A method for in-situ inducing the generation of nanodiamonds by electron beam irradiation

Abstract

The present invention discloses a method for in-situ inducing the formation of nanodiamond by electron beam irradiation, belonging to the field of nanodiamond preparation. First, WC-(8-20)Co / Ni mixed powder is introduced onto the surface of clean alloy structural steel by using plasma thermal spraying technology. Then, the carbon material on the surface of the substrate is irradiated by an electron beam. The high-energy density electron beam instantaneously bombards the material surface, and the kinetic energy is converted into heat energy in the subsurface, causing the material surface to rapidly heat up and then rapidly cool down. By instantaneously inputting high energy, the conditions for phase transformation of the carbon material are generated, and the in-situ formation of nanodiamond is induced. The nanodiamond prepared by the present invention has controllable size; the entire preparation process is simple, environmentally friendly, low in cost and high in efficiency, breaking through the problems of cumbersome nanodiamond preparation process and high preparation cost, etc.

Description

Technical Field

[0001] The present invention belongs to the field of nano-diamond preparation, and specifically relates to a method for in-situ inducing the preparation of nano-diamonds by electron beam irradiation. Background Art

[0002] Nano-diamond refers to the morphological form of diamond grains with a particle size of 1 - 100 nm. It has the characteristics of both diamond and nano-materials, such as high hardness, high corrosion resistance, high thermal conductivity, low friction coefficient, low surface roughness, large specific surface area, biocompatibility, high surface activity, etc. It has extremely high application value in the fields of precision machining, lubricant material preparation, biomedicine, etc., and has great potential research and application value. Based on this, the preparation methods of nano-diamonds have always received strong attention from scientists around the world.

[0003] Currently, the main synthesis methods of nano-diamonds are high temperature and high pressure method, diamond single crystal grinding, and detonation method. The high temperature and high pressure method is mainly a method of transforming graphite powder into diamond particles under quasi-hydrostatic pressure and high temperature. This method usually uses transition metals, such as Fe, Ni, etc. as catalysts to accelerate the transformation from graphite phase to diamond phase; or uses substances such as hexogen, trinitrotoluene, etc. to generate pressure through explosion to impact graphite powder and transform it into diamond particles. The high temperature and high pressure method can controllably prepare diamond particles with different grain sizes, different morphologies and qualities. It is the diamond particle preparation method with the longest development time and the most widespread use. However, this method has harsh reaction conditions (pressure exceeding 104 atmospheres, temperature exceeding 1200 °C), and the equipment is cumbersome, the production cost is too high, and the safety factor is relatively low.

[0004] Diamond single crystal grinding is a method of crushing bulk diamond into nano-diamond particles by means of grinding, vibration, etc. The commonly used equipment is a ball mill. By using different ball milling media, controlling the abrasive ratio and other experimental parameters, nano-diamond particles of different sizes can be obtained. This method is simple to operate and has mild conditions, and is commonly used in the industrial production of diamond particles. However, the nano-diamond particles synthesized by this method have a large size difference and are prone to agglomeration, and special treatment is required. And due to the extremely high hardness and wear resistance of diamond materials, the equipment parts and ball milling media are extremely vulnerable to damage, which not only weakens the dispersion effect of nano-diamond particles, but also leads to too high impurity content in the dispersed particles.

[0005] The detonation method is a method of directly synthesizing nano-diamond particles from carbon elements in explosives by the high temperature (higher than 3000 °C) and high pressure (greater than 20 GPa) generated instantaneously by explosive detonation. The process of synthesizing nano-diamonds by this method is cumbersome and complex, and the nano-diamonds obtained by the detonation method are relatively small in size, generally concentrated in 2 - 10 nm, and the purity is about 95%.

[0006] The biggest problem troubling the world today is that although nanodiamonds are excellent, their preparation cost is too high, the preparation process is cumbersome, most of the preparation processes need to be carried out in a high-temperature and high-pressure environment, the controllability of each preparation process is insufficient, and the safety is poor. In the commercial method for preparing nanodiamonds, the synthesized nanodiamond particles have more impurities. It is necessary to screen and purify to remove non-carbon substances, then use strong acid to wash to remove amorphous carbon impurities in the product, then rinse the nanodiamond particles with clean water, and finally dry them to obtain relatively pure nanodiamond particles. Strong acid and other substances need to be used during the preparation process, resulting in serious environmental pollution and low efficiency. If impurity-free nanodiamonds are required, the cost will be even greater. Therefore, it is urgent to develop a simple, efficient, environmentally friendly, controllable and low-cost nanodiamond preparation process.

[0007] As a clean surface modification technology with high energy utilization rate, the electron beam technology uses a high-energy density electron beam current to instantaneously bombard the surface of the material, and convert the kinetic energy into heat energy in the subsurface, so that the surface of the material rapidly heats up and then rapidly cools down. By instantaneously inputting high energy, the conditions for carbon material phase transformation are generated (changing from carbon powder to nanodiamonds requires sufficiently high temperature and pressure). Based on this principle, Zhang Guifeng et al. from Dalian University of Technology invented a method for preparing nanodiamonds by intense pulsed electron beam (CN201610537883). However, this method requires the preparation and treatment of nanocarbon powder, and it is also difficult to separate the subsequent nanocarbon powder and nanodiamonds, resulting in a cumbersome preparation process, high equipment requirements, and increased costs; Gao Bo et al. from Northeastern University invented a method for synthesizing nanodiamonds by irradiating a graphite suspension with an intense pulsed electron beam (CN201110155541). However, this method requires the preparation of a graphite suspension (graphite particles, catalyst powder, deionized water) first, which takes a long time and has low efficiency. Therefore, it is of great significance to develop a new method for preparing nanodiamonds with high efficiency and low cost. Summary of the Invention

[0008] To overcome the deficiencies in the prior art, the present invention provides a method for in-situ inducing the formation of nanodiamonds by electron beam irradiation. Compared with the existing preparation methods, the nanodiamonds prepared by the method of the present invention have controllable sizes; the entire preparation process is simple, environmentally friendly, low-cost and high-efficiency, breaking through the problems of cumbersome nanodiamond preparation process and high preparation cost.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A method for in-situ inducing the formation of nanodiamonds by electron beam irradiation, comprising the following steps:

[0011] The first step: Select a pre-coated material and a substrate

[0012] The matrix material used is alloy structural steel. Before the test, the matrix material is quenched and tempered. The process parameters of quenching and tempering are: holding at 600 - 1100°C for 15 - 60 min and then quenching in oil, and tempering at 500 - 700°C for 30 - 90 min;

[0013] The pre - coated material selected is WC-(8 - 20)Co / Ni mixed powder. The nickel powder in the pre - coated material is a powder with a purity greater than 99.9% and a particle size of 30 - 100μm. The particle size of the WC-(8 - 20)Co powder added to the pre - coated material is 20 - 90μm. The alloy powder is introduced onto the surface of the clean steel specimen by plasma thermal spraying technology;

[0014] Step 2: Use electron beam to irradiate the surface of the specimen

[0015] Place the coated workpiece on the electron beam platform, turn on the equipment, and turn on the vacuum system; when the vacuum degree reaches the specified value, turn on the magnetic field, spark source, and cathode high - voltage in sequence, so that the electron beam directly irradiates the carbon material, generating a high - temperature and high - pressure environment, inducing the carbon material to transform into nanodiamond. Nanodiamond generated in situ is detected on the surface of the matrix after irradiation;

[0016] The electron beam process parameters are: vacuum degree 3×10 -3 ~7×10 -3 Pa, acceleration voltage 0 - 120 KV, scanning frequency 0 - 3000 Hz, beam current 0 - 120 mA, focusing current 0 - 1000 mA.

[0017] Furthermore, for the quenching and tempering treatment of the matrix material, the process parameters are preferably: holding at 870°C for 30 min and then quenching in oil, and tempering at 600°C for 60 min.

[0018] Furthermore, the nickel powder in the pre - coated material is a powder with a purity greater than 99.9% and a particle size of 50μm, and the particle size of the WC-(8 - 20)Co powder added to the pre - coated material is 60μm.

[0019] Furthermore, the electron beam process parameters are preferably: vacuum degree 6×10 -3 Pa, acceleration voltage 80 KV, scanning frequency 1800 Hz, beam current 60 mA, focusing current 600 mA.

[0020] When the electron beam irradiates the surface of the specimen, the high energy (10 8 ~10 9 W / cm 2) and high-density electrons bombard the material surface instantaneously (2 - 5 μs). The kinetic energy of the electrons is converted into heat energy and released instantaneously. The temperature of the material surface changes due to direct heating by the electron beam heat source, rising rapidly to the phase change critical point. The material surface melts, causing the pre-coated layer to fuse with the substrate. The molten metal liquid flows to form a molten pool. The surface tension of the molten pool, the Marangoni flow inside the molten pool, and the recoil pressure generated by the solid-liquid phase change create a high-temperature and high-pressure environment on the material surface, meeting the basic conditions for the generation of nanodiamonds. WC decomposes at high temperatures to form free carbon and W. At the same time, the Fe element in the substrate steel is released and rises to the inside of the molten pool, forming a metal catalyst with the Co powder and Ni powder in the mixed powder, catalyzing the conversion of carbon materials into nanodiamonds. The W element in the mixed powder has good compatibility with elements such as Fe, Co, and Ni, and carbide formation reactions occur on the surface of the nanodiamonds and with the nanodiamonds, protecting the in-situ generated nanodiamonds and facilitating the improvement of the conversion rate.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The size of the prepared nanodiamonds is controllable. The carbon material is irradiated by an electron beam to ultrashortly generate nanodiamonds in-situ; the original material is carbon powder, and the parameters of the electron beam irradiation can be adjusted within an appropriate range, thereby producing ideal nanodiamond sizes;

[0023] (2) The preparation process is clean and pollution-free. The working environment of the electron beam is a vacuum chamber, reducing the possibility of being contaminated by active gases in the air during the preparation of nanodiamonds. At the same time, it does not release pollutants such as heavy metals into the atmosphere, meeting the environmental protection concept advocated by the country;

[0024] (3) High efficiency and low preparation cost. This method does not require any pretreatment of the carbon material. At the same time, the electron beam spot diameter is large, and the single-pulse time is 3 - 5 μs. Nanodiamonds can be in-situ induced to form from carbon materials in a few μs, with high efficiency. Therefore, the cost of the nanodiamonds prepared by this method is extremely low, breaking through the worldwide problem that the preparation of nanodiamonds is difficult, time-consuming, and costly, which restricts its extended application. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the nanodiamond generation process of the present invention;

[0026] Figure 2 It is a scanning electron microscope image of the pre-coated material in the example;

[0027] (a) is WC - 12Co, (b) is Ni;

[0028] Figure 3 It is a secondary electron image of the nanodiamonds generated in Example 1. Detailed implementation manners

[0029] The following will further elaborate on the content of the present invention in combination with embodiments and drawings, but it is not a limitation to the present invention.

[0030] Embodiment 1

[0031] Refer to Figure 1-2 , a method for in-situ inducing the formation of nanodiamond by electron beam irradiation, comprising the following steps:

[0032] (1) Select pre-coated materials and substrates

[0033] The substrate material used is 32CrMo steel sheet. Before the test, the substrate material is quenched and tempered. The quenching and tempering process parameters are: holding at 850 °C for 40 min and quenching in oil, and tempering at 650 °C for 45 min;

[0034] Refer to Figure 2 , the pre-coated material selected is WC-10Co / Ni mixed powder, WC-10Co accounts for 20 wt.%, Ni accounts for 80 wt.%. The nickel powder in the pre-coated material is a powder with a purity of 99.99% and a particle size of 50 μm. The particle size of the cemented carbide WC-12Co powder added to the pre-coated material is 60 μm. The alloy powder is introduced onto the surface of the clean steel specimen by plasma thermal spraying technology;

[0035] (2) Use electron beam to irradiate the surface of the specimen

[0036] Place the coated workpiece on the electron beam platform, turn on the equipment, and turn on the vacuum system. When the vacuum degree reaches 6×10 - 3 Pa, turn on the magnetic field, spark source and cathode high voltage in sequence, so that the intense current pulsed electron beam directly irradiates the carbon material to generate a high-temperature and high-pressure environment, inducing the carbon material to be converted into nanodiamond; Electron beam process parameters: acceleration voltage 80 KV, scanning frequency 1800 Hz, beam current 60 mA, focusing current 600 mA. In-situ generated nanodiamond is detected on the surface of the substrate after irradiation, as Figure 3 shown.

[0037] Embodiment 2

[0038] A method for ultra-fast in-situ inducing the formation of nanodiamond by electron beam irradiation, comprising the following steps:

[0039] (1) Select pre-coated materials and substrates

[0040] The substrate material used is 30CrMnSi steel sheet. Before the test, the substrate material is quenched and tempered. The quenching and tempering process parameters are: holding at 870 °C for 30 min and quenching in oil, and tempering at 600 °C for 1 h;

[0041] The selected pre-coated material is a WC-12Co / Ni mixed powder, with WC-12Co accounting for 30 wt.%, and Ni accounting for 70 wt.%. The nickel powder in the pre-coated material is a powder with a purity of 99.99% and a particle size of 45 - 60 μm. The particle size of the cemented carbide WC-12Co powder added to the pre-coated material is 30 - 80 μm. The alloy powder is introduced onto the surface of a clean steel specimen using plasma thermal spraying technology;

[0042] (2) Irradiate the surface of the specimen with an electron beam

[0043] Place the coated workpiece on the electron beam platform, turn on the equipment, and turn on the vacuum system. When the vacuum degree reaches 7×10 - 3 Pa, turn on the magnetic field, spark source, and cathode high voltage in sequence, so that the intense pulsed electron beam directly irradiates the carbon material, generating a high-temperature and high-pressure environment, and inducing the carbon material to transform into nanodiamond; Electron beam process parameters: acceleration voltage 60 KV, scanning frequency 1500 Hz, beam current 50 mA, focusing current 500 mA. In-situ generated nanodiamond is detected on the surface of the substrate after irradiation.

[0044] Example 3

[0045] A method for ultra-fast in-situ induction of nanodiamond generation by electron beam irradiation, comprising the following steps:

[0046] (1) Select the pre-coated material and the substrate

[0047] The substrate material used is 40Cr steel sheet. Before the test, the substrate material is quenched and tempered. The quenching and tempering process parameters are: holding at 900 °C for 45 min and quenching in oil, and tempering at 550 °C for 1 h;

[0048] The selected pre-coated material is a WC-18Co / Ni mixed powder, with WC-18Co accounting for 40 wt.%, and Ni accounting for 60 wt.%. The nickel powder in the pre-coated material is a powder with a purity greater than 99.9% and a particle size of 45 - 60 μm. The particle size of the cemented carbide WC-12Co powder added to the pre-coated material is 30 - 80 μm. The alloy powder is introduced onto the surface of a clean steel specimen using plasma thermal spraying technology;

[0049] (2) Irradiate the surface of the specimen with an electron beam

[0050] Place the coated workpiece on the electron beam platform, turn on the equipment, and turn on the vacuum system. When the vacuum degree reaches 6.5×10 -3Pa, turn on the magnetic field, spark source, and cathode high voltage in sequence, so that the intense current pulsed electron beam directly irradiates the carbon material to generate a high-temperature and high-pressure environment, inducing the carbon material to transform into nanodiamond; the process parameters of the electron beam are: acceleration voltage 60 KV, scanning frequency 1600 Hz, beam current 80 mA, focusing current 750 mA, and in-situ generated nanodiamond is detected on the surface of the substrate after irradiation.

[0051] The above-described embodiments only represent the implementation manners of the present invention, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for in-situ inducing the generation of nanodiamonds by electron beam irradiation, characterized in that, It includes the following steps: The first step: Select the pre-coated material and the substrate The substrate material used is alloy structural steel. Before the test, the substrate material is quenched and tempered. The process parameters of quenching and tempering are: holding at 600 - 1100 °C for 15 - 60 min and then quenching in oil, and tempering at 500 - 700 °C for 30 - 90 min; The selected pre-coated material is WC-(8 - 20)Co / Ni mixed powder. The nickel powder in the pre-coated material is a powder with a particle size of 30 - 100 μm and a purity greater than 99.9%. The particle size of the WC-(8 - 20)Co powder added to the pre-coated material is 20 - 90 μm. The alloy powder is introduced onto the surface of a clean steel specimen by plasma thermal spraying technology; The second step: Use electron beam to irradiate the surface of the specimen Place the coated workpiece on the electron beam platform, turn on the equipment, turn on the vacuum system. When the vacuum degree reaches the specified value, turn on the magnetic field, spark source and cathode high voltage in sequence, so that the high-current pulsed electron beam directly irradiates the carbon material to generate a high-temperature and high-pressure environment, inducing the carbon material to transform into nanodiamond. Nanodiamond generated in-situ is detected on the surface of the substrate after irradiation; Electron beam process parameters: vacuum degree 3×10 -3 ~7×10 -3 Pa, acceleration voltage 60 - 120 KV, scanning frequency 1500 - 3000 Hz, beam current 50 - 120 mA, focusing current 500 - 1000 mA.

2. The method for in-situ inducing the formation of nanodiamond by electron beam irradiation according to claim 1, wherein: The substrate material is quenched and tempered, and the process parameters of quenching and tempering are: holding at 870 °C for 30 min and then quenching in oil, and tempering at 600 °C for 60 min.

3. The method for in-situ inducing the generation of nanodiamond by electron beam irradiation according to claim 1, characterized in that: The nickel powder in the pre-coated material is a powder with a particle size of 50 μm and a purity greater than 99.9%. The particle size of the WC-(8 - 20)Co powder added to the pre-coated material is 60 μm.

4. The method for in-situ inducing the formation of nanodiamond by electron beam irradiation according to claim 1, wherein Electron beam process parameters: vacuum degree 6×10 -3 Pa, acceleration voltage 80 KV, scanning frequency 1800 Hz, beam current 60 mA, focusing current 600 mA.

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