1. A method of producing a continuous pyrolytic carbon coating on continuous fibers comprising the steps of:

(1) preparing a CVD apparatus for allowing continuous passage of the continuous fiber in a reaction chamber, wherein one end of the continuous fiber is passed through the reaction chamber to make the continuous fiber in the reaction chamber in a flat and tensioned state:

(2) vacuumizing a reaction cavity of CVD equipment to be below 20Pa, heating to 800-900 ℃ at a heating rate of 10-20 ℃/min, then heating to a reaction temperature at a heating rate of 5-10 ℃/min, wherein the reaction temperature is 950-1200 ℃, introducing carbon source gas and carrier gas, enabling continuous fibers to continuously pass through the reaction cavity, and continuously depositing pyrolytic carbon on the fibers in the reaction cavity, so that a continuous pyrolytic carbon coating is formed on the continuous fibers, and the continuous pyrolytic carbon coated SiC fibers are obtained.

2. The method of producing a continuous pyrolytic carbon coating on continuous fibers according to claim 1 wherein the continuous fibers are SiC fibers, the carbon source gas is propylene and the carrier gas is nitrogen.

3. The method for preparing a continuous pyrolytic carbon coating on continuous fibers according to claim 2, wherein in the step (2), the amount of the propylene fed is 100sccm to 4000sccm, the amount of the nitrogen fed is 100sccm to 4000sccm, and the pressure of the mixed gas of propylene and nitrogen is in the range of 500Pa to 5000 Pa.

4. The method for preparing the continuous pyrolytic carbon coating on the continuous fiber according to any one of claims 1 to 3, wherein in the step (1), the CVD apparatus is a roll-to-roll continuous growth CVD apparatus, the two ends of a furnace chamber of the roll-to-roll continuous growth CVD apparatus are respectively provided with an unwinding roll and a winding roll, before reaction, the continuous fiber is wound on the unwinding roll, and one end of the continuous fiber is wound on the winding roll after passing through the furnace chamber.

5. The method of producing a continuous pyrolytic carbon coating on continuous fibers according to claim 4, wherein the roll-to-roll continuous growth CVD apparatus is a roll-to-roll continuous growth CVD apparatus manufactured by Anhui Biez apparatus technology Limited.

6. The method for preparing a continuous pyrolytic carbon coating on continuous fibers according to claim 4, wherein in the step (2), the advancing rate of the continuous fibers in the reaction chamber is controlled by the take-up speed of the take-up drum of the CVD apparatus, and the take-up drum rotates at a constant speed of 1rpm to 10rpm, so that the continuous fibers move straightly in the reaction chamber and new parts on the continuous fibers continuously pass through the reaction chamber.

7. The method for preparing a continuous pyrolytic carbon coating on continuous fibers according to claim 6, wherein in the step (2), when the reaction temperature is 1100-1200 ℃, the gas inlet ratio of propylene to nitrogen is 1: 3-7, the pressure range of the mixed gas of propylene and nitrogen is 500-1000Pa, and the filament winding rate is 3-5 rpm, the thickness of the pyrolytic carbon coating is 100-200 nm.

8. The method for preparing the continuous pyrolytic carbon coating on the continuous fiber according to any one of claims 1 to 3, wherein the temperature is reduced to room temperature at 10-20 ℃/min after the reaction of step (2) is completed.

Background

In a continuous fiber reinforced composite system, in addition to the fiber and matrix portions, the interface is also a critical component of the composite of the system. Generally, a good interface can play an important role in protecting fibers, effectively transferring loads, adjusting thermal matching between the fibers and a matrix, improving chemical compatibility between the fibers and the matrix, and preventing or inhibiting fiber oxidation, and not only influences the mechanical properties of the composite material, but also influences the high temperature resistance and oxidation resistance of the composite material.

At present, for SiC_fVarious SiC fibers are known in the composite material system of the/SiC, such as weak interface, lamellar crystal structure interface, (X-Y)_nVarious interface structures such as multilayer interface phases, porous materials and other novel interfaces are specifically proposed. The general idea of the method is to deflect, expand or split the crack of the matrix at the interface phase, so that the crack is propagated between the interface and the matrix, between the interface and the fiber or inside the interface, thereby achieving the purposes of increasing the fracture energy of the composite material system and further playing the toughening role of the SiC fiber.

The laminated crystal structure has the advantages that the inside of an interface of the laminated crystal structure is of a laminated structure, the bonding force between atomic planes is Van der Waals force, the bonding force between the layers of the interface is not strong, and the shearing strength is low. When the crack is expanded to the interface of the lamellar crystal structure, deflection and bifurcation are easy to occur in the lamellar structure, more energy is consumed in the process, the fracture energy of the material is increased, and the toughness of the composite material system is improved. Pyrolytic carbon coatings (PyC) and hexagonal boron nitride coatings (h-BN) are typical interfaces of layered crystal structures, not only in SiC_fthe/SiC composite material system shows good capability of improving the brittleness of the material, and can be stably prepared by a proper method, so that the existing SiC composite material system becomes the existing SiC_fThe two most widely applied interfaces in the SiC composite material system.

SiC for nuclear reactor_fIn the/SiC composite system, PyC has gained attention as one of the most common interfaces with a layered crystal structure. PyC can be obtained by a variety of preparative processes such as chemical vapor deposition, precursor cleavage, sol-gel processes and in situ synthesis. Among them, the chemical vapor deposition process is the most common method for preparing PyC, and generally employs a carbon-containing precursor (such as methane, propylene propane) as a reaction gas and N₂Ar or H₂Used as carrier gas, deposited at a certain reaction temperature and atmosphere pressure to obtain PyC.

However, the method of preparing the interface phase by the conventional CVD method has some disadvantages: generally, when the coating is prepared by the CVD method, the whole SiC fiber preform or three-dimensional woven body is placed in a closed furnace chamber, and deposited under certain reaction gas and process conditions to obtain the coated SiC fiber preform or woven body. Thus, the size and shape of the prefabricated member or the woven body are limited by the size of the closed furnace chamber during the preparation of the coating, and the same batch of products may have different deposition effects due to the uneven distribution of the furnace atmosphere; for a prefabricated part with larger size or good air tightness in a certain direction (such as a SiC fiber thin-wall tube prefabricated part with a metal lining), because the reaction atmosphere is difficult to enter the interior of a woven structure or is easy to deposit on one side of the prefabricated part, the deposition conditions of interface phases in different areas of the prefabricated part are different, and a controllable and uniform interface phase coating is difficult to obtain according to the setting of process conditions.

In contrast, researchers have clustered continuous SiC fibers into spheres or uniformly wound the fibers around a graphite body for CVD deposition in order to produce uniform coatings on the bundled continuous SiC fibers, and then subsequently produce composite materials using the coated SiC fibers. However, the SiC fibers prepared by the method are bent, kinked and overlapped with each other due to clustering and winding, so that the deposited SiC fibers are subjected to residual deformation and cross-linking and bonding among fiber bundles, and the subsequent use of the SiC fibers is influenced. Therefore, in order to obtain a SiCf/SiC composite material with stable components and uniform thickness interfaces on the fibers in each region, a new SiC fiber coating preparation method needs to be developed to improve the current CVD process. This new method needs to solve the problems of the CVD process described above and allows for the deposition of a stable, uniform coating on a continuous SiC fiber bundle.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects of the traditional CVD method and provides a method for preparing a continuous pyrolytic carbon coating on continuous fibers by adopting a continuous CVD method, and the method can be expanded to coat novel interfaces on other novel fibers and is expected to realize large-batch continuous production.

In order to solve the technical problems, the invention adopts the following technical scheme.

A method of preparing a continuous pyrolytic carbon coating on continuous fibers comprising the steps of:

(1) preparing a CVD apparatus for allowing continuous passage of the continuous fiber in a reaction chamber, wherein one end of the continuous fiber is passed through the reaction chamber to make the continuous fiber in the reaction chamber in a flat and tensioned state:

(2) vacuumizing a reaction cavity of CVD equipment to be below 20Pa, heating to 800-900 ℃ at a heating rate of 10-20 ℃/min, then heating to a reaction temperature at a heating rate of 5-10 ℃/min, wherein the reaction temperature is 950-1200 ℃, introducing carbon source gas and carrier gas, enabling continuous fibers to continuously pass through the reaction cavity, and continuously depositing pyrolytic carbon on the fibers in the reaction cavity, so that a continuous pyrolytic carbon coating is formed on the continuous fibers, and the continuous pyrolytic carbon coated SiC fibers are obtained.

In the above method for preparing a continuous pyrolytic carbon coating on continuous fibers, preferably, the continuous fibers are SiC fibers, the carbon source gas is propylene, and the carrier gas is nitrogen.

In the method for preparing the continuous pyrolytic carbon coating on the continuous fiber, preferably, in the step (2), the air inflow of the propylene is 100sccm to 4000sccm, the air inflow of the nitrogen is 100sccm to 4000sccm, and the pressure range of the mixed gas of the propylene and the nitrogen is 500Pa to 5000 Pa.

Preferably, in the step (1), the CVD equipment is roll-to-roll continuous growth CVD equipment, two ends of a furnace chamber of the roll-to-roll continuous growth CVD equipment are respectively provided with a unwinding roll and a winding roll, before reaction, the continuous fiber is wound on the unwinding roll, and one end of the continuous fiber passes through a furnace chamber and is wound on the winding roll.

In the above method for preparing a continuous pyrolytic carbon coating on continuous fibers, preferably, the roll-to-roll continuous growth CVD equipment is roll-to-roll continuous growth CVD equipment manufactured by amberweike equipment technology ltd.

In the method for preparing the continuous pyrolytic carbon coating on the continuous fiber, preferably, in the step (2), the advancing speed of the continuous fiber in the reaction chamber is controlled by the filament winding speed of a winding drum of the CVD equipment, and the winding drum rotates at a constant speed of 1rpm to 10rpm, so that the continuous fiber moves straightly in the reaction chamber, and a new part on the continuous fiber continuously passes through the reaction chamber.

In the above method for preparing a continuous pyrolytic carbon coating on continuous fibers, preferably, in the step (2), when the reaction temperature is 1100-1200 ℃, the air inlet ratio of propylene to nitrogen is 1: 3-7, the pressure range of the mixed gas of propylene and nitrogen is 500-1000Pa, and the filament winding rate is 3-5 rpm, the thickness of the obtained pyrolytic carbon coating is 100-200 nm. And the filament winding speed is also taken as the filament running speed, and when the filament winding speed is 3-5 rpm, the corresponding fiber advancing speed is 6-10 cm/min.

In the method for preparing the continuous pyrolytic carbon coating on the continuous fiber, preferably, after the reaction in the step (2) is completed, the temperature is reduced to room temperature at a speed of 10-20 ℃/min.

The invention has the main innovation points that:

the invention adopts a continuous CVD method to prepare the pyrolytic carbon coating with complete shape and uniform and controllable thickness on a continuous fiber bundle, and the process can stably control the thickness of the pyrolytic carbon on a single fiber bundle by adjusting related parameters so as to adapt to the subsequent forming process of the composite material and meet the performance requirements of the composite material member.

Compared with the prior art, the invention has the advantages that:

the PyC coated SiC fibers prepared by the continuous CVD method can be kept straight, the fibers have no bending, kinking, twisting and other phenomena, the finished product has stable appearance, and the method has good operability in subsequent composite material weaving, winding and other forming processes.

The PyC coating prepared by the method has complete shape and uniform and controllable thickness, and the PyC thickness can be accurately controlled by adjusting process parameters; under the conditions of high deposition temperature 1100-1150 ℃, proper air inlet proportion of 1:3-1:7 and low atmosphere total pressure of 500-1000Pa, the PyC coating can be controlled at 100-200 nm, and the coated SiC fiber has good mechanical property.

The PyC coated fiber prepared by the method is not limited by the size of equipment, batch production is not needed, uninterrupted continuous operation can be realized, and mass production is expected to be realized.

Drawings

Figure 1 shows rolled PyC coated SiC fibres prepared according to example 1 of the invention.

Figure 2 is a photograph of PyC coated SiC fibers prepared by a conventional CVD process and a continuous CVD process according to example 1 of the present invention.

Fig. 3 is a SEM image (left) of a cross-section of a PyC coated SiC fiber bundle prepared by a conventional CVD method and actual and calculated values of PyC coating thickness for SiC fibers of different thickness (right).

FIG. 4 is a SEM image of a cross section of a single-strand PyC coated SiC fiber prepared by a continuous CVD method in example 1 of the present invention, wherein (a) is 1000 times and (b) is 3000 times.

FIG. 5 is an SEM image of cross-sections of PyC coated SiC fibers prepared in example 2 of the present invention at different feed ratios, wherein the feed ratios of propylene to nitrogen are (a) 1:7, (b) 1: 5, (c) 1:3, and (d) 1: 1.

FIG. 6 is a SEM image of cross-sections of PyC coated SiC fibers prepared at different take-up speeds of example 3 according to the invention, wherein the take-up speeds are (a)2rpm, (b)3rpm, (c)4rpm, and (d)5 rpm.

Detailed Description

The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention. The materials and equipment used in the following examples are commercially available.

Example 1:

a method of the present invention for producing a continuous pyrolytic carbon coating on continuous fibers comprising the steps of:

(1) the CVD equipment is produced by Anhui Beard equipment technology limited company and is commercially available, a unwinding cylinder and a winding cylinder are respectively arranged at two ends of a hearth of the CVD equipment, the unwinding cylinder is also called a shaft cylinder at an unwinding end, the winding cylinder is also called a shaft cylinder at a winding end, continuous SiC fibers (single-bundle SiC fibers) are wound on the unwinding cylinder, the SiC fibers are drawn to pass through a horizontal furnace chamber to the winding cylinder and are wound tightly, and the SiC fibers in the hearth are kept in a straight and tensioned state.

(2) And sealing the furnace chamber and vacuumizing to below 20Pa, heating the furnace chamber to 800 ℃ at the heating rate of 10 ℃/min, heating to 1100 ℃ at the heating rate of 5 ℃/min, introducing reaction gas propylene and carrier gas nitrogen after the temperature is constant, wherein the air inflow of the propylene is 500sccm, the air inflow of the nitrogen is 1000sccm, and the pressure of the mixed gas of the propylene and the nitrogen is 1000 Pa. And opening a motor of the CVD equipment while introducing the atmosphere, driving a winding drum to rotate, and winding the SiC fibers on the winding drum at a certain speed, wherein the speed of the winding drum can be controlled at 4rpm by the motor. The reaction can be continuously carried out, the pyrolytic carbon is continuously deposited on the advancing fiber in the reaction cavity until all rolled SiC fibers are completely rolled, the preparation is completed, the temperature is reduced to the room temperature at the speed of 10 ℃/min, and the rolled SiC fibers are taken out to obtain rolled PyC coated SiC fibers, as shown in figure 1.

In fig. 2, the upper sample is the PyC coated SiC fiber prepared by the conventional CVD method, and the lower sample is the PyC coated SiC fiber prepared by the continuous CVD method in this example, and it is clearly seen that, compared with the above sample, the SiC fiber prepared by the continuous CVD method has a straight appearance and no significant bending, kinking or twisting phenomenon. FIG. 3 shows the variation trend of the coating thickness of the sample prepared by the conventional CVD method, which is large and small. Fig. 4 is an SEM image of a single-bundle PyC-coated SiC fiber prepared by the continuous CVD method according to this example, and it can be seen that a complete and uniform PyC coating with a thickness of about 1000nm is formed on the outer side of each fiber.

Example 2

A method of the present invention for producing a continuous pyrolytic carbon coating on continuous fibers is substantially the same as the method of example 1 except that: in this example, the reaction temperature is 1150 ℃, the take-up speed is 2rpm, the pressure of the atmosphere in the furnace is 1500Pa, the flow rate of propylene is 500sccm, and the flow rate of nitrogen is 3500sccm, 2500sccm, 1500sccm, and 500sccm, respectively, so that the carbon content is not changed₃H₆∶N₂The air intake ratios were 1:7, 1: 5, 1:3, 1: 1, respectively, as shown in Table 2.

It can be seen that the weight gain of the SiC fiber after deposition increases with increasing air intake ratio, and the calculated PyC thickness also increases, significantly from-120 nm to-1000 nm. Fig. 5 is a cross-sectional image of SiC fiber deposited at different air inlet ratios, and it can be clearly seen that the PyC coating with uniform thickness and complete shape is coated on the SiC fiber in a high-magnification micro-field. When the air inlet ratio is increased from 1:7 to 1: 1, the coating thickness is obviously increased, and the coating thickness can be controlled within the range of 100-1100nm by adjusting the air inlet ratio.

TABLE 2 weight gain and PyC thickness of SiC fibers after deposition at different air-in ratios

And (3) carrying out monofilament tensile strength test on the SiC fibers deposited at different air inlet ratios, wherein 20 parallel monofilament samples are taken from each group of samples, the length of each monofilament sample is about 25mm, and the loading rate is 5 mm/min. Substituting the SiC monofilament diameter measurement results, the monofilament tensile strength of the SiC fiber can be calculated according to the following formula:

wherein σ is the monofilament tensile strength (GPa), Pmax is the maximum load at break (N), and D is the individual fiber diameter (nm). The result shows that the thickness of the PyC coating is increased along with the increase of the proportion of the reaction gas, when the air inlet ratio is low (1: 7-1: 3), the calculated thickness is closer to the measured thickness, the monofilament strength of the SiC fiber is not obviously changed, and the strength is 3.5GPa-3.6 GPa; when the inlet gas ratio was increased to 1: 1, the PyC thickness increased significantly, the PyC deposition rate increased, and the difference between the calculated thickness and the measured thickness was large, but the PyC monofilament strength was significantly lower than the other values, only 1.735 GPa. This shows that at lower air inlet ratios (1: 7-1: 3), the PyC growth rate is slower, but the coating structure is denser, the mechanical properties of the PyC coated SiC fiber are better, and at higher air inlet ratios (1: 1), the PyC coating has a faster deposition rate, but the coating structure is looser, and the properties of the PyC coated SiC fiber are reduced.

Example 3

A method of the present invention for producing a continuous pyrolytic carbon coating on continuous fibers is substantially the same as the method of example 1 except that: in this embodiment, the PyC deposition thickness is controlled by adjusting the filament winding rate, in this embodiment, the reaction temperature is 1150 ℃, the pressure of the atmosphere in the furnace is 1000Pa, the flow rates of propylene and nitrogen are both 500sccm, the advancing speed of the SiC fiber in the furnace is adjusted by setting the rotating speed of the motor of the winding drum, the diameter of the winding drum is 8.2cm, and the length of the constant temperature zone of the furnace body is 60cm, so that the advancing speed and the deposition time of the fiber can be calculated, as shown in table 3.

The weight gain of the reacted SiC fiber of this example decreased with the increase in the take-up rate, along with the theoretical calculated thickness of PyC also decreased significantly. Fig. 6 is SEM images of the deposited SiC fiber at different magnifications, and it can be seen that coatings with complete shapes and uniform thickness are formed on the surface of the deposited SiC fiber at different filament take-up speeds, and as the filament take-up speed increases, the thickness of the PyC coating decreases, and the PyC thickness can be controlled within the range of 100nm to 900nm according to the adjustment of the filament take-up speed. When the filament drawing speed is 2rpm, the thickness of PyC is more than 800nm, the strength of the SiC fiber single filament is less than 2.0GPa, and when the filament drawing speed is 3rpm to 5rpm, namely the advancing speed of the fiber is 6cm/min to 10cm/min, the thickness of the PyC coating can be controlled to be 100nm to 200nm, the strength of the corresponding SiC fiber single filament is 3.5 to 3.6GPa, and the mechanical property is improved. It can be seen that in the process of increasing the filament winding speed from 2rpm to 3rpm, there is a sudden change in the deposition effect of PyC, and under the process conditions of this embodiment, when the air inlet ratio is 1: 1, although the performance of PyC coated SiC is not good at the slow speed (2rpm), the mechanical properties of SiC fiber can be better improved by selecting a suitable filament winding speed range (3rpm-5 rpm).

TABLE 3 calculated thickness of PyC and weight gain after deposition of SiC fibers at different take-up rates

In conclusion, the pyrolytic carbon coated SiC fibers prepared by the continuous CVD method have straight appearance, no residual deformation and no mutual adhesion, and the components, the thickness and the structure of the coating can be controlled by regulating and controlling reaction conditions.

The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make many possible variations and modifications to the disclosed embodiments, or equivalent modifications, without departing from the spirit and scope of the invention, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention.