High density fluorescent pyrochlore phase europium zirconate and method of making same

Abstract

The application discloses high-density fluorescent pyrochlore phase europium zirconate and a preparation method thereof. The preparation method comprises the following steps: mixing zirconium oxide powder and europium oxide powder, then performing first tabletting treatment, to obtain mixed powder first intermediate; performing first sintering treatment on the mixed powder first intermediate, to obtain europium zirconate second intermediate; performing second sintering treatment on the europium zirconate second intermediate, to obtain the high-density fluorescent pyrochlore phase europium zirconate; wherein the temperature of the first sintering treatment is 1400-1750 DEG C, and the pressure is 1-5 atm; the temperature of the second sintering treatment is 500-1600 DEG C, and the pressure is 3.5-8 GPa. Since the europium zirconate is prone to coexisting in two phases, the first sintering treatment (muffle furnace sintering) and the second sintering treatment (high-temperature and high-pressure sintering) are combined to directly synthesize more stable pyrochlore phase europium zirconate, so that the application directly synthesizes the target product by using the two sintering combination modes, and the generation of a transition phase is avoided.

Description

Technical Field

[0001] This invention relates to the field of functional ceramics technology, and in particular to a high-density fluorescent pyrochlore phase europium zirconate and its preparation method. Background Technology

[0002] Oxide ceramics with the chemical formula A2B2O7 (also known as pyrochlore structure ceramics) have a series of advantages such as low thermal conductivity, excellent ionic conductivity, high catalytic activity, high coefficient of thermal expansion, high melting point, unique cell structure, and low conduction temperature. Therefore, these ceramics are widely used in high-temperature thermal expansion coatings, solid fuel oxide battery electrolytes, catalysis in complex environments, and nuclide fixation.

[0003] In general, elements A and B in the above chemical formula are metallic elements (e.g., transition metals such as Zr and Y, or rare earth metals such as lanthanum and actinides). Well-sintered A₂Zr₂O₇ zirconate polycrystalline ceramics, with lanthanides and actinides as A and Zr as B, possess excellent light transmittance in addition to the advantages mentioned above. Therefore, research on this type of zirconate as an optical window is currently very extensive. The factors affecting the light transmittance of ceramic materials, besides the need for a transparent band gap, also require the sample to have low porosity and be free of other impurities. The specific mechanisms affecting light transmittance are detailed in the appendix. Figure 1 As shown.

[0004] In fact, the most significant factor affecting the light transmittance of this type of zirconate ceramic is the sample's density (i.e., the sample needs extremely low porosity to reduce light scattering by the pores and increase the intensity of emitted light); while for europium zirconate (Eu₂Zr₂O₇) ceramics, porosity also greatly affects various properties of the sample. Europium zirconate ceramics, as a rare-earth zirconate ceramic with a pyrochlore structure, have very wide applications in industry, such as as temperature detectors and photoluminescent elements (excited at a wavelength of 355 nm; the photoluminescence wavelength range of europium zirconate is between 575-725 nm, as shown in the attached figure). Figure 2 As shown. Due to its high melting point and stability, europium zirconate can be used as a temperature detector and photoluminescent element in relatively harsh environments. As an A₂B₂O₇ structured pyrochlore ceramic, europium zirconate needs to follow the Subramanian theory, meaning the ionic sizes of the A and B metal ions must conform to the following rules:

[0005] rA + / rB + <1.46 Formation of defective fluorite phase

[0006] 1.46 < rA + / rB + <1.78 Formation of pyrochlore phase

[0007] in and Europium zirconium has an ion size ratio of 1.48; due to its very close ratio of 1.46, it can undergo interconversion between defective fluorite and pyrochlore phases under certain conditions. This unique phase-transformation property results in low density (actual density / theoretical density) and high porosity in europium zirconium, limiting its widespread industrial application. For example, as a solid-state battery electrolyte, low-density materials have low ionic conductivity, reducing the battery's energy density; and as a photoluminescent material, low density results in fewer stimulated emission ions per unit volume, further limiting the luminous flux and reducing luminous efficiency. In recent years, many scientists have focused on improving the density of europium zirconium, but currently, even with complex processes, the highest density achievable is only 95.5%.

[0008] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the present invention provides a high-density fluorescent pyrochlore phase europium zirconate and its preparation method, aiming to solve the problem that europium zirconate is prone to two-phase transformation when using the existing preparation method, resulting in low density.

[0010] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0011] In a first aspect, the present invention provides a method for preparing europium zirconate with high density fluorescent pyrochlore phase, the method comprising the following steps:

[0012] Zirconia powder and europium oxide powder are mixed and then subjected to a first tableting process to obtain a first intermediate of mixed powder.

[0013] The first intermediate of the mixed powder is subjected to a first sintering treatment to obtain the second intermediate of europium zirconate;

[0014] The europium zirconate second intermediate is subjected to a second sintering treatment to obtain the high-density fluorescent pyrochlore phase europium zirconate;

[0015] The temperature of the first sintering treatment is 1400-1750℃, and the pressure is 1-5 atm.

[0016] The second sintering treatment is performed at a temperature of 500-1600℃ and a pressure of 3.5-8 GPa.

[0017] Preferably, the molar ratio of the zirconium oxide powder to the europium oxide powder is 2:1.

[0018] Preferably, the pressure of the first tableting process is 0.5-2.8 GPa.

[0019] Preferably, the density of the first intermediate of the mixed powder is 50-75%.

[0020] Preferably, the step of performing a first sintering treatment on the first intermediate of the mixed powder specifically involves: placing the first intermediate of the mixed powder in a muffle furnace, heating it to 1400-1750°C at a heating rate of 5-20°C / min, and holding it at that temperature for 3-5 hours to obtain the second intermediate of europium zirconate.

[0021] Preferably, the step of performing a second sintering treatment on the europium zirconate second intermediate specifically includes:

[0022] The europium zirconate second intermediate was placed in a DIA-type 200-ton cubic press and pressurized to 624 bar at a pressurization rate of 2.1-3.47 bar / min, with a sample chamber pressure of 4 GPa. During the pressure holding stage, the temperature was increased to 500-1600℃ at a heating rate of 40-80℃ / min and held for 5-30 min. After the holding period, the pressure was released at 1.3-1.73 MPa / min.

[0023] Alternatively, the europium zirconate second intermediate is placed in a hinged six-sided press and pressurized to 27-73 MPa at a pressurization rate of 1.87-3.73 MPa / min, with a sample chamber pressure of 3-6 GPa. During the pressure holding stage, the temperature is increased to 500-1200℃ at a heating rate of 20-100℃ / min and held for 5-30 min. After the holding period, the pressure is released at 1.8-3.73 MPa / min.

[0024] Preferably, before performing the second sintering treatment on the europium zirconate second intermediate, the method further includes the following step:

[0025] The first intermediate of the mixed powder after the first sintering treatment is successively crushed, ground and then compressed into tablets.

[0026] Preferably, the pressure of the second tableting process is 0.5-2.8 GPa.

[0027] Preferably, after performing a second sintering treatment on the europium zirconate second intermediate, the method further includes the following step:

[0028] The europium zirconate intermediate after the second sintering treatment was sequentially cleaned, dried and polished.

[0029] In a second aspect, the present invention provides a high-density fluorescent pyrochlore phase europium zirconate, which is prepared by the above-described preparation method.

[0030] Beneficial effects:

[0031] This invention discloses a high-density fluorescent pyrochlore phase europium zirconate and its preparation method. Since europium zirconate is prone to two-phase coexistence, a more stable pyrochlore phase europium zirconate can be directly synthesized by a first sintering treatment (muffle furnace sintering) and a second sintering treatment (high temperature and high pressure sintering). Therefore, this invention utilizes a combination of two sintering methods to directly synthesize the target product, avoiding the generation of transition phases, improving density, and saving production costs and time. Attached Figure Description

[0032] Figure 1 These are the factors affecting the transparency of ceramics mentioned in the background section of this invention.

[0033] Figure 2 It refers to the europium zirconate fluorescence peak in the pyrochlore phase mentioned in the background section of this invention.

[0034] Figure 3 The image shows the XRD pattern of europium zirconate prepared in Example 1 of this invention.

[0035] Figure 4 The XRD patterns of europium zirconate prepared in Example 2 of the present invention at 1000, 1500 and 2000 °C.

[0036] Figure 5 This is a backscattered scanning electron microscope image of europium zirconate prepared in Example 2 of the present invention at 1600 °C.

[0037] Figure 6 This is a density diagram of europium zirconate prepared at different synthesis temperatures under 4 GPa in Example 2 of the present invention.

[0038] Figure 7 The images show the XRD patterns of europium zirconate after sintering in a muffle furnace and after high-pressure sintering in Example 3 of the present invention.

[0039] Figure 8 This is the XRD pattern of europium zirconate after high-pressure sintering in a muffle furnace according to Example 4 of the present invention.

[0040] Figure 9 The hinged six-sided top press mentioned in Embodiment 5 of the present invention is heated and assembled. Detailed Implementation

[0041] This invention provides a high-density fluorescent pyrochlore phase europium zirconate and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0042] Pyrochlore-phase A2B2O7 oxide ceramics are more stable than defective fluorite phases under extreme conditions. Therefore, this invention aims to prepare europium zirconate pyrochlore phase ceramics with high density, high mechanical properties and stable existence under various extreme environments.

[0043] This invention provides a method for preparing europium zirconate with high density fluorescent pyrochlore phase, the method comprising the following steps:

[0044] Zirconia powder and europium oxide powder are mixed and then subjected to a first tableting process to obtain a first intermediate of mixed powder.

[0045] The first intermediate of the mixed powder is subjected to a first sintering treatment to obtain the second intermediate of europium zirconate;

[0046] The europium zirconate second intermediate is subjected to a second sintering treatment to obtain the high-density fluorescent pyrochlore phase europium zirconate;

[0047] The temperature of the first sintering treatment is 1400-1750℃, and the pressure is 1-5 atm.

[0048] The second sintering treatment is performed at a temperature of 500-1600℃ and a pressure of 3.5-8 GPa.

[0049] Compared to the traditional muffle furnace sintering method alone (i.e., the first sintering treatment) (ball milling for 24 hours, sintering at 1700°C for 10 hours; density 95%), this embodiment of the invention also introduces high-temperature and high-pressure sintering (i.e., the second sintering treatment) to prepare europium zirconate with near-full density in the pyrochlore phase (muffle furnace sintering for 4 hours, high-pressure sintering at 800°C for 0.5 hours; density 99.98%). This reduces the sintering temperature and time, and mitigates problems such as the decline in the mechanical properties of europium zirconate due to the growth of europium zirconate grain size. At the same time, increasing the density of europium zirconate will simultaneously reduce the specific surface area of ​​europium zirconate, which will significantly improve the stability of europium zirconate under various extreme environments.

[0050] High-density europium zirconium zirconium in pyrochlore phase has higher ionic conductivity, thereby increasing the energy density of solid fuel cells. On the other hand, europium zirconium in pyrochlore phase with higher density has more stimulated emission ions, which further increases the luminous flux of stimulated light. While improving luminous efficiency, it can also increase thermal conductivity, reduce the accumulation of luminous heat caused by low density, and thus protect the overall luminous system.

[0051] Furthermore, since europium zirconate readily exhibits a two-phase coexistence state, a more stable pyrochlore-phase europium zirconate can be directly synthesized through muffle furnace sintering and high-temperature, high-pressure sintering (i.e., a first sintering treatment and a second sintering treatment). Therefore, this embodiment of the invention utilizes a combined approach to directly synthesize the target product, avoiding the generation of a transition phase. Compared to traditional methods for preparing ceramics, the method of this embodiment saves 86.3% of the time and increases the density to nearly 100%.

[0052] Specifically, high pressure (high pressure intensity), as a physical method, is now widely used in the preparation of various polycrystalline superhard materials. By using a press to squeeze the pressure-transmitting medium to generate ultra-high pressure at the center of the sample cavity, the sample in the cavity is pulverized and the pores are filled, thereby increasing the overall density of the sample. On the other hand, while using the press to generate high pressure, heating components can also be used to heat and sinter the sample. Under high temperature conditions, the sample will exhibit significant yielding, and combined with the high pressure environment, the pores in the sample cavity can be closed, thereby improving the sample density. According to the Hall-Petch effect, the various mechanical properties of the sample are inversely proportional to the grain size, indicating that smaller grains result in samples with better mechanical properties. Therefore, high temperature and high pressure environments can be used to solve the problem of low density in the prepared europium zirconate ceramics and can improve various mechanical properties of europium zirconate ceramics.

[0053] In some embodiments, the molar ratio of the zirconium oxide powder to the europium oxide powder is 2:1.

[0054] In some embodiments, the pressure of the first tableting process is 0.5-2.8 GPa.

[0055] Normally, samples must be pressed before the first sintering treatment (using a muffle furnace). Without pressing, the mixed powder intermediate cannot form europium zirconate even when treated in the muffle furnace at the same temperature and time. Higher pressure promotes the combination of europium oxide and zirconium oxide to form europium zirconate more quickly (pressure reduces the mean free path of atoms, thus lowering the reaction barrier). However, in practice, other aspects must also be considered, such as whether the mold can withstand excessive pressure, and whether the sample can be formed under excessive pressure. Therefore, to address these issues, the pressure (exposed to the sample) selected in this embodiment is 0.5-2.8 GPa, with the hydraulic pressure corresponding to the jack being 3-10 MPa.

[0056] In some preferred embodiments, the pressure of the first tableting process is 2.5 GPa.

[0057] In some embodiments, the density of the first intermediate of the mixed powder is 50-75%.

[0058] In some preferred embodiments, the density of the europium zirconate first intermediate is 70%.

[0059] In some embodiments, the step of performing a first sintering treatment on the first intermediate of the mixed powder specifically involves: placing the first intermediate of the mixed powder in a muffle furnace, heating it to 1400-1750°C at a heating rate of 5-20°C / min, and holding it at that temperature for 3-5 hours to obtain the second intermediate of europium zirconate.

[0060] In some embodiments, the step of performing a second sintering treatment on the europium zirconate second intermediate specifically includes:

[0061] The europium zirconate second intermediate was placed in a DIA-type 200-ton cubic press and pressurized to 624 bar at a pressurization rate of 2.1-3.47 bar / min, with a sample chamber pressure of 4 GPa. During the pressure holding stage, the temperature was increased to 500-1600℃ at a heating rate of 40-80℃ / min and held for 5-30 min. After the holding period, the pressure was released at 1.3-1.73 MPa / min.

[0062] Alternatively, the europium zirconate second intermediate is placed in a hinged six-sided press and pressurized to 27-73 MPa at a pressurization rate of 1.87-3.73 MPa / min, with a sample chamber pressure of 3-6 GPa. During the pressure holding stage, the temperature is increased to 500-1200℃ at a heating rate of 20-100℃ / min and held for 5-30 min. After the holding period, the pressure is released at 1.8-3.73 MPa / min.

[0063] In some embodiments, before performing a second sintering treatment on the europium zirconate second intermediate, the method further includes the following step:

[0064] The first intermediate of the mixed powder after the first sintering treatment is successively crushed, ground and then compressed into tablets.

[0065] In some embodiments, the pressure of the second tableting process is 0.5-2.8 GPa.

[0066] Generally speaking, the higher the pre-compression pressure of the powder before the second sintering process, the better. This is because higher pressure results in higher sample density. A denser sample, after being placed in high-pressure assembly, exhibits less deformation inside the sample cavity under high pressure (mainly less deformation of the heating tube and sample enclosure). This ensures more uniform and stable heat distribution from the heating tube, preventing localized overheating and resulting in uneven performance of the sintered sample. Simultaneously, higher density reduces the mean free path of the sample reaction, thereby lowering the reaction barrier and increasing the reaction rate. However, in practice, other factors must also be considered, such as whether the mold can withstand excessive pressure and whether the sample can be formed under such pressure. Therefore, to address these issues, the pressure (applied to the sample) selected in this embodiment is 0.5-2.8 GPa, with the hydraulic pressure corresponding to the jack being 3-10 MPa.

[0067] In some preferred embodiments, the pressure of the first tableting process is 2.5 GPa.

[0068] In some embodiments, after performing a second sintering treatment on the europium zirconate second intermediate, the method further includes the following steps:

[0069] The europium zirconate intermediate after the second sintering treatment was sequentially cleaned, dried and polished.

[0070] In a second aspect, the present invention provides a high-density fluorescent pyrochlore phase europium zirconate, which is prepared by the above-described preparation method.

[0071] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are intended only to illustrate the present invention and not to limit it. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0072] Example 1

[0073] The preparation of europium zirconate includes the following steps:

[0074] Commercially available nano-zirconia (~50nm) and europium oxide powders were uniformly mixed in a mixer at a molar ratio of 2:1 for 12 hours. After mixing, the powder was placed in a vacuum oven and dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor from the sample. Subsequently, the sample was pre-compressed in a Φ10mm mold using a jack with a pre-compression pressure of 12 MPa and a pressure of 643 MPa in the mold. The density of the sample after pre-compression was 54%.

[0075] The pre-compressed sample was placed in a muffle furnace and kept at 900-1500℃ (each 100℃ increment) for 3 hours for the experiment. The experiment was conducted at a heating and cooling rate of 10℃ / min.

[0076] After the experiment, the samples were subjected to XRD analysis (as shown in the attached image). Figure 3 When the holding time is 3 hours, the temperature needs to be increased to 1500℃ to prepare pure-phase europium zirconate with pyrochlore phase (PDF#24-0418). The XRD superlattice diffraction peaks indicated by the arrows in the figure are used to distinguish between pyrochlore phase and defective fluorite phase europium zirconate. At the same time, the density of the sample at 1500℃ was found to be only 87.4%. This indicates that it is difficult to prepare high-density fluorescent pyrochlore phase europium zirconate using traditional muffle furnace sintering conditions.

[0077] Example 2

[0078] The preparation of europium zirconate includes the following steps:

[0079] Commercially available nano-zirconia (~50nm) and europium oxide powders were uniformly mixed in a mixer at a molar ratio of 2:1 for 12 hours. The mixed powder was then placed in a vacuum oven and dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor. The dried powder was then pre-compressed in a Φ3.5mm mold with a pre-compression jack pressure of 5 MPa. The pre-compression pressure on the sample powder in the mold was 2.2 GPa. The density of the sample after pre-compression was ~70%, and the sample size was Φ3.5*3.5mm.

[0080] The sample was wrapped in hBN and placed in a high-temperature, high-pressure assembly. The entire assembly was then placed in a DIA-type 200-ton cubic press, and the oil pressure was increased to 624 bar at a pressurization rate of 2.6 bar / min, at which point the sample chamber pressure reached 4 GPa. Heating was then carried out at a heating / cooling rate of 70℃ / min. This step of the europium zirconate polycrystalline ceramic synthesis experiment was conducted at 900, 1000, 1100, 1500, 1600, and 2000℃, with a holding time of 1 hour for each temperature. After holding, the temperature was lowered at a rate of 70℃ / min. Once cooled to room temperature, the pressure was released at a rate of 1.3 bar / min. After depressurization, the sample was polished and then tested.

[0081] Appendix Figure 4 The XRD patterns of samples taken at 1000, 1500, and 2000℃ are shown. The figures reveal that at 1000℃, the sample formed europium zirconate of the defective fluorite phase (PDF#78-1292), which is not the target product, europium zirconate of the pyrochlore phase. When the temperature is increased to 1500℃, the sample decomposes, generating a product that is not of the pyrochlore phase, and the decomposition is more pronounced at 2000℃. (Attached) Figure 5 The image shows a backscattered electron microscope (SEM) image of the product formed at 1600℃. It clearly reveals the presence of two phases in the sample, indicating that this is not an ideal pure-phase europium zirconate pyrochlore phase. (Attached) Figure 6 To determine the density of samples synthesized at different synthesis temperatures under 4 GPa, it was found that even samples synthesized at non-decomposition synthesis temperatures (900-1100℃) were europium zirconate with defective fluorite phase and their density did not exceed 99%.

[0082] Example 3

[0083] The preparation of a high-density fluorescent pyrochlore phase europium zirconate includes the following steps:

[0084] Commercially available nano-zirconia (~50nm) and europium oxide powders were uniformly mixed in a mixer at a molar ratio of 2:1 for 12 hours. After mixing, the powder was placed in a vacuum oven and dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor from the sample. Subsequently, the sample was pre-compressed in a Φ10mm mold using a jack with a pre-compression pressure of 12 MPa and a pressure of 643 MPa in the mold. The density of the sample after pre-compression was 54%.

[0085] The pre-compressed sample was then placed in a muffle furnace and kept at 1500℃ for 3 hours, with a heating and cooling rate of 10℃ / min to prepare pure phase pyrochlore phase europium zirconate.

[0086] After XRD analysis confirmed the prepared europium zirconate sample to be pure pyrochlore-phase europium zirconate, the sample was pulverized using a corundum mortar and then finely ground using an agate mortar. The processed powder was then sieved through a 100-mesh sieve. The sieved powder was then vacuum-dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor. The dried sample was then pre-compressed in a Φ3.5mm mold with a pre-compression jack pressure of 5 MPa and a pre-compression pressure of 2.2 GPa. The density of the pre-compressed sample was ~72%, and the sample size was Φ3.5*3.5mm.

[0087] The pre-compressed sample was wrapped with hBN (hexagonal boron nitride) and placed in a high-temperature, high-pressure assembly. The entire assembly was then placed in a DIA-type 200-ton cubic press, and the oil pressure was increased to 624 bar at a pressurization rate of 2.6 bar / min, at which point the sample chamber pressure reached 4 GPa. During the pressure holding phase, heating and cooling were performed at a rate of 70℃ / min. The sintering temperature of the sample was 550℃, with holding times of 5 min and 30 min, respectively. After heating, the pressure was released to atmospheric pressure at a rate of 1.73 bar / min. After the experiment, the high-pressure assembly was removed, and the sample was cleaned (ultrasonically cleaned in anhydrous ethanol for 15 min), dried, and polished. After polishing, the sample underwent XRD and density analysis.

[0088] Appendix Figure 7 The XRD patterns of the samples prepared in the muffle furnace and after high-pressure sintering show that the sintered samples still contain pure pyrochlore europium zirconate. Density tests revealed that the samples at 550℃ for 5 minutes and 30 minutes had densities of 95% and 96.7%, respectively.

[0089] Example 4

[0090] The preparation of a high-density fluorescent pyrochlore phase europium zirconate includes the following steps:

[0091] Commercially available nano-zirconia (~50nm) and europium oxide powders were uniformly mixed in a mixer at a molar ratio of 2:1 for 12 hours. The mixed powder was then placed in a vacuum oven and dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor. Subsequently, the sample was pre-compressed in a Φ10mm mold using a jack at a pre-compression pressure of 12 MPa, resulting in a mold pressure of 643 MPa. The density of the sample after pre-compression was 54%.

[0092] The pre-compressed sample was then placed in a muffle furnace and kept at 1500℃ for 3 hours, with a heating and cooling rate of 10℃ / min to prepare pure phase pyrochlore phase europium zirconate.

[0093] After XRD analysis confirmed the prepared sample to be pure europium zirconate of the pyrochlore phase, the sample was pulverized using a corundum mortar and then finely ground using an agate mortar. The processed sample powder was then sieved through a 100-mesh sieve. The sieved powder was then vacuum dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor. Subsequently, the dried sample was placed in a Φ3.5 mm mold for pre-compression. The pre-compression jack pressure was 5 MPa, and the pre-compression pressure on the sample powder in the mold was 2.2 GPa. The density of the sample after pre-compression was ~74%, and the size of the pre-compressed sample was Φ3.5*3.5 mm.

[0094] The pre-compressed sample was wrapped with hBN and placed in a high-temperature, high-pressure assembly. The entire assembly was then placed in a DIA-type 200-ton cubic press, and the oil pressure was increased to 624 bar at a pressurization rate of 2.6 bar / min, at which point the sample chamber pressure reached 4 GPa. During the pressure holding stage, heating and cooling were performed at a rate of 70℃ / min, with the sample sintering temperature at 800℃ and a holding time of 30 min. After heating, the pressure was released to atmospheric pressure at a rate of 1.73 bar / min.

[0095] After the experiment, the high-pressure assembly was removed, and the sample was cleaned (ultrasonically cleaned in anhydrous ethanol for 15 min), dried, and polished. After polishing, the sample was subjected to XRD and density testing. (See attached image.) Figure 8 The XRD patterns of the samples prepared in the muffle furnace and after high-pressure sintering show that the sintered samples still contain pure pyrochlore europium zirconate. Simultaneously, density testing revealed that the actual density of the samples reached 6.749 ± 0.0159 g / cm³. 3 (Theoretical density is 6.7497±0.0044 g / cm³) 3 The density reached 99.98%, which is close to full density. Grain size analysis revealed that the initial grain size of the sample synthesized in the muffle furnace was 426 nm, while the grain size of the sample after grinding and high-pressure sintering was 258 nm. This indicates that grinding can significantly reduce the grain size of the sintered sample, while high pressure conditions can effectively inhibit grain growth, thereby refining the grains to improve the mechanical properties of the sample.

[0096] Example 5

[0097] The preparation of a high-density fluorescent pyrochlore phase europium zirconate includes the following steps:

[0098] Commercially available nano-zirconia (~50nm) and europium oxide powders were uniformly mixed in a mixer at a molar ratio of 2:1 for 12 hours. The mixed powder was then placed in a vacuum oven and dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor. Subsequently, the sample was pre-compressed in a Φ10mm mold using a jack at a pre-compression pressure of 12 MPa, resulting in a mold pressure of 643 MPa. The density of the sample after pre-compression was 54%.

[0099] The pre-compressed sample was then placed in a muffle furnace and kept at 1500℃ for 3 hours, with a heating and cooling rate of 10℃ / min to prepare pure phase pyrochlore phase europium zirconate.

[0100] After XRD analysis confirmed the prepared sample to be pure europium zirconate of the pyrochlore phase, the sample was pulverized using a corundum mortar and then finely ground using an agate mortar. The processed sample powder was then sieved through a 100-mesh sieve. The sieved powder was then vacuum dried at 100°C for 8 hours under a vacuum of 4.2 Pa to remove volatile impurities such as water vapor. Subsequently, the dried sample was placed in a Φ3.5 mm mold for pre-compression. The pre-compression jack pressure was 5 MPa, and the pre-compression pressure on the sample powder in the mold was 2.2 GPa. The density of the sample after pre-compression was ~74%, and the size of the pre-compressed sample was Φ3.5*3.5 mm.

[0101] The pre-compressed sample was wrapped with hBN and placed in a high-temperature, high-pressure assembly machine; subsequently, the entire assembly was placed in a domestically produced hinged six-sided top press (heated assembly as shown in the attached image). Figure 9 The experiments were conducted at oil pressures of 56 MPa and 66 MPa, respectively; the pressure was increased at a rate of 2.24 MPa / min, at which point the sample chamber pressures reached 5 GPa and 5.5 GPa, respectively. During the pressure holding phase, the temperature was increased and decreased at a rate of 60 °C / min, with a holding time of 25 min; after the holding period, the pressure was released at 2.8 MPa / min.

[0102] After the experiment, the high-pressure assembly was removed, and the samples were cleaned (ultrasonically cleaned in anhydrous ethanol for 15 min), dried, and polished. After polishing, the samples underwent XRD and density testing. The tests revealed that, thanks to the excellent quasi-hydrostatic pressure conditions provided by the hinged six-sided press and the quasi-hydrostatic environment provided by the high-temperature NaCl melting, the density of europium zirconate in the pyrochlore phase reached 99.62% under 5 GPa and 760℃ temperature-pressure conditions; and 99.79% under 5.5 GPa and 740℃ temperature-pressure conditions. Grain size analysis revealed that the initial grain size of the sample synthesized in the muffle furnace was 457 nm, while the grain sizes of the samples after grinding and high-pressure sintering were 323 nm (5 GPa) and 296 nm (5.5 GPa), respectively. This indicates that grinding can significantly reduce the grain size of the sintered sample, while the relatively higher pressure conditions can significantly inhibit grain growth, thereby achieving the goal of refining the grains to improve the mechanical properties of the sample.

[0103] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing europium zirconate with high density fluorescent pyrochlore phase, characterized in that, The preparation method includes the following steps: Zirconia powder and europium oxide powder are mixed and then subjected to a first tableting process to obtain a first intermediate of mixed powder. The first intermediate of the mixed powder is subjected to a first sintering treatment to obtain the second intermediate of europium zirconate; The europium zirconate second intermediate is subjected to a second sintering treatment to obtain the high-density fluorescent pyrochlore phase europium zirconate; The temperature of the first sintering treatment is 1400-1750℃, and the pressure is 1-5 atm. The second sintering treatment is carried out at a temperature of 500-1600℃ and a pressure of 3.5-8 GPa. The pressure of the first tableting process is 0.5-2.8 GPa.

2. The method for preparing high-density fluorescent pyrochlore phase europium zirconate according to claim 1, characterized in that, The molar ratio of zirconium oxide powder to europium oxide powder is 2:

1.

3. The method for preparing high-density fluorescent pyrochlore-phase europium zirconate according to claim 1, characterized in that, The density of the first intermediate of the mixed powder is 50-75%.

4. The method for preparing high-density fluorescent pyrochlore phase europium zirconate according to claim 1, characterized in that, The first sintering treatment of the mixed powder first intermediate is specifically as follows: the mixed powder first intermediate is placed in a muffle furnace, heated to 1400-1750°C at a heating rate of 5-20°C / min, and held for 3-5 hours to obtain europium zirconate second intermediate.

5. The method for preparing high-density fluorescent pyrochlore-phase europium zirconate according to claim 1, characterized in that, The step of performing a second sintering treatment on the europium zirconate second intermediate is as follows: The europium zirconate second intermediate was placed in a DIA-type 200-ton cubic press and pressurized to 624 bar at a pressurization rate of 2.1-3.47 bar / min, with a sample chamber pressure of 4 GPa. During the pressure holding stage, the temperature was increased to 500-1600℃ at a heating rate of 40-80℃ / min and held for 5-30 min. After the holding period, the pressure was released at 1.3-1.73 MPa / min. Alternatively, the europium zirconate second intermediate is placed in a hinged six-sided press and pressurized to 27-73 MPa at a pressurization rate of 1.87-3.73 MPa / min, with a sample chamber pressure of 3-6 GPa. During the pressure holding stage, the temperature is increased to 500-1200℃ at a heating rate of 20-100℃ / min and held for 5-30 min. After the holding period, the pressure is released at 1.8-3.73 MPa / min.

6. The method for preparing high-density fluorescent pyrochlore phase europium zirconate according to claim 1, characterized in that, Before performing the second sintering treatment on the europium zirconate second intermediate, the method further includes the following steps: The first intermediate of the mixed powder after the first sintering treatment is successively crushed, ground and then compressed into tablets.

7. The method for preparing high-density fluorescent pyrochlore phase europium zirconate according to claim 6, characterized in that, The pressure of the second tableting process is 0.5-2.8 GPa.

8. The method for preparing high-density fluorescent pyrochlore phase europium zirconate according to claim 1, characterized in that, After performing a second sintering treatment on the europium zirconate second intermediate, the process further includes the following steps: The europium zirconate intermediate after the second sintering treatment was sequentially cleaned, dried and polished.

9. A high-density fluorescent pyrochlore phase europium zirconate, characterized in that, The high-density fluorescent pyrochlore phase europium zirconate was prepared by the preparation method described in any one of claims 1-8.

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