Production technology processes for soft magnetic ferrites

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Comparison of existing process technologies: In China, the industrial production of manganese-zinc ferrites currently relies on the oxide method (dry process), which involves grinding the materials and then sintering them to produce magnetic cores. High-purity iron oxide, manganese carbonate (or manganese oxide), zinc oxide, and other materials are used as raw materials, which are mixed in specific proportions and then sintered into the desired shape. The production process of the powder is shown in the figure below, and the resulting powder is then sintered into magnetic cores. Raw materials → Formulation → Mixing → Pre-baking → Coarse crushing → Fine crushing → Spray granulation → Inspection → Particle size adjustment → Bottling. The advantages of the oxide method are its simple process, accurate formulation, and suitability for large-scale industrial production. However, the high purity of iron oxide, manganese carbonate (or manganese oxide), and zinc oxide is very expensive, resulting in extremely high product costs. At the same time, since solid substances are used as raw materials, the reactive activity of the oxide components is low, and it is not possible to achieve microscopic homogeneity in the mixture. Therefore, during high-temperature synthesis, the temperature must be very high (over 1,000 degrees), yet this still does not prevent the problem of uneven reaction rates due to the different diffusion speeds of the various components at high temperatures, resulting in non-homogeneity. Therefore, the quality of traditional products is unstable, and the reproducibility of their performance in production is poor. The improved chemical coprecipitation method is most advanced in China at the School of Chemistry and Chemical Engineering of Central South University. This method involves dissolving the metal salts and mixing them evenly, then selecting a suitable precipitant to cause the metal ions to precipitate or crystallize uniformly. The resulting precipitate is subsequently dehydrated to produce the precursor powder. The precursor powder was reacted in a pressurized water container to produce manganese-zinc ferrite nanocrystals with a particle size of 10–20 nm. This powder is already available for sale as a commodity, but at a lower price. By further sintering the manganese-zinc ferrite nanocrystals, the final product of this project, namely the core, is obtained. The manufacturing process flow of the improved chemical coprecipitation method is shown in the figure below. Manganese sulfate, zinc, and iron mixed solution; precipitation, aging, filtration, washing, drying; precursor powder; mineralization reaction, sintering; magnetic core products. The advantage of this method is that it allows for the direct production of well-crystallized powders, without the need for high-temperature firing or ball milling (which helps to avoid powder agglomeration, impurities, and structural defects), and the resulting powders exhibit high sintering activity ； Simple process, low energy consumption, low pollution, and low investment.

Main production process: Manganese and zinc ores (reacted with auxiliary materials) — pressure filtration — repeated filtering and pressure filtration — purification — re-precipitation — washing and filtration — pre-sintering and decomposition — further washing and filtration — pressure filtration — secondary calcination — final product. Natural gas, steam, compressed air, as well as large amounts of water and soft water are required in this process.