SiO2-Nd2Ce2O7 glass ceramic material and preparation method thereof

Abstract

The invention belongs to the technical field of ceramic low-temperature sintering, and particularly relates to a SiO2-Nd2Ce2O7 glass ceramic material and a preparation method thereof. The invention provides a glass ceramic material, which is prepared from the following components in parts by weight: 30 to 40 parts of SiO2 and 60 to 70 parts of Nd2Ce2O7, wherein SiO2 comprises powder with the diameter of 15 nm or microspheres with the diameter of 80 nm. The preparation method comprises the following steps: firstly, preparing Nd2Ce2O7 powder by adopting a precipitation method, then uniformly mixing the Nd2Ce2O7 powder with SiO2 powder or microspheres by adopting a ball milling method, and carrying out cold sintering to obtain the SiO2-Nd2Ce2O7 glass ceramic solidified body. Compared with a traditional method for preparing the ceramic solidified body at high temperature, the method has the advantages that the preparation temperature is reduced, the preparation time is greatly shortened, the heat treatment temperature is reduced, and the volatilization amount of volatile nuclide and energy consumption can be effectively reduced. The SiO2-Nd2Ce2O7 glass ceramic solidified body prepared by the method is high in relative density, and the method is suitable for popularization.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature sintering technology of ceramics, specifically relating to a low-temperature preparation method of SiO2-Nd2Ce2O7 glass ceramics. Background Art

[0002] In the field of nuclear waste solidification, borosilicate glass waste has achieved commercial application due to its good chemical stability, becoming one of the important materials for nuclear waste solidification. However, the current manufacturing process of borosilicate glass waste still faces significant technical challenges. In traditional preparation processes, the manufacturing temperature is usually maintained in the high-temperature range of 1100 to 1400℃. This high-temperature environment not only brings about high energy consumption problems, but also poses serious nuclear safety hazards—during the high-temperature production of nuclear waste, various volatile nuclides (such as iodine, cesium, and molybdenum) are prone to leakage. Relevant research data show that the fission product cesium (Cs) will significantly volatilize in the form of solid aerosol at 1000℃; when iodine (I)-containing waste is heat-treated at 750℃, the volatilization of iodine exceeds 50%; and in the form of synthetic rock waste sintered at 1237℃, there is a 7.8% volatilization loss. This risk of radionuclide release during the high-temperature preparation process, and the resulting high energy consumption problem, has become a key bottleneck restricting the development of traditional nuclear waste solidification technology.

[0003] To address the inherent drawbacks of high-temperature sintering, cold sintering (CSP) has emerged as an innovative consolidation technology. This technology achieves ceramic sintering at temperatures as low as 300°C under uniaxial pressure by partially dissolving ceramic components in a solvent to form a temporary liquid phase. This improves energy efficiency while effectively avoiding the potential release of volatile nuclides at high temperatures. Its basic principle is similar to liquid-phase sintering, utilizing solvents such as water to saturate the sintered powder, creating a viscous phase at the interface to promote the dissolution-precipitation mechanism. However, in practical applications, the solubility of most radioactive waste solidification matrix materials (such as neodymium cerate) is significantly limited, making it difficult to obtain dense, solidified ceramic bodies with excellent leaching resistance through cold sintering. This technological limitation greatly restricts the application of cold sintering in the field of nuclear waste solidification.

[0004] Therefore, there is an urgent need for a new glass-ceramic preparation technology that can solve the problems of easy volatilization, high energy consumption and long preparation time of volatile radionuclide waste in traditional high-temperature preparation, and break through the solubility limitations of waste solidification matrix materials, so as to achieve safe, efficient and low-consumption solidification treatment of nuclear waste. Summary of the Invention

[0005] In view of this, the present invention provides a SiO2-Nd2Ce2O7 glass ceramic and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first technical objective of this invention is to provide a method for preparing SiO2-Nd2Ce2O7 glass-ceramic materials, comprising the following steps:

[0008] Step 1: Weigh Nd(NO3)3·6H2O and Ce(NO3)·6H2O, dissolve them in 1L of deionized water and stir to obtain mixture I;

[0009] Step 2: Measure a certain amount of ammonia water and deionized water, stir and mix to obtain mixture II;

[0010] Step 3: Add the mixture I obtained in Step 1 to the mixture II obtained in Step 2 using a peristaltic pump. After mixing is complete, stop stirring and age at room temperature (25°C) for 48 hours to obtain mixture III.

[0011] Step 4: Use a centrifuge to separate mixture III to obtain precipitate IV, wash it with deionized water and alcohol, then mix it with alcohol and put it into a reaction vessel with a polytetrafluoroethylene inner liner. Place it in an oven to react and obtain mixture V.

[0012] Step 5: Place mixture V in an 85℃ oven to dry for 12 hours. Then grind the dried sample and place it in a crucible. Calcine it in a muffle furnace to obtain Nd2Ce2O7 powder. The calcination conditions are: heating from room temperature (25℃) to 800℃ at a heating rate of 5℃ / min under air atmosphere, holding at that temperature for 6 hours, and then naturally cooling to room temperature.

[0013] Step 6: Add the neodymium cerate (Nd2Ce2O7) nanopowder obtained in step 5 and SiO2 nanopowder / SiO2 nanospheres to a liquid for treatment to make them mix evenly, so as to obtain SiO2-Nd2Ce2O7 mixed nanopowder.

[0014] Step 7: Mix the SiO2-Nd2Ce2O7 mixed nanopowder obtained in Step 6 with sodium hydroxide (NaOH) solution, and prepare the SiO2-Nd2Ce2O7 glass-ceramic solidified body through a cold sintering process, namely the SiO2-Nd2Ce2O7 glass-ceramic material.

[0015] Preferably, in step 1, the molar ratio of Nd(NO3)3·6H2O to Ce(NO3)4·6H2O is 1:1, and the ion concentrations of Nd and Ce are both 0.1-0.3 mol / L.

[0016] Preferably, in step 2, the volume ratio of ammonia water to deionized water is 1:4, so that the ammonia concentration in mixture II is 2.6-2.9 mol / L and the volume of mixture II is 1.25L.

[0017] Preferably, the reaction conditions in step 4 are: 200℃, 24h.

[0018] Preferably, the volume ratio of the two mixtures in step 3 is mixture I: mixture II = 1:1.25.

[0019] Preferably, in step 6, the SiO2 mass percentage in the SiO2-Nd2Ce2O7 mixed nanopowder is 30-40 wt%; the mixed powder is ball-milled to achieve uniform dispersion; and the liquid in step 6 is anhydrous ethanol.

[0020] Preferably, in step 7, the concentration of the sodium hydroxide (NaOH) solution is 3-5 mol / L, and the mass of the sodium hydroxide (NaOH) solution is 20-40% of the sum of the masses of the sodium hydroxide (NaOH) solution and the mixed powder.

[0021] Preferably, the cold sintering conditions are 250-350℃, 600-750MPa, holding time of 0.5h, and air atmosphere.

[0022] The second technical objective of this invention is to provide a SiO2-Nd2Ce2O7 glass-ceramic material prepared by the method described above.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) This invention first prepares Nd2Ce2O7 powder with small and uniform particle size by precipitation method, mixes it with SiO2 to obtain SiO2-Nd2Ce2O7 mixed powder, and prepares SiO2-Nd2Ce2O7 glass ceramic solidified body by cold sintering. Compared with the traditional high temperature sintering preparation method, the preparation time is shortened.

[0025] 2) Cold sintering is a low-temperature, pressure-assisted consolidation process that can synthesize dense bulk materials at lower temperatures, thereby reducing the heat treatment temperature and effectively reducing the volatilization of volatile nuclides and energy consumption. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 The XRD pattern is that of the Nd2Ce2O7 powder prepared in Examples 1 and 2.

[0028] Figure 2 This is a cross-sectional SEM image of the SiO2-Nd2Ce2O7 glass-ceramic solidified body prepared in Example 1.

[0029] Figure 3 This is an EDS elemental distribution diagram of the cross section of the SiO2-Nd2Ce2O7 glass-ceramic solidified body prepared in Example 1.

[0030] Figure 4 This is a TEM image of the cross-section of the SiO2-Nd2Ce2O7 glass-ceramic solidified body prepared in Example 2.

[0031] Figure 5 This is an EELS elemental distribution diagram of the cross section of the SiO2-Nd2Ce2O7 glass-ceramic solidified body prepared in Example 2. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0034] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0035] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0036] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0037] This invention discloses a low-temperature preparation method for SiO2-Nd2Ce2O7 glass-ceramic materials.

[0038] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0039] Example 1

[0040] In this embodiment, the method for preparing the SiO2-Nd2Ce2O7 glass-ceramic solidified body is as follows:

[0041] (1) Nd2Ce2O7 powder synthesis

[0042] Weigh 13.15g of Nd(NO3)3·6H2O powder with a purity of 99.99% and 13.05g of Ce(NO3)4·6H2O powder with a purity of 99.99% as raw materials. Dissolve the above raw materials in 1L of deionized water and stir to dissolve. Add the solution dropwise to an ammonia solution obtained by mixing 250ml of ammonia water and 1L of deionized water using a peristaltic pump. Stir continuously during the dropwise addition process. Stop stirring when the dropwise addition is completed and let the suspension stand for 48h.

[0043] The suspension was separated into precipitate and supernatant using a centrifuge. The precipitate was washed with deionized water and alcohol, then mixed with alcohol and placed in a reaction vessel with a polytetrafluoroethylene inner liner. The mixture was placed in a 200°C oven for 24 hours. After the reaction was completed, the suspension was removed and dried in an 85°C oven. The dried powder was then filled into an alumina crucible and transferred to a muffle furnace. The furnace was heated to 800°C at a heating rate of 5°C / min and held for 4 hours to perform calcination heat treatment on the powder.

[0044] After the heat preservation is completed, the powder is naturally cooled to room temperature to complete the preparation of Nd2Ce2O7 powder.

[0045] (2) Preparation of SiO2-Nd2Ce2O7 mixed powder

[0046] Weigh 4g of SiO2 nanoparticles and 6g of Nd2Ce2O7 powder and add them to a nylon ball mill jar. Then add 300ml of anhydrous ethanol and an agate ball milling tool. Mix the mixture by mechanical ball milling at 300 rads for 8 hours. Transfer the mixed suspension to a forced-air drying oven and keep it at 100℃ for 24 hours to obtain a dry mixed powder.

[0047] (3) Preparation of SiO2-Nd2Ce2O7 glass-ceramic solidified body

[0048] 1.2g of SiO2-Nd2Ce2O7 mixed powder and 0.8g of 3mol / L NaOH solution were placed in an agate mortar and ground to obtain a mixed powder. 1.5g of the mixed powder was weighed and placed in a cold sintering mold for sintering preparation. The cold sintering preparation conditions were: 300℃, 750MPa, holding time 30min, and air atmosphere.

[0049] The XRD pattern of the Nd2Ce2O7 powder prepared in this embodiment is as follows: Figure 1 As shown, it matches the standard PDF card, confirming that the prepared powder is a pure phase; Figure 2 and Figure 3 The images shown are SEM and EDS images of the cross-section of the SiO2-Nd2Ce2O7 glass-ceramic solidified body in this embodiment. The Nd2Ce2O7 particles are distributed in the continuous SiO2 phase, and there are only a few micropores on the surface, which confirms that the prepared ceramic solidified body is dense.

[0050] Example 2

[0051] In this embodiment, the method for preparing the SiO2-Nd2Ce2O7 glass-ceramic solidified body is as follows:

[0052] (1) Nd2Ce2O7 powder synthesis

[0053] Weigh 13.15g of Nd(NO3)3·6H2O powder with a purity of 99.99% and 13.05g of Ce(NO3)4·6H2O powder with a purity of 99.99% as raw materials. Dissolve the above raw materials in 1L of deionized water and stir to dissolve. Add the solution dropwise to an ammonia solution obtained by mixing 250ml of ammonia water and 1L of deionized water using a peristaltic pump. Stir continuously during the dropwise addition process. Stop stirring when the dropwise addition is completed and let the suspension stand for 48h.

[0054] The suspension was separated into precipitate and supernatant using a centrifuge. The precipitate was washed with deionized water and alcohol, then mixed with alcohol and placed in a reaction vessel with a polytetrafluoroethylene inner liner. The mixture was placed in a 200°C oven for 24 hours. After the reaction was completed, the suspension was removed and dried in an 85°C oven. The dried powder was then filled into an alumina crucible and transferred to a muffle furnace. The furnace was heated to 800°C at a heating rate of 5°C / min and held for 4 hours to perform calcination heat treatment on the powder.

[0055] After the heat preservation is completed, the powder is naturally cooled to room temperature to complete the preparation of Nd2Ce2O7 powder.

[0056] (2) Preparation of SiO2-Nd2Ce2O7 mixed powder

[0057] Weigh 4g of SiO2 nanospheres (diameter ~80nm) and 6g of Nd2Ce2O7 powder and add them to a nylon ball mill jar. Then add 300ml of anhydrous ethanol and an agate ball milling tool and mechanically ball mill at 300 rads for 8 hours to mix. Transfer the mixed suspension to a forced-air drying oven and keep it at 100℃ for 24 hours to obtain a dry mixed powder.

[0058] (3) Preparation of SiO2-Nd2Ce2O7 glass-ceramic solidified body

[0059] 1.2g of SiO2-Nd2Ce2O7 mixed powder and 0.8g of 3mol / L NaOH solution were placed in an agate mortar and ground to obtain a mixed powder. 1.5g of the mixed powder was weighed and placed in a cold sintering mold for sintering preparation. The cold sintering preparation conditions were: 300℃, 750MPa, holding time 30min, and air atmosphere.

[0060] The XRD pattern of the Nd2Ce2O7 powder prepared in this embodiment is as follows: Figure 1 As shown, it matches the standard PDF card, confirming that the prepared powder is a pure phase; Figure 3 and Figure 4 The images shown are TEM and EELS images of the cross-section of the SiO2-Nd2Ce2O7 glass-ceramic solidified body in this embodiment. The TEM image confirms that the black particles (Nd2Ce2O7 particles) are uniformly distributed in the white SiO2 continuous phase. The EELS image further confirms that the black particles are Nd2Ce2O7 particles and the white continuous phase is SiO2.

[0061] To further demonstrate the beneficial effects of the present invention and to better understand it, the technical features disclosed in the present invention are further illustrated by the following comparative examples, but these should not be construed as limiting the present invention. Other improvements made by those skilled in the art based on the above description of the invention, without inventive effort, are also considered to fall within the protection scope of the present invention.

[0062] Comparative Example 1

[0063] In this embodiment, the method for preparing the Nd2Ce2O7 ceramic solidified body is as follows:

[0064] (1) Nd2Ce2O7 powder synthesis

[0065] Weigh 13.15g of Nd(NO3)3·6H2O powder with a purity of 99.99% and 13.05g of Ce(NO3)4·6H2O powder with a purity of 99.99% as raw materials. Dissolve the above raw materials in 1L of deionized water and stir to dissolve. Add the solution dropwise to an ammonia solution obtained by mixing 250ml of ammonia water and 1L of deionized water using a peristaltic pump. Stir continuously during the dropwise addition process. Stop stirring when the dropwise addition is completed and let the suspension stand for 48h.

[0066] The suspension was separated into precipitate and supernatant using a centrifuge. The precipitate was washed with deionized water and alcohol, then mixed with alcohol and placed in a reaction vessel with a polytetrafluoroethylene inner liner. The mixture was placed in a 200°C oven for 24 hours. After the reaction was completed, the suspension was removed and dried in an 85°C oven. The dried powder was then filled into an alumina crucible and transferred to a muffle furnace. The furnace was heated to 800°C at a heating rate of 5°C / min and held for 4 hours to perform calcination heat treatment on the powder.

[0067] After the heat preservation is completed, the powder is naturally cooled to room temperature to complete the preparation of Nd2Ce2O7 powder.

[0068] (2) Preparation of cold sintered Nd2Ce2O7 ceramic samples

[0069] 1.2g of Nd2Ce2O7 powder and 0.8g of 3mol / L NaOH solution were placed in an agate mortar and ground to obtain a mixed powder. 1.5g of the mixed powder was weighed and placed in a cold sintering mold for sintering preparation. The cold sintering preparation conditions were: 300℃, 750MPa, holding time 30min, and air atmosphere.

[0070] The sample prepared in this embodiment exhibits extremely poor solubility in sodium hydroxide solution due to the inherent chemical properties of the Nd₂Ce₂O₇ powder, failing to achieve an effective dissolution-precipitation mechanism for particle bonding through the solution medium. During sintering, the powder particles primarily rely on externally applied high pressure to generate mechanical forces for physical bonding, lacking the support of chemical bonding forces. This bonding method results in numerous pores and a loose structure within the sample, ultimately exhibiting a low density and failing to achieve the desired sintering densification effect.

[0071] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a SiO2-Nd2Ce2O7 glass-ceramic material, characterized in that, The following steps are involved: Step 1) Weigh Nd(NO3)3·6H2O and Ce(NO3)4·6H2O, dissolve them in deionized water and stir to obtain mixture I; Step 2) Measure a certain amount of ammonia water and deionized water and stir to obtain mixture II; Step 3) Add the mixture I obtained in step 1) to the mixture II obtained in step 2). Stop stirring after mixing and let it age to obtain mixture III. Step 4) Separate mixture III to obtain precipitate IV, wash it with deionized water and alcohol, then mix it with alcohol and put it into a reaction vessel with a polytetrafluoroethylene inner liner. Place it in an oven to react and obtain mixture V. Step 5) Dry the mixture V, then grind the dried sample and calcine it to obtain Nd2Ce2O7 powder; Step 6) Add the Nd2Ce2O7 nanopowder obtained in step 5) and SiO2 nanopowder or nanospheres to a liquid for treatment to make them mix evenly, so as to obtain SiO2-Nd2Ce2O7 mixed nanopowder. Step 7) The SiO2-Nd2Ce2O7 mixed nanopowder obtained in step 6) is mixed with sodium hydroxide solution, and SiO2-Nd2Ce2O7 glass ceramic solidified body is prepared by cold sintering process, that is, the SiO2-Nd2Ce2O7 glass ceramic material.

2. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of Nd(NO3)3·6H2O to Ce(NO3)4·6H2O is 1:1, and the ion concentrations of Nd and Ce are both 0.1-0.3 mol / L.

3. The preparation method according to claim 1, characterized in that, In step 2), the volume ratio of ammonia water to deionized water is 1:4, so that the ammonia concentration in mixture II is 2.6-2.9 mol / L.

4. The preparation method according to claim 1, characterized in that, In step 3), the volume ratio of the two mixtures is mixture I: mixture II = 1:1.

25.

5. The preparation method according to claim 1, characterized in that, In step 3), the aging time is 48 h and the aging temperature is 25 ℃.

6. The preparation method according to claim 1, characterized in that, In step 4), the reaction temperature is 200 °C and the reaction time is 24 h.

7. The preparation method according to claim 1, characterized in that, In step 5), the drying temperature is 85℃ and the drying time is 12 h; the calcination conditions are: heating from room temperature (25℃) to 800℃ in an air atmosphere at a heating rate of 5℃ / min, holding at that temperature for 6 h, and then naturally cooling to room temperature.

8. The preparation method according to claim 1, characterized in that, In step 6), the mass percentage of SiO2 in the SiO2-Nd2Ce2O7 mixed nanopowder is 30-40%; the liquid in step 6 is anhydrous ethanol.

9. The preparation method according to claim 1, characterized in that, In step 7), the concentration of the sodium hydroxide solution is 3-5 mol / L, and the mass of the sodium hydroxide solution is 20-40% of the sum of the mass of the sodium hydroxide solution and the mass of the mixed nanopowder.

10. The preparation method according to claim 1 or 9, characterized in that, The cold sintering conditions are 250-350 ℃, 600-750 MPa, holding time of 0.5 h, and air atmosphere.

11. A SiO2-Nd2Ce2O7 glass-ceramic material prepared by the method described in claim 1.

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