Method for preparing nano composite material through synchronous pulse discharge of dissimilar wires

Abstract

The invention discloses a method for preparing a nano composite material through synchronous pulse discharge of dissimilar wires, and belongs to the technical field of nano composite material processes. According to the invention, two or more than two discharge wires are used for performing pulse discharge at the same time and enabling the two or more than two discharge wires to generate electric explosion synchronously, so that the nano composite material is formed. The resistivity and thermophysical properties of dissimilar materials are generally greatly different, so that the heating speeds of different discharge wires may be different, and then asynchronous explosion of the wires is caused. The sublimation energy of the discharge wire and the energy of the actual injection wire in the discharge process are calculated by adjusting the geometric dimension of the discharge wire, so that the sublimation energy is matched with the energy; the numerical value of K is adjusted by adjusting the length of the discharge wire, so that K is within the range of 0.8-1.25, and the purposes that the dissimilar wires explode synchronously and the composite material is formed are achieved. The method has the advantages of wide applicability, simple process, wide application and the like.

Description

Technical Field

[0001] The present invention relates to a method for preparing nano-composites by synchronous pulsed discharge of dissimilar wires, belonging to the technical field of nano-composite processes. Background Art

[0002] The research history of wire pulsed discharge (electrical explosion) is long, dating back to 1774 at the earliest. Naime, through the electrical explosion experiment of metal wires, first demonstrated the principle that the current is equal in each part of a series circuit, laying the foundation for subsequent research. In 1857, Faraday first applied the electrical explosion technology to the preparation of small-sized materials, initiating the application of electrical explosion technology in the field of materials science. Since then, the electrical explosion phenomenon has attracted wide attention and has been gradually studied and applied in multiple fields, such as for the development of fast fuses, explosion arc extinguishing chambers, etc.

[0003] According to Kotov's summary and research, wire pulsed discharge (also known as electrical explosion) refers to the physical process of generating a high-density current (10 4 -10 6 A / mm 2 ) through a conductive material (such as a metal wire or metal foil) in a specific medium or vacuum environment, thereby triggering the Joule heating effect, causing a large amount of energy to be rapidly deposited in the wire, and melting and vaporizing the wire within an extremely short time (microsecond or nanosecond level), forming a high-temperature and high-pressure state (the temperature can reach about 10 4 K, and the pressure is about 10 2 GPa), and thus an explosion occurs. As can be seen from the above definition, electrical explosion mainly includes two stages: the Joule heating stage and the explosion stage. In the Joule heating stage, a large amount of energy is rapidly deposited when the current passes through the wire, melting and vaporizing the wire, and even possibly forming a plasma. Immediately following in the explosion stage, the products under high temperature and high pressure expand rapidly outward, accompanied by the generation of shock waves and a strong flash effect. The whole process will produce significant mechanical, thermal, optical, and electromagnetic effects.

[0004] With the continuous development of technology, wire pulsed discharge technology has been gradually applied to a wider range of fields. Currently, this technology has achieved remarkable results in the preparation of nano-materials, explosion spraying, transient light sources, and high-temperature sources. Its characteristics of low cost, high efficiency, and environmental friendliness have enabled it to be widely applied in the industrial and scientific research fields, especially showing great potential in large-scale production and the development of functional materials.

[0005] Many of the current achievements can usually be realized through the pulsed discharge of a single wire. With the continuous deepening of research, it has been found that the synchronous pulsed discharge technology of dissimilar wires has a wider range of application fields, such as the preparation of nanocomposites, the synthesis of bimetallic or multi-metallic nanoparticles, the spraying of functional coatings, bimetallic nanocatalysts, high-energy electromagnetic pulse sources, diversified shock wave research, and so on. If the synchronous pulsed discharge of dissimilar wires can be achieved, the explosion processes of the two can affect and interact with each other, and the mixing or mutual reaction of different material elements can occur instantaneously during the explosion, thus forming nanocomposites. This method can generate nanocomposites with specific structures and functions through the interaction between different material elements or through the alloying process.

[0006] However, there are the following technical difficulties in the synchronous pulsed discharge of dissimilar wires: The resistivity differences of different wires are relatively large, which will directly affect their heating rates and explosion times during the pulsed discharge process; There are significant differences in the thermophysical properties (such as melting point, boiling point, specific heat capacity, thermal conductivity, sublimation energy, etc.) of different wires, which means that under the same current conditions, the phase change processes of different wires will be different. For the above reasons, when a current pulse passes through the discharge wire, the heating rates of different discharge wires may be significantly different, which may lead to the asynchronous explosion of the wires. In this case, the wire that explodes first will affect the wire that explodes later, and the explosion products cannot be well mixed and interacted, thus affecting the formation of the target product.

[0007] Currently, there is little research on the synchronous pulsed discharge of dissimilar wires and it is still in its infancy, but some preliminary results have also been obtained, such as the preparation of FeCoNi magnetic nanoparticles by the synchronous pulsed discharge method. However, there is no report on the research of the matching technology for the synchronous pulsed discharge of dissimilar wires. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing nanocomposites by the synchronous pulsed discharge of dissimilar wires, using two or more discharge wires to simultaneously perform pulsed discharge and making them synchronously undergo electrical explosion, thereby forming nanocomposites.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing nanocomposites by the synchronous pulsed discharge of dissimilar wires disclosed by the present invention includes the following steps:

[0011] Step 1: Select two discharge wires according to the experimental target material. The cross-sectional areas of the two discharge wires are S1 and S2 respectively, the lengths are l1 and l2 respectively, and the sublimation energy per unit volume is E S1 and E S2 ;

[0012] Step 2: Calculate the ratio k1 of the sublimation energies of the two discharge wires,

[0013]

[0014] Step 3: Calculate the energy injected into the discharge wire during the pulsed discharge joule heating stage.

[0015] E′ = ∫I 2 R t dt

[0016] I is the current; R t is the resistance of the discharge wire. The resistivity of the material changes with temperature. During synchronous parallel discharge, the transient characteristics of capacitor discharge will significantly affect the dynamic process of energy deposition. The dynamic coupling of resistance change and current change will reduce the influence of resistance change. In the application of preparing nanocomposites by synchronous pulsed discharge of dissimilar metal wires, the process requirement does not require the two wires to explode strictly synchronously, but it is necessary to ensure that the shock wave generated by the first exploding material does not interfere with the melting or gasification process of the other wire in the joule heating stage. Since this process has a high tolerance for the explosion timing of the two wires and the resistance change is relatively gentle before the material phase change (especially in the initial stage of microsecond-level discharge), using the initial resistance value R to estimate the energy E′ can still meet the engineering accuracy requirements.

[0017] E′ = I 2 Rt

[0018] Step 4: Calculate the ratio k2 of the actual energy injected into the discharge wire during the pulsed discharge joule heating stage.

[0019]

[0020] The subscript 1 represents the first discharge wire, R1 is the resistance of the first discharge wire; the subscript 2 represents the second discharge wire, R2 is the resistance of the second discharge wire; t is the time; ρ1 and ρ2 are the initial resistivity of the two discharge wires respectively.

[0021] Step 5: Calculate the pulsed discharge matching parameter K.

[0022]

[0023] From the above formula, the pulsed discharge matching parameter K is related to the resistivity of the discharge material, the sublimation energy, and the length of the discharge wire. Adjust the value of K by adjusting the length of the discharge wire.

[0024] Step 6: According to the determined lengths l1 and l2 of the discharge wires, as well as the cross-sectional areas S1 and S2, and the sublimation energy E per unit volume S1 and E S2 , calculate the sublimation energy E required for the electro-explosion of the discharge wire.

[0025] E1 = E S1S1l1

[0026] E2 = E S2 S2l2

[0027] E = E1 + E2

[0028] Step 7: Install the discharge wires with lengths l1 and l2 in step 6 into the pulsed discharge system, charge the high-voltage energy storage capacitor so that the initial energy storage is greater than the sublimation energy E in step 6, and conduct a synchronous pulsed discharge experiment to prepare the nanocomposite material.

[0029] Preferably, the value of K is adjusted by adjusting the length of the discharge wire so that K is in the range of 0.8 - 1.25.

[0030] Beneficial effects:

[0031] 1. A method for preparing a nanocomposite material by synchronous pulsed discharge of dissimilar wires according to the present invention. By adjusting the geometric dimensions of the discharge wires, calculating the sublimation energy of the discharge wires and the energy actually injected into the wires during the discharge process, and making them match, the purpose of synchronous explosion of dissimilar wires and the formation of a composite material is achieved. The operation is simple and no complex process control is required.

[0032] 2. A method for preparing a nanocomposite material by synchronous pulsed discharge of dissimilar wires according to the present invention. Since this method uses the form of synchronous discharge of two or more discharge wires to realize the preparation of the composite material, it only requires that the wires can explode under the action of high-density current, and is applicable to various metal materials, non-metal conductors and semiconductor materials, with wide adaptability.

[0033] 3. A method for preparing a nanocomposite material by synchronous pulsed discharge of dissimilar wires according to the present invention. Through the synchronous pulsed discharge of graphite strips and various discharge wires, the preparation of various graphene-based composite materials can be realized. Through the synchronous pulsed discharge of bimetal wires or various metal wires, the synthesis of bimetal or multi-metal nanoparticles, the spraying of functional coatings, etc. can be realized.

[0034] 4. A method for preparing a nanocomposite material by synchronous pulsed discharge of dissimilar wires according to the present invention. The pulsed discharge method adopted belongs to a one-step green synthesis method, with low production cost, no need to introduce complex chemical reagents and processes, and is more competitive than traditional synthesis methods when used for the preparation of nanocomposite materials and multi-metal nanoparticles. Description of the drawings

[0035] Figure 1 Schematic diagram of the pulsed discharge system used in the present invention;

[0036] Figure 2 TEM image of the nano-silicon / graphene composite material obtained in Example 1 of the present invention;

[0037] Figure 3 TEM image of the recovered sample obtained in Comparative Example 1 of the present invention;

[0038] Figure 4 TEM image of the recovered sample obtained in Comparative Example 2 of the present invention;

[0039] Figure 5 Flowchart of a method for preparing a nanocomposite by synchronous pulsed discharge of dissimilar wires according to the present invention. Detailed implementation manners

[0040] To better illustrate the purpose and advantages of the present invention, the following further describes the content of the invention in conjunction with the accompanying drawings and examples.

[0041] In the following examples, the schematic diagram of the pulsed discharge system used is as Figure 1 shown. The pulsed discharge system consists of three parts: a charging power supply, a discharge capacitor, and a discharge tank.

[0042] Graphite paper: with a purity of 99%, a thickness of 0.5 mm, purchased from Beijing Innochem Science & Technology Co., Ltd., and its resistivity is 0.005 Ω·cm.

[0043] Silicon wafer: with a purity of 99%, N-type, a thickness of 0.5 mm, purchased from Zhejiang Lijing Optoelectronic Technology Co., Ltd., and its resistivity is 0.02 Ω·cm.

[0044] The following tests are conducted on the following examples:

[0045] Transmission electron microscope (TEM): FEI Talos F200X.

[0046] Example 1:

[0047] This example discloses a method for preparing a nano-silicon / graphene nanocomposite by synchronous pulsed discharge of graphite strips and silicon strips. This method solves the problems of high cost and low efficiency of traditional methods through efficient and environmentally friendly process innovation, significantly improves the material properties (inhibiting silicon volume expansion and enhancing conductivity), promotes the industrialization process of high-energy-density lithium-ion batteries, reduces production costs and environmental pollution at the same time, and contributes to the cross-application of new energy technologies and nanocomposites.

[0048] A method for preparing a nanocomposite by synchronous pulsed discharge of dissimilar wires disclosed in this example is specifically implemented as follows:

[0049] Step 1: Select high-purity graphite paper and high-purity silicon wafers as raw materials according to the experimental target materials. The thickness of both is 0.5 mm. Considering the difficulty of material processing and the requirements of pulsed discharge for the discharge wire, cut the graphite strips and silicon strips into long strips with a width of 2 mm. The cross-sectional areas of the two discharge wires are 1 mm 2 and 1 mm 2 , respectively. Refer to the literature to obtain that the sublimation energy per unit mass of graphite and silicon are 57.9 kJ / g and 16.43 kJ / g, respectively. The densities of the graphite strips and silicon strips here are 2.1 g / cm 3 and 2.3 g / cm 3 , respectively. The sublimation energy per unit volume E S1 and E S2 are equal to 121.6 kJ / cm 3 and 37.8 kJ / cm 3 respectively; Preset their lengths to be l1 and l2,

[0050] Step 2: Calculate the ratio k1 of the sublimation energy of the two discharge wires.

[0051]

[0052] Step 3: Determine the energy injected into the discharge wire during the pulsed discharge Joule heating stage.

[0053] E′ = ∫I 2 R t dt

[0054] I is the current; R t is the resistance of the discharge wire. Generally, the resistivity of the material changes with temperature. During synchronous parallel discharge, the transient characteristics of capacitor discharge will significantly affect the dynamic process of energy deposition. The dynamic coupling of resistance change and current change will reduce the influence of resistance change. In the application of preparing nanocomposites by synchronous pulsed discharge of dissimilar metal wires, the process requirement does not require the two wires to explode strictly synchronously, but it is necessary to ensure that the shock wave generated by the material that explodes first does not interfere with the melting or vaporization process of the other wire during the Joule heating stage. Since this process has a high tolerance for the explosion timing of the two wires and the resistance change is relatively gentle before the material phase change (especially in the initial stage of microsecond-level discharge), using the initial resistance value R for energy estimation can still meet the engineering accuracy requirements, that is,

[0055] E′ = I 2 Rt

[0056] Step 4: Calculate the ratio k2 of the actual energy injected into the discharge wire during the pulsed discharge Joule heating stage. Since the magnitude of the current in a parallel circuit is inversely proportional to the magnitude of the resistance, the following derivation can be carried out.

[0057]

[0058] The subscript 1 represents the graphite strip; the subscript 2 represents the silicon strip; t is the time; ρ1 and ρ2 are the initial resistivity of the two discharge wires respectively;

[0059] Step Five: Calculate the pulse discharge matching parameter K.

[0060]

[0061] From the above formula, it can be seen that the pulse discharge matching parameter K is related to the resistivity, sublimation energy of the discharge material and the length of the discharge wire. By adjusting the length of the discharge wire, the value of K is adjusted to be in the range of 0.8 - 1.25; here, both l1 and l2 are equal to 75 mm.

[0062] Step Six: According to the determined lengths l1 and l2 of the discharge wires, as well as the cross-sectional areas S1 and S2, and the sublimation energy per unit volume E S1 and E S2 , calculate the sublimation energy E required for the electro-explosion of the discharge wire.

[0063] E1 = E S1 S1l1 = 9.12 kJ

[0064] E2 = E S2 S2l2 = 2.84 kJ

[0065] E = E1 + E2 = 11.96 kJ

[0066] Step Seven: According to the above calculation results, process the graphite strip and the silicon strip to the preset size of 0.5 mm × 2 mm × 85 mm (with 5 mm installed on each end on the electrode, and the effective length is 75 mm). Since K = 1.24 > 1, that is, the explosion time of the graphite strip is slightly earlier than that of the silicon strip. Therefore, when installing the discharge wires, keep the graphite strip and the silicon strip parallel, and the distance between them is 3 mm. In this way, it can not only prevent the shock wave generated by the prior explosion of the graphite strip from damaging the Joule heating process of the silicon strip; at the same time, the smaller distance can also enable the synergistic effect between the explosion products of the two to form a composite material.

[0067] Step Eight: After installing the discharge wires, inject distilled water into the discharge tank so that the water surface submerges the discharge wires by about 5 cm. Seal the discharge tank, check whether there is any abnormality in the pulse discharge system, then start the pulse discharge system, set the initial energy storage to be greater than 11.96 kJ, and then carry out the discharge. After the discharge is over, open the tank lid. There are no obvious fragments in the tank, and the discharge products are evenly suspended in the distilled water, indicating that both the graphite strip and the silicon strip have completed the explosion. Subsequently, the sample is recovered, and after drying treatment, it is obtained as Figure 2The shown nano-silicon / graphene composite material has nano-particle sizes between 1 - 200 nm, and the lateral size of few-layer graphene is several to dozens of micrometers. Among them, the lattice spacing of spherical nano-particles is 0.19 nm, corresponding to the (220) crystal plane of silicon. It can be seen that some silicon nano-particles are wrapped by graphene with 5 layers.

[0068] Comparative Example 1:

[0069] Steps 1 to 4 are the same as those in Example 1.

[0070] Step 5: Calculate the pulse discharge matching parameter K.

[0071]

[0072] As can be seen from the above formula, the pulse discharge matching parameter K is related to the resistivity, sublimation energy of the discharge material, and the length of the discharge wire. The value of K is adjusted by adjusting the length of the discharge wire; here, let l1 equal 70 mm and l2 equal 75 mm.

[0073] Step 6: According to the determined lengths l1 and l2 of the discharge wires, as well as the cross-sectional areas S1 and S2, and the sublimation energy per unit volume E S1 and E S2 , calculate the sublimation energy E required for the electro-explosion of the discharge wire.

[0074] E1 = E S1 S1l1 = 8.51 kJ

[0075] E2 = E S2 S2l2 = 2.84 kJ

[0076] E = E1 + E2 = 11.35 kJ

[0077] Step 7: According to the above calculation results, process the graphite strip to the preset size of 0.5 mm × 2 mm × 80 mm (with 5 mm at each end installed on the electrode, and the effective length is 70 mm), and process the silicon strip to the preset size of 0.5 mm × 2 mm × 85 mm (with 5 mm at each end installed on the electrode, and the effective length is 75 mm). K = 1.42. When installing the discharge wire, keep the graphite strip and the silicon strip parallel, and the distance between them is 3 mm.

[0078] Step 8: After installing the discharge wire, inject distilled water into the discharge tank so that the water surface submerges the discharge wire by about 5 cm. Seal the discharge tank, check for any abnormalities in the pulse discharge system, then start the pulse discharge system, set the initial energy storage to be greater than 11.35 kJ, and then conduct the discharge. After the discharge is over, open the tank lid. There are small fragments of silicon at the bottom of the tank, and the distilled water becomes turbid. Recover and characterize the suspension in the discharge tank to obtain as Figure 3For the material shown, the sample is a graphene film, and no large amount of silicon particles are found on its surface. This indicates that under these conditions, when the graphite strip undergoes electrical explosion, the silicon strip is still in the primary stage of Joule heating. Therefore, the shock wave generated by the electrical explosion of the graphite strip destroys the silicon strip, forming silicon fragments that settle at the bottom of the tank, while the prematurely exploded graphite strip forms a graphene film that suspends in the distilled water.

[0079] Comparative Example 2:

[0080] Steps 1 to 4 are the same as those in Example 1.

[0081] Step 5: Calculate the pulse discharge matching parameter K.

[0082]

[0083] As can be seen from the above formula, the pulse discharge matching parameter K is related to the resistivity of the discharge material, the sublimation energy, and the length of the discharge wire. The value of K is adjusted by adjusting the length of the discharge wire. Here, let l1 be equal to 80 mm and l2 be equal to 60 mm.

[0084] Step 6: According to the determined lengths l1 and l2 of the discharge wires, as well as the cross-sectional areas S1 and S2, and the sublimation energy per unit volume E S1 and E S2 , calculate the sublimation energy E required for the electrical explosion of the discharge wire.

[0085] E1 = E S1 S1l1 = 9.73 kJ

[0086] E2 = E S2 S2l2 = 2.27 kJ

[0087] E = E1 + E2 = 12.00 kJ

[0088] Step 7: According to the above calculation results, process the graphite strip to the preset size of 0.5 mm × 2 mm × 90 mm (with 5 mm installed on each end on the electrode, and the effective length is 80 mm), and process the silicon strip to the preset size of 0.5 mm × 2 mm × 70 mm (with 5 mm installed on each end on the electrode, and the effective length is 60 mm). K = 0.7. When installing the discharge wire, keep the graphite strip and the silicon strip parallel, and the distance between them is 3 mm.

[0089] Step 8: After installing the discharge wire, pour distilled water into the discharge tank so that the water surface is about 5 cm above the discharge wire. Seal the discharge tank, check for any abnormalities in the pulse discharge system, then start the pulse discharge system, set the initial energy storage to be greater than 12.00 kJ, and then conduct the discharge. After the discharge is completed, open the tank lid. The distilled water becomes turbid, and there are visible graphite debris in the tank. Recover and characterize the suspension in the discharge tank to obtain as Figure 4For the material shown, the sample mainly consists of silicon nanoparticles with a particle size between 1 - 200 nm. There are also micron-sized graphite flakes in the sample. This indicates that under these conditions, the silicon strip undergoes electrical explosion earlier. The silicon strip experiences a complete Joule heating stage and explodes to form silicon nanoparticles, while at this time the graphite strip is still in the initial or middle stage of the Joule heating stage. The temperature and pressure inside it increase, causing the graphite strip to expand. The shock wave generated by the electrical explosion of the silicon strip also acts on it, thus forming graphite flakes. Due to insufficient discharge of the graphite strip, the two do not explode simultaneously, and the discharge products of the two cannot be well mixed and interact with each other, so a nano-silicon / graphene composite material cannot be formed.

[0090] The above specific description further details the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above is only a specific embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nanocomposite by synchronous pulsed discharge of dissimilar wires, characterized in that, It includes the following steps: Step 1: Select two discharge wires according to the experimental target materials. The cross-sectional areas of the two discharge wires are S1 and S2 respectively, the lengths are l1 and l2 respectively, and the sublimation energy per unit volume is E S1 and E S2 ; Step 2: Calculate the ratio k1 of the sublimation energies of the two discharge wires; Step 3: Calculate the energy injected into the discharge wire during the pulsed discharge Joule heating stage; E′ = ∫I 2 R t dt I is the current; R t is the resistance of the discharge wire; Use the initial resistance value R for energy estimation to obtain the energy E'; E′ = I 2 Rt Step 4: Calculate the ratio k2 of the actual energy injected into the discharge wire during the pulsed discharge Joule heating stage; The subscript 1 represents the first type of discharge wire, R1 is the resistance of the first type of discharge wire; the subscript 2 represents the second type of discharge wire, R2 is the resistance of the second type of discharge wire; t is time; ρ1 and ρ2 are the initial resistivity of the two types of discharge wires respectively; Step 5: Calculate the pulsed discharge matching parameter K; From the above formula, it can be seen that the pulsed discharge matching parameter K is related to the resistivity, sublimation energy of the discharge material and the length of the discharge wire. The value of K is adjusted by adjusting the length of the discharge wire; Step 6. Calculate the sublimation energy E required for the electro-explosion of the discharge wire based on the determined lengths l1 and l2 of the discharge wire, as well as the cross-sectional areas S1 and S2 and the sublimation energy per unit volume E S1 and E S2 , and calculate the sublimation energy E required for the electro-explosion of the discharge wire; E1 = E S1 S1l1 E2 = E S2 S2l2 E = E1 + E2 Step 7: Install the discharge wires with lengths l1 and l2 in step 6 into the pulsed discharge system, charge the high-voltage energy storage capacitor so that the initial energy storage is greater than the sublimation energy E in step 6, and conduct a synchronous pulsed discharge experiment to prepare the nanocomposite material.

2. The method for preparing a nanocomposite by synchronous pulse discharge of dissimilar wires according to claim 1, characterized in that, Adjust the value of K by adjusting the length of the discharge wire so that K is within the range of 0.8 - 1.25.

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