NdFeB Powder Cyclone Separation for Recycled Magnet Coercivity
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Solution Overview
Problem
Recycling of rare earth metal magnets, specifically NdFeB magnets, faces challenges due to difficulties in separating nickel-coated, fully magnetized, and glued magnets, leading to reduced density and coercivity in re-sintered magnets due to oxygen content and particle aggregation during the hydrogen decrepitation process.
Innovation Solution
A method involving hydrogenated NdFeB powder separation using a cyclone separator to distinguish between Nd-rich grain boundary phase particles and Nd2Fe14B matrix phase particles, with optional multiple passes to enrich the underflow in matrix phase particles, followed by blending with fresh Nd-hydride and re-sintering to form high-quality recycled magnets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hydrogen decrepitation is used to process sintered NdFeB magnets into powder, then the nickel coating peels away and the magnet can be liberated from electronics scrap, but the re-sintered magnets exhibit reduced density and coercivity due to higher oxygen content
Solution Approach 1:
The patent segments the hydrogenated powder into different particle size fractions using sieving and classification. The fine fraction (<10 microns) containing oxygen-rich grain boundary phase particles is separated from the coarse fraction containing intact matrix phase particles. This segmentation allows selective processing to remove harmful oxygen-containing particles while preserving the magnetic matrix phase.
Solution Approach 2:
The patent extracts and removes the harmful oxygen-rich particles from the hydrogenated powder. By classifying the powder and identifying that oxygen is mainly entrained in the fine grain boundary phase particles, the process removes these particles through sieving and classification, thereby extracting the harmful component that causes reduced density and coercivity in re-sintered magnets.
2Manufacturing precision
If the fine fraction is removed by sieving, then oxygen-rich particles are removed, but Nd is also lost requiring powder blending with extra Nd or rare earth alloy
Solution Approach 1:
The patent implements feedback control by analyzing the composition of the fine fraction removed during classification. By determining the Nd content in the removed fraction and comparing it to the original powder composition, the process can calculate the required amount of Nd or rare earth alloy to add back during powder blending. This feedback mechanism ensures that the final powder composition is optimized to achieve the desired magnetic properties in re-sintered magnets.
3Manufacturing precision
If extra rare earth material is added to compensate for Nd loss, then density can be maintained, but the magnetic strength (remanence) is reduced
Solution Approach 1:
The patent applies parameter changes by carefully controlling the composition and amount of rare earth material added during powder blending. Rather than simply adding extra rare earth to compensate for losses, the process optimizes the rare earth content to achieve the desired magnetic properties. By adjusting the rare earth parameter in the powder composition and controlling the classification process to minimize unnecessary Nd loss, the patent maintains both density and magnetic strength in the re-sintered magnets.
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
This method effectively separates and removes oxygen-rich particles, improving the magnetic properties of recycled NdFeB magnets by enhancing density and coercivity, and maintaining remanence, thus overcoming the limitations of conventional recycling methods.
Implementation Method 1
separating the powder into an overflow enriched in Nd-rich grain boundary phase particles and an underflow enriched in Nd2Fe14B matrix phase particles
Implementation Method 2
feeding said powder into an inlet of a cyclone separator
Implementation Method 3
During hydrogenation, the Nd-rich grain boundary phase forms NdH2.7, then the matrix phase forms Nd2Fe14BHx
Implementation Method 4
The differential expansion of these two phases due to hydride formation causes inter-granular cracking at the grain boundaries
Implementation Method 5
During sintering the Nd-rich phase would normally form a liquid, which allows for liquid phase sintering
Data Source
AI summary
A method of processing NdFeB magnetic powder comprises: providing a source of hydrogenated NdFeB powder (101, 102, 103); feeding said powder into an inlet of a cyclone separator (104); separating the powder into an overflow enriched in Nd-rich grain boundary phase and an underflow enriched in NdxFeyBHz matrix phase particles (106); optionally feeding the underflow back into the inlet of the cyclone separator whereby to further enrich the underflow in the NdxFeyBHz matrix phase particles (108a); and collecting the underflow (108).