The Insulation Coating Process Optimization And Soft Magnetic Properties Of Iron Powder Cores

Soft magnetic materials are widely applied in electronic, machinery and communication industry as important basic materials in national economy. Magnetic powder core is a kind of soft magnetic composites prepared with a method similar to powder metallurgy, mainly applied in electromagnetic transitions and attracting more and more interesting for the shape, composite and properties can be designed based on the applications. Iron powder core is a kind of magnetic powder cores have been researched for several hundred years and is widely applied in electronic components for the advantages of high flux density, high original permeability, good DC bias performance and low costs. New requirements are put forward while the electronic components are smaller, more energy-efficient and being applied in higher frequency. However, high core loss limits the application of iron powder cores. Insulation coating is a key to reduce the core loss of iron powder core in high frequency. At present, the research of magnetic powder cores is focused on the invention of new insulators and insulation coating process optimization. Phosphate-silicon resin coated iron powder cores are prepared with inorganic-organic double coating method in this paper. Optimizing phosphatizing process is used to improve the quality of phosphate layer and the magnetic properties of soft magnetic properties through orthogonal experiment.Sodium dihydrogen phosphate solution is used as phosphatizing agent. The experiment results indicate that phosphate-silicon resin coating reduce the AC core loss of iron powder cores. The AC core loss and DC core loss are reduced by 72.8% and 87.5% respectively, compared with the pure iron powder cores. But the flux density and permeability are reduced at the same time.The phosphatizing conditions include concentration, ingredient and p H of phosphatizing solution, phosphatizing temperature and phosphatizing time. Orthogonal experiment is used to research the influence of phosphatizing conditions on the morphology and composition of phosphate layer and the magnetic properties of phosphate-silicon resin coated iron powder cores. Uniform Phosphatizing conditions cannot be obtained from orthogonal experiment for the amount of soft magnetic property parameters. The results of orthogonal experiment indicate that the optimal p H of phosphatizing solution is 2 and the optimal phosphatizing temperature is 120 ℃。The accelerating effect of hydrogen peroxide is not obvious for its instability in phosphatizing solution.The influence of phosphatizing solution concentration on the phosphatizing coating is remarkable. The optimal concentration of phosphatizing solution is 6%. Adding oxalic acid as surface treatment agent, sodium molybdate and nickel nitrate as accelerator to adjust ingredient of phosphatizing solution. Experiment results indicate that a small amount of oxalic acid can change the surface morphology of phosphatized iron powders and lower the core loss of double coated iron powder cores. Excessive oxalic acid leads to the generation of oxalate, obstructing the phosphatizing on the powder surface. The addition of sodium molybdate changes the surface morphology of phosphatized iron powders, and makes the phosphate layer smooth and densification. The AC core loss is reduced by 8.4% under the frequency of 100 k Hz, while the concentration of sodium molybdate is 1%. The addition of nickel nitrate into the solution as phosphatizing accelerator refines the phosphate grain, makes the phosphate layer uniform and densification and enhances the content of phosphate. The permeability is promoted by 4.6% under the frequency of 100 k Hz, while the concentration of nickel nitrate is 1.0%. The AC core loss is reduced by 16.8% under the frequency of 100 k Hz, while the concentration of nickel nitrate is 1.5%.