In the world of NdFeB magnet production, achieving ultra-fine grains is crucial for optimal magnetic properties. To attain an average grain size of 3 to 5 micrometers, the Hydrogen Decrepitation technique has become the go-to method before jet milling, thanks to its economic and technical advantages.
When neodymium magnets were first discovered, researchers investigated different approaches to produce these magnets efficiently and economically. Two primary methods were explored: conventional powder metallurgy and Hydrogen Decrepitation. After extensive research, Hydrogen Decrepitation emerged as the superior choice, eventually becoming the exclusive technique employed in the industry.
Understanding Hydrogen Decrepitation in NdFeB Magnet Manufacturing
Hydrogen is a highly reactive, tiny atom, consisting of only one proton and one electron. This small size allows it to easily penetrate the grain boundaries of numerous metals. In most cases, metallurgists strive to prevent hydrogen from infiltrating metal, as it causes embrittlement by entering grain boundaries and generating pressure at vulnerable points. This leads to the formation of micro-cracks that propagate throughout the grain structure.
Despite these negative effects, hydrogen can be harnessed to achieve the desired reduction in grain size. By deliberately introducing a significant amount of hydrogen into the metal, it effectively disintegrates – or decrepitates – due to hydrogen’s proficiency in breaking down the metal into remarkably small fragments.
The role of Hydrogen Decrepitation in creating high-performance neodymium magnets cannot be understated. This innovative technique allows manufacturers to economically produce magnets with exceptional magnetic properties by exploiting hydrogen’s unique characteristics to reduce grain size. As a result, Hydrogen Decrepitation has become an indispensable process in the manufacturing of neodymium magnets.
The Process – Implementing Hydrogen Decrepitation in NdFeB Magnet Production
Although strip casting with rapid solidification results in very small grains, the material produced emerges as flakes that need to be converted into powder for magnet manufacturing. To achieve this, the metal flakes are placed inside a vacuum chamber, and a controlled amount of hydrogen is introduced.
As hydrogen accumulates within the grain boundaries, the metal starts to disintegrate, as demonstrated in the brief video above.
Once the material has undergone decrepitation, it is prepared for the subsequent stage in the process. During this phase, the decrepitated material is subjected to jet milling to attain the desired grain size and shape for optimal neodymium magnet production.