Colored silicon carbide fiber and preparation method thereof

Abstract

The invention discloses a colored silicon carbide fiber and a preparation method thereof, and belongs to the technical field of high-performance ceramic fiber materials. The method comprises the following steps: sequentially carrying out photoresist removal and cleaning pretreatment on silicon carbide fibers, placing the silicon carbide fibers in an atmosphere with the oxygen concentration of 10-80%, and carrying out heat treatment at 900-1100 DEG C for 10-360 minutes, so that a silicon dioxide film with the thickness of 30-550 nm is generated on the surface of the silicon carbide fibers in situ through a thermal oxidation reaction. The film makes the fiber present a structural color based on an optical interference effect. According to the method, no external coloring agent is introduced, the process is simple and environment-friendly, the prepared colored silicon carbide fiber is firm in coloring and adjustable in color, excellent mechanical properties and high temperature resistance are kept, the retention rate of monofilament tensile strength is not lower than 80%, and the method is suitable for continuous and large-scale production.

Description

Technical Field

[0001] This invention relates to the field of high-performance ceramic fiber preparation technology, specifically to a colored silicon carbide fiber and its preparation method, particularly a method for achieving structural coloring and functional synergy by in-situ growth of a silicon dioxide film on the surface of silicon carbide fiber through thermal oxidation treatment. Background Technology

[0002] Silicon carbide fiber, as a key high-performance inorganic ceramic fiber, is widely used in aerospace, nuclear energy, and advanced composite materials. With its expansion into civilian sectors such as 3C electronics and high-end consumer goods, the market has created an urgent demand for diverse appearance and colors.

[0003] Currently, silicon carbide fibers, due to the free carbon formed during the preparation process and their inherent properties, only exhibit a monotonous black color, failing to meet the aesthetic demands of modern industry. Silicon carbide fibers have a smooth surface and high chemical inertness, making traditional chemical dyeing methods difficult, resulting in poor colorfastness and significant pollution. In existing technologies, for carbon fibers with similar physicochemical properties, external coloring processes are often introduced. Chinese patent CN114411409A discloses a "gradient rainbow-colored carbon fiber based on single-layer thin-film interference and its preparation method," which uses sol-gel methods, vapor deposition, etc., to add a transparent inorganic oxide film (such as SiO2) to the surface of the carbon fiber, utilizing the interference effect to generate color. Another example is achieving coloring by introducing cyclic cluster polyphosphazene films (CN201510127348.1) or carbon microsphere layers (CN202111357814.7) onto the surface. However, these methods are complex, require continuous introduction of foreign substances, and may damage the fiber's intrinsic properties.

[0004] For example, Chinese patent CN120738914A discloses a "high electromagnetic shielding colored fiber and its preparation method and application," which achieves high electromagnetic shielding performance by depositing an optically inert material layer and an electromagnetic shielding functional coating on the surface of a matrix fiber. The electromagnetic shielding functional coating uses a metal element or metal oxide, achieving both color and high electromagnetic shielding performance. However, this method has inherent drawbacks: it is unsuitable for the typical high-temperature application environment (>1000℃) of silicon carbide fibers, leading to failure and potentially contaminating or damaging the fibers. Furthermore, the introduced conductive coating alters the dielectric properties of the silicon carbide fiber and may cause adverse interfacial reactions with the matrix when used as a reinforcement in composite materials, impairing its excellent bulk properties. The patent mentions using silicon dioxide as the optically inert material layer, primarily to enrich the fiber surface with hydroxyl groups, enhancing the adhesion and density of the subsequent electromagnetic shielding functional coating on the fiber surface. Under high-temperature oxidation conditions, common silicon carbide fibers naturally form an extremely thin (typically <10nm) colorless amorphous silica (SiO2) film on their surface, effectively blocking oxygen diffusion and thus providing passive antioxidant protection for the fiber body. This characteristic is one of the core mechanisms of silicon carbide fiber's high-temperature resistance. However, based on the traditional understanding of silicon carbide fiber manufacturing processes, there are generally technical limitations in this field: the SiO2 layer is only regarded as a passively generated "protective shell" that aims to be as thin as possible. The focus of technological development has always been on how to optimize fiber composition and structure to inhibit or delay the initial occurrence of the oxidation process, with the fundamental goal of maximizing the preservation of the fiber's initial mechanical strength. Existing technologies have neglected the possibility of actively designing and precisely constructing the SiO2 layer to develop its active functions beyond basic antioxidant protection. Summary of the Invention

[0005] The main objective of this invention is to provide a colored silicon carbide fiber and its preparation method. This method eliminates the need for introducing external coloring substances, actively utilizing the inherent characteristic of in-situ silicon dioxide generation on the surface of silicon carbide fibers. By precisely controlling the degree of oxidation on the fiber surface, the silicon dioxide layer is transformed into a thin protective film, thereby solving the problems of difficulty in coloring the surface of silicon carbide fibers, weak coloring, and damage to the high-temperature resistance of the fiber itself in existing technologies. To achieve the above objective, this invention adopts the following technical solution:

[0006] A method for preparing colored silicon carbide fibers includes the following steps:

[0007] (1) Pretreatment: The silicon carbide fiber is degummed and cleaned to remove the organic adhesive and contaminants attached to the surface, so as to ensure the uniformity of the subsequent oxidation reaction.

[0008] (2) Thermal oxidation treatment: After heat treatment in an oxygen-containing atmosphere, silicon carbide fibers with different thicknesses are generated on the fiber surface to obtain silicon carbide fibers with structural color.

[0009] Furthermore, in the degumming step, the silicon carbide fiber is placed at 600°C and kept at that temperature for 1 hour to remove impurities such as adhesive from the surface of the finished silicon carbide fiber. The degree of impurity removal from the fiber surface affects the thickness and uniformity of the oxide film formed.

[0010] Furthermore, in the cleaning step, the silicon carbide fibers are ultrasonically cleaned with alcohol of concentration above 95%, followed by low-temperature drying. This step mainly cleans dust, grease, and other contaminants from the fiber surface; simultaneously, using alcohol of concentration above 95% allows for rapid drying, reducing the introduction of impurities; low-temperature drying avoids affecting the subsequent high-temperature processing effect and prevents safety hazards.

[0011] Furthermore, in the thermal oxidation treatment, by controlling the treatment temperature, treatment time and oxygen concentration, the SiC on the fiber surface is oxidized with oxygen to generate a SiO2 layer. The in-situ generated SiO2 layer will be bonded to the underlying SiC at the interface through strong covalent bonds (Si-O-Si and Si-C), ensuring that the interface bonding is very strong and not easy to peel off under stress or thermal shock.

[0012] Furthermore, through the aforementioned thermal oxidation treatment, an in-situ continuous amorphous silicon dioxide film with a thickness of 30 nm to 550 nm is constructed on the surface of the silicon carbide fiber, thereby giving the silicon carbide fiber a uniform and stable structural color. The interference color is most pronounced at layer thicknesses within this range. As the thickness increases, the color changes according to the pattern: blue → green → yellow → purple → blue, with different colors formed by interference.

[0013] Furthermore, the oxygen volume concentration in the oxygen-containing atmosphere is 10% to 80%. Higher oxygen concentrations result in faster oxidation rates, while lower oxygen concentrations result in slower oxidation rates.

[0014] Furthermore, the high-temperature heat treatment is carried out at a temperature of 900℃ to 1100℃ for 10 to 360 minutes. Too low a reaction temperature results in a slow oxidation rate and slow oxide layer thickness growth, while too high a reaction temperature can significantly damage the fiber structure, leading to a sharp decrease in fiber strength. The reaction time affects the oxide layer thickness; too short a reaction time results in an insufficient oxide layer thickness, while too long a reaction time leads to excessive reduction in fiber strength.

[0015] Furthermore, the controllable thermal oxidation process in step (2) employs multiple intermittent heat treatments, with the number of heat treatments ranging from 1 to 5. This method helps alleviate thermal stress and yields a thicker film and a more vibrant color. By precisely controlling the temperature and time of each heat treatment, a SiO2 film with a specific optical thickness can be constructed, thereby achieving a dynamic color-changing effect (angle-dependent color effect) that varies with the viewing angle. Under the same reaction temperature, reaction time, and reaction oxygen concentration, multiple oxidation processes result in a faster oxidation rate and a thicker oxide layer.

[0016] Furthermore, the SiO2 film can serve as an ideal weak interface layer in SiC fiber-reinforced SiC ceramic matrix composites (CMCs). Through its controllable failure during crack propagation, it effectively promotes toughening mechanisms such as crack deflection, fiber bridging, and fiber pull-out, thereby improving the fracture toughness of the composite material by 5-10% and achieving customized performance at the reinforcement-matrix interface.

[0017] The present invention also claims protection for a colored silicon carbide fiber prepared by the above method, characterized in that the fiber surface has an amorphous silicon dioxide continuous film with a thickness of 30 nm to 550 nm that is covalently bonded to the fiber matrix, the fiber exhibits a visible structural color, and its monofilament tensile strength retention rate is not less than 80% after being kept at 1100°C for 1 hour.

[0018] Compared with the closest prior art, the beneficial effects of the present invention are as follows:

[0019] (1) A silicon dioxide film of different thicknesses is generated in situ on the surface of silicon carbide fiber by thermal oxidation treatment, so as to achieve the preparation of multiple colors on the fiber surface. The film is firmly bonded to the fiber matrix surface and is not easy to fall off.

[0020] (2) The SiO2 layer generated in situ on the surface of silicon carbide fiber prepared by the present invention can provide better and more durable long-term high temperature oxidation resistance, which greatly delays the performance degradation of the fiber under extreme environment. The fiber product retains no less than 80% of its strength after being kept at 1100℃ for 1 hour.

[0021] (3) The present invention adopts a one-step thermal oxidation method, which does not require the addition of external colorants and complex equipment. The process is simple and environmentally friendly. Continuous and large-scale production can be achieved by precisely controlling the temperature and time. The cost is low and the product performance is stable. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the preparation method of the present invention.

[0023] Figure 2 These are photographs of the colored silicon carbide fiber samples prepared in Examples 1-5.

[0024] Figure 3 This is a scanning electron microscope image of the cross-section of the sample obtained in Example 1.

[0025] Figure 4 This is a scanning electron microscope image of the cross-section of the sample obtained in Example 2.

[0026] Figure 5 This is a scanning electron microscope image of the cross-section of the sample obtained in Example 3.

[0027] Figure 6 This is a scanning electron microscope image of the cross-section of the sample obtained in Example 4.

[0028] Figure 7 These are photographs of the sample with different colors at different angles obtained in Example 5.

[0029] Figure 8 This is a scanning electron microscope image of the cross-section of the sample obtained in Comparative Example 1. Detailed Implementation

[0030] The present invention will be further illustrated by the following examples, but the scope of protection of the present invention is not limited thereto.

[0031] Pretreatment: The finished silicon carbide fibers used in all examples and comparative examples were placed in a muffle furnace and kept at 600°C for 1 hour in air atmosphere to remove the surface adhesive. After cooling, they were ultrasonically cleaned with 95% ethanol for 5 minutes and dried at 50°C for later use.

[0032] Example 1: Preparation of blue silicon carbide fibers

[0033] The pretreated fibers were placed in a high-temperature box furnace and heated to 960°C at a heating rate of 5°C / min under static air (oxygen concentration of approximately 21%), and held at this temperature for 40 minutes, followed by furnace cooling to room temperature. A SiO2 multifunctional layer with a thickness of approximately 102 nm was successfully constructed on the surface of the resulting fibers, exhibiting a uniform blue color.

[0034] Example 2: Preparation of green silicon carbide fibers

[0035] The operation method is the same as in Example 1, except that the thermal oxidation conditions are changed to holding at 1060℃ for 120 minutes. The resulting SiO2 multifunctional layer on the fiber surface is approximately 195 nm thick and appears green.

[0036] Example 3: Preparation of yellow silicon carbide fibers

[0037] The operation method is the same as in Example 1, except that the thermal oxidation conditions are changed to holding at 960°C for 170 minutes. The resulting SiO2 multifunctional layer on the fiber surface is approximately 226 nm thick and appears yellow.

[0038] Example 4: Preparation of purple silicon carbide fibers

[0039] The operation method is the same as in Example 1, except that the thermal oxidation conditions are changed to holding at 960℃ for 120 min, followed by raising the temperature to 1060℃ and holding for another 90 min. The resulting SiO2 multifunctional layer on the fiber surface has a thickness of approximately 271 nm and appears purple.

[0040] Example 5: Preparation of blue angle-changing silicon carbide fiber

[0041] The operation method is the same as in Example 1, except that the thermal oxidation conditions are changed to a three-stage oxidation method. The pretreated fibers are heat-treated in the following order, and after each heat treatment, they are taken out and cooled to room temperature in air:

[0042] First time: 960℃, 60 minutes;

[0043] Second time: 960℃, 80 minutes;

[0044] Third time: 960℃, 120 minutes.

[0045] The cumulative oxidation time was 260 minutes. The resulting SiO2 multifunctional layer on the fiber surface was approximately 323 nm thick, and the film exhibited a dynamic color-changing effect from blue-green to blue under different viewing angles.

[0046] Comparative Example 1: Primitive Fibers

[0047] Black silicon carbide fibers from the same batch, after undergoing general pretreatment steps, without subsequent thermal oxidation treatment, were used as a benchmark for performance comparison.

[0048] Comparative Example 2: Increasing oxygen concentration and improving oxidation rate

[0049] Compared with Example 1, the pretreated fibers were placed in a high-temperature box furnace, the oxygen concentration was increased to 60%, and the temperature was raised to 960°C at a rate of 5°C / min, and held at this temperature for 10 minutes, followed by furnace cooling to room temperature. A SiO2 multifunctional layer with a thickness of approximately 120 nm was successfully constructed on the surface of the resulting fibers, exhibiting a uniform blue color.

[0050] Comparative Example 3: Insufficient Oxidation

[0051] The pretreated fibers were heat-treated at 900℃ for 600 minutes, resulting in a SiO2 film with a thickness of only 35nm, no obvious interference color, and the process was too time-consuming and not economical.

[0052] Comparative Example 4: Excessive Oxidation

[0053] The pretreated fibers were heat-treated at 1200℃ for 60 minutes, resulting in severe fiber embrittlement. The thickness of the SiO2 multifunctional layer on the fiber surface was approximately 450 nm, but the tensile strength retention rate of the single filaments was less than 50%, failing to meet the basic requirements for structural materials. The experiment fully demonstrates the protective effect of the SiO2 multifunctional layer constructed in this invention on the fibers.

[0054] Table 1. Correspondence between thermal oxidation process conditions and fiber color

[0055]

[0056] Table 2 Relationship between fiber oxide film thickness and mechanical properties

[0057]

[0058] Data shows that, by using the method of the present invention, while obtaining different colors, the high-temperature strength retention rate of the fibers is significantly higher than that of the untreated original fibers (Comparative Example 1).

Claims

1. A method for preparing colored silicon carbide fibers, characterized in that, Includes the following steps: (1) Pretreatment: Silicon carbide fibers are degummed and cleaned to remove surface impurities; (2) Thermal oxidation treatment: The pretreated silicon carbide fiber is placed in an oxygen-containing atmosphere, and the oxygen volume concentration is controlled at 10%-80% for 10-360 minutes at 900℃-1100℃. The colored silicon carbide fiber surface is subjected to an in-situ thermal oxidation reaction to generate a silicon dioxide film with a thickness of 30-550 nm.

2. The preparation method according to claim 1, characterized in that, The degumming process described in step (1) is as follows: the silicon carbide fiber is kept at 600°C for 1 hour in an air atmosphere.

3. The preparation method according to claim 1, characterized in that, The cleaning process described in step (1) is as follows: the silicon carbide fiber is ultrasonically cleaned with ethanol of 95% or higher concentration, and then dried at 50℃-80℃.

4. The preparation method according to claim 1, characterized in that, The heat treatment is a multiple intermittent heat treatment, with the number of heat treatments ranging from 1 to 5.

5. A colored silicon carbide fiber, characterized in that, It is prepared by the method according to any one of claims 1 to 4.

6. A colored silicon carbide fiber, characterized in that, It includes: a silicon carbide fiber matrix; an amorphous silicon dioxide film formed on the surface of the silicon carbide fiber matrix; the thickness of the amorphous silicon dioxide film is 30 nm to 550 nm, and it is generated in situ through a thermal oxidation reaction to give the silicon carbide fiber a structural color.

7. The colored silicon carbide fiber according to claim 6, characterized in that, After the colored silicon carbide fiber is kept at 1100℃ for 1 hour, the retention rate of its monofilament tensile strength is not less than 80%.

8. The colored silicon carbide fiber according to claim 6, characterized in that, The amorphous silicon dioxide thin film exhibits an angular color difference effect.

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