Method for promoting low-temperature densification of yttria-stabilized zirconia and application

Abstract

The invention provides a method for promoting low-temperature densification of yttria-stabilized zirconia and application, and belongs to the technical field of high-temperature solid oxide fuel cells. The nano-powder prepared by a sol-gel method is small in particle size, large in specific surface area and high in activity, so that the densification temperature of the nano-powder is reduced, the nano-powder is sintered in a vapor-containing atmosphere, the oxygen partial pressure under high-temperature vapor is reduced, lattice oxygen escapes to form oxygen vacancies, meanwhile, hydrogen proton defects generated by hydrolysis reduce the formation energy of cation defects, and the oxygen vacancies are reduced. Formation of defects is promoted, and oxygen vacancies and the defects provide channels for atomic diffusion; and hydroxyl adsorbed on the surface of the YSZ and cations form ionic bonds, the diffusion rate of OH <-> is far higher than that of O2 <->, and due to electrostatic interaction, diffusion of cations is further promoted, so that sintering of the YSZ is promoted, and low-temperature densification of the YSZ is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature solid oxide fuel cells, and particularly relates to a method for promoting low-temperature densification of yttria-stabilized zirconia and application. BACKGROUND

[0002] A high-temperature solid oxide fuel cell (SOFC) is an electrochemical device for directly converting chemical energy into electrical energy, and has the advantages of high efficiency, no pollution, full solid-state structure, and wide adaptability to various fuel gases. Yttria-stabilized zirconia (YSZ) is often used as an electrolyte material for SOFCs due to its high ionic conductivity, reduced electron mobility, good chemical and thermal stability, and easy manufacturing and processing.

[0003] Currently, commercially available submicron YSZ powders are mainly used as raw materials to prepare electrolyte materials, and a very high sintering temperature (≥1550℃) is often required to obtain a material with high density. However, a too high sintering temperature will cause excessive grain growth, resulting in a decrease in the mechanical properties of the material, making the SOFCs prone to cracking during assembly or operation, causing cross leakage of fuel gas, reducing the performance and efficiency of the cells, and even leading to failure of the cells. On the other hand, a middle-temperature SOFC often adopts an anode-supported electrolyte thin film cell, and uses an anode and electrolyte co-sintering process. The anode is a mixture of NiO and YSZ, and its sintering temperature is much lower than that of pure YSZ. If the sintering temperature is too high, the anode porosity will be too low and the anode will be over-sintered. Therefore, the technology of low-temperature densification of YSZ powders is very crucial. SUMMARY

[0004] The application aims to provide a method for promoting low-temperature densification of yttria-stabilized zirconia and application. The method provided by the application realizes low-temperature densification of yttria-stabilized zirconia.

[0005] In order to achieve the above-mentioned application purposes, the application provides the following technical solutions: The application provides a preparation method of yttria-stabilized zirconia, comprising the following steps: (1) mixing yttria with a nitric acid solution to perform a double decomposition reaction to obtain yttrium nitrate; (2) mixing the yttrium nitrate obtained in the step (1) with water and a chelating agent to obtain a yttrium nitrate solution; (3) mixing a zirconium source with water and a dispersing agent to obtain a zirconium source solution; (4) mixing the yttrium nitrate solution obtained in the step (2) with the zirconium source solution obtained in the step (3) to perform a sol-gel and drying to obtain a gel; (5) sequentially performing heat pre-sintering and heat treatment on the gel obtained in the step (4) to obtain a nano-powder; (6) the nanometer powder obtained in step (5) is sequentially subjected to compression molding and pre-sintering to obtain a green body; (7) the green body obtained in step (6) is sintered in an atmosphere containing water vapor to obtain yttria-stabilized zirconia.

[0006] Preferably, the chelating agent in step (2) comprises at least one of citric acid, oxalic acid and acetylacetone; and the molar ratio of the chelating agent to yttrium ions in yttrium nitrate is (1-3):1.

[0007] Preferably, the zirconium source in step (3) is ZrOCl2·8H2O.

[0008] Preferably, the dispersing agent in step (3) comprises at least one of polyethylene glycol, anhydrous ethanol and isopropyl alcohol; and the mass ratio of the zirconium source to the dispersing agent is (11-13):1.

[0009] Preferably, the temperature of the sol-gel in step (4) is 50-100℃, and the time of the sol-gel is 10-20h.

[0010] Preferably, the temperature of the heat pre-sintering in step (5) is 400-700℃, and the time of the heat pre-sintering is 1-3h; the temperature of the heat treatment is 600-1000℃, and the time of the heat treatment is 1-5h.

[0011] Preferably, the temperature of the pre-sintering in step (6) is 800-1200℃, the time of the pre-sintering is 1-5h, and the rate of the temperature rising to the pre-sintering temperature is 5-10℃ / min.

[0012] Preferably, the volume content of the water vapor in the atmosphere containing water vapor in step (7) is 10-100%; the temperature of the sintering is 1000-1600℃, the time of the sintering is 1-500h, and the rate of the temperature rising to the sintering temperature is 1-10℃ / min.

[0013] The application further provides the yttria-stabilized zirconia prepared by the preparation method.

[0014] The application further provides the application of the yttria-stabilized zirconia as an electrolyte of a high-temperature solid oxide fuel cell.

[0015] This invention provides a method for preparing yttrium oxide-stabilized zirconium oxide, comprising the following steps: (1) mixing yttrium oxide with nitric acid solution to perform a metathesis reaction to obtain yttrium nitrate; (2) mixing the yttrium nitrate obtained in step (1) with water and a chelating agent to obtain a yttrium nitrate solution; (3) mixing a zirconium source with water and a dispersant to obtain a zirconium source solution; (4) mixing the yttrium nitrate solution obtained in step (2) with the zirconium source solution obtained in step (3), performing sol-gel and drying to obtain a gel; (5) subjecting the gel obtained in step (4) to heat pre-calcination and heat treatment in sequence to obtain nanoparticles; (6) subjecting the nanoparticles obtained in step (5) to pressing and pre-sintering in sequence to obtain a green body; (7) sintering the green body obtained in step (6) in an atmosphere containing water vapor to obtain yttrium oxide-stabilized zirconium oxide. This invention utilizes the sol-gel method to prepare nanoparticles with small particle size, large specific surface area, and high activity, resulting in a significantly lower densification temperature. Sintering the YSZ nanoparticles in a water vapor atmosphere lowers the oxygen partial pressure, causing lattice oxygen to escape and form oxygen vacancies. Simultaneously, the hydrogen proton defects generated by hydrolysis reduce the formation energy of cation defects, promoting defect formation. Oxygen vacancies and defects provide channels for atomic diffusion, thereby promoting atomic diffusion. Furthermore, hydroxyl groups adsorbed on the YSZ surface form ionic bonds with cations, OH... - The diffusion rate is much higher than that of O 2- Due to electrostatic interaction, the diffusion of cations is also promoted, which in turn promotes the sintering of YSZ, accelerates the densification process of the material, and improves the density of the material. This achieves low-temperature densification of YSZ and solves the problem caused by high-temperature sintering of electrolytes in high-temperature solid oxide fuel cells. Attached Figure Description

[0016] Figure 1 This invention provides schematic diagrams of the YSZ grain sintering stage under the action of water vapor and hydroxyl-accelerated sintering. Figure 2 SEM images of the green blank prepared in Example 1, and the yttrium oxide-stabilized zirconium oxide prepared in Examples 1-3 and Comparative Examples 1-3; Figure 3 Density and grain size diagrams of the green blank prepared in Example 1, and the yttrium-stabilized zirconia prepared in Examples 1-3 and Comparative Examples 1-3; Figure 4 Two-dimensional surface profiles of yttrium oxide-stabilized zirconium oxide prepared in Examples 1-3 and Comparative Examples 1-3; Figure 5 The g-values ​​and static magnetic field diagrams of yttrium-stabilized zirconia prepared in Examples 1-3 and Comparative Examples 1-3 are shown. Detailed Implementation

[0017] This invention provides a method for preparing yttrium oxide-stabilized zirconium oxide, comprising the following steps: (1) Yttrium oxide is mixed with nitric acid solution to carry out a metathesis reaction to obtain yttrium nitrate; (2) Mix the yttrium nitrate obtained in step (1) with water and a chelating agent to obtain a yttrium nitrate solution; (3) Mix the zirconium source with water and dispersant to obtain a zirconium source solution; (4) The yttrium nitrate solution obtained in step (2) is mixed with the zirconium source solution obtained in step (3), and the mixture is sol-gelled and then dried to obtain a gel; (5) The gel obtained in step (4) is subjected to heat pre-calcination and heat treatment in sequence to obtain nanoparticles; (6) The nanoparticles obtained in step (5) are pressed and pre-sintered in sequence to obtain a green body; (7) The green body obtained in step (6) is sintered in an atmosphere containing water vapor to obtain yttrium-stabilized zirconium oxide.

[0018] Unless otherwise specified, the present invention does not impose any special restrictions on the source of the raw materials, and commercially available products well known to those skilled in the art can be used.

[0019] This invention involves mixing yttrium oxide with nitric acid solution to perform a metathesis reaction, thereby obtaining yttrium nitrate.

[0020] In this invention, the particle size of the yttrium oxide is preferably ≤50nm; the purity of the yttrium oxide is preferably ≥99%.

[0021] In this invention, the nitric acid solution is preferably prepared by mixing concentrated nitric acid and water.

[0022] In this invention, the mass concentration of the concentrated nitric acid is preferably 68%.

[0023] In this invention, the preferred mass ratio of yttrium oxide to concentrated nitric acid is 0.80321 g : (2~10) mL. As one embodiment, the specific mass ratio of yttrium oxide to concentrated nitric acid can be 0.80321 g : 2 mL, 0.80321 g : 3 mL, 0.80321 g : 4 mL, 0.80321 g : 5 mL, 0.80321 g : 6 mL, 0.80321 g : 7 mL, 0.80321 g : 8 mL, 0.80321 g : 9 mL, or 0.80321 g : 10 mL.

[0024] In this invention, the water is preferably deionized water.

[0025] In this invention, the preferred mass-to-volume ratio of yttrium oxide to water is 0.80321 g : (20~50) mL. As one embodiment, the specific mass-to-volume ratio of yttrium oxide to water can be 0.80321 g : 20 mL, 0.80321 g : 25 mL, 0.80321 g : 30 mL, 0.80321 g : 35 mL, 0.80321 g : 40 mL, 0.80321 g : 45 mL, or 0.80321 g : 50 mL.

[0026] In this invention, the mixing temperature is preferably 50-80°C. As one embodiment, the mixing temperature can specifically be 50°C, 60°C, 70°C, or 80°C. This invention does not have a specific limitation on the mixing time, as long as yttrium oxide is completely dissolved.

[0027] In this invention, the preferred temperature for the metathesis reaction is 100-150°C. This invention does not impose a specific time limit on the metathesis reaction; as long as the solvent in the system is completely removed to obtain a solid powder, it is acceptable.

[0028] This invention controls the amount of each raw material and the reaction temperature within the above-mentioned range, which enables yttrium oxide to react fully to form yttrium nitrate.

[0029] After obtaining yttrium nitrate, the present invention mixes the yttrium nitrate with water and a chelating agent to obtain a yttrium nitrate solution.

[0030] In this invention, the water is preferably deionized water.

[0031] In this invention, the preferred mass-to-volume ratio of yttrium oxide to water is 0.80321 g : (50~100) mL. As one embodiment, the specific mass-to-volume ratio of yttrium oxide to water can be 0.80321 g : 50 mL, 0.80321 g : 60 mL, 0.80321 g : 70 mL, 0.80321 g : 80 mL, 0.80321 g : 90 mL, or 0.80321 g : 100 mL.

[0032] In this invention, the chelating agent preferably includes at least one of citric acid, oxalic acid and acetylacetone, more preferably citric acid.

[0033] In this invention, the preferred molar ratio of the chelating agent to yttrium ions in yttrium nitrate is (1~3):1. As one embodiment, the molar ratio of the chelating agent to yttrium ions in yttrium nitrate can specifically be 1:1, 1.5:1, 2:1, 2.5:1, or 3:1.

[0034] The present invention does not have any special limitations on the operation of mixing yttrium nitrate with water and chelating agent. Any mixing technology known to those skilled in the art can be used to ensure that the three are mixed evenly.

[0035] This invention involves mixing a zirconium source with water and a dispersant to obtain a zirconium source solution.

[0036] In this invention, the zirconium source is preferably ZrOCl2·8H2O.

[0037] In this invention, the mass ratio of yttrium oxide to zirconium source is preferably 1:(36~37), more preferably 1:36.9.

[0038] In this invention, the water is preferably deionized water.

[0039] In this invention, the preferred mass-to-volume ratio of the zirconium source to water is 29.63504 g : (50~100) mL. As one embodiment, the specific mass-to-volume ratio of the zirconium source to water can be 29.63504 g : 50 mL, 29.63504 g : 60 mL, 29.63504 g : 70 mL, 29.63504 g : 80 mL, 29.63504 g : 90 mL, or 29.63504 g : 100 mL.

[0040] In this invention, the dispersant preferably includes at least one of polyethylene glycol, anhydrous ethanol and isopropanol, more preferably polyethylene glycol; the molecular weight (Mw) of the polyethylene glycol is preferably 1000~3000 g / mol, more preferably 2000 g / mol.

[0041] In this invention, the preferred mass ratio of the zirconium source to the dispersant is (11~13):1. As one embodiment, the mass ratio of the zirconium source to the dispersant may specifically be 11:1, 11.5:1, 12:1, 12.5:1, or 13:1.

[0042] The present invention does not have any special limitations on the operation of mixing the zirconium source with water and dispersant. The three can be mixed evenly by means of mixing techniques known to those skilled in the art.

[0043] This invention controls the amount of each raw material in the zirconium source solution within the above-mentioned range, which is more conducive to obtaining small-particle-size nanoparticles.

[0044] After obtaining the yttrium nitrate solution and the zirconium source solution, the present invention mixes the yttrium nitrate solution and the zirconium source solution, performs sol-gelation, and then dries to obtain a gel.

[0045] In this invention, the mixing of the yttrium nitrate solution and the zirconium source solution is preferably carried out by adding the zirconium source solution dropwise to the yttrium nitrate solution and stirring until the solution is transparent and there is no precipitate.

[0046] In this invention, the dripping rate is preferably 0.5~2 mL / min, more preferably 1 mL / min.

[0047] In this invention, the temperature of the sol-gel is preferably 50-100°C; the gelation time is preferably 10-20 hours. As one embodiment, the temperature of the sol-gel can specifically be 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C; the gelation time can specifically be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours. By controlling the temperature and time of the sol-gel within the above ranges, this invention enables sufficient gel formation.

[0048] In this invention, the drying temperature is preferably 100~150℃; the drying time is preferably 24~48h. As one embodiment, the drying temperature can specifically be 100℃, 110℃, 120℃, 130℃, 140℃, or 150℃; the drying time can specifically be 24h, 25h, 28h, 30h, 35h, 40h, 45h, or 48h.

[0049] After obtaining the gel, the present invention sequentially pre-calcines and heat-treats the gel to obtain nanoparticles.

[0050] In this invention, the preheating temperature is preferably 400-700°C; the preheating time is preferably 1-3 hours. As one embodiment, the preheating temperature can specifically be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, or 700°C; the preheating time can specifically be 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours. By performing preheating and controlling the temperature and time within the above ranges, this invention can remove residual organic matter.

[0051] After the pre-calcination is completed, the present invention preferably grinds the pre-calcined product and then performs heat treatment.

[0052] The present invention does not impose any particular limitation on the grinding operation; any grinding technique well known to those skilled in the art can be used. As one embodiment, the grinding is performed in an agate mortar.

[0053] In this invention, the heat treatment temperature is preferably 600~1000℃; the heat treatment time is preferably 1~5h. As one embodiment, the heat treatment temperature can specifically be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃; the heat treatment time can specifically be 1h, 2h, 3h, 4h, or 5h. By controlling the heat treatment temperature and time within the above ranges, this invention can further obtain nanoparticles with small particle size and high crystallinity.

[0054] After heat treatment, the product of the heat treatment is preferably cooled to obtain nanoparticles.

[0055] The present invention does not impose any special limitations on the cooling operation; any cooling technique known to those skilled in the art can be used to cool the material to room temperature.

[0056] After obtaining the nanoparticles, the present invention sequentially presses and pre-sintersects the nanoparticles to obtain green bodies.

[0057] In this invention, the pressing pressure is preferably 10-50 MPa; the pressing holding time is preferably 1-5 min. As one embodiment, the pressing pressure can specifically be 10 MPa, 20 MPa, 30 MPa, 40 MPa, or 50 MPa; the pressing holding time can specifically be 1 min, 2 min, 3 min, 4 min, or 5 min.

[0058] In one embodiment, the present invention places 0.5~1.5g of nanoparticles into a mold with a diameter of 15~18mm, and presses them into shape using a uniaxial pressure of 10~50MPa for 1~5min.

[0059] In this invention, the pre-sintering temperature is preferably 800~1200℃; the pre-sintering time is preferably 1~5h; and the heating rate to the pre-sintering temperature is preferably 5~10℃ / min. As one embodiment, the pre-sintering temperature can specifically be 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, or 1200℃; the pre-sintering time can specifically be 1h, 2h, 3h, 4h, or 5h; and the heating rate to the pre-sintering temperature can specifically be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. By performing pre-sintering and controlling the temperature and time within the above ranges, this invention can further improve the density of the product.

[0060] After pre-sintering is completed, the present invention preferably cools the pre-sintered product to obtain a green blank.

[0061] In one implementation, the cooling is performed by cooling the furnace to room temperature.

[0062] After obtaining the green blank, the present invention sintersulates the green blank in an atmosphere containing water vapor to obtain yttrium oxide stabilized zirconium oxide.

[0063] In this invention, the water vapor atmosphere preferably includes a water vapor atmosphere or a mixture of water vapor and air; the volume content of water vapor in the water vapor atmosphere is preferably 10-100%. As one embodiment, the volume content of water vapor in the water vapor atmosphere can specifically be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

[0064] In this invention, the flow rate of the water vapor atmosphere is preferably 0.1~1L / min.

[0065] In one embodiment, the steam is generated by a precision steam generator; the vaporization temperature of the precision steam generator is 100~180℃; the precision steam generator is connected to a tubular furnace via a pipe; the pipe is insulated with heating tape to prevent steam condensation; the heating temperature is 100~180℃. This invention does not impose any special limitations on the model or source of the precision steam generator; commercially available products well-known to those skilled in the art can be used.

[0066] In this invention, the sintering temperature is preferably 1000~1600℃; the sintering time is preferably 1~500h; and the rate of heating to the sintering temperature is preferably 1~10℃ / min. In one embodiment, the sintering temperature can specifically be 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃, or 1600℃; the sintering time can specifically be 1h, 50h, 100h, 150h, 200h, 250h, 300h, 350h, 400h, 450h, or 500h; and the rate of heating to the sintering temperature can specifically be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. By controlling the sintering temperature and time within the above ranges, this invention can further improve the density of the product.

[0067] After sintering, the present invention preferably cools the sintered product to obtain yttrium oxide stabilized zirconium oxide.

[0068] In one implementation, the cooling is performed by cooling the furnace to room temperature.

[0069] In one implementation, the sintering is carried out in a tube furnace.

[0070] As one implementation method, after sintering is completed, the precision steam generator is turned off to prevent water accumulation and cracking of the tubular furnace tubes during the cooling process.

[0071] Existing technologies for preparing YSZ powder typically employ solid-state reaction methods, resulting in micron-sized powders with relatively large particle sizes. This invention utilizes a sol-gel method to prepare nano-sized powders. Nanoparticles, due to their small particle size, large specific surface area, and high activity, significantly reduce their densification temperature. Furthermore, existing technologies typically sinter YSZ in air, which, due to low defect concentration and a lack of pathways to accelerate atomic diffusion, results in a relatively low densification rate, posing a challenge for high-temperature sintering. This invention, however, sintersulates under high-temperature water vapor. Firstly, the reduced oxygen partial pressure under high-temperature water vapor leads to lattice oxygen overflow, forming oxygen vacancies. Simultaneously, the hydrogen proton defects generated by hydrolysis lower the formation energy of cation defects, promoting defect formation. Oxygen vacancies and defects provide pathways for atomic diffusion, thus promoting atomic diffusion. Secondly, hydroxyl groups adsorbed on the YSZ surface form ionic bonds with cations, resulting in OH groups... - The diffusion rate is much higher than that of O 2- Due to electrostatic interaction, the diffusion of cations is also promoted, which in turn promotes the sintering of YSZ, accelerates the densification process of the material, and improves the density of the material. This achieves low-temperature densification of YSZ and solves the problem caused by high-temperature sintering of electrolytes in high-temperature solid oxide fuel cells.

[0072] A schematic diagram of the YSZ grain sintering stage under water vapor in the preparation method provided by this invention is shown below. Figure 1 As shown in (b), the schematic diagram of hydroxyl-accelerated sintering is as follows. Figure 1 As shown in (a) and (c). Among them Figure 1 (a) and (c) further illustrate the main pathways of accelerated diffusion of hydroxyl groups. First, as... Figure 1 As shown in (a), due to the oxygen permeability of YSZ at high temperatures, hydroxyl groups dissociate from water vapor and readily diffuse into the crystal lattice. Subsequently, the hydroxyl groups may react with yttrium to form volatile hydroxides and react with lattice oxygen to generate oxygen vacancies. Furthermore, driven by the decrease in the total free energy of the system, hydroxyl groups, vacancies, and gaseous hydroxides always tend to diffuse into the crystal lattice. Dehydration reactions between hydroxyl groups formed on adjacent grains may lead to grain bonding, such as... Figure 1 As shown in (c), defects containing vacancies can accelerate the lattice diffusion rate, while gaseous hydroxides promote sintering through gas-phase transport mechanisms. Sintering diffusion in air is dominated by grain boundary diffusion, while diffusion in water vapor is dominated by lattice diffusion. The diffusion coefficient of lattice diffusion is greatly increased, and the space occupied by the lattice is much larger than that of the grain boundary. Therefore, the shift from grain boundary diffusion to lattice diffusion as the dominant diffusion mechanism directly leads to a significant increase in the material's diffusion efficiency. The phase transformation and sintering rate controlled by diffusion efficiency are accelerated. The water vapor corrosion reaction and the effect of hydroxyl groups are also enhanced, further promoting sintering in water vapor, thereby achieving low-temperature densification.

[0073] The present invention also provides yttrium-stabilized zirconium oxide prepared by the preparation method described in the above technical solution.

[0074] The present invention also provides the application of yttrium-stabilized zirconium oxide as an electrolyte in high-temperature solid oxide fuel cells as described in the above technical solution.

[0075] The present invention does not impose any special limitations on the operation of the application, and any technical solution known to those skilled in the art can be used.

[0076] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0077] Example 1 A method for preparing yttrium-stabilized zirconium oxide is as follows: (1) 0.80321g of Y2O3 (≤50nm, purity 99%) is added to 5mL of concentrated nitric acid (mass concentration of 68%) and 30mL of deionized water, heated at 65℃ until dissolved, and then subjected to a metathesis reaction at 120℃ to obtain solid yttrium nitrate; (2) Mix the solid yttrium nitrate obtained in step (1) with 80 mL of deionized water, and add 38.4252 g of citric acid (the molar ratio of citric acid to yttrium ions is 2:1) to obtain a yttrium nitrate solution; (3) Mix 29.63504 g of ZrOCl2·8H2O and 80 mL of deionized water, and add 2.462622 g of polyethylene glycol (Mw is 2000 g / mol) to obtain zirconium oxychloride solution; (4) Add the zirconium oxychloride solution obtained in step (3) to the yttrium nitrate solution obtained in step (2) (dropping rate 1 mL / min), stir until the solution is transparent and there is no precipitate, then gel at 80℃ for 15 h, and then dry at 120℃ for 36 h to obtain a yellow gel; (5) The yellow gel obtained in step (4) was preheated at 600°C for 2 hours, crushed with an agate mortar, and then heat-treated at 800°C for 3 hours. After cooling, sol-gel YSZ nanopowder was obtained. (6) Pour 1g of the sol-gel YSZ nanopowder obtained in step (5) into a mold with a diameter of 16mm, press it with a uniaxial pressure of 30MPa for 2min, and then heat it to 1000℃ in a tube furnace at a rate of 8℃ / min for 2h for pre-sintering. Cool it to room temperature with the furnace to obtain the green body. (7) Connect the tubular furnace to the precision steam generator and the gas cylinder, and introduce steam and compressed air into the tubular furnace together at a flow rate of 0.8 L / min. The volume content of steam in the mixture of steam and compressed air is 20%, the vaporization temperature of the precision steam is 120℃, and the heating temperature is 120℃. Place the green blank into the tubular furnace and heat it to 1200℃ at a rate of 5℃ / min for sintering for 100h. Turn off the precision steam generator and cool it to room temperature with the furnace to obtain yttrium-stabilized zirconia.

[0078] Example 2 Replace the sintering time in step (7) of Example 1 with 300h, and everything else is the same as in Example 1.

[0079] Example 3 Replace the sintering time in step (7) of Example 1 with 500h, and everything else is the same as in Example 1.

[0080] Comparative Example 1 A method for preparing yttrium oxide-stabilized zirconium oxide is as follows: (1)~(6) are the same as in Example 1, to obtain a green blank; (7) The green blank obtained in step (6) is placed in a tube furnace and sintered at 1200°C for 100 hours in an air atmosphere at a rate of 5°C / min. The green blank is then cooled to room temperature in the furnace to obtain yttrium-stabilized zirconia.

[0081] Comparative Example 2 Replace the sintering time in step (7) of Comparative Example 1 with 300h, and keep everything else the same as Comparative Example 1.

[0082] Comparative Example 3 Replace the sintering time in step (7) of Comparative Example 1 with 500h, and keep everything else the same as Comparative Example 1.

[0083] SEM images of the green blank prepared in Example 1, and the yttrium oxide-stabilized zirconia prepared in Examples 1-3 and Comparative Examples 1-3 are shown below. Figure 2 As shown. From Figure 2 It can be seen that the surface porosity decreases with increasing sintering time. Compared with sintering in air (e~g), the porosity of sintering in steam (b~d) is significantly reduced, indicating that heat treatment in steam significantly promotes the densification process. That is, sintering in steam achieves a density comparable to that in air. The densification sintering temperature in steam is lower, that is, low-temperature densification is achieved.

[0084] The density and grain size of the green blank prepared in Example 1, and the yttrium-stabilized zirconia prepared in Examples 1-3 and Comparative Examples 1-3 are as follows: Figure 3 As shown. From Figure 3 It can be seen that, compared with sintering in air, sintering under water vapor results in greater density and grain size, meaning that water vapor promotes the sintering of YSZ.

[0085] Two-dimensional surface profiles of yttrium oxide-stabilized zirconium oxide prepared in Examples 1-3 and Comparative Examples 1-3 are shown below. Figure 4 As shown. From Figure 4 It can be seen that sintering kinetics are mainly related to the pore healing rate, and the coarsening scale and rate are the two main factors affecting the sintering process. The pore surfaces are coarsened under the conditions of Examples 1-3 and Comparative Examples 1-3, but the coarsening rates under water vapor and air are significantly different. The arithmetic mean linear roughness under water vapor... R a and surface roughness S a Both were significantly greater than those in air. After sintering for 100 hours, the roughness of the sample under water vapor was 0.0891 μm, significantly greater than that in air (~0.0372 μm). Higher surface roughness indicates a larger contact area and a higher healing rate, suggesting that the densification rate under water vapor was significantly higher than that in air during the early stages of sintering. However, the roughness under water vapor did not change much after sintering for 300 and 500 hours, consistent with the significant decrease in densification rate during the later stages of water vapor sintering. The surface roughness after 300 hours of sintering in air was similar to that after 100 hours, but after 500 hours, the surface roughness increased significantly, consistent with the fact that densification in air mainly occurs in the later stages of sintering.

[0086] The g-values ​​and static magnetic fields of yttrium oxide-stabilized zirconium oxide prepared in Examples 1-3 and Comparative Examples 1-3 are as follows: Figure 5 As shown. From Figure 5 It can be seen that g=2.004 indicates the formation of oxygen vacancies. At the same location, the peak intensity of the static magnetic field under high-temperature steam is significantly higher than that in air, indicating that high-temperature steam promotes the formation of oxygen vacancies. This is mainly because high-temperature steam reduces the oxygen partial pressure, promoting the overflow of lattice oxygen. Furthermore, regardless of whether it is under steam or air, the peak intensity of the YSZ static magnetic field increases with increasing sintering time, indicating that oxygen vacancies increase with prolonged sintering time. As previously mentioned, the densification mechanism under high-temperature steam changes from grain boundary diffusion to lattice diffusion. This is mainly because the oxygen vacancies generated by the reduced oxygen partial pressure under high-temperature steam accelerate the diffusion of ions through the lattice, thereby accelerating the densification process.

[0087] In summary, the method provided by this invention achieves low-temperature densification of YSZ.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing yttrium oxide-stabilized zirconium oxide, comprising the following steps: (1) Yttrium oxide is mixed with nitric acid solution to carry out a metathesis reaction to obtain yttrium nitrate; (2) Mix the yttrium nitrate obtained in step (1) with water and a chelating agent to obtain a yttrium nitrate solution; (3) Mix the zirconium source with water and dispersant to obtain a zirconium source solution; (4) The yttrium nitrate solution obtained in step (2) is mixed with the zirconium source solution obtained in step (3), and the mixture is sol-gelled and then dried to obtain a gel; (5) The gel obtained in step (4) is subjected to heat pre-calcination and heat treatment in sequence to obtain nanoparticles; (6) The nanoparticles obtained in step (5) are pressed and pre-sintered in sequence to obtain a green body; (7) The green body obtained in step (6) is sintered in an atmosphere containing water vapor to obtain yttrium-stabilized zirconium oxide.

2. The preparation method according to claim 1, characterized in that, The chelating agent in step (2) includes at least one of citric acid, oxalic acid and acetylacetone; the molar ratio of the chelating agent to yttrium ions in yttrium nitrate is (1~3):

1.

3. The preparation method according to claim 1, characterized in that, The zirconium source in step (3) is ZrOCl2·8H2O.

4. The preparation method according to claim 1, characterized in that, The dispersant in step (3) includes at least one of polyethylene glycol, anhydrous ethanol and isopropanol; the mass ratio of the zirconium source to the dispersant is (11~13):

1.

5. The preparation method according to claim 1, characterized in that, In step (4), the temperature of the sol-gel is 50~100℃ and the sol-gel time is 10~20h.

6. The preparation method according to claim 1, characterized in that, In step (5), the preheating temperature is 400~700℃ and the preheating time is 1~3h; the heat treatment temperature is 600~1000℃ and the heat treatment time is 1~5h.

7. The preparation method according to claim 1, characterized in that, In step (6), the pre-sintering temperature is 800~1200℃, the pre-sintering time is 1~5h, and the rate of heating to the pre-sintering temperature is 5~10℃ / min.

8. The preparation method according to claim 1, characterized in that, In step (7), the volume content of water vapor in the atmosphere containing water vapor is 10-100%; the sintering temperature is 1000-1600℃, the sintering time is 1-500h, and the rate of heating to the sintering temperature is 1-10℃ / min.

9. Yttrium-stabilized zirconium oxide prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the yttrium-stabilized zirconium oxide as described in claim 9 as an electrolyte for high-temperature solid oxide fuel cells.

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