1. Weakening of Magnetic Force
When the temperature rises, the magnetic force of ferrite magnets will gradually weaken. In general ferrite magnets, when the temperature reaches around 200 °C, the magnetic force will decrease to about 70% of the initial magnetic force. When the temperature continues to rise above 500 °C, the magnetic force will decrease sharply and may even disappear. This is because high temperatures cause changes in the crystal structure of ferrite, resulting in a decrease in the magnetization degree and magnetic permeability, thereby reducing the magnetic performance of the magnets.
2. Instability of Magnetic Characteristics
In a high-temperature environment, the magnetic characteristics of ferrite magnets will become unstable. The magnetization degree of the magnets will change with the variation of temperature, leading to the instability of the magnetic force. Especially at high temperatures, ferrite magnets will exhibit magnetic hysteresis. That is, due to the thermal motion of the magnetized molecules, the magnetization state of the magnets undergoes frequent reversals, making the magnetic force unstable.
3. Thermal Expansion and Stress Cracks
In a high-temperature environment, ferrite magnets will undergo thermal expansion, resulting in changes in size. The thermal expansion coefficients are different at different temperatures. When the temperature rises, the size of ferrite magnets will expand, which may easily lead to the failure of mechanical fits. Meanwhile, the thermal stress between the magnets and the outside environment in a high-temperature environment will cause stress concentration inside the magnets and then trigger stress cracks.
In conclusion, when using ferrite magnets in a high-temperature environment, attention should be paid to the reduction and fluctuation of the magnetic force, the size changes caused by thermal expansion, and the occurrence of stress cracks.
Low-temperature Usage Limitations
1. Attenuation of Magnetic Performance
Low temperatures will cause the magnetic performance of ferrite magnets to attenuate. As the temperature drops, the magnetic force of the magnets gradually weakens. At a certain low temperature, the magnetic force will drop sharply until it disappears. The relationship between the magnetic force of ferrite magnets and temperature is mainly affected by the material composition and sintering process.
2. Change in Magnetization Direction
In a low-temperature environment, the magnetization direction of ferrite magnets will change. When the temperature drops to a certain limit, the magnetization direction of the magnets will change abruptly, resulting in changes in magnetic performance. This is mainly related to the crystal structure and magnetic domain structure of ferrite magnet materials.
3. Changes in Physical Properties
In a low-temperature environment, the physical properties of ferrite magnets will change. For example, the resistivity increases as the temperature decreases, the magnetic permeability gradually decreases, and the magnetic susceptibility increases. Meanwhile, low temperatures also have an impact on the mechanical strength of ferrite magnets, making them prone to brittle fracture.
In conclusion, when using ferrite magnets in a low-temperature environment, it is necessary to consider the weakening and direction change of the magnetic force, the changes in physical properties, and the brittle fracture problem of the magnets.
In general, ferrite magnets have certain usage limitations in both high-temperature and low-temperature environments. In high-temperature environments, issues such as the weakening of magnetic force, instability of magnetic characteristics, thermal expansion, and stress cracks of ferrite magnets need to be noted. In low-temperature environments, problems like the attenuation of magnetic performance, change in magnetization direction, changes in physical properties, and brittle fracture of ferrite magnets also require attention. Therefore, in practical applications, it is necessary to select appropriate ferrite magnet materials according to the specific working environment and requirements or take corresponding improvement measures to ensure the normal operation and service life of the magnets.
