High-emissivity YSZ / MoSi2 composite ceramic coating and preparation method thereof

Abstract

The invention discloses a high-emissivity YSZ / MoSi2 composite ceramic coating and a preparation method thereof, and relates to the technical field of nano material and coating preparation. The preparation method of the composite ceramic coating specifically comprises the following steps: ball-milling and mixing YSZ and MoSi2 to obtain mixed nano ceramic powder; adding a binder into the mixed nano ceramic powder to form slurry; carrying out spray granulation on the slurry to form atomized particles; drying and sieving the atomized particles to obtain composite ceramic powder; and coating the composite ceramic powder on a base material through plasma spraying to obtain the high-emissivity YSZ / MoSi2 composite ceramic coating. According to the preparation method disclosed by the invention, the ceramic powder with nanoscale crystal grains and the YSZ / MoSi2 composite coating with high emissivity are obtained through the synergistic effect of ball milling, spray granulation and plasma spraying technologies.

Description

Technical Field

[0001] This invention relates to a high emissivity YSZ / MoSi2 composite ceramic coating and its preparation method, belonging to the field of nanomaterials and coating preparation technology. Background Technology

[0002] The tobacco industry is a crucial foundational industry in Yunnan Province, and also a major contributor to energy consumption and greenhouse gas emissions. With the advancement of national policies on carbon peaking and carbon neutrality, the requirements for energy conservation and emission reduction in tobacco curing barns are becoming increasingly stringent. Traditional tobacco curing barns use electric or coal heating, and lack efficient energy-saving measures for their walls, resulting in high energy consumption and carbon emissions. Currently, there are still no breakthroughs in the efficient utilization of heat energy in tobacco curing barns within the tobacco industry; traditional barns use cement walls, leading to low heat utilization rates.

[0003] Energy conservation and efficiency research in high-temperature industries has become an inevitable trend. Using special functional coatings inside equipment can achieve highly efficient energy utilization. These coatings have high emissivity, which enhances surface radiation, improves heat transfer efficiency, reduces heat loss, and increases energy utilization. Currently, there are many high-emissivity coating materials available, among which MoSi2 exhibits high emissivity across a wide wavelength range and can generate SiO2 as a protective film, improving the coating's oxidation resistance. However, the large difference in thermal expansion coefficients between SiO2 and MoSi2 can generate thermal and internal stresses, leading to cracking or peeling of the coating material and eventual failure. Introducing YSZ into MoSi2 can theoretically generate zirconium silicate in situ at high temperatures, effectively bridging the significant difference in thermal expansion coefficients between MoSi2 and SiO2. Furthermore, the generated zirconium silicate exhibits extremely high emissivity in the far-infrared band, thereby suppressing cracking and peeling of the coating due to thermal stress and constructing a more stable and dense high-temperature anti-oxidation barrier. However, challenges remain regarding the uniform composite of YSZ and MoSi2, the precise control of phase structure during spraying, and the generation kinetics and structural stability of the zirconium silicate protective layer during long-term thermal cycling.

[0004] In summary, this invention proposes a high-emissivity YSZ / MoSi2 composite ceramic coating and its preparation method, achieving uniform composite of YSZ and MoSi2 and precise control of phase structure during spraying. This effectively improves the emissivity of the coating, enhances its oxidation resistance and high-temperature resistance, and extends its service life. Summary of the Invention

[0005] To address the shortcomings of related technologies, this invention provides a high emissivity YSZ / MoSi2 composite ceramic coating and its preparation method, which has the advantages of high emissivity, low radiative heat loss, and high energy utilization. It solves the problems of uneven YSZ and MoSi2 composite and poor precise control of phase structure during spraying.

[0006] One objective of this invention is to provide a method for preparing a high-emissivity YSZ / MoSi2 composite ceramic coating, specifically comprising the following steps: (1) YSZ and MoSi2 were ball-milled and mixed to obtain mixed nano-ceramic powder.

[0007] (2) Add a binder to the mixed nano-ceramic powder to form a slurry.

[0008] (3) Spray granulation of the slurry (preferably using a centrifugal atomizer) to form atomized particles.

[0009] (4) The atomized particles are dried and sieved to obtain composite ceramic powder.

[0010] (5) The composite ceramic powder is coated onto the substrate by plasma spraying to obtain a high emissivity YSZ / MoSi2 composite ceramic coating.

[0011] Preferably, in step (1), YSZ and MoSi2 are mixed in a mass ratio of (1-4):1; the ball milling conditions are: ball milling at a speed of 250-350 rpm for 24-36 hours.

[0012] Preferably, the binder in step (2) is a polyvinyl alcohol aqueous solution with a mass percentage concentration of 3-10%; the amount of binder added to the slurry is 0.3-0.4% by mass percentage.

[0013] Preferably, the room temperature for spray granulation in step (3) is 220-280℃, the rotation frequency is 35-65Hz, and the powder feeding rate is 15-25%.

[0014] Preferably, the composite ceramic powder after sieving in step (4) has a size of 15-35 μm.

[0015] Preferably, in step (5), the power of plasma spraying is 30-40kW, the powder feeding rate is 60-80g / min, and the spraying distance is 10-15cm; the substrate is low carbon steel.

[0016] More preferably, the substrate in step (5) is Q235 steel.

[0017] The second objective of this invention is to provide a high-emissivity YSZ / MoSi2 composite ceramic coating prepared using the method of this invention.

[0018] Mechanism of the invention: This invention utilizes the synergistic effects of ball milling, spray granulation, and plasma spraying technologies to form nano-ceramic powder from micron-sized YSZ and MoSi2. This creates numerous MoSi2 / YSZ phase interfaces, where rapid element diffusion and in-situ reactions occur, generating zirconium silicate and achieving a "metallurgical bond." This effectively bridges the significant difference in thermal expansion coefficients between MoSi2 and SiO2, suppressing cracking and peeling of the coating caused by thermal stress. The molten particles cool on the substrate surface while maintaining the original composite structure, ultimately resulting in a composite ceramic coating with significantly improved fracture toughness, oxidation resistance, and emissivity.

[0019] The beneficial effects of this invention are: This invention achieves the fragmentation and composite formation of YSZ and MoSi2 nanoscale grains through the synergistic effect of ball milling, spray granulation, and plasma spraying technologies, generating zirconium silicate in situ. This effectively bridges the significant difference in thermal expansion coefficients between MoSi2 and SiO2, improving the emissivity of the coating over a wide wavelength range and increasing energy utilization. The resulting YSZ / MoSi2 composite ceramic coating contains pores, which enhances thermal insulation and further reduces energy consumption. The composite ceramic coating prepared by this invention exhibits excellent oxidation resistance and fracture toughness, thus extending the coating's service life. Attached Figure Description

[0020] Figure 1 This is a SEM image of spherical particles obtained by spray granulation in Embodiment 1 of the present invention.

[0021] Figure 2 This is a cross-sectional morphology diagram of the coating obtained after plasma spraying in Embodiment 1 of the present invention.

[0022] Figure 3 The images show the emissivity of the coatings prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0023] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. In the embodiments and comparative examples of this invention, unless otherwise specified, all chemical reagents used were commercially available analytical grade reagents.

[0024] Example 1 A method for preparing a high-emissivity YSZ / MoSi2 composite ceramic coating specifically includes the following steps: (1) YSZ (micron-sized) and MoSi2 (micron-sized) were mixed at a mass ratio of 1.5:1 and ball-milled at room temperature for 30 hours at a speed of 300 rpm to obtain mixed nano-ceramic powder.

[0025] (2) Add a 5% (w / w) aqueous solution of polyvinyl alcohol to the mixed nano-ceramic powder to form a slurry, wherein the amount of polyvinyl alcohol added in the slurry is 0.3% (w / w).

[0026] (3) The slurry is sprayed and granulated in a centrifugal atomizer under the conditions of room temperature of 220℃, atomizer rotation frequency of 50Hz and powder feeding rate of 20% to form atomized particles.

[0027] (4) Dry the atomized particles to remove moisture, and then sieve to obtain composite ceramic powder with a diameter of 15-35 μm.

[0028] (5) Plasma spraying was carried out under the conditions of power of 35kW, powder feeding rate of 80g / min and spraying distance of 10cm to coat the composite ceramic powder onto the Q235 steel substrate to obtain a high emissivity YSZ / MoSi2 composite ceramic coating.

[0029] The SEM image of the particles formed by spray granulation in this embodiment is as follows: Figure 1 As shown, by Figure 1 It can be concluded that the particulate powder formed after spray granulation in this embodiment consists of a large number of broken small particles. The small particles of the two different components are uniformly mixed, and the particle size distribution is uniform. This indicates that this embodiment achieves uniform composite of YSZ and MoSi2 through the synergistic effect of ball milling and spray granulation technologies, which is beneficial to the homogenization of the coating composition. The cross-sectional morphology of the coating after plasma spraying in this embodiment was observed, such as... Figure 2 As shown, the thickness of the YSZ / MoSi2 composite coating is approximately 200-300 μm. A thicker coating helps reduce light transmittance, thereby increasing the coating's emissivity. In this embodiment, porosity exists within the coating after plasma spraying, indicating that the synergistic effect of ball milling, spray granulation, and plasma spraying technologies gives the coating material excellent thermal insulation capabilities. The emissivity of the coating material prepared in this embodiment was tested, as shown... Figure 3 As shown, the emissivity of the coating material in this embodiment remains high in the range of 0.8-0.9 across the entire wavelength range, and the change is very gradual. This indicates that the coating material prepared in this embodiment, due to the synergistic effect of ball milling, spray granulation, and plasma spraying technologies, generates zirconium silicate in situ, resulting in a wide-band high emissivity characteristic. It can maintain a high emissivity in the 2-15μm wavelength range, increasing energy utilization.

[0030] Example 2 A method for preparing a high-emissivity YSZ / MoSi2 composite ceramic coating specifically includes the following steps: (1) YSZ (micron-sized) and MoSi2 (micron-sized) were mixed at a mass ratio of 1:1 and ball-milled at room temperature for 36 hours at a speed of 250 rpm to obtain mixed nano-ceramic powder.

[0031] (2) Add a 3% (w / w) aqueous solution of polyvinyl alcohol to the mixed nano-ceramic powder to form a slurry, wherein the amount of polyvinyl alcohol added in the slurry is 0.4% (w / w).

[0032] (3) The slurry is sprayed and granulated in a centrifugal atomizer under the conditions of room temperature of 280℃, atomizer rotation frequency of 35Hz and powder feeding rate of 15% to form atomized particles.

[0033] (4) Dry the atomized particles to remove moisture, and then sieve to obtain composite ceramic powder with a diameter of 15-35 μm.

[0034] (5) Plasma spraying was carried out under the conditions of power 40kW, powder feeding rate 60g / min and spraying distance 15cm to coat the composite ceramic powder onto the Q235 steel substrate to obtain a high emissivity YSZ / MoSi2 composite ceramic coating.

[0035] SEM images of the particles formed after spray granulation in this embodiment show that the powder particles are spherical with a uniform size distribution. This indicates that the uniform composite of YSZ and MoSi2 is achieved through the synergistic effect of ball milling and spray granulation technologies. Cross-sectional morphology observation of the plasma-sprayed coating in this embodiment reveals the presence of pores within the coating. This indicates that the coating material exhibits excellent thermal insulation capabilities through the synergistic effect of ball milling, spray granulation, and plasma spraying technologies. Emissivity testing of the coating material prepared in this embodiment shows that the emissivity remains high in the range of 0.8-0.9 across the entire wavelength range, with very gradual changes. This indicates that the coating material prepared in this embodiment has the characteristic of high emissivity over a wide wavelength range due to the synergistic effect of ball milling, spray granulation and plasma spraying technologies, which generates zirconium silicate in situ. It can maintain a high emissivity in the wavelength range of 2-15μm, thereby increasing the energy utilization rate.

[0036] Example 3 A method for preparing a high-emissivity YSZ / MoSi2 composite ceramic coating specifically includes the following steps: (1) YSZ (micron-sized) and MoSi2 (micron-sized) were mixed at a mass ratio of 4:1 and ball-milled at room temperature for 24 hours at a speed of 350 rpm to obtain mixed nano-ceramic powder.

[0037] (2) Add a 10% (w / w) aqueous solution of polyvinyl alcohol to the mixed nano-ceramic powder to form a slurry, wherein the amount of polyvinyl alcohol added in the slurry is 0.35% (w / w).

[0038] (3) The slurry is sprayed and granulated in a centrifugal atomizer under the conditions of room temperature of 250℃, atomizer rotation frequency of 35Hz and powder feeding rate of 25% to form atomized particles.

[0039] (4) Dry the atomized particles to remove moisture, and then sieve to obtain composite ceramic powder with a diameter of 15-35 μm.

[0040] (5) Plasma spraying was carried out under the conditions of power of 30kW, powder feeding rate of 70g / min and spraying distance of 12cm to coat the composite ceramic powder onto the Q235 steel substrate to obtain a high emissivity YSZ / MoSi2 composite ceramic coating.

[0041] SEM images of the particles formed after spray granulation in this embodiment show that the powder particles are spherical with a uniform size distribution. This indicates that the uniform composite of YSZ and MoSi2 is achieved through the synergistic effect of ball milling and spray granulation technologies. Cross-sectional morphology observation of the plasma-sprayed coating in this embodiment reveals the presence of pores within the coating. This indicates that the coating material exhibits excellent thermal insulation capabilities through the synergistic effect of ball milling, spray granulation, and plasma spraying technologies. Emissivity testing of the coating material prepared in this embodiment shows that the emissivity remains high in the range of 0.8-0.9 across the entire wavelength range, with very gradual changes. This indicates that the coating material prepared in this embodiment has the characteristic of high emissivity over a wide wavelength range due to the synergistic effect of ball milling, spray granulation and plasma spraying technologies, which generates zirconium silicate in situ. It can maintain a high emissivity in the wavelength range of 2-15μm, thereby increasing the energy utilization rate.

[0042] Comparative Example 1 A method for preparing a YSZ ceramic coating specifically includes the following steps: (1) Add a 5% (w / w) aqueous solution of polyvinyl alcohol to YSZ powder (micron grade) to form a slurry, wherein the amount of polyvinyl alcohol added in the slurry is 0.3% (w / w).

[0043] (2) The slurry is sprayed and granulated in a centrifugal atomizer under the conditions of room temperature of 220℃, atomizer rotation frequency of 50Hz and powder feeding rate of 20% to form atomized particles.

[0044] (3) Dry the atomized particles to remove moisture, and then sieve to obtain composite ceramic powder with a diameter of 15-35 μm.

[0045] (4) Plasma spraying was carried out under the conditions of power of 35kW, powder feeding rate of 80g / min and spraying distance of 10cm to coat the composite ceramic powder onto the Q235 steel substrate to obtain YSZ ceramic coating.

[0046] The emissivity of the coating material prepared in this comparative example was tested, and the test results are as follows: Figure 3 As shown in the test results, the emissivity of the coating material in this comparative example remained within the range of 0.4-0.6 across the entire wavelength range, with significant fluctuations. This indicates that the emissivity of this comparative example in the long-wavelength region (10-15 μm) is significantly higher than that in the short-wavelength region, and its thermal radiation characteristics vary significantly with wavelength; the high emissivity effect in the wide-band is not significant, resulting in poor energy utilization.

[0047] Comparative Example 2 A method for preparing a MoSi2 ceramic coating specifically includes the following steps: (1) Add a 5% (w / w) aqueous solution of polyvinyl alcohol to MoSi2 powder (micron-sized) to form a slurry, wherein the amount of polyvinyl alcohol added in the slurry is 0.3% (w / w).

[0048] (2) The slurry is sprayed and granulated in a centrifugal atomizer under the conditions of room temperature of 220℃, atomizer rotation frequency of 50Hz and powder feeding rate of 20% to form atomized particles.

[0049] (3) Dry the atomized particles to remove moisture, and then sieve to obtain composite ceramic powder with a diameter of 15-35 μm.

[0050] (4) Plasma spraying was carried out under the conditions of power of 35kW, powder feeding rate of 80g / min and spraying distance of 10cm to coat the composite ceramic powder onto the Q235 steel substrate to obtain MoSi2 ceramic coating.

[0051] This comparative example uses only MoSi2 as a raw material to prepare ceramic coatings. During the preparation process, SiO2 is generated. Since the coefficient of thermal expansion of SiO2 and the original MoSi2 are quite different, thermal stress and internal stress are generated, which causes the coating on the substrate to crack and makes it impossible to achieve uniform coating material application.

[0052] Comparative Example 3 A method for preparing a YSZ / MoSi2 composite ceramic coating specifically includes the following steps: (1) YSZ (micron-sized) and MoSi2 (micron-sized) were mixed in a mass ratio of 1.5:1 to form a mixed powder. Polyvinylpyrrolidone (PVP) powder was weighed in a mass ratio of 1:200 to the mixed powder. Isopropanol was weighed in a mass ratio of 1:1 to the mixed powder. The weighed polyvinylpyrrolidone (PVP) powder was added to the isopropanol to form a mixed liquid. Then the mixed liquid was added to the mixed powder. The mixture was stirred at room temperature at 200 rpm for 30 h to obtain a mixture. The mixture was dried at 60 °C to obtain a mixed ceramic powder.

[0053] (2) Add a 5% (w / w) aqueous solution of polyvinyl alcohol to the mixed ceramic powder to form a slurry, wherein the amount of polyvinyl alcohol added in the slurry is 0.3% (w / w).

[0054] (3) The slurry is sprayed and granulated in a centrifugal atomizer under the conditions of room temperature of 220℃, atomizer rotation frequency of 50Hz and powder feeding rate of 20% to form atomized particles.

[0055] (4) Dry the atomized particles to remove moisture, and then sieve to obtain composite ceramic powder with a diameter of 15-35 μm.

[0056] (5) Plasma spraying was carried out under the conditions of power of 35kW, powder feeding rate of 80g / min and spraying distance of 10cm to coat the composite ceramic powder onto the Q235 steel substrate to obtain YSZ / MoSi2 composite ceramic coating.

[0057] In this comparative example, the mixing of YSZ and MoSi2 by stirring resulted in uneven distribution of raw materials. The sprayed YSZ / MoSi2 composite ceramic coating showed partial cracking and obvious particle blocks. The wide-band high emissivity effect was not significant, and the energy utilization rate was poor.

[0058] Comparative Example 4 A method for preparing a YSZ / MoSi2 composite ceramic coating specifically includes the following steps: (1) YSZ (micron-sized) and MoSi2 (micron-sized) were mixed at a mass ratio of 1.5:1 and ball-milled at room temperature for 30 hours at a speed of 300 rpm to obtain mixed nano-ceramic powder.

[0059] (2) Add a 5% polyvinyl alcohol aqueous solution to the mixed nano-ceramic powder to form a slurry, wherein the amount of polyvinyl alcohol added in the slurry is 0.3% by mass.

[0060] (3) The slurry is sprayed and granulated in a centrifugal atomizer under the conditions of room temperature of 220℃, atomizer rotation frequency of 50Hz and powder feeding rate of 20% to form atomized particles.

[0061] (4) Dry the atomized particles to remove moisture, and then sieve to obtain composite ceramic powder with a diameter of 15-35 μm.

[0062] (5) The composite ceramic powder was coated onto the Q235 steel substrate by laser cladding technology to obtain the YSZ / MoSi2 composite ceramic coating. The conditions for laser cladding were: laser power 2000W, scanning speed 5mm / s, spot diameter 4mm, powder feeding rate 20g / min, preheating temperature 500℃, and protective gas was high-purity argon with a flow rate of 20L / min.

[0063] The YSZ / MoSi2 composite ceramic coating prepared in this comparative example was coated with composite ceramic powder using a laser cladding method, which generated extremely high thermal stress during the coating process, resulting in cracking of the coating material on the substrate.

[0064] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing a high-emissivity YSZ / MoSi2 composite ceramic coating, characterized in that, Specifically, the following steps are included: (1) YSZ and MoSi2 were ball-milled and mixed to obtain mixed nano-ceramic powder; (2) Add a binder to the mixed nano-ceramic powder to form a slurry; (3) Spray granulation of the slurry to form atomized particles; (4) The atomized particles are dried and sieved to obtain composite ceramic powder; (5) The composite ceramic powder is coated onto the substrate by plasma spraying to obtain a high emissivity YSZ / MoSi2 composite ceramic coating.

2. The method for preparing the high emissivity YSZ / MoSi2 composite ceramic coating according to claim 1, characterized in that, In step (1), YSZ and MoSi2 are mixed in a mass ratio of (1-4):1; the ball milling conditions are: ball milling at a speed of 250-350 rpm for 24-36 hours.

3. The method for preparing the high emissivity YSZ / MoSi2 composite ceramic coating according to claim 1, characterized in that, The binder in step (2) is a polyvinyl alcohol aqueous solution with a mass percentage concentration of 3-10%; the amount of binder added to the slurry is 0.3-0.4% by mass percentage.

4. The method for preparing the high emissivity YSZ / MoSi2 composite ceramic coating according to claim 1, characterized in that, The temperature of the spray granulation chamber in step (3) is 220-280℃, the rotation frequency is 35-65Hz, and the powder feeding rate is 15-25%.

5. The method for preparing the high emissivity YSZ / MoSi2 composite ceramic coating according to claim 1, characterized in that, The composite ceramic powder after sieving in step (4) has a size of 15-35μm.

6. The method for preparing the high emissivity YSZ / MoSi2 composite ceramic coating according to claim 1, characterized in that, In step (5), the plasma spraying power is 30-40kW, the powder feeding rate is 60-80g / min, and the spraying distance is 10-15cm; the substrate is low carbon steel.

7. The high emissivity YSZ / MoSi2 composite ceramic coating prepared by the method according to any one of claims 1 to 6.

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