A chemically inert, high-temperature resistant, easily collapsible ceramic core and its preparation method

Abstract

This invention discloses a highly chemically inert, high-temperature resistant, and easily collapsible ceramic core and its preparation method, meeting the requirements for use above 1600℃. It avoids the problem of core collapse caused by hydration reaction upon contact with water-based coatings, and improves the core removal performance of complex internal cavity structures. The invention first involves uniformly mixing calcium oxide powder, plasticizer, and activated carbon fiber, molding, and sintering to obtain a base blank. Then, 2,6-di-tert-butyl-p-cresol and oleamide are prepared into an ethanol solution using anhydrous ethanol. The base blank is then completely immersed in the ethanol solution. After thorough immersion, it is removed and allowed to dry naturally. This process is repeated 2-3 times to obtain a waterproof blank. Next, yttrium oxide powder and yttrium sol are mixed to form a slurry. Finally, the slurry is uniformly sprayed onto the surface of the waterproof blank, dried, and sintered to obtain the final product.

Description

Technical Field

[0001] This invention relates to a ceramic core, specifically to a highly chemically inert, high-temperature resistant, easily collapsible ceramic core and its preparation method. It belongs to the field of precision casting technology. Background Technology

[0002] Precision casting is a crucial manufacturing method for complex components in modern industry. Hollow castings with intricate internal cavities require ceramic cores to ensure the shape and dimensions of these cavities. Currently, the most mature ceramic cores primarily use alumina and silicon dioxide as raw materials, and these alumina and silicon dioxide-based ceramic cores are widely used in the precision casting of materials including steel and high-temperature alloys. However, alumina and silicon dioxide-based ceramic cores exhibit low strength and are prone to deformation above 1600℃. Furthermore, due to the high chemical reactivity of alumina and silicon dioxide at high temperatures, they easily undergo interfacial reactions with the high-temperature melt of alloys, leading to a decline in casting quality or even scrapping. For alloys containing multiple highly reactive elements (such as titanium alloys, zirconium alloys, and niobium alloys), the casting temperature during precision casting exceeds 1600℃. The manufacturing of hollow castings of these alloys requires ceramic cores that can withstand temperatures above 1600℃ and possess low chemical reactivity. Therefore, alumina-based and silicon dioxide-based ceramic cores are no longer sufficient to meet the requirements for applications above 1600℃.

[0003] Calcium oxide has attracted the attention of researchers due to its good chemical inertness to molten titanium alloys and excellent core-removing properties. For example, patent application CN102531648A discloses a calcium oxide-based ceramic core for titanium alloy casting and its preparation method. In this patent, the calcium oxide content is 74.9–98.45 wt%. Because the precision casting process for titanium alloys is complex, the core needs to come into contact with water-based coatings during use. The core prepared by the above patent undergoes a hydration reaction upon contact with water, causing it to disintegrate. Therefore, this type of core is difficult to apply practically in the field of precision casting of titanium alloys. Patent application CN1793033A discloses a ceramic core material for precision casting of titanium alloys, with zirconium oxide as the main component, containing 60–85 wt%, of which calcium oxide contains 4–20 wt%. The above core has a relatively high zirconium oxide content, and zirconium oxide is a stable compound that is insoluble in acid and alkali solutions. Therefore, core removal is difficult, and because the core contains a certain amount of calcium oxide, it also faces the problem of hydration during use.

[0004] Patent application CN103159461A discloses a method for preparing calcium oxide-based ceramic cores. This patent modifies the hydration resistance of the core by coating the surface of a pure calcium oxide core blank. While this method can alter the core's hydration resistance, the magnetron sputtering surface coating requires sophisticated equipment. It necessitates sanding the surface of the calcium oxide-based ceramic core blank, cleaning and drying the blank, and applying a vacuum during the coating process, resulting in high costs. Furthermore, the calcium oxide-based ceramic core blank undergoes sintering after high-temperature firing, which is detrimental to the subsequent hydrolysis and core removal process. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a highly chemically inert, high-temperature resistant, easily collapsible ceramic core and its preparation method, which meets the usage requirements above 1600℃, avoids the problem of core collapse caused by hydration reaction when in contact with water-based coatings, and improves the core removal performance of complex internal cavity structures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a highly chemically inert, high-temperature resistant, and easily collapsible ceramic core, comprising the following specific steps:

[0008] (1) First, mix calcium oxide powder, plasticizer and activated carbon fiber evenly, shape and sinter to obtain the base blank;

[0009] (2) Then, 2,6-di-tert-butyl-p-cresol and oleamide are prepared into an ethanol solution using anhydrous ethanol. The substrate blank is then completely immersed in the ethanol solution. After it is fully soaked, it is taken out and dried naturally. This process is repeated 2 to 3 times to form a waterproof coating on the surface of the substrate blank, thus obtaining a waterproof blank.

[0010] (3) Then mix yttrium oxide powder and yttrium sol to make a slurry. Finally, spray the slurry evenly on the surface of the waterproof blank, dry it, and sinter it to obtain the ceramic core.

[0011] Preferably, in step (1), the mass ratio of calcium oxide powder, plasticizer and activated carbon fiber is 80-90:5-10:5-10.

[0012] Preferably, in step (1), the particle size of the calcium oxide is D50 = 10-20 μm.

[0013] Preferably, in step (1), the plasticizer is a mixture of dioctyl phthalate and triglyceride, with a mass ratio of 60-80:20-40.

[0014] Preferably, in step (1), the activated carbon fiber has a diameter of 1–5 μm and a specific surface area of ​​1000–1500 m². 2 / g, with an average pore size of 1.0–2.0 nm and a length of 10–20 μm.

[0015] Preferably, in step (1), the sintering process conditions are as follows: first, the temperature is raised from room temperature to 670°C at a constant rate over 2 hours and held for 4 hours; then, the temperature is raised to 1000°C at a constant rate over 4 hours and held for 4 hours; finally, the temperature is raised to 1500°C at a constant rate over 4 hours and held for 4 hours.

[0016] Preferably, in step (2), the mass ratio of the substrate blank to the ethanol solution is 1:2-3, the mass concentration of the ethanol solution is 15-20%, and the mass ratio of 2,6-di-tert-butyl-p-cresol to oleic acid amide is 1-2:2-3.

[0017] Preferably, in step (2), the time required for full soaking is 30 to 60 minutes, and the natural drying time is 24 to 48 hours.

[0018] Preferably, in step (3), the mass ratio of yttrium oxide powder to yttrium sol is 2.5 to 3:1, the particle size of yttrium oxide powder is D50 = 10 to 20 μm, and the yttrium sol is prepared by the method in Example 3 of patent application CN115319018A.

[0019] Preferably, in step (3), the spraying process conditions are: spraying voltage 40V, spraying current 400A, spraying distance 150mm, spray gun moving speed 80mm / s; the thickness of the coating formed by spraying is 300~400μm.

[0020] Preferably, in step (3), the drying process conditions are: temperature 19-23℃, humidity 45-55%, and drying time 24-48 hours.

[0021] Preferably, in step (3), the sintering process conditions are as follows: first, the temperature is raised from room temperature to 670°C at a constant rate for 2 hours and held for 4 hours; then, the temperature is raised to 1000°C at a constant rate for 4 hours and held for 4 hours; finally, the temperature is raised to 1500°C at a constant rate for 4 hours and held for 4 hours.

[0022] A highly chemically inert, high-temperature resistant, and easily collapsible ceramic core is obtained through the aforementioned preparation method.

[0023] The beneficial effects of this invention are as follows: First, calcium oxide powder, plasticizer, and activated carbon fiber are mixed evenly, shaped, and sintered to obtain a base blank. Then, 2,6-di-tert-butyl-p-cresol and oleamide are prepared into an ethanol solution using anhydrous ethanol. The base blank is then completely immersed in the ethanol solution. After thorough immersion, it is removed and allowed to air dry. This process is repeated 2-3 times to obtain a waterproof blank. Next, yttrium oxide powder and yttrium sol are mixed to form a slurry. Finally, the slurry is evenly sprayed onto the surface of the waterproof blank, dried, and sintered to obtain a ceramic core. This ceramic core has the following advantages:

[0024] (1) It solves the problem that the current alumina-based ceramic core and silicon oxide-based ceramic core cannot meet the use requirements above 1600℃, and that calcium oxide-based ceramic core is prone to hydration reaction and core collapse during contact with water-based coatings. At the same time, it can easily achieve physical and chemical corrosion core removal and improve the core removal performance of complex internal cavity structures.

[0025] (2) Activated carbon fiber has small pore size and narrow distribution, large specific surface area, fast adsorption speed and large adsorption capacity. Activated carbon fiber is a microporous structure with narrow distribution and single pore size. Its pores can produce capillary coagulation effect, which can better adsorb calcium oxide and plasticizer molecules, so that they are evenly dispersed and prevent agglomeration. This prevents calcium oxide from sintering during subsequent calcination. During subsequent calcination, the activated carbon fiber can be burned off, forming a porous structure inside the core. Since the fiber has a long length, it can form a seepage channel after calcination. Thus, during the subsequent core removal process, water can easily reach the core and react with calcium oxide along the seepage channel, which greatly accelerates the core demolding speed.

[0026] (3) Yttrium oxide coatings are prepared by spraying, which requires simple equipment and has low coating preparation costs. The thickness of the prepared coating can reach 300-400 μm.

[0027] (4) In the subsequent core removal process, the core removal agent can be a mixed aqueous solution of ammonium nitrate and sodium hydroxide. During the core removal process, the solution can easily reach the interior of the core along the seepage channel and react with calcium oxide to generate a large amount of heat and generate ammonia gas that overflows, thereby causing the core to collapse and greatly accelerating the core demolding speed.

[0028] The effect of specific parameters and dosage of activated carbon fiber on the effect:

[0029] When the diameter of activated carbon fibers is less than 1 μm (or the specific surface area is less than 1000 m²), 2 When the activated carbon fiber diameter is less than 5 μm and the average pore size is less than 1.0 nm and the length is less than 10 μm, the adsorption effect is weak and the anti-agglomeration effect is not obvious. However, when the activated carbon fiber diameter is greater than 5 μm (or the specific surface area is greater than 1500 m²), the adsorption effect is weak and the anti-agglomeration effect is not obvious. 2When the carbon density is 1 / g, with an average pore size greater than 2.0 nm and a length greater than 20 μm, the sintering strength of the core decreases because the activated carbon is burned off after core calcination. This is detrimental to the preparation and molding of the core.

[0030] When the activated carbon fiber content is less than 5%, the adsorption effect is weak and the anti-agglomeration effect is not obvious. When the activated carbon fiber content is greater than 10%, it will reduce the sintering strength of the core.

[0031] The sintering strength was tested using the "three-point bending test method" and the testing instrument was a bending test machine.

[0032] 1. Preparation: a) Place the sample on the support device and adjust its position to align it with the loading point.

[0033] b) Set an appropriate span (i.e., the distance between two support points) and loading rate (i.e., the rate of change of load per second) according to the specimen size.

[0034] c) Calibrate the measuring instrument and connect it to the computer for data acquisition and processing.

[0035] 2. Applying load: a) Begin applying load and record the load-displacement curve.

[0036] b) Record the maximum bending angle of the specimen when it is bent.

[0037] c) When the specimen fails, stop applying the load and record the failure load and displacement of the specimen.

[0038] 3. Data processing: Calculate the strength of the specimen based on the load-displacement curve.

[0039] The aggregation rate was determined by scanning the sample with a scanning electron microscope and identifying the number of aggregated particles through the spectrum. The aggregation rate was then obtained by dividing the number of aggregated particles by the total number of particles.

[0040] See Tables 1-5 for details.

[0041] Table 1. Relationship between activated carbon fiber diameter and the sintering strength and agglomeration rate of the resulting core.

[0042] .

[0043] Table 2. Relationship between specific surface area of ​​activated carbon fiber and sintering strength and agglomeration rate of the resulting core

[0044] .

[0045] Table 3. Relationship between average pore size of activated carbon fibers and sintering strength and agglomeration rate of the resulting core.

[0046] .

[0047] Table 4. Relationship between activated carbon fiber length and the sintering strength and agglomeration rate of the resulting core

[0048] .

[0049] Table 5. Relationship between activated carbon fiber dosage and the sintering strength and agglomeration rate of the resulting core.

[0050] .

[0051] Both 2,6-di-tert-butyl-p-cresol and oleamide are white powders, readily soluble in ethanol but insoluble in water. After ethanol evaporates, a dense, waterproof coating forms on the surface. If 2,6-di-tert-butyl-p-cresol is insufficient or lacking, the strength of the waterproof coating will decrease, making the membrane prone to rupture. Conversely, if oleamide is insufficient or lacking, the density of the waterproof coating will decrease, reducing the membrane's waterproof performance. See Table 6 for details.

[0052] The waterproofing rate is in accordance with the national standard GB / T1741 2007 "Test Methods for Waterproofing Membranes and Coatings for Buildings". The coating strength is tested using the "three-point bending test method", as detailed in the previous section on sintering strength testing.

[0053] Table 6. Influence of Raw Material Composition on Waterproof Coating Effect

[0054] Detailed Implementation

[0055] The present invention will be further described below with reference to embodiments. It should be noted that the following description is only for explaining the present invention and does not limit its content. Example 1:

[0056] A method for preparing a highly chemically inert, high-temperature resistant, and easily collapsible ceramic core, comprising the following specific steps:

[0057] (1) First, mix 800g of calcium oxide powder, 50g of plasticizer and 50g of activated carbon fiber evenly, shape and sinter to obtain the base blank;

[0058] (2) Then, 2,6-di-tert-butyl-p-cresol and oleamide are prepared into an ethanol solution using anhydrous ethanol. The substrate blank is then completely immersed in the ethanol solution. After it is fully soaked, it is taken out and dried naturally. This process is repeated twice to form a waterproof coating on the surface of the substrate blank, thus obtaining a waterproof blank.

[0059] (3) Take 250g of yttrium oxide powder and 100g of yttrium sol and mix them to make a slurry. Finally, spray the slurry evenly on the surface of the waterproof blank, dry it, and sinter it to obtain the ceramic core.

[0060] In step (1), the particle size of the calcium oxide is D50 = 10 μm.

[0061] In step (1), the plasticizer is a mixture of dioctyl phthalate and triglyceride, with a mass ratio of 60:20.

[0062] In step (1), the activated carbon fiber has a diameter of 1 μm and a specific surface area of ​​1000 m². 2 / g, with an average pore size of 1.0nm and a length of 10μm.

[0063] In step (1), the sintering process conditions are as follows: first, use 2 hours to uniformly raise the temperature from room temperature to 670℃ and hold for 4 hours; then use 4 hours to continue uniformly raising the temperature to 1000℃ and hold for 4 hours; finally, use 4 hours to continue uniformly raising the temperature to 1500℃ and hold for 4 hours.

[0064] In step (2), the mass ratio of the substrate blank to the ethanol solution is 1:2, and the mass concentration of the ethanol solution is 15%, wherein the mass ratio of 2,6-di-tert-butyl-p-cresol to oleamide is 1:2. The time required for full impregnation is 30 minutes, and the natural drying time is 24 hours.

[0065] In step (3), the particle size of yttrium oxide powder is D50=10μm, and the yttrium sol is prepared by the method in Example 3 of patent application CN115319018A.

[0066] In step (3), the spraying process conditions are: spraying voltage 40V, spraying current 400A, spraying distance 150mm, spray gun moving speed 80mm / s; the thickness of the coating formed by spraying is 300μm.

[0067] In step (3), the drying process conditions are: temperature 19℃, humidity 45%, and drying time 24 hours.

[0068] In step (3), the sintering process conditions are as follows: first, use 2 hours to uniformly raise the temperature from room temperature to 670℃ and hold for 4 hours; then use 4 hours to continue uniformly raising the temperature to 1000℃ and hold for 4 hours; finally, use 4 hours to continue uniformly raising the temperature to 1500℃ and hold for 4 hours.

[0069] The prepared highly chemically inert, high-temperature resistant, and easily collapsible ceramic core solves the problems of current alumina-based and silicon-based ceramic cores failing to meet the usage requirements above 1600℃, and calcium oxide-based ceramic cores being prone to hydration reactions and core collapse during contact with water-based coatings. It also facilitates physicochemical corrosion core removal, improving the core removal performance of complex internal cavity structures. Its operating temperature reaches 1800℃. In the subsequent core removal process, a mixed aqueous solution of ammonium nitrate and sodium hydroxide with a concentration of 20% and a mass ratio of 1:2 is used as the core remover. During core removal, the remover easily reaches the core interior along the seepage channels and reacts with calcium oxide, generating a large amount of heat and releasing ammonia gas, thus causing the core to collapse. The demolding time is reduced from the previous 48 hours to 0.5 hours, greatly accelerating the core demolding speed. Example 2:

[0070] A method for preparing a highly chemically inert, high-temperature resistant, and easily collapsible ceramic core, comprising the following specific steps:

[0071] (1) First, mix 900g of calcium oxide powder, 100g of plasticizer and 100g of activated carbon fiber evenly, shape and sinter to obtain the base blank;

[0072] (2) Then, 2,6-di-tert-butyl-p-cresol and oleamide are prepared into an ethanol solution using anhydrous ethanol. The substrate blank is then completely immersed in the ethanol solution. After it is fully soaked, it is taken out and dried naturally. This process is repeated 3 times to form a waterproof coating on the surface of the substrate blank, thus obtaining a waterproof blank.

[0073] (3) Take 300g of yttrium oxide powder and 100g of yttrium sol and mix them to make a slurry. Finally, spray the slurry evenly on the surface of the waterproof blank, dry it, and sinter it to obtain the ceramic core.

[0074] In step (1), the particle size of the calcium oxide is D50 = 20 μm.

[0075] In step (1), the plasticizer is a mixture of dioctyl phthalate and triglyceride, with a mass ratio of 80:40.

[0076] In step (1), the activated carbon fiber has a diameter of 5 μm and a specific surface area of ​​1500 m². 2 / g, with an average pore size of 2.0nm and a length of 20μm.

[0077] In step (1), the sintering process conditions are as follows: first, use 2 hours to uniformly raise the temperature from room temperature to 670℃ and hold for 4 hours; then use 4 hours to continue uniformly raising the temperature to 1000℃ and hold for 4 hours; finally, use 4 hours to continue uniformly raising the temperature to 1500℃ and hold for 4 hours.

[0078] In step (2), the mass ratio of the substrate blank to the ethanol solution is 1:3, and the mass concentration of the ethanol solution is 20%, wherein the mass ratio of 2,6-di-tert-butyl-p-cresol to oleamide is 2:3. The time required for full impregnation is 60 minutes, and the natural drying time is 48 hours.

[0079] In step (3), the particle size of yttrium oxide powder is D50=20μm, and the yttrium sol is prepared by the method in Example 3 of patent application CN115319018A.

[0080] In step (3), the spraying process conditions are: spraying voltage 40V, spraying current 400A, spraying distance 150mm, spray gun moving speed 80mm / s; the thickness of the coating formed by spraying is 400μm.

[0081] In step (3), the drying process conditions are: temperature 23℃, humidity 55%, and drying time 48 hours.

[0082] In step (3), the sintering process conditions are as follows: first, use 2 hours to uniformly raise the temperature from room temperature to 670℃ and hold for 4 hours; then use 4 hours to continue uniformly raising the temperature to 1000℃ and hold for 4 hours; finally, use 4 hours to continue uniformly raising the temperature to 1500℃ and hold for 4 hours. Example 3:

[0083] A method for preparing a highly chemically inert, high-temperature resistant, and easily collapsible ceramic core, comprising the following specific steps:

[0084] (1) First, mix 850g of calcium oxide powder, 80g of plasticizer and 80g of activated carbon fiber evenly, shape and sinter to obtain the base blank;

[0085] (2) Then, 2,6-di-tert-butyl-p-cresol and oleamide are prepared into an ethanol solution using anhydrous ethanol. The substrate blank is then completely immersed in the ethanol solution. After it is fully soaked, it is taken out and dried naturally. This process is repeated twice to form a waterproof coating on the surface of the substrate blank, thus obtaining a waterproof blank.

[0086] (3) Take 280g of yttrium oxide powder and 100g of yttrium sol and mix them to make a slurry. Finally, spray the slurry evenly on the surface of the waterproof blank, dry it, and sinter it to obtain the ceramic core.

[0087] In step (1), the particle size of the calcium oxide is D50 = 15 μm.

[0088] In step (1), the plasticizer is a mixture of dioctyl phthalate and triglyceride, with a mass ratio of 70:30.

[0089] In step (1), the activated carbon fiber has a diameter of 2 μm and a specific surface area of ​​1200 m².2 / g, with an average pore size of 1.5nm and a length of 15μm.

[0090] In step (1), the sintering process conditions are as follows: first, use 2 hours to uniformly raise the temperature from room temperature to 670℃ and hold for 4 hours; then use 4 hours to continue uniformly raising the temperature to 1000℃ and hold for 4 hours; finally, use 4 hours to continue uniformly raising the temperature to 1500℃ and hold for 4 hours.

[0091] In step (2), the mass ratio of the substrate blank to the ethanol solution is 1:2.5, and the mass concentration of the ethanol solution is 18%, wherein the mass ratio of 2,6-di-tert-butyl-p-cresol to oleamide is 1.5:2.5. The time required for full impregnation is 40 minutes, and the natural drying time is 32 hours.

[0092] In step (3), the particle size of yttrium oxide powder is D50=15μm, and the yttrium sol is prepared by the method in Example 3 of patent application CN115319018A.

[0093] In step (3), the spraying process conditions are: spraying voltage 40V, spraying current 400A, spraying distance 150mm, spray gun moving speed 80mm / s; the thickness of the coating formed by spraying is 400μm.

[0094] In step (3), the drying process conditions are: temperature 20℃, humidity 50%, and drying time 35 hours.

[0095] In step (3), the sintering process conditions are as follows: first, use 2 hours to uniformly raise the temperature from room temperature to 670℃ and hold for 4 hours; then use 4 hours to continue uniformly raising the temperature to 1000℃ and hold for 4 hours; finally, use 4 hours to continue uniformly raising the temperature to 1500℃ and hold for 4 hours.

[0096] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Based on the technical solutions of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for preparing a highly chemically inert, high-temperature resistant, easily collapsible ceramic core, characterized in that, The specific steps are as follows: (1) First, mix calcium oxide powder, plasticizer and activated carbon fiber evenly, shape and sinter to obtain the base blank; (2) Then, 2,6-di-tert-butyl-p-cresol and oleamide are prepared into an ethanol solution using anhydrous ethanol. The substrate blank is then completely immersed in the ethanol solution. After it is fully soaked, it is taken out and dried naturally. This process is repeated 2 to 3 times to form a waterproof coating on the surface of the substrate blank, thus obtaining a waterproof blank. (3) Then mix yttrium oxide powder and yttrium sol to make a slurry. Finally, spray the slurry evenly on the surface of the waterproof blank, dry it, and sinter it to obtain the ceramic core.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of calcium oxide powder, plasticizer and activated carbon fiber is 80-90:5-10:5-10.

3. The preparation method according to claim 1, characterized in that, In step (1), the plasticizer is a mixture of dioctyl phthalate and triglyceride, with a mass ratio of 60-80:20-40.

4. The preparation method according to claim 1, characterized in that, In step (1), the activated carbon fiber has a diameter of 1–5 μm and a specific surface area of ​​1000–1500 m². 2 / g, with an average pore size of 1.0–2.0 nm and a length of 10–20 μm.

5. The preparation method according to claim 1, characterized in that, In step (1), the sintering process conditions are as follows: first, use 2 hours to uniformly raise the temperature from room temperature to 670℃ and hold for 4 hours; then use 4 hours to continue uniformly raising the temperature to 1000℃ and hold for 4 hours; finally, use 4 hours to continue uniformly raising the temperature to 1500℃ and hold for 4 hours.

6. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the substrate blank to the ethanol solution is 1:2-3, the mass concentration of the ethanol solution is 15-20%, and the mass ratio of 2,6-di-tert-butyl-p-cresol to oleic acid amide is 1-2:2-3.

7. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of yttrium oxide powder to yttrium sol is 2.5 to 3:

1.

8. The preparation method according to claim 1, characterized in that, In step (3), the spraying process conditions are: spraying voltage 40V, spraying current 400A, spraying distance 150mm, spray gun moving speed 80mm / s; the thickness of the coating formed by spraying is 300~400μm.

9. The preparation method according to claim 1, characterized in that, In step (3), the drying process conditions are: temperature 19-23℃, humidity 45-55%, and drying time 24-48 hours; The sintering process conditions are as follows: first, heat the temperature from room temperature to 670℃ at a constant rate over 2 hours and hold for 4 hours; then, continue heating the temperature at a constant rate to 1000℃ over 4 hours and hold for 4 hours; finally, continue heating the temperature at a constant rate to 1500℃ over 4 hours and hold for 4 hours.

10. A highly chemically inert, high-temperature resistant, easily collapsible ceramic core, characterized in that, It is obtained by the preparation method described in any one of claims 1 to 9.

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