Sm-Fe-N Magnetic Powder With Uniform Nitriding and Low Ca
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Solution Overview
Problem
Conventional methods for producing Sm—Fe—N-based magnetic powders face challenges in achieving fine particle size, uniform nitriding, and low impurity content, particularly with the gas atomization method, which results in non-uniform magnetic properties and high reactivity with refractory materials, while reduction diffusion methods leave residual alkaline earth metals that affect bonded magnet manufacturability.
Innovation Solution
A method involving gas atomization followed by classification and nitriding, where the Sm—Fe-based alloy powder is synthesized with a narrow particle size distribution and low Ca content, ensuring uniform nitriding and high circularity, resulting in a magnetic powder with improved coercive force and manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If gas atomization method is used to produce Sm—Fe—N-based magnetic powder, then spherical particles can be obtained, but the particle size is too large (80-110 μm) and nitriding is non-uniform
Solution Approach 1:
The gas atomization process is segmented into multiple stages with different gas pressures and flow rates. The first stage uses high pressure to create fine initial droplets, while subsequent stages use lower pressure to prevent over-atomization and maintain spherical shape. This multi-stage segmentation allows achieving both fine particle size (2-10 μm) and spherical morphology simultaneously.
Solution Approach 2:
The alloy is pre-melted and homogenized before atomization to ensure uniform composition distribution. This preliminary action prevents non-uniform nitriding by ensuring consistent chemical composition throughout the particles, allowing uniform nitrogen diffusion during subsequent nitriding treatment.
2Manufacturing precision
If reduction diffusion method using Ca is used, then fine powder (10 μm or less) can be obtained, but Ca remains as impurity affecting bonded magnet manufacturability
Solution Approach 1:
The harmful Ca element is completely excluded from the raw material composition. Instead of using Ca-based reduction diffusion method, the patent employs direct gas atomization of Sm-Fe alloy followed by nitriding. This extraction of the harmful element from the process eliminates Ca impurity contamination while still achieving fine particle size (2-10 μm) through optimized atomization parameters.
Solution Approach 2:
The patent uses a disposable atomization droplet approach where molten alloy is converted into fine droplets that solidify into powder particles. This single-use droplet method replaces the multi-step reduction diffusion process, eliminating the need for Ca reducing agent and subsequent washing steps, thereby eliminating Ca impurity while maintaining fine particle size.
3Manufacturing precision
If gas atomization is used with N2 gas spraying, then ultrafine powder (2-10 μm) can be obtained, but Sm reacts with refractory materials causing composition deviation
Solution Approach 1:
The gas atomization process is conducted in an inert atmosphere using Ar gas instead of N2 gas. This inert environment prevents Sm from reacting with refractory materials and atmospheric oxygen during the high-temperature atomization process. The inert atmosphere maintains the intended Sm/Fe molar ratio by preventing unwanted chemical reactions, while still enabling fine particle formation through gas-droplet interaction.
Solution Approach 2:
Ar gas serves as an intermediary medium that transfers kinetic energy to the molten alloy without causing chemical reactions. The Ar atoms collide with the molten droplets to atomize them into fine particles, but unlike N2 or O2, Ar does not form compounds with Sm or Fe. This intermediary role allows achieving ultrafine particle size (2-10 μm) while maintaining compositional stability.
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 yields Sm—Fe—N-based magnetic powders with fine, spherical particles and low impurity content, enhancing coercive force and magnetic property uniformity, and preventing resin gelation during bonded magnet production.
Implementation Method 1
a gas atomization step of obtaining an Sm—Fe-based powder by a gas atomization method in which in an atmosphere of an inert gas excluding nitrogen, a gas stream of the inert gas excluding nitrogen is sprayed onto a molten metal containing Sm and Fe as main components, thereby rapidly cooling and solidifying particles of the molten metal
Implementation Method 2
a nitriding step of subjecting the powder obtained in the classification step to a nitriding treatment by heating and holding the powder in a temperature range of 500° C. or lower in a non-oxidizing gas atmosphere containing a nitrogen compound
Data Source
AI summary
An Sm—Fe—N-based magnetic powder includes particles containing Sm, Fe, and N as main components. The powder has a composition wherein a molar ratio of Sm to Fe (Sm/Fe) is 0.09 or more and 0.25 or less, a molar ratio of N to Fe (N/Fe) is 0.06 or more and 0.30 or less, and a Ca content in the powder is 0.002 mass % or less. When a cumulative 10% particle diameter is represented by D10, a cumulative 50% particle diameter is represented by D50, and a cumulative 90% particle diameter is represented by D90 in a volume-based particle size distribution according to a laser diffraction/scattering method, D50 is 2.0 to 11.0 μm, and D10, D50, and D90 satisfy a relationship of the following formula: (D90−D10)/D50<1.10. The Sm—Fe—N-based magnetic powder is advantageous in improving coercive force, containing few impurities, and improving the performance and manufacturability of a bonded magnet.