Empty ceramic dishes can get hot in a microwave due to a phenomenon called "thermal runaway" or "resonance heating." This occurs when certain materials, like ceramics, do not absorb microwaves evenly, leading to localized hot spots in the material.
Here's how it happens:
Microwave interaction: Microwaves emitted by the oven are absorbed by the water molecules present in the food. When there is no food or liquid to absorb the microwave energy, it gets reflected back and forth within the microwave cavity.
Uneven absorption: Some materials, particularly ceramics and certain types of glass, do not absorb microwaves as effectively as food does. Instead, they may partially reflect the microwaves and create standing waves within the microwave cavity.
Hotspots: Standing waves create areas of intense microwave energy concentration, known as "hotspots." These hotspots occur at specific points within the microwave cavity where the microwave radiation combines constructively, leading to a higher energy concentration.
Heating the ceramic: When an empty ceramic dish is placed in the microwave, the hotspots form within the ceramic material due to its uneven absorption of microwaves. As a result, these hotspots can rapidly heat up the ceramic dish.
Potential damage: If the hotspots become too intense, they can cause the ceramic dish to crack, shatter, or even ignite if the dish is not microwave-safe or has any metallic parts or decorations.
To prevent empty ceramic dishes from overheating in the microwave:
Always place food or a cup of water in the microwave alongside the ceramic dish to absorb the microwave energy effectively.
Use microwave-safe ceramic dishes that are specifically designed for microwave use, and avoid using dishes with metallic trim or decorations.
Stir or rotate the food during heating to ensure even distribution of microwave energy and prevent hotspots from forming.
Follow the manufacturer's instructions and recommended cooking times for your microwave and dishes.
By taking these precautions, you can safely use ceramic dishes in the microwave without risking damage to the dish or the microwave itself.