Curie point also called the Curie temperature or magnetic transition point, refers to the material can be changed between the ferromagnet and paramagnetic temperature, that is, ferromagnet from the ferromagnetic phase into paramagnetic phase transition temperature. It can also be said that the transition temperature of the secondary phase transition occurs.
The material becomes ferromagnetic when below the Curie point temperature, and the material-related magnetic field is difficult to change at that time.
When the temperature is higher than the Curie point temperature, the material becomes a paramagnetic magnet, the magnetic field of the magnet is easy to change with the surrounding magnetic field. The magnetic susceptibility at this time is about 10-6 square.
Once the core temperature exceeds its Curie temperature, its permeability decreases drastically (in accordance with the broad definition of the magnetic material manufacturer, it has begun to drop sharply before reaching the defined Curie temperature). It means that that after reaching the Curie temperature, the electromagnetic effect of the core has been unable to play a role, the consequences are serious.
Different materials of the core to withstand the Curie temperature is not fixed. For manganese and zinc to consider the Curie temperature effect of the common (other materials Curie temperature is higher), power class material Curie temperature below 230 ℃, high conductivity class below 120 ℃. It need to consider if use of high-conductivity core, and the transformer has a higher temperature requirements.
More than Curie temperature from ferromagnetism into paramagnetic, should not involve phase change, because some of the volume will expand contraction, resulting in density will change, as the quality should not change, unless the temperature is too much something volatile.
As for the Tc magnetic materials are different, such as iron Curie temperature of about 770 ℃, cobalt Curie temperature of about 1131 ℃.
The magnetic material has a critical temperature Tc, that is, the Curie temperature. At this temperature, the arrangement of the atomic magnetic moments is chaotic and disorder due to the intense thermal motion of the atoms at high temperatures. The magnetization of the magnetic material decreases with increasing temperature, which determines the upper limit of the temperature of the magnetic device. If the temperature exceeds the Curie temperature, the inductance of the core will decrease until it disappears and the circuit will not work properly.
Commonly used PC40, PC44 Curie temperature at 210 ℃.
According to the circuit needs and working conditions, select the appropriate core.
Usually small and medium power switching power supply transformer core, usually selected 200 ℃ near the core material.
With this feature, people have developed a lot of control elements, for example, we use the rice cooker to use the magnetic material Curie point characteristics. In the middle of the bottom of the rice cooker installed a magnet and a Curie point of 103 ℃ magnetic material. When the water in the pot is dry, the temperature of the food will rise from 100 ° C. When the temperature reaches about 103 ° C, the magnetic force of the magnetic material sucked by the magnet disappears, and the magnet loses its suction, and the spring between the magnet and the magnetic material separates them and drives the power switch off Open and stop heating.