Silicon-coated silicon dioxide coating material as well as preparation method and application thereof

Abstract

The invention provides a silicon-coated silicon dioxide coating material as well as a preparation method and application thereof, and relates to the technical field of thermal spraying surface engineering. The silicon-coated silicon dioxide coating material disclosed by the invention is of a core-shell structure and comprises the following components: 5wt.%-20wt.% of a silicon shell and the balance of a silicon dioxide core, the particle size of the silicon-coated silicon dioxide coating material is 30-60 [mu] m, the sphericity degree is 99%-100%, and the thickness of the silicon coating layer is 3-10 [mu] m. The technical problems that silicon dioxide is in a glassy state, does not have a fixed melting point, is gasified at a high temperature, cannot form a coating and cannot be efficiently sprayed at normal temperature and normal pressure due to high brittleness are solved by constructing a silicon-coated silicon dioxide core-shell structure coating material, a silicon shell is used as a binding phase, and is fully melted during plasma spraying by utilizing the low-melting-point characteristic of the silicon shell, so that the coating cannot be efficiently sprayed at normal temperature and normal pressure; the bonding force among silicon dioxide particles is effectively improved, meanwhile, the brittleness of silicon dioxide is relieved through good plasticity of silicon, and the bonding strength and thermal shock resistance of the coating are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of thermal spraying surface engineering technology, and in particular to a silicon-coated silica coating material, its preparation method, and its application. Background Technology

[0002] Silica (SiO2), as an important inorganic non-metallic material, has broad application prospects in thermal barrier coatings, protective coatings, and functional coatings in aerospace, energy, and electronics fields due to its high melting point, low thermal conductivity, good corrosion resistance, and excellent electrical insulation properties. Plasma spraying technology, as an efficient surface modification method, can prepare high-performance coatings on substrate surfaces; however, applying silica materials to plasma spraying presents several challenges.

[0003] Silica has a melting point higher than the effective heating temperature range of conventional plasma spraying processes, making it difficult for silica particles to fully melt during spraying and forming a good coating structure. Furthermore, silica itself is brittle and lacks plastic deformation ability; even if some particles reach a molten state, the resulting coating is prone to cracking due to stress concentration after cooling. In addition, because the bonding between silica particles relies mainly on mechanical interlocking and lacks an effective binder phase, the bonding strength between the coating and the substrate, as well as within the coating itself, is generally low, failing to meet the requirements of practical engineering applications.

[0004] To improve the performance of silica coatings, existing technologies mainly employ the addition of binders, such as physically mixing high-melting-point oxides like alumina and zirconium oxide into silica powder as a binder phase. However, this simple physical mixing method has significant shortcomings. For example, the interfacial bonding between the binder and silica particles is weak, making them prone to interfacial separation under high-temperature service conditions; the introduction of binders alters the overall composition of the coating, affecting the original functional properties of silica; and the flowability and spray uniformity of the mixed powder are difficult to guarantee. Furthermore, silica coatings prepared by traditional methods have high porosity, poor density, and insufficient thermal shock resistance, making them prone to cracking and peeling after high-temperature thermal cycling, severely limiting their service life and application range.

[0005] Therefore, how to effectively solve the spraying difficulties and performance defects caused by the high melting point and high brittleness of silica while maintaining its excellent functional properties, and develop a silica-based coating material that is easy to spray, has high bonding strength and excellent thermal shock resistance, is one of the technical problems that urgently need to be solved in this field. Summary of the Invention

[0006] In view of this, the present invention provides a silicon-coated silica coating material, its preparation method, and its application. The present invention solves the technical problem of inefficient spraying of silica at room temperature and pressure due to its high melting point and brittleness by constructing a silicon-coated silica core-shell structure coating material. The silica shell acts as a binder phase, utilizing its low melting point to fully melt during plasma spraying, effectively improving the bonding force between silica particles. Simultaneously, the good plasticity of silicon alleviates the brittleness of silica, significantly improving the coating's bonding strength and thermal shock resistance.

[0007] The first aspect of this invention is to provide a silicon-coated silica coating material, which has a core-shell structure and comprises: The outer shell is 5wt.%-20wt.% silicon, with the balance being a silicon dioxide core; The silica core serves as the functional phase of the coating, providing properties such as high melting point, low thermal conductivity, corrosion resistance, and electrical insulation. The silicon shell acts as a binder phase, improving the bonding strength between the composite particles and the matrix. At the same time, the low melting point of silicon allows it to fully melt during plasma spraying, filling the gaps between the silicon dioxide particles and forming a dense coating. The particle size of the silicon-coated silica coating material is 30-60 μm to meet the powder feeding requirements of plasma spraying, and the sphericity is 99%-100% to improve the flowability of the particles and the uniformity of spraying. The thickness of the silicon coating layer is 3-10 μm to ensure the bonding effect and protective function.

[0008] A second aspect of the present invention is to provide a method for preparing the above-mentioned silicon-coated silica coating material, comprising the following steps: S1. Silane gas cracking: Silicon dioxide seed crystals are added to a rotating fluidized bed, silane gas (SiH4) is introduced, and the temperature is raised to the cracking temperature to crack the gas, yielding hydrogen gas (H2) and silicon atoms (reaction formula: SiH4→Si+2H2). S2, Silicon Atom Deposition: Hydrogen gas is used to blow up the silicon dioxide seed crystal, making the seed crystal fluidized, so that silicon atoms are uniformly deposited on the surface of silicon dioxide particles to form a silicon coating shell, thus obtaining composite particles. S3. Collection and Cooling: Cool and collect the composite particles of S2 to obtain the silicon-coated silica coating material.

[0009] Preferably, in step S1, the particle size of the silicon dioxide seed crystal is 10-20 μm, the purity is ≥99.9%, and the pyrolysis temperature is 500℃-600℃.

[0010] Preferably, in step S2, the hydrogen pressure is 0.08-0.12 MPa, the silicon atom deposition temperature is 450℃-550℃, and the deposition time is 1-2 h to ensure that the coating thickness reaches the target thickness.

[0011] Preferably, in step S3, the cooling temperature is ≤50℃.

[0012] A third aspect of this invention provides a method for preparing a composite coating with high bonding strength, high temperature resistance, high hardness, and corrosion resistance using the aforementioned silicon-coated silica coating material, comprising the following steps: After the silicon-coated silica coating material is dried, it is sprayed onto the pretreated substrate and nitrided to obtain a composite coating. The porosity of the silicon-coated silica coating is 2%-6%, and the bonding strength with the substrate is 20-35 MPa.

[0013] Preferably, the drying temperature is 70℃-90℃ and the drying time is 1-2 hours. Drying can remove moisture from the silicon-coated silica coating material and prevent pores from forming during spraying.

[0014] Preferably, the substrate pretreatment method is as follows: The substrate workpiece is roughened by sandblasting with silica particles to improve the mechanical adhesion between the coating and the substrate. Subsequently, the substrate surface is cleaned with alcohol or acetone to remove oil and impurities. After drying, the coating is installed onto the workpiece to be coated. The silica particles have a particle size of 20-40 μm, the substrate is metal or ceramic, the sandblasting gas pressure is 0.4-0.7 MPa, and the substrate roughness R after sandblasting is... a The thickness is 3.0-6.0 μm, the drying temperature is 80℃-100℃, and the drying time is 0.5 h.

[0015] Preferably, the spraying is plasma spraying; the spraying is carried out in an inert atmosphere to form an inert environment and prevent particle oxidation, more preferably nitrogen; the spraying parameters are: power 25-40 kW, cooling gas flow rate 70-100 lpm, spraying distance 80-120 mm, powder feeding rate 25-45 g / min, coating thickness 200-400 μm, the cooling gas is an inert gas, more preferably argon; during the spraying process, the substrate temperature is controlled below 150℃ to prevent substrate deformation.

[0016] Preferably, the nitriding treatment method is as follows: the coated substrate workpiece is placed in a nitriding furnace and nitrided at 1000-1200℃ for 180-360 min, so that the silicon in the coating reacts with nitrogen to generate silicon nitride (reaction formula: 3Si+2N2→Si3N4), forming a mixed phase of silicon nitride, silicon, and silicon nitride, which further improves the high-temperature stability and bonding strength of the coating.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention uses a silicon shell as a binder phase, which has a low melting point and can be fully melted during plasma spraying. This effectively reduces the overall material spraying temperature requirements, enabling efficient spraying under conventional plasma spraying conditions and significantly improving process feasibility and production efficiency.

[0018] After melting, the silicon shell fully wets the surface of the silicon dioxide core and flows and fills the gaps between particles, forming a continuous adhesive network. This significantly improves the density of the coating and effectively reduces its porosity. This core-shell structure ensures a tight bond between silicon and silicon dioxide at the microscale. Compared to traditional physical mixing methods, the interfacial bonding is stronger, avoiding interfacial separation problems during high-temperature service. This significantly improves the bonding strength between the coating and the substrate, as well as the bonding strength within the coating itself.

[0019] Silicon materials possess excellent plasticity and toughness, and their presence in coatings can effectively alleviate the brittleness of silica. During thermal cycling, the silicon phase can absorb some of the thermal stress through plastic deformation, preventing stress concentration in the brittle silica phase. This significantly improves the thermal shock resistance of the coating, enabling it to withstand more high-temperature and low-temperature cycles without cracking or peeling, thus greatly extending its service life.

[0020] This invention uses chemical vapor deposition to prepare core-shell structured materials. Silicon atoms are uniformly deposited on the surface of silicon dioxide particles to form composite particles with controllable coating thickness and high sphericity. This ensures the fluidity and uniformity of the material and achieves uniform composite of silicon and silicon dioxide at the nanometer to micrometer scale, avoiding component segregation and ensuring the consistency and stability of coating performance.

[0021] Since the silicon shell accounts for only 5%-15% of the total material mass, and the coating is still mainly composed of silicon dioxide, it can fully retain the excellent functional properties of silicon dioxide, such as its high melting point, low thermal conductivity, corrosion resistance, and electrical insulation. This allows for the improvement of coating processability and mechanical properties without sacrificing its core advantages as a functional coating. Consequently, the coating prepared by this invention possesses both excellent thermal insulation and high-temperature resistance, as well as good bonding strength and thermal shock resistance.

[0022] The method for preparing silicon-coated silica coating material provided by this invention is simple, easy to industrialize, and has excellent material properties. It is suitable for high-temperature insulation of industrial furnaces and kilns, corrosion protection of chemical equipment, insulation of electronic equipment, and other working conditions, and has broad application prospects. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0025] Example 1: Preparation of silicon-coated silica coating material, the method is as follows: The silicon-coated silica coating material prepared in this embodiment has a core-shell structure, with a silicon shell content of 10.0 wt.% and the remainder being a silica core. The coating material has a particle size of 30-45 μm, a sphericity of 99.5%, a silicon coating thickness of 5 ± 0.5 μm, and a purity of 99.95%.

[0026] The preparation method of the silicon-coated silica coating material is as follows: Silica seed crystals (particle size 15 μm, purity 99.95%), silane gas (purity 99.99%), and hydrogen gas (purity 99.999%) were selected. Rotary fluidized bed settings: Adjust the rotation speed of the rotary fluidized bed to 500 rpm, and set the pyrolysis temperature to 600℃ and the deposition temperature to 500℃; Silane gas cracking: 10 kg of silicon dioxide seed crystals were added to a rotating fluidized bed, and silane gas (flow rate 500 mL / min) was introduced. The gas was cracked at 600℃ for 40 min to obtain hydrogen gas and silicon atoms. Silicon atom deposition: Hydrogen gas at a pressure of 0.1 MPa (flow rate of 1000 mL / min) is introduced to blow up the silicon dioxide seed crystal, making the seed crystal fluidized, so that silicon atoms are uniformly deposited on the surface of silicon dioxide particles. After deposition for 1.5 h, a silicon-encapsulated outer shell is formed, resulting in composite particles with silicon dioxide as the core and silicon as the outer shell. Collection and cooling: The composite particles settle to the bottom under the centrifugal force of a rotating fluidized bed, are cooled (≤50℃) and then collected, nitrided, to obtain the composite coating material.

[0027] Example 2 The difference from Example 1 is that the particle size of the coating material is 35-50 μm and the deposition time is 2 h.

[0028] Example 3 Silicon-coated silica coating A composite coating was prepared using the silicon-coated silica coating material prepared in Example 1. The coating preparation method is as follows: Material drying: The silicon-coated silica coating material prepared in Example 1 was dried at 80°C for 1 h to remove moisture and prevent pores from forming during spraying; Matrix pretreatment: The matrix workpiece is roughened by sandblasting with silica particles (30 μm in diameter) to achieve a matrix roughness R. a =4 μm, to improve the mechanical adhesion between the coating and the substrate; then clean the substrate surface with alcohol to remove oil and impurities, dry at 80°C for 30 min, and then install it onto the sprayed workpiece; Plasma spraying: The pretreated substrate is placed in the spraying chamber, evacuated to 25±5 mbar, and backfilled with argon to 45±5 mbar; the plasma spraying method is adopted, and the spraying parameters are set as follows: power 30 kW, cooling gas (argon) flow rate 85 lpm, spraying distance 100 mm, powder feeding rate 30 g / min, coating thickness 300 μm; during the spraying process, the substrate temperature is controlled below 150℃ to prevent substrate deformation; Cooling: Allow to cool naturally to room temperature after spraying.

[0029] Nitriding treatment: The coated substrate workpiece is placed in a nitrogen furnace and nitrided at 1100℃ for 240 min. The silicon in the coating reacts with nitrogen to generate silicon nitride, forming a mixed phase of silicon nitride, silicon, and silicon nitride, which further improves the high-temperature stability and bonding strength of the coating.

[0030] Performance testing: The coating has a porosity of 3.5% (tested according to GB / T34887-2017); its bonding strength with the substrate is 28 MPa (tested according to GB / T1720-2020 nano-scratch method); it withstood 185 thermal shock cycles in the 1600℃ thermal shock test (air cooling to room temperature) (no cracking or peeling of the coating); and its thermal insulation coefficient is 0.13 W / m·K (tested using the hot wire method).

[0031] Example 4 The difference from Example 3 is that the silicon-coated silica coating material of Example 2 is used, and the spraying parameters are set as follows: power 28 kW, cooling gas (argon) flow rate 80 lpm, spraying distance 90 mm, powder feeding rate 40 g / min, and coating thickness 300 μm.

[0032] Performance testing: Based on the above, the coating obtained in this embodiment has a thermal shock resistance of more than 185 cycles in the 1600℃ thermal shock test, and the bonding strength with the substrate is 29±7 MPa.

[0033] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A silicon-coated silica coating material, characterized in that, The material has a core-shell structure and is composed as follows: The outer shell is 5wt.%-20wt.% silicon, with the balance being a silicon dioxide core; The silicon-coated silica coating material has a particle size of 30-60 μm, a sphericity of 99%-100%, and a silicon coating thickness of 3-10 μm.

2. The method for preparing a silicon-coated silica coating material according to claim 1, characterized in that, Includes the following steps: S1. Silane gas cracking: Add silicon dioxide seed crystals to a rotating fluidized bed, introduce silane gas, and heat to the cracking temperature to crack the gas and obtain hydrogen and silicon atoms. S2, Silicon Atom Deposition: Hydrogen gas is used to blow up the silicon dioxide seed crystal, making the seed crystal fluidized, so that silicon atoms are uniformly deposited on the surface of silicon dioxide particles to form a silicon coating shell, thus obtaining composite particles. S3. Collection and Cooling: Cool and collect the composite particles of S2 to obtain the silicon-coated silica coating material.

3. The method for preparing a composite coating with high bonding strength, high temperature resistance, high hardness, and corrosion resistance using the silicon-coated silica coating material as described in claim 1, characterized in that... The steps are as follows: After the silicon-coated silica coating material is dried, it is sprayed onto the pretreated substrate and nitrided to obtain a composite coating.

4. The method for preparing the composite coating according to claim 3, characterized in that, The drying temperature is 70℃-90℃, and the drying time is 1-2 hours.

5. The method for preparing a composite coating according to claim 3, characterized in that, The substrate pretreatment method is as follows: the substrate workpiece is roughened by sandblasting with silica particles, then the substrate surface is cleaned with alcohol or acetone and dried.

6. The method for preparing a composite coating according to claim 5, characterized in that, Matrix roughness R after sandblasting a The thickness ranges from 3.0 to 6.0 μm.

7. The method for preparing a composite coating according to claim 5, characterized in that, The spraying is plasma spraying.

8. The method for preparing a composite coating according to claim 7, characterized in that, The spraying is carried out in an inert atmosphere, and the spraying parameters are: power 25-40 kW, cooling gas flow rate 70-100 lpm, spraying distance 80-120 mm, powder feeding rate 25-45 g / min, coating thickness 200-400 μm, and the substrate temperature is controlled below 150℃ during the spraying process.

9. The method for preparing a composite coating according to claim 3, characterized in that, The nitriding treatment method is as follows: the sprayed substrate is heated and nitrided in nitrogen gas to form a mixed phase coating of silicon nitride, silicon, and silicon dioxide.

10. The method for preparing a composite coating according to claim 9, characterized in that, The heating nitriding temperature is 1000℃-1200℃, and the heating nitriding time is 180-360 min.