Soaking crucible for sintering nano-grain large-size yttrium-magnesium multiphase ceramic ball cover and sintering method

Abstract

The invention relates to a soaking crucible for sintering a nano-grain large-size yttrium-magnesium multiphase ceramic ball cover and a method for sintering the ceramic ball cover by using the soaking crucible. The soaking crucible comprises a supporting piece, a crucible cover and a crucible base, and the crucible cover and the crucible base are made of metal; the supporting piece is made of the same powder as the biscuit, and the size of the supporting piece is designed according to the size of the ceramic ball cover needing to be sintered. During use, the ceramic supporting piece is placed in the center of the crucible base, a ceramic biscuit is placed on the ceramic supporting piece, the crucible cover is placed on the crucible base, the relative height of the crucible and the supporting piece is adjusted, the sphere centers of all devices are overlapped in the center of the bottom of the supporting piece, and then sintering is conducted. The uniform heating crucible can greatly eliminate the problem of poor compactness or cracking caused by non-uniform heating in the sintering process of ceramic.

Description

Technical Field

[0001] The invention relates to a soaking crucible for sintering a nano-grain large-size yttrium-magnesium composite ceramic sphere cover and a method for sintering the ceramic sphere cover using the soaking crucible, belonging to the field of ceramic sintering. Background Art

[0002] Yttrium-magnesium composite ceramics are a recently emerging infrared window. They feature broadband high transmittance, high strength, and low emissivity at high temperatures. They are a key component of infrared optoelectronic systems and play a vital role in the national defense industry. The structural characteristics of composite ceramics determine their density and grain size, which directly influence their optical and mechanical properties. The key to producing high-performance ceramics is to achieve high density while reducing grain size.

[0003] The sintering process is a key step in the ceramic preparation process. Traditional sintering uses a sintering method that slowly heats up and keeps the temperature for a long time. However, this sintering method is very likely to cause excessive growth of grains, which reduces the performance of the ceramics. Hot pressing sintering has to deal with the problems of uneven force, difficulty in preparing large-sized ceramics with complex shapes, and carbon residue. Patent CN.112174644B proposes a method of rapidly sintering a ceramic blank directly into a muffle furnace that has been pre-heated to a high temperature to obtain a small grain size. However, there are the following problems: the structure of a general muffle furnace makes it difficult to obtain uniform heating of large-sized ceramic blanks, and the different shrinkage rates in different areas can easily cause ceramics to break; the heating rate of the ceramic surface is much higher than that of the ceramic interior, and the surface is sintered before the interior, which easily generates residual stress and is not conducive to the discharge of internal pores.

[0004] On the other hand, traditional infrared ceramics are covered with alumina crucibles during the sintering process to prevent temperature field disturbances caused by air convection and ceramic cracking caused by uneven heating due to direct radiation from the heating wire. However, the thermal conductivity of alumina crucibles is poor. When using large-sized alumina crucibles, different positions of the crucible are at different distances from the heating wire of the heating furnace, resulting in different temperatures at different positions of the crucible itself, affecting the sintering process of the ceramic. In addition, for yttrium-magnesium composite ceramics, alumina crucibles have a high emissivity in the range of 6-14um. The infrared radiation band emitted is in the strong absorption zone of yttrium-magnesium composite ceramics and is easily absorbed by the surface of the ceramic blank, causing uneven temperatures inside and outside the blank.

[0005] Patent CN211120648U proposes a method for achieving a uniform temperature field by utilizing a hollow crucible bottom to promote convective heat transfer. However, at high temperatures, radiative heat transfer is more important than convective heat transfer, and the presence of large-sized ceramic blanks can affect airflow distribution and heat distribution, making it difficult to achieve the desired heat distribution. The present invention proposes a heat distribution crucible that effectively solves the problem of rapid temperature rise sintering of ceramic spheres, which is of great significance for the sintering of large-sized ceramic spheres with high density and small grains. Summary of the Invention

[0006] The purpose of the present invention is to provide a soaking crucible for sintering large-sized nanocrystalline yttrium-magnesium composite ceramic spherical covers, so as to overcome the problem of uneven thermal field in the rapid heating and sintering of existing large-sized ceramic head covers and avoid uneven density or cracking of the ceramics.

[0007] The technical solutions of the present invention are as follows:

[0008] A soaking crucible for sintering large-size nano-crystalline yttrium-magnesium composite ceramic spheres, comprising a support, a crucible cover and a crucible base.

[0009] The crucible base has an integrally formed central raised portion and a peripheral annular bearing portion, wherein the central raised portion forms an upwardly protruding double-opening spherical shell structure;

[0010] The support member vertically passes through the central raised portion, the upper end of the support member forms a bearing curved surface conforming to the inner surface of the ceramic ball cover blank, and the lower end forms a positioning base;

[0011] The crucible cover is a spherical shell structure with a single-side opening, and the open end thereof fits in with the outer annular bearing portion to form a sintering cavity surrounding the ceramic spherical cover blank;

[0012] The support member and the crucible base form a relative height-adjustable structure, and through pre-sintering calibration, the center point of the bottom surface of the support member positioning base, the geometric center of the ceramic spherical cover blank, the curvature center of the spherical crown of the crucible cover, and the curvature center of the central raised part of the crucible base are achieved to coincide with each other.

[0013] The crucible cover and the crucible base are made of metal material.

[0014] Furthermore, the metal material is selected from at least one of molybdenum, tungsten, platinum or alloys thereof.

[0015] The support member is made of the same sinterable material as the ceramic ball cover green body, so as to ensure synchronous shrinkage during the sintering process, thereby achieving relatively uniform heating.

[0016] A radial gap of 0.1-10 mm is provided between the support member and the central raised portion to compensate for thermal expansion differences during sintering.

[0017] The ceramic ball cover blank is a spherical cap shell structure, and the support member is a cylindrical structure, whose bearing curved surface is a spherical cap surface with the same curvature radius as the inner surface of the ceramic ball cover blank.

[0018] The outer diameter of the annular bearing portion on the periphery of the crucible base is larger than the bottom diameter of the crucible cover, forming a stepped radiation protection structure.

[0019] Furthermore, the outer ring diameter of the outer annular bearing portion differs from the bottom diameter of the crucible cover by 0-2 cm.

[0020] The outer radius of the spherical segment shell of the central raised portion of the crucible base is 5-10 cm smaller than the inner radius of the unsintered ceramic spherical cover blank, and the inner radius of the spherical segment shell of the crucible cover is 1-4 cm larger than the outer radius of the unsintered ceramic spherical cover blank.

[0021] The wall thickness of the crucible cover and the crucible base is 0.1-5 mm.

[0022] The sintering of the nanocrystalline large-sized yttrium-magnesium composite ceramic sphere using the above-mentioned soaking crucible mainly includes the following steps:

[0023] S1. The yttrium-magnesium composite nanopowder is placed in a mold and a ceramic ball blank and support are obtained by cold isostatic pressing;

[0024] S2. Place the support member in the center of the crucible base, place the ceramic spherical cover blank on the support member, place the crucible lid on the crucible base, and cover the ceramic spherical cover blank. Adjust the relative height of the support member and the crucible base so that the center point of the bottom surface of the support member positioning base, the geometric center of the ceramic spherical cover blank, the center of curvature of the spherical cap of the crucible lid, and the center of curvature of the central raised portion of the crucible base coincide with each other;

[0025] S3 step S2 of the ceramic ball cover green billet and soaking crucible device as a whole for the first conventional sintering, rapidly heated to the sintering temperature, after a period of heat removal, to obtain a pre-fired ceramic;

[0026] S4. The pre-fired ceramic is subjected to a second hot isostatic pressing sintering, annealing, and double-sided polishing to obtain a ceramic sample.

[0027] Furthermore, in step S1, the cold isostatic pressing pressure is 50-300 MPa, and the time is 1-60 min.

[0028] Furthermore, in step S2, the relative height adjustment between the support member and the crucible base can be achieved by placing refractory bricks under the support member and the crucible base.

[0029] Furthermore, in step S3, during the first conventional sintering, if muffle furnace sintering is adopted, platinum or its alloy is selected as the crucible material; if vacuum sintering is adopted, tungsten or its alloy is selected as the crucible material; the first sintering heating rate is 0.5-20°C / min, the calcination temperature is 1200-1450°C, and the holding time is 0-180min.

[0030] Furthermore, in step S4, the second hot isostatic pressing sintering temperature is 800-1400° C., the sintering time is 30-200 min, and the pressure is 50-200 MPa; the annealing temperature is 800-1300° C., and the annealing time is 1-20 h.

[0031] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0032] The present invention uses a metal crucible to cover the ceramic body. Compared with the commonly used alumina crucible, on the one hand, it can obtain a more uniform heating source by virtue of the better thermal conductivity of the metal. The metal crucible itself has a high thermal conductivity, which can effectively avoid the influence of the uneven temperature field of the heating furnace on the shrinkage of the ceramic body, or the problems caused by the low thermal conductivity of the alumina crucible, especially in the use scenario where rapid heating is required.

[0033] On the other hand, ceramic sintering at high temperatures primarily relies on radiation heat transfer, and the radiation intensity is inversely proportional to the square of the distance. When the crucible temperature is uniform, large-scale samples at different locations at different distances from the crucible will also affect the uniformity of the temperature field. The support member designed in the present invention is made of the same material and the same process as the ceramic blank, and the length of the support member is the same as the radius of curvature of the ceramic blank. When the blank is placed on the support member, the center of the support member's positioning base coincides with the center of the ceramic blank's sphere. The ceramic spherical cover blank only contacts the support member, avoiding the interference of contact heat transfer on the uniformity of the temperature field when the sample is placed on the crucible for sintering in the general sintering step. In addition, because the materials and manufacturing processes used are the same, the support member and the ceramic blank can sinter and shrink in equal proportions during the sintering process. That is, during the sintering process, the center of the support member's positioning base always coincides with the center of the ceramic blank's sphere, and always coincides with the center of curvature of the spherical crown of the crucible cover and the center of curvature of the central raised portion of the crucible base. This ensures that the green billet is always heated evenly during the shrinkage process, effectively avoiding the cracking problem caused by uneven heating and shrinkage in different areas of large-sized samples.

[0034] In view of the influence of uneven heating inside and outside the ceramic on the densification and cracking of the ceramic, the present invention adopts metal as the crucible material. The emissivity of the metal in the strong absorption band of yttrium-magnesium composite ceramics is low, and the emissivity in the near-infrared band is high. The infrared radiation emitted can more easily penetrate the sample, so that the inside and outside of the sample are heated more evenly. In traditional vacuum sintering, tungsten is also often used as the crucible material, but this is mainly because tungsten has the characteristics of high temperature resistance and chemical stability. The influence of its infrared radiation characteristics on sintering has not been taken seriously. In this patent, more emphasis is placed on the high thermal conductivity and unique infrared radiation characteristics of metals. Therefore, metals that are not easily oxidized, such as platinum, are used when sintering in an air environment, and relatively cheap and commonly used metals, such as tungsten, are used to make crucibles when sintering in a vacuum environment. In addition, in order to obtain a better and more excellent heat-dissipating effect, one or more layers of larger-sized metal crucible covers can be covered on the outside of the metal crucible cover.

[0035] A more uniform heating environment allows large-scale ceramic green bodies to be sintered at faster heating rates without cracking. This faster heating rate allows for greater sintering activity of the ceramic grains upon reaching the sintering temperature, allowing for compaction while maintaining a smaller grain size. The prepared yttrium-magnesium composite ceramic samples have an extremely small average grain size (<150nm) and exhibit excellent transmission properties in the near-infrared and mid-infrared bands, particularly in the near-infrared region, far exceeding that of yttrium-magnesium composite ceramics prepared using conventional sintering systems. They also exhibit excellent mechanical properties, and the ceramic sintering process is carbon-free, making them very suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a cross-sectional view of the overall structure of the present invention;

[0037] Figure 2 A three-dimensional half-section schematic diagram of the overall structure of the present invention;

[0038] Figure 3 This is the SEM morphology of the composite ceramic prepared in Example 1;

[0039] Figure 4 This is the infrared transmittance graph of the composite ceramic prepared in Example 1;

[0040] Figure 5 This is a picture of an unpolished composite ceramic sample prepared in Comparative Example 1;

[0041] Explanation of the reference numerals: 1-support member, 1a-bearing curved surface, 1b-positioning base, 2-crucible cover, 3-crucible base, 3a-central protrusion, 3b-outer annular bearing portion, 4-ceramic ball cover blank. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the embodiments and accompanying drawings. These examples are only used to illustrate the present invention but should not be used to limit the scope of protection of the present invention.

[0043] Example 1

[0044] Yttrium-magnesium composite nanopowder is placed in a cold isostatic mold and isostatically pressed at 200 MPa for 5 minutes to obtain a ceramic spherical cover blank and a support. The inner surface radius of the blank is 100 mm, the thickness is 8 mm, and the bowl diameter is 180 mm. The cross-sectional diameter of the support is 20 mm, the total length is 100 mm, the bottom surface is flat, and the top surface has a curvature radius of 100 mm. The crucible is made of platinum and has a thickness of 0.1 mm. The crucible lid is a hemispherical shell with an outer surface diameter of 250 mm. The spherical part of the crucible base is open on both sides, with an upper opening diameter of 25 mm and a lower opening diameter of 40 mm. The outer surface curvature radius of the ring part in the crucible base is 250 mm. The support is placed in the center of the crucible base, the spherical cover blank is placed on the support, and the crucible lid is placed on the crucible base, covering the ceramic blank. Adjust the relative height of the support and the crucible base so that the center of the ceramic blank, the crucible base, and the crucible cover coincide with the bottom of the support. At this time, the distance between the ceramic blank and the crucible cover is 17 mm. Place the entire device in a muffle furnace for the first sintering. The heating rate is controlled at 10°C / min, the sintering temperature is set at 1330°C, and the holding time is 30 minutes. After sintering, the density is tested by the drainage method and is 96%. The second step uses 200MPa 1250°C hot isostatic pressing to assist sintering for 90 minutes. After annealing at 1000°C for 10 hours, polishing is performed to obtain a Y2O3-MgO infrared transparent composite ceramic with a thickness of 3 mm. The composite ceramic prepared by this method has an extremely fine grain size and excellent transmittance.

[0045] Figure 3 This is the SEM morphology of the composite ceramic prepared in Example 1. The calculated average grain size of the composite ceramic is about 130 nm.

[0046] Figure 4 This is the infrared transmittance graph of the composite ceramic prepared in Example 1. The transmittance at 2.5 μm reaches 84%. Some of the carbon contamination is caused by carbon residue in the powder, rather than the sintering system using a soaking crucible.

[0047] Example 2

[0048] Yttrium-magnesium composite nanopowder was placed in a cold isostatic mold and cold isostatically pressed at 200 MPa for 5 minutes to produce a ceramic spherical cover blank and a support. The blank had an inner radius of 100 mm, a thickness of 10 mm, and a bowl-shaped diameter of 180 mm. The support had a cross-sectional diameter of 20 mm and a total length of 100 mm. The bottom surface was flat, and the top surface had a radius of curvature of 100 mm. The crucible was made of tungsten and was 5 mm thick. The crucible lid was a hemispherical shell with an outer diameter of 310 mm. The double-sided spherical segment of the crucible base had an upper opening diameter of 22 mm and a lower opening diameter of 100 mm. The outer radius of curvature of the outer surface was 50 mm. The outer diameter of the ring in the crucible base was 330 mm. The support was placed in the center of the crucible base, the spherical cover blank was placed on the support, and the crucible lid was placed on the crucible base, covering the ceramic blank. The relative heights of the support and crucible base were adjusted so that the centers of the spheres of the ceramic blank, crucible base, and crucible lid coincided with the bottom of the support. The entire device was placed in a vacuum furnace for the first sintering step. The heating rate was controlled at 10°C / min, the sintering temperature was set at 1330°C, and the holding time was 30 minutes. After sintering, hot isostatic pressing (HSP) was performed at 200 MPa and 1250°C for 90 minutes. Annealing was performed at 1000°C for 10 hours, followed by polishing to produce a 3mm thick Y2O3-MgO infrared-transparent composite ceramic. The ceramic exhibited a transmittance of 78% at 2.5μm, and SEM analysis revealed an average grain size of 170nm.

[0049] Example 3

[0050] Yttrium-magnesium composite nanopowder was placed in a cold isostatic mold and cold isostatically pressed at 200 MPa for 5 minutes to produce a ceramic spherical cover blank and a support. The blank had an inner radius of 100 mm, a thickness of 10 mm, and a bowl-shaped diameter of 180 mm. The support had a cross-sectional diameter of 20 mm and a total length of 100 mm. The bottom surface was flat, and the top surface had a radius of curvature of 100 mm. The crucible was made of tungsten and was 5 mm thick. The crucible lid was a hemispherical shell with an outer diameter of 310 mm. The double-sided spherical segment of the crucible base had an upper opening diameter of 22 mm and a lower opening diameter of 100 mm. The outer radius of curvature of the outer surface was 50 mm. The outer diameter of the ring in the crucible base was 330 mm. The support was placed in the center of the crucible base, the spherical cover blank was placed on the support, and the crucible lid was placed on the crucible base, covering the ceramic blank. The relative heights of the support and crucible base were adjusted so that the centers of the spheres of the ceramic blank, crucible base, and crucible lid coincided with the bottom of the support. The entire device was placed in a vacuum furnace for the first sintering step. The heating rate was controlled at 10°C / min, the sintering temperature was set at 1300°C, and the holding time was 45 minutes. After sintering, hot isostatic pressing (HSP) was performed at 200 MPa and 1250°C for 90 minutes. Annealing was performed at 1000°C for 10 hours, followed by polishing to produce a 3mm thick Y2O3-MgO infrared-transparent composite ceramic. The ceramic exhibited a transmittance of 83% at 2.5μm, and SEM analysis revealed an average grain size of 147nm.

[0051] Example 4

[0052] Yttrium-magnesium composite nanopowder was placed in a cold isostatic mold and cold isostatically pressed at 50 MPa for 60 minutes to produce a ceramic spherical cover blank and a support. The blank had an inner radius of 120 mm, a thickness of 10 mm, and a bowl-shaped diameter of 180 mm. The support had a cross-sectional diameter of 10 mm and a total length of 100 mm. The bottom surface was flat, and the top surface had a radius of curvature of 100 mm. The crucible was made of tungsten and was 5 mm thick. The crucible lid was a hemispherical shell with an outer diameter of 290 mm. The double-sided spherical segment of the crucible base had an upper opening diameter of 30 mm and a lower opening diameter of 40 mm. The outer radius of curvature was 20 mm, and the outer diameter of the ring in the crucible base was 310 mm. The support was placed in the center of the crucible base, the spherical cover blank was placed on the support, and the crucible lid was placed on the crucible base, covering the ceramic blank. The relative heights of the support and crucible base were adjusted so that the centers of the spheres of the ceramic blank, crucible base, and crucible lid coincided with the bottom of the support. The entire device was placed in a vacuum furnace for the first sintering step. The heating rate was controlled at 0.5°C / min, the sintering temperature was set at 1200°C, and the holding time was 180 minutes. After sintering, the device was subjected to hot isostatic pressing (HSP) at 50 MPa and 800°C for 200 minutes. Annealing at 800°C for 20 hours and polishing were performed to produce a 3mm thick Y2O3-MgO infrared-transparent composite ceramic. The ceramic achieved a transmittance of 24% at 2.5μm.

[0053] Example 5

[0054] Yttrium-magnesium composite nanopowder was placed in a cold isostatic mold and cold isostatically pressed at 300 MPa for 1 minute to produce a ceramic spherical cover blank and a support. The blank had an inner radius of 120 mm, a thickness of 10 mm, and a bowl-shaped diameter of 180 mm. The support had a cross-sectional diameter of 10 mm and a total length of 100 mm. The bottom surface was flat, and the top surface had a radius of curvature of 100 mm. The crucible was made of tungsten and was 5 mm thick. The crucible lid was a hemispherical shell with an outer diameter of 290 mm. The double-sided spherical segment of the crucible base had an upper opening diameter of 30 mm and a lower opening diameter of 40 mm. The outer radius of curvature was 20 mm, and the outer diameter of the ring in the crucible base was 310 mm. The support was placed in the center of the crucible base, the spherical cover blank was placed on the support, and the crucible lid was placed on the crucible base, covering the ceramic blank. The relative heights of the support and crucible base were adjusted so that the centers of the spheres of the ceramic blank, crucible base, and crucible lid coincided with the bottom of the support. The entire device was placed in a vacuum furnace for the first sintering step. The heating rate was controlled at 20°C / min, the sintering temperature was set at 1450°C, and the holding time was 0 min. After sintering, hot isostatic pressing (HSP) was performed at 200 MPa and 1400°C for 30 min. Annealing was performed at 1300°C for 1 h, followed by polishing to produce a 3mm thick Y2O3-MgO infrared-transparent composite ceramic. The ceramic exhibited a transmittance of 37% at 2.5μm, and SEM analysis revealed an average grain size of 327nm.

[0055] Comparative Example 1

[0056] Yttrium-magnesium composite nanopowder was placed in a cold isostatic mold and cold isostatically pressed at 200 MPa for 5 minutes to obtain a ceramic ball cover blank and a support. The inner surface radius of the blank is 100 mm, the thickness is 8 mm, and the bowl diameter is 180 mm. The cross-sectional diameter of the support is 20 mm, the total length is 100 mm, the bottom surface is flat, and the top surface curvature radius is 100 mm. The ball cover blank was placed on the support without adding a crucible. The entire device was placed in a muffle furnace for the first sintering. The heating rate was controlled at 10 ° C / min, the sintering temperature was set at 1330 ° C, and the sintering time was 30 minutes. After the sintering was completed, the head cover cracked. No further heat treatment, annealing, etc. were performed. The average grain size of the SEM test was 120 nm.

[0057] Compared with Example 1, Comparative Example 1 uses the same green body production and sintering process, but does not use a metal soaking crucible. Under rapid heating conditions, different locations of the ceramic green body are heated unevenly and shrink at different rates, generating stress and causing cracking.

[0058] Figure 5 This is the cracking diagram of the composite ceramic prepared in Comparative Example 1.

[0059] Comparative Example 2

[0060] Yttrium-magnesium composite nanopowder was placed in a cold isostatic mold and cold isostatically pressed at 200 MPa for 5 minutes to obtain a ceramic ball cover blank and a support. The inner surface radius of the blank is 100 mm, the thickness is 8 mm, and the bowl mouth diameter is 180 mm. The cross-sectional diameter of the support is 20 mm, the total length is 100 mm, the bottom surface is flat, and the top surface curvature radius is 100 mm. The ball cover blank was placed on the support without adding a crucible. The entire device was placed in a muffle furnace for the first sintering. The heating rate was controlled at 0.5 ° C / min, the sintering temperature was set at 1330 ° C, and the sintering time was 30 minutes. After sintering, the ball cover was complete, and the density was 84% ​​tested by the drainage method. The average grain size was 135 nm by SEM test.

[0061] Compared to Example 1 and Comparative Example 1, Comparative Example 2 employed the same green body preparation process, but omitted the use of a metal soaking crucible and employed a slower sintering heating rate. This slow heating allowed for sufficient heat conduction between different locations on the ceramic green body, preventing the cracking observed in Comparative Example 1. However, this also resulted in excessive growth time for the ceramic grains before reaching the sintering temperature. This increased grain size led to a decrease in sintering activity after reaching the target sintering temperature, resulting in a lower density of the ceramic produced at the same sintering temperature and soaking time.

[0062] In Example 1, a metal soaking crucible with a special structural design was used, combined with a rapid heating and short-time heat preservation sintering process, to prepare a large-sized yttrium-magnesium composite ceramic ball cover with excellent permeability and extremely small grain size. In Comparative Example 1, compared with Example 1, no soaking crucible was used, and the ceramic cracked under the same sintering system. In Comparative Example 2, no soaking crucible was used. The conventional method of reducing the heating rate was used to avoid the occurrence of ceramic cracking, but it resulted in a decrease in grain sintering activity and poor ceramic density, indicating that it is difficult to obtain large-sized, high-performance yttrium-magnesium composite ceramics without a crucible. Examples 2, 3, 4, and 5 used a metal soaking crucible combined with vacuum sintering to study the effects of different sintering processes on ceramic properties. In summary, the use of the metal soaking crucible designed in this patent effectively avoids the problem of ceramic body cracking in the rapid heating sintering process, and prepares a large-sized yttrium-magnesium composite ceramic ball cover with excellent permeability and extremely small grain size, which is very suitable for industrial production.

Claims

1. A soaking crucible for sintering large-scale nano-crystalline yttrium-magnesium composite ceramic spheres, characterized in that: include: Support (1), crucible cover (2) and crucible base (3), The crucible base (3) has an integrally formed central raised portion (3a) and a peripheral annular bearing portion (3b), wherein the central raised portion (3a) forms an upwardly protruding double-opening spherical shell structure; The support member (1) is a columnar structure, vertically passing through the central raised portion (3a), with its upper end forming a bearing curved surface (1a) conforming to the inner surface of the ceramic spherical cover blank (4), and its lower end forming a positioning base (1b), and the ceramic spherical cover blank (4) is suspended and supported only by the bearing curved surface (1a) of the support member (1); The crucible cover (2) is a spherical shell structure with a single-side opening, and its open end fits in contact with the outer annular bearing portion (3b) to form a sintering cavity surrounding the ceramic spherical cover blank (4); The support member (1) and the crucible base (3) form a relatively height-adjustable structure, and the center point of the bottom surface of the positioning base (1b) of the support member (1), the geometric center of the ceramic spherical cover blank (4), the center of curvature of the spherical cap of the crucible cover (2), and the center of curvature of the central raised portion (3a) of the crucible base (3) are achieved by calibration before sintering.

2. The soaking crucible for sintering large-scale nanocrystalline yttrium-magnesium composite ceramic spheres according to claim 1, characterized in that: The crucible cover (2) and the crucible base (3) are made of metal material.

3. The soaking crucible for sintering large-scale nanocrystalline yttrium-magnesium composite ceramic spheres according to claim 2, characterized in that: The metal material is selected from at least one of molybdenum, tungsten, platinum or alloys thereof.

4. The soaking crucible for sintering large-scale nanocrystalline yttrium-magnesium composite ceramic spheres according to claim 1, characterized in that: The support member (1) is made of the same sinterable material as the ceramic spherical cover blank (4), so that the support member and the blank shrink synchronously during the sintering process.

5. The soaking crucible for sintering large-scale nano-crystalline yttrium-magnesium composite ceramic spheres according to claim 1, characterized in that: A radial gap of 1-10 mm is provided between the support member (1) and the central raised portion (3a) to compensate for thermal expansion differences during sintering.

6. The soaking crucible for sintering large-scale nanocrystalline yttrium-magnesium composite ceramic spheres according to claim 1, characterized in that: The ceramic ball cover blank (4) is a spherical cap shell structure, and the support member (1) is a cylindrical structure, and its bearing curved surface (1a) is a spherical cap surface with the same curvature radius as the inner surface of the ceramic ball cover blank (4).

7. The soaking crucible for sintering large-scale nanocrystalline yttrium-magnesium composite ceramic spheres according to claim 1, characterized in that: The outer diameter of the annular bearing portion (3b) on the periphery of the crucible base (3) is greater than the bottom diameter of the crucible cover (2), forming a stepped radiation protection structure.

8. The soaking crucible for sintering large-scale nanocrystalline yttrium-magnesium composite ceramic spheres according to claim 7, characterized in that: The outer diameter of the outer annular bearing portion (3b) differs from the bottom diameter of the crucible cover (2) by 0-2 cm.

9. The soaking crucible for sintering large-scale nanocrystalline yttrium-magnesium composite ceramic spheres according to claim 1, characterized in that: The outer surface radius of the spherical segment shell of the central raised portion (3a) of the crucible base (3) is 5-10 cm smaller than the inner surface radius of the unsintered ceramic spherical cover blank, and the inner surface spherical segment shell radius of the crucible cover (2) is 1-4 cm larger than the outer surface radius of the unsintered ceramic spherical cover blank.

10. The soaking crucible for sintering nanocrystalline large-size yttrium-magnesium composite ceramic spheres according to claim 1, characterized in that: The wall thickness of the crucible cover (2) and the crucible base (3) is 0.1-5 mm.

11. A sintering method for a nano-crystalline large-size yttrium-magnesium composite ceramic sphere, characterized in that: Sintering is performed using the soaking crucible according to any one of claims 1 to 10, comprising the following steps: S1. The yttrium-magnesium composite nanopowder is placed in a mold and a ceramic ball blank and support are obtained by cold isostatic pressing; S2. Place the support member in the center of the crucible base, place the ceramic spherical cover blank on the support member, place the crucible lid on the crucible base, and cover the ceramic spherical cover blank. Adjust the relative height of the support member and the crucible base so that the center point of the bottom surface of the support member positioning base, the geometric center of the ceramic spherical cover blank, the center of curvature of the spherical cap of the crucible lid, and the center of curvature of the central raised portion of the crucible base coincide with each other; S3 step S2 of the ceramic ball cover green billet and soaking crucible device as a whole for the first conventional sintering, rapidly heated to the sintering temperature, after a period of heat removal, to obtain a pre-fired ceramic; S4. The pre-fired ceramic is subjected to a second hot isostatic pressing sintering, annealing, and double-sided polishing to obtain a ceramic sample.

12. The sintering method of a nano-crystalline large-size yttrium-magnesium composite ceramic ball cover according to claim 11, characterized in that: (1) The cold isostatic pressing parameters of step S1 are: pressure of 50-300 MPa, time of 1-60 min; (2) Step S2: placing refractory bricks under the support member and the crucible base to achieve adjustable relative heights between the support member and the crucible base; (3) The first conventional sintering process parameters of step S3 are: When using a muffle furnace for sintering, platinum or its alloys are selected as the crucible material; When vacuum sintering is used, tungsten or its alloy is selected as the crucible material; The heating rate is 0.5-20°C / min, the calcination temperature is 1200-1450°C, and the holding time is 0-180min. (4) The process parameters of the second hot isostatic pressing sintering in step S4 are: Hot isostatic pressing: temperature is 800-1400℃, sintering time is 30-200min, pressure is 50-200MPa; Annealing: temperature is 800-1300℃, annealing time is 1-20h.

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