Preparation method of compact-structure metal ceramic inert anode material for aluminum electrolysis

Abstract

The invention relates to a preparation method of a compact-structure metal ceramic inert anode material for aluminum electrolysis, and belongs to the technical field of aluminum electrolysis. The anode preparation method comprises the steps that firstly, metal powder is pretreated, the metal powder and graphite powder are mixed and then heated, subjected to heat preservation and rapidly cooled, and a C / metal solid solution is obtained; nickel oxide and iron oxide are used as precursors to prepare ferronickel spinel, the ferronickel spinel is mixed with C / metal powder, and Joule thermal sintering is performed after pressing. Under the action of a large temperature gradient, C is separated out from metal lattice gaps and reacts with ferronickel spinel at an interface to generate a ferronickel alloy, a metal / alloy / ceramic continuous sintering interface is formed, anode densification is achieved, meanwhile, crystal grain growth and coarsening of metal ceramic are effectively restrained through the extremely high temperature rising and falling rate, and the metal ceramic anode is formed. And the prepared anode material is high in conductivity and excellent in mechanical property.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum electrolysis, and in particular to a method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis. Background Art

[0002] In the electrolytic aluminum industry, the Hall-Heroult molten salt electrolysis method is the only industrial production method. This process uses carbon materials as anodes. The electrolysis process not only consumes a large amount of high-quality carbon, but also produces a large amount of greenhouse gases including carbon dioxide, carbon tetrafluoride, hexafluoroethane, asphalt fumes and carbonyl sulfide, causing serious pollution to the environment. In addition, since the anode is constantly consumed during the electrolysis process, it needs to be frequently adjusted and replaced, which not only increases the workload of workers, but also may lead to instability in the production process, thereby increasing the energy consumption of aluminum electrolysis and reducing the current efficiency. In view of these problems, the research and application of inert anode materials has become a hot area in aluminum electrolysis technology, which is of great significance for the aluminum industry to achieve energy conservation, environmental protection, reduce emissions and improve efficiency.

[0003] Although there are many patents and research reports on inert anodes worldwide, nickel-iron spinel has attracted much attention as an anode material due to its excellent resistance to fluoride salt corrosion. The metal ceramic inert anode formed by nickel-iron spinel as a ceramic phase and other metal composites has been widely studied, such as the patents with publication numbers CN 113186569A and CN103556184 A. The current process usually adopts a method of sintering nickel-iron spinel powder and metal powder at high temperature to prepare anode materials. Due to the high melting point of spinel, the sintering process remains solid, and the metal phase melts to form a liquid phase, which plays the role of a particle binder and improves the conductivity of the anode. However, due to the poor wettability of the metal phase and the nickel-iron spinel phase interface, it is very easy to cause metal phase agglomeration and uneven distribution during the sintering process. In addition, long-term sintering causes ceramic grains to grow and coarsen, resulting in low anode density, resulting in poor conductivity, corrosion resistance, and mechanical properties. Summary of the invention

[0004] In view of the shortcomings of the prior art in the preparation process of metal ceramic inert anodes, the present invention provides a method for preparing a metal ceramic inert anode material with a dense structure for aluminum electrolysis.

[0005] In order to achieve the above object, the technical solution provided by the present invention is:

[0006] 1. A method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis, characterized by comprising the following steps:

[0007] S1: weighing metal powder and graphite powder raw materials according to a certain mass ratio, ball milling and mixing in a ball mill to obtain C-metal mixed powder, and heat treating the C-metal mixed powder to obtain C / metal solid solution powder;

[0008] S2: Weigh nickel oxide and iron oxide powder raw materials according to a certain mass ratio, mix them in a ball mill, obtain oxide mixed slurry, and sieving and calcining to obtain NiFe2O4 ceramic powder;

[0009] S3: C / metal solid solution powder and NiFe2O4 ceramic powder are mixed according to a set mass ratio, put into a ball mill jar with a dispersion medium added, and ball milled to obtain a mixed slurry, vacuum dried and sieved to obtain anode mixed raw material powder, and a binder is added to the mixed raw material according to a certain mass ratio to obtain C / metal-ceramic mixed powder;

[0010] S4: Pressing the C / metal-ceramic mixed powder into a shape under a certain pressure, vacuum drying to remove moisture, and then heating at a certain temperature to remove the binder to obtain an anode green body;

[0011] S5: The anode green body is subjected to Joule heat sintering, heated to a sintering temperature in an inert atmosphere, kept at that temperature for a certain period of time, and then cooled to room temperature to obtain a metal ceramic inert anode.

[0012] 2. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that the mass proportion of graphite powder in the metal powder and graphite powder raw materials is 0-5% (not 0), the mass proportion of metal powder is 95%-100% (not 100%), and the composition is at least one of Ni, Fe, Mn, Cu, Zn, Cr, and Co.

[0013] 3. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that the C-metal mixed powder is heat-treated under vacuum or inert atmosphere, the heat treatment temperature is 900-1500°C, and the insulation time is 1-3h.

[0014] 4. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that: in the composition of the nickel oxide and iron oxide powder raw materials, the molar mass ratio of nickel oxide to iron oxide is 1.0 to 1.5:1, the calcination temperature of the mixed powder is 1100 to 1300°C, and the calcination time is 2 to 6 hours.

[0015] 5. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that: in the composition of the C / metal solid solution powder and the NiFe2O4 ceramic powder, the mass proportion of the C / metal solid solution powder is 10% to 30%, and the total mass proportion of the NiFe2O4 ceramic powder is 70% to 90%.

[0016] 6. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that the ball milling liquid dispersion medium is one of water, ethanol, isopropanol, acetone, toluene, n-hexane, cyclohexane, mineral oil, silicone oil, ethylene glycol, etc., and the ball milling time is 1 to 20 hours.

[0017] 7. The method for preparing a densely structured metal-ceramic inert anode material for aluminum electrolysis is characterized in that during the C / metal-ceramic mixed powder compression molding process, the binder is one of dextrin, starch, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and hydroxymethyl cellulose, and the amount of binder added is 5% to 20% of the mass of the C / metal-ceramic mixed powder.

[0018] 8. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that the compression molding includes at least one of molding and isostatic pressing, the molding pressure is 5 to 20 MPa, and the isostatic pressing pressure is 350 to 450 MPa.

[0019] 9. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that the binder in the green body is removed under an inert atmosphere, the degreasing temperature is 200 to 600°C, and the heating time is 1 to 5 hours.

[0020] 10. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis is characterized in that the Joule heat sintering temperature is 1200-1500°C, the insulation time is 10-100s, the heating and cooling rates are 50-150°C / min, and the inert atmosphere includes one of vacuum, Ar, N2, CO, and CO2.

[0021] Principles and advantages

[0022] The present invention pre-treats the metal phase, mixes the metal powder with the graphite powder and performs heat treatment to obtain the C / metal solid solution powder, dissolves the C in the metal phase lattice gap, then mixes the C / metal powder with the nickel-iron spinel powder and performs Joule heat sintering, wherein the C precipitates from the metal lattice gap under the action of a large temperature gradient and diffuses to the ceramic interface, and undergoes an oxidation-reduction reaction with the nickel-iron spinel at the phase interface to form a nickel-iron alloy (2C+NiFe2O4=Ni+2Fe+2CO2), the nickel-iron alloy and the metal phase are in-situ sintered at the phase interface, and the ceramic particles are rearranged under the action of capillary force, so that the ceramic particles are aggregated and bonded to form a metal-alloy-ceramic continuous interface; at the same time, the extremely fast heating and cooling rates of the Joule heat are utilized to effectively inhibit the grain growth and coarsening of the metal ceramic, thereby significantly improving the density, electrical conductivity and mechanical properties of the metal ceramic material (see Table 1). Table 1 Comprehensive performance comparison between the embodiment and the comparative example

[0023] The advantages of the method of the present invention are as follows: (1) The wettability of the metal phase and the ceramic phase in the obtained anode material is significantly improved. C is dissolved in the metal phase as a reducing agent, reacts with spinel at high temperature to form a nickel-iron alloy at the metal / ceramic interface, and is in-situ sintered with the metal phase to form a continuous metal-alloy-ceramic interface. (2) The density of the obtained metal ceramic is as high as 98%. Compared with the inert anode in the prior art, the dense anode not only has a better conductive channel, but also can better resist the corrosion of molten salt electrolyte. (3) The mechanical properties of the metal ceramic are significantly improved. The large temperature gradient thermal field generated by Joule heat sintering promotes the redox reaction between C and spinel to form a nickel-iron alloy at the interface. The surface tension of the alloy liquid phase diffusion promotes the contraction of the ceramic phase, and in-situ sintering with the metal phase forms a continuous and stable interface, so that the phase distribution is uniform, the phase particles are fine, and the particle specific surface area is increased, which is beneficial to prevent crack propagation and relieve stress concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The process flow chart of the present invention for preparing a high-density metal ceramic inert anode for aluminum electrolysis;

[0025] Figure 2 This is a microscopic morphology of the metal ceramic inert anode prepared in Example 2 of the present invention;

[0026] Figure 3 This is a microscopic morphology of the metal ceramic inert anode prepared in Comparative Example 1 of the present invention; DETAILED DESCRIPTION

[0028] Example 1

[0029] The raw material powders used in this embodiment include nickel oxide powder, iron oxide powder, metal nickel powder, and graphite powder, wherein the molar mass ratio of NiO to Fe2O3 is 1:1, the graphite powder accounts for 1% of the mass of the metal Ni powder, and the C / Ni solid solution powder accounts for 10% of the total mass of the raw material powder. The preparation method steps of this embodiment are as follows:

[0030] (1) Preparation of C / Ni solid solution powder. Anhydrous ethanol was used as the dispersion medium, and metal Ni powder with a graphite powder accounting for 1 wt% was added. The mixture was ball-milled at a speed of 330 r / min for 5 h to obtain a uniformly mixed C / Ni mixed slurry. After the mixed slurry was dried, it was heated to 900°C in a resistance furnace and kept at this temperature for 3 h, cooled to room temperature, and ground through a 200-mesh sieve to obtain a C / Ni solid solution powder.

[0031] (2) Preparation of NiFe2O4 ceramic powder. Using anhydrous ethanol as the dispersion medium, NiO and Fe2O3 were mixed in a molar mass ratio of 1:1, and ball milled at a speed of 330 r / min for 5 h to obtain a mixed slurry and dried. The dried powder was then placed in a resistance furnace and calcined at 1100°C for 6 h, crushed and ground, and passed through a 200-mesh sieve to obtain NiFe2O4 ceramic powder.

[0032] (3) Preparation of C / metal-ceramic composite powder. Using anhydrous ethanol as the dispersion medium, C / Ni solid solution powder and NiFe2O4 ceramic powder were mixed and ball-milled at a speed of 330 r / min for 5 h to obtain C / metal-ceramic slurry. The slurry was vacuum-dried and ground through a 200-mesh sieve. Then, 5% by mass of dextrin was added to the sieved material and stirred evenly to obtain C / metal-ceramic composite powder.

[0033] (4) Compression molding: The C / metal-ceramic powder is subjected to molding and isostatic pressing in sequence, with a molding pressure of 5 MPa and a holding time of 1 min; the isostatic pressing pressure is 350 MPa and the holding time is 30 s, to obtain a C / metal-ceramic compact.

[0034] (5) Pre-sintering and debinding: The C / metal-ceramic compact is debinded at low temperature in an argon atmosphere, wherein the debinding temperature is 200°C and the debinding time is 5 hours.

[0035] (6) Joule heat sintering. The degreased green body is rapidly sintered at high temperature under vacuum, wherein the sintering temperature is 1200°C and the sintering time is 100 seconds. After sintering, a metal ceramic inert anode material can be obtained.

[0036] The average grain size of the metal ceramic inert anode obtained in this example is 1.3um. The density of the metal ceramic is better than 96.43%, the conductivity is 37.6S / cm, and the Vickers hardness is 758.4N·mm -2 , fracture toughness is 5.3MPa·m 1 / 2 , the three-point bending strength is 98.7MPa.

[0037] Example 2

[0038] The raw material powders used in this embodiment include nickel oxide powder, iron oxide powder, metal nickel powder, and graphite powder, wherein the molar mass ratio of NiO to Fe2O3 is 1.32:1, the graphite powder accounts for 2% of the mass of the metal Ni powder, and the C / Ni solid solution powder accounts for 17% of the total mass of the raw material powder. The preparation method steps of this embodiment are as follows:

[0039] (1) Preparation of C / Ni solid solution powder. Anhydrous ethanol was used as the dispersion medium, and metal Ni powder with a graphite powder accounting for 2 wt% was added. The mixture was ball-milled at a speed of 330 r / min for 12 h to obtain a uniformly mixed C / Ni mixed slurry. After the mixed slurry was dried, it was heated to 1200°C in a resistance furnace and kept at this temperature for 2 h, cooled to room temperature, and ground through a 200-mesh sieve to obtain a C / Ni solid solution powder.

[0040] (2) Preparation of NiFe2O4 ceramic powder. Using anhydrous ethanol as the dispersion medium, NiO and Fe2O3 were mixed at a molar mass ratio of 1.32:1, and ball milled at a speed of 330 r / min for 12 h to obtain a mixed slurry and dried. The dried powder was then placed in a resistance furnace and calcined at 1200°C for 4 h, crushed and ground, and passed through a 200-mesh sieve to obtain NiFe2O4 ceramic powder.

[0041] (3) Preparation of C / metal-ceramic composite powder. Using anhydrous ethanol as the dispersion medium, C / Ni solid solution powder and NiFe2O4 ceramic powder were mixed and ball-milled at a speed of 330 r / min for 12 h to obtain C / metal-ceramic slurry. The slurry was vacuum-dried and ground through a 200-mesh sieve. Then, 10% by mass of dextrin was added to the sieved material and stirred evenly to obtain C / metal-ceramic composite powder.

[0042] (4) Compression molding: The C / metal-ceramic powder is subjected to molding and isostatic pressing in sequence, with a molding pressure of 10 MPa and a holding time of 1 min; the isostatic pressing pressure is 400 MPa and the holding time is 30 s, to obtain a C / metal-ceramic compact.

[0043] (5) Pre-sintering and debinding: The C / metal-ceramic compact is debinded at low temperature in an argon atmosphere, wherein the debinding temperature is 600°C and the debinding time is 1 h.

[0044] (6) Joule heat sintering: The degreased green body is rapidly sintered at high temperature under vacuum, wherein the sintering temperature is 1350°C and the sintering time is 40 seconds. After sintering, a metal ceramic inert anode material can be obtained.

[0045] The average grain size of the metal ceramic inert anode obtained in this example is 1.2um. The density of the metal ceramic is better than 98.58%, the conductivity is 48.9S / cm, and the Vickers hardness is 856.3N·mm -2 , fracture toughness is 7.1MPa·m 1 / 2 , the three-point bending strength is 118.5MPa.

[0046] Example 3

[0047] The raw material powders used in this embodiment include nickel oxide powder, iron oxide powder, metal nickel powder, and graphite powder, wherein the molar mass ratio of NiO to Fe2O3 is 1.5:1, the graphite powder accounts for 5% of the mass of the metal Ni powder, and the C / Ni solid solution powder accounts for 30% of the total mass of the raw material powder. The preparation method of this embodiment has the following steps:

[0048] (1) Preparation of C / Ni solid solution powder. Anhydrous ethanol was used as the dispersion medium, and metal Ni powder with a graphite powder ratio of 5 wt% was added. The mixture was ball-milled at a speed of 330 r / min for 20 h to obtain a uniformly mixed C / Ni mixed slurry. After the mixed slurry was dried, it was heated to 1500°C in a resistance furnace and kept at this temperature for 1 h, cooled to room temperature, and ground through a 200-mesh sieve to obtain a C / Ni solid solution powder.

[0049] (2) Preparation of NiFe2O4 ceramic powder. Using anhydrous ethanol as the dispersion medium, NiO and Fe2O3 were mixed at a molar mass ratio of 1.5:1, and ball milled at a speed of 330 r / min for 20 h to obtain a mixed slurry and dried. The dried powder was then placed in a resistance furnace and calcined at 1300°C for 2 h, crushed and ground, and passed through a 200-mesh sieve to obtain NiFe2O4 ceramic powder.

[0050] (3) Preparation of C / metal-ceramic composite powder. Using anhydrous ethanol as the dispersion medium, C / Ni solid solution powder and NiFe2O4 ceramic powder were mixed and ball-milled at a speed of 330 r / min for 20 h to obtain C / metal-ceramic slurry. The slurry was vacuum-dried and ground through a 200-mesh sieve. Then, 20% by mass of dextrin was added to the sieved material and stirred evenly to obtain C / metal-ceramic composite powder.

[0051] (4) Compression molding: The C / metal-ceramic powder is subjected to molding and isostatic pressing in sequence, with a molding pressure of 20 MPa and a holding time of 1 min; the isostatic pressing pressure is 450 MPa and the holding time is 30 s, to obtain a C / metal-ceramic compact.

[0052] (5) Pre-sintering and debinding: The C / metal-ceramic compact is debinded at low temperature in an argon atmosphere, wherein the debinding temperature is 400°C and the debinding time is 3 h.

[0053] (6) Joule heat sintering: The degreased green body is rapidly sintered at high temperature under vacuum, wherein the sintering temperature is 1500°C and the sintering time is 10 seconds to obtain a metal ceramic inert anode material.

[0054] The average grain size of the metal ceramic inert anode obtained in this example is 1.5um. The density of the metal ceramic is better than 95.27%, the conductivity is 27.5S / cm, and the Vickers hardness is 697.8N·mm -2 , fracture toughness is 4.4MPa·m1 / 2 , the three-point bending strength is 89.2MPa.

[0055] Comparative Example 1

[0056] The raw material powder used in this embodiment includes nickel-iron spinel powder, nickel oxide powder, and metal nickel powder, wherein NiFe2O4 is the matrix phase, the mass fraction of NiO is 10%, and the metal Ni powder accounts for 17% of the total mass of the raw material powder. The preparation method steps of this embodiment are as follows:

[0057] (1) Preparation of metal-ceramic composite powder. Anhydrous ethanol was used as a dispersion medium, and raw material powder was added to obtain a mixed slurry. The mixture was ball-milled at a speed of 330 r / min for 12 h to obtain a uniformly mixed metal-ceramic slurry. The slurry was vacuum-dried and ground through a 200-mesh sieve. Then, 10% by mass of dextrin was added to the sieved material and stirred evenly to obtain a metal-ceramic composite powder.

[0058] (2) Compression molding: The metal ceramic powder is subjected to molding and isostatic pressing in sequence, with the molding pressure being 10 MPa and the holding time being 1 min; the isostatic pressing pressure being 400 MPa and the holding time being 30 s, to obtain a metal ceramic compact.

[0059] (3) Pre-sintering and debinding: The metal ceramic compact is debinded at low temperature in an argon atmosphere, wherein the debinding temperature is 600°C and the debinding time is 1 hour.

[0060] (4) Atmosphere sintering: The degreased green body is sintered at high temperature in an argon atmosphere, wherein the sintering temperature is 1350°C and the sintering time is 3 hours to obtain a metal ceramic inert anode material.

[0061] The average grain size of the metal ceramic inert anode obtained in this example is 2.1um. The density of the metal ceramic is better than 93.62%, the conductivity is 22.6S / cm, and the Vickers hardness is 672.5N·mm -2 , fracture toughness is 3.8MPa·m 1 / 2 , the three-point bending strength is 82.5MPa.

Claims

1. A method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis, characterized in that: The following steps are involved: S1: weighing metal powder and graphite powder raw materials according to a certain mass ratio, ball milling and mixing in a ball mill to obtain C-metal mixed powder, and heat treating the C-metal mixed powder to obtain C / metal solid solution powder; S2: Weigh nickel oxide and iron oxide powder raw materials according to a certain mass ratio, mix them in a ball mill, obtain oxide mixed slurry, and sieving and calcining to obtain NiFe2O4 ceramic powder; S3: C / metal solid solution powder and NiFe2O4 ceramic powder are mixed according to a set mass ratio, put into a ball mill jar with a dispersion medium added, and ball milled to obtain a mixed slurry, vacuum dried and sieved to obtain anode mixed raw material powder, and a binder is added to the mixed raw material according to a certain mass ratio to obtain C / metal-ceramic mixed powder; S4: Pressing the C / metal-ceramic mixed powder into a shape under a certain pressure, vacuum drying to remove moisture, and then heating at a certain temperature to remove the binder to obtain an anode green body; S5: The anode green body is subjected to Joule heat sintering, heated to a sintering temperature in an inert atmosphere, kept at that temperature for a certain period of time, and then cooled to room temperature to obtain a metal ceramic inert anode.

2. The method for preparing a dense structure metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: In the metal powder and graphite powder raw materials, the mass proportion of graphite powder is 0-5% (not 0), the mass proportion of metal powder is 95%-100% (not 100%), and the composition is at least one of Ni, Fe, Mn, Cu, Zn, Cr, and Co.

3. The method for preparing a dense structure metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: The C-metal mixed powder is heat treated in vacuum or inert atmosphere at a temperature of 900-1500° C. and a heat preservation time of 1-3 hours.

4. The method for preparing a dense structure metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: In the raw material composition of nickel oxide and iron oxide powder, the molar mass ratio of nickel oxide to iron oxide is 1.0-1.5:1, the calcination temperature of the mixed powder is 1100-1300° C., and the calcination time is 2-6 hours.

5. The method for preparing a dense structure metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: In the composition of the C / metal solid solution powder and the NiFe2O4 ceramic powder, the mass proportion of the C / metal solid solution powder is 10% to 30%, and the total mass proportion of the NiFe2O4 ceramic powder is 70% to 90%.

6. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: The ball milling liquid dispersion medium is one of water, ethanol, isopropanol, acetone, toluene, n-hexane, cyclohexane, mineral oil, silicone oil, ethylene glycol, etc., and the ball milling time is 1 to 20 hours.

7. The method for preparing a dense structure metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: During the C / metal-ceramic mixed powder compression molding process, the binder is one of dextrin, starch, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and hydroxymethyl cellulose, and the amount of the binder added is 5% to 20% of the mass of the C / metal-ceramic mixed powder.

8. The method for preparing a dense structure metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: The compression molding includes at least one of molding and isostatic pressing. The molding pressure is 5-20 MPa, and the isostatic pressing pressure is 350-450 MPa.

9. The method for preparing a dense structure metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: The binder in the green body is removed under an inert atmosphere, the degreasing temperature is 200-600° C., and the heating time is 1-5 hours.

10. The method for preparing a densely structured metal ceramic inert anode material for aluminum electrolysis according to claim 1, characterized in that: The Joule heat sintering temperature is 1200-1500° C., the holding time is 10-100s, the heating and cooling rates are 50-150° C. / min, and the inert atmosphere includes one of vacuum, Ar, N2, CO, and CO2.

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