Rare Earth Sintered Magnet Two-Layer Protective Structure
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Solution Overview
Problem
Rare earth sintered magnets used in harsh environments face challenges with corrosion, leading to reduced magnetic properties and reliability, as existing protective layers do not provide sufficient corrosion resistance.
Innovation Solution
A rare earth sintered magnet with a two-layer protective structure is developed, where the surface portion has a higher heavy rare earth element content than the interior, and the first layer consists of rare earth oxide with a mass ratio of heavy to light rare earth elements of 1 or greater, while the second layer comprises an oxide containing iron and/or boron with lower rare earth oxide content, enhancing corrosion resistance and adhesiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth elements are added to improve corrosion resistance, then corrosion resistance improves, but manufacturing cost increases
Solution Approach 1:
Heavy rare earth elements are selectively concentrated in the surface portion of the magnet body and in the first protective layer, rather than being uniformly distributed throughout the entire magnet. This local quality approach ensures that corrosion-resistant properties are enhanced where they are most needed (at the surface exposed to harsh environments) while minimizing the overall amount of expensive heavy rare earth elements required, thus controlling manufacturing costs.
Solution Approach 2:
The invention optimizes the mass ratio of heavy rare earth elements to light rare earth elements in the surface portion to be 1 or greater, creating a specific compositional parameter that maximizes corrosion resistance. By controlling this parameter locally at the surface rather than throughout the entire magnet, the invention achieves high corrosion resistance with controlled material costs.
2Strength
If the first layer has high rare earth oxide content for good adhesiveness, then adhesiveness between magnet body and protective layer improves, but the outer surface corrosion resistance may be compromised
Solution Approach 1:
The protective layer is segmented into two layers with different compositions: the first layer contains rare earth oxide for strong adhesiveness to the magnet body, while the second layer contains iron oxide and/or boron oxide for enhanced outer surface corrosion resistance. This segmentation resolves the contradiction by assigning different functional requirements to different layers.
Solution Approach 2:
The second layer is formulated as a composite containing iron oxide and/or boron oxide with lower rare earth oxide content compared to the first layer. This composite composition provides superior corrosion resistance on the outer surface while the first layer maintains strong adhesiveness through its rare earth oxide content, achieving both requirements simultaneously.
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 two-layer structure significantly improves corrosion resistance and maintains high magnetic properties, ensuring the reliability of motors and automobiles that utilize these magnets in corrosive environments.
Implementation Method 1
the surface portion of the magnet body has a higher heavy rare earth element content than the interior of the magnet body that is surrounded by the surface portion
Implementation Method 2
the first layer comprises a rare earth oxide
Data Source
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AI summary
A rare earth sintered magnet 10 including a magnet body that includes a rare earth compound, and a protective layer on the magnet body, having a first layer and a second layer in that order from the magnet body side, wherein the surface portion of the magnet body has a higher heavy rare earth element content than the interior of the magnet body that is surrounded by the surface portion, the first layer includes a rare earth oxide, the mass ratio of the heavy rare earth element being 1 or greater with respect to the light rare earth element, and the second layer includes an oxide containing iron and/or boron which is different from the rare earth oxide, the second layer having a lower rare earth oxide content than the first layer.