Surface target-free activation process and surface chemical plating process of ferronickel spinel powder

Abstract

The invention belongs to the technical field of aluminum electrolysis inert anode materials, and particularly relates to a surface target-free activation process and a surface chemical plating process of ferronickel spinel powder. The surface target-free activation process of the ferronickel spinel powder comprises the following steps: carrying out reaction on NiFe2O4 powder, nickel salt and hydroxide in a solvent to form a colloidal solution, carrying out solid-liquid separation, and drying to obtain Ni (OH) 2-coated NiFe2O4 powder; and calcining the obtained Ni (OH) 2-coated NiFe2O4 powder to obtain NiO-coated NiFe2O4 powder, and then carrying out a reduction reaction to obtain NiFe2O4 particles with nano Ni particles distributed on the surfaces of the NiO-coated NiFe2O4 powder. Nanoscale active Ni particles are formed on the surfaces of NiFe2O4 particles through a chemical bath precipitation method, calcination and reduction, replace palladium to become a surface activation center and are uniformly distributed, and a continuous and complete metal coating can be formed on the surface of powder during chemical plating.

Description

Technical Field

[0001] The invention relates to the technical field of inert anode materials for aluminum electrolysis, and in particular to a surface target-free activation process and a surface chemical plating process of nickel-iron spinel powder. Background Art

[0002] Nickel iron spinel (NiFe 2 O 4 ) has a stable structure and has the advantages of resistance to molten salt corrosion, high-temperature oxidation and thermal shock. As an inert anode material for aluminum electrolysis, it has received widespread attention and research. However, spinel has low electrical conductivity and cannot meet the requirements of anode materials. Metal ceramic anode materials are usually prepared by pressing and sintering after metal powder doping, but nickel-iron spinel has poor wettability with metals and poor sintering performance. Forming a metal coating on the surface of nickel-iron spinel powder is one of the ways to improve conductivity and sintering performance. Methods for plating a metal layer on the surface of nickel-iron spinel include magnetron sputtering, electroplating, vacuum evaporation, chemical plating, etc. Among them, chemical plating is the cheapest and most effective method.

[0003] Since nickel-iron spinel powder has no catalytic activity on its surface, it needs to be pretreated before chemical plating. The traditional pretreatment technology is precious metal catalytic activation treatment, which mainly includes sensitization activation of Pd, Sn, and Ag, one-step method, and colloidal Pd activation method. For example, in the colloidal Pd activation method, the activation solution is composed of SnCl 2 and PdCl 2 Solution composition: put the dispersed raw material powder into the colloidal palladium activation solution, and the colloidal palladium will be directly adsorbed on the particle surface. After activation, it is treated with a degumming solution to remove the Sn adsorbed around the colloidal palladium. 2+ Dissolved in the dissolving solution, the Pd particles with catalytic activity are exposed as the catalytic center on the particle surface. During chemical plating, the metal ions are reduced and deposited at the catalytic center and continuously grow on the surface to form a continuous metal film. Although the above activation method is relatively mature, it involves the consumption of a large amount of precious metals, resulting in high pretreatment costs for chemical plating, and the discharge of precious metals causes environmental pollution.

[0004] In April 2019, Ma Junfei published a paper titled Metal Mesh Structure NiFe 2 O 4 The article "Preparation and Performance Study of NiFe-based Inert Anode" discloses a method for target-free activation treatment of NiFe 2 O 4 A method for chemically plating Ni on particles, wherein NiFe 2 O 4 The target-free activation process of the particles is carried out in Fe 2 O 3 Preparation of NiFe by sintering NiO powder 2 O 4In the process of adding metal Ni powder, after sintering, crushing and screening, NiFe 2 O 4 There is Ni powder on the surface of the particles, so Ni is used to replace Pd as the active center in the initial stage of chemical Ni plating. This target-free activation process replaces the traditional palladium activation process, solving the high cost caused by precious metal palladium activation and the pollution caused by waste liquid discharge.

[0005] However, the above-mentioned powder metallurgy method is used to prepare NiFe 2 O 4 The metal Ni particles are embedded in the particle surface, which makes the metal Ni 2 O 4 The particle surface is unevenly distributed, the activation effect is poor, and the NiFe 2 O 4 A continuous metal coating is formed on the surface. Summary of the invention

[0006] The purpose of the present invention is to provide a target-free activation process for the surface of nickel-iron spinel powder, so as to solve the problem of poor activation effect of the existing target-free activation process.

[0007] The second purpose of the present invention is to provide a surface chemical plating process for nickel-iron spinel powder to solve the problem of discontinuous and uneven coating in the existing chemical plating process.

[0008] In order to solve the above technical problems, the technical solution of the surface target-free activation process of nickel-iron spinel powder of the present invention is: A target-free activation process for the surface of nickel-iron spinel powder comprises the following steps: (1) NiFe 2 O 4 The powder, nickel salt and hydroxide react in a solvent to form a colloidal solution, and then the solid-liquid is separated and dried to obtain Ni(OH) 2 @NiFe 2 O 4 Powder; (2) Ni(OH) obtained in step (1) 2 @NiFe 2 O 4 The powder is calcined to obtain NiO@NiFe 2 O 4 powder, and then NiO@NiFe 2 O 4 The powder is reduced to obtain NiFe with nano-Ni particles distributed on the surface. 2 O 4 Particles.

[0009] The present invention provides a pioneering process for the surface target-free activation of nickel-iron spinel powder, wherein the surface of NiFe is firstly activated by a chemical bath precipitation method. 2 O 4 Ni(OH) is formed on the powder surface 2 , then calcined and reduced to NiFe 2 O 4 Nano-scale active Ni particles are formed on the surface of the particles, and the generated active nickel nanoparticles replace palladium to become the activation center on the surface of the ceramic powder and are evenly distributed, serving as activation sites for the reduction and deposition of nickel ions or copper ions during chemical nickel plating or chemical copper plating, and expanding and growing along the particle surface direction with the site as the core, which is conducive to the final formation of a continuous and complete metal coating on the powder surface. The target-free activation process provided by the present invention is simple to operate, does not need to add nickel powder, and the active nickel particles are obtained by nickel salt reaction, calcination, and reduction, which is low in cost and less in environmental pollution, and can meet the requirements of industrial application.

[0010] In order to further make NiFe 2 O 4 The powder surface reaction is more sufficient and complete, so that the nickel source is evenly distributed on the particle surface. Preferably, in step (1), the molar ratio of nickel ions of the nickel salt to hydroxide ions is 1: (1.4-3); per 10g NiFe 2 O 4 The amount of nickel salt added to the powder is 0.1~0.2g.

[0011] In order to further improve the reaction efficiency, preferably, the reaction time in step (1) is 0.5-1.5 h and the reaction temperature is room temperature.

[0012] In order to further enhance the Ni(OH) 2 The oxidation is more complete. Preferably, the calcination temperature in step (2) is 200-400° C. and the calcination time is 3-5 h.

[0013] In order to reduce the NiO on the surface of the powder simply and efficiently, preferably, the reduction reaction in step (2) is NiO@NiFe 2 O 4 The powder is heated and reduced in a reducing gas, the temperature of the heating and reduction is 400-600° C., and the time of the heating and reduction is 2-4 hours. More preferably, the reducing gas is hydrogen or carbon monoxide.

[0014] In order to further improve the stability of the reactants after the reaction in step (1), preferably, the solid-liquid separation in step (1) is carried out by filtering until the solid obtained by filtration is neutral; the drying temperature is 60-120° C., and the drying time is 6-10 h.

[0015] In order to further improve the reaction efficiency of step (1), preferably, the nickel salt is Ni(NO 3 ) 2 6H 2 O, the hydroxide is sodium hydroxide.

[0016] The technical scheme of the surface chemical plating process of nickel-iron spinel powder of the present invention is: A surface chemical plating process for nickel-iron spinel powder comprises the following steps: after activating the nickel-iron spinel powder by the target-free activation process for the surface of the nickel-iron spinel powder, chemically plating the nickel-iron spinel powder.

[0017] The surface chemical plating process of nickel-iron spinel powder provided by the present invention is to activate the NiFe by adopting the surface target-free activation process. 2 O 4 Nano-scale active Ni particles are formed on the surface of the particles, replacing palladium as the activation center on the surface of the ceramic powder and are evenly distributed. They serve as activation sites for the reduction and deposition of nickel / copper ions during chemical nickel / copper plating, forming a continuous and complete metal coating on the powder surface, which is beneficial to improving the conductivity of the inert anode made of nickel-iron spinel powder.

[0018] In order to further improve the uniformity and stability of the copper plating layer and thus improve the anode conductivity, preferably, when the chemical plating is chemical copper plating, the plating solution comprises the following components: 32-40 g / L copper salt, 32-40 g / L EDTA-2Na, C 4 H 4 O 6 KNa 10~20g / L, K 4 [Fe(CN 6 )] 10~20mg / L, HCHO 20~30 mL / L, CH 3 OH 100~120 mL / L; plating solution pH is 11~12; the temperature for chemical copper plating is 70~80℃, and the time for chemical copper plating is 120~140min.

[0019] In order to further improve the uniformity and stability of the nickel plating layer and thus improve the anode conductivity, preferably, when the chemical plating is chemical nickel plating, the plating solution comprises the following components: 32-40 g / L of nickel salt, C 6 H 5 O 7 Na 3 25~30g / L, CH 3 COONa 15~20 g / L, NaH 2 PO 2 32~40 g / L; pH of the plating solution is 8~9; the temperature for chemical nickel plating is 70~80℃, and the time for chemical nickel plating is 90~100min. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The NiFe obtained by the target-free activation process of Example 1 of the present invention 2 O 4 SEM morphology of powder; Figure 2 The NiFe obtained by the target-free activation process of Example 1 of the present invention 2 O 4 Morphology of powder after chemical nickel plating; Figure 3 The NiFe of Example 1 of the present invention 2 O 4 Metallographic image of the inert anode made by chemical nickel plating of powder; Figure 4 NiFe for comparison 2 O 4 Metallographic image of an inert anode made by chemical nickel plating of powder. DETAILED DESCRIPTION

[0021] The technical concept of the surface target-free activation process of nickel-iron spinel powder of the present invention is as follows: The existing target-free activation process is to use powder metallurgy to produce NiFe 2 O 4 Nickel powder is added during the preparation process, but the nickel powder distribution on the surface of the nickel-iron spinel particles produced by this process is not uniform, and the activation effect is poor, resulting in local agglomeration of the metal nickel phase in the produced anode and the inability to form a continuous metal coating.

[0022] The present invention innovatively uses NiFe 2 O 4 The nickel source is introduced into the particle surface by chemical reaction, and then calcined and reduced to form active nano-nickel particles. At this time, the nano-nickel particles are well dispersed on the surface of nickel-iron spinel, which greatly improves the activation effect. The prepared anode has a continuous metal network structure, which is beneficial to the improvement of the anode conductivity.

[0023] The target-free surface activation process of nickel-iron spinel powder provided by the present invention comprises the following steps: (1) NiFe 2 O 4 The powder, nickel salt and hydroxide are reacted in a solvent, and the molar ratio of nickel ions of the nickel salt to hydroxide ions of the hydroxide is 1: (1.4-3); for every 10g NiFe 2 O 4 The nickel salt corresponding to the powder is 0.1-0.2 g to obtain a colloidal solution, which is filtered until the solid obtained by filtration is neutral, and then vacuum dried at 60-120 ° C for 6-10 h to obtain Ni(OH)2 @NiFe 2 O 4 Powder.

[0024] (2) Ni(OH) obtained in step (1) 2 @NiFe 2 O 4 The powder was calcined at 200-400℃ for 3-5h to obtain NiO@NiFe 2 O 4 Powder, NiO@NiFe 2 O 4 The powder is heated and reduced at 400-600°C in a reducing gas for 2-4 hours to obtain NiFe with nano-Ni particles distributed on the surface. 2 O 4 Particles.

[0025] In a specific embodiment, the reaction in step (1) is to convert NiFe 2 O 4 The powder, nickel salt solution and hydroxide solution are reacted, and the concentrations of nickel salt solution and hydroxide solution are 0.2~2 g / L and 0.1~0.8 g / L respectively; for every 10gNiFe 2 O 4 The volumes of nickel salt solution and hydroxide solution added to the powder are 160~300mL and 100~200mL, respectively.

[0026] It is understandable that the nickel-iron spinel powder prepared by the target-free surface activation process of the present invention can be used for chemical nickel plating and also for chemical copper plating.

[0027] The embodiments of the present invention are further described below in conjunction with specific examples. The chemical reagents involved in the following examples are all commercially available conventional products unless otherwise specified.

[0028] 1. Specific embodiment of the target-free surface activation process of nickel-iron spinel powder of the present invention Example 1 The target-free activation process of the surface of the nickel-iron spinel powder of this embodiment is as follows: (1) Weigh 10g of nano NiFe 2 O 4 The powder was repeatedly ultrasonically cleaned, and then 0.5 g / L and 200 mL of Ni(NO 3 ) 2 6H 2 O solution, and then add 0.2g / L, 100mL NaOH solution, stir and react for 1.5h at room temperature to obtain a binary colloidal solution (NiFe 2 O 4 -Ni(OH)2 ), let it stand and filter until the filtered solid is neutral, and then dry it in a vacuum oven at 120°C for 6 hours to obtain Ni(OH) 2 @NiFe 2 O 4 Powder; (2) Ni(OH) obtained in step (1) 2 @NiFe 2 O 4 The powder was calcined at 200 °C in an inert atmosphere for 4 h to form fine NiO@NiFe 2 O 4 Composite powder, then NiO@NiFe 2 O 4 The composite powder was reduced in hydrogen at 400°C for 3 hours. 2 O 4 Active Ni nanoparticles are formed on the particle surface. The NiFe 2 O 4 The SEM morphology of the powder is as follows Figure 1 As shown, from Figure 1 It can be seen that uniformly distributed Ni nanodots are generated on the originally smooth surface of the nickel-iron spinel, which serve as targets for metal attachment in the subsequent chemical plating process. This shows that the target-free activation process of the present invention forms uniform Ni nanodots on the surface of the nickel-iron spinel through a chemical bath precipitation method, replacing palladium as the activation center on the surface of the ceramic powder.

[0029] Example 2 The target-free activation process of the surface of the nickel-iron spinel powder of this embodiment is as follows: (1) Weigh 30g of nano NiFe 2 O 4 The powder was repeatedly ultrasonically cleaned, and then 1 g / L, 500 mL of Ni(NO 3 ) 2 6H 2 O solution, then add 0.5g / L, 400mL NaOH solution, stir and react for 1.5h at room temperature to obtain a binary colloidal solution (NiFe 2 O 4 -Ni(OH) 2 ), let it stand and filter until the filtered solid is neutral, and then dry it in a vacuum oven at 120 ° C for 6 hours to obtain Ni(OH) 2 @NiFe 2 O 4 Powder; (2) Ni(OH) obtained in step (1) 2 @NiFe 2 O4 The powder was calcined at 200 °C in an inert gas for 4 h to form fine NiO@NiFe 2 O 4 Composite powder, then NiO@NiFe 2 O 4 The composite powder was reduced in hydrogen at 400 °C for 3 hours. 2 O 4 Active Ni nanoparticles are formed on the particle surface.

[0030] 2. Specific embodiment of the surface chemical plating process of nickel-iron spinel powder of the present invention Example 3 The surface chemical nickel plating process of the nickel-iron spinel powder of this embodiment is as follows: 25g / L complexing agent C 6 H 5 O 7 Na 3 Solution, 15 g / L stabilizer CH 3 Mix the COONa solution evenly, then add 32g / L of main salt NiSO 4 The solution was stirred thoroughly and then the target-free activated NiFe 2 O 4 powder, then add 32 g / L reducing agent NaH 2 PO 2 The solution was mixed evenly, and 10% NaOH solution was added to adjust the pH value of the chemical plating solution to 8. The plating temperature was 70°C and the plating time was 90 min. The powder was fully stirred during the plating. After the plating was completed, the powder was washed with deionized water until neutral, and dried in an oven at 80°C for 6 hours to obtain NiFe with a nickel layer. 2 O 4 Powder. NiFe with nickel coating 2 O 4 The SEM image of the powder is as follows Figure 2 As shown, from Figure 2 It can be seen that in NiFe 2 O 4 Under the action of the nano-nickel formed on the particle surface as the active center, the metal ions are reduced to metal through metal autocatalysis and deposited on the surface of the ceramic particles to form a continuous and uniform metal coating. 2 O 4 A smooth, continuous and dense nickel plating layer can be obtained on the powder surface.

[0031] Example 4 The surface chemical copper plating process of the nickel-iron spinel powder of this embodiment is as follows: 32g / L EDTA-2Na, 10g / L 4 H 4 O 6 KNa solution and 10mg / L stabilizer K 4 [Fe(CN 6 )] The solution was mixed evenly, and then 32g / L of main salt (metal salt) CuSO was added 4 The solution was stirred thoroughly and then the target-free activated NiFe 2 O 4 Then add 20 mL / L HCHO and 100 mL / L CH 3 OH, mix evenly, add 20% NaOH solution to adjust the pH value of the chemical plating solution to 12, the plating temperature is 80℃, the plating time is 120min, and the plating is fully stirred. After the plating is completed, the powder is washed with deionized water to neutrality, and dried in an oven at 80℃ for 6 hours to obtain NiFe with a copper layer. 2 O 4 Powder.

[0032] Example 5 The surface chemical nickel plating process of the nickel-iron spinel powder of this embodiment is as follows: 27g / L complexing agent C 6 H 5 O 7 Na 3 Solution, 18 g / L stabilizer CH 3 Mix the COONa solution evenly, then add 35g / L of main salt NiSO 4 The solution was stirred thoroughly and then the target-free activated NiFe 2 O 4 powder, then add 35 g / L reducing agent NaH 2 PO 2 The solution was mixed evenly, and 10% NaOH solution was added to adjust the pH value of the chemical plating solution to 8. The plating temperature was 70°C and the plating time was 90 min. The powder was fully stirred during the plating. After the plating was completed, the powder was washed with deionized water until neutral, and dried in an oven at 80°C for 6 hours to obtain NiFe with a nickel layer. 2 O 4 Powder.

[0033] 3. Experimental Examples In this experimental example, the activation effects of different target-free activation processes were evaluated by observing the microstructure of nickel-iron spinel powder after chemical plating and the anode made.

[0034] The target-free activation process of directly adding nickel metal powder is used as a comparative example. The specific method of the target-free activation process of the comparative example is as follows: weigh 10g NiFe 2 O 4 The powder was fully mixed with 0.4 g of metal Ni powder, sintered at 1200 ° C in an argon atmosphere, and after crushing and screening, NiFe 2 O 4 Particles.

[0035] The target-free activated nickel-iron spinel powder obtained in the comparative example was prepared by referring to the NiFe 2 O 4 The powder is nickel plated by a chemical nickel plating method to obtain nickel-iron spinel powder with a nickel-plated layer.

[0036] The NiFe with a coating obtained by chemical plating in Examples 3 to 5 and Comparative Example 2 O 4 The powder was pressed at 60 MPa for 2 h and sintered at 900° C. for 2 h to obtain an inert anode. The metallographic image of the inert anode made of nickel-iron spinel powder with a nickel coating in Example 3 is shown in FIG. Figure 3 As shown, from Figure 3 It can be seen that the anode material has a dense structure, NiFe 2 O 4 The grain size is uniform, and a continuous metal network structure is formed at the interface.

[0037] The metallographic image of the inert anode made of nickel-iron spinel powder with a nickel coating in the comparative example is as follows: Figure 4 As shown, from Figure 4 It can be seen that the metal Ni phase in the anode is locally agglomerated and no metal network is formed, indicating that the Ni powder and NiFe 2 O 4 The method of pre-doping raw materials and then chemically plating is not effective in NiFe 2 O 4 A continuous metal coating is formed on the surface of the powder.

[0038] The test results of the conductivity and bending strength of the inert anodes prepared in Examples 3 to 5 and the comparative example are shown in Table 1. It can be seen from Table 1 that the conductivity of the inert anodes prepared in Examples 3 to 5 can reach 1011 S·cm -1 The bending strength can reach more than 83MPa, while the conductivity of the inert anode made in the comparative example is only 102 S·cm -1 , the flexural strength is only 20 MPa, indicating that the surface target-free activation process provided by the present invention can greatly improve the conductivity and flexural resistance of the inert anode compared with directly adding metal nickel powder.

[0039] Table 1 Test results of conductivity and bending strength of inert anode <![CDATA[Conductivity / S·cm -1 > Bending strength / MPa Example 3 1011 83 Example 4 1042 91 Example 5 1356 85 Comparative Example 102 20 Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A target-free activation process for the surface of nickel-iron spinel powder, characterized in that: The following steps are involved: (1) NiFe2O4 powder, nickel salt and hydroxide are reacted in a solvent to form a colloidal solution, and the solid-liquid solution is separated and dried to obtain Ni(OH)2@NiFe2O4 powder; (2) calcining the Ni(OH)2@NiFe2O4 powder obtained in step (1) to obtain NiO@NiFe2O4 powder, and then subjecting the NiO@NiFe2O4 powder to a reduction reaction to obtain NiFe2O4 particles having nano-Ni particles distributed on the surface.

2. The surface target-free activation process of nickel-iron spinel powder as claimed in claim 1, characterized in that: In the step (1), the molar ratio of nickel ions of the nickel salt to hydroxide ions of the hydroxide is 1:(1.4-3); and 0.1-0.2 g of nickel salt is added for every 10 g of NiFe2O4 powder.

3. The surface target-free activation process of nickel-iron spinel powder as claimed in claim 1 or 2, characterized in that: The reaction time in step (1) is 0.5-1.5 h, and the reaction temperature is room temperature.

4. The surface target-free activation process of nickel-iron spinel powder as claimed in claim 1, characterized in that: In the step (2), the calcination temperature is 200-400° C. and the calcination time is 3-5 hours.

5. The surface target-free activation process of nickel-iron spinel powder as claimed in claim 1, characterized in that: The reduction reaction in step (2) is that the NiO@NiFe2O4 powder is heated and reduced in a reducing gas, the temperature of the heating reduction is 400-600°C, and the time of the heating reduction is 2-4h.

6. The surface target-free activation process of nickel-iron spinel powder as claimed in claim 1, characterized in that: In the step (1), the solid-liquid separation is carried out by filtering until the solid obtained by filtration is neutral; the drying temperature is 60-120° C., and the drying time is 6-10 hours.

7. The target-free surface activation process of nickel-iron spinel powder according to claim 1 or 2, characterized in that: The nickel salt is Ni(NO3)2·6H2O, and the hydroxide is sodium hydroxide.

8. A surface chemical plating process for nickel-iron spinel powder, characterized in that: The following steps are involved: After the nickel-iron spinel powder is activated by the target-free surface activation process described in any one of claims 1 to 7, the nickel-iron spinel powder is chemically plated.

9. The surface chemical plating process of nickel-iron spinel powder as claimed in claim 8, characterized in that: When the chemical plating is chemical copper plating, the plating solution includes the following components: copper salt 32~40g / L, EDTA-2Na 32~40g / L, C4H4O6KNa 10~20g / L, K4[Fe(CN6)] 10~20mg / L, HCHO 20~30 mL / L, CH3OH 100~120 mL / L; the pH of the plating solution is 11~12; the temperature during chemical copper plating is 70~80℃, and the time for chemical copper plating is 120~140min.

10. The surface chemical plating process of nickel-iron spinel powder according to claim 8, characterized in that: When the chemical plating is chemical nickel plating, the plating solution includes the following components: nickel salt 32~40g / L, C6H5O7Na3 25~30g / L, CH3COONa 15~20 g / L, NaH2PO2 32~40 g / L; the pH value of the plating solution is 8~9; the temperature of the chemical nickel plating is 70~80℃, and the time of the chemical nickel plating is 90~100min.

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