Ferrite Sintered Magnet Grain Boundary Control
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Solution Overview
Problem
Current ferrite sintered magnets face challenges in achieving a balance between residual magnetic flux density (Br) and coercive force (HcJ), with existing studies focusing primarily on element composition without adequate consideration of structural designs and conditions beyond the main and added elements.
Innovation Solution
A ferrite sintered magnet comprising main phase grains with a hexagonal structure, two-grain boundaries, and multi-grain boundaries, made of Ca, R, Sr, Fe, and Co, where R is a rare earth element or Bi, and La, with specific ratios of main phase grains and multi-grain boundaries in the cross section along the easy magnetization axis, optimized to achieve uniform grain orientation and size for improved magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If various elements are added to improve Br and HcJ, then magnetic properties are enhanced, but it remains unclear which combination provides high properties and the balance between Br and HcJ is not optimized
Solution Approach 1:
The patent changes the parameters by specifying precise compositional ranges (La: 0.01-0.5 mass%, Co: 0.1-1.0 mass%, Sr: 0.1-0.5 mass%) and a specific structural parameter (Nm/(Nm+Ng) ratio: 50-65%). This transforms the uncertain element combination problem into a controlled parameter optimization, achieving both high Br and HcJ with a balanced and reproducible formulation.
Solution Approach 2:
The patent applies local quality by distinguishing between different types of grain boundaries (two-grain boundaries vs. multi-grain boundaries) and controlling their distribution. By specifically managing the Nm/(Nm+Ng) ratio, the invention creates different local structures with optimized functions: main phase grains for magnetic properties and controlled grain boundaries for microstructure stability, achieving balanced Br and HcJ.
Data Source
AI summary
The present invention provides a ferrite sintered magnet comprising (1) main phase grains containing a ferrite having a hexagonal structure, (2) two-grain boundaries formed between two of the main phase grains, and (3) multi-grain boundaries surrounded by three or more of the main phase grains. The above ferrite sintered magnet comprises Ca, R, Sr, Fe and Co, with R being at least one element selected from the group consisting of rare earth elements and Bi, and comprising at least La. The number Nm of the above main phase grains and the number Ng of the above multi-grain boundaries in the cross section including the direction of the easy magnetization axis of the above ferrite sintered magnet satisfy the formula (1A):50%≤Nm/(Nm+Ng)≤65% (1A).