June 18, 2021

Is the hot red strong magnet still magnetic?

Powerful magnets are very magnetic and have a wide range of uses in life. However, many people will be curious, what kind of scene will appear if the strong magnet is burned red and then used to attract the iron? Has the magnetism of the red-hot magnet become stronger or weaker, or does it simply disappear? Let’s reveal the answer together.

Magnets are generally made of rare earth metal praseodymium, neodymium, dysprosium and other rare elements mixed and sintered. Its interior is neatly arranged with “magnetic domains” in the same direction (magnetic domains are regions with uniform magnetization in the material. In the area, the magnetic moments of the atoms are arranged neatly and the direction is consistent). When an iron object approaches the magnet, the magnetic field of the magnet magnetizes the iron, so that there is a mutual attraction between them, and this attraction makes them stick firmly together.

When the temperature of the magnet rises, the molecular motion inside the magnet is very active, and the original magnetic domains in the magnet that are neat and in the same direction will change. As the temperature rises further, the magnetic domains in the magnet are not as neat and stable as before, so the magnetism is weaker than before. When the magnet is burnt red, that is, the temperature of the magnet rises to a certain value, the arrangement of the magnetic domains will be completely disordered, and the magnet will lose its magnetism.

In the same way, when the iron block is burned red, it cannot be attracted by the magnet, because the burned iron block cannot be magnetized. Scientists call the temperature at which the magnet completely loses its magnetism as the “Curie temperature”. After experiments, it is found that the Curie temperature of the magnet is 769 degrees Celsius.

In steelmaking plants, electromagnetic cranes use electromagnets to often put heavy pig iron into the steelmaking furnace. But for the steel ingots just produced from the steelmaking furnace, the magnet crane is useless. Because the temperature of the steel ingot just out of the furnace is as high as 1400 degrees Celsius, which has far exceeded the Curie temperature of steel, the steel ingot loses the magnetism of iron and cannot be magnetized. After the red-hot magnet has no magnetism, will the magnetism be restored after the temperature drops? At this time, you only need to re-magnetize the magnet, and the magnet will restore its previous magnetism.

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