Metal can be melted and metal powders can be sintered in a household microwave oven. In addition to being a fun and somewhat dangerous science project, this may one day lead to more energy efficient materials processing methods. Research published in the scientific journal Nature has shown that sintering metal with microwaves at 2.45 Ghz, the frequency used in household microwave ovens, can lead to mechanical properties that are superior to metal parts sintered in conventional furnaces. The suspected reason for the superior mechanical properties is that the pores formed during microwave sintering are very round and thus they do not act as stress concentrators.
- The inside of the microwave oven must be very well insulated. Ceramic refractory materials should be used.
- The vent holes of the microwave should be sealed, or a system to pump nitrogen in through the vent holes should be built. This will minimize or prevent the amount of oxidation that occurs. When working with metal powder, this is absolutely necessary to prevent oxidation.
- Use a microwave that operates at at least 850 Watts.
- It is easy to get metal dangerously hot, but it can be hard to get it hot enough to melt. Try putting silicon carbide, graphite, or magnetite inside of the insulated area to increase the temperature. They will act as a susceptor. This means that they will soak up the microwaves like a sponge and get hot really fast.
- Do not mix metal powders without doing your homework first. This may seem like a quick and dirty way to make an alloy but it may lead to the production of excess heat a la thermite reaction.
- Do not try this with aluminum, magnesium, or any other highly flammable metal.
- Keep in mind that this is Very Dangerous
- Keep a fire extinguisher, phone, and cold water handy.
The cold water is not to put fires out, it is to treat burns.
- Wear eye protection.
- Do a lot of internet or library research before attempting this or any other science project. As the saying goes, "Ten hours in the lab can save you one in the library."
Why Sparks Occur
- Try making metal matrix composites by surrounding a ceramic material or a metal that has a high melting point with a metal powder that has a lower melting point. You may find that metals don't like to stick to most things. Good reinforcement materials should stick to the surrounding matrix material. Otherwise, there will be little benefit for making the composite.
- Try casting your own action figures, keychains ornaments, or some other neat objects.
- Try recycling scrap metal after you have thoroughly cleaned it.
Any good conductor will act like an antenna when put into a microwave oven. A large voltage will build up in the conductor, and the electricity will then arc to the grounded metal parts of the oven.