Ferrite Sintered Magnet Coercivity via SiO2 and CaCO3
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Solution Overview
Problem
Conventional sintered Ca-La-Co ferrite magnets fail to achieve high coercivity (HcJ) and squareness ratio (Hk/HcJ) while maintaining high residual magnetic flux density (Br), making them unsuitable for thinning applications such as motors, where demagnetization is a concern.
Innovation Solution
The addition of more than 1% by mass of SiO2 and 1% or more by mass of CaCO3 during the pulverization step, along with a composition that includes a third phase with a higher atomic ratio of La, forms a sintered magnet with improved HcJ and Hk/HcJ, maintaining high Br.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the amounts of sintering aids (SiO2, CaCO3) are increased to improve HcJ, then coercivity improves, but residual magnetic flux density Br decreases due to increased non-magnetic components
Solution Approach 1:
The patent applies parameter changes by precisely controlling the amounts of sintering aids within specific ranges (SiO2: 0.3-1.5% by mass, CaCO3: 0.2-1.5% by mass) and optimizing the elemental composition ratios (La: 0.1-0.65 atomic ratio, Co: 0.25-0.65 atomic ratio) to achieve the optimal balance between coercivity and residual magnetic flux density
Solution Approach 2:
The patent uses composite materials by combining multiple elements (Ca, La, Sr, Ba, Fe, Co, Si, C) to form a complex ferrite system with specific phase composition, where the interaction between different elements creates synergistic effects that improve both coercivity and magnetic flux density beyond what single-element substitutions could achieve
2Force
If the amounts of sintering aids are increased to improve HcJ, then coercivity improves, but the squareness ratio Hk/HcJ decreases
Solution Approach 1:
The patent optimizes multiple parameters simultaneously including sintering aid amounts, elemental composition ratios, sintering temperature (1150-1250°C), and sintering time (0.5-2 hours) to achieve the optimal balance between coercivity improvement and squareness ratio maintenance
3Quantity of substance
If the amounts of sintering aids are reduced to maintain high Br, then residual magnetic flux density is maintained, but coercivity HcJ decreases
Solution Approach 1:
The patent employs composite material strategy by incorporating multiple rare earth elements (La, Sr, Ba) and transition metal elements (Co) in specific ratios to create a multi-phase ferrite structure that enhances coercivity through magnetic anisotropy while maintaining high residual flux density
Solution Approach 2:
The patent changes the chemical composition parameters by substituting specific proportions of Ca with La (0.1-0.65 atomic ratio) and Fe with Co (0.25-0.65 atomic ratio) to intrinsically enhance the magnetic properties, reducing dependence on sintering aid quantities
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 approach results in sintered ferrite magnets with significantly enhanced HcJ and Hk/HcJ, enabling them to be made thinner without demagnetization, suitable for high-performance applications in electric parts like motors and generators.
Implementation Method 1
the addition of more than 1% by mass of SiO2 and 1% or more by mass of CaCO3 during the pulverization step
Implementation Method 2
a third phase containing La at a higher atomic ratio than in said main phase
Data Source
Figure 1(A)~1(B)
Figure 1(C)~1(D)
Figure 2(A)~2(B)
AI summary
A sintered ferrite magnet having a main phase composed of ferrite having a hexagonal, M-type magnetoplumbite structure, a grain boundary phase containing Si and Ca with a lower atomic ratio of La than in said main phase, and a third phase containing La at a higher atomic ratio than in said main phase, and a method for producing a sintered ferrite magnet having said third phase by calcining starting materials with more La than Ca, adding more than 1% and 1.8% or less by mass of SiO2 and 1-2% by mass (calculated as CaO) of CaCO3 to the calcined body, and pulverizing, molding and sintering it.