarboxylic acid ammonium salt (weight average molecular weight 30000), 2% by mass of hydroxypropylmethylcellulose (weight average molecular weight 750000) and isobutylene maleic anhydride copolymer (dispersion stabilizing component 2 (binder)). ) 5% by weight (both based on 100% by weight of water 3) was added to prepare suspension 4 and put it in a mold. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 44800 mPa · s.

  Next, the mold containing the suspension 4 was cooled in a freezer set to −10 ° C. for 50 minutes to produce a plate-like frozen body 6 having a thickness of 10 mm. The viscosity (25 ° C.) after 50 minutes of the suspension 4 was 43500 mPa · s.

  Subsequently, the frozen body 6 was taken out of the mold and dried with a vacuum drying device for 24 hours. Furthermore, after degreasing at 600 ° C. for 2 hours in an electric furnace in an air atmosphere, firing was performed at a firing temperature of 1600 ° C. for 2 hours so that the firing shrinkage was 11%, that is, the volume shrinkage was 70.5%. A porous ceramic 11 was obtained.

(Comparative Example 1)
A porous ceramic 11 was produced in the same manner as in Example 1 except that the compounding amount of the polycarboxylic acid ammonium salt was changed to 0.5% by mass. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 5.5 mPa · s, and the viscosity (25 ° C.) after 50 minutes of the suspension 4 was 9.5 mPa · s.

(Comparative Example 2)
Porous ceramics 11 in the same manner as in Example 1 except that the polymer dispersant was changed to carboxylic acid copolymer (weight average molecular weight 8000) 0.5% (based on 100 mass% water 3). Was made. Here, the viscosity immediately after preparation of the suspension 4 (25 ° C.) was 5.5 mPa · s, and the viscosity of the suspension 4 after 50 minutes (25 ° C.) was 10 mPa · s.

(Comparative Example 3)
A porous ceramic 11 was produced in the same manner as in Comparative Example 2 except that the blending amount of the carboxylic acid copolymer was changed to 1.5% by mass. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 5.5 mPa · s, and the viscosity (25 ° C.) after 50 minutes of the suspension 4 was 10.5 mPa · s.

(Comparative Example 4)
A porous ceramic 11 was produced in the same manner as in Example 2 except that the compounding amount of the polycarboxylic acid ammonium salt was changed to 0.5% by mass. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 9.5 mPa · s, and the viscosity (25 ° C.) after 50 minutes of the suspension 4 was 4.5 mPa · s.

(Comparative Example 5)
20 vol% of zirconia particles having an average particle diameter of 9 μm and 80.0 vol% of deionized water were mixed. To this, 0.5% by mass of polycarboxylic acid ammonium salt (weight average molecular weight 30000) and 5% by mass of isobutylene maleic anhydride copolymer (both based on 100% by mass of water 3) were added to form suspension 4 Was prepared and placed in a mold. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 290 mPa · s.

  Next, the mold containing the suspension 4 was cooled in a freezer set to −10 ° C. for 50 minutes to produce a plate-like frozen body 6 having a thickness of 10 mm. The viscosity (25 ° C.) after 50 minutes of the suspension 4 was 50 mPa · s.

  Subsequently, the frozen body 6 was taken out of the mold and dried with a vacuum drying device for 24 hours. Furthermore, after degreasing at 600 ° C. for 2 hours in an electric furnace in an air atmosphere, firing was performed at a firing temperature of 1600 ° C. for 2 hours so that the firing shrinkage was 11%, that is, the volume shrinkage was 70.5%. A porous ceramic 11 was obtained.

(Comparative Example 6)
A porous ceramic 11 was produced in the same manner as in Comparative Example 5 except that the blending amount of the polycarboxylic acid ammonium salt was changed to 1.5% by mass. Here, the viscosity (25 ° C.) immediately after preparation of the suspension 4 was 25 mPa · s, and the viscosity (25 ° C.) after 50 minutes of the suspension 4 was 12 mPa · s.

  Table 1 shows the average particle diameter of the ceramic particles 1 used in Examples and Comparative Examples, the type of the dispersion stabilizing component 2, the weight average molecular weight Mw, and the blending amount thereof.

  In the porous ceramics 11 obtained in Examples 1 to 4, the average pore diameter and the average aspect ratio of the pores 10 were measured. As a result, all satisfy the desired numerical ranges of an average pore diameter of 10 μm to 300 μm and an aspect ratio of the pore 11 of 1.5 or more. The average aspect ratio of the pores 10 was measured as follows.

<Average aspect ratio of pore 10>
The average aspect ratio of the pores 10 was calculated based on the image analysis of the porous ceramics 11 photographed with SEM (Scanning Electron Microscope). More specifically, a predetermined range of the longitudinal section of the produced porous ceramic 11 was photographed with an SEM (see FIG. 3). Next, the cross section of the pore 10 was approximated to an ellipsoid, the area, the major axis and the minor axis were measured, and the value obtained by dividing the major axis by the minor axis was calculated as the “aspect ratio of the pore 10”. The average value of the aspect ratios of the pores 10 calculated for 50 arbitrarily selected pores 10 was defined as “the average aspect ratio of the pores 10”.

  Furthermore, the porosity, the presence or absence of cracks, and the degree of deformation of the porous ceramics 11 obtained in the examples and comparative examples were measured. The results are shown in Table 2 together with the dispersion stability of the suspension 4. Here, the crack of the porous ceramics 11 was evaluated by visual observation. Further, the degree of deformation of the porous ceramic 11 was measured as follows.

<Degree of deformation of porous ceramic 11>
A hole was formed in the center of a 300 mm aluminum bar, and a measuring instrument in which a digital gauge was fitted in this hole was applied to the surface of the porous ceramic 11, and the value with the largest amount of deformation was taken as the amount of warpage. In this example and the comparative example, it was defined as “no deformation” that the obtained “warp” was 1 mm or less. In addition, when the crack was recognized in the obtained porous ceramics 11, this measurement was not implemented.

  As shown in Tables 1 and 2, when the viscosity of the suspension 4 after the time required to produce the frozen body 6 is defined as the dispersion stability, the ratio to the viscosity immediately after the preparation of the suspension 4 is defined as the dispersion stability. When the type and blending amount of the dispersion stabilizing component 2 are adjusted so that the dispersion stability value is 50% to 150%, the porous ceramic 11 having no cracks or deformation is produced even if the gelation step is omitted. .

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Ceramic particle 2 Dispersion stabilization component 3 Water 4 Suspension body 5 Ice 6 Frozen body 7 Lower surface 8 Upper surface 9 Ceramic frame 10 Pore 11 Porous ceramic (fired body)
12 Cooling device

Claims (12)

A step of preparing a suspension in which ceramic particles having a weight average molecular weight of 500 to 2,000,000 and water and having an average particle diameter of 0.05 μm to 100 μm are dispersed;
A freezing step of freezing the suspension within a predetermined time to produce a frozen body;
A drying step of removing the ice grown on the frozen body to generate pores;
A degreasing step of removing the compound from the frozen body from which the ice has been removed;
Firing the product produced by removing the compound to produce a fired body, and
The predetermined time is a time during which the viscosity of the suspension is 50% to 150% with respect to the viscosity immediately after the preparation of the suspension.   The method for producing a porous ceramic according to claim 1, wherein the volume of the fired body is 78% or less of the volume of the frozen body.   The method for producing a porous ceramic according to claim 1 or 2, wherein the compound contains a polycarboxylate or acrylate having a weight average molecular weight of 1000 to 40000.   The method for producing porous ceramics according to any one of claims 1 to 3, wherein the suspension includes one or more of ammonia, sodium hydroxide, and potassium hydroxide. The ceramic particles have an average particle size of 1 to 100 μm,
The method for producing porous ceramics according to any one of claims 1 to 4, wherein the suspension includes one or more of a cellulose derivative, an acrylic polymer, and a thickening polysaccharide. A suspension in which ceramic particles having an average particle size of 0.05 μm to 100 μm are dispersed, including one or more of ammonia, sodium hydroxide and potassium hydroxide, a compound having a weight average molecular weight of 500 to 2,000,000 and water. A step of preparing;
A freezing step of freezing the suspension within a predetermined time to produce a frozen body;
A drying step of removing the ice grown on the frozen body to generate pores;
Firing the frozen body from which the ice has been removed to produce a fired body,
The predetermined time is a time during which the viscosity of the suspension is 50% to 150% with respect to the viscosity immediately after the preparation of the suspension. A step of preparing a suspension in which ceramic particles are dispersed, including one or more of ammonia, sodium hydroxide and potassium hydroxide, a compound having a weight average molecular weight of 500 to 2,000,000 and water;
A freezing step of freezing the suspension within a predetermined time to produce a frozen body;
A drying step of removing the ice grown on the frozen body to generate pores;
Firing the frozen body from which the ice has been removed to produce a fired body,
The predetermined time is a time when the viscosity of the suspension is 50% to 150% with respect to the viscosity immediately after the preparation of the suspension,
The volume of the fired body is 78% or less of the volume of the frozen body. A step of preparing a suspension in which ceramic particles having an average particle diameter of 1 to 100 μm are dispersed, including at least one of a cellulose derivative, an acrylic polymer, and a thickening polysaccharide and water;
A freezing step of freezing the suspension within a predetermined time to produce a frozen body;
A drying step of removing the ice grown on the frozen body to generate pores;
Firing the frozen body from which the ice has been removed to produce a fired body,
The predetermined time is a time during which the viscosity of the suspension is 50% to 150% with respect to the viscosity immediately after the preparation of the suspension. The suspension is composed of N-alkylamide polymer, N-isopropylacrylamide polymer, sulfomethylated acrylamide polymer, N-dimethylaminopropyl methacrylamide polymer, polyalkylacrylamide polymer, alginic acid, alginic acid. Sodium, ammonium alginate, polyethyleneimine, cellulose derivative system, polyacrylate, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, carboxyvinyl polymer, starch, gelatin, agar, pectin, glucomannan, xanthan gum, locust bean gum, Carrageenan gum, guar gum, gellan gum, lignin sulfonate, polyacrylamide, polyvinyl ester, isobutylene-maleic anhydride Coalescence, vinyl acetate, epoxy resins, method for producing a porous ceramic according to any one of claims 1 to 8, characterized in that it comprises one or more of phenolic resins and urethane resins.   The method for producing a porous ceramic according to any one of claims 1 to 9, wherein the porosity of the porous ceramic is 50% to 99%.   The ceramic particles include zirconia, alumina, silica, titania, silicon carbide, boron carbide, silicon nitride, boron nitride, cordierite, sialon, zircon, aluminum titanate, or mullite. The method for producing a porous ceramic according to any one of 10.   The method for producing porous ceramics according to any one of claims 1 to 11, wherein the average aspect ratio of the pores is 1.5 or more.