Flexible SiC Composite Film with In-situ Pressure Monitoring Function and Its Preparation Method

Abstract

The present invention discloses a flexible SiC composite film with in-situ pressure monitoring function and a preparation method thereof, belonging to the technical field of flexible composite films. The flexible SiC composite film with in-situ pressure monitoring function of the present invention comprises a flexible SiC piezoelectric layer, an electroluminescent layer and a temperature-resistant encapsulation layer arranged in sequence; the flexible SiC piezoelectric layer is composed of SiC particles and a polymer matrix; the electroluminescent layer is filled with a luminescent material; the temperature-resistant encapsulation layer includes a modified polytetrafluoroethylene layer and a SiO2 aerogel layer connected to the electroluminescent layer. The composite film of the present invention adopts a piezoelectric layer composed of SiC particles and a high-temperature polymer matrix, combined with a double-layer temperature-resistant encapsulation structure composed of SiO2 aerogel and modified polytetrafluoroethylene, can work stably in a medium-high temperature environment to a certain extent, and has excellent flexibility, and can be conformally pasted on the surface of complex curved structural parts.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible composite films, and particularly relates to a flexible SiC composite film with an in-situ pressure monitoring function and a preparation method thereof. Background Art

[0002] Existing pressure sensors are mostly based on the principles of resistance strain, capacitance or piezoelectricity, and rely on wire connections or embedded electrodes to transmit electrical signals, which have significant limitations in high-temperature, strong vibration or complex curved surface applications. For example, traditional piezoelectric ceramic sensors (such as PZT) have high sensitivity, but are brittle, have poor flexibility, are difficult to fit curved surface structures, and are prone to depolarization at high temperatures; while metal strain gauges can adapt to a certain temperature range, but require complex wiring and are easily affected by electromagnetic interference. In recent years, flexible sensor technology has gradually developed, but its temperature resistance performance is generally insufficient. Some studies have tried to improve the temperature resistance through encapsulation materials, but a single encapsulation layer is difficult to balance the functions of heat insulation and mechanical protection, and the increase in surface roughness at high temperatures is likely to introduce noise. Summary of the Invention

[0003] The purpose of the present invention is to provide a flexible SiC composite film with an in-situ pressure monitoring function and a preparation method thereof, which are used to solve the technical problems of complex wiring and insufficient temperature resistance in existing pressure sensors.

[0004] To achieve the above object, in one embodiment of the present invention, a flexible SiC composite film with an in-situ pressure monitoring function is provided, which includes a flexible SiC piezoelectric layer, an electroluminescent layer, and a temperature-resistant encapsulation layer arranged in sequence;

[0005] The flexible SiC piezoelectric layer is composed of SiC particles and a polymer matrix;

[0006] The electroluminescent layer is filled with a luminescent material;

[0007] The temperature-resistant encapsulation layer includes a modified polytetrafluoroethylene layer and a SiO2 aerogel layer connected to the electroluminescent layer.

[0008] One of the preferred solutions of the present invention is that the thickness of the flexible SiC piezoelectric layer is 80μm - 150μm, and the piezoelectric coefficient d 33 is 15pC / N - 25pC / N.

[0009] One of the preferred solutions of the present invention is that the mass ratio of SiC particles to the polymer matrix is 5:5 - 7:3, and the particle size of SiC particles is 50nm - 200nm.

[0010] One of the preferred solutions of the present invention is that the polymer matrix includes any one of polysilazane, polyimide, and polyetheretherketone.

[0011] One of the preferred embodiments of the present invention is that the thickness of the electroluminescent layer is 20 μm - 50 μm.

[0012] One of the preferred embodiments of the present invention is that the luminescent material is copper-doped zinc sulfide or chromium-doped yttrium aluminum garnet.

[0013] One of the preferred embodiments of the present invention is that the particle size of copper-doped zinc sulfide is 1 μm - 3 μm, and the particle size of chromium-doped yttrium aluminum garnet is 3 μm - 5 μm.

[0014] One of the preferred embodiments of the present invention is that the thickness of the SiO2 aerogel layer is 40 μm - 100 μm, and the thermal conductivity is lower than 0.02 W / (m·K).

[0015] The present invention also discloses a preparation method of a flexible SiC composite film with an in-situ pressure monitoring function, including the following steps:

[0016] Composite SiC particles and a polymer matrix prepolymer to prepare a flexible SiC piezoelectric layer;

[0017] Deposit an electroluminescent layer on the flexible SiC piezoelectric layer;

[0018] Spray a temperature-resistant encapsulation layer on the electroluminescent layer to obtain a flexible SiC composite film with an in-situ pressure monitoring function;

[0019] The electroluminescent layer is prepared by mixing a luminescent material, silica gel, and a scattering agent, and the temperature-resistant encapsulation layer includes a SiO2 aerogel layer and a modified polytetrafluoroethylene layer.

[0020] One of the preferred embodiments of the present invention is that the preparation of the flexible SiC piezoelectric layer by composite SiC particles and a polymer matrix prepolymer includes:

[0021] Mix SiC particles, a polymer matrix prepolymer, and a solvent to obtain a slurry;

[0022] Coat the slurry on a substrate and perform stepwise curing;

[0023] The film after stepwise curing is subjected to polarization treatment to obtain a flexible SiC piezoelectric layer.

[0024] One of the preferred embodiments of the present invention is that the mixing of SiC particles, a polymer matrix prepolymer, and a solvent to obtain a slurry includes: calculating the mass of the polymer prepolymer according to the mass ratio of SiC particles and the polymer matrix, mixing the SiC particles and the polymer prepolymer, and then adding a solvent to adjust the solid content of the material to 25% - 45%, and obtaining the slurry after dispersion.

[0025] One of the preferred embodiments of the present invention is that the polymer matrix prepolymer includes any one of polysilazane prepolymer, polyimide prepolymer, and polyetheretherketone prepolymer, and the solvent includes any one of N-methylpyrrolidone, xylene, acetone, hexane, and cyclohexane.

[0026] One of the preferred embodiments of the present invention is that the slurry is coated on a substrate for stepwise curing, including: coating the slurry on the substrate by casting, with the wet film thickness being 150 μm - 300 μm, preheating at 110°C - 130°C for 0.5 h - 1.5 h after coating, and then heating up to 200°C - 250°C and maintaining for 1 h - 2 h.

[0027] One of the preferred embodiments of the present invention is that the film after stepwise curing is subjected to polarization treatment to obtain a flexible SiC piezoelectric layer, including: applying a DC polarization electric field of 6 kV / mm - 10 kV / mm to the film after stepwise curing, and performing isothermal polarization treatment at 100°C - 120°C for 0.5 h - 1.5 h to obtain a flexible SiC piezoelectric layer.

[0028] One of the preferred embodiments of the present invention is that an electroluminescent layer is deposited on the flexible SiC piezoelectric layer, including: mixing a luminescent material and silica gel in a mass ratio of 1:2 - 3, adding a scattering agent at 0.5% - 1% of the mass of the luminescent material and stirring to mix, obtaining a slurry, depositing the obtained slurry on the surface of the flexible SiC piezoelectric layer, and performing ultraviolet curing after deposition.

[0029] One of the preferred embodiments of the present invention is that the luminescent material is copper-doped zinc sulfide or chromium-doped yttrium aluminum garnet, and the scattering agent includes any one of TiO2, SiO2, BaSO4, and CaCO3.

[0030] One of the preferred embodiments of the present invention is that a temperature-resistant encapsulation layer is sprayed on the electroluminescent layer to obtain a flexible SiC composite film with an in-situ pressure monitoring function, including:

[0031] Using tetraethyl orthosilicate as a precursor, preparing a SiO2 sol by the sol-gel method, and dip-coating the prepared sol on the electroluminescent layer and drying to obtain a SiO2 aerogel layer;

[0032] Spraying a modified polytetrafluoroethylene suspension onto the surface of the SiO2 aerogel layer, and drying and heating to obtain a flexible SiC composite film with an in-situ pressure monitoring function.

[0033] In summary, the beneficial effects of the present invention are:

[0034] 1. The flexible SiC composite film with in-situ pressure monitoring function of the present invention forms a flexible SiC piezoelectric layer by compounding nano-SiC particles with a high-temperature polymer matrix. It generates charges under pressure and stimulates the luminescent material in the adjacent electroluminescent layer to emit light. The light intensity distribution directly reflects the pressure. It is further combined with a double-layer heat-resistant packaging layer structure composed of SiO2 aerogel and modified polytetrafluoroethylene to block heat flow and reduce surface roughness, ensuring stability and anti-interference ability in high-temperature environments, and solving the problems of complex wiring and insufficient temperature resistance of traditional sensors.

[0035] 2. The electroluminescent layer of the flexible SiC composite film with in-situ pressure monitoring function of the present invention selects ZnS:Cu (copper-doped zinc sulfide) or YAG:Cr (chromium-doped yttrium aluminum garnet) material according to the operating temperature, and combines TiO2 scattering agent to improve luminescence uniformity.

[0036] 3. The flexible SiC composite film with in-situ pressure monitoring function of the present invention integrates a flexible SiC piezoelectric layer, an electroluminescent layer and a temperature-resistant packaging layer into one. By combining the piezoelectric effect with the electroluminescent technology, it can realize in-situ pressure monitoring in a high-temperature environment. It also has excellent flexibility and can be adhered to the surface of complex curved structural parts. It is suitable for real-time pressure monitoring in medium, high temperature and high pressure scenarios such as aerospace and industrial equipment.

[0037] 4. The high temperature and anti-interference ability of the flexible SiC composite film with in-situ pressure monitoring function of the present invention is achieved through a double-layer temperature-resistant packaging structure composed of SiO2 aerogel and modified polytetrafluoroethylene, so that the film can work stably for a long time at a high temperature of 400°C, and has low surface roughness, which effectively reduces the noise caused by airflow disturbance and significantly improves the monitoring accuracy under high temperature and high pressure environment.

[0038] 5. The flexible SiC composite film with in-situ pressure monitoring function of the present invention utilizes the piezoelectric effect to directly convert the pressure signal into a light intensity distribution density signal, thereby realizing wireless optical signal output without the need for wires or electrode connections, thus simplifying the complex wiring problems of traditional sensors and avoiding the influence of electromagnetic interference on signal transmission.

[0039] 6. The flexible SiC composite film with in-situ pressure monitoring function of the present invention has high flexibility through the composite design of the flexible SiC piezoelectric layer and the high-temperature resistant polymer matrix, which can closely fit complex curved structures (such as aircraft engine blades), thereby expanding its application scenarios on curved components.

[0040] 7. The flexible SiC composite film with in-situ pressure monitoring function of the present invention realizes sensitive detection of tiny pressures through the piezoelectric properties of nano-SiC particles combined with the uniform scattering of electroluminescent materials, and provides real-time feedback through changes in light intensity to meet dynamic monitoring needs.

[0041] Other features and advantages of the present invention will be set forth in the following description, and in part will be obvious from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention may be illustrated by the effects described in the description and the accompanying drawings. Description of the Drawings

[0042] Figure 1 It is a schematic diagram of a flexible SiC composite film with in-situ pressure monitoring function in an embodiment of the present invention;

[0043] Figure 2 It is a structural schematic diagram of a flexible SiC composite film with in-situ pressure monitoring function in an embodiment of the present invention;

[0044] Figure 3 It is a flow chart of a preparation method of a flexible SiC composite film with in-situ pressure monitoring function in an embodiment of the present invention.

[0045] Wherein, 1 - flexible SiC piezoelectric layer, 2 - electroluminescent layer, 3 - temperature-resistant encapsulation layer, 4 - SiO2 aerogel layer, 5 - modified polytetrafluoroethylene layer. Detailed Embodiments

[0046] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0047] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0048] As Figure 1 shown, the present invention discloses a flexible SiC composite film with in-situ pressure monitoring function. As Figure 2 shown, it includes a flexible SiC piezoelectric layer 1, an electroluminescent layer 2, and a temperature-resistant encapsulation layer 3 arranged in sequence. The thickness of the flexible SiC piezoelectric layer 1 is 80 μm - 150 μm, and the piezoelectric coefficient d 33 is 15 pC / N - 25 pC / N, and the thickness of the electroluminescent layer 2 is 20 μm - 50 μm;

[0049] The flexible SiC piezoelectric layer 1 is composed of a composite of SiC particles and a polymer matrix, and the mass ratio of SiC particles to the polymer matrix is 5:5 - 7:3; among them, the SiC particles are nano-SiC particles with a particle size of 50 nm - 200 nm, and the polymer matrix is a high-temperature resistant polymer matrix, which is a polymer material with certain high-temperature resistance and can maintain flexibility at an appropriate high temperature, including any one of polysilazane, polyimide, and polyetheretherketone;

[0050] The general formula of polysilazane is [-Si(CH3)2-NH-] n or [-Si(CH2=CH)2-NH-] n , and the companies selling commercially available organic polysilazane include Hangzhou Qingci New Materials Technology Co., Ltd. (product models: vinyl polysilazane TC-P11, methyl polysilazane TC-P01A, TC-L11, TC-P05, etc.), Merck KGaA (product models: Durazane®1000 series, etc.);

[0051] The electroluminescent layer 2 is filled with a luminescent material, and the luminescent material is selected according to the target temperature. The luminescent material is copper-doped zinc sulfide (ZnS:Cu) or chromium-doped yttrium aluminum garnet (YAG:Cr). The particle size of copper-doped zinc sulfide is 1 μm - 3 μm, and the particle size of chromium-doped yttrium aluminum garnet is 3 μm - 5 μm;

[0052] The high-temperature resistant encapsulation layer 3 includes a modified polytetrafluoroethylene layer 5 and a SiO2 aerogel layer 4 connected to the electroluminescent layer 2. The thickness of the SiO2 aerogel layer 4 is 40 μm - 100 μm, and the thermal conductivity is lower than 0.02 W / (m·K). The SiO2 aerogel layer 4 can block the influence of high-temperature heat flow on the internal functional layers. The modified polytetrafluoroethylene layer 5 can still maintain a surface roughness less than 0.5 μm after continuously bearing temperature at 400 °C for 10 h, thus avoiding additional noise caused by air flow disturbance.

[0053] The flexible SiC composite film with in-situ pressure monitoring function of the present invention integrates the flexible SiC piezoelectric layer 1, the electroluminescent layer 2, and the high-temperature resistant encapsulation layer 3. The flexible SiC piezoelectric layer 1 is formed by the composite of nano-SiC particles and a high-temperature polymer matrix, generates charges under pressure, and excites the luminescent material in the adjacent electroluminescent layer 2 to emit light. The light intensity distribution directly reflects the magnitude of the pressure. Further, combined with the double-layer high-temperature resistant encapsulation layer 3 structure composed of SiO2 aerogel and modified polytetrafluoroethylene, it blocks heat flow and reduces the surface roughness, ensuring stability and anti-interference ability in a high-temperature environment.

[0054] The present invention also discloses a preparation method of a flexible SiC composite film with in-situ pressure monitoring function, as Figure 3 shown, which includes the following steps:

[0055] Step (1): Prepare a flexible SiC piezoelectric layer 1 by compounding SiC particles and a polymer matrix prepolymer.

[0056] Step (2): Deposit an electroluminescent layer 2 on the flexible SiC piezoelectric layer 1.

[0057] Step (3): Spray a temperature-resistant encapsulation layer 3 on the electroluminescent layer 2 to obtain a flexible SiC composite film with in-situ pressure monitoring function.

[0058] The electroluminescent layer 2 is prepared by mixing a luminescent material, silica gel, and a scattering agent. The temperature-resistant encapsulation layer 3 includes a SiO2 aerogel layer 4 and a modified polytetrafluoroethylene layer 5. Among them, the silica gel is high-temperature-resistant silica gel.

[0059] Among them, step (1) of compounding SiC particles and a polymer matrix prepolymer to prepare a flexible SiC piezoelectric layer 1 includes:

[0060] Step (101): Mix SiC particles, a polymer matrix prepolymer, and a solvent to obtain a slurry. Specifically, calculate the mass of the polymer prepolymer according to the mass ratio of SiC particles to the polymer matrix of 5:5 - 7:3. Mix nano-SiC particles with a particle size of 50 nm - 200 nm and the polymer matrix prepolymer, and then add a solvent to adjust the solid content of the material to 25% - 40%. Then, treat it in an ultrasonic disperser at a power of 500 W for 30 min to obtain a uniformly dispersed slurry. Among them, the polymer matrix prepolymer includes any one of a polysilazane prepolymer, a polyimide prepolymer, and a polyetheretherketone prepolymer. The polysilazane prepolymer is a type of inorganic or organic-inorganic hybrid polymer with a Si-N bond as the main chain, in an incompletely crosslinked intermediate state, and can form functional materials such as ceramics and coatings through further curing or pyrolysis. Among them, the solvent includes any one of N-methylpyrrolidone, xylene, acetone, hexane, and cyclohexane.

[0061] Step (102): Coat the slurry on a substrate for stepwise curing. Specifically, coat the slurry obtained in step (101) on a glass substrate with a surface treated with silane by a casting process, and the wet film thickness is 150 μm - 300 μm. Then, transfer it to a vacuum drying oven for stepwise curing. The stepwise curing is: first preheat at 110°C - 130°C for 0.5 h - 1.5 h to volatilize the solvent, and then raise the temperature to 200°C - 250°C and hold for 1 h - 2 h to complete the polymer crosslinking.

[0062] Step (103): The film after stepwise curing is subjected to polarization treatment to obtain the flexible SiC piezoelectric layer 1. Specifically, the film cured in step (102) is applied with a DC polarization electric field of 6 kV / mm - 10 kV / mm under the condition of a silicone oil bath, and is subjected to isothermal polarization treatment at 100 °C - 120 °C for 0.5 h - 1.5 h, so that the internal polarization direction of the SiC particles is oriented along the direction of the applied electric field, and finally a flexible SiC piezoelectric layer 1 with a thickness of 80 μm - 150 μm and a piezoelectric coefficient d 33 of 15 pC / N - 25 pC / N is obtained;

[0063] Step (2): Deposit the electroluminescent layer 2 on the flexible SiC piezoelectric layer 1, including: Select the luminescent material according to the target operating temperature: for application scenarios below 400 °C, use copper-doped zinc sulfide (ZnS:Cu) powder with a particle size of 1 μm - 3 μm; for high-temperature working conditions above 400 °C, select chromium-doped yttrium aluminum garnet (YAG:Cr) powder with a particle size of 3 μm - 5 μm;

[0064] Mix the luminescent material and silicone gel in a mass ratio of 1:2 - 3, add a scattering agent according to 0.5 wt% - 1 wt% of the mass of the luminescent material, and mix at a rotation speed of 1500 r / min - 2000 r / min for 10 min - 20 min by a planetary mixer to form a uniform slurry; adopt an electrostatic spraying process, and deposit the slurry uniformly on the surface of the flexible SiC piezoelectric layer 1 under the conditions of a spraying voltage of 25 kV - 40 kV and a substrate temperature of 70 °C - 90 °C, control the single spraying thickness to be about 10 μm, repeat spraying 2 to 5 times, control the total thickness to reach 20 μm - 50 μm as needed, and then perform ultraviolet curing in a nitrogen atmosphere, and use an ultraviolet light source with a wavelength of 365 nm and an intensity of 50 mW / cm 2 - 60 mW / cm 2 to irradiate for 5 min - 8 min to crosslink and cure the silicone gel; wherein, the scattering agent includes any one of TiO2, SiO2, BaSO4, and CaCO3;

[0065] Step (3): Spray the temperature-resistant encapsulation layer 3 on the electroluminescent layer 2 to obtain a flexible SiC composite film with an in-situ pressure monitoring function, including:

[0066] Step (301): Using tetraethyl orthosilicate as a precursor, prepare a SiO2 sol by the sol-gel method, dip-coat the prepared sol on the electroluminescent layer, and dry to obtain a SiO2 aerogel layer. Specifically: Prepare a SiO2 precursor solution by the sol-gel method, using tetraethyl orthosilicate as the silicon source and ethanol as the solvent, with a volume ratio of 1:5 - 1:10, add hydrochloric acid with a volume concentration of 0.01M - 0.1M as a catalyst to promote the hydrolysis reaction to form a sol, form a film on the surface of the electroluminescent layer 2 by dip-coating, and use an ultraviolet-assisted low-temperature heat treatment process to complete the transformation of the gel into SiO2 aerogel, while avoiding thermal damage to the SiC piezoelectric layer and the electroluminescent layer 2 during the preparation process, to obtain the SiO2 aerogel layer 4;

[0067] Step (302): Spray the modified polytetrafluoroethylene suspension onto the surface of the SiO2 aerogel layer 4, and obtain a flexible SiC composite film with in-situ pressure monitoring function after drying and heating. Specifically, spray a polytetrafluoroethylene suspension with a solid content of 20% - 30% (adding 15wt% of Fe3O4 to modify the temperature resistance of polytetrafluoroethylene) onto the surface of the SiO2 aerogel layer 4 by spraying process. The spraying pressure of the air pressure spraying method is 0.4MPa - 0.7MPa, the spraying distance is about 20cm, dry for 10min - 15min under ventilation conditions after spraying to completely evaporate the solvent, and then heat in a muffle furnace at 200℃ - 250℃ for 15min - 30min to form a dense composite layer and cool with the furnace to obtain a flexible SiC composite film with in-situ pressure monitoring function. Preferably, the pressure needs to be gradually reduced during the spraying process of the tetrafluoroethylene suspension to optimize the coating uniformity.

[0068] Example 1: Surface pressure monitoring of aeroengine blades

[0069] Step 1: Prepare the flexible SiC piezoelectric layer 1

[0070] Mix SiC nanoparticles with a particle size of 100nm and a polysilazane prepolymer in a ratio of 7:3, add N-methylpyrrolidone to adjust the solid content to 30%, and cast and mold after ultrasonic dispersion. The wet film thickness is 200μm. After preheating at 120℃ for 1h and crosslinking and curing at 250℃ for 2h, apply an 8kV / mm polarization electric field in a 100℃ silicone oil bath to obtain a piezoelectric film with a thickness of 100μm;

[0071] Step 2: Deposit the electroluminescent layer 2

[0072] Select YAG:Cr powder (particle size 4μm), mix it with high-temperature resistant silica gel in a ratio of 1:3, add 0.5wt% TiO2, and then electrostatically spray it on the surface of the piezoelectric layer. The spraying voltage is 30kV, the substrate temperature is 80℃, and the total thickness is 40μm. After ultraviolet curing, a uniform light-emitting layer is formed;

[0073] Step 3: Encapsulation treatment

[0074] Prepare a 50-μm-thick SiO2 aerogel on the surface of the light-emitting layer by the sol-gel method, then spray a modified polytetrafluoroethylene coating, and heat it at 250 °C for 20 min to form a dense outer layer.

[0075] Attach the film to the surface of the aeroengine blade. After applying airflow to the blade to generate pressure, the light intensity of the light-emitting layer increases with the increase of pressure. Collect the optical signal through an external optical device to realize in-situ monitoring of the dynamic pressure of the blade.

[0076] Example 2: Monitoring of air flow pressure distribution on the car body

[0077] Step 1: Preparation of flexible SiC piezoelectric layer

[0078] Mix SiC nanoparticles with a particle size of 150 nm and a polyimide prepolymer in a mass ratio of 6:4, use xylene as a solvent to adjust the solid content to 35%, and the wet film thickness is 250 μm after casting. After preheating at 110 °C for 1 h and crosslinking and curing at 250 °C for 2 h, use a polarization electric field strength of 10 kV / mm, and finally obtain a film piezoelectric coefficient d 33 is 22 pC / N;

[0079] Step 2: Preparation of electroluminescent layer

[0080] Select YAG:Cr powder (particle size 5 μm) and high-temperature resistant silica gel and mix them in a mass ratio of 1:2, add 0.8 wt% TiO2 scattering agent, and then electrostatically spray it on the surface of the piezoelectric layer. The spraying voltage is 35 kV, the substrate temperature is 80 °C, and the total thickness is 50 μm. After ultraviolet curing, a uniform light-emitting layer is obtained;

[0081] Step 3: Preparation of temperature-resistant encapsulation layer

[0082] Prepare a 40-μm-thick SiO2 aerogel on the surface of the light-emitting layer by the sol-gel method, then spray a modified polytetrafluoroethylene coating, and heat it at 250 °C for 25 min to form a dense outer layer.

[0083] Attach the film to the complex curved surface of the car body (such as the arc surface of the car door and the ridge line of the engine hood). During the aerodynamic analysis of the car body shape, monitor the air flow pressure distribution in real time to achieve dead-angle-free monitoring, and the applicable temperature range is from room temperature to 200 °C.

[0084] Comparative example: Single-layer temperature-resistant encapsulation without SiO2 aerogel

[0085] Step 1: Preparation of flexible SiC piezoelectric layer

[0086] The parameters are the same as those in Example 2, and the piezoelectric coefficient d 33 is 21 pC / N;

[0087] Step 2: Preparation of the electroluminescent layer

[0088] The parameters are the same as those in Example 2;

[0089] Step 3: Preparation of the encapsulation layer

[0090] Only a single-layer modified polytetrafluoroethylene coating is used, and the SiO2 aerogel layer is not added. The surface roughness of the polytetrafluoroethylene coating is 0.8 μm after heating at 250 °C.

[0091] The composite films prepared in Example 2 and the comparative example were subjected to surface roughness, thermal conductivity, maximum temperature rise inside the film under the same air flow conditions, and luminescence response stability tests. The test results are shown in Table 1:

[0092] Table 1: Test results of the composite films prepared in Example 2 and the comparative example

[0093]

[0094] It can be seen from Table 1 that in the comparative example, the temperature-resistant encapsulation layer does not include the SiO2 aerogel layer, resulting in a significant increase in the surface roughness of the film. Due to the lack of the heat insulation effect of the SiO2 aerogel layer, the thermal conductivity increases, and the maximum temperature rise inside the film under the same air flow conditions increases by 115 °C, which is not conducive to the long-term operation of the film at high temperatures. At the same time, it significantly affects the stability of the luminescence signal, increasing the light intensity signal fluctuation from 5% to 30% and affecting the determination of the effective signal.

[0095] In summary, the flexible SiC composite film with the in-situ pressure monitoring function of the present invention can work stably in a medium-high temperature environment to a certain extent, has excellent flexibility, can be conformally pasted on the surface of complex curved structural parts, and is suitable for real-time pressure monitoring in medium-high temperature and high-pressure scenarios such as aerospace and industrial equipment.

[0096] The above-described embodiments are only used to describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A flexible SiC composite film with in-situ pressure monitoring function, characterized in that: It includes a flexible SiC piezoelectric layer, an electroluminescent layer, and a temperature-resistant encapsulation layer arranged in sequence; The flexible SiC piezoelectric layer is composed of SiC particles and a polymer matrix; The electroluminescent layer is filled with a light-emitting material; The temperature-resistant encapsulation layer includes a modified polytetrafluoroethylene layer and a SiO2 aerogel layer connected to the electroluminescent layer; The mass ratio of the SiC particles to the polymer matrix is 5:5 - 7:3, and the particle size of the SiC particles is 50nm - 200nm; The polymer matrix includes any one of polysilazane, polyimide, and polyetheretherketone; The electroluminescent layer is prepared by mixing a light-emitting material, silica gel, and a scattering agent. The light-emitting material is copper-doped zinc sulfide or chromium-doped yttrium aluminum garnet.

2. The flexible SiC composite film with in-situ pressure monitoring function as described in claim 1, characterized in that: The thickness of the flexible SiC piezoelectric layer is 80 μm - 150 μm, and the piezoelectric coefficient d 33 is 15 pC / N - 25 pC / N.

3. The flexible SiC composite film with in-situ pressure monitoring function according to claim 1, characterized in that: The thickness of the electroluminescent layer is 20μm - 50μm.

4. The flexible SiC composite film with in-situ pressure monitoring function according to claim 1, wherein: The particle size of the copper-doped zinc sulfide is 1μm - 3μm, and the particle size of the chromium-doped yttrium aluminum garnet is 3μm - 5μm.

5. The flexible SiC composite film with in-situ pressure monitoring function according to claim 1, characterized in that: The thickness of the SiO2 aerogel layer is 40μm - 100μm, and the thermal conductivity is lower than 0.02W / (m·K).

6. A preparation method of a flexible SiC composite film with in-situ pressure monitoring function, characterized in that, It includes the following steps: Compound SiC particles and a polymer matrix prepolymer to prepare a flexible SiC piezoelectric layer; Deposit an electroluminescent layer on the flexible SiC piezoelectric layer; Spray a temperature-resistant encapsulation layer on the electroluminescent layer to obtain a flexible SiC composite film with an in-situ pressure monitoring function; The electroluminescent layer is prepared by mixing a light-emitting material, silica gel, and a scattering agent. The temperature-resistant encapsulation layer includes a SiO2 aerogel layer and a modified polytetrafluoroethylene layer; The depositing the electroluminescent layer on the flexible SiC piezoelectric layer includes: mixing the light-emitting material and silica gel in a mass ratio of 1:2 - 3, adding a scattering agent according to 0.5% - 1% of the mass of the light-emitting material and stirring to mix, obtaining a slurry, depositing the obtained slurry on the surface of the flexible SiC piezoelectric layer, and performing ultraviolet curing after deposition; The light-emitting material is copper-doped zinc sulfide or chromium-doped yttrium aluminum garnet; The mass ratio of the SiC particles to the polymer matrix is 5:5 - 7:3, and the particle size of the SiC particles is 50nm - 200nm; The polymer matrix includes any one of polysilazane, polyimide, and polyetheretherketone.

7. The preparation method of the flexible SiC composite film with in-situ pressure monitoring function according to claim 6, characterized in that: The compounding SiC particles and a polymer matrix prepolymer to prepare a flexible SiC piezoelectric layer includes: Mix SiC particles, a polymer matrix prepolymer, and a solvent to obtain a slurry; Coat the slurry on a substrate and perform stepwise curing; The film after stepwise curing is subjected to polarization treatment to obtain a flexible SiC piezoelectric layer.

8. The preparation method of the flexible SiC composite film with in-situ pressure monitoring function according to claim 7, characterized in that: Mixing SiC particles, a polymer matrix prepolymer, and a solvent to obtain a slurry includes: calculating the mass of the polymer prepolymer according to the mass ratio of the SiC particles to the polymer matrix, mixing the SiC particles and the polymer prepolymer, and then adding a solvent to adjust the solid content of the material to 25% - 45%, and obtaining a slurry through dispersion.

9. The preparation method of the flexible SiC composite film with in-situ pressure monitoring function according to any one of claims 7 or 8, characterized in that: The polymer matrix prepolymer includes any one of a polysilazane prepolymer, a polyimide prepolymer, and a polyetheretherketone prepolymer, and the solvent includes any one of N-methylpyrrolidone, xylene, acetone, hexane, and cyclohexane.

10. The preparation method of the flexible SiC composite film with in-situ pressure monitoring function according to claim 7, characterized in that: The stepwise curing by coating the slurry on the substrate includes: coating the slurry on the substrate by tape casting, with the wet film thickness being 150 μm - 300 μm, preheating at 110°C - 130°C for 0.5 h - 1.5 h after coating, and then heating up to 200°C - 250°C and holding for 1 h - 2 h.

11. The preparation method of the flexible SiC composite film with in-situ pressure monitoring function according to claim 7, characterized in that: The flexible SiC piezoelectric layer is obtained by polarizing the film after stepwise curing, which includes: applying a DC polarization electric field of 6 kV / mm - 10 kV / mm to the film after stepwise curing, and performing isothermal polarization treatment at 100°C - 120°C for 0.5 h - 1.5 h to obtain the flexible SiC piezoelectric layer.

12. The preparation method of the flexible SiC composite film with in-situ pressure monitoring function according to claim 6, characterized in that: The scattering agent includes any one of TiO2, SiO2, BaSO4, and CaCO3.

13. The preparation method of the flexible SiC composite film with in-situ pressure monitoring function according to claim 6, characterized in that: Spraying a temperature-resistant encapsulation layer on the electroluminescent layer to obtain a flexible SiC composite film with in-situ pressure monitoring function, which includes: Using tetraethyl orthosilicate as a precursor, preparing SiO2 sol by the sol-gel method, and dip-coating the prepared sol on the electroluminescent layer and drying to obtain a SiO2 aerogel layer; Spraying the modified polytetrafluoroethylene suspension onto the surface of the SiO2 aerogel layer, drying and heating to obtain a flexible SiC composite film with in-situ pressure monitoring function.

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