CN104451596A - Composite material based on diamond crystals and preparation method of composite material - Google Patents

Abstract

The invention provides a preparation method of a composite material based on diamond crystals. The preparation method comprises the following steps: forming a barrier layer on the surface of a carbon nano tube and/or a carbon fiber; forming nucleation sites for guiding the diamond crystals to deposit on the barrier layer; and depositing a diamond coating on the barrier layer. By adopting the preparation method disclosed by the invention, high-quality diamond crystals can coat the barrier layer on the condition of not damaging carbon nanowires or carbon fibers, and very high binding force is formed between the diamond crystals and the carbon nanowires or the carbon fibers; meanwhile, the nucleation sites are used for guiding the diamond coating to deposit, so that the quality of the diamond coating is prevented from being lowered due to a secondary nucleation phenomenon.

Description

A kind of composite material based on diamond crystal and preparation method thereof

technical field

The invention belongs to the technical field of composite materials, and in particular relates to a diamond crystal-based composite material and a preparation method thereof.

Background technique

Carbon nanotubes and carbon fiber materials have a series of distinctive properties, such as high mechanical strength, excellent toughness and strong electrical conductivity. On the other hand, it is well known that diamond has special physical properties, such as high hardness, and is widely used in wear-resistant hard coatings, cutting and polishing tools. Although the diamond film has high hardness, it has low toughness and mechanical brittleness. The composite of carbon nanotubes and/or carbon fibers and diamond is very suitable for manufacturing materials with excellent mechanical properties, electrical conductivity and thermal properties through mutual complementarity, so it has high use value. Diamond-coated carbon nanotubes and/or carbon fiber yarns in composite materials have high use value in terms of comprehensive performance, production efficiency and cost.

In the existing methods for preparing diamond coatings, deposition chemical vapor deposition (CVD) is usually carried out under conditions of strong hydrogen-rich plasma and a temperature higher than 700 ° C. Hydrogen acts as a catalyst to promote the formation of SP3 hybrid bonds of carbon. Formation, destruction of SP2 hybrid bond formation. But this environment can also cause damage to the carbon nanotubes/carbon fibers that are also SP2 bonds, thereby reducing the quality of the carbon nanotubes and/or carbon fibers.

In order to make up for the above shortcomings of the traditional chemical vapor deposition method, M. Terranova (Chemistry of Materials 17.2005.3214) et al. used a hot wire chemical vapor deposition (HFCVD) device to coat iron as a catalyst on a silicon substrate. , using carbon nanoparticle flow in an argon atmosphere to synthesize carbon nanotubes and diamond nanocrystals in one step, and realize the growth of diamond nanocrystal particles on single-walled carbon nanotube bundles. N. Shankar (Diamond Related Matter, 17.2008, PP.79-83,) and others first dispersed multi-walled carbon nanotubes on a silicon substrate, and then deposited diamond on this structure with a hot wire chemical vapor deposition (HFCVD) device. A carbon nanotube/diamond composite was successfully grown. They found that under typical deposition conditions for diamond growth, 1% methane and 99% hydrogen, the carbon nanotubes were destroyed. However, increasing the methane flow rate to 2%-5%, that is, reducing the partial etching effect of hydrogen, they found that the carbon nanotubes were not etched, and diamond could nucleate and grow on the carbon nanotubes. However, reducing the etching activity will have a negative effect on the surface morphology of diamond particles, making its microcrystalline structure into a "cauliflower" morphology, that is, many nanometer-sized (100-400nm) diamond particles on carbon nanotubes. Random nucleation, growth.

For the diamond-coated carbon nanotube and/or carbon fiber material prepared by the above method, the quality of the carbon nanotube, the diamond or both will still be damaged. At the same time, in the two works done by Terranova et al. and Shankar et al., the formed diamond is a single crystal composed of extremely small nanocrystals, without the formation of microcrystalline diamond, and the further recombination process can only be performed within a narrow parameter window, there is very little flexibility in synthesizing composites of different types or structures, and there are still drawbacks in application.

Contents of the invention

The purpose of the embodiments of the present invention is to overcome the above-mentioned deficiencies in the prior art, and provide a carbon nanotube wire and diamond crystal that can achieve high-quality diamond crystals firmly attached to the surface of carbon nanotubes or carbon fibers without damaging the quality. Composite materials and methods for their preparation.

In order to achieve the above-mentioned purpose of the invention, the technical solutions of the embodiments of the present invention are as follows:

A method for preparing a composite material based on diamond crystals, comprising the steps of:

forming a barrier layer on the surface of the carbon nanotubes and/or carbon fibers;

forming nucleation sites for directing deposition of diamond crystals on said barrier layer;

A diamond coating is deposited on the barrier layer.

Using the above-mentioned preparation method of the present invention, the carbon nanowire or carbon fiber can be coated with high-quality diamond crystals without damaging the carbon nanowire or carbon fiber through the barrier layer, and the gap between the diamond crystal and the carbon nanowire or carbon fiber can also be very high. At the same time, the deposition of the diamond coating is guided through the nucleation site to prevent the phenomenon of secondary nucleation from reducing the quality of the diamond coating.

The present invention further protects the diamond crystal-based composite material prepared according to the above method, and the micron-scale wire saw prepared from the composite material.

The above diamond crystal-based composite material prepared by the present invention can achieve high-quality diamond crystals firmly attached to the surface of carbon nanotubes or carbon fibers, or on the structure formed by the two without damaging the carbon nanotubes and carbon fibers. Compared with the existing composite materials, the quality is greatly improved. The micron wire saw that prepares simultaneously, compares with the diamond wire saw that existing method makes, and the diameter of the wire saw that prepares in the present invention is about 20 microns, and the diameter of wire saw in existing practice is all more than 1 millimeter; Therefore The invention not only reduces the manufacturing cost of the wire saw, but also in terms of application, such as cutting of silicon wafers, can realize sawdust-free cutting, can save about one-third of the cost of silicon wafer materials on average, and can greatly reduce the cost of silicon substrates. The cost of device materials such as solar photovoltaic panels.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

1 is a schematic diagram of a method for preparing a composite material based on diamond crystals according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of the morphological change of a diamond coating prepared on a carbon nanotube array according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The embodiment of the present invention provides a method for preparing a composite material based on diamond crystals, as shown in Figure 1, comprising the following steps:

S10, forming a barrier layer on the surface of carbon nanotubes and/or carbon fibers;

S20, forming nucleation sites for guiding diamond crystal deposition on the barrier layer;

S30, depositing a diamond coating on the barrier layer.

In the above method of the present invention, in step S10, a barrier layer is first formed on the surface of carbon nanotubes and/or carbon fibers during the preparation of the composite material, the purpose of which is to protect the carbon nanotubes during the subsequent diamond deposition process. And/or carbon fiber structures are not affected by the reactive gases and temperatures required to form high quality diamond. Among them, the advantage of this measure is that no compromise between CNT and diamond growth parameters is used, and the process conditions of diamond crystal deposition can be freely selected to obtain high-quality diamond crystals, regardless of the necessary active gas atmosphere that will damage carbon nanotubes and / or the effect of carbon fiber structure. At the same time, the barrier layer can also support diamond nucleation or act as an adhesion promoter to allow greater load transfer between diamond and carbon nanotubes and/or carbon fibers. Therefore, the flexibility in the preparation process of composite materials is greatly improved.

Among them, based on the above requirements and conditions, the requirement for the barrier layer is to realize the function of protecting the carbon nanotube and/or carbon fiber structure against the harsh conditions in the diamond deposition process; therefore, the material selection of the barrier layer should theoretically be able to meet the above conditions. All technicians can use common sense. Further in the present invention, in order to ensure quality such as bonding strength, the barrier layer adopts an amorphous silicon-based buffer film, which uses tetramethylsilane and oxygen as precursors, and is deposited by an inductively coupled PECVD process with a thickness of several nanometers. layer; or the barrier layer adopts a layer of amorphous silicon oxide or silicon carbide, which can meet the quality requirements of China in terms of performance and use effect. At the same time, in order to achieve the desired protective effect, the barrier layer is required to be coated on the carbon nanotube and/or carbon fiber or the structure of the carbon nanotube and/or carbon fiber composite with a minimum thickness, and the thickness of the barrier layer is generally required to be less than 100nm. Due to the quality of diamond deposition during implementation, the preferred thickness of the barrier layer is less than 20 nm, more preferably less than 10 nm or only a few nanometers.

At the same time, the formation of the barrier layer is preferably realized by capacitively coupled plasma chemical vapor deposition method. Under the action of high frequency or DC electric field, the source gas is ionized to form plasma, and the low temperature plasma is used as the energy source to introduce an appropriate amount of barrier layer material The reactive gas of the barrier layer material is activated by plasma discharge to realize chemical vapor deposition. This method can promote the breakage and recombination of the chemical bonds of the reactive gas molecules of the barrier layer material, generate more active chemical groups, and enhance the binding; at the same time, the entire reaction system maintains a lower temperature to avoid damage to carbon fibers/carbon nanotubes. make an impact.

Further after step S10, in step S20, a nucleation site for guiding diamond crystal deposition is formed on the surface of the barrier layer, so as to guide the initial nucleation site to promote grain growth during the deposition process and prevent secondary diamond crystals from occurring. The phenomenon of secondary nucleation leads to a reduction in the quality of the diamond coating.

In the step S20, the guided nucleation sites can be realized simply by using nano-diamond seed crystals, which serve as guiding crystal nuclei during the deposition process to guide the deposition and growth of the diamond coating. The way to form the nucleation site, in the implementation of the invention, can be carried out by using overbias to enhance the nucleation method, or immerse the carbon nanotubes and/or carbon fibers coated with a silicon-based thin film barrier layer in the suspended nano-diamond Diamond seed crystals can be planted in the ethanol solution of the microparticles by means of an ultrasonic bath; technicians can choose according to the preparation conditions and effects, and there is no limitation here.

In the last step S30, a diamond deposition step is performed to form a diamond coating on the barrier layer of carbon nanotubes and/or carbon fibers. This process can use chemical vapor deposition to realize the deposition or synthesis of diamond crystals on the barrier layer on the carbon nanotube/carbon fiber or carbon nanotube carbon fiber composite under the reaction gas atmosphere that is conducive to the formation of SP3 hybrid bonds of carbon; Alternatively, other coating techniques can also be used.

Further in the present invention, in order to avoid damage to carbon nanotubes and/or carbon fibers during the coating step, plasma-enhanced chemical vapor deposition (PECVD) is preferably used to coat carbon nanotubes/carbon fibers or carbon nanotubes/carbon fibers. At the same time, in the implementation process, it is more guaranteed that high-quality diamond crystals promote grain growth at the initial nucleation site without secondary nucleation. In the plasma-enhanced reactive gas atmosphere, more than 98% hydrogen is used to generate a strong hydrogen-rich plasma environment, which can finally form a carbon nanotube and/or carbon fiber structure completely covered and closed by diamond particles. Of course, in order to avoid damaging the carbon nanotubes and/or carbon fibers during the coating step, the PECVD process should be performed at low pressure and moderate temperature.

In the step of depositing diamond crystals on the carbon nanotube/carbon fiber or carbon nanotube/carbon fiber structure with a barrier layer, a microwave-like chemical vapor deposition method can be preferably used. In the process of depositing high-quality diamond, the selected reaction gas atmosphere may include any gas components that are conducive to diamond deposition, and should not contain gas components that can produce secondary nucleation. For example, the reaction gas contains more than 98% hydrogen and less than 2% methane, avoiding the induction of secondary nucleation. Simultaneously in this process, in order to realize obtaining high-quality diamond layer on carbon nanotube/carbon fiber or its structure, should select suitable temperature and pressure, according to barrier layer thickness in the present invention's implementation, and required formation diamond body layer crystal For crystal quality control, the preferred pressure is lower than 100hPa, and the temperature is higher than 700°C.

Based on the realization of the above-mentioned same purpose of the present invention, the capacitively coupled PECVD process is used to coat the barrier layer on carbon nanotubes and/or carbon fibers, or carbon nanotubes and/or carbon fiber composite structures, and the subsequent diamond synthesis process adopts microwave CVD Or in hot wire CVD.

According to the needs in the process of preparing composite materials, the implementation process may also include the following steps before step S10:

S00, process carbon nanotubes and/or carbon fibers according to the structure of the composite material to be prepared to generate the expected carbon nanotubes and/or carbon fiber structures; for example, process carbon nanotubes to form carbon nanotube arrays or carbon nanowires Structural morphology, or the structure formed by carbon nanotubes may be any arrangement of such nanotubes, including large sheets of towering carbon nanotubes, dispersed carbon nanotube spin-coated films on different substrates, carbon nanotube networks or carbon fibers yarn and more. Of course, its structure and shape can be selected according to the requirements of the composite material to be prepared, which is not limited here.

Using the above-mentioned preparation method of the present invention, the carbon nanowire or carbon fiber can be coated with high-quality diamond crystals without damaging the carbon nanowire or carbon fiber through the barrier layer, and the gap between the diamond crystal and the carbon nanowire or carbon fiber can also be very high. At the same time, the deposition of the diamond coating is guided through the nucleation site to prevent the phenomenon of secondary nucleation from reducing the quality of the diamond coating.

And prepared by the above method of the present invention, the diamond coating can be applied to various carbon nanotube and/or carbon fiber structures, such as carbon nanotubes arranged in large sheets, carbon nanotube network and carbon fiber yarn. It also provides the flexibility to adjust the volume ratio of carbon nanotubes and/or carbon fibers in composite materials and layered composites in research and development, as well as to achieve large-scale production of thin, hard, wear-resistant coatings, etc.

At the same time, the present invention can further use the micron-scale wire saw prepared from the above-mentioned composite material. Among them, the obtained micron-scale wire saw can replace the traditional wire saw to cut silicon wafers; compared with the existing manufacturing method that relies on electroplating or inlaying to connect diamond crystals to metal wires to prepare diamond wire saws or saw wires, the present invention The diameter of the wire saw prepared in the method is about 20 microns, while the diameter of the wire saw in the existing practice is more than 1 millimeter; In terms of cutting, sawdust-free cutting can be realized, which can save about one-third of the cost of silicon wafer materials on average, and can greatly reduce the cost of silicon-based device materials (such as solar photovoltaic panels).

The preparation of the present invention can obtain uniformly distributed diamond wires, which have a variety of use values, such as: 1. nanotube/carbon nanowire reinforced diamond is used in superhard wear-resistant film coatings; 2. diamond-coated wires are made of Micron-sized diamonds are composed of carbon nanotubes and/or carbon fibers, which can replace traditional inlaid or electroplated diamond metal wire cutters with diamonds on stainless steel to cut semiconductor materials such as silicon materials; ③High temperature and high pressure sensors; ④Field emission devices ; ⑤ micromechanics and sensing applications; ⑥ flexible and bendable diamond coating; ⑦ nanowires based on carbon nanotubes and/or carbon fibers covered with silicon-based films.

In order to make the implementation details of the above-mentioned method process of the present invention more clear and complete, to facilitate the implementation reference of those skilled in the art, and to make the outstanding progressive effect of the present invention more remarkable, the implementation of the above-mentioned process is specifically illustrated by examples below.

Example 1

S00, processing the carbon nanotubes to generate a desired carbon nanotube array (as shown in Figure 2);

S10, cover the carbon nanotube and/or carbon fiber structure with a silicon-based thin barrier layer by capacitively coupled PECVD under the conditions of tetramethylsilane and oxygen at a relatively low pressure and a suitable temperature;

S20, immersing the carbon nanotubes and/or carbon fibers coated with a silicon-based film buffer layer in an ethanol solution in which nano-diamond particles are suspended, and planting diamond seed crystals with an ultrasonic bath method;

S30, using the microwave CVD method to prepare a deposited diamond coating under suitable conditions in the reactor (more than 98% hydrogen and less than 2% methane at a pressure of 70hpa and 850°C).

Fig. 2 shows a schematic diagram of the process of preparing carbon nano-array covered with diamond in this embodiment. In Figure 2, the array of single carbon nanotubes is placed on a suitable substrate; the silicon-based thin film barrier layer can ensure that the top of the carbon nanotubes will not be damaged when synthesizing diamond; and finally form a diamond coating.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. based on a preparation method for the matrix material of diamond crystal, it is characterized in that, comprise the steps:

The surface of carbon nanotube and/or carbon fiber forms barrier layer;

Described barrier layer is formed the forming core site for guiding diamond crystal to deposit;

Deposition of diamond coatings on described barrier layer.

2., as claimed in claim 1 based on the preparation method of the matrix material of diamond crystal, it is characterized in that, described barrier layer is unbodied silica-based buffer film, amorphous silicon oxide or silicon carbide.

3., as claimed in claim 2 based on the preparation method of the matrix material of diamond crystal, it is characterized in that, the thickness of described barrier layer is less than 100nm.

4. the preparation method of the matrix material based on diamond crystal as described in any one of claims 1 to 3, is characterized in that, described forming core site is Nano diamond seed crystal.

5. as claimed in claim 4 based on the preparation method of the matrix material of diamond crystal, it is characterized in that, described barrier layer being formed in the forming core site step for guiding diamond crystal to deposit, adopting the method for bias enhanced nucleation or nano-diamond particles suspension excusing from death bath to generate forming core site.

6. the preparation method of the matrix material based on diamond crystal as described in any one of claims 1 to 3, is characterized in that, on described barrier layer in deposition of diamond coatings step, using plasma enhanced chemical vapor deposition prepares diamond coatings.

7., as claimed in claim 6 based on the preparation method of the matrix material of diamond crystal, it is characterized in that, in described plasma enhanced chemical vapor deposition process, the density of hydrogen of reactant gas atmosphere is greater than 98%;

And/or in described plasma enhanced chemical vapor deposition process, reaction pressure is lower than 100hPa, and temperature is higher than 700 DEG C.

8. the preparation method of the matrix material based on diamond crystal as described in any one of claims 1 to 3, it is characterized in that, the surface of described carbon nanotube and/or carbon fiber is formed in barrier layer step, adopts capacitance coupling plasma chemical Vapor deposition process to form described barrier layer.

9. the matrix material based on diamond crystal that the preparation method of the matrix material based on diamond crystal according to any one of claim 1 to 8 prepares.

10. one kind adopts the micron order scroll saw prepared based on the matrix material of diamond crystal according to claim 9.