Method and device for in-situ construction of graphene coated nickel powder by utilizing self-pressure effect of polyhydric alcohol pyrolysis

Abstract

The method comprises the following steps: mixing nickel powder, an inorganic bulking agent and a liquid-phase polyol carbon source, carrying out high-shear stirring or ultrasonic dispersion to obtain a precursor composite material, introducing high-purity argon into the precursor composite material for replacement, and carrying out in-situ construction on the graphene-coated nickel powder by virtue of a polyhydric alcohol pyrolysis self-pressure effect, so as to obtain the graphene-coated nickel powder. The method comprises the following steps: heating a gas inlet until the oxygen content of an exhaust port is lower than 10ppm, limiting free diffusion of the gas by utilizing a semi-closed structure, then heating under the protection of an inert atmosphere to maintain a micro-positive pressure state, carrying out pyrolytic reaction, constructing a reducing atmosphere by reducing gas generated in situ by pyrolysis, rapidly filling gaps of powder with H2 and CO generated by pyrolysis, maintaining the micro-positive pressure state, and carrying out reaction, after the reaction is finished, a product is rapidly cooled, washed and dried to obtain graphene coated nickel powder; the industrial problem that the micro-nano metal powder is extremely easy to sinter and inactivate under high-temperature treatment is solved, and the prepared powder keeps the original sphericity and dispersity and can be directly used for precision machining processes such as silk-screen printing and ink-jet printing.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and powder metallurgy technology, specifically relating to a method and apparatus for in-situ construction of graphene-coated nickel powder using the self-pressure effect of polyol pyrolysis, in order to significantly improve the conductivity and antioxidant capacity of nickel powder, as well as related production equipment. Background Technology

[0002] With the rapid development of 5G communication, power semiconductors, new energy vehicle electronics, and flexible electronic devices, the electronics industry has an increasingly urgent need for high-performance conductive pastes, conductive adhesives, and electromagnetic shielding materials. Nickel powder, due to its excellent chemical stability, migration resistance, and relatively low cost, has become a core filler to replace precious metals such as gold and silver in the preparation of multilayer ceramic capacitor terminals, high-frequency antennas, and conductive adhesives. However, in practical applications, the conductivity of micro / nano-scale nickel powder falls far short of theoretical expectations. The intrinsic conductivity of metallic nickel is approximately 1.43 × 10⁻⁶. 7 However, after being prepared into a slurry or compacted, its apparent conductivity is usually only maintained at 50-100 S / cm, which severely limits its application in high-frequency, high-power circuits.

[0003] The primary cause of the deterioration in the conductivity of nickel powder is in-situ oxidation due to its extremely high surface activity. In an air environment, a dense nickel oxide film with a thickness of approximately 3-10 nm spontaneously forms on the surface of micro- and nano-sized nickel powder. According to solid-state physics theory, NiO is a typical wide-bandgap semiconductor (bandgap of approximately 3.7-4.0 eV), exhibiting a near-insulating state at room temperature. This oxide film forms an extremely high potential barrier at the powder particle interface, hindering the tunneling effect of charge carriers and leading to an increase in contact resistance. Even after treatment in a reducing atmosphere, nickel powder can still undergo secondary oxidation due to the presence of trace amounts of oxygen during subsequent powder metallurgy or slurry sintering processes. Therefore, how to construct a passivation layer on the surface of nickel powder that can both block oxygen penetration and provide a high-speed electron transport channel is a key research focus in this field.

[0004] Graphene, with its superior carrier mobility (>2×10⁻⁶), 5 cm 2 With its high viscosity (V·S) and chemical stability, graphene is considered an ideal protective layer for metals. Theoretically, growing graphene on nickel surfaces via chemical vapor deposition can achieve a dual effect of "corrosion resistance and electrical conductivity." However, in the practical application of graphene coating on nickel powder, there are two major insurmountable physical obstacles: 1) Supersaturated solid solution and precipitation mechanism of carbon atoms in nickel matrix (solubility bottleneck): According to the Ni-C binary phase diagram, the solubility of carbon in nickel increases sharply with increasing temperature. In the high-temperature range commonly used in traditional CVD processes (800°C-1000°C), the solubility of carbon in nickel is as high as 0.2 wt% or more. In stark contrast, the solubility of carbon in copper is extremely low (<0.001 wt%). On the copper surface, graphene follows a "surface-catalyzed self-limiting" growth mechanism, easily forming high-quality monolayers. However, on the nickel surface, graphene growth follows a "dissolution-segregation / precipitation" mechanism: at high temperatures, a large number of carbon atoms dissolve into the nickel interior, and during cooling, carbon atoms are driven by supersaturation to segregate violently to the surface. Because the precipitation kinetics are difficult to control precisely, the final result is often a graphite sheet or amorphous carbon with a thickness of tens of nanometers. These thick carbon layers not only disrupt the linear dispersive band structure of graphene, but also increase interfacial scattering due to interlayer van der Waals forces, which limits the improvement of the electrical conductivity of the composite powder and makes it difficult to achieve the intrinsic high conductivity of graphene.

[0005] 2) Low-Temperature Sintering and Morphology Failure Caused by Nanotechnology (Morphology Pain Point): Micro- and nano-sized nickel powders possess extremely high specific surface energy. According to Tammann's temperature theory, metal powders begin to undergo surface atomic diffusion and grain boundary migration when they reach 0.3-0.5 times their melting point (nickel's melting point is approximately 1455°C, and its sintering initiation temperature is around 450°C). Traditional CVD growth of graphene typically requires temperatures above 800°C to activate precursors such as methane. Under these high-temperature conditions, micro- and nano-sized nickel powders undergo severe thermal sintering, leading to bridging, agglomeration, and even fusion into lumps between particles. This not only completely destroys the powder's flowability and specific surface area but also makes it impossible to redisperse it for subsequent application in electronic paste preparation. Even mechanical pulverization will damage the formed graphene coating, resulting in the loss of antioxidant properties.

[0006] Currently, the academic community is attempting to improve the conductivity of nickel powder through methods such as reduced graphene oxide (rGO) coating or solution mixing. However, rGO suffers from a large number of lattice defects (sp). 3 The electrical conductivity of CVD-grown highly crystalline graphene (including hybrid sites and residual oxygen-containing functional groups) is much lower than that of CVD-grown graphene. Furthermore, existing CVD methods fail to resolve the conflict between "high-temperature sintering" and "thick-layer precipitation," resulting in persistently low compaction conductivity of the products.

[0007] Therefore, developing a coating technology that can both suppress the diffusion of carbon atoms into the metal to obtain high-quality graphene and effectively prevent thermal sintering between powder particles at low temperatures below 600°C has become a key scientific problem that urgently needs to be solved in the preparation of high-performance conductive nickel powder. Summary of the Invention

[0008] This invention overcomes the defects of poor quality of graphene on nickel surface, high process temperature, and easy sintering in the prior art, and provides a method and apparatus for in-situ construction of graphene-coated nickel powder using the self-pressure effect of polyol pyrolysis.

[0009] The technical solution of this invention is as follows: A method for in-situ constructing graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, the specific steps of which are as follows: (1) Nickel powder, inorganic loosening agent and liquid polyol carbon source are mixed in a preset ratio and dispersed by high shear stirring or ultrasonication so that the polyol molecules can form a liquid phase impregnation layer with a thickness of nanometers by using the hydrogen bonding between their hydroxyl groups and the oxide layer on the nickel surface, thus obtaining the precursor composite material. (2) The precursor composite material is placed in the reactor. First, high-purity argon gas (purity ≥ 99.99%) is introduced for replacement until the oxygen content at the exhaust port is less than 10 ppm. The semi-closed reactor structure restricts the free diffusion of gas, providing a spatial basis for the subsequent in-situ self-generated atmosphere. Then, the temperature is raised under the protection of an inert atmosphere, and the pyrolysis reaction is carried out under a slightly positive pressure. Within this specific temperature range, the surface of nickel powder acts as a catalytic active center, inducing the polyol to undergo dehydrogenation and bond breaking reactions. The loosening agent not only prevents sintering but also acts as a "gas microchannel," facilitating the in-situ gas penetration to the surface of nickel powder. The instantaneous pressure formed by the gaseous products generated by the thermal decomposition of polyol in the confined space not only provides a reducing atmosphere but also serves as the driving force for the subsequent gas phase deposition reaction. The in-situ pyrolysis of polyol is used to generate the gaseous products. The generated reducing gas creates a reducing atmosphere, and the H2 and CO produced by pyrolysis quickly fill the gaps between the powder particles. A pressure relief valve is set to maintain a slightly positive pressure state inside the reactor for the reaction. As the gas production increases, the pressure inside the chamber rises to a slightly positive pressure state. This pressure effectively increases the collision frequency of active carbon atoms on the nickel surface, compensating for the insufficient reaction kinetics at low temperatures. The following synergistic reactions occur during this stage: high concentrations of H2 and CO reduce NiO on the nickel surface to highly active metallic Ni crystal planes; active carbon atoms nucleate on the reduced Ni crystal planes. Because the temperature is lower than the bulk diffusion activation energy of carbon in nickel, the carbon atoms are confined to the surface for two-dimensional rearrangement, avoiding dissolution into the interior; oxygen-containing free radicals generated by the pyrolysis of polyols have a selective etching effect on amorphous carbon, ensuring that the number of graphene layers is 1-10 and the lattice defects are low. (3) After the reaction is complete, the product is rapidly cooled under a reducing atmosphere or an inert atmosphere, then washed to remove the loosening agent and dried to obtain graphene-coated nickel powder.

[0010] Step (1) The nickel powder has a specific surface area of ​​0.5-2.0 m². 2 / g of nickel powder, the inorganic loosening agent is selected from inorganic materials with high thermal stability, including but not limited to MgO, Al2O3, Na2CO3, NaCl or K2SO4, and its particle size should be one order of magnitude smaller than the nickel powder particle size to achieve physical separation of the nickel powder particle surface; the liquid phase polyol carbon source is selected from at least one of ethylene glycol, propylene glycol, glycerol or diethylene glycol.

[0011] Step (1) The amount of polyol added is 0.5%-5% of the mass of nickel powder, and the mass ratio of nickel powder to inorganic loosening agent is 1:2-1:10.

[0012] Step (2) The pyrolysis reaction is carried out under a slightly positive pressure by heating the temperature to 450°C-600°C at a heating rate of 5-20°C / min, the pressure of the reaction is 0.01-0.5MPa, and the reaction time is 5-30min.

[0013] After the reaction in step (3) is completed, the cooling system is forcibly turned on to cool the sample to below 200°C within 5 minutes. The diffusion state of carbon atoms is "frozen" by physical rapid cooling to prevent secondary segregation of dissolved carbon during the cooling process.

[0014] Step (3) Remove the loosening agent with dilute hydrochloric acid or deionized water with a concentration of 0.5-1.0 mol / L, and obtain graphene-coated nickel powder by washing and vacuum drying.

[0015] This invention also provides an apparatus for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, comprising: Feeding system 1: Used for continuous oxygen-free supply of precursor composite materials; Spiral propulsion reaction system 2: includes a spiral tube heater 2-1 with multiple independent temperature control zones, wherein the spiral tube heater 2-1 is equipped with a spiral shaft 2-2 for mixing and continuously propulsing materials, and the spiral shaft 2-2 is driven to rotate by a drive motor; an exhaust pipe is provided on the side of the tail of the spiral tube heater 2-1; Temperature control system 3: includes multiple temperature sensors installed inside the spiral tube furnace 2-1 to monitor the temperature inside the spiral tube furnace 2-1; Pressure control system 4 includes a pressure monitor 4-1 installed on the spiral tube furnace 2-1 and a constant pressure relief valve 4-2 installed on the exhaust pipe of the spiral tube furnace 2-1, so as to maintain the pressure in the reaction tube at a slightly positive pressure state by utilizing the in-situ gas generated by the pyrolysis of polyols. Cooling discharge system 5: includes cooling jacket 5-1 and tail gas purification device 5-2. Cooling jacket 5-1 is installed outside the discharge pipe of spiral tube heater 2-1. Tail gas purification device 5-2 is installed at the outlet end of the discharge pipe of spiral tube heater 2-1. Tail gas purification device 5-2 is used to purify pyrolysis tail gas.

[0016] The feeding system 1 includes a liquid phase impregnation mixer 1-1 and a double-stage vacuum lock hopper 1-2. The liquid phase impregnation mixer 1-1 is installed inside the double-stage vacuum lock hopper 1-2. The liquid phase impregnation mixer 1-1 is used to stir and coat the polyol spray onto the surface of the solid powder. The double-stage vacuum lock hopper 1-2 includes an upper lock hopper, a transition chamber, and a lower lock hopper. The transition chamber is equipped with an inert gas replacement port. The liquid phase impregnation mixer 1-1 is equipped with an air inlet and an exhaust port for atmosphere adjustment. The bottom of the lower lock hopper of the double-stage vacuum lock hopper 1-2 is connected to the feed port.

[0017] The spiral tube heater 2-1 is divided into a preheating section, a pyrolysis reaction section, and a heat preservation section along the material feeding direction. Each section is equipped with an independent temperature sensor and an electric heating element. The spiral shaft 2-2 is equipped with spiral blades from the feed inlet at the bottom of the feeding system 1 to the tail of the spiral tube heater 2-1. A closed tube is installed on the outside of the spiral shaft 2-2.

[0018] The spiral tube heating furnace 2-1 also has a cooling sealing surface inside the discharge pipe, which is used to reduce the temperature of the product to below 200°C under the protection of a reducing atmosphere.

[0019] The device also includes a controller, which is connected to various temperature sensors, electric heating elements, pressure monitoring gauge 4-1, and constant pressure relief valve 4-2.

[0020] This invention achieves the following specific beneficial effects through the coupled optimization of carbon source form, reaction kinetics, and equipment structure: 1. Breakthrough conductivity enhancement effect and interfacial carrier transport characteristics The graphene-coated nickel powder prepared by this invention exhibits an order-of-magnitude improvement in compacted conductivity. The physical mechanism lies in the fact that low-temperature pyrolysis avoids the high solubility temperature range of nickel for carbon, allowing graphene to be anchored on the nickel surface in a near-ideal single layer or structure. This in-situ growth-formed chemical bonding interface eliminates the van der Waals force gaps present in the physical coating method, greatly reducing the interfacial contact resistance. Its conductivity is close to or even exceeds that of traditional silver-coated nickel powder, providing a solid material basis for realizing "nickel instead of silver" in electronic pastes.

[0021] 2. Extremely high technological economy and environmental friendliness. Unlike traditional CVD processes that require continuous consumption of high-purity hydrogen and high-purity methane, this invention utilizes liquid-phase polyols as an "integrated" carbon and reduction source. The H2 and CO generated during the cracking of polyol molecules have extremely high reducing activity, which can remove the oxide film on the nickel surface in situ without the need to purchase an additional high-pressure hydrogen system. In addition, as an industrial-grade bulk chemical, polyols are much cheaper than high-purity specialty gases. Combined with the condensation and recovery system in the equipment, the carbon source utilization rate is increased by more than 40%, and the overall preparation cost is only 20%-30% of that of traditional CVD processes.

[0022] 3. Precise thermal morphology control and zero-sintering characteristics This invention successfully solves the industry problem of micro-nano metal powders being prone to sintering and deactivation under high-temperature treatment. By limiting the reaction temperature to below 600℃ (far lower than the rapid sintering start temperature of nickel powder) and supplementing it with an inorganic loosening agent with high thermal stability, a dual protection mechanism of "physical isolation + low-temperature coating" is constructed. The powder prepared retains its original sphericity and dispersibility, with a specific surface area change rate of less than 5%, and can be directly used in precision processing such as screen printing and inkjet printing without the need for secondary ball milling.

[0023] 4. Excellent chemical stability and corrosion resistance life. The high-quality graphene coating is like a dense, atomic-level "preservative film" covering the surface of nickel powder. The resulting product, after being exposed to a strong oxidizing environment at 200°C for 100 hours, shows a conductivity change rate of less than 3%, demonstrating excellent oxidation resistance. Under acid and alkali corrosion environments, its electrochemical stability is more than 10 times higher than that of the original nickel powder, greatly extending the service life of end products such as conductive adhesives and electromagnetic shielding coatings under extreme working conditions. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the device. In the diagram: 1-Feeding system, 2-Screw propulsion reaction system, 2-1-Screw tube heater, 2-2-Screw shaft, 3-Temperature control system, 4-Pressure regulation system, 4-1-Pressure monitor, 4-2-Pressure relief valve, 5-Cooling discharge system, 5-1-Jacket cooling, 5-2-Tail gas purification device; Figure 2 The resistivity curve of the product obtained in Example 1 as a function of pressure is shown. Figure 3 The electrical conductivity of the product obtained in Example 1 varies with pressure. Figure 4 The curve showing the change in compacted density of the product obtained in Example 1 as a function of pressure; Figure 5 SEM images of the product and raw nickel powder were obtained for Example 1. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] Example 1 A device for in-situ construction of graphene-coated nickel powder using the self-pressure effect of polyol pyrolysis, such as... Figure 1 As shown, it includes: Feeding system 1 includes a connected liquid phase impregnation mixer 1-1 and a double-stage vacuum lock hopper 1-2. The liquid phase impregnation mixer 1-1 is installed inside the double-stage vacuum lock hopper 1-2. The liquid phase impregnation mixer 1-1 stirs the polyol molecules to form a liquid phase impregnation layer with a thickness of nanometers by using the hydrogen bonding between their hydroxyl groups and the nickel surface oxide layer, thus obtaining the precursor composite material. The double-stage vacuum lock hopper 1-2 includes an upper lock hopper, a transition chamber, and a lower lock hopper. The transition chamber is equipped with an inert gas replacement interface. The liquid phase impregnation mixer 1-1 is equipped with an air inlet and an air outlet for atmosphere adjustment. The bottom of the lower lock hopper of the double-stage vacuum lock hopper 1-2 is connected to the feed port. Feeding system 1 is used for the continuous oxygen-free supply of the precursor composite material. Spiral propulsion reaction system 2: The spiral propulsion reaction system 2 is connected to the bottom feed inlet of the lower lock hopper of the double-stage vacuum lock hopper 1-2. The spiral propulsion reaction system 2 includes a spiral tube heater 2-1 with multiple independent temperature control zones. The spiral tube heater 2-1 is equipped with a spiral shaft 2-2 for material mixing and continuous propulsion. The spiral shaft 2-2 is driven to rotate by a drive motor. An exhaust pipe is provided on the side of the tail of the spiral tube heater 2-1. The spiral tube heater 2-1 is divided into a preheating section, a pyrolysis reaction section, and a heat preservation section along the material propulsion direction. Each section is equipped with an independent temperature sensor and an electric heating element. The spiral shaft 2-2 is connected to the feed system. From the bottom feed inlet of the lower vacuum lock hopper 1-2 to the tail of the spiral tube heater 2-1, spiral blades are installed. After the material comes out of the feeding system 1, it reacts and is propelled on the spiral blades. A closed tube is installed on the outside of the spiral shaft 2-2 to prevent the material from scattering. The inside of the discharge pipe of the spiral tube heater 2-1 is also equipped with a cooling sealing surface to rapidly reduce the temperature of the product to below 200°C under the protection of a reducing atmosphere. A pressure-resistant seal is installed between the drive motor and the spiral shaft 2-2. The double-stage vacuum lock hopper 1-2 is sealed to the spiral tube heater 2-1, forming a closed space inside the spiral tube heater 2-1. Temperature control system 3: includes multiple temperature sensors. Temperature sensors are installed in the preheating section, pyrolysis reaction section and heat preservation section of the spiral tube heater 2-1, and a temperature sensor is also installed in the discharge pipe to monitor the temperature inside the spiral tube heater 2-1. Pressure control system 4: includes a pressure monitor 4-1 installed on the spiral tube heater 2-1; a constant pressure relief valve 4-2 installed on the exhaust pipe of the spiral tube heater 2-1; utilizing the instantaneous expansion effect of the gas produced by polyol cracking, a dynamic pressure balance is formed by the constant pressure relief valve 4-2 installed at the tail of the spiral tube heater 2-1 and the material seal at the feed end, thus constructing a micro-positive pressure reaction environment; Cooling discharge system 5: includes cooling jacket 5-1 and tail gas purification device 5-2. Cooling jacket 5-1 is set outside the discharge pipe of spiral tube heater 2-1. Cooling water is filled inside cooling jacket 5-1. Tail gas purification device 5-2 is set at the outlet end of discharge pipe of spiral tube heater 2-1. Tail gas purification device 5-2 is a container filled with alkaline substances (such as sodium hydroxide solution or calcium oxide). Tail gas is discharged after being purified by tail gas purification device 5-2. The device in this embodiment can also be equipped with a controller, which is connected to various temperature sensors, electric heating elements, pressure monitoring gauge 4-1, and constant pressure relief valve 4-2. The controller is a commercially available product that collects, stores, and feeds back various monitoring data.

[0027] Example 2 A method for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, employing the apparatus of Example 1, includes the following specific steps: (1) Weigh 100g of spherical nickel powder with an average particle size of 1.0μm, add 500g of active nano MgO (its particle size should be one order of magnitude smaller than the nickel powder particle size) and 5mL of anhydrous ethylene glycol and mix. Feed the mixture into the double-stage vacuum lock bucket 1-2 and disperse it in the liquid phase impregnation mixer 1-1 by high shear stirring for 1h. This allows the polyol molecules to form a liquid phase impregnation layer with a thickness of 5-20nm by using the hydrogen bonding between their hydroxyl groups and the oxide layer on the nickel surface, thus obtaining the precursor composite material. (2) The mixed precursor composite material is fed into the screw shaft 2-2 from the bottom inlet of the feeding system 1. The screw shaft 2-2 rotates into the pyrolysis section of the spiral tube heater 2-1. High-purity argon gas (purity ≥ 99.99%) is first introduced into the spiral tube heater 2-1 for replacement until the oxygen content at the exhaust port is lower than 10 ppm. The semi-closed structure restricts the free diffusion of gas, providing a spatial basis for the subsequent construction of the in-situ self-generated atmosphere. Then, the temperature is raised under the protection of the argon atmosphere to carry out the pyrolysis reaction. The opening pressure is set to 0.12 MPa, and the heating rate is 10°C / min. The temperature is raised to 500°C, and the pyrolysis reaction takes 15 minutes. Within this specific temperature range, the surface of the nickel powder acts as a catalytic active center, inducing dehydrogenation and bond breaking reactions in the polyol. The loosening agent not only prevents sintering but also acts as a "gas microchannel," facilitating the in-situ permeation of gas to the surface of the nickel powder. The instantaneous pressure formed by the gaseous products generated by the thermal decomposition of the polyol in the confined space not only provides a reducing atmosphere but also serves as the driving force for subsequent vapor deposition reactions. During the reaction, the pressure monitoring instrument 4-1 monitors the internal pressure of the reaction, and the constant pressure relief valve 4-2 regulates the pressure. A reducing atmosphere is constructed using the reducing gas generated in situ by the pyrolysis of polyols. The H2 and CO produced by the pyrolysis quickly fill the gaps between the powder particles. A pressure relief valve is set to maintain a slightly positive pressure state inside the reactor for the reaction. As the gas production increases, the pressure inside the chamber rises to a slightly positive pressure state. This pressure effectively increases the collision frequency of active carbon atoms on the nickel surface, compensating for the insufficient reaction kinetics at low temperatures. The following synergistic reactions occur during this stage: high concentrations of H2 and CO reduce NiO on the nickel surface to highly active metallic Ni crystal planes; active carbon atoms nucleate on the reduced Ni crystal planes. Because the temperature is lower than the bulk diffusion activation energy of carbon in nickel, the carbon atoms are confined to the surface for two-dimensional rearrangement, avoiding dissolution into the interior; oxygen-containing free radicals generated by the pyrolysis of polyols have a selective etching effect on amorphous carbon, ensuring that the number of graphene layers is 1-10 and the lattice defects are low. (3) After the reaction is completed, the product is sent from the spiral shaft 2-2 to the tail discharge pipe of the spiral tube heating furnace 2-1. Under the action of the cooling jacket 5-1, the product is rapidly cooled to below 100°C under the protection of argon atmosphere. After collection, it is washed with 1 mol / L dilute hydrochloric acid until the filtrate is neutral. Then it is dehydrated with anhydrous ethanol and dried under vacuum at 60°C to obtain graphene-coated nickel powder. The gas generated in the process enters the tail gas purification device 5-2 for purification and is then discharged into the air.

[0028] The composite powder obtained in Example 1 was tested. SEM showed that the nickel powder surface coating was continuous and intact, with a thickness of 1.2-2.5 nm, corresponding to 3-5 graphene layers. D / I G=0.11, the four-probe method was used to test the conductivity under a compaction pressure of 0-30MPa. The results are shown in Table 1. The highest conductivity was 6090S / cm. When the powder was placed in a 200℃ forced-air drying oven for 100h to accelerate aging, the conductivity was 5961S / cm, and the decrease rate was only 2.1%.

[0029] Table 1

[0030] Figure 2 The graph shows the resistivity of the product in Example 1 as a function of pressure. As can be seen from the graph, the resistivity of the powder decreases significantly with increasing pressure. When the pressure is 30 MPa, the resistivity of the powder is less than 0.0002 Ω·cm.

[0031] Figure 3 The graph shows the change in electrical conductivity of the product of Example 1 with pressure. As can be seen from the graph, the electrical conductivity of the powder increases significantly with increasing pressure. When the pressure is 30 MPa, the electrical conductivity of the powder exceeds 6000 S / cm.

[0032] Figure 4 The graph shows the change in compacted density of the product from Example 1 as a function of pressure. It can be seen from the graph that the powder density increases linearly with pressure, reaching 3.3 g / cm³ at a pressure of 30 MPa. 3 .

[0033] Figure 5 The SEM images of the product and raw nickel powder obtained in Example 1 are shown in the left image and the right image. As can be seen from the images, a transparent graphene veil appeared on the surface of the powder after processing, and the pores and grain boundaries under the graphene coating layer are clearly visible.

[0034] Example 3 A method for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, employing the apparatus of Example 1, includes the following specific steps: (1) Weigh out a specific surface area of ​​1.5m² 2 Spherical nickel powder of / g is mixed with micronized K2SO4 (its particle size should be one order of magnitude smaller than the nickel powder particle size) at a mass ratio of 1:5, and then glycerol with a mass fraction of 3% of spherical nickel powder is added. The mixture is fed into a double-stage vacuum lock hopper 1-2 and dispersed in a liquid phase impregnation mixer 1-1 by high shear stirring for 0.5h. This allows the polyol molecules to form a liquid phase impregnation layer with a thickness of nanometers by utilizing the hydrogen bonding between their hydroxyl groups and the oxide layer on the nickel surface, thus obtaining the precursor composite material. (2) The mixed precursor composite material is fed into the screw shaft 2-2 from the bottom inlet of the feeding system 1. The screw shaft 2-2 rotates into the pyrolysis section of the spiral tube heater 2-1. The spiral tube heater 2-1 is first purged with high-purity argon (purity ≥ 99.99%) to replace the oxygen content at the exhaust port until it is below 10 ppm. The semi-closed structure restricts the free diffusion of the gas, providing a spatial basis for the subsequent construction of the in-situ self-generated atmosphere. Then, the temperature is raised under the protection of the argon atmosphere to carry out the pyrolysis reaction. The opening pressure is set to 0.18 MPa, and the heating rate is 15°C / min. The temperature was raised to 530°C, and the pyrolysis reaction time was 15 minutes. Within this specific temperature range, the surface of the nickel powder served as a catalytic active center, inducing dehydrogenation and bond breaking reactions in the polyol. The loosening agent not only prevented sintering but also acted as a "gas microchannel," facilitating the in-situ permeation of gas to the surface of the nickel powder. The instantaneous pressure generated by the gaseous products of the polyol's thermal decomposition within the confined space not only provided a reducing atmosphere but also served as the driving force for subsequent vapor deposition reactions. During the reaction, the pressure monitoring instrument 4-1 monitored the internal pressure of the reaction, and the constant pressure relief valve 4-2 regulated the pressure. A reducing atmosphere is constructed using the reducing gas generated in situ by the pyrolysis of polyols. The H2 and CO produced by the pyrolysis quickly fill the gaps between the powder particles. A pressure relief valve is set to maintain a slightly positive pressure state inside the reactor for the reaction. As the gas production increases, the pressure inside the chamber rises to a slightly positive pressure state. This pressure effectively increases the collision frequency of active carbon atoms on the nickel surface, compensating for the insufficient reaction kinetics at low temperatures. The following synergistic reactions occur during this stage: high concentrations of H2 and CO reduce NiO on the nickel surface to highly active metallic Ni crystal planes; active carbon atoms nucleate on the reduced Ni crystal planes. Because the temperature is lower than the bulk diffusion activation energy of carbon in nickel, the carbon atoms are confined to the surface for two-dimensional rearrangement, avoiding dissolution into the interior; oxygen-containing free radicals generated by the pyrolysis of polyols have a selective etching effect on amorphous carbon, ensuring that the number of graphene layers is 1-10 and the lattice defects are low. (3) After the reaction is completed, the product is sent from the spiral shaft 2-2 to the tail discharge pipe of the spiral tube heating furnace 2-1. Under the action of the cooling jacket 5-1, the product is rapidly cooled to below 100℃ at a rate of 100℃ / min under the protection of argon atmosphere. After collection, it is washed multiple times with deionized water at 80℃ to remove K2SO4. Then it is dehydrated with anhydrous ethanol and vacuum dried at 60℃ to obtain graphene-coated nickel powder. The gas generated in the process enters the tail gas purification device 5-2 for purification and is then discharged into the air.

[0035] Example 4 A method for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, employing the apparatus of Example 1, includes the following specific steps: (1) Weigh out spherical nickel powder with an average particle size of 1.0 μm, add 4 times the mass of Al2O3 (the particle size should be one order of magnitude smaller than the particle size of nickel powder), add 1% of the mass of nickel powder diethylene glycol as a carbon source and mix. Feed the material into the double-stage vacuum lock bucket 1-2 and disperse it in the liquid phase impregnation mixer 1-1 by high shear stirring for 1 h, so that the polyol molecules can form a liquid phase impregnation layer with a thickness of nanometers by using the hydrogen bonding between their hydroxyl groups and the oxide layer on the surface of nickel, and obtain the precursor composite material; (2) The mixed precursor composite material is fed into the spiral shaft 2-2 from the bottom inlet of the feeding system 1. The spiral shaft 2-2 rotates into the pyrolysis section of the spiral tube heater 2-1. High-purity argon gas (purity ≥ 99.99%) is first introduced into the spiral tube heater 2-1 for replacement until the oxygen content at the exhaust port is lower than 10 ppm. The semi-closed structure restricts the free diffusion of gas, providing a spatial basis for the subsequent construction of the in-situ self-generated atmosphere. Then, the temperature is raised under the protection of the argon atmosphere to carry out the pyrolysis reaction. The opening pressure is set to 0.15 MPa, and the heating rate is 10°C / min. The temperature was raised to 480°C, and the pyrolysis reaction time was 25 minutes. Within this specific temperature range, the surface of the nickel powder served as a catalytic active center, inducing dehydrogenation and bond breaking reactions in the polyol. The loosening agent not only prevented sintering but also acted as a "gas microchannel," facilitating the in-situ permeation of gas to the surface of the nickel powder. The instantaneous pressure formed by the gaseous products generated by the thermal decomposition of the polyol in the confined space not only provided a reducing atmosphere but also served as the driving force for subsequent vapor deposition reactions. During the reaction, the pressure monitoring instrument 4-1 monitored the internal pressure of the reaction, and the constant pressure relief valve 4-2 regulated the pressure. A reducing atmosphere is constructed using the reducing gas generated in situ by the pyrolysis of polyols. The H2 and CO produced by the pyrolysis quickly fill the gaps between the powder particles. A pressure relief valve is set to maintain a slightly positive pressure state inside the reactor for the reaction. As the gas production increases, the pressure inside the chamber rises to a slightly positive pressure state. This pressure effectively increases the collision frequency of active carbon atoms on the nickel surface, compensating for the insufficient reaction kinetics at low temperatures. The following synergistic reactions occur during this stage: high concentrations of H2 and CO reduce NiO on the nickel surface to highly active metallic Ni crystal planes; active carbon atoms nucleate on the reduced Ni crystal planes. Because the temperature is lower than the bulk diffusion activation energy of carbon in nickel, the carbon atoms are confined to the surface for two-dimensional rearrangement, avoiding dissolution into the interior; oxygen-containing free radicals generated by the pyrolysis of polyols have a selective etching effect on amorphous carbon, ensuring that the number of graphene layers is 1-10 and the lattice defects are low. (3) After the reaction is completed, the product is sent from the spiral shaft 2-2 to the tail discharge pipe of the spiral tube heating furnace 2-1. Under the action of the cooling jacket 5-1, the product is rapidly cooled to below 100°C under the protection of argon atmosphere. After collection, it is soaked in 1.0 mol / L sodium hydroxide solution to remove Al2O3, and then washed with water until neutral to obtain a continuous graphene film on the surface of nickel powder with a coating rate of more than 99%. Antioxidant experiment shows that the powder does not have a significant weight gain when heated in air at 250°C for 2 hours. The gas generated in the process enters the tail gas purification device 5-2 for purification and then is discharged into the air.

[0036] Example 5 A method for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, employing the apparatus of Example 1, includes the following specific steps: (1) Weigh out spherical nickel powder with an average particle size of 1.0 μm, add 3 times the mass of MgO (its particle size should be one order of magnitude smaller than the nickel powder particle size), add a mixture of ethylene glycol and propylene glycol (1:1) as a carbon source, the amount of carbon source added is 5% of the mass of nickel powder, after mixing, feed through a double-stage vacuum lock bucket 1-2, and disperse in a liquid phase impregnation mixer 1-1 by high shear stirring for 1 h, so that the polyol molecules can form a liquid phase impregnation layer with a thickness of nanometers by using the hydrogen bonding of their hydroxyl groups with the oxide layer on the surface of nickel, and obtain the precursor composite material; (2) The precursor composite material is fed into the spiral shaft 2-2 from the bottom feed port of the feeding system 1. The spiral shaft 2-2 rotates into the pyrolysis section of the spiral tube heater 2-1. High-purity argon gas (purity ≥99.99%) is first introduced into the spiral tube heater 2-1 for replacement until the oxygen content at the exhaust port is lower than 10ppm. The semi-closed structure restricts the free diffusion of gas, providing a spatial basis for the subsequent construction of the in-situ self-generated atmosphere. Then, the pyrolysis reaction is carried out under the protection of the argon atmosphere. The opening pressure is set to 0.5MPa, and the temperature is increased at a rate of 10°C / min. The pyrolysis reaction was carried out at 510°C for 5 minutes. Within this specific temperature range, the surface of the nickel powder served as a catalytic active center, inducing dehydrogenation and bond breaking reactions in the polyol. The loosening agent not only prevented sintering but also acted as a "gas microchannel," facilitating the in-situ permeation of gas to the surface of the nickel powder. The instantaneous pressure generated by the gaseous products of the polyol's thermal decomposition within the confined space not only provided a reducing atmosphere but also served as the driving force for subsequent vapor deposition reactions. During the reaction, the pressure monitoring instrument 4-1 monitored the internal pressure of the reaction, and the constant pressure relief valve 4-2 regulated the pressure. A reducing atmosphere is constructed using the reducing gas generated in situ by the pyrolysis of polyols. The H2 and CO produced by the pyrolysis quickly fill the gaps between the powder particles. A pressure relief valve is set to maintain a slightly positive pressure state inside the reactor for the reaction. As the gas production increases, the pressure inside the chamber rises to a slightly positive pressure state. This pressure effectively increases the collision frequency of active carbon atoms on the nickel surface, compensating for the insufficient reaction kinetics at low temperatures. The following synergistic reactions occur during this stage: high concentrations of H2 and CO reduce NiO on the nickel surface to highly active metallic Ni crystal planes; active carbon atoms nucleate on the reduced Ni crystal planes. Because the temperature is lower than the bulk diffusion activation energy of carbon in nickel, the carbon atoms are confined to the surface for two-dimensional rearrangement, avoiding dissolution into the interior; oxygen-containing free radicals generated by the pyrolysis of polyols have a selective etching effect on amorphous carbon, ensuring that the number of graphene layers is 1-10 and the lattice defects are low. (3) After the reaction is completed, the product is sent from the spiral shaft 2-2 to the tail discharge pipe of the spiral tube heating furnace 2-1. Under the action of the cooling jacket 5-1, the product is rapidly cooled to below 100°C under the protection of argon atmosphere. After collection, it is washed with 1 mol / L dilute hydrochloric acid until the filtrate is neutral. Then it is dehydrated with anhydrous ethanol and dried under vacuum at 60°C to obtain graphene-coated nickel powder. The gas generated in the process enters the tail gas purification device 5-2 for purification and is then discharged into the air.

[0037] Example 6 A method for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, employing the apparatus of Example 1, includes the following specific steps: (1) Weigh 100g of spherical nickel powder with an average particle size of 1.0μm, add 100g of MgO and 100g of NaCl as a loosening agent (the particle size should be one order of magnitude smaller than the nickel powder particle size), 5mL of ethylene glycol, feed into the double-stage vacuum lock bucket 1-2, and disperse in the liquid phase impregnation mixer 1-1 by high shear stirring for 1h, so that the polyol molecules can form a liquid phase impregnation layer with a thickness of nanometers by using the hydrogen bonding between their hydroxyl groups and the oxide layer on the surface of nickel, and obtain the precursor composite material; (2) The precursor composite material is fed into the spiral shaft 2-2 from the bottom inlet of the feeding system 1. The spiral shaft 2-2 rotates into the pyrolysis section of the spiral tube heater 2-1. High-purity argon gas (purity ≥ 99.99%) is first introduced into the spiral tube heater 2-1 for replacement until the oxygen content at the exhaust port is lower than 10 ppm. The semi-closed structure restricts the free diffusion of gas, providing a spatial basis for the subsequent construction of the in-situ self-generated atmosphere. Then, the temperature is raised under the protection of the argon atmosphere to carry out the pyrolysis reaction. The opening pressure is set to 0.1 MPa, and the temperature is raised at a rate of 10°C / min to 0.1 MPa. At 500°C, the pyrolysis reaction time is 15 minutes. Within this specific temperature range, the surface of the nickel powder acts as a catalytic active center, inducing dehydrogenation and bond breaking reactions in the polyol. The loosening agent not only prevents sintering but also acts as a "gas microchannel," facilitating the in-situ permeation of gas to the surface of the nickel powder. The instantaneous pressure formed by the gaseous products generated by the thermal decomposition of the polyol in the confined space not only provides a reducing atmosphere but also serves as the driving force for subsequent vapor deposition reactions. During the reaction, the pressure monitoring instrument 4-1 monitors the internal pressure of the reaction, and the constant pressure relief valve 4-2 regulates the pressure. A reducing atmosphere is constructed using the reducing gas generated in situ by the pyrolysis of polyols. The H2 and CO produced by the pyrolysis quickly fill the gaps between the powder particles. A pressure relief valve is set to maintain a slightly positive pressure state inside the reactor for the reaction. As the gas production increases, the pressure inside the chamber rises to a slightly positive pressure state. This pressure effectively increases the collision frequency of active carbon atoms on the nickel surface, compensating for the insufficient reaction kinetics at low temperatures. The following synergistic reactions occur during this stage: high concentrations of H2 and CO reduce NiO on the nickel surface to highly active metallic Ni crystal planes; active carbon atoms nucleate on the reduced Ni crystal planes. Because the temperature is lower than the bulk diffusion activation energy of carbon in nickel, the carbon atoms are confined to the surface for two-dimensional rearrangement, avoiding dissolution into the interior; oxygen-containing free radicals generated by the pyrolysis of polyols have a selective etching effect on amorphous carbon, ensuring that the number of graphene layers is 1-10 and the lattice defects are low. (3) After the reaction is completed, the product is sent from the spiral shaft 2-2 to the tail discharge pipe of the spiral tube heating furnace 2-1. Under the action of the cooling jacket 5-1, the product is rapidly cooled to below 100°C under the protection of argon atmosphere. After collection, it is washed with 1mol / L dilute hydrochloric acid until the filtrate is neutral. Then it is dehydrated with anhydrous ethanol and vacuum dried at 60°C to obtain graphene-coated nickel powder. The gas generated in the process enters the tail gas purification device 5-2 for purification and is then discharged into the air. Continuous production with a yield of >2kg / h is achieved. The product consistency is better than that of batch reactors, and the graphene coating thickness fluctuates by less than 1nm.

[0038] Example 7 A method for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, employing the apparatus of Example 1, includes the following specific steps: (1) Weigh out high specific surface area nickel powder, add 3 times the mass of nickel powder MgO (its particle size should be one order of magnitude smaller than the nickel powder particle size) as a loosening agent, add 2% of the mass of nickel powder ethylene glycol as a carbon source, mix and feed through a double-stage vacuum lock bucket 1-2, disperse in a liquid phase impregnation mixer 1-1 by high shear stirring for 1 hour, so that the polyol molecules can form a liquid phase impregnation layer with a thickness of nanometers by using the hydrogen bonding of its hydroxyl groups with the oxide layer on the nickel surface, and obtain the precursor composite material; (2) The precursor composite material is fed into the spiral shaft 2-2 from the bottom feed port of the feeding system 1. The spiral shaft 2-2 rotates into the pyrolysis section of the spiral tube heater 2-1. High-purity argon gas (purity ≥ 99.99%) is first introduced into the spiral tube heater 2-1 for replacement until the oxygen content at the exhaust port is lower than 10 ppm. The semi-closed structure restricts the free diffusion of gas, providing a spatial basis for the subsequent construction of the in-situ self-generated atmosphere. Then, the pyrolysis reaction is carried out under the protection of the argon atmosphere. The opening pressure is set to 0.12 MPa, and the temperature is increased at a rate of 10°C / min. The pyrolysis reaction was carried out at 520°C for 20 minutes. Within this specific temperature range, the surface of the nickel powder served as a catalytic active center, inducing dehydrogenation and bond breaking reactions in the polyol. The loosening agent not only prevented sintering but also acted as a "gas microchannel," facilitating the in-situ permeation of gas to the surface of the nickel powder. The instantaneous pressure generated by the gaseous products of the polyol's thermal decomposition within the confined space not only provided a reducing atmosphere but also served as the driving force for subsequent vapor deposition reactions. During the reaction, the pressure monitoring instrument 4-1 monitored the internal pressure of the reaction, and the constant pressure relief valve 4-2 regulated the pressure. A reducing atmosphere is constructed using the reducing gas generated in situ by the pyrolysis of polyols. The H2 and CO produced by the pyrolysis quickly fill the gaps between the powder particles. A pressure relief valve is set to maintain a slightly positive pressure state inside the reactor for the reaction. As the gas production increases, the pressure inside the chamber rises to a slightly positive pressure state. This pressure effectively increases the collision frequency of active carbon atoms on the nickel surface, compensating for the insufficient reaction kinetics at low temperatures. The following synergistic reactions occur during this stage: high concentrations of H2 and CO reduce NiO on the nickel surface to highly active metallic Ni crystal planes; active carbon atoms nucleate on the reduced Ni crystal planes. Because the temperature is lower than the bulk diffusion activation energy of carbon in nickel, the carbon atoms are confined to the surface for two-dimensional rearrangement, avoiding dissolution into the interior; oxygen-containing free radicals generated by the pyrolysis of polyols have a selective etching effect on amorphous carbon, ensuring that the number of graphene layers is 1-10 and the lattice defects are low. (3) After the reaction is completed, the product is sent from the spiral shaft 2-2 to the tail discharge pipe of the spiral tube heating furnace 2-1. The double-layer water-cooled jacket at the end of the spiral tube is opened and a large flow of cold argon gas is introduced. The monitoring shows that the cooling rate reaches 147℃ / min, so that the sample drops from 520℃ to below 180℃ within 2 minutes. The test found that due to the rapid cooling "freezing" of carbon atoms, there are no messy amorphous carbon precipitates at the interface. The graphene is tightly bonded to the nickel substrate, and the contact resistance is further reduced by 12% compared with Example 1. The gas generated in the process enters the tail gas purification device 5-2 for purification and then is discharged.

[0039] Comparative Example 1 Using nickel powder of the same particle size, without using loosening agents and polyols, a methane / hydrogen mixture (V / V=1 / 10) was introduced into a tube furnace and reacted at 900℃ for 30 minutes. The nickel powder underwent severe thermal sintering and formed lumps. After mechanical crushing, the compacted electrical conductivity was tested to be 155 S / cm. Raman spectroscopy showed that the carbon layer quality was extremely poor and contained a large amount of amorphous carbon.

[0040] Comparative Example 2 The process steps are the same as in Example 1, but the constant pressure relief valve is closed and the reactor is connected to the atmosphere (atmospheric pressure environment). Test data: the product conductivity is 3134 S / cm. The reason is that the polyol cracking products are rapidly lost under atmospheric pressure, which cannot form sufficient reduction potential on the nickel powder surface, and the carbon atom nucleation rate is slow, resulting in a discontinuous coating layer.

[0041] Table 2 shows the performance test data of the products of each embodiment.

[0042] Table 2

[0043] As can be seen from the comparison of data from the examples and comparative examples, the present invention successfully constructed a high-quality graphene coating layer on the surface of nickel powder by combining "low-temperature liquid phase impregnation of polyols" with "spontaneous micro-positive pressure environment". The present invention solves the technical problems of high-temperature sintering and thick-layer precipitation while significantly improving the electrical conductivity, and the technical effect has obvious substantial characteristics.

[0044] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for in-situ construction of graphene-coated nickel powder using the self-compression effect of polyol pyrolysis, characterized in that, The specific steps are as follows: (1) Nickel powder, inorganic loosening agent and liquid polyol carbon source are mixed to obtain precursor composite material; (2) Place the precursor composite material in the reactor, first replace it with an inert atmosphere, then raise the temperature to the pyrolysis temperature, use the gaseous products generated by the pyrolysis of polyol to increase the pressure in the reactor, and control the reactor to maintain a slightly positive pressure state for the pyrolysis reaction through the pressure control system, so that the carbon atoms of the polyol cracking are deposited in situ on the surface of nickel powder. (3) After the reaction is complete, the product is rapidly cooled under a reducing atmosphere or an inert atmosphere, then washed to remove the inorganic loosening agent, and dried to obtain graphene-coated nickel powder.

2. The method according to claim 1, characterized in that, Step (1) The nickel powder has a specific surface area of ​​0.5-2.0 m². 2 / g of nickel powder, the inorganic loosening agent is MgO, Al2O3, Na2CO3, NaCl or K2SO4, and its particle size should be one order of magnitude smaller than the nickel powder particle size; the liquid phase polyol carbon source is at least one of ethylene glycol, propylene glycol, glycerol or diethylene glycol or a mixture thereof.

3. The method according to claim 1, characterized in that, Step (1) The amount of polyol added is 0.5%-5% of the mass of nickel powder, and the mass ratio of nickel powder to inorganic loosening agent is 1:2-1:

10.

4. The method according to claim 1, characterized in that, Step (2) The pyrolysis reaction is carried out under a slightly positive pressure by heating the temperature to 450°C-600°C at a heating rate of 5-20°C / min, the pressure of the reaction is 0.01-0.5MPa, and the reaction time is 5-30min.

5. A device for in-situ construction of graphene-coated nickel powder using the self-pressure effect of polyol pyrolysis, characterized in that, include: Feeding system (1): used for continuous oxygen-free supply of precursor composite materials; Spiral propulsion reaction system (2): includes a spiral tube heater (2-1) with multiple independent temperature control zones, wherein the spiral tube heater (2-1) is provided with a spiral shaft (2-2) for mixing and continuously propulsing materials, and the spiral shaft (2-2) is driven to rotate by a drive motor; an exhaust pipe is connected to the side of the tail of the spiral tube heater (2-1); Temperature control system 3: includes multiple temperature sensors, installed inside the spiral tube furnace (2-1); Pressure control system 4: includes a pressure monitoring instrument (4-1) installed on the spiral tube heater (2-1); and a constant pressure relief valve (4-2) installed on the exhaust pipe of the spiral tube heater (2-1). Cooling discharge system (5): includes cooling jacket (5-1) and exhaust gas purification device (5-2). Cooling jacket (5-1) is set outside the discharge pipe of spiral tube heater (2-1), and exhaust gas purification device (5-2) is set at the outlet end of the discharge pipe of spiral tube heater (2-1).

6. The apparatus according to claim 5, characterized in that, The feeding system 1 includes a liquid phase impregnation mixer (1-1) and a double-stage vacuum lock hopper (1-2). The liquid phase impregnation mixer (1-1) is installed inside the double-stage vacuum lock hopper (1-2). The liquid phase impregnation mixer (1-1) is equipped with an air inlet and an exhaust outlet. The bottom of the double-stage vacuum lock hopper (1-2) is connected to the feed inlet.

7. The apparatus according to claim 6, characterized in that, The spiral tube heater (2-1) is divided into a preheating section, a pyrolysis reaction section and a heat preservation section in sequence along the material feeding direction. Each section is equipped with an independent temperature sensor and an electric heating element. The spiral shaft (2-2) starts from the feed port at the bottom of the feeding system (1) and extends to the tail of the spiral tube heater (2-1). A closed pipe is set on the outside of the spiral shaft (2-2).

8. The apparatus according to claim 7, characterized in that, It also includes a controller, which is connected to various temperature sensors, electric heating elements, pressure monitors (4-1), and pressure relief valves (4-2).

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