Gadolinium oxysulfide cold storage ceramic microspheres as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ceramics and refrigeration, and particularly relates to gadolinium oxysulfide cold storage ceramic microspheres as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing GOS ceramic powder, acrylic light-cured resin and absolute ethyl alcohol in proportion, and calendering to obtain a plastic material body; the GOS is extruded from an extrusion opening of the die to form a wire rod, and the wire rod is cured by ultraviolet light to obtain a GOS cured wire rod; and cutting into micro-cylinders, drying, and spheroidizing by radio frequency plasma to obtain the GOS cold storage microspheres with uniform particle size distribution. The microspheres prepared through the method are regular in sphericity, uniform in particle size height and high in density, when the microspheres are used as cold storage filler of a two-stage cold end heat exchanger of a two-stage G-M low-temperature refrigerator, the refrigeration efficiency and the temperature stability can be improved, the high-precision low-temperature scene requirement is met, the process reproducibility is good, and industrial production is facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of ceramics and refrigeration technology, and particularly relates to gadolinium oxysulfide cold storage ceramic microspheres and a preparation method and application thereof. Background Art

[0002] Gadolinium oxysulfide (GOS) is a high-entropy magnetic material characterized by large heat absorption and release effects when its magnetic entropy changes, making it suitable for refrigeration applications. By exploiting this change in magnetic entropy during a magnetic phase transition, high-entropy magnetic materials can be used as magnetic regenerators in small regenerative cryogenic gas refrigerators operating at 4.2K to 20K. In these refrigerators, GOS ceramics must be spherical to ensure smooth liquid helium flow, and their particle size must be highly consistent.

[0003] Unlike metallic cold storage materials like HoCu2 and Er3Ni, ceramics cannot be directly produced using the molten metal drop process. Currently, GOS ceramics are commonly produced using hot isostatic pressing and hot pressing, which are inefficient and expensive.

[0004] Traditional GOS microspheres are mostly prepared by spray granulation or drop granulation, which have the following defects: the microsphere particle size distribution is relatively wide (usually 0.2-0.4mm), resulting in uneven filling of the cold storage bed and low heat transfer efficiency; the binder dosage is relatively high (5-20wt%), which easily leaves impurities after high-temperature debinding, destroying the chemical uniformity of the material; the density is less than 95% of the theoretical value, and the porosity is high, affecting the cold storage capacity.

[0005] In addition, the solution disclosed in Chinese patent CN118955132A is to use GOS ceramic powder to prepare microspheres by direct plasma spheroidization after sintering and crushing, but the particle size distribution cannot be guaranteed, the yield is low and the roundness is poor. In the solution disclosed in Japanese patent JP2024056758A, alginate is used as a binder. After the raw material powders are mixed to form a slurry, the slurry is added dropwise to the gelling solution using a syringe, a pipette and other tools to granulate, and then degreased and sintered to obtain GOS cold storage microspheres. However, in order to ensure that the powder slurry has the good fluidity required for dropwise addition, it is necessary to control the amount of binder and the water content in the system, maintain the fluidity by a large amount of water, and ensure the stability of the slurry and the subsequent gelation cross-linking basis by alginate. The drying and evaporation of a large amount of water can easily cause internal stress and pores. The high-temperature decomposition and gas production of alginate during subsequent degreasing will also form certain pores. These stresses and pores will reduce the density and strength of the microspheres and also weaken their cold storage capacity per unit volume. In addition, the particle size of the microspheres produced by this production method cannot be precisely controlled.

[0006] In summary, the improvement of the performance of small-scale regenerative low-temperature gas refrigerators has put forward increasingly stringent requirements on the spherical regularity, particle size consistency, density and cold storage capacity per unit volume of GOS cold storage microspheres. In the existing technology, traditional preparation methods, mainstream production methods and existing patent solutions are difficult to take into account the above increasingly stringent requirements and need further improvement. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the present invention provides a gadolinium oxysulfide cold storage ceramic microsphere and its preparation method and application.

[0008] A first aspect of the present invention provides a method for preparing gadolinium oxysulfide cold storage ceramic microspheres, comprising the following steps: Step 1: GOS ceramic powder, light-curable resin and anhydrous ethanol are mixed evenly, and then subjected to calendering and homogenization treatment to obtain a plastic body; Step 2: Using an extrusion device, the plastic body is extruded from a die extrusion port. The die extrusion port is set downward so that the extruded material forms a wire rod and moves vertically downward. A light source is set below the die extrusion port to irradiate the extruded material so that the material is photocured to form a GOS cured wire rod. Step 3: Cut the GOS solidified wire rod into micro cylinders of preset lengths, and dry the GOS ceramic micro cylinders for later use; Step 4: Place the micro-cylinder into a radio frequency plasma spheroidization furnace, melt and spheroidize under the protection of an inert atmosphere, and collect GOS cool storage microspheres with uniform particle size distribution.

[0009] As a further optimization scheme for the preparation method of gadolinium oxysulfide cool storage ceramic microspheres, in step 1, the mass ratio of GOS ceramic powder to acrylic photocurable resin is 100:(2.0-6.0), and the mass ratio of GOS ceramic powder to anhydrous ethanol is 100:(2.0-5.0); in step 1, the photocurable resin is an acrylic photocurable resin; in step 2, the light source is an ultraviolet light source; and in step 3, the ratio of microcylinder diameter to height is 1:(0.75-1.25). Among them, the mass ratio of GOS ceramic powder to acrylic photocurable resin is more preferably 100:(2.5-5.5), and further preferably 100:(3.0-5.0); the mass ratio of GOS ceramic powder to anhydrous ethanol is more preferably 100:(2.5-4.0), and further preferably 100:(3.0-3.5).

[0010] As a further optimization scheme for the preparation method of gadolinium oxysulfide cold storage ceramic microspheres, in step 1, the particle size distribution D50 of the GOS ceramic powder is 0.2-10 μm and the purity is ≥99.9%; more preferably, D50 is 0.5-5 μm and the purity is ≥99.95%.

[0011] As a further optimization scheme for the preparation method of gadolinium oxysulfide cold storage ceramic microspheres, in step 1, the acrylic light-curing resin is selected from light-curing epoxy acrylic resin, light-curing polyester acrylic resin, and light-curing polyurethane acrylic resin.

[0012] As a further optimization scheme for the preparation method of gadolinium oxysulfide cold storage ceramic microspheres, in step 2, an annular ultraviolet light source is provided below the extrusion port of the mold, and the extruded material passes downward through the annular ultraviolet light source and is surrounded by the annular ultraviolet light source.

[0013] As a further optimization scheme for the preparation method of gadolinium oxysulfide cold storage ceramic microspheres, in step 2, the extrusion speed of the screw extruder of the extrusion equipment is 3 to 30 mm / s, the diameter of the die extrusion port is 0.15 to 0.35 mm, and the number of extrusion ports is one or more.

[0014] As a further optimization scheme for the preparation method of gadolinium oxysulfide cold storage ceramic microspheres, in step 3, the GOS solidified wire rods are arranged neatly and fed into a rotary blade cutting machine. By precisely controlling the feed speed, the GOS solidified wire rods are cut into GOS ceramic microcylinders of preset lengths.

[0015] As a further optimization scheme for the preparation method of gadolinium oxysulfide cold storage ceramic microspheres, in step 3, the cutting length of the microcylinder is 0.15-0.35 mm, and the ratio of diameter to height is 1:(0.85-1.1).

[0016] As a further optimization scheme for the preparation method of gadolinium oxysulfide cold storage ceramic microspheres, in step 4, the RF power of the RF plasma spheroidization furnace is 20-40 kW; the protective atmosphere is argon or helium; the feeding speed of the microcylinders is 2-30 g / min, and the feeding speed is more preferably 2-10 g / min.

[0017] A second aspect of the present invention provides gadolinium oxysulfide cold storage ceramic microspheres, wherein the provided gadolinium oxysulfide cold storage ceramic microspheres are prepared according to any one of the above preparation methods.

[0018] A third aspect of the present invention provides an application of the gadolinium oxysulfide cold storage ceramic microspheres, wherein the gadolinium oxysulfide cold storage ceramic microspheres are used as cold storage fillers in the secondary cold end heat exchanger of a double-stage Gifford-McMahon cryogenic refrigerator.

[0019] Beneficial effects The present invention achieves long-term stable and precise extrusion under low-impurity conditions by mixing GOS ceramic powder with a low-proportion acrylic light-curing resin and ethanol, and coordinating fixed-section vertical extrusion molding with online ultraviolet light rapid curing to lock the cross-sectional size. On this basis, the length of the micro-cylinder is accurately controlled in conjunction with a precision cutting process, thereby achieving precise regulation of the volume of the micro-cylinder. After plasma spheroidization, gadolinium oxysulfide cold storage ceramic microspheres with rounded shapes, highly uniform particle sizes, high density, and high strength can be produced in large quantities. When applied to low-temperature refrigerators, the refrigeration performance can be significantly improved due to the microspheres' dense and wear-resistant properties, uniform filling, smooth liquid helium flow, and high heat transfer efficiency. It exhibits multiple advantages such as faster cooling rate, higher temperature control accuracy, lower energy consumption, and stronger durability. It can meet the needs of high-precision low-temperature scenarios such as quantum testing and superconducting experiments for efficient and stable refrigeration, and the preparation process has good reproducibility, which is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an optical microscope image of the GOS ceramic cool storage microspheres prepared in Example 1.

[0021] Figure 2 This is an optical microscope magnified image of the GOS ceramic cool storage microspheres prepared in Example 1.

[0022] Figure 3 This is an optical microscope magnified image of the GOS ceramic cool storage microspheres prepared in Example 2.

[0023] Figure 4 This is an optical microscope magnified image of the GOS ceramic cool storage microspheres prepared in Example 3.

[0024] Figure 5 This is an optical microscope magnified image of the GOS ceramic cool storage microspheres prepared in Example 4.

[0025] Figure 6 This is the particle size distribution diagram of the GOS ceramic cold storage microspheres prepared in Example 1.

[0026] Figure 7 This is the particle size distribution diagram of the GOS ceramic cold storage microspheres prepared in Example 2.

[0027] Figure 8 This is the particle size distribution diagram of the GOS ceramic cold storage microspheres prepared in Example 3.

[0028] Figure 9 This is the particle size distribution diagram of the GOS ceramic cold storage microspheres prepared in Example 4.

[0029] Figure 10 Schematic diagram of the structure of a two-stage Gifford-McMahon cryogenic refrigerator.

[0030] In the figure, 1. Rotating motor; 2. Rotary valve; 3. Air distribution valve; 4. Cover; 5. Cylinder; 6. Phosphor bronze wire mesh; 7. Primary cold-end heat exchanger; 8. Lead; 9. Holmium copper; 10. Gadolinium oxysulfide; 11. Secondary cold-end heat exchanger; 12. High-pressure intake air; 13. Low-pressure return air. DETAILED DESCRIPTION

[0031] Step 1: Mix the ingredients GOS ceramic powder, a small amount of light-curing resin and a small amount of anhydrous ethanol are mixed evenly and placed in a roller press for pre-pressing to obtain a semi-consolidated material block, which is then placed in a roller press for calendering and homogenization to obtain a clay-like solid sheet.

[0032] Step 2: Extrusion The solid sheet prepared in step 1 is put into a screw extruder, and the material is extruded from the die extrusion port. The die extrusion port is set downward so that the extruded material forms a wire rod and moves vertically downward; a light source is set below the die extrusion port to irradiate the extruded material so that the material is quickly solidified to form a GOS solidified wire rod.

[0033] Step 3: Precision Cutting The GOS solidified wire rods obtained in step 2 are neatly arranged and fed into a high-precision rotary blade cutting machine. By controlling the feeding speed, the GOS solidified wire rods are cut into GOS ceramic micro cylinders of preset lengths. The GOS ceramic micro cylinders are dried and set aside.

[0034] Step 4: Plasma Spherification The GOS ceramic micro cylinders prepared in step 3 are put into a radio frequency plasma spheroidization furnace, melted and spheroidized at high temperature under the protection of an inert atmosphere, and spherical GOS cold storage microspheres with uniform particle size distribution are obtained after cooling, i.e., the target product.

[0035] In step 1, a low-proportion photocurable resin is mixed with the raw materials to reduce subsequent porosity and impurities, facilitating the subsequent formation of high-density cool-storage microspheres. In step 2, the raw materials are precisely extruded and rapidly photocured externally to lock in the cross-sectional dimensions, resulting in a cured rod with precise and consistent diameter. In step 3, the length of the cylinders is precisely cut to control their volume, ensuring highly consistent particle size after spheroidization. The final microsphere size can be precisely adjusted as needed by adjusting the mold outlet size and cutting length. In step 4, plasma spheroidization rapidly melts the cylinders, allowing them to naturally shrink under surface tension to form a regular spherical shape. This not only ensures a circularity R close to 1, but also minimizes internal impurities and defects, resulting in a fully melted microsphere with a density close to the theoretical density. Furthermore, the entire process, from raw material mixing to spheroidization, is precisely controlled, eliminating raw material waste and morphology screening losses. This ensures near-100% GOS powder raw material utilization and finished microsphere yield. The result is adjustable microsphere size, excellent sphericity, a narrow particle size distribution, high density, and superior cool-storage performance, meeting the requirements of high-performance chillers.

[0036] In step 1, the photocurable resin preferably uses acrylic photocurable resin, which can achieve rapid polymerization and curing under ultraviolet light. Mixing GOS ceramic powder with ethanol and acrylic photocurable resin has the following two advantages: First, acrylic photocurable resin is easily soluble in ethanol and the raw materials contain ethanol. Therefore, the photocurable resin will not remain in the equipment for a long time, effectively avoiding problems such as screw jamming, mold outlet blockage, or outlet size reduction during long-term operation, and ensuring molding quality and dimensional stability. Second, this type of resin cures extremely quickly under ultraviolet light. By controlling the light power, it can be cured within 1-3 seconds. This prevents dimensional deviation of the wire rods during the falling process due to slow curing and prevents adhesion between wire rods, facilitating collection and creating the basic conditions for subsequent precise cutting operations. In contrast, if thermosetting resin is used in conjunction with a heating device installed under the mold outlet, although it can theoretically be cured, the thermal curing speed is slow, and a small amount of curing will also occur inside the screw extruder. After long-term operation, it is very easy to cause the screw to jam, especially to cause the mold outlet to be blocked or the outlet size to be reduced, affecting production continuity and dimensional stability.

[0037] In step 1, the acrylic light-curing resin is preferably selected from light-curing epoxy acrylic resin, light-curing polyester acrylic resin, and light-curing polyurethane acrylic resin. Preferably, the mass ratio of GOS ceramic powder to acrylic light-curing resin is 100:(2.0-6.0), and the mass ratio of GOS ceramic powder to anhydrous ethanol is 100:(2.0-4.0). Preferably, the GOS ceramic powder used has a particle size distribution (D50) of 0.2-10 μm and a purity of 99.9% or greater; more preferably, the particle size distribution (D50) is 0.5-5 μm and a purity of 99.95% or greater.

[0038] In step 2, the light source is selected to cure the photocurable resin, preferably a UV light source, with a dominant wavelength of preferably 365-405 nm. The light source is preferably an annular light source, positioned approximately 10 cm below the extrusion port. The extruded material can pass downward through the annular UV light source, where the surface is uniformly irradiated with UV light and uniformly cured. Preferably, the extrusion speed of the screw extruder is in the range of 3 to 30 mm / s, and the extrusion port diameter of the mold is 0.15 to 0.35 mm. The number of extrusion ports can be one or more, generally not exceeding 20 (too many may result in insufficient light coverage on the surface of the wire rod, affecting molding). Preferably, the number is 1, 2, 3, 4, 5, or 6.

[0039] In step 3, the GOS solidified wire rod is preferably cut to a length of 0.15-0.35 mm, resulting in a diameter-to-height ratio of 1:0.75-1.25 for the resulting GOS ceramic micro-cylinders. More preferably, the ratio is 1:0.85-1.1. By precisely adjusting the die outlet size and cutting feed speed, the cylinder diameter-to-height ratio can be controlled, preventing the cylinders from being too tall or too flat. This reduces the migration distance of the material during the plasma spheroidization process when it is melted and converted into a spherical shape, helping to more quickly form a more regular spherical shape under tension.

[0040] In step 4, the RF power of the RF plasma furnace is preferably 20-40 kW to ensure that the GOS ceramic micro-cylinders are fully melted in the high-temperature plasma to achieve complete globalization; the protective atmosphere can be an inert gas such as argon or helium, preferably argon; the feeding speed is controlled to be 2-30 g / min, and the preferred feeding speed is 2-10 g / min.

[0041] The present invention is further illustrated by the following specific examples, which are exemplary and intended to illustrate the problem and explain the present invention, and are not intended to limit the scope of the present invention. The raw materials, reagents, and instruments used in the examples are commercially available conventional products unless the manufacturer is indicated.

[0042] Example 1 (1) 500 g of GOS ceramic powder (D50 = 3 μm), 25 g of light-curable polyurethane acrylic resin (Kaster U-CURE 93412), and 15 g of anhydrous ethanol were transferred into a three-roller press and pressed into a clay-like solid film with a thickness of 3 mm.

[0043] (2) The film was fed into a screw extruder with a barrel temperature of 25°C, an extrusion speed of 15 mm / s, an extrusion port diameter of 0.15 mm, and three extrusion ports distributed in a regular triangle on a horizontal plane. During extrusion, a circular ultraviolet light source (main wavelength 365 nm) below the extrusion port was turned on and continuously irradiated to obtain a circular GOS ceramic wire rod with a diameter of 0.15 mm.

[0044] (3) The solidified GOS ceramic rods were arranged horizontally and fed into a rotary blade cutting machine to cut the rods into GOS ceramic micro cylinders with a length of 0.15 mm and a diameter of 0.15 mm. The obtained GOS ceramic micro cylinders were placed in a vacuum oven at 45 °C and vacuum dried for 5 h.

[0045] (4) The dried GOS ceramic micro-cylinders were put into a radio frequency plasma spheroidization device with an output power of 35 kW, Ar atmosphere protection, and a feeding speed of 10 g / min. After high-temperature melting and spheroidization and cooling, GOS ceramic cold storage microspheres were collected.

[0046] Example 2 (1) 500 g of GOS ceramic powder (D50 = 7 μm), 20 g of light-curable polyester acrylic resin (Kaster U-Cure9230), and 15 g of anhydrous ethanol were transferred into a three-roller press and pressed into a clay-like solid film with a thickness of 3 mm.

[0047] (2) The film was fed into a screw extruder at a barrel temperature of 25°C, an extrusion speed of 12 mm / s, an extrusion port diameter of 0.2 mm, and three extrusion ports distributed in a regular triangle on a horizontal plane. During extrusion, a circular ultraviolet light source (main wavelength 365 nm) below the extrusion port was turned on and continuously irradiated to obtain a circular GOS ceramic wire rod with a diameter of 0.2 mm.

[0048] (3) The solidified GOS ceramic rods were arranged horizontally and fed into a rotary blade cutting machine to cut the rods into GOS ceramic micro cylinders with a length of 0.22 mm and a diameter of 0.2 mm. The obtained GOS ceramic micro cylinders were placed in a vacuum oven at 45 °C and vacuum dried for 5 h.

[0049] (4) The dried GOS ceramic micro-cylinders were put into a radio frequency plasma spheroidization device with an output power of 40 kW, Ar atmosphere protection, and a feeding speed of 8 g / min. After high-temperature melting and spheroidization and cooling, GOS ceramic cold storage microspheres were collected.

[0050] Example 3 (1) Take 500g of GOS ceramic powder (D50=7um), 25g of light-cured polyurethane acrylic resin (AgiSyn230A2), and 15g of anhydrous ethanol and transfer them into a three-roller press to press them into a clay-like solid film with a thickness of 3mm.

[0051] (2) The film was fed into a screw extruder with a barrel temperature of 25°C, an extrusion speed range of 10 mm / s, an extrusion port diameter of 0.25 mm, and three extrusion ports distributed in a regular triangle on a horizontal plane. During extrusion, a circular ultraviolet light source (main wavelength 365 nm) below the extrusion port was turned on and continuously irradiated to obtain a circular GOS ceramic wire rod with a diameter of 0.25 mm.

[0052] (3) The solidified GOS ceramic rods were arranged horizontally and fed into a rotary blade cutting machine to cut the rods into GOS ceramic micro cylinders with a length of 0.25 mm and a diameter of 0.25 mm. The obtained GOS ceramic micro cylinders were placed in a vacuum oven at 45 °C and vacuum dried for 3 h.

[0053] (4) The dried GOS ceramic micro-cylinders were put into a radio frequency plasma spheroidization device with an output power of 40 kW, Ar atmosphere protection, and a feeding speed of 6 g / min. After high-temperature melting and spheroidization and cooling, GOS ceramic cold storage microspheres were collected.

[0054] Example 4 (1) Take 500g of GOS ceramic powder (D50=10μm), 20g of light-cured epoxy acrylic resin (AgiSyn 1030), and 15g of anhydrous ethanol and transfer them into a three-roller press to press them into a clay-like solid film with a thickness of 3mm.

[0055] (2) The film was fed into a screw extruder with a barrel temperature of 25°C, an extrusion speed range of 6 mm / s, an extrusion port diameter of 0.35 mm, and three extrusion ports distributed in a regular triangle on a horizontal plane. During extrusion, a circular ultraviolet light source (main wavelength of 365 nm) below the extrusion port was turned on and continuously irradiated to obtain a circular GOS ceramic wire rod with a diameter of 0.35 mm.

[0056] (3) The solidified GOS ceramic rods were arranged horizontally and fed into a rotary blade cutting machine to cut the rods into GOS ceramic micro cylinders with a length of 0.32 mm and a diameter of 0.35 mm. The obtained GOS ceramic micro cylinders were placed in a vacuum oven at 45 °C and vacuum dried for 3 h.

[0057] (4) The dried GOS ceramic micro-cylinders were put into a radio frequency plasma spheroidization device with an output power of 40 kW, Ar atmosphere protection, and a feeding speed of 3 g / min. After high-temperature melting and spheroidization and cooling, GOS ceramic cold storage microspheres were collected.

[0058] Characterization and testing Figure 1 This is a whole picture of the GOS ceramic cool storage microspheres prepared in Example 1 under an optical microscope. It can be seen that a large number of densely packed uniform spherical GOS ceramic cool storage microspheres are distributed in the field of view. Figures 2 to 5Magnified optical microscope photographs of the cool-storage microspheres prepared in Examples 1 to 4 are shown. The morphology of the individual microspheres can be clearly observed in the photographs. All microspheres exhibit a regular spherical shape, with a smooth surface without obvious depressions or protrusions, and a roundness close to 1. The particle size differences between the microspheres in the same example are minimal, and the size is highly uniform, with no obvious irregular particles or adhesion. This intuitively demonstrates the excellent performance of the GOS ceramic microspheres obtained by the preparation method of the present invention in terms of spherical regularity and particle size consistency.

[0059] The particle size distribution of the cool storage microspheres prepared in Examples 1 to 4 was statistically analyzed, and the particle size distribution diagrams were as follows: Figures 6 to 9 The statistical results of particle size distribution are shown in Table 1.

[0060] Table 1 Particle size distribution test results The particle size distribution of the cool storage microspheres prepared in Example 1 is as follows: Figure 6 As shown in the figure, the statistical sample number (Sample N) is 1000, the particle size mean (Sample Mean) is 0.165742 mm, the overall standard deviation (StDev(Overall)) is 0.00196133 mm, and the within-group standard deviation (StDev(Within)) is 0.00196464 mm. The two values ​​are nearly identical, with the former reflecting long-term global fluctuations in production, while the latter reflects short-term process variation. The two values ​​are highly consistent. The black column (actual distribution) and the red curve (theoretical fit) are close, and the microsphere particle sizes are closely clustered near the mean. These results demonstrate the extremely high particle size uniformity of the prepared cold storage microspheres, with extremely low standard deviations across over a thousand samples. This ensures highly consistent performance across each microsphere, minimizing performance fluctuations caused by particle size variations and providing support for precise temperature control scenarios such as quantum bit testing platforms, superconducting magnet quench protection experiments, and low-temperature infrared detector calibration. On the other hand, it is shown that the process of the present invention has excellent reproducibility, and each operation link such as extrusion, curing, precision cutting, and plasma spheroidization can be easily achieved with high consistency, and can be mass-produced, providing reliable process guarantee for industrial scale-up.

[0061] The particle size distribution of the cool storage microspheres prepared in Example 2, Example 3 and Example 4 are as follows: Figure 7 、 Figure 8 、 Figure 9 As shown, the sample size for all three samples was 1000, with mean particle sizes of 0.23466 mm, 0.28457 mm, and 0.35591 mm, respectively. The within-group standard deviations and overall standard deviations were small and highly similar. Similar to the test results in Example 1, the test results in Examples 2, 3, and 4 also demonstrate that the prepared GOS ceramic cool storage microspheres all possess extremely high particle size uniformity and excellent reproducibility through the preparation process.

[0062] Density and hardness (HV1 / 15s) were tested for the GOS cold storage microspheres prepared in Examples 1 to 4 and the new, original GOS cold storage microsphere fillers (original fillers) for commercially available G-M cryogenic refrigerators. The ratio of the measured density to the theoretical density was calculated based on the theoretical density of Gd2O2S of 7.32 g / cm³. The test and calculation results are shown in Table 2.

[0063] Table 2 Hardness and density results The GOS cold-storage microspheres produced in Examples 1-4 of the present invention exhibit excellent density and mechanical properties, significantly outperforming commercially available original fillers. The GOS cold-storage microspheres in these examples exhibit high hardness, with HV1 / 15s hardness values ​​ranging from 729.38 to 748.74. Their density approaches theoretical density, with a measured density-to-theoretical density ratio of 97.54% to 98.36%. The entire preparation process, through a unique formulation design and coordinated molding and sintering processes, achieves rounded microspheres with highly uniform particle size while also controlling the content of all ingredients other than GOS to extremely low levels. This results in microspheres approaching theoretical density and possessing extremely high hardness. This high density improves the microspheres' cold storage capacity per unit volume, while their high hardness enhances their wear resistance during refrigerator operation, helping to extend their service life and ensure long-term stable operation of the refrigeration system. The operation of a G-M refrigerator relies on the cyclical compression and expansion of the medium (typically at a frequency of 1-2 Hz). The microspheres are subjected to repeated mechanical shock in a high-pressure helium environment. Microspheres with insufficient hardness will gradually break down, producing fine particles, which can lead to numerous problems, including: decreased cold storage efficiency (changes in particle packing density, reducing heat exchange area); risk of system blockage (debris can clog gas circuits or valves); wear on remote cryocooler components (such as pistons and cylinders) caused by entry into the helium circulation; localized accumulation of broken microspheres (uneven airflow and unbalanced cooling distribution); and abnormal pressure drop (increased cryocooler power consumption). Therefore, improving the compactness and strength of GOS cryocooler microspheres is crucial for the operation of G-M cryocoolers.

[0064] To test the refrigeration performance of the GOS cold-storage microspheres prepared in this invention, a two-stage Gifford-McMahon (GM) cryogenic refrigerator was used as the test platform (the structure is shown in Figure 10). A single-variable replacement test method was employed: only the gadolinium oxysulfide microspheres in the secondary cold-end heat exchanger were replaced, while the lead and holmium copper fillers in the primary cold-end were retained. The remaining parameters of the refrigeration system were kept consistent to compare the effects of different GOS cold-storage microspheres on refrigeration performance.

[0065] The GOS cool-storage microspheres of Examples 2 and 3 were selected as the experimental groups. Control samples were also prepared: Comparative Example 1 mixed the microspheres of Examples 2 and 3 at a mass ratio of 4:3; Comparative Example 2 mixed the microspheres of Examples 2, 3, and 4 at a mass ratio of 4:5:5 to simulate uneven particle size. Comparative Example 3 used GOS cool-storage microspheres originally supplied with commercially available GM cryogenic refrigerators.

[0066] All test groups used a uniform GOS microsphere charge weight of 70g. The chiller configuration included: RDE-412A4 cold head, F70 compressor, 1.6MPa equilibrium pressure, 40W primary input power, and 10W secondary input power. After the chiller was started and operating stably, the temperature of the secondary cold-end heat exchanger was recorded every 10 minutes for 90 minutes. The results are shown in Table 2.

[0067] Table 3 Refrigeration test results Analysis of the cooling test data in Table 3 demonstrates that the samples in the examples exhibit rapid cooling and efficient refrigeration. The examples experienced rapid cooling in the initial 10-30 minutes. For example, by 20 minutes, the secondary temperatures of Examples 2 and 3 had dropped to 3.76-3.95K and 3.73-3.94K, respectively, 0.2-0.3K lower than those of Comparative Example 1 (3.88-4.16K), Comparative Example 2 (3.92-4.33K), and the original packing (3.92-4.33K). At 60 minutes, the experimental groups stabilized at 3.82-3.97K (Example 2) and 3.81-3.93K (Example 3), 0.1-0.2K lower than the comparative examples and the original packing, approaching the low-temperature range. At 90 minutes, the temperatures of the experimental groups reached 3.79-3.92K (Example 2) and 3.78-3.90K (Example 3), 0.1-0.3K lower than the control samples.

[0068] At the same time, the temperature data of the examples also showed remarkable stability. At 60 minutes, the temperature of Example 2 fluctuated between 3.82-3.97K (range 0.15K), and that of Example 3 was 3.81-3.93K (range 0.12K), while that of Comparative Example 1 fluctuated by 0.18K, Comparative Example 2 fluctuated by 0.23K, and that of the original packing fluctuated by 0.21K, showing significantly better temperature stability in the examples. At 90 minutes, the temperature of Example 2 fluctuated between 3.79-3.92K (range 0.13K), that of Example 3 fluctuated by 3.78-3.90K (range 0.12K), that of Comparative Example 1 fluctuated by 0.16K, that of Comparative Example 2 fluctuated by 0.32K, and that of the original packing fluctuated by 0.26K, further demonstrating that the highly uniform particle size of GOS cold storage microspheres can reduce local heat transfer differences and make the refrigeration system temperature more stable.

[0069] It can be seen that the microspheres prepared in the embodiment of the present invention are highly uniform in particle size, regular in spherical shape, and highly dense, which is conducive to the rapid flow and heat exchange of liquid helium, thereby improving the refrigeration efficiency. The filling uniformity reduces the local heat transfer difference, thereby ensuring temperature stability. The strong cold storage capacity per unit volume improves the refrigeration speed, which can effectively improve the refrigeration performance of the low-temperature refrigerator, reduce energy consumption and improve temperature control accuracy. The mixed particle size or commercially available filler in the comparative example has poor particle size dispersion or sphericity, which not only weakens the cold storage and heat exchange efficiency, but also leads to intensified temperature fluctuations.

[0070] In summary, the GOS cold storage microspheres prepared by the present invention have the advantages of uniform particle size and regular spherical shape, as well as the performance characteristics of high density and strong hardness. They have multiple advantages such as faster cooling rate, higher temperature control accuracy, lower energy consumption level, and stronger durability. They significantly improve the comprehensive performance of low-temperature refrigerators and can better meet the needs of high-precision low-temperature application scenarios for efficient, stable and precise refrigeration, and have important practical value.

[0071] The above embodiments are exemplary and intended to illustrate the technical concepts and features of the present invention so that those skilled in the art can understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for preparing gadolinium oxysulfide cold storage ceramic microspheres, characterized in that: The following steps are involved: Step 1: GOS ceramic powder, light-curable resin and anhydrous ethanol are mixed evenly, and then subjected to calendering and homogenization treatment to obtain a plastic body; Step 2: Using an extrusion device, the plastic body is extruded from a die extrusion port, wherein the die extrusion port is downwardly arranged so that the extruded material forms a wire rod and moves vertically downward; a light source is arranged below the die extrusion port to irradiate the extruded material so that the material is photocured to form a GOS cured wire rod; Step 3: cutting the GOS solidified wire rod into micro cylinders of a preset length, and drying the GOS ceramic micro cylinders for later use; Step 4: The micro-cylinders are placed in a radio frequency plasma spheroidization furnace, melted and spheroidized under the protection of an inert atmosphere, and GOS cool storage microspheres with uniform particle size distribution are collected.

2. The method for preparing gadolinium oxysulfide cold storage ceramic microspheres according to claim 1, characterized in that: In step 1, the particle size distribution D50 of the GOS ceramic powder is 0.2-10 μm and the purity is ≥99.9%.

3. The method for preparing gadolinium oxysulfide cold storage ceramic microspheres according to claim 1, characterized in that: In step 1, the light-curing resin is selected from light-curing epoxy acrylic resin, light-curing polyester acrylic resin, and light-curing polyurethane acrylic resin.

4. The method for preparing gadolinium oxysulfide cold storage ceramic microspheres according to claim 1, characterized in that: In step 2, an annular ultraviolet light source is provided below the extrusion port of the die, and the extruded material passes downward through the annular ultraviolet light source and is surrounded and irradiated by the annular ultraviolet light source.

5. The method for preparing gadolinium oxysulfide cold storage ceramic microspheres according to claim 1, characterized in that: In step 2, the extrusion equipment is a screw extruder, the extrusion speed of the screw extruder is 3 to 30 mm / s, the diameter of the die extrusion port is 0.15 to 0.35 mm, and the number of the extrusion ports is one or more.

6. The method for preparing gadolinium oxysulfide cold storage ceramic microspheres according to claim 1, characterized in that: In step 3, the GOS solidified wire rods are neatly arranged and fed into a rotary blade cutting machine, where the GOS solidified wire rods are cut into GOS ceramic micro cylinders of preset length by precisely controlling the feeding speed.

7. The method for preparing gadolinium oxysulfide cold storage ceramic microspheres according to claim 1, characterized in that: In step 3, the cutting length of the micro-cylinder is 0.15-0.35 mm, and the ratio of diameter to height is 1:(0.85-1.1).

8. The method for preparing gadolinium oxysulfide cold storage ceramic microspheres according to claim 1, characterized in that: In step 4, the radio frequency power of the radio frequency plasma spheroidization furnace is 20 to 40 kW, the protective atmosphere is argon or helium, and the feeding speed of the micro cylinders is 2 to 30 g / min.

9. A gadolinium oxysulfide cold storage ceramic microsphere, characterized in that: The gadolinium oxysulfide cold storage ceramic microspheres are prepared according to the preparation method according to any one of claims 1 to 8.

10. The use of gadolinium oxysulfide cold storage ceramic microspheres according to claim 9, characterized in that: The gadolinium oxysulfide cold storage ceramic microspheres are used as cold storage fillers for the secondary cold end heat exchanger of a double-stage Gifford-McMahon cryogenic refrigerator.

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