Inner protective layer of iridium crucible and preparation method thereof

Abstract

The application provides an inner protective layer of an iridium crucible and a preparation method thereof, and belongs to the technical field of single crystal growth. The inner protective layer of the iridium crucible is composed of an IrAl alloy layer and a ceramic coating, the IrAl alloy layer is located between the ceramic coating and the inner wall of the iridium crucible and covers the inner wall of the iridium crucible, the thickness of the inner protective layer increases from 300-500 microns at the opening of the iridium crucible to 700-1100 microns at the bottom of the iridium crucible along the inner wall, the ceramic coating is divided into three layers from inside to outside, the height of the three layers of the ceramic coating on the inner wall of the iridium crucible gradually decreases in the direction from the opening of the iridium crucible to the bottom of the side wall of the iridium crucible, and the first layer of the ceramic coating covers the entire surface of the IrAl alloy layer. The gradually increasing thickness of the inner protective layer of the iridium crucible from the opening to the bottom can reduce the longitudinal temperature field difference of the melt in the crystal growth process, improve the stability of the crystal growth and the crystallization quality, reduce the corrosion of the melt and oxygen to the iridium crucible, and reduce the loss of iridium metal in the crystal growth process.

Description

Technical Field

[0001] This invention belongs to the field of single crystal growth technology, specifically relating to an inner protective layer of an iridium crucible and its preparation method. Background Technology

[0002] In melt crystal growth, a crucible capable of withstanding the high temperatures of melting and the erosion caused by the melt is crucial for crystal quality control. Iridium has a melting point of 2450℃; therefore, iridium crucibles are commonly used for melt growth of crystals such as sapphire, gallium oxide, and yttrium aluminum garnet (YAG) with melting points in the range of 1800–2100℃. However, in practical use, iridium crucibles are prone to oxidation and volatilization in an oxygen atmosphere, leading to problems such as melt floating, iridium-doped crystals, and crucible corrosion. Therefore, effective protective measures need to be studied to reduce iridium metal loss and improve crystal growth quality.

[0003] Chinese patent application CN114086249A discloses a method for suppressing iridium crucible oxidation. This method involves dividing the gallium oxide growth temperature into at least two temperature ranges and setting different growth atmospheres for each range. The growth atmosphere can be an inert protective atmosphere composed of argon and / or nitrogen, an oxidizing atmosphere composed of oxygen and / or carbon dioxide, or a mixture of both. This approach can suppress iridium oxidation to some extent and improve crystal growth quality, but it cannot completely prevent iridium oxidation. Furthermore, continuously introducing gas during crystal melting carries away a significant amount of energy and accelerates melt evaporation, increasing process costs.

[0004] Chinese Patent Publication CN206872982U discloses an iridium crucible with a protective coating on its surface. This method improves the crucible's lifespan by coating its outer surface with a 0.1-3 mm thick coating. The coating material is Y₂O₃, ZrO₂, or a composite material of Y₂O₃ and ZrO₂ in a 4:6 mass ratio. This approach effectively reduces the volatilization of iridium on the outer surface of the crucible, significantly reduces the crucible's deformation, and is beneficial for temperature field stability and reducing crystal growth costs. However, this method cannot prevent the melt from corroding the inner wall of the crucible, nor can it reduce the temperature gradient of the melt or suppress melt volatilization, thus failing to improve the crystal growth quality.

[0005] Chinese Patent Publication CN113774484B discloses a combined crucible for growing gallium oxide crystals. This method fundamentally avoids corrosion of the iridium crucible by the oxide melt by embedding a ceramic crucible within an iridium crucible. This solution is applicable to both Czochralski and casting methods for crystal growth. However, because the ceramic-embedded crucible and the iridium crucible exist independently with a certain distance between them, the ceramic crucible needs to be quite thick, increasing the cost. Furthermore, the poor thermal conductivity and thickness of the ceramic crucible require the iridium crucible to withstand higher heating temperatures to prepare the melt, leading to increased iridium volatilization, reduced heating efficiency, energy waste, and decreased stability of the melt temperature field. Moreover, since the melt does not directly contact the iridium crucible, it is impossible to directly test the iridium crucible's temperature to adjust the melt temperature, increasing the process complexity. Additionally, this solution also fails to reduce the temperature gradient of the melt and suppress melt volatilization to improve crystal growth quality. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention provides an inner protective layer for an iridium crucible. This inner protective layer can reduce the temperature gradient across the melt, thereby suppressing melt volatilization to improve crystal growth quality, and can also reduce corrosion of the iridium crucible by the melt and oxygen.

[0007] Specifically, the present invention adopts the following technical solution to achieve the above objectives:

[0008] An inner protective layer for an iridium crucible, the inner protective layer comprising an IrAl alloy layer and a ceramic coating, wherein the IrAl alloy layer is located between the ceramic coating and the inner wall of the iridium crucible and covers the inner wall of the iridium crucible; the thickness of the inner protective layer on the side wall of the iridium crucible increases from 300-500 μm to 700-1100 μm from the opening of the iridium crucible along the inner wall toward the bottom of the iridium crucible; the ceramic coating is divided into three layers from the inside out, the height of the three ceramic coating layers on the inner wall of the iridium crucible gradually decreasing from the opening of the iridium crucible toward the bottom of the side wall of the iridium crucible, and the first ceramic coating layer covers the entire surface of the IrAl alloy layer.

[0009] In this invention, the IrAl alloy layer in the inner protective layer of the iridium crucible prevents oxygen atom diffusion and buffers the thermal stress between the ceramic coating and the iridium crucible. The ceramic coating reduces the longitudinal temperature difference between the upper and lower surfaces of the melt and prevents the melt from eroding the inner surface of the iridium crucible. Therefore, the multi-layered material design of the inner sidewall protective layer of the crucible makes the coating more stable and able to withstand the high temperatures above 1800°C required for single crystal growth. The thickness of the sidewall protective layer gradually increases from the crucible opening to the bottom of the sidewall, which reduces the longitudinal temperature gradient of the melt, improves the stability and crystal quality of crystal growth, and solves the problem of corrosion of the iridium crucible interior by the melt and oxygen.

[0010] In a preferred embodiment, the IrAl alloy layer is a uniform coating with a thickness of 100~200μm; each ceramic coating layer has the same thickness of 200~300μm.

[0011] In a preferred embodiment, the Al content in the IrAl alloy layer is: 0 < Al ≤ 15 wt%.

[0012] In a preferred embodiment, the ceramic coating is a rare earth element tantalate ceramic thermal barrier layer, the main material components of which are RETaO4, RE3TaO7 or RETa3O9, wherein RE is a rare earth element.

[0013] In a further preferred embodiment, the rare earth element is at least one of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, or Lu.

[0014] The present invention further provides an iridium crucible comprising an inner protective layer of the iridium crucible.

[0015] The present invention also provides a method for preparing the inner protective layer of the iridium crucible according to any of the above embodiments, comprising the following steps:

[0016] S1. Clean and spray the inner surface of the iridium crucible to obtain a clean and rough inner surface;

[0017] S2. Within 2 hours, the first IrAl alloy layer is uniformly sprayed onto the inner surface of the side wall of the iridium crucible using an atmospheric plasma spraying method, so that the first IrAl alloy layer covers the entire inner surface of the side wall of the iridium crucible.

[0018] S3. Using atmospheric plasma spraying, a first ceramic coating layer is sprayed onto the surface of the first IrAl alloy layer, so that the first ceramic coating layer covers the entire surface of the first IrAl alloy layer; a second ceramic coating layer is sprayed onto the surface of the first ceramic coating layer at a first distance from the top of the first IrAl alloy layer; and a third ceramic coating layer is sprayed onto the surface of the second ceramic coating layer at a second distance from the top of the first ceramic coating layer.

[0019] S4. A second IrAl alloy layer is sprayed onto the inner bottom of the iridium crucible using an atmospheric plasma spraying method, and a second ceramic coating is sprayed onto the surface of the second IrAl alloy layer; the first IrAl alloy layer and the second IrAl alloy layer constitute the IrAl alloy layer; the first ceramic coating and the second ceramic coating constitute the ceramic coating.

[0020] S5. Anneal and polish the iridium crucible to obtain a stable inner protective layer.

[0021] In some implementations, the spraying conditions in step S1 are as follows: the spraying pressure is 0.2-1 MPa, the angle between the nozzle and the direction perpendicular to the sprayed area on the inner wall of the iridium crucible is 60°-85°, and the distance between the nozzle and the sprayed area is 100-200 mm.

[0022] In some implementations, the spraying conditions of the atmospheric plasma spraying method in step S2 are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 200-300 mm, and the gas flow rate is 150-320 SCFH.

[0023] In some implementations, the spraying conditions of the atmospheric plasma spraying method in step S3 are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 100-180 mm, and the gas flow rate is 100-230 SCFH.

[0024] In some implementations, the first distance and the second distance are equal, and depending on the size of the iridium crucible, the first distance and the second distance are both 5mm-15mm.

[0025] In some implementations, the spraying conditions of the atmospheric plasma spraying method in step S4 are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 100-180 mm, and the gas flow rate is 100-230 SCFH.

[0026] In some implementations, the annealing conditions in step S5 are: 1200-1600℃, held for 2-5 hours.

[0027] The technical solution of the present invention has the following beneficial effects: (1) In the present invention, by forming a thermal barrier material layer with a slope thickness, a longitudinal temperature gradient is formed between the iridium crucible and the thermal barrier material layer, which can reduce the longitudinal temperature field difference of the melt during crystal growth and improve the stability and crystal quality of crystal growth. (2) By coating a protective layer inside the iridium crucible, the present invention can reduce the corrosion of the iridium crucible by the melt and oxygen, reduce the loss of iridium metal during crystal growth, extend the service life of the iridium crucible, and reduce the cost of crystal growth. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the internal protection structure of the iridium crucible provided by the present invention.

[0029] In the figure: 1. Iridium crucible; 11. Side wall; 12. Bottom; 2. IrAl alloy layer; 21. First IrAl alloy layer; 22. Second IrAl alloy layer; 3. Ceramic coating; 31. First ceramic coating; 311. First layer of first ceramic coating; 312. Second layer of first ceramic coating; 313. Third layer of first ceramic coating; 32. Second ceramic coating. Detailed Implementation

[0030] The following description, in conjunction with embodiments, clearly and completely describes the technical solutions of the present invention, so that those skilled in the art can fully understand the present invention. Obviously, the described embodiments are only some preferred embodiments of the present invention, and not all embodiments. Any equivalent modifications or substitutions made by those skilled in the art to the following embodiments without creative effort are within the protection scope of the present invention.

[0031] The methods not described in detail in the following embodiments are all conventional methods well known to those skilled in the art.

[0032] Example 1

[0033] Reference Figure 1This embodiment provides an inner protective layer for an iridium crucible. The iridium crucible 1 includes a sidewall 11 and a bottom 12. An inner protective layer is coated on the inner surface of the iridium crucible 1. This inner protective layer consists of an IrAl alloy layer 2 and a ceramic coating 3. The IrAl alloy layer 2 consists of a first IrAl alloy layer 21 on the inner surface of the sidewall 11 and a second IrAl alloy layer 22 on the inner surface of the bottom 12. The IrAl alloy layer 2 is located between the ceramic coating 3 and the inner surface of the sidewall 11 and covers the entire inner surface of the iridium crucible 1. The IrAl alloy layer 2 is used to bond the ceramic coating 3 to the inner surface of the sidewall 11. The ceramic coating 3 consists of a first ceramic coating 31 on the inner surface of the sidewall 11 and a second ceramic coating 32 on the inner surface of the bottom 12. The ceramic coating 3 is divided into three layers from the inside out. The thickness of the three ceramic coating layers on the sidewall 11 increases uniformly from the opening of the iridium crucible 1 along the inner wall to the bottom 12, and the thickness on the inner surface of the bottom 12 is uniform. The first ceramic coating 31 consists of three layers from the inside out, each with the same thickness. The first ceramic coating 311 covers the entire surface of the IrAl alloy layer 2. The top of the second ceramic coating 312 is spaced from the top of the first ceramic coating 311, and the top of the third ceramic coating 313 is spaced from the top of the second ceramic coating 312, resulting in a gradient distribution of the thickness of the ceramic coating 3 along the height direction of the sidewall 11 (from the opening of the iridium crucible 1 towards the bottom 12). The second ceramic coating 32 is a uniformly thick ceramic coating. The IrAl alloy layer (with an Al atomic percentage of 8%) has a thickness of 100 μm. The ceramic coating 3 is a rare-earth element tantalate ceramic thermal barrier layer, with its main material composition being YTaO4 containing 6 wt% Y2O3. The thicknesses of the first ceramic coating 311, the second ceramic coating 312, and the third ceramic coating 313 are all 200 μm. The distance between the top of the second layer of the first ceramic coating 312 and the top of the first layer of the first ceramic coating 311 is 10 mm, and the distance between the top of the third layer of the first ceramic coating 313 and the top of the second layer of the first ceramic coating 312 is 10 mm. The thickness of the inner protective layer at the opening of the iridium crucible 1 is 300 μm, the thickness at the bottom 12 of the iridium crucible is 700 μm, and the thickness of the protective layer on the inner surface of the sidewall 11 gradually increases from 300 μm to 700 μm.

[0034] The method for preparing the inner protective layer of this iridium crucible includes the following steps:

[0035] S1. Clean the inner surface of the iridium crucible with deionized water, and then spray iridium gold onto the inner surface using a spraying method. The sandblasting pressure is 0.8MPa, the angle of the nozzle relative to the direction perpendicular to the sprayed area on the inner wall of the iridium crucible is 70°, and the distance between the nozzle and the sprayed area is 120mm, to obtain a clean and rough inner surface.

[0036] S2. Within 2 hours, an IrAl alloy (Al content of 8wt%) is uniformly sprayed onto the inner surface of the iridium crucible using atmospheric plasma spraying to obtain the first IrAl alloy layer. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 250mm, and the gas flow rate (inert gas as carrier gas, such as nitrogen) is 200SCFH.

[0037] S3. A first ceramic coating layer, consisting of a rare-earth element tantalate ceramic containing 6 wt% Y₂O₃ and YTaO₄, is sprayed onto the surface of the first IrAl alloy layer using an atmospheric plasma spraying method. A second first ceramic coating layer is then sprayed onto the surface of this first ceramic coating layer 10 mm from the opening of the iridium crucible using the same atmospheric plasma spraying method. A third first ceramic coating layer is then sprayed onto the surface of this second first ceramic coating layer 10 mm from the top of the first first ceramic coating layer using the same atmospheric plasma spraying method, thus obtaining a protective layer on the sidewall. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 150 mm, and the gas flow rate (using an inert gas as the carrier gas, such as argon) is 150 SCFH.

[0038] S4. An IrAl alloy (8wt% Al content) is sprayed onto the inner surface of the bottom of the iridium crucible using atmospheric plasma spraying to obtain a second IrAl alloy layer. A rare-earth element tantalate ceramic thermal barrier layer containing 6wt% Y₂O₃ (YTaO₄) is then sprayed onto the surface of the second IrAl alloy layer to obtain the bottom protective layer. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 150 mm, and the gas flow rate (inert gas as carrier gas, such as argon) is 150 SCFH.

[0039] S5. Anneal the iridium crucible at 1500℃ for 3 hours, and then polish it to obtain a stable inner protective layer.

[0040] Gallium oxide crystals are grown using the melt method with an iridium crucible containing the aforementioned inner protective layer, as follows:

[0041] P1: Weigh 500g of high-quality gallium oxide powder (purity ≥99.9999%) and place it in an iridium crucible.

[0042] P2: Place it properly <010> The β-Ga2O3 seed crystals are placed in the furnace, the furnace door is closed, a vacuum is drawn, and then high-purity CO2 gas is introduced into the furnace. The induction heating switch is turned on to start heating the furnace body.

[0043] P3: When the temperature inside the furnace reaches 1850℃, the furnace is left to stand for 2 hours to remove bubbles from the gallium oxide melt. Then, gallium oxide single crystals are grown using methods such as crystal pulling, necking, shoulder formation, and constant diameter growth. The pulling speed is eventually stabilized at 5-10 mm / h (e.g., 5 mm / h, 6 mm / h, 8 mm / h, 10 mm / h; in this embodiment, it is 6 mm / h). A gallium oxide single crystal ingot with a half-width at half-maximum (FWHM) of 15 arcsec is obtained. After removing bubbles from the gallium oxide melt and when the temperature field is stable, the temperatures of the upper and lower surfaces of the melt are measured to be 1803℃ and 1855℃, respectively, with a longitudinal temperature difference of 52℃.

[0044] Example 2

[0045] Reference Figure 1 This embodiment provides an inner protective layer for an iridium crucible. The difference from Embodiment 1 is that the IrAl alloy layer contains 15% Al atoms and has a thickness of 150 μm. The ceramic coating 3 is a rare-earth element tantalate ceramic thermal barrier layer, with its main material composition being NdTaO4 containing 4 wt% Nd₂O₃. The thicknesses of the first ceramic coating 311, the second ceramic coating 312, and the third ceramic coating 313 are all 250 μm. The distance between the top of the second ceramic coating 312 and the top of the first ceramic coating 311 is 5 mm, and the distance between the top of the third ceramic coating 313 and the top of the second ceramic coating 312 is 15 mm. The thickness of the inner protective layer is 400 μm at the opening of the iridium crucible 1, 900 μm at the bottom 12 of the iridium crucible, and the thickness of the protective layer on the inner surface of the sidewall 11 gradually increases from 400 μm to 900 μm.

[0046] The method for preparing the inner protective layer of this iridium crucible includes the following steps:

[0047] S1. Clean the inner surface of the iridium crucible with deionized water, and then spray iridium gold onto the inner surface using a spraying method. The sandblasting pressure is 0.2MPa, the angle of the nozzle relative to the direction perpendicular to the sprayed area on the inner wall of the iridium crucible is 85°, and the distance between the nozzle and the sprayed area is 100mm, to obtain a clean and rough inner surface.

[0048] S2. Within 2 hours, an IrAl alloy (Al content of 15wt%) is uniformly sprayed onto the inner surface of the iridium crucible using atmospheric plasma spraying to obtain the first IrAl alloy layer. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 200mm, and the gas flow rate (inert gas as carrier gas, such as helium) is 150SCFH.

[0049] S3. A first ceramic coating layer, consisting of a rare-earth element tantalate ceramic containing 4 wt% Nd₂O₃ and NdTaO₄, is sprayed onto the surface of the first IrAl alloy layer using an atmospheric plasma spraying method. A second first ceramic coating layer is then sprayed onto the surface of this first ceramic coating layer 5 mm from the opening of the iridium crucible using the same atmospheric plasma spraying method. A third first ceramic coating layer is then sprayed onto the surface of this second first ceramic coating layer 15 mm from the top of the first first ceramic coating layer using the same atmospheric plasma spraying method, thus obtaining a protective layer on the sidewall. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 100 mm, and the gas flow rate (using an inert gas as the carrier gas, such as argon) is 100 SCFH.

[0050] S4. An IrAl alloy (15wt% Al content) is sprayed onto the inner surface of the bottom of the iridium crucible using atmospheric plasma spraying to obtain a second IrAl alloy layer. A rare-earth element tantalate ceramic thermal barrier layer containing a 4wt% Nd₂O₃ NdTaO₄ coating is then sprayed onto the surface of the second IrAl alloy layer to obtain the bottom protective layer. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 100mm, and the gas flow rate (inert gas as carrier gas, such as argon) is 100SCFH.

[0051] S5. Anneal the iridium crucible at 1200℃ for 5 hours, and then polish it to obtain a stable inner protective layer.

[0052] Gallium oxide crystals were grown according to the method in Example 1, with a pulling speed of 5 mm / h in step P3 and a measured longitudinal temperature difference of 63°C in the melt.

[0053] Example 3

[0054] Reference Figure 1 This embodiment provides an inner protective layer for an iridium crucible. The difference from Embodiment 1 is that the IrAl alloy layer contains 5% Al atoms and has a thickness of 200 μm. The ceramic coating 3 is a rare-earth element tantalate ceramic thermal barrier layer, its main material composition being SmTaO4 containing 2 wt% Sm₂O₃. The thicknesses of the first ceramic coating 311, the second ceramic coating 312, and the third ceramic coating 313 are all 300 μm. The distance between the top of the second ceramic coating 312 and the top of the first ceramic coating 311 is 15 mm, and the distance between the top of the third ceramic coating 313 and the top of the second ceramic coating 312 is 5 mm. The thickness of the inner protective layer at the opening of the iridium crucible 1 is 500 μm, the thickness at the bottom 12 of the iridium crucible is 1100 μm, and the thickness of the protective layer on the inner surface of the sidewall 11 gradually increases from 500 μm to 1100 μm.

[0055] The method for preparing the inner protective layer of this iridium crucible includes the following steps:

[0056] S1. Clean the inner surface of the iridium crucible with deionized water, and then spray iridium gold onto the inner surface using a spraying method. The sandblasting pressure is 1MPa, the angle of the nozzle relative to the direction perpendicular to the sprayed area on the inner wall of the iridium crucible is 60°, and the distance between the nozzle and the sprayed area is 200mm, to obtain a clean and rough inner surface.

[0057] S2. Within 2 hours, an IrAl alloy layer (Al content of 5wt%) is uniformly sprayed onto the inner surface of the iridium crucible using atmospheric plasma spraying to obtain the first IrAl alloy layer. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 100mm, and the gas flow rate (inert gas as carrier gas, such as helium) is 320SCFH.

[0058] S3. A first ceramic coating layer, consisting of a rare-earth element tantalate ceramic containing 2 wt% Sm₂O₃ and SmTaO₄, is sprayed onto the surface of the first IrAl alloy layer using an atmospheric plasma spraying method. A second first ceramic coating layer is then sprayed onto the surface of this first ceramic coating layer 15 mm from the opening of the iridium crucible using the same atmospheric plasma spraying method. A third first ceramic coating layer is then sprayed onto the surface of this second first ceramic coating layer 5 mm from the top of the first first ceramic coating layer using the same atmospheric plasma spraying method, thus obtaining a protective layer on the sidewall. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 180 mm, and the gas flow rate (using an inert gas as the carrier gas, such as argon) is 230 SCFH.

[0059] S4. An IrAl alloy (5wt% Al content) is sprayed onto the inner surface of the bottom of the iridium crucible using atmospheric plasma spraying to obtain a second IrAl alloy layer. A rare-earth element tantalate ceramic thermal barrier layer containing a 2wt% Sm₂O₃ SmTaO₄ coating is then sprayed onto the surface of the second IrAl alloy layer to obtain the bottom protective layer. The atmospheric plasma spraying process conditions are as follows: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 180 mm, and the gas flow rate (inert gas as carrier gas, such as argon) is 230 SCFH.

[0060] S5. Anneal the iridium crucible at 1600℃ for 2 hours, and then polish it to obtain a stable inner protective layer.

[0061] Gallium oxide crystals were grown according to the method in Example 1. In step P3, the pulling speed was 10 mm / h, and the measured longitudinal temperature difference of the melt was 58°C.

[0062] In the present invention, when the main material component of the ceramic coating is RE3TaO7 or RETa3O9 (RE is a rare earth element) and the rare earth element is at least one of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb or Lu, the same protective effect can be achieved.

[0063] Comparative Example 1

[0064] Following the same method as in Example 1, gallium oxide single crystals were grown using an iridium crucible without any inner protective layer, and the longitudinal temperature difference of the melt measured in step P3 was 98°C.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Various modifications and variations can be made to the present invention by any person skilled in the art. Any simple equivalent changes and modifications made based on the scope of protection of the present invention and the content of the specification should be included within the scope of protection of the present invention.

Claims

1. An inner protective layer for an iridium crucible, characterized in that, The inner protective layer consists of an IrAl alloy layer and a ceramic coating. The IrAl alloy layer is located between the ceramic coating and the inner wall of the iridium crucible and covers the inner surface of the iridium crucible. The thickness of the inner protective layer on the side wall of the iridium crucible increases from 300-500 μm to 700-1100 μm from the opening of the iridium crucible along the inner wall towards the bottom of the iridium crucible. The ceramic coating is divided into three layers from the inside out. The height of the three ceramic coating layers on the inner wall of the iridium crucible gradually decreases from the opening of the iridium crucible towards the bottom of the side wall of the iridium crucible. The first ceramic coating layer covers the entire surface of the IrAl alloy layer.

2. The inner protective layer of the iridium crucible according to claim 1, characterized in that, The IrAl alloy layer is a uniform coating with a thickness of 100~200μm; each ceramic coating layer has the same thickness of 200~300μm.

3. The inner protective layer of the iridium crucible according to claim 1, characterized in that, The Al content in the IrAl alloy layer is: 0 < Al ≤ 15 wt%.

4. The inner protective layer of the iridium crucible according to claim 1, characterized in that, The ceramic coating is a rare earth element tantalate ceramic thermal barrier layer, and its main material components are RETaO4, RE3TaO7 or RETa3O9, wherein RE is a rare earth element.

5. An iridium crucible, characterized in that, The iridium crucible comprises an inner protective layer as described in any one of claims 1 to 4.

6. A method for preparing the inner protective layer of the iridium crucible according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Clean and spray the inner surface of the iridium crucible to obtain a clean and rough inner surface; S2. Within 2 hours, the first IrAl alloy layer is uniformly sprayed onto the inner surface of the side wall of the iridium crucible using an atmospheric plasma spraying method, so that the first IrAl alloy layer covers the entire inner surface of the side wall of the iridium crucible. S3. Using atmospheric plasma spraying, a first ceramic coating layer is sprayed onto the surface of the first IrAl alloy layer, so that the first ceramic coating layer covers the entire surface of the first IrAl alloy layer; a second ceramic coating layer is sprayed onto the surface of the first ceramic coating layer at a first distance from the top of the first IrAl alloy layer; and a third ceramic coating layer is sprayed onto the surface of the second ceramic coating layer at a second distance from the top of the first ceramic coating layer. S4. A second IrAl alloy layer is sprayed onto the inner bottom of the iridium crucible using an atmospheric plasma spraying method, and a second ceramic coating is sprayed onto the surface of the second IrAl alloy layer; the first IrAl alloy layer and the second IrAl alloy layer constitute the IrAl alloy layer; the first ceramic coating and the second ceramic coating constitute the ceramic coating. S5. Anneal and polish the iridium crucible to obtain a stable inner protective layer.

7. The preparation method according to claim 6, characterized in that, The spraying conditions in step S1 are: spraying pressure of 0.2-1 MPa, the angle between the nozzle and the direction perpendicular to the sprayed area on the inner wall of the iridium crucible of 60°-85°, and the distance between the nozzle and the sprayed area of ​​100-200 mm; or / and the spraying conditions of the atmospheric plasma spraying method in step S2 are: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible of 200-300 mm, and the gas flow rate of 150-320 SCFH.

8. The preparation method according to claim 6, characterized in that, The spraying conditions for the atmospheric plasma spraying method in step S3 are: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 100-180 mm, and the gas flow rate is 100-230 SCFH; or / and the spraying conditions for the atmospheric plasma spraying method in step S4 are: the distance between the nozzle and the sprayed area on the inner wall of the iridium crucible is 100-180 mm, and the gas flow rate is 100-230 SCFH.

9. The preparation method according to claim 6, characterized in that, The first distance and the second distance are equal, and depending on the size of the iridium crucible, the first distance and the second distance are both 5mm-15mm.

10. The preparation method according to claim 6, characterized in that, The annealing conditions in step S5 are: 1200-1600℃, holding for 2-5 hours.

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