When it comes to neodymium-iron-boron magnets, the stability of their magnetic properties over time is a key indicator of quality. Stability here refers to how the magnet’s properties change due to internal and external influences after magnetization. Factors like temperature, time, electromagnetic fields, radiation, mechanical vibration, and impact all play a role. Let’s dive into what affects the long-term stability of these magnets.
Factors Affecting Long-Term Stability
Magnets can experience changes in their physical and chemical properties over time, especially due to environmental factors like temperature, humidity, and corrosive substances. After a magnet is magnetized, most of its regions align in a specific direction, but some small areas (reverse magnetization nuclei) remain misaligned. Environmental conditions can cause these nuclei to grow or new ones to form, leading to a slow, irreversible decay of the magnet’s properties from the surface inward. This decay impacts crucial performance parameters such as residual magnetism, coercive force, and maximum magnetic energy product, and can eventually cause the magnet to fail. This loss is irreversible, meaning re-magnetizing the magnet won’t restore it to its original state.
Long-Term Stability at Room Temperature
In 2013, Finnish researchers found that sintered neodymium-iron-boron magnets (HcJ=15.6kOe) stored at room temperature for one year (10,000 hours) showed no detectable loss of magnetization across different Pc values (Pc=-0.33, -1.1, -3.3). The Trilateral Research Institute conducted a similar study over 12 years (4,441 days) on sintered neodymium-iron-boron magnets with an intrinsic coercive force HcJ=18kOe. These uncoated cubic magnets (10.2mm edge length, Pc=-2) were exposed to the lab’s ambient environment, with temperatures ranging from 22℃ to 28℃, and measured annually.
The study found minimal magnetic flux loss in the first six years, with a noticeable change around 2,208 days (about the 6th year). Surface rust spots appeared after six years, indicating oxidation and corrosion that would continue over time, accelerating the performance decay. Extrapolating the data, the researchers estimated a loss of less than 1% over 30 years and about 1.3% over 50 years, with a 2% loss expected around 150 years.
These results suggest that high-quality sintered neodymium-iron-boron magnets can have a lifespan of 30-50 years, even without surface coating.
Long-Term Stability at High Temperatures
High-temperature stability is also crucial for neodymium-iron-boron magnets. Data shows that higher storage temperatures accelerate the relative magnetic flux loss. Magnets with lower absolute Pc values experience greater initial and long-term losses, which increase significantly with temperature. When feasible, increasing the absolute value of Pc can effectively reduce magnetic loss by further enhancing HcJ.
The relationship between time and relative magnetic loss indicates that higher HcJ values result in lower magnetic losses, highlighting the importance of high HcJ for maintaining stability at elevated temperatures. The magnetic permeability coefficient Pc also plays a role in determining long-term magnetic loss at high temperatures.
Conclusion
Understanding the long-term stability of neodymium-iron-boron magnets is essential for applications in fields like aerospace, electric vehicles, and high-power wind generators where longevity is critical. By optimizing the composition and applying surface protection treatments, we can significantly improve the oxidation and corrosion resistance of these magnets, ensuring a lifespan of 30-50 years or more under optimal conditions. High HcJ values and appropriate Pc coefficients are key for maintaining magnetic properties over extended periods, even at high temperatures.
At MainRich, we focus on these factors to produce durable, high-performance sintered neodymium-iron-boron magnets suitable for a variety of demanding applications. Contact us for more information.
