A method for preparing gadolinium oxysulfide scintillating ceramic

Abstract

This invention provides a method for preparing gadolinium oxysulfide scintillation ceramics, comprising the following steps: Step 1: preparing precursor powder containing gadolinium oxysulfide matrix powder; Step 2: adding the precursor powder into a mold and performing segmented pressure sintering in an inert atmosphere to obtain a pre-densified sintered body; then performing hot isostatic pressing sintering of the pre-densified sintered body in an inert atmosphere to obtain a fully dense ceramic body; Step 3: placing the fully dense ceramic body in an atmosphere-controlled annealing furnace; performing a first stage of heat preservation in air at a temperature of 800-1000 °C for 12-30 hours; then switching to an inert atmosphere and raising the temperature from the first stage heat preservation temperature to 1000-1250 °C for a second stage heat preservation for 20-40 hours, followed by cooling to room temperature to obtain gadolinium oxysulfide scintillation ceramics. The GOS scintillation ceramic prepared by this invention achieves a comprehensive and synergistic leap in performance, including relative density ≥99.9%, light output >30000 ph / MeV, and afterglow <0.01%, and can stably prepare large-size ceramic sheets with a diameter ≥50 mm.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramic material preparation technology, specifically to a method for preparing gadolinium oxysulfide scintillation ceramic. Background Technology

[0002] Scintillation ceramics are optically functional ceramic materials capable of converting high-energy rays (X-rays, gamma rays, etc.) into visible light, and have wide applications in medical CT, industrial CT, security inspection equipment, and high-energy physics detection. Among them, gadolinium oxysulfide (Gd2O2S, abbreviated as GOS) scintillation ceramics, as a hexagonal crystal system, have become one of the mainstream materials for commercial CT detectors due to their high density (7.34 g / cm³), high effective atomic number (60), high X-ray blocking ability, high band gap (4.6 eV), excellent luminous efficiency, low afterglow, and suitable decay time.

[0003] As medical imaging equipment develops towards higher resolution and lower dose, the performance requirements for GOS scintillation ceramics are constantly increasing, mainly including: high density (≥99.9%) to ensure optical transmittance; high luminous efficiency to reduce radiation dose; excellent luminous uniformity to ensure imaging quality; and good stability to ensure long-term reliability.

[0004] Existing GOS ceramic preparation technologies, such as atmospheric pressure sintering, are difficult to achieve complete densification; hot isostatic pressing (HIP) can eliminate closed pores, but requires the preparation of a green blank with a certain strength beforehand, and has limited ability to eliminate open pores; while single hot pressing (HP) or spark plasma sintering (SPS) and other pressure-assisted sintering technologies, while improving densification rate and suppressing grain growth, also generally face the following challenges: (1) carbon pollution risk from the mold; (2) thermal stress generated during rapid sintering; (3) intrinsic defects such as lattice oxygen vacancies; (4) for multi-element co-doped systems, it is difficult to ensure uniform distribution of elements at the molecular scale.

[0005] Although existing studies have adopted a combined process of "pressure-assisted sintering + HIP + annealing", sintering and subsequent heat treatment are usually regarded as isolated steps. The entire process of defect generation and elimination is not designed in a coordinated manner, resulting in insufficient targeted treatment of defects with different properties such as carbon contamination and oxygen vacancies, which limits the further improvement of the overall performance of ceramics.

[0006] To address the aforementioned issues, existing research has attempted to improve the process by optimizing the sintering process or subsequent heat treatment. For example, CN105330289A discloses a method for preparing gadolinium oxysulfate scintillation ceramics, employing SPS combined with hot isostatic pressing and annealing. However, this patented annealing process does not perform step-by-step optimization for different defect types, resulting in limited effectiveness in eliminating carbon contamination and oxygen vacancies. CN105800663A discloses a hot-pressing reaction sintering method for gadolinium oxysulfate scintillation ceramics. This method solves the problems of high energy consumption and the influence of sintering aids in the preparation of gadolinium oxysulfate ceramics. The raw material powder is obtained by uniformly mixing Gd₂O₂SO₄ with reducing agent powder, and then the raw material powder is sintered in stages, including at 820°C. The first stage sintering was carried out at 950 ℃ and 10-75 MPa, and the second stage was 1000 MPa. 1500 ℃, 30 The second-stage sintering was performed at 150 MPa, with an inert atmosphere or vacuum environment maintained during the sintering process. However, the prepared gadolinium oxysulfate ceramics did not exhibit good optical properties, and the elimination of carbon contamination and oxygen vacancies was not significant. CN110282650A discloses a method for preparing gadolinium oxysulfate powder and its scintillation ceramics for X-ray detection. This method prepares gadolinium oxysulfate scintillation ceramics by self-doping gadolinium oxysulfate powder and isostatic pressing followed by high-temperature atmosphere sintering, achieving high-purity, uniform particle preparation and an efficient sintering process. However, this method does not meet the practical application requirements of gadolinium oxysulfate scintillation ceramics with high density, low carburization, and high optical performance.

[0007] Therefore, developing an integrated fabrication process that can synergistically control densification, microstructure evolution, and defect repair is of great significance for obtaining high-performance, highly consistent GOS scintillation ceramics. Summary of the Invention

[0008] The technical problem this invention aims to solve is to address the issues of insufficient density, poor doping uniformity, coexistence of carbon contamination and oxygen vacancy defects, and weak process synergy in existing GOS ceramics. This invention provides a GOS scintillation ceramic preparation method with high process integration and the ability to simultaneously optimize microstructure and luminescence performance. The technical solution of this invention is as follows: A method for preparing gadolinium oxide scintillation ceramics includes the following steps: Step 1: Prepare precursor powder containing gadolinium oxysulfide matrix powder; Step 2: Add the precursor powder into the mold and perform segmented pressure sintering in an inert atmosphere: first, heat to 800-950 ℃ under a pressure of 10-20 MPa, then continue to heat to 1000-1150 ℃, gradually increase the pressure to 30-50 MPa during the heating process, then maintain the pressure and continue to heat to 1400-1650 ℃, and hold at the temperature and pressure for 10-24 hours to obtain a pre-densified sintered body; Then, the pre-densified sintered body is subjected to hot isostatic pressing sintering in an inert atmosphere at a temperature of 1300-1500 ℃ and a pressure of 150-200 MPa for a holding time of 1-5 hours to obtain a fully dense ceramic body. Step 3: Place the fully dense ceramic body in an atmosphere-controlled annealing furnace; in air, perform the first stage of heat treatment at a temperature of 800-1000 ℃ for 12-30 hours; then switch to an inert atmosphere and raise the temperature from the first stage heat treatment temperature to 1000-1250 ℃ for the second stage heat treatment for 20-40 hours, and then cool to room temperature to obtain gadolinium oxide scintillation ceramic.

[0009] Optionally, in step one: the gadolinium oxysulfate matrix powder is mixed evenly with praseodymium source, cerium source and fluorine source to obtain precursor powder; The particle size D of the gadolinium sulfide matrix powder 50 2-6 μm; The praseodymium source is Pr6O. 11 The cerium source is Ce2(CO3)3 and / or CeO2, and the fluorine source is LiF and / or Li2GeF6; The molar ratio of Pr to Ce is 1:(2-5), the total doping amount of Pr and Ce is 0.1-1.0 mol%, and the doping amount of F is 0.05-0.2 wt%. Preferably, the particle size D of the gadolinium oxysulfate matrix powder is... 50 3-5 μm The molar ratio of Pr to Ce is 1:(3-4); the total doping amount of Pr and Ce is 0.3-0.8 mol%, and the doping amount of F is preferably 0.08-0.15 wt%.

[0010] Optionally, in step one, wet ball milling is used to mix the materials for 12-24 hours at a ball-to-material ratio of (2-5):1 at a speed of 200-400 rpm to obtain a mixed slurry; the mixed slurry is then dried at 80-120 ℃ for 12-24 hours to obtain a dried powder. The dried powder is passed through a 100-300 mesh sieve to obtain the precursor powder; Preferably, the wet ball milling mixing time is 16-24 hours.

[0011] Optionally, the sintering process in step two includes: the holding temperature of hot isostatic pressing sintering is 50-150 ℃ lower than the holding temperature of segmented pressure sintering.

[0012] Preferably, in step two, the temperature is first raised to 900 ℃ under a pressure of 10-20 MPa, and then raised to 1100 ℃. During the heating process, the pressure is gradually increased to 40-45 MPa, and then the pressure is maintained and the temperature is raised to 1550-1600 ℃. The temperature and pressure are maintained for 15-18 hours to obtain a pre-densified sintered body. The pre-densified sintered body is then subjected to hot isostatic pressing in an inert atmosphere at a temperature of 1400-1450 ℃ and a pressure of 175-185 MPa for 2-3 hours to obtain a fully dense ceramic body.

[0013] Optionally, in step three, the temperature is first kept at 800-950 ℃ for 18-24 hours; then the temperature is switched to an inert atmosphere and raised to 1050-1200 ℃, and kept at that temperature for 20-35 hours.

[0014] Optionally, the heating rate in the air atmosphere in step three is 2-5 °C / min; In step three, the heating rate in the inert atmosphere is 3-8 ℃ / min; In step three, the annealing process starts from the highest temperature and cools down at a rate of 0.3-2 ℃ / min, down to 400-600 ℃, and then naturally cools down to room temperature with the furnace. Preferably, the heating rate in the air atmosphere in step three is 3-4 °C / min; In step three, the heating rate in the inert atmosphere is 4-6 ℃ / min; In step three, the annealing process starts from the highest temperature and cools down at a rate of 0.5-1.5 ℃ / min, down to 400-600 ℃, and then naturally cools down to room temperature with the furnace.

[0015] Optionally, step four is also included: grinding and polishing the gadolinium oxide scintillation ceramic; The thickness tolerance of the processed ceramic sheet is ±0.02 mm, and the surface roughness Ra≤0.1 μm.

[0016] Preferably, the present invention includes the following steps: Step 1: Prepare precursor powder containing gadolinium oxysulfide matrix powder; Step 2: Hot pressing sintering: The precursor powder is loaded into an isolated mold and pressurized in stages under a protective atmosphere: 15 MPa at room temperature to 900 ℃; gradually increase the pressure to 45 MPa and maintain it during the heating process from 900 to 1100 ℃; continue heating to the sintering temperature of 1550 ℃, hold for 12 hours, and cool with the furnace.

[0017] HIP treatment: After cleaning the surface of the green body, it is treated at 1450 ℃ and 180 MPa high-purity argon atmosphere for 2 hours to obtain a fully dense ceramic body; Step 3: Two consecutive stages of annealing: In an air atmosphere, heat to 900 ℃ at 3 ℃ / min and hold for 24 hours; without interrupting the program, switch to a high-purity argon atmosphere, heat to 1100 ℃ at 3 ℃ / min and hold for 30 hours; after completion, cool to 500 ℃ at 1 ℃ / min and cool with the furnace.

[0018] Precision machining: Double-sided grinding to a thickness of 2.00±0.01 mm, with a surface roughness Ra≤0.08 μm. Gadolinium oxide scintillation ceramic is obtained.

[0019] The present invention also proposes a high-performance gadolinium oxysulfide scintillation ceramic prepared by the above method.

[0020] Optionally, the high-performance gadolinium oxysulfide scintillation ceramic has the following performance indicators: Relative density ≥ 99.9%; Optical output >30000 ph / MeV; Afterglow (@20ms) < 0.01%; Carbon content less than 0.018 wt% Preferably, the high-performance gadolinium oxysulfide scintillation ceramic has a relative density ≥ 99.95%; Carbon content less than 0.010 wt% Optical output >35820 ph / MeV; Its appearance ranges from light yellow to yellow and semi-transparent.

[0021] Optionally, the ceramic is a sheet-like structure with a diameter of not less than 50 mm.

[0022] This invention also proposes the application of the above-mentioned high-performance gadolinium oxysulfide scintillation ceramics in detectors of medical CT, industrial CT, or security inspection equipment.

[0023] The beneficial effects of this invention include: This invention applies low pressure (10-20 MPa) in the low-temperature range (800-950 ℃) to facilitate gas discharge and green body stability, and gradually increases the pressure to 30-50 MPa in the high-temperature range (above 1000-1150 ℃) to achieve rapid densification. This strategy not only avoids mold damage and powder cracking, but also inhibits excessive carbon penetration from the mold into the ceramic surface (carbon content <0.010wt%), laying a purity foundation for subsequent defect repair.

[0024] This invention combines two steps: rapid densification via hot pressing and full densification via hot isostatic pressing (HIP). The HIP temperature is explicitly limited to 50-150 °C below the hot pressing temperature. The hot pressing stage achieves skeletal densification (relative density >95%), while the HIP stage eliminates all closed pores without causing abnormal grain growth, resulting in a final relative density ≥99.95%. This resolves the technical contradiction of achieving both high density and fine-grained structure in GOS ceramics.

[0025] This invention features a continuous two-stage annealing process with a step-by-step defect repair mechanism: It innovatively proposes a continuous procedure of "low-temperature air annealing (800-1000 ℃) + high-temperature inert atmosphere annealing (1000-1250 ℃)," sequentially repairing defects of two different mechanisms—surface carbon contamination and bulk oxygen vacancies—within a single heat treatment cycle. First, external carbon impurities are removed using an oxidizing atmosphere, then an inert atmosphere is switched to repair internal intrinsic defects and optimize Pr³. + / Ce³ + The localized coordination environment of the luminescent center avoids the limitations of single-atmosphere treatment and achieves systematic purification of defects inside and outside the ceramic.

[0026] The GOS scintillation ceramics prepared by this invention achieve a synergistic leap in comprehensive performance: the GOS ceramics prepared by this method have a relative density ≥99.95%, light output >35820 ph / MeV, and afterglow (@20ms) <0.01%. The core indicators comprehensively surpass the level of existing technologies and commercial products, and can stably prepare large-size ceramic sheets with a diameter ≥50 mm, with good batch consistency and stability.

[0027] This invention, through systematic comparative experiments, reveals the fundamental principle that excessively high pressure during sintering exacerbates carbon contamination, leading to a sharp drop in light output, and defines the optimal process condition window. This differentiated parameter combination yields products with superior performance. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a flowchart of the preparation process of the present invention; Figure 2 SEM images of the cross-sectional microstructure of the ceramic prepared in Example 1; Figure 3 A photograph of the actual Φ50mm large-size ceramic sheet prepared in Example 1; Figure 4 SEM images of the cross-sectional microstructure of the ceramic prepared in Comparative Example 1; Figure 5 Photograph of the Φ50mm large-size ceramic sheet prepared for Comparative Example 1. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0031] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] The terms “comprising,” “including,” “having,” “containing,” etc., used in this document are all open-ended, meaning they include but are not limited to. The terms “first” and “second” used in this document are for descriptive purposes only, and features specified as “first” or “second” may explicitly or implicitly include at least one of those features.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the equipment, apparatus, materials, reagents, etc., used are all commercially available.

[0034] A process for preparing high-performance gadolinium oxysulfide scintillation ceramics using a combination of sintering and segmented annealing, such as... Figure 1 As shown, it includes the following steps: S1. Powder pretreatment and homogenization Raw material selection: High-purity Gd2O2S powder (purchased externally) was used as the base material, with a purity ≥ 99.99%. 50 The micrometer size should be controlled within 2-6 μm. D is preferred. 50 The particle size is 3-5 μm, which is beneficial for sintering activity and ensures powder flowability.

[0035] Doping element design: This invention employs a three-element co-doping strategy of Pr, Ce, and F. Pr acts as the main activator, providing luminescent centers; Ce acts as a sensitizer, enhancing energy absorption and transfer efficiency; and F acts as a flux and charge compensation agent, promoting sintering and optimizing luminescence performance.

[0036] Specific doping method: Pr is doped with Pr6O 11 The doping of Pr and Ce is introduced in the form of Ce2(CO3)3 or CeO2, and the doping of F is introduced in the form of LiF or Li2GeF6. The molar ratio of Pr to Ce is 1:(2-5), preferably 1:(3-4); the total doping amount of Pr and Ce is 0.1-1.0 mol%, preferably 0.3-0.8 mol%; and the doping amount of F is 0.05-0.2 wt%, preferably 0.08-0.15 wt%.

[0037] If the molar ratio of Pr to Ce deviates from 1:(2-5) or the total doping amount exceeds the range of 0.1-1.0 mol%, it will lead to quenching of luminescence concentration, a significant decrease in luminescence intensity or a prolonged afterglow time, making it difficult to obtain ideal scintillation performance. At the same time, if the F doping amount is less than 0.05 wt%, the fluxing effect will be insufficient, and if it is greater than 0.2 wt%, it will easily introduce impurity phases and reduce the light transmittance of ceramics. Therefore, it is necessary to strictly control the content of each dopant within the range mentioned above.

[0038] Mixing method: Wet mixing process is adopted. According to the stoichiometric ratio, the weighed Gd2O2S powder, Pr source, Ce source and F source are added to the polyurethane ball mill jar. Anhydrous ethanol or pure water is added as the dispersion medium. The weight of anhydrous ethanol: the weight of raw materials = (2-4):1. The mixture is mixed by planetary ball milling for 12-24 hours. The weight of the ball mill: the weight of raw materials = (2-5):1. The speed is 200-400 rpm.

[0039] Drying and sieving: Dry the mixed slurry at 80-120 ℃ for 12-24 hours to obtain a dried powder. Pass the dried powder through a 100-300 mesh sieve to obtain a uniformly mixed precursor powder without agglomeration.

[0040] The innovation of this invention in the raw material processing stage is as follows: by using wet ball milling combined with the use of dispersants, uniform doping of Pr, Ce and F is achieved; and by drying and sieving processes, precursor powder with good flowability and narrow particle size distribution is obtained, laying the foundation for subsequent sintering.

[0041] S2. Combined two-step sintering: The first step, sintering (hot pressing sintering, pressure-assisted rapid densification): The precursor powder obtained from S1 is loaded into a specially isolated mold and pressure-assisted sintering is performed under a protective atmosphere. A segmented pressurization strategy is adopted: a lower pressure is applied in the low-temperature zone (e.g., room temperature to 900 ℃) to stabilize the green body; when the powder begins to flow plastically in the medium-temperature zone (900 ℃ to 1100 ℃), the pressure is increased to the final value (e.g., 30-50 MPa), and a high-temperature (e.g., 1400-1650 ℃) long-term holding time is completed at this pressure for 10-24 hours, preferably 12-18 hours, to achieve rapid densification of the material and preliminary control of grain size.

[0042] Innovative Segmented Hot Pressing: This invention employs a segmented pressurization method. Specifically, in the temperature range from room temperature to 900°C, a low pressure (10-20 MPa) is maintained to facilitate the expulsion of internal gases and initial compaction of the powder. When the temperature rises above 900°C, the powder begins to enter the plastic flow and densification stage, at which point the pressure is gradually increased to a set value (30-50 MPa). This segmented pressurization method avoids mold damage or powder splitting due to excessive pressure in the low-temperature stage, while ensuring uniform pressure transmission in the high-temperature stage, thus improving the density uniformity of the sintered body.

[0043] The second step, sintering (hot isostatic pressing, HIP densification): After surface cleaning, the pre-sintered body obtained in the first step is placed in a hot isostatic pressing apparatus. It is held under an inert atmosphere, at a relatively low temperature (usually 50-150 °C lower than the first step sintering temperature, preferably 50-100 °C lower), and at an isostatic pressure (150-200 MPa) for 1-5 hours, preferably 2-3 hours. The aim is to eliminate all closed pores remaining after the first step sintering through hydrostatic pressure without causing abnormal grain growth, thus achieving the theoretical density.

[0044] This invention sets the HIP treatment temperature to be 50-100 °C lower than the hot pressing sintering temperature. This temperature selection ensures sufficient atomic diffusion to eliminate closed pores while avoiding abnormal grain growth caused by excessively high temperatures. After HIP treatment, residual micron- and nano-sized closed pores inside the ceramic are effectively eliminated, and the relative density reaches over 99.9%.

[0045] S3. Continuous Two-Stage Annealing: The fully dense ceramic treated in S2 is placed in a programmable atmosphere annealing furnace and subjected to a continuous, uninterrupted annealing process. This process consists of two temperature-atmosphere stages: The first stage (non-reducing atmosphere medium-temperature treatment): This involves prolonged holding at a medium temperature (e.g., 800-1000 ℃) in an oxidizing atmosphere or air atmosphere. The main functions of this stage are: to eliminate surface carbon contamination impurities introduced by mold contact through oxidation; and to initially release residual thermal stress introduced by rapid heating and cooling and pressure processing.

[0046] The mechanism of annealing: 1. Removes surface carbon contamination. Carbon elements that may have penetrated into the ceramic surface during hot pressing are oxidized into CO or CO2 gas and escape, restoring the yellow-green appearance and transparency of the ceramic; 2. Initially releases thermal stress. The thermal stress generated during the combined sintering process is initially released during annealing; 3. Repairs surface defects. Oxygen vacancies on the ceramic surface are partially compensated in the air atmosphere.

[0047] Execution parameters: Temperature 800-1000 ℃, preferably 800-950 ℃; Holding time 12-30 hours, preferably 18-24 hours; Heating rate 2-5 ℃ / min, preferably 3-4 ℃ / min.

[0048] The second stage (high-temperature optimization in inert atmosphere, reducing atmosphere, or vacuum environment): Without interrupting the program, the furnace atmosphere is switched to a reducing atmosphere, a high-purity inert atmosphere, or a vacuum environment. The temperature is then increased to a higher range (e.g., 1000-1250 ℃) and held for an extended period. The main function of this stage is to repair oxygen vacancy defects in the bulk phase through high-temperature diffusion of lattice atoms under low oxygen partial pressure; and to optimize the dopant ions (Pr³). + / Ce³ + The local coordination environment of the luminescent material activates its luminescence efficiency.

[0049] Execution parameters: Temperature 1000-1250 ℃, preferably 1050-1200 ℃; Holding time 20-40 hours, preferably 20-35 hours; Heating rate 3-8 ℃ / min, preferably 4-6 ℃ / min.

[0050] Cooling control: After the heat preservation is completed, control the cooling rate to slowly reduce to 400-600 ℃ at a rate of 0.3-2 ℃ / min, and then let it cool naturally to room temperature with the furnace.

[0051] The heating and cooling rates throughout the annealing process are precisely controlled to achieve a gradual release of stress and repair of defects.

[0052] The mechanism of two-stage annealing: 1. Elimination of oxygen vacancy defects: The activity of lattice atoms is enhanced at high temperatures, and oxygen vacancies formed during sintering are eliminated through diffusion; 2. Optimization of Pr / Ce ion valence state: Pr and Ce ions are placed in a suitable valence state and coordination environment to form efficient luminescent centers; 3. Lattice integrity: Promotes lattice structure adjustment and reduces non-radiative recombination centers.

[0053] The innovation of the segmented annealing process lies in combining low-temperature air atmosphere annealing and high-temperature inert atmosphere annealing to address surface carbon contamination and bulk oxygen vacancies in stages. First, low-temperature air annealing removes surface carbon contamination, followed by high-temperature argon annealing to eliminate bulk defects. This avoids oxidation problems that may occur with high-temperature air annealing and also overcomes the limitation of simple inert atmosphere annealing in effectively removing carbon contamination.

[0054] S4. Grinding and Precision Machining: Double-sided grinding, polishing, and precision machining are performed on the fully annealed ceramics to obtain a final ceramic product with specified dimensions and high surface finish.

[0055] Double-sided grinding of ceramics is performed using a diamond double-sided grinding disc. Grinding process parameters: grinding disc speed 1000-3000 rpm, feed rate 0.01-0.05 mm / min, and deionized water as coolant.

[0056] Machining accuracy control: Through precision grinding, the final ceramic sheet thickness tolerance is controlled to ±0.02mm, and the surface roughness Ra≤0.1μm. High-precision dimensional control and low surface roughness are prerequisites for ensuring good optical coupling between the ceramic sheet and the photodetector array.

[0057] Examples 1-13: Gadolinium oxide scintillation ceramics were prepared according to the process parameters listed in Table 1, with the same basic raw materials and pretreatment steps. Matrix: Purchased D 501000 g of high-purity Gd2O2S powder with a particle size of ≈4.2-5.8 μm.

[0058] Doping: Based on a Pr:Ce molar ratio of 1:3, weigh out Pr6O 11 0.85 g of Ce2(CO3)3 and 2.36 g of LiF were weighed as F source (F doping amount of about 0.1 wt%). Weighing was done using a balance with a weight of 0.001 to minimize error.

[0059] Wet ball milling: Mix anhydrous ethanol and a ball milling device with the dispersion medium, and ball mill for 20 hours using a planetary ball milling machine. The ratio of anhydrous ethanol weight to raw material weight is 2.5:1, and the ratio of ball milling device weight to raw material weight is 3:1. The rotation speed is 320 rpm.

[0060] Drying and sieving: After drying at 100 ℃, pass through a 120-mesh sieve to obtain precursor powder.

[0061] Example 1 (1) Hot pressing sintering: The precursor powder is loaded into the isolated mold and pressurized in stages under a protective atmosphere: room temperature ~ 900 ℃ pressure 15 MPa; during the heating process of 900~1100 ℃, the pressure is gradually increased to 45 MPa and maintained; continue to heat up to the sintering temperature of 1550 ℃, hold for 12 hours, and cool with the furnace.

[0062] (2) HIP treatment: After cleaning the surface of the billet, it is treated for 2 hours at 1450 ℃ and 180 MPa high-purity argon atmosphere.

[0063] (3) Two consecutive annealing stages: In an air atmosphere, the temperature is increased to 900 ℃ at 3 ℃ / min and held for 24 hours; without interrupting the program, the temperature is switched to a high-purity argon atmosphere and increased to 1100 ℃ at 3 ℃ / min and held for 30 hours; after the process, the temperature is cooled to 500 ℃ at 1 ℃ / min and cooled with the furnace.

[0064] (4) Precision machining: double-sided grinding to a thickness of 2.00±0.01 mm, surface roughness Ra≤0.08 μm.

[0065] Example 2 The difference from Example 1 is that the hot pressing sintering temperature is 1500 ℃, while the rest is the same as Example 1.

[0066] Example 3 The difference from Example 1 is that the hot pressing sintering temperature is 1600 ℃ and the holding time is 10 hours, while the rest is the same as Example 1.

[0067] Example 4 The difference from Example 1 is that the HIP treatment temperature is 1400 ℃, the pressure is 180 MPa, and the heat treatment time is 2 hours. The rest is the same as Example 1.

[0068] Example 5 The difference from Example 1 is that the HIP treatment temperature is 1500 ℃, the pressure is 180 MPa, and the heat treatment time is 2 hours. The rest is the same as Example 1.

[0069] Example 6 The difference from Example 1 is that the two-stage annealing process is as follows: the first stage is 850 ℃, air atmosphere, and heat preservation for 24 hours; the second stage is 1050 ℃, inert atmosphere, and heat preservation for 36 hours; the rest is the same as Example 1.

[0070] Example 7 The difference from Example 1 is that the two-stage annealing process is as follows: the first stage is 950 ℃, air atmosphere, and heat preservation for 20 hours; the second stage is 1150 ℃, inert atmosphere, and heat preservation for 25 hours; the rest is the same as Example 1.

[0071] Example 8 The difference from Example 1 is that the two-stage annealing process is as follows: the first stage is 900 ℃, air atmosphere, and heat preservation for 20 hours; the second stage is 1200 ℃, inert atmosphere, and heat preservation for 20 hours; the rest is the same as Example 1.

[0072] Example 9 The difference from Example 1 is that the hot pressing sintering temperature is 1600 ℃ and the HIP treatment temperature is 1300 ℃; the rest is the same as Example 1.

[0073] Example 10 Compared with Example 1, in the hot pressing sintering process, the pressure was gradually increased to 50 MPa during the heating process from 900 to 1100 ℃; and the HIP treatment pressure was maintained at 200 MPa; the rest was the same as in Example 1.

[0074] Example 11 Compared to Example 1, in the two-stage annealing process: under air atmosphere, the temperature was increased to 950 °C at 4 °C / min and held for 24 hours; without interruption, the process was switched to high-purity argon atmosphere, and the temperature was increased to 1200 °C at 4 °C / min and held for 30 hours; after completion, the temperature was cooled to 500 °C at 1 °C / min and cooled with the furnace. The rest was the same as in Example 1.

[0075] Example 12 Compared to Example 1, after the second stage of annealing, the furnace was cooled to 500 °C at a rate of 5 °C / min, and then cooled in the furnace. The rest was the same as in Example 1.

[0076] Example 13 Compared to Example 1, the second stage of annealing was adjusted to be annealing under vacuum, with the vacuum level below 10 Pa. The remaining steps were the same as in Example 1.

[0077] Comparative Example 1 (without HIP processing) The difference from Example 1 is that the HIP step is omitted, and two-stage annealing is performed directly after hot pressing and sintering. The rest is the same as Example 1.

[0078] Comparative Example 2 (Traditional Single-Stage Air Annealing) The difference from Example 1 is that the annealing process is changed to directly heating to 1100 ℃ and holding for 30 hours in air atmosphere, while the rest is the same as Example 1.

[0079] Comparative Example 3 (Traditional Single-Stage Inert Atmosphere Annealing) The difference from Example 1 is that the annealing process is changed to directly heating to 1100 ℃ and holding for 30 hours in an inert atmosphere (without an air section), while the rest is the same as Example 1.

[0080] Comparative Example 4 (Hot-pressing temperature too low) The difference from Example 1 is that the hot pressing sintering temperature is 1350 ℃, while the rest is the same as Example 1.

[0081] Comparative Example 5 (HIP temperature is too high, equal to hot pressing temperature) The difference from Example 1 is that the HIP processing temperature is 1550 ℃ (equal to the hot pressing temperature), and the rest is the same as Example 1.

[0082] Comparative Example 6 Compared with Example 1, the adjustment steps are as follows: (1) Hot pressing sintering: The precursor powder is loaded into the isolated mold and pressurized in stages under a protective atmosphere: room temperature ~ 900 ℃ pressure 15 MPa; during the heating process of 900~1100 ℃, the pressure is gradually increased to 45 MPa and maintained; continue to heat up to the sintering temperature of 1550 ℃, hold for 12 hours, and cool with the furnace.

[0083] (2) In an air atmosphere, the temperature is increased to 900 ℃ at 3 ℃ / min and held for 24 hours; after the end, the temperature is cooled to 500 ℃ at 1 ℃ / min and cooled with the furnace.

[0084] (3) HIP treatment: After cleaning the surface of the billet, it is treated for 2 hours at 1450 ℃ and 180 MPa high-purity argon atmosphere.

[0085] (4) In a high-purity argon atmosphere, the temperature is increased to 1100 ℃ at 3 ℃ / min and held for 30 hours; after the end, the temperature is cooled to 500 ℃ at 1 ℃ / min and cooled with the furnace.

[0086] (5) Precision machining: double-sided grinding to a thickness of 2.00±0.01 mm, surface roughness Ra≤0.08 μm.

[0087] Performance testing The performance of the GOS ceramic sheets prepared in Examples 1-13 and Comparative Examples 1-6 was tested using the following methods:

[0088] The test results are shown in the table below:

[0089] Results Analysis Of all the implementations, Example 1 showed the best overall performance, with the highest light output (35820 ph / MeV), a relative density of 99.96%, afterglow <0.01%, carbon content <0.010%, and a light yellow, semi-transparent appearance. Examples 3 and 7 were the next best.

[0090] High performance can be obtained at hot pressing temperatures of 1550~1600 ℃, with 1550 ℃ (Example 1) providing the best light output, and 1600 ℃ (Example 3) providing higher density but slightly lower light output.

[0091] The HIP temperature is preferably 50~150 ℃ lower than the hot pressing temperature, with the optimal temperature being 1450 ℃ (Example 1); if the temperature is too low (1300 ℃), densification will be insufficient, and if it is too high (equal to the hot pressing temperature), the light output will decrease significantly.

[0092] Sintering pressure is not always better the higher it is. In Example 10 (hot pressing 50 MPa, HIP 200 MPa), the carbon content increased to 0.018%, and the light output dropped to 32100, which was worse than Example 1 (45 MPa, 180 MPa).

[0093] The optimal combination of two-stage annealing (air at 900°C in the first stage and argon at 1100°C in the second stage) is shown in Example 1. Too low a temperature results in insufficient repair, while too high a temperature leads to decreased light output. Single-stage annealing (Comparative Examples 2 and 3) results in high carbon content and low light output.

[0094] According to the sintering and annealing combination scheme of one-step sintering + one-stage air annealing + two-step HIP sintering + two-stage argon annealing in Comparative Example 6, the carbon content distribution of the sintered body formed in the first step of sintering can be reduced after the first stage of air annealing. However, after the second step of HIP sintering, carburization will still be introduced into the sintered body during the heating and cooling process. The second stage of argon annealing cannot effectively oxidize and remove the carburization, resulting in an increase in carbon content and a decrease in light output in the ceramic body.

[0095] The cooling rate is preferably ≤2 ℃ / min. If the rate is too fast (Example 12), stress patterns will be introduced, resulting in decreased light transmittance and light output. Furthermore, Example 13 uses vacuum annealing, and the vacuum environment is beneficial for Pr³ + / Ce³ + The valence state balance was affected to some extent, resulting in its light output (33630 ph / MeV) being lower than that of Example 1.

[0096] The above cross-tests fully demonstrate that the three-step process of "hot pressing sintering + HIP + continuous two-stage annealing" described in this invention has a significant synergistic effect, and the process parameters of each step must be within the optimal range to obtain GOS scintillation ceramics with the best overall performance.

[0097] In summary, the preparation method of this invention demonstrates the effectiveness and synergy of the process. The proposed three-step integrated process of "hot pressing sintering + hot isostatic pressing (HIP) + continuous two-stage annealing" can synergistically achieve full densification, carbon contamination removal, oxygen vacancy repair, and luminescent center optimization of GOS scintillation ceramics, overcoming problems such as insufficient density, uneven doping, and coexistence of residual defects in existing technologies. Comparative Examples 1-6 confirm that the absence of any key step (the interleaved execution of HIP, two-stage annealing, and sintering annealing processes) or deviation of parameters from the optimal range will lead to a decrease in density and light output, proving that the three-step process needs to work synergistically and be precisely matched.

[0098] The present invention has selected the following processing conditions for each step: hot pressing sintering temperature 1550~1600 ℃, pressure 40~50MPa (preferably 45 MPa), holding time 12~18 hours; hot isostatic pressing: temperature 50~150 ℃ lower than hot pressing temperature (preferably 1450 ℃), pressure 150~200 MPa (preferably 180 MPa), holding time 1~5 hours; two-stage annealing: the first stage is in air atmosphere, temperature 800~950 ℃ (preferably 900 ℃), holding time 12~30 hours; the second stage is in high-purity inert atmosphere (such as argon), temperature 1000~1150 ℃ (preferably 1100 ℃), holding time 20~40 hours; the heating and cooling rates are both ≤5 ℃ / min, and the cooling rate is preferably ≤2 ℃ / min (more preferably 1 ℃ / min).

[0099] like Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown, the performance indicators of the GOS scintillation ceramic prepared by the above-mentioned optimal technical solution (Example 1) are: relative density ≥99.96%, light output ≥35820 ph / MeV, afterglow (@20ms) <0.01%, carbon content <0.010%, light yellow and semi-transparent appearance, and large-size ceramic sheets with a diameter of not less than 50 mm can be stably prepared.

[0100] This invention employs segmented pressurized hot pressing sintering, using low-temperature, low-pressure venting and high-temperature, high-pressure densification to avoid mold damage while ensuring density uniformity. Low-temperature HIP full densification eliminates residual closed pores without causing abnormal grain growth, achieving a relative density of over 99.9%. This invention also utilizes a continuous two-stage annealing process: first, an air atmosphere removes surface carbon contamination, then an inert atmosphere repairs bulk oxygen vacancies and optimizes Pr³. + / Ce³ + The luminescent center addresses the issue of incomplete repair of defects inherent in single-stage annealing. It is the first to clearly demonstrate that excessive pressure exacerbates carbon contamination, and an optimal pressure combination of 45 MPa / 180 MPa is proposed to avoid over-carburization.

[0101] The GOS scintillation ceramic prepared by this invention exhibits significantly superior light output (35820 ph / MeV) compared to existing technologies and comparative examples, with extremely low afterglow (<0.01%), meeting the stringent requirements of high-resolution, low-dose imaging for detectors in medical CT, industrial CT, and security inspection equipment. This process can stably produce large-size (Φ≥50 mm) ceramic sheets, demonstrating good batch consistency and promising industrialization prospects.

[0102] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing gadolinium oxide scintillation ceramic, characterized in that, Includes the following steps: Step 1: Prepare precursor powder containing gadolinium oxysulfide matrix powder; Step 2: Add the precursor powder into the mold and perform segmented pressure sintering in an inert atmosphere: First, heat to 800-950 ℃ under a pressure of 10-20 MPa, then continue to heat to 1000-1150 ℃. During the heating process, gradually increase the pressure to 30-50 MPa, then maintain the pressure and continue to heat to 1400-1650 ℃, and hold at the temperature and pressure for 10-24 hours to obtain a pre-densified sintered body; Then, the pre-densified sintered body is subjected to hot isostatic pressing sintering in an inert atmosphere at a temperature of 1300-1500 ℃ and a pressure of 150-200 MPa for a holding time of 1-5 hours to obtain a fully dense ceramic body. Step 3: Place the fully dense ceramic body in an atmosphere-controlled annealing furnace; in air, perform the first stage of heat treatment at a temperature of 800-1000 ℃ for 12-30 hours; then switch to an inert atmosphere and raise the temperature from the first stage heat treatment temperature to 1000-1250 ℃ for the second stage heat treatment for 20-40 hours, and then cool to room temperature to obtain gadolinium oxide scintillation ceramic.

2. The method for preparing gadolinium oxysulfide scintillation ceramic according to claim 1, characterized in that, In step one: The gadolinium oxysulfide matrix powder is mixed uniformly with praseodymium source, cerium source and fluorine source to obtain precursor powder; The particle size D of the gadolinium sulfide matrix powder 50 2-6 μm; The praseodymium source is Pr6O. 11 The cerium source is Ce2(CO3)3 and / or CeO2, and the fluorine source is LiF and / or Li2GeF6; The molar ratio of Pr to Ce is 1:(2-5), the total doping amount of Pr and Ce is 0.1-1.0 mol%, and the doping amount of F is 0.05-0.2 wt%. Preferably, the particle size D of the gadolinium oxysulfate matrix powder is... 50 3-5 μm The molar ratio of Pr to Ce is 1:(3-4); the total doping amount of Pr and Ce is 0.3-0.8 mol%, and the doping amount of F is preferably 0.08-0.15 wt%.

3. The method for preparing gadolinium oxysulfide scintillation ceramic according to claim 1, characterized in that, In step one, the gadolinium oxysulfide matrix powder is mixed with praseodymium source, cerium source, fluorine source and solvent, and then wet ball milled for 12-24 hours at a ball-to-material ratio of (2-5):1 at a speed of 200-400 rpm to obtain a mixed slurry; the mixed slurry is then dried at 80-120℃ for 12-24 hours to obtain a dried powder. The dried powder is passed through a 100-300 mesh sieve to obtain the precursor powder; Preferably, the wet ball milling mixing time is 16-24 hours.

4. The method for preparing gadolinium oxysulfide scintillation ceramic according to claim 1, characterized in that, Step two sintering treatment includes: the holding temperature of hot isostatic pressing sintering is 50-150 ℃ lower than the holding temperature of segmented pressure sintering; Preferably, in step two, the temperature is first raised to 900 ℃ under a pressure of 10-20 MPa, and then raised to 1100 ℃. During the heating process, the pressure is gradually increased to 40-45 MPa, and then the pressure is maintained and the temperature is raised to 1550-1600 ℃. The temperature and pressure are maintained for 15-18 hours to obtain a pre-densified sintered body. The pre-densified sintered body is then subjected to hot isostatic pressing in an inert atmosphere at a temperature of 1400-1450 ℃ and a pressure of 175-185 MPa for 2-3 hours to obtain a fully dense ceramic body.

5. The method for preparing gadolinium oxysulfide scintillation ceramic according to claim 1, characterized in that, In step three, the temperature is first kept at 800-950 ℃ for 18-24 hours; then the atmosphere is switched to inert and the temperature is raised to 1050-1200 ℃, kept at that temperature for 20-35 hours, and then cooled to room temperature.

6. The method for preparing gadolinium oxysulfide scintillation ceramic according to claim 1, characterized in that, In step three, the heating rate in the air atmosphere is 2-5 ℃ / min; In step three, the heating rate in the inert atmosphere is 3-8 ℃ / min; In step three, the annealing process starts from the highest temperature and cools down at a rate of 0.3-2 ℃ / min, down to 400-600 ℃, and then naturally cools down to room temperature with the furnace. Preferably, the heating rate in the air atmosphere in step three is 3-4 °C / min; In step three, the heating rate in the inert atmosphere is 4-6 ℃ / min; In step three, the annealing process starts from the highest temperature and cools down at a rate of 0.5-1.5 ℃ / min, down to 400-600 ℃, and then naturally cools down to room temperature with the furnace.

7. The method for preparing gadolinium oxysulfide scintillation ceramic according to claim 1, characterized in that, It also includes step four: grinding and polishing the gadolinium oxide scintillation ceramic; The thickness tolerance of the processed ceramic sheet is ±0.02 mm, and the surface roughness Ra ≤ 0.1 μm.

8. A high-performance gadolinium oxide scintillation ceramic, characterized in that, Prepared by the method described in any one of claims 1-7.

9. The high-performance gadolinium oxysulfide scintillation ceramic according to claim 8, characterized in that, It has the following performance indicators: Relative density ≥ 99.9%; Optical output >30000 ph / MeV; Afterglow (@20ms) < 0.01%; Carbon content less than 0.018 wt% Preferably, the high-performance gadolinium oxysulfide scintillation ceramic has a relative density ≥ 99.95%; Carbon content less than 0.010 wt% Optical output >35820 ph / MeV; Its appearance ranges from light yellow to yellow and semi-transparent.

10. The high-performance gadolinium oxysulfide scintillation ceramic according to claim 8, characterized in that, The ceramic is a sheet-like structure with a diameter of not less than 50 mm.

11. The application of high-performance gadolinium oxysulfide scintillation ceramics according to any one of claims 8 to 10 in detectors of medical CT, industrial CT, or security inspection equipment.

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