Baking dishes made from an exotic ceramic material could speed up the rate at which microwave ovens cook food, reducing the energy needed for cooking.
Microwave ovens use a neat trick to rapidly heat food. Microwaves have an alternating electric component that causes any molecules with a positive charge at one end and a negative charge at the other, such as water, to rotate and align themselves with the field.
The rotating water molecules jostle other nearby molecules, which also begin to move. Simply because these molecules are in motion, the food becomes hot.
But microwave ovenware is "transparent" to microwaves and so only heats up by conduction as it touches the hot food.
That means that the food loses some heat to its container. Ovenware that is directly heated by microwaves could reverse that loss by conductively heating the food instead, which would improve the efficiency of microwave cooking.
Baking dish baked
Now, Sridhar Komarneni at Pennsylvania State University, together with Hiroaki Katsuki and Nobuaki Kamochi at the Saga Ceramic Research Laboratory in Saga, Japan, have developed a new ceramic with microwave-absorbing properties.
Komarneni's team took powdered petalite, a lithium-rich mineral, and mixed it with a small quantity of magnetic iron oxide. They dried the powder and fired it in a kiln for 5 hours, before sintering it at 1250°C to create an iron oxide-petalite foam suitable for use as a microwave ceramic.
The iron oxide component interacts with the microwaves' electric field and rapidly heats, while the insulating petalite component helps to retain that heat after the oven is switched off.
Porcelain is so slow
The researchers tested their new foam against standard porcelain ovenware in a 600-watt microwave oven. After 70 seconds of power, the porcelain had reached 50-60°C, but the new foam had risen to over 200°C.
The foam continued to gain temperature for another 30 seconds after the power was switched off, peaking at 294°C. That's because it takes a few seconds for the heat to spread from the iron oxide component throughout the foam, says Komarneni.
"The microwave-ware saves about 50% energy compared to the conventional microwave ware," says Komarneni. A ceramic rice cooker constructed using the new foam takes just 10 minutes to prepare rice instead of 20-30 minutes using conventional ovenware.
And it may not be long before you can buy the new ovenware. The new material is already being commercialised by a company in Japan, says Komarneni.