Silicon Oxide-Coated Iron Powder for High-Frequency Inductors
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Solution Overview
Problem
The existing methods for producing inductors with high permeability at high frequencies face limitations due to the low permeability of nickel-based metal powders and the deterioration of magnetic characteristics caused by insulating coatings, which affect the packing density and insulating properties of the powder compact.
Innovation Solution
The development of silicon oxide-coated iron powder with a particle diameter of 0.25 to 0.80 μm and an axial ratio of 1.5 or less, coated with a silicon oxide content of 1.0% to 10% by mass, achieved through a wet method involving a phosphorus-containing ion, to enhance permeability and insulating properties while maintaining high powder compact density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iron powder with minute particle diameter (0.8 μm or less) is used to enhance permeability, then the permeability of the inductor is improved, but the insulating property deteriorates due to phosphorus contamination from wet method production
Solution Approach 1:
The patent extracts and removes phosphorus from the iron powder surface through oxidation treatment. The phosphorus-containing ions that contaminate the iron powder during wet method production are selectively removed by oxidizing the surface, thereby restoring the insulating property while preserving the high permeability enabled by the fine particle size
Solution Approach 2:
The patent changes the chemical state of the iron powder surface by controlling oxidation. By adjusting oxidation conditions (temperature, time, atmosphere), the surface composition is modified to reduce phosphorus content while maintaining the desired particle size and magnetic properties, thus resolving the contradiction between permeability and insulating property
2Object-affected harmful factors
If insulating material coating is applied to soft magnetic powder, then the insulating property is improved, but the powder compact density decreases due to large average film thickness
Solution Approach 1:
The patent changes the approach from adding thick insulating coatings to modifying the surface composition through controlled oxidation. This reduces the film thickness while achieving adequate insulating properties, thereby maintaining high powder compact density without sacrificing electrical insulation
Solution Approach 2:
The patent creates a composite surface structure on the iron powder particles through oxidation, forming a multi-layered surface composition that provides both insulating properties and maintains particle packing efficiency. The oxidized surface layer acts as an intrinsic insulating barrier without requiring additional coating material
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The silicon oxide-coated iron powder achieves high permeability in the high-frequency band with improved insulating properties and high powder compact density, effectively addressing the limitations of existing technologies.
Implementation Method 1
having coated on a surface thereof a silicon oxide... a powder compact obtained through vertical compression molding of the silicon oxide-coated iron powder... has a volume resistivity of 1.0×10^5 Ω·cm or more
Implementation Method 2
a powder compact obtained through vertical compression molding of the silicon oxide-coated iron powder at 64 MPa
Data Source
AI summary
A silicon oxide-coated iron powder has a small particle diameter, can achieve high in a high frequency band, and has high insulating property. In a method for producing the powder, a silicon alkoxide is added to a slurry containing iron powder having an average particle diameter of 0.25 μm or more and 0.80 μm or less and an average axial ratio of 1.5 or less dispersed in a mixed solvent of water and an organic material containing water in an amount of 1% by mass or more and 40% by mass or less. Then, a hydrolysis catalyst for the silicon alkoxide is added to perform silicon oxide coating, the method resulting in a silicon oxide-coated iron powder having the high μ′ in a high frequency band and the high insulating property.