Aluminum foil in the microwave?
Understand what can happen if you put paper or aluminum items in the microwave
Edited and resized image from Sincerely Media, available on Unsplash
Placing metal utensils or even aluminum foil in the microwave can be very dangerous. Metals are excellent conductors of energy and, if microwaved, contact with the device's electric and magnetic fields can create an electrical current in these conductive materials. So an innocent tin foil lunch box that you'd like to defrost in the microwave could end up starting a fire.
Forgetting an aluminum cutlery inside the container to be heated is also dangerous. The electrical phenomenon starts with a few sparks, crackles and small explosions, evolving into larger explosions, which can end up setting fire to the device - or even to the entire house. So, if you hear some crackling noises when heating food, pause the appliance and check that you didn't end up forgetting an aluminum object in the microwave by mistake!
Why not put aluminum in the microwave
To understand what happens if you do this, you need to know the working principle of the device. The microwave oven contains a magnetron, that is, a tube where electrons are affected by magnetic and electric fields in order to produce radiation in the form of microwaves, which are tiny electromagnetic waves (hence the name!).
The electromagnetic waves released by the microwave interact with the water molecules present in the food, causing the agitation between them to increase. This internal movement of food molecules generates energy that, when radiation ceases, is emitted in the form of heat, which heats the food.
That is why it is necessary to use utensils that are made of materials that are transparent to this type of electromagnetic radiation, such as glass, ceramics, paper and some plastics. They are materials that let the waves pass and allow the food to heat up.
Metals such as aluminum, in addition to not being transparent to microwaves, are also excellent conductors. As the appliance walls are also lined with metal, placing a large heavy metal pan inside the microwave will only reflect the waves through the appliance itself, preventing the food from heating.
The big danger, however, is in smaller metal items such as cutlery, utensils and even aluminum foil. In the case of these materials, which act as small conductors, the electric and magnetic fields of the microwave can create an electric current - large pieces of metal, such as the oven wall itself, usually support this current. On the other hand, if you microwave small aluminum items, such as cutlery or lunchboxes, they can become overloaded by electrical current, overheat, and generate sparks that can cause a fire. Be careful!
