Ultra-thin atomic oxygen protective coating for space and preparation method thereof

Abstract

The present invention discloses an ultra-thin atomic oxygen protective coating for space and a preparation method thereof, and relates to the field of space solar cell technology. The preparation method comprises: S1, pre-cleaning the surface of the space material to remove surface impurities and pollutants; S2, plasma activation and modification of the surface of the space material after pre-cleaning in step S1; S3, depositing a 1‑10 nm ALD‑Al2O3 coating on the surface of the space material as a seed layer, and alternately growing ALD‑Al2O3 and ALD‑TiO2 coatings on the seed layer to prepare an ultra-thin atomic oxygen protective coating with a total coating thickness of 50‑100 nm. The present invention adopts the above-mentioned ultra-thin atomic oxygen protective coating for space and a preparation method thereof, and grows a dense and ultra-thin nano-aluminum oxide / titanium oxide laminated film on the surface of space materials such as polyimide by atomic layer deposition technology to enhance the atomic oxygen protection effect.

Description

Technical Field

[0001] The invention relates to the technical field of space solar cells, and in particular to an ultra-thin atomic oxygen protective coating for space and a preparation method thereof. Background Art

[0002] Atomic oxygen (AO) in the low Earth orbit environment is highly oxidizing and often carries high energy. The erosion effect caused by its high-energy collision can cause the performance degradation of organic materials such as polyimide and polyvinylidene chloride in space battery arrays, seriously affecting the normal operation of spacecraft. In order to increase the service life of space materials, it is necessary to prepare a protective coating on their surface for protection.

[0003] Currently, for space materials such as polyimide, protective coatings such as silicon oxide, aluminum oxide and silicone are basically covered on the surface through different methods such as sol-gel, physical vapor deposition and chemical vapor deposition to improve the resistance to atomic oxygen corrosion.

[0004] However, due to the high density of film defects, these methods often require the deposition of a coating of considerable thickness to provide a good protective effect. On the one hand, a coating that is too thick will increase costs, and on the other hand, it will lead to reduced coating toughness, poor adhesion, and prone to defects such as cracks and peeling, causing film performance failure.

[0005] Therefore, the preparation of universal, high-performance atomic oxygen protective coatings is particularly critical to the service life of space materials and the on-orbit operation of satellites. Summary of the invention

[0006] The purpose of the present invention is to provide an ultra-thin atomic oxygen protective coating for space and a preparation method thereof. Through atomic layer deposition technology, a dense and ultra-thin inorganic coating can be grown on the surface of space materials such as polyimide, and it can play a good atomic oxygen protection effect.

[0007] To achieve the above object, the present invention provides a method for preparing an ultra-thin atomic oxygen protective coating for space, comprising the following steps:

[0008] S1. Pre-clean the surface of space materials to remove surface impurities and contaminants;

[0009] S2, plasma activation and modification of the surface of the space material pre-cleaned in step S1;

[0010] The specific steps of activation modification include:

[0011] The pre-cleaned space material is placed in the ALD chamber, and the surface of the space material is activated and modified by the inductively coupled O2 / Ar mixed plasma generator inside the ALD chamber; the O2 / Ar mixed plasma power is set to 300W, the O2 / Ar mixed gas composition is 6 / 4, and the O2 / Ar mixed plasma action time is 10-20min;

[0012] S3. Deposit 1-10 nm ALD-Al2O3 coating as a seed layer on the surface of the space material, and alternately grow ALD-Al2O3 and ALD-TiO2 coatings on the seed layer to prepare an ultra-thin atomic oxygen protective coating with a total coating thickness of 50-100 nm.

[0013] Preferably, the pre-cleaning in step S1 includes:

[0014] S1-1, use deionized water to clean the space material in the first step to remove impurities;

[0015] S1-2. Use organic solvent ethanol to soak and clean the surface of space materials to remove surface chemical pollutants.

[0016] Preferably, the specific steps of depositing the ultra-thin atomic oxygen protective coating in step S3 include:

[0017] S3-1, the ALD chamber temperature is set in the range of 70-150°C, and the chamber is evacuated to 0-20Pa; argon is used as a carrier gas to alternately introduce aluminum precursor and oxidant, and ALD-Al2O3 is deposited in multiple cycles to deposit 1-10nm of ALD-Al2O3 on the surface of the space material as a seed layer;

[0018] S3-2. Using argon as a carrier gas, titanium precursor and oxidant are alternately introduced to deposit ALD-TiO2, and ALD-TiO2 coating and ALD-Al2O3 coating are alternately deposited to deposit an ALD-Al2O3 / TiO2 stack with a thickness of 40-90nm.

[0019] Preferably, in step S3-2, during the ALD-Al2O3 / TiO2 stack deposition process, eight ALD-TiO2 and two ALD-Al2O3 cycles are considered as one super cycle, and several super cycles are deposited in sequence until the ALD-Al2O3 / TiO2 stack thickness reaches 40 nm.

[0020] Preferably, in step S3-1, the ALD chamber temperature is set to 100°C.

[0021] Preferably, the space material includes one of polyimide, polyvinylidene chloride, polytetrafluoroethylene, and a resin-based composite material.

[0022] As an inorganic atomic oxygen protective coating, a coating that is too thick will easily crack, resulting in coating defects and protection failure; at the same time, the inorganic coating must have good adhesion to the substrate. Therefore, it is necessary to prepare an ultra-thin and dense ALD protective coating for use in atomic oxygen protection of materials such as polyimide. The key lies in the need for a suitable ALD deposition temperature and a substrate surface rich in active sites that facilitates the growth of the ALD coating.

[0023] In this regard, the ALD growth temperature is optimized. 70-150℃ is a temperature range suitable for ALD growth on the polymer surface. Too low a temperature is not conducive to the deposition of the ALD coating. Too high a temperature will cause the polymer to expand due to heat, resulting in discontinuous infiltration growth of the ALD coating. The preferred 100℃ is a more suitable ALD coating growth temperature. At this temperature, it is conducive to the growth of amorphous ALD-Al2O3 / TiO2 coatings. At the same time, the ALD-TiO2 coating has a faster growth rate at this temperature. The incorporation of ALD-Al2O3 coatings can further improve the density of the coating growth.

[0024] Therefore, the present invention adopts the above-mentioned ultra-thin atomic oxygen protective coating for space and its preparation method, which has the following technical effects:

[0025] (1) Using the ALD coating growth process, the growth temperature is relatively low, which is suitable for coating modification of polymer surface materials such as polyimide, effectively avoiding damage to the substrate during the process;

[0026] (2) ALD coatings have excellent density and uniformity, so that ultra-thin coatings at the nanometer level can provide good atomic oxygen protection, effectively avoiding defects caused by excessive coating deposition thickness;

[0027] (3) Optimize the ALD coating preparation process to prepare nanoscale Al2O3 / TiO2 stacked films to further improve the atomic oxygen protection effect of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of a method for preparing an ultra-thin atomic oxygen protective coating for space use in the present invention;

[0029] Figure 2 It is a designed film system of an ultra-thin atomic oxygen protective coating for space use in the present invention;

[0030] Figure 3 The test results of the water contact angle of the sample before and after the plasma activation of the polyimide film surface, wherein (a) is the water contact angle of the polyimide film surface before the plasma activation; (b) is the water contact angle of the polyimide film surface after the plasma activation;

[0031] Figure 4is the ratio of surface element content before and after plasma activation of the polyimide surface;

[0032] Figure 5 This is the C1s fine spectrum of XPS test before and after polyimide surface plasma activation;

[0033] Figure 6 The figures are the test results of atomic oxygen irradiation of polyimide film and polyimide coated with ALD coating, wherein (a) is the surface morphology of polyimide film after irradiation by ground atomic oxygen simulation test; (b) is the surface morphology of polyimide film coated with ALD atomic oxygen protective coating after irradiation by ground atomic oxygen simulation test; (c) is the 3D morphology of polyimide surface after irradiation by ground atomic oxygen simulation test; (d) is the 3D morphology of polyimide surface coated with ALD atomic oxygen protective coating after irradiation by ground atomic oxygen simulation test;

[0034] Figure 7 The water contact angle on the polyimide surface under the action of O2 / Ar mixed plasma with different gas flow components;

[0035] Figure 8 The mass loss rate of polyimide substrate (a) and the surface roughness variation trend (b) of ALD coatings with different thicknesses;

[0036] Fig. 9 Mass loss (a) and surface roughness trend (b) of coating samples with a total thickness of 50 nm and different doping ratios of Al2O3 after AO etching. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0038] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0039] Embodiment 1

[0040] A method for preparing an ultra-thin atomic oxygen protective coating for space use, the process is as follows Figure 1 As shown, the specific steps include:

[0041] S1. Pre-cleaning of polyimide membrane surface:

[0042] The polyimide membrane surface is first cleaned with deionized water to remove impurities, and the polyimide membrane surface is soaked and cleaned with organic solvent ethanol to remove surface chemical pollutants.

[0043] S2. Polyimide film surface plasma activation:

[0044] The cleaned polyimide film was placed in an ALD chamber, and the polyimide surface was activated and modified by an inductively coupled (ICP) plasma generator inside the chamber. The plasma power was set to 300 W, and the surface was activated and modified by O2 / Ar mixed plasma. The O2 / Ar mixed gas composition was 6 / 4, and the O2 / Ar mixed plasma action time was 20 min.

[0045] After plasma treatment, the polyimide film further removes surface contamination particles, while the surface hydrophilicity is improved, generating more active sites to facilitate the deposition of the ALD coating and further improve the coating adhesion.

[0046] like Figures 3 to 5 As shown, Figure 3 In the figure, (a) is the water contact angle of the polyimide film surface before plasma activation; (b) is the water contact angle of the polyimide film surface after plasma activation. Figure 4 is the ratio of surface element content before and after plasma activation of the polyimide surface. Figure 5 This is the C1s fine spectrum of XPS test before and after polyimide surface plasma activation.

[0047] Surface XPS analysis showed that after plasma activation, the proportion of O elements on the surface of the polyimide membrane increased, the proportion of C elements decreased significantly, and the content of polar groups such as CO / C=O increased, thereby forming more active sites on the surface and improving the surface hydrophilicity.

[0048] S3, ALD coating deposition:

[0049] The ALD chamber temperature was set to 100°C and the chamber was evacuated to 20 Pa. Using argon as the carrier gas, the aluminum precursor and the oxidant were introduced alternately, and ALD-Al2O3 was deposited in multiple cycles. Similarly, the titanium precursor and the oxidant were introduced in sequence to deposit ALD-TiO2. Eight ALD-TiO2 and two ALD-Al2O3 cycles were considered as one super cycle, and several such super cycles were deposited in sequence to perform ALD-Al2O3 / TiO2 stacked film deposition.

[0050] like Figure 2 The coating design film system is shown, in which 10nm ALD-Al2O3 is pre-deposited on the surface of the activated polyimide film as a seed layer; then a 40nm thick ALD-Al2O3 / TiO2 stack is deposited according to the above-mentioned super cycle, and the total coating thickness is 50nm.

[0051] Experimental Testing

[0052] (i) The polyimide sample coated with the ALD coating prepared in Example 1 was placed in a ground atomic oxygen simulation test device for atomic oxygen irradiation test.

[0053] like Figure 6 As shown, (a) is the surface morphology of the polyimide film after irradiation by the ground atomic oxygen simulation test; (b) is the surface morphology of the polyimide film covered with ALD atomic oxygen protective coating after irradiation by the ground atomic oxygen simulation test; (c) is the 3D morphology of the surface of the polyimide after irradiation by the ground atomic oxygen simulation test; (d) is the 3D morphology of the surface of the polyimide covered with ALD atomic oxygen protective coating after irradiation by the ground atomic oxygen simulation test.

[0054] It can be seen that the surface of the polyimide sample without ALD coating was completely corroded by AO after atomic oxygen irradiation, the structure was damaged, and the 3D morphology showed a significant increase in roughness; the surface of the sample covered with ALD coating was intact after atomic oxygen irradiation, and the 3D morphology showed that the roughness did not change significantly. The prepared ALD atomic oxygen protective coating has a good protective effect.

[0055] (II) The key to the dense growth of inorganic protective coatings, especially ALD coatings, on the surface of polymer substrates depends first on the active sites on the polymer surface. The improvement of active sites helps to promote the rapid adsorption of ALD precursors on the substrate surface to form a dense film, so the substrate surface needs to be treated.

[0056] Through the designed plasma source located inside the ALD chamber, that is, using in-situ O2 / Ar mixed plasma, the plasma parameters are optimized, and the substrate surface is directly activated before the ALD coating is deposited. The plasma treatment efficiency is improved and the timeliness problem is effectively avoided. On the one hand, the adhesion between the substrate and the coating is improved, and on the other hand, the hydrophilicity of the substrate surface is increased, more active sites are generated, and more abundant polar groups such as CO / C=O are convenient for the adsorption and growth of the ALD coating, which plays a key role in the subsequent dense growth.

[0057] like Figure 7 The figure shows the surface water contact angle data of polyimide after activation treatment under 300W O2 / Ar mixed plasma for 10 minutes. It can be seen that the effect of O2 / Ar mixed plasma with different gas flow components is the best when the O2 / Ar mixed gas component is 6 / 4, and the water contact angle of the polyimide surface is the lowest.

[0058] (III) Taking ALD-TiO2 coating as an example, a ground atomic oxygen simulation test was carried out on a polyimide substrate covered with ALD-TiO2 coating of different thicknesses ranging from 5nm to 100nm (5, 10, 25, 50, 75, 100nm).

[0059] After atomic oxygen corrosion, the mass loss rate of samples with different thicknesses is as follows Figure 8As shown in (a), as the thickness of the ALD-TiO2 coating increases to more than 50 nm, the mass loss rate of the polyimide sample is basically stable at 0.2 mg / cm 2 Below, it has excellent atomic oxygen protection ability. Figure 8 (b) shows the surface roughness change trend of samples of different thicknesses after atomic oxygen etching. As the thickness increases, the surface roughness of the sample after etching stabilizes in the range of 0.02-0.03μm, which is consistent with the roughness of the sample before AO irradiation.

[0060] (IV) Design of ALD-Al2O3 / TiO2 coating structure, verify the optimal structure by controlling the doping ratio of ALD-Al2O3. After the deposition of ALD-Al2O3 seed layer, super cycles of ALD-Al2O3 / TiO2 with aluminum / titanium ratios of 1 / 9, 2 / 8, 3 / 7, and 4 / 6 were designed to verify its protection ability after atomic oxygen corrosion. Fig. 9 The mass loss and surface roughness trends of coating samples with a total thickness of 50 nm and different doping ratios of Al2O3 after AO etching. Fig. 9 As shown in (a), when the ALD-Al2O3 doping ratio is 20% (i.e., the aluminum / titanium ratio is 2 / 8), the sample has the lowest carbon content of 0.08 mg / cm after AO erosion test. 2 Mass loss rate, the sample after AO irradiation under this coating structure has the lowest surface roughness of 0.026μm ( Fig. 9 (b)).

[0061] Therefore, the present invention adopts the above-mentioned ultra-thin atomic oxygen protective coating for space and its preparation method, and adopts oxygen / argon mixed plasma to activate and modify the substrate, increase the active groups on the substrate surface, and promote the uniform and dense growth of the ALD coating on the polyimide substrate; the prepared coating has good density, effectively improves the atomic oxygen protection ability of space materials such as polyimide and polyvinylidene chloride, and can avoid the defects caused by excessively thick coatings; the design of the atomic layer deposition aluminum oxide / titanium oxide laminated film system further optimizes the density of the coating and the adhesion of the substrate, further improving the atomic oxygen protection ability.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing an ultra-thin atomic oxygen protective coating for space, characterized in that: The steps include: S1. Pre-clean the surface of space materials to remove surface impurities and contaminants; S2, plasma activation and modification of the surface of the space material pre-cleaned in step S1; The specific steps of activation modification include: The pre-cleaned space material is placed in the ALD chamber, and the surface of the space material is activated and modified by the inductively coupled O2 / Ar mixed plasma generator inside the ALD chamber; the O2 / Ar mixed plasma power is set to 300W, the O2 / Ar mixed gas flow ratio is 6:4, and the O2 / Ar mixed plasma action time is 10-20min; S3, depositing a 1-10 nm ALD-Al2O3 coating as a seed layer on the surface of the space material, and alternately growing an ALD-Al2O3 and an ALD-TiO2 coating on the seed layer to prepare an ultra-thin atomic oxygen protective coating with a total coating thickness of 50-100 nm; The specific steps of depositing the ultra-thin atomic oxygen protective coating in step S3 include: S3-1, the ALD chamber temperature is set in the range of 70-150°C, and the chamber is evacuated to 0-20Pa; argon is used as a carrier gas to alternately introduce aluminum precursor and oxidant, and ALD-Al2O3 is deposited in multiple cycles to deposit 1-10nm of ALD-Al2O3 on the surface of the space material as a seed layer; S3-2, using argon as a carrier gas, alternately introducing a titanium precursor and an oxidant to deposit ALD-TiO2, alternately depositing an ALD-TiO2 coating and an ALD-Al2O3 coating, and depositing an ALD-Al2O3 / TiO2 stack with a thickness of 40-90 nm; In step S3-2, during the ALD-Al2O3 / TiO2 stack deposition process, eight ALD-TiO2 and two ALD-Al2O3 cycles are considered as one super cycle, and several super cycles are deposited in sequence until the ALD-Al2O3 / TiO2 stack thickness reaches 40 nm.

2. The method for preparing an ultra-thin atomic oxygen protective coating for space use according to claim 1, characterized in that: The pre-cleaning in step S1 includes: S1-1, use deionized water to clean the space material in the first step to remove impurities; S1-2. Use organic solvent ethanol to soak and clean the surface of space materials to remove surface chemical pollutants.

3. The method for preparing an ultra-thin atomic oxygen protective coating for space use according to claim 1, characterized in that: In step S3-1, the ALD chamber temperature is set to 100°C.

4. The method for preparing an ultra-thin atomic oxygen protective coating for space use according to claim 1, characterized in that: The space material includes one of polyimide, polyvinylidene chloride, and polytetrafluoroethylene.

5. An ultra-thin atomic oxygen protective coating prepared by the method for preparing an ultra-thin atomic oxygen protective coating for space use as described in any one of claims 1 to 4.

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