Long-term stability of magnets at room temperature
A study published by Finnish scholars in 2013 showed that sintered neodymium iron boron magnets (HcJ=15.6kOe) placed at room temperature for 1 year (10000h), samples with different Pc values (Pc=-0.33, -1.1, -3.3) There is no perceptible loss of magnetization. The Sanhuan Research Institute also conducted a similar measurement and research, which lasted more than 12 years (4441 days). The experimental sintered NdFeB magnet has an intrinsic coercivity HcJ=18kOe, and the sample is an uncoated sample with a side length of 10.2mm. Cube, permeability coefficient Pc=-2 (click on magnetic moment, magnetic flux and remanence to understand what is the Pc value), the number of samples is 8 pieces, directly exposed to the atmospheric environment where the laboratory is located, the temperature is 22 ℃ ~ 28 ℃, observe and measure once a year for 12 years.
It can be found from the above data that the relative magnetic flux loss measured in the first 6 years is basically not large, and an inflection point appears around 2208 days (about 6 years). From the outside, rust spots can be seen on the surface of the black magnet after 6 years of storage, which means that the surface and the inside of the magnet have already begun to oxidize and corrode. As time goes by, the range of oxidation or corrosion will continue to expand, and the rate of performance degradation is also obvious. accelerate. In addition, the experiment also extrapolated the magnetic flux loss from the currently measured 4441 days (12 years and 2 months) to 30-50 years. The estimated magnetic flux loss in 30 years is less than 1%, and the magnetic flux loss in 50 years is about 1.3. %, 2% corresponds to about 150 years.
This result shows that if the service life of the magnet is defined as the time corresponding to the flux loss rate equal to 5%, even if the magnet is on the surface without corrosion-resistant coating, the currently measured sintered NdFeB magnet still has a very long Life expectancy is conservatively estimated to be 30-50 years.
Generally, the larger magnetic flux loss comes from oxidation or corrosion on the surface of the magnet, which is an irreversible loss. Among all kinds of rare earth permanent magnet materials, this loss of sintered NdFeB is the most serious, but after composition optimization and Surface protection treatment, oxidation resistance and corrosion resistance of sintered NdFeB magnets have been greatly improved. Therefore, under the condition that the surface of the magnet is well protected, for a sintered NdFeB with sufficiently high HcJ, the service life can exceed 30-50 years.
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