A method for producing microwave-absorbing zinc oxide composite powder

Abstract

The present invention discloses a method for producing a wave-absorbing zinc oxide composite powder, belonging to the technical field of zinc oxide composite powders. Polyvinyl alcohol is used as a dispersant to uniformly disperse nano-zinc oxide, and then glutaraldehyde is used as a cross-linking agent to cross-link the polyvinyl alcohol. An alcohol-soluble phenolic resin is used to coat the nano-zinc oxide. After spray drying, the nano-zinc oxide is hydrothermally reacted with ferrous sulfate and manganese sulfate, and then heat-treated to prepare the wave-absorbing zinc oxide composite powder. The phenolic resin coating of the zinc oxide reduces the density of the zinc oxide particles, and zinc oxide does not agglomerate due to prolonged mixing time, thereby improving the uniformity of the raw material mixing. Furthermore, the alcohol-soluble phenolic resin is heat-cured during the spray drying process. The cured phenolic resin is insoluble in water. After heat treatment, the phenolic resin forms a carbon layer, which promotes grain growth and increases particle size. The heat treatment temperature is reduced, and the wave-absorbing zinc oxide composite powder can be synthesized at a lower temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of zinc oxide composite powders, and in particular relates to a production method of wave-absorbing zinc oxide composite powders. Background Art

[0002] Zinc oxide has excellent microwave absorption, antibacterial, and thermal stability properties. Nano-zinc oxide is also lightweight, light-colored, and has strong microwave absorption capabilities, making it suitable for the development of new invisible absorbent materials. Wang Shan et al. mixed carbonyl iron powder, zinc oxide, and hydrogenated nitrile rubber to prepare a 1-mm-thick single-layer microwave-absorbing material. Huang Yunhua et al. studied the microwave absorption properties of CNTs / nano-zinc oxide composite coatings. Zeng et al. used electroplating to coat high-temperature annealed zinc oxide on the surface of carbon fiber to create a microwave-absorbing material. Zhou Chang et al. used high-energy ball milling to prepare a zinc oxide-carbonyl iron composite absorber and found that the particle size of the absorber gradually decreased with increasing ball milling time. Guo et al. used a hydrothermal method to prepare a sea urchin-shaped zinc oxide-carbonyl iron powder composite material. Zhou Meilin studied the modification of zinc oxide microwave-absorbing materials by doping with magnetic materials to improve the material's microwave absorption strength and expand the microwave absorption frequency range, such as mixing with ferrites and nickel and cobalt oxides. Xiong Guoxuan et al. used iron oxide, zinc oxide, and manganese carbonate as raw materials, and prepared manganese zinc ferrite through ball milling and calcination processes. The material was then compounded with cement to produce a cement-based composite absorber. However, although the process is relatively simple, the high-temperature sintering and subsequent crushing process still faces significant difficulties due to the large amount of energy required and the high cost. In addition, mixing in the past required a long mixing time. However, as the mixing time increases, the nano-zinc oxide will agglomerate, resulting in poor mixing effect. After the prepared raw materials are vigorously mixed in a mixer and then transferred to a vibrating ball mill for grinding, the agglomeration of the nano-zinc oxide often causes a small amount of "white spots" to appear in the mixed powder, affecting the uniformity of the raw material mixing. In addition, zinc oxide has a large specific gravity and sinks to the bottom. During the processing of the mixed material, due to the different specific gravities of the various raw materials, stratification often occurs. As a person skilled in the art, it is urgent to develop a new method for producing a composite absorber zinc oxide powder. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for producing a wave-absorbing zinc oxide composite powder in response to the existing problems.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for producing a wave-absorbing zinc oxide composite powder comprises the following steps: first, adding clean water into a reactor and stirring, and adding polyvinyl alcohol powder under stirring to obtain a polyvinyl alcohol solution with a mass fraction of 0.3-0.5%, then weighing nano zinc oxide and slowly adding it to the solution, continuing to stir for 20-30 minutes to fully and evenly mix, then adding a glutaraldehyde solution with a mass proportion of 0.02-0.04% of the polyvinyl alcohol solution to the reactor, and then adding an alcohol-soluble phenolic resin under stirring, and continuing to stir for 5-10 minutes to obtain a zinc oxide slurry with a solid content of 30-35%, and spray-drying the zinc oxide slurry to obtain phenolic resin-coated zinc oxide;

[0006] The second step is to weigh ferrous sulfate and manganese sulfate according to the ratio of Fe2O3:MnO:ZnO=52-53:25-27:20-23, add deionized water, and stir in a stirring tank to form a uniform solution. During this time, the solution is heated and maintained at 50-60°C. During the stirring process, 1.5-2 mol / L NaOH is slowly added dropwise to adjust the pH value of the solution to 10.5-11. After that, the solution is stirred at a constant speed for 5-10 minutes, and then the weighed phenolic resin is added to coat the solution. The zinc oxide is transferred to a reactor and heated to 160°C and kept warm for 2 to 4 hours. The reaction is then naturally cooled to room temperature. The reactor is opened and washed with deionized water. The precipitate is then placed in a ball mill with a ball-to-material ratio of 6:1. The precipitate is ball milled in a ball mill for 6 to 8 hours to fully mix the raw materials. The precipitate is then placed in a vacuum tube furnace for heat treatment at a temperature of 750 to 850°C. Inert gas argon is introduced into the tube furnace for a heat treatment time of 60 to 90 minutes, and then cooled to room temperature.

[0007] Carbonization: Under the action of the dehydration carbonization catalyst, the carbonizing agent is dehydrated and carbonized to form a hard carbon skeleton structure.

[0008] Furthermore, the nano zinc oxide in the first step has an average particle size of 50nm to 80nm, an agglomeration index of 40 to 60, and a specific surface area of ​​55m 2 / g~80m 2 / g of nano zinc oxide.

[0009] Furthermore, the alcohol-soluble phenolic resin in the first step is an alcohol-soluble phenolic resin with a solid content of 68% to 72% and a pH of 8 to 9.

[0010] Furthermore, the ash content of the phenolic resin-coated zinc oxide obtained in the second step is 90% to 92%.

[0011] Furthermore, the first step of the spray drying process has an air inlet temperature of 240°C to 250°C, an air outlet temperature of 105°C to 110°C, a peristaltic pump speed of 80r / min to 90r / min, and an atomization pressure of 0.05MPa to 0.1MPa.

[0012] Furthermore, the polyvinyl alcohol in the first step has an alcoholysis degree of 86 to 90 and a molecular weight of 17,600 to 26,400.

[0013] Furthermore, the glutaraldehyde solution in the first step is an aqueous solution with a mass fraction of 25% to 40%.

[0014] Beneficial effects of the present invention:

[0015] The present invention discloses a method for producing a wave-absorbing zinc oxide composite powder. The method uses polyvinyl alcohol as a dispersant to uniformly disperse nano-zinc oxide, then cross-links the polyvinyl alcohol using glutaraldehyde as a cross-linking agent, and coats the nano-zinc oxide with an alcohol-soluble phenolic resin. After spray drying, the nano-zinc oxide is hydrothermally reacted with ferrous sulfate and manganese sulfate, and then heat-treated to prepare the wave-absorbing zinc oxide composite powder. The phenolic resin coating of the zinc oxide reduces the density of the zinc oxide particles, and zinc oxide does not agglomerate due to prolonged mixing time, thereby improving the uniformity of the raw material mixing. Furthermore, the alcohol-soluble phenolic resin is thermally cured during the spray drying process. The cured phenolic resin is insoluble in water. After heat treatment, the phenolic resin forms a portion of carbonaceous material, and partial combustion occurs, which helps promote grain growth and increase particle size. Furthermore, by lowering the reaction temperature of the oxide raw materials, the wave-absorbing zinc oxide composite powder can be synthesized at a lower temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attachment Figure 1 1 and 2 are X-ray diffraction patterns of Example 1, Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0017] The present invention is described below with specific examples, but is not intended to be limiting of the present invention. Example 1

[0018] Raw materials: Hangmo Y652 alcohol-soluble phenolic resin with a solid content of 68% and a pH of 8; Jinhua Zinc Oxide Co., Ltd. has an average particle size of 50nm, an agglomeration index of 40, and a specific surface area of ​​55m 2 / g of nano zinc oxide that meets the GB / T 19589-2004 standard; 05-88 (L) polyvinyl alcohol has a degree of alcoholysis of 86 and a molecular weight of 17600.

[0019] The production method of wave-absorbing zinc oxide composite powder includes the following steps: the first step is to put clean water into a reactor and start stirring at a stirring speed of 200 rpm, and add polyvinyl alcohol powder under stirring to obtain a polyvinyl alcohol solution with a mass fraction of 0.3%, then weigh nano zinc oxide, slowly add it to the above solution, continue stirring for 20 minutes to fully and evenly mix, then add glutaraldehyde solution accounting for 0.02% of the mass proportion of the polyvinyl alcohol solution to the reactor, the glutaraldehyde solution is a 25% mass fraction aqueous solution, and then add alcohol-soluble phenolic resin under stirring at a stirring speed of 400 rpm, and continue stirring for 5 minutes to obtain a zinc oxide slurry with a solid content of 30%, and spray dry the zinc oxide slurry. The spray drying process is an air inlet temperature of 240°C, an air outlet temperature of 105°C, a peristaltic pump speed of 80 r / min, and an atomization pressure of 0.05 MPa to obtain phenolic resin-coated zinc oxide. The ash content of the phenolic resin-coated zinc oxide is 90%; the second step, according to the molar mass ratio of Fe2O3: MnO: ZnO, ferrous sulfate and manganese sulfate were weighed and added to deionized water, and stirred at a stirring speed of 200 rpm in a stirred tank to form a uniform solution, during which the solution was heated and maintained at 50°C. During the stirring process, 1.5 mol / L NaOH was slowly added dropwise to adjust the pH of the solution to pH 10.5, and then stirred at a uniform speed for 5 minutes. The weighed phenolic resin-coated zinc oxide was added and transferred to the reactor and heated to 160°C and kept warm for 2 hours. After that, the reaction was naturally cooled to room temperature, the reactor was opened, washed with deionized water, and the precipitate was placed in a ball mill with a ball-to-material ratio of 6:1. The precipitate was ball milled in a ball mill for 6 hours to fully mix the raw materials and placed in a GSL-1100X-S vacuum tube furnace for heat treatment at a heat treatment temperature of 750°C. Inert gas argon was introduced into the tube furnace for a heat treatment time of 60 minutes, and then cooled to room temperature.

[0020] Product performance: initial magnetic permeability (10kHz0.1mT) 4050; specific loss coefficient (0.1MHz) 7×10 -6 Curie temperature 145°C; resistivity 72Ω·m; reflection loss (30-800MHz) -11dB.

[0021] Comparative Example 1

[0022] Iron oxide, manganese carbonate and zinc oxide were weighed in a molar mass ratio of Fe2O3:MnO:ZnO=53:27:20, ball-milled and sintered at 1350°C for 6 hours, and then crushed through a 325-mesh sieve. Example 2

[0023] Raw materials: Hangmo Y6522 alcohol-soluble phenolic resin with a solid content of 72% and a pH of 9; Jinhua Zinc Oxide Co., Ltd. has an average particle size of 80nm, an agglomeration index of 60, and a specific surface area of ​​80m 2 / g of nano zinc oxide that meets the GB / T 19589-2004 standard; Wanwei 05-88 (L) polyvinyl alcohol has a degree of alcoholysis of 90 and a molecular weight of 26400.

[0024] The production method of the wave-absorbing zinc oxide composite powder includes the following steps: first, adding clean water into a reactor and stirring at a speed of 200 rpm, and adding polyvinyl alcohol powder under stirring to obtain a polyvinyl alcohol solution with a mass fraction of 0.5%, then weighing nano zinc oxide and slowly adding it to the above solution, continuing to stir for 30 minutes to fully and evenly mix, then adding glutaraldehyde solution with a mass ratio of 0.04% of the polyvinyl alcohol solution to the reactor, the glutaraldehyde solution is a 40% aqueous solution, and then adding alcohol-soluble phenolic resin under stirring at a speed of 300 rpm and continuing to stir. 10min, to obtain a zinc oxide slurry with a solid content of 35%, and the zinc oxide slurry was spray-dried. The spray drying process was as follows: an inlet air temperature of 250°C, an outlet air temperature of 110°C, a peristaltic pump speed of 90r / min, and an atomization pressure of 0.1MPa to obtain phenolic resin-coated zinc oxide. The ash content of the phenolic resin-coated zinc oxide was 92%; in the second step, according to the molar mass ratio of Fe2O3:MnO:ZnO=52:25:23, ferrous sulfate and manganese sulfate were weighed and added to deionized water, and stirred in a stirred tank to form a uniform solution. During this period, the solution was heated and maintained at 60°C, and the stirring speed was 200rpm. During the stirring process, 2 mol / L NaOH was slowly added dropwise to adjust the pH value of the solution to pH 11, and then stirred at a uniform speed for 10 minutes. The weighed amount of phenolic resin-coated zinc oxide was added and transferred to a reactor, heated to 160°C and kept warm for 4 hours. The reaction was then naturally cooled to room temperature. The reactor was opened and washed with deionized water. The precipitate was placed in a ball mill with a ball-to-material ratio of 6:1 and ball milled in a ball mill for 8 hours to fully mix the raw materials. The mixture was placed in a GSL-1100X-S vacuum tube furnace for heat treatment at a temperature of 850°C. Inert gas argon was introduced into the tube furnace at a flow rate of 150 mL / min. After the heat treatment time was 60 minutes, the mixture was cooled to room temperature.

[0025] Product performance: initial magnetic permeability (10kHz0.1mT) 5000; specific loss factor (0.1MHz) 15×10 -6 ; Curie temperature 140℃; resistivity 20Ω·m, reflection loss (30-800MHz) -12dB.

[0026] Note: Three blanks of Φ25×15×10 mm were pressed from the absorbing zinc oxide composite powder and processed through the same sintering process to form magnetic ring samples. Measurement method: 10 Ts of enameled wire with a diameter of Φ0.35 mm was uniformly wound around the magnetic ring sample and the inductance was measured. The initial magnetic permeability was calculated according to the method specified in Section 7.3 of GB 9632.1-2002. A coil was wound around the magnetic ring sample. The relative loss factor was calculated according to the method specified in Section 7.3 of GB 9632.1-2002. To measure the inductance and power loss, a double coil was uniformly wound around the magnetic ring sample with a number of turns N of 5 Ts. The power loss per unit volume was calculated according to the method specified in Section 11.2 of GB 9632.1-2002. The magnetic permeability or inductance was measured according to the method specified in Section 7.3 of GB 9632.1-2002. Rise the temperature by 10°C, then hold for 15 minutes before measuring again. When the inductance reaches its peak and then drops sharply, measure again every 2°C until the inductance approaches zero. Plot a curve of inductance versus temperature. In the region of inductance drop, draw a straight line through the two points at 80% and 20% of the peak value. The temperature corresponding to the intersection of this line and the horizontal axis is the Curie temperature. An XRD-D8 X-ray diffractometer was used, using a Cu target, an accelerating voltage of 60 kV, a current of 50 mA, and a scanning speed of 10° / min.

Claims

1. A method for producing a microwave-absorbing zinc oxide composite powder, characterized in that: The invention comprises the following steps: first, adding clean water into a reaction kettle and stirring, and adding polyvinyl alcohol powder under stirring to obtain a polyvinyl alcohol solution with a mass fraction of 0.3-0.5%, then weighing nano zinc oxide, slowly adding it to the above solution, continuing to stir for 20-30 minutes to fully and evenly mix, then adding glutaraldehyde solution with a mass proportion of 0.02-0.04% of the polyvinyl alcohol solution into the reaction kettle, and then adding alcohol-soluble phenolic resin under stirring, and continuing to stir for 5-10 minutes to obtain zinc oxide slurry with a solid content of 30-35%, spray drying the zinc oxide slurry to obtain phenolic resin-coated zinc oxide; second, mixing the zinc oxide slurry according to the molar mass ratio of Fe2O3:MnO:ZnO=52-53:25-27:20- 23. Weigh ferrous sulfate and manganese sulfate, add deionized water, and stir in a stirred kettle to form a uniform solution. During this time, heat the solution and maintain it at 50-60°C. Slowly add 1.5-2 mol / L NaOH dropwise during stirring to adjust the pH of the solution to 10.5-11. Then, stir at a constant speed for 5-10 minutes. Then, add weighed phenolic resin-coated zinc oxide, transfer the mixture to a reactor, heat to 160°C, and keep warm for 2-4 hours. Then, cool the reactor naturally to room temperature. Open the reactor, wash with deionized water, mix the raw materials thoroughly, and place in a vacuum tube furnace for heat treatment at 750-850°C. Inert gas argon is introduced into the tube furnace for 60-90 minutes. Then, cool to room temperature. The alcohol-soluble phenolic resin in the first step is an alcohol-soluble phenolic resin with a solid content of 68% to 72% and a pH of 8 to 9.

2. The method for producing the wave-absorbing zinc oxide composite powder according to claim 1, wherein: The nano zinc oxide in the first step has an average particle size of 50 to 80 nm, an agglomeration index of 40 to 60, and a specific surface area of ​​55 to 80 m2 / g.

3. The method for producing the wave-absorbing zinc oxide composite powder according to claim 1, wherein: The ash content of the phenolic resin-coated zinc oxide obtained in the second step is 90% to 92%.

4. The method for producing the wave-absorbing zinc oxide composite powder according to claim 1, wherein: The first step of the spray drying process is as follows: the inlet air temperature is 240-250° C., the outlet air temperature is 105-110° C., the peristaltic pump speed is 80-90 r / min, and the atomization pressure is 0.05-0.1 MPa.

5. The method for producing the microwave-absorbing zinc oxide composite powder according to claim 1, wherein: The polyvinyl alcohol prepared in the first step has an alcoholysis degree of 86 to 90 and a molecular weight of 17,600 to 26,400.

6. The method for producing the microwave-absorbing zinc oxide composite powder according to claim 1, wherein: The first step glutaraldehyde solution is an aqueous solution with a mass fraction of 25 to 40%.

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