CN113402304B

CN113402304B - Method for preparing continuous pyrolytic carbon coating on continuous fiber

Info

Publication number: CN113402304B
Application number: CN202110774871.9A
Authority: CN
Inventors: 周新贵; 黎畅; 王洪磊
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2021-07-08
Filing date: 2021-07-08
Publication date: 2023-05-16
Anticipated expiration: 2041-07-08
Also published as: CN113402304A

Abstract

The invention discloses a method for preparing a continuous pyrolytic carbon coating on continuous fibers, which comprises the steps of preparing a CVD device, wherein the CVD device is a CVD device which allows Xu Qianwei to continuously pass through a reaction cavity, and enabling one end of the continuous fibers to pass through the reaction cavity so that the continuous fibers in the reaction cavity are in a straight and tensioned state: the reaction chamber of the CVD equipment is vacuumized to below 20Pa, heated to 800-900 ℃ firstly, then heated to the reaction temperature of 950-1200 ℃, and the reaction gas and the carrier gas are introduced, and the continuous fiber continuously passes through the reaction chamber, thereby forming the continuous pyrolytic carbon coating on the continuous fiber. The method can ensure that the obtained pyrolytic carbon coating fiber has straight appearance, no phenomena of bending, kinking, twisting and the like, complete shape, controllable thickness and good mechanical property, and can be used for mass continuous production.

Description

Method for preparing continuous pyrolytic carbon coating on continuous fiber

Technical Field

The invention belongs to the technical field of fiber coating preparation, relates to a novel preparation method of a continuous pyrolytic carbon coating, and in particular relates to a method for preparing a continuous pyrolytic carbon coating on continuous fibers.

Background

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

Currently, for SiC _f Various SiC fibers in SiC composite systems are known, for example, as weak interfaces, lamellar crystal structure interfaces, (X-Y) _n Multiple interface structures such as multi-layer interfacial phases, porous materials, and other novel interfaces have been proposed specifically. The general thinking is that the crack of the matrix deflects, expands or diverges at the interface phase, so that the crack propagates 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 interface of the lamellar crystal structure is internally lamellar, the bonding force between the atomic planes is Van der Waals force, and the interface has weak interlayer bonding force and lower shearing strength. When cracks propagate to the interface of the lamellar crystal structure, the cracks are easy to occur in the lamellar structureDeflection and bifurcation, which requires more energy consumption, increases the fracture energy of the material, thereby increasing the toughness of the composite system. Pyrolytic carbon coating (PyC) and hexagonal boron nitride coating (h-BN) are typical lamellar crystal structure interfaces, which are not only at SiC _f The SiC composite material system has good capability of improving the brittleness of the material, can be stably prepared by a proper method and becomes the current SiC _f The two interfaces most widely used in the SiC composite systems.

SiC for nuclear use _f In the SiC composite system PyC has received widespread attention from researchers as one of the most common lamellar crystal structure interfaces. The PyC can be obtained by various preparation processes, such as a chemical vapor deposition method, a precursor cracking process, a sol-gel process and an in-situ synthesis method. Among them, the chemical vapor deposition process is the most commonly used method for preparing PyC, which generally adopts a carbon-containing precursor (such as methane and propylene propane) as a reaction gas, and uses N ₂ Ar or H ₂ And (3) carrying out deposition at a certain reaction temperature and atmosphere pressure to obtain the PyC.

However, the process of preparing the interfacial phase by conventional CVD methods also suffers from several disadvantages: generally, when a coating is prepared by a CVD method, a SiC fiber preform or three-dimensional woven body is integrally placed in a closed furnace chamber, and deposited under certain reaction gas and process conditions, thereby obtaining a SiC fiber preform or woven body with a coating. In this way, the size and shape of the preform or braid are limited by the size of the closed oven cavity during the preparation of the coating, and the same batch of products may have differences in deposition effect due to uneven distribution of the oven atmosphere; for a prefabricated member with larger size or good air tightness in a certain direction (such as a prefabricated member of a SiC fiber thin-wall tube with a metal lining), the reactive atmosphere is difficult to enter the inside of a woven structure or is easy to deposit on one side of the prefabricated member, so that the deposition conditions of interface phases in different areas of the prefabricated member are different, and a controllable and uniform interface phase coating is difficult to obtain according to the setting of process conditions.

In this regard, researchers have clustered continuous SiC fibers into spheres or uniformly entangled fibers onto a graphite body for CVD deposition in an attempt to produce a uniform coating on the bundled continuous SiC fibers, and then subsequently prepare a composite material with such coated SiC fibers. However, the SiC fibers prepared by the method are bent, kinked and overlapped mutually due to the clusters and the fibers during winding, so that residual deformation and crosslinking and bonding between fiber bundles are generated on the deposited SiC fibers, and the subsequent use of the SiC fibers is affected. Therefore, in order to obtain the finally prepared SiCf/SiC composite material with stable components and uniform thickness interfaces on the fibers in each region, a new preparation method of the SiC fiber coating needs to be developed to perfect the current CVD process. This new method needs to solve the problems of the CVD process described above and to deposit a stable, uniform coating on a continuous SiC fiber bundle.

Disclosure of Invention

The technical problem to be solved by the invention is to overcome the defects of the traditional CVD method, and provide a method for preparing a continuous pyrolytic carbon coating on continuous fibers by adopting the continuous CVD method, wherein the method can be further expanded to coating novel interfaces on other novel fibers, and is expected to realize mass 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 which allows Xu Qianwei to continuously pass through the reaction chamber, and enabling one end of the continuous fiber to pass through the reaction chamber so as to enable the continuous fiber in the reaction chamber to be in a straight and tensioned state:

(2) Vacuumizing a reaction cavity of a CVD device to below 20Pa, heating to 800-900 ℃ at a heating rate of 10-20 ℃/min, heating to a reaction temperature at a heating rate of 5-10 ℃/min, introducing carbon source gas and carrier gas to make continuous fibers 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 obtaining the continuous pyrolytic carbon coated SiC fibers.

In the above method for preparing a continuous pyrolytic carbon coating on a continuous fiber, preferably, the continuous fiber is SiC fiber, 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 propylene is 100 sccm-4000 sccm, the air inflow of nitrogen is 100 sccm-4000 sccm, and the pressure range of the mixed gas of propylene and nitrogen is 500 Pa-5000 Pa.

In the above method for preparing a continuous pyrolytic carbon coating on a continuous fiber, preferably, in the step (1), the CVD apparatus is a roll-to-roll continuous growth CVD apparatus, both ends of a hearth of the roll-to-roll continuous growth CVD apparatus are respectively provided with an unreeling drum and a reeling drum, before the reaction, the continuous fiber is wound on the unreeling drum, and one end of the continuous fiber passes through the furnace chamber to be wound on the reeling drum.

In the above method for preparing a continuous pyrolytic carbon coating on a continuous fiber, preferably, the roll-to-roll continuous growth CVD apparatus is a roll-to-roll continuous growth CVD apparatus manufactured by ambebeck equipment technologies, inc.

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 cavity is controlled by the filament collecting speed of a winding drum of the CVD equipment, and the winding drum rotates at a constant speed of 1 rpm-10 rpm, so that the continuous fiber moves flatly in the reaction cavity, and a new part of the continuous fiber continuously passes through the reaction cavity.

In the method for preparing the continuous pyrolytic carbon coating on the continuous fiber, 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 Pa-1000 Pa, and the filament collecting rate is 3-5 rpm, the thickness of the obtained pyrolytic carbon coating is 100-200 nm. The wire collecting speed is also taken as the wire running speed, and when the wire collecting speed is 3rpm-5rpm, the corresponding fiber advancing speed is 6cm/min-10 cm/min.

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

The main innovation point of the invention is that:

the invention adopts a continuous CVD method to prepare the pyrolytic carbon coating with complete shape and uniform and controllable thickness on the continuous fiber bundles, and the process can stably control the thickness of the pyrolytic carbon on the single-bundle fibers 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 components.

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

according to the invention, each bundle of the PyC-coated SiC fibers prepared by adopting the continuous CVD method can be ensured to be straight, the fibers are free from bending, kinking, twisting and other phenomena, the appearance of the finished product is stable, and the PyC-coated SiC fibers have good operability in the subsequent forming processes of braiding, winding and the like of the composite material.

The PyC coating prepared by the invention has complete shape and uniform and controllable thickness, and can realize accurate control of the thickness of the PyC by adjusting the technological parameters; under the conditions of high deposition temperature of 1100-1150 ℃, proper air inlet ratio of 1:3-1:7 and low total atmosphere pressure of 500-1000Pa, the PyC coating can be controlled between 100nm and 200nm, and the coated SiC fiber has good mechanical properties.

The preparation method of the PyC coated fiber is not limited by the size of equipment, does not need batch production, can realize uninterrupted continuous operation, and is expected to realize mass production.

Drawings

FIG. 1 is a rolled PyC coated SiC fiber prepared in example 1 of the present invention.

FIG. 2 is a photograph of a PyC coated SiC fiber prepared by a conventional CVD method and a continuous CVD method according to example 1 of the present invention.

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

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

FIG. 5 is a SEM image of a section of a PyC coated SiC fiber prepared in accordance with example 2 of the invention at different inlet ratios, where the inlet ratio of propylene to nitrogen is (a) 1:7, (b) 1:5, (c) 1:3, and (d) 1:1.

FIG. 6 is a SEM image of a section of a PyC coated SiC fiber prepared at various take-up speeds according to example 3 of the invention, where the take-up speed is (a) 2rpm, (b) 3rpm, (c) 4 rpm, and (d) 5 rpm.

Detailed Description

The invention is further described below in connection with the drawings and the specific preferred embodiments, but the scope of protection of the invention is not limited thereby. The materials and instruments used in the examples below are all commercially available.

Example 1:

the method for preparing the continuous pyrolytic carbon coating on the continuous fiber comprises the following steps:

(1) The CVD equipment is manufactured by Anhui Baeck equipment technology Co., ltd, and is commercially available, wherein an unwinding drum and a winding drum are respectively arranged at two ends of a hearth of the CVD equipment, the unwinding drum is also called an unwinding end shaft drum, the winding drum is also called a winding end shaft drum, continuous SiC fibers (single-beam SiC fibers) are wound on the unwinding drum, and the SiC fibers are pulled to pass through a horizontal furnace chamber to the winding drum and wound tightly, so that the SiC fibers in the hearth are kept in a straight and tensioned state.

(2) Sealing the furnace chamber, vacuumizing to below 20Pa, heating the furnace chamber to 800 ℃ at a heating rate of 10 ℃/min, heating to a reaction temperature of 1100 ℃ at a heating rate of 5 ℃/min, and introducing the reaction gas propylene and carrier gas nitrogen after the temperature is constant, wherein the propylene air inflow is 500sccm, the nitrogen air inflow is 1000sccm, and the pressure of the mixed gas of propylene and nitrogen is 1000Pa. And when the atmosphere is introduced, a motor of the CVD equipment is opened, the winding drum is driven to rotate, the SiC fibers are wound on the winding drum at a certain speed, and the speed of the winding drum can be controlled at 4 rpm by the motor. The reaction can be continuously carried out, pyrolytic carbon is continuously deposited on travelling fibers in the reaction cavity until all rolled SiC fibers are rolled, the preparation is completed, the temperature is reduced to room temperature at 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 a PyC-coated SiC fiber prepared by a conventional CVD method, and the lower sample is a PyC-coated SiC fiber prepared by a continuous CVD method according to this embodiment, and it is obvious that, compared with the two, the SiC fiber prepared by a continuous CVD method has a straight appearance, and no phenomena of significant bending, kinking and twisting. FIG. 3 shows the variation of the thickness of a sample coating prepared by the conventional CVD method, wherein the variation of the thickness of the outer coating is large and the variation of the thickness of the inner coating is small. Fig. 4 is an SEM image of single-strand PyC coated SiC fibers prepared by the continuous CVD method of this example, and it can be seen that a PyC coating of complete shape and uniform thickness is formed on the outside of each fiber, with a thickness of about 1000 a nm a.

Example 2

The process of the present invention for producing a continuous pyrolytic carbon coating on continuous fibers is substantially the same as that of example 1 except that: in this example, the reaction temperature in this example was 1150℃and the filament take-up rate was 2rpm, the furnace atmosphere pressure was 1500Pa, the propylene flow rate was 500sccm and the nitrogen flow rates were set to 3500sccm, 2500sccm, 1500sccm and 500sccm, respectively, so that C was obtained ₃ H ₆ ∶N ₂ The inlet ratios were 1:7, 1:5, 1:3, 1:1, respectively, as shown in Table 1.

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

Table 1 rate of weight gain and PyC thickness of SiC fibers after deposition at different air intake ratios

No.	C3H6 (sccm)	N2 (sccm)	Air inlet ratio (C3H 6:N2)	Weight gain of fiber (%)	PyC calculated thickness (nm)
						1	500	3500	1∶7	4.0	121
2	500	2500	1∶5	3.9	118
						3	500	1500	1∶3	14.9	436
4	500	500	1∶1	37.6	1042

Monofilament tensile strength tests were performed on SiC fibers deposited at different air intake ratios, with 20 parallel monofilament samples taken for each group, the monofilament samples being approximately 25 mm long and loading rate 5 mm/min. Substituting the SiC monofilament diameter measurement, the monofilament tensile strength of the SiC fiber can be calculated according to the following formula:

wherein sigma is the tensile strength (GPa) of a monofilament, pmax is the maximum load at break (N), and D is the diameter (nm) of a single fiber. The result shows that the thickness of the PyC coating shows an increasing trend 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 relatively close to the measured thickness, the variation of the monofilament strength of the SiC fiber is not obvious, and the strength is 3.5GPa-3.6GPa; when the air inlet ratio is increased to 1:1, the thickness of the PyC is obviously increased, the deposition rate of the PyC is accelerated, the calculated thickness and the measured thickness are greatly different, but the strength of the PyC monofilament is obviously lower than other values and is 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 fibers 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 fibers are reduced.

Example 3

The process of the present invention for producing a continuous pyrolytic carbon coating on continuous fibers is substantially the same as that of example 1 except that: in the embodiment, the deposition thickness of the PyC is controlled by adjusting the wire winding rate, in the embodiment, the reaction temperature is 1150 ℃, the pressure of the atmosphere in the furnace is 1000Pa, the flow rates of propylene and nitrogen are 500sccm, the advancing speed of the SiC fiber in the furnace is adjusted by setting the rotating speed of a winding drum motor, the diameter of the winding drum is 8.2cm, the constant temperature area of the furnace body is 60cm, and the advancing speed and the deposition time of the fiber can be calculated as shown in Table 2.

The weight gain rate of the SiC fiber after reaction of the embodiment is reduced along with the increase of the wire collecting rate, and the theoretical calculation thickness of PyC is also obviously reduced. Fig. 6 is SEM images of deposited SiC fibers at different magnifications, and it can be seen that the surface of the deposited SiC fibers at different filament take-up speeds generates a coating with complete shape and uniform thickness, and the PyC thickness can be controlled in the range of 100nm to 900nm according to the adjustment of the filament take-up speed as the filament take-up speed increases and the PyC coating thickness decreases. When the filament collecting speed is 2rpm, the thickness of the PyC is more than 800nm, the strength of the SiC fiber monofilament is less than 2.0GPa, and when the filament collecting speed is 3rpm-5rpm, namely the fiber advancing speed is 6cm/min-10cm/min, the thickness of the PyC coating can be controlled to be 100nm-200nm, the corresponding strength of the SiC fiber monofilament is 3.5-3.6GPa, and the mechanical property is improved. It can be seen that there is a sudden change in the deposition effect of PyC during the increase of the wire take-up rate from 2rpm to 3rpm, and under the process conditions of this embodiment, the mechanical properties of the SiC fibers can be better improved by selecting a suitable wire take-up rate range (3 rpm-5 rpm) although the performance of the PyC coated with SiC is poor at a slower rate (2 rpm) when the air intake ratio is 1:1.

Table 2 weight gain and PyC calculated thickness of SiC fibers after deposition at different take-up rates

No.	Wire take-up rate (r/m)	Fiber travel speed (cm/min)	Deposition time (min)	Weight gain of fiber (%)	PyC calculated thickness (nm)
						1	2	3.75	16	37.6	827
2	3	6.0	10	10.5	258
						3	4	7.5	8	9.7	208
4	5	10.0	6	6.6	144

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

The above description is only of the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. While the invention has been described in terms of preferred embodiments, it is not intended to be limiting. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention or equivalent embodiments using the method and technical solution disclosed above without departing from the spirit and technical solution of the present invention. Therefore, any simple modification, equivalent substitution, equivalent variation and modification of the above embodiments according to the technical substance of the present invention, which do not depart from the technical solution of the present invention, still fall within the scope of the technical solution of the present invention.

Claims

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

(1) Preparing a CVD device which is a CVD device allowing Xu Qianwei to continuously pass through a reaction cavity, and enabling one end of continuous fibers to pass through the reaction cavity so as to enable the continuous fibers in the reaction cavity to be in a straight and tensioned state;

(2) Vacuumizing a reaction cavity of a CVD device to below 20Pa, heating to 800-900 ℃ at a heating rate of 10-20 ℃/min, heating to a reaction temperature at a heating rate of 5-10 ℃/min, introducing carbon source gas and carrier gas to continuously pass continuous fibers 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 to obtain continuous pyrolytic carbon coated SiC fibers;

the continuous fibers are SiC fibers, the carbon source gas is propylene, and the carrier gas is nitrogen;

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 Pa-1000 Pa, and the wire collecting speed is 3-5 rpm, the thickness of the obtained pyrolytic carbon coating is 100-200 nm.

2. The method for producing a continuous pyrolytic carbon coating on a continuous fiber according to claim 1, wherein in the step (1), the CVD apparatus is a roll-to-roll continuous growth CVD apparatus, both ends of a hearth of the roll-to-roll continuous growth CVD apparatus are provided with an unreeling drum and a reeling drum, respectively, and before the reaction, the continuous fiber is wound on the unreeling drum, and one end of the continuous fiber is wound up through a furnace chamber onto the reeling drum.

3. The method of producing a continuous pyrolytic carbon coating on continuous fibers according to claim 2, wherein the roll-to-roll continuous growth CVD apparatus is a roll-to-roll continuous growth CVD apparatus manufactured by ambebeck apparatus technologies, inc.

4. The method for preparing a continuous pyrolytic carbon coating on continuous fibers according to claim 1, wherein after the completion of the reaction in step (2), the temperature is lowered to room temperature at 10 ℃/min to 20 ℃/min.