A method for preparing a dense ceramic film by low-temperature melt reaction

Abstract

The application provides a low-temperature melt reaction method for preparing a dense ceramic film. The application introduces a low-temperature melt, makes high-melting-point reactants dissolve in the melt and react, and after reaching supersaturation, the target product crystals are precipitated and gradually grow and connect, and finally a dense ceramic film with a thickness of 1-10 microns is obtained. The application changes the solid-solid system in the traditional sintering method into a solid-liquid system, and the mass transfer and reaction rate are faster; meanwhile, the problems such as deformation and element segregation caused by the traditional high-temperature sintering (>1200 DEG C) can be avoided; energy is saved, the method is simple, the cost is low, special instruments and equipment are not needed, and large-scale preparation is easy to realize.

Description

Technical Field

[0001] This invention belongs to the field of functional ceramic materials, and specifically relates to a method for densifying ceramic thin films at low temperatures using melt reaction. Background Technology

[0002] Functional ceramics have wide applications in key fields such as optoelectronics and energy. For example, BaTiO3, with its high dielectric constant, is often used in the fabrication of ceramic capacitors; SrTiO3, due to its excellent photocatalytic properties, is used as a photoelectrode material; and SrZrO3 and BaZrO3 can serve as proton conductor materials for next-generation solid-state oxide batteries. However, most functional ceramics have sintering temperatures above 1200℃, making it difficult to achieve a dense sinter and requiring significant time and energy. Over-firing and deformation may occur after high-temperature sintering, affecting mechanical properties; furthermore, elements may easily volatilize and segregate during high-temperature sintering, ultimately deviating from the stoichiometric ratio and affecting the performance of functional ceramics.

[0003] Common methods for lowering densification temperature include adding sintering aids or using nanoparticles for sintering, but both have limited effectiveness, and the addition of sintering aids may adversely affect ceramic properties. Researchers have continuously optimized densification techniques, developing advanced sintering methods such as hot pressing, spark plasma sintering, microwave sintering, and cold sintering. These methods provide external driving forces such as heat, pressure, microwaves, and pulses to the powder to promote ceramic densification, which can reduce the sintering difficulty and shorten the sintering time to some extent. However, some new sintering technologies can operate at temperatures as high as 2000℃, failing to truly solve problems such as deformation and elemental segregation caused by high-temperature sintering; moreover, they require specific and expensive equipment, making large-scale industrial application difficult. Therefore, there is a need to develop a truly low-temperature densification technology that is inexpensive, simple, easy to implement on a large scale, and truly effective. Summary of the Invention

[0004] Melt growth has significant advantages such as rapid growth, high crystal purity, and good integrity, making it one of the important and commonly used methods for growing large single crystal materials and crystals of specific shapes. This invention provides a low-temperature densification method for ceramic thin films based on melt reaction, comprising the following steps:

[0005] (1) The reactant powder is mixed with surfactants, binders and other organic substances and ball-milled to obtain a reactant slurry. The reactant slurry is then evenly coated onto a substrate and calcined to remove the organic substances.

[0006] (2) Press a certain amount of low melting point melt powder into a sheet and place it on the upper surface of the coating in step (1).

[0007] (3) Place the composition of step (2) into a tube furnace and ventilate for reaction; the reaction temperature is not higher than 600℃; after the melt powder reaches the melting point, it becomes molten, the reactants dissolve in it and react with the melt, and after reaching a certain supersaturation, the product crystals precipitate and continue to grow and grow. After the reaction is completed, wash with deionized water to obtain a dense ceramic film.

[0008] The reactant powder is a raw material used to prepare ceramic thin films and is a metal oxide;

[0009] The melt powder is a raw material used to prepare ceramic thin films, and is a metal oxide or metal salt; at the same time, after the melt powder melts, it also plays a role in dissolving the high-melting-point reactant powder and providing a molten environment for crystal growth.

[0010] The melting point of the reactant powder is higher than that of the molten powder; the melting point of the molten powder is not higher than 600°C.

[0011] The reactant powders are TiO2, ZrO2, Y2O3, CeO2, and (ZrO2). 0.92 (Y2O3) 0.08 One or more of (8YSZ) are added to the reactant slurry, and the organic matter added to the slurry is two or more of ethanol, methyl ethyl ketone, triethanolamine, polyvinyl butyral resin (PVB), and butyl benzyl phthalate (BBP), and the solid content of the slurry is 16 to 38 wt%.

[0012] The reactant slurry can be uniformly coated onto the substrate surface using spin coating or dipping methods. The substrate can be selected according to the application scenario; generally, a corundum substrate is chosen, but if it is to be fabricated into a battery, a solid oxide battery anode can also be used as the substrate.

[0013] The low-melting-point melt powder includes any one or a mixture of several of Ba(NO3)2 (melting point: 590℃), BaO2 (melting point: 450℃), and Sr(NO3)2 (melting point: 570℃). The mass of the melt powder is weighed to ensure it can be pressed into a complete disc, generally 0.2–0.5 g.

[0014] Furthermore, in the above technical solution, the reactant powder has a coating thickness of micrometers and a mass of milligrams; after the melt powder melts, it can dissolve the reactant powder and react with it, and it needs to continuously provide a melting environment for the growth of product crystals. Therefore, the melt powder in this system must be in much excess of the reactant powder.

[0015] Furthermore, in the above technical solution, the mass of the melt powder is at least 10 times or more of the mass of the reactant powder.

[0016] The atmosphere of the tubular furnace is oxygen or an inert atmosphere, the purpose of which is to prevent the reaction with CO2 in the air to generate carbonate impurities, and at the same time to inhibit the melt from decomposing too quickly after reaching the melting point.

[0017] The reaction temperature in step (3) is no higher than 600℃. The reaction temperature is sufficient to melt the selected melt powder without decomposition. For example, if the melt is Ba(NO3)2, the reaction temperature can be ≥590℃. The reaction time is 6 to 24 hours.

[0018] The thickness of the dense ceramic film is determined according to the coating thickness in step (1). The film thickness can be controlled by adjusting the spin coating speed, immersion time or slurry concentration, and is generally 1 to 10 μm.

[0019] The advantages of this invention are: (1) It utilizes a simple low-temperature melt reaction to prepare dense ceramic films, dissolving high-melting-point reactants in a suitable molten salt for reaction, thereby transforming the solid-solid system in the traditional sintering method into a solid-liquid system, greatly improving mass transfer and reaction rate, and enhancing interfacial contact. (2) Most importantly, it develops a truly meaningful low-temperature densification technology. Depending on the selected melt, the densification temperature can be reduced to below 600℃, far lower than the traditional sintering temperature (>1200℃). (3) This method is inexpensive and simple, requires no specific equipment, is suitable for large-scale production, and is expected to be widely applied in the field of ceramic densification. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the principle of preparing dense ceramic films using the low-temperature melt reaction method described in this invention.

[0021] Figure 2 The images shown are electron microscope (EM) images of the reactant coating prepared in step 1 of Example 2 of the present invention, where a) is a surface EEM image and b) is a cross-sectional EEM image.

[0022] Figure 3 This is an electron microscope image of the dense ceramic film prepared in step 3 of Example 6 of the present invention.

[0023] Figure 4 The images shown are electron microscope (EM) images of the dense film prepared in step 3 of Example 6 of the present invention after cleaning, where a) is a surface EEM image and b) is a cross-sectional low-magnification EEM image. Detailed Implementation

[0024] The following embodiments will further illustrate the present invention, but are not intended to limit the invention.

[0025] Example 1

[0026] Preparation of dense BaTiO3 ceramic films from Ba(NO3)2 melt:

[0027] Step 1: Preparation of nano-TiO2 coating. Using 30g of nano-TiO2 (particle size approximately 40nm) as the starting material, 50g of anhydrous ethanol and 20g of butanone as solvents, and 0.3g of triethanolamine as a surfactant, the mixture was ball-milled for 24h. Subsequently, 5g of butyl benzyl phthalate and 2.7g of polyvinyl butyral were added as dispersants and binders, and the mixture was ball-milled for another 24h to obtain a uniformly dispersed nano-TiO2 slurry. 0.5mL of the above nano-TiO2 slurry was spin-coated onto a corundum substrate (approximately 20mm in diameter) at 3000rpm for 60 seconds. The resulting film was calcined at 500℃ for 2h to remove organic matter, yielding a uniform nano-TiO2 coating with a thickness of approximately 1μm. The coating morphology was similar to that of the substrate. Figure 2 resemblance.

[0028] Step 2: Preparation of a dense BaTiO3 film. 0.2 g of Ba(NO3)2 tablets were placed on the nano-TiO2 coating obtained in Step 1, and the mixture was placed in a tube furnace and reacted at 590°C for 6 hours with oxygen flowing at a rate of 100 mL / min. -1 After the reaction, the film was washed with deionized water and dried to obtain a dense BaTiO3 ceramic film with a thickness of approximately 1 μm, exhibiting a density similar to... Figure 4 Consistent.

[0029] Example 2

[0030] Preparation of dense BaZrO3 ceramic films from Ba(NO3)2 melt:

[0031] Step 1: Preparation of nano-ZrO2 coating. Using 40g of nano-ZrO2 (particle size approximately 200nm) as the starting material, 50g of anhydrous ethanol and 20g of butanone as solvents, and 0.3g of triethanolamine as a surfactant, the mixture was ball-milled for 24h. Subsequently, 5g of butyl benzyl phthalate and 5.4g of polyvinyl butyral were added as dispersants and binders, and the mixture was ball-milled for another 30h to obtain a uniformly dispersed nano-ZrO2 slurry. 1mL of this slurry was spin-coated onto a corundum substrate at 2600rpm for 45s, repeated twice. The resulting film was calcined in a muffle furnace at 500℃ for 2h to remove organic matter, yielding a ZrO2 coating with a thickness of approximately 10μm. Figure 2 As shown.

[0032] Step 2: Preparation of a dense BaZrO3 film. Place 0.4 g of Ba(NO3)2 tablets onto the ZrO2 coating obtained in Step 1, and incubate in 200 mL of water for [unclear - likely a specific process or time]. -1 The reaction was carried out in oxygen for 24 hours at a temperature of 590℃. After the reaction, the film was washed with deionized water and dried overnight to obtain a dense BaZrO3 film with a thickness of approximately 10 μm. The density of the film was similar to that of the standard BaZrO3 film. Figure 4 resemblance.

[0033] Example 3

[0034] Preparation of dense BaCeO3 ceramic films from Ba(NO3)2 melt:

[0035] Step 1: Preparation of nano-CeO2 coating. Using 17g of nano-CeO2 (particle size <50nm) as the starting material, 40g of anhydrous ethanol and 20g of butanone as solvents, and 0.3g of triethanolamine as a surfactant, the mixture was ball-milled for 24h. Then, 5g of butyl benzyl phthalate and 2g of polyvinyl butyral were added as dispersants and binders, and ball-milling continued for another 24h to obtain a uniformly dispersed nano-CeO2 slurry. 0.5mL of the above nano-CeO2 slurry was spin-coated onto a corundum substrate at 3000rpm for 60s, repeating the spin-coating twice. The resulting film was calcined in a muffle furnace at 500℃ for 2h to remove organic matter, yielding a CeO2 coating with a thickness of approximately 3μm. The coating morphology is similar to... Figure 2 Consistent.

[0036] Step 2: Preparation of a dense BaCeO3 film. 0.2 g of Ba(NO3)2 tablets were compressed and placed on the nano-CeO2 coating obtained in Step 1. The mixture was then placed in a tube furnace and purged with 100 mL of hot air for 1 minute. -1 Oxygen was reacted at 590℃ for 10 h. After the reaction, the mixture was washed with deionized water and dried to obtain a dense BaCeO3 ceramic film with a thickness of approximately 3 μm. The density was characterized by electron microscopy. Figure 4 Consistent.

[0037] Example 4

[0038] Preparation of dense BaZrO3 ceramic films from BaO2 melt:

[0039] Step 1: Prepare a nano-ZrO2 coating. Same as Step 1 in Example 2.

[0040] Step 2: Preparation of a dense BaZrO3 film. 0.5 g of pure BaO2 was compressed into a tablet and placed on the nano-ZrO2 coating obtained in Step 1. The mixture was then placed in a tube furnace and purged with 100 mL of hot air for a short time. -1 Argon gas was used to react at 500℃ for 24 hours. After the reaction, the mixture was soaked in deionized water overnight and then dried to obtain a dense BaZrO3 ceramic film with a thickness of about 10 μm. The degree of density was characterized by electron microscopy.

[0041] Example 5

[0042] Dense Ba2O3 was prepared from a mixed melt of Ba(NO3)2 and Sr(NO3)2. 0.5 Sr 0.5 TiO3 ceramic membrane

[0043] Step 1: Prepare a nano-TiO2 coating. Same as Step 1 in Example 1.

[0044] Step 2: Preparation of Ba 0.5 Sr 0.5 A dense TiO3 film was formed. A 0.24 g mixture of Ba(NO3)2 and Sr(NO3)2 melt powder (molar ratio 1:1) was ground, pressed into discs, and placed on the TiO2 coating obtained in step 1. The mixture was then placed in a tube furnace and reacted at 600°C for 6 hours with oxygen flowing at a rate of 100 mL / min. -1 After the reaction was complete, the sample was washed with deionized water and dried overnight. Ba was characterized by electron microscopy. 0.5 Sr 0.5 The TiO3 ceramic film has a density of approximately 1 μm and a density similar to that of other ceramic films. Figure 4 .

[0045] Example 6

[0046] Dense BaZr prepared from Ba(NO3)2 melt 0.85 Y 0.15 O 3-δ (BZY) Solid Oxide Electrolyte Membrane

[0047] Step 1: Preparation of the BZY solid oxide battery anode support layer. Using BaCO3, Y2O3, ZrO2, and NiO as raw materials, the BZY anode support layer was prepared by tape casting and sintered at 1500℃ for 6 hours, wherein BZY:NiO = 1:1wt%.

[0048] Step 2: Preparation of nano-(ZrO2) 0.92 (Y2O3) 0.08 (8YSZ) Coating. Using 50g of nano-8YSZ (particle size approximately 50nm) as the starting material, 50.4g of anhydrous ethanol and 20g of butanone as solvents, and 0.3g of triethanolamine as a surfactant, the mixture was ball-milled for 24h. Subsequently, 5g of butyl benzyl phthalate and 5.4g of polyvinyl butyral were added as dispersants and binders, and the mixture was ball-milled for another 24h to obtain a uniformly dispersed nano-8YSZ slurry. 1mL of the 8YSZ slurry was spin-coated onto a polished BZY anode substrate at 2600rpm for 60s, repeated twice. The resulting film was calcined in a muffle furnace at 500℃ for 2h to remove organic matter. Electron microscopy characterized the coating thickness as approximately 8μm, with morphology similar to... Figure 2 Consistent.

[0049] Step 3: Preparation of a dense BZY electrolyte membrane. 0.4 g of Ba(NO3)2 was pressed into a disc and placed on the 8YSZ coating obtained in Step 2. The disc was then placed in a tube furnace and reacted at 590 °C for 12 h with oxygen flowing at a rate of 200 mL / min. -1 After the reaction, the morphology is as follows: Figure 3As shown. A dense BZY solid oxide electrolyte membrane can be obtained by washing with deionized water and drying. The surface and cross-sectional morphology are shown in [Figure number missing]. Figure 4 . at 50mL min -1 10% H2 / Ar (containing 3% H2O) and 50 mL min -1 Using air as fuel, the open-circuit voltage of the half-cell was measured at 550℃ to be 1.05V, which is close to the theoretical value.

[0050] Example 7

[0051] Dense BaCe prepared from Ba(NO3)2 melt 0.6 Zr 0.4 O 3-δ (BCZ) Solid Oxide Electrolyte Membrane

[0052] Step 1: Preparation of the BCZ solid oxide battery anode support layer. A porous BCZ anode support layer was prepared using BaCO3, CeO2, ZrO2, NiO, and spherical graphite (8 μm) as raw materials via a tape casting method and sintered at 1450℃ for 6 h. The ratio of BCZ to NiO was 1:1 wt%, and the spherical graphite accounted for 20% of the total weight.

[0053] Step 2: Preparation of CeO2 and ZrO2 composite coating. Using CeO2 and ZrO2 as starting materials, with a total solid content of 15.2 g, the materials were added according to a stoichiometric ratio. 50 g of anhydrous ethanol and 20 g of butanone were used as solvents, and 0.3 g of triethanolamine was used as a surfactant. The mixture was ball-milled for 24 h, followed by the addition of 5 g of butyl benzyl phthalate and 2 g of polyvinyl butyral as dispersants and binders, and ball-milled for another 24 h to obtain a uniformly dispersed CeO2 and ZrO2 composite slurry. This CeO2 and ZrO2 composite slurry was then dipped into the BCZ anode substrate prepared in Step 1 at a pressure of -0.05 MPa for 60 s. The resulting membrane was calcined in a muffle furnace at 500 °C for 2 h to remove organic matter. Excess coating on the opposite side was then polished away to obtain the CeO2 and ZrO2 composite coating with a thickness of approximately 10 μm.

[0054] Step 3: Preparation of a dense BCZ electrolyte membrane. Place 0.5 g Ba(NO3)2 tablets onto the CeO2 and ZrO2 composite coating obtained in Step 2, and place the membrane in a tube furnace with 200 mL of hot water flowing through it. -1 Oxygen was reacted at 590℃ for 24 hours. After the reaction, the membrane was washed with deionized water and dried to obtain a dense BCZ solid oxide electrolyte membrane. The membrane was then processed at 50 mL / min. -1 H2 (containing 3% H2O) and 50 mL min -1 Using air as fuel, the open-circuit voltage of the BCZ half-cell was measured at 550℃ to be 1.03V, which is close to the theoretical value.

[0055] Many examples can be listed above. As long as a uniformly densely packed reactant coating is prepared and a suitable low-temperature melt is found, a dense ceramic film can theoretically be prepared according to the low-temperature melt reaction method proposed in this invention.

Claims

1. A melt reaction-based, low temperature densification method for ceramic membranes, characterized by, The method includes the following steps: (1) Prepare the reactant powder into a slurry, coat it evenly on the substrate and calcine to remove organic matter; (2) Press a certain amount of low melting point melt powder into a sheet and place it on the upper surface of the coating in step (1); (3) Place the composition of step (2) into a tube furnace and ventilate for reaction; the reaction temperature is not higher than 600℃; after the melt powder reaches the melting point, it becomes molten, the reactants dissolve in it and react with the melt, and after reaching a certain supersaturation, the product crystals precipitate and continue to grow and grow together. Finally, wash with deionized water to obtain a dense ceramic film. The reactant powder is a raw material used to prepare ceramic thin films and is a metal oxide; The melt powder is a raw material used to prepare ceramic thin films and can provide a molten environment for crystal growth after melting. It is a metal oxide or metal salt. The melting point of the reactant powder is higher than that of the molten powder; the melting point of the molten powder is not higher than 600°C.

2. The method of claim 1, wherein, Step (1) The reactant powders are TiO2, ZrO2, Y2O3, CeO2, and (ZrO2). 0.92 (Y2O3) 0.08 One or more of (8YSZ); the organic substances added to the slurry are two or more of ethanol, methyl ethyl ketone, triethanolamine, polyvinyl butyral resin, and butyl benzyl phthalate, and the solid content of the slurry is 16-38 wt%; the reactant slurry is uniformly coated on the substrate surface by spin coating or impregnation.

3. The method of claim 1, wherein, The low melting point melt powder in step (2) includes any one or a mixture of several of Ba(NO3)2, BaO2, and Sr(NO3)2.

4. The method of claim 1, wherein, The atmosphere in the tubular furnace is oxygen or an inert atmosphere.

5. The method of claim 1, wherein, The reaction temperature in step (3) is no higher than 600℃; the reaction time is 6 to 24 hours.

6. The method of claim 1, wherein, The thickness of the obtained dense ceramic film is determined according to the coating thickness in step (1), and is 1 to 10 μm.

7. The method of claim 1, wherein, The mass of the melt powder is more than 10 times that of the reactant powder.

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