Process method for improving corrosion resistance of ferrite

Abstract

The invention relates to the technical field of material surface treatment, and discloses a process method for improving the corrosion resistance of ferrite, which comprises the steps of raw material formula preparation, deep chemical precipitation purification, ion exchange purification, superfine grinding and mixing, precise compression molding, multi-stage sintering, chemical nickel-phosphorus alloy plating and the like. The grain boundary stability is optimized by introducing a CeO2 additive, the impurity content is reduced by adopting chemical precipitation and ion exchange, the microstructure compactness is improved by combining high-energy mixing and atmosphere control, and a uniform nickel-phosphorus alloy protection layer is formed. According to the invention, the corrosion resistance and long-term stability of the ferrite material in a humid, acidic or alkaline complex environment are improved.

Description

Technical Field

[0001] This invention belongs to the field of material surface treatment technology, specifically a process method for improving the corrosion resistance of ferrite. Background Technology

[0002] Ferrite materials, due to their excellent magnetic properties and wide range of applications, have become important materials in the manufacture of electronic components. However, in practical applications, ferrite materials often face corrosion problems, especially in humid, acidic, or alkaline environments. Insufficient corrosion resistance can lead to surface deterioration, thereby affecting their magnetic properties and service life. Therefore, improving the corrosion resistance of ferrite materials has become one of the key research focuses.

[0003] Patent publication number CN1700370B discloses a Ni-Cu-Zn ferrite material that achieves high initial permeability temperature characteristics and small grain size by controlling the proportion of the main components and adding trace amounts of secondary components such as Al2O3, CaO, and MgO. Although this approach exhibits excellent magnetic properties, its formulation design and process flow do not consider the corrosion resistance of ferrite materials, and the long-term stability of the material in humid or corrosive environments remains insufficient.

[0004] The main problem with the existing technical solutions is that the formulation design focuses on optimizing magnetic properties and lacks the introduction of targeted corrosion-resistant components, resulting in weak corrosion resistance of the materials. The existing technology needs further improvement to develop ferrite materials and their preparation processes with excellent corrosion resistance. Summary of the Invention

[0005] This application provides a process method for improving the corrosion resistance of ferrite materials. The method aims to enhance the corrosion resistance of ferrite materials in complex environments through optimized formulation design, deep purification of raw materials, enhanced microstructure control, and surface treatment. This process method combines key steps such as chemical precipitation purification, ion exchange deep purification, ultrafine grinding and high-energy mixing, precision forming, and multi-stage sintering, ultimately forming a dense and uniform nickel-phosphorus alloy protective layer to further enhance the corrosion resistance of ferrite components.

[0006] This application provides a method for preparing ferrite materials with excellent corrosion resistance, comprising the following steps: S10: Raw material formulation preparation. Based on the desired performance of the ferrite, the main metal oxide raw materials are accurately weighed, with a molar percentage composition of 53% Fe2O3, 37% MnO, and 10% ZnO. 2% by mass of CeO2 is introduced into the main metal oxide raw materials as a corrosion-resistant additive. All main metal oxide raw materials are reagent-grade powders with a chemical purity greater than 99.9%, and the average particle size of CeO2 is controlled below 50 nm. The introduction of CeO2 not only improves the grain boundary stability of the ferrite material but also enhances its corrosion resistance through its unique redox properties.

[0007] S20: Raw material pretreatment involves deep chemical precipitation purification of the prepared metal oxide raw material and CeO2 additive mixture. Specific steps include dissolving the mixture in high-purity deionized water to prepare a precursor solution, and adjusting the pH of the solution to 8.5 to 9.5 by adding high-purity ammonia or sodium hydroxide solution with a molar concentration of 1 mol / L, while maintaining the solution temperature between 60°C and 80°C and continuously stirring mechanically for 30 minutes to promote uniform growth of the precipitate particles. After precipitation, the mixture is repeatedly centrifuged and washed with deionized water until the conductivity of the washing solution is below 0.5 microsiemens per centimeter.

[0008] Subsequently, the powder, after chemical precipitation purification and drying, undergoes deep purification via ion exchange. The specific operation involves dispersing the powder in high-purity deionized water to form a dilute slurry, which is then sequentially passed through an exchange column filled with a strongly acidic cation exchange resin and a strongly basic anion exchange resin. The strongly acidic cation exchange resin is a sulfonic acid type polystyrene-divinylbenzene copolymer resin, and the strongly basic anion exchange resin is a quaternary ammonium salt type polystyrene-divinylbenzene copolymer resin. The slurry is pumped through the exchange column sequentially at a flow rate of 0.5 L / h to 1 L / h using a peristaltic pump, ensuring that the total content of easily corrosive trace impurities in the raw material, such as sodium, potassium, chloride, and sulfide ions, is reduced to below 0.01% (mass fraction).

[0009] S30: Mixing and Shaping. The pre-treated raw material powder is added to a planetary ball mill for ultrafine grinding and high-energy mixing. The ball mill uses a zirconia grinding jar, and the grinding media are high-purity zirconia grinding balls with a diameter range of 0.5 mm to 1.5 mm. High-purity deionized water is added as a dispersion medium during the grinding process, and the powder-to-water mass ratio is controlled within the range of 1:1 to 1:2. The ball milling operation is carried out at an ambient temperature of 20℃ to 30℃, with the rotation speed maintained at 300 r / min to 500 r / min, for a continuous grinding time of 5 hours. This reduces the average particle size to below 200 nm, achieving uniform mixing of all components at the nanoscale.

[0010] Subsequently, the ball-milled slurry was granulated using a spray drying tower. During spray granulation, 1% to 3% polyvinyl alcohol (PVA) was added to the slurry as a temporary organic binder. The PVA had an average degree of polymerization of 1700 ± 50 and a degree of hydrolysis of 98% ± 1%. The inlet temperature of the spray drying process was controlled at 180°C to 220°C, and the outlet temperature was controlled at 80°C to 100°C, ultimately yielding granulated particles with a particle size distribution between 100 μm and 200 μm, high sphericity, and good flowability, with a bulk density of 1.5 g / m³. 3 Up to 1.8g / m 3 .

[0011] The granulated particles are introduced into a precision mold with an optimized structure for pressing and molding. The main material of the mold is a tungsten carbide-cobalt alloy, and its surface is coated with a titanium nitride coating with a thickness of 2μm to 3μm. The coating has a Vickers hardness of Hv2000 to 2500 and a coefficient of friction of 0.4 to 0.6. The internal structure of the mold is optimized through computer-aided design and finite element analysis. During the pressing process, a high-precision hydraulic-electric hybrid press is used, with a single-axis pressure of 120MPa, a pressure rise rate controlled at 5MPa per second to 10MPa per second, and a holding time of 2 to 5 seconds, so that the relative density of the obtained ferrite preform can reach more than 60%.

[0012] S40: Sintering. The pressed ferrite blank is placed in a sintering boat and sent to a multi-segment high-precision programmable atmosphere sintering furnace for pre-sintering. During the pre-sintering stage, the atmosphere inside the furnace is air or a weak oxidizing atmosphere, and the temperature is increased from room temperature to 850°C at a heating rate of 7°C / min, and then held at this temperature for 2 hours.

[0013] After pre-sintering, the furnace temperature is continuously increased to the main sintering temperature of 1380℃ at a rate of 8℃ / min under program control. During the main sintering stage, the furnace atmosphere is precisely controlled to be a reducing atmosphere, specifically composed of 7% hydrogen (by volume) with the remainder being high-purity nitrogen or argon. Furnace temperature control accuracy is achieved through real-time monitoring and feedback using multi-point K-type or S-type thermocouples, combined with a PID control algorithm to ensure that the temperature fluctuation of the sintering furnace is within ±1℃, and the furnace is held at 1380℃ for 4 hours. After sintering, the furnace is slowly cooled to room temperature at a rate of 1℃ / min to 3℃ / min.

[0014] S50: Post-treatment involves multi-stage precision cleaning of the sintered ferrite components. The cleaning process includes cleaning for 10-15 minutes at a dilute alkaline solution (1%-2% sodium carbonate solution by mass) at 60-70°C using ultrasonic waves at 40 kHz, with the option to add 0.1% surfactant; followed by cleaning for 5-10 minutes in high-purity deionized water at room temperature using ultrasonic waves at 40 kHz; and finally, ultrasonic cleaning for 5 minutes in anhydrous ethanol at room temperature, followed by drying with high-purity nitrogen. The surface cleanliness after cleaning is verified by contact angle measurement, with a contact angle less than 10 degrees.

[0015] The cleaned ferrite components were subjected to electroless nickel-phosphorus alloy plating. The plating solution formulation, by mass concentration, included 28 g / L nickel sulfate, 32 g / L sodium hypophosphite, 18 g / L sodium citrate, and 12 g / L sodium acetate. The pH value of the plating solution was strictly controlled at 5.0 ± 0.1 by precisely adding dilute sulfuric acid or sodium hydroxide solution. The plating operation was carried out at a constant temperature of 88℃ ± 1℃ and continued for 55 minutes. The obtained nickel-phosphorus alloy coating thickness was approximately 5 μm to 10 μm, with a phosphorus mass fraction between 8% and 12%.

[0016] The nickel-phosphorus-plated ferrite components were subjected to low-temperature heat treatment to further optimize the coating structure and enhance its adhesion to the substrate. The heat treatment was carried out in an inert atmosphere at a temperature range of 200°C to 300°C for 1 to 2 hours.

[0017] This application provides a ferrite material prepared according to the method described above. This ferrite material exhibits improved corrosion resistance and is suitable for complex environments such as humid, acidic, or alkaline conditions.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention optimizes the grain boundary stability of the material by introducing CeO2 as a corrosion-resistant additive; effectively reduces the content of trace impurities in the raw materials through chemical precipitation purification and deep ion exchange purification; achieves uniform distribution of powder particles at the nanoscale through ultrafine grinding and high-energy mixing; improves the density and surface smoothness of the green body through precision molds and high-precision pressing; constructs a dense microstructure through multi-stage sintering and atmosphere control; and forms a uniform and dense corrosion-resistant protective layer through chemical nickel-phosphorus alloy plating and low-temperature heat treatment. These combined techniques enhance the corrosion resistance of the ferrite material, enabling it to exhibit excellent long-term stability in complex environments. Detailed Implementation The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] The implementation examples are designed around the reasonable adjustment of the core process parameters of the patent (CeO2 additive, ion exchange purification, ball milling mixing, sintering control, and electroless plating treatment), highlighting the impact of process variables on performance. All parameters are within the scope of the patent-protected technology.

[0020] The comparative model was designed to address the core improvements of the patent (CeO2 additives and deep purification through ion exchange) to verify the necessity of the key processes.

[0021] Performance testing methods: All samples underwent the following performance tests under uniform conditions: Relative density: determined by the water displacement method, reflecting the microscopic compactness of the material; Neutral salt spray test (NSS): 5% sodium chloride solution, 35°C, spray for 240 hours, calculate corrosion rate (g / m²·h). Stability in acidic environments: Immersed in 5% sulfuric acid solution (25℃) for 72 hours, calculate the weight loss rate (%); Alkaline environment stability: Immerse in 5% sodium hydroxide solution (25℃) for 72 hours and calculate the weight loss rate (%). Coating adhesion: Cross-cut test (1mm grid), rating standard is 0-5 (0 is the best, no peeling).

[0022] Performance data comparison table: From the table above, we can obtain: The relative densities of all six embodiments were higher than 5.25 g / cm³, the NSS corrosion rate was lower than 0.0045 g / m²·h, the acid-base weight loss rate was lower than 0.12%, and the coating adhesion was all grade 0. This indicates that by adjusting the patented process parameters (such as CeO2 addition of 1.5%-2%, ion exchange flow rate of 0.7-1.0 L / h, ball milling speed of 400-500 r / min, etc.), ferrite materials with excellent corrosion resistance can be prepared, and the process stability is strong.

[0023] Comparative Example 1, lacking CeO2, exhibited a relative density reduced to 5.15 g / cm³, a 5.8-fold increase in NSS corrosion rate compared to Example 1, a 5-6 fold increase in acid-base weight loss rate, and a coating adhesion reduced to Grade 1. This verifies the design objective of this technical solution: CeO2 optimizes grain boundary stability and enhances corrosion resistance. CeO2 can reduce corrosion channels by regulating the grain boundary structure, making it a core component for improving corrosion resistance.

[0024] Comparative Example 2, lacking ion exchange purification, had a relative density of only 5.02 g / cm³, resulting in a 6.6-fold increase in NSS corrosion rate and a 7-8-fold increase in acid-base weight loss compared to Example 1. The coating adhesion also decreased to level 2. This was because trace impurities such as sodium, potassium, and chlorine were not removed. These impurities form micro-batteries within the material, accelerating the corrosion reaction. This demonstrates that "deep impurity removal through ion exchange" is a crucial step in ensuring corrosion resistance in this technical solution.

[0025] The performance of Examples 4 (high ball milling speed), 5 (slightly higher sintering temperature), and 6 (thick coating) was further optimized (e.g., the NSS corrosion rate of Example 6 was only 0.0021 g / m²·h), indicating that the synergistic effect of ultrafine grinding (improving mixing uniformity), precise sintering (enhancing density), and chemical plating (constructing a protective layer) can further strengthen corrosion resistance, which is in line with the patent's technical concept of "multi-step synergistic performance improvement".

[0026] In summary, the process described in this technical solution, through a combination of "CeO2 addition + deep purification + precise forming and sintering + chemical plating," can effectively solve the problem of insufficient corrosion resistance of ferrites. The comparative example shows performance degradation due to the absence of key steps, thus verifying the innovation and practicality of this process.

[0027] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ferrite materials with corrosion resistance, characterized in that, Includes the following steps: S10: Raw material formulation preparation: According to the target performance of the required ferrite, weigh the main metal oxide raw materials, whose molar percentage composition is 53% Fe2O3, 37% MnO, and 10% ZnO, and introduce CeO2 with a mass fraction of 2% as an additive into the main metal oxide raw materials. S20: Raw material pretreatment, chemical precipitation purification and ion exchange deep purification are carried out on the main metal oxide raw materials and CeO2 mixture; S30: Mixing and molding, the pre-treated raw material powder is ultra-finely ground and mixed with high energy, then spray-dried and granulated, and pressed into shape; S40: Sintering, the formed green body is pre-sintered and main sintered in a multi-section atmosphere sintering furnace in sequence; S50: Post-treatment, the sintered ferrite components are cleaned and chemically plated with nickel-phosphorus alloy, followed by low-temperature heat treatment.

2. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S10, the chemical purity of the main metal oxide raw material is greater than 99.9%, and the average particle size of CeO2 is less than 50 nm.

3. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S20, during the chemical precipitation purification process, the mixture is dissolved in deionized water, the pH of the solution is adjusted to 8.5 to 9.5, the temperature is controlled at 60°C to 80°C, the stirring time is 30 minutes, and the conductivity of the washing solution is less than 0.5 microsiemens per centimeter.

4. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S20, during the ion exchange deep purification process, the slurry passes through an exchange column filled with strong acid cation exchange resin and strong base anion exchange resin, with the flow rate controlled at 0.5 L / h to 1 L / h, and the final total content of trace impurities is less than 0.01%.

5. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S30, the ball milling operation uses a zirconia ball mill jar and zirconia grinding balls with a diameter ranging from 0.5 mm to 1.5 mm. The mass ratio of powder to water is 1:1 to 1:2, the rotation speed is 300 r / min to 500 r / min, the time is 5 hours, and the average size of the powder particles is less than 200 nm.

6. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S30, the inlet temperature of the spray drying tower is controlled at 180℃ to 220℃, and the outlet temperature is controlled at 80℃ to 100℃. Polyvinyl alcohol (PVA) with a mass fraction of 1% to 3% is added as a binder. The resulting granulated particles have a particle size distribution of 100μm to 200μm and a loose packing density of 1.5g / m³. 3 Up to 1.8g / m 3 .

7. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S40, the heating rate during the pre-sintering stage is 7℃ / min, the temperature is raised to 850℃ and held for 2 hours; the heating rate during the main sintering stage is 8℃ / min, the temperature is raised to 1380℃ and held for 4 hours, the hydrogen gas component in the furnace atmosphere is 7%, and the remainder is nitrogen or argon gas, and the temperature fluctuation is controlled within ±1℃.

8. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S50, the cleaning process includes ultrasonic cleaning in a sodium carbonate solution at 60°C to 70°C for 10 to 15 minutes, followed by ultrasonic cleaning in deionized water and anhydrous ethanol for 5 to 10 minutes respectively, resulting in a final surface contact angle of less than 10 degrees.

9. The method for preparing a ferrite material with corrosion resistance according to claim 1, characterized in that, In step S50, during the electroless nickel-phosphorus alloy plating process, the plating solution contains 28 g / L nickel sulfate, 32 g / L sodium hypophosphite, 18 g / L sodium citrate, and 12 g / L sodium acetate. The pH value is controlled at 5.0 ± 0.1, the plating temperature is 88℃ ± 1℃, and the time is 55 min, forming a nickel-phosphorus alloy coating with a thickness of 5 μm to 10 μm.

10. A ferrite material, characterized in that, The ferrite material with corrosion resistance is prepared according to any one of claims 1 to 9.

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