Ceramic crucible with large-particle skeleton structure and high porosity and preparation method

Abstract

The invention belongs to the technical field of high-temperature alloy precision casting, and particularly relates to a high-porosity ceramic crucible with a large-particle skeleton structure and a preparation method. According to the method, a traditional crucible forming method is abandoned, a framework made of a large-particle material is firstly constructed, then gaps between the frameworks are accurately filled with a specific filling material, and therefore forming of the crucible is completed. Wherein the framework material comprises the following raw materials in parts by weight: 50-65 parts of 3-5mm white corundum, 30-45 parts of 1-3mm white corundum, 3-4.5 parts of gel powder, 0.5-2 parts of high-alumina cement and 5-8 parts of additional water; the filling material comprises the following raw materials in parts by weight: 20-45 parts of 0-120-mesh white corundum, 25-35 parts of alpha-alumina powder, 30-40 parts of silica sol and 0.5-1 part of an external surfactant. The basic strength of the crucible is stabilized, and the thermal shock resistance of the crucible is remarkably enhanced by optimizing the internal pore structure of the crucible.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature alloy precision casting, and in particular relates to a ceramic crucible with a large-particle skeleton structure and high porosity and a preparation method thereof. Background Art

[0002] In the field of high-temperature alloy precision casting, ceramic crucibles are regarded as indispensable consumables. Their main function is to serve as a medium for carrying molten metal during medium-frequency melting. In view of the extremely high melting point and extremely fast heating rate of high-temperature alloys, extremely stringent requirements are placed on the thermal shock resistance of crucibles. At present, the market for ceramic crucibles used for high-temperature alloy melting mainly relies on imported products. This phenomenon has posed a significant obstacle to the sustainable development of my country's high-end equipment manufacturing industry. Although China has made certain technological progress in the field of ceramic crucibles in recent years, compared with similar foreign products, there is still a significant gap in the service life of domestic crucibles, which is specifically manifested in that their thermal shock resistance is far inferior to that of imported products.

[0003] Regarding the thermal shock performance of ceramics, relevant research data show that the sensitivity of ceramic strength to thermal shock damage decreases with increasing temperature. At the same time, higher porosity can inhibit the instantaneous diffusion of cracks during rapid cooling and heating, and can also absorb thermal expansion to a certain extent, thereby reducing thermal stress. However, traditional domestic ceramic crucibles are generally formed by cold isostatic pressing, hot die casting, and injection molding. During the raw material mixing process, coarse particles and fine particles are mixed together for forming. After sintering, they not only have high strength, but also low porosity. At the same time, the sintering temperature is generally extremely high during the sintering process, causing a large amount of shrinkage in the ceramic crucible, which further leads to the concentration of stress inside the crucible, thereby seriously weakening the thermal stability of the ceramic crucible, which is manifested in that it is very easy to experience performance fluctuations or structural damage under temperature changes. Summary of the invention

[0004] In order to solve the above technical problems, the present invention adopts a unique molding process, which aims to accurately separate and arrange the coarse particles and fine particles in the ceramic crucible. Specifically, the coarse particles are cleverly used as the support frame of the crucible to lay the foundation for the basic strength of the crucible; and the fine particles are used as filling materials, tightly and evenly filled in the skeleton pores formed by the coarse particles, thereby effectively ensuring that the porosity of the crucible is maintained in an ideal state. In addition, all raw materials used to manufacture ceramic crucibles have undergone strict high-temperature pretreatment, and the sintering process strictly follows the solid-phase sintering principle. After sintering, it almost achieves a "zero" shrinkage effect. This feature further optimizes the internal stress distribution of the crucible, and ultimately achieves the goal of significantly improving the service life of the ceramic crucible.

[0005] The invention discloses a ceramic crucible with a large-particle skeleton structure and high porosity. The ceramic crucible skeleton material is composed of the following raw materials in percentage by mass, wherein 3-5 mm white corundum is 50-65 parts, 1-3 mm white corundum is 30-45 parts, gel powder is 3-4.5 parts, high-alumina cement is 0.5-2 parts, and water is added in an amount of 5-8 parts; the filling material is composed of the following raw materials in percentage by mass, wherein 0-120 mesh white corundum is 20-45 parts, α-alumina powder is 25-35 parts, silica sol is 30-40 parts, and a surfactant is added in an amount of 0.5-1 parts.

[0006] According to another aspect of the present invention, there is also provided a method for making the crucible, comprising the following steps:

[0007] a) Mixing skeleton raw materials: by weight, take 50-65 parts of 3-5mm white corundum, 30-45 parts of 1-3mm white corundum, 3-4.5 parts of gel powder, and 0.5-2 parts of high-alumina cement, and send them into a zero-gravity mixing device, and add 5-8 parts of water at the same time, mix the skeleton raw materials evenly, and set aside;

[0008] b) Aggregate molding: The mixed skeleton raw materials are fed into the crucible mold and vibrated to achieve uniform filling.

[0009] c) Aggregate demoulding: placing the crucible mold equipped with the skeleton in a room temperature environment, removing the crucible mold after standing and hardening, and obtaining a skeleton-type crucible blank for standby use;

[0010] d) Mixing filling materials: by weight, take 20-45 parts of 0-120 mesh white corundum, 25-35 parts of α-alumina powder, 30-40 parts of silica sol, and add 0.5-1 part of surfactant, send them into a mixing and stirring device, mix the filling materials evenly, and obtain a slurry for standby use;

[0011] e) Filling coating: After the formed crucible skeleton is completely immersed in the filling slurry for a period of time, the crucible skeleton is taken out. At this time, the coarse particle surface of the crucible skeleton will be completely covered by the filling slurry, and the crucible skeleton is placed in a hardening chamber, and carbon dioxide gas is introduced into the hardening chamber. The filling coating process needs to be repeated according to the size requirements of the crucible.

[0012] f) Crucible repair: After coating, there are still defects such as pinholes and pores on the surface of the crucible. It is necessary to use a brush dipped in the coating slurry to repair the defective position to obtain the desired crucible body;

[0013] g) Crucible drying: The formed crucible blank is sent into a blast drying oven to remove excess moisture in the blank;

[0014] h) Crucible sintering: The dried ceramic crucible blank is sent into a kiln and sintered to obtain a finished crucible.

[0015] Preferably, the main components of the gel powder in step a) are silica-alumina gel powder and the high-alumina cement is SC-71 type, and the weightless mixing time is 10-30 minutes.

[0016] Further preferably, the mold in step b) is a silicone mold with a Shore hardness of 36A, and graphite powder needs to be evenly coated on the surface of the silicone mold to facilitate demolding of the blank after molding.

[0017] More preferably, in step c), the room temperature should be controlled above 16° C. and the molding time should be controlled within 18-24 hours.

[0018] More preferably, the silica sol in step d) is 40% alkaline silica sol, and the surfactant is a non-anionic surfactant.

[0019] More preferably, the time of introducing carbon dioxide in step e) is 30-45 minutes, and the number of coating times needs to be more than 3 times.

[0020] More preferably, step f) requires repairing and leveling the uneven areas on the crucible surface.

[0021] More preferably, in step g), the drying temperature should be controlled at 105° C. and the drying time should be 16-48 hours.

[0022] More preferably, the sintering temperature of the crucible in step h) is 850-1050°C.

[0023] The present invention provides a method for preparing a high-porosity ceramic crucible with a large-particle skeleton structure. The ceramic crucible is known for its excellent chemical stability, and its core component is mainly aluminum oxide, which ensures that it does not undergo any chemical reaction with molten steel during the casting process. By adopting a unique skeleton structure design, the ceramic crucible of the present invention can maintain its basic strength and meet various requirements for daily use. In addition, the filler is cleverly filled in the pores between the particle skeletons. This design not only ensures the high porosity of the crucible, but also effectively suppresses the instantaneous expansion of cracks under rapid cooling and heating conditions, and can absorb thermal expansion to a certain extent, thereby significantly improving the thermal stability of the crucible. Furthermore, the present invention adopts low-temperature sintering technology, which significantly reduces the internal stress distribution of the crucible, thereby effectively extending the service life of the crucible. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a photo of the surface state of the coarse particle skeleton structure of the present invention;

[0025] Figure 2 This is a photo of the surface state of the present invention after filling;

[0026] Figure 3This is a photo of the crucible of the present invention before being repaired;

[0027] Figure 4 This is a photo of the finished crucible of the present invention;

[0028] Figure 5 This is a scanning electron microscope image of the finished crucible of the present invention;

[0029] Figure 6 This is the SEM scanning electron microscope image of the crucible cross section. DETAILED DESCRIPTION

[0030] 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.

[0031] Example 1

[0032] A method for preparing a ceramic crucible with a large particle skeleton structure and high porosity is prepared according to the following steps:

[0033] a) Mixing skeleton raw materials: by weight, take 60 parts of 3-5mm white corundum, 35 parts of 1-3mm white corundum, 4 parts of gel powder, and 1 part of high-alumina cement, send them into a zero-gravity mixing device, and add 6 parts of water at the same time, mix the skeleton raw materials evenly, and set aside;

[0034] b) Aggregate molding: The mixed skeleton raw materials are fed into the crucible mold and vibrated to achieve uniform filling.

[0035] c) Aggregate demoulding: placing the crucible mold equipped with the skeleton in a room temperature environment, removing the crucible mold after standing and hardening for 20 hours to obtain a skeleton type crucible blank for standby use;

[0036] d) Mixing filling materials: by weight, take 45 parts of 0-120 mesh white corundum, 25 parts of α-alumina powder, 30 parts of silica sol, and add 0.5 parts of surfactant, send them into a mixing and stirring device, mix the filling materials evenly, and obtain a slurry for standby use;

[0037] e) Filling material coating: After the formed crucible skeleton is completely immersed in the filling slurry, the crucible skeleton is taken out. At this time, the coarse particle surface of the crucible skeleton will be completely covered by the filling slurry. The crucible skeleton is placed in a hardening chamber, and carbon dioxide gas is introduced into the hardening chamber for 30 minutes. Repeat the coating and hardening operation 5 times;

[0038] f) Crucible repair: Use a brush to dip the coating slurry to repair the defective position to obtain the required crucible body;

[0039] g) Crucible drying: The formed crucible blank is sent into a blast drying oven at a drying temperature of 105° C. for 16 hours to remove excess moisture from the blank;

[0040] h) Crucible sintering: The dried ceramic crucible blank is sent into a kiln and sintered at 1050°C. After keeping the temperature for 2 hours, a finished crucible is obtained.

[0041] Example 2

[0042] A method for preparing a ceramic crucible with a large particle skeleton structure and high porosity is prepared according to the following steps:

[0043] a) Mixing skeleton raw materials: by weight, take 50 parts of 3-5mm white corundum, 45 parts of 1-3mm white corundum, 4.5 parts of gel powder, and 0.5 parts of high-alumina cement, send them into a zero-gravity mixing device, and add 8 parts of water at the same time, mix the skeleton raw materials evenly, and set aside;

[0044] b) Aggregate molding: The mixed skeleton raw materials are fed into the crucible mold and vibrated to achieve uniform filling.

[0045] c) Aggregate demoulding: placing the crucible mold equipped with the skeleton in a room temperature environment, removing the crucible mold after standing and hardening for 24 hours to obtain a skeleton type crucible blank for standby use;

[0046] d) Mixing filling materials: by weight, take 30 parts of 0-120 mesh white corundum, 35 parts of α-alumina powder, 35 parts of silica sol, and 0.8 parts of surfactant, and send them into a mixing and stirring device, mix the filling materials evenly, and obtain a slurry for standby use;

[0047] e) Filling material coating: After the formed crucible skeleton is completely immersed in the filling slurry, the crucible skeleton is taken out. At this time, the coarse particle surface of the crucible skeleton will be completely covered by the filling slurry. The crucible skeleton is placed in a hardening chamber, and carbon dioxide gas is introduced into the hardening chamber for 40 minutes. Repeat the coating and hardening operation 5 times;

[0048] f) Crucible repair: Use a brush to dip the coating slurry to repair the defective position to obtain the required crucible body;

[0049] g) Crucible drying: The formed crucible blank is sent into a blast drying oven at a drying temperature of 105° C. for 20 hours to remove excess moisture from the blank;

[0050] h) Crucible sintering: The dried ceramic crucible blank is sent into a kiln and sintered at 950°C. After keeping the temperature for 2 hours, a finished crucible is obtained.

[0051] Example 3

[0052] A method for preparing a ceramic crucible with a large particle skeleton structure and high porosity is prepared according to the following steps:

[0053] a) Mixing skeleton raw materials: by weight, take 55 parts of 3-5mm white corundum, 40 parts of 1-3mm white corundum, 3.5 parts of gel powder, and 1.5 parts of high-alumina cement, send them into a zero-gravity mixing device, and add 7 parts of water at the same time, mix the skeleton raw materials evenly, and set aside;

[0054] b) Aggregate molding: The mixed skeleton raw materials are fed into the crucible mold and vibrated to achieve uniform filling.

[0055] c) Aggregate demoulding: placing the crucible mold equipped with the skeleton in a room temperature environment, removing the crucible mold after standing and hardening for 22 hours to obtain a skeleton type crucible blank for standby use;

[0056] d) Mixing filling materials: by weight, take 25 parts of 0-120 mesh white corundum, 35 parts of α-alumina powder, 40 parts of silica sol, and 1 part of surfactant, and send them into a mixing and stirring device, mix the filling materials evenly, and obtain a slurry for standby use;

[0057] e) Filling material coating: After the formed crucible skeleton is completely immersed in the filling slurry, the crucible skeleton is taken out. At this time, the coarse particle surface of the crucible skeleton will be completely covered by the filling slurry. The crucible skeleton is placed in a hardening chamber, and carbon dioxide gas is introduced into the hardening chamber for 45 minutes. Repeat the coating and hardening operation for 6 times;

[0058] f) Crucible repair: Use a brush to dip the coating slurry to repair the defective position to obtain the required crucible body;

[0059] g) Crucible drying: The formed crucible blank is sent into a blast drying oven at a drying temperature of 105° C. for 24 hours to remove excess moisture from the blank;

[0060] h) Crucible sintering: The dried ceramic crucible blank is sent into a kiln and sintered at 850°C. After keeping the temperature for 2 hours, a finished crucible is obtained.

[0061] Example 4

[0062] A method for preparing a ceramic crucible with a large particle skeleton structure and high porosity is prepared according to the following steps:

[0063] a) Mixing skeleton raw materials: by weight, take 65 parts of 3-5mm white corundum, 30 parts of 1-3mm white corundum, 3 parts of gel powder, and 2 parts of high-alumina cement, send them into a weightless mixing device, and add 5 parts of water at the same time, mix the skeleton raw materials evenly, and set aside;

[0064] b) Aggregate molding: The mixed skeleton raw materials are fed into the crucible mold and vibrated to achieve uniform filling.

[0065] c) Aggregate demoulding: placing the crucible mold equipped with the skeleton in a room temperature environment, removing the crucible mold after standing and hardening for 18 hours to obtain a skeleton type crucible blank for standby use;

[0066] d) Mixing filling materials: by weight, take 35 parts of 0-120 mesh white corundum, 30 parts of α-alumina powder, 35 parts of silica sol, and 0.8 parts of surfactant, and send them into a mixing and stirring device, mix the filling materials evenly, and obtain a slurry for standby use;

[0067] e) Filling material coating: After the formed crucible skeleton is completely immersed in the filling slurry, the crucible skeleton is taken out. At this time, the coarse particle surface of the crucible skeleton will be completely covered by the filling slurry. The crucible skeleton is placed in a hardening chamber, and carbon dioxide gas is introduced into the hardening chamber for 40 minutes. Repeat the coating and hardening operation for 6 times;

[0068] f) Crucible repair: Use a brush to dip the coating slurry to repair the defective position to obtain the required crucible body;

[0069] g) Crucible drying: The formed crucible blank is sent into a blast drying oven at a drying temperature of 105° C. for 20 hours to remove excess moisture from the blank;

[0070] h) Crucible sintering: The dried ceramic crucible blank is sent into a kiln and sintered at 950°C. After keeping the temperature for 2 hours, a finished crucible is obtained.

[0071] Performance Test Table

[0072]

[0073] Attached Figure 1 Attached is a photo of the surface state of the coarse particle skeleton structure of the present invention; Figure 2 This is a photo of the surface state of the present invention after filling; Figure 3 This is a photo of the crucible of the present invention before repairing. Figure 4 This is a photo of the finished crucible of the present invention.

[0074] The X-ray diffraction pattern of the ceramic crucible product prepared by this method is as follows: Figure 5 The main crystal phase of the crucible of the present invention is aluminum oxide;

[0075] The cross-section SEM image of the ceramic crucible prepared by this method is as follows: Figure 6 The microstructure of the crucible of the present invention also presents a skeleton filling structure.

[0076] 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 ceramic crucible with a large particle skeleton structure and high porosity, characterized in that: By weight, the ceramic crucible skeleton material includes the following raw materials, including 50-65 parts of 3-5mm white corundum, 30-45 parts of 1-3mm white corundum, 3-4.5 parts of gel powder, 0.5-2 parts of high alumina cement, and 5-8 parts of water; the filling material includes the following raw materials, including 20-45 parts of 0-120 mesh white corundum, 25-35 parts of α-alumina powder, 30-40 parts of silica sol, and 0.5-1 part of surfactant.

2. A method for preparing a ceramic crucible with a large particle skeleton structure and high porosity, characterized in that: The steps include: a) Mixing skeleton raw materials: by weight, take 50-65 parts of 3-5mm white corundum, 30-45 parts of 1-3mm white corundum, 3-4.5 parts of gel powder, and 0.5-2 parts of high-alumina cement, and send them into a zero-gravity mixing device, and add 5-8 parts of water at the same time, mix the skeleton raw materials evenly, and set aside; b) Aggregate forming: The mixed skeleton raw materials are fed into the crucible mold and vibrated to achieve uniform filling; c) Aggregate demoulding: placing the crucible mold containing the skeleton raw material in a room temperature environment, removing the crucible mold after standing and hardening, and obtaining a skeleton type crucible blank for standby use; d) Mixing filling materials: by weight, take 20-45 parts of 0-120 mesh white corundum, 25-35 parts of α-alumina powder, 30-40 parts of silica sol, and add 0.5-1 part of surfactant, send them into a mixing and stirring device, mix the filling materials evenly, and obtain a slurry for standby use; e) Filling material coating: After the formed crucible skeleton is completely immersed in the filling slurry for a period of time, the crucible skeleton is taken out; at this time, the coarse particle surface of the crucible skeleton will be completely covered by the filling slurry, and the crucible skeleton is placed in a hardening chamber, and carbon dioxide gas is introduced into the hardening chamber; the filling coating process needs to be repeated according to the size requirements of the crucible. Coating and hardening operations; f) Crucible repair: Use a brush to dip the coating slurry to repair the pinholes and pores on the surface of the coated crucible to obtain the desired crucible body; g) Crucible drying: The formed crucible blank is sent into a blast drying oven to remove excess moisture in the blank; h) Crucible sintering: The dried ceramic crucible blank is sent into a kiln and sintered to obtain a finished crucible.

3. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: In step a), the main components of the gel powder are silica-alumina gel powder and the high-alumina cement is SC-71 type, and the weightless mixing time is 10-30 minutes.

4. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: The mold in step b) is a silicone mold with a Shore hardness of 36A. Graphite powder needs to be evenly coated on the surface of the silicone mold to facilitate demoulding of the blank after molding.

5. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: In step c), the room temperature should be controlled above 16° C. and the molding time should be controlled within 18-24 hours.

6. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: In step d), the silica sol is 40% alkaline silica sol, and the surfactant is a non-anionic surfactant.

7. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: In step e), the carbon dioxide is introduced for 30-45 minutes, and the coating frequency needs to be more than 3 times.

8. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: In step f), the uneven areas on the crucible surface need to be repaired and made smooth.

9. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: In step g), the drying temperature should be controlled at 105° C. and the drying time is 16-48 hours.

10. The method for preparing a ceramic crucible with a large particle skeleton structure and high porosity according to claim 2, characterized in that: The sintering temperature of the crucible in step h) is 850-1050°C.

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