A preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics and silicon carbide honeycomb ceramics

Abstract

The present invention relates to the field of honeycomb ceramic technology, and in particular, to a preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics and silicon carbide honeycomb ceramics. The method is prepared by using inorganic solid components, starch, a binder, a lubricant and water, and the inorganic solid components include silicon carbide, metallic silicon and precipitated silicon dioxide. The method can effectively increase the degreasing strength of silicon carbide honeycomb ceramics; significantly improve the qualified rate of products and reduce production costs; the silicon carbide honeycomb ceramics of the present invention have a median pore size in the range of 9-15 μm and a porosity in the range of 38-45%, which meets general requirements, and the wall thickness is 9-12 mil, and the sintering success rate is high.

Description

Technical Field

[0001] The invention relates to the technical field of honeycomb ceramics, and in particular to a preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics and the silicon carbide honeycomb ceramics. Background Art

[0002] With the rapid development of the automobile industry, automobile exhaust pollution is becoming more and more serious. At present, wall-flow particulate filters are mostly used to filter vehicle exhaust. Its structure is to block the holes of the grid-shaped honeycomb ceramic intervals. Each grid only blocks one end. The porous characteristics of the material are used to allow the exhaust gas to pass through the honeycomb wall to achieve the filtering effect of the exhaust gas. At present, the preparation of silicon carbide honeycomb ceramics mainly adopts the production process of silicon combined with silicon carbide. The green products of this process need to go through three different sintering processes, namely degreasing sintering, atmosphere sintering and oxidation sintering. Among them, degreasing sintering mainly burns out organic additives and pore-forming agents in the product to improve the plasticity of the mud. This process will lead to a decrease in the strength of the product and it is very easy to cause the product to crack during the product transportation process, resulting in a low product qualification rate and high production cost.

[0003] Silicon carbide honeycomb ceramics are generally formed by extrusion, with a median pore size of 9-15μm and a porosity of 38-45%. Theoretically, the median pore size and porosity requirements can be achieved by stacking large particles. However, due to the current wall thickness requirement of 9-12mil for silicon carbide honeycomb ceramics, due to its thin wall thickness and the irregular morphology of silicon carbide particles themselves, it will be difficult to extrude when using large particles to stack and form pores. When small silicon carbide particles are stacked to form pores, the median pore size and porosity do not meet the requirements, so an additional 7-15% of organic pore formers are required. In addition, extrusion molding has high requirements on the plasticity of the mud, and organic binders and lubricants need to be added to improve the plasticity of the mud. These added organic pore formers, binders and lubricants will volatilize during the degreasing and sintering process, which will lead to a decrease in product strength. The more organic additives are added, the lower the strength of the product after degreasing, and the lower the qualified rate of the product. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics and silicon carbide honeycomb ceramics.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] The invention provides a preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics, which is prepared by using inorganic solid components, starch, a binder, a lubricant and water, wherein the inorganic solid components include silicon carbide, metallic silicon and precipitated silicon dioxide.

[0007] Based on the above technical solution, the present invention can also be improved as follows.

[0008] Furthermore, in the inorganic solid component, the mass percentage of each component is 77%-79% of silicon carbide, 19%-20% of metallic silicon, and 1.5%-3.5% of precipitated silicon dioxide, and the total mass percentage of each component is 100%.

[0009] Furthermore, in the inorganic solid component, the mass percentage of each component is 77.59%-78.52% of silicon carbide, 19.40%-19.63% of metallic silicon, and 1.85%-3.01% of precipitated silicon dioxide, and the total mass percentage of each component is 100%.

[0010] Furthermore, based on the mass of the inorganic solid component being 100%, the mass percentage of the starch is 5%-7%, and the mass percentage of the binder is 5%-9%.

[0011] Furthermore, based on the mass of the inorganic solid component being 100%, the mass percentage of the starch is 6%, and the mass percentage of the binder is 7%.

[0012] Further, the following steps are included:

[0013] S1, mixing the inorganic solid component, starch and a binder to obtain a powder;

[0014] S2, adding water to the powder and kneading, then adding the lubricant and continuing to knead to obtain a mud material;

[0015] S3, preparing the mud material into mud segments;

[0016] S4, extruding the mud segment, performing microwave treatment and drying to obtain a green body;

[0017] S5, cutting the green body and then sintering it to obtain the silicon carbide honeycomb ceramic.

[0018] Furthermore, based on the mass of the powder being 100%, the amount of water added is 22%-23%, and the amount of lubricant added is 0.5%-1.5%.

[0019] Furthermore, the sintering temperature is 450-500°C.

[0020] The present invention also provides a silicon carbide honeycomb ceramic, which is prepared by the above method.

[0021] Furthermore, the wall thickness of the silicon carbide honeycomb ceramic is 9-12 mil.

[0022] The beneficial effects of the present invention are:

[0023] (1) The preparation method of increasing the degreasing strength of silicon carbide honeycomb ceramics of the present invention is prepared by adding precipitated silica, which does not decompose at high temperatures and has a special microstructure and a high specific surface area, and can effectively increase the degreasing strength of silicon carbide honeycomb ceramics;

[0024] (2) The preparation method of increasing the degreasing strength of silicon carbide honeycomb ceramics of the present invention can significantly improve the qualified rate of products and reduce production costs;

[0025] (3) The silicon carbide honeycomb ceramic of the present invention has a median pore size in the range of 9-15 μm and a porosity in the range of 38-45%, which meets general requirements. At the same time, the wall thickness is 9-12 mil and the sintering success rate is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the SEM picture of the silicon carbide honeycomb ceramic of Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0028] The preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics of the present invention adopts inorganic solid components, starch, binder, lubricant and water for preparation, wherein the inorganic solid components include silicon carbide, metallic silicon and precipitated silicon dioxide.

[0029] The preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics of the present invention comprises adding precipitated silica for preparation. The precipitated silica does not decompose at high temperatures and has a special microstructure and a high specific surface area. The degreasing strength of silicon carbide honeycomb ceramics can be effectively increased, thereby significantly improving the qualified rate of products and reducing production costs.

[0030] Specifically, precipitated silica is a white powder of hydrated amorphous silicic acid, the main component of which is silicon dioxide. It will not decompose during the degreasing process. Due to the presence of a silicate form of a silicate molecular skeleton -Si-O-Si-, it has more two-dimensional structures. At the same time, there are -OH groups on the surface of precipitated silica, which makes its surface have extremely strong chemical adsorption. It can be adsorbed on the surface of silicon carbide particles, and then through its own two-dimensional structure, the silicon carbide powder after degreasing is connected, thereby increasing its strength after degreasing.

[0031] Preferably, in the inorganic solid component, the mass percentage of each component is 77%-79% of silicon carbide, 19%-20% of metallic silicon, and 1.5%-3.5% of precipitated silicon dioxide, and the total mass percentage of each component is 100%.

[0032] Preferably, in the inorganic solid component, the mass percentage of each component is 77.59%-78.52% of silicon carbide, 19.40%-19.63% of metallic silicon, and 1.85%-3.01% of precipitated silicon dioxide, and the total mass percentage of each component is 100%.

[0033] Preferably, based on 100% by mass of the inorganic solid component, the mass percentage of starch is 5%-7%, and the mass percentage of the binder is 5%-9%.

[0034] Preferably, based on 100% by mass of the inorganic solid component, the mass percentage of starch is 6% and the mass percentage of the binder is 7%.

[0035] Preferably, the preparation method of the present invention comprises the following steps:

[0036] S1. Mixing inorganic solid components, starch and a binder by a dry method to obtain a powder having a tightly packed structure.

[0037] S2. Add water to the powder and place it in a kneading machine for kneading, then add a lubricant and continue kneading to obtain a mud material; based on the mass of the powder as 100%, the amount of water added is 22%-23%, and the amount of lubricant added is 0.5%-1.5%.

[0038] Preferably, kneading is performed for 7 minutes after adding water, and kneading is continued for 10 minutes after adding the lubricant.

[0039] S3. Knead the clay into plastic clay segments.

[0040] S4, extruding the mud segment with the outer skin into a honeycomb shape, performing microwave treatment and drying to obtain a green body.

[0041] S5. After cutting the green body, sintering it in a degreasing kiln to obtain silicon carbide honeycomb ceramics; the sintering temperature is 450-500°C.

[0042] The silicon carbide honeycomb ceramic of the present invention is prepared by the above method.

[0043] The silicon carbide honeycomb ceramic of the present invention has a median pore size within the range of 9-15 μm and a porosity within the range of 38-45%, which meets general requirements. Meanwhile, the wall thickness is 9-12 mil and the sintering success rate is high.

[0044] The present invention is described below by means of specific examples.

[0045] Example 1

[0046] The preparation method of this embodiment is:

[0047] (1) A uniform mixture having a close packing is prepared by dry mixing 78.52% by weight of silicon carbide, 19.63% by weight of metallic silicon, 1.85% by weight of precipitated silica, 6% by weight of starch, and 7% by weight of a binder, wherein the amount of starch and the binder added is based on the amount of the inorganic components.

[0048] (2) The mixed powder is placed in a kneading machine, 22.94% by weight of water based on the total powder is added, and the mixture is kneaded for 7 minutes. 1% by weight of a lubricant is added, and the mixture is kneaded for 10 minutes. The amount of lubricant added is based on the total powder.

[0049] (3) The clay material kneaded in step (2) is formed into clay segments.

[0050] (4) Extruding the plastic mud segment into a honeycomb structure with the outer skin, and then microwave and dry it.

[0051] (5) After drying, the green body is cut into fixed heights and sintered in a degreasing kiln at 450-500°C.

[0052] Example 2

[0053] The preparation method of this embodiment is:

[0054] (1) A uniform mixture having a close packing is prepared by dry mixing 78.06% by weight of silicon carbide, 19.51% by weight of metallic silicon, 2.42% by weight of precipitated silica, 6% by weight of starch, and 7% by weight of a binder, wherein the amount of starch and the binder added is based on the amount of the inorganic components.

[0055] (2) The mixed powder is placed in a kneading machine, 22.94% by weight of water based on the total powder is added, and the mixture is kneaded for 7 minutes. 1% by weight of a lubricant is added, and the mixture is kneaded for 10 minutes. The amount of lubricant added is based on the total powder.

[0056] (3) The clay material kneaded in step (2) is formed into clay segments.

[0057] (4) Extruding the plastic mud segment into a honeycomb structure with the outer skin, and then microwave and dry it.

[0058] (5) After drying, the green body is cut into fixed heights and sintered in a degreasing kiln at 450-500°C.

[0059] Example 3

[0060] The preparation method of this embodiment is:

[0061] (1) A uniform mixture having a close packing is prepared by dry mixing 77.59% by weight of silicon carbide, 19.40% by weight of metallic silicon, 3.01% by weight of precipitated silica, 6% by weight of starch, and 7% by weight of a binder, wherein the amount of starch and the binder added is based on the amount of the inorganic components.

[0062] (2) The mixed powder is placed in a kneading machine, 22.94% by weight of water based on the total powder is added, and the mixture is kneaded for 7 minutes. 1% by weight of a lubricant is added, and the mixture is kneaded for 10 minutes. The amount of lubricant added is based on the total powder.

[0063] (3) The clay material kneaded in step (2) is formed into clay segments.

[0064] (4) Extruding the plastic mud segment into a honeycomb structure with the outer skin, and then microwave and dry it.

[0065] (5) After drying, the green body is cut into fixed heights and sintered in a degreasing kiln at 450-500°C.

[0066] Comparative Example

[0067] The preparation method of this comparative example is:

[0068] (1) 80% by weight of silicon carbide, 20% by weight of metallic silicon, 6% by weight of starch, and 7% by weight of a binder are mixed by a dry method to obtain a uniform mixture having a dense packing, wherein the amount of starch and the binder added is based on the amount of the inorganic components.

[0069] (2) The mixed powder is placed in a kneading machine, 22.94% by weight of water based on the total powder is added, and the mixture is kneaded for 7 minutes. 1% by weight of a lubricant is added, and the mixture is kneaded for 10 minutes. The amount of lubricant added is based on the total powder.

[0070] (3) The clay material kneaded in step (2) is formed into clay segments.

[0071] (4) Extruding the plastic mud segment into a honeycomb structure with the outer skin, and then microwave and dry it.

[0072] (5) After drying, the green body is cut into fixed heights and sintered in a degreasing kiln at 450-500°C.

[0073] The SEM image of the silicon carbide honeycomb ceramic of Example 2 is as follows: Figure 1 The parameters of each embodiment and comparative example are shown in Table 1.

[0074] Table 1

[0075]

[0076] It can be seen from the comparative example and Examples 1-3 that the more precipitated silica is added, the higher the qualified rate of product degreasing. Precipitated silica is an amorphous powdery material that can reduce the CTE of the product and is beneficial to improving the thermal shock resistance of the product. Although the qualified rate of product degreasing increases with the increase in the amount of precipitated silica added, when the amount of precipitated silica added reaches a certain value, the median pore size and porosity of the product will decrease, mainly because excessive precipitated silica will react with the residual carbon after organic degreasing during the sintering process to form silicon carbide whiskers, which will fill in the pores, reduce the pore size and porosity, and lead to poor connectivity of the micropores, which is very unfavorable for reducing the pressure drop of the product.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method for increasing the degreasing strength of silicon carbide honeycomb ceramics, characterized in that: The method is prepared by using an inorganic solid component, starch, a binder, a lubricant and water, wherein the inorganic solid component includes silicon carbide, metallic silicon and precipitated silicon dioxide; The mass percentage of each component in the inorganic solid component is 77.59%-78.52% of silicon carbide, 19.40%-19.63% of metallic silicon, and 1.85%-3.01% of precipitated silicon dioxide, and the total mass percentage of each component is 100%; Based on the mass of the inorganic solid component being 100%, the mass percentage of the starch is 5%-7%, and the mass percentage of the binder is 5%-9%; The preparation method comprises the following steps: S1, mixing the inorganic solid component, starch and a binder to obtain a powder; S2, adding water to the powder and kneading, then adding the lubricant and continuing to knead to obtain a mud material; S3, preparing the mud material into mud segments; S4, extruding the mud segment, subjecting it to microwave treatment and drying, to obtain a green body; S5, cutting the green body and sintering it in a degreasing kiln to obtain the silicon carbide honeycomb ceramic; the sintering temperature is 450-500°C.

2. A method for increasing the degreasing strength of silicon carbide honeycomb ceramics according to claim 1, characterized in that: Based on the mass of the inorganic solid component being 100%, the mass percentage of the starch is 6%, and the mass percentage of the binder is 7%.

3. A method for increasing the degreasing strength of silicon carbide honeycomb ceramics according to claim 1, characterized in that: Based on the mass of the powder being 100%, the amount of water added is 22%-23%, and the amount of lubricant added is 0.5%-1.5%.

4. A silicon carbide honeycomb ceramic, characterized in that: The method is prepared by any one of claims 1 to 3.

5. The silicon carbide honeycomb ceramic according to claim 4, characterized in that: The silicon carbide honeycomb ceramic has a median pore size of 9-15 μm, a porosity of 38-45%, and a wall thickness of 9-12 mil.

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