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CN-122013137-A - Method and device for in-situ construction of graphene-coated nickel powder by utilizing polyol pyrolysis self-compaction effect

CN122013137ACN 122013137 ACN122013137 ACN 122013137ACN-122013137-A

Abstract

The invention discloses a method and a device for in-situ construction of graphene coated nickel powder by utilizing a polyol pyrolysis self-pressure effect, which are characterized in that nickel powder, an inorganic loosening agent and a liquid-phase polyol carbon source are mixed, a precursor composite is obtained through high-shear stirring or ultrasonic dispersion, high-purity argon is introduced into the precursor composite for replacement until the oxygen content of an exhaust port is lower than 10ppm, a semi-closed structure is utilized to limit free diffusion of gas, then the gas is heated and maintained in a micro-positive pressure state under the protection of inert atmosphere for pyrolysis reaction, reducing gas generated in situ by pyrolysis is used for constructing a reducing atmosphere, H 2 and CO generated by pyrolysis are rapidly filled in a powder gap for reaction in the micro-positive pressure state, and products are rapidly cooled, washed and dried after the reaction is finished, so that the graphene coated nickel powder is obtained.

Inventors

  • BAO RUI
  • LIU LIANG
  • YI JIANHONG

Assignees

  • 昆明理工大学

Dates

Publication Date
20260512
Application Date
20260206

Claims (8)

  1. 1. The method for in-situ construction of the graphene-coated nickel powder by utilizing the polyol pyrolysis self-compaction effect is characterized by comprising the following specific steps: (1) Mixing nickel powder, an inorganic loosening agent and a liquid-phase polyol carbon source to obtain a precursor composite; (2) Placing the precursor composite material into a reactor, firstly replacing the precursor composite material in an inert atmosphere, then heating to a pyrolysis temperature, utilizing a gas phase product generated by the pyrolysis of the polyol to raise the pressure in the reactor, and controlling the reactor to maintain a micro-positive pressure state through a pressure regulating system to carry out pyrolysis reaction so as to enable carbon atoms cracked by the polyol to be deposited on the surface of nickel powder in situ; (3) And after the reaction is finished, rapidly cooling the product under the protection of a reducing atmosphere or an inert atmosphere, then washing to remove the inorganic loosening agent, and drying to obtain the graphene coated nickel powder.
  2. 2. The method of claim 1, wherein the nickel powder in step (1) is nickel powder with a specific surface area of 0.5-2.0m 2 /g, the inorganic bulking agent is MgO, al 2 O 3 、Na 2 CO 3 , naCl or K 2 SO 4 , the particle size of the inorganic bulking agent is smaller than one order of magnitude of the particle size of the nickel powder, and the liquid-phase polyol carbon source is at least one of ethylene glycol, propylene glycol, glycerol or diethylene glycol or a mixture thereof.
  3. 3. The method according to claim 1, wherein the polyol in the step (1) is added in an amount of 0.5% -5% by mass of nickel powder, and the mass ratio of the nickel powder to the inorganic loosening agent is 1:2-1:10.
  4. 4. The method according to claim 1, wherein the pyrolysis reaction is carried out in the micro positive pressure state in the step (2) at a temperature rising rate of 5-20 ℃ per minute to 450-600 ℃, the pressure of the reaction is 0.01-0.5MPa, and the reaction time is 5-30min.
  5. 5. The device for in-situ construction of graphene-coated nickel powder by utilizing polyol pyrolysis self-compaction effect is characterized by comprising: A feed system (1) for oxygen-free continuous supply of precursor composite; The spiral propulsion reaction system (2) comprises a spiral tube type heating furnace (2-1) with a plurality of sections of independent temperature control areas, wherein a spiral shaft (2-2) for mixing and continuously propelling materials is arranged in the spiral tube type heating furnace (2-1), and the spiral shaft (2-2) is driven by a driving motor to rotate; The temperature control system 3 comprises a plurality of temperature sensors which are arranged in the spiral tube type heating furnace (2-1); the pressure regulating and controlling system 4 comprises a pressure monitoring instrument (4-1) arranged on the spiral tube type heating furnace (2-1), a constant pressure relief valve (4-2) arranged on an exhaust pipe of the spiral tube type heating furnace (2-1); The cooling discharging system (5) comprises a cooling jacket (5-1) and a tail gas purifying device (5-2), wherein the cooling jacket (5-1) is arranged outside a discharging pipe of the spiral pipe type heating furnace (2-1), and the tail gas purifying device (5-2) is arranged at the outlet end of the discharging pipe of the spiral pipe type heating furnace (2-1).
  6. 6. The device according to claim 5, wherein the feeding system 1 comprises a liquid-phase dipping stirrer (1-1) and a double-stage vacuum lock hopper (1-2), the liquid-phase dipping stirrer (1-1) is arranged in the double-stage vacuum lock hopper (1-2), the liquid-phase dipping stirrer (1-1) is provided with an air inlet hole and an air outlet hole, and the bottom of the double-stage vacuum lock hopper (1-2) is connected with the feeding hole.
  7. 7. The device according to claim 6, wherein the spiral tube type heating furnace (2-1) is sequentially divided into a preheating section, a pyrolysis reaction section and a heat preservation section along the material advancing direction, each section is provided with an independent temperature sensor and an electric heating element, the spiral shaft (2-2) starts from a feed inlet at the bottom of the feed system (1) to the tail of the spiral tube type heating furnace (2-1), and a closed tube is arranged outside the spiral shaft (2-2).
  8. 8. The device according to claim 7, further comprising a controller connected to each of the temperature sensor, the electric heating element, the pressure monitor (4-1), the constant pressure relief valve (4-2).

Description

Method and device for in-situ construction of graphene-coated nickel powder by utilizing polyol pyrolysis self-compaction effect Technical Field The invention belongs to the technical field of nano functional materials and powder metallurgy, and particularly relates to a method and a device for in-situ construction of graphene-coated nickel powder by utilizing a polyol pyrolysis self-compaction effect, a preparation process for remarkably improving the conductivity and the oxidation resistance of the nickel powder, and related production equipment. Background With the rapid development of 5G communication, power semiconductors, new energy automobile electronics and flexible electronic devices, the electronic industry has increasingly stringent requirements for high-performance conductive pastes, conductive adhesives and electromagnetic shielding materials. Nickel powder has become a core filler for preparing multilayer ceramic capacitor terminal electrodes, high-frequency antennas and conductive adhesives to replace noble metals such as gold, silver and the like due to its excellent chemical stability, migration resistance and relatively low cost. However, in practical application, the conductivity of the micro-nano nickel powder is far from theoretical expectation. The intrinsic conductivity of metallic nickel is about 1.43×10 7 S/m, but after being made into slurry or compacted, the apparent conductivity of the metallic nickel is usually only maintained at 50-100S/cm, which severely limits the application of the metallic nickel in high-frequency and high-power circuits. The primary cause of deterioration in conductivity of nickel powder is in-situ oxidation due to its extremely high surface activity. In the air environment, the surface of the micro-nano nickel powder spontaneously forms a compact nickel oxide film with the thickness of about 3-10 nm. According to solid physical theory, niO belongs to a typical wide bandgap semiconductor (band gap is about 3.7-4.0 eV), and is in a nearly insulating state at normal temperature. The oxide film forms an extremely high potential barrier at the contact interface of the powder particles, so that the tunneling effect of carriers is blocked, and the contact resistance is increased. Even nickel powder treated in a reducing atmosphere is subjected to secondary oxidation due to the presence of a small amount of oxygen in the subsequent powder metallurgy or slurry sintering process. Therefore, how to construct a passivation layer on the surface of nickel powder, which can not only obstruct oxygen permeation, but also provide a high-speed electron transmission channel, is the center of gravity of research in the field. Graphene is considered as an ideal metal protection layer by virtue of its excellent carrier mobility (> 2×10 5cm2/(v·s) and chemical stability, graphene is grown on a nickel surface by chemical vapor deposition, and the dual efficacy of "corrosion prevention-conduction" can be theoretically achieved: 1) Supersaturated solid solution and precipitation mechanism (solubility pain point) of carbon atoms in nickel matrix according to Ni-C binary phase diagram, the solubility of carbon in nickel increases sharply with increasing temperature. The solubility of carbon in nickel is as high as 0.2wt% or more in the high temperature range (800-1000 ℃) common to conventional CVD processes. In sharp contrast to copper, the solubility of carbon in copper is very low (< 0.001 wt%). On the copper surface, graphene follows a surface catalysis self-limiting growth mechanism, and a high-quality monolayer is easy to form. On the surface of nickel, graphene grows by following a 'dissolution-segregation/precipitation' mechanism, namely, a large amount of carbon atoms are dissolved into the nickel at high temperature, and the carbon atoms are severely segregated to the surface under the drive of supersaturation in the cooling process. Since the kinetics of precipitation are difficult to control precisely, the final formation is often a graphite platelet or amorphous carbon with a thickness of up to tens of nanometers. The thick-layer carbon not only damages the linear dispersion energy band structure of the graphene, but also increases interface scattering due to interlayer Van der Waals force, so that the conductivity of the composite powder is limited to be improved, and the intrinsic high conductivity of the graphene is difficult to achieve. 2) The nano effect-induced low-temperature sintering and morphology failure (morphology pain point) is that the micro-nano nickel powder has extremely high specific surface energy, and according to the Tammann temperature theory, when the metal powder reaches 0.3-0.5 times of the melting point (the melting point of nickel is about 1455 ℃ and the sintering initial temperature is about 450 ℃), the surface atomic diffusion and grain boundary migration start to occur. Conventional CVD growth of graphene typically requires high temperatures