High porosity high strength thin-walled cordierite honeycomb ceramic and method of making

Abstract

This invention relates to the field of honeycomb ceramic technology, specifically to a high-porosity, high-strength thin-walled cordierite honeycomb ceramic and its preparation method. Its inorganic solid component includes spherical magnesium hydroxide, silicon-alumina hollow microspheres, spherical alumina, and spherical silica; the particle size D of the silicon-alumina hollow microspheres is... 50 The particle size D of the hollow silicon-aluminum microspheres is 15-40 μm. 100 The mesh size is less than the set mesh size, which is 150-180 mesh. This honeycomb ceramic has a high firing yield, and its porosity and isostatic compressive strength are significantly improved. The method has a high extrusion speed, high molding efficiency, and short production cycle, which is conducive to large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of honeycomb ceramic technology, and more specifically, to a thin-walled cordierite honeycomb ceramic with high porosity and high strength, and its preparation method. Background Technology

[0002] Honeycomb ceramics, due to their unique structure, are widely used in purifying automotive exhaust gases. They can serve as carriers, providing reaction sites for catalysts used in exhaust gas purification, and also as filters to remove particulate matter from exhaust gases. With increasing demands, reducing the back pressure of wall-flow honeycomb ceramics requires thinning the wall thickness (from 9 mil to 6-8 mil) and increasing the porosity (from 45-55% to 55-65%). However, existing technologies face the following challenges: Thinning the wall thickness leads to a significant decrease in strength and an increased risk of firing cracks, especially for asymmetric structures. Increased porosity combined with thinning further reduces strength. High porosity requires a composite of organic pore-forming agents and graphite, but the amount of graphite added is limited. Meanwhile, the decomposition temperature of organic pore-forming agents is concentrated in the range of 200-600℃, which easily leads to concentrated decomposition and heat release, causing thin-walled, high-porosity honeycomb ceramics to crack during firing and resulting in a low yield. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a thin-walled cordierite honeycomb ceramic with high porosity and high strength and a method for its preparation.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: This invention provides a thin-walled cordierite honeycomb ceramic with high porosity and high strength. The material of the thin-walled honeycomb ceramic includes inorganic solid components, which include spherical magnesium hydroxide, silicon aluminum hollow microspheres, spherical alumina and spherical silicon dioxide. The particle size D of the silicon-aluminum hollow microspheres 50 The particle size is 15-40 μm, and the difference between the maximum and minimum particle size D50 is less than or equal to 10 μm; the particle size D of the silicon-aluminum hollow microspheres is... 100 Less than the set mesh count, which is 150-180 mesh.

[0005] Based on the above technical solution, the present invention can be further improved as follows.

[0006] Furthermore, the particle size D of the silicon-aluminum hollow microspheres 50 The particle size is 15-25 μm, D. 100 Less than 180 mesh.

[0007] Furthermore, the particle size D of the silicon-aluminum hollow microspheres 50 The particle size is 30-40 μm, D 100 Less than 150 mesh.

[0008] Furthermore, the particle size D of the spherical magnesium hydroxide... 50 The particle size is 15-25 μm, D. 100 The particle size D of the spherical alumina is less than 180 mesh. 50 The particle size is 4-8 μm, and the particle size D is... 100 The particle size D of the spherical silica is less than 325 mesh. 50 The particle size is 8-16 μm, and the particle size D is... 100 Less than 200 mesh.

[0009] Furthermore, in the inorganic solid component, the mass percentages of each component are as follows: 15%-25% spherical magnesium hydroxide, 15%-45% silicon-aluminum hollow microspheres, 15.1%-28.9% spherical alumina, and 23.0%-41.2% spherical silicon dioxide.

[0010] Furthermore, the inorganic solid component also includes kaolin and boehmite, wherein the mass percentage of kaolin in the inorganic solid component is less than or equal to 16%, and the mass percentage of boehmite in the inorganic solid component is less than or equal to 5%.

[0011] Furthermore, the material of the thin-walled honeycomb ceramic also includes organic solid components, lubricants, and water; the organic solid components include pore-forming agents and / or binders; the pore-forming agents are spherical or near-spherical with a particle size D. 50 The particle size is 15-25 μm, D. 100 Less than 180 mesh.

[0012] Furthermore, the thin-walled honeycomb ceramic has a wall thickness of 6-8 mil, a pore density of 300 cpsi, a porosity of 51.7%-68.6%, a mesopore diameter of 7.6 μm-11.8 μm, an isostatic compressive strength of 1.22 MPa-1.96 MPa, and a coefficient of thermal expansion of 0.22 × 10⁻⁶ at 25-800℃. -6 -0.64×10 -6 / ℃.

[0013] The present invention also provides a method for preparing thin-walled cordierite honeycomb ceramics with high porosity and high strength as described above, wherein a clay segment containing the inorganic solid components is extruded into a honeycomb structure to prepare a green body, and the green body is fired to obtain the thin-walled honeycomb ceramics; the extrusion speed is 10.5-15.5 mm / s.

[0014] Furthermore, the firing temperature is 1400℃-1430℃, and the holding time is 16-24 hours.

[0015] The beneficial effects of this invention are as follows: (1) The high porosity and high strength thin-walled cordierite honeycomb ceramic of the present invention effectively inhibits the concentrated decomposition and heat release of organic pore-forming agents and lubricants by using spherical magnesium hydroxide instead of traditional talc and magnesium oxide, thus avoiding cracking of thin-walled high porosity honeycomb ceramic during firing and greatly improving the firing qualification rate. (2) The high porosity and high strength thin-walled cordierite honeycomb ceramic of the present invention uses silicon-aluminum hollow microspheres of a specific particle size to achieve inorganic pore formation during the preparation process, avoiding the cracking problem caused by the concentrated decomposition of organic pore-forming agents in the low temperature range, while providing a skeleton support function, thereby improving porosity and isostatic compressive strength. (3) The high porosity and high strength thin-walled cordierite honeycomb ceramic of the present invention uses spherical raw materials such as spherical alumina and spherical silica, which enables the raw material particles to be tightly packed and uniformly dispersed, significantly improving the plasticity and fluidity of the clay, increasing the extrusion speed, and solving the problem of difficult extrusion molding of thin-walled honeycomb ceramics. (4) The high porosity and high strength thin-walled cordierite honeycomb ceramic of the present invention can meet the diversified needs of different regions and different fields of the market; (5) The method for preparing high porosity and high strength thin-walled cordierite honeycomb ceramics of the present invention has a high extrusion speed, which makes the honeycomb ceramics have high molding efficiency and short production cycle, which is conducive to large-scale industrial production. At the same time, the speed range takes into account the molding quality, so that the thin-walled honeycomb ceramics can be extruded stably without deformation or cracking, achieving high firing qualification rate and low cost manufacturing. Attached Figure Description

[0016] Figure 1 This is a microscopic morphology diagram of the high-porosity, high-strength thin-walled cordierite honeycomb ceramic of Embodiment 2 of the present invention. Detailed Implementation

[0017] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0018] The high-porosity, high-strength thin-walled cordierite honeycomb ceramic of the present invention comprises an inorganic solid component, which includes spherical magnesium hydroxide, silicon-aluminum hollow microspheres, spherical alumina, and spherical silica; wherein the particle size D of the silicon-aluminum hollow microspheres is... 50 The particle size is 15-40 μm, and the difference between the maximum and minimum values ​​of particle size D50 is less than or equal to 10 μm; the particle size D of silicon-aluminum hollow microspheres is... 100 The particle size is less than the set mesh size, which is 150-180 mesh. It should be noted that "particle size D" is... 100 "Less than the set mesh size" means that 100% of the particles in the powder pass through the set mesh size sieve.

[0019] The high-porosity, high-strength thin-walled cordierite honeycomb ceramic of the present invention achieves a synergistic improvement in high porosity and high strength by using spherical magnesium hydroxide, silicon aluminum hollow microspheres, spherical alumina, and spherical silica as inorganic solid components. This effectively solves the problems of slow extrusion molding speed, easy cracking during firing, and low strength of thin-walled, high-porosity honeycomb ceramics.

[0020] Specifically, the present invention utilizes hollow silicon-aluminum microspheres, whose spherical structure significantly improves extrusion speed. These microspheres can also serve as silicon and aluminum sources, replacing other components in the synthesis of cordierite materials or cordierite composites, effectively enhancing the strength of the honeycomb ceramic. The hollow silicon-aluminum microspheres have a closed, hollow structure and high strength, ensuring their morphology remains intact during the honeycomb ceramic fabrication process. Furthermore, the hollow silicon-aluminum microspheres can be used as pore-forming agents. During high-temperature firing, the outer shell reacts and breaks down to form the designed material, leaving pores in the hollow areas, creating a porous structure in the ceramic material. The hollow microspheres are relatively lightweight, with a large volume for the same weight, reducing or eliminating the need for pore-forming agents, significantly improving the yield of thin-walled, high-porosity honeycomb ceramics. This offers numerous advantages for the preparation of high-porosity honeycomb ceramics.

[0021] This invention uses magnesium hydroxide as a magnesium source to replace traditional talc and magnesium oxide. Magnesium hydroxide is a highly efficient and environmentally friendly flame-retardant material with a decomposition temperature of approximately 330℃-350℃, which highly overlaps with the decomposition temperature of organic matter. During the decomposition process, magnesium hydroxide absorbs a large amount of heat, achieving cooling and oxygen isolation through physical means. This inhibits the temperature rise during the decomposition of organic pore-forming agents and lubricants, preventing cracking of honeycomb ceramics caused by the concentrated decomposition of these agents.

[0022] The microstructure of each component in this invention is basically spherical or near-spherical. Such materials can improve the fluidity of the clay from the source, thereby significantly increasing the extrusion speed and solving the problem of difficult extrusion molding of thin-walled, asymmetric honeycomb ceramics. Furthermore, the spherical and near-spherical components can also reduce the amount of lubricant added and improve the firing qualification rate of the product.

[0023] Preferably, in some embodiments of the present invention, the particle size D of the silicon-aluminum hollow microspheres is... 50 The particle size is 15-25 μm, D. 100 Less than 180 mesh.

[0024] Preferably, in other embodiments of the present invention, the particle size D of the silicon-aluminum hollow microspheres is... 50 The particle size is 30-40 μm, D 100 Less than 150 mesh.

[0025] Preferably, the particle size D of the near-spherical magnesium hydroxide is... 50The particle size is 15-25 μm, D. 100 Less than 180 mesh; particle size D of spherical alumina 50 The particle size is 4-8 μm, and the particle size D is... 100 Smaller than 325 mesh; particle size D of spherical silica 50 The particle size is 8-16 μm, and the particle size D is... 100 It is less than 200 mesh.

[0026] In this invention, quasi-spherical refers to a sphericity of 0.75-0.90, and spherical refers to a sphericity of ≥0.90.

[0027] Preferably, the inorganic solid components have the following mass percentages: 15%-25% spherical magnesium hydroxide, 15%-45% silica-alumina hollow microspheres, 15.1%-28.9% spherical alumina, and 23.0%-41.2% spherical silicon dioxide. The above proportions design creates a synergistic effect among the inorganic solid components, ensuring the high porosity of the honeycomb ceramic material while avoiding the decrease in strength caused by excessive content.

[0028] Preferably, the inorganic solid component also includes kaolin and boehmite, with kaolin comprising 8%-16% by mass and boehmite comprising 5% by mass.

[0029] Adding kaolin can further improve the firing success rate, and adding boehmite can further reduce the coefficient of thermal expansion.

[0030] Preferably, the material of the thin-walled cordierite honeycomb ceramic further includes an organic solid component, a lubricant, and water, wherein the organic solid component includes a pore-forming agent and / or a binder.

[0031] Preferably, the pore-forming agent is spherical or near-spherical, with a particle size D. 50 The particle size is 15-25 μm, D. 100 It is less than 180 mesh.

[0032] Preferably, the pore-forming agent is one or more of the following: starch, graphite, polymethyl methacrylate, polyethylene polymer, graphene precursor, and nutshell powder.

[0033] Preferably, the lubricant is soybean oil, mineral oil, or water-based lubricant.

[0034] Preferably, the binder is a cellulose ether.

[0035] The thin-walled cordierite honeycomb ceramic of this invention has a porosity of 51.7%-68.6%, a mesopore diameter of 7.6μm-11.8μm, an isostatic compressive strength of 1.22MPa-1.96MPa, and a coefficient of thermal expansion of 0.22×10⁻⁶ at 25-800℃. -6-0.64×10 -6 / ℃.

[0036] This thin-walled cordierite honeycomb ceramic, with its advantages of thin walls, high porosity, and high performance, can be coated with different types of catalysts or used as a filter, making it suitable for solving environmental problems in different scenarios. It provides a guarantee for the diversified needs of the market and offers good technical support for the treatment of air pollution.

[0037] The present invention discloses a method for preparing thin-walled cordierite honeycomb ceramics with high porosity and high strength. The method involves extruding a clay segment containing inorganic solid components into a honeycomb structure to prepare a green body, and then firing the green body to obtain thin-walled honeycomb ceramics. The extrusion speed is 10.5-15.5 mm / s.

[0038] In the preparation process of honeycomb ceramics, molding and firing are the core technologies. The thinner the wall thickness, the higher the porosity and the larger the micropore size of the product, and the more difficult the extrusion molding becomes. This is because the finer the raw material, the denser the prepared ceramic, the lower the porosity and the smaller the micropore size. Therefore, extrusion molding and ceramic performance are contradictory. At the same time, the thinner the wall thickness and the higher the porosity, the lower the strength and the higher the risk of firing cracking. This invention not only solves the problem of difficult extrusion molding of thin-walled honeycomb ceramics by using spherical or near-spherical components, but also solves the problem of easy cracking during firing of thin-walled, high-porosity honeycomb ceramics by introducing flame retardant magnesium hydroxide and silicon-aluminum hollow microspheres.

[0039] In the preparation method of the present invention, the high extrusion speed makes the forming efficiency of the honeycomb ceramic high and the production cycle short, which is conducive to large-scale industrial production. At the same time, the speed range takes into account the forming quality, so that the high porosity thin-walled honeycomb ceramic with a wall thickness of 6mil-8mil and a pore density of 300cpsi can be stably extruded without deformation or cracking, providing a forming process guarantee for achieving a high firing qualification rate of 99.8% and low-cost manufacturing.

[0040] Preferably, the firing temperature is 1400℃-1430℃, and the holding time is 16-24 hours.

[0041] Specifically, the preparation method of the present invention includes the following steps: S1. The inorganic solid components and organic solid components are mixed evenly using a dry method to obtain powder.

[0042] S2. Mix the evenly mixed powder with lubricant and water, knead and knead to form a plastic clay block.

[0043] S3. The plastic clay segment is extruded at the above extrusion speed to obtain a honeycomb structure. After drying and shaping, honeycomb ceramic is obtained.

[0044] S4. Cut and process the honeycomb ceramic to conform to the pre-designed height and size to obtain the blank.

[0045] Preferably, for wall-flow honeycomb ceramics, the specific processing method is drilling and plugging, while for through-flow honeycomb ceramics, no drilling or plugging process is required.

[0046] S5. The blank is fired and kept warm to obtain the finished product.

[0047] Preferably, for honeycomb ceramics requiring skin grafting, post-processing is also necessary. Post-processing methods generally include rounding the outer periphery, edge grinding, and edge banding.

[0048] The honeycomb ceramic of this invention possesses excellent comprehensive performance, achieving a synergistic improvement in thin-walled structure, high porosity, and high strength, thus meeting the diversified needs of different market sectors. By using spherical magnesium hydroxide to replace traditional talc and magnesium oxide, introducing uniformly sized silicon-alumina hollow microspheres, and spherical raw materials such as spherical alumina and silicon dioxide, combined with dry mixing, wet kneading and extrusion molding processes, the extrusion speed reaches 10.5-15.5 mm / s, and the firing qualification rate reaches 90.4%-100%. This effectively solves the technical problems of difficult extrusion molding and easy cracking during firing of thin-walled high-porosity honeycomb ceramics, significantly improving production efficiency and yield.

[0049] The effects of the present invention will be illustrated below through specific embodiments and comparative examples.

[0050] The specific composition of each embodiment and comparative example is shown in Table 1. The SEM image of the high-porosity, high-strength thin-walled cordierite honeycomb ceramic of Example 2 is shown below. Figure 1 As shown.

[0051] Among them, the silicon-aluminum hollow microspheres #1 are spherical with a particle size D. 50 The particle size is 15-25 μm, D. 100 Less than 180 mesh; silicon-aluminum hollow microspheres #2 are spherical with a particle size D. 50 The particle size is 30-40 μm, D 100 Less than 150 mesh.

[0052] The talc used in the comparative example was in flake form with a particle size D. 50 The particle size is 30-40 μm, D 100 Less than 150 mesh.

[0053] The pore-forming agent used in each embodiment and comparative example is starch, which has a spherical microstructure and a particle size D. 50 The particle size is 15~25μm, D 100 Less than 180 mesh.

[0054] The lubricant used in each embodiment and comparative example is soybean oil.

[0055] Table 1. Specific ingredient ratios for each embodiment and comparative example. The preparation methods for each embodiment and comparative example are as follows: 1) Use a dry method to mix all inorganic solid components and organic solid components evenly.

[0056] 2) Mix the evenly mixed powder with lubricant and water, knead and knead to form a plastic clay segment.

[0057] 3) Extrude the plastic clay segments into a honeycomb structure at the extrusion speeds shown in Table 2 and then dry and shape them.

[0058] 4) Cut and process the honeycomb ceramics; 5) Firing the green body at 1405℃ and holding it for 18 hours.

[0059] To facilitate better comparative analysis, the honeycomb ceramics of the examples and comparative examples were uniformly extruded to a wall thickness of 7 mil and a pore density of 300 cpsi.

[0060] The properties of the obtained honeycomb ceramic material were tested, and the test results are shown in Table 2.

[0061] Table 2. Extrusion speed and performance test results of each embodiment and comparative example. The comparison between the examples and comparative examples shows that the formulation and preparation method of the present invention have an absolute advantage in the extrusion molding of honeycomb ceramics. This is because the microstructure of the raw materials of the present invention is spherical and near-spherical. During the extrusion molding process through the die, the microstructure avoids the bridging phenomenon between traditional sheet-like raw materials and angular raw materials, which significantly improves the extrusion speed and shortens the production cycle.

[0062] Specifically, in Examples 1-4, the content of silicon-aluminum hollow microspheres increased from 15% to 45%, resulting in improvements in porosity, median pore size, isostatic compressive strength, and coefficient of thermal expansion, while the extrusion speed decreased significantly. Furthermore, the firing pass rate in these examples remained above 99.0%. This indicates that increasing the content of silicon-aluminum hollow microspheres can significantly improve porosity and strength, but it may have some impact on molding performance and thermal expansion stability. However, this impact is not significant, allowing these honeycomb ceramics to maintain high overall performance.

[0063] Comparing Example 2 and Example 5, when the content of magnesium hydroxide increased from 15% to 25% and the content of silicon-aluminum hollow microspheres remained at 25%, the porosity increased significantly from 58.9% to 68.6%, and the isostatic compressive strength increased from 1.38 MPa to 1.96 MPa. However, the extrusion speed decreased significantly, and the firing qualification rate also dropped to 97.1%. This indicates that increasing the content of magnesium hydroxide is beneficial for pore formation and reinforcement, but excessive amounts will reduce the plasticity of the clay.

[0064] In Examples 6-9, as the kaolin content increased, the extrusion speed and firing qualification rate both decreased significantly, while the isostatic strength and thermal expansion coefficient increased. This indicates that adding an appropriate amount of kaolin helps to improve strength, but excessive amounts will deteriorate molding performance and firing quality.

[0065] Compared with Example 2, Example 10 showed that after adding 5% boehmite to replace part of the kaolin, the coefficient of thermal expansion was significantly reduced, while the porosity and isostatic compressive strength were improved, indicating that boehmite has a significant effect on reducing the coefficient of thermal expansion.

[0066] Example 12 uses particle size D 50 Replacing #1 with #2 large-particle-size silicon-aluminum hollow microspheres (30-40μm) significantly increases the median pore size and reduces the coefficient of thermal expansion to 0.25×10⁻⁶. -6 / ℃, but the isostatic strength decreased, indicating that increasing the particle size is beneficial for obtaining large pore size and low expansion, but will affect the strength.

[0067] Comparative Examples 1-4 used traditional talc formulations, which had low extrusion speeds and significantly inferior performance compared to the Examples.

[0068] In summary, the technical solution of this invention, which uses magnesium hydroxide to replace talc and introduces silicon-aluminum hollow microspheres and spherical raw materials, is significantly superior to the traditional formula in terms of molding performance, firing qualification rate, porosity, strength and coefficient of thermal expansion.

[0069] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A thin-walled cordierite honeycomb ceramic with high porosity and high strength, characterized in that, The material of the thin-walled honeycomb ceramic includes inorganic solid components, which include spherical magnesium hydroxide, silicon aluminum hollow microspheres, spherical alumina, and spherical silicon dioxide. The particle size D of the silicon-aluminum hollow microspheres 50 The particle size is 15-40 μm, and the particle size D 50 The difference between the maximum and minimum values ​​is less than or equal to 10 μm; the particle size D of the silicon-aluminum hollow microspheres 100 Less than the set mesh count, which is 150-180 mesh.

2. The high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to claim 1, characterized in that, The particle size D of the silicon-aluminum hollow microspheres 50 The particle size is 15-25 μm, D. 100 Less than 180 mesh.

3. The high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to claim 1, characterized in that, The particle size D of the silicon-aluminum hollow microspheres 50 The particle size is 30-40 μm, D. 100 Less than 150 mesh.

4. A high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to any one of claims 1-3, characterized in that, The particle size D of the spherical magnesium hydroxide 50 The particle size is 15-25 μm, D. 100 The particle size D of the spherical alumina is less than 180 mesh. 50 The particle size is 4-8 μm, and the particle size D is... 100 The particle size D of the spherical silica is less than 325 mesh. 50 The particle size is 8-16 μm, and the particle size D is... 100 Less than 200 mesh.

5. A high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to claim 4, characterized in that, The inorganic solid components are as follows: 15%-25% spherical magnesium hydroxide, 15%-45% hollow aluminum silica microspheres, 15.1%-28.9% spherical alumina, and 23.0%-41.2% spherical silicon dioxide.

6. A high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to claim 5, characterized in that, The inorganic solid component also includes kaolin and boehmite, wherein the mass percentage of kaolin in the inorganic solid component is less than or equal to 16%, and the mass percentage of boehmite in the inorganic solid component is less than or equal to 5%.

7. A high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to any one of claims 1-3, characterized in that, The material of the thin-walled honeycomb ceramic also includes organic solid components, lubricants, and water; the organic solid components include pore-forming agents and / or binders; the pore-forming agents are spherical or near-spherical with a particle size D. 50 The particle size is 15-25 μm, D. 100 Less than 180 mesh.

8. A high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to any one of claims 1-3, characterized in that, The thin-walled honeycomb ceramic has a wall thickness of 6-8 mil, a pore density of 300 cpsi, a porosity of 51.7%-68.6%, a mesopore diameter of 7.6 μm-11.8 μm, an isostatic compressive strength of 1.22 MPa-1.96 MPa, and a coefficient of thermal expansion of 0.22 × 10⁻⁶ at 25-800℃. -6 -0.64×10 -6 / ℃.

9. A method for preparing high-porosity, high-strength thin-walled cordierite honeycomb ceramics as described in any one of claims 1-8, characterized in that, The clay segment containing the inorganic solid components is extruded into a honeycomb structure to prepare a green body, and the green body is fired to obtain the thin-walled honeycomb ceramic; the extrusion speed is 10.5-15.5 mm / s.

10. The method for preparing a high-porosity, high-strength thin-walled cordierite honeycomb ceramic according to claim 9, characterized in that, The firing temperature is 1400℃-1430℃, and the holding time is 16-24 hours.

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