Misch-Metal Permanent Magnets With Multi-Step Grain Boundary Diffusion
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Solution Overview
Problem
Misch-metal permanent magnetic materials exhibit low coercivity due to the high proportion of La and Ce, which limits the magneto-crystalline anisotropy field and leads to poor magnetic properties, making them unsuitable for commercialization, and traditional grain boundary diffusion methods are ineffective in enhancing coercivity.
Innovation Solution
A method involving multi-step diffusion and sintering processes, including induction melting, strip casting, hydrogen decrepitation, jet milling, magnetic alignment, and isostatic pressing to create a sintered substrate magnet, followed by vacuum diffusion with light rare-earth metals and their alloys, and subsequent tempering to form double magnetically hardening shell layers, reducing the accumulation of heavy rare-earths and enhancing grain boundary diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If misch-metal is used as the raw material for permanent magnetic materials, then the cost is reduced and abundant rare-earth resources are utilized, but the coercivity and magnetic properties are significantly degraded
Solution Approach 1:
The patent divides the rare-earth elements into different functional zones: La/Ce-rich main phase for cost-effectiveness and Nd/Pr-rich grain boundary phases for coercivity enhancement. This segmentation allows each region to perform its specific function optimally, resolving the contradiction between using abundant misch-metal and achieving required magnetic properties.
Solution Approach 2:
The patent applies local quality by creating Nd/Pr-enriched grain boundary phases specifically at the grain boundaries, while the main phase remains La/Ce-rich. This localized distribution of different rare-earth elements allows the bulk material to be cost-effective while specific regions provide the necessary magnetic properties.
2Device complexity
If traditional one-step grain boundary diffusion is applied to misch-metal magnets, then the process is simple, but the diffusion depth is limited and coercivity enhancement is insufficient
Solution Approach 1:
The patent implements periodic action through multi-step grain boundary diffusion processes, where different rare-earth elements are diffused in sequence at different stages. This stepwise approach allows better control of diffusion depth and composition distribution, achieving superior coercivity enhancement compared to single-step diffusion.
Solution Approach 2:
The patent uses intermediate Nd/Pr phases as mediators during the diffusion process. These intermediate phases form during the multi-step diffusion and facilitate the controlled distribution of rare-earth elements, enabling better penetration and more uniform composition distribution throughout the grain boundaries.
3Quantity of substance
If high proportion of La and Ce is used in misch-metal magnets, then the cost is reduced, but the magneto-crystalline anisotropy field is limited and coercivity is low
Solution Approach 1:
The patent applies local quality by concentrating Nd/Pr elements specifically at the grain boundaries while maintaining high La/Ce content in the main phase. This localized distribution allows the bulk material to utilize abundant and cheap La/Ce, while the grain boundary regions provide the necessary magneto-crystalline anisotropy for high coercivity.
Solution Approach 2:
The patent creates a composite microstructure with La/Ce-rich main phase and Nd/Pr-rich grain boundary phases. This composite structure combines the advantages of both rare-earth combinations: the cost-effectiveness and abundance of La/Ce with the high magnetic properties of Nd/Pr, achieving both economic and performance goals.
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 method significantly increases the coercivity of misch-metal permanent magnetic materials, promoting their commercial application while efficiently utilizing abundant rare-earth resources, reducing the need for heavy rare-earths, and forming continuous non-ferromagnetic grain boundary phases to weaken exchange coupling between main-phase grains.
Implementation Method 1
the grain boundary diffusion (GBD) technology is widely recognized as an effective method to enhance the coercivity of NdFeB permanent magnetic materials
Implementation Method 2
a misch-metal permanent magnetic material and a method for preparing the same based on sintering and multi-step diffusion
Data Source
AI summary
A preparation method of a misch-metal permanent magnetic material based on sintering and multi-step diffusion is provided. A sintered substrate magnet is prepared by induction melting, strip casting, hydrogen decrepitation, jet milling, magnetic alignment, isostatic pressing and sintering. A first diffusion source and a second diffusion source are prepared, where the first diffusion source is a light rare-earth metal or its alloy, and the second diffusion source is a light-heavy rare-earth combination or its alloy. The sintered substrate magnet is sequentially subjected to a first vacuum diffusion with the first diffusion source and a second vacuum diffusion with the second diffusion source. The resultant product is subjected to low-temperature tempering to give the desired misch-metal permanent magnetic material.