A nickel ferrite composite zirconium boride / silicon carbide material, preparation method and application thereof in aluminum electrolysis

Abstract

The invention provides a nickel ferrite composite zirconium boride / silicon carbide material, a preparation method and application thereof in aluminum electrolysis, and belongs to the technical field of composite materials; the preparation method comprises the steps of preparing the zirconium boride / silicon carbide material, coating, mixing, and forming and sintering; the coating step comprises the steps of adding nickel nitrate, ferric nitrate and polyethylene glycol 200 to deionized water, stirring evenly, adding 18-22wt% ammonia aqueous solution to adjust the pH value to 9.8-10.2, and obtaining a coating liquid; adding the zirconium boride / silicon carbide material to the coating liquid, performing a homogenization treatment, drying, and performing a heating and heat preservation treatment to obtain a coating; the nickel ferrite composite zirconium boride / silicon carbide material of the invention has a high degree of densification, excellent strength performance, good corrosion resistance and high electrical conductivity.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and in particular relates to a nickel ferrite composite zirconium boride / silicon carbide material, a preparation method and application thereof in aluminum electrolysis. Background Art

[0002] Under the theme of low-carbon and environmental protection, carbon-free aluminum electrolysis technology is a new aluminum production technology that replaces carbon anodes with inert anodes. During the electrolysis process, the inert anode does not participate in the anode reaction and only produces oxygen at the anode, avoiding the emission of carbon dioxide, carbon monoxide and asphalt fumes, which meets the requirements of green development. It can also reduce carbon consumption, save a large amount of high-quality carbon materials, reduce the disturbance of the thermal balance of the electrolytic cell caused by anode replacement, enhance the stability of production operation, effectively improve current efficiency, save manpower, and reduce production costs; therefore, the use of inert anode materials in aluminum electrolysis process has become the key development direction of the current aluminum industry.

[0003] Nickel ferrite is an important compound composed of nickel ions and iron ions. It usually appears as black granules or powder. It has high magnetic susceptibility and electrical conductivity, and good thermal shock resistance. It is an important type of inert anode material, which makes it have good application prospects in the field of aluminum electrolysis.

[0004] Most of the inert anodes in the prior art are made of nickel ferrite-based metal ceramic materials, which have good chemical stability, excellent electrical conductivity and thermal shock resistance, but poor corrosion resistance. They are corroded by the electrolyte during use, causing the iron in the anode to dissolve into the electrolyte, and then the iron is precipitated at the cathode, which in turn affects the purity of the aluminum product and limits its application in the aluminum electrolysis industry.

[0005] Zirconium boride is a ceramic material with high melting point, high hardness and high strength. Silicon carbide has good thermal conductivity, low thermal expansion coefficient and excellent thermal shock resistance. Both have good chemical stability and excellent corrosion resistance. They can be used in aluminum electrolysis to effectively improve the efficiency and stability of aluminum electrolysis and ensure the purity of aluminum products. They have broad development prospects in the field of aluminum electrolysis.

[0006] However, the sintering temperature of zirconium boride / silicon carbide materials is relatively high, and they need to be sintered at relatively high temperatures and pressures. The density of the zirconium boride / silicon carbide materials obtained by sintering is relatively low, and their loose internal structure becomes an area of ​​stress concentration, which not only becomes an obstacle to electron transmission, but also affects the stability during use, and is also susceptible to corrosion and penetration by molten salts, affecting the quality and output of aluminum liquid; and the bonding force between zirconium boride and silicon carbide is poor, and the compatibility between the two is poor, resulting in uneven dispersion during mixing, affecting the uniformity of the mixture, and thus affecting the strength performance of the product, shortening the service life, and increasing the resistance to electron transmission, prolonging the transmission time, and reducing the electrical conductivity of the material; when zirconium boride / silicon carbide materials are composited with nickel ferrite, the interface bonding performance is poor, affecting the overall performance and stability of the composite material;

[0007] Therefore, providing a nickel ferrite composite zirconium boride / silicon carbide material with high densification, excellent strength performance, good corrosion resistance and high electrical conductivity is a technical problem that needs to be urgently solved in the prior art. Summary of the invention

[0008] In order to solve the technical problems existing in the prior art, the present invention provides a nickel ferrite composite zirconium boride / silicon carbide material, a preparation method and its application in aluminum electrolysis. The nickel ferrite composite zirconium boride / silicon carbide material has a high degree of densification, excellent strength performance, good corrosion resistance and high electrical conductivity.

[0009] In view of the above technical problems, the present invention adopts the following technical solutions:

[0010] On the one hand, a method for preparing a nickel ferrite composite zirconium boride / silicon carbide material includes the steps of preparing the zirconium boride / silicon carbide material, coating, mixing, and forming and sintering, as follows:

[0011] 1. Preparation of zirconium boride / silicon carbide materials

[0012] (1) Zirconium boride pretreatment

[0013] The zirconium boride is placed in a concentrated sulfuric acid solution, the temperature is increased to 90-95°C, and the reaction is refluxed for 5.7-6.2 hours. After the reflux reaction is completed, the temperature is lowered to 32-37°C, a lithium aluminum hydride solution is added, and the mixture is stirred at this temperature for 3.7-4.2 hours. After filtering and washing, the mixture is dried at 93-97°C to a constant weight to obtain hydroxyl-rich zirconium boride. The hydroxyl-rich zirconium boride is immersed in a pretreatment solution, the temperature is increased to 60-65°C, and the mixture is stirred for 4.7-5.2 hours. After the stirring is completed, the mixture is filtered out, washed with deionized water, and dried at 107-112°C for 9.5-11.0 hours to obtain pretreated zirconium boride.

[0014] The particle size of the zirconium boride is 160-180 nm;

[0015] The lithium aluminum hydride solution is a mixture of lithium aluminum hydride and tetrahydrofuran, and the mass ratio of the lithium aluminum hydride to tetrahydrofuran is 1.0-1.3:45-50;

[0016] The pretreatment liquid is a mixture of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate, and the mass ratio of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate is 100:1.2-1.4:0.5-0.7:0.5-0.8;

[0017] The mass ratio of the zirconium boride, concentrated sulfuric acid solution, and lithium aluminum hydride solution is 9.8-10.3:87-92:15.5-16.0;

[0018] The mass concentration of the concentrated sulfuric acid solution is 70-75%;

[0019] The mass ratio of the hydroxyl-rich zirconium boride to the pretreatment liquid is 8.5-9.0:98-104;

[0020] (2) Silicon carbide pretreatment

[0021] The silicon carbide is placed in a hydrogen peroxide solution, the temperature is increased to 46-50°C and stirred for 2.7-3.2 hours. After the stirring is completed, it is filtered and washed, and then dried at 78-82°C for 1.8-2.2 hours, and then put into an ethanol solution, Tween 60 and glyceryl monostearate are added, and after stirring evenly, methacrylic acid is added, and after continuing to stir evenly, benzoyl peroxide is added, and ultrasonic dispersion is performed. The ultrasonic time is 1.8-2.2 hours, the ultrasonic power is 116-123W, and the ultrasonic frequency is 20-24kHz. After the ultrasonic treatment is completed, the temperature is increased to 80-84°C, and the reaction is stirred for 3.2-3.6 hours. After the reaction is completed, it is filtered and washed with deionized water, and dried at 82-87°C for 7.8-8.2 hours to obtain pretreated silicon carbide;

[0022] The particle size of the silicon carbide is 210-230nm;

[0023] The mass ratio of silicon carbide, hydrogen peroxide solution, ethanol solution, Tween 60, glyceryl monostearate, methacrylic acid, and benzoyl peroxide is 5.0-5.5:52-57:295-306:0.2-0.4:0.4-0.6:0.8-1.2:0.47-0.52;

[0024] The mass concentration of the hydrogen peroxide solution is 20-25%;

[0025] The mass concentration of the ethanol solution is 23-27%;

[0026] (3) Combination

[0027] The pretreated silicon carbide is placed in N,N-dimethylformamide, the temperature is raised to 62-67°C at a rate of 0.8-1.2°C / min, vinyltrimethoxysilane is added and stirred, and the stirring is carried out at 260-300rpm for 2.8-3.2h. After the stirring is completed, the temperature is raised to 94-98°C at a rate of 0.8-1.2°C / min, and the pretreated zirconium boride is added. The reaction is stirred at 230-250rpm for 2.4-2.6h. After the reaction is completed, the zirconium boride / silicon carbide material is obtained by filtering, washing and drying;

[0028] The mass ratio of the pretreated silicon carbide, N,N-dimethylformamide, vinyltrimethoxysilane and pretreated zirconium boride is 4.0-4.5:98-102:1.12-1.22:5.2-5.5.

[0029] 2. Coating

[0030] Add nickel nitrate, iron nitrate and polyethylene glycol 200 to deionized water, stir evenly, add ammonia solution to adjust the pH value to 9.8-10.2, and obtain a coating solution; add zirconium boride / silicon carbide material to the coating solution, perform homogenization treatment, the homogenization time is 4.7-5.3 minutes, the homogenization pressure is 4.3-4.7 MPa, the homogenization times are 2 times, after the homogenization treatment is completed, dry to constant weight at 83-87°C, then heat to 336-342°C at a rate of 4.5-5.5°C / min, keep warm for 25-30 minutes, then heat to 605-613°C at a rate of 1.8-2.2°C / min, keep warm for 1.5-2.0 hours, and after the insulation is completed, obtain a coating;

[0031] The mass ratio of the deionized water, nickel nitrate, ferric nitrate and polyethylene glycol 200 is 114-125:3.8-4.2:1.5-2.0:1.1-1.4;

[0032] The mass concentration of the ammonia solution is 18-22%;

[0033] The mass ratio of the coating liquid to the zirconium boride / silicon carbide material is 98-103:8.0-8.5.

[0034] 3. Mixing

[0035] Add nickel ferrite, coating, and sodium dodecylbenzene sulfonate to deionized water, and perform ball milling. The ball milling time is 23-28 minutes, the ball milling speed is 110-120 rpm, and the ball milling temperature is 34-38° C. Then, polyvinyl alcohol and hydroxyethyl cellulose are added, and the ball milling is continued for 16-20 minutes. After the ball milling is completed, the mixed powder is dried at 98-102° C. to constant weight to obtain a mixed powder;

[0036] The particle size of the nickel ferrite is 350-370nm;

[0037] The mass ratio of the deionized water, nickel ferrite, coating, sodium dodecylbenzene sulfonate, polyvinyl alcohol and hydroxyethyl cellulose is 60-65:57.5-58.4:3.5-4.0:0.8-1.2:0.3-0.5:0.2-0.4.

[0038] 4. Molding and sintering

[0039] The mixed powder is placed in a mold for isostatic pressing, and the molding pressure is controlled to be 165-174MPa for 8-12min to obtain a green body; the green body is heated to 970-990℃ at a rate of 6.3-6.6℃ / min under an argon atmosphere, and kept warm for 28-32min. After the insulation is completed, the temperature is increased to 1960-2020℃ at a rate of 3.8-4.2℃ / mn, and kept warm for 3.0-3.4h, and cooled to room temperature with the furnace to obtain a nickel ferrite composite zirconium boride / silicon carbide material.

[0040] On the other hand, a nickel ferrite composite zirconium boride / silicon carbide material is prepared by the above method.

[0041] The nickel ferrite composite zirconium boride / silicon carbide material prepared by the present invention is used in aluminum electrolysis, which can effectively improve the efficiency of aluminum electrolysis, ensure the stability of aluminum electrolysis, and improve the purity of aluminum products.

[0042] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0043] 1. The present invention first prepares the zirconium boride / silicon carbide material by a specific method, and pre-treats the zirconium boride, specifically, acidifying the zirconium boride, treating it with a reducing agent, so that the surface of the zirconium boride contains more hydroxyl groups, and then immersing it in a pre-treatment liquid containing amino groups, so that the pre-treated zirconium boride contains more amino groups; the pre-treatment of silicon carbide is to first disperse it, and then add methacrylic acid monomer to polymerize it on the surface of silicon carbide, so that the surface of the pre-treated silicon carbide has more carboxyl groups; in the bonding step, a vinyl silane coupling agent is introduced, and the hydroxyl group at one end of the coupling agent can be combined with the carboxyl group of the pre-treated silicon carbide, and the vinyl group can react with the pre-treated zirconium boride, thereby enhancing the compatibility and bonding force between the pre-treated zirconium boride and the pre-treated silicon carbide, and through the bridge effect of the vinyl silane coupling agent, the pre-treated zirconium boride and the pre-treated silicon carbide are bonded. A uniform and dense distribution is formed in the material, and defects at the bonding interface are reduced, thereby improving the strength and stability of the composite material and ensuring the electrical conductivity of the composite material. In the coating step, nickel ferrite is generated in situ on the surface of zirconium boride / silicon carbide, so that the nickel ferrite coating layer can be tightly attached to the surface of the zirconium boride / silicon carbide material, thereby enhancing the interface bonding force and improving the interface bonding performance, which can effectively reduce the defects and stress concentration inside the composite material and enhance the overall stability of the material; in the mixing step, the uniform dispersion of the coating in the nickel ferrite matrix is ​​enhanced, which helps to improve the homogeneity of the mixed powder, and ultimately ensures the densification degree and stability of the composite material, so that it has excellent corrosion resistance, good strength and good electrical conductivity. When used in aluminum electrolysis, it can effectively improve the efficiency of aluminum electrolysis, enhance the stability of electrolysis, and ensure the purity of aluminum products;

[0044] 2. The nickel ferrite composite zirconium boride / silicon carbide material prepared by the present invention has a density of 98.7-99.0%;

[0045] 3. The nickel ferrite composite zirconium boride / silicon carbide material prepared by the present invention has a flexural strength of 453.8-456.4 MPa and a room temperature conductivity of 177.5-178.6 S / cm;

[0046] 4. The nickel ferrite composite zirconium boride / silicon carbide material prepared by the present invention was subjected to an electrolysis test in a molten salt system at 1000°C. The molten salt system was NaF·AlF3+CaF2+Al2O3, wherein the molar ratio of NaF·AlF3 was 2.0, the mass concentration of CaF2 was 5.0%, the mass concentration of Al2O3 was 5.0%, and the anode current density was 1.0 A / cm 2 The electrolysis time is 48 hours. The annual corrosion rate is calculated by testing the corrosion amount in 48 hours to be 7.6-8.1mm / a.

[0047] 5. The nickel ferrite composite zirconium boride / silicon carbide material prepared in the present invention is heated to 1000°C at a rate of 20°C / min in an air atmosphere, kept at this temperature for 24.0 hours, and then cooled to 20°C at a rate of 40°C / min. This is considered a cycle. After repeating the cycle 20 times, the flexural strength is measured again to be 437.0-444.5MPa. DETAILED DESCRIPTION

[0048] In order to more clearly understand the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described.

[0049] Example 1

[0050] 1. Preparation of zirconium boride / silicon carbide materials

[0051] (1) Zirconium boride pretreatment

[0052] 10.0 g of zirconium boride was placed in 90 g of 72 wt% concentrated sulfuric acid solution, the temperature was raised to 93° C., and refluxed for 6.0 h. After the reflux reaction was completed, the temperature was lowered to 35° C., 15.8 g of lithium aluminum hydride solution was added, and the mixture was stirred at this temperature for 4.0 h. After filtering and washing, the mixture was dried at 95° C. to constant weight to obtain hydroxyl-rich zirconium boride. 8.8 g of hydroxyl-rich zirconium boride was immersed in 100 g of pretreatment solution, the temperature was raised to 63° C. and stirred for 5.0 h. After the stirring was completed, the mixture was filtered out, washed with deionized water, and dried at 110° C. for 10.0 h to obtain pretreated zirconium boride.

[0053] The particle size of the zirconium boride is 170 nm;

[0054] The lithium aluminum hydride solution is a mixture of lithium aluminum hydride and tetrahydrofuran, and the mass ratio of the lithium aluminum hydride to tetrahydrofuran is 1.2:47;

[0055] The pretreatment liquid is a mixture of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate, and the mass ratio of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate is 100:1.3:0.6:0.7;

[0056] (2) Silicon carbide pretreatment

[0057] 5.2 g of silicon carbide was placed in 55 g of 23 wt% hydrogen peroxide solution, the temperature was raised to 48 ° C and stirred for 3.0 h. After the stirring was completed, it was filtered and washed, and then dried at 80 ° C for 2.0 h. Then, it was put into 300 g of 25 wt% ethanol solution, 0.3 g of Tween 60 and 0.5 g of glyceryl monostearate were added, and after stirring, 1.0 g of methacrylic acid was added. After continuing to stir, 0.50 g of benzoyl peroxide was added, and ultrasonic dispersion was performed. The ultrasonic time was 2.0 h, the ultrasonic power was 120 W, and the ultrasonic frequency was 22 kHz. After the ultrasonic treatment was completed, the temperature was raised to 82 ° C, and the reaction was stirred for 3.5 h. After the reaction was completed, it was filtered, washed with deionized water, and dried at 85 ° C for 8.0 h to obtain pretreated silicon carbide;

[0058] The particle size of the silicon carbide is 220 nm;

[0059] (3) Combination

[0060] Place 4.3 g of pretreated silicon carbide in 100 g of N,N-dimethylformamide, heat to 65°C at a rate of 1.0°C / min, add 1.17 g of vinyltrimethoxysilane and stir, stir at 280 rpm for 3.0 h. After stirring, heat to 96°C at a rate of 1.0°C / min, add 5.4 g of pretreated zirconium boride, stir and react at 240 rpm for 2.5 h. After the reaction, filter, wash and dry to obtain zirconium boride / silicon carbide material.

[0061] 2. Coating

[0062] 4.0 g of nickel nitrate, 1.7 g of ferric nitrate, and 1.3 g of polyethylene glycol 200 were added to 120 g of deionized water, and after stirring evenly, a 20 wt % ammonia solution was added to adjust the pH value to 10 to obtain a coating liquid; 8.3 g of zirconium boride / silicon carbide material was added to 100 g of the coating liquid, and homogenization was performed. The homogenization time was 5.0 min, the homogenization pressure was 4.5 MPa, and the number of homogenizations was 2 times. After the homogenization treatment was completed, it was dried to constant weight at 85°C, and then heated to 340°C at a rate of 5.0°C / min, and kept warm for 27 min, and then heated to 610°C at a rate of 2.0°C / min, and kept warm for 1.8 h. After the insulation was completed, a coating was obtained.

[0063] 3. Mixing

[0064] Add 58.0 g of nickel ferrite, 3.7 g of coating, and 1.0 g of sodium dodecylbenzene sulfonate to 62 g of deionized water, and perform ball milling. The ball milling time is 25 min, the ball milling speed is 114 rpm, and the ball milling temperature is 36 ° C. Then, add 0.4 g of polyvinyl alcohol and 0.3 g of hydroxyethyl cellulose, and continue ball milling for 18 min. After the ball milling is completed, dry at 100 ° C to constant weight to obtain a mixed powder;

[0065] The particle size of the nickel ferrite is 360 nm.

[0066] 4. Molding and sintering

[0067] The mixed powder is placed in a mold for isostatic pressing, and the molding pressure is controlled to be 170 MPa for 10 min to obtain a green body; the green body is heated to 980°C at a rate of 6.5°C / min under an argon atmosphere and kept warm for 30 min. After the insulation is completed, the temperature is increased to 2000°C at a rate of 4.0°C / mn and kept warm for 3.2 h. The green body is cooled to room temperature with the furnace to obtain a nickel ferrite composite zirconium boride / silicon carbide material.

[0068] Example 2

[0069] 1. Preparation of zirconium boride / silicon carbide materials

[0070] (1) Zirconium boride pretreatment

[0071] 9.8 g of zirconium boride was placed in 87 g of 70 wt% concentrated sulfuric acid solution, the temperature was raised to 90°C, and refluxed for 5.7 h. After the reflux reaction was completed, the temperature was lowered to 32°C, 15.5 g of lithium aluminum hydride solution was added, and the mixture was stirred at this temperature for 3.7 h. After filtering and washing, the mixture was dried at 93°C to constant weight to obtain hydroxyl-rich zirconium boride. 8.5 g of hydroxyl-rich zirconium boride was immersed in 98 g of pretreatment solution, the temperature was raised to 60°C, and the stirring time was 4.7 h. After the stirring was completed, the mixture was filtered out, washed with deionized water, and dried at 107°C for 11.0 h to obtain pretreated zirconium boride.

[0072] The particle size of the zirconium boride is 160 nm;

[0073] The lithium aluminum hydride solution is a mixture of lithium aluminum hydride and tetrahydrofuran, and the mass ratio of the lithium aluminum hydride to tetrahydrofuran is 1.0:45;

[0074] The pretreatment liquid is a mixture of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate, and the mass ratio of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate is 100:1.2:0.5:0.5;

[0075] (2) Silicon carbide pretreatment

[0076] 5.0 g of silicon carbide was placed in 52 g of 20 wt% hydrogen peroxide solution, the temperature was raised to 46 ° C and stirred for 3.2 h. After the stirring was completed, it was filtered and washed, and then dried at 78 ° C for 2.2 h. Then, it was put into 295 g of 23 wt% ethanol solution, 0.2 g of Tween 60 and 0.4 g of glyceryl monostearate were added, and after stirring evenly, 0.8 g of methacrylic acid was added. After continuing to stir evenly, 0.47 g of benzoyl peroxide was added, and ultrasonic dispersion was performed. The ultrasonic time was 1.8 h, the ultrasonic power was 116 W, and the ultrasonic frequency was 20 kHz. After the ultrasonic was completed, the temperature was raised to 80 ° C, and the reaction was stirred for 3.2 h. After the reaction was completed, it was filtered and washed with deionized water, and dried at 82 ° C for 7.8 h to obtain pretreated silicon carbide;

[0077] The particle size of the silicon carbide is 210 nm;

[0078] (3) Combination

[0079] Place 4.0g of pretreated silicon carbide in 98g of N,N-dimethylformamide, heat to 62°C at a rate of 0.8°C / min, add 1.12g of vinyltrimethoxysilane and stir, stir at 260rpm for 3.2h. After stirring, heat to 94°C at a rate of 0.8°C / min, add 5.2g of pretreated zirconium boride, stir at 230rpm for 2.4h. After the reaction, filter, wash and dry to obtain zirconium boride / silicon carbide material.

[0080] 2. Coating

[0081] 3.8 g of nickel nitrate, 1.5 g of ferric nitrate, and 1.1 g of polyethylene glycol 200 were added to 114 g of deionized water, and after stirring evenly, 18 wt % ammonia solution was added to adjust the pH value to 9.8 to obtain a coating liquid; 8.0 g of zirconium boride / silicon carbide material was added to 98 g of the coating liquid, and homogenization was performed. The homogenization time was 4.7 min, the homogenization pressure was 4.3 MPa, and the number of homogenizations was 2 times. After the homogenization treatment was completed, it was dried to constant weight at 83 ° C, and then heated to 336 ° C at a rate of 4.5 ° C / min, and kept warm for 25 min, and then heated to 605 ° C at a rate of 1.8 ° C / min, and kept warm for 1.5 h. After the insulation was completed, a coating was obtained.

[0082] 3. Mixing

[0083] Add 57.5 g of nickel ferrite, 3.5 g of coating, and 0.8 g of sodium dodecylbenzene sulfonate to 60 g of deionized water, and perform ball milling. The ball milling time is 23 min, the ball milling speed is 110 rpm, and the ball milling temperature is 34 ° C. Then, add 0.3 g of polyvinyl alcohol and 0.2 g of hydroxyethyl cellulose, and continue ball milling for 16 min. After the ball milling is completed, dry at 98 ° C to constant weight to obtain a mixed powder;

[0084] The particle size of the nickel ferrite is 350 nm.

[0085] 4. Molding and sintering

[0086] The mixed powder is placed in a mold for isostatic pressing, and the molding pressure is controlled to be 165MPa for 8min to obtain a green body; the green body is heated to 970℃ at a rate of 6.3℃ / min under an argon atmosphere and kept warm for 28min. After the insulation is completed, the temperature is increased to 1960℃ at a rate of 3.8℃ / mn and kept warm for 3.0h. The green body is cooled to room temperature with the furnace to obtain a nickel ferrite composite zirconium boride / silicon carbide material.

[0087] Example 3

[0088] 1. Preparation of zirconium boride / silicon carbide materials

[0089] (1) Zirconium boride pretreatment

[0090] 10.3 g of zirconium boride was placed in 92 g of 75 wt% concentrated sulfuric acid solution, the temperature was raised to 95°C, and refluxed for 6.2 h. After the reflux reaction was completed, the temperature was lowered to 37°C, 16.0 g of lithium aluminum hydride solution was added, and the mixture was stirred at this temperature for 4.2 h. After filtering and washing, the mixture was dried at 97°C to constant weight to obtain hydroxyl-rich zirconium boride. 9.0 g of hydroxyl-rich zirconium boride was immersed in 104 g of pretreatment solution, the temperature was raised to 65°C, and the stirring time was 5.2 h. After the stirring was completed, the mixture was filtered out, washed with deionized water, and dried at 112°C for 9.5 h to obtain pretreated zirconium boride.

[0091] The particle size of the zirconium boride is 180 nm;

[0092] The lithium aluminum hydride solution is a mixture of lithium aluminum hydride and tetrahydrofuran, and the mass ratio of the lithium aluminum hydride to tetrahydrofuran is 1.3:50;

[0093] The pretreatment liquid is a mixture of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate, and the mass ratio of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate is 100:1.4:0.7:0.8;

[0094] (2) Silicon carbide pretreatment

[0095] 5.5 g of silicon carbide was placed in 57 g of 25 wt% hydrogen peroxide solution, the temperature was raised to 50°C and stirred for 2.7 h. After the stirring was completed, it was filtered and washed, and then dried at 82°C for 1.8 h. Then, it was placed in 306 g of 27 wt% ethanol solution, 0.4 g of Tween 60 and 0.6 g of glyceryl monostearate were added, and after stirring evenly, 1.2 g of methacrylic acid was added. After continuing to stir evenly, 0.52 g of benzoyl peroxide was added, and ultrasonic dispersion was performed. The ultrasonic time was 2.2 h, the ultrasonic power was 123 W, and the ultrasonic frequency was 24 kHz. After the ultrasonic treatment was completed, the temperature was raised to 84°C, and the reaction was stirred for 3.6 h. After the reaction was completed, it was filtered, washed with deionized water, and dried at 87°C for 8.2 h to obtain pretreated silicon carbide;

[0096] The particle size of the silicon carbide is 230 nm;

[0097] (3) Combination

[0098] Place 4.5g of pretreated silicon carbide in 102g of N,N-dimethylformamide, heat to 672°C at a rate of 1.2°C / min, add 1.22g of vinyltrimethoxysilane and stir, stir at 300rpm for 2.8h. After stirring, heat to 98°C at a rate of 1.2°C / min, add 5.5g of pretreated zirconium boride, stir and react at 250rpm for 2.6h. After the reaction, filter, wash and dry to obtain zirconium boride / silicon carbide material.

[0099] 2. Coating

[0100] 4.2 g of nickel nitrate, 2.0 g of ferric nitrate, and 1.4 g of polyethylene glycol 200 were added to 125 g of deionized water, and after stirring evenly, a 22 wt % ammonia solution was added to adjust the pH value to 10.2 to obtain a coating liquid; 8.5 g of zirconium boride / silicon carbide material was added to 103 g of the coating liquid, and homogenization was performed. The homogenization time was 5.3.7 min, the homogenization pressure was 4.7 MPa, and the number of homogenizations was 2 times. After the homogenization treatment was completed, it was dried to constant weight at 87 ° C, and then heated to 342 ° C at a rate of 5.5 ° C / min, and kept warm for 30 min, and then heated to 613 ° C at a rate of 2.2 ° C / min, and kept warm for 2.0 h. After the insulation was completed, a coating was obtained.

[0101] 3. Mixing

[0102] Add 58.4 g of nickel ferrite, 4.0 g of coating, and 1.2 g of sodium dodecylbenzene sulfonate to 65 g of deionized water, and perform ball milling. The ball milling time is 28 min, the ball milling speed is 120 rpm, and the ball milling temperature is 38 ° C. Then, add 0.5 g of polyvinyl alcohol and 0.4 g of hydroxyethyl cellulose, and continue ball milling for 20 min. After the ball milling is completed, dry at 102 ° C to constant weight to obtain a mixed powder;

[0103] The particle size of the nickel ferrite is 370 nm.

[0104] 4. Molding and sintering

[0105] The mixed powder is placed in a mold for isostatic pressing, and the molding pressure is controlled to be 174MPa for 12min to obtain a green body; the green body is heated to 990℃ at a rate of 6.6℃ / min under an argon atmosphere and kept warm for 32min. After the insulation is completed, the temperature is increased to 2020℃ at a rate of 4.2℃ / mn and kept warm for 3.4h. The green body is cooled to room temperature with the furnace to obtain a nickel ferrite composite zirconium boride / silicon carbide material.

[0106] Comparative Example 1

[0107] Based on Example 1, the changes are as follows:

[0108] In the step of preparing the zirconium boride / silicon carbide material, the zirconium boride pretreatment and silicon carbide pretreatment steps are omitted;

[0109] In the combining step, an equal amount of pretreated silicon carbide is replaced by silicon carbide without any treatment, and an equal amount of pretreated zirconium boride is replaced by zirconium boride without any treatment;

[0110] The particle size of the zirconium boride is 170 nm; the particle size of the silicon carbide is 220 nm;

[0111] The rest of the operations are the same.

[0112] Comparative Example 2

[0113] Based on Example 1, the changes are as follows:

[0114] In the step of preparing the zirconium boride / silicon carbide material, the combining step is to place 4.3 g of pretreated silicon carbide in 100 g of N,N-dimethylformamide, heat it to 96° C. at a rate of 1.0° C. / min, add 5.4 g of pretreated zirconium boride, stir and react at 240 rpm for 2.5 hours, and after the reaction is completed, filter, wash and dry to obtain the zirconium boride / silicon carbide material;

[0115] The coating step is omitted, and in the mixing step, the coating material is replaced with zirconium boride / silicon carbide material in equal amounts;

[0116] The rest of the operations are the same.

[0117] Performance Testing

[0118] The performance of the nickel ferrite composite zirconium boride / silicon carbide materials prepared in Examples 1-3 and Comparative Examples 1-2 was tested as follows:

[0119]

[0120] The corrosion rate was determined by electrolyzing the nickel ferrite composite zirconium boride / silicon carbide material in a molten salt system at 1000°C. The molten salt system was NaF·AlF3+CaF2+Al2O3, where the molar ratio of NaF·AlF3 was 2.0, the mass concentration of CaF2 was 5.0%, the mass concentration of Al2O3 was 5.0%, and the anode current density was 1.0 A / cm 2 , the electrolysis time is 48h, and the annual corrosion rate is calculated by testing the corrosion amount in 48h;

[0121] The hot and cold cycle flexural strength test is to raise the temperature of the nickel ferrite composite zirconium boride / silicon carbide material to 1000℃ at a rate of 20℃ / min in an air atmosphere, keep it at this temperature for 24.0h, and then lower the temperature to 20℃ at a rate of 40℃ / min. This is one cycle. After repeating the cycle 20 times, the flexural strength is tested again.

[0122] The invention first prepares the zirconium boride / silicon carbide material by a specific method, and pre-treats the zirconium boride, specifically, acidifying the zirconium boride, treating it with a reducing agent, so that the surface of the zirconium boride contains more hydroxyl groups, and then immersing it in a pre-treatment liquid containing amino groups, so that the pre-treated zirconium boride contains more amino groups; the pre-treatment of silicon carbide is to add methyl acrylate monomer after dispersion treatment, so that it is polymerized on the surface of silicon carbide, so that the surface of the pre-treated silicon carbide has more carboxyl groups; in the bonding step, a vinyl silane coupling agent is introduced, and the hydroxyl group at one end of the coupling agent can be combined with the carboxyl group of the pre-treated silicon carbide, and the vinyl group can react with the pre-treated zirconium boride, so as to enhance the compatibility and bonding force between the pre-treated zirconium boride and the pre-treated silicon carbide, and through the bridge effect of the vinyl silane coupling agent, the pre-treated zirconium boride and the pre-treated silicon carbide are bonded together. A uniform and dense distribution is formed in the material, and defects at the bonding interface are reduced, so that the strength and stability of the composite material can be improved, and the electrical conductivity of the composite material can be guaranteed. In the coating step, nickel ferrite is in-situ generated on the surface of zirconium boride / silicon carbide, so that the nickel ferrite coating layer can be tightly attached to the surface of the zirconium boride / silicon carbide material, thereby enhancing the interface bonding force and improving the interface bonding performance, which can effectively reduce the defects and stress concentration inside the composite material and enhance the overall stability of the material; in the mixing step, the uniform dispersion of the coating in the nickel ferrite matrix is ​​enhanced, which helps to improve the homogeneity of the mixed powder, and finally ensures the densification degree and stability of the composite material, so that the composite material has excellent corrosion resistance, good strength and good electrical conductivity. When used in aluminum electrolysis, it can effectively improve the aluminum electrolysis efficiency, enhance the electrolysis stability and ensure the purity of the aluminum product.

[0123] Comparative Example 1 omits the pretreatment step of zirconium boride and silicon carbide. In the bonding step, zirconium boride and silicon carbide without any treatment are directly used, and a vinyl silane coupling agent is introduced. The hydroxyl group at one end of the coupling agent can be combined with zirconium boride and silicon carbide, and the vinyl group at the other end has poor bonding with zirconium boride and silicon carbide, so that the bridging effect of the vinyl silane coupling agent cannot be achieved, and the interfacial bonding performance of zirconium boride and silicon carbide is weakened, thereby affecting the coating of zirconium boride / silicon carbide materials by nickel ferrite, and ultimately affecting the density of the composite material. There are many defects in the bonding interface, the overall stability is poor, the strength performance and conductivity are poor, and the corrosion rate is fast. When used in aluminum electrolysis, it greatly affects the efficiency of aluminum electrolysis and reduces the purity of aluminum products.

[0124] In Comparative Example 2, in the combining step, the pretreated zirconium boride and pretreated silicon carbide are only stirred and dispersed, and the interface bonding force between the two is weak, which increases the defects of the bonding interface. The coating step is omitted, and the zirconium boride / silicon carbide material is directly mixed with the nickel ferrite. Its dispersibility in the nickel ferrite matrix is ​​poor, and a dense and uniform distribution cannot be achieved, which reduces the homogeneity of the mixed powder, reduces the strength uniformity and overall stability of the composite material, and the degree of densification is not high, and the electrical conductivity is reduced, which affects the stability of the aluminum electrolysis process and the electrolysis efficiency.

[0125] Unless otherwise specified, all ratios and percentages described in the present invention are by mass ratios and percentages are by mass percentages.

[0126] 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 is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a nickel ferrite composite zirconium boride / silicon carbide material, characterized in that: It includes the steps of preparing zirconium boride / silicon carbide material, coating, mixing, molding and sintering; The preparation of the zirconium boride / silicon carbide material comprises zirconium boride pretreatment, silicon carbide pretreatment and bonding steps; The zirconium boride pretreatment step is to place the zirconium boride in a concentrated sulfuric acid solution, reflux at 90-95° C. for 5.7-6.2 hours, reduce the temperature to 32-37° C., add a lithium aluminum hydride solution, and stir at the temperature for 3.7-4.2 hours to obtain hydroxyl-rich zirconium boride; immerse the hydroxyl-rich zirconium boride in the pretreatment solution, and stir at 60-65° C. for 4.7-5.2 hours to obtain pretreated zirconium boride; The pretreatment liquid is a mixture of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate; The silicon carbide pretreatment step is to place the silicon carbide in a hydrogen peroxide solution, stir at 46-50° C. for 2.7-3.2 hours, dry, put into an ethanol solution, add Tween 60 and glyceryl monostearate, stir evenly, add methacrylic acid, continue to stir evenly, add benzoyl peroxide, perform ultrasonic dispersion, and react at 80-84° C. for 3.2-3.6 hours to obtain pretreated silicon carbide; The combining step comprises placing the pretreated silicon carbide in N,N-dimethylformamide, heating to 62-67° C., adding vinyltrimethoxysilane and stirring evenly, heating to 94-98° C., adding the pretreated zirconium boride and stirring to react, thereby obtaining a zirconium boride / silicon carbide material; The coating step comprises adding nickel nitrate, iron nitrate and polyethylene glycol 200 to deionized water, stirring evenly, adjusting the pH value to 9.8-10.2 to obtain a coating solution; adding zirconium boride / silicon carbide material to the coating solution, performing homogenization treatment, drying, and performing a heating and heat preservation treatment to obtain a coating; The mixing step comprises adding nickel ferrite, coating material and sodium dodecylbenzene sulfonate into deionized water, and performing ball milling treatment. The ball milling time is 23-28 minutes, the ball milling speed is 110-120 rpm, and the ball milling temperature is 34-38° C., and then adding polyvinyl alcohol and hydroxyethyl cellulose, and continuing ball milling for 16-20 minutes. After the ball milling is completed, drying at 98-102° C. to constant weight to obtain a mixed powder.

2. The method for preparing a nickel ferrite composite zirconium boride / silicon carbide material according to claim 1, characterized in that: In the zirconium boride pretreatment step, the particle size of the zirconium boride is 160-180 nm; The lithium aluminum hydride solution is a mixture of lithium aluminum hydride and tetrahydrofuran, and the mass ratio of the lithium aluminum hydride to tetrahydrofuran is 1.0-1.3:45-50; In the pretreatment liquid, the mass ratio of toluene, kH550, ethylenediamine and sodium N-dodecylaminopropionate is 100:1.2-1.4:0.5-0.7:0.5-0.8; The mass ratio of the zirconium boride, concentrated sulfuric acid solution, and lithium aluminum hydride solution is 9.8-10.3:87-92:15.5-16.0; The mass concentration of the concentrated sulfuric acid solution is 70-75%; The mass ratio of the hydroxyl-rich zirconium boride to the pretreatment liquid is 8.5-9.0:98-104.

3. The method for preparing a nickel ferrite composite zirconium boride / silicon carbide material according to claim 1, characterized in that: In the silicon carbide pretreatment step, the ultrasonic dispersion has an ultrasonic time of 1.8-2.2 h, an ultrasonic power of 116-123 W, and an ultrasonic frequency of 20-24 kHz; The particle size of the silicon carbide is 210-230nm; The mass ratio of silicon carbide, hydrogen peroxide solution, ethanol solution, Tween 60, glyceryl monostearate, methacrylic acid, and benzoyl peroxide is 5.0-5.5:52-57:295-306:0.2-0.4:0.4-0.6:0.8-1.2:0.47-0.52; The mass concentration of the hydrogen peroxide solution is 20-25%; The mass concentration of the ethanol solution is 23-27%.

4. The method for preparing a nickel ferrite composite zirconium boride / silicon carbide material according to claim 1, characterized in that: In the combining step, the mass ratio of the pretreated silicon carbide, N,N-dimethylformamide, vinyltrimethoxysilane, and pretreated zirconium boride is 4.0-4.5:98-102:1.12-1.22:5.2-5.

5.

5. The method for preparing a nickel ferrite composite zirconium boride / silicon carbide material according to claim 1, characterized in that: In the coating step, the mass ratio of the deionized water, nickel nitrate, ferric nitrate and polyethylene glycol 200 is 114-125:3.8-4.2:1.5-2.0:1.1-1.4; The mass ratio of the coating liquid to the zirconium boride / silicon carbide material is 98-103:8.0-8.5; The homogenization process has a homogenization time of 4.7-5.3 min, a homogenization pressure of 4.3-4.7 MPa, and a homogenization frequency of 2 times; The heating and heat preservation treatment is to heat the temperature to 336-342°C at a rate of 4.5-5.5°C / min, keep the temperature for 25-30 minutes, then heat the temperature to 605-613°C at a rate of 1.8-2.2°C / min, and keep the temperature for 1.5-2.0 hours.

6. The method for preparing a nickel ferrite composite zirconium boride / silicon carbide material according to claim 1, characterized in that: In the mixing step, the particle size of the nickel ferrite is 350-370 nm; The mass ratio of the deionized water, nickel ferrite, coating, sodium dodecylbenzene sulfonate, polyvinyl alcohol and hydroxyethyl cellulose is 60-65:57.5-58.4:3.5-4.0:0.8-1.2:0.3-0.5:0.2-0.

4.

7. The method for preparing a nickel ferrite composite zirconium boride / silicon carbide material according to claim 1, characterized in that: The molding and sintering step comprises placing the mixed powder in a mold for isostatic pressing, controlling the molding pressure to be 165-174 MPa, and the time to be 8-12 min to obtain a green body; heating the green body to 970-990° C. at a rate of 6.3-6.6° C. / min under an argon atmosphere, and keeping the temperature for 28-32 min. After the insulation is completed, heating the green body to 1960-2020° C. at a rate of 3.8-4.2° C. / mn, and keeping the temperature for 3.0-3.4 h, and cooling to room temperature with the furnace to obtain a nickel ferrite composite zirconium boride / silicon carbide material.

8. A nickel ferrite composite zirconium boride / silicon carbide material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

9. Application of nickel ferrite composite zirconium boride / silicon carbide material in aluminum electrolysis, characterized in that: The nickel ferrite composite zirconium boride / silicon carbide material is prepared by the preparation method according to any one of claims 1 to 7.

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