Boron carbide ceramic coating paste as well as preparation method and application thereof

Abstract

The invention belongs to the field of boron carbide ceramic materials, and particularly relates to boron carbide ceramic coating paste as well as a preparation method and application thereof. The boron carbide ceramic coating slurry is prepared from the following components in parts by weight: 10 to 12 parts of a nano reinforced binder system, 4 to 6 parts of aggregate, 0.9 to 1.8 parts of a composite curing agent and 0.2 to 0.8 part of an interface coupling agent. According to the invention, nano silicon dioxide and carbon nanotubes are added into a binder system, zinc borate is added into a composite curing agent, and the problems of low bonding strength and poor high-temperature stability of a traditional boron carbide coating are solved through a multi-scale synergistic strategy of nano enhancement, interface chemical bonding and glass phase optimization; and the interface bonding strength, the high-temperature stability and the complex base material adaptability of the coating are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of boron carbide ceramic materials, and particularly relates to a boron carbide ceramic slurry, a preparation method thereof and an application thereof. Background Art

[0002] As a superhard material, boron carbide (B4C) ceramic material has high hardness, high melting point, corrosion resistance and good thermal stability, so it has wide applications in the fields of military, aerospace, nuclear industry and protective materials, etc. Boron carbide ceramic coatings are often used to protect matrix materials from harsh environments such as high temperature, wear and chemical corrosion. However, there are still some technical problems in the existing preparation technologies of boron carbide ceramic coatings. The existing preparation methods of boron carbide ceramic coatings mainly include:

[0003] Vapor deposition method: Boron carbide is deposited on the surface of the matrix by chemical vapor deposition (CVD) or physical vapor deposition (PVD) methods. This method can obtain a dense and uniform coating, but the process is complex, the equipment is expensive, and the requirements for the surface of the matrix are high.

[0004] Thermal spraying method: Boron carbide particles are sprayed onto the surface of the matrix by methods such as flame spraying and plasma spraying to form a coating. The thermal spraying method can adapt to the preparation of coatings with a large area. However, due to the melting process of the coating, the adhesion and uniformity of the coating may not be ideal, and the coating may fall off or crack at high temperature.

[0005] Sol-gel method: Boron carbide coatings are synthesized by the sol-gel method. The preparation process is relatively simple, and a relatively uniform coating can be obtained. However, the prepared coating has poor stability under high temperature and high pressure, and the adhesion and wear resistance of the coating are weak, which limits its wide use in practical applications.

[0006] Although the existing technologies can prepare boron carbide ceramic coatings to a certain extent, there are still the following disadvantages: Poor coating adhesion: The adhesion between the coating and the matrix is often insufficient. Especially under high temperature or harsh environments, the coating is easy to fall off. Poor coating uniformity: The existing preparation methods are difficult to ensure the uniformity of the coating, which may lead to local weakness and affect its overall performance. Poor high-temperature stability: The coatings prepared by the existing technologies are easy to oxidize, exfoliate or deform at high temperature, affecting the reliability of their long-term use. High cost: The preparation processes of the existing technologies are relatively complex, the equipment requirements are high, and the production cost is high, which is not suitable for large-scale industrial production. Aiming at the disadvantages of the existing technologies, the present invention provides a new preparation method of boron carbide ceramic coatings, which can significantly improve the adhesion, uniformity and high-temperature stability of the coatings and solve the deficiencies in the existing technologies. Summary of the Invention

[0007] To solve the technical problems existing in the above-mentioned background art, the present invention provides an improved boron carbide ceramic slurry and preparation process, which significantly improves the interfacial bonding strength, high-temperature stability and adaptability to complex substrates of the coating through nano-enhancement, interfacial chemical bonding and glass phase optimization.

[0008] An object of the present invention is to provide a boron carbide ceramic slurry, which is characterized in that it comprises the following components by weight: 10-12 parts of a nano-enhanced binder system, 4-6 parts of aggregate, 0.9-1.8 parts of a composite curing agent, and 0.2-0.8 parts of an interfacial coupling agent.

[0009] Furthermore, the nano-enhanced binder system is an acid aluminum phosphate binder added with 1-3 wt% of nano-silica and 0.5-1.5 wt% of carbon nanotubes.

[0010] In the nano-enhanced binder system involved in the present invention, a key component, nano-silica, is innovatively added, which plays a crucial role in improving the performance of the binder. From the perspective of the microstructure, during the preparation and curing process of the binder, due to the complexity of the molecular arrangement and reaction, some microporous structures will inevitably be formed. The existence of these micropores will not only reduce the density of the binder, but may also have a negative impact on its mechanical properties, chemical stability and other aspects.

[0011] Due to its nano-scale size characteristics, nano-silica has a very high specific surface area and surface activity. When it is added to the binder system, the nano-silica particles can easily penetrate into the micropores inside the binder by virtue of their small particle size. On the one hand, the nano-silica particles can generate strong interaction forces with the binder molecules, including van der Waals forces, hydrogen bonds, etc. This interaction force enables the nano-silica particles to be stably filled in the micropores, effectively occupying the space of the micropores, thereby reducing the volume and number of micropores.

[0012] On the other hand, the active groups on the surface of nano-silica can undergo chemical reactions or physical adsorption with the binder molecules, further enhancing the binding force between nano-silica and the binder matrix. This tight binding not only enables nano-silica to better fill the micropores, but also forms a uniform dispersion state inside the binder, avoiding the agglomeration of particles. As nano-silica continuously fills the micropores, the porosity of the binder is significantly reduced. A lower porosity means that the binder has higher density, which can effectively block the intrusion of harmful substances such as moisture and gas in the external environment, thereby improving the durability and stability of the binder. At the same time, the dense structure also helps to improve the mechanical properties of the binder, such as strength, toughness, etc., enabling it to better withstand external forces in practical applications.

[0013] At both ends of the carbon nanotubes in the binder, they are tightly combined with the binder matrix on both sides of the crack. When the crack attempts to further expand, it is necessary to overcome the binding effect of the carbon nanotubes. Due to the high strength of the carbon nanotubes, the energy required for crack propagation increases significantly, thereby effectively delaying the crack propagation speed. In addition, the carbon nanotubes do not exist in isolation in the binder system. They will intertwine and entangle with each other to form a three-dimensional network structure. In this three-dimensional toughening network, the carbon nanotubes are connected to each other, like a fine "protective net". When an external force acts on the binder, the stress can be more evenly distributed through the carbon nanotube network, avoiding the occurrence of stress concentration. Even if the carbon nanotubes at a certain location break under the action of stress, the other connected carbon nanotubes can still continue to bear the stress, thus maintaining the integrity of the entire binder system. At the same time, there is a strong interfacial interaction between the carbon nanotubes and the binder matrix. This interaction enables the carbon nanotubes to better transfer stress, further enhancing the toughness of the binder. Through the bridging of cracks by carbon nanotubes and the formation of a three-dimensional toughening network, the nano-enhanced binder system in the present invention can exhibit higher crack propagation resistance and toughness when facing external forces, thereby significantly improving the service life and reliability of the binder.

[0014] Further, the particle size of the nano-silica is 20 - 50 nm; the diameter of the carbon nanotubes is 5 - 15 nm.

[0015] Further, the composition of the composite curing agent is: alumina, magnesia and zinc borate are mixed in a mass ratio of

[0016] 1:0.3 - 0.8:0.1 - 0.4.

[0017] Further, the mesh number of the alumina and magnesia is 200 - 400 mesh; the zinc borate is 300 - 500 mesh.

[0018] Zinc borate in the composite curing agent of the present invention decomposes into B 2 O 3 and ZnO at 300 °C, which can react with aluminum phosphate in the nano-enhanced binder system to generate a borophosphate glass phase, and this glass phase can seal the grain boundary pores.

[0019] Further, the interfacial coupling agent is 0.2 - 0.8 wt% γ-aminopropyltriethoxysilane.

[0020] The amino group in the interfacial coupling agent γ-aminopropyltriethoxysilane can form a covalent bond with the hydroxyl group on the surface of the metal substrate, and the ethoxy group can complex with aluminum phosphate to achieve a "inorganic-organic-metal" gradient bond.

[0021] Further, the aggregate is boron carbide powder, and its particle size is 1 - 3 μm.

[0022] Another object of the present invention is to provide a method for preparing a boron carbide ceramic slurry, which is characterized by comprising the following steps:

[0023] S1: Preparation of an acid aluminum phosphate binder: React phosphoric acid with Al(OH) 3 in a molar ratio of 2.08:1 to obtain a colorless colloidal solution.

[0024] S2: Step-by-step ball milling: Pre-disperse nano-silica for 30-50 minutes, and then add the acid aluminum phosphate binder, carbon nanotubes, aggregate and composite curing agent according to the above ratio and ball mill for 1.5 hours until D50 = 35-50 nm.

[0025] Further, in step S1, the molar ratio of phosphoric acid to aluminum hydroxide is 2-3:1.

[0026] Another object of the present invention is to provide an application of the boron carbide ceramic slurry on the surface of a metal substrate.

[0027] The technical solution of the present invention has the following technical effects:

[0028] 1. In the nano-enhanced binder system involved in the present invention, a key component, nano-silica, is innovatively added. From the perspective of the microstructure, during the preparation and curing processes of the binder, due to the complexity of the intermolecular arrangement and reaction, some microporous structures will inevitably be formed. The existence of these micropores will not only reduce the density of the binder but also may have a negative impact on its mechanical properties, chemical stability, etc. Due to its nano-scale size characteristics, nano-silica has an extremely high specific surface area and surface activity. When it is added to the binder system, the nano-silica particles can easily penetrate into the micropores inside the binder by virtue of their tiny particle size. On the one hand, the nano-silica particles can generate strong interaction forces with the binder molecules, including van der Waals forces, hydrogen bonds, etc. This interaction force enables the nano-silica particles to be stably filled in the micropores, effectively occupying the space of the micropores, thereby reducing the volume and number of micropores. On the other hand, the active groups on the surface of nano-silica can undergo chemical reactions or physical adsorption with the binder molecules, further enhancing the binding force between the nano-silica and the binder matrix. This tight binding not only enables the nano-silica to better fill the micropores but also can form a uniform dispersion state inside the binder, avoiding the agglomeration of particles. With the continuous filling of the micropores by nano-silica, the porosity of the binder is significantly reduced. A lower porosity means that the binder has higher density, can effectively block the intrusion of harmful substances such as moisture and gas in the external environment, thereby improving the durability and stability of the binder. At the same time, the dense structure also helps to improve the mechanical properties of the binder, such as strength and toughness, enabling it to better withstand external forces in practical applications.

[0029] 2. At both ends of the carbon nanotubes in the binder of the present invention, they are tightly combined with the binder matrix on both sides of the crack. When the crack attempts to further expand, it is necessary to overcome the binding effect of the carbon nanotubes. Due to the high strength of the carbon nanotubes, the energy required for crack propagation increases significantly, thus effectively delaying the crack propagation speed. In addition, the carbon nanotubes do not exist in isolation in the binder system. They will intertwine and entangle with each other to form a three-dimensional network structure. In this three-dimensional toughening network, the carbon nanotubes are connected to each other, just like a fine "protective net". When an external force acts on the binder, the stress can be more evenly distributed through the carbon nanotube network, avoiding the occurrence of stress concentration. Even if the carbon nanotubes at a certain location break under the action of stress, the other connected carbon nanotubes can still continue to bear the stress, thus maintaining the integrity of the entire binder system. At the same time, there is a strong interfacial interaction between the carbon nanotubes and the binder matrix, and this interaction enables the carbon nanotubes to better transfer stress, further enhancing the toughness of the binder. Through the action of the carbon nanotubes bridging the cracks and forming a three-dimensional toughening network, the nano-enhanced binder system in the present invention can exhibit higher crack propagation resistance and toughness when facing external forces, thus significantly improving the service life and reliability of the binder.

[0030] 3. In the composite curing agent system involved in the present invention, a component of zinc borate is added. When the system temperature rises to 300 °C, zinc borate will undergo a decomposition reaction, and the generated boron trioxide and zinc oxide have high chemical activity and can chemically react with aluminum phosphate in the nano-enhanced binder system. From the perspective of the chemical reaction mechanism, a series of atomic rearrangements and the formation and breakage of chemical bonds will occur between the boron atoms in boron trioxide and the aluminum atoms and phosphorus atoms in AlPO 4 . During this process, the boron atoms will combine with phosphate ions and form new chemical bonds with the surrounding oxygen atoms, gradually forming a substance with a glassy structure, namely the boron phosphate glass phase. The boron phosphate glass phase has good fluidity and filling ability. At a certain temperature, it can flow like a liquid and penetrate into the grain boundary pores. As the temperature decreases, the boron phosphate glass phase gradually solidifies, completely filling and sealing the grain boundary pores. This process not only eliminates the pores at the grain boundaries, improves the density of the binder, but also enhances the bonding force at the grain boundaries. In addition, the boron phosphate glass phase can form strong chemical bonds with the crystal surfaces on both sides of the grain boundary, making the atomic connection at the grain boundary more compact, thus effectively preventing external substances (such as moisture, gas, etc.) from entering the binder interior through the grain boundary pores, improving the chemical stability and durability of the binder. At the same time, the closed grain boundary pores also reduce the possibility of cracks initiating and propagating at the grain boundaries, further enhancing the mechanical properties of the binder.

[0031] 4. Through a multi-scale collaborative strategy of nano toughening, interfacial bonding, and glass phase optimization, the present invention solves the problems of low bonding strength and poor high-temperature stability of traditional boron carbide coatings. Detailed implementation manners

[0032] The embodiments of the present invention are described in detail below, which are intended to explain the present invention and should not be construed as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0033] It should be noted that the nano-enhanced binder system in the following embodiments of the present invention is prepared by the following method: React phosphoric acid with Al(OH)3 in a molar ratio of 2.08:1 to obtain a colorless colloidal solution. Pre-disperse nano-silica for 30 minutes, and then add acid aluminum phosphate binder and carbon nanotubes and ball mill to a particle size D50 = 50 nm.

[0034] Example 1

[0035] The composition of the boron carbide coating slurry is: 103 g of nano-enhanced binder system, 45 g of boron carbide powder with a particle size of 3 - 5 μm, 12 g of curing agent, and in the curing agent, Al 2 O 3 :MgO:Zn 3 (BO 3 ) 2 = 1:0.5:0.2, 4 g of γ-aminopropyltriethoxysilane.

[0036] The preparation method of the boron carbide coating slurry is: Weigh the materials according to the above ratio, first pre-disperse the nano-enhanced binder system for 30 minutes, and then add the remaining components and ball mill (rotation speed 800 rpm, ball-to-material ratio 5:1) until the particle size of the system is D50 = 35 nm.

[0037] Preparation of boron carbide ceramic coating: Brush the coating slurry on the surface of 304 stainless steel pretreated (polished with 800# sandpaper + cleaned with acetone), and cure at room temperature for 20 hours. Then heat to 150 °C at a heating rate of 4 °C / minute, hold for 2 hours, then heat to 200 °C at a heating rate of 15 °C / minute, hold for 0.5 h, and then heat to 300 °C at a heating rate of 15 °C / minute, hold for 1 hour.

[0038] Example 2

[0039] The composition of the boron carbide slurry is as follows: 89 g of a nano-enhanced binder system, 32 g of boron carbide powder with a particle size of 3 - 5 μm, 12 g of a curing agent. In the curing agent, Al 2 O 3 :MgO:Zn 3 (BO 3 ) 2 = 1:0.3:0.2, and 3 g of γ-aminopropyltriethoxysilane.

[0040] The preparation method of the boron carbide slurry is as follows: Weigh the materials according to the above ratio. First, pre-disperse the nano-enhanced binder system for 30 minutes, and then add the remaining components and ball mill (rotation speed 800 rpm, ball-to-material ratio 5:1) until the particle size of the system is D50 = 35 nm.

[0041] Preparation of the boron carbide ceramic coating: Brush the slurry onto the surface of 304 stainless steel pretreated (polished with 800# sandpaper + cleaned with acetone), and cure it at room temperature for 20 hours. Then heat it to 150 °C at a heating rate of 4 °C / minute and hold for 2 hours, then heat it to 200 °C at a heating rate of 15 °C / minute and hold for 0.5 h, and then heat it to 300 °C at a heating rate of 15 °C / minute and hold for 1 hour.

[0042] Example 3

[0043] The composition of the boron carbide slurry is as follows: 98 g of a nano-enhanced binder system, 36 g of boron carbide powder with a particle size of 3 - 5 μm, 16 g of a curing agent. In the curing agent, Al 2 O 3 :MgO:Zn 3 (BO 3 ) 2 = 1:0.5:0.4, and 5.3 g of γ-aminopropyltriethoxysilane.

[0044] The preparation method of the boron carbide slurry is as follows: Weigh the materials according to the above ratio. First, pre-disperse the nano-enhanced binder system for 30 minutes, and then add the remaining components and ball mill (rotation speed 800 rpm, ball-to-material ratio 5:1) until the particle size of the system is D50 = 35 nm.

[0045] Preparation of the boron carbide ceramic coating: Brush the slurry onto the surface of 304 stainless steel pretreated (polished with 800# sandpaper + cleaned with acetone), and cure it at room temperature for 20 hours. Then heat it to 150 °C at a heating rate of 4 °C / minute and hold for 2 hours, then heat it to 200 °C at a heating rate of 15 °C / minute and hold for 0.5 h, and then heat it to 300 °C at a heating rate of 15 °C / minute and hold for 1 hour.

[0046] The thermal cycling performance of the coatings described in the examples and comparative examples (the retention rate of the bonding strength after 100 cycles of the coating at 25 - 500 °C), the interfacial bonding strength (ASTM C633, loading rate 1 mm / min), and the Vickers hardness measurement results are shown in the following table:

[0047] Example Thermal cycling performance (%) Interface bonding strength (MPa) Vickers hardness (MPa) Example 1 96.32 365±17 730 ± 21 MPa Example 2 97.64 381±21 724 ± 13 MPa Example 3 96.97 372±18 719 ± 29 MPa

[0048] Comparing the performance of the relevant coatings in the above examples, it can be seen that the present invention provides an improved boron carbide ceramic slurry and preparation process. Through nano-reinforcement, interfacial chemical bonding, and glass phase optimization, the interfacial bonding strength, high-temperature stability, and adaptability to complex substrates of the coating are significantly improved.

[0049] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as specified, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A boron carbide ceramic slurry, characterized in that: The composition includes the following components by weight: 10-12 parts of nano-enhanced binder system, 4-6 parts of aggregate, 0.9-1.8 parts of composite curing agent, and 0.2-0.8 parts of interface coupling agent.

2. A boron carbide ceramic slurry as claimed in claim 1, characterized in that: The nano-enhanced binder system is prepared by adding 1-3 wt% nano-silicon dioxide and 0.5-1.5 wt% carbon nanotubes to an acid aluminum phosphate binder.

3. A boron carbide ceramic slurry as claimed in claim 2, characterized in that: The particle size of the nano silicon dioxide is 20-50 nm; the diameter of the carbon nanotube is 5-15 nm.

4. The boron carbide ceramic slurry according to claim 1, characterized in that: The composite curing agent is composed of aluminum oxide, magnesium oxide and zinc borate mixed in a mass ratio of 1:0.3-0.8:0.1-0.

4.

5. A boron carbide ceramic slurry as claimed in claim 4, characterized in that: The mesh size of the aluminum oxide and magnesium oxide is 200-400 meshes; the mesh size of the zinc borate is 300-500 meshes.

6. The boron carbide ceramic slurry according to claim 1, characterized in that: The interface coupling agent is 0.2-0.8 wt % of γ-aminopropyltriethoxysilane.

7. The boron carbide ceramic slurry according to claim 1, characterized in that: The aggregate is boron carbide powder, and the particle size thereof is 1-3 um.

8. A method for preparing the boron carbide ceramic slurry as claimed in any one of claims 1 to 7, characterized in that The steps include: S1: Preparation of acid aluminum phosphate binder: phosphoric acid and Al(OH)3 are reacted in a molar ratio of 2.08:1 to obtain a colorless adhesive solution; S2: Step-by-step ball milling: Nano-silicon dioxide is pre-dispersed for 30-50 minutes, and then acid aluminum phosphate binder carbon nanotubes, aggregates and composite curing agent are added according to the above ratio and ball milled for 1.5 hours until D50 = 35-50 nm.

9. The preparation method as claimed in claim 8, characterized in that: The molar ratio of phosphoric acid to aluminum hydroxide in step S1 is 2-3:

1.

10. Use of the boron carbide ceramic slurry according to any one of claims 1 to 7 on the surface of a metal substrate.