A rare earth-doped alkali metal chloride composite ceramic and a cold sintering preparation method thereof

Abstract

A rare earth-doped alkali metal chloride composite ceramic and a cold sintering preparation method thereof belong to the technical fields of inorganic non-metallic materials and luminescent ceramics. By purifying raw materials and optimizing processes, different rare earth concentration-doped alkali metal halide composite ceramics are prepared by the cold sintering method under variable temperature and variable pressure conditions. Tests on the obtained ceramics show that: as the doping concentration of Eu increases, the emission spectrum intensity gradually increases. When the Eu concentration is 0.008 mol%, the sintering temperature is 125 °C, and the pressure is 300 MPa, the luminescent properties of the ceramic are the best. The raw material purification and ceramic preparation process in the present invention are simple, do not adopt harsh preparation conditions, can reduce production costs, and have broad application prospects in the fields of lighting, lasers, and biological fluorescence labeling, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic non-metallic materials and luminescent ceramics, and particularly relates to a rare-earth doped alkali metal chloride composite ceramic and a cold sintering preparation method thereof. Background Art

[0002] Problems such as high temperature, low energy efficiency, phase decomposition, and diffusion exist in the traditional sintering preparation process of ceramic materials. Existing sintering technologies, such as microwave sintering, spark plasma sintering, and rapid sintering, can reduce the sintering temperature of ceramic materials. However, the sintering temperature of these processes is still too high for some special ceramic materials. Therefore, there is an urgent need for a low-energy-consuming and low-cost sintering process while ensuring the density and stability of the ceramic structure. Traditional ceramic sintering needs to be carried out at high temperatures (>1000 °C), resulting in coarsening of grains, high energy consumption, and uneven distribution of rare-earth doping. The cold sintering method is a process that densifies various inorganic materials, especially ceramic materials that are unstable at high temperatures, using transient liquid phase and uniaxial pressure at low temperatures (<300 °C) or even at room temperature, and can also improve the mechanical properties and durability of ceramic materials. Therefore, the cold sintering technology has attracted much attention since its birth. Alkali metal chlorides have the advantages of simple structure, low cost, wide bandgap, etc., and are a good raw material for preparing ceramics. It is easy to achieve ion doping. Pure and ion-doped alkali metal halide ceramics have broad application prospects in the fields of electricity, optics, detection, etc. Lei Li et al. prepared NaCl and LiF ceramics by the cold sintering method and studied the influence law of water content on electrical and mechanical properties. Yongtao Li et al. prepared NaCl:Eu ceramics by cold sintering and analyzed their structures and properties. However, the preparation process and property research of rare-earth doped alkali metal composite halide ceramics have rarely been reported.

[0003] Alkali metal chloride composite ceramics have a relatively large lattice energy, which can provide more coordination space for Eu, making it easier for Eu ions to maintain a stable luminescent state in the composite ceramics and less likely to undergo self-excitation effects or optical damage. Especially under low-temperature sintering conditions, the lattice structure can be better maintained, and the lattice is more stable compared to the NaCl:Eu ceramic, less prone to lattice distortion. Moreover, the composite ceramics have a higher solubility. Therefore, during the cold sintering process, Eu ions are more evenly distributed in the lattice, avoiding the problems of uneven doping or ion aggregation that occur in traditional sintering processes. In addition, due to their relatively large lattice constants and lower thermal expansion coefficients, alkali metal halide composite ceramics are more stable than traditional ceramics in environments with large temperature fluctuations, such as high-temperature changes or extreme temperature environments, and are suitable for optical components or other high-temperature applications in high-temperature working environments. However, further research is still needed in aspects such as raw material purification, process optimization, and improvement of luminescence efficiency for rare-earth-doped alkali metal halide composite ceramics. Therefore, in view of the deficiencies of the prior art, the present invention provides a rare-earth-doped alkali metal chloride composite ceramic and its cold sintering preparation method. Through raw material purification, process optimization, etc., a high-performance rare-earth-doped alkali metal halide composite ceramic has been successfully prepared, effectively solving problems such as low raw material purity, low luminescence efficiency, and complex preparation processes, and facilitating the wide application of ceramics in new-generation information technology fields such as electronics, lighting, flat panel displays, and lasers. Summary of the Invention

[0004] The object of the present invention is to provide a rare-earth-doped alkali metal chloride composite ceramic and its cold sintering preparation method, which have low equipment costs, low preparation energy consumption, a simple preparation process, and the prepared ceramic material has high stability and high luminescence efficiency.

[0005] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0006] The present invention provides a rare-earth-doped alkali metal chloride composite ceramic and its cold sintering preparation method, including the following steps:

[0007] (1) Raw material purification: Add KOH, NaOH, and NH4Cl with a purity of 99.7% to the HCl solution. The mixed solution is concentrated and evaporated at 60 °C to 100 °C to obtain a solid mixture. The solid mixture is placed in a quartz container and vacuum dehydrated at 230 °C to 260 °C to obtain a dehydrated product. Then, in an inert atmosphere, the product is calcined at 420 °C to 480 °C to obtain K x Na 1-x Cl (0.1 ≤ x ≤ 0.9) raw materials;

[0008] (2) K with a purity of 99.9% x Na1-x Cl and EuCl3 are weighed according to the stoichiometric ratio, and the K x Na 1-x The molar ratio of Cl to EuCl3 is 0.5:(0.002 - 0.02), and an organic flux accounting for 0.1 - 1% of the total mass of the raw materials is added;

[0009] (3) Add the weighed raw materials in step (2) to deionized water (resistivity not less than 18 MΩ·cm), stir and completely dissolve them. The mass ratio of the raw materials to deionized water is 1:(3 - 5). Dry at 60 - 100 °C for 15 - 25 h, grind for 10 - 20 min, and then put them into a mold;

[0010] (4) Perform uniaxial hot pressing sintering on the mixture in the mold in step (3), and apply ultrasonic assistance with a frequency of 20 - 40 kHz and a power of 100 - 500 W at the same time. The uniaxial pressure is 50 - 400 Mpa, the pressurization and depressurization rates are 5 - 10 Mpa / min, the sintering temperature is 100 - 225 °C, the sintering time is 20 - 30 min, the sintering heating and cooling rates are 8 - 15 °C / min. After sintering, cut off the power, relieve the pressure, cool down, and demold and dry to obtain a ceramic chip.

[0011] Furthermore, in step (2), the organic flux is polyethylene glycol (PEG).

[0012] Furthermore, in step (4), the application time of the ultrasonic wave is 50 - 80% of the entire sintering process.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention synthesizes K x Na 1-x Cl:Eu ceramics by using the cold sintering method under variable temperature and pressure conditions. The tests on the obtained ceramics show that as the Eu concentration increases, the emission spectrum intensity increases. When the doping concentration is 0.008 mol%, the sintering temperature is 125 °C, and the pressure is 300 MPa, the luminescence performance is the best. In addition, the raw material preparation process in the present invention is simple, can reduce production costs, is suitable for large-scale industrial production, and has broad application prospects in the fields of lighting, flat panel display, laser, and biological fluorescence labeling, etc. Description of the Drawings

[0015] Figure 1 is the XRD of the KNaCl:Eu ceramics of the present invention sintered at 125 °C.

[0016] Figure 2is the XPS spectrum of the KNaCl:Eu ceramic of the present invention. In the figure, (a) is the XPS of KNaCl:0.008Eu, and (b) is K 2p 3 / 2 and K 2p 1 / 2 XPS fitting peaks, (c) is the XPS fitting peak of Cl 2p 3 / 2 XPS fitting peak, (d) is the XPS fitting peak of Na 1s, and (e) is Eu3d 5 / 2 and Eu 3d 3 / 2 XPS fitting peaks.

[0017] Figure 3 is the SEM image of the fracture surface of the KNaCl:Eu ceramic of the present invention. In the figure, (a)-(c) are the SEM images and tomography scans of the KNaCl:0.008Eu ceramic sample, (d) is the SEM image of KNaCl:0.008Eu at a sintering temperature of 225 °C, (e) is the SEM image of KNaCl:0.008Eu ceramic under a uniaxial pressure of 50 MPa, (f) is the SEM image of KNaCl:0.008Eu ceramic under a uniaxial pressure of 100 MPa, (g) is the SEM image of KNaCl:0.008Eu ceramic under a uniaxial pressure of 200 MPa, and (h) is the SEM image of KNaCl:0.008Eu ceramic under a uniaxial pressure of 300 MPa.

[0018] Figure 4 is the fluorescence spectrum of the KNaCl:Eu ceramic of the present invention. In the figure, (a) is the excitation spectrum of KNaCl:Eu at 613 nm, (b) is the emission spectrum of KNaCl:Eu at 391 nm, and (c) is the emission spectra of KNaCl:0.008Eu at different sintering temperatures.

[0019] Figure 5 is the TG curve of the KNaCl:Eu ceramic of the present invention.

[0020] Figure 6 (a) is the KNaCl:0.008Eu ceramic sheet, Figure 6 (b) is the KNaCl:0.008Eu ceramic sheet under ultraviolet light excitation. Specific Embodiments

[0021] The following further describes the specific embodiments of the present invention with reference to the accompanying drawings:

[0022] Example 1: A rare earth doped alkali metal chloride composite ceramic and its cold sintering preparation method, specifically including the following steps:

[0023] (1) Add KOH, NaOH, and NH4Cl with a purity of 99.7% into the HCl solution, concentrate and evaporate at 80 °C to obtain a solid mixture. Place the solid mixture in a quartz container and perform vacuum dehydration at 250 °C for 2 h. Then, calcine the product at 450 °C in an inert atmosphere to obtain K 0.5 Na 0.5 Cl raw material;

[0024] (2) Weigh K 0.5 Na 0.5 Cl and EuCl3 according to the stoichiometric ratio of 1:(0.002 - 0.02), and add polyethylene glycol (PEG) accounting for 0.4% of the total mass of the raw materials;

[0025] (3) Add the weighed raw materials in step (2) into deionized water, stir to completely dissolve them, perform drying treatment at 80 °C for 24 h, grind the dried mixture for 20 min, and then put it into a mold;

[0026] (4) Press the mixture in the mold in step (3) into tablets using a tablet press and perform uniaxial hot pressing sintering, while applying ultrasonic assistance with a frequency of 30 kHz and a power of 300 W;

[0027] (5) The uniaxial pressure in step (4) is 300 MPa, the temperature is controlled by an external heating coil and a temperature controller, the sintering temperature is 125 °C, sinter for 30 min, and the heating and cooling rates during sintering are 10 °C / min;

[0028] (6) After sintering, cut off the power, relieve the pressure, cool down, demold and dry to obtain a ceramic tablet. The fluorescence intensity of the sample increases with the increase of the doping concentration, and the luminescence intensity is the best when the doping concentration is 0.008 mol%.

[0029] Example 2: A rare earth doped alkali metal chloride composite ceramic and its cold sintering preparation method, specifically including the following steps:

[0030] (1) Add KOH, NaOH, and NH4Cl with a purity of 99.7% into the HCl solution, concentrate and evaporate at 80 °C to obtain a solid mixture. Place the solid mixture in a quartz container and perform vacuum dehydration at 250 °C for 2 h. Then, calcine the product at 450 °C in an inert atmosphere to obtain K 0.5 Na 0.5 Cl raw material;

[0031] (2) Weigh K 0.5 Na 0.5Cl and EuCl3 were weighed according to a stoichiometric ratio of 1:0.008, and polyethylene glycol (PEG) accounting for 0.4% of the total mass of the raw materials was added;

[0032] (3) The weighed raw materials in step (2) were added to deionized water, stirred and completely dissolved, dried at 80 °C for 24 h, the dried mixture was ground for 20 min, and then placed in a mold;

[0033] (4) The mixture in the mold in step (3) was pressed into tablets using a tablet press and subjected to uniaxial hot pressing sintering, with ultrasonic assistance at a frequency of 30 kHz and a power of 300 W applied simultaneously;

[0034] (5) In step (4), the uniaxial pressure was 300 MPa, the temperature was controlled by an external heating coil and a temperature controller, and was heated from room temperature to 100 °C, 125 °C, 150 °C, 175 °C, 200 °C, 225 °C respectively, the sintering time was 30 min, and the sintering heating and cooling rates were 10 °C / min;

[0035] (6) After sintering, the power was cut off, the pressure was released, cooled, and after demolding and drying, ceramic tablets were obtained. The fluorescence intensity of the samples increased with the increase of the sintering temperature, and the luminescence intensity was the best at 125 °C.

[0036] Example 3: A rare earth doped alkali metal chloride composite ceramic and its cold sintering preparation method, specifically including the following steps:

[0037] (1) KOH, NaOH, and NH4Cl with a purity of 99.7% were added to the HCl solution, concentrated and evaporated at 80 °C to obtain a solid mixture. The solid mixture was placed in a quartz container and vacuum dehydrated at 250 °C for 2 h, and then the product was calcined at 450 °C under an inert atmosphere to obtain K 0.5 Na 0.5 Cl raw materials;

[0038] (2) K 0.5 Na 0.5 Cl and EuCl3 were weighed according to a stoichiometric ratio of 1:0.008, and polyethylene glycol (PEG) accounting for 0.4% of the total mass of the raw materials was added;

[0039] (3) The weighed raw materials in step (2) were added to deionized water, stirred and completely dissolved, dried at 80 °C for 24 h, the dried mixture was ground for 20 min, and then placed in a mold;

[0040] (4) Press the mixture in the mold in step (3) into tablets using a tablet press and perform uniaxial hot pressing sintering, while applying ultrasonic assistance with a frequency of 30 kHz and a power of 300 W;

[0041] (5) The different uniaxial pressures in step (4) are 50 MPa, 100 MPa, 200 MPa, 300 MPa, and 400 MPa respectively. The temperature is controlled at 125 °C by an external heating coil and a temperature controller, and the sintering time is 30 min;

[0042] (6) After sintering, cut off the power, relieve the pressure, cool down, and after demolding and drying, obtain ceramic tablets. The luminescence intensity of the sample is the best when the uniaxial pressure is 300 MPa.

[0043] Example 4: A rare earth-doped alkali metal chloride composite ceramic and its cold sintering preparation method, specifically including the following steps:

[0044] (1) Add KOH, NaOH, and NH4Cl with a purity of 99.7% to the HCl solution, concentrate and evaporate at 80 °C to obtain a solid mixture. Place the solid mixture in a quartz container and perform vacuum dehydration at 250 °C for 2 h. Then, in an inert atmosphere, calcine the product at 450 °C to obtain K 0.5 Na 0.5 Cl raw materials;

[0045] (2) Weigh K 0.5 Na 0.5 Cl with a purity of 99.9% and EuCl3 according to a stoichiometric ratio of 1:0.008, and add polyethylene glycol (PEG) accounting for 0.4% of the total mass of the raw materials;

[0046] (3) Add the weighed raw materials in step (2) to deionized water, stir to completely dissolve them, perform a drying treatment at 80 °C for 24 h, grind the dried mixture for 20 min, and then put it into a mold;

[0047] (4) Press the mixture in the mold in step (3) into tablets using a tablet press and perform uniaxial hot pressing sintering, while applying ultrasonic assistance with a frequency of 40 kHz and a power of 400 W;

[0048] (5) The uniaxial pressure in step (4) is 300 MPa, the temperature is controlled at 125 °C by an external heating coil and a temperature controller, and the sintering time is 30 min;

[0049] (6) After sintering, cut off the power, relieve the pressure, cool down, and after demolding and drying, obtain ceramic tablets.

[0050] The above embodiments are the preferred embodiments of the present invention, and the protection scope of the present invention cannot be limited thereby. Any equivalent changes or equivalent modifications made by those skilled in the art to the present invention without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A rare earth-doped alkali metal chloride composite ceramic, characterized in that, Adopt a cold sintering preparation method, and its preparation method includes the following steps: (1) Raw material purification: Add KOH, NaOH, and NH4Cl with a purity of 99.7% into the HCl solution. The mixed solution is concentrated and evaporated at 60°C to 100°C to obtain a solid mixture. The solid mixture is placed in a quartz container and vacuum dehydrated at 230°C to 260°C to obtain a dehydrated product. Then, in an inert atmosphere, the product is calcined at 420°C to 480°C to obtain K 0.5 Na 0.5 Cl raw materials; (2) Weigh K with a purity of 99.9% 0.5 Na 0.5 Cl and EuCl3 according to the stoichiometric ratio. The molar ratio of the 0.5 Na 0.5 Cl to EuCl3 is 1:(0.002 - 0.02), and an organic flux accounting for 0.1 - 1% of the total mass of the raw materials is added; (3) Add the weighed raw materials in step (2) into deionized water with a resistivity of not less than 18 MΩ·cm, stir and completely dissolve it. The mass ratio of the raw materials to deionized water is 1:(3 - 5). Dry it at 60 - 100 °C for 15 - 25 h, grind it for 10 - 20 min, and then put it into a mold; (4) Perform uniaxial hot pressing sintering on the mixture in the mold in step (3), while applying ultrasonic assistance with a frequency of 20 - 40 kHz and a power of 100 - 500 W. The uniaxial pressure is 300 MPa, the pressurization and depressurization rates are 5 - 10 MPa / min, the sintering temperature is 125 °C, the sintering time is 20 - 30 min, the sintering heating and cooling rates are 8 - 15 °C / min. After sintering, cut off the power supply, depressurize, cool, and obtain a ceramic sheet after demolding and drying.

2. The rare earth-doped alkali metal chloride composite ceramic according to claim 1, characterized in that: The organic flux is polyethylene glycol.

3. The rare earth-doped alkali metal chloride composite ceramic according to claim 1, characterized in that: The application time of the ultrasonic wave is 50 - 80% of the whole sintering process.

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