High-infrared-emissivity coating for surface of carbon / carbon composite material as well as preparation and application of high-infrared-emissivity coating

Abstract

The invention relates to a high-infrared-emissivity coating for the surface of a carbon / carbon composite material as well as preparation and application of the high-infrared-emissivity coating. The high-infrared-emissivity coating is a Fe3O4 coating prepared by adopting a plasma spraying process; the adopted plasma spraying raw materials are nano Fe3O4 and diamond powder, and the particle size range is 50-100 microns after ball milling; the plasma spraying is carried out in argon and nitrogen atmospheres, the spraying power is 25-36 kW, the argon flow is 35-50 L / min, and the nitrogen flow is 5-10 L / min. According to the method, the low-cost Fe3O4 powder is selected as a main raw material, the high-infrared-emissivity coating is prepared on the surface of the carbon / carbon composite material through the plasma spraying technology, the bonding strength of the coating and a matrix is high, and the emissivity is high; the problems that an existing high-infrared-emissivity coating is complex in process, high in cost, insufficient in performance and the like are effectively solved, and the high-infrared-emissivity coating is suitable for the field of aerospace.

Description

Technical Field

[0001] The present invention belongs to the technical field of infrared radiation coating materials, and relates to a high-infrared emissivity coating for the surface of carbon / carbon composite materials, and its preparation and application. Background Art

[0002] In the aerospace field, especially for space nuclear reactors performing deep space exploration missions, its thermal management system is particularly crucial. As the core component in this system, the heat dissipation fins are responsible for efficiently transferring and radiating the heat generated by the nuclear reactor into space. To achieve this goal, the fin material not only needs to have excellent thermal conductivity and mechanical strength, but also must have a high infrared emissivity to improve the thermal radiation efficiency. According to the Stefan-Boltzmann law W = εσT 4 , the thermal radiation efficiency can be improved by increasing the infrared emissivity of the fins.

[0003] Carbon / carbon composite materials, due to their excellent high-temperature stability, low density and high thermal conductivity, have become ideal materials for manufacturing such fins. However, their emissivity in the infrared band is relatively low, which limits the application of carbon / carbon composite materials in this direction. A common method to improve the thermal radiation efficiency of materials is to prepare a high-infrared emissivity coating on the surface of the matrix material, and a large number of studies on high-infrared emissivity coatings have been carried out at home and abroad.

[0004] For example, Yang Zhenxiao et al. [1] prepared a coating with an emissivity of up to 0.88 - 0.89 in the range of 400 - 800 °C by plasma spraying spinel-structured Cr2O3-TiO2-based composite powders, and the bonding strength reached 33.1 MPa; Wang et al. [2] from Tianjin University prepared a MoSi2-SiO2-SiOC composite coating by high-temperature sintering method, with an emissivity greater than 0.9 at 700 °C, but the bonding strength was relatively low, only 0.6 MPa; Chang Yunpeng et al. [3] from Beijing Institute of Technology used La 0.8 Ca 0.2 CrO3 powders to prepare a coating with an emissivity higher than 0.87 in the full wavelength range; Zhang Hu [4] prepared a NiO-CrO2-SiC ceramic coating by sol-gel method, with a maximum emissivity of up to 0.96; Huang Jianping [5] prepared a La-CeO2 coating by electron beam physical vapor deposition (EB-PVD), and the emissivity in the range of 2.5 - 25 μm at 600 °C reached 0.9.

[0005] However, the above-mentioned schemes have deficiencies such as complex coating preparation processes, expensive raw materials and / or low bonding strength between the coating and the matrix. Therefore, how to obtain a high-infrared emissivity coating that meets the application requirements of space reactor fins at low cost and high efficiency has become an urgent problem to be solved in the field of deep space exploration. Summary of the Invention

[0006] The object of the present invention is to provide a high-infrared emissivity coating for the surface of carbon / carbon composites, its preparation and application. Using nano-Fe3O4 as the main raw material, a coating with both high infrared emissivity and high bonding strength is prepared on the surface of C / C composites by plasma spraying technology.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] In one aspect, the present invention provides a high-infrared emissivity coating for the surface of carbon / carbon composites, which is prepared by a plasma spraying process based on spraying powder. The spraying powder is composed of the following raw material components by mass percentage: 85-92% of Fe3O4 powder and 8-15% of diamond powder.

[0009] Further, the particle size range of the Fe3O4 powder is 50-75μm. Preferably, the Fe3O4 powder of the present invention is obtained by screening after spray granulation of nano-powder. Compared with other granulation methods, the powder obtained by spray granulation has a high sphericity, is more easily combined with diamond powder in the subsequent ball milling process, and at the same time, the prepared composite powder has a better sphericity and stronger fluidity, and is more easily sprayed evenly during the spraying process.

[0010] Further, the particle size range of the diamond powder is 8-25μm.

[0011] Further, the spraying powder is prepared through the following process:

[0012] Weigh the Fe3O4 powder and diamond powder, dry them, and then load them into the ball milling tank of a planetary ball mill for ball milling under the protection of an inert atmosphere.

[0013] Furthermore, during the ball milling process, the diameter of the stainless steel balls added is 2.5-3.5mm, preferably 3mm, and the mass ratio of the stainless steel balls to the spraying powder is 4-6:1, preferably 5:1. Specifically, the volume of the ball milling tank can be 20L.

[0014] Furthermore, the process parameters of the ball milling process are: forward rotation for 5-8min, reverse rotation for 5-8min, interval for 2-5min, ball milling speed of 120-160r / min, and ball milling time of 60-180min.

[0015] In another aspect, the present invention provides a preparation method of a high-infrared emissivity coating for the surface of carbon / carbon composites, including the following steps:

[0016] (1) Degrease and roughen the carbon / carbon composite matrix to increase the surface roughness of the matrix and improve the bonding strength between the coating and the matrix;

[0017] (2) Prepare a coating on the roughened carbon / carbon composite matrix using a plasma spraying device to obtain the high infrared emissivity coating.

[0018] Further, in step (1), the degreasing process is: ultrasonic cleaning in industrial alcohol for 10 - 20 min;

[0019] The roughening process is: cold spraying with small particle pure copper, usually the particle size of pure copper powder is 5 - 45 μm, and the cold spraying temperature is from room temperature to 600 °C.

[0020] Further, in step (2), the spraying powder is first dried at 80 - 100 °C for 30 - 60 min, and then sprayed using a plasma spraying device to prepare the coating.

[0021] Further, in step (2), the process parameters of plasma spraying are: spraying power 25 - 36 kW, argon gas flow rate 35 - 50 L / min, nitrogen gas flow rate 5 - 10 L / min, spraying distance 80 - 120 mm, spray gun moving speed 600 mm / s, substrate temperature < 200 °C, spraying passes 5 - 20 times, and coating thickness 10 - 45 μm.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The raw material Fe3O4 used in the coating is inexpensive, and the near-infrared and mid-infrared emissivities are greater than 0.91. However, during the conventional spraying process, Fe3O4 is prone to oxidation to form Fe2O3 or reduction to form FeO, making it difficult to obtain a Fe3O4 coating with high purity. The present invention avoids the oxidation / reduction of Fe3O4 during the spraying process by adding diamond powder, controlling the particle size of the spraying powder, spraying parameters, plasma atmosphere, etc., and thus obtains a high infrared emissivity coating mainly composed of the Fe3O4 phase.

[0024] (2) The prepared coating has a high infrared emissivity, with an emissivity > 0.9; the bonding strength between the coating and the substrate is high, with a bonding strength > 25 MPa; the raw materials are inexpensive and easily available; the preparation process is simple, efficient, highly repeatable, and easy for mass production.

[0025] (3) Using the plasma spraying technology to spray and ball-mill the prepared Fe3O4 composite powder, adding reducing diamond powder to avoid the oxidation of Fe3O4 during the spraying process, and controlling the spraying process, spraying atmosphere, and particle size of the powder to reduce the oxidation / reduction during the spraying process. Finally, a coating mainly composed of the Fe3O4 phase is obtained. This coating has a strong bond with the substrate, an infrared emissivity > 0.9, and at the same time, the preparation process is simple, efficient, and inexpensive. Compared with the prior art, it effectively solves the deficiencies of the existing high infrared emissivity coatings, such as poor performance and high cost. Description of the Drawings

[0026] Figure 1 It is a scanning electron microscope photograph of the cross-section of the coating prepared in Example 1 at 1000 times magnification.

[0027] Figure 2 It is a scanning electron microscope photograph of the cross-section of the coating prepared in Example 2 at 1000 times magnification.

[0028] Figure 3 It is a scanning electron microscope photograph of the surface of the coating prepared in Example 3 at 500 times magnification.

[0029] Figure 4 It is a scanning electron microscope photograph of the surface of the coating prepared in Example 3 at 5000 times magnification.

[0030] Figure 5 It is the SEM photograph of the coatings obtained in Example 1 and Comparative Example 1. Detailed implementation manners

[0031] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0032] In the following embodiments, the particle size of the used Fe3O4 powder is about 50 - 75 μm, and the particle size range of the diamond powder is about 8 - 25 μm.

[0033] In addition, the infrared emissivity test is to measure the total infrared hemispherical emissivity of the coating surface at room temperature using a UV-visible-near-infrared spectrophotometer (PE Lambda 950), and the wavelength range is 700 - 1600 μm. The test principle is based on Kirchhoff's law of thermal radiation.

[0034] For the remaining raw materials or processing techniques without special instructions, it means that they are all conventional commercially available raw materials or conventional processing techniques in the art.

[0035] Example 1

[0036] A high-infrared emissivity coating on the surface of a carbon / carbon composite material is prepared by the following method:

[0037] Step 1: Weigh 300 g of diamond powder and 2700 g of Fe3O4 powder, and place them in an oven to dry at 100 °C for 30 minutes.

[0038] Step 2: Weigh 15 kg of stainless steel beads, and load the diamond powder and Fe3O4 powder from Step 1 into a ball mill tank. Vacuum the ball mill tank and fill it with argon, and repeat three times to ensure that the ball milling process is under an argon protection atmosphere.

[0039] Step 3: Place the ball mill jar into the ball mill and start ball milling the powder. The specific parameters are as follows: rotate forward for 6 minutes, rotate backward for 6 minutes, with a 2-minute interval, a ball milling speed of 120 r / min, and a ball milling time of 120 minutes.

[0040] Step 4: Take out the powder. Since the particle size of Fe3O4 powder is much larger than that of diamond powder, diamond powder will combine with the surface of Fe3O4 powder to form composite powder during the ball milling process, similar to sticking diamond powder on the surface of Fe3O4 powder. Therefore, sieve the powder with a particle size range of 50 - 100 μm and dry it in an oven at 80°C for 30 minutes for standby.

[0041] Step 5: Ultrasonically clean the C / C composite matrix with dimensions of 50 mm × 50 mm × 3 mm in alcohol for 15 minutes. After drying, use small-particle pure copper to perform cold spraying on the surface to roughen the surface.

[0042] Step 6: Spray the powder prepared in Step 4 on the matrix processed in Step 5 by plasma spraying. The spraying parameters are as follows: spraying power 25 kW, argon gas flow rate 35 L / min, nitrogen gas flow rate 6 L / min, spraying distance 80 mm, spray gun moving speed 600 mm / s, control the matrix temperature < 200°C (generally around 160°C), the number of spraying passes is 5 times, and the coating thickness is 15 μm. The prepared coating has a dense structure and good bonding. After testing, the bonding strength is 16 MPa, and the infrared emissivity is 0.902.

[0043] Example 2

[0044] A high-infrared-emissivity coating on the surface of a carbon / carbon composite material is prepared by the following method:

[0045] Example 2 is only different from Example 1 in the spraying parameters in Step 6, and the other steps are the same.

[0046] Step 6: Spray the powder prepared in Step 4 on the matrix processed in Step 5 by plasma spraying. The spraying parameters are as follows: spraying power 28 kW, argon gas flow rate 35 L / min, nitrogen gas flow rate 5 L / min, spraying distance 80 mm, spray gun moving speed 600 mm / s, the matrix temperature < 200°C, the number of spraying passes is 8 times, and the coating thickness is 20 μm. The prepared coating has a dense structure and good bonding. After testing, the bonding strength is 22 MPa, and the infrared emissivity is 0.913.

[0047] Example 3

[0048] A high-infrared-emissivity coating on the surface of a carbon / carbon composite material is prepared by the following method:

[0049] Step 1: Weigh 400 g of diamond powder and 2,600 g of Fe3O4 powder, and place them in an oven to dry at 100 °C for 30 minutes.

[0050] Step 2: Weigh 15 kg of stainless steel balls, and load the diamond powder and Fe3O4 powder from Step 1 into a ball milling jar. Evacuate the ball milling jar and fill it with argon, and repeat this three times to ensure that the ball milling process is under an argon protection atmosphere.

[0051] Step 3: Load the ball milling jar into a ball mill and start ball milling the powder. The specific parameters are as follows: forward rotation for 4 minutes, reverse rotation for 4 minutes, an interval of 2 minutes, a ball milling speed of 120 r / min, and a ball milling time of 120 minutes.

[0052] Step 4: Take out the powder, and screen the powder with a particle size range of 50 - 100 μm, and dry it in an oven at 80 °C for 30 minutes for standby.

[0053] Step 5: Conduct alcohol ultrasonic cleaning on a C / C composite matrix with dimensions of 20 mm × 20 mm × 3 mm for 15 minutes. After drying, use small particle pure copper to perform cold spraying on the surface to roughen the surface.

[0054] Step 6: Spray the powder prepared in Step 4 on the matrix processed in Step 5 by plasma spraying. The spraying parameters are as follows: spraying power 28 kW, argon flow rate 35 L / min, nitrogen flow rate 6 L / min, spraying distance 80 mm, spray gun moving speed 600 mm / s, matrix temperature < 200 °C, number of spraying passes 5 times, and coating thickness 17 μm. The prepared coating has a dense structure and good bonding. After testing, the bonding strength is 18 MPa, and the infrared emissivity is 0.916.

[0055] As can be seen from the above examples, the present invention uses plasma spraying to prepare a high infrared emissivity coating on the surface of a carbon / carbon composite material. Compared with other methods, it has the advantages of simple process, easy reproducibility, low cost, a dense structure of the prepared coating, good bonding with the matrix, an infrared emissivity > 0.9, being able to meet the application requirements of space stacked carbon / carbon fins, and being able to be mass-produced, having great application value.

[0056] Comparative Example 1:

[0057] Compared with Example 1, most of them are the same, except that the addition of diamond powder is omitted.

[0058] Characterize the cross-section of the prepared coating and compare it with the coating prepared by adding diamond powder. The results are as Figure 5 shown.

[0059] As can be seen, the porosity of the coating without diamond powder (i.e., Comparative Example 1) is significantly higher than that of the coating with diamond (i.e., Example 1). The high-magnification SEM photos of the coating were analyzed using Image J. The porosity of the coating without diamond powder is 12.15%, and the porosity of the coating with diamond powder is 5.34%.

[0060] Comparative Example 2:

[0061] Compared with Example 1, most of them are the same, except that the diamond powder is replaced with carbon powder of equal mass and equal particle size. The carbon content in the prepared powder was tested. The mass fraction of carbon in the powder with diamond powder is 8.36%, and the mass fraction of carbon in the powder with carbon powder is 3.31%. This is because the crystal structures of diamond and carbon powder are different. Diamond has a regular tetrahedron structure, and carbon powder has a layered structure. During ball milling, the compounding effect of carbon powder and Fe3O4 is poor, and the required powder cannot be obtained.

[0062] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A high-infrared emissivity coating for the surface of a carbon / carbon composite material, characterized in that, Prepared by using the plasma spraying process based on spraying powder, and the spraying powder is composed of raw material components in the following mass percentages: 85-92% of Fe3O4 powder and 8-15% of diamond powder.

2. The high-infrared emissivity coating for the surface of a carbon / carbon composite material according to claim 1, wherein The particle size range of the Fe3O4 powder is 50-75μm.

3. The high-infrared emissivity coating for the surface of a carbon / carbon composite material according to claim 1, wherein The particle size range of the diamond powder is 8-25μm.

4. A high-infrared emissivity coating for the surface of a carbon / carbon composite material according to claim 1, characterized in that, The spraying powder is prepared through the following process: Weigh the Fe3O4 powder and diamond powder, dry them, then load them into the ball mill tank of a planetary ball mill, and carry out ball milling treatment under the protection of an inert atmosphere.

5. A high-infrared emissivity coating for the surface of a carbon / carbon composite material according to claim 4, characterized in that, During the ball milling treatment process, the diameter of the stainless steel balls added is 2.5-3.5mm, and the mass ratio of the stainless steel balls to the spraying powder is 4-6:

1.

6. The high-infrared emissivity coating for the surface of a carbon / carbon composite material according to claim 4, characterized in that, The process parameters of the ball milling treatment are: forward rotation for 5-8min, reverse rotation for 5-8min, interval for 2-5min, ball milling speed of 120-160r / min, and ball milling time of 60-180min.

7. The preparation method of the high-infrared emissivity coating for the surface of the carbon / carbon composite material according to any one of claims 1-6, characterized in that, It includes the following steps: (1) Degrease and roughen the carbon / carbon composite material substrate. (2) Use a plasma spraying device to prepare a coating on the carbon / carbon composite material substrate after roughening treatment to obtain the high infrared emissivity coating.

8. The preparation method of the high-infrared emissivity coating for the surface of the carbon / carbon composite material according to claim 7, characterized in that In step (1), the degreasing treatment process is: ultrasonic cleaning in industrial alcohol for 10-20min. The roughening treatment process is: cold spraying with small particle pure copper.

9. The preparation method of the high-infrared emissivity coating for the surface of the carbon / carbon composite material according to claim 7, characterized in that In step (2), the spraying powder is first dried at 80-100°C for 30-60min, and then a coating is prepared by spraying using a plasma spraying device.

10. The preparation method of the high-infrared emissivity coating for the surface of the carbon / carbon composite material according to claim 7, characterized in that, In step (2), the process parameters of plasma spraying are: spraying power of 25-36kW, argon gas flow rate of 35-50L / min, nitrogen gas flow rate of 5-10L / min, spraying distance of 80-120mm, gun moving speed of 600mm / s, substrate temperature <200°C, spraying passes of 5-20 times, and coating thickness of 10-45μm.

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