Preparation method of high-stability carbon rod for preparing single-walled carbon nanotube through arc discharge

Abstract

The invention discloses a preparation method of a high-stability carbon rod for preparing a single-walled carbon nanotube by arc discharge, the carbon rod prepared by the method is prepared by a secondary granulation and gradient sintering process, and the preparation method comprises the following steps: 1) uniformly mixing graphite powder (C), micron-sized nickel powder (Ni), yttrium oxide (Y2O3), phenolic resin and absolute ethyl alcohol according to a certain proportion, the mixing method is ball milling; 2) drying the mixture in a hot air box for secondary granulation; 3) placing the dried mixture in a square or cylindrical mold for compression molding to obtain a carbon ingot; and 4) carrying out gradient sintering on the pressed and molded carbon ingot to obtain the carbon rod with good conductivity. The resistivity is 6.9 E <-4 > omega.m after sintering treatment at 900 DEG C, and the resistivity is 3.4 E <-4 > omega.m after sintering treatment at 1000 DEG C. The gradient sintered carbon rod with good conductivity has good conductivity, high mechanical strength and machinability, and also has the advantages of simple preparation process flow, low price, strong stability, batch production and the like. Through secondary granulation and gradient sintering processes, the prepared carbon rod meets the requirement of arc discharge for synthesis of a single-walled carbon nanotube, the conductivity of the obtained carbon rod is obviously changed along with different sintering temperatures, and the yield of the single-walled carbon nanotube is further influenced.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon material preparation, and particularly relates to a method for preparing a high-stability carbon rod for preparing single-walled carbon nanotubes by arc discharge, and its applications in the fields of energy storage and conversion, composite materials and structural reinforcement, biomedical and sensors, etc. In particular, by optimizing the reaction activation mechanism, the densification sintering of the carbon rod is realized at a temperature significantly lower than that of the traditional process (traditionally 1200 - 1500 °C), and batch production is achieved. Background Art

[0002] As a high-performance carbon material, carbon rods are widely used in key fields such as electrochemical electrodes (such as batteries and electrolyzers), high-temperature metallurgical furnace components, aerospace thermal protection systems, and nuclear reactor moderators due to their excellent electrical conductivity, high-temperature stability, chemical inertness, and mechanical strength. With the rapid development of new energy technologies and high-end manufacturing industries, the market has put forward higher requirements for the comprehensive performance of carbon rods (such as axial flexural strength, volume density uniformity, electrical / thermal conductivity isotropy) and the environmental friendliness of preparation.

[0003] At present, the mainstream preparation processes of industrial carbon rods include the molding-sintering method, the impregnation-carbonization method, and the chemical vapor deposition (CVD) method. Among them, the molding-sintering method usually uses tar, coal tar pitch, etc. as binders and sinters at 1200 - 1500 °C. This method is prone to an increase in the porosity gradient inside the carbon rod (generally >15%) due to uneven distribution of the binder, thereby reducing the anti-cracking performance under axial load. At the same time, the high-temperature sintering process has significant energy consumption (unit energy consumption ≥2.5 kWh / kg), and the thermal decomposition of coal tar pitch releases polycyclic aromatic hydrocarbon pollutants, and the thermal decomposition of tar releases sulfides, etc., which restricts its green production. The impregnation-carbonization method has a long production cycle and poor thermal shock resistance. The chemical vapor deposition (CVD) method has extremely high equipment investment costs (the cost of the reaction chamber exceeds one million US dollars) and low deposition rates (<0.1 mm / h), making it difficult to meet the requirements of large-scale continuous production.

[0004] In addition, the above methods generally rely on petroleum-based binders or precursors, facing the problems of non-renewable raw materials and high carbon emission intensity. In recent years, although some studies have tried to introduce biomass-derived carbon sources or water-soluble binders, the following bottlenecks exist: ① The high ash content of biomass (>5%) leads to the electrical conductivity of the carbon rod dropping below 800 S / m; ② The coking rate of the water-based binder is low (<50%), and the densification effect is insufficient.

[0005] Therefore, there is an urgent need to develop a preparation method that combines low energy consumption, short process, environmental friendliness, and can simultaneously optimize the microstructure uniformity and macroscopic mechanical properties of carbon rods to break through the comprehensive performance and sustainability limitations of the existing technology. Summary of the Invention

[0006] To solve the above problems, the purpose of the present invention is to provide a method for preparing a high-stability carbon rod for preparing single-walled carbon nanotubes by arc discharge. The technical solution adopted by the present invention is as follows:

[0007] A method for preparing a high-stability carbon rod for preparing single-walled carbon nanotubes by arc discharge, comprising the following steps:

[0008] Step 1: At room temperature, mix graphite powder (C), micron-sized nickel powder (Ni), yttrium oxide (Y2O3), and thermosetting phenolic resin with absolute ethanol in a certain proportion, and put them into a planetary ball mill for ball milling to make the sample evenly mixed;

[0009] Step 2: Put the sample obtained in Step 1 into a hot air oven for drying and secondary granulation;

[0010] Step 3: Put the sample obtained in Step 2 into a mold and press it into a carbon rod or a carbon plate;

[0011] Step 4: Put the pressed carbon rod or carbon plate into the cavity of a carbonization furnace, start the vacuum carbonization furnace, heat it up to 250 - 300°C in an inert atmosphere and keep it warm for 30 - 90 minutes, further increase the furnace cavity temperature to 700 - 1100°C, and keep it warm for 90 - 150 minutes, and then naturally cool it to room temperature to obtain a carbon rod or a carbon plate with good conductivity and gradient sintering.

[0012] Step 5: The prepared carbon rod or carbon plate can be obtained as a carbon rod with good conductivity through mechanical processing.

[0013] Preferably, the inert gas in Step 4 is one or more of nitrogen and argon.

[0014] Furthermore, the ball milling speed in Step 1 is 250 - 350 r / min.

[0015] Furthermore, the temperature for drying and secondary granulation in Step 2 is 30 - 60°C.

[0016] Furthermore, the flow rate of the inert gas in Step 3 is 60 - 90 mL / min.

[0017] Furthermore, the heating rate of the vacuum carbonization furnace in Step 4 is 1 - 5°C / min to 250 - 300°C, and 10°C / min to 700 - 1000°C; the inert gas is 60 - 90 mL / min.

[0018] More specifically, the preparation of single-walled carbon nanotubes by arc discharge includes the following steps:

[0019] Put the carbon rod with high stability as the anode into the arc reaction device, and use a high-purity graphite rod as the cathode; lower the vacuum hood, evacuate the cavity to 20 Pa and then circulate to fill with argon gas for cleaning (repeat 3 times); then fill in a certain amount of helium or argon / hydrogen as the buffer gas, turn on the DC power switch in an environment of 750 - 850 mbar (absolute pressure) to start arc discharge, and the discharge current is 80 - 110 A; the electrode spacing is 3 - 5 mm; after the reaction chamber cools down, collect the flaky products and scattered fluffy products in the deposition area, which are the single-walled carbon nanotube samples.

[0020] The present invention provides a preparation method of a carbon rod with high stability for arc discharge preparation of single-walled carbon nanotubes and its applications in the fields of energy storage and conversion, composite materials and structural reinforcement, biomedical and sensors, etc., which has the characteristics of high stability and good electrical conductivity.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0022] The present invention provides a preparation method of a carbon rod with high stability for arc discharge preparation of single-walled carbon nanotubes. The preparation process conditions are simple, the cost is low, the operation is convenient, it can be industrialized, and it has good commercial value.

[0023] The carbon rod with high stability for arc discharge preparation of single-walled carbon nanotubes provided by the present invention has the characteristics of good electrical conductivity and high mechanical strength; by optimizing the reaction activation mechanism, the atoms inside the carbon rod obtain sufficient energy to rearrange and adjust, effectively eliminating internal stress to improve the structural stability of the carbon rod and reducing the possibility of problems such as cracking and deformation during subsequent use. In addition, the contact between graphite powders will be closer and more stable due to atomic thermal motion, building a more efficient electron conduction network; thereby enhancing the mechanical strength of the carbon rod and significantly enhancing its electrical conductivity; overall, from the yield of the synthesized single-walled carbon nanotubes, it can be seen that the carbon rod material prepared by the present invention reflects the replaceability of the anode consumable material for single-walled carbon nanotubes. Description of the Drawings

[0024] Figure 1 It is a physical picture of the 10*10*150 mm carbon rod formed by pressing for the present invention.

[0025] Figure 2 It is a physical picture of the carbon rod sintered in an inert atmosphere at 700 - 1000 °C for the present invention.

[0026] Figure 3 It is a physical picture of the single-walled carbon nanotubes prepared from the carbon rod sintered at 900 °C for the present invention.

[0027] Figure 4 It is a physical picture of the single-walled carbon nanotubes prepared from the carbon rod sintered at 1000 °C for the present invention.

[0028] Figure 5 It is the graph of the change in electrical conductivity of the carbon rods obtained in Examples 1-4 of the present invention.

[0029] Figure 6 It is the graph of the change in the yield of single-walled carbon nanotubes prepared from the carbon rods obtained in Examples 1-4 of the present invention.

[0030] Figure 7 It is the SEM image of single-walled carbon nanotubes prepared with the carbon rods obtained in Examples 1-4 of the present invention as the anode.

[0031] Figure 8 It is the TEM image of single-walled carbon nanotubes prepared with the carbon rods obtained in Examples 1-4 of the present invention as the anode.

[0032] Figure 9 It is the Raman graph of single-walled carbon nanotubes prepared with the carbon rods obtained in Examples 1-4 of the present invention as the anode in the Raman shift range of 0-3000 cm -1 Raman graph within the Raman shift range. Figure 10 It is the flow chart of the carbon rods obtained in Examples 1-4 of the present invention. Detailed implementation manners

[0033] To make the objectives, technical solutions and advantages of this application clearer, the present invention will be further described below with reference to the accompanying drawings and embodiments. Here, the specific embodiments are only used to explain and illustrate the present invention and are not used to limit the present invention. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field. The materials and reagents used are all commercially available. Example 1

[0034] The present invention provides a preparation method for a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge, and the method includes the following steps:

[0035] Step 1: At room temperature, mix high-purity graphite powder (C), micron-sized nickel powder (Ni), yttrium oxide (Y2O3) and a thermosetting phenolic resin sample with absolute ethanol in a certain proportion, and put them into a planetary ball mill, and ball mill at 350 rpm for 6 h to make the samples evenly mixed;

[0036] Step 2: Put the sample obtained in Step 1 into a hot air oven and dry it at 40 °C for 4 h;

[0037] Step 3: Place the sample obtained in Step 2 in a vacuum carbonization furnace, and introduce argon gas with a gas flow rate of 70 mL / min for 10 min to evacuate the air in the furnace;

[0038] Step 4: Start the vacuum carbonization furnace, heat it up to 90°C at a rate of 2°C / min under an inert atmosphere, and keep it at this temperature for 30 min; this enables the phenolic resin to fully soften and fill the inside of the carbon rod, improving the overall density.

[0039] Step 5: Under an inert atmosphere, continue to heat the product of Step 4 to 160°C at a rate of 2°C / min, and keep it at this temperature for 90 min; this allows the phenolic resin to fully crosslink, enhancing the stability of the carbon rod structure.

[0040] Step 7: Under an inert atmosphere, continue to heat the product of Step 5 to 320°C at a rate of 2°C / min, and keep it at this temperature for 90 min; the slow heating rate ensures uniform heating of the carbon rod and prevents uneven decomposition of the resin caused by rapid temperature fluctuations; a certain holding time ensures complete decomposition of the resin.

[0041] Step 8: Under an inert atmosphere, continue to heat the product of Step 7 to 700°C at a rate of 10°C / min and keep it at this temperature for 150 min; after the holding period, stop the supply of the inert gas, allow it to cool naturally to room temperature, take out the product, and a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge can be obtained.

[0042] Step 9: Place the collection rack (iron wire rack) into the arc reaction device, then put the highly stable carbon rod as the anode and a high-purity graphite rod as the cathode into the arc reaction device; lower the vacuum hood, evacuate the cavity to 20 Pa and then repeatedly fill it with argon gas for cleaning (repeat 3 times); then fill in a certain amount of argon gas as a buffer gas, turn on the DC power switch in an environment of 850 mbar (absolute pressure) to start arc discharge, and the discharge current is 110 A; after the reaction chamber cools down, collect the flaky products and the scattered fluffy products in the deposition area, which are the single-walled carbon nanotube samples. Example 2

[0043] This example provides a method for preparing a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge. The preparation method is basically the same as that of Example 1, except that: during the gradient sintering process, it is heated to 800°C at a rate of 10°C / min. Example 3

[0044] This example provides a method for preparing a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge. The preparation method is basically the same as that of Example 1, except that: during the gradient sintering process, it is heated to 900°C at a rate of 10°C / min. Example 4

[0045] This example provides a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge. The preparation method is basically the same as that of Example 1, except that: during the gradient sintering process, it is heated to 1000°C at a rate of 10°C / min.

[0046] Figure 1 Shows a physical picture of a carbon rod before sintering after being pressed into shape, Figure 2 Is a physical picture of the carbon rod after sintering. It can be found that there are no cracks in the carbon rod after sintering, and the carbon rod is highly densified.

[0047] Figure 3 、 Figure 4 Respectively show the physical pictures of single-walled carbon nanotubes prepared by arc discharge in Example 3 and Example 4. It can be seen that the single-walled carbon nanotubes prepared by this invention are in sheet form, and have high stability. The single-walled carbon nanotubes can be exfoliated and collected completely, and they are thin, light and have high toughness, having important prospects in the fields of composite materials, flexible electronic devices, biomedicine and sensors, etc.

[0048] Figure 5 Shows the change of the conductivity of the carbon rod with the increase of the sintering temperature (700 - 1000 °C). It can be found that after sintering treatment at 1000 °C, the resistivity of the carbon rod drops to 3.4E-4 Ω·m, having good conductivity. High-temperature annealing can adjust the internal structure of the carbon rod, eliminate residual stress, make the carbon lattice more regular, improve the mechanical strength and conductivity of the carbon rod, etc., and can be applied in the field of energy storage and conversion.

[0049] Figure 6 Shows the yield change diagram of single-walled carbon nanotubes prepared from the carbon rods obtained in Examples 1 - 4 after sintering with the increase of the annealing temperature (700 - 1000 °C). It can be found that with the increase of the sintering temperature of the carbon rod, the yield of single-walled carbon nanotubes prepared using the carbon rod as the anode increases, and the yield in Example 4 can reach 36%.

[0050] Figure 7 Shows the SEM images of single-walled carbon nanotubes prepared using the carbon rods obtained in Examples 1 - 4 as the anode. In Examples 1 and 2, it can be found that impurities such as graphite particles of different sizes adhere to the wall of the single-walled carbon nanotube bundle. While in Examples 3 and 4, with the increase of the sintering temperature of the anode graphite rod, the impurity particles adhering to the surface of the single-walled carbon nanotube bundle decrease, and the surface is smoother. It shows that the content of single-walled carbon nanotubes is very high and evenly distributed.

[0051] Figure 8 Shows the TEM images of single-walled carbon nanotubes prepared using the carbon rods obtained in Examples 1 - 4 as the anode. It can be found that there are amorphous carbon particles in the single-walled carbon nanotubes in Example 1, while the amorphous carbon in the single-walled carbon nanotubes provided in Examples 2 and 3 significantly decreases, and the purity of the single-walled carbon nanotubes provided in Example 4 is quite high, with almost no amorphous carbon present.

[0052] Figure 9The Raman spectra of single-walled carbon nanotubes prepared with the carbon rods obtained in Examples 1-4 as anodes are shown. The single-walled carbon nanotubes provided in Examples 1-4 exhibit distinct Raman peaks around 1590 and 160 cm -1 -1. Among them, the absorption peak at 1590 cm -1 -1 is attributed to the in-plane stretching vibration of the graphite layer of the carbon nanotubes (G peak), and the peak at 1340 cm -1 -1 is the peak (D peak) generated by the disordered structure of carbon. It can be seen from the figure that for the single-walled carbon nanotubes provided in Examples 1-4, the I(D) / I(G) value gradually decreases; in Example 3, the full width at half maximum of the G peak is sharpened, indicating an increase in the in-plane grain size; the G peak in Example 4 is the strongest, while the D peak is quite weak, which indicates that the content of amorphous carbon in the product of Example 4 is negligible.

[0053] Therefore, it can be seen that the highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge provided by the present invention has the advantages of high purity, high yield, good electrical conductivity, etc.

[0054] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing a carbon rod with high stability for preparing single-walled carbon nanotubes by arc discharge, characterized in that Achieving a highly conductive graphite anode through a secondary granulation and gradient sintering process, including the following steps: Step 1: At room temperature, mix graphite powder (C), micron-sized nickel powder (Ni), yttrium oxide (Y2O3), and thermosetting phenolic resin with absolute ethanol in a certain ratio and place them in a planetary ball mill for ball milling to make the sample evenly mixed; Step 2: Put the sample obtained in Step 1 into a hot air oven for drying and secondary granulation; Step 3: Put the sample obtained in Step 2 into a mold for pressing to form a carbon rod or carbon plate; Step 4: Place the pressed carbon rod or carbon plate into the cavity of a vacuum carbonization furnace, start the vacuum carbonization furnace, heat up to 250 - 300°C under an inert atmosphere and hold for 30 - 90 min, further increase the furnace cavity temperature to 700 - 1100°C, and hold for 90 - 150 min, stop gas supply after natural cooling to room temperature, and a carbon rod or carbon plate with good conductivity and gradient sintering can be obtained. Step 5: The prepared carbon rod or carbon plate can be obtained as a carbon rod with good conductivity through mechanical processing.

2. Preparation of a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge according to claim 1, characterized in that, The ball milling speed in Step 1 is 250 - 350 r / min, and the time is 3 - 6 hours.

3. Preparation of a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge according to claim 1, characterized in that, The drying temperature in Step 2 is 30 - 60°C, and the drying time is 1 - 4 h.

4. Preparation of a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge according to claim 1, characterized in that, The pressing pressure of the carbon rod in Step 3 is 10 - 30 MPa, and the mold is square plate-shaped or cylindrical.

5. Preparation of a highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge according to claim 1, characterized in that, The heating rate in the low-temperature stage (<300°C) of the sintering furnace in Step 4 is 1 - 5°C / min, and in the high-temperature stage (>300°C) it is 10°C / min to 700°C - 1000°C; the flow rate of the inert gas is 60 - 90 mL / min.

6. Using the highly stable carbon rod for preparing single-walled carbon nanotubes by arc discharge as described in any one of claims 1 - 5 as an anode in an arc discharge furnace can obtain a considerable yield of single-walled carbon nanotubes.

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