阅读说明：本技术 一种高导热碳纤维表面氧化铝-氧化锆复合涂层的制备方法 (Preparation method of high-thermal-conductivity carbon fiber surface alumina-zirconia composite coating ) 是由 欧阳求保 朱城楠 曹贺 于 2020-05-11 设计创作，主要内容包括：本发明公开了一种高导热碳纤维表面氧化铝-氧化锆复合涂层的制备方法,该方法为溶胶凝胶法。过程包括碳纤维表面的预处理；复合溶胶的制备；预处理后碳纤维的涂覆和干燥处理；涂覆复合溶胶后碳纤维的较低温度热处理。通过这个过程从而获得氧化铝-氧化锆复合涂层涂覆的碳纤维。本发明制备的复合涂层晶型是γ-Al<Sub>2</Sub>O<Sub>3</Sub>·t-ZrO<Sub>2</Sub>的复合涂层。该方法工艺较简单,对设备和操作环境要求低,可实施性强,原材料价格便宜,且易于获取,容易实现,节能环保,可在高导热碳纤维表面制得涂覆完整,厚度可调的复合涂层,提高了碳纤维的抗氧化性能,改善了碳纤维增强铝基复合材料的导热性能。(The invention discloses a preparation method of an alumina-zirconia composite coating on the surface of high-thermal-conductivity carbon fiber, which is a sol-gel method. The process comprises the pretreatment of the surface of the carbon fiber; preparing composite sol; coating and drying the pretreated carbon fibers; and (4) performing low-temperature heat treatment on the carbon fiber coated with the composite sol. By this procedure, an alumina-zirconia composite coating-coated carbon fiber was obtained. The composite coating crystal form prepared by the inventionIs gamma-Al 2 O 3 ·t‑ZrO 2 The composite coating of (1). The method has the advantages of simple process, low requirements on equipment and operating environment, strong feasibility, low price of raw materials, easy acquisition, easy realization, energy conservation and environmental protection, can prepare a composite coating with complete coating and adjustable thickness on the surface of the high-heat-conductivity carbon fiber, improves the oxidation resistance of the carbon fiber, and improves the heat conductivity of the carbon fiber reinforced aluminum-based composite material.)

1. A preparation method of an alumina-zirconia composite coating on the surface of a heat-conducting carbon fiber specifically comprises the following steps:

(1) heating the carbon fiber to 380-450 ℃, and preserving heat for 10-30 min to remove the glue; soaking the cooled carbon fiber into acetone for 60-120 min to completely remove the glue; washing the carbon fiber after complete degumming by deionized water, and then drying the carbon fiber in vacuum at the temperature of 70-90 ℃ for 2-4 h;

(2) mixing zirconium nitrate and yttrium nitrate to prepare a solution, dropwise adding an oxalic acid solution into the solution, then adding polyvinyl alcohol and glycerol, and finally placing the solution into a water bath at the temperature of 80-100 ℃ to keep stirring for 0.5-1 h to obtain blue transparent zirconium-containing sol;

dropwise adding an ammonia water solution into an aluminum nitrate solution, continuously stirring for 30-50 min to obtain a milky solution, then carrying out suction filtration, washing with deionized water for several times, drying at 60-90 ℃ to obtain a milky precipitate, adding deionized water into the milky precipitate, dropwise adding a nitric acid solution, adding polyvinyl alcohol, and finally placing into a water bath at 80-100 ℃ to keep stirring for 1-2 h to obtain a clear and transparent boehmite sol; mixing the sol containing zirconium and the sol containing boehmite, and putting the mixture into a water bath at the temperature of 80-100 ℃ to keep stirring for 10-30 min to obtain light blue transparent composite sol;

(3) ultrasonically dipping the carbon fiber treated in the step (1) into the composite sol obtained in the step (2) for coating, filtering out the composite sol, and then drying in vacuum at 50-80 ℃ for 12-24 h to obtain the carbon fiber coated with the composite gel;

(4) carrying out heat treatment on the carbon fiber obtained in the step (3) in an argon atmosphere, heating to 400 ℃ at a heating rate of 1-3 ℃/min, and keeping the temperature for 20-50 min; and heating to the heat treatment temperature of 600-800 ℃ at the heating rate of 4-8 ℃/min, and preserving the heat for 1-3 h to obtain the carbon fiber coated with the alumina-zirconia composite coating.

2. The method of claim 1, wherein: the hot carbon fiber in the step (1) refers to a carbon fiber with the thermal conductivity of more than 300W/(m.K).

3. The method of claim 1, wherein: the molar ratio of the zirconium nitrate to the yttrium nitrate in the step (2) is between 94:6 and 97: 3;

the molar ratio of the zirconium nitrate to the oxalic acid in the step (2) is between 4:1 and 6: 1.

4. The method of claim 1, wherein: the molar ratio of the ammonia water to the aluminum nitrate in the step (2) is between 3:1 and 6: 1.

5. The method of claim 1, wherein: in the step (2), the mass fraction of the polyvinyl alcohol in the zirconium-containing sol is 1-4%, and the mass fraction of the glycerol in the zirconium-containing sol is 1-4%.

6. The method of claim 1, wherein: in the step (2), the concentration of the zirconium-containing sol is 0.2-0.3 mol/L, the concentration of the boehmite sol is 0.2-0.3 mol/L, and the molar ratio of Al to Zr in the composite sol is 4: 1-1: 1.

7. The method of claim 1, wherein: the intermediate coating and drying treatment process of the sol in the step (3) can be repeated for multiple times, and then subsequent heat treatment is carried out, so that the thickness of the composite coating is controlled.

8. The method of claim 1, wherein: and (4) coating the sol in the step (3) for ultrasonic dipping for 5-60 min, and then performing subsequent treatment, thereby controlling the thickness of the composite coating.

9. The production method according to any one of claims 1 to 8, characterized in that: the thickness of the aluminum oxide-zirconium oxide composite coating is 30-300 nm; the alumina-zirconia composite coating is gamma-Al₂O₃·t-ZrO₂And (4) composite coating.

10. Use of a carbon fiber coated with an alumina-zirconia composite coating prepared by the method of claim 1, wherein: the method is used for preparing the hot carbon fiber reinforced aluminum matrix composite material to enhance the thermal conductivity.

Technical Field

The invention relates to the field of high-thermal-conductivity carbon fiber reinforced aluminum-based composite materials, in particular to a preparation method of an alumina-zirconia composite coating on the surface of high-thermal-conductivity carbon fibers.

Background

The high-thermal-conductivity carbon fiber has the advantages of high strength, high modulus, low thermal expansion coefficient, low density, corrosion resistance and the like of the polypropylene cyano-carbon fiber, and also has the advantage of unique unidirectional high thermal conductivity, so that the high-thermal-conductivity carbon fiber is often used as a reinforcement to improve the thermal property and the mechanical property of a composite material, and the composite material is widely applied to the fields of aviation, aerospace, machinery, electronics and the like. However, carbon fibers have poor oxidation resistance, begin to oxidize at about 400 ℃ in air, have poor wettability with aluminum, and react at high temperature to form brittle, deliquescent Al even at the interface during compounding₄C₃Phase, Al₄C₃The thermal conductivity of the composite material is poor, the surface structure of the high-thermal-conductivity carbon fiber is damaged, the weight of the carbon fiber is reduced, and the thermal conductivity of the carbon fiber is reduced, so that the thermal performance of the composite material is influenced, and the application range of the composite material is limited.

Research shows that the carbon fiber is treated with surface coating to solve the problems, and proper surface coating can raise the antioxidant performance of carbon fiber, improve the wettability between carbon fiber and aluminum base, block the interface reaction between carbon fiber and aluminum base during high temperature compounding, reduce Al content and raise the heat resistance of aluminum alloy₄C₃The surface structure of the carbon fiber is kept complete, so that the heat-conducting property of the carbon fiber reinforced aluminum matrix composite is improved, and the application range of the carbon fiber reinforced aluminum matrix composite is expanded.

At present, methods for performing surface coating treatment on carbon fibers mainly include a physical vapor deposition method, a chemical vapor deposition method, and a sol-gel method. The sol-gel method has the advantages of low requirements on equipment and operating environment and can better solve the problem of uniform coating on the surface of the carbon fiber. In 2014, Chinese invention patent CN 103643481A discloses carbon fiber surface oxygenThe preparation method of the aluminum oxide coating comprises the steps of using aluminum nitrate as a raw material, adopting a sol-gel method, carrying out hydrolysis at 75-95 ℃, carrying out heat preservation for 1-2 hours, ageing for a period of time to form sol, coating carbon fibers, and carrying out heat treatment at 1000 ℃ to obtain α -Al₂O₃And (4) coating. The main problems are that the heat treatment temperature is high, and the energy-saving requirement is not met; in addition, when the binary or more than binary multi-element sol is coated on the carbon fiber, the problem of high-temperature heat treatment exists, and the prepared coating is easy to crack and fall off, so that the application of the carbon fiber in the aluminum matrix composite material is influenced.

The alumina-zirconia composite coating has better stability, and not only has the advantages of good high-temperature performance, phase change toughness and the like of the zirconia coating, but also has the advantages of corrosion resistance, oxidation resistance, good wettability with aluminum and the like of the alumina coating.

The patent CN 109160529A of China invention in 2018 discloses a preparation method of an alumina-zirconia high-temperature oxidation-resistant composite layer by searching the existing patents and documents, wherein ZrAl is used₂The alloy block is ground and polished, and after the surface is bright and flat without scratches, the alloy block is cleaned and dried; and then placing the composite material in a vacuum closed environment, introducing pure oxygen, and oxidizing for 6-24 hours at the constant temperature and the constant pressure at the temperature of 850-950 ℃ to obtain the alumina-zirconia high-temperature oxidation resistant composite layer. Document "Preparation of ZrO₂–Al₂O₃composite membranes by sol-gel process and the preparation of ZrO by the sol-gel process₂-Al₂O₃Composite membrane and characterization thereof) (Materials Science and Engineering A, Vol.367(2004)243-247) aluminum isopropoxide as a raw material, adding deionized water and nitric acid, and hydrolyzing at 80 ℃ for 12h to prepare boehmite sol; adding deionized water and anion exchange resin into zirconium hypochlorite serving as a raw material to obtain zirconium-containing sol; and mixing the boehmite sol and the zirconium-containing sol, and adding polyvinyl alcohol to obtain mixed sol. Literature "MicroStructure of sol-gel synthesized Al₂O₃–ZrO₂(Y₂O₃) Nano-composites studied by Transmission Electron microscopy (study of nanocomposite Al prepared by the Sol-gel method by Transmission Electron microscopy)₂O₃–ZrO₂(Y₂O₃) The microstructure of (1) (Materials Letters, Vol.59(2005)355-360) using aluminum sec-butoxide as a raw material, adding ethylene glycol monoethyl ether and isopropanol, hydrolyzing at 90 +/-8 ℃ for 4h to obtain alumina sol, then dropwise adding zirconium n-butoxide, finally adding deionized water and yttrium nitrate, and stirring to obtain the composite sol.

The main disadvantages of the methods for preparing alumina-zirconia composite coatings in the above patents and documents are: (1) the alumina-zirconia composite coating prepared by adopting a chemical deposition method has harsh preparation conditions and high energy consumption, is not suitable for preparing the alumina-zirconia composite coating by adopting a carbon fiber material (2) sol-gel method, has expensive raw materials and low efficiency, is toxic and can be obtained by (3) long-time hydrolysis and aging in the process of preparing alumina sol, and wastes energy.

In addition, the above patents and literature only relate to the method for preparing the alumina-zirconia composite coating, and are not applied to carbon fibers. Because the alumina-zirconia composite coating belongs to binary sol coating, the carbon fiber is easy to crack in the heat treatment process after being coated.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a preparation method of an alumina-zirconia composite coating on the surface of high-thermal-conductivity carbon fiber. The method has the advantages of simple process, low heat treatment temperature, low requirements on equipment and operation environment and low manufacturing cost, and the prepared composite coating is completely coated on the continuous fibers, has controllable thickness, can improve the oxidation resistance of the carbon fibers and improve the heat-conducting property of the carbon fiber reinforced aluminum-based composite material.

The invention is realized by the following technical scheme: firstly, pretreating (removing glue, cleaning and drying) high-thermal-conductivity carbon fibers, then preparing zirconium-containing sol by using zirconium nitrate as a raw material, preparing boehmite sol by using aluminum nitrate as a raw material, mixing the two sols to obtain composite sol, then coating the pretreated carbon fibers to obtain carbon fibers coated with the composite sol, drying to obtain carbon fibers coated with the composite gel, and finally carrying out low-temperature heat treatment on the carbon fibers coated with the gel under the atmosphere protection to obtain the carbon fibers with the alumina-zirconia composite coating.

The preparation method of the high-thermal-conductivity carbon fiber surface alumina-zirconia composite coating specifically comprises the following steps:

(1) heating the carbon fiber to 380-450 ℃, and preserving heat for 10-30 min to remove the glue; soaking the cooled carbon fiber into acetone for 60-120 min to completely remove the glue; washing the carbon fiber after complete degumming by deionized water, and then drying the carbon fiber in vacuum at 70-90 ℃ for 2-4 h;

(2) mixing zirconium nitrate and yttrium nitrate to prepare a solution, dropwise adding an oxalic acid solution into the solution, then adding polyvinyl alcohol and glycerol, and finally placing the solution into a water bath at the temperature of 80-100 ℃ to keep stirring for 0.5-1 h to obtain blue transparent zirconium-containing sol;

dropwise adding an ammonia water solution into an aluminum nitrate solution, continuously stirring for 30-50 min to obtain a milky solution, then carrying out suction filtration, washing with deionized water for several times, drying at 60-90 ℃ to obtain a milky precipitate, adding deionized water into the milky precipitate, dropwise adding a nitric acid solution, adding polyvinyl alcohol, and finally placing into a water bath at 80-100 ℃ to keep stirring for 1-2 h to obtain a clear and transparent boehmite sol; and mixing the zirconium-containing sol and the boehmite sol, and putting the mixture into a water bath at the temperature of 80-100 ℃ to keep stirring for 10-30 min to obtain light blue transparent composite sol.

(3) Ultrasonically dipping the carbon fiber treated in the step (1) into the composite sol obtained in the step (2), filtering the composite sol, and then drying in vacuum at 50-80 ℃ for 12-24 h to obtain the carbon fiber coated with the composite gel;

(4) carrying out heat treatment on the carbon fiber obtained in the step (3) in an argon atmosphere, heating to 400 ℃ at a heating rate of 1-3 ℃/min, and keeping the temperature for 20-50 min; and heating to the heat treatment temperature of 600-800 ℃ at the heating rate of 4-8 ℃/min, and preserving the heat for 1-3 h to obtain the carbon fiber coated with the alumina-zirconia composite coating.

Preferably, the hot carbon fiber in step (1) of the present invention is a carbon fiber having a thermal conductivity of more than 300W/(m.K).

Preferably, the molar ratio of zirconium nitrate to yttrium nitrate in step (2) of the present invention is between 94:6 and 97: 3.

Preferably, the molar ratio of zirconium nitrate to oxalic acid in step (2) of the present invention is between 4:1 and 6: 1.

Preferably, the molar ratio of the ammonia water to the aluminum nitrate in the step (2) of the present invention is between 3:1 and 6: 1.

Preferably, in the step (2) of the present invention, the mass fraction of the polyvinyl alcohol in the zirconium-containing sol is between 1 and 4%, and the mass fraction of the glycerol in the zirconium-containing sol is between 1 and 4%.

Preferably, in the step (2) of the present invention, the concentration of the zirconium-containing sol is between 0.2 and 0.3mol/L, the concentration of the boehmite sol is between 0.2 and 0.3mol/L, and the molar ratio of Al to Zr in the composite sol is between 4:1 and 1: 1.

Preferably, the coating and drying process of the sol in step (3) of the present invention may be repeated several times, and then a subsequent heat treatment is performed, thereby controlling the thickness of the composite coating layer.

Preferably, in the invention, the sol coating ultrasonic immersion time in the step (3) is 5-60 min, and then the subsequent treatment is carried out, so as to control the thickness of the composite coating.

Preferably, the thickness of the alumina-zirconia composite coating is 30-300 nm.

Preferably, the alumina-zirconia composite coating in the invention refers to gamma-Al₂O₃·m-ZrO₂And (4) composite coating.

According to the second aspect of the invention, the carbon fiber coated with the alumina-zirconia composite coating prepared by the method can be used for preparing the heat-conducting carbon fiber reinforced aluminum-based composite material, the heat conductivity of the prepared heat-conducting carbon fiber reinforced aluminum-based composite material is obviously improved compared with that of an aluminum alloy matrix, and the heat conductivity of the prepared carbon fiber reinforced aluminum-based composite material is also improved compared with that of the carbon fiber reinforced aluminum-based composite material prepared by carbon fiber without the coating.

In the method of the invention, zirconium nitrate, yttrium nitrate, oxalic acid, aluminum nitrate and ammonia water are used as raw materials, and compared with the raw materials in the prior art patents and documents, the method has the advantages of low price and low toxicity. In the process of preparing the zirconium-containing sol, the temperature is only required to be kept at 80-100 ℃ for 0.5-1 h; in the process of preparing the boehmite sol, only heat preservation is carried out for 1-2 h at 80-100 ℃; the two sols are mixed and then only need to be kept at 80-100 ℃ for 10-30 min, and most of the existing technologies keep the temperature for at least 6h, so that the time is undoubtedly saved, the efficiency is increased, and the energy is saved. In the invention, the thickness of the alumina-zirconia composite coating can be controlled by repeatedly carrying out the steps of coating and drying treatment, and can also be controlled by the ultrasonic dipping time, and the thickness of the prepared alumina-zirconia composite coating is controllable, and the crystal form is single.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention adopts a sol-gel method and takes zirconium nitrate, yttrium nitrate, oxalic acid, aluminum nitrate, ammonia water, nitric acid, polyvinyl alcohol and glycerol as raw materials to prepare the composite sol, and the raw materials have low price, easy acquisition, easy realization and smaller toxicity.

(2) The time required by high-temperature hydrolysis, mixing and stirring and aging in the process of preparing the composite sol is shorter than that in the prior art, the time is saved, the operability is strong, special equipment is not required, and the method is suitable for batch production;

(3) in the invention, the heat treatment temperature of the carbon fiber coated with the composite sol is relatively low, so that the energy consumption is saved;

(4) according to the invention, the obtained alumina-zirconia composite coating on the surface of the high-thermal-conductivity carbon fiber is complete and compact, has no obvious cracks, and improves the oxidation resistance of the carbon fiber and the thermal conductivity of the carbon fiber reinforced aluminum matrix composite.

Drawings

FIG. 1 is a process flow diagram of a sol-gel method for preparing an alumina-zirconia composite coating on the surface of a carbon fiber with high thermal conductivity;

fig. 2 is a scanning electron microscope image of uncoated high thermal conductivity carbon fiber.

Fig. 3 is a scanning electron microscope image of the high thermal conductivity carbon fiber containing the alumina-zirconia composite coating.

FIG. 4 is a phase analysis diagram of gel after heat treatment at 900 ℃ in the preparation of the alumina-zirconia composite coating by a sol-gel method.

Fig. 5 is an oxidation resistance experiment chart of uncoated high thermal conductive carbon fiber and high thermal conductive carbon fiber containing alumina-zirconia composite coating.

FIG. 6 is a comparison of the thermal conductivity of an aluminum alloy matrix, an uncoated high thermal conductivity carbon fiber reinforced aluminum matrix composite and an alumina-zirconia composite coated high thermal conductivity carbon fiber reinforced aluminum matrix composite.

Fig. 7 is a schematic diagram of a high thermal conductivity carbon fiber reinforced aluminum matrix composite prepared by a vacuum pressure infiltration method.

Detailed Description

The carbon fibers described in the following examples are continuous fibers, model TC-HM-70, and were carried out according to the process flow diagram shown in FIG. 1. The coating condition and the thickness of the aluminum oxide-zirconium oxide are detected by a Scanning Electron Microscope (SEM), the phase composition of the composite sol after heat treatment is determined by X-ray diffraction analysis (XRD), the oxidation resistance experiment of the carbon fiber containing the composite coating is determined by a thermogravimetric analyzer, and the heat conductivity of the carbon fiber reinforced aluminum-based composite material is determined by a laser thermal conductivity meter.