A method for preparing large-size transparent YAG nanoceramics by crystallization of amorphous materials

Abstract

The present invention provides a large-scale transparent YAG nanoceramic, characterized by being directly obtained from amorphous glass prepared by a one-step high-temperature heat treatment and then subjected to a one-step hot pressing crystallization process; the amorphous glass has a refractive index of 1.8-2.3, a hardness of 9GPa-14GPa, a transmittance of 79%-93%, and an amorphous degree of 100%; the YAG nanoceramic is composed of a YAG nanocrystalline phase with a grain size of 20-60nm; the YAG nanoceramic has a diameter of 1-3cm and a transmittance of 77%-83% within a wavelength range of 450-800nm. The present invention uses a one-step hot pressing crystallization process to directly obtain a large-scale nanoceramic with excellent optical, mechanical, and thermal stability, and has broad application prospects in multiple fields.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and in particular to a method for preparing large-size transparent YAG nano-ceramics by crystallizing amorphous materials. Background Art

[0002] Y3Al5O 12 (YAG) transparent ceramics have a wide range of applications in windows, fluorescence, lasers, scintillation and other fields due to their excellent mechanical properties, physicochemical stability, thermal stability and optical properties. However, YAG transparent ceramics are currently mainly prepared by traditional powder sintering methods. The traditional powder sintering method has several important problems: it requires a high temperature and high pressure environment, the sintering time is long, and the grains are easily coarsened during the sintering process. The obtained garnet transparent ceramics are generally micron-crystalline ceramics, and it is difficult to obtain ultrafine-grained or nano-crystalline transparent ceramic materials. Moreover, these sintering methods are heavily dependent on the quality of the powder raw materials, and usually require high-purity, high-dispersity and nano-scale powders. These problems make the preparation of highly transparent YAG ceramics complex and difficult.

[0003] In recent years, amorphous crystallization technology has emerged. This process involves heat treating amorphous glass materials at a moderate temperature (≤1200°C) and then crystallizing them into nanocrystalline transparent ceramic materials in a relatively short period of time (<5 hours). Transparent ceramics with nanoscale crystals exhibit superior mechanical and optical properties. However, the YAG transparent ceramics currently produced by the amorphous crystallization method are generally small in size, with a diameter of 3-5 mm, which often makes them difficult to apply effectively in practice.

[0004] The above problems seriously restrict the practical application of YAG nano-transparent ceramics. Therefore, a method for preparing large-sized YAG transparent nano-ceramics by crystallization of amorphous materials is urgently needed. Summary of the Invention

[0005] In response to the problem that YAG transparent ceramics prepared in the prior art have small diameters and are difficult to be effectively applied, the present invention proposes a new preparation method that can obtain transparent YAG nanoceramics with large diameters and excellent mechanical and optical properties.

[0006] A large-sized transparent YAG nanoceramic is directly obtained by hot-pressing and crystallizing amorphous glass prepared by a one-step high-temperature heat treatment. The amorphous glass has a refractive index of 1.8-2.3, a hardness of 9GPa-14GPa, a transmittance of 79%-93%, and an amorphous degree of 100%. The YAG nanoceramic is composed of a YAG nanocrystalline phase with a grain size of 20-60nm. The YAG nanoceramic has a diameter of 1-3cm and a transmittance of 77%-83% within a wavelength range of 450-800nm.

[0007] Optionally, the one-step hot pressing crystallization is to first pressurize and keep the temperature at a first temperature for a period of time, and then further heat the temperature to a second temperature and keep the temperature for a period of time.

[0008] Furthermore, the present invention also provides a method for preparing the aforementioned YAG nanoceramic, comprising:

[0009] Step S1, uniformly mixing Al2O3 and Y2O3, and optionally, other metal oxides / non-metal oxides, in a certain proportion, and forming the mixture into a molded body under a certain pressure; the other oxides are metal oxides / non-metal oxides other than Al and Y, and are preferably any one or more of gadolinium oxide, cerium oxide, dysprosium oxide, erbium oxide, europium oxide, iron oxide, lanthanum oxide, lutetium oxide, neodymium oxide, praseodymium oxide, samarium oxide, terbium oxide, thorium oxide, thulium oxide, ytterbium oxide, chromium oxide, silicon oxide, zirconium oxide, boron oxide, germanium oxide, phosphorus oxide, vanadium oxide, arsenic oxide, antimony oxide, hafnium oxide, zinc oxide, lead oxide, and beryllium oxide;

[0010] Step S2: crushing the molded body to a sample of suitable particle size, placing the sample in a containerless solidification system, melting the sample at high temperature in a stable suspension state, and cooling and solidifying the melted sample into spherical amorphous glass; optionally, crushing the spherical amorphous glass into glass powder; it is worth noting that the amorphous glass prepared in the present invention does not require the pre-high-temperature sintering process used in the prior art;

[0011] In step S3, the spherical amorphous glass / glass powder is placed in a mold, then heated to a first holding temperature and maintained there, while applying pressure. After the holding temperature is complete, the temperature is further raised to a second holding temperature and maintained there. After cooling, a large-sized YAG nanoceramic is obtained. This method utilizes two stages of heating and pressurizing in a hot pressing furnace to produce a large-sized transparent ceramic in a single step, significantly simplifying the process compared to existing technologies.

[0012] Optionally, in step S1, the ratio of Al2O3 to Y2O3 is 70-80 mol%: 20-30 mol%.

[0013] Optionally, in step S1, an appropriate amount of ethanol is added when the raw materials are mixed, and the raw materials are dried after being evenly mixed; the dried raw materials are molded under a pressure of 10-35 MPa, preferably into a cylinder with a diameter of 10-30 mm and a height of 1-5 mm.

[0014] Optionally, in step S2, the containerless solidification system is a suspension-heating system, the system also has a nozzle, the sample particle size is not larger than the nozzle diameter, and the sample is placed in the nozzle; the suspension method is selected from at least one of gas suspension, ultrasonic suspension, electrostatic suspension, and electromagnetic suspension, preferably gas suspension, which has good universality and can suspend a large mass; the heating method is selected from at least one of laser heating and induction heating, preferably laser heating, which heats up quickly, can reach a high temperature, and can cool down quickly when turned off.

[0015] Optionally, in step S2, high-purity oxygen (purity ≥99.99wt%) or air is used as the carrier gas, and the flow rate is adjusted to stabilize the gas suspension of the sample. The carrier gas is preferably high-purity oxygen to avoid blackening and devitrification of the material caused by oxygen vacancies. The laser heating power is adjusted to heat the sample to 2700-2900°C to completely melt the sample, and the heating time is preferably 10-60s.

[0016] Optionally, in step S3, the mold is a graphite mold with an inner diameter of 1-3 cm.

[0017] Optionally, in step S3, the hot pressing crystallization process is specifically as follows:

[0018] S31, raising the temperature to 900-1000°C at a certain heating rate (10-15°C / min), and keeping it warm for 0.5-2h, applying a pressure of 10-90MPa, preferably 40MPa, during the holding period, to perform the first heating stage;

[0019] S32. After the first stage of heating is completed, the temperature is further raised to 1100-1300℃ and kept at this temperature for 0.5h-5h, and finally cooled to room temperature with the furnace.

[0020] Furthermore, the present invention also provides applications of transparent YAG nano-ceramics in optical windows, lenses, fluorescence, lasers, scintillators, and X-ray detection and imaging.

[0021] The beneficial effects brought about by the technical solution provided by the present invention include at least:

[0022] The YAG nano-transparent ceramic preparation method of the present invention is that when preparing the transparent glass precursor amorphous glass, no high-temperature pretreatment is required, and the transparent glass precursor is directly crystallized by one-step hot pressing to obtain large-sized (1-3 cm) nanocrystalline transparent ceramics with excellent mechanical properties (hardness of 22 GPa), optical properties (transmittance of 77%-83% in the wavelength range of 450-800 nm), thermal conductivity and thermal stability (5.7 W / m·k at 25°C, 4.6 W / m·k at 500°C); the present invention avoids the defects of the prior art of high-temperature sintering before pneumatic suspension preparation of amorphous glass and viscous sintering before amorphous crystallization through one-step hot pressing crystallization, significantly simplifying the process and avoiding the problems of cracking and devitrification caused by first preparing a large-sized glass precursor and then further pressureless temperature crystallization after removal. The ceramic material has great application potential in the fields of optical windows, lenses, fluorescence, lasers, scintillators, X-ray detection and imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 Figure 1 is a diagram of a stably suspended molten sample of the present invention, wherein (a) is a schematic diagram and (b) is a physical diagram;

[0025] Figure 2 is a process flow chart of the present invention;

[0026] Figure 3 This is a morphology diagram of the YAG nano-transparent ceramic obtained in Example 14 of the present invention;

[0027] Figure 4 : This is the transmittance curve of the YAG nano-transparent ceramic obtained in Example 14 of the present invention;

[0028] Figure 5 The XRD pattern of the YAG nano-transparent ceramic obtained in Example 14 of the present invention is

[0029] Figure 6 This is a TEM image of the YAG nano-transparent ceramic obtained in Example 14 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Examples 1-13

[0032] First, amorphous glass is prepared by a containerless solidification method, as shown below:

[0033] (1) According to the raw material ratios (molar percentages) of Examples 1-6 in Table 1, Y2O3 raw material powder, Al2O3 raw material powder, and cerium oxide (CeO2) raw material powder were weighed separately. The raw material powders were all high-purity (99.99%) powders or analytically pure (99.9%) powders. They were then mixed uniformly using a wet mixing method. The specific method was as follows: anhydrous ethanol was added to the raw material powders, and the mixture was stirred and ground in a corundum crucible until the alcohol was completely volatilized. The uniformly mixed powders were pressed into cylindrical blocks by a hydraulic press at room temperature, and this process did not require heating and roasting. Although only cerium oxide was used as the oxide for doping, it will be understood by those skilled in the art that other similar oxides may also be used.

[0034] (2) The cylindrical block described in step (1) is then broken into cubic blocks with a mass of 10 mg to 500 mg, placed in the nozzle of an air suspension device, and high-purity oxygen is introduced. The laser is then turned on to heat the block raw material into a molten state. The air flow size is adjusted to allow the small pieces of raw material to be suspended stably in the molten state. The laser is then turned off to allow the melt to quickly cool to room temperature to obtain amorphous glass. The specific schematic diagram and actual picture are as follows: Figure 1 and Figure 2 shown.

[0035] The amorphous glass has a refractive index of 1.8-2.3, a hardness of 9 GPa-14 GPa, a transmittance of 79%-93%, and an amorphous degree of 100%.

[0036] Then, large-sized transparent YAG-based nanoceramics were prepared by direct amorphous crystallization using vacuum hot pressing. The specific method is as follows:

[0037] The spherical amorphous glass / glass powder prepared in step (2) of the containerless solidification method is placed in a mold, and the temperature is increased to 900-1000°C at a certain heating rate (10-15°C / min), and kept warm for 0.5-2h. During the heat preservation period, a pressure of 10-90MPa is applied to perform the first heating stage. After the first heating stage is completed, the temperature is further increased to 1100-1300°C and kept warm for 0.5h-5h. Finally, the large-sized transparent YAG-based nanoceramics are obtained. The specific schematic diagram and actual picture are as follows: Figure 2 shown.

[0038] The large-sized transparent YAG-based nanoceramics obtained in Examples 1-13 have a diameter of 1-3 cm, a grain size of 20-60 nm, and a transmittance of 77%-82% within the wavelength range of 450-800 nm.

[0039] The YAG-based nano-ceramic materials obtained in Examples 7-13 can be fully excited under blue light (450 nm) to produce yellow fluorescence.

[0040] Example 14

[0041] Except that during the crystallization process, the heating rate of the first stage was set to 10°C / min, the target temperature was set to 940°C, the holding time was set to 0.5h, the pressure applied during the holding period was set to 40MPa, the target temperature of the second stage was set to 1100°C, and the holding time was set to 1h, the other preparation methods and conditions were the same as those in Example 3 to obtain YAG-based nanoceramics.

[0042] Figure 3 This is an optical photograph of the YAG-based nano-ceramic material of Example 14, with a diameter of 1 cm.

[0043] Figure 4 This is the transmittance curve of the YAG-based nano-ceramic material of Example 14. It can be seen from the figure that the sample has good transmittance from the visible light region to the infrared region, with the highest transmittance reaching 86% and the transmittance reaching 83% at 780nm.

[0044] Figure 5 14 is the XRD pattern of the YAG-based nano-ceramic material of this embodiment. It can be seen from the figure that the crystal phase of the nano-ceramic material of this embodiment is the YAG crystal phase.

[0045] Figure 6 This is a microstructure photograph of the YAG-based nano-ceramic material of Example 14. As can be seen from the figure, the YAG-based nano-ceramic material of this example is composed of a YAG main crystal phase and an Al2O3 secondary crystal phase.

[0046] Comparative Example 1

[0047] Except that during the crystallization process, the large-sized glass obtained by heating is taken out and placed in a muffle furnace for pressureless heating crystallization, other preparation methods and conditions are the same as those of Examples 1-13. The obtained YAG-based nanoceramics are cracked and non-transparent.

[0048] Table 1 Raw material ratios (molar percentages) of Examples 1-13

[0049]

[0050] Table 2 Transmittance of YAG-based nanoceramics obtained in Examples 1-13

[0051]

[0052] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing large-sized transparent YAG nanoceramics, characterized in that: include: Step S1, Al2O3 and Y2O3, as well as other metal oxides / non-metal oxides other than Al and Y, are uniformly mixed in a certain proportion and formed into a molded body under a certain pressure; Step S2, crushing the molded body into a sample of suitable particle size, and placing the sample into a containerless solidification system, so that the sample is melted at high temperature in a stable suspension state, and the melted sample is cooled and solidified into spherical amorphous glass; Step S3: placing the spherical amorphous glass in a mold: S31, raising the temperature to 900-1000°C at a certain heating rate and keeping it at that temperature for 0.5-2h, applying a pressure of 10-90MPa during the holding period, and performing the first heating stage; S32, after the first heating is completed, further heating to 1100-1300 ° C, and keeping the temperature for 0.5h-5h, and finally cooling to room temperature with the furnace to obtain large-sized YAG nanoceramics; The amorphous glass has a refractive index of 1.8-2.3, a hardness of 9GPa-14GPa, a transmittance of 79%-93%, and an amorphous degree of 100%; the YAG nanoceramic is composed of a YAG nanocrystalline phase with a grain size of 20-60nm; the YAG nanoceramic has a diameter of 1-3cm and a transmittance of 77%-83% within a wavelength range of 450-800nm.

2. The method according to claim 1, characterized in that In step S2, the spherical amorphous glass is further crushed into glass powder.

3. The method according to claim 1, characterized in that In step S1, the ratio of Al2O3 to Y2O3 is 70-80 mol%:20-30 mol%; other oxides are metal oxides / non-metal oxides other than Al and Y.

4. The method according to claim 3, characterized in that Other oxides are any one or more of gadolinium oxide, cerium oxide, dysprosium oxide, uranium oxide, europium oxide, iron oxide, lanthanum oxide, lutetium oxide, neodymium oxide, praseodymium oxide, samarium oxide, terbium oxide, thorium oxide, thulium oxide, ytterbium oxide, chromium oxide, silicon oxide, zirconium oxide, boron oxide, germanium oxide, phosphorus oxide, vanadium oxide, arsenic oxide, antimony oxide, hafnium oxide, zinc oxide, lead oxide, and beryllium oxide.

5. The method according to claim 1, wherein In step S1, an appropriate amount of ethanol is added when the raw materials are mixed, and the raw materials are dried after being evenly mixed; the dried raw materials are molded under a pressure of 10-35 MPa to form a cylinder with a diameter of 10-30 mm and a height of 1-5 mm.

6. The method according to claim 1, characterized in that In step S2, the containerless solidification system is a suspension-heating system, which also has a nozzle. The sample particle size is no larger than the nozzle diameter, and the sample is placed in the nozzle; the suspension method is selected from at least one of gas suspension, ultrasonic suspension, electrostatic suspension, and electromagnetic suspension; the heating method is selected from at least one of laser heating and induction heating.

7. The method according to claim 6, characterized in that In step S2, the suspension method is selected from gas suspension, high-purity oxygen or air is used as the carrier gas, and the flow rate is adjusted to ensure stable gas suspension of the sample; the heating method is selected from laser heating, and the laser heating power is adjusted to heat the sample to 2700-2900°C to completely melt the sample, and the heating time is 10-60s.

8. The method according to claim 1, characterized in that In step S3, the mold is a graphite mold with an inner diameter of 1-3 cm.

9. Application of the nanoceramics prepared by the method according to any one of claims 1 to 8 in optical windows, lenses, fluorescence, lasers, scintillators, and X-ray detection imaging.

Images