Experiment 57: Microwave Furnace Melting Metal
To make my microwave furnace, I grabbed the alumina-silica light-density firebrick that was my arc furnace body and cleaned the metal residue from its inside. The furnace body is simply one brick with a 2" diameter hole 1.5" deep in it and another brick as the lid. Each brick is about 4" by 4" by 2.5", so this leaves a 1" thick bottom on the furnace body.
I added a 1/8" layer of crushed lump charcoal to the bottom of the furnace's inside and put my soup can crucible on top of that. Then, I added some aluminum TIG welding filler rod scraps and set the furnace in an experiments-only microwave. With everything in place, I nuked my furnace for six minutes on high heat. Amazingly, the aluminum was completely molten and glowed bright orange! I was quite impressed, so I tried zinc in the microwave furnace. After four minutes, it was a mere puddle.
I read on a forum somewhere that charcoal can heat things to at least 1000°C as a microwave susceptor, so I suppose I shouldn't be surprised that the furnace works so well. With a simple soup can as its crucible, though, it has limitations. I tried melting copper, and while the copper melted (around 20 minutes on high), it also ate through the steel and leaked out everywhere. A graphite crucible might be a better choice. However, I am still impressed that a common microwave can melt a metal like aluminum in less than ten minutes!