A method for preparing a yttria coating on the inner wall of a ceramic crucible

Abstract

The application provides a preparation method of a yttrium oxide coating on the inner wall of a ceramic crucible and relates to the technical field of coating preparation.The preparation method of the yttrium oxide coating on the inner wall of the ceramic crucible comprises the following steps: mixing yttrium oxide powder, polyethylene glycol, polyvinyl alcohol and water, heating and stirring to obtain a slurry; using a centrifugal spin coating process, coating the slurry on the inner wall of the ceramic crucible, and baking to obtain a pre-coating layer; carbonizing the pre-coating layer to obtain a carbonized coating layer; and sintering the carbonized coating layer to obtain a yttrium oxide coating.The application is suitable for ceramic crucibles with a large length-diameter ratio, and the prepared yttrium oxide coating has a smooth surface, a uniform thickness distribution and a strong bonding force with the crucible, and is not easy to fall off under a large temperature gradient.

Description

Technical Field

[0001] This invention relates to the field of coating preparation technology, and specifically to a method for preparing a yttrium oxide coating on the inner wall of a ceramic crucible. Background Technology

[0002] With the rapid development of my country's aviation industry, higher requirements have been placed on parameters such as thrust-to-weight ratio, compressor stage number, and turbine stage number of aero-engines. The service environment for materials is also becoming increasingly harsh, and the performance of traditional Ni-based and Ti-based high-temperature alloys is gradually approaching their limits. To further improve engine performance, it is necessary to develop new high-temperature alloys and more advanced preparation processes. Ti-Al based alloys, with their low density, good high-temperature strength, creep resistance, oxidation resistance, and high elastic modulus, have become a research hotspot in the field of high-temperature alloys. Directional solidification is an important technique for preparing high-temperature single-crystal / directional columnar blades. Ti-Al alloys prepared by directional solidification exhibit advantages in high-temperature performance and creep resistance, and research on the directional solidification of Ti-Al alloys has attracted widespread attention in recent years. However, titanium, as a reactive element, reacts with most elements in the molten state, and the directional solidification experiment requires the alloy to remain in a molten state for a long time. If the alloy reacts with the crucible, it will not only introduce impurities or affect the alloy's microstructure and properties, but may even cause the crucible to crack, leading to melt leakage. Therefore, preparing directional solidification crucibles and melting crucibles that do not react with titanium alloys is the key to the success of directional solidification forming or melting experiments of titanium alloys.

[0003] Ceramic crucibles such as Al2O3 and SiO2 possess numerous advantages, including high strength, high temperature resistance, corrosion resistance, mature manufacturing processes, customizable dimensions, and low cost. They are often chosen for high-temperature melting and directional solidification processes. However, alloy melts of highly reactive metals such as Ti react violently with ceramic crucibles. Therefore, there is a need to develop a low-cost crucible that combines good thermal shock resistance and high chemical stability to meet the melting or forming requirements of alloys containing reactive elements such as titanium alloys and titanium-aluminum alloys. Yttrium oxide is a refractory oxide with a melting point exceeding 2400℃. It not only exhibits excellent heat resistance and high-temperature stability but also good chemical stability, particularly at high temperatures, where it does not readily react with reactive metal elements such as Ti, Al, Zr, Nb, and Hf. Combining the properties of ceramic crucibles and yttrium oxide, using a ceramic crucible as the substrate and yttrium oxide as the coating, a composite ceramic crucible is prepared. This ensures good thermal shock resistance under large temperature gradients and effectively isolates the reaction between the molten metal and the crucible. Previous reports indicate that Beijing University of Aeronautics and Astronautics (patent number: CN101531534A) prepared yttrium oxide coatings inside corundum crucibles using a slip casting process; Nanjing University of Science and Technology (patent number: CN103771886A) prepared yttrium oxide coatings on the inner walls of corundum crucibles using a manual application method. While these two methods successfully prepared yttrium oxide coatings on the inner walls of corundum crucibles, they are not suitable for coating preparation inside ceramic crucibles with large aspect ratios (≥18). They cannot achieve uniform and complete coverage of the entire inner wall of the crucible with yttrium oxide slurry, thus hindering the rapid mass production of yttrium oxide coatings on the inner walls of ceramic crucibles with large aspect ratios. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a yttrium oxide coating on the inner wall of a ceramic crucible. This invention is not only applicable to ceramic crucibles with a large aspect ratio, but also produces a yttrium oxide coating with a smooth surface, uniform thickness distribution, strong adhesion to the crucible, and resistance to peeling off under large temperature gradients.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a yttrium oxide coating on the inner wall of a ceramic crucible, comprising the following steps:

[0007] Yttrium oxide powder, polyethylene glycol, polyvinyl alcohol and water are mixed and heated and stirred to obtain a slurry.

[0008] The slurry was coated onto the inner wall of a ceramic crucible using a centrifugal spin coating process and then baked to obtain a pre-coating.

[0009] The pre-coating is carbonized to obtain a carbonized coating.

[0010] The carbonized coating is sintered to obtain a yttrium oxide coating.

[0011] Preferably, the mass ratio of yttrium oxide powder, polyethylene glycol, polyvinyl alcohol, and water is 30-40:5-10:1-5:45-64.

[0012] Preferably, the yttrium oxide powder has an average particle size of 1–300 μm; the polyethylene glycol has an average molecular weight of 8500–11600; and the polyvinyl alcohol has a degree of hydrolysis of 98.0–99.8%.

[0013] Preferably, the heating and stirring temperature is 35–80°C.

[0014] Preferably, the ceramic crucible is open at one end or open at both ends.

[0015] Preferably, the conditions for the centrifugal spin coating process include: a spin speed of 500 to 2000 rpm; and a spin coating time of 10 to 30 minutes.

[0016] Preferably, the baking temperature is 60–90°C; the baking time is 5–8 hours; and the baking is carried out under a protective atmosphere.

[0017] Preferably, the carbonization temperature is 800–900°C; the carbonization time is 3–6 hours; and the carbonization is carried out under a protective atmosphere.

[0018] Preferably, the sintering temperature is 1500–1700°C; and the sintering time is 6–10 hours.

[0019] Preferably, the thickness of the yttrium oxide coating is 20–500 μm.

[0020] This invention provides a method for preparing a yttrium oxide coating on the inner wall of a ceramic crucible. The yttrium oxide coating prepared by this invention using a centrifugal spin-coating process is suitable for ceramic crucibles with large aspect ratios, exhibits good stability, strong adhesion to the inner wall of the crucible, is not easily detached, and has a uniform thickness. It not only effectively isolates the reaction between the alloy containing reactive elements and the ceramic crucible but also ensures the dimensional integrity and performance of the alloy. The ceramic crucible with the yttrium oxide coating on its inner wall prepared by this invention has good corrosion resistance and thermal shock resistance, can operate at temperatures up to 1650℃, and will not crack under large temperature gradients. The slurry used in this invention has both fluidity and viscosity, providing complete and uniform coverage of the inner wall of the ceramic crucible. The preparation process of this invention is simple, low-cost, and highly efficient, allowing for rapid mass production. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation of the yttrium oxide coating on the inner wall of the Al2O3 ceramic crucible using the centrifugal spin coating method in this embodiment;

[0022] Figure 2This is a schematic diagram of the structure of the yttrium oxide coating on the inner wall of the Al2O3 ceramic crucible prepared by centrifugal spin coating in the example;

[0023] Figure 3 This is a photograph of an Al2O3 ceramic crucible with a yttrium oxide coating on its inner wall, as shown in the example.

[0024] Figure 4 To complete the Ti process using the yttrium oxide-coated Al2O3 ceramic crucible prepared according to the examples. 50 Al 48 Experimental sample of Mo2 alloy under directional solidification. Detailed Implementation

[0025] This invention provides a method for preparing a yttrium oxide coating on the inner wall of a ceramic crucible, comprising the following steps:

[0026] Yttrium oxide powder, polyethylene glycol, polyvinyl alcohol and water are mixed and heated and stirred to obtain a slurry.

[0027] The slurry was coated onto the inner wall of a ceramic crucible using a centrifugal spin coating process and then baked to obtain a pre-coating.

[0028] The pre-coating is carbonized to obtain a carbonized coating.

[0029] The carbonized coating is sintered to obtain a yttrium oxide coating.

[0030] This invention involves mixing yttrium oxide powder, polyethylene glycol, polyvinyl alcohol, and water, followed by heating and stirring to obtain a slurry. In this invention, the preferred mass ratio of yttrium oxide powder, polyethylene glycol, polyvinyl alcohol, and water is 30–40:5–10:1–5:45–64, and more preferably 40:10:1:50.

[0031] In this invention, the average particle size of the yttrium oxide powder is preferably 1-300 μm, more preferably 50 μm; the average molecular weight of the polyethylene glycol is preferably 8500-11600, more preferably 10000; and the degree of alcoholysis of the polyvinyl alcohol is preferably 98.0-99.8%, more preferably 99%. In this invention, the water is preferably distilled water.

[0032] In this invention, the heating and stirring temperature is preferably 35–80°C. In this invention, the heating and stirring time is preferably 5–10 minutes. In this invention, the heating and stirring is preferably carried out under water bath conditions.

[0033] After obtaining the slurry, this invention utilizes a centrifugal spin coating process to coat the slurry onto the inner wall of a ceramic crucible, followed by baking to obtain a pre-coating layer. In this invention, the aspect ratio of the ceramic crucible is preferably ≥18. In this invention, the aspect ratio refers to the ratio of length to diameter. In this invention, the ceramic crucible is preferably open at one end or both ends. In this invention, the ceramic crucible is preferably composed of Al2O3.

[0034] In this invention, the preferred conditions for the centrifugal spin coating process include: a spin speed of 500-2000 rpm, more preferably 1000-1500 rpm; and a spin coating time of 10-30 minutes, more preferably 20-25 minutes.

[0035] In this invention, the centrifugal spin coating preferably includes: pouring the slurry into a ceramic crucible, blocking both ends of the ceramic crucible with non-woven fabric, and then clamping the ceramic crucible containing the slurry on a lathe and rotating it, using the centrifugal force generated to make the slurry evenly coated on the inner wall of the ceramic crucible.

[0036] In this invention, the baking temperature is preferably 60–90°C, more preferably 70–80°C; the baking time is preferably 5–8 hours, more preferably 6–7 hours. In this invention, the baking is preferably carried out under a protective atmosphere; the gas providing the protective atmosphere preferably includes nitrogen, argon, or helium. In this invention, the baking is preferably carried out in a tube furnace. This invention forms a pre-coating on the inner wall of the ceramic crucible by baking.

[0037] After obtaining the pre-coating, the present invention carbonizes the pre-coating to obtain a carbonized coating. In the present invention, the carbonization temperature is preferably 800–900°C, more preferably 850–900°C; the carbonization time is preferably 3–6 hours, more preferably 4–5 hours. In the present invention, the carbonization is preferably carried out under a protective atmosphere; the gas providing the protective atmosphere preferably includes nitrogen, argon, or helium. The present invention utilizes carbonization treatment to completely carbonize the organic matter in the pre-coating.

[0038] In this invention, the pre-coating is carbonized directly on the ceramic crucible with the pre-coating attached to its inner wall.

[0039] Preferably, the carbonized coating is obtained by cooling it in the furnace after carbonization.

[0040] After obtaining the carbide coating, the present invention sintersulates the carbide coating to obtain a yttrium oxide coating. In the present invention, the sintering temperature is preferably 1500–1700°C, more preferably 1600–1650°C; the sintering time is preferably 6–10 hours, more preferably 7–8 hours. In the present invention, the sintering is preferably carried out in a resistance furnace. In the present invention, the sintering atmosphere is preferably a protective atmosphere; the gas providing the protective atmosphere preferably includes nitrogen, argon, or helium. In the sintering process of the present invention, the carbide is sintered into dense yttrium oxide.

[0041] In this invention, the ceramic crucible with the carbonized coating attached to its inner wall is sintered directly during the sintering process.

[0042] Preferably, the yttrium oxide coating is obtained by cooling the furnace after sintering.

[0043] In this invention, the thickness of the yttrium oxide coating is preferably 20-500 μm, more preferably 25-200 μm.

[0044] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0045] Comparative Example 1

[0046] Step 1: Preparation of coating slurry

[0047] Yttrium oxide powder (average particle size of 50 μm), polyethylene glycol (average molecular weight of 10,000) and distilled water were mixed in a mass ratio of 39:6:55 and stirred until homogeneous at room temperature.

[0048] Step 2: Preparation of the pre-coating

[0049] Pour 8 mL of the slurry described in the first step into an Al2O3 ceramic crucible (length-to-diameter ratio of 18) with openings at both ends. Block the openings at both ends of the Al2O3 ceramic crucible with non-woven fabric. Then, clamp the Al2O3 ceramic crucible containing the slurry on a lathe and rotate it at a speed of 1000 rpm for 20 minutes. Use the centrifugal force generated to coat the slurry evenly on the inner wall of the Al2O3 ceramic crucible. Then, place the Al2O3 ceramic crucible in a tube furnace and bake it at 90°C under an argon atmosphere for 8 hours to form a pre-coating on the inner wall of the Al2O3 ceramic crucible.

[0050] Step 3: Carbonization of the coating

[0051] The Al2O3 ceramic crucible with pre-coated inner wall obtained in the second step is heated to 900℃ under argon atmosphere and held for 3 hours to completely carbonize the organic matter in the pre-coating. It is then cooled with the furnace to form a carbonized coating.

[0052] Step 4: Sintering of the coating

[0053] The Al2O3 ceramic crucible with a carbonized coating on its inner wall obtained in the third step was placed in a resistance furnace and sintered at 1700℃ for 10 hours. After cooling with the furnace, yttrium oxide coatings that had peeled off in multiple places were obtained.

[0054] Upon inspection of the coated crucible prepared in Comparative Example 1, it was found that the coating had peeled off in many places, and the coating on the inner wall of the crucible was poor where it did not peel off. These results indicate that the viscosity of the coating slurry is low, which makes it impossible for the coating to maintain a good bond with the inner wall of the crucible. This does not meet the requirements of the directional solidification experiment, and the crucible prepared in this comparative example was not used for the directional solidification experiment.

[0055] Comparative Example 2

[0056] Step 1: Preparation of coating slurry

[0057] Yttrium oxide powder (average particle size 50 μm), polyethylene glycol (average molecular weight 10,000), polyvinyl alcohol (degree of alcoholysis 99%) and distilled water were mixed in a mass ratio of 40:10:1:50 and stirred until homogeneous at room temperature.

[0058] Step 2: Preparation of the pre-coating

[0059] Pour 8 mL of the slurry described in the first step into an Al2O3 ceramic crucible (length-to-diameter ratio of 18) with openings at both ends. Block the openings at both ends of the Al2O3 ceramic crucible with non-woven fabric. Then, clamp the Al2O3 ceramic crucible containing the slurry on a lathe and rotate it at a speed of 1000 rpm for 20 minutes. Use the centrifugal force generated to coat the slurry evenly on the inner wall of the Al2O3 ceramic crucible. Then, place the Al2O3 ceramic crucible in a tube furnace and bake it at 90°C under an argon atmosphere for 8 hours to form a pre-coating on the inner wall of the Al2O3 ceramic crucible.

[0060] Step 3: Carbonization of the coating

[0061] The Al2O3 ceramic crucible with pre-coated inner wall obtained in the second step is heated to 900℃ under argon atmosphere and held for 3 hours to completely carbonize the organic matter in the pre-coating. It is then cooled with the furnace to form a carbonized coating.

[0062] Step 4: Sintering of the coating

[0063] The Al2O3 ceramic crucible with a carbonized coating on its inner wall obtained in the third step was placed in a resistance furnace and sintered at 1700℃ for 10 hours. After cooling with the furnace, a yttrium oxide coating with uneven thickness was obtained.

[0064] The coated crucible prepared in Comparative Example 2 was examined. Although no obvious coating peeling was found, there were many obvious protrusions and the coating thickness was uneven. The above results indicate that adding polyvinyl alcohol to the coating slurry effectively increases the viscosity and improves the adhesion between the coating and the inner wall of the crucible. However, the polyvinyl alcohol in the slurry was not completely dissolved under room temperature mixing conditions and agglomerated with other components during the coating preparation process. The coating thickness was uneven and did not meet the requirements of the directional solidification experiment. Therefore, the crucible prepared in this comparative example was not used for the directional solidification experiment.

[0065] Example

[0066] Step 1: Preparation of coating slurry

[0067] Yttrium oxide powder (average particle size 50 μm), polyethylene glycol (average molecular weight 10,000), polyvinyl alcohol (degree of alcoholysis 99%) and distilled water were mixed in a mass ratio of 40:10:1:50 and stirred until homogeneous under a water bath heating condition at 50°C.

[0068] Step 2: Preparation of the pre-coating

[0069] Pour 8 mL of the slurry described in the first step into an Al2O3 ceramic crucible (length-to-diameter ratio of 18) with openings at both ends. Block the openings at both ends of the Al2O3 ceramic crucible with non-woven fabric. Then, clamp the Al2O3 ceramic crucible containing the slurry on a lathe and rotate it at a speed of 1000 rpm for 20 minutes. Use the centrifugal force generated to coat the slurry evenly on the inner wall of the Al2O3 ceramic crucible. Then, place the Al2O3 ceramic crucible in a tube furnace and bake it at 90°C under an argon atmosphere for 8 hours to form a pre-coating on the inner wall of the Al2O3 ceramic crucible.

[0070] Step 3: Carbonization of the coating

[0071] The Al2O3 ceramic crucible with pre-coated inner wall obtained in the second step is heated to 900℃ under argon atmosphere and held for 3 hours to completely carbonize the organic matter in the pre-coating. It is then cooled with the furnace to form a carbonized coating.

[0072] Step 4: Sintering of the coating

[0073] The Al2O3 ceramic crucible with a carbonized coating on its inner wall obtained in the third step was placed in a resistance furnace and sintered at 1700℃ for 10 hours. After cooling with the furnace, a yttrium oxide coating with a thickness of 25μm was obtained.

[0074] The crucibles with yttrium oxide coatings prepared in this example were examined, and no coating peeling or protrusions were found. The coating thickness was uniform, and it maintained good adhesion to the inner wall of the crucible. These results indicate that under water bath heating conditions, the polyvinyl alcohol was completely dissolved in the mixed slurry, allowing the mixed slurry to maintain both good fluidity and a certain viscosity. This resulted in a uniform coating thickness and good adhesion to the inner wall of the crucible, meeting the requirements for directional solidification experiments. The crucibles prepared in this example were used for Ti... 50 Al 48 After the directional solidification experiment of Mo2 alloy, it was removed. Visual inspection of the crucible and the directional solidification experimental sample revealed no cracks on the crucible surface, and the sample had a regular shape and a smooth surface, showing no reaction with the coating, effectively ensuring the cleanliness of the alloy.

[0075] Figure 1 This is a flowchart illustrating the preparation of the yttrium oxide coating on the inner wall of an Al2O3 ceramic crucible using a centrifugal spin coating method, as shown in the examples.

[0076] Figure 2 This is a schematic diagram of the structure of the yttrium oxide coating on the inner wall of the Al2O3 ceramic crucible prepared by the centrifugal spin coating method in the embodiment. The yttrium oxide coating is attached to the inner wall of the Al2O3 ceramic crucible.

[0077] Figure 3 This is a photograph of the Al2O3 ceramic crucible with a yttrium oxide coating on its inner wall, as shown in the example. Figure 3 (a) is a macroscopic morphology diagram of the Al2O3 ceramic crucible; Figure 3 (b) shows the cross-sectional morphology of the Al2O3 ceramic crucible with a yttrium oxide coating after the directional solidification test in Example 1. Figure 3 It can be seen that the yttrium oxide coating prepared by the present invention has a smooth surface, uniform thickness distribution, and is tightly bonded to the crucible, and did not fall off in the directional solidification experiment.

[0078] Figure 4 To complete the Ti process using the yttrium oxide-coated Al2O3 ceramic crucible prepared according to the examples. 50 Al 48 Experimental samples of Mo2 alloy with directional solidification. Figure 4 It can be seen that the alloy has a regular shape and did not react with the coating during the directional solidification process.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a yttrium oxide coating on the inner wall of a ceramic crucible, comprising the following steps: Yttrium oxide powder, polyethylene glycol, polyvinyl alcohol, and water were mixed and heated to obtain a slurry; the mass ratio of yttrium oxide powder, polyethylene glycol, polyvinyl alcohol, and water was 40:10:1:50; the average molecular weight of polyethylene glycol was 10000; the degree of alcoholysis of polyvinyl alcohol was 99%; the heating and stirring temperature was 50°C; and the average particle size of yttrium oxide powder was 50 μm. The slurry was coated onto the inner wall of a ceramic crucible using a centrifugal spin coating process and then baked to obtain a pre-coating. The aspect ratio of the ceramic crucible is 18; The centrifugal spin coating process includes: pouring the slurry into a ceramic crucible, blocking both ends of the ceramic crucible with non-woven fabric, clamping the ceramic crucible containing the slurry on a lathe and rotating it, using the centrifugal force generated to coat the slurry evenly on the inner wall of the ceramic crucible; the conditions of the centrifugal spin coating process include: the rotation speed of the centrifugal spin coating is 1000 rpm; the centrifugal spin coating time is 20 minutes. The pre-coating is carbonized to obtain a carbonized coating; the carbonization temperature is 900°C; the carbonization time is 3 hours; the carbonization is carried out under a protective atmosphere. The carbonized coating is sintered to obtain a yttrium oxide coating.

2. The preparation method according to claim 1, characterized in that, The ceramic crucible is open at one end or at both ends.

3. The preparation method according to claim 1, characterized in that, The baking temperature is 60–90°C; the baking time is 5–8 hours; and the baking is carried out under a protective atmosphere.

4. The preparation method according to claim 1, characterized in that, The sintering temperature is 1500–1700℃; the sintering time is 6–10 hours.

5. The preparation method according to claim 1, characterized in that, The thickness of the yttrium oxide coating is 20–500 μm.

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