What happens if an aluminum object is placed in a microwave oven?

Placing metal objects in the microwave can cause a fire or explosion or will it be nothing?

The microwave oven is one of the great inventions of the 20th century, now when using a microwave oven, manufacturers still warn that metal and especially aluminum objects in the oven should not be used. microwave. Otherwise, it may cause fire or explosion, but why so, we will try to understand through the working principle of microwave oven.

The technology used in microwaves is quite simple, it uses microwaves to heat food. The microwaves are generated from a magnetron light, which is guided by a waveguide, into the cooking compartment and reflected back and forth between the metal walls of the cooking compartment and absorbed by the food. Microwaves in microwaves are vibrations of the electromagnetic field with a normal frequency of 2450 MHz (wavelength of 12.24 cm). Food molecules (water, fat, sugar and other organic substances) are capable of absorbing this type of wave and vibrating the molecules inside. Rotary oscillation is transformed into chaotic thermal motion through molecular collisions, heating food.

Another special feature is glass molecules, some special plastics or paper that are difficult to be heated by microwave at 2450 MHz. As a result, food can be stored in items with the above materials in the microwave, but only food is cooked. However, for metals, especially aluminum, things are different.

Although the internal structure of the microwave is a Faraday cage consisting of metal or metal mesh surrounded, ensuring waves do not leak out. The holes in this grid are much smaller than the wavelength (12cm), so the microwaves do not leak, but the light (at a much shorter wavelength) still passes through, helping to observe the food inside.

Like a mirror, however, instead of reflecting light, these metal plates reflect microwaves. If you use a thick aluminum pot and place it in the microwave, the food will never be heated up because the microwave waves are blocked by the pot.

It is for thick metal objects, but with thin metal leaves, things get a lot worse. The electromagnetic field in the microwave creates a conductive current in the metal. For large and thick metal objects, they can withstand this current without any problems.However, for thin metal pieces, aluminum foil, they can be overwhelmed by internal currents and quickly heated up. Therefore, it can cause fire , especially for aluminum foil, which is wrinkled, this phenomenon is more and more powerful.

The oscillation of microwaves can create an electric field focused at the corners or edges of a metal object, ionizing the surrounding air, so you can hear crackling sounds, or see slightly spark like lightning. However, no explosion will occur.

The truth is that your microwave can be burnt if you put a thin sheet of metal inside , but there will not be a similar explosion. And for thick metal, there will be no phenomenon, only the food inside is not heated.

Many microwave ovens are now integrated with grill mode, in which mode the microwave uses heat from the resistance wire or halogen lamp, not the microwave. When the microwave oven is like a normal electric oven, so in this mode you can use paper wrappers, metal blisters inside the microwave.