Yttrium lutetium silicate precursor as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of crystal materials, and discloses a lutetium yttrium silicate precursor and a preparation method and application thereof. The preparation method of the yttrium lutetium silicate precursor comprises the following steps: preparing a sodium silicate solution; adding lutetium chloride, yttrium chloride and cerium chloride into deionized water to form a mixed solution, then adding the sodium silicate solution, and stirring for 3-8 minutes to obtain a mixed material liquid; mixing the mixed material liquid with a precipitant, carrying out precipitation treatment, stirring for 5-15 minutes, carrying out suction filtration, and washing with deionized water until the pH value is 7-8, so as to obtain a precipitate; and burning the precipitate to obtain the catalyst. The yttrium lutetium silicate precursor produced by the invention is used for crystal growth, the obtained crystal bar is free of miscellaneous agglomerate fog cracking and the like, the uniformity is better, the light output of the crystal is better, and the resolution ratio is better.

Description

Technical Field

[0001] The present application belongs to the technical field of crystal materials and relates to a yttrium-lutetium silicate precursor and a preparation method and application thereof. Background Art

[0002] PET (Positron Emission Tomography, PET for short) detector is the most core and expensive component of PET / CT. Its structure and technology will directly determine the working mode of the PET data acquisition system, the key performance indicators of the whole machine and other important factors. A typical PET detector includes scintillation crystals, photoelectric conversion devices and front-end electronics. Scintillation crystals are one of the key components in PET detectors and the most important component that determines the quality grade of PET. At present, the scintillation crystals used in PET equipment mainly include: slow scintillation crystals-bismuth germanate (BGO), fast scintillation crystals-lutetium silicate (LSO) and lutetium yttrium silicate (LYSO). Among them, fast scintillation crystals (LSO and LYSO) have shorter luminescence decay time and can provide higher time resolution in high-energy particle detection, so they are favored by researchers.

[0003] LYSO crystal is a rare earth orthosilicate crystal with a monoclinic system. It has attracted great attention from the international scintillation crystal community for its high light output, fast luminescence decay, large effective atomic number, and high density. It has stable physical and chemical properties, is non-deliquescent, and has high gamma ray detection efficiency. It is considered to be the inorganic scintillation crystal material with the best comprehensive performance. The transmittance of LYSO crystal in the range of 400-800nm ​​reaches 83%, which can ensure that the generated scintillation light is absorbed by itself to a minimum. LYSO crystal is a crystal material commonly used in the new generation of all-digital PET because it can provide excellent time resolution and energy resolution.

[0004] At present, the main method for growing LYSO crystals is the Czochralski method. The Czochralski method is to heat and melt the raw materials of rare earth oxides that constitute the crystals, connect seed crystals to the surface of the melt and pull the melt. Under controlled conditions, the atoms or molecules of the seed crystals and the melt are continuously rearranged at the interface, and the single crystals are grown as the temperature drops and the crystals gradually solidify. However, this growth method has the following three main defects. First, during the crystal growth process, impurities including crucible materials will cause the quality of the crystals to decline, and even produce afterglow problems; second, the volatilization of components will not only cause changes in the composition of the melt, but also may cause changes in the temperature gradient and concentration gradient in the melt. These changes may have an adverse effect on the growth rate and growth quality of the crystal, resulting in unevenness or defects inside the crystal; third, the melting point of rare earth oxides is relatively high, basically above 2000°C, so the requirements for production equipment (high temperature stability) and growth conditions (such as temperature, pulling speed, rotation speed, etc.) are relatively high.

[0005] Therefore, it is relatively difficult to grow high-quality defect-free yttrium lutetium silicate crystals using the existing Czochralski process. Some researchers have proposed using the hydrothermal method to prepare high-quality defect-free yttrium lutetium silicate precursor materials, and then further treat them by other methods (such as hot pressing sintering, recrystallization or Czochralski method, etc.) to grow the required LYSO crystals. The current hydrothermal method uses lutetium nitrate, yttrium nitrate, and cerium nitrate as raw materials, and urea as a precipitant to prepare high-quality yttrium lutetium silicate precursors under hydrothermal conditions. However, the raw materials for the hydrothermal method are a nitric acid system composed of nitrates, and urea is used as a precipitant, which is easy to produce ammonium nitrate, and ammonium nitrate is an explosive raw material. Therefore, the preparation method has extremely high requirements for control during the process, and the hydrothermal method needs to be completed under high temperature and high pressure conditions, with a high risk factor and a long reaction time. In addition, the use of urea as a precipitant will also produce a large amount of wastewater containing ammonia nitrogen, which will greatly increase the cost of water treatment.

[0006] Therefore, how to provide a process that is simple in preparation, environmentally friendly and safe, and can produce high-quality yttrium lutetium silicate precursor materials is a problem that needs to be solved urgently. Summary of the invention

[0007] In order to overcome the above technical problems, the present application provides a yttrium lutetium silicate precursor and a preparation method and application thereof.

[0008] In the first aspect, the present application provides a method for preparing a yttrium-lutetium silicate precursor, using the following technical solution: A method for preparing a yttrium-lutetium silicate precursor comprises the following steps: Step S1: preparing a sodium silicate solution; Step S2: adding lutetium chloride, yttrium chloride and cerium chloride into deionized water to form a mixed solution, then adding the sodium silicate solution and stirring for 3-8 minutes to obtain a mixed solution; Step S3: mixing the mixed liquid with a precipitant for precipitation treatment, stirring for 5-15 minutes, filtering, and washing with deionized water until the pH value is 7-8 to obtain a precipitate; Step S4: calcining the precipitate to obtain a yttrium-lutetium silicate precursor.

[0009] The present application adopts chloride of rare earth elements as a preparation raw material to react with sodium silicate to form silicate ions containing rare earth elements, and then uses a precipitant to precipitate the rare earth silicate ions into a precipitate, and finally obtains a high-quality yttrium-lutetium silicate precursor material free of impurities and defects through a calcination treatment.

[0010] In the above reaction process, there is no volatilization of components, so the amount of rare earth chloride can be directly determined by the rare earth element ratio in the target product yttrium lutetium silicate precursor. These rare earth elements can be 100% transferred to the final yttrium lutetium silicate precursor; and no impurities in any container or environment will be introduced during the entire reaction process, so the quality of the product can be greatly improved.

[0011] Compared with the existing hydrothermal process, the present application does not use nitrates of rare earth elements as raw materials, so there is no risk of producing explosives, and no wastewater containing ammonia nitrogen will be produced, so the environmental protection and safety problems existing in the prior art are solved; and the present application is different from the existing hydrothermal method for preparing yttrium lutetium silicate precursor, and does not require high temperature and high pressure. The reaction can be promoted only by sufficient stirring treatment, so the control requirements during the reaction are low, the process is simple and easy to control, and provides a basis for realizing large-scale production of high-quality yttrium lutetium silicate.

[0012] Optionally, the specific steps of step S1 are as follows: dissolving silicon dioxide and sodium hydroxide in deionized water, heating and stirring at a heating temperature of 80-100° C. until the solution is transparent and clear, and adjusting the pH value to 7-8 to obtain the sodium silicate solution.

[0013] More preferably, the heating temperature is 85-95°C, 90°C.

[0014] Optionally, the molar ratio of the silicon dioxide to the sodium hydroxide is 1:2.

[0015] The present invention provides a silicon source for yttrium lutetium silicate by reacting silicon dioxide with sodium hydroxide, thereby obtaining a pure sodium silicate solution free of impurities, and providing a basis for preparing a high-quality yttrium lutetium silicate precursor.

[0016] Optionally, in step S2, the molar ratio of the lutetium chloride, the yttrium chloride and the cerium chloride is (1-xy): x:y, wherein 0.09≤x≤0.2, 0.001≤y≤0.005.

[0017] Optionally, in step S2, the sum of the molar amounts of the lutetium chloride, the yttrium chloride and the cerium chloride is twice that of silicon dioxide.

[0018] In the preparation process of yttrium lutetium silicate precursor, the amount of rare earth chloride and silicon dioxide used in lutetium chloride, yttrium chloride and cerium chloride is determined according to the proportion of rare earth elements and silicon elements in the target product. Since there is no volatilization of components in the preparation process, the rare earth element content in yttrium lutetium silicate can be accurately controlled, thereby avoiding crystal defects caused by component volatilization.

[0019] Optionally, the precipitant is selected from any one of oxalic acid, ammonia water, sodium carbonate and urea.

[0020] The present application can precipitate rare earth silicate ions into precipitates through the above-listed precipitants, thereby transferring rare earth elements into the precipitates, thereby forming the required crystals containing lutetium, yttrium, cerium and silicon elements, and the above-listed precipitants will not bring impurity elements, and the only carbon, hydrogen and nitrogen will also be converted into gas phase components in the subsequent burning treatment. Moreover, when oxalic acid and sodium carbonate are used as precipitants, since the entire system does not contain any nitrogen elements, the obtained product is very pure and does not produce wastewater containing ammonia nitrogen, which is environmentally friendly and cost-saving.

[0021] Optionally, in step S3, the amount of the precipitant is 1.2-1.5 times the total molar amount of the lutetium chloride, the yttrium chloride, and the cerium chloride; Further preferably, the amount of the precipitant used is 1.4 times the total molar amount of the lutetium chloride, the yttrium chloride and the cerium chloride.

[0022] By limiting the amount of the precipitant as above, it is possible to ensure that the rare earth elements react fully and are completely converted into precipitates, thereby avoiding crystal defects caused by the lack of rare earth components.

[0023] Optionally, the calcination treatment is carried out at a temperature of 950-960° C. and for a time of 3-5 hours.

[0024] By adopting the high temperature calcination treatment under the above conditions, the amorphous phase or metastable phase in the precipitate can be transformed into a more stable and ordered crystalline phase, and the orderliness of the atomic or ionic arrangement inside the crystal can be enhanced, thereby improving the crystallinity. In addition, the calcination treatment can also fully remove organic matter, moisture and other volatile impurities in the yttrium lutetium silicate precursor.

[0025] In a second aspect, the present application also provides a yttrium lutetium silicate precursor prepared by the aforementioned preparation method.

[0026] The ratio of rare earth elements and silicon elements in the yttrium lutetium silicate precursor of the present application is precisely controllable and has a low defect rate.

[0027] The yttrium lutetium silicate precursor particles provided in the present application are evenly distributed without agglomeration.

[0028] In a third aspect, the present application also provides an application of a yttrium lutetium silicate precursor, specifically an application of the yttrium lutetium silicate precursor in the production of yttrium lutetium silicate crystals.

[0029] The yttrium lutetium silicate precursor of the present application has a low defect rate, and the rare earth element ratio is precisely controllable, which provides a basis for the production of high-quality defect-free yttrium lutetium silicate crystals. DETAILED DESCRIPTION

[0030] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present invention. The experimental methods in the following examples where specific conditions are not specified are usually performed under conventional conditions, conditions described in laboratory manuals, or conditions recommended by manufacturers.

[0031] Example 1 Embodiment 1 provides a yttrium-lutetium silicate precursor, and its preparation method comprises the following steps: Step S1: dissolving 1 mol of silicon dioxide and 2 mol of sodium hydroxide in 4 mol of deionized water, heating and stirring on a magnetic stirrer at 90° C. until the solution becomes transparent and clear, and adjusting the pH value to 7 with hydrochloric acid to obtain a sodium silicate solution; Step S2: adding 1.812 mol parts of lutetium chloride, 0.18 mol parts of yttrium chloride, and 0.008 mol parts of cerium chloride to 4 mol parts of deionized water to form a mixed solution, and then adding the sodium silicate solution prepared in step S1, stirring for 5 minutes, to obtain a mixed solution; Step S3: dissolving 2.8 mol of oxalic acid in deionized water, heating to 80° C. to completely dissolve the oxalic acid to obtain an oxalic acid solution, mixing the mixed liquid with the oxalic acid solution for precipitation treatment, stirring for 10 minutes, and then filtering and washing with deionized water until the pH value is 7 to obtain a precipitate; Step S4: calcining the precipitate at 950° C. for 4 hours to obtain the target product, yttrium lutetium silicate precursor.

[0032] Example 2 Example 2 is substantially the same as Example 1, except that the amounts of rare earth raw materials used in Example 2 are: 1.598 molar parts of lutetium chloride, 0.4 molar parts of yttrium chloride, and 0.002 molar parts of cerium chloride.

[0033] Example 3 Example 3 is substantially the same as Example 1, except that the amounts of rare earth raw materials used in Example 2 are: 1.79 molar parts of lutetium chloride, 0.2 molar parts of yttrium chloride, and 0.01 molar parts of cerium chloride.

[0034] Example 4 Example 4 is substantially the same as Example 1, except that an equimolar amount of sodium carbonate is used to replace oxalic acid in Example 4.

[0035] Example 5 Example 5 is substantially the same as Example 1, except that an equimolar amount of aqueous ammonia is used to replace the oxalic acid solution in Example 5.

[0036] Example 6 Example 6 is substantially the same as Example 1, except that an equal molar amount of urea is used to replace oxalic acid in Example 6.

[0037] Figure 1 The following is a SEM image of the yttrium-lutetium silicate precursor product prepared in Example 1, wherein the left image is a SEM image magnified 500 times, and the right image is a SEM image magnified 10,000 times. Figure 1 It can be seen that the yttrium lutetium silicate precursor product is in powder form, the powder particles are evenly distributed, and there is no agglomeration phenomenon.

[0038] Figure 2 This is the XRD pattern of the yttrium-lutetium silicate precursor product prepared in Example 1. Figure 1 It can be seen that the yttrium lutetium silicate precursor was successfully prepared using the preparation method of the present application.

[0039] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing a yttrium-lutetium silicate precursor, characterized in that: The following steps are involved: Step S1: preparing a sodium silicate solution; Step S2: adding lutetium chloride, yttrium chloride and cerium chloride into deionized water to form a mixed solution, then adding the sodium silicate solution and stirring for 3-8 minutes to obtain a mixed solution; Step S3: mixing the mixed liquid with a precipitant for precipitation treatment, stirring for 5-15 minutes, filtering, and washing with deionized water until the pH value is 7-8 to obtain a precipitate; Step S4: calcining the precipitate to obtain a yttrium-lutetium silicate precursor.

2. The method for preparing a yttrium-lutetium silicate precursor according to claim 1, characterized in that: The specific steps of step S1 are as follows: dissolving silicon dioxide and sodium hydroxide in deionized water, heating and stirring at a heating temperature of 80-100° C. until the solution is transparent and clear, and adjusting the pH value to 7-8 to obtain the sodium silicate solution.

3. The method for preparing a yttrium-lutetium silicate precursor according to claim 2, characterized in that: The molar ratio of the silicon dioxide to the sodium hydroxide is 1:

2.

4. The method for preparing a yttrium-lutetium silicate precursor according to claim 1, characterized in that: In the step S2, the molar ratio of the lutetium chloride, the yttrium chloride and the cerium chloride is (1-xy): x:y, wherein 0.09≤x≤0.2, 0.001≤y≤0.

005.

5. The method for preparing a yttrium-lutetium silicate precursor according to claim 1, characterized in that: In the step S2, the sum of the molar amounts of the lutetium chloride, the yttrium chloride and the cerium chloride is twice that of silicon dioxide.

6. The method for preparing a yttrium-lutetium silicate precursor according to claim 1, characterized in that: The precipitant is selected from any one of oxalic acid, ammonia water, sodium carbonate and urea.

7. The method for preparing a yttrium-lutetium silicate precursor according to claim 6, characterized in that: In the step S3, the amount of the precipitant is 1.2-1.5 times the total molar amount of the lutetium chloride, the yttrium chloride and the cerium chloride.

8. The method for preparing a yttrium-lutetium silicate precursor according to claim 1, characterized in that: The temperature of the calcination treatment is 950-960° C. and the time is 3-5 hours.

9. The yttrium lutetium silicate precursor prepared by the method for preparing the yttrium lutetium silicate precursor according to any one of claims 1 to 8.

10. Use of the yttrium lutetium silicate precursor according to claim 9 in producing yttrium lutetium silicate crystals.

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